Abstract A61: Targeting the c-Met signaling pathway by humanized anti-HGF antibody inhibits irinotecan resistance in colorectal cancer.
Authors: Woo Jong Kyu , Jang Yeong-Su , Kang Ju-Hee , Kim Hwan Mook , Oh Seung-Hyun 
Published: May 2015

Background and Purpose: Preclinical and clinical findings indicate that multiple tumour micro-environmental factors, including growth factors, protect solid tumors from therapeutic interventions. Experimental evidence has clarified some of the resistance mechanisms, which have led to the development of innovative approaches to treat cancer. Irinotecan (CPT-11) is a semi-synthetic derivative of camptothecin, originally isolated from the Chinese/Tibetan ornamental tree Camptothecaacuminata. It is a key component of first- and second-line treatment regimens for metastatic colorectal cancer (CRC). Studies of irinotecan have demonstrated that its efficacy to treat cancer is superior to that of best supportive care. However, de novo or acquired clinical resistance to camptothecins still exists expecting new target. The hepatocyte growth factor (HGF)/c-Met signaling system is known to be implicated in the development and progression of colon cancer, but the relationship between the expressions of HGF or c-MET and clinicopathologic feature remains controversial. Growth Factors derived from the extracellular matrix (ECM) create an environment conducive to tumor growth and invasion. We hypothesized that over-expression of HGF in cancer-associated fibroblast (CAF) is related to tumor metastasis and chemo-resistance. We also hypothesized that HGF deprivation using neutralizing antibody inhibited chemoresistance in colorectal cancer.

Results: We measured the levels of mRNA and secreted protein of HGF by real-time PCR and ELISA in fibroblast and CRC cell lines. The mRNA and secreted protein level of HGF were significantly higher in fibroblast than in CRC cell lines. HGF was not detected in conditioned media (CM) from CRC cell cultures established without fibroblasts, but was detected in CM from fibroblast harvested without CRC cells, suggesting that the measured HGF is fibroblast-derived. Fibroblast-derived HGF induced invasion and chemo-resistance of CRC cell lines. We also found elevated levels of HGF in the CM from fibroblast treated with irinotecan. However, anti-HGF antibody removed this resistance to irinitecan. Down regulation of MET expression by a MET-specific siRNA canceled HGF-induced resistance to irinotecan in CRC cells. Fibroblast originated HGF activated c-Met, PI3K/AKT and MAPK signaling in CRC cells. Phosphorylated-MET mediated activation of PI3K/AKT and MAPK rescued HGF effect in CRC cells. Furthermore, fibroblast-derived HGF affected migration and invasion of CRC cells. We further showed that an anti-HGF antibody enhanced anti-tumor activity of irinotecan in vivo, resulting in shrinkage of well-established human colon cancer in mice without enhancing toxicity.

Conclusion: We identified HGF as an important determinant of irinotecan resistance and metastasis of CRC. Anti-HGF monoclonal antibody treatment confirmed the importance of this growth factor for chemo-resistance in CRC. These results present new options toward the early diagnosis of chemoresistance and suggest novel combinations of chemotherapy and anti-HGF agents to prevent or significantly delay the onset of therapy resistance. These observations open new avenues toward the diagnosis of chemoresistant tumors and therapies targeting HGF overexpressing cancers.

Citation Format: Jong Kyu Woo, Yeong-Su Jang, Ju-Hee Kang, Hwan Mook Kim, Seung-Hyun Oh. Targeting the c-Met signaling pathway by humanized anti-HGF antibody inhibits irinotecan resistance in colorectal cancer.. [abstract]. In: Abstracts: AACR Special Conference on Cellular Heterogeneity in the Tumor Microenvironment; 2014 Feb 26-Mar 1; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2015;75(1 Suppl):Abstract nr A61. doi:10.1158/1538-7445.CHTME14-A61