466P - Interim results from trial of SL-801, a novel XPO-1 inhibitor, in patients with advanced solid tumours

SL-801 is a novel, oral, small molecule that reversibly inhibits Exportin-1 (XPO-1), a nuclear export protein, overexpressed in a variety of solid and hematologic malignancies. XPO-1 is a mediator of nuclear-cytoplasmic transport of over 200 nuclear proteins and has been associated with aggressive tumor behavior and poor prognosis. SL-801 has demonstrated potent in vitro and in vivo activity. Interim results from the dose-escalation stage are reported. STML-801-0115 is a first-in-human, multicenter dose and schedule finding study in patients with localized unresectable, or metastatic solid tumors that are refractory to or are relapsed after treatment with standard therapy. Objectives are to identify the maximum tolerated dose or optimal dose/schedule, and assess pharmacokinetics, pharmacodynamics, and preliminary anti-tumor activity. SL-801 was initially orally administered on days 1-4 and 8-11 of a 21-day cycle (Schedule A). The dosing schedule has been amended to potentially allow a longer recovery time between dosing periods while maintaining dose intensity. Patients are now receiving SL-801 once daily on days 1-2, 8-9, 15-16 and 22-23 of a 28-day cycle (Schedule B). The starting dose in the study was 5mg/day in Schedule A; current study dose level is 70mg/day in Schedule B. 45 patients received 5-65mg/day of SL-801 in Schedule A (median age 63 YO [range: 39-83], 51% females, median number of prior systemic therapies, 4 [range: 2-10]; 57% received 3 or more. Common treatment-emergent adverse events (TEAEs) were nausea (62%), vomiting (64%), fatigue (44%), decreased appetite (33%), and diarrhea (29%). Grade 3 TEAEs included nausea (9%), anemia (7%), and fatigue, diarrhea, hyponatremia and hypophosphatasemia (each 4%). Most TEAEs were grade 1-2; no grade 4-5 toxicities reported. 12 patients (27%) had stable disease (SD) and remained on study for 2-11 months including 5 with SD for 4+ months. 1 patient with basal cell carcinoma had SD for 11 months. 3 patients had radiographic tumor shrinkage of 14-20% in target lesions. SL-801 reversibly binds XPO1, a clinically validated target in oncology. To date 27% of heavily pre-treated patients have achieved SD as best response. Enrollment and dose escalation continue. NCT02667873. Stemline Therapeutics. Stemline Therapeutics. J. Wang: Speaker Bureau / Expert testimony: AstraZeneca. E. Chiorean: Research grant / Funding (institution): Boehringer-Ingelheim, Merck, BMS, Lilly, Stemline, Ignyta/Roche, Incyte, Halozyme