ABCG2 and cancer: Additionally, polymers are internalized by cancer cells through nonspecific or specific endocytosis, allowing bypass of ABC transporters and, consequently, increased intracellular drug concentrations for MDR cancer cell killing (Shi et al., 2015; Gupta et al., 2017) Modified ligands (such as peptides, antibodies, aptamers, folic acid, and hyaluronic acid (HA)) on surfaces of nanomedicines are also able to accurately target tumors and enhance cell uptake.