RNA MOLECULES FOR THE TREATMENT OF CANCER

Abstract

An RNA molecule is disclosed having a sequence having at least 80% sequence identity to SEQ ID NO: 2. The invention is also directed to an RNA molecule obtainable by transcription of a DNA sequence having at least 80% sequence identity to SEQ ID NO: 1 for use as a medicament and to pharmaceutical compositions comprising such an RNA molecule.

Claims

1. An RNA molecule having a sequence having at least 80% sequence identity to SEQ ID NO: 2.

2. An RNA molecule obtainable by transcription of a DNA sequence having at least 80% sequence identity to SEQ ID NO: 1 or the RNA molecule according to claim 1 for use as a medicament.

3. The RNA molecule according to claim 2 for use in the treatment of cancer.

4. The RNA molecule for use according to claim 3, wherein the cancer is selected from the group consisting of colon cancer, lung cancer, stomach cancer, esophageal cancer, pancreatic cancer, gallbladder cancer, renal cancer, bladder cancer, prostate cancer, testicular cancer, cervical cancer, endometrial cancer, choriocarcinoma, ovarian cancer, breast cancer, thyroid cancer, brain cancer, head and neck cancer, malignant melanoma, skin cancer, liver cancer, leukemia, lymphoma, multiple myeloma, chronic myelogenous leukemia, neuroblastoma and aplastic anemia.

5. The RNA molecule for use according to claim 3, wherein the cancer comprises cancer cells and wherein the treatment induces differentiation and/or cell death in the cancer cells.

6. The RNA molecule for use according to claim 2, wherein the treatment comprises incubating the RNA molecule with cell extracts prior to administration.

7. A pharmaceutical composition comprising as active ingredient an RNA molecule obtainable by transcription of a DNA sequence having at least 80% sequence identity to SEQ ID NO: 1.

8. The pharmaceutical composition according to claim 7, wherein the RNA molecule has a sequence having at least 80% sequence identity to SEQ ID NO: 2.

9. A pharmaceutical composition comprising as active ingredient a plurality of RNA fragments, wherein the plurality of RNA fragments covers at least 80% of the sequence of SEQ ID NO: 2.

10. The pharmaceutical composition according to claim 7, wherein the RNA molecule or the RNA fragments are RNA purified from cells or in vitro transcribed RNA.

11. The pharmaceutical composition according to claim 7, wherein the RNA molecule or the RNA fragments are encapsulated in lipid nanoparticles, cellular or synthetic exosome mimics or in virus-like particles.

12. The pharmaceutical composition according to claim 7, wherein the RNA molecule or the RNA fragments are activated by incubating the RNA molecule or the RNA fragments with cell extracts prior to administration.

13. A pharmaceutical composition comprising as active ingredient a vector loaded with a DNA sequence having at least 80% sequence identity to SEQ ID NO: 1.

14. The pharmaceutical composition according to claim 13, wherein the vector is selected from the group consisting of a plasmid vector, a cosmid vector, a virus, and analogs thereof.

15. The pharmaceutical composition according to claim 7 for use in the treatment of cancer.

16. The RNA molecule for use according to claim 6, wherein the treatment comprises incubating the RNA molecule with cell extracts from cells from S. frugiperda, D. melanogaster, M. musculus or H. sapiens prior to administration.

17. The pharmaceutical composition according to claim 12, wherein the RNA molecule or the RNA fragments are activated by incubating the RNA molecule or the RNA fragments with cell extracts from cells from S. frugiperda, D. melanogaster, M. musculus or H. sapiens prior to administration.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0011] FIG. 1 shows that let-7-C may encode two non-coding transcripts. (A) Genomic region of the let-7-C in Drosophila, containing 3 exons (black boxes), one large intron and one small intron (dashed line). Transcriptome analysis of eye-antennal disc cells at 48 hours after pupal formation (metamorphed control) and metamorphed ph.sup.505 cells by RNA-seq revealed many reads (black and grey bars indicate two replicates) mapping to the first intron. (B) let-7-C intron sequences can be observed in publicly available RNA-seq data in the Flybase. Notably, the intron sequences are enriched in samples from pupal stages, but not in embryonic, larval, and adult stages. (C) RNA-seq analysis of ecdysone-treated ph.sup.505 culture cells showed many sequencing reads mapping in the first intron. Analysis of modENCODE data for RNA Pol II ChIP of adult heads and Kc167 cells reveals multiple regions with strong Pol II localization within the first intron, indicating potential transcription start sites. Based on the Pol II localization sites, as well as the sequencing reads, we named one IncRNA let-A and the other transcript let-B. In addition, the second half of the intron 1 was named I1 B that was used in following experiments.

[0012] FIG. 2 shows the dynamic expression of let-7-C IncRNAs during development. (A-E) qPCR quantification of the expression levels of different intronic regions of the let-7-C in whole larvae or pupae from different larval and pupal stages. Primers were used to amplify let-A coding region (A), intermediate region between let-A and let-B (B), let-B coding region (C), and 3′ region outside of let-B (D). Eip75B, a known ecdysone-induce gene, was used here as a control (E). (F) qPCR quantification of the expression levels of different intronic regions of the let-7-C in ecdysone-treated ph.sup.505 culture cells at different time points. Primers used were the same as in (A-D). (C) Expression dynamic of let-7 miRNA at the different developmental time points. (D) Confocal image of in situ hybridization of intron 1 sequences to whole salivary glands of white prepupae shows a strong signal (arrow) at the periphery of the nuclei (grey).

[0013] FIG. 3 shows that induced expression of let-A resulted in rapid cell death in ph.sup.505 cells. (A-F) Light microscope pictures showing ph.sup.505 culture cells in different conditions: (A) untransfected; (B) silver-treated; (C) induced let-A; (D) induced I1 B; (E) induced let-B; (F) induced mCherry (mC). All pictures showed the cells at two hours after induction. Arrow in (A) indicates a ph.sup.505 cell which has an extended shape and attaches to the plate; arrowhead in (A) indicates a round shape floating ph.sup.505 cell. Asterisks in (C) indicate dying cells; dashed arrow in (C) indicates a ph.sup.505 cell with abnormal shape. Scale bar is 20 μm. (G) alamarBlue quantification of cell viability at three hours (3 h) after different RNAs were induced in ph.sup.505 cells. This assay incorporates an oxidation-reduction indicator that both fluoresces and changes color in response to chemical reduction of medium resulting from cell growth. The fluorescence was measured and higher value correlated with more living cells in the culture. (H) alamarBlue quantification of cell viability at three days (3 d) after different RNAs were induced in ph.sup.505 cells. (I) alamarBlue quantification of cell viability at three hours after different RNAs were induced in S2 cells.

[0014] FIG. 4 shows that let-A expression induced apoptotic cell death in ph.sup.505 cells. (A) Annexin V staining in mCherry-expressing ph.sup.505 cells. (B) Annexin V staining in let-A-expressing ph.sup.505 cells showing many cells undergo apoptotic cell death. (C) CellRox staining in mCherry-expressing ph.sup.505 cells. (D) CellRox staining in let-A-expressing ph.sup.505 cells. (E) Cell viability measurements of ph.sup.505 cells when different apoptosis inhibitors were applied during the induction of mCherry or let-A.

[0015] FIG. 5 shows that cell death was induced by let-A RNA molecules. (A-C) Light microscope images showing ph.sup.505 culture cells treated with let-A/medium (A), mCherry/medium (B), or UV medium (C). Scale bars are 20 gm. (D) Light microscope pictures showing ph.sup.505 culture cells treated with purified RNA fraction from mCherry/medium. (E) Light microscope pictures showing ph.sup.505 culture cells treated with purified DNA fraction from mCherry/medium. (F) Light microscope pictures showing ph.sup.505 culture cells treated with purified RNA fraction from let-A/medium. (G) Light microscope pictures showing ph.sup.505 culture cells treated with purified DNA fraction from let-A/medium. (H) Cell viability measurements of ph.sup.505 cells when RNase or DNase were added to the medium during the induction of let-A or mCherry. Note that adding RNase could significantly increase cell viability in the culture, but DNase could not. (I) Cell viability measurements of ph.sup.505 cells treated with RNAs purified from let-A, let-B, I1B, or mCherry/medium. Only purified RNA from let-A/medium was toxic to the cells. (J) Cell viability measurements of S2 cells treated with RNAs purified from let-A, let-B, I1B, or mCherry/medium. Purified RNA from let-A/medium was not toxic to S2 Cells.

