Abstract PR2: Stroma-derived matrix metalloproteinase 9 (MMP9) confers resistance to anti-EGFR therapy through cell-extrinsic activation of ERBB2/ERK/JUN pathway

Abstract Matrix metalloproteinases (MMPs) have been studied historically for their role in tissue invasion and metastasis. The tumor microenvironment also produces MMPs that may influence other tumor behaviors, as recent mouse models suggest in the intestine and other sites. We examined MMP9 expression in 642 cases of human colorectal cancer (CRC) in relation to clinicopathological features and mutations. MMP9 antibody (Ab) unambiguously stained mesenchymal cells in 104 cases (16.2%) and gave weaker stromal staining in another 12.8%. High stromal MMP9 expression correlated most strongly with the CpG island methylator phenotype (CIMP-high) in tumors (multivariate odds ratio – OR – 2.45, 95% confidence interval – CI – 1.41 to 4.27, p=0.0015) and also with absence of tumor KRAS mutations (multivariate OR 0.54, 95% CI 0.33 to 0.87, p=0.011). The latter association suggested KRAS allelic status as one reason for heterogeneity in CRC cell line responses to MMP9. Four out of 6 KRASWT cell lines proliferated significantly more in the presence of exogenous MMP9, while 4 of 5 KRASMut lines failed to respond. This led us to ask if stromal MMP9 expression might predict the outcome of treatment with anti-EGFR mAb cetuximab, allowing KRASWT tumors to bypass mAb blockade of EGFR-KRAS pathway activation. We retrospectively evaluated MMP9 expression by immunohistochemistry on primary tumors and progression-free survival (PFS) in 86 patients who had received chemotherapy combined with cetuximab as first-line or salvage therapy. Tumors from 29 patients (33.8%) harbored mutant KRAS. PFS of patients with MMP9high;KRASWT tumors (median 3.5 months) was lower than that of patients with low or no stromal MMP9 expression and KRASWT tumors (median 5.8 months, 95% CI for the hazard ratio 1.135-2.179). Patients with KRASMut tumors showed no significant difference in PFS with respect to MMP9 expression (2.55 months and 2.25 months in the MMP9high and MMP9neg/low subgroups, respectively). Thus, low stromal MMP9 expression in KRASWT tumors predicted a better outcome with cetuximab treatment than high MMP9 expression. In CRC cell lines that grow faster in response to MMP9, this factor activates ERBB2 and ERK/JUN signaling. Together, these findings suggest that stroma-derived MMP9 may help tumors bypass common mutational mechanisms for constitutive growth factor pathway activation and confer resistance to anti-EGFR therapy through cell-extrinsic activation of the ERBB2/ERK/JUN pathway. Stromal MMP9 expression may thus predict cetuximab response in KRASWT CRCs and have value in selecting patients for treatment. This proffered talk is also presented as Poster A26.