Therapeutic effect of gedatolisib, a pan-PI3K/mTOR inhibitor, on prostate cancer models with PI3K or PTEN mutational status.

Abstract

149 Background: Metastatic castration-resistant prostate cancer (mCRPrC) is characterized by a loss of androgen receptor (AR) sensitivity and oncogenic activation of the PI3K, AKT, and mTOR (PAM) pathway. Loss of the PI3K regulator, PTEN, is frequent during prostate cancer (PrC) initiation, progression, and therapeutic resistance. Co-targeting PAM/AR pathways is a promising PrC treatment strategy but hampered by complex PAM-AR pathway crosstalk driving either reciprocal negative feedback inhibition or feedback relief. Most PAM inhibitors (PAM-i) selectively spare (or weakly inhibit) one or more key PAM pathway components, potentiating drug resistance depending on the PAM mutation status of patients. AKT-i demonstrated limited efficacy in PTEN-deficient PrC and even less efficacy in PTEN-wild type (wt) in recent clinical studies, suggesting that more comprehensive inhibition of the PI3K isoforms and mTOR may be required. We posited that gedatolisib, a well-tolerated and potent inhibitor of all Class I PI3K isoforms, mTORC1, and mTORC2, would be effective in both PTEN-wt and PTEN-deficient PrC. Methods: A panel of PrC cell lines with different PI3K or PTEN status ( wt: 22RV1, MDA-PCa-2b, DU145; null: LNCaP, PC3, C4-2) were assayed under different conditions for their sensitivity to gedatolisib and other PAM-I ( PI3K: alpelisib, copanlisib; AKT: capivasertib, ipatasertib; mTOR: everolimus; pan-PI3K/mTOR: samotolisib, gedatolisib). A combination of cell viability, growth rate, cytotoxicity and phospho-FACS analytical assays were used. Xenograft studies evaluating gedatolisib with a subset of these models were also performed in castrated mice. Results: We confirmed that AKT-i is more effective in PTEN-null than PTEN-wt PrC. In contrast, the two pan-PI3K/mTOR-i evaluated were effective independent of PI3K or PTEN status. Gedatolisib exhibited superior potency and efficacy compared to each of the other PAM-i for cell proliferation, death, or PAM pathway activation. In vivo, gedatolisib substantively inhibited tumor growth regardless of PTEN or PI3K status. Conclusions: We demonstrated that gedatolisib exerts superior activity regardless of PI3K or PTEN status in all PrC cell lines evaluated compared to the other PAM pathway inhibitors evaluated. Our results indicate potent and simultaneous blockade of all Class I PI3K isoforms, mTORC1, and mTORC2 could circumvent PTEN dependent resistance. Gedatolisib as a single agent and in combination with other therapies reported promising preliminary efficacy and safety in various solid tumor types. In light of the PrC findings reported here, development of gedatolisib may be warranted in PrC patients regardless of their PTEN or PI3K status.