Open-label phase 1/2 study evaluating the tolerability and antitumor activity of selinexor and pembrolizumab in colorectal cancer.

Abstract

110 Background: Single agent selinexor, an oral selective inhibitor of nuclear export (SINE), showed activity against heavily pretreated CRC with RAS mutations (mut) or wildtype (wt) in 2 clinical studies. In preclinical studies, selinexor showed superior potency in KRAS mut over wt with improved activity in combination with PD-1/PD-L1 blockade. A phase 1b study (NCT02419495) showed the safety and antitumor activity of combined selinexor and a PD-1/PD-L1 inhibitor. This phase 1/2 open-label study is evaluating selinexor with pembrolizumab in patients with microsatellite instability (MSI)-stable CRC. Methods: The study enrolled patients with advanced/metastatic CRC who progressed after prior chemotherapy (1-3 lines for RAS wt, 1-2 for RAS mut) and are ineligible for anti-PD-1/PD-L1 therapy. Patients received weekly oral selinexor 80 mg and pembrolizumab 200 mg IV every 3 weeks. Antitumor activity, safety and tolerability were assessed. Results: Thirty-four patients, median age 57.5 years, male 59%, RAS mut 53%, median prior lines 2, are enrolled. At data cutoff (1-SEP-21) median treatment duration was 57 days (range: 1-246) and 25 patients were evaluable for response. Best response was stable disease in 8/13 patients with RAS mut CRC (62%) and in 3/12 patients with RAS wt CRC (25%). Median overall survival (months) has not been reached for the overall population (95% CI: 6.3, NE), for RAS mut (95% CI: 7.6, NE), and for the RAS wt (95% CI: 6.1, NE). Median progression-free survival is 3.0 and 1.4 months for patients with CRC with RAS mut and wt, respectively (p=0.04; HR: 0.43 [959% CI: 0.18, 1.01]). Thirty patients (88%) discontinued therapy, mostly due to progressive disease (44%). The most common treatment-emergent adverse events (TEAEs) (total; Grade ≥3) were nausea (77%; 3%), vomiting (41%; 0%), fatigue (41%; 12%), decreased appetite (35%; 0%), diarrhea (32%; 0%). Nine patients (26%) had serious treatment-emergent adverse events. Conclusions: Combined selinexor with pembrolizumab demonstrated higher disease control rates and prolonged overall survival in patients with chemotherapy-refractory advanced/metastatic CRC with RAS mut vs RAS wt tumors. These patients would not have been eligible for anti-PD-1 mAb therapy because their tumors were not MSI-high, suggesting that the combination may be active in RAS mut CRC. Therapy was well tolerated with no unanticipated adverse events. Further investigation of this combined treatment is warranted, particularly in patients with CRC with RAS mut. Clinical trial information: NCT04256707.