Methotrexate Analogues. 25. Chemical and Biological Studies on the γ-tert-Butyl Esters of Methotrexate and Aminopterin

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Abstract
.gamma.-tert-Butylaminopterin (.gamma.-tBAMT), the 1st example of an aminopterin (AMT) .gamma.-monoester, was synthesized, and new routes to the known N10-methyl analog .gamma.-tert-butyl methotrexate (.gamma.-tBMTX) were developed. The inhibitory effects of .gamma.-tBAMT on the activity of purified dihydrofolate reductase (DHFr) from L1210 murine leukemia cells, the growth of L1210 cells and CEM human leukemic lymphoblast in suspension culture, and the growth of several lines of human squamous cell carcinoma of the head and neck in monolayer culture were compared with the effects of .gamma.-tBMTX and the parent acids AMT and methotrexate (MTX). Patterns of cross-resistance to .gamma.-tBAMT, .gamma.-tBMTX, and AMT among several MTX-resistant cell lines were examined. In vivo antitumor activities of .gamma.-tBAMT and .gamma.-tBMTX were compared in mice with L1201 leukemia. While the activity of .gamma.-tBAMT was very close to that of .gamma.-tBMTX in the DHFR inhibition assay, the AMT ester was more potent than the MTX ester against cells in culture and against L1210 leukemia in vivo. Only partial cross-resistance was shown against .gamma.-tBMTX and .gamma.-tBAMT in cultured cells that were resistant to MTX by virtue of a transport defect or a combination of defective transport and elevated DHFR activity.