The ability of cancer cells to pump out chemotherapeutics has made that capability an increasingly popular target for cancer drugs. However, in any given cancer cell, it is unknown which or how many human proteins might contribute to multidrug resistance (MDR).

Thus companies hoping to increase the efficacy of chemotherapeutics by inhibiting the MDR transporters have two strategic choices: to develop broad-spectrum agents capable of inhibiting the entire family or focus their efforts on cancers where the specific transporters being targeted are known to be responsible for resistance.