Combination artemisinin and chemiluminescent photodynamic therapy and uses therefor

Abstract

Photodynamic therapy-based methods of treating diseases such as cancer and malaria are disclosed. These methods include administering 5-aminolevulinic acid (ALA), luminol and artemisinin (ART). ART and ALA administered in combination with luminol can kill malaria parasites without host toxicity. In some aspects, the methods further include administration of a luminol enhancer such as 4-iodophenol. The disclosed methods can also be used to remove potential malaria pathogens from the blood supply.

Claims

1. A method of killing intraerythrocytic parasites, the method comprising contacting the parasites with therapeutically effective amount of a combination of 5-aminolevulinic acid or a derivative thereof, luminol or a derivative thereof, and artemisinin or a derivative thereof.

2. The method of claim 1, further comprising administering a therapeutically effective amount of 4-iodophenol.

3. The method of claim 1, wherein the artemisinin or derivative thereof is selected from the group consisting of artemisinin, artesunate, artemether, dihydroartesmisinin, artelinic acid, and artemotil.

4. The method of claim 1, wherein the artemisinin or derivative thereof is dihydroartesmisinin.

5. The method of claim 1, wherein the artemisinin or derivative thereof is administered at a sub-therapeutic dose.

6. The method of claim 5, wherein the sub-therapeutic dose is 10% of the EC.sub.50 of the artemisinin or derivative thereof.

7. The method of claim 1, wherein the luminol or derivative thereof is selected from the group consisting of lumino, luminol sodium salt, luminol hemihydrate, luminol hydrochloride, isoluminol, isoluminol monohydrate, and N-(4-aminobutyl)-N-ethyl-isoluminol (ASEI).

8. The method of claim 1, wherein the 5-aminolevulinic acid or derivative thereof is selected from the group consisting of 5-aminolevulinic acid (5-ALA), methylaminolevulinate, hexylaminolevulinate, 5-ALA esters, and 5-ALA amides.

9. The method of claim 1, wherein the killing of intraerythrocytic parasites is indicative by pyknosis.

10. The method of claim 1, wherein the parasites are drug-resistant.

11. The method of claim 1, wherein the parasites are artemisinin-resistant.

12. A method of treating blood-stage malaria, the method comprising administering to a subject in need thereof, therapeutically effective amount of a combination of 5-aminolevulinic acid or a derivative thereof, luminol or a derivative thereof, and artemisinin or a derivative thereof.

13. The method of claim 12, further comprising administering a therapeutically effective amount of 4-iodophenol.

14. The method of claim 12, wherein the artemisinin or derivative thereof is selected from the group consisting of artemisinin, artesunate, artemether, dihydroartesmisinin, artelinic acid, and artemotil.

15. The method of claim 12, wherein the artemisinin or derivative thereof is dihydroartesmisinin.

16. The method of claim 12, wherein the artemisinin or derivative thereof is administered at a sub-therapeutic dose.

17. The method of claim 16, wherein the sub-therapeutic dose is 10% of the EC.sub.50 of the artemisinin or derivative thereof.

18. The method of claim 12, wherein the luminol or derivative thereof is selected from the group consisting of lumino, luminol sodium salt, luminol hemihydrate, luminol hydrochloride, isoluminol, isoluminol monohydrate, and isoluminol ABEI.

19. The method of claim 12, wherein the 5-aminolevulinic acid or derivative thereof is selected from the group consisting of 5-aminolevulinic acid (5-ALA), methylaminolevulinate, hexylaminolevulinate, 5-ALA esters, and 5-ALA amides.

20. The method of claim 12, wherein the parasites are artemisinin-resistant.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) The application file contains at least one drawing executed in color. Copies of this patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.

(2) FIG. 1A illustrates a schematic representation of heme synthesis and FIG. 1B illustrates the spectrographic analysis of PPIX.

(3) FIG. 2 illustrates parasite growth in the presence or absence of ALA.

(4) FIG. 3A and FIG. 3B illustrate that hemozoin dynamics in ALA-treated parasites can be rapidly ablated by light.

(5) FIG. 4 illustrates the growth of untreated versus ALA-treated parasites over several days with 2-minute daily exposures to broad-wavelength white light on an overhead projector light box.

(6) FIG. 5A, FIG. 5B, FIG. 5C, FIG. 5D and FIG. 5E illustrate that stable disruption of parasite enzymes and the apicoplast do not affect heme biosynthesis from ALA.

(7) FIG. 6 illustrates that biosynthesis of PPIX and coproporphyrin III can be blocked by succinylacetone.

(8) FIG. 7A, FIG. 7B, FIG. 7C and FIG. 7D illustrate that ALA uptake by erythrocytes requires permeability pathways established by Plasmodium infection.

(9) FIG. 8A, FIG. 8B and FIG. 8C illustrate that plasmodium-encoded heme biosynthesis pathway can have no detectable activity during blood-stage infection.

(10) FIG. 9A and FIG. 9B illustrate chemiluminescence-based photodynamic therapy for treatment of bloodstage malaria.

