We have previously demonstrated that solamargine (SM), the major steroidal glycoalkaloid extracted from Chinese herb Solanum plants, reveals down-regulation of HER2 and up-regulation of Fas and tumor necrosis factor receptor (TNFR) expressions, triggers the mitochondria-mediated cell apoptosis pathway, and sensitizes human nonsmall cell lung cancer (NSCLC) H441 and A549 adenocarcinoma cells to chemotherapy. The present study shows that SM enhances HER2 expression in NSCLC large cell carcinoma H661 and small cell lung cancer (SCLC) H69 cells and may increase the susceptibility of the cells to trastuzumab, the humanized anti-HER2 antibody. The combinational treatment of SM and trastuzumab synergistically augments and inhibits H661 and H69 cell proliferation. After treatment with SM, coexpression of HER2 and topoisomerase IIα (TOP2A) H661 and H69 cells is more sensitive to the TOP2 inhibitor, epirubicin. The combinatory use of low concentrations of SM with the low-toxic epirubicin accelerated greater apoptotic cell death than each drug did alone in H661 and H69 cells. Relevant studies have shown that HER2 overexpressing cancer cells are more resistant than HER2 low-expressing cells to the chemotherapeutic agent and tumor necrosis factor-induced apoptosis. These investigations have indicated that HER2 overexpression does not suffice to induce intrinsic and pleomorphic drug resistance. The data presented herein suggest that the expression of HER2 did not influence the SM-induced apoptosis of different types of lung cancer cells and that the SM up-regulation of HER2 and TOP2A expressions simultaneously augmented trastuzumab and epirubicin-induced deaths of lung cancer H661 and H69 cells.
