Metronomic small molecule inhibitor of Bcl-2 (TW-37) is antiangiogenic and potentiates the antitumor effect of ionizing radiation.
OBJECTIVE
To investigate the effect of a metronomic (low-dose, high-frequency) small-molecule inhibitor of Bcl-2 (TW-37) in combination with radiotherapy on microvascular endothelial cells in vitro and in tumor angiogenesis in vivo.


METHODS
Primary human dermal microvascular endothelial cells were exposed to ionizing radiation and/or TW-37 and colony formation, as well as capillary sprouting in three-dimensional collagen matrices, was evaluated. Xenografts vascularized with human blood vessels were engineered by cotransplantation of human squamous cell carcinoma cells (OSCC3) and human dermal microvascular endothelial cells seeded in highly porous biodegradable scaffolds into the subcutaneous space of immunodeficient mice. Mice were treated with metronomic TW-37 and/or radiation, and tumor growth was evaluated.


RESULTS
Low-dose TW-37 sensitized primary endothelial cells to radiation-induced inhibition of colony formation. Low-dose TW-37 or radiation partially inhibited endothelial cell sprout formation, and in combination, these therapies abrogated new sprouting. Combination of metronomic TW-37 and low-dose radiation inhibited tumor growth and resulted in significant increase in time to failure compared with controls, whereas single agents did not. Notably, histopathologic analysis revealed that tumors treated with TW-37 (with or without radiation) are more differentiated and showed more cohesive invasive fronts, which is consistent with less aggressive phenotype.


CONCLUSIONS
These results demonstrate that metronomic TW-37 potentiates the antitumor effects of radiotherapy and suggest that patients with head and neck cancer might benefit from the combination of small molecule inhibitor of Bcl-2 and radiation therapy.
Zeitlin
Benjamin D
BD
Angiogenesis Research Laboratory, Department of Restorative Sciences, University of Michigan School of Dentistry, Ann Arbor, MI.
Spalding
Aaron C
AC
Campos
Marcia S
MS
Ashimori
Naoki
N
Dong
Zhihong
Z
Wang
Shaomeng
S
Lawrence
Theodore S
TS
Nör
Jacques E
JE
D020533:Angiogenesis Inhibitors / Q000008:administration & dosage*; D000818:Animals; D001549:Benzamides / Q000008:administration & dosage*; D002294:Carcinoma, Squamous Cell / Q000098:blood supply / Q000188:drug therapy / Q000473:pathology / Q000532:radiotherapy; D002453:Cell Cycle / Q000187:drug effects / Q000528:radiation effects; D049109:Cell Proliferation / Q000187:drug effects / Q000528:radiation effects; D003131:Combined Modality Therapy / Q000379:methods; D042783:Endothelial Cells / Q000187:drug effects* / Q000528:radiation effects; D006258:Head and Neck Neoplasms / Q000098:blood supply / Q000188:drug therapy / Q000473:pathology / Q000532:radiotherapy; D006801:Humans; D008297:Male; D051379:Mice; D016513:Mice, SCID; D009389:Neovascularization, Pathologic / Q000188:drug therapy* / Q000532:radiotherapy; D010641:Phenotype; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000037:antagonists & inhibitors*; D011838:Radiation-Sensitizing Agents / Q000008:administration & dosage*; D013450:Sulfones / Q000008:administration & dosage*; D047368:Tumor Burden / Q000187:drug effects / Q000528:radiation effects; D023041:Xenograft Model Antitumor Assays / Q000379:methods
D020533:Angiogenesis Inhibitors; D001549:Benzamides; D019253:Proto-Oncogene Proteins c-bcl-2; D011838:Radiation-Sensitizing Agents; D013450:Sulfones; C515128:TW-37 compound