Prostate cancers adapt to
androgen receptor (AR) pathway inhibitors and progress to
castration resistance due to ongoing AR expression and function. To counter this, we developed a new approach to modulate the AR and inhibit
castration-resistant
prostate cancer (CRPC) using multivalent
peptoid conjugates (MPC) that contain multiple copies of the AR-targeting
ligand ethisterone attached to a
peptidomimetic scaffold. Here, we investigated the antitumor effects of compound MPC309, a trivalent display of
ethisterone conjugated to a
peptoid oligomer backbone that binds to the AR with nanomolar affinity. MPC309 exhibited potent antiproliferative effects on various
enzalutamide-resistant
prostate cancer models, including those with AR splice variants,
ligand-binding mutations, and noncanonical AR gene expression programs, as well as mouse prostate organoids harboring defined genetic alterations that mimic lethal human
prostate cancer subtypes. MPC309 is taken up by cells through macropinocytosis, an endocytic process more prevalent in
cancer cells than in normal ones, thus providing an opportunity to target
tumors selectively. MPC309 triggers a distinct AR transcriptome compared with DHT and
enzalutamide, a clinically used
antiandrogen. Specifically, MPC309 enhances the expression of differentiation genes while reducing the expression of genes needed for cell division and metabolism. Mechanistically, MPC309 increases AR
chromatin occupancy and alters AR interactions with coregulatory
proteins in a pattern distinct from DHT. In xenograft studies, MPC309 produced significantly greater
tumor suppression than
enzalutamide. Altogether, MPC309 represents a promising new AR modulator that can combat resistant disease by promoting an AR antiproliferative gene expression program.