Results of a Phase I Dose Escalation Study of the Novel, Oral CRM1 Selective Inhibitor of Nuclear Export (SINE) KPT-335 in Dogs with Spontaneous Non-Hodgkin's Lymphomas (NHL)

Nuclear-cytoplasmic transport is highly regulated by karyopherin proteins – importins and exportins – through the nuclear pore complex. Of the seven known exportins, most tumor suppressor proteins (TSP) and IkB, the inhibitor of NF-kB, are transported out of the nucleus exclusively by exportin 1 (XPO1), more commonly called CRM1. SINE compounds bind irreversibly CRM1/XPO1, forcing the nuclear retention and activation of TSP and IkB, leading to selective tumor cell death. In vitro, SINEs demonstrate potent cytotoxic activity against tumor cells at nanomolar concentrations with minimal effects on normal cells in vitro. KPT-335 and related SINEs show oral bioavailability, good tolerability, and potent activity in multiple mouse xenograft models. Hematologic cancers are particularly vulnerable to SINE induced apoptosis, and effects on normal tissues are minimal at antitumor doses.

Cytotoxicity was assessed in vitro with MTT and apoptosis assays. In order to evaluate the therapeutic potential of SINE in a spontaneous, large animal malignancy with many similarities to human disease including NF-kB activation, dogs with relapsed or newly diagnosed NHL were treated with KPT-335 in this dose escalation study. The primary objective was to evaluate the adverse events (AEs) and to establish the maximum tolerated dose (MTD) of KPT-335 orally in capsules. The secondary objectives were to determine the optimal dosing regimen, correlate pharmacodynamic markers and drug levels, and provide evidence of biological activity. We report the interim results defining the MTD and AEs of KPT-335 in dogs with NHL.

All dogs had progressive disease (PD) on entry into the trial. Dogs with newly diagnosed or relapsed NHL, metastatic osteosarcoma (OSA), melanoma (MEL) and mast cell tumor (MCT) were eligible with preference given to NHL. The initial KPT-335 dose was 1 mg/kg (equivalent to 20mg/m²) orally with food on a Monday/Thursday schedule. At least 3 dogs were included in each cohort, and dose was escalated by 0.25mg/kg increments. CBC, serum chemistries, clotting times, drug peak plasma level and response to therapy were assessed at each weekly visit. Tumor samples will be obtained before and after treatment in an expansion cohort once the optimal dosing regimen has been determined.

Three structurally related SINE compounds including KPT-335 showed potent cytotoxicity of primary and immortalized canine B cell lymphomas in vitro (EC₅₀<100 nM). The Phase 1 dose escalation study with KPT-335 oral included doses of 1mg/kg twice weekly and continued up to 2mg/kg (Table 1). Doses up to 1.75mg/kg were very well tolerated for over 3 months. At 1.75mg/kg, mild to moderate anorexia, weight loss and alkaline phosphatase elevation (possibly related to prednisone use) were observed. DLTs occurred at 2mg/kg including anorexia and vomiting without diarrhea. Laboratory parameters showed minimal or no changes at doses below the DLT.

Oral KPT-335 shows single agent disease stabilization and tumor reduction in dogs with NHL, the majority of who have diffuse large B cell lymphoma (DLBCL) relapsed after chemotherapy (typically CHOP). The activation of TSP and the neutralization of NF-kB activity by nuclear localization of IkB may contribute to the antitumor activity of SINE in canine NHL. AEs associated with drug administration include primarily anorexia, with vomiting at the DLT dose; diarrhea and significant laboratory changes were not observed. These observations are consistent with the effects of SINEs in other animal species.

The novel SINE KPT-335 exhibits single agent biological activity with good tolerability in a relevant spontaneous large animal model of newly diagnosed and chemotherapy refractory cancer. The MTD and no adverse effect level of KPT-335 given by mouth twice weekly to dogs with NHL are ∼1.75 and 1.25 mg/kg, respectively, with anorexia, weight loss and vomiting as DLTs. Additional cohorts at doses of ≥1.25mg/kg given with increased frequency are being enrolled. These data are directly relevant to the development of oral KPT-330, a related SINE, currently in Phase 1 human clinical trials.

Shacham:Karyopharm Therapeutics: Employment. Barnard:Karyopharm: Research Funding. Kisseberth:Karyopharm: Research Funding. Ito:Karyopharm: Research Funding. Jensen:Karyopharm: Research Funding. Borgotti:Karyopharm: Research Funding. Henson:Karyopharm: Research Funding. Wilson:Karyopharm: Research Funding. McCauley:Karyopharm Therapeutics Inc: Employment. Modiano:Karyopharm: Research Funding. Kauffman:Karyopharm Therapeutics Inc: Employment. London:Karyopharm: Research Funding.