[0016] FIG. 6 shows that cell toxicity was induced by in vitro transcribed full length let-A RNA. (A) Cell viability of ph.sup.505 cells treated with in vitro transcribed sense or antisense let-A and mCherry RNAs. Only the sense let-A RNA was toxic to the cells. (B) Cell viability of ph.sup.505 cells treated with sonicated let-A RNA. The RNA lost its toxicity with increasing number of sonication cycles. (C) Cell viability of ph.sup.505 cells treated with in vitro transcribed let-A, let-B, or mCherry RNA. RNAs were transcribed with biotinylated ribonucleotides, incubated with cell extracts, and purified by affinity purification before applied to the cells. Input, without purification; RNA, affinity purified RNA; FT, flow through after affinity purification. (D) RNA-seq of the input or affinity purified in vitro transcribed RNA as in (C). Number of reads per kilobase million (RPKM) showed the enrichment of let-A after purification. Among the RNAs with the top number of sequencing counts, let-7-C had the most reads. (E) A map of the deletion constructs and shorter parts and fragments within let-A sequence. IVT let-A IP shows the sequencing reads enriched within let-A. (F) Cell viability of ph.sup.505 cells transfected with constructs encoding a series of let-A deletion sequences. (G) Cell viability of ph.sup.505 cells transfected with vectors encoding let-A parts p1-p3. (H) Cell viability of ph.sup.505 cells transfected with vectors encoding let-A short fragments.

[0017] FIG. 7 shows that let-A was toxic to in vivo growing ph.sup.505 tumors. (A, B) Confocal images showing ph.sup.505 tumor after 24 hours incubation in let-A/medium (A) or mCherry/medium (B). Note the tumor cells became dissociated and no longer formed a sphere structure after incubation in let-A/medium. Scale bars are 50 p.m. (C, D) Adult host flies transplanted with let-A/medium-incubated ph.sup.505 tumor (C) or mCherry/medium-incubated ph.sup.505 tumor (D). let-A/medium-incubated ph.sup.505 tumor could not grow, but mCherry medium-incubated ph.sup.505 tumor could form tumors in the host flies. (E, F) Confocal picture showing ph.sup.505 tumor after overnight incubation with purified RNAs from let-A/medium (E) or from mCherry/medium (F). Note the tumor cells became dissociated and no longer formed a sphere structure after incubation with purified RNA from let-A/medium. Scale bars are 50 μm.

[0018] FIG. 8 shows that let-A RNA is also toxic to mammalian cells. (A) Cell viability of HEK293T cells transfected with Drosophila let-A or GFP. Induced expression of let-A was toxic to HEK cells. (B) Cell viability of various mammalian cell lines treated with purified RNA from let-A/medium, I1B/medium, or mCherry/medium. The purified RNA from let-A/medium could kill HEK293T, HeLa, C2C12 myoblast, Mcf7, BTBA, and K562 cells.

[0019] FIG. 9 shows that Toll signaling pathway is required for let-A induced cell toxicity. (A) Cell viability of ph.sup.505 cells treated with inhibitors against Toll signaling components TLR3, MyD88, and TBK1. Cells were first incubated with different inhibitors for one hour, then treated with purified RNAs from mCherry/medium or let-A/medium for three hours. (B) Cell viability of ph.sup.505 cells treated with two NF-κB inhibitors. Cells were treated by the same processes as (A). (C) Cell viability of HEK393T cells treated with inhibitors against Toll signaling components. Cells were treated by the same inhibitors and processes as (A). (D) SEAP activity in HEK-Dual hTLR3 cells treated with purified RNA from let-A/medium or mCherry/medium, with or without Toll signaling inhibitors. (E) Cell viability of ph.sup.505 cells with or without pre-treatment with LPS before let-A or mCherry expression was induced. Note that let-A induction could kill the LPS pre-treated cells even faster. (F) Cell viability of HEK393T cells with or without pre-treated with Poly(I:C), before treated with purified RNA from mCherry/medium or let-A/medium. let-A/medium purified RNA could kill the pre-treated cells much faster.

[0020] FIG. 10 shows let-A/medium can reduce the nucleolus's volume in treated cells. (A, B) confocal images showing ph.sup.505 cells treated with mCherry/medium (mCh) (A) or let-A/medium (let-A) (B). Immunostaining using Fibrillarin antibody (nucleolus). The boundary of a single cell and its nucleus are outlined, and the arrow points to the nucleolus stained by fibrillarin immunofluorescence. (C) Quantification of the nucleolus volume showing that the nucleolus volume was reduced in let-A/medium treated ph.sup.505 cells. (D, E) confocal images showing HEK cells treated with mCh (D) or let-A (E). Immunostaining using Fibrillarin antibody (nucleolus). In mCh treated cells, each nucleus contains one large Fibrillarin staining (volume larger than 25 um.sup.3) and a few smaller ones. The arrow points to the nucleolus stained by fibrillarin immunofluorescence. But in let-A treated cells, the larger structure disappears and more smaller staining are observed in the nucleolus. (F) Quantification of the number of nucleoli with different volume in mCh or let-A treated HEK cells, showing that the nucleolus volume was reduced in let-A/medium treated cells.

[0021] FIG. 11 compares the cellular toxicity of mutagenized let-A. (A) 20% of let-A is removed from the 3′-end (let-A80) or replaced by a neutral sequence (part of hygromycin; letA80-H or part of mCherry; letA80-M). let-Amut 7 and let-Amut 13 represent two variants containing approx. 20% base exchanges over the entire length of let-A. white box:

[0022] consensus let-A sequence, black box: mutagenized sequences compared to consensus let-A, line: deleted sequence. (B) let-A variants shown in A were transfected in HEK293T cells, expression of variants induced and cell toxicity measured by alamarBlue.

DETAILED DESCRIPTION OF THE INVENTION

[0023] The invention relates to an RNA molecule having a sequence having at least 80% sequence identity to SEQ ID NO: 2.

[0024] The RNA molecule having a sequence according to SEQ ID NO: 2 is herein also referred to as Drosophila let-A IncRNA, let-A IncRNA or simply let-A. In a preferred embodiment, the RNA molecule is single-stranded.

[0025] The inventors found that induced expression of let-A results in rapid death of Drosophila ph.sup.505 cancer cells and that dead cells further release this RNA, thus becoming toxic to neighboring cancer cells. In particular, it was found that when let-A RNA was over-expressed in cultured ph.sup.505 cells, this results in rapid cell death of the entire population within a few hours. It was surprising that only a subset of the ph.sup.505 cells in the culture were transfected by the virus vector and thus expressing the RNA, but still all the cells in the culture died. In addition, the culture medium also became toxic and could further induce cell death when applied to a new culture of ph.sup.505 cells. These results indicate that cells expressing let-A release some molecules leading to the death of the untransfected cells in the same culture.

[0026] Without wanting to be bound by a mechanism, it is believed that let-A RNA may act through the Toll signaling pathway to induce apoptosis. Toll-like receptors (TLRs) are a family of membrane proteins that can induce an immune response upon recognition of microbial pathogens. First discovered in Drosophila, this family of proteins is evolutionarily conserved from flies to humans. In particular, several TLRs (TLR3, TLR7, TLR8, and TLR9) are known to recognize either double stranded or single stranded RNAs to initiate downstream signaling (Alexopoulou, L., Holt, A. C., Medzhitov, R., and Flavell, R. A. (2001). Recognition of double-stranded RNA and activation of NF-kappaB by Toll-like receptor 3. Nature. 413, 732-738.).

