In this review article, we provide an overview of the current preclinical and clinical status of statins as antitumor agents. In addition, we evaluated various patents that describe the role of mevalonate pathway inhibitors and methods to determine if cancer cells are sensitive to statins treatment.

Background Despite the introduction of several novel therapeutic approaches that improved survival, metastatic castration-resistant prostate cancer (mCRPC) remains an incurable disease. Herein we report the synergistic antitumor interaction between two well-known drugs used for years in clinical practice, the antiepileptic agent with histone deacetylase inhibitory activity valproic acid and the cholesterol lowering agent simvastatin, in mCRPC models. Methods Synergistic anti-tumor effect was assessed on PC3, 22Rv1, DU145, DU145R80, LNCaP prostate cancer cell lines and EPN normal prostate epithelial cells, by calculating combination index (CI), caspase 3/7 activation and colony formation assays as well as on tumor spheroids and microtissues scored with luminescence 3D-cell viability assay. Cancer stem cells (CSC) compartment was studied evaluating specific markers by RT-PCR, western blotting and flow cytometry as well as by limiting dilution assay. Cholesterol content was evaluated by 1H-NMR. Overexpression of wild-type YAP and constitutively active YAP5SA were obtained by lipofectamine-based transfection and evaluated by immunofluorescence, western blotting and RT-PCR. 22Rv1 R_39 docetaxel resistant cells were selected by stepwise exposure to increasing drug concentrations. In vivo experiments were performed on xenograft models of DU145R80, 22Rv1 parental and docetaxel resistant cells, in athymic mice. Results We demonstrated the capacity of the combined approach to target CSC compartment by a novel molecular mechanism based on the inhibition of YAP oncogene via concurrent modulation of mevalonate pathway and AMPK. Because both CSCs and YAP activation have been associated with chemo-resistance, we tested if the combined approach can potentiate docetaxel, a standard of care in mCRCP treatment. Indeed, we demonstrated, both in vitro and in vivo models, the ability of valproic acid/simvastatin combination to sensitize mCRPC cells to docetaxel and to revert docetaxel-resistance, by mevalonate pathway/YAP axis modulation. Conclusion Overall, mCRPC progression and therapeutic resistance driven by CSCs via YAP, can be tackled by the combined repurposing of two generic and safe drugs, an approach that warrants further clinical development in this disease.

Introduction: docetaxel (DTX) represents the standard of care first line treatment of castration-resistant prostate cancer (PCa). However, the onset of systemic side effects hampers patient's compliance and DTX resistance invariably emerges, leading to disease relapse, suggesting the need of novel combination strategies. Cancer stem cells (CSC) drive PCa survival and metastasis and are thought to be responsible for the development of resistance to DTX. The mevalonate pathway (MVP) plays a critical role in PCa progression and is implicated in cell stemness, proliferation, and organ size regulation through the YAP-TAZ signaling axis. Here, we evaluate the combination treatment of valproic acid (VPA), an histone deacetylase (HDAC) inhibitor and the cholesterol-lowering drug simvastatin (SIM), an inhibitor of HMGCoA reductase (HMGCR), the rate limiting enzyme in MVP, alone and plus DTX in PCa models. Method: synergistic antiproliferative effects were assessed on LNCAP, 22Rv1, DU145, PC3 and DU14580 SIM-resistant cell lines and normal epithelial prostate EPN cells, by calculating combination index (CI) according to Chou and Talalay method. Apoptosis was measured by FACS analysis and caspase assay. Tumor spheroids were obtained by low attach systems and scored with luminescence 3D-cell viability assay. Proteins and genes expression was assessed by western blot and real time PCR analysis. In vivo experiments were performed on xenograft models in athymic mice. Cholesterol content was evaluated by nuclear magnetic resonance (1H-NMR). Results: synergistic antiproliferative and proapoptotic effect of VPA-SIM was observed in all PCa cell lines tested, except in EPN cells and was confirmed in PCa spheroids. SIM-dependent cholesterol content downmodulation was potentiated by VPA and mevalonic acid, the product of HMGCR activity, reverts all the antitumor combined effect, suggesting the involvement of MVP in the synergistic interaction. Mechanistically, the combination is able to induce a reduction of HMGCR mRNA expression and the inhibitory phosphorylation of HMGCR and YAP, followed by a reduction of CTGF, BRCA5 and Cyr61 YAP-target genes, as well as a reduction of a CSC-marker gene such as NANOg. Notably, the VPA-SIM combination, sensitizes PCa cells to DTX treatment in sensitive and DTX-resistant cells, as shown by CI calculation, apoptosis, and CSC enriched-spheroid experiments. The synergistic interaction of the triple combination was also confirmed in vivo in both DU145R80 and 22Rv1 xenograft models. Conclusions: Overall, this study suggests that the combination of two safe generic drugs such as VPA and SIM, may improve the therapeutic index of DTX and revert DTX-resistance, representing an innovative and feasible antitumor strategy for the treatment of prostate cancer that warrants further clinical evaluation. Citation Format: Federica Iannelli, Maria Serena Roca, Chiara Ciardiello, Simona De Rienzo, Rita Lombardi, Angela Sorice, Susan Costantini, Tania Moccia, Maria Rita Milone, Biagio Pucci, Alfredo Budillon, Francesca Bruzzese. Synergistic antitumor interaction of valproic acid and simvastatin sensitizes prostate cancer to docetaxel by targeting cancer stem cells compartment via YAP-pathway modulation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2877.