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424 An allosteric, orally administered CBL-B inhibitor remodels the tumor microenvironment and enhances immune-mediated tumor growth inhibition
  1. Yilin Qi,
  2. Jun Kuai,
  3. Yingzhi Bi,
  4. Huadong Sun,
  5. Samira Jaeger,
  6. David Greco,
  7. Ken Carson,
  8. Timothy Reilly,
  9. Geraldine Harriman and
  10. Fang Wang
  1. Hotspot Therapeutics, Boston, MA, United States


Background Casitas B-lineage lymphoma proto-oncogene b (CBL-B), an E3 ubiquitin-protein ligase, is a critical regulator of immunity. Genetic ablation or inactivation of CBL-B bypasses the requirement of a co-stimulatory signal for T cell activation in an antigen-dependent manner. CBL-B knockout mice spontaneously reject tumor growth, and the effect is largely dependent on CD8+T cells. Therefore, CBL-B represents a novel target for cancer immunotherapy. Previously, Hotspot has disclosed a series of allosteric CBL-B inhibitors which exhibited potent in vitro and in vivo properties.

Methods Our CBL-B inhibitor (CBL-Bi) was evaluated in a set of syngeneic mouse tumor models. In addition to the measurement of tumor growth, tumor gene expression immune signatures were characterized by Nanostring analysis. Immunohistochemistry and flow-based immunophenotyping were used in profiling the tumor microenvironment.

Results CBL-Bi, as a single agent, demonstrated a spectrum of anti-tumor responses. It not only showed anti-tumor activity in immunologically hot tumor models, such as H22 and CT26, but also in immunologically cold tumor models, such as B16-F10. Responding tumors showed enhancement of antigen presentation, T cell cytotoxicity, and interferon and TNF pathway activation. Furthermore, an in vivo study using the CT26 model demonstrated that the anti-tumor effect was mediated by the immune system, as there was no tumor growth inhibition observed in immune deficient NCG mice. We further investigated the combinational effect of CBL-Bi with anti-PD1 in the CT26 syngeneic mouse tumor model. Additive or synergistic anti-tumor activity was observed. Tumor microenvironment profiling demonstrated significant enhancement of T cell tumor infiltration, and a shift of tumor associated macrophages to a pro-inflammatory status was observed in the combination group.

Conclusions Taken together, the pre-clinical in vivo data presented here demonstrate that inhibition of CBL-B induces immune mediated tumor growth inhibition; the anti-tumor effect is further enhanced when combined with anti-PD1. Thus, CBL-B inhibition has the potential to overcome the low-antigen and high immune suppressive tumor environment.

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