Supplementary Figure 5. Intermittent CKI27 allows for immune cell recovery in the spleen, increases frequencies in the TDLN, and inhibits TILs similarly to continuous treatment. (A) Schema of LLC tumor bearing mice treated with vehicle, daily 2mg/kg CKI27, or intermittent 5mg/kg 4on/3off CKI27. Mice were treated in a staggered schedule and all timepoints were harvested on day 23. (B-D) All fold changes were calculated by normalizing to DMSO. (B) Fold changes of absolute number (cells/uL) of spleen immune cell populations. (C) Fold changes of absolute number (cells/uL) of TDLN immune cell populations. (D) Fold changes of tumor weights (mg) and TILs (cells/mg); n=4-5. Data are shown as mean±SEM. Unpaired, nonparametric Mann-Whitney test was used to compare each time point. Significance levels are indicated by asterisks (*p ≤ 0.05; **p ≤ 0.01; ***p ≤ 0.001; ****p ≤ 0.0001)
Funding
Swim Across America (SAA)
Ludwig Institute for Cancer Research (LICR)
Parker Institute for Cancer Immunotherapy (PICI)
ARTICLE ABSTRACT
MEK inhibitors (MEKi) have shown limited success as a treatment for MAPK/ERK pathway–dependent cancers due to various resistance mechanisms tumor cells can employ. CH5126766 (CKI27) is an inhibitor that binds to MEK and prevents release of RAF, reducing the relief of negative feedback commonly observed with other MEKis. We observed that CKI27 increased MHC expression in tumor cells and improved T cell–mediated killing. Yet, CKI27 also decreased T-cell proliferation, activation, and cytolytic activity by inhibiting the MAPK/ERK pathway that is activated downstream of T-cell receptor signaling. Therefore, we aimed to balance the positive and negative immunomodulatory effects of MEKis for optimal combination with immunotherapy. Intermittent administration of CKI27 allowed T cells to partially recover and costimulation via GITR and OX-40 agonist antibodies completely alleviated inhibition of function. In Kras mutant lung and colon tumor mouse models, intermittent CKI27 and anti-GITR significantly decreased tumor growth and prolonged survival when further combined with CTLA-4 immune checkpoint blockade. Moreover, this triple combination increased CD8+ and CD4+ T-cell proliferation, activation, and effector/memory subsets in the tumor-draining lymph nodes and tumors and led to intratumoral regulatory T-cell destabilization. These data, collectively, will allow for more informed decisions when optimizing combination regimens by overcoming resistance, reducing toxicity, and generating long-term immune responses.
