While this conservation might cause an NBD-targeting P-gp inhibitor to bind other ABC transporters, one might argue that this ‘off-target’ activity against other ABC transporters is acceptable within the context of multidrug resistant cancer – for these patients, chemotherapy has failed, options are limited, and more than one ABC transporter is potentially at play in conferring multidrug resistance. The gene discussed is ABCG2; the disease is cancer.