Background Casitas B-lineage lymphoma b (CBL-B) is an E3 ubiquitin ligase, which is highly expressed in peripheral T cells.1 CBL-B knockout T cells upregulate TCR-mediated T cell activation regardless of CD28,2 and have shown to increase IL-2 and IFN- γ levels.3 4 Loss of CBL-B can prevent CD8+ T cell exhaustion and increase immune cells infiltration in tumors that suppressed tumor growth in mouse models.5–7 The YF550-C1, which is our developed small molecule that targeted CBL-B protein, showed dramatically immunotherapy effects in cancer.
Methods The CBL-B knockout T cells isolated from spleen of CBL-B knockout mice stimulated with anti-CD3 or anti-CD3/28 for 48 hours. Human PBMC or Pan T were stimulated with anti-CD3 or anti-CD3/28 in the presents of 8 titration doses of CBL-B inhibitors, and the culture medium were used for detection of IL-2 or IFN-γ by ELISA. Anti-CD3 was used to stimulate T cell activation in vivo, and YF550-C1 was orally administrated with three doses of YF550-C1 before stimulation. The activation was evaluated by measuring serum concentration of IL-2 and IFN-γ, or the ratio changes of CD69+ T cells. Syngeneic and PD-1 resistant PDX (patient-derived-xenograft) tumor mouse models was used to evaluate tumor growth.
Results CBL-B deficiency suppressed tumor growth in mouse tumor models and enhanced cytokines release in T cells upon TCR engagement. (figure 1). YF550-C1 elevated IL-2 and IFN-γ in TCR stimulated human PBMCs. (figure 2). YF550-C1 alleviated PGE2-mediated immunosuppression of human T cell activation (figure 3). YF550-C1 enhanced cytokines release and T cells activation in in vivo anti-CD3 stimulated mouse model. (figure 4). Single-agent YF550-C1 treatment was sufficient to suppress tumor growth in syngeneic mouse models. (figure 5). Single-agent YF550-C1 treatment was sufficient to suppress PD-1/PD-L1 resistant NSCLC patient-derived tumor growth. (figure 6). Combination of YF550-C1 and anti-PD-L1 treatment showed synergy effect in mouse model. (figure 7)
Conclusions YF550-C1 increases cell activation, inhibits T cell immunosuppression and enhances antitumor activity in multiple preclinical tumor models. YF550-C1 is a promising candidate for cancer treatment as monotherapy or in combination with PD-L1 blockade.
Acknowledgements YF550-C1 was developed by Zhuhai Yufan Biotechnologies Co., Ltd and supported by MingMed Biotechnology Co., Ltd.
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