[0027] Transcriptome analyses of metamorphed cells derived from ph.sup.505 tumor cells passing through metamorphosis showed, among other signaling pathways, a prominent activation of Toll signaling. The fact that this innate immune pathway is highly conserved also provides an explanation why mammalian cells also react to the exposure of the Drosophila let-A IncRNA.

[0028] The RNA molecule according to the invention has a sequence having at least 80% sequence identity to SEQ ID NO: 2. In the context of the invention, the term “sequences having at least 80% sequence identity” comprises sequences having at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, at least 99.5%, most preferably 100% sequence identity to the respective sequence. In all cases, the identity is the identity over the total length of the sequences.

[0029] In one aspect, the RNA molecule according to the invention is a variant of the RNA molecule having a sequence according to SEQ ID NO: 2, i.e. let-A. The term “variant” herein refers to biologically active derivatives of the respective RNA. In general, the term “variant” refers to molecules having a native sequence and structure with one or more additions, substitutions (generally conservative in nature) and/or deletions, relative to the native molecule, so long as the modifications do not destroy biological activity and which are “substantially homologous” to the reference molecule. In general, the sequences of such variants will have a high degree of sequence homology to the reference sequence, e.g., sequence homology of more than 50%, generally more than 60%-70%, even more particularly 80%-85% or more, such as at least 90%-95% or more, when the two sequences are aligned. In case of let-A, a variant thereof shows a similar capability to induce apoptosis in cancer cells, in particular Drosophila ph.sup.505 cancer cells.

[0030] In a preferred embodiment, the RNA molecule has the same secondary structure as let-A. For example, the RNA molecule according to the invention has a double-stranded stem structure formed by complementary base pairing and a loop structure formed by unpairing bases. Within the stem structures, a small bulge loop or an internal loop may exist due to one or two unpairing bases. In addition, the RNA molecule may contain a pseudoknot structure.

[0031] The RNA molecules according to the invention are preferably long non-coding RNA (IncRNA) molecules. IncRNA molecules are herein defined as RNA molecules of more than 200 nucleotides without substantial ORFs.

[0032] In a further embodiment, the invention relates to an RNA molecule obtainable by transcription of a DNA sequence having at least 80% sequence identity to SEQ ID NO: 1 for use as a medicament. In a preferred embodiment, the RNA molecule is for the use in the treatment of cancer.

[0033] The term “obtainable by transcription of a DNA sequence” is herein understood as meaning that the RNA molecule is the transcription product or transcript of the respective DNA. Thus, the term “RNA molecule obtainable by transcription of a DNA sequence having at least 80% sequence identity to SEQ ID NO: 1” refers to any RNA molecule that can be transcribed from a DNA sequence having at least 80% sequence identity to SEQ ID NO: 1 or any processing product of such an RNA molecule. In particular, the RNA molecule according to the invention may have been processed by undergoing posttranscriptional modifications such as RNA methylation, folding, cleavage or wrapping into extracellular cargo vesicles such as exosomes.

[0034] The term “obtainable by transcription of a DNA sequence” is herein understood not to be limited with regard to the source of the RNA molecule. The RNA molecules according to the invention, including the RNA molecules used in the pharmaceutical compositions according to the invention, can be in vivo transcribed RNA molecules purified from cells or in vitro transcribed RNA.

[0035] The skilled person knows how RNA can be purified from cells or transcribed in vitro. For example, RNA purification can be performed by using TRIzol Reagent (Invitrogen, Calif., catalogue no. 15596018). For this, samples are lysed and homogenized in the appropriate volume of TRIzol Reagent. Samples are incubated at room temperature for 5 minutes, then ⅕ of the volume of chloroform is added, incubated and mixed vigorously. To separate the phases samples are centrifuged for 15 minutes at 13 000×g at 18° C. The aqueous phase containing the RNA is transferred to a new tube and RNA is precipitated using isopropanol. The resulting pellet is washed using ice cold 70% ethanol, air dried and dissolved in a suitable buffer.

[0036] The RNA molecules according to the invention may be purified from any eukaryotic cell expressing let-A artificially or naturally. In one embodiment, the RNA molecules according to the invention are purified from cells of S. frugiperda, D. melanogaster, M. musculus and H. sapiens. In a preferred embodiment, RNA molecules may be purified from Sf21, ph505, S2, CI.8, NIH-3T3, HEK293T or HeLa cells.

[0037] Likewise, RNA purification can be performed using commercially available kits such as RNeasy Mini Kit (Qiagen, Germany, catalogue no. 74106) or Dynabeads™ mRNA DIRECT™ Purification Kit (Invitrogen, Calif., catalogue no. 61012).

[0038] For RNA in vitro transcription, numerous commercial kits are available, e.g. MEGAscript® T7 Transcription kit (Invitrogen, Calif., catalogue no. AM1334). Likewise, RNA can be produced by oligonucleotide synthesis.

[0039] In a preferred embodiment, the RNA molecule obtainable by transcription of a DNA sequence having at least 80% sequence identity to SEQ ID NO: 1 is an RNA molecule having at least 80% sequence identity to SEQ ID NO: 2.

[0040] The invention relates to use of these RNA molecules as a medicament, preferably for use in the treatment of cancer.

[0041] Surprisingly, the present inventors found the Drosophila let-A IncRNA to be toxic for different types of mammalian cancer cell lines, indicating an evolutionarily conserved oncolytic function. Consequently, the RNA molecules according to the invention are useful for the treatment of cancer.

[0042] The cancer may be selected from the group consisting of colon cancer, lung cancer, stomach cancer, esophageal cancer, pancreatic cancer, gallbladder cancer, renal cancer, bladder cancer, prostate cancer, testicular cancer, cervical cancer, endometrial cancer, choriocarcinoma, ovarian cancer, breast cancer, thyroid cancer, brain cancer, head and neck cancer, malignant melanoma, skin cancer, liver cancer, leukemia, lymphoma, multiple myeloma, chronic myelogenous leukemia, neuroblastoma and aplastic anemia.

[0043] The invention is also directed to methods of treatment of cancer, wherein the treatment comprises administration of a therapeutically effective amount of an RNA molecule according to the invention.

[0044] The term “administering” herein refers to administering an effective amount of the RNA molecules or the pharmaceutical compositions according to the invention, to a subject in need thereof.

[0045] Administering a nucleic acid, such as DNA or RNA molecule, in particular a IncRNA to a cell may be performed by transducing, transfecting, electroporating, translocating, fusing, phagocytosing, shooting or ballistic methods, etc., i.e., by any means by which a nucleic acid can be transported across a cell membrane.

[0046] In one aspect of the invention, the treatment induces differentiation and cell death in the cancer cells present in the cancer.

[0047] Differentiation of cancer cells may be measured by determining the nucleolus size by immunostaining with an antibody against the nucleolus protein Fibrillarin, followed by microscopy imaging and image processing. Cancer cells often have an enlarged nucleolus compared to normal cells. Another way to measure differentiation is to use cell markers specific for differentiated cells, for example, neuronal cell markers or muscle cell markers. The person skilled in the art is aware which markers can be used to this end. Differentiation of cancer cells can also be determined using transcriptomics, immunofluorescence or other cellular tests.

[0048] Surprisingly, treatment with let-A IncRNA resulted in a reduced volume of nucleolus in most of the cells. Thus, the RNA molecules of the invention are capable of conveying the nucleolar morphology of a healthy cell onto cancer cells.

[0049] The invention also relates to a pharmaceutical composition comprising as active ingredient an RNA molecule obtainable by transcription of a DNA sequence having at least 80% sequence identity to SEQ ID NO: 1. In one embodiment, the pharmaceutical composition comprises as active ingredient an RNA molecule having at least 80% sequence identity to SEQ ID NO: 2.

