Bavituximab: a Novel, Investigational Immunotherapy Agent Targeting Phosphatidylserine in the Vasculature of the Tumor Microenvironment

Bavituximab is a first-in-class phosphatidylserine (PS)-targeting monoclonal antibody that blocks PS-mediated immunosuppression by multifocal reprogramming of immune cells in the tumor microenvironment to support immune activation.¹ PS is a highly immunosuppressive molecule usually located inside the membrane of healthy cells, but “flips” and becomes exposed on the outside of cells that line tumor blood vessels, creating a specific target for anticancer treatments. PS-targeting agents block PS-mediated immunosuppression by multifocal reprogramming of immune cells in the tumor microenvironment to support immune activation.¹

Preclinical data demonstrate that bavituximab:

• Blocks PS-mediated immunosuppressive signaling
• Provides specificity for innate immune responses
• Activates T-cell–driven adaptive immunopathways to stimulate an effective immune response to the tumor.²

After binding exposed PS in tumors, bavituximab engages Fc-γ receptors on tumor-promoting myeloid-derived suppressor cells (MDSCs), M2-like tumor-associated macrophages (which fail to differentiate into M1-like tumor-killing macrophages and natural killer cells), and immature dendritic cells, leading to multiple immunostimulatory changes in the tumor environment.² These changes include:

• An increase in immunostimulatory cytokines (including tumor necrosis factor alpha [TNF-α] and interleukin (IL)-12)
• Macrophage polarization from an M2 state to a tumor-fighting M1 state
• Differentiation of tumor-promoting MDSCs into M1 macrophages and mature dendritic cells.²

Thus, antibody-mediated PS blockade reduces the levels of MDSCs, transforming growth factor beta (TGF-β) and IL-10 and increases the levels of TNF-α and IL-12.¹ M1 macrophages contribute to tumor destruction through antibody-dependent cellular cytotoxicity, while mature dendritic cells educate T cells, inducing tumor-specific cytotoxic T-cell responses^.2,3

References

1. Yopp A, Kallinteris N, Huang X, et al. Antibody-mediated blockade of phosphatidylserine enhances the antitumor activity of targeted therapy and immune checkpoint inhibitors by affecting myeloid and lymphocyte populations in the tumor microenvironment. J Immunother Cancer. 2014;2(suppl 3):P266.
2. Belzile O, Zhang Z, Huang X, et al. Antibody-mediated blockade of phosphatidylserine combined with radiation improves survival and tumor eradication in a rat model of non-small cell lung cancer. Cancer Res. 2014;74(19 suppl). Abstract 639.
3. Yin Y, Barbero G, Brownlee Z, et al. Targeting phosphatidylserine to improve androgen deprivation therapy of prostate cancer. Cancer Res. 2011;71(8 suppl). Abstract 621.

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