Pauline K. Chang

5-Diazo-4-Oxo-L-Norvaline: Reactive Asparagine Analog with Biological Specificity

The L-asparagine analog, 5-diazo-4-oxo-L-norvaline, specifically inactivates L-asparaginase and inhibits the growth of L-asparagine-dependent or L-asparaginase-sensitive tumor cells in culture. With 5-14C-labeled compound, a biphasic incorporation into sensitive cells occurs, but the inhibition of cell multiplication is manifest much later than the rapid phase of incorporation of the analog.

Effects of asparagine synthetase inhibitors on asparaginase resistant tumors

Abstract Inhibitors of asparagine synthetase have been selected with an asparagine-independent sub-line of L5178Y lymphoblasts in culture. Five of nineteen asparagine analogs showed selective inhibition of asparagine synthetase. The order of inhibition in vitro of cell growth and asparagine synthetase is: l -β- aspartyl methylamide > l -β- aspartyl hydroxamate > l -β- aspartyl hydrazide > d,l - threo -β- met > d,l -α-N- methylasparagine . The most effective inhibitor of asparagine synthetase, β-aspartyl methylamide, was competitive with glutamine ( K i , = 2 × 10 −4 M) and ammonia. The β-amide was also relatively resistant to hydrolysis by Escherichia coli and Erwinia carotovora asparaginases. The β-amide had a plasma half-life of 90 min in mice; was concentrated 5-fold in leukemic cells from ascites fluid; and was metabolized to an α - N -acetyl derivative which was excreted in the urine. The compound increased life span from 31 to 79 per cent when administered to mice bearing various asparaginase resistant tumors.

some inhibitory properties of 6-N-Hydroxylaminopurine: An analog of adenine and hypoxanthine☆

Abstract 6-N-Hydroxylaminopurine (HAP) prolonged the survival time of mice bearing sarcoma 180 ascites cells; several other ascitic neoplasms were less sensitive to this agent. The rate of incorporation of 2- 14 C-glycine into both polynucleotide adenine and guanine of sarcoma 180 was depressed 90% or more by treatment with HAP, and the utilization of 8- 14 C-hypoxanthine and 8- 14 C-adenine for nucleotide formation was decreased by approximately 85% and 50% respectively. HAP competitively inhibited the formation of adenylic acid from adenine in cell-free extracts of sarcoma 180; the inhibition of inosinic acid formation from hypoxanthine by this analog was complex, being only partially competitive. Dialyzed extracts of either sarcoma 180 or of a variant resistant to purine analogs formed nucleotide from HAP at similar rates, whereas extracts of the L1210 lymphoma formed 5.6-fold more HAP-nucleotide than did those from a 6-mercaptopurine-resistant subline. The extracts from drug-sensitive and -resistant L1210 cells converted adenine to the nucleotide level at equal rates ; only the susceptible neoplasm converted guanine to guanylic acid at a significant rate. In cultured 14L5178Y lymphoblasts, capable of synthesizing purine nucleotides de novo , both hypoxanthine and adenine prevented inhibition of cell reproduction by HAP; on a molar basis adenine was the more effective. In amethopterin-treated L5178Y cells, high levels of HAP supported cell growth in the presence of thymidine and serine. The results suggest that HAP may function as both an antagonist of adenine and hypoxanthine in mammalian cells. Furthermore, the inhibition of cell reproduction caused by this compound appears to be attributable to interference with the biosynthesis of purine nucleotides.

Synthesis and evaluation of 2,4-diaminoquinazoline antifolates with activity against methotrexate-resistant human tumor cells

In an attempt to find potent antifolates with selectivity against tumor cells with intrinsic or acquired resistance to methotrexate, eleven nonclassical 2,4-diaminoquinazoline antifolates were synthesized and tested as inhibitors of dihydrofolate reductase from L5178Y cells. Several compounds appeared to be good enzyme inhibitors, with I50 values around 1 nM. Two of the compounds were also good inhibitors of cell growth in vitro. One of these (PKC-32, 9-(2,4-diamino-5-methylquinazoline-6-methylene)aminophenanthren e) appeared to be 100-fold more potent than methotrexate as an inhibitor of growth of a methotrexate-resistant cell line with impaired transport for methotrexate. PKC-32 and PKC-155 were also tested against mouse tumors in vivo. PKC-32 was modestly active in vivo as compared with methotrexate. This drug may be a useful agent in the treatment of methotrexate-resistant tumors.