Abstract 2665: High dose intermittent scheduling of AZD8835, a novel potent and selective inhibitor of PI3Kα and PI3Kδ, identifies potential treatment strategies for PIK3CA-dependent cancers

Abstract

Abstract The PIK3CA gene, encoding the p110 catalytic unit of PI3Kα, is one of the most frequently mutated oncogenes described in human cancer. Hence PI3Kα is a target subject to intensive efforts in identifying inhibitors and evaluating their therapeutic potential. To date most studies with PI3K inhibitors have used a continuous (daily) dosing schedule and although clinical responses have been reported the overall activity observed has been moderate. This may in part be due to suboptimal pathway inhibition which is capped by normal tissue toxicities such as rash, diarrhoea and hyperglycaemia. Furthermore, additional dose reduction may be required when such agents are used in combination with other therapies. Therefore in our efforts to optimise inhibition of PI3K pathway signalling, we have explored high dose intermittent scheduling as an alternative to continuous dosing. Here we describe pre-clinical studies that exemplify such concepts, centred around use of AZD8835, a PI3K inhibitor currently in Phase 1 clinical evaluation. AZD8835 is a novel and potent inhibitor of PI3Kα and PI3Kδ, with selectivity vs. PI3Kβ, PI3Kγ(IC50s of 6nM, 6nM, 431nM and 90nM respectively in enzyme assays) and other kinases. AZD8835 preferentially displays activity in tumour models with a mutant PIK3CA background, such as ER+ve breast cancer models. Such models were used in our investigations, in both cell culture and in mouse xenograft contexts. We demonstrate that a high dose intermittent schedule of single agent AZD8835 achieves greater pathway inhibition yielding significant anti-tumour responses. In the sensitive BT474 xenograft model, a dose of 100mg/kg AZD8835 BID on days 1 and 4 in a weekly schedule delivered -36% tumour regression, accompanied by a strongly elevated rapid onset apoptosis signal with 4-16% cells staining positively for cleaved-caspase3. We also evaluated AZD8835 in combination with other targeted therapeutic agents, in MCF7, BT474 and T47D breast models, observing increased sensitivity relative to single agent AZD8835; firstly with agents that target other nodes in the PI3K pathway; secondly with agents targeting parallel but interconnected driver pathways in breast disease (ER, CDK4/6). Overall the data indicate that high dose intermittent scheduling can deliver strong anti-tumour efficacy in a range of combination settings and provides a promising alternative to continuous dosing. Such schedules merit clinical evaluation. Citation Format: Kevin Hudson, Urs Hancox, Cath Trigwell, Phillippa Dudley, Lyndsey Hanson, Robert McEwen, Alys Jones, Marie Cumberbatch, Urszula Polanska, Rebecca Ellston, Oona Delpuech, Pablo Morentin Gutierrez, Lara Ward, Francisco Cruzalegui, Stephen Green. High dose intermittent scheduling of AZD8835, a novel potent and selective inhibitor of PI3Kα and PI3Kδ, identifies potential treatment strategies for PIK3CA-dependent cancers. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2665. doi:10.1158/1538-7445.AM2015-2665