Growth inhibition of human lung adenocarcinoma cells by antibodies against epidermal growth factor receptor and by ganglioside G(M3): Involvement of receptor-directed protein tyrosine phosphatase(s)

Growth of the EGF receptor-expressing non-small-cell lung carcinoma cell line H125 seems to be at least partially driven by autocrine activation of the resident EGF receptors. Thus, the possibility of an EGF receptor-directed antiproliferative treatment was investigated in vitro using a monoclonal antibody (αEGFR ior egf/r3) against the human EGF receptor and gangliosides which are known to possess antiproliferative and anti-tyrosine kinase activity. The moderate growth-inhibitory effect of αEGFR ior egf/r3 was strongly potentiated by the addition of monosialoganglioside G(M3). Likewise, the combination of αEGFR ior egf/r3 and G(M3) inhibited EGF receptor autophosphotylation activity in H125 cells more strongly than either agent alone. A synergistic inhibition of EGF receptor autophosphorylation by αEGFR ior egf/r3 and G(M3) was also observed in the human epidermoid carcinoma cell line A431. In both cell lines, the inhibition of EGF receptor autophosphorylation by G(M3) was prevented by pretreatment of the cells with pervanadate, a potent inhibitor of protein tyrosine phosphatases (PTPases). Also, G(M3) accelerated EGF receptor dephosphorylation in isolated A431 cell membranes. These findings indicate that G(M3) has the capacity to activate EGF receptor-directed PTPase activity and suggest a novel possible mechanism for the regulation of cellular PTPases.