Quantitative structure-activity relationship of multidrug resistance reversal agents.

Multidrug resistance (MDR) is one of the major obstacles to long term successful cancer chemotherapy. The use of MDR reversal (MDRR) agents is a promising approach to overcome the undesired MDR phenotype. To design more effective MDRR agents that are urgently needed for clinical use, a data set of 609 diverse compounds tested for MDRR activity against P388/ADR-resistant cell lines was submitted to the MULTICASE computer program for structure-activity analysis. Some substructural features related to MDRR activity were identified. For example, the CH2-CH2-N-CH2-CH2 group was found in most of the active compounds, and the activity was further enhanced by the presence of (di)methoxylphenyl groups, whereas the presence of a stable quaternary ammonium salt, a carboxylic, a phenol, or an aniline group was found to be detrimental to activity. Possible explanations for these observations are proposed. Some physicochemical properties, e.g., the partition coefficient (log P) and the graph index (which in some sense measures the "complexity" of a molecule) were also found to be relevant to activity. Their role in MDRR was also rationalized. Based on our quantitative structure-activity relationship study of MDRR agents, some compounds with desired substructural features and activity were identified from the MACCS-II and National Cancer Institute DIS databases and tested experimentally. Our study may also help the rational design of anti-cancer drugs. Based on this study and on observations by other researchers, we postulate that P-glycoprotein-mediated resistance to paclitaxel could probably be eliminated by proper substitution of its benzamido and phenyl groups. Several novel compounds with the paclitaxel skeleton are proposed, which may lead to a new generation of paclitaxel anti-cancer drugs with less MDR potential.