Abstract B065: Combining the androgen receptor inhibitor darolutamide with PI3K/AKT/mTOR pathway inhibitors has superior efficacy in preclinical models of prostate cancer

The phosphoinositide 3 kinase (PI3K)/AKT/mammalian target of rapamycin (mTOR) signaling pathway is dysregulated in the majority of advanced prostate cancer patients, often linked to phosphate and tensin homolog (PTEN) inactivation. An increasing number of studies demonstrates the reciprocal crosstalk between the PI3K/AKT/mTOR and the androgen receptor (AR) pathways with the inhibition of one of them leading to the compensatory activation of the other one. We compared the effects of different PI3K/AKT/mTOR pathway inhibitors as single agents or in combination with the AR inhibitor darolutamide.In vitro impact of the compounds was evaluated in prostate cancer cell lines by proliferation and apoptosis assays, and by RNA-seq analysis. In vivo effects were determined in a patient-derived (PDX) prostate cancer model in an efficacy study followed by immunohistochemistry analysis. Analysis of VCaP cells treated with the androgen R1881 showed that beside androgen response, the PI3K/AKT/mTOR pathway was an essential hallmark characteristic of androgen action. Additional darolutamide treatment opposed androgen effects on both pathways. We therefore evaluated the impact of selective inhibitors of PI3K or AKT and saw strong in vitro antiproliferative effects in the prostate cancer cell lines tested. We then focused on the pan-PI3K inhibitor copanlisib and observed pronounced synergistic effects with darolutamide in the VCaP model. This was accompanied by induction of PARP cleavage and activation of caspase 3/7. A detailed transcriptomic analysis revealed that the combination of both inhibitors resulted in more pronounced transcript changes, compared to individual treatments. Principal component analysis furthermore showed the combination to be closer to the DMSO control along the axis that represents androgen regulation. We observed a pronounced downregulation of cell proliferation and cell division genes following combination treatment compared to individual treatments, a prominent example being the proliferation marker KI67. In vivo studies performed with the PDX LuCaP 35 model revealed a superior inhibitory effect of the combination treatment with darolutamide and copanlisib when compared to single agents. Immunohistochemistry analysis revealed a significant upregulation of a pro-apoptotic pathway in tumors treated with darolutamide and copanlisib which was not observed in single treatment arms, when compared to vehicle control. In summary, we found that different P