PROJECT ONE: Metronomic Small Molecule Inhibitor of Bc12 in Head and Neck Cancer Therapy
Jacques Nör, DDS, PhD, School of Dentistry
Frank Worden, M.D., Hematology-Oncology
Head & neck tumors are highly vascularized malignancies with poor survival rates with current therapies. It is known that vascular endothelial growth factor (VEGF) is a strong inducer of tumor angiogenesis, and that VEGF enhances endothelial cell survival and resistance to treatment by upregulating the expression of Bcl-2. We have recently demonstrated that Bcl-2 functions as a pro-angiogenic signaling molecule, in addition to its well-known anti-apoptotic effect (Karl et al., 2005). Inhibition of VEGF signaling with an antibody (e.g. Avastin), or with an inhibitor of one its receptors (e.g. PTK787) results in selective ablation of tumor blood vessels and inhibition of tumor growth. These results demonstrate that the VEGF/Bcl-2 pathway is critical for the maintenance of tumor vasculature. Structure based 3D-database searching led to the development of novel small molecule inhibitors of Bcl-2 (TW-37 and TM-1252). We have demonstrated that TW-37 induces apoptosis of head & neck tumor cells and neovascular endothelial cells (but not dermal fibroblasts) in vitro, and that TW-37 is anti-angiogenic in vivo (Zeitlin et al., 2006). This work demonstrated that a small molecule inhibitor of Bcl-2 represents a novel class of drugs that induces tumor cell apoptosis and is anti-angiogenic, two distinct and perhaps synergistic anti-tumor effects. However, we do not know the effect of a small molecule inhibitor of Bcl-2 on the resistance of head & neck tumors to radiation therapy and to conventional chemotherapy, and what is the better treatment sequence and timing.
The broad long-term goals of this translational project are to understand the effect of therapeutic inhibition of Bcl-2 on the clinical outcome of patients with head & neck cancer. The objectives of this application are to evaluate the effect of a small molecule inhibitor used in a metronomic regimen (low dose, high frequency) in combination with radiation therapy and Cisplatin on angiogenesis in vitro and in vivo, and on the growth of head & neck tumors in vivo. We plan to accomplish these objectives by studying mechanisms involved in the process of small molecule inhibitor of Bcl-2-mediated endothelial cell and tumor cell apoptosis, when used in combination with ionizing radiation and chemotherapy. The SCID Mouse Model of Human Angiogenesis and in vivo bioluminescence will be used to evaluate the effect of timing and sequence of treatment on angiogenesis and tumor growth. And a Phase I clinical trial will be conducted in patients that were previously treated with radiation therapy and standard chemotherapy to begin evaluation of the safety and efficacy of a small molecule inhibitor of Bcl-2 for treatment of head & neck cancer. The knowledge generated here will enhance our understanding about the function of Bcl-2 in head & neck tumor angiogenesis and growth, and will demonstrate if therapeutic blockade of Bcl-2 function affects resistance to ionizing radiation and chemotherapy.
We have worked on S.A. #1 and #2 during the first year of this project, as planned in the original grant application. These experiments were designed to evaluate the effects TW-37 by itself, or in combination therapies, in head and neck squamous cell carcinomas (HNSCC). We observed that, when utilized by itself, TW-37 inhibits tumor angiogenesis and slows down HNSCC tumor growth, leading to a significant effect in "time to failure". Notably, combination of TW-37 with Cisplatin leads to synergistic effects of drug combination in vitro, and additive effect in vivo. Surprisingly, we observed that TW-37 mediates an "S" phase cell cycle arrest of both HNSCC and primary endothelial cells, which is associated with an increase in phosphorylated Chk1, and inhibition of Cyclin D1 and CDK4.
In addition, we have performed experiments with combination of radiation therapy and TW37. We observed that TW-37 acts as a radiosensitizer in head and neck squamous cell carcinomas in vivo. TW-37 sensitized endothelial cells to the effects of relatively low dose radiation. Our results further suggested that this effect might derive from a sensitive sub-population of endothelial cells that are highly responsive to TW-37 treatment. Notably, the anti-angiogenic effects of radiation and TW-37 appeared to compliment the known anti-tumor cell effects of both TW-37 and radiation in vitro, and may account for the enhanced anti-tumor effect for the combination therapy observed in vivo. The manuscript reporting these results is being reviewed internally (by the authors) and should be submitted for publication within the next two months.
It is known that several tumor-derived pro-angiogenic factors trigger signaling pathways that converge to Bcl-2 and result in its upregulated expression in tumor-associated microvascular endothelial cells (Nör et al., 1999; Karl et al., 2005). We have demonstrated that this pathway has a direct impact in head and neck tumor growth (Nör et al., 2001; Kaneko et al., 2007). We propose that small molecule inhibitors of Bcl-2 have two complimentary effects that are mediated by the direct induction of tumor cell apoptosis and selective disruption of tumor blood vessels. We have recently published a review manuscript in the Journal of Clinical Oncology that is focused on the presentation and discussion of the effects of therapeutic inhibition of Bcl-2 in tumor biology (Zeitlin et al., 2008).
The translational significance of this project is that this work is characterizing a novel class of compounds that have both, an anti-angiogenic and an anti-tumor cell effect. Collectively, these studies are providing the pre-clinical data to support the use of small molecule inhibitors of Bcl-2 for treatment of highly vascularized malignancies, such as head and neck tumors.