Tumor angiogenesis plays a critical role in colorectal cancer progression. Recent randomized clinical trials have revealed the additive effect of bevacizumab, a humanized monoclonal antibody against vascular endothelial growth factor (VEGF)-A, to conventional chemotherapy in the improved survival of patients with metastatic colorectal cancer. However, a number of preclinical reports indicate the development of resistance to anti-angiogenic therapy. In this study, we addressed the effects of anti-VEGF antibodies on the growth and malignant behavior of colorectal cancer cells. TK-4, a solid tumor strain derived from a colon cancer patient, was subcutaneously or orthotopically implanted into nude mice. Short-term administration of anti-VEGF antibodies inhibited the growth of cecal tumors at day 14 by suppressing mitosis, but prolonged treatment resulted in the recovery of cellular proliferation and suppression of apoptosis at day 35. Intratumoral hypoxia induced by anti-VEGF antibody treatment resulted in activation of hypoxia inducible factor-1α protein and an increased number of aldehyde dehydrogenase 1-positive tumor cells. In microarray analysis,stanniocalcin 2(STC2) was the most highly upregulated gene in anti-VEGF antibody-treated tumors.In vitroanalyses showed that the growth and migration of SW480 colon cancer cells under hypoxic conditions were significantly inhibited by knockdown of STC2.In vivoserial transplantation of TK-4 revealed that long-term administration of anti-VEGF antibodies increased the tumorigenicity of colon cancers and accelerated tumor growth when transplanted into secondary recipient mice. Our data provide a potential molecular explanation for the limited clinical effectiveness of anti-VEGF antibodies.What's new?
Antibodies against vascular endothelial growth factor (VEGF) are used in the treatment of colorectal cancer, but tumors may become resistant to them. In this study, anti-VEGF antibodies were found to effectively suppress the growth of cecal tumors at day 14 in a colorectal cancer xenograft mouse model. At day 35, however, indications of drug resistance emerged. Intratumoral hypoxia induced by treatment played an important role in regulating multiple processes that accelerated the malignant potential of colon cancers. The data may explain the molecular mechanism behind the limited clinical effectiveness of anti-VEGF antibodies.