PIK3CA Mutation/PTEN Expression Status Predicts Response of Colon Cancer Cells to the Epidermal Growth Factor Receptor Inhibitor Cetuximab

Abstract

Cetuximab is a monoclonal antibody that targets the human epidermal growth factor receptor (EGFR). Although approved for use in EGFR-overexpressing advanced colorectal cancer, recent studies have shown a lack of association between EGFR overexpression and cetuximab response, requiring the identification of novel biomarkers predictive of response to this agent. To do so, 22 colon cancer cell lines were screened for cetuximab response in vitro and sensitive and resistant lines were identified. In sensitive cell lines, cetuximab induced a G 0 -G 1 arrest without inducing apoptosis. Notably, cetuximabsensitive but not cetuximab-resistant cell lines were preferentially responsive to EGF-stimulated growth. Whereas neither EGFR protein/mRNA expression nor gene copy number correlated with cetuximab response, examination of the mutation status of signaling components downstream of EGFR showed that cell lines with activating PIK3CA mutations or loss of PTEN expression (PTEN null) were more resistant to cetuximab than PIK3CA wild type (WT)/PTENexpressing cell lines (14 F 5.0% versus 38.5 F 6.4% growth inhibition, mean F SE; P = 0.008). Consistently, PIK3CA mutant isogenic HCT116 cells showed increased resistance to cetuximab compared with PIK3CA WT controls. Furthermore, cell lines that were PIK3CA mutant/PTEN null and Ras/BRAF mutant were highly resistant to cetuximab compared with those without dual mutations/PTEN loss (10.8 F 4.3% versus 38.8 F 5.9% growth inhibition, respectively; P = 0.002), indicating that constitutive and simultaneous activation of the Ras and PIK3CA pathways confers maximal resistance to this agent. A priori screening of colon tumors for PTEN expression status and PIK3CA and Ras/BRAF mutation status could help stratify patients likely to benefit from this therapy.

KRAS mutation testing for predicting response to anti-EGFR therapy for colorectal carcinoma: proposal for an European quality assurance program

“…In MSI colorectal carcinoma, BRAF mutations occur independently of KRAS mutations and provide proliferation and survival signals through activation of several signaling pathways [44,45]. Cell lines with RAS/BRAF mutations are highly resistant to cetuximab in vitro compared with wild-type cells [46]. One study showed no relationship between BRAF mutations and median survival of patients with metastatic colorectal cancer receiving bevacizumab, an antibody against vascular endothelial growth factor-A (VEGF) [47].…”

“…This catalytic subunit can be activated by an interaction with RAS proteins. PIK3CA mutations have been found in 10-18% of colorectal cancers [38,46,49], but it is unclear whether these mutations can predict response to EGFRtargeted therapies. According to one in vitro study, cell lines with activating PIK3CA mutations are resistant to cetuximab compared with wild-type cell lines [46].…”

“…PIK3CA mutations have been found in 10-18% of colorectal cancers [38,46,49], but it is unclear whether these mutations can predict response to EGFRtargeted therapies. According to one in vitro study, cell lines with activating PIK3CA mutations are resistant to cetuximab compared with wild-type cell lines [46]. However, two studies failed to observe a link between PIK3CA mutation status and cetuximab response in patients with colon cancer [33,48].…”

“…1b). Cell lines deficient in PTEN expression are more resistant to cetuximab in vitro than those with normal PTEN expression [46]. The loss of PTEN protein expression negatively predicts efficacy of cetuximab therapy in patients with metastatic colorectal cancer [50].…”

Prognostic vs predictive molecular biomarkers in colorectal cancer: is KRAS and BRAF wild type status required for anti-EGFR therapy?

“…A priori screening of colon tumors for PTEN expression status and PIK3CA and Ras/BRAF mutation status could help stratify patients likely to benefit from this therapy. 53 Razis et al 54 reported that normal PTEN protein expression was associated with a higher response rate and longer time to progression in patients treated with cetuximabbased therapy, despite a 50% response rate observed in patients who had lost PTEN protein expression. Loupakis 55 metastases from patients with irinotecan refractatory mCRC treated with irinotecan and cetuximab: 12 (36%) of 33 patients with PTEN-positive metastases were responders compared with one (5%) of 22 who had PTEN-negative metastases.…”