DETAILED DESCRIPTION OF THE INVENTION

(11) The present inventors describe methods of photodynamic therapy for use against diseases, such as and without limitation, cancer and malaria. In various embodiments, the photosensitizer can be 5-aminolevulinic acid. In some embodiments, photodynamic therapy can comprise administration of artemisinin (ART) or a therapeutically acceptable salt or derivative thereof, luminol and 5-aminolevulinic acid (ALA) for chemiluminescence therapy. In some embodiments, 4-iodophenol can be administered in addition to ART, luminol and ALA. Without being limited by theory, treatment with ALA, a heme biosynthesis intermediate, can lead to cellular accumulation of protoporphyrin IX (PPIX). In turn, PPIX can generate cytotoxic oxygen radicals when illuminated. In various configurations, illumination can be from an external light source or light from a chemiluminescent compound. In various embodiments, the present teachings include the use of ALA treatment as a photosensitizer, luminol as the CL agent, and ART as the activator of chemiluminescence by luminol, without or with the enhancer 4-iodophenol. In various configurations, methods of the present teachings can be used to treat malaria, clean ex vivo blood of malaria parasites, or to treat cancer.

(12) The present inventors disclose photodynamic treatment strategies that include photosensitizing Plasmodium parasites with ALA and then killing them with light. The present inventors have developed treatment methods which, in various embodiments, can circumvent conventional PDT requirements for external light and can ablate parasite growth. In various configurations, these methods can include luminol-based chemiluminescence, stimulated by combinatorial delivery of artemisinin, e.g., low-dose artemisinin. In various embodiments, these methods can include administration of ALA, luminol and artemisinin (or a clinical derivative) for treating malaria. In various configurations, multidrug-resistant parasites can remain susceptible to this photodynamic strategy. In some configurations, a photodynamic strategy disclosed by the inventors can have an additional advantage of exploiting host enzyme activity refractory to development of resistance-conferring mutations.

(13) In various embodiments, the use of artemisinin to stimulate intracellular light emission by luminol for ALA-based photodynamic therapy can be applicable to treatment of a deep-tissue cancer. In some configurations of the present teachings, such as when poor accessibility to external light can limit current PDT approaches for cancer therapy, artemisinin (ART) administration in combination with ALA and luminol can synergistically provide cancer chemotherapy which can be unexpectedly powerful in its beneficial effects.

(14) Abbreviations: ALA aminolevulinic acid ALAD ALA dehydratase ALAS ALA synthase ART artemisinin CL-PDT chemiluminescence-based photodynamic therapy cobA uroporphyrinogen III methyltransferase CPO coproporphyrinogen III oxidase DDD DHFR degradation domain DHA dihyroartemisinin FC ferrochelatase IPP isopentenyl pyrophosphate NPP new permeability pathways PBGD porphobilinogen deaminase PDT Photodynamic therapy PPIX protoporphyrin IX TMP trimethoprim
Methods

(15) The methods and compositions described herein utilize laboratory techniques well known to skilled artisans, and can be found in laboratory manuals such as Sambrook, J., et al., Molecular Cloning: A Laboratory Manual, 3rd ed. Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y., 2001; Spector, D. L. et al., Cells: A Laboratory Manual, Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y., 1998; Nagy, A., Manipulating the Mouse Embryo: A Laboratory Manual (Third Edition), Cold Spring Harbor, N.Y., 2003; Harlow, E., Using Antibodies: A Laboratory Manual, Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y., 1999; and Carruthers, W., and Coldham, I., Modern Methods of Organic Synthesis (4th Edition), Cambridge University Press, Cambridge, U.K., 2004. Methods of administration of pharmaceuticals and dosage regimes, can be determined according to standard principles of pharmacology well known skilled artisans, using methods provided by standard reference texts such as Remington: the Science and Practice of Pharmacy (Alfonso R. Gennaro ed. 19th ed. 1995); Hardman, J. G., et al., Goodman & Gilman's The Pharmacological Basis of Therapeutics, Ninth Edition, McGraw-Hill, 1996; and Rowe, R. C., et al., Handbook of Pharmaceutical Excipients, Fourth Edition, Pharmaceutical Press, 2003. As used in the present description and the appended claims, the singular forms a, an and the are intended to include the plural forms as well, unless the context indicates otherwise. All publications cited herein are hereby incorporated by reference, each in their entirety.

(16) Materials

(17) All reagents were of the highest purity commercially available. Succinylacetone, 5-aminolevulinic acid, trimethoprim, furosemide, saponin, isopentenyl pyrophosphate, doxycycline, luminol, and dihydroartemisinin were purchased from Sigma-Aldrich Co., St. Louis, Mo. 5-[.sup.13C4]aminolevulinic acid and .sup.13C2-glycine were purchased from Cambridge Isotope Laboratories, Inc., Tewksbury, Mass.

