Increase of doxorubicin sensitivity for folate receptor positive cells when given as the prodrug N-(phenylacetyl) doxorubicin in combination with folate-conjugated PGA.

Folate receptor (FR) has been proposed as a promising target for tumor drug targeting. The aim of this study was to increase the chemo-sensitivity of FR-positive cells to doxorubicin by folate-directed enzyme prodrug therapy (FDEPT). Folate conjugated penicillin-G amidase was prepared and its ability to hydrolyze N-(phenylacetyl) doxorubicin was measured by HPLC. Fluorescence and confocal image analysis revealed that Folate-PGA can be specifically delivered into FR-positive HeLa and SKOV3 tumor cells. In vitro cytotoxity assays, IC50 was reduced with N-(phenylacetyl) doxorubicin versus doxorubicin for HeLa (3.1-fold reduction; p<0.001) and SKOV3 (3.3-fold reduction; p<0.001) when Folate-PGA was specifically bound to the cells. Complete activation was confirmed in HeLa and SKOV3 cells pretreated with free folic acid (1 mM), where the combination of N-(phenylacetyl) doxorubicin with Folate-PGA did not show any significant cell toxicity to the IC50 of doxorubicin. Pharmacokinetic clearance and biodistribution studies in vivo showed that 125I-Folate-PGA was cleared from blood within 24 h and had significantly higher tumor uptake compared to 125I-PGA (p<0.05). These results demonstrate that the FDEPT approach may be a potential promising strategy to improve chemotherapy-resistant cancers therapeutic ratio and warranted future studies.