Abstract B181: Association of AKT1E17K and PIK3CAH1047R mutations with efficacy of ARQ 092 in vitro, in vivo and in patients

Abstract

Abstract Background: The AKT pathway is critical in cancer initiation and progression, it can be constitutively activated by mutations in AKT (8% breast, 6% colorectal, 6.8% meningioma) and PIK3CA (27% breast, 28% endometrial, 13% colorectal)12. ARQ 092 is a potent and selective AKT inhibitor in phase 1 clinical development. Also, ARQ 092 has been shown to have anti-growth activity in cells from patients with Proteus syndrome, a non-cancer disease solely driven by AKT1E17K3. Methods: Biochemical IC50 for AKT 1/2/3 and the selectivity profile of ARQ 092 or ARQ 751 (more potent next generation AKT inhibitor) against over 300 kinases were determined. The binding of both inhibitors to wild-type AKT1 and AKT1E17K was assessed using intrinsic tryptophan fluorescence quench. Inhibitory effect on AKT1E17K was determined in transient transfection cell system. AKT1 membrane translocation was performed in cells transiently transfected with GFP-fused AKT1 or AKT1E17K. AKT pathway in select cell lines was assessed using Western blot analysis. Anti-proliferative effects were tested in a panel of 18 breast cancer cell lines, 4 with H1047R. In vivo efficacy was tested in 2 mouse xenografts and 2 patient-derived tumors with endometrial and breast cancer cells bearing AKT1E17K or PIK3CAH1047R mutations. In a phase 1 clinical trial, patients have been enrolled to receive oral ARQ 092 at multiple doses and schedules4. Results: ARQ 092 inhibited AKT1, 2, and 3 activity with IC50 values of 5.0, 4.5, and 16 nM, respectively whereas ARQ 751 had IC50 values of 0.54, 0.79, and 1.3 nM, respectively; MK-2206 exerted less potency (40.5, 29.5 and 36.4 nM) and GDC-0068 showed potency of 2.0, 27.0, and 6.3 nM. For the AKT1E17K mutant, Kd values were 42 and 8.6 nM for ARQ 092 and ARQ 751 respectively, accompanied with inhibition of its phosphorylation; whereas over 1 μM for MK-2206. ARQ 092 and ARQ 751 but not MK-2206 at 1 μM blocked AKT1E17K membrane translocation. ARQ 092 and ARQ 751 were efficacious on all 4 PIK3CAH1047R cells with GI50 of less than 1 μM. In an endometrial PDX model bearing AKT1E17K, ARQ 092 at 100 mg/kg and ARQ 751 at 75 mg/kg obtained respectively 78% and 98% tumor growth inhibition. In vivo models with PIK3CAH1047R treated with ARQ 092 at 100-120 mg/Kg exhibited tumor growth inhibition between 32% and 84%. In the ongoing clinical trial, in 7 patients with AKT1E17K enrolled at doses close to MTD for each schedule, 2 RECIST partial responses (breast cancer and follicular lymphoma), 2 minor responses (parotid cancer, 19.3% tumor reduction; endometrial cancer, 17.5% reduction), 3 stable diseases (ovarian, neuroendocrine, meningioma, 120-277 days on therapy) were observed. One patient with PIK3CAH1047R mutant endometrial carcinoma was treated and obtained a partial response. Conclusions: ARQ 092, and the next generation ARQ 751, are potent, selective allosteric AKT inhibitors. They both bind tightly to and inhibit membrane translocation and activation of AKT1E17K and of PI3K-stimulated AKT. Preclinical and clinical findings from oncology and non-oncology studies show that AKT1 E17K and PIK3CAH1047R mutations may be used for patient selection. 1Kim MS, Br J Cancer 2008. 2Yuan TL, Oncogene 2008. 3Biesecker L, ASHG 2014 4Tolcher A, ESMO 2015. Citation Format: Giovanni Abbadessa, Yi Yu, Sudharshan Eathiraj, Justin Meade, Michael J. Wick, Anthony Tolcher, Kyri Papadopoulos, Mansoor Saleh, Jasgit Sachdev, Feng Chai, Brian Schwartz. Association of AKT1E17K and PIK3CAH1047R mutations with efficacy of ARQ 092 in vitro, in vivo and in patients. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr B181.