Comprehensive Testing of Chemotherapy and Immune Checkpoint Blockade in Preclinical Cancer Models Identifies Additive Combinations

Our plain-English summary of Comprehensive Testing of Chemotherapy and Immune Checkpoint Blockade in Preclinical Cancer Models Identifies Additive Combinations, by N. Principe, W.J. Aston, D.E. Hope, et al (Frontiers in Immunology, 2022).

The study

• Authors: N. Principe, W.J. Aston, D.E. Hope, C.M. Tilsed, S.A. Fisher, L. Boon, I.M. Dick, W.L. Chin, A.M. McDonnell, A.K. Nowak, R.A. Lake, J. Chee, W.J. Lesterhuis
• Journal: Frontiers in Immunology
• Published: 2022;13:872295
• Cited by: 18 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Antibodies that target immune checkpoints such as cytotoxic T lymphocyte antigen 4 (CTLA-4) and the programmed cell death protein 1/ligand 1 (PD-1/PD-L1) are now a treatment option for multiple cancer types. However, as a monotherapy, objective responses only occur in a minority of patients. Chemotherapy is widely used in combination with immune checkpoint blockade (ICB). Although a variety of isolated immunostimulatory effects have been reported for several classes of chemotherapeutics, it is unclear which chemotherapeutics provide the most benefit when combined with ICB. We investigated 10 chemotherapies from the main canonical classes dosed at the clinically relevant maximum tolerated dose in combination with anti-CTLA-4/anti-PD-L1 ICB. We screened these chemo-immunotherapy combinations in two murine mesothelioma models from two different genetic backgrounds, and identified chemotherapies that produced additive, neutral or antagonistic effects when combined with ICB. Using flow cytometry and bulk RNAseq, we characterized the tumor immune milieu in additive chemo-immunotherapy combinations. 5-fluorouracil (5-FU) or cisplatin were additive when combined with ICB while vinorelbine and etoposide provided no additional benefit when combined with ICB. The combination of 5-FU with ICB augmented an inflammatory tumor microenvironment with markedly increased CD8+ T cell activation and upregulation of IFNγ, TNFα and IL-1β signaling. The effective anti-tumor immune response of 5-FU chemo-immunotherapy was dependent on CD8+ T cells but was unaffected when TNFα or IL-1β cytokine signaling pathways were blocked. Our study identified additive and non-additive chemotherapy/ICB combinations and suggests a possible role for increased inflammation in the tumor microenvironment as a basis for effective combination therapy.

Copyright © 2022 Principe, Aston, Hope, Tilsed, Fisher, Boon, Dick, Chin, McDonnell, Nowak, Lake, Chee and Lesterhuis.