(18) Microscopy

(19) Images of live or fixed parasites were acquired on an Axio Imager.M1 epifluorescence microscope (Carl Zeiss Microimaging, Inc.) equipped with a Hamamatsu ORCA-ER digital CCD camera and running Axiovision 4.8 software, as described previously (Sigala, P. A., et al., J. Biol. Chem. 287, 37793-37807, 2012). Live parasite nuclei were stained with 5 M Hoechst 33342 added immediately prior to image acquisition. For photodynamic imaging studies, parasites were cultured in 200-500 M ALA in the absence or presence of 50 M succinylacetone for 6-12 hours prior to visualization. Hemozoin movement in parasite digestive vacuoles were imaged by acquiring 10-20 sequential frames at 1 second intervals on the bright-field channel. Images were cropped and superimposed in Adobe Photoshop and exported as movie files with a 0.1 second frame delay. Immunofluorescence images were acquired by fixing and staining parasites as previously described (Tonkin, C. J., et al., Mol. Biochem. Parasitol 137, 13-21, 2004; Ponpuak, M., et al., Mol. Microbiol. 63, 314-334, 2007). Electron microscopy images were obtained as previously described (Beck., J. R., et al., Nature 511, 592-595, 2014). Uninfected erythrocytes were washed and resuspended in 1 cytomix (120 mM KCl (anhydr); 0.15 mM CaCl2; 10 mM KH2PO4 (anhydr); 25 mM HEPES; 2 mM EGTA; 5 mM MgCl2; Adjust pH to 7.6 with KOH) containing 500 M ALA, electroporated in a manner identical to parasite transfections (see below), washed in PBS, incubated overnight at 37 C., and imaged as described above for live parasites. Images acquired on different channels for common samples were processed with identical brightness and contrast settings.

(20) Parasite Growth Analysis

(21) Parasite growth was monitored by diluting asynchronous parasites to 0.5% parasitemia and allowing culture expansion with daily or twice daily media changes. Parasitemia was measured daily by diluting 10 l of each resuspended culture in 200 l acridine orange (1.5 g/ml) and analyzing by flow cytometry, as previously described (Muralidharan, V., et al., Nat. Commun. 3, 1310, 2012). To assess the light sensitivity of ALA-treated parasites, asynchronous parasites were cultured in 200-500 M ALA in the absence or presence of 50 M succinylacetone and subjected to 2-5 minute daily exposures to broad wavelength white light on an overhead projector. Daily parasitemia measurements were plotted as a function of time and fit to an exponential growth equation using Graph Pad Prism 5.0 (Graph Pad Software, Inc., La Jolla, Calif.).

(22) For chemiluminescence experiments, asynchronous parasites were diluted to 0.5% parasitemia and incubated 50-100 M ALA and 50 M succinylacetone for 8 hours. After 8 hours, parasite media was changed to also include 750 M luminol and 500 pM dihydroartemisinin in the indicated combinations. Parasite cultures were allowed to expand over 5 days, with twice-daily (7 am and 4 pm) media changes in the indicated combinations. Parasitemia was measured daily as indicated above. Experiments were performed using 3D7 (drug sensitive) parasites, Dd2 (multidrug resistant) parasites (Sidhu, A. B. S., et al., Science 298, 210-213, 2002), and a clinical isolate (MRA-1241; Ariey, F. et al., Nature 505, 50-55, 2014) bearing the I543T mutation in the Kelch-13 gene locus.

(23) Parasite Strains, Culture, Genetic Modification, and Transgene Expression

(24) Parasite culture and transfection were performed as previously described (Sigala, P. A., et al., J. Biol. Chem. 287, 37793-37807, 2012). Cloning was performed using either restriction endonuclease digestion and ligation or the In-Fusion system (Clontech Laboratories, Inc., Mountain View, Calif.).

(25) For episomal expression of P. falciparum ALA dehydratase (PF3D7_1440300) fused to a C-terminal GFP tag, cDNA encoding the complete ALAD gene (exons only) was RT-PCR amplified from total parasite RNA using the Superscript III system (Life Technologies, Grand Island, N.Y.) and primers 5-CACTATAGAACTCGAGATGTTAAAATCAGATGTAGTGCTTTTATTGTATATAC-3 (SEQ ID NO:7) and 5-CTGCACCTGGCCTAGGTAGAGTTAATTCTATATTAAAATTATTATTTGAATTATCATC-3 (SEQ ID NO:8), digested with XhoI/AvrlI, and ligated into the XhoI/AvrlI sites of a digested pTEOE vector that was identical to a previously described pTyEOE vector (Beck, J. R., et al., Nature 511, 592-595, 2014) except that the pTEOE plasmid contained human DHFR in place of yeast DHOD as the positive selection marker. Plasmid-based expression of the ALAD-GFP fusion was driven by the HSP86 promoter. This plasmid (50 g) was co-transfected into 3D7 parasites along with plasmid pHTH (10 g) for transient expression of the piggyback transposase that mediates integration of the pTEOE plasmid into the parasite genome (Balu, B., et al., Proc. Nat'l Acad. Sci. USA 102, 16391-16396, 2005). Parasites were selected (Mamoun, C. B., et al., Proc. Nat'l. Acad. Sci. USA 96, 8716-8720, 1999) with 5 nM WR.

