Various conventional chemotherapeutic drugs can block angiogenesis or even kill activated, dividing endothelial cells. Such effects may contribute to the antitumor efficacy of chemotherapy in vivo and may delay or prevent the acquisition of drug-resistance by cancer cells. We have implemented a treatment regimen that augments the potential antivascular effects of chemotherapy, that is devoid of obvious toxic side effects, and that obstructs the development of drug resistance by tumor cells. Xenografts of 2 independent neuroblastoma cell lines were subjected to either continuous treatment with low doses of vinblastine, a monoclonal neutralizing antibody (DC101) targeting the flk-1/KDR (type 2) receptor for VEGF, or both agents together. The rationale for this combination was that any antivascular effects of the low-dose chemotherapy would be selectively enhanced in cells of newly formed vessels when survival signals mediated by VEGF are blocked. Both DC101 and low-dose vinblastine treatment individually resulted in significant but transient xenograft regression, diminished tumor vascularity, and direct inhibition of angiogenesis. Remarkably, the combination therapy resulted in full and sustained regressions of large established tumors, without an ensuing increase in host toxicity or any signs of acquired drug resistance during the course of treatment, which lasted for >6 months.
Giannoula Klement, Sylvain Baruchel, Janusz Rak, Shan Man, Katherine Clark, Daniel J. Hicklin, Peter Bohlen, Robert S. Kerbel
Submitter: Adam P. Dicker, M.D., Ph.D. | email@example.com
Thomas Jefferson University
Published April 24, 2000
We were excited to read of the work by Klement et al, that low-dose chemotherapy can cause inhibition of tumor angiogenesis. We have additional experimental data that indirectly support a similar hypothesis. Paclitaxel (taxol) and Docetaxel (taxotere) are microtubule- binding drugs (taxanes) shown to have clinical activity in a variety human solid tumors. Both drugs can also amplify the cytotoxic effect of ionizing radiation in-vitro, presumably by inducing arrest at metaphase, which is known to be a very radiosensitive phase of the cell cycle. High doses of taxanes or of radiation are commonly used in the clinic, to treat tumors at a number of sites. We have evaluated combinations of taxanes and radiation, to target the endothelial cell population with the goal of a reduction of radiation and paclitaxel doses, while selectively targeting the endothelial cell compartment. We isolated human umbilical vein endothelial cells (HUVEC) and incubated these cells at a subconfluent density with different concentrations of paclitaxel and docetaxel (.001-10 ng/ml). We compared the effects of these drugs, with or without a low dose of radiation (2-10 Gy), on cell proliferation, migration and tube formation in Matrigel. We also evaluated the effect of taxanes and radiation on cellular behavior in the aortic ring angiogenesis assay. Both taxanes inhibited endothelial cell proliferation, migration, and tube formation (differentiation) in a dose dependent manner. The half-maximal inhibition doses (IC-50) for paclitaxel and docetaxel was 1-nM and 0.01-nM (p <0.001), respectively. In combination with radiation, inhibition of sprouting and tube formation increased 3.6-fold using the IC-50 and 10 Gy. Inhibition of proliferation of endothelial cells suggested a greater than additive effect at low doses of both drug and radiation. The addition of radiation potentiated these antiangiogenic effects in a dose dependent manner. The anti-proliferative effects of taxane–induced radiosensitization of endothelial cells may result from induction of apoptosis or inhibition of cell-cycle progression. These results suggest that the activity of taxanes may in part be due to the antiangiogenic as well as direct cytotoxic effects on tumor cells. However, the exact mechanism(s) responsible for this effect remains to be elucidated. We plan to test our findings in-vivo to further evaluate this concept in the manner of Klement et al. Taken together, these results further support the hypothesis that low doses of chemotherapeutic drugs can act as antiangiogenic therapies.
Adam P. Dicker, M.D., Ph.D.and Derrick Grant, Ph.D. Department of Radiation Oncology, Kimmel Cancer Center and The Cardeza Foundation for Hematological Research Jefferson Medical College, Thomas Jefferson University, Philadelphia, PA