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We examined the expression of the estrogen and epidermal growth factor (EGF) receptors in a drug-resistant subline of MCF-7 cells in order to study potential alterations in hormone dependence or in the growth factor pathway that could be related to the development of drug resistance in human breast cancer. The drug-resistant subline was derived from MCF-7 cells by selection with Adriamycin in the presence of the P-glycoprotein antagonist, verapamil, to prevent acquisition of the classical multidrug resistance phenotype. The Adriamycin-resistant cells retain estrogen-binding, estrogen-responsive monolayer growth, and estrogen-dependent tumorigenesis. Estrogen-binding studies demonstrate 1.4 x 10(6) sites per cell with unaltered affinity when compared to parental MCF-7 cells, which have 2.7 x 10(5) sites per cell. An increase in expression of EGF receptor, eight to 12-fold, occurred early in the selection for drug resistance, and appears to be unrelated to verapamil exposure, since cells maintained in Adriamycin without verapamil also have increased EGF receptor expression. Partially drug-sensitive revertants carried a verapamil, but out of Adriamycin, demonstrate a decline in EGF receptor expression. We postulate that activation of growth factor pathways in drug-resistant cells may enhance mechanisms of drug resistance, or provide mitogenic stimuli for cells to recover after damage by drug exposure.

A Graffi murine leukemia was utilized as a model system to investigate the effect of chemoimmunostimulation therapy. Subcutaneous inoculation of approximately 1.0 times 10(6) tumor cells resulted in a rapidly growing tumor at the site of inoculation and subsequent development of splenomegaly and lymphoadenopathy. All animals succumbed to the leukemia within 24 to 30 days. Treatment of diseased animals with two courses of cytoxan over a 2-week period resulted in a remission period of approximately 16 to 18 days before relapse and eventual death of approximately 70% of the drug-treated animals. A significant number of long-term survivors (50 to 83%) was obtained in groups of animals that received combined drug plus BCG or C. parvum therapy. In contrast, the administration of MER (a methanol-extracted residue of BCG) to animals in a drug-induced remission period was no more effective than drug alone. The protective effect afforded by BCG and C. parvum was dependent on the time interval between drug therapy and the administration of the immunostimulators. Treatment of leukemic animals with BCG, C. parvum, or MER alone proved ineffective as all mice died at approximately the same time as untreated control animals. No leukemic cells were observed in any of the histologically examined tissues taken from long-term survivors. The implication of these results for cancer therapy is discussed.