[0050] It is herein understood that a pharmaceutical composition comprises a therapeutically effective amount of the active ingredient as well as pharmacological excipients. The person skilled in the art knows how to formulate a pharmaceutical composition comprising an RNA molecule. In particular, the person skilled in the art is aware of methods for stabilizing an RNA molecule in a pharmaceutical composition.

[0051] In the pharmaceutical composition according to the invention, the RNA molecule may be encapsulated in lipid nanoparticles, cellular or synthetic exosome mimics or in virus-like particles.

[0052] Herein, the term “lipid nanoparticles” is defined as molecules that are spherical in shape and comprise a solid lipid core stabilized by a surfactant. The core lipids can be steroids, fatty acids, acylglycerols, waxes, and combinations of them. Surfactants may be biological membrane lipids such as phospholipids, sphingomyelins and bile salts (e.g., sodium taurocholate). All of these may be utilized as stabilizers in the lipid nanoparticles used for pharmaceutical compositions of the invention.

[0053] Herein, the term “cellular or synthetic exosome mimics” is defined as nano-sized vesicles (exosomes), derived or purified from cells with modifications (cellular exosome mimics) or generated by artificial methods like cell extrusion (synthetic exosome mimics) that serve as cargos to deliver proteins, nucleic acids or other cellular components to neighboring or distant cells.

[0054] Herein, the term “virus-like particles” is defined as multiprotein structures that closely resemble the organization and conformation of viruses but contain no viral genetic material.

[0055] It may enhance the efficacy of the pharmaceutical composition or the RNA molecules according to the invention to activate the RNA molecule prior to administration. This can be achieved by incubating the RNA molecule with cell extracts. Therefore, in one aspect, the treatment comprises incubating the RNA molecule with cell extracts prior to administration. For example, the RNA molecules according to the invention may be incubated with cell extracts from cells from S. frugiperda, D. melanogaster, M. musculus and H. sapiens. In particular, the RNA molecules may be incubated with cell extracts fromSf21, ph505, S2, Cl.8, NIH-3T3, HEK293T or HeLa cells.

[0056] The term “incubating with cell extracts” herein refers to a process in which cells are first homogenized in extraction buffer comprising protease and phosphatase inhibitors. In a second step, the thus obtained active cell lysate is mixed with the respective RNA molecules, e.g., the RNA molecules of the invention, for an appropriate amount of time, e.g., 5 to 15 min. Lastly, the RNA molecules are purified as described above.

[0057] Without wanting to be bound by a mechanism, it is believed that incubation with cell extracts activates and/or stabilizes the RNA molecules according to the invention and thus further enhances efficacy of the RNA molecules.

[0058] In another embodiment, the invention relates to a pharmaceutical composition comprising as active ingredient a vector loaded with a DNA sequence encoding an RNA molecule having at least 80% sequence identity to SEQ ID NO: 2. In one embodiment, the polynucleotide sequence has a sequence having at least 80% sequence identity to SEQ ID NO: 1.

[0059] The vector may be selected from the group consisting of a plasmid vector, a cosmid vector, or any other vector-based RNA expression system, a virus, and analogs thereof. The virus may be a retrovirus or a lentivirus. In a preferred embodiment, the virus is an adenovirus or an adeno-associated virus.

[0060] The term “loaded” is herein understood to mean that in case of the vector being a plasmid vector or a cosmid vector, said vector comprises said DNA sequence. In case the vector is a virus, the term is understood to mean that the virus carries said DNA sequence and is able to transduce cells with said DNA sequence.

[0061] In another embodiment, the pharmaceutical composition comprises a plurality of RNA fragments, wherein the plurality of RNA fragments covers at least 80% of the sequence of SEQ ID NO: 2. The present inventors have surprisingly found that fragments of the let-A RNA molecule show a similar cytotoxicity as the full length let-A molecule, as long as the fragments cover at least 80% of the sequence of SEQ ID NO: 2. Thus, the invention also covers embodiments wherein the let-A RNA molecule is not present as a one molecule, but rather as individual fragments, wherein the fragments cover or span at least 80% of the sequence of SEQ ID NO: 2.

[0062] The pharmaceutical compositions according to the invention are useful in the treatment of cancer.

[0063] The cancer may be selected from the group consisting of colon cancer, lung cancer, stomach cancer, esophageal cancer, pancreatic cancer, gallbladder cancer, renal cancer, bladder cancer, prostate cancer, testicular cancer, cervical cancer, endometrial cancer, choriocarcinoma, ovarian cancer, breast cancer, thyroid cancer, brain cancer, head and neck cancer, malignant melanoma, skin cancer, liver cancer, leukemia, lymphoma, multiple myeloma, chronic myelogenous leukemia, neuroblastoma and aplastic anemia.

EXAMPLES

Example 1

[0064] Materials and methods

[0065] Fly Genetics

[0066] Fly strains were maintained on standard medium. All genetic experiments were performed at 25° C. To generate homozygous ph.sup.505 MARCM clones, virgin females of ph.sup.505 FRT19A/FM7 act-GFP were crossed with tub-Gal80 FRT19A; ey-flp act>STOP>Gal4 UAS-GFP males.

[0067] To measure the expression of the IncRNA during development, we collected larvae and pupae (w.sup.1118) at different developmental time points and extracted RNA for qPCR analyses. For larvae, third instar larvae staying in the food were collected as late larvae (LL); and wandering larvae were larvae leaving the food and wandering in the vial. For pupae, white pupae were collected and aged in a separate plate for 1, 2, 3, 24, 48, 72, and 96 hours.

[0068] The following fly strains were used in this study: (1) Ore-R, (2) w.sup.1118, (3) ph505 FRT19A/FM7 act-GFP, (4) tub-Gal80 FRT19A; ey-flp act>STOP>Gal4 UAS-GFP.

[0069] Transplantation

[0070] For transplantation experiments 4-6 days old adult w.sup.1118 females were used as hosts (n>20 for each transplantation). The host flies were immobilized on an ice-cold metal plate and stuck on a piece of double-sided sticky tape, with their ventral sides up. The dissected tumor tissue was cut into small pieces of similar size and each piece was transplanted into the abdomen of one host using a custom-made glass needle. All transplantation was made under a GFP microscope to ensure labelled cells were injected into the hosts. After transplantation, host flies were allowed to recover at room temperature for 1-2 hours in fresh standard Drosophila medium before transferred to and maintained at 25° C.

[0071] To test the toxicity of the let-A medium on in vivo growing tumors, host flies carrying 1-week-old transplanted ph.sup.505 tumors were dissected and the tumors were incubated with either control medium (mCherry medium) or let-A medium for 24 hours. The tumors were then cut into small pieces and re-transplanted into new host flies.

[0072] ph.sup.505 Cell Line Generation

[0073] In order to establish a ph.sup.505 cell line, two to three 1-week old transplanted ph.sup.505 tumors were isolated from the host flies and dissected into small pieces in sterilized PBS following 3 times wash with Shields and Sang M3 Insect medium (US Biological) containing

[0074] Penicillin/streptomycin(P/S). The cells were resuspended in 1 ml of M3 (P/S) medium and plated into the 96 well plate 200 μl per well. After the stable cell growth, single cell line was isolated using Terasaki plate (Greiner Bio-One). To confirm the cell line, genomic DNA was isolated and sequence analysis performed.

[0075] RNA In Situ in Salivary Glands

[0076] For single molecule FISH analysis (Fluorescence in situ Hybridization) a set of oligonucleotides spanning the first intron of let-7-C was designed using the Stellaris Probe Designer software (Biosearch Technologies). The oligonucleotides were ordered from Biosearch Technologies labeled with Quasar-670.

[0077] RNA FISH was preformed following the Stellaris protocol for suspension cells with minor modifications. Briefly, salivary glands from white pupa were dissected and washed in PBS and fixed with 4% formaldehyde in PBS for 10 min at room temperature. After washing with PBS samples were incubated with 70% EtOH for 24 hours at 4° C. Then, samples were washed in washing buffer (2×SSC, 10% formamide) at room temperature. For hybridization 125 nM of the probe set in hybridization buffer (Biosearch Technologies) was added and incubated overnight at 37° C. The next day, samples were washed twice for 30 min at 37° C. with washing buffer, the second wash containing 500 ng/ml DAPI (Sigma-Aldrich). After one wash with PBS samples were mounted with Vectashield Mounting Medium (Vectorlabs).

