Nanoengineered photosensitizers for photodynamic priming to overcome P-glycoprotein-mediated multidrug resistance.

P-glycoprotein (P-gp, ABCB1)-mediated multidrug resistance (MDR) remains a significant barrier to successful chemotherapy outcomes for cancer patients. While photoactivation of verteporfin (VP), a photosensitizer, has demonstrated success for overcoming MDR through direct protein aggregation upon photoactivation and through adenosine triphosphate (ATP) depletion, the impact of VP's formulation on P-gp function and cellular energetics has not been fully characterized in this context. In this study, we screened four well-established VP formulations-liposomal VP (L-VP), lysophosphatidylcholine-conjugated VP (lysoPC VP), liposomal formulation of lysoPC VP (L-lysoPC VP), and a self-assembled VP nanoaggregate (NanoVP), with a free form of VP as a control-for their ability to inhibit P-gp. Using a combination of in vitro intracellular VP accumulation assays, P-gp substrate retention experiments, and Seahorse-based metabolic profiling, we identified NanoVP as the lead formulation for P-gp modulation in cancer cells. NanoVP effectively depleted ATP in drug-resistant cancer cells, while being recognized as a P-gp substrate. Photodynamic priming with NanoVP at sub-cytotoxic light doses enhanced P-gp substrate retention within the cells without damaging P-gp protein, indicating ATP depletion as the primary mode of functional inhibition. These findings highlighted NanoVP's clinical potential to enhance chemotherapeutic efficacy via photoactivation-based modulation of P-gp's function in multidrug-resistant cancers.