Brain Exposure to the Macrocyclic ALK Inhibitor Zotizalkib is Restricted by ABCB1, and Its Plasma Disposition is Affected by Mouse Carboxylesterase 1c

Zotizalkib (TPX-0131), a fourth-generation macrocyclic anaplastic lymphoma kinase (ALK) inhibitor, is designed to overcome resistance due to secondary ALK mutations in non-small cell lung cancer (NSCLC). We here evaluated the pharmacokinetic roles of the ABCB1 (P-gp/MDR1) and ABCG2 (BCRP) efflux transporters, OATP1 influx transporters and the metabolizing enzymes CES1 and CYP3A in plasma and tissue disposition of zotizalkib after oral administration in relevant mouse models. Zotizalkib was efficiently transported by hABCB1 in vitro. In vivo, a significant ∼9-fold higher brain-to-plasma ratio was observed in <i>Abcb1a/b</i>^-/- and <i>Abcb1a/b;Abcg2</i>^-/- compared to wild-type mice. No change in brain disposition was observed in <i>Abcg2</i>^-/- mice, suggesting that mAbcb1a/b markedly restricts the brain accumulation of zotizalkib. ABCB1-mediated efflux of zotizalkib was completely inhibited by elacridar, a dual ABCB1/ABCG2 inhibitor, increasing brain exposure without any signs of acute CNS-related toxicities. In <i>Oatp1a/b</i>^-/- mice, no marked changes in plasma exposure or tissue-to-plasma ratios were observed, indicating that zotizalkib is not a substantial <i>in vivo</i> substrate for mOatp1a/b. Zotizalkib may further be metabolized by CYP3A4 but only noticeably at low plasma concentrations. In <i>Ces1</i>^-/- mice, a 2.5-fold lower plasma exposure was seen compared to wild-type, without alterations in tissue distribution. This suggests increased plasma retention of zotizalkib by binding to the abundant mouse plasma Ces1c. Notably, the hepatic expression of human CES1 did not affect zotizalkib plasma exposure or tissue distribution. The obtained pharmacokinetic insights may be useful for the further development and optimization of therapeutic efficacy and safety of zotizalkib and related compact macrocyclic ALK inhibitors.