[0078] Cell Culture and Treatments

[0079] Drosophila Clone 8 (CI.8) and ph.sup.505 cell lines were maintained at 25° C. in Shields and Sang M3 Insect medium (US Biological), supplemented with 2% Fetal Bovine Serum (FBS) (PAN Biotech), 2.5% fly extract, 5 μg/ml human insulin (Sigma), 100 U/ml penicillin and 100 μg/ml streptomycin (Gibco, Life Technologies). S2 cells were cultured in Schneider's medium (Gibco, Life Technologies) supplemented with 10% FBS (PAN Biotech) at 25° C. Spodoptera frugiperda Sf21 cells (Clontech) were propagated in Grace's medium (Gibco, Life Technologies) with 10% FBS (PAN Biotech) at 27° C. All mammalian cell lines except for the mesenchymal stem cells were grown in Dulbecco's Modified Eagle's Medium (DMEM) high glucose (Sigma) supplemented with 10% FBS (Sigma) and 2 mM L-glutamine (Gibco). For HEK-Dual hTLR3 cells (InvivoGen) the growth medium was additionally supplemented with 100 μg/ml Normocin, 100 μg/ml Hygromycin B and 50 μg/ml Zeocin (all from InvivoGen). Primary human bone marrow-derived mesenchymal stem cells were obtained from ATCC (PCS-500-012). They were maintained according to manufacturer's instructions and differentiated as previously described (Almalki, S. G. & Agrawal, D. K. (2016). Effects of matrix metalloproteinases on the fate of mesenchymal stem cells. Stem Cell Res Ther. 7(1): 129).

[0080] HEK293T cells were transfected using Fugene HD (Promega) following manufacturer's instructions. After two days, transcription was induced with 1 μg/ml tetracycline (Sigma) and cell viability was measured after overnight incubation.

[0081] SEAP activity was detected using QuantiBlue (InvivoGen) and the absorbance quantified on a Tecan Infinite M1000 PRO microplate reader at 650 nm.

[0082] For the ecdysone time course, cells were treated one day after seeding with 5 μM 20-Hydroxyecdysone (Sigma) and incubated for the specified time before RNA was extracted.

[0083] To induce apoptosis, ph.sup.505 cells were treated twice with UV-C (90 mJ/cm2, 254 nm). For the UV treatment, cells were washed in PBS and irradiated with UV light in PBS, which was afterwards replaced by medium.

[0084] For the RNase and DNase treatment 100 μg/ml RNase mix (Roche) or 100 U/ml DNase I (Roche) and 100 μM AgNO3 were added together to the transduced cells. After 3 hours cell viability was measured using alamarBlue.

[0085] The following inhibitors were used: Apoptosis inhibitors: Pan-Caspase Inhibitor Z-VAD-FMK (Enzo Life Sciences) 50 μM; Caspase 8 Inhibitor Z-IETD-FMK (Enzo Life Sciences) 15 μM; Clusterin (secretory form, human recombinant, Enzo Life Sciences) 0.5 μM; oxidative stress was reduced with 1 mM Trolox (6-Hydroxy-2,5,7,8-tetramethylchromane-2-carboxylic acid, Sigma). Toll signaling pathway inhibitors: TLR3/dsRNA Complex Inhibitor (Sigma) 30 μM; MyD88 inhibitor T6167923 (Anawa) 50 μM; TBK1 inhibitor MRT67307 (Sigma) 2 μM; and the NF-kB inhibitors Rolipram (Abcam) 1 μM; pyrrolidine dithiocarbonate (PDTC, Sigma) 25 μM. For all the inhibitor experiments, cells were pretreated one hour with the respective inhibitor before induction or addition of the extracted medium. For induction, the cell viability was determined after three hours, for extracted medium treatment after one hour, for Drosophila cell lines and for mammalian cell lines after overnight incubation.

[0086] For activation of the Toll pathway cells were pretreated for one hour with 10 μg/ml LPS (Sigma) or 5 μg/ml poly(I:C) HMW (InvivoGen). Two hours after induction cell viability was measured with alamarBlue.

[0087] Generation of Recombinant Baculoviruses

[0088] Cloning was performed following the strategy described in Lee et al. (2000). The let-A and I1B fragments were amplified from S2 cell genomic DNA using the Expand Long Template PCR System (Roche) and cloned in pBacPAK8_EGFP under a metallothionein promoter. let-B was cloned from pBacPAK8_EGFP_I1B. Viruses were generated, amplified, analyzed and harvested using the BacPAK Baculovirus Expression System (Clonetech) according to manufacturer's instruction.

[0089] Cloning for Mammalian Cell Expression

[0090] For inducible expression in mammalian cells, let-A, let-B, I1B, mCherry and EGFP were cloned from pBacPAK8 into pSBtet (Addgene) under the control of an inducible TRE promoter.

[0091] For in vitro transcription the fragments were cloned in pGEM-T Easy plasmids under the control of a T7 promoter.

[0092] Transduction of Drosophila cells with Baculoviruses

[0093] Cells were plated one day prior to transduction. For transductions cells were first washed twice with Grace's medium and incubated for two hours at room temperature with the virus inoculum. After removal of the virus, fresh medium was added and cells were incubated at 25° C. for one more day before induction. Unless otherwise specified, transcription of the constructs was induced with 100 μM AgNO3 (Sigma). The conditioned medium was always harvested one day after induction.

[0094] Cell Viability Measurement

[0095] Cell viability was measured after the indicated time using alamarBlue cell viability assay reagent (Thermo Fisher Scientific) following the manufacturer's instructions. Fluorescence at 650 nm was measured with Tecan Infinite M1000 PRO microplate reader.

[0096] RNA Extraction, cDNA Synthesis and Quantitative Real-Time PCR

[0097] RNA from cells or medium was extracted using TRIzol (Invitrogen) following manufacturer's instructions. Reverse transcription was done with the first Strand synthesis kit (Fermentas) using oligo (dT)18 as a primer and qPCR was carried out with LightCycler 96 (Roche) using FastStart Essential DNA Green Master Mix (Roche). Expression levels were normalized to ATPasecf6.

[0098] For miRNA expression analysis, RNA was reverse transcribed using TaqMan miRNA Reverse Transcription kit (Applied Biosystems) and qPCR was performed using let-7 and 2S rRNA TaqMan MicroRNA Assay primer mix (Thermo Fisher Scientific) with the TaqMan Small RNA Assay (Applied Biosystems).

[0099] DNA Isolation

[0100] DNA was purified from conditioned medium by phenol-chloroform extraction.

[0101] Annexin V and CelIROX staining.

[0102] To detect an early stage of apoptosis, cells were incubated one day after transduction with 2.5 mM CaCl2 (Sigma), 5 μl/ml Alexa Fluor-conjugated Annexin V (Biolegend) and 1 μg/ml Hoechst33342 for 10 minutes at room temperature and then induced with 100 μM AgNO3 and imaged on several time points. To detect the presence of ROS, CelIROX DeepRed Reagent (Life Technologies) was used. Before induction, cells were incubated for 30 minutes with 2.5 μM CelIROX reagent. Nuclei were also stained with 1 μg/ml Hoechst33342. Images were taken using a Leica MZ16 FA fluorescent microscope.

[0103] In Vitro RNA Transcription and Purification

[0104] RNA was transcribed from linearized pGEM plasmids using the MEGAscript T7 Transcription kit (Ambion) following the manufacturer's instructions. The IVT products were purified using the MEGAclear kit (Ambion). Concentration and size of the transcripts were determined using TapeStation 4200 (Agilent).

