Method and a kit to quantify and qualify exosomes for diagnosis of prostate cancer and prostate hyperplasia

Abstract

A method and a kit are provided to quantify and qualify exosomes. Specifically the method and the kit quantify PSA-carrying exosomes for a purpose to diagnose prostate cancer and to distinguish between patients having a tumor and those having a benign prostate condition with increased blood levels of PSA. The method and the kit provide a fast, easy to use and accurate method for clinical settings.

Claims

1. A method to distinguish between prostate hyperplasia and prostate cancer, said method comprising the steps of: a) determining an abnormality or enlargement of a person's prostate gland and identifying the person as a potential prostate cancer patient when the prostate gland is abnormal or enlarged, b) collecting a body fluid or cell derived sample from the patient and from a healthy person with normal prostate gland for a control sample; c) capturing total exosomes of the samples with a primary antibody against a protein exclusively present on outer surface of exosomes; d) capturing primary antibody bound exosomes of step b) carrying prostate specific antigen (PSA) protein on their outer membrane surface with an anti-PSA detection antibody; e) allowing an enzyme linked secondary antibody to react with the detection antibody; f) adding substrate; g) detecting the reaction and quantifying primary antibody-exosome-anti-PSA antibody complex; h) accurately eliminating prostate cancer diagnosis when quantity of the complex in the patient sample is substantially similar to or lower than quantity in the healthy person's sample and accurately diagnosing prostate cancer when the quantity of the complex in the patient's sample is substantially higher than in the healthy person's sample.

2. A method to accurately diagnose prostate cancer, said method comprising the steps of: a) collecting a unfractionated body fluid or cell derived sample form a patient and form a multitude of healthy persons; b) capturing total exosomes of sample with a primary antibody against a protein exclusively present on outer surface of exosomes; c) capturing prostate specific antigen (PSA) carrying exosomes from primary antibody-exosome complexes with an anti-PSA detection antibody; d) allowing an enzyme linked secondary antibody to react with the detection antibody; e) adding substrate; f) detecting the reaction and quantifying primary antibody-exosome-anti-PSA antibody complex; g) determining maximum quantity of the complex of step f) in the sample of the healthy persons and setting a cutoff point close to such maximum; and h) accurately diagnosing cancer when the quantity of the complex in patient's sample is higher than such cutoff point.

3. The method of claim 1, wherein the method is conducted on a test kit, said test kit comprising: a) a primary antibody preparation for capturing total exosomes from a body fluid or cell derived sample of a patient, wherein the primary antibody is Rab 5; b) a detection antibody preparation for prostate tumor related bound exosomes, wherein the detection antibody is anti-PSA; c) an enzyme linked secondary antibody preparation for reaction with the detection antibody; d) a substrate for the enzyme; and e) a control sample.

4. The method of claim 1 wherein the primary antibody is antiRab 5.

5. The method of claim 1, wherein the sample is a plasma or urine sample.

6. The method of claim 2, wherein the primary antibody is anti Rab 5.

7. The method of claim 2, wherein the sample is a plasma or a urine sample.

8. A test kit to quantify and qualify exosomes in human cell derived samples or in body fluids for accurate diagnosis and prognosis of prostate tumor, said kit comprising: a) a primary antibody preparation for capturing total exosomes from a body fluid or cell derived sample of a patient, wherein the primary antibody is against a protein exclusively present on outer surface of exosomes; b) a detection antibody preparation for detecting prostate tumor related bound exosomes, wherein the detection antibody is anti-PSA; c) an enzyme linked secondary antibody preparation for reaction with the detection antibody; d) a substrate for the enzyme; and e) a control sample.

9. The test kit of claim 8, wherein the primary antibody is antiRab5.

10. The test kit of claim 8, wherein the kit is for diagnosis and prognosis of prostate tumor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] FIG. 1 Exotest and cytofluorimetric analysis confirmed PSA expression on tumor-derived exosomes.

