Small molecule inhibition of PD-1 transcription is an effective alternative to antibody blockade in cancer therapy

The impact of PD-1 immune checkpoint therapy prompts exploration of other strategies to downregulate PD-1 for cancer therapy. We previously showed that the serine/threonine kinase, glycogen synthase kinase GSK-3α/β, is a central regulator of PD-1 transcription in CD8+ T cells. Here, we show that the use of small molecule inhibitors of GSK-3α/β (GSK-3i) to reduce pcdc1 (PD-1) transcription and expression was as effective as anti-PD-1 and PDL-1 blocking antibodies in the control of B16 melanoma, or EL4 lymphoma, in primary tumor and metastatic settings. Further, the conditional genetic deletion of GSK-3α/β reduced PD-1 expression on CD8+ T cells, and limited B16 pulmonary metastasis to the same degree as PD-1 gene deficiency. In each model, GSK-3i inhibited PD-1 expression on tumor infiltrating lymphocytes (TILs), while increasing Tbx21 (T-bet) transcription, and the expression of CD107a+ (LAMP1) and granzyme B (GZMB) on CD8+ T-cells. Lastly, the adoptive transfer of T-cells treated ex vivo with a GSK-3 inhibitor delayed the onset of EL4 lymphoma growth to a similar extent as anti-PD-1 pre-treatment. Overall, our findings show how GSK-3 inhibitors that downregulate PD-1 expression can enhance CD8+ T-cell function in cancer therapy to a similar degree as PD-1 blocking antibodies.

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