[0105] Active cellular extract was prepared as described (Crevel, G. & Cotterill, S. (1991). DNA replication in cell-free extracts from Drosophila melanogaster. EMBO J. 10, 4361-4369.) with slight modifications. Cells were washed twice with PBS and then 43*10{circumflex over ( )}6 cells were dounced on ice in a dounce homogenizer (Pestle B) in extraction buffer (10 mM HEPES, pH 7.5, 10% v/v ethyleneglycol, 250 mM sucrose, 100 mM NaCl, 2.5 mM MgCl2, 1 mM EDTA, 2 mM DTT, 2 mM ATP, PhosSTOP Phosphatase Inhibitor Cocktail (Roche) and cOmplete™ Protease Inhibitor Cocktail (Roche)). The lysate was centrifuged for 10 min at 20,000g at 4° C. The supernatant was taken and total protein concentration was determined by Pierce BCA Protein Assay Kit (Thermo Fisher Scientific). 35 μl of extract (about 4 mg/ml protein) was mixed with 375 ng of IVT RNA (diluted in 15 μl extraction buffer), incubated at 25° C. for 15 minutes and then the RNA was purified by TRIzol extraction.

[0106] Biotinylated RNA was produced by in vitro transcription in the presence of Desthiobiotin-16-UTP (TriLink Biotechnologies). The resulting transcripts were incubated with active cellular extract. To isolate the biotin labelled RNA, the mixture was incubated with 20 μl of Dynabeads MyOne Streptavidin T1 (Invitrogen) for 15 minutes at 25° C. Afterwards, another 20 μl beads were added and again incubated 15 minutes at 25° C. Next, the beads were washed twice with extraction buffer and eluted in elution buffer (extraction buffer with 2 mM avidin (IBA)) at 25° C. for 15 minutes. The eluates and flow-through were purified by TRIzol extraction.

[0107] The purified RNA was sequenced by first depleting ribosomal RNA with the Ribo-Zero Gold rRNA Removal Kit and then subjecting the remaining RNA to the Illumina TruSeq Stranded Library Prep Kit. The resulting libraries were sequenced on a NextSeq500 at paired end 38.

[0108] Immunohistochemistry and Antibodies

[0109] Tumours were fixed in 2% paraformaldehyde (in 1×PBS) for 25 minutes at room temperature, and washed several times in PBST (1×PBS with 0.5% Triton X-100). Tumours were incubated overnight with primary antibodies at 4° C., followed by several washes at room temperature, incubated with secondary antibodies at 4° C. overnight. After several washes, samples were incubated with DAPI (1:200 in PBST) at room temperature for 20 minutes, then mounted in Vectashield and stored at −20° C. before imaging.

[0110] Primary antibody used in this study was: chicken anti-green fluorescent protein (GFP) (1:1000; Abcam ab13970); Secondary antibodies were: Alexa 488-conjugated anti-chicken (1:500; Molecular Probes).

[0111] Microscopy

[0112] Immunofluorescent images were recorded on a Leica TCS SP8 confocal microscope. Adult flies with transplanted tumours were taken on a Nikon SMZ1270 microscope. Images were processed using ImageJ, Imaris, Photoshop, and Adobe Illustrator.

[0113] Transcriptome Analyses

[0114] Transcriptome analyses were performed by mRNA sequencing. RNAs were isolated from the ph.sup.505 culture cells at 16 hours after treated with ecdysone (5 μM 20-Hydroxyecdysone (Sigma)). RNA was extracted using an Arcturus PicoPure RNA Isolation kit (Applied Biosystems), library prepared with SMARTSeq2 NexteraXT and sequenced on an Illumina NextSeq2500 or NextSeq500.

[0115] Bioinformatics Analyses

[0116] Short reads were aligned to BDGP dm6 genome assembly using TopHat 2.0.12 for Bowtie 2.2.3 with parameters “--very-sensitive” and a segment length of 18 for the IVT reads. From the aligned reads, differential expression was called using R 3.5.1 and edgeR 3.24.3.

[0117] RPKM values for external miRNA expression data were retrieved from FlyBase (Release 2018_06).

Example 2

[0118] The let-7 Complex Encodes Two Putative Non-Coding RNAs

[0119] In our previous study, we discovered an endogenous tumor eviction mechanism in Drosophila (Jiang et al., 2018). Ecdysone signaling during metamorphosis, transforms tumorigenic ph.sup.505 cells into non-tumorigenic “metamorphed” ph.sup.505 cells, which become eliminated in adults. The let-7 miRNA and mir-125 were identified as important effectors of the process. The let-7 complex (let-7-C) in Drosophila is located on the second chromosome, the primary transcript encoding, besides let-7 and mir-125 also mir-100, spans -17 kb of genomic region and consisting of three exons and two introns (FIG. 1A). During a detailed transcriptome analysis of the metamorphed ph.sup.505 cells by RNA-seq, to our surprise, we observed many reads mapping to the intronic region of let-7-C (FIG. 1A). These reads were particularly enriched in the 5′ region of the first intron in one group of samples, and in the second half of the first intron in another (FIG. 1A). This indicates that the let-7-C may encode, besides the pri-RNA for the miRNAs, additional non-coding transcripts. To determine if these new non-annotated transcripts are present in other transcriptome database, we searched publicly available RNA-seq data in Flybase, which had been generated from various tissues and cells at different developmental stages.

[0120] Indeed, the intronic sequences can also be observed in a few samples and cell lines (FIG. 1B). Interestingly, the intronic sequences were detected particularly in samples from pupal stages, but not in embryonic, larval, or adult stages, suggesting that the expression of these transcripts might be related to the expression of ecdysone signaling at metamorphosis (FIG. 1B).

[0121] In our previous study, we showed that larval ph.sup.505 mutant cells can continue to proliferate and give rise to neoplastic tumors after being transplanted into adult host flies (Jiang et al., 2018). We isolated the transplanted tumors from adult hosts, dissociated the tumors, cultured the dissociated cells in fly medium, and thereby established a ph.sup.505 primary cell line. To test if ecdysone can induce the expression of the non-coding transcripts in let-7-C, we treated ph.sup.505 cell culture with ecdysone overnight, isolated the polyadenylated RNAs, and performed transcriptome analysis by RNA-seq. Similarly, this analysis showed many reads mapping to the second half of the first intron (FIG. 1C), suggesting ecdysone signaling can induce the expression of certain non-coding transcripts. Furthermore, an analysis of modENCODE data for RNA Pol II ChIP of adult heads and Kc167 cells reveals multiple regions with strong Pol II localization within the first intron (FIG. 1C). These observations suggest the let-7-C locus is more complex and encodes at least two IncRNA transcripts in addition to the primary transcript for the three miRNAs (FIG. 1C). Based on the Pol II localization sites, as well as the sequencing reads, we named one IncRNA let-A which consists of the first exon and the first half of the intron, and the other transcript let-B which consists of sequences in the second half of the first intron (FIG. 1C). Interestingly, three previously discovered ecdysone responsive elements (EcRE), which are required for the ecdysone-induced expression of let-7-C, are all located in the let-B transcript (FIG. 1C).

[0122] In Vivo Expression of the Two IncRNAs During Development

[0123] To further examine if the two IncRNAs in the let-7-C are expressed in vivo, we treated ph.sup.505 culture cells with ecdysone, collected RNAs at several time points, and quantified the expression of several regions within the first intron using different primer pairs by qPCR. Compared to the untreated ph.sup.505cells, the expression of both transcripts could be detected after exposure to ecdysone (FIG. 2A). The expression of let-B transcript was the first to be observed one day after ecdysone treatment, while let-A remained at basal levels (FIG. 2A). The expression level of let-B was similar for the first two days, and slightly increased in day three and four (FIG. 2A). On the other hand, the expression level of let-A was lower than let-B during the first two days after ecdysone treatment, but continuously increased thereafter (FIG. 2A). This shows that the IncRNA let-B, containing all three EcREs, is the first to be expressed in response to ecdysone and let-A is expressed at a later time point.

