Targeted inhibition of mitochondrial Hsp90 suppresses localised and metastatic prostate cancer growth in a genetic mouse model of disease

BACKGROUND: The molecular chaperone heat shock protein-90 (Hsp90) is a promising cancer drug target, but current Hsp90-based therapy has so far shown limited activity in the clinic. METHODS: We tested the efficacy of a novel mitochondrial-targeted, small-molecule Hsp90 inhibitor, Gamitrinib (GA mitochondrial matrix inhibitor), in the Transgenic Adenocarcinoma of the Mouse Prostate (TRAMP) model. The TRAMP mice receiving 3-week or 5-week systemic treatment with Gamitrinib were evaluated for localised or metastatic prostate cancer, prostatic intraepithelial neoplasia (PIN) or localised inflammation using magnetic resonance imaging, histology and immunohistochemistry. Treatment safety was assessed histologically in organs collected at the end of treatment. The effect of Gamitrinib on mitochondrial dysfunction was studied in RM1 cells isolated from TRAMP tumours. RESULTS: Systemic administration of Gamitrinib to TRAMP mice inhibited the formation of localised prostate tumours of neuroendocrine or adenocarcinoma origin, as well as metastatic prostate cancer to abdominal lymph nodes and liver. The Gamitrinib treatment had no effect on PIN or prostatic inflammation, and caused no significant animal weight loss or organ toxicity. Mechanistically, Gamitrinib triggered acute mitochondrial dysfunction in RM1 cells, with loss of organelle inner membrane potential and release of cytochrome-c in the cytosol. CONCLUSIONS: The Gamitrinib has pre-clinical activity and favourable tolerability in a genetic model of localised and metastatic prostate cancer in immunocompetent mice. Selective targeting of mitochondrial Hsp90 could provide novel molecular therapy for patients with advanced prostate cancer

Preventive and therapeutic efficacy of finasteride and dutasteride in TRAMP mice

Background: The prostate cancer prevention trial (PCPT) and Reduction by dutasteride of Prostate Cancer Events (REDUCE) trial found that 5α-reductase (5αR) inhibitors finasteride and dutasteride respectively, decreased prostate cancer prevalence but also increased the incidence of high-grade tumors. 5αR2 is the main isoenzyme in normal prostate tissue; however, most prostate tumors have high 5αR1 and low 5αR2 expression. Because finasteride inhibits only 5αR2, we hypothesized that it would not be as efficacious in preventing prostate cancer development and/or progression in C57BL/6 TRAMP x FVB mice as dutasteride, which inhibits both 5αR1 and 5αR2. Method/Principal Findings: Six-week-old C57BL/6 TRAMP x FVB male mice were randomized to AIN93G control or pre- and post- finasteride and dutasteride diet (83.3 mg drug/kg diet) groups (n =30–33) that began at 6 and 12 weeks of age, respectively, and were terminated at 20 weeks of age. The pre- and post- finasteride and dutasteride groups were designed to test the preventive and therapeutic efficacy of the drugs, respectively. Final body weights, genitourinary tract weights, and genitourinary tract weights as percentage of body weights were significantly decreased in the Pre- and Post-dutasteride groups compared with the control. The Post-dutasteride group showed the greatest inhibition of prostatic intraepithelial neoplasia progression and prostate cancer development. Surprisingly, the Post-dutasteride group showed improved outcomes compared with the Pre-dutasteride group, which had increased incidence of high-grade carcinoma as the most common and most severe lesions in a majority of prostate lobes. Consistent with our hypothesis, we found little benefit from the finasteride diets, and they increased the incidence of high-grade carcinoma. Conclusion: Our findings have commonalities with previously reported PCPT, REDUCE, and the Reduction by dutasteride of Clinical Progression Events in Expectant Management (REDEEM) trial results. Our results may support the therapeutic use of dutasteride, but not finasteride, for therapeutic or preventive use

False-positive TUNEL staining observed in SV40 based transgenic murine prostate cancer models

The TRAMP (Transgenic Adenocarcinoma of the Mouse Prostate) and LADY (Probasinlarge T antigen transgenic mouse) mice are widely used autochthonous models of prostate cancer. Both models utilise probasin promoters to direct androgenregulated expression of oncogenic SV40 specifically to epithelial cells of the mouse prostate. The oncogenic processes and phenotypes which result mimic many features of human prostate cancer, making these transgenic mouse models useful experimental systems. The terminal deoxynucleotidyl transferase (Tdt) -mediated dUTP in situ nick end labelling (TUNEL) assay is a commonly used method for the detection of cells undergoing apoptosis. In this study, we demonstrate false-positive TUNEL staining in frozen prostate tissue from TRAMP and LADY mice, which was not observed in non-transgenic control animals and is not due to non-specific binding of labelled-dUTP substrate. The false-positive signal co-localised with large SV40 T-antigen expression. False-positive signal was apparent using multiple commercial TUNEL kits with different detection systems. These results caution against the use of the TUNEL assay for detection of apoptosis in frozen prostate tissue of large T-antigen based autochthonous transgenic models of prostate cancerM. D. Lawrence, B. J. Blyth, R. J. Ormsby, W. D. Tilley, P. J. Syke