Modulation Of The Hedgehog Signaling Pathway In Models Of Basal Cell Carcinoma By Atp-Competitive Pkci Inhibitors

We will describe for the first time the optimization and pharmacological characterisation of azaquinazoline based ATP-competitive inhibitors of the aPKC isoforms. The serine/threonine kinase protein kinase C iota (PKCι) and protein kinase C zeta (PKCζ) together define the atypical sub-class of the protein kinase C superfamily (aPKC). Both isoforms have emerged as master regulators of cellular polarity with PKCι implicated in the maintenance of aberrant Hedgehog (HH) pathway activity in basal cell carcinoma (BCC). Common activating mutations in the HH signalling pathway drive BCC growth through the transcription factor GLI. Inhibitors of membrane protein smoothened (SMO) are clinically effective suppressors of HH signalling in BCC. However, acquired and de novo resistance to SMO inhibitors poses severe limitations to the clinical use of these agents. PKCι has been shown to directly activate GLI1 in BCC and has been linked to SMO inhibitor resistance making a strong case for the development of a selective PKCι inhibitor. Insights from structural biology identified critical amino acid residues in the PKCι binding pocket that could be exploited through structure-based drug design to optimise inhibitor potency and selectivity over structurally related kinase targets. The phosphorylation status of the known PKCι proximal substrate LLGL2 was used as a cellular pharmacodynamic biomarker and to demonstrate in vivo PKCι inhibition. To investigate the effects of PKCι inhibitors on the HH pathway a panel of compounds covering a diversity of chemotypes were profiled using a Hedgehog pathway GLI1 reporter assay in an engineered NIH3T3 cell line. Murine and human BCC cells, dependent on HH signalling for survival, were sensitive to PKCι inhibitor treatment with concomitant dose and time dependent effects on the expression of the HH pathway activity biomarker GLI1. Taken together, these results have therapeutic implications making a strong case for further evaluation of PKCι inhibitors in the setting of SMO-inhibitor-resistant BCC cancers. Citation Format: Jon Roffey, Christian Dillon, Anthony E. Oro, Amar N. Mirza, Kavita Y. Sarin, Sumaira Z. Aasi, Peter J. Parker, Philippe Riou, Caroline Barton, Bhavisha Patel, Caroline Barton, Andrew Turnbull, Emma Stanway, Katherine Fowler, Gregory Ott, Mark Ator. Modulation of the Hedgehog signaling pathway in models of basal cell carcinoma by ATP-competitive PKCi inhibitors [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr LB-B32.