Background: Bevacizumab (BV) is broadly used to treat a number of cancers; however, BV resistance mechanisms and strategies to overcome this resistance are yet to be determined. Methods: We established xenograft mice models harboring Kirsten rat sarcoma oncogene homolog (KRAS) mutations based on the A549 cell line, and tested the responses of xenograft tumors to a series of drugs in ex vivo and in vivo experiments. Changes in transcriptive level were analyzed by ribonucleic acid (RNA) sequencing and the expressions of connexins were determined by immunohistochemistry staining. Results: A549 cell mutation type (KRAS G12S) was confirmed by sequencing. After treating the xenograft tumors with BV, the median interval time from BV administration to tumor volume more than 2.5-fold of the original was 37 days, compared with 21 days in the control (P = 0.025). A549 cells showed resistantance to selumitinib (MEK inhibitor) but were sensitive to selumitinib plus BEZ235 (phosphoinositide 3-kinase/mammalian target of rapamycin dual inhibitor). However, selumitinib could effectively reverse the resistance to BV in in vivo experiments. RNA sequencing showed that mouse genes, but not human genes, activated the mitogen-activated protein kinase signaling pathway, accompanied by activation of the Wnt and Hedgehog pathways. Connexin43 (S261) was phosphorylated before and during BV treatment, and subsequently transitioned to negative phosphorylated-connexin 43-S261 after resistance to BV. Conclusion: Combining an MEK inhibitor with BV was a potential strategy to reverse initial BV resistance. Phosphorylated-connexin 43 might be associated with the response to BV.