Sulfo-Quinovosyl-Acyl-Glycerol (SQAG), a Eukaryotic DNA Polymerase Inhibitor and Anti-Cancer Agent

It was found that a class of sulfolipids known as sulfo-quinovosyl-acyl-glycerols (SQAGs) from ferns and algae are potent inhibitors of eukaryotic DNA polymerase α & β and effective anti-neoplastic agents. In developing a procedure for the chemical synthesis of sulfolipids, many derivatives and stereoisomers of SQAGs have been obtained including sulfo-quinovosyl-monoacyl-glycerols (SQMGs) and sulfo-quinovosyl-diacyl-glycerols (SQDGs). This review describes studies on the structure-function relationship between synthetic SQAGs and DNA polymerase α & β, and the relationship to cytotoxic activity. The major action was probably dependent on the fatty acid effect, which was reported previously, although each of the SQAGs was a much stronger inhibitor than just the fatty acid present in the SQAGs. The inhibitory effect could be influenced by the chain size of fatty acids in the SQAGs. The sulfonyl group in quinovose was also needed to inhibit the enzymes. Lineweaver-Burk plots of SQAGs indicated that DNA polymerase α was noncompetitively inhibited, but the SQAGs were effective as antagonists of both the template-primer DNA-binding and the nucleotide substrate-binding of DNA polymerase β. Based on these results, the molecular actions of SQAGs and drug design strategies for developing new anti-neoplastic agents were discussed.