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Better together
Inhibitors of the epidermal growth factor receptor (EGFR) are already used to treat colorectal cancer. Unfortunately, although many patients’ tumors respond to these drugs, most of these responses are only partial and result in a slowing of tumor growth rather than a regression of the cancer. Now, Zanella et al. used a combination of patient samples and mouse xenografts to determine the reasons for the incomplete response to treatment and how it can be overcome. In some cases, more effective treatment just required a more complete inhibition of EGFR. Many of the other cancers overexpressed insulin-like growth factor 2 (IGF2), and the authors discovered that combining inhibitors of EGFR and IGF was an effective way to overcome resistance in these tumors.
Abstract
Among patients with colorectal cancer who benefit from therapy targeted to the epidermal growth factor receptor (EGFR), stable disease (SD) occurs more frequently than massive regressions. Exploring the mechanisms of this incomplete sensitivity to devise more efficacious treatments will likely improve patients’ outcomes. We tested therapies tailored around hypothesis-generating molecular features in patient-derived xenografts (“xenopatients”), which originated from 125 independent samples that did not harbor established resistance-conferring mutations. Samples from xenopatients that responded to cetuximab, an anti-EGFR agent, with disease stabilization displayed high levels of EGFR family ligands and receptors, indicating high EGFR pathway activity. Five of 21 SD models (23.8%) characterized by particularly high expression of EGFR and EGFR family members regressed after intensified EGFR blockade by cetuximab and a small-molecule inhibitor. In addition, a subset of cases in which enhanced EGFR inhibition was unproductive (6 of 16, 37.5%) exhibited marked overexpression of insulin-like growth factor 2 (IGF2). Enrichment of IGF2 overexpressors among cases with SD was demonstrated in the entire xenopatient collection and was confirmed in patients by mining clinical gene expression data sets. In functional studies, IGF2 overproduction attenuated the efficacy of cetuximab. Conversely, interception of IGF2-dependent signaling in IGF2-overexpressing xenopatients potentiated the effects of cetuximab. The clinical implementation of IGF inhibitors awaits reliable predictors of response, but the results of this study suggest rational combination therapies for colorectal cancer and provide evidence for IGF2 as a biomarker of reduced tumor sensitivity to anti-EGFR therapy and a determinant of response to combined IGF2/EGFR targeting.
- Copyright © 2015, American Association for the Advancement of Science
