To the editor,


Selinexor (KPT-330) is an oral selective inhibitor of nuclear export (SINE) and was shown to hinder the DNA damage repair (DDR) system by diminishing DDR proteins expression while enhancing the killing of cancer cells by DDR-based therapeutics in vivo preclinical models [1,2,3]. Previous early phase studies demonstrated the modest activity of single agent selinexor in patients with solid tumors [4,5,6]. In vivo studies of selinexor in combination with different chemotherapeutics demonstrated synergistic activity [3, 7, 8]. An open-label, multi-arm phase 1b study utilizing selinexor in combination with different standard chemotherapies was conducted at MD Anderson Cancer Center to evaluate the safety and tolerability of the combination. Herein, we report results from 5 closed separate arms of the study.

Eligible patients were adult (age  ≥ 18 years) patients with histologically documented, relapsed/metastatic refractory solid tumors following standard therapy or adding selinexor to systemic therapy was appropriate. The primary aim was to evaluate the safety and tolerability of selinexor when given in combination with different standard chemotherapies and the secondary aim was to determine the preliminary antitumor activity [DCR (CR  +  PR  +  SD  ≥ 6 months), and progression-free survival (PFS)].

Nineteen patients with relapsed/refractory solid tumors were enrolled between July 2015 and January 2017. The demographic and clinical characteristics of all patients enrolled are summarized in Table 1. No patients are currently in the study where the majority of patients withdrew from the study due to progression of disease while 5 patients withdrew due to clinically intolerable treatment-emergent adverse events (TEAE). All patients experienced at least one TEAE and TRAE (Table 2 and Additional file 1: Table S2). The commonest TRAE were thrombocytopenia (84%), nausea (68%), leukopenia (68%), neutropenia (63%), fatigue (58%), vomiting (53%), and anemia (53%). The most prevalent grade 3/4 TRAE were neutropenia (42%), leukopenia (26%), hyponatremia (21%), anemia (16%), and thrombocytopenia (16%). Three patients experienced DLTs; a patient dosed at selinexor 60 mg twice weekly (BIW) with DC reported grade 3 leukopenia and grade 4 neutropenia; a patient receiving selinexor at 40 mg once weekly (QW) with FOLFIRI reported grade 3 febrile neutropenia (FN); and a patient receiving selinexor at 40 mg QW with XELOX reported grade 3 diarrhea. Four patients were reported to have serious adverse events (SAEs). One patient receiving selinexor with DC had an SAE from treatment-related grade 3 FN. Two patients in the combination of selinexor with FOLFIRI had SAEs; one patient had treatment-related grade 3 FN while the other had treatment-unrelated grade 2 pancreatitis. One patient receiving selinexor with XELOX had an SAE from treatment-related grade 3 diarrhea and treatment-unrelated grade 3 dyspnea and skin infection. No patients died during the study.

Table 1 Patients baseline demographics and disease characteristics
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Table 2 Summary of treatment-related adverse events (TRAE) in all grades of severity
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All patients enrolled had measurable disease, but 5 patients had not completed their first restaging scans due to earlier withdrawal of consent and toxicity. Fourteen patients were considered efficacy evaluable patients (Additional file 1: Figure S1). No patients had objective responses, however, 7 patients had SD. Of the 7 SD patients, 2 received selinexor with DC (ovarian cancer), 2 received selinexor with FOLFIRI [colorectal cancer (CRC); neuroendocrine carcinoma of the pancreas], 2 received selinexor with XELOX (CRC; cholangiocarcinoma), and 1 received selinexor with irinotecan (CRC). All had progressed on multiple prior lines of therapy including FOLFOX, FOLFIRI, cisplatin  +  gemcitabine, FOLFRINOX, temozolomide, everolimus, octreotide, capecitabine, sunitinib, and ziv-aflibercept. The median time-to-treatment failure (TTF) was 20 weeks (range, 6–29 weeks). Two patients who received selinexor with XELOX experienced disease control resulting in a DCR of 14%. A patient with CRC who progressed on prior 4 lines of therapies, had stable disease with TTF of 26 weeks. Another patient with cholangiocarcinoma who progressed on prior 3 lines of therapies including cisplatin  +  gemcitabine, FOLFRINOX, had stable disease with TTF of 29 weeks. The median PFS for all patients was 2.0 months (95% CI 1.2, 2.8) while the median OS for all patients was 5.2 months (95% CI 4.0, 11.2) (Additional file 1: Figure S2).

In conclusion, selinexor in combination with standard chemotherapy showed limited clinical activity with some toxicity. Although RP2D of selinexor was 40 mg QW in combination with XELOX or FOLFIRI, the study arms were not pursued for dose expansion due to toxicities and lack of response. Optimizing supportive care, proper use of growth factors, and aggressive measures on antiemetics strategies are important to mitigate TRAE.