Data from Recurrent Mutations in Cyclin D3 Confer Clinical Resistance to FLT3 Inhibitors in Acute Myeloid Leukemia

<div>AbstractPurpose:<p>Biomarkers of response and resistance to FLT3 tyrosine kinase inhibitors (TKI) are still emerging, and optimal clinical combinations remain unclear. The purpose of this study is to identify co-occurring mutations that influence clinical response to the novel FLT3 inhibitor pexidartinib (PLX3397).</p>Experimental Design:<p>We performed targeted sequencing of pretreatment blasts from 29 patients with <i>FLT3</i> internal tandem duplication (ITD) mutations treated on the phase I/II trial of pexidartinib in relapsed/refractory <i>FLT3</i>-ITD+ acute myeloid leukemia (AML). We sequenced 37 samples from 29 patients with available material, including 8 responders and 21 non-responders treated at or above the recommended phase II dose of 3,000 mg.</p>Results:<p>Consistent with other studies, we identified mutations in <i>NRAS, TP53, IDH2</i>, and a variety of epigenetic and transcriptional regulators only in non-responders. Among the most frequently mutated genes in non-responders was Cyclin D3 (<i>CCND3)</i>. A total of 3 individual mutations in <i>CCND3</i> (Q276*, S264R, and T283A) were identified in 2 of 21 non-responders (one patient had both Q276* and S264R). No <i>CCND3</i> mutations were found in pexidartinib responders. Expression of the Q276* and T283A mutations in <i>FLT3</i>-ITD MV4;11 cells conferred resistance to apoptosis, decreased cell-cycle arrest, and increased proliferation in the presence of pexidartinib and other FLT3 inhibitors. Inhibition of CDK4/6 activity in <i>CCND3</i> mutant MV4;11 cells restored pexidartinib-induced cell-cycle arrest but not apoptosis.</p>Conclusions:<p>Mutations in <i>CCND3</i>, a gene not commonly mutated in AML, are a novel cause of clinical primary resistance to FLT3 inhibitors in AML and may have sensitivity to CDK4/6 inhibition.</p></div>