Combination AZD5363 with Enzalutamide Significantly Delays Enzalutamide-resistant Prostate Cancer in Preclinical Models

Abstract The phosphatidylinositol-4,5-bisphosphate 3-kinase/Akt (PI3K/Akt) pathway is a key pathway activated in castrate-resistant prostate cancer (CRPC). This preclinical study evaluates targeting of Akt with AZD5363 alone and in combination with enzalutamide (ENZ) to prevent and delay resistance. Our results demonstrate AZD5363 has significant proapoptotic, antiproliferative activity as monotherapy in ENZ-resistant cell lines in vitro and significantly decreased tumour growth in ENZ-resistant xenograft. The combination of AZD5363 and ENZ showed synergistic decreases in cell proliferation and induced cell-cycle arrest and apoptosis in prostate cancer cell lines LNCaP and C4-2. Notably, the combination of AZD5363 and ENZ resulted in an impressive regression of castrate-resistant LNCaP xenograft tumours without any recurrence demonstrated, whereas progression occurred with both monotherapies. Serum prostate-specific antigen (PSA) levels were also continuously suppressed, and nadir PSA levels were lower in the combination arm compared to ENZ alone. Combination AZD5363 and ENZ at time of castration similarly resulted in significant regression of tumours, with greater relative suppression of PSA compared to when administered to castrate-resistant xenografts. In summary, combination AZD5363 and ENZ significantly delays the development of ENZ resistance in preclinical models through synergistic increases in apoptosis and cell cycle arrest. Our results also suggest greater efficacy may be seen with earlier combination treatment. This study provides preclinical data to support evaluation of combination targeting of the PI3K/Akt pathway and the androgen-receptor axis in the clinic using AZD5363 and ENZ, respectively. Patient summary Targeting of the Akt and androgen receptor pathways with AZD5363 and enzalutamide, respectively, significantly delayed the development of enzalutamide-resistant prostate cancer through increased apoptosis and cell cycle arrest. This preclinical synergy provides a strong rationale for clinical evaluation of this combination.