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January 15, 2011 (Vol. 31, No. 2)

Finessing Gene Editing in Human Cells

Genetically Defined X-Man Disease Models Find Niche in Personalized Medicine Applications

  • Methods

    K-Ras wild-type and Erbitux-sensitive SW48 colon cancer cells were selected for engineering using the Genesis platform, wherein two different variants of K-Ras mutation (G13D and G12V) were spliced into the endogenous K-Ras locus. These two isogenic cell lines and WT parental cells were then tested for their sensitivity to Erbitux in vitro and in vivo.

  • Results

    Click Image To Enlarge +
    Figure 2. Predicting K-Ras resistance to EGFR-targeted agents in colon cancer [De Rook W., et al., JAMA Oct. 2010]

    In both in vitro proliferation assays and in xenografted tumors, G12V containing SW48 cells were found to be completely unresponsive to Erbitux. However, G13D containing SW48 cells, along with the parental WT SW48 cells, were highly responsive to Erbitux. This experimental data was unambiguous, showing clearly that G13D mutations do not impart resistance to Erbitux therapy in these patient-relevant disease models. Bardelli and colleagues were thus prompted to subsequently perform a new and larger retrospective sequence analysis on colon cancer patient tumor samples for their K-Ras mutational status and compare this with their known clinical response data to Erbitux.

    This patient study demonstrated a clear concordance with the X-Man disease model data and confirmed that G13D patients are benefitting from anti-EGFR therapy. Prospective clinical trials will need to be performed to confirm this suspicion and, if conclusive, may lead to a further refinement in the rules for prescribing EGFR-targeted therapies in colon cancer.

  • Conclusions

    Click Image To Enlarge +
    Figure 3. X-Man genetically defined and patient-relevant human cell lines

    X-Man cell lines are a powerful tool to predict patient responses to targeted therapies and they provide a definitive understanding of the genetic factors that mediate their sensitivity or resistance to such agents. Further in vitro studies are now ongoing using a suite of SW48 based X-Man cell lines covering several other variations of mutant K-Ras and other genotypes for their effects on EGFR-targeted agents.

    Other targeted agents are also being tested in this system so as to potentially inform the prospective integration of clinical biomarkers into new clinical trials. Expanding on this ambition, Horizon and several translational and clinical collaborators have been awarded a large consortium grant to define and integrate new genetic biomarkers into X-Man models and build algorithm for prospective clinical trials.

    Genetically defined X-Man human cell lines are important tools to predict which patients will benefit from new targeted or personalized medicines. Building upon the K-Ras/Erbitux data, examples of personalized medicine will become increasingly manifold as such models are extended upon and increasingly disseminated within the academic and industrial research community.

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