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  • Title: Efficacy of the combination of MEK and CDK4/6 inhibitors in vitro and in vivo in KRAS mutant colorectal cancer models.
    Author: Lee MS, Helms TL, Feng N, Gay J, Chang QE, Tian F, Wu JY, Toniatti C, Heffernan TP, Powis G, Kwong LN, Kopetz S.
    Journal: Oncotarget; 2016 Jun 28; 7(26):39595-39608. PubMed ID: 27167191.
    Abstract:
    PURPOSE: Though the efficacy of MEK inhibitors is being investigated in KRAS-mutant colorectal cancers (CRC), early clinical trials of MEK inhibitor monotherapy did not reveal significant antitumor activity. Resistance to MEK inhibitor monotherapy developed through a variety of mechanisms converging in ERK reactivation. Since ERK increases cyclin D expression and increases entry into the cell cycle, we hypothesized that the combination of MEK inhibitors and CDK4/6 inhibitors would have synergistic antitumor activity and cause tumor regression in vivo. RESULTS: The combination of MEK and CDK4/6 inhibitors synergistically inhibited cancer cell growth in vitro and caused tumor regression in vivo in cell line and patient-derived xenograft models. Combination therapy markedly decreased levels of phosphorylated ribosomal protein S6 both in vitro and in vivo and decreased Ki67 staining in vivo. EXPERIMENTAL DESIGN: We performed in vitro proliferation, colony formation, apoptosis, and senescence assays, and Western blots, on a panel of 11 KRAS mutant CRC cell lines treated with the MEK inhibitor MEK162, the CDK4/6 inhibitor palbociclib, or the combination. We also treated 4 KRAS mutant CRC cell line and patient-derived xenografts with the MEK inhibitor trametinib, the CDK4/6 inhibitor palbociclib, or the combination, and performed immunohistochemical and reverse phase protein array analysis. CONCLUSIONS: Combined inhibition of both MEK and CDK4/6 is effective in preclinical models of KRAS mutant CRC and justifies a planned phase II clinical trial in patients with refractory KRAS-mutant CRC.Efficacy of the combination of MEK and CDK4/6 inhibitors in vitro and in vivo in KRAS mutant colorectal cancer models.
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