[0124] Next, we analyzed how the two IncRNAs are expressed during fly development. As the expression of the let-7-C locus is regulated by ecdysone signaling at the larva to pupa transition, we collected wild-type larvae and pupae at different developmental time points during the larva to pupa transition and after pupal formation, extracted RNA, and performed qPCR for different regions in the let-7 intron (FIG. 2B). At late 3.sup.rd larval instar (LL) and wandering larval (WL) stage, both of the two IncRNAs were expressed at a basal level (FIG. 2B). In the white pupae (WP), expression of both let-A and let-B started to increase (FIG. 2B). Similar to the ecdysone-treated culture cells, the fold-change of let-B expression was higher than that of let-A in the beginning, suggesting let-B was the first to be expressed (FIG. 2B). During the first 3 hours after pupae formation (APF) (P1-P3), the expression of let-B did not increase. In contrast, let-A expression continued to increase during the early hours of pupariation (FIG. 2B). The expression of both IncRNAs decreased at 24 hours APF, and we could only detect basal levels at 48 hours, 72 hours, and 96 hours APF (FIG. 2B). The expression dynamics of the two IncRNA looks very similar to that of the known ecdysone responsive gene Eip75B (FIG. 2B), but shows significant differences to the expression pattern of the miRNA let-7 (FIG. 2C). In situ hybridization of both let-A and let-B sequences to whole salivary glands of white prepupae show a strong signal at the periphery of the nuclei, reflecting most probably the highly active site of synthesis (FIG. 2D). These results show that the two IncRNAs are expressed transiently during early pupal stage in normal development and exhibit a different expression profile compared to that of the let-7 miRNA.

Example 3

[0125] Effects of Induced Expression of the Two IncRNAs in Culture Cells

[0126] To characterize the potential function of the two IncRNAs, we transduced ph.sup.505 culture cells with a silver-inducible viral vector that expresses either let-A or let-B IncRNA. In addition, we transduced either mCherry as control, or the entire second half of the first intron (named I1B) (FIG. 1C). In untransfected cells (FIG. 3A) or ph.sup.505 cell cultures treated only with silver (FIG. 3B), most cells had either an extended shape and attached to the plate (arrow in 3A), or a round shape and floated in the medium (arrowhead in 3A), with only few dead cells. However, when we induced the expression of let-A, surprisingly almost all the ph.sup.505 cells died within three hours (FIG. 3C, asterisks), with few remaining cells having an abnormal shape (FIG. 3C, dashed arrow). When inducing let-B, I1B, or mCherry in ph.sup.505 cells, no such effect was observed (FIG. 3D-F). We used the alamarBlue assay to quantify cell viability when different RNAs were activated in ph.sup.505 cells. In contrast to the untreated control cells, the cell viability was significantly reduced at three hours after let-A was expressed in ph.sup.505 cells (FIG. 3G). However, the cell viability was not affected when let-B, I1B, or mCherry was induced (FIG. 3G). To test if any of these RNAs might have a long-term effect, we measured the cell viability at three days after induction. As expected, most of the cells were dead when let-A was induced (FIG. 3H). While the expression of let-B only weakly reduced the cell viability, the induction of I1B or mCherry did not affect the cell viability at all (FIG. 3H). These results show that the expression of IncRNA let-A is toxic to the ph.sup.505 culture cells, but let-B is not. As let-A showed such a strong phenotype to cultured cells, we decided to focus on this IncRNA for further investigation.

[0127] Interestingly, the effect of let-A seemed to be cell type specific. When we transduced the RNAs in S2 or Cl8 cells and induced the expression, the cells did not die and the viability was not affected (FIG. 3I).

[0128] To determine how cells died upon let-A expression, we performed immunostaining for the apoptosis marker Annexin V. In the control culture with mCherry expressed only very few dead cells could be observed (FIG. 4A). In contrast, in let-A expressing cultures, as early as 40 minutes after induction, most of the cells were undergoing apoptotic cell death (FIG. 4B). Next, we tested if the cells die due to oxidative stress using the CelIRox assay. Expression of mCherry did not induce any change in oxidative stress in the ph.sup.505 cells (FIG. 4C). However, when let-A was expressed in the ph.sup.505 cells, a significant increase in cellular oxidative stress could be observed (FIG. 4D). We next applied several apoptosis inhibitors against pan-caspases, caspase 8, Bax, or oxidative stress inhibitor to the ph.sup.505 cells during let-A expression, and in all conditions, inhibition of apoptotic cell death resulted in more surviving cells in the culture (FIG. 4E). All together, these results show that expression of let-A in ph.sup.505 cells can induce a rapid apoptotic cell death.

[0129] Cellular Toxicity is Induced by the let-A RNA Molecule

[0130] As only a small subset of ph.sup.505 cells was transduced by the viral vector, it was surprising to observe that almost all the cells in the culture died within a short time after let-A induction (FIG. 3G). We speculated that the transduced cells released some molecules, therefore making the medium toxic, further inducing the death in the untransfected cells in the culture. To test this, we induced the expression of let-A (or mCherry RNA as control) in ph.sup.505 cells, collected the medium (henceforth called let-A/medium or mCherry/medium), and added the collected medium to another plate of untreated ph.sup.505 cells. Adding the let-A/medium led to the death of most ph.sup.505 cells within the hour (FIG. 5A). Conversely, adding mCherry/medium had no effect (FIG. 5B). To test whether the medium toxicity was due to cell apoptosis in general, we killed untreated ph.sup.505 cells by UV, collected the medium, and added it to a new plate of ph.sup.505 cells. Unlike the let-A/medium, the UV/medium had no effect on the ph.sup.505 cells (FIG. 5C), indicating the toxicity of the medium is due to the induced expression of let-A.

[0131] To characterize the effector molecule in the medium, we induced the expression of let-A in ph.sup.505 cells and collected the medium after most cells had died. We next isolated either RNA or DNA from the medium, purified twice by Trizol extraction, and added the purified fractions to ph.sup.505 cells. The purified RNA or DNA from the mCherry/medium did not show any effect to ph.sup.505 culture cells (FIG. 5D, E). However, the purified RNA from let-A/medium was able to kill all the cells (FIG. 5F), whereas DNA was not (FIG. 5G), indicating that the toxicity was mediated by RNA molecules. To further confirm this result, we added RNase or DNase in the medium during the induction. Clearly, adding RNase to the medium increased the cell viability but DNase did not, confirming the effector to be an RNase-sensitive molecule (FIG. 5H). Furthermore, cell viability tests showed that the toxicity was due to the specific expression of let-A, because purified RNA from the medium of other RNAs (let-B, I1B, or mCherry) would not kill ph.sup.505 cells (FIG. 5I). The toxicity of the RNA was also cell-specific similarly to the let-A transductions as there was no effect when S2 cells were treated with the purified RNA from let-A medium (FIG. 5J).

[0132] Cell Toxicity can be Induced by In Vitro Transcribed Full Length Let-A RNA

[0133] To further test if the toxicity was caused by let-A itself, we in vitro transcribed (ivt) sense and antisense let-A or mCherry, and tested their toxicity on ph.sup.505 cells. When ph.sup.505 cells were treated with isolated ivt let-A RNA, the viability was not affected. However, when the ivt let-A RNA was first incubated with cell extracts, then added to ph.sup.505 cells, the cells could be killed (FIG. 6A). In addition, only RNA with the sense sequence could kill the cells, but RNA with the antisense sequence could not (FIG. 6A). Moreover, when ivt let-A RNA was fragmented by sonication before incubation and application to ph.sup.505 cells, it was no longer able to kill ph.sup.505 cells (FIG. 6B). These results indicate the effector molecule is let-A, however, requiring further processing and/or modifications to induce the cell toxicity.

[0134] To further confirm this, we in vitro transcribed biotinylated let-A, incubated with cell extracts, and isolated the RNA by biotin-streptavidin affinity purification. The purified let-A RNA showed stronger toxic effect on ph.sup.505 cells compared to the input RNA (FIG. 6C). In contrast, neither I1B nor mCherry RNA that were in vitro transcribed and processed by the same procedure was able to kill the ph.sup.505 culture cells (FIG. 6C). We next did total RNA-seq with the affinity purified RNA. As shown in FIG. 6D, after affinity purification let-A sequence was enriched compare to the input sample. Among the RNAs with the highest number of sequencing counts, let-7-C had the most sequencing reads (FIG. 6D).

