Dominant Expression of Multiple Drug Resistance After In Vitro X-irradiation Exposure in Intraspecific Chinese Hamster Ovary Hybrid Cells

Background: Exposure of Chinese hamster ovary (CHO) cells to fractionated x irradiation in vitro has led to expression of a distinctive multiple-drug-resistant phenotype. This phenotype is characterized by overexpression of P-glycoprotein without an increase in P-glycoprotein messenger RNA or gene amplification; increased glutathione S-transferase (GST) activity; and resistance to vincristine, colchicine, and etoposide but not to doxorubicin. Purpose: To investigate whether this phenotype is dominant or recessive, we established intraspecific hybrids by fusion of x-ray-treated, drug-resistant CHO cells (DXR-10I or DXR-10II) with drug-sensitive CHO cells (E29)