Inheritance of cellular resistance to the antitumor agent ICRF 159 in somatic cell hybrids

Two independently derived sublines of Syrian hamster BHK 21 S cells that demonstrate resistance to the antitumor agent ICRF 159 (NSC-129943) were fused to sensitive cells in both intraspecific and interspecific crosses, and the responses of the resultant hybrids to the drug were determined. In intraspecific hybrids from crosses involving either of the sublines, resistance to ICRF 159 was expressed codominantly ith the hybrid response being halfway between the parental responses. In interspecific hybrids from crosses with sensitive mouse cells, resistance was also expressed but to a lesser extent than in the intraspecific hybrids. However, subsequent passaging of an interspecific hybrid resulted in an increase in the degree of resistance, which appeared to be accompanied by a loss of telocentric mouse chromosomes. The results suggested that resistance in these lines was due to an alteration in the cellular target involved in the response to ICRF 159.