[0024] A) An illustration showing the principle of the ELISA based test according to this invention (Exotest®). The wells of the test kit are coated with Anti-Rab-5-antibody which is the primary antibody capturing total exosomes. Anti-PSA or CD63 antibodies are included as secondary antibodies and labeled with the enzyme horseradish peroxidase (HRP).

[0025] B) Exosomes isolated from RWPE-1 (non-neoplastic prostate cells), RWPE-2 (early prostate tumor), MDA231 (Breast cancer) an Mel-1 (melanoma cancer) were analyzed for PSA expression by Exotest of FIG. 1A. The values were reported as arbitrary values and reaction buffer was used as negative control (Ctr.neg.).

[0026] C) Cytofluorimetric analysis of PSA expression on exosomes isolated from RWPE-2 and MDA231 cells and coated on aldehyde/sulfate latex beads for 12 hours. One representative experiment of three was reported. A control antibody was used as negative staining control.

[0027] D) Cytofluorimetric analysis of PSA expression on aldehyde/sulfate latex beads-coated exosomes isolated from three patients with tumors and healthy donors. One representative experiment is shown of each. Anti-Rab-5b antibody was used as exosomes control. A control antibody was used as negative staining control.

[0028] FIG. 2 PSA-positive exosomes robustly distinguished cancers and hypertrophies.

[0029] A) RWPE-2, infected with luciferase gene, were inoculated in anterior prostate of NSG mice and evaluated three weeks after injection by IVIS system. One representative image is shown. Evaluation of exosomes positive for CD63 and PSA in plasma of inoculated mice and analyzed by Exotest of FIG. 1A. PBS injected mice were used as negative test control. Three independent experiments were conducted and the data is shown as mean±S.D.

[0030] B) Non-neoplastic RWPE-1(RW-1) and tumor RWPE-2 (RW-2), transduced with EGFP reporter gene, were inoculated under renal capsule (SRC) and analyzed by stereomicroscopy system. Evaluation of exosomes positive for CD63 and PSA in plasma of inoculated mice and analyzed by Exotest of FIG. 1A. Three independent experiments were conducted and the data was were reported as mean±S.D.

[0031] FIG. 3 A) Exosomes isolated from patients' plasma and evaluated for PSA expression by the method of this invention. 22, 26 and 31 patients were analyzed for healthy, hypertrophy and cancer groups respectively. Optical density values are shown. *** represents P<0.001 as evaluated by unpaired t-test.

[0032] B) Exosomes isolated from patients′plasma and evaluated for CD63 expression by the method of this invention. 22, 26 and 31 patients were analyzed for healthy, hypertrophy (Control) and cancer groups respectively. Optical density values are shown as arbitrary units.

[0033] C) PSA positive exosomes (PSA-EX) evaluation in plasma of 12 women and 22 healthy donors performed by the method of this invention. Optical density values are shown as arbitrary units.

DETAILED DESCRIPTION OF THE INVENTION

Definitions

[0034] ExoTest® is a trademarked ELISA-based test that was first described and claimed in the U.S. provisional patent application No. 61/062,528 and subsequent US Serial Number 2009/0220944, both of which are incorporated herein by reference. ExoTest platform comprises ELISA plates pre-coated with antibodies against housekeeping exosome proteins enabling specific capture of exosomes from different biological samples, including cell culture supernatants and human biological fluids. Quantification and characterization of exosomal proteins is subsequently performed by using appropriate detection antibodies against exosome associated antigens that can be either common for all exosomes or cell type- or cell condition specific.

[0035] Exosomes are microvesicles of a size ranging between 30-120 nm, actively secreted in the extracellular environment by normal as well as tumor cells.

[0036] The invention is now described by means of non limiting examples.

