The Synergistic Mechanism of Pemetrexed Followed by Kanglaite was due to KLT Subsequently Inhibiting the Pemetrexed-Activated MAPK Signaling Pathway.

Abstract Kanglaite (KLT) can enhance the cytotoxic effects of chemotherapy; however, the underlying mechanism remains unclear. We investigated the mechanism underlying the cytotoxic synergy between KLT and pemetrexed in NSCLC cell lines. A549 and H1975 cell lines were treated with pemetrexed and/or KLT in vitro. IC50 values, the combination index, cell cycle distribution, and signaling pathway analysis were assessed. Cytotoxic interactions between KLT and pemetrexed were dose-dependent in A549 and H1975 NSCLC cell lines. The administration of pemetrexed followed by KLT had a synergistic effect and an advantage over KLT followed by pemetrexed. Concomitant administration in both cell lines indicated that the cytotoxic interactions between KLT and pemetrexed were schedule-dependent. Cell cycle analysis showed that KLT arrested cells mainly in the G2/M phase, whereas pemetrexed arrested cells mainly in the S phase. Exposure to KLT first induced G2/M arrest and subsequently prevented the cytotoxicity of the S phase-specific drug pemetrexed. Signaling pathway analysis showed that exposure to pemetrexed resulted in increased phospho-p44/42MAPK levels which were inhibited by subsequent exposure to KLT. Thus pemetrexed followed by KLT inhibited the MAPK signaling pathway more obviously than KLT followed by pemetrexed. Pemetrexed followed by KLT had a synergistic effect and an advantage over other sequences in NSCLC cell lines. The synergistic mechanism was due to KLT subsequently inhibiting the pemetrexed-activated MAPK signaling pathway. These findings may provide molecular evidence to support clinical treatment strategies for patients with NSCLC.