Homeobox B9: A potential surrogate marker for bevacizumab in combination with chemotherapy in colorectal cancer.

Abstract

10531 Background: Homeobox B9 (HOXB9) is known to be overexpressed in human breast cancer and profoundly related to tumorigenicity, lung metastasis and radio-resistance. (Hayashida, PNAS 2010, and Chiba, PNAS 2011). However, little is known about the relation between the expression of HOXB9 and angiogenesis in colorectal cancer (CRC). We aimed to clarify the impact of HOXB9 in CRC and evaluate the importance for bevacizumab treatment. Methods: The expression of HOXB9 in human CRC specimens was analyzed. Then, we introduced HOXB9 construct into human CRC cell lines and examined TGFβ signaling and angiogenic factors. Xenograft model was established by these cell lines either with or without the administration of bevacizumab (5mg/kg, weekly) intraperitoneally. Finally, we examined the mRNA levels of consecutive patients who were treated by chemotherapy with bevacizumab in our institute and calculated the Kaplan- Meier curve with log-rank test. Results: 47 of 69 surgical specimens (67%) showed positive expression of HOXB9 mRNA. The high HOXB9 mRNA levels significantly correlated with poor differentiation and liver metastasis. The HOXB9-overexpressed cell lines showed significantly higher expression of TGFβ signaling target genes and angiogenic factors. HOXB9 overexpression significantly increased tumor volume and burden with higher microvessel density in vivo, even though the cell proliferation decreased in vitro. Notably, HOXB9-overexpressed tumor was dramatically shrunk by administration of bevacizumab (tumor shrinkage rate; 93% vs. 42% in HT29, 83% vs. 27% in HCT116). Patients with high expression of HOXB9 in tumor showed significantly longer progression free and overall survival periods (n=39). Conclusions: Our results demonstrated that patients with high expression of HOXB9 in tumor had better prognosis with bevacizumab treatment but worse without. In vivo and in vitro experiments revealed that HOXB9 might orchestrate angiogenesis and establish positive feedback between cancer cells and microenvironment. Bevacizumab might inhibit the feedback to reduce tumor growth dramatically. Therefore, HOXB9 may work as a potential surrogate marker of bevacizumab treatment in CRC.