(26) For episomal expression of Propionibacterium freudenreichii (shermanii) uroporphyrinogen III methyltransferase (cobA) (Genbank: CBL55989.1) targeted to the parasite apicoplast, the cobA gene was PCR-amplified from plasmid pISA41728 using the primers 5-ACGATTTTTTCTCGAGATGACCACCACACTGTTGCCCGGCACTGTC-3 (SEQ ID NO: 1) and 5-CTGCACCTGGCCTAGGGTGGTCGCTGGGCGCGCGATGG-3(SEQ ID NO: 2), digested with XhoI/AvrlI, and ligated into the XhoI/AvrlI-cut pTEOE vector described above. An insert encoding the P. falciparum acyl carrier protein (ACP) leader sequence (residues 1-60) with 5- and 3-XhoI sites, previously PCR-amplified from parasite cDNA, 42 was digested with XhoI and ligated into the XhoI-cut cobA/pTEOE vector to generate an in-frame ACPL-cobA-GFP fusion gene. This plasmid was co-transfected with pHTH into 3D7 parasites as described above.

(27) For disruption of the P. falciparum genes encoding PBGD (PF3D7_1209600) and CPO (PF3D7_1142400), primer pairs (PBGD: 5-CACTATAGAACTCGAGGATCATAATAATGATACATTATGTACTATTGGGACATCGTCC-3 (SEQ ID NO: 3) and 5-CTGCACCTGGCCTAGGAACTGCTATAATGCCTTGACCTAAGGCAGGATAAATCAGG-3 (SEQ ID NO: 4); CPO: 5-CACTATAGAACTCGAGTTTTTTCAAATATTTATAAAAACAGGAAAAAAGAAGAAAAAATA-3 (SEQ ID NO: 5) and 5-CTGCACCTGGCCTAGGATAACATTTACAATCCTTATTATTATTATTATTATTGTTGATGG-3 (SEQ ID NO: 6)) were used to PCR-amplify 360 bp and 471 bp sequences from the middle of the 1.3 kb PBGD and 1.6 kb CPO genes, respectively. These inserts were cloned by IN-FUSION (PCR based cloning) into the XhoI/AvrlI sites of the pPM2GT vector (Klemba et al. 2004 J. Cell Biol. 164, 47-56), which contains a human DHFR marker for positive selection with 5 nM WR, and plasmids (50 g) were transfected into 3D7 parasites by electroporation. Parasites were subjected to three rounds of positive selection with 5 nM WR, with the first and second selections followed by three-week periods of maintenance in the absence of drug pressure. After the third round of positive selection, parasites were cloned by limiting dilution. Clonal parasites that had integrated the plasmid at the desired locus to disrupt the target genes by single crossover homologous recombination were verified by PCR and southern blot, as previously described (Klemba, M., et al., J. Cell Biol. 164, 47-56, 2004), and retained for further analysis.

(28) For apicoplast disruption experiments, parasites were cultured in 1 jiM doxycycline and 200 M IPP for 7-21 days. After 7 days, genomic DNA was harvested and analyzed by PCR to confirm selective loss of the apicoplast genome.

(29) Analysis of Heme Biosynthesis by .sup.13C-Labeling and Tandem Mass Spectrometry

(30) Parasites were cultured in 200 M 5-[.sup.13C4]-ALA for 12-24 hours, harvested by centrifugation, lysed in 0.05% cold saponin, washed in PBS, and extracted with DMSO. Deuteroporphyrin was added as an internal standard, and extracts were analyzed for .sup.13C-labeled heme, PPIX, and CPPIII using a previously published liquid chromatography-multiple reaction monitoring tandem mass spectrometry assay (Ke, H. et al., J. Biol. Chem. 289, 34827-34837, 2014).

(31) Fractionation of Parasite-Infected Erythrocytes

(32) To assess whether parasites could synthesize heme from ALA in the absence of host enzymes in the erythrocyte cytoplasm, parasite-infected red blood cells were lysed with 0.05% saponin (0.2 M filtered), spun briefly and gently to pellet, washed in PBS, and resuspended in 12 ml of RPMI/Albumax (Life Technologies, Grand Island, N.Y.), growth media supplemented with 200 M 5-[.sup.13C4]-ALA. Parasites were incubated overnight at 37 C., harvested by centrifugation, and extracted and analyzed by tandem mass spectrometry as described above.

(33) Preparation of Lysates from Uninfected Erythrocytes

(34) To assess the heme biosynthesis capacity of the erythrocyte cytoplasm, 500 l packed red blood cells (described previously; Sigala, P. A., et al., J. Biol. Chem. 287, 37793-37807, 2012) were lysed in 20 ml of 0.04% saponin/PBS (0.2 M filtered) and centrifuged at 25,000g for 60 minutes to pellet unlysed cells and any organelles. The superficial 15 ml of the lysate supernatant was removed and 0.2 M filtered, supplemented with 200 M 5-[.sup.13C4]-ALA in the absence or presence of 50 M succinylacetone, incubated overnight at 37 C., and analyzed by tandem mass spectrometry as described above.

