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Alteration of EGF-receptor binding in human breast cancer cells by antineoplastic agents
A R Hanauske1, C K Osborne, G C Chamness
1University of Texas Health Science Center, San Antonio.
Abstract:
Polypeptide growth factors bind to membrane receptors on human breast cancer cells and stimulate cell proliferation, suggesting that they may be important in growth regulation. Inhibition of the stimulatory effects of these factors might result in antineoplastic activity. Since cytotoxic drugs have been shown to alter cell membrane characteristics, we have examined the effects of a variety of antitumor drugs on the binding of epidermal growth factor (EGF) to the membrane receptor of human breast cancer cells. Twenty-four standard or investigational cytotoxic drugs were screened at a concentration of one-tenth the achievable peak plasma level for their ability to inhibit binding of 125I-EGF to its receptor in MCF-7 human breast cancer cells. Although at this concentration statistically significant inhibition of binding was observed with 11 drugs, the maximum inhibition observed was only 27%. Five agents, representing classes of drugs with different modes of action, were then studied in more detail. Of these, preincubation with 5-fluorouracil, 4-hydroperoxy-cylophosphamide and doxorubicin inhibited MCF-7 colony formation in a dose-dependent manner, but these drugs had no effect on EGF-binding even at a concentration of 10 times the peak plasma level. Preincubation of cells with vinblastine and cisplatin, however, resulted in both reduced colony survival and a parallel reduction in EGF receptor binding. Membrane integrity, as measured by trypan blue exclusion, was not altered. Scatchard analysis of EGF binding demonstrated that the major effect of cisplatin was a reduction in binding affinity. We conclude that cisplatin and vinblastine at high concentrations can inhibit the binding of EGF to human breast cancer cells offering an additional possible mechanism for their antiproliferative activity.
Insights
Certain chemotherapy drugs, like cisplatin and vinblastine, can inhibit epidermal growth factor (EGF) binding to breast cancer cells. This suggests a new mechanism for their anti-cancer effects beyond direct cell killing.
Area of Science:
- Oncology
- Molecular Biology
- Pharmacology
Background:
- Polypeptide growth factors stimulate breast cancer cell proliferation by binding to membrane receptors.
- Inhibiting growth factor signaling may offer a strategy for antineoplastic therapy.
- Cytotoxic drugs can alter cell membrane properties, potentially affecting growth factor receptor binding.
Purpose of the Study:
- To investigate the effects of various antitumor drugs on epidermal growth factor (EGF) binding to its receptor in human breast cancer cells.
- To screen standard and investigational cytotoxic drugs for their ability to inhibit EGF receptor binding.
- To explore the mechanisms by which certain drugs affect EGF binding and cell proliferation.
Main Methods:
- Screening of 24 cytotoxic drugs for inhibition of 125I-EGF binding to MCF-7 cells at sub-therapeutic concentrations.
- Detailed study of five selected agents (5-fluorouracil, 4-hydroperoxy-cyclophosphamide, doxorubicin, vinblastine, and cisplatin) at higher concentrations.
- Assessment of drug effects on MCF-7 colony formation and membrane integrity (trypan blue exclusion).
- Scatchard analysis to determine the impact of drugs on EGF receptor binding affinity and number.
Main Results:
- Eleven of 24 screened drugs showed statistically significant inhibition of EGF binding, but with a maximum of only 27% inhibition.
- 5-fluorouracil, 4-hydroperoxy-cyclophosphamide, and doxorubicin inhibited colony formation but did not affect EGF binding.
- Vinblastine and cisplatin reduced both colony survival and EGF receptor binding.
- Scatchard analysis indicated that cisplatin primarily reduced EGF binding affinity.
Conclusions:
- Cisplatin and vinblastine, at high concentrations, inhibit EGF binding to human breast cancer cells.
- This inhibition of EGF binding represents a potential additional mechanism for the antiproliferative activity of these drugs.
- The findings highlight the complex interactions between chemotherapy and growth factor signaling pathways in cancer treatment.