Background: KRAS is frequently mutated in the tumors of patients with metastatic colorectal cancer (mCRC) and thus represents a valid target for therapy. However, the strategies of targeting KRAS directly and targeting the downstream effector mitogen-activated protein kinase kinase (MEK) via monotherapies have shown limited efficacy. Thus, there is a strong need for novel, effective combination therapies to improve MEK-inhibitor efficacy in patients with KRAS-mutated mCRC.
Objective: Our objective was to identify novel drug combinations that enhance MEK-inhibitor efficacy in patients with KRAS-mutated mCRC.
Design: In this study, we performed unbiased high-throughput screening (HTS) to identify drugs that enhance the efficacy of MEK inhibitors in vitro, and we validated the drugs' efficacy in vivo.
Methods: HTS was performed using three-dimensional CRC spheroids. Trametinib, the anchor drug, was probed with two "clinically ready" libraries of 252 drugs to identify effective drug combinations. The effects of the drug combinations on CRC cell proliferation and apoptosis were further validated using cell growth assays, flow cytometry, and biochemical assays. Proteomic and immunostaining studies were performed to determine the drugs' effects on molecular signaling and cell division. The effects of the drug combinations were examined in vivo using CRC patient-derived xenografts.
Results: HTS identified paclitaxel as being synergistic with trametinib. In vitro validation showed that, compared with monotherapies, this drug combination demonstrated strong inhibition of cell growth, reduced colony formation, and enhanced apoptosis in multiple KRAS-mutated CRC cell lines. Mechanistically, combining trametinib with paclitaxel led to alterations in signaling mediators that block cell-cycle progression. Trametinib also enhanced paclitaxel-mediated microtubule stability resulting in significantly higher defects in mitosis. Finally, the combination of trametinib with paclitaxel exhibited significant inhibition of tumor growth in several KRAS-mutant patient-derived xenograft mouse models.
Conclusion: Our data provide evidence supporting clinical trials of trametinib with paclitaxel as a novel therapeutic option for patients with KRAS-mutated, metastatic CRC.
Keywords: KRAS; colorectal cancer; combination therapy; paclitaxel; trametinib.
Combining paclitaxel enhances the efficacy of trametinib in colorectal cancer cells with mutations in the oncogenic KRAS protein Metastatic colorectal cancer (mCRC) is the second leading cause of cancer death in the USA. About half of these patients have mutations in the oncogenic protein KRAS. In recent developments targeted therapies that block KRAS demonstrate modest benefit in a small percentage of patients with mCRC and when benefit is obtained, it is transient. Thus, there is an urgent need for developing novel effective therapeutic strategies that can significantly improve survival of most patients with mCRC. The MEK protein is activated by KRAS and is a key protein for cancer cell survival. As inhibitors for the MEK protein by themselves are not effective in improving outcomes in patients with mCRC, the research team performed a drug screen to identify drugs that can significantly enhance the efficacy of MEK-inhibitors in blocking the growth of cultured CRC cells and colorectal tumors grown in animal models. Through unbiased high throughput screening, this study identified the anti-cancer drug paclitaxel to strongly enhance the efficacy of the MEK-inhibitor trametinib. Compared to the drugs by themselves, when combined, these drugs led to significant increases in death of multiple CRC cell types that have mutations in the oncogenic KRAS gene. Also, the drug combination blocked colorectal tumors growth in mice significantly more than the drugs used as single agents. The study also made a novel observation that the MEK-inhibitor can enhance the cell killing ability of paclitaxel by likely increasing its bioavailability inside of CRC cells. Thus, blocking of oncogenic survival signaling by the MEK-inhibitor and increased cytotoxic effects of paclitaxel, work together in inducing higher cell death in CRC cells. These preclinical studies indicate that the combination of trametinib and paclitaxel may be a strong candidate regimen for further evaluation in clinical studies and has the potential to improve outcomes in patients with metastatic colorectal cancer with KRAS mutations.
© The Author(s), 2024.