(35) Chemical Block of Parasite Nutrient Uptake Pathways

(36) The 3D7 parasite line expressing the endogenous HSP101 from its genomic locus and bearing a C-terminal E. coli DHFR degradation domain (DDD) fusion tag was previously published (Beck, J. R., et al., Nature 511, 592-595, 2014). To test whether ALA-uptake by parasite infected erythrocytes depends on parasite-established nutrient acquisition pathways in the host cell membrane, the inventors split a synchronous culture of HSP101-DDD into two populations of late schizonts (purified over a magnetic column) and washed out trimethoprim (TMP) from one of the two cultures. Both cultures (TMP) were permitted to lyse and reinvade fresh erythrocytes overnight. The following morning, parasites were placed in 200 M ALA as early rings, incubated for 8 hours at 37 C., and imaged by live parasite microscopy as described above. Alternatively, asynchronous wild-type 3D7 parasites were incubated in the absence or presence of 100 M furosemide for one hour to block nutrient acquisition pathways, followed by addition of 500 M ALA and further incubation for eight hours. Parasites were then imaged by live parasite microscopy as described above.

(37) Antibodies

(38) The following antibodies were used for immunofluorescence (IFM) and western blot (WB) analysis at the indicated dilutions: goat anti-GFP (Abcam 5450, Abcam, Cambridge, Mass.) (IFM 1:500, WB 1:1000), rabbit anti-ACP44,48 (IFM: 1:500), ALEXA FLUOR 488-conjugated chicken anti-goat (IFM: 1:500), ALEXA FLUOR 555-conjugated donkey anti-rabbit (Life Technologies, Grand Island, N.Y.) (IFM: 1:500), donkey anti-goat-IRDye 800 (Licor Biosciences, Lincoln, Nebr.) (WB: 1:10,000).

EXAMPLES

(39) The following examples are included to demonstrate various embodiments of the present disclosure. It should be appreciated by those of skill in the art that the techniques disclosed in the examples that follow represent techniques discovered by the inventors to function well in the practice of the invention, and thus can be considered to constitute preferred modes for its practice. However, those of skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments which are disclosed and still obtain a like or similar result without departing from the spirit and scope of the invention.

Example 1. Exogenous ALA can be Used to Stimulate Heme Biosynthesis and Photosensitize Parasites

(40) The present inventors investigated whether ALA treatment could serve as a probe of heme biosynthesis activity in Plasmodium-infected erythrocytes by enabling direct visualization of PPIX production and the cellular consequences of light activation. Untreated parasites imaged on an epifluorescence microscope display only background auto-fluorescence from hemozoin crystals in the parasite digestive vacuole (FIG. 2). Parasites grown in 200 M ALA, however, display bright red fluorescence distributed throughout the infected erythrocyte, as expected for accumulation of PPIX (additional discussion below).

(41) The cytotoxic effects of light-activating PPIX were readily apparent by monitoring the motion of hemozoin crystals that dynamically tumble within the digestive vacuole of individual parasites. Although the origin and physiological significance of this motion remain unknown, hemozoin dynamics serve as an internal biomarker of food vacuole integrity and parasite viability (Sigala, P. A. and Goldberg, D. E., Annu. Rev. Microbiol. 68, 259-278, 2014). Hemozoin motion in untreated parasites is unaffected by a several second acquisition of a fluorescent image whose excitation wavelength overlaps that of PPIX. In contrast, the hemozoin dynamics in ALA-treated parasites are rapidly ablated by light (FIG. 3A). FIG. 3A depicts bright field and fluorescence microscopy images of untreated and 200 M ALA-treated parasites. Fluorescence images were acquired with a Zeiss filter set 43 HE (excitation 537-562 nm, emission 570-640 nm). Ultrastructural analysis by electron microscopy revealed a loss of electron density within the digestive vacuole of ALA-treated and illuminated parasites, illustrating disruption of the food vacuole membrane and outward diffusion of the vacuolar protein contents. FIG. 3B depicts Transmission electron microscopy images of untreated (left) and 500 M ALA-treated (right) P. falciparum-infected erythrocytes after light exposure on an overhead projector lightbox. The white arrow identifies the digestive vacuole. Scale bar equals 1 m. These changes indicate a photodynamic mechanism of PPIX-mediated generation of reactive oxygen species that lead to pleiotropic cytotoxic damage, including loss of lipid bilayer integrity.

(42) To test the effects of these changes on bulk parasite culture, the present inventors monitored the growth of untreated versus ALA-treated parasites over several days with 2-minute daily exposures to broad-wavelength white light on an overhead projector light box. FIG. 4 depicts growth of asynchronous 3D7 parasites in the presence or absence of 200 M ALA and 50 M succinylacetone (SA), with 2-minute exposures to white light on an overhead projector on days 0-2. Parasitemia (percentage of total erythrocytes infected with parasites) as a function of time was fit with an exponential growth equation. Whereas untreated parasite cultures grew normally in the presence of light, the growth of ALA-treated cultures was strongly attenuated by light (FIG. 4), consistent with a prior report (Smith, T. G. and Kain, K. C., Journal of Infectious Diseases 190, 184-191, 2004). Microscopic examination by blood smear revealed that ALA-treated cultures predominantly contained pyknotic parasites, indicative of widespread cell death. The photosensitivity of parasite growth in ALA was fully rescued by 50 M succinylacetone, an ALA dehydratase (ALAD) inhibitor shown in previous work to substantially reduce PPIX biosynthesis from ALA in parasite-infected erythrocytes (Ke, H. et al. J. Biol. Chem. 289, 34827-34837, 2014; Nagaraj, V. A., et al. PLoS Patholg. 9, e1003522, 2013). This chemical rescue confirmed that parasite photosensitivity in ALA requires biosynthetic conversion of ALA to PPIX.

