THE COMBINATION OF ENHANCED ANDROGEN DEPRIVATION WITH OXIDATIVE PHOSPHORYLATION INHIBITION MIGHT BE A PROMISING NEW STRATEGY AGAINST PROSTATE CANCER
INTRODUCTION: We have recently shown that oxidative phosphorylation (OXPHOS) inhibition with oligomycin displayed synergistic antitumor effects with androgen deprivation in prostate cancer models in vitro (Sakellakis et al. Esmoopen. 2018). Although the introduction of potent OXPHOS inhibitors to clinical practice has long been considered impossible, recently some agents showed promising results in pre-clinical studies. IACS-010759 is a novel OXPHOS inhibitor developed at the MD Anderson Institute for Applied Cancer Search that has entered Phase 1 clinical trials (Molina et al. Nature Medicine. 2018).
METHODS: We evaluated the effects of oligomycin, as well as the effects of clinically meaningful concentrations of IACS-010759 in VCAP, LNCaP, LNCaP-C4-2B, PC3 and HEK293 cells under the following conditions in vitro: 1) castration (charcoal stripped serum media, CSS), 2) the presence of low testosterone levels (CSS+80ng/dL testosterone), 3) OXPHOS inhibition (CSS+80ng/dL testosterone+25nM IACS-010759 or 50ng/ml oligomycin) and combined androgen signaling and OXPHOS inhibition (CSS+25nM IACS-010759 or 50ng/ml oligomycin). We tested the tumor cell viability and proliferation after 72 hours using MTT assay. We also assessed apoptosis rates (48 hours) using flow cytometry and optical microscopy, and biochemical changes in TCA metabolites (48 hours) using mass spectrometry.
RESULTS: The addition of oligomycin in the presence of testosterone in VCAP cells caused a remarkable decrease in the pyruvate-to-lactate ratio as well as the ratios of other TCA metabolites to lactate (p<0.001). This suggests that VCAP cells display a high post-OXPHOS inhibition glycolytic drive (POIGD) in order to compensate for OXPHOS inhibition. Thus, the effect of oligomycin in VCAP viability was minimal. However, in the total absence of testosterone, a massive decrease in cell viability and increase in apoptosis rates were seen (p<0.001). In the latter case there was no decrease in the pyruvate to lactate ratio. The addition of clinically relevant concentrations of IACS-010759 (25nM) in the presence of testosterone paradoxically caused a strong increase in tumor cell viability and proliferation. This increase was greatly reduced in the absence of testosterone. In the latter case, we observed a minimal viability increase vs enhanced castration (CSS) alone after 72 hours, but most VCAP cells eventually became non-viable in the absence of testosterone in the long term (irrespective of the presence of IACS). LNCaP and LNCaP-C4-2B cells when placed in 50ng/ml oligomycin in the presence of testosterone showed a relative increase in pyruvate to lactate ratio, thus displayed a low post-OXPHOS inhibition glycolytic drive. The addition of 25nM IACS-010759 eliminated both LNCAP and LNCAP-C4-2B cells after 72 hours irrespective of the presence or absence of testosterone. The addition of IACS-010759 also caused a small proliferation delay in AR negative PC3 cells and normal human embryonal kidney cells HEK293.
CONCLUSIONS: Different OXPHOS inhibitors have different effects in cell lines. The addition of androgen deprivation to OXPHOS inhibition has anti-tumor effects. IACS-010759 is a potent agent against a subset of prostate tumors with low POIGD. Given that tumors are usually heterogeneous, the administration of IACS-010759 should be only given in combination with androgen deprivation to prevent the accelerated growth of subsets of clones with high POIGD, while at the same time possibly kill those clones that are androgen dependent.