Efflux-Enhanced Imidazoquinolines To Exploit Chemoresistance

Abstract

The imidazoquinoline family of toll-like receptor (TLR) immune cell agonists has long demonstrated moderate anticancer immunogenic effects by activating tumoricidal immune cells and depleting immunosuppressive cells within the tumor microenvironment. At a molecular level, we have also established that several imidazoquinolines traffic from within cancer cells to the extracellular space via P-glycoprotein (P-gp)-mediated efflux, a process commonly upregulated as multidrug-resistant (MDR) cancers acquire chemoresistance. However, imidazoquinoline P-gp efflux has never been deliberately enhanced to exploit this process. This study pioneers efforts to optimize imidazoquinoline efflux, ultimately balancing immunogenic potency alongside functional efflux susceptibility. Starting from an established imidazoquinoline scaffold previously optimized for potency, efflux was significantly enhanced by elaborating the N1 benzylic position with amide- and sulfonamide-linked P-gp affinity fragments consisting of empirically established P-gp substrates as well as computationally predicted P-gp binders. Lead compounds were identified from this series that exhibited enhanced P-gp efflux with functional retention of TLR agonism. Similar to the parent imidazoquinoline scaffold, leads had limited direct cytotoxicity in both treatment-naive and MDR B16 melanoma models and did not significantly affect the efficacy or trafficking of the chemotherapeutic doxorubicin. Efflux-enhanced imidazoquinolines were preferentially expelled from MDR-B16 cells relative to treatment-naive cells, resulting in immunogenicity that was enhanced as a consequence of the acquired MDR phenotype. Because enhanced P-gp-mediated efflux is common to most MDR cancer types, we envision that these results could inspire the design of immunotherapeutic drugs with mechanisms of action that are broadly enhanced in MDR cancers that have failed treatment or acquired resistance to chemotherapeutics.