Pharmacokinetics and toxicity of the novel oral demethylating agent zebularine in laboratory and tumor bearing dogs

Christopher M Fulkerson, Purdue University

Abstract

The aim of this thesis is to investigate the pharmacokinetics and toxicity of the novel oral demethylating agent zebularine (zeb) in laboratory dogs and tumor bearing dogs. This thesis focuses on the application of this therapeutic strategy in dogs with naturally occurring invasive transitional cell carcinoma (InvTCC), which serve as a relevant model of the human disease. DNA hypermethylation in the promoter region is a common epigenetic change in cancer that silences tumor suppressor genes. Zeb is an oral cytidine analog that acts as a demethylating agent. Zeb has been investigated extensively in vitro as well as in mice, rodents and rhesus monkeys. Prior to the investigation described in this thesis, zeb had not been investigated in the dog. The authors set out to investigate zeb in dogs with naturally occurring InvTCC with an eventual goal of applying this treatment strategy to humans with this devastating cancer. The first part of this thesis reviews the importance of DNA methylation in cancer development, the development and application of zeb as a novel oral demethylating agent and the application of demethylating agents in InvTCC in the dog. The second part of this thesis presents initial pharmacokinetics and toxicity data following high dose oral zeb in laboratory dogs (n=3) and tumor bearing dogs (n=3). Daily high dose oral zeb at 4 mg kg-1 resulted in remarkable, but reversible, hematologic toxicity in the form of neutropenia in laboratory dogs. Dose adjustment revealed that a dose intensity of 4 mg kg-1 once every 21 days was well tolerated in tumor bearing dogs. The third part of this thesis presents the results to date of a phase I dose escalation trial of oral zeb in 26 dogs with InvTCC. At daily doses up to 0.5 mg kg-1, zeb was well tolerated. At higher doses, dose-limiting toxicity (DLT) was detected. In a population in which 73% of dogs had failed previous treatment, overall disease control rate of 73.3% was detected, and median progression free survival time was 86 days (95% CI, 47.5-124.5). Of particular interest is that one dog has experienced disease stabilization for more than 511 days. Remarkable, but reversible, neutropenia was detected in laboratory dogs treated with high dose daily zeb. Low dose daily zeb at doses up to 0.5 mg kg-1 was well tolerated in dogs with InvTCC. Initial results indicate promising disease control rates and progression free survival in a population of dogs that was heavily pretreated. These results warrant further investigation as a treatment strategy in dogs with InvTCC with potential applications to the human disease. Further investigation is required to determine if the optimal effects of zeb may be in combination with cytotoxic chemotherapy drugs and to document that tumor responses are due to DNA demethylation and reactivation of silenced genes.

Degree

M.S.

Advisors

Knapp, Purdue University.

Subject Area

Veterinary services|Oncology

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