Direct assessment of P-glycoprotein efflux to determine tumor response to chemotherapy.

Multidrug resistance is a major impediment to the success of cancer chemotherapy. The overproduced P-glycoprotein that extrudes anticancer drugs from cells, is the most common mechanism detected in multidrug-resistant cancers. Direct measurement of cellular efflux of tumors in vivo, rather than estimation of MDR1 mRNA and P-glycoprotein levels in samples stored or embedded, can functionally characterize the mechanism of drug resistance and determine the choice of anticancer drugs for cancer patients. Herewith, we introduce a new approach to directly determine P-glycoprotein efflux of tumors. Employing Flutax-2 (Oregon green-488 paclitaxel) and fluorescence spectrophotometry, this method has successfully measured cellular transportability including efflux and accumulation in diverse cancer cell lines, tumors and other tissues with high reproducibility. With this method, we have quantitatively determined cellular efflux that is correlated with P-glycoprotein levels and the reversal effects of agents in cell lines of breast, ovarian, cervical and colon cancers, and in tumor-bearing mice. It has sensitively detected these alterations of P-glycoprotein efflux in approximately 5mg tumor or other tissues with high confidence. This direct and quick functional assessment has a potential to determine drug resistance in different types of cancers after surgical resection. Further validation of this method in clinic settings for the diagnosis of drug resistance purpose is needed.