Example 2. Stable Disruption of Parasite Enzymes and the Apicoplast do not Affect Heme Biosynthesis from ALA

(43) Upstream enzymes in the parasite-encoded heme biosynthesis pathway are amenable to genetic disruptions that block production of PPIX from exogenous ALA (FIG. 1A) and thus prevent parasite photosensitivity. The parasite genes encoding the apicoplast-targeted porphobilinogen deaminase (PBGD) and cytosolic coproporphyrinogen III oxidase (CPO) were successfully disrupted using single-crossover homologous recombination to truncate the open reading frame for each gene. Southern blot and PCR analysis confirmed correct integration and gene disruption in clonal parasite lines. These genetic disruptions had no effect on the ability of parasite-infected erythrocytes to incorporate .sup.13C-labelled ALA into heme, PPIX, or coproporphyrinogen III (FIG. 5A), as monitored by a previously developed tandem mass spectrometry assay (Ke, H. et al., J. Biol. Chem. 289, 34827-34837, 2014), and clonal growth of both parasite lines remained fully photosensitive in ALA (FIG. 5B). FIG. 5B depicts growth of asynchronous PBGD (left) and CPO (right) 3D7 parasites in the presence or absence of 200 M ALA, with 2-minute light exposures on an overhead projector on days 0-2. WT growth was fit to an exponential equation.

(44) The present inventors stably disrupted this organelle by treating parasites with doxycycline and isopentenyl pyrophosphate (IPP). Doxycycline inhibits the prokaryotic replication machinery of the apicoplast and prevents organelle segregation, resulting in apicoplast loss and parasite death (Dahl, E. L., et al., Antimicrob. Agents Chemother. 50, 31243131, 2006). The lethal effects of doxycycline, however, can be chemically rescued by IPP, which enables parasites to make essential isoprenoids despite apicoplast disruption and leads to a stable metabolic state in which parasites lack the intact organelle such that nuclear-encoded proteins ordinarily targeted to the apicoplast become stranded in small vesicles. (Yeh, E. and DeRisi, J. L., PLoS Biol. 9, e1001138, 2011). Apicoplast loss in doxycycline and IPP-treated parasites was confirmed with microscopy to verify disrupted targeting of the nuclear-encoded ALAD enzyme (FIG. 5C). FIG. 5C depicts bright field and fluorescence images of live 3D7 parasites expressing ALAD-GFP from a plasmid before or after two-week treatment with IPP and doxycycline. Despite apicoplast disruption, these parasites retained their capacity for heme biosynthesis (FIG. 5D) and remained fully photosensitive in ALA (FIG. 5E). FIG. 5D illustrates LC-MS/MS detection of .sup.13C-labelled heme, PPIX, and CPP in parasites grown in 200 M 5[.sup.13C4]-ALA. Parasites were extracted in DMSO, supplemented with deuteroporphyrin as an internal standard, and analyzed by LC-MS/MS. Integrated analyte peak areas were normalized to PPIX in each sample. RBC: uninfected red blood cells, WT: parental clone 3D7, IPP/dox: isopentenyl pyrophosphate/doxycycline-treated 3D7 parasites. FIG. 5E illustrates growth of asynchronous IPP/doxycycline-treated parasites in the presence or absence of 200 M ALA and 50 M succinylacetone (SA), with 2-minute light exposures on an overhead projector on days 02. These results illustrate that parasite infected erythrocytes have a parallel biosynthetic pathway that bypasses functional disruption of the parasite enzymes targeted to the apicoplast and cytoplasm.

Example 3. Erythrocytes Retain Vestigial Heme Biosynthesis Enzymes with Latent Activity in ALA

(45) In these investigations, red porphyrin fluorescence in ALA-treated intraerythrocytic parasites was not limited to the parasitophorous vacuole but was detectable throughout the erythrocyte cytoplasm (FIG. 3A), as expected for host enzyme activity in this compartment and production of PPIX. To directly test the model that enzymes remaining in the erythrocyte cytoplasm could catalyze PPIX biosynthesis from ALA, the present inventors permeabilized uninfected erythrocytes using the plant-derived detergent saponin, clarified lysates by centrifugation (25,000g for 60 min.) followed by sterile filtration (0.2 M), and then used tandem mass spectrometry to monitor heme and porphyrin biosynthesis from .sup.13C-labelled ALA added to the filtered lysate supernatant. The inventors detected formation of .sup.13C-labelled PPIX and coproporphyrin III (the spontaneous oxidation product of the pathway intermediate coproporphyrinogen III) but not heme, and this biosynthetic activity was fully blocked by succinylacetone (FIG. 6). FIG. 6 depicts LC-MS/MS detection of .sup.13C-labelled PPIX and CPP in erythrocyte lysate supernatants incubated with 200 M 5-[.sup.13C4]-ALA without or with 50 M succinylacetone (SA). Erythrocytes were lysed in 0.04% saponin, centrifuged at 25,000g for 60 min., and 0.2 M syringe filtered prior to ALA addition. These data illustrate that erythrocytes retain a vestigial and partial biosynthesis pathway capable of converting exogenous ALA into PPIX but unable to convert PPIX to heme due to lack of mitochondria and ferrochelatase.

