CHROMOSOMAL ALTERATION AND THE DEVELOPMENT OF TUMORS

XVI. KARYOLOGICAL STUDIES ON SENSITIVE AND RESISTANT SUBLINES OF THE MOUSE LYMPHOCYTIC LEUKEMIA, L-1210, TO SEVERAL ANTITUMOR AGENTS

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Chromosomes in a drug sensitive and 5 drug resistant sublines of mouse leukemia L-1210 were studied. The 5 sublines used in the present study were resistant to methotrexate (L-1210/AM), 6-mercaptopurine and fluorouracil (L-1210/6MP-FU), 6-mercaptopurine, fluorouracil and methotrexate (L-1210/6MP-FU-AM), antileukemic agent NSC-38280 (L-1210/38280) and thioguanine (L-1210/TG). The chromosome numbers in sensitive L-1210/s cells varied from 34 to 46 with the mode at 40. Resistant sublines L-1210/AM, L-1210/6MP-FU, L-1210/6MP-FU-AM and L-1210/38280 also had 40 chromosomes as the mode of variation, fluctuating from 36 to 45. The L-1210/TG subline had only 41 chromosomes as a mode. A large submetacentric marker chromosome was usually found to characterize the sensitive line. In none of resistant lines, however, this marker chromosome was observed, while a small minute telocentric or metacentric and long telocentric T-markers were often observed in them. The relationship of these changes in karyotypes and type to resistance was discussed.