Example 1. Isolation of Exosomes and Labeling of the Exosomes

Exosomes Isolation

[0037] Exosomes were purified by three successive centrifugations at 300×g (5 min), 1200×g (20 min) and 10.000×g (30 min) to eliminate cells and debris, followed by centrifugation for 1 h at 100 000×g. The exosome pellets were washed once in a large volume of PBS, centrifuged at 100.000×g for 1 h and re-suspended in 50-200 μl of PBS. To obtain plasma exosomes, the classical protocol was modified because of plasma viscosity and protein and lipid abundance compared with the cell supernatant. After the separation from total blood, plasma was centrifuged for 30 min at 500×g, 45 min at 12 000×g and 2 h at 110 000×g. Pellets were re-suspended in a large volume of PBS, filtered on a 0.22-μm filter (Millipore) and centrifuged at 110 000×g for 1 h. Microvesicle pellets were washed once in a large volume of PBS, centrifuged at 110 000×g for 1 h and re-suspended in 50-200 μl of PBS. The amount of 110.000×g pellet proteins recovered are measured by Bradford assay (Bio-Rad). Exosomes were used as fresh preparation for immunoisolation by sytofluorimetry analysis or ELISA-based test, the principal of which is shown in FIG. 1A.

Exosomes Labeling

[0038] For immunoisolation and FACS analysis of microvesicles exosome pellets were resuspended in 10 μl of 4-μm-diameter aldehyde/sulfate latex beads (Interfacial Dynamics, Portland, Oreg., USA) were incubated with purified anti-CD63 or prostate specific protein hAbs at room temperature in a small volume (50 μl). After 15 min, the volume was made up to 400 μl with PBS and incubated overnight at 4° C. under gentle agitation. Exosome-coated beads were washed twice in FACS washing buffer (1% BSA and 0.1% NaN3 in PBS) and re-suspended in 400 μl FACS washing buffer, stained with fluorescent antibodies and analyzed on a FACSCalibur flow cytometer (BD Biosciences) and CellQuest software.

Example 2 Prostate Specific Antigen PSA is Expressed on Exosomes Detected by Exotest

[0039] The presence of PSA on exosomes was further validated by using an ELISA test (Exotest®) where the primary capturing antibody was RAB5b antibody capturing total exosomes of the sample and the secondary antibody was either PSA-antibody or CD-63 antibody. Exosomes isolated from a normal cell line, RWPE-1 and RWPE-2 cells were loaded on RAB5b-antibody coated plates (FIG. 1A). We used a breast and melanoma cancer cells as PSA negative controls. RAB5b attached exosomes were incubated with antibodies against either CD63 or PSA and evaluated by peroxidises enzymatic reaction (FIG. 1A). Tumor cell lines released significantly higher amount of exosomes (CD63+) as compared to non-neoplastic cells (FIG. 1B), while PSA-bearing exosomes were exclusively detected in the supernatant of non-neoplastic prostate and tumor cell lines (FIG. 1B).

[0040] This data was highly consistent with that obtained by FACS analysis of aldehyde/sulfate latex beads, following overnight exosome coating and staining with an additional anti-PSA antibody (FIG. 1 C, D). Results confirmed PSA expression on exosomes surface of both RWPE-2 and patients' plasma (FIG. 1 C, D). Breast cancer cells and healthy man donors were used as negative controls. Rab5b staining on plasma samples was used as control.

Example 3 Detection of PSA Exosomes in Mice Inoculated with RWPE-2 Cells

In Vivo Mice Models

[0041] Six-eight week old male NOD.Cg-Prkdcscid Il2rgtm1Wj1/SzJ, NSG mice (Charles River Laboratoty, Wilmington, Mass.) were used for experiments.

Sub-Renal Capsule Injection:

[0042] To perform renal capsule injection, a skin incision of approximately 1 cm was made along the dorsal midline of an anesthetized mouse. Then, an incision was made in the body wall slightly shorter than the long axis of the kidney. After exteriorization of the kidney, the capsule was lifted from renal parenchyma to allow an injection or a 2-4 mm incision to injected 105 cells with or without matrigel. Three weeks from injection, mice were analyzed and blood samples withdrawals were performed.

