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Normalization of epidermal growth factor receptor and transforming growth factor production in drug resistant variants derived from adenovirus transformed cells

Variants (G2, G5) resistant to the cancer chemotherapeutic drug methylglyoxal bis (guanylhydrazone) (MGBG) were isolated from adenovirus type 2 transformed rat brain cells (F4; Sircar et al., 1987). Although at least one of these variants continued to express the adenovirus Ela and Elb transforming proteins, they both exhibited a detransformed phenotype as witnessed by flat morphology, loss of anchorage independent growth, and tumor forming capacity. Reverse transformation suggested the possibility of changes in growth factor receptors and the production of transforming growth factors. To test this possibility, we investigated the status of epidermal growth factor receptors (EGF‐r) and transforming growth factor alpha (TGF‐α) production in F4, G2 and G5 cells. The level of 125I‐labeled EGF binding to intact drug resistant cells increased by 2‐ to 3‐fold compared to the transformed parental cell. Scatchard analysis suggests that increased binding was the result of increased receptor levels rather than altered affinity of receptor for ligand. The production of growth factors which compete with 125I‐labeled EGF binding declined in the detransformed G2 and G5 cells to a level intermediate between transformed (F4) and normal cells (FR3T3). EGF‐receptor increase and the complementary decrease in growth factor production in the drug resistant variants may be associated with detransformation.