Studies examining intracellular delivery of methotrexate with a folate/FITC nanostructure. Panel A shows that the devices are readily taken into KB cells regardless of drug conjugate. Panel B shows that at 1000 uM only the conjugate where methotrexate is linked by an ester is acutely cytotoxic to the tumor cells. Panels C and D compare the efficiency in killing tumor cells and the acute cytotoxicity (respectively) of ester-conjugated drug and free methotrexate. The polymer delivered drug is 5 to 10 times more efficient at killing the KB cells.
 Reprinted with permission from Quintana et al.²⁰