Orthotopic Injection:

[0043] For orthotopic injection, abdominal wall muscles were incised, and the bladder and seminal vesicles were delivered through the incision to expose the prostate. 105 cells were injected via a 0.3 mm needle directly into the anterior prostate. The incision was closed using a running suture of 4-0 silk. Cells were infected with luciferase gene and monitored with IVIS Imaging System 100 Series (Xenogen). All animal procedures were performed according to protocols approved by the ISS Animal Care Committee.

[0044] A set of experiments were performed by inoculating RWPE-2 cells into the anterior prostate lobe of NSG mice and PSA positive exosome were quantified 9 weeks after injection into the plasma by capturing total exosomes with antiRab5b antibody and selectively capturing PSA positive exosomes with antiPSA-antibody on an Exotest kit. CD63 positive exosomes were captured from the total exosomes by using CD63 antibody as secondary antibody. PBS inoculated mice were used as internal control. Data showed the presence of human CD63 and PSA-positive exosomes in the mice injected with tumor cells (FIG. 2A).

[0045] Since it is reported that tumors release marked levels of exosomes, we wanted to test the sensitivity of our approach comparing the tumor RWPE-2 and non-neoplastic RWPE-1 cells. We injected both cell lines into an highly permissive and vascularised site, under the renal capsule (SRC) (FIG. 2B) and we evaluated PSA positive plasmatic exosomes 4 weeks after injection by Exotest. Results showed that tumor cells released exosomes 2 fold more than non-neoplastic cells and that this system robustly distinguished aggressive and non-neoplastic cells (FIG. 2 B). This data supports that the method of this invention guarantees high sensitivity to distinguish between tumor and non-neoplastic cells.

Example 4. PSA Positive Exosomes Identify Patients with Prostate Cancer

[0046] In order to investigate the diagnostic significance of our data, we collected plasmatic samples from a large cohort of patients, representative of all phases of prostatic neoplastic disease. In detail, plasma was collected from 31 patients with diagnosed cancers (Tumor) and 26 patients with non-neoplastic prostatic disease (Hypertrophy). A group of healthy men (22) (Healthy) were used as control population. From the plasma samples exosomes were isolated by ultracentrifugation and were analyzed for the presence of either CD63 or PSA. Plasma collected from patients with tumor showed higher levels of exosomes as compared to healthy donors as analyzed by the CD63 Exotest analysis (FIG. 3B). However, patients with cancer showed a significant increase in the level of PSA-positive exosomes than hypertrophic patients (FIG. 3A). Exosomes isolated from six women were used as exosomal PSA negative controls (FIG. 3C). Setting a cut-off at 500 as arbitrary unit value, chosen as maximum value in the hypertrophic patients value distribution (in FIG. 3A), PSA-positive exosomes level well discriminates the patients with tumors from ones with hypertrophy as determined by Exotest analysis of this invention. This data offers a new and alternative diagnostic tool by passing the conventional screening test limits with a non-invasive approach for patients.

Example 5. Quantification of Exosomes by Using Unfractionated Biological Fluids

[0047] In order to provide a fast and simple test for clinical purposes we verified that the test can be used for exosome detection in unfractionated biological fluids that would allow an easy and reproducible analysis avoiding the steps of ultracentrifugation. We compared the detection and quantification of PSA exosomes from unfractionated samples (human plasma, urine samples) and purified exosomes samples. The presence of PSA-exosomes in unfractionated samples was detectable by ExoTest (results not shown). The results suggest that ExoTest is useful and reliable in clinical setting using whole plasma or urine samples and avoiding the complex and time consuming procedures of exosome purification. Thus the test disclosed here provides an easy to use, fast and patient friendly test for accurately diagnose prostate cancer and to discriminate it from benign conditions where plasma PSA levels may be increased.