INTRODUCTION: Cancer cells are able to survive oxidative phosphorylation (OXPHOS) inhibition by up-regulation of glycolysis. Androgens stimulate glycolysis in prostate cancer cells through activation of the androgen receptor (AR). Here we hypothesize that androgens might help subsets of prostate cancer cells to survive OXPHOS inhibition. In addition, the combined androgen signaling and OXPHOS inhibition might pose synergistic anti-tumor effects in vitro.
MATERIAL AND METHOD: The effects of suppressing OXPHOS with 100ng/ml oligomycin in charcoal stripped serum media (CSS), before and after the addition of 40ng/dl testosterone in VCAP, LNCaP, and LNCaP-C4-2B cells in vitro were evaluated. Tumor cell viability after 72 hours was estimated using MTT assay.
RESULTS AND DISCUSSION: The addition of 100ng/ml oligomycin to VCAP cells in a steroid-depleted environment (CSS) dramatically decreased cell viability compared to CSS alone (p<0.001). The addition of castrate testosterone levels (40ng/dl) increased tumor cell viability both with and without concurrent OXPHOS suppression (p<0.001 for both). VCAP cells are androgen-sensitive and harbor AR amplification. In LNCaP cells the addition of 100ng/ml oligomycin in CSS resulted in a remarkable reduction in cell viability compared to CSS alone (p<0.001). Testosterone at 40ng/dl increased cell viability and proliferation compared to CSS alone, both with and without concurrent OXPHOS inhibition (p<0.001 for both). The experiments were repeated using LNCaP-C4-2B cells. LNCaP-C4-2B cells are isogenic to LNCaP cells, but show persistent AR-mediated transcription even in androgen-deprived conditions. We found that the addition of 100ng/ml oligomycin in CSS caused a smaller decrease in cell viability compared to LNCaP cells. Addition of 40ng/dl testosterone significantly decreased the anti-tumor effects of OXPHOS inhibition (p<0.001). These in vitro results generate the hypothesis that active AR signaling might be involved in resistance towards the antitumor effects of OXPHOS inhibition.
CONCLUSIONS: The combined androgen depletion and OXPHOS inhibition shows promising synergistic anti-tumor effects in vitro. Although our data are preliminary and only hypothesis generating, they suggest that this therapeutic combination might be able to amplify the anti-tumor effects of androgen signaling inhibition alone in a subset of androgen sensitive prostate tumors. Further studies will further assess the safety and efficacy of this therapeutic combination.
This work was conducted at the MD Anderson Cancer Center, Department of Genitourinary Oncology, Metabolomics and mass spectrometry lab 3871 (under my PI supervision) and its an ongoing project.