Comparative Oncology Assessment of a Novel Inhibitor of Valosin-Containing Protein in Tumor-Bearing Dogs.

Pet dogs with naturally occurring cancers play an important role in studies of cancer biology and drug development. We assessed tolerability, efficacy, and pharmacokinetic/pharmacodynamic relationships with a first-in-class small molecule inhibitor of valosin-containing protein (VCP/p97), CB-5339, administered to 24 tumor-bearing pet dogs. Tumor types assessed included solid malignancies, lymphomas, and multiple myeloma. Through a stepwise dose and schedule escalation schema, we determined the maximum tolerated dose to be 7.5 mg/kg when administered orally on a 4 days on, 3 days off schedule per week for 3 consecutive weeks. Adverse events were minimal and mainly related to the gastrointestinal system. Pharmacokinetic/pharmacodynamic data suggest a relationship between exposure and modulation of targets related to induction of the unfolded protein response, but not to tolerability of the agent. An efficacy signal was detected in 33% (2/6) of dogs with multiple myeloma, consistent with a mechanism of action relating to induction of proteotoxic stress in a tumor type with abundant protein production. Clinical trials of CB-5339 in humans with acute myelogenous leukemia and multiple myeloma are ongoing.

Target-Agnostic P-Glycoprotein Assessment Yields Strategies to Evade Efflux, Leading to a BRAF Inhibitor with Intracranial Efficacy.

The blood-brain barrier (BBB) presents a major hurdle in the development of central nervous system (CNS) active therapeutics, and expression of the P-glycoprotein (P-gp) efflux transporter at the blood-brain interface further impedes BBB penetrance of most small molecules. Designing efflux liabilities out of compounds can be laborious, and there is currently no generalizable approach to directly transform periphery-limited agents to ones active in the CNS. Here, we describe a target-agnostic, prospective assessment of P-gp efflux using diverse compounds. Our results demonstrate that reducing the molecular size or appending a carboxylic acid in many cases enables evasion of P-gp efflux in cell-based experiments and in mice. These strategies were then applied to transform a periphery-limited V600EBRAF inhibitor, dabrafenib, into versions that possess potent and selective anti-cancer activity but now also evade P-gp-mediated efflux. When compared to dabrafenib, the compound developed herein (everafenib) has superior BBB penetrance and superior efficacy in an intracranial mouse model of metastatic melanoma, suggesting it as a lead candidate for the treatment of melanoma metastases to the brain and gliomas with BRAF mutation. More generally, the results described herein suggest the actionability of the trends observed in these target-agnostic efflux studies and provide guidance for the conversion of non-BBB-penetrant drugs into versions that are BBB-penetrant and efficacious.

Discovery and canine preclinical assessment of a nontoxic procaspase-3-activating compound.

A critical event in the apoptotic cascade is the proteolytic activation of procaspases to active caspases. The caspase autoactivating compound PAC-1 induces cancer cell apoptosis and exhibits antitumor activity in murine xenograft models when administered orally as a lipid-based formulation or implanted s.c. as a cholesterol pellet. However, high doses of PAC-1 were found to induce neurotoxicity, prompting us to design and assess a novel PAC-1 derivative called S-PAC-1. Similar to PAC-1, S-PAC-1 activated procaspase-3 and induced cancer cell apoptosis. However, S-PAC-1 did not induce neurotoxicity in mice or dogs. Continuous i.v. infusion of S-PAC-1 in dogs led to a steady-state plasma concentration of ∼10 µmol/L for 24 to 72 hours. In a small efficacy trial of S-PAC-1, evaluation of six pet dogs with lymphoma revealed that S-PAC-1 was well tolerated and that the treatments induced partial tumor regression or stable disease in four of six subjects. Our results support this canine setting for further evaluation of small-molecule procaspase-3 activators, including S-PAC-1, a compound that is an excellent candidate for further clinical evaluation as a novel cancer chemotherapeutic.

Hematological toxicity and therapeutic efficacy of lomustine in 20 tumor-bearing cats: critical assessment of a practical dosing regimen.

Twenty cats with spontaneously arising tumors received oral lomustine at a dose range of 32 to 59 mg/m2 every 21 days. Due to biohazard concerns associated with lomustine capsule reformulation, a standardized 10-mg capsule dosage was used for all cats regardless of body weight. Severe hematological toxicity was infrequent, with the incidence of either grade III or IV neutropenia and thrombocytopenia being 4.1% and 1.0%, respectively. Cats receiving higher cumulative doses of lomustine trended toward a greater likelihood for progressive neutropenia (P=0.07). Two cats with lymphoma, two cats with fibrosarcoma, and one cat with multiple myeloma achieved a measurable partial response to lomustine therapy. Cats treated with higher dosages of lomustine trended toward statistically significant higher response rates (P=0.07).