Phase II study of the oral selective inhibitor of nuclear export (SINE) KPT-335 (verdinexor) in dogs with lymphoma.

BACKGROUND: Chemotherapeutic options for the treatment of canine lymphoma have not changed in several decades necessitating the identification of new therapeutics to improve patient outcome. KPT-335 (verdinexor) is a novel orally bioavailable selective inhibitor of nuclear export (SINE) that exhibited anti-tumor activity against non-Hodgkin lymphoma in a prior phase I study. The objective of this phase II study was to expand upon the initial findings and assess the activity and safety in a larger population of dogs with lymphoma. RESULTS: Fifty-eight dogs with naïve or progressive B-cell and T-cell lymphoma were enrolled in this clinical trial. KPT-335 was administered orally in one of three dosing groups, based on the previously established biologically active dose of 1.5 mg/kg three times weekly. Treatment with single-agent, orally administered KPT-335 resulted in an objective response rate (ORR) of 37%, of which dogs with T-cell lymphoma had an ORR of 71%. KPT-335 was well tolerated in all dose groups with grade 1-2 anorexia being the most common adverse event. Anorexia was responsive to symptomatic and supportive medications, including prednisone. CONCLUSIONS: These data demonstrate that KPT-335 has biologic activity in canine lymphoma, and support continued evaluation of SINE compounds such as KPT-335 in combination with standard chemotherapeutics in canine lymphoma.

Mutations in the fifth immunoglobulin-like domain of kit are common and potentially sensitive to imatinib mesylate in feline mast cell tumours.

The purpose of the current study was to investigate the mutation status of KIT in feline mast cell tumours (MCTs) and to examine the effects of tyrosine kinase inhibition on the phosphorylation of mutant kit in vitro and in clinical cases of cats. Sequence analysis of KIT identified mutations in 42/62 MCTs (67.7%). The vast majority of the mutations were distributed in exons 8 and 9, both of which encode the fifth immunoglobulin-like domain (IgD) of kit. All five types of kit with a mutation in the fifth IgD were then expressed in 293 cells and examined for phosphorylation status. The mutant kit proteins showed ligand-independent phosphorylation. The tyrosine kinase inhibitor imatinib mesylate suppressed the phosphorylation of these mutant kit proteins in transfectant cells. In a clinical study of 10 cats with MCTs, beneficial response to imatinib mesylate was observed in 7/8 cats that had a mutation in the fifth IgD of kit in tumour cells. Mutations in the fifth IgD of kit thus appear to be common and potentially sensitive to imatinib mesylate in feline MCTs. These data provide an in vivo model for paediatric mastocytosis where mutations in the fifth IgD of kit also occur.

A phase I clinical trial evaluating imatinib mesylate (Gleevec) in tumor-bearing cats.

A phase I clinical trial evaluating the toxicity of orally-administered imatinib mesylate was performed in 9 tumor-bearing cats. Imatinib is a small molecule, tyrosine kinase inhibitor, which selectively blocks the function of overexpressed proteins associated with various malignancies. Cats included in the study had diagnoses of fibrosarcoma, squamous cell carcinoma, and mast cell tumor, and each cat was staged using CBC and serum biochemistry; urinalysis, thoracic radiographs, and abdominal ultrasonography were performed in some cats. Most cats were treated previously by surgery, radiation therapy, chemotherapy, or some combination of these treatments. None of the cats received any concurrent chemotherapy. Six cats were treated with imatinib mesylate at 1-2 mg/kg PO q24h. Dose escalations were made to 2, 4, and 10 mg/kg PO q24h in 5 cats. Two cats started therapy at 10 mg/kg PO q24h, and 1 cat started therapy at 15 mg/kg PO q24h; all 3 cats remained at these dosages. No signs of toxicity, as evaluated by CBC and serum biochemistry, were noted in 8 of the 9 cats, and minimal gastrointestinal toxicity was observed. Due to the low frequency of adverse effects, further evaluation of imatinib is ongoing at a dosage of 10 mg/kg PO q24h.

Intratumoral injection of Clostridium novyi-NT spores induces antitumor responses.

Species of Clostridium bacteria are notable for their ability to lyse tumor cells growing in hypoxic environments. We show that an attenuated strain of Clostridium novyi (C. novyi-NT) induces a microscopically precise, tumor-localized response in a rat orthotopic brain tumor model after intratumoral injection. It is well known, however, that experimental models often do not reliably predict the responses of human patients to therapeutic agents. We therefore used naturally occurring canine tumors as a translational bridge to human trials. Canine tumors are more like those of humans because they occur in animals with heterogeneous genetic backgrounds, are of host origin, and are due to spontaneous rather than engineered mutations. We found that intratumoral injection of C. novyi-NT spores was well tolerated in companion dogs bearing spontaneous solid tumors, with the most common toxicities being the expected symptoms associated with bacterial infections. Objective responses were observed in 6 of 16 dogs (37.5%), with three complete and three partial responses. On the basis of these encouraging results, we treated a human patient who had an advanced leiomyosarcoma with an intratumoral injection of C. novyi-NT spores. This treatment reduced the tumor within and surrounding the bone. Together, these results show that C. novyi-NT can precisely eradicate neoplastic tissues and suggest that further clinical trials of this agent in selected patients are warranted.

An orally bioavailable parthenolide analog selectively eradicates acute myelogenous leukemia stem and progenitor cells.

Leukemia stem cells (LSCs) are thought to play a central role in the pathogenesis of acute leukemia and likely contribute to both disease initiation and relapse. Therefore, identification of agents that target LSCs is an important consideration for the development of new therapies. To this end, we have previously demonstrated that the naturally occurring compound parthenolide (PTL) can induce death of human LSCs in vitro while sparing normal hematopoietic cells. However, PTL has relatively poor pharmacologic properties that limit its potential clinical use. Consequently, we generated a family of PTL analogs designed to improve solubility and bioavailability. These studies identified an analog, dimethylamino-parthenolide (DMAPT), which induces rapid death of primary human LSCs from both myeloid and lymphoid leukemias, and is also highly cytotoxic to bulk leukemic cell populations. Molecular studies indicate the prevalent activities of DMAPT include induction of oxidative stress responses, inhibition of NF-kappaB, and activation of p53. The compound has approximately 70% oral bioavailability, and pharmacologic studies using both mouse xenograft models and spontaneous acute canine leukemias demonstrate in vivo bioactivity as determined by functional assays and multiple biomarkers. Therefore, based on the collective preclinical data, we propose that the novel compound DMAPT has the potential to target human LSCs in vivo.