Selective Targeting of Protein Kinase C (PKC)-theta Nuclear Translocation Reduces Mesenchymal Gene Signatures and Reinvigorates Dysfunctional CD8+ T Cells in Immunotherapy-Resistant and Metastatic Cancers.

Abstract

Protein kinase C (PKC)-theta is a serine/threonine kinase with both cytoplasmic and nuclear functions. Nuclear chromatin-associated PKC-theta (nPKC-theta) is increasingly recognized to be pathogenic in cancer, whereas its cytoplasmic signaling is restricted to normal T-cell function. Here we show that nPKC-theta is enriched in circulating tumor cells (CTCs) in patients with triple-negative breast cancer (TNBC) brain metastases and immunotherapy-resistant metastatic melanoma and is associated with poor survival in immunotherapy-resistant disease. To target nPKC-theta, we designed a novel PKC-theta peptide inhibitor (nPKC-thetai2) that selectively inhibits nPKC-theta nuclear translocation but not PKC-theta signaling in healthy T cells. Targeting nPKC-theta reduced mesenchymal cancer stem cell signatures in immunotherapy-resistant CTCs and TNBC xenografts. PKC-theta was also enriched in the nuclei of CD8+ T cells isolated from stage IV immunotherapy-resistant metastatic cancer patients. We show for the first time that nPKC-theta complexes with ZEB1, a key repressive transcription factor in epithelial-to-mesenchymal transition (EMT), in immunotherapy-resistant dysfunctional PD1+/CD8+ T cells. nPKC-thetai2 inhibited the ZEB1/PKC-theta repressive complex to induce cytokine production in CD8+ T cells isolated from patients with immunotherapy-resistant disease. These data establish for the first time that nPKC-theta mediates immunotherapy resistance via its activity in CTCs and dysfunctional CD8+ T cells. Disrupting nPKC-theta but retaining its cytoplasmic function may offer a means to target metastases in combination with chemotherapy or immunotherapy.Copyright © 2022 by the authors. Licensee MDPI, Basel, Switzerland.