Potential for reactive oxygen speciesmediated DNA damage and cellular multidrug resistance produced by the pyrroloiminoquinone class of marine natural products

The pyrroloiminoquinones (PIQs) are a group of secondary metabolites possessing a para-quinoneimine substituted with a fused pyrrole ring. These compounds vary in their functionalization around the heterocyclic framework and so provide a basis for the comparison of these derivatizations, on biological activity. In this dissertation, preliminary evidence is provided to suggest that genetic deoxyribonucleic acid (DNA) damage involving the iminoquinone may occur through a reactive oxygen species mediated redox pathway. Substantial evidence is also provided to show that these compounds have the potential to generate the multidrug resistance phenotype in cultured cells. Relevant biochemical and electrochemical attributes of the PIQs are described. Experimental evidence is provided for the cleavage of DNA, after PIQ reduction, in the presence of molecular O2. Ultraviolet absorbance measurements give structural information about the reduced species and demonstrate the reversibility of the reduction in the presence of molecular oxygen. It is also demonstrated that the extent of DNA cleavage produced by each of the pyrroloiminoquinones is directly related to the amount of energy necessary to reduce the PIQs by one electron and the reversibility of that one electron reduction. DNA intercalation is shown not to correlate suggesting that this attribute of the PIQs is of lesser importance. Prevention of DNA damage in solution by reduced PIQ is then achieved with ascorbate, suggesting a radical-mediated process. Cellular responses to PIQ treatment are addressed. The lack of correlation between >in vitro cytotoxicity and reductive DNA cleavage is presented and addressed in terms of possible additional mechanisms of PIQ activity. In contradiction to this, indirect evidence of ROS-mediated cellular damage in vitro is provided using ascorbate and glutathione in a protection assay. Cellular resistance, a common problem with many chemotherapeutic agents, is investigated. The PIQs are found to be substrates for the P-glycoprotein transporter and this mode of cellular resistance, in effect a cytotoxic stress-response, is investigated. The PIQs are shown to not only be acceptable substrates for Pgp170, but also inducers of Pgp170 expression after continuous treatment. Preliminary evidence supports the hypothesis that substrate recognition of the PIQs by Pgp170 may be an important factor in regulating the extent of Mdr1 expression.