Abstract 4488: Folate receptor targeted therapy using small molecule drug conjugates constructed with high affinity antifolate ligands

Proceedings: AACR 106th Annual Meeting 2015; April 18-22, 2015; Philadelphia, PA Folate receptor (FR)-targeted small molecule drug conjugates (SMDC) have shown promising clinical results. To date, all related SMDCs have been constructed with folic acid. Whereas folic acid displays very high affinity for the FR (kd ∼ 0.1 nM), antifolates with similar high binding affinity and specificity have also been reported. This knowledge prompted our investigation towards substituting the folic acid targeting moiety in our SMDCs with high affinity antifolates, such as CB3717 (a thymidylate synthase inhibitor), and the glycinamide ribonucleotide formyltransferase (GARFTase) inhibitors, AG94 and AG147, thereby testing the hypothesis that greater antitumor activity should result from the combination of inhibitors. Using mice bearing FR-positive human tumor xenografts, we observed curative activity with a CB3717-based vinca alkaloid SMDC under conditions where no cures resulted with vintafolide (EC145) treatment. Similarly, tubulysin SMDCs constructed with AG94 and AG147 were found to produce curative activity using a dosing regimen where a folic acid-tubulysin conjugate did not. Of note, treatment of mice with simple co-mixtures of the antifolates and untargeted drugs was found to be ineffective, thereby confirming the need for linking the two moieties together to produce maximal activity. Taken together, these studies demonstrate that high affinity antifolates can be used in an SMDC format serving as both a high affinity targeting ligand and as a second drug having different, and perhaps a complementary mechanism of action to yield greater antitumor activity. Citation Format: Christopher P. Leamon, Joseph A. Reddy, Iontcho R. Vlahov, Fei You, Hanna F. Klein, Paul J. Kleindl, Melissa Nelson, Marilynn Vetzel, Patrick J. Klein, Larry H. Matherly, Aleem Gangjee. Folate receptor targeted therapy using small molecule drug conjugates constructed with high affinity antifolate ligands. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4488. doi:10.1158/1538-7445.AM2015-4488