Thymidylate synthase: a target for anticancer drug design

Area of Science:

• Biochemistry
• Pharmacology
• Medicinal Chemistry

Background:

• N10-Propargyl-5,8-dideazafolic acid (CB3717) is an antifolate drug with thymidylate synthase (TS) as its primary target.
• CB3717 exhibits clinical activity but is limited by poor aqueous solubility and associated toxicities.
• Intracellular polyglutamation potentiates the inhibitory effect of CB3717 on TS.

Purpose of the Study:

• To explore novel C2-modified quinazoline analogues of CB3717 for improved therapeutic profiles.
• To investigate the structure-activity relationships of CB3717 analogues concerning TS inhibition and cytotoxicity.
• To separate structural features responsible for antitumor activity from those causing systemic toxicities.

Main Methods:

• Synthesis and evaluation of C2-modified quinazoline analogues, including desamino (CB3804), C2-methyl (CB3819), and C2-methoxy (CB3828) derivatives.
• Assessment of TS inhibitory activity in vitro and in vivo.
• Evaluation of cytotoxicity in continuous cell culture.
• Measurement of aqueous solubility and systemic toxicities in mouse models.
• Analysis of polyglutamation by folylpolyglutamate synthetase (FPGS) and intracellular retention.

Main Results:

• CB3717 analogues (CB3804, CB3819, CB3828) exhibit comparable TS inhibitory activities to CB3717.
• CB3804 and CB3819 show significantly enhanced cytotoxicity and improved aqueous solubility compared to CB3717.
• CB3804 and CB3819 demonstrate reduced toxicity and are rapidly cleared from plasma, suggesting polyglutamation is crucial for activity.

Conclusions:

• C2-modified quinazolines, particularly CB3804 and CB3819, represent a new generation of selective thymidylate synthase inhibitors.
• These analogues successfully separate antitumor efficacy from systemic toxicities, offering a promising therapeutic window.
• The development of these analogues highlights the potential for optimizing antifolate drugs through targeted structural modifications.