Antitumor effects of bevacizumab in a microenvironment-dependent human adult T-cell leukemia/lymphoma mouse model.

Objective The objective of this study was to evaluate the therapeutic potential of bevacizumab with or without systemic chemotherapy for adult T-cell leukemia/lymphoma (ATL) and clarify the significance of angiogenesis for ATL pathogenesis. Methods NOD/Shi-scid, IL-2Rγnull (NOG) mice were used as recipients of tumor cells from a patient with ATL, which engraft and proliferate in a microenvironment-dependent manner. The ATL cells could be serially transplanted in NOG mice, but could not be maintained in in vitro cultures. Results Injection of bevacizumab alone significantly increased necrosis and decreased vascularization in the tumor tissue. Levels of human soluble interleukin two receptor in the serum (reflecting the ATL tumor burden) of bevacizumab-treated mice were significantly lower than in untreated mice. Although bevacizumab monotherapy showed these clear anti-angiogenesis effects, it did not prolong survival. In contrast, injection of bevacizumab together with cyclophosphamide, doxorubicin, vincristine, prednisolone (CHOP) led to a significant prolongation of survival of the ATL mice relative to CHOP alone. Conclusions This is the first report to evaluate the efficacy of bevacizumab for ATL in a tumor microenvironment-dependent model. Bevacizumab therapy combined with chemotherapy could be a valuable treatment strategy for that subgroup of ATL probably depending to a large extent on angiogenesis via vascular endothelial growth factor.