Stemline Therapeutics, Inc., presented updated clinical data on the felezonexor (SL-801) Phase 1 trial in patients with advanced solid tumors at the European Society of Medical Oncology (ESMO) 2019 Annual Congress in Barcelona, Spain. The presentation is now available on the Stemline website, www.stemline.com, under the Scientific Presentations tab. Felezonexor is a novel, oral, small molecule that reversibly inhibits Exportin-1 (XPO1), a nuclear export protein, overexpressed in a variety of solid and hematologic malignancies. XPO1 is a mediator of nuclear-cytoplasmic transport of nuclear proteins and has been associated with aggressive tumor behavior and poor prognosis. XPO1 is a clinically validated target in oncology, and the FDA recently approved an XPO1 inhibitor drug, in combination with other agents, for the treatment of certain oncology patients (with relapsed refractory multiple myeloma). Felezonexor has demonstrated potent in vitro and in vivo preclinical activity. Interim results from the ongoing Phase 1 clinical trial reported at ESMO are summarized below. Key Felezonexor Highlights from Ongoing Phase 1 Trial in Patients with Advanced Solid Tumors: Partial response (PR) achieved with single agent felezonexor in a 4th line patient with KRAS-positive, microsatellite stable (MSS) colorectal cancer (18+ weeks, ongoing). PR (RECIST 1.1 criteria) reported after 2 cycles of felezonexor (70mg then 65mg due to elevated creatinine), with the patient demonstrating serial reductions in the two target lesions (liver and spleen). Treatment with felezonexor ongoing (cycle 6); Next staging pending. Stable disease (SD) achieved in 12 patients, with 11/12 of these patients 3rd line or greater. Five patients had SD for 4 and 11 months, including 1 patient with basal cell carcinoma with SD for 11 months. 20% disease shrinkage noted in one patient with heavily pre-treated neuroendocrine tumor. Pharmacokinetic (PK) analyses suggest dose-dependent increases in exposure. Dosing regimen previously adjusted (Schedule B) to improve tolerability while maintaining dose intensity; 1 patient in Schedule B (n=7) experienced grade 3 weakness, the 75mg cohort has been expanded and enrollment continues. Ideal therapeutic dose and regimen not yet determined, and dose escalation ongoing. Further updates expected as Phase 1 trial continues to enroll.