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Mutations in ERK signaling drive a significant percentage of malignancies. LY3009120, a pan-RAF and dimer inhibitor, has preclinical activity in RAS - and BRAF -mutated cell lines including BRAF -mutant melanoma resistant to BRAF inhibitors. This multicenter, open-label, phase I clinical trial (NCT02014116) consisted of part A (dose escalation) and part B (dose confirmation) in patients with advanced/metastatic cancer. In part A, oral LY3009120 was dose escalated from 50 to 700 mg twice a day on a 28-day cycle. In part B, 300 mg LY3009120 was given twice a day. The primary objective was to identify a recommended phase II dose (RP2D). Secondary objectives were to evaluate safety, pharmacokinetics, and preliminary efficacy. Identification of pharmacodynamic biomarkers was exploratory. In parts A and B, 35 and 16 patients were treated, respectively ( N = 51). In part A, 6 patients experienced eight dose-limiting toxicities. The RP2D was 300 mg twice a day. Common (>10%) any-grade drug-related treatment-emergent adverse events were fatigue ( n = 15), nausea ( n = 12), dermatitis acneiform ( n = 10), decreased appetite ( n = 7), and maculopapular rash ( n = 7). The median duration of treatment was 4 weeks; 84% of patients completed one or two cycles of treatment. Exposures observed at 300 mg twice a day were above the preclinical concentration associated with tumor regression. Eight patients had a best overall response of stable disease; there were no complete or partial clinical responses. Despite adequate plasma exposure levels, predicted pharmacodynamic effects were not observed., (©2019 American Association for Cancer Research.)

Identifying molecular factors of sensitivity and resistance of cancer cells to enzastaurin, a drug inhibiting protein kinase C (PKC) beta, remains a major challenge to improve its clinical development. Investigating the cellular effects of enzastaurin in a panel of 20 human cancer cell lines, we found that most cells displaying oncogenic K-Ras mutations also display resistance to enzastaurin. Wild-type (WT) K-Ras cancer cells displaying high sensitivity to enzastaurin also expressed high mRNA levels of epithelial markers, such as E-cadherin (CDH1), and low mRNA expressions of mesenchymal markers, such as vimentin, N-cadherin (CDH2), and other genes frequently expressed in mesenchymal transition such as ZEB1, TWIST, SLUG, SNAIL, and TGFbeta. WT K-Ras enzastaurin-resistant cells also expressed high levels of mesenchymal markers. Based on this observation, the effects of enzastaurin were investigated in epithelial colon COLO205-S cells that expressed WT Ras/Raf and its derived COLO205-R mesenchymal counterpart selected for resistance to most PKC modulators and displaying oncogenic K-Ras (G13D/exon 2). In COLO205-S cells, inhibition of phosphorylated PKCbeta led to the inactivation of AKT and glycogen synthase kinase 3beta and was associated with apoptosis without significant effect on cell cycle progression. In COLO205-R cells, enzastaurin induced mainly necrosis at high concentrations. In COLO205-R cells, a strong activation of extracellular signal-regulated kinase 1/2 possibly due to oncogenic K-Ras was predominantly associated with transcription of potent antiapoptotic genes, such as BCL2, GADD45B, and CDKN1A, as well as the multidrug resistance gene ABCB1. From this study, colon cancer cells undergoing apoptosis under enzastaurin exposure seem to frequently express a WT Ras and an epithelial phenotype.

PEP005 (ingenol-3-angelate) is a novel anticancer agent extracted from Euphorbia peplus that was previously shown to modulate protein kinase C (PKC), resulting in antiproliferative and proapoptotic effects in several human cancer cell lines. In Colo205 colon cancer cells, exposure to PEP005 induced a time- and concentration-dependent decrease of cells in S phase of cell cycle and apoptosis. In Colo205 cells exposed to PEP005, a variety of signaling pathways were activated as shown by increased phosphorylation of PKCdelta, Raf1, extracellular signal-regulated kinase 1/2 mitogen-activated protein kinase (MAPK), c-Jun NH(2)-terminal kinase, p38 MAPK, and PTEN. PEP005-induced activation of PKCdelta was associated with its translocation from the cytosol to the nucleus and other cellular membranes. Interestingly, PEP005 treatment also resulted in reduced expression of PKCalpha and reduced levels of phosphorylated active form of AKT/protein kinase B. These data suggest that PEP005-induced activation of PKCdelta and reduced expression of PKCalpha resulted in apoptosis by mechanisms mediated by activation of Ras/Raf/MAPK and inhibition of the phosphatidylinositol 3-kinase/AKT signaling pathways. This study supports ongoing efforts targeting PKC isoforms in cancer therapy with PEP005 alone and in combination with other cytotoxic agents.