Evaluation Of The Novel, Orally Bioavailable Selective Inhibitor Of Nuclear Export (SINE) Verdinexor (KPT-335) In Spontaneous Canine Cancer: Results Of Phase I and Phase II Clinical Trials

SINE (Selective Inhibitors of Nuclear Export) block the activity of XPO1/CRM1, 1 of 7 nuclear export proteins in cells, forcing the nuclear retention of key tumor suppressor proteins (TSP), leading to selective apoptosis of tumor cells.  The purpose of these studies was to evaluate the in vitro activity of SINE against canine tumor cell lines and investigate the biological activity of Verdinexor (KPT-335) in dogs with spontaneous cancers as proof of principle for human clinical studies with SINE. Several different canine tumor cell lines including those derived from Non-Hodgkin Lymphoma (NHL) exhibited growth inhibition and apoptosis in response to nanomolar concentrations of SINE; NHL cells were particularly sensitive with IC50 concentrations ranging from 2-42 nM. A Phase I clinical trial of Verdinexor was performed in dogs with cancer with an emphasis on NHL given in vitro activity demonstrated against the tumor cell lines. The maximum tolerated dose (MTD) was 1.75 mg/kg twice per week although biological activity was observed at 1 mg/kg. Clinical benefit including Partial Response (PR) and Stable Disease (SD) for at least 4 weeks was observed in 9/14 dogs with NHL with a median time to progression of 66 days (range 35-256). A dose expansion study was performed in 6 dogs with NHL given 1.5 mg/kg Verdinexor on a Monday/Wednesday/Friday (MWF) regimen; clinical benefit (PR + SD) was observed in 4/6 dogs with a median time to progression of 83 days (range 35-250+). Toxicities were primarily gastrointestinal in nature consisting of anorexia, weight loss, vomiting and diarrhea and were manageable with supportive care and dose modulation.  A validated health related Quality of Life (QOL) form used to assess dogs during treatment demonstrated that the overall quality of life did not decrease in dogs in this study supporting the notion that clinical toxicities associated with Verdinexor are generally well tolerated.  Based on these findings, a Phase IIb study was performed in 58 dogs with either newly diagnosed or relapsed NHL.  Drug was administered initially at 1.5 mg/kg MWF, but this dosing regimen was changed to 1.25 mg/kg M/Th due to the high rate of anorexia and weight loss on the MWF regimen; dose escalation was permitted to 1.5 mg/kg on the M/Th regimen.  The objective response rate was 34% (1 CR, 19 PR) with an additional 33 dogs experiencing SD for a minimum of 4 weeks, resulting in a of 91% disease control rate. While the median time to progression was approximately 5 weeks, 19 dogs (32%) remained on study drug for >8 weeks; several dogs continue to receive Verdinexor.  Laboratory abnormalities were minimal and clinical toxicities were mild on the M/Th regimen.  Together, these data provide robust evidence that the novel orally bioavailable XPO1 inhibitor Verdinexor exhibits single agent biological activity in a spontaneous large animal model of human NHL. Furthermore, Verdinexor was well tolerated even in the absence of supportive care, suggesting that SINE compounds could exhibit good long-term tolerability in people.