Background: Prostate tumor-initiating cells (TICs) have the exclusive abilities to self-renew and to initiate tumors in immune-deficient recipients. Prostate TICs survive treatment due to their intrinsic resistance to current therapies. Elevated expression of Bmi-1 (B-cell specific MMLV insertion site) occurs in prostate tumor stem cells. Bmi-1 promotes tumorigenesis by repressing genes regulating cell cycle and apoptosis and by suppressing growth inhibitor proteins. Thus, Bmi-1 is an ideal drug target to eliminate self-renewal of prostate TICs. Pressing questions are whether Bmi-1 inhibitors are effective against prostate cancer and if combining Bmi-1 inhibitors with chemotherapy causes tumor eradication.
Objective/Hypothesis: Our goal is to identify and subsequently develop a new class of bioavailable small molecules that inhibit tumor growth by selectively reducing Bmi-1 production. In preliminary studies, we found Bmi-1 to be overexpressed in 44% of advanced prostate tumors. We hypothesize that Bmi-1 plays a vital role in prostate TIC maintenance and that drugs targeting Bmi-1 will eliminate TICs in patient tumors. We have identified three potent and selective compounds that reduce Bmi-1 expression in prostate cancer cell lines in vitro and in vivo. We propose to use mice and zebrafish xenografts of primary cells to (1) select a compound(s) that potently, selectively, and safely reduce Bmi-1 expression in primary prostate TICs and (2) develop a clinical strategy for combination therapy.
Specific Aims: (1) Determine the extent of aberrant expression of Bmi-1 in primary prostate tumors and study of the role of Bmi-1 in regulating prostate TIC self-renewal. (a) Analyses of Bmi-1 expression in primary and metastatic prostate cancer patients. (b) Study of the effects of Bmi-1 knockdown on putative TICs in vitro and in vivo with serially engrafted zebrafish and mice xenografts. (2) Evaluate the therapeutic response to combining small molecule Bmi-1 inhibitors with chemotherapy to eradicate prostate TIC xenografts. We have identified three Bmi-1 inhibitors with antitumor activity at ED50 of <1mM. We will study the additive or synergetic effects of combining Bmi-1 inhibitors, to target self-renewal in primary prostate TICs, with cisplatin and taxanes that can debulk tumors in order to reach total tumor eradication.
Study Design: TICs isolated by phenotypic and time-of-adherence assays from fresh tumors and DU145 cells will be used to generate zebrafish xenografts. The tumor initiation potential will be confirmed in established mouse xenografts. The effect of Bmi-1 inhibitors against primary xenografts generated in zebrafish and mice will be investigated as monotherapy and in combination with cisplatin and taxotere. These studies will allow us to (1) identify a Bmi-1 inhibitor(s) with in vivo potency, selectivity, and antitumor activity in animal models and (2) develop a clinical strategy for combination therapy.
Synergy: This proposal utilizes the expertise of three laboratories: the Sabaawy laboratory, with expertise in using zebrafish as a vertebrate model to study carcinogenesis and drug effects; the Bertino laboratory, with experience in cell biology and molecular pharmacology; and the Kim laboratory, with experience in prostate cancer biology and mouse xenografts, together with the availability of Bmi-1 inhibitors from PTC Therapeutics, and the clinical prostate cancer translation team at the Gallo Prostate Cancer Center.
Innovation: There are two novel and potentially broad-reaching concepts in this proposal. First, zebrafish provide an ideal vertebrate for prostate cancer xenografts. Second, we will escalate the development of novel Bmi-1 inhibitor(s) that target TICs in prostate cancer for clinical trials.
Impact: Bmi-1 inhibitors that target prostate cancer TICs may provide a new class of inhibitors that when used alone and in combination would be effective therapies for many patients with prostate cancer.
Focus Area: This proposal is focused in the areas of therapeutics and prostate tumor biology.
Animal Model; Apoptosis; Area; Bioavailable; Biological Assay; B-Lymphocytes; Cancer Biology; Cancer Center; Cancer Patient; Cell Cycle; Cell Maintenance; Cells; Cellular biology; chemotherapy; Cisplatin; Clinical; Clinical Trials; Combined Modality Therapy; Development; docetaxel; drug carcinogenesis; Drug Delivery Systems; DU145; effective therapy; experience; Genes; Goals; Growth Inhibitors; Immune; In Vitro; in vivo; inhibitor/antagonist; innovation; Laboratories; Malignant neoplasm of prostate; Metastatic Prostate Cancer; Modeling; Molecular; Mus; novel; overexpression; Patients; PC3 cell line; Pharmacology; Play; Production; Prostatic Neoplasms; Proteins; Research Design; Resistance; response; Role; self-renewal; Site; small molecule; taxane; Taxane Compound; Therapeutic; Time; Translations; tumor; Tumor Biology; Tumor Debulking; tumor eradication; tumor growth; tumor initiation; Tumor Stem Cells; tumorigenesis; Xenograft procedure; Zebrafish