[0135] As let-A has a length of ˜6 kb and needs further modifications and/or processing to become active, we tried to identify essential regions or short sequences within full length let-A. We first generated a series of deletion constructs starting from the 3′ end of le-A, and transfected ph.sup.505 cells with viral vectors expressing each single construct (FIG. 6E, r1-r16). In contrast to let-A full length RNA, all the deletion constructs showed a gradually reduced toxicity and were able to kill the cells only three days after induction (FIG. 6F). From the RNA-seq analysis (FIG. 6D), we observed several regions within let-A where short sequencing reads were enriched (FIG. 6E, IVT let-A Seq). Based on these sequencing results, we next split full length let-A into three shorter fragments (let-Ap1-p3) (FIG. 6E). Again, when these shorter fragments were expressed in ph.sup.505 cells, all three shorter RNAs showed reduced toxicity (FIG. 6G). Only when two or all three shorter RNAs were expressed together, ph.sup.505 cells could be killed as efficiently as the full length let-A (FIG. 6G). Last we tested constructs that only express single short sequences from the most enriched regions in the sequencing results (FIG. 6E). When induced in ph.sup.505 cells, all these short sequences also showed significantly reduced activity to kill the cells, except when combined (all mixed) (FIG. 6H). Together these experiments show that multiple regions within let-A have an additive effect towards toxicity and the full-length sequence is required to act with maximum efficiency. Example 4

[0136] ph.sup.505 Tumor Tissue can be Extinguished by Let-A/Medium and Purified let-A RNA

[0137] Since ph.sup.505 culture cells can be killed by the let-A/medium and by purified RNA, we hypothesized that the RNA may also be toxic to in vivo growing tumors. We first transplanted imaginal discs containing ph.sup.505 mutant clones into adult host flies and collected the tumors growing in those flies. We dissected host flies carrying 1-week-old tumors and incubated the tumors with either control medium (mCherry medium) or let-A/medium for 24 hours. The tumor tissue became dissociated after incubation with let-A/medium (FIG. 7A). In contrast, the cells in the tumor incubated in the control medium still form tumor spheres and the bulk of tumor tissue does not show visible changes (FIG. 7B). In addition, after re-transplantation into adult host flies, let-A/medium-incubated tumors were no longer able to grow in host flies (FIG. 7C), but the control medium-incubated tumors still gave rise to the formation of tumors (FIG. 7D). These results show that the let-A/medium is also toxic to in vivo formed tumors.

[0138] Next, we tested if RNA purified from the let-A/medium has the same effect. Similarly, tumors incubated with the let-A/medium-purified RNA became dissociated (FIG. 7E) and could not form tumors after re-transplantation. In contrast, tumors incubated overnight with RNA from control medium remained tumorigenic and were able to grow after re-transplantation (FIG. 7F).

Example 5

[0139] Let-A RNA Exerts its Toxic Effect also on Mammalian Cells

[0140] As the IncRNA let-A can induce rapid apoptosis in Drosophila cancer cells, it is intriguing to test if this RNA has the same effect on mammalian cells. Therefore, we transfected HEK293T cells with Drosophila let-A and measured the cellular viability. To our surprise, Drosophila let-A was also toxic to the HEK293T cells and most cells died after overnight incubation (FIG. 8A). Furthermore, the RNA fraction purified from let-A/medium was also able to kill the HEK293T cells, but RNAs from the I1B or mCherry/medium could not (FIG. 8B). We next treated several other mammalian cell lines with RNAs purified from the let-A/medium, including HeLa, C2C12 myoblast, Mcf7, BT8A, and K562 cells. Indeed, purified RNA was able to kill all those cell lines (FIG. 8B) with RNAs purified from I1B/medium or mCherry/medium not having the same effect (FIG. 8B). These results show that Drosophila let-A has an evolutionarily conserved oncolytic function active also in mammalian cells.

Example 6

[0141] The Toll Signaling Pathway is Activated During the Cellular Response to Let-A

[0142] To uncover the underlying mechanism in both Drosophila and mammalian cells, we investigated what signaling pathways might be involved during this process. To test if the Toll signaling pathway is required for the let-A induced cell death, we applied several inhibitors that targeted different components in ph.sup.505 cells (FIG. 10A). When the receptor TLR3 was blocked, an increase in cell viability was observed (FIG. 9A). When inhibitors against more downstream components were applied, including the adaptor protein MyD88 and the kinase TBK1, we observed a further increase in cell viability (FIG. 9A). In addition, we used two inhibitors for the most downstream transcription factor NF-κB, which also resulted in a better cell survival (FIG. 9B). Next, we used the same inhibitors to block Toll signaling in mammalian HEK293T cells. Similarly, the treatment could inhibit let-A induced toxicity in the HEK cells and significantly increase the cell viability (FIG. 9C).

[0143] We next used a HEK-Dual hTLR3 cell line that expresses SEAP (Secreted embryonic alkaline phosphatase) as a reporter for Toll signaling. The SEAP activity was low in the untreated condition, but increased upon treatment with Poly(I:C) (polyinosine-polycytidylic acid), a known inducer of the Toll signaling pathway (FIG. 9D). Treating HEK-Dual hTLR3 cells with Poly(I:C) could increase the SEAP activity in these cells (FIG. 9D). When HEK-Dual hTLR3 cells were treated with mCherry/medium, we did not observe an increase in SEAP activity (FIG. 9D). However, treating cells with let-A/medium could increase SEAP activity in the cells (FIG. 9D), indicating that Toll signaling was induced. Furthermore, when the Toll pathway inhibitors were added, SEAP activity was strongly reduced in both Poly(I:C) treated and let-A treated cells (FIG. 9D).

[0144] Lastly, we pre-treated ph.sup.505 cells with LPS (lipopolysaccharide), which is an inducer of Toll signaling but does not cause cell death (FIG. 9E), to sensitize the cells to other activators of Toll signaling. When mCherry was induced in LPS pre-treated ph.sup.505 cells, it did not have any effect (FIG. 9E). In contrast, when let-A was induced in LPS pre-treated ph.sup.505 cells, it killed the cells even faster and all cells died within one hour (FIG. 9E). Similarly, Poly(I:C) pre-treated HEK cells also became more sensitive to let-A and showed a further reduced viability compared to cells untreated with Poly(I:C) (FIG. 9F). Together these results show that Toll signaling pathway is required for let-A induced cell death in both Drosophila and human cancer cells.

Example 7

[0145] Generation and Analysis of Mutagenized Sequences

[0146] For the 80% let-A construct (letA80) 20% of let-A was removed from the 3′ end by PCR. For letA80-H part of HygR and for letA80-M part of mCherry was fused to letA80 on the 3′end to keep transcript size at around 6 kb. Both constructs were cloned into a tetracycline inducible CMV-driven expression plasmid.

[0147] For the mutagenized let-A variant, mutagenesis was performed manually in a semi-random fashion. Briefly, let-A was divided into three fragments (Let-A 5′ 1-1913, 1914-3860, 3861-5947) and bases were manually semi-randomly exchanged while respecting local intramolecular base pairings. To enable synthesis, introduced bases were preferably G/C and fragment size was kept around 2000 bases. Each fragment was extended by 60 bp to overlap with the neighboring fragment. Synthesis was performed by IDT (Integrated DNA Technologies). The DNA fragments and a tetracycline inducible CMV-driven expression vector were assembled using HiFi DNA Assembly Master Mix (NEB E2621). After the purification, all three vectors were used for T-REx HEK293T cell transfection. After overnight induction with 1 μg/mL tetracycline (Sigma) cell viability was determined using alamarBlue Cell Viability Reagent (ThermoFisher).