Year of Publication

2013

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Pharmacy

Department

Pharmaceutical Sciences

First Advisor

Dr. Markos Leggas

Second Advisor

Dr. Val Adams

Abstract

Simvastatin is a 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor that is used for the treatment of hyperlipidemia. Simvastatin has recently been studied for its potential use in cancer therapy. In-vitro studies have shown that simvastatin displays anticancer activity, but at concentrations unlikely to be achieved in patients being receiving typical antihyperlipidemic treatment doses. Thus, several clinical trials were conducted to study the tolerability of high dose statins in cancer patients. The maximum tolerated dose of simvastatin was determined to be 15 mg/kg/day, 25-fold higher than a typical dose. However, it is not known if simvastatin plasma concentrations can reach those found to be effective in-vitro. In this context, we initiated a clinical study to determine the pharmacokinetics of high dose simvastatin in patients with chronic lymphocytic leukemia. For this purpose, an LC-MS/MS method was developed and validated for the quantitation of simvastatin and its acid form in plasma and peripheral blood mononuclear cells obtained from CLL patients. Results show that simvastatin concentrations were dose proportional relative to the antihyperlipidemic doses, but lower than those required for in-vitro cytotoxicity against cancer cells. These findings demonstrate that the in-vitro effective concentrations of simvastatin are not achievable clinically, which might explain the limited effectiveness of high dose simvastatin in this study and in previous clinical trials. In view of these data, the use of simvastatin as a sole therapy in cancer treatment was not encouraging and led us to examine the use in combination with other anticancer drugs.

After screening several chemotherapeutic agents in combination with simvastatin, we showed that tipifarnib (a farnesyltransferase inhibitor) interacts synergistically in several leukemia cell lines. Mechanistically we showed that simvastatin augments the cytotoxicity of tipifarnib by disrupting the localization of RAS in the cell membrane and by subsequent deactivation of the ERK pathway. Consistent with this observation, drug treatment led to the induction of apoptosis through the caspase cascade activation and the cleaved PARP upregulation. Notably, this synergistic effect

was observed at clinically achievable concentrations of simvastatin and tipifarnib. Thus, the effectiveness of this combination should be explored further in future clinical studies.

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