Selective Accumulation of Near Infrared-Labeled Multivalent Quinidine Copolymers in Tumors Overexpressing P-Glycoprotein: Potential for Noninvasive Diagnostic Imaging.

P-glycoprotein (P-gp) is a promiscuous small molecule transporter whose overexpression in cancer is associated with multidrug resistance (MDR). In these instances, anticancer drugs can select for P-gp-overexpressing cells, leading to cancer recurrence with an MDR phenotype. To avoid selection for MDR cancers and inform individual patient treatment plans, it is critical to noninvasively identify P-gp-overexpressing tumors prior to administration of chemotherapy. We report the facile free radical copolymerization of quinidine, a competitive inhibitor of P-gp, and acrylic acid to generate multiplexed polymeric P-gp-targeted imaging agents with tunable quinidine content. Copolymer targeting was demonstrated in a nude mouse xenograft model. In xenografts overexpressing P-gp, copolymer distribution was enhanced over two-fold compared to the negative control of poly(acrylic acid) regardless of quinidine content. In contrast, accumulation of the copolymers in xenografts lacking P-gp was equivalent to poly(acrylic acid). This work forms the foundation for a unique approach toward the phenotype-specific noninvasive imaging of MDR tumors and is the first in vivo demonstration of copolymer accumulation through the active targeting of P-gp.