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Targeting Replication Stress Using CHK1 Inhibitor Promotes Innate and NKT Cell Immune Responses and Tumour Regression
Martina Proctor1, Jazmina L Gonzalez Cruz2, Sheena M Daignault-Mill2
1Mater Research Institute, The University of Queensland, Brisbane, QLD 4102, Australia.
Abstract:
Drugs selectively targeting replication stress have demonstrated significant preclinical activity, but this has not yet translated into an effective clinical treatment. Here we report that targeting increased replication stress with a combination of Checkpoint kinase 1 inhibitor (CHK1i) with a subclinical dose of hydroxyurea targets also promotes pro-inflammatory cytokine/chemokine expression that is independent of cGAS-STING pathway activation and immunogenic cell death in human and murine melanoma cells. In vivo, this drug combination induces tumour regression which is dependent on an adaptive immune response. It increases cytotoxic CD8+ T cell activity, but the major adaptive immune response is a pronounced NKT cell tumour infiltration. Treatment also promotes an immunosuppressive tumour microenvironment through CD4+ Treg and FoxP3+ NKT cells. The number of these accumulated during treatment, the increase in FoxP3+ NKT cells numbers correlates with the decrease in activated NKT cells, suggesting they are a consequence of the conversion of effector to suppressive NKT cells. Whereas tumour infiltrating CD8+ T cell PD-1 and tumour PD-L1 expression was increased with treatment, peripheral CD4+ and CD8+ T cells retained strong anti-tumour activity. Despite increased CD8+ T cell PD-1, combination with anti-PD-1 did not improve response, indicating that immunosuppression from Tregs and FoxP3+ NKT cells are major contributors to the immunosuppressive tumour microenvironment. This demonstrates that therapies targeting replication stress can be well tolerated, not adversely affect immune responses, and trigger an effective anti-tumour immune response.
Insights
Combining a Checkpoint kinase 1 inhibitor (CHK1i) with hydroxyurea triggers an anti-tumor immune response in melanoma. This therapy promotes tumor regression by increasing NKT cell infiltration and CD8+ T cell activity, despite some immunosuppressive effects.
Area of Science:
- Oncology
- Immunology
- Cancer Therapy
Background:
- Replication stress-targeting drugs show preclinical promise but lack clinical efficacy.
- Translating preclinical success of replication stress inhibitors into effective cancer treatments remains a challenge.
Purpose of the Study:
- To investigate the immune effects of combining a CHK1 inhibitor with hydroxyurea in melanoma.
- To determine the impact of this combination therapy on tumor microenvironment and adaptive immunity.
Main Methods:
- Treatment of human and murine melanoma cells and tumors with a CHK1 inhibitor and hydroxyurea.
- Analysis of cytokine/chemokine expression, cell death pathways (cGAS-STING), and immune cell infiltration (CD8+ T cells, NKT cells, Tregs).
- Assessment of T cell activity, PD-1/PD-L1 expression, and combination therapy with anti-PD-1.
Main Results:
- The drug combination induced pro-inflammatory cytokine/chemokine expression independent of cGAS-STING or immunogenic cell death.
- In vivo, the combination led to tumor regression dependent on adaptive immunity, characterized by increased NKT cell infiltration and CD8+ T cell activity.
- Treatment promoted an immunosuppressive tumor microenvironment via CD4+ Treg and FoxP3+ NKT cells, with FoxP3+ NKT accumulation correlating with decreased activated NKT cells.
Conclusions:
- Replication stress-targeting therapies can be well-tolerated and trigger effective anti-tumor immune responses.
- Immunosuppression mediated by Tregs and FoxP3+ NKT cells is a key factor limiting response, not peripheral T cell activity.
- Combination with anti-PD-1 did not improve outcomes, highlighting the role of NKT and Treg cells in the immunosuppressive tumor microenvironment.
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