Beyond the boundary: The emerging roles of ATP-binding cassette transporters in multidrug resistance (MDR) and therapeutic targeting in cancer

Multidrug resistance (MDR) remains a primary obstacle to successful cancer chemotherapy, with the overexpression of ATP-binding cassette (ABC) transporters being a principal cause. These transporters actively efflux a wide range of anticancer drugs, reducing their intracellular efficacy. Consequently, targeting ABC transporters represents a critical strategy for overcoming therapeutic resistance. This comprehensive review details the molecular architecture and functional mechanisms of all seven human ABC transporter subfamilies (ABCA-ABCG), elucidating their distinct roles in both cancer progression and the development of MDR. We trace the evolution of therapeutic interventions, from first, second, and third-generation small molecule inhibitors to the potential of natural products. Furthermore, this review explores advanced and emerging strategies designed to circumvent or neutralize ABC transporter activity. These include genetic approaches such as RNA interference and CRISPR-Cas9 gene editing, immunotherapy-based tactics like monoclonal antibodies and antibody-drug conjugates (ADCs), and the application of sophisticated nanoparticle delivery systems designed to bypass efflux mechanisms. By providing a holistic overview of the entire ABC transporter family and the broad array of strategies being developed to counteract their function, this article aims to equip researchers with a full-scope perspective on the field, identifying current challenges and illuminating future directions for combating MDR in cancer.