A combination of p53-activating APR-246 and phosphatidylserine-targeting antibody potently inhibits tumor development in hormone-dependent mutant p53-expressing breast cancer xenografts

Abstract

Background

Between 30 and 40% of human breast cancers express a defective tumor suppressor p53 gene. Wild-type p53 tumor suppressor protein promotes cell-cycle arrest and apoptosis and inhibits vascular endothelial growth factor–dependent angiogenesis, whereas mutant p53 protein (mtp53) lacks these functions, resulting in tumor cell survival and metastasis. Restoration of p53 function is therefore a promising drug-targeted strategy for combating mtp53-expressing breast cancer.

Methods

In this study, we sought to determine whether administration of APR-246, a small-molecule drug that restores p53 function, in combination with 2aG4, an antibody that targets phosphatidylserine residues on tumor blood vessels and disrupts tumor vasculature, effectively inhibits advanced hormone-dependent breast cancer tumor growth.

Results

APR-246 reduced cell viability in mtp53-expressing BT-474 and T47-D human breast cancer cells in vitro, and significantly induced apoptosis in a dose-dependent manner. However, APR-246 did not reduce cell viability in MCF-7 breast cancer cells, which express wild-type p53. We next examined APR-246’s anti-tumor effects in vivo using BT-474 and T47-D tumor xenografts established in female nude mice. Tumor-bearing mice were treated with APR-246 and/or 2aG4 and tumor volume followed over time. Tumor growth was more effectively suppressed by combination treatment than by either agent alone, and combination therapy completely eradicated some tumors. Immunohistochemistry analysis of tumor tissue sections demonstrated that combination therapy more effectively induced apoptosis and reduced cell proliferation in tumor xenografts than either agent alone. Importantly, combination therapy dramatically reduced the density of blood vessels, which serve as the major route for tumor metastasis, in tumor xenografts compared with either agent alone.

Conclusion

Based on our findings, we contend that breast tumor growth might effectively be controlled by simultaneous targeting of mtp53 protein and tumor blood vessels in mtp53-expressing cancers.

Keywords:

• breast cancer
• blood vessel targeting agent
• p53
• APR-246
• apoptosis
• angiogenesis

Acknowledgments

This research was initially conducted with Dr Philip Thorpe from the University of Texas Southwestern Medical Center (Dallas, TX, USA), who sadly passed away recently. We would like to thank him for providing antibodies, including 2aG4, used in our research. We would also like to thank Peregrine Pharmaceuticals Inc., (Tustin, CA, USA) for providing additional 2aG4 and acknowledge APREA AB (Solna, Sweden) for providing partial funding and APR-246 for our in vivo studies. Additional financial support was provided by a peer-reviewed faculty research grant from the College of Veterinary Medicine, University of Missouri. SMH is the Zalk Missouri Professor of Tumor Angiogenesis.

Disclosure

The authors report no conflicts of interest in this work.