In plain English

This was a study in mice, not a study of asbestos exposure. The authors, based at Australia's National Centre for Asbestos Related Diseases, grew two mouse mesothelioma tumor lines (AB1 and AE17) under the skin of female mice. They tested 10 chemotherapy drugs, each combined with two immune checkpoint antibodies (anti-CTLA-4 and anti-PD-L1), and compared survival with the best single treatment. In AB1, 5-FU plus the antibodies gave a hazard ratio of 0.101, and tumors disappeared completely in over 80% of treated mice. Cisplatin plus the antibodies was additive in both models, with hazard ratios of 0.610 in AB1 and 0.286 in AE17. Vinorelbine or etoposide combinations were antagonistic in AB1 but had no effect in AE17. Tumors treated with the effective combinations contained more activated T cells. Removing CD8+ T cells weakened both combinations. Blocking the inflammatory signals TNF-alpha or IL-1 beta did not significantly reduce the 5-FU combination's effect (one experiment, five mice per group). The authors noted that tumors under the skin may not mirror the pleural environment, and that 5-FU is not currently used clinically for mesothelioma.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Animal experiment: preclinical drug-combination screen in mouse mesothelioma tumor models, with flow cytometry, bulk RNA sequencing, and cell- and cytokine-blocking experiments
• Who was studied: Female BALB/c and C57BL/6 mice, 8 to 10 weeks old, housed in Perth, Western Australia. Murine mesothelioma cell lines AB1, AB1-HA and AE17 were injected subcutaneously into the right flank. Group sizes in the survival experiments ranged from 5 to 15 mice. Dates of the experiments are not given.
• Exposure: No asbestos or fiber exposure was studied. The exposures were 10 chemotherapy drugs: 5-FU, cisplatin, gemcitabine, irinotecan, doxorubicin, bleomycin, cyclophosphamide, vinorelbine, etoposide and pemetrexed. Each was given at its maximum tolerated dose, except 5-FU, which was given at 75 mg/kg because of severe toxicity. Each drug was combined with anti-CTLA-4 and anti-PD-L1 immune checkpoint blockade given on the same day.
• Main results:
  • In the AB1 model, 5-FU plus checkpoint blockade gave a hazard ratio of 0.101 compared with the best single treatment.
  • In AB1, complete tumor regression occurred in more than 80% of mice given 5-FU plus checkpoint blockade. The figures were 0 to 20% with 5-FU alone and 20 to 30% with checkpoint blockade alone.
  • In the AE17 model, 5-FU plus checkpoint blockade was also additive (hazard ratio 0.308). The survival difference against 5-FU alone had p = 0.199, which is not statistically significant.
  • Cisplatin plus checkpoint blockade was additive in both models: hazard ratio 0.610 in AB1 and 0.286 in AE17.
  • Vinorelbine or etoposide combined with checkpoint blockade was antagonistic in AB1 (hazard ratios 3.65 and 4.08) but had no effect in AE17 (hazard ratios 1.96 and 0.391).
  • Cyclophosphamide plus checkpoint blockade gave no further benefit in AB1 (hazard ratio 0.895) but significantly improved median survival in AE17 (hazard ratio 0.244).
  • Activated, proliferating CD8+ T cells made up 23.3% (plus or minus 8.69%) of tumor immune cells in mice given 5-FU plus checkpoint blockade, compared with 3.62% (plus or minus 1.21%) with 5-FU alone (p = 0.03).
  • In AB1-HA tumor-bearing mice, removing CD8+ T cells significantly reduced the anti-tumor effect of both the 5-FU and the cisplatin combinations.
  • In AB1-HA tumor-bearing mice, survival on 5-FU plus checkpoint blockade did not differ significantly when TNF-alpha was blocked (P = 0.136) or when IL-1 beta was blocked (P greater than 0.999). The authors' discussion states that TNF-alpha neutralization further improved efficacy.
  • The TNF-alpha and IL-1 beta blocking experiments were a single experiment with five mice per group.
• The authors' conclusion: The authors concluded that their study identified additive and non-additive chemotherapy and checkpoint blockade combinations. They suggested that increased inflammation in the tumor environment may play a role in effective combination therapy.
• Limitations the authors state:
  • 5-FU could not be given at its maximum tolerated dose alongside checkpoint blockade, so a lower dose was used, which may have affected the additive result.
  • The tumors were grown under the skin, which may not fully reproduce the tumor environment in the pleural mesothelium.
  • Chemotherapy and checkpoint blockade were given at the same time. The authors noted that dosing and scheduling could affect the immune response to chemotherapy.
  • RNA sequencing of whole tumors could not separate effects on tumor cells from effects on immune cells.
  • 5-FU is not currently used clinically for mesothelioma, so the 5-FU results may apply more to other cancers.

Topics

Medical terms in this study, explained in our Lexicon: Chemotherapy, CTLA-4, PD-1/PD-L1, PD-L1, Immunotherapy, Mesothelioma, Fluorouracil (5-FU), Cisplatin.

Related studies

• Combination immune checkpoint blockade as an effective therapy for mesothelioma — V.S. Fear, C. Tilsed, et al. (2018)
• Synergistic effect of CTLA-4 blockade and cancer chemotherapy in the induction of anti-tumor immunity — W.J. Lesterhuis, J. Salmons, et al. (2013)
• Cyclophosphamide chemotherapy sensitizes tumor cells to TRAIL-dependent CD8 T cell-mediated immune attack resulting in suppression of tumor growth — R.G. van der Most, A.J. Currie, et al. (2009)
• Immune checkpoint inhibitor associated reactivation of primary membranous nephropathy responsive to rituximab — J.S. Lin, D.Y. Wang, et al. (2020)
• Pre-treatment high-sensitivity troponin T for the short-term prediction of cardiac outcomes in patients on immune checkpoint inhibitors — S. Petricciuolo, M.G. Delle Donne, et al. (2021)
• Immune checkpoint inhibitors a new player in the therapeutic game of mesothelioma: New reality with new challenges — K. Parikh, L.E.L. Hendriks, et al. (2021)

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