A novel and selective inhibitor of PKC ζ potently inhibits human breast cancer metastasis in vitro and in mice

Cell motility and chemotaxis play pivotal roles in the process of tumor development and metastasis. Protein kinase C ζ (PKC ζ) mediates epidermal growth factor (EGF)-stimulated chemotactic signaling pathway through regulating cytoskeleton rearrangement and cell adhesion. The purpose of this study was to develop anti-PKC ζ therapeutics for breast cancer metastasis. In this study, a novel and high-efficient PKC ζ inhibitor named PKC Z I195.17 was screened out through a substrate-specific strategy. MTT assay was used to determine the cell viability of human breast cancer MDA-MB-231, MDA-MB-435, and MCF-7 cells while under PKC Z I195.17 treatment. Wound-healing, chemotaxis, and Matrigel invasion assays were performed to detect the effects of PKC Z I195.17 on breast cancer cells migration and invasion. Adhesion, actin polymerization, and Western blotting were performed to detect the effects of PKC Z I195.17 on cells adhesion and actin polymerization, and explore the downsteam signaling mechanisms involved in PKC ζ inhibition. MDA-MB-231 xenograft was used to measure the in vivo anti-metastasis efficacy of PKC Z I195.17. The compound PKC Z I195.17 selectively inhibited PKC ζ kinase activity since it failed to inhibit PKC α, PKC β, PKC δ, PKC η, AKT2, as well as FGFR2 activity. PKC Z I195.17 significantly impaired spontaneous migration, chemotaxis, and invasion of human breast cancer MDA-MB-231, MDA-MB-435, and MCF-7 cells, while PKC Z I195.17 did not obviously inhibited cells viability. PKC Z I195.17 also inhibited cells adhesion and actin polymerization through attenuating the phosphorylations of integrin β1, LIMK, and cofilin, which might be the downstream effectors of PKC ζ-mediated chemotaxis in MDA-MB-231 cells. Furthermore, PKC Z I195.17 suppressed the breast cancer metastasis and increased the survival time of breast tumor-bearing mice. In summary, PKC Z I195.17 was a PKC ζ-specific inhibitor which dampened cancer cell migration and metastasis and may serve as a novel therapeutic drug for breast cancer metastasis.