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

Background: 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.

Methods: 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.

Results: 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.

Conclusions: 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.