Discovery and pharmacological characterization of AZD3229, a potent KIT/PDGFRα inhibitor for treatment of gastrointestinal stromal tumors

Abstract

Gastrointestinal stromal tumor (GIST) is the most common human sarcoma driven by mutations in KIT or platelet-derived growth factor α (PDGFRα). Although first-line treatment, imatinib, has revolutionized GIST treatment, drug resistance due to acquisition of secondary KIT/PDGFRα mutations develops in a majority of patients. Second- and third-line treatments, sunitinib and regorafenib, lack activity against a plethora of mutations in KIT/PDGFRα in GIST, with median time to disease progression of 4 to 6 months and inhibition of vascular endothelial growth factor receptor 2 (VEGFR2) causing high-grade hypertension. Patients with GIST have an unmet need for a well-tolerated drug that robustly inhibits a range of KIT/PDGFRα mutations. Here, we report the discovery and pharmacological characterization of AZD3229, a potent and selective small-molecule inhibitor of KIT and PDGFRα designed to inhibit a broad range of primary and imatinib-resistant secondary mutations seen in GIST. In engineered and GIST-derived cell lines, AZD3229 is 15 to 60 times more potent than imatinib in inhibiting KIT primary mutations and has low nanomolar activity against a wide spectrum of secondary mutations. AZD3229 causes durable inhibition of KIT signaling in patient-derived xenograft (PDX) models of GIST, leading to tumor regressions at doses that showed no changes in arterial blood pressure (BP) in rat telemetry studies. AZD3229 has a superior potency and selectivity profile to standard of care (SoC) agents—imatinib, sunitinib, and regorafenib, as well as investigational agents, avapritinib (BLU-285) and ripretinib (DCC-2618). AZD3229 has the potential to be a best-in-class inhibitor for clinically relevant KIT/PDGFRα mutations in GIST.

The Pharmacokinetic–Pharmacodynamic (PKPD) Relationships of AZD3229, a Novel and Selective Inhibitor of KIT, in a Range of Mouse Xenograft Models of GIST

“…The potency of AZD3229 along with approved (imatinib, sunitinib and regorafenib) and investigational agents (ripretinib and avapritinib) have been previously reported in a cell viability assay across a Ba/F3 cell panel as the GI 50 (10,13) and GI 90 (14). The known clinical exposures ( Supplementary Table S2) for KIT inhibitors at the approved dose for SoC agents and the recommended phase II dose for the investigational agents have been taken from the literature and the plasma concentration at trough (C, trough ) compared and color coded as green if the C, trough exceeds the GI 90 ( Supplementary Table S3).…”

“…The in vivo studies used in these analyses are described in detail with the primary data, including tumor growth curves and immunoblots by Banks et al, (14). All animal studies HGiXF-106 (GS11331) (KIT exon 11 del 557-558/V654A; Crown Bioscience).…”

“…The PK-pKIT relationship has been explored in four in vivo models, and this covers a narrow range of known mutations. Additional mutations are known to confer resistance to imatinib, sunitinib and regorafenib and the potency of these agents along with AZD3229 and investigational agents (ripretinib and avapritinib) have been previously reported in a cell viability assay across a Ba/F3 cell-panel as the GI 50 (13) and GI 90 (14) ( Supplementary Table S3). It would be desirable to demonstrate a correlation between the cell-viability GI 90 and in vivo EC 90 to be able to use the in vitro data to more fully assess relative activity and exposure requirements across a more extensive number of…”

“…The PKPD insights described above for AZD3299 should be generalizable to other KIT inhibitors. For the SoC agents (imatinib, sunitinib and regorafenib), the potency against the various KIT mutations in the Ba/F3 cell-panel are available, along with in vivo antitumor activity measured at doses in a mouse that deliver clinically relevant exposures ( Supplementary Table S2) (14). The mouse equivalent doses for imatinib (300 mg/kg), sunitinib (80 mg/kg), and regorafenib (100 mg/kg), were calculated using a PK guided approach by matching clinical dose normalized unbound exposure in human to mouse, rather than using an empirical factor (18).…”

“…AZD3229 is an oral, potent KIT/PDGFRα inhibitor that is active against a wide spectrum of primary and secondary KIT/PDGFRα mutations that are known to confer resistance to standard of care (SoC) agents (13). It is also expected to avoid significant VEGFR-2 activity at clinically relevant exposures (13,14).…”