Else G Dapat is a PhD degree holder trained at the Institute of Biology,University of the Philippines Diliman, Quezon City and German Cancer ResearchCenter, Heidelberg, Germany, under the supervision of Prof. Dr. Thomas Efferth.She is presently an Assistant Professor III at the University of the PhilippinesManila. She is engaged in a research project on the isolation of bioactivecompounds from Philippine Traditional Medicine to test toward selected cancercell lines.


The existence of multidrug resistance (MDR) is a major contributory factorin the failure of chemotherapy. Concrete interpretation of P-glycoprotein (P-gp)substrate specificity, whether a substance is a substrate or an inhibitor, can bevisualized as an important component of a compound's pharmaceutical profilingin drug design. In this work, P-gp substrate specificity of Maldi 531.2[M+H]+, aphenol ester from Aglaialoherileaves was investigated. The basis for thisinvestigation is the effect of Maldi 531.2[M+H]+ on P-gp ATPase activity whichwas examined by measuring the amount of inorganic phosphates (Pi) releasedas a result of ATP hydrolysis. To test the effects of Maldi 531.2[M+H]+ on MDRactivity, an attempt to combine Maldi 531.2[M+H]+ with a potent P-gp substratesuch as verapamil was performed. As a result of this combination treatment, twodistinct patterns of interaction with P-gp activity was determined by calcein-acetoxymethyl ester (AM) assay. Both stimulation and inhibition of MDR activitywere observed at certain drug concentrations suggesting biphasic reactionswhich can be called cooperative stimulation and competitive inhibitionrespectively. Verapamil is a strong substrate to P-gp. Substrate specificity ofMaldi 531.2[M+H]+ maybe less than the substrate specificity of verapamil but itacts additively with the low concentration of verapamil in stimulating ATPaseactivity.