Antifolates targeted specifically to the folate receptor

Area of Science:

• Pharmacology
• Oncology
• Drug Discovery

Background:

• Most antifolate drugs rely on the reduced-folate carrier (RFC) for transport.
• Some antifolates also bind the alpha-isoform of the folate receptor (alpha-FR), contributing to activity when alpha-FR is overexpressed or folate is low.
• Ubiquitous RFC expression in normal tissues limits antifolate drug tolerability.

Purpose of the Study:

• To develop novel antifolates specifically targeting alpha-FR overexpressing tumors.
• To evaluate the efficacy and tumor-specific inhibition of a new class of cyclopenta[g]quinazoline-based thymidylate synthase (TS) inhibitors.

Main Methods:

• Discovery of cyclopenta[g]quinazoline-based TS inhibitors with differential affinity for alpha-FR and RFC.
• In vitro testing of compound potency against alpha-FR positive and negative cell lines.
• In vivo studies using tumor xenografts in mice to assess drug localization and TS inhibition.

Main Results:

• CB300638, a potent TS inhibitor, demonstrated high affinity for alpha-FR and low affinity for RFC.
• CB300638 showed approximately 300-fold greater potency against alpha-FR overexpressing cells (A431-FBP, KB) compared to alpha-FR negative cells (A431).
• In vivo, CB300638 localized to tumors and specifically inhibited TS in tumor tissue, not normal tissues.

Conclusions:

• Cyclopenta[g]quinazoline-based antifolates targeting alpha-FR represent a promising therapeutic strategy for epithelial tumors overexpressing this receptor.
• These novel agents offer potential for reduced toxicity compared to conventional antifolates due to targeted delivery.
• Further clinical development is supported by preclinical data, though unique compound properties present challenges.