[Strain of Yoshida sarcoma with induced pafencil resistance].

Pafencyl, a new antineoplastic drug, approved for use in the USSR, was administered orally to Wistar rats bearing subcutaneous Ioshida's sarcomas (during 5 days, 1 to 10 mg/kg bw). Administration of the drug during several days induced drug resistance. Since the 28th transplant generation accompanied by pafencyl administration drug resistance became stable and the maximal tolerable dose (MTD) 40 mg/kg, which causes regression of the sensitive strain, was ineffective. In rats bearing bilaterally transplanted resistant and sensitive tumors, pafencyl in MTD and lower doses completely inhibited the growth of the sensitive line with a zero or stimulation effect on the tumor-resistant one. The resistance index was 30.9. The drug resistance remained unchanged for 2 years under cryopreservation in liquid nitrogen at -196 degrees C. This tumor-resistant model can be used for studying the mechanisms of drug resistance, cross resistance and preclinical testing of new drugs.