Assessing the potential for in vivo modulation of expression with small peptides to restore and enhance androgen receptor pathway inhibition in prostate cancer.

Increased levels of intratumoral free iron drive more aggressive behavior with the development of treatment resistance and spread in a range of cancers including prostate cancer (PCa). This phenotype is associated with an increase in TFRC expression and a decrease in FTH1, a profile supporting increased iron acquisition. In this study we investigated the anti-oncogenic effects of two small peptides (FT-002 and FT-005) that upregulate FTH1 expression and downregulate TFRC expression when combined with standard androgen receptor pathway inhibitors (ARPIs) in xenograft models of PCa in male athymic nude mice. The PC3 cell line was used to establish xenografts representing highly aggressive, androgen-resistant PCa and the LNCaP cell line as a model of androgen-sensitive PCa. Both peptides enhanced the anti-tumor efficacy of ARPI therapy. Efficacy was more marked with the combination of the second-generation APRI enzalutamide than the first-generation agent bicalutamide, a result consistent with known resistance mechanisms to different ARPI therapy. Further, the FT-peptide/enzalutamide combination drove tumor regression whereas enzalutamide monotherapy only slowed growth, even in the hormone-sensitive xenograft. The FT-002a-enzalutamide combination was more effective than FT-005 in reducing tumor mass and volume and modulating FTH1 and TFRC expression. The reversal by the peptides of this oncogenic expression pattern points to a reduction in the tumor free iron via increased iron storage in ferritin and a reduction in iron influx via the transferrin receptor. Peptide-mediated modulation of tumor iron metabolism may therefore offer a novel means to enhance ARPI efficacy and delay resistance in advanced prostate cancer.