CRISPR/Cas9 mutagenesis invalidates a putative cancer dependency targeted in on-going clinical trials

Area of Science:

• Oncology
• Molecular Biology
• Genetics

Background:

• Maternal Embryonic Leucine Zipper Kinase (MELK) is implicated as a genetic dependency in various cancers.
• MELK inhibition via RNAi or small molecules reportedly blocks cancer cell proliferation, especially in triple-negative breast cancer.
• The MELK inhibitor OTS167 is undergoing clinical trials based on these preclinical findings.

Purpose of the Study:

• To investigate the essentiality of MELK in cancer cell fitness using CRISPR/Cas9 gene editing.
• To validate MELK as a therapeutic target for cancer treatment.
• To assess the mechanism of action for the MELK inhibitor OTS167.

Main Methods:

• CRISPR/Cas9 mutagenization was employed to create MELK-null cancer cell lines.
• Cell fitness parameters including doubling time, cytokinesis, and anchorage-independent growth were evaluated.
• Sensitivity of MELK-knockout lines to the MELK inhibitor OTS167 was assessed.

Main Results:

• CRISPR/Cas9-mediated MELK knockout had no discernible impact on the fitness of basal breast cancer cell lines or six other cancer types.
• MELK-null cells maintained wild-type proliferation rates, normal cytokinesis, and anchorage-independent growth.
• MELK-knockout cells remained sensitive to OTS167, indicating an off-target mechanism for the drug.

Conclusions:

• MELK is not a critical determinant of fitness in the tested cancer cell lines, challenging its role as a universal cancer dependency.
• The preclinical rationale for clinical trials targeting MELK, including those with OTS167, is undermined by these findings.
• CRISPR/Cas9 serves as a robust tool for preclinical target validation, with implications for drug development strategies.