Abstract 4515: SPR965: an oral PI3K/ mTOR C1/C2 inhibitor for the treatment of solid tumors
Authors: Arora Reena , Dutta Bakul K. , Goel Ravinder , Hollinger Frank P. , Kulia Bilash , Mahajan Dinesh , Mahapatra Amal R. , Sagar Milind , Sen Somdutta , Sharma Amit , Dugar Sundeep 
Published: May 2015

Background

The discovery and development of inhibitors for the PI3K/AKT/mTOR signaling pathway is an attractive area of research due to its association with several oncogenic malignancies. This signaling pathway controls cellular growth as well as survival via regulation of widely divergent physiological processes, i.e. cell cycle progression, differentiation, transcription, translation and apoptosis. Constitutive activation of the PI3 kinase alpha and/or the downstream protein mTOR has been implicated in the progression of a large variety of solid tumors. Literature reports suggest the importance of developing combined and specific inhibitor of both PI3K and mTOR kinases.

Described herein is the discovery of a novel small molecule, SPR965, a potent, and orally bioavailable inhibitor for class 1 PI3 Kinase and mTOR kinases with the potential for the clinical treatment of various solid tumors, specifically prostate, ovarian and colon cancers. The complete preclinical profile of SPR965 is presented in detail.

Methods

Drug candidates were evaluated in an in vitro enzyme assays to determine their inhibitory activity PI3 and mTOR C1/ C2 kinases. Promising candidates were then evaluated in proliferation assays using various human cancer cell lines (PC3 - prostate, SKOV3 - ovarian, HCT-116 - colon and A2780 - ovarian). The most promising leads were then evaluated against a panel of 456 kinases to determine the level of selectivity for our primary targets - PI3K and mTOR C1/C2. Compounds meeting the desired threshold of potency and selectivity were evaluated for their in vivo pharmacokinetic profile (iv/ po) in rodents followed by studies in mouse xenograft models (SKOV3 and HCT-116).

Results

SPR965 is a potent inhibitor of PI3K alpha and mTOR with an IC50 of 24 and 25 nM respectively. SPR965 is also a highly selective inhibitor of PI3 and mTOR C1/C2 kinases when evaluated in a screen against 456 kinases. Further studies demonstrated that SPR965 is a potent inhibitor of proliferation in a multiple cell lines and in several xenograft models. The proliferation inhibition activity (EC50) in A2780 is 17 nM, PC3 is 30 nM, SKOV3 is 74 nM, and HCT-116 is 163 nM. SPR965 is one of the most efficacious PI3/mTOR kinase inhibitor yet reported, with ED50 = 0.5 mg/Kg as determined in a SKOV3 xenograft mouse model and ED50 = 0.6 mg/ Kg in HCT-116 xenograft mouse model. This dose level is markedly lower than those reported for other reported inhibitors of this pathway. Pharmacokinetic studies in Sprague Dawley rats and in NUDE mice indicated that the oral bioavailability of SPR965was ∼100% and 75% respectively.

Conclusion

SPR965 is one of the most efficacious inhibitor of the PI3 and mTOR kinases when compared to the reported ED50s of other reported compounds. It also is one of the most selective and highly bioavailable inhibitor of the PI3 and mTOR kinases. Further studies are underway to support first-in-human trials with SPR965 where we hope to demonstrate its unique therapeutic benefits.

Citation Format: Reena Arora, Bakul K. Dutta, Ravinder Goel, Frank P. Hollinger, Bilash Kulia, Dinesh Mahajan, Amal R. Mahapatra, Milind Sagar, Somdutta Sen, Amit Sharma, Sundeep Dugar. SPR965: an oral PI3K/ mTOR C1/C2 inhibitor for the treatment of solid tumors. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4515. doi:10.1158/1538-7445.AM2014-4515