gsk-2334470 and Skin-Neoplasms

Melanoma development involves members of the AGC kinase family, including AKT, PKC, and, most recently, PDK1, as elucidated recently in studies of Braf::Pten mutant melanomas. Here, we report that PDK1 contributes functionally to skin pigmentation and to the development of melanomas harboring a wild-type PTEN genotype, which occurs in about 70% of human melanomas. The PDK1 substrate SGK3 was determined to be an important mediator of PDK1 activities in melanoma cells. Genetic or pharmacologic inhibition of PDK1 and SGK3 attenuated melanoma growth by inducing G1 phase cell-cycle arrest. In a synthetic lethal screen, pan-PI3K inhibition synergized with PDK1 inhibition to suppress melanoma growth, suggesting that focused blockade of PDK1/PI3K signaling might offer a new therapeutic modality for wild-type PTEN tumors. We also noted that responsiveness to PDK1 inhibition associated with decreased expression of pigmentation genes and increased expression of cytokines and inflammatory genes, suggesting a method to stratify patients with melanoma for PDK1-based therapies. Overall, our work highlights the potential significance of PDK1 as a therapeutic target to improve melanoma treatment.

Topics: Animals; Benzoates; Bridged Bicyclo Compounds, Heterocyclic; Cell Line, Tumor; Drug Screening Assays, Antitumor; G1 Phase Cell Cycle Checkpoints; Humans; Immediate-Early Proteins; Indazoles; Lymphatic Metastasis; Melanoma; Mice, Knockout; Molecular Targeted Therapy; Protein Kinase Inhibitors; Protein Serine-Threonine Kinases; Proto-Oncogene Proteins B-raf; Pyrimidines; Pyruvate Dehydrogenase Acetyl-Transferring Kinase; Skin; Skin Neoplasms

Phosphoinositide-dependent kinase-1 (PDK1) is a serine/threonine protein kinase that phosphorylates members of the conserved AGC kinase superfamily, including AKT and protein kinase C (PKC), and is implicated in important cellular processes including survival, metabolism and tumorigenesis. In large cohorts of nevi and melanoma samples, PDK1 expression was significantly higher in primary melanoma, compared with nevi, and was further increased in metastatic melanoma. PDK1 expression suffices for its activity, owing to auto-activation, or elevated phosphorylation by phosphoinositide 3'-OH-kinase (PI3K). Selective inactivation of Pdk1 in the melanocytes of Braf(V600E)::Pten(-/-) or Braf(V600E)::Cdkn2a(-/-)::Pten(-/-) mice delayed the development of pigmented lesions and melanoma induced by systemic or local administration of 4-hydroxytamoxifen. Melanoma invasion and metastasis were significantly reduced or completely prevented by Pdk1 deletion. Administration of the PDK1 inhibitor GSK2334470 (PDKi) effectively delayed melanomagenesis and metastasis in Braf(V600E)::Pten(-/-) mice. Pdk1(-/-) melanomas exhibit a marked decrease in the activity of AKT, P70S6K and PKC. Notably, PDKi was as effective in inhibiting AGC kinases and colony forming efficiency of melanoma with Pten wild-type (WT) genotypes. Gene expression analyses identified Pdk1-dependent changes in FOXO3a-regulated genes, and inhibition of FOXO3a restored proliferation and colony formation of Pdk1(-/-) melanoma cells. Our studies provide direct genetic evidence for the importance of PDK1, in part through FOXO3a-dependent pathway, in melanoma development and progression.

Topics: Animals; Carcinogenesis; Cell Line, Tumor; Forkhead Box Protein O3; Forkhead Transcription Factors; Gene Knockout Techniques; Humans; Indazoles; Lung Neoplasms; Lymphatic Metastasis; Melanoma, Experimental; Mice; Mice, Knockout; Mutation, Missense; Protein Serine-Threonine Kinases; Proto-Oncogene Proteins B-raf; PTEN Phosphohydrolase; Pyrimidines; Pyruvate Dehydrogenase Acetyl-Transferring Kinase; Signal Transduction; Skin Neoplasms; Tissue Array Analysis