Academic Background and Problem Statement

Triple-negative breast cancer (TNBC) is a highly aggressive subtype of breast cancer, accounting for 15-20% of all breast cancer cases. Due to the lack of expression of estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2), TNBC is insensitive to hormone therapy and HER2-targeted therapies, relying primarily on chemotherapy. However, TNBC has a high recurrence rate and mortality, particularly among younger women, and is often associated with distant metastases to the brain, liver, lungs, and bones. Therefore, there is an urgent need to develop new therapeutic strategies to improve the prognosis of TNBC patients.

The MYC proto-oncogene is overexpressed in more than 60% of TNBC cases, directly promoting tumor cell proliferation and suppressing anti-tumor immune responses. Although MYC is an attractive therapeutic target, direct inhibition of MYC function has been challenging due to the lack of a drug-binding pocket. Consequently, researchers have explored indirect mechanisms to inhibit MYC, such as suppressing MYC-dependent transcription or inducing immunogenic cell death (ICD) to enhance anti-tumor immune responses.

Source and Author Information

This study was conducted by a collaborative team from multiple research institutions, including QIMR Berghofer Medical Research Institute, Peter MacCallum Cancer Centre, and Children’s Cancer Institute. The primary authors include Prahlad V. Raninga, Biju Zeng, Davide Moi, and others. The paper was published in 2024 in the journal Oncogene, titled CBL0137 and NKG2A blockade: a novel immuno-oncology combination therapy for MYC-overexpressing triple-negative breast cancers.

Research Process and Experimental Design

1. Inhibition of MYC-High TNBC Cells by CBL0137

The study first evaluated the inhibitory effect of CBL0137, a non-genotoxic anti-cancer small molecule, on the proliferation of TNBC cells. By analyzing a panel of 10 TNBC cell lines, it was found that CBL0137 significantly inhibited the proliferation of MYC-high cell lines, while having a lesser effect on MYC-low cell lines. Further experiments demonstrated that CBL0137 suppressed cell proliferation by downregulating the transcription of MYC and its downstream target genes, and this inhibition was dependent on MYC but independent of NF-κB and SSRP1.

2. In Vivo Inhibition of TNBC Tumor Growth by CBL0137

The study assessed the in vivo anti-tumor effects of CBL0137 using immunodeficient (NSG mice) and immunocompetent (BALB/c mice) mouse models. The results showed that CBL0137 significantly inhibited the growth of MYC-high MDA-MB-231 TNBC tumors and exhibited stronger anti-tumor effects in the immunocompetent 4T1.2 TNBC model. Further immune profiling indicated that CBL0137 inhibited tumor growth by inducing type I interferon responses and enhancing tumor-specific immune responses.

3. Induction of Immunogenic Cell Death (ICD) by CBL0137

The study also found that CBL0137 induced immunogenic cell death (ICD) in MYC-high TNBC cells both in vitro and in vivo, as evidenced by increased expression of calreticulin and high-mobility group box 1 (HMGB1) on the cell surface. Additionally, CBL0137-treated tumor cells induced a partially protective immune response in mice, further supporting its immunogenicity.

4. Synergistic Effect of CBL0137 and NKG2A Blockade

The study revealed that CBL0137 treatment led to upregulation of NKG2A on tumor-infiltrating effector T cells and NK cells, while the expression of its ligand, QA-1b, was increased in tumor cells. The activation of the NKG2A/QA-1b axis may suppress the activity of effector T cells and NK cells. Therefore, the study further evaluated the combined therapeutic effect of CBL0137 and anti-NKG2A antibody. The results showed that the combination therapy significantly inhibited the growth of 4T1.2 tumors and increased tumor cell apoptosis.

Main Results and Conclusions

1. CBL0137 Inhibits TNBC Cell Proliferation by Downregulating MYC Transcription: CBL0137 significantly inhibited the proliferation of MYC-high TNBC cells, and this inhibition was dependent on MYC but independent of NF-κB and SSRP1.

2. CBL0137 Inhibits Tumor Growth In Vivo Through Direct Cytotoxicity and Immune Modulation: CBL0137 exhibited significant anti-tumor effects in both immunodeficient and immunocompetent mouse models, with stronger effects in immunocompetent mice, indicating that CBL0137 exerts its anti-tumor effects by enhancing anti-tumor immune responses.

3. CBL0137 Induces Immunogenic Cell Death (ICD): CBL0137 enhanced the immunogenicity of tumor cells by inducing ICD, thereby eliciting a partially protective immune response in mice.

4. Synergistic Effect of CBL0137 and NKG2A Blockade: The combination of CBL0137 and anti-NKG2A antibody significantly inhibited tumor growth, suggesting that NKG2A blockade can enhance the anti-tumor effects of CBL0137.

Scientific Value and Application Prospects

This study provides new insights into the treatment of MYC-high TNBC, particularly through the inhibition of MYC transcription and induction of ICD by CBL0137, combined with NKG2A blockade to enhance anti-tumor immune responses. This combination therapy not only demonstrates significant anti-tumor effects but also offers a new strategy for immunotherapy in TNBC patients. CBL0137 has already entered several clinical trials, and future clinical studies may validate the potential of its combination with NKG2A blockade.

Research Highlights

1. Novel Therapeutic Strategy: CBL0137, by inhibiting MYC transcription and inducing ICD, combined with NKG2A blockade, offers a new combination immunotherapy strategy.

2. Comprehensive Experimental Validation: The study comprehensively validated the anti-tumor mechanisms and effects of CBL0137 through in vitro cell experiments, in vivo mouse models, and immune profiling.

3. Potential Clinical Application: The combination therapy of CBL0137 and NKG2A blockade provides a new treatment option for TNBC patients, particularly those with MYC overexpression, and holds significant clinical implications.

Conclusion

This study reveals the anti-tumor effects of CBL0137 in MYC-high TNBC through the inhibition of MYC transcription and induction of ICD, and demonstrates the synergistic therapeutic effects of combining CBL0137 with NKG2A blockade. This discovery provides new insights into immunotherapy for TNBC and holds significant scientific and clinical value.