Example 4. ALA Uptake by Erythrocytes Requires New Permeability Pathways Established by Plasmodium Infection

(46) In contrast to parasite-infected erythrocytes, uninfected erythrocytes showed no detectable porphyrin fluorescence in the presence of ALA (FIG. 7A), consistent with reports that the erythrocyte membrane has a general low permeability to small molecule zwitterions (Desai, S. A., et al., Nature 406, 1001-1005, 2000; Kirk, K., et al., J. Biol. Chem. 269, 3339-3347, 1994; Ginsburg, H., et al., Mol. Biochem. Parasitol. 14, 313-322, 1985). FIG. 7A depicts Bright field and fluorescence (Zeiss filter set 43 HE) images of uninfected erythrocytes incubated in 500 M ALA before or after electroporation. Electroporation of uninfected erythrocytes in the presence of ALA resulted in robust intracellular porphyrin fluorescence (FIG. 7A), illustrating that host enzymes have latent biosynthetic activity that requires a mechanism for ALA uptake across the normally impermeable erythrocyte membrane.

(47) Upon invasion, Plasmodium parasites export hundreds of effector proteins into host erythrocytes. These proteins dramatically alter the architecture of the infected erythrocyte and establish new permeability pathways (NPP) that enhance host cell uptake of amino acids and other nutrients from host serum (Spillman, N. J., et al., Ann. Rev. Biochem., 84, 813-841, 2015 expected publication June 2015).

(48) In an investigation of selective uptake of ALA by infected erythrocytes via parasite-dependent nutrient acquisition pathways, the inventors utilized a parasite line in which the export of parasite proteins into host erythrocytes, including establishment of nutrient permeability pathways, can be conditionally regulated with the small-molecule ligand trimethoprim (TMP; Beck, J. R., et al., Nature 511, 592-595, 2014). In these parasites, protein export and NPP mechanisms are retained in the presence of TMP but blocked in its absence. TMP was retained or washed out of a synchronized culture of late schizonts to retain or block protein export, respectively, parasites were allowed to rupture and reinvade new erythrocytes, and then both sets of parasites (i.e., TMP and thus NPP) were incubated in ALA for 8 hours. Whereas TMP-treated parasites with normal protein export and permeability displayed robust PPIX fluorescence indistinguishable from wild-type parasites, parasites whose protein export and establishment of NPP mechanisms were blocked by removing TMP showed no detectable PPIX fluorescence (FIG. 7B). FIG. 7B depicts Bright field and fluorescence images of parasites cultured in 500 M ALA with normal (+TMP) or blocked (TMP) establishment of parasite permeability pathways in the erythrocyte membrane. Infected erythrocyte permeability was modulated using a 3D7 parasite line expressing Hsp101 tagged at its endogenous locus with a trimethoprim (TMP)-dependent destabilization domain. TMP was maintained or washed out from synchronous schizont-stage parasites, which were allowed to rupture and invade new erythrocytes. 500 M ALA was added to both cultures after invasion, and parasites were imaged 8 hours later. Similar results were achieved in wild-type parasites using the small-molecule drug furosemide, which blocks parasite-derived NPP mechanisms directly (FIG. 7C; Staines H M 2004 Mol. Biochem. Parasitol. 133, 315-318). These observations illustrate, without being limited by theory, that ALA can be selectively taken up by infected erythrocytes via parasite-dependent nutrient acquisition pathways and metabolized to PPIX within the erythrocyte cytoplasm (FIG. 7D). The present data further illustrate, without being limited by theory, that PPIX produced by host enzyme activity can then be taken up by parasites and converted to heme by Plasmodium ferrochelatase within the parasite mitochondrion (FIG. 7D).

Example 5. Plasmodium-Encoded Heme Biosynthesis Pathway has no Detectable Activity During Blood-Stage Infection

(49) In these experiments, parasite-infected erythrocytes were biochemically fractionated using saponin to selectively permeabilize host cell membranes while leaving parasite membranes intact. Under these conditions, soluble erythrocyte proteins can be washed away to leave the intact parasite natively embedded within the resulting erythrocyte ghost. Parasites treated in this fashion remain metabolically active for 5-6 hours or longer, retain a transmembrane potential, accumulate fluorescent dyes such as MitaTracker Red (Life Technologies), and carry out DNA synthesis (Cobbold, S. A., et al., Int. J. Parasitol. 41, 125-135, 2011; Izumo, A. et al., Trans. R. Soc. Trop. Med. Hyg. 81, 264-267, 1987). After saponin treatment and washout, parasites were placed back into culture medium containing .sup.13C-ALA and incubated overnight before extraction for analysis by tandem mass spectrometry. Biosynthesis of heme, PPIX, or CPP in fractionated parasites was not detected (FIG. 8A), illustrating that the apicoplast-localized portion of the parasite heme biosynthesis pathway is largely or completely inactive during blood-stage infection.

