Interactions between drugs of abuse and HIV protease inhibitors

Abstract

Drug abuse is an escalating problem prevalent in both large metropolitan and rural places and is a major cause of mortality and morbidity all over the world. Drugs of abuse such as morphine and nicotine are consumed by people for prolonged periods of times to improve their physical and mental condition as well as to get relief from pain and other medical conditions. This prolonged intake often overlaps with the clinical regimen of several chronic neuropsychological, cardiovascular, pulmonary, infectious and neoplastic diseases. One in four patients living with human immunodeficiency virus (HIV) infection reported use of drugs of abuse. Achieving target intracellular concentrations during long term therapy of several diseases can be challenging due to number of factors such as poor adherence, drug resistance and drug-drug interactions. One important mechanism of multidrug resistance involves the up-regulation of multidrug resistance transporter, pglycoprotein (p-gp), member of ATP binding cassette (ABC) superfamily that effluxes most of the therapeutic drugs and reduce their intracellular accumulation. Drug-drug interactions can result from inhibition and induction of the cytochrome P450 enzymes and/or efflux transporters. Drugs of abuse have the ability to potentiate or attenuate the effects of co-administered therapeutic drugs that can lead to toxic effects or a reduction in the therapeutic activity of the co-administered drugs. This thesis investigates the chronic effect of morphine and nicotine on the expression and functional activity of efflux transporters (MDR1, MRP2, and BCRP) and metabolizing enzymes (CYP3A4). Induction of Pregnane-X-Receptor (PXR) was found to regulate the induction of MDR1 and CYP3A4 gene expression. Interactions between drugs of abuse and therapeutic drugs provide crucial insights into the failure of clinical regimen in patients suffering from HIV, cancer and other infections. Results from this thesis elucidate the mechanism behind the interactions between morphine and nicotine and HIV protease inhibitors. Studies were performed primarily through the use of in vitro models; e.g. LS180 and Caco-2 (for intestine) and HepG2 (for liver). In the second set of my studies, expression and functional activity of efflux transporters in Calu-3, human airway epithelial cell line was investigated. Expression and functionality of efflux and influx transporters in the airways is poorly identified and characterized. Results from this project allow understanding of the drug absorption in airways. As part of the study, molecular and functional activity of breast cancer resistance protein was identified for the first time. Folic acid receptor-alpha and proton coupled folic acid transporter expression was identified at molecular and protein level across human bronchial epithelial cell line, Calu-3. Since nicotine is smoked through lungs, effect of nicotine on the expression and functional activity of efflux transporters and metabolizing enzymes was determined. Nicotine was found to induce MDR1, BCRP expression and CYP3A4/A5 metabolism in Calu-3 cells. Male Sprague Dawley rats were treated with nicotine to investigate the effect of nicotine on CYP3A4 mediated rat lung metabolism. Cortisol was used as a model substrate to evaluate CYP3A4 mediated metabolism. Cortisol metabolism enhanced in nicotine treated rats than control rats signifying the enhanced CYP3A4/A5 metabolism. Furthermore, cortisol metabolism enhanced in microsomes obtained from smokers when compared to microsomes obtained from non-smokers