(50) To test this conclusion within undisrupted parasites, the present inventors created a transgenic parasite line expressing an apicoplast-targeted copy of the uroporphyrinogen III methyltransferase (cobA) gene from Propionibacterium freudenreichii to serve as a biosensor of heme biosynthesis pathway activity within the parasite apicoplast. The cobA protein catalyzes a key step in bacterial cobalamin biosynthesis, converting the uroporphyrinogen III intermediate produced by the heme biosynthesis pathway into the red fluorescent product trimethylpyrrocorphin, and has been shown to function when heterologously expressed in bacteria, yeast, and mammalian cells (Sattler, I., et al., 1995 J. Bacteria. 177, 1564-1569; Wildt, S. and Deuschele, U., Nat. Biotechnol. 17, 1175-1178, 1999). These data confirm correct targeting of a cobA-GFP fusion protein to the apicoplast in ALA-treated parasites but were unable to detect any red fluorescence in the apicoplast indicative of cobA-mediated conversion of uroporphyrinogen III to trimethylpyrrocorphin (FIG. 8B), suggesting that parasite enzymes targeted to this organelle are inactive in both asexual and sexual blood stages. Growth of FC parasites (Ke, H., et al., 2014, J. Biol. Chem. 289, 34827-34837), which would be expected to accumulate PPIX during native pathway activity (FIG. 1A), was insensitive to light in the absence of ALA (FIG. 8C). WT or FC D10 parasites were cultured under normal growth conditions (without exogenous ALA) with two-minute light exposures on an overhead projector lightbox on days 0-2. Culture parasitemia as a function of time was fit to an exponential growth model. Both WT and FC parasites had parasitemia doubling times of 1.1 days under these conditions (FIG. 8C). These observations illustrate that heme biosynthesis in blood-stage P. falciparum parasites is only operative when exogenous ALA is present to stimulate PPIX production by remnant host enzymes in the erythrocyte cytoplasm with subsequent PPIX uptake and conversion to heme by ferrochelatase in the parasite mitochondrion (FIG. 7D).

Example 6. Development of Chemiluminescence-Based Photodynamic Therapy for Treatment of Bloodstage Malaria

(51) The present inventors tested whether intraerythrocytic parasites might be uniquely susceptible to chemiluminescence-based photodynamic therapy (CL-PDT) (FIG. 9A). Artemisinin and its derivatives are current frontline drugs used for treatment of malaria, usually in combination with a partner drug. To test the efficacy of an artemisinin CL-PDT strategy for treatment of blood-stage malaria, we incubated intraerythrocytic parasites in 50-100 M ALA with or without luminol and sub-therapeutic doses (10% of EC50) of dihyroartemisinin (DHA), with twice-daily media changes. Parasites treated with each compound in isolation or in combination with only one other compound showed little difference in growth rate compared to mock-treated parasites. The combination of all three compounds, however, resulted in potent inhibition of parasite growth (FIG. 9B), and microscopic examination by blood-smear revealed widespread evidence of pyknosis and parasite death. The cytotoxicity of this combination could be rescued by treatment with succinylacetone, supporting a photodynamic mechanism requiring heme biosynthetic flux.

(52) The development of parasite resistance to frontline antimalarial drugs continues to hamper malaria treatment and eradication efforts worldwide. To test whether a CL-PDT mechanism remains effective against parasites with diverse resistance to distinct drugs, the inventors designed studies with Dd2 parasites, which have multidrug resistance to antifolate and quinolone antibiotics (Sidhu, A. B. S., et al., Science 298, 210-213, 2002), and with clinical isolates containing kelch-13 protein mutations that confer artemisinin tolerance (Ariey, F., et al., Nature 505, 50-55, 2014). In both parasite lines, combination treatment with ALA, luminol, and DHA potently ablated parasite growth. These data demonstrate that a CL-PDT combination with artemisinin provides a potent strategy for treatment of blood-stage malaria. All three compounds have excellent toxicity profiles and have each been used clinically (Larkin, T. and Gannicliffe, C., Sci. Justice 48, 71-75, 2008; Bissonnette, R., et al., Photochem. Photobiol. 74, 339-345, 2001; Gordi, T. and Lepist, E. I., Toxicol. Lett. 147, 99-107, 2004). Also, a CL-PDT strategy has the advantage of relying on the activity of host enzymes in the erythrocyte that are outside the genetic control of the parasite and thus refractory to development of resistance-conferring mutation.

(53) All publications cited herein are incorporated by reference, each in their entirety.