PEP005, a selective small-molecule activator of protein kinase C, has potent antileukemic activity mediated via the delta isoform of PKC

Pharmacological Significance, Medicinal Use, and Toxicity of Extracted and Isolated Compounds from Euphorbia Species Found in Southern Africa: A Review

This study documents the Euphorbiaceae family of plants in Southern Africa, with a focus on their traditional medicinal applications, pharmacological properties, toxicity, and active secondary metabolites. A review of the literature from scientific journals, books, dissertations, and conference papers spanning from 1962 to 2023 was conducted for 15 Euphorbia species. Recent findings indicate that specific compounds found in Euphorbia plants exhibit significant biological and pharmacological properties. However, the white sticky latex sap they contain is highly toxic, although it may also have medicinal applications. Phytochemical analyses have demonstrated that these plants exhibit beneficial effects, including antibacterial, antioxidant, antiproliferative, anticancer, anti-inflammatory, antiviral, antifungal, and anti-HIV activities. Key phytochemicals such as euphol, cycloartenol, tirucallol, and triterpenoids contribute to their therapeutic efficacy, along with various proteins like lectin and lysozyme. Despite some Euphorbiaceae species undergoing screening for medicinal compounds, many remain insufficiently examined, highlighting a critical gap in the research literature. Given their historical usage, further investigations are essential to evaluate the medicinal significance of Euphorbia species through detailed studies of isolated compounds and their pharmacokinetics and pharmacodynamics. This research will serve as a valuable resource for future inquiries into the benefits of lesser-studied Euphorbia species.

Activating PKC-ε induces HIV expression with improved tolerability

Despite suppressive antiretroviral therapy (ART), HIV-1 persists in latent reservoirs that seed new HIV infections if ART is interrupted, necessitating lifelong therapy for people with HIV. Activation of latent HIV during ART could improve recognition and elimination of infected cells by the immune system. Protein kinase C (PKC) isozymes increase HIV transcription and hence are potential latency reversal agents. However, the clinical utility of PKCs for this application is limited due to toxicity, which is poorly understood. Our studies showed that PKC activation with multiple classes of agonists leads to widespread platelet activation, consistent with disseminated intravascular coagulation, at concentrations that were similar to those required for T-cell activation. Differential expression analysis indicated that PKC-ε and PKC-η isoforms are expressed at high levels in human CD4+ T cells but not in platelets. Using structure-based drug design, we developed a novel PKC agonist, C-233, with increased selectivity for PKC-ε. C-233 increased both supernatant HIV RNA and p24 expression ex vivo after treatment of CD4+ T cells from ART-suppressed people with HIV. C-233 was 5-fold more potent for T-cell activation relative to platelet activation. Our studies support the use of structure-based drug design to create selective novel PKC agonists for the safe activation of HIV reservoirs and improved tolerability.

An Ingenane-Type Diterpene from Euphorbia kansui Promoted Cell Apoptosis and Macrophage Polarization via the Regulation of PKC Signaling Pathways

Euphorbia kansui, a toxic Chinese medicine used for more than 2000 years, has the effect of "purging water to promote drinking" and "reducing swelling and dispersing modules". Diterpenes and triterpenes are the main bioactive components of E. kansui. Among them, ingenane-type diterpenes have multiple biological activities as a protein kinase C δ (PKC-δ) activator, which have previously been shown to promote anti-proliferative and pro-apoptotic effects in several human cancer cell lines. However, the activation of PKC subsequently promoted the survival of macrophages. Recently, we found that 13-hydroxyingenol-3-(2,3-dimethylbutanoate)-13-dodecanoate (compound A) from E. kansui showed dual bioactivity, including the inhibition of tumor-cell-line proliferation and regulation of macrophage polarization. This study identifies the possible mechanism of compound A in regulating the polarization state of macrophages, by regulating PKC-δ-extracellular signal regulated kinases (ERK) signaling pathways to exert anti-tumor immunity effects in vitro, which might provide a new treatment method from the perspective of immune cell regulation.

Preparation of chitosan-hyaluronic acid microcapsules and its dynamic release behavior analysis in a 3D-printed microchannel system: Exploration and verification

This research focuses on the challenges of efficiently constructing drug carriers and evaluating their dynamic release in vitro simulation. By using pickering emulsion and layer-by-layer self-assembly methods. The microcapsules had tea tree oil as the core material, SiO2 nanoparticles as stabilizers, and chitosan and hyaluronic acid as shell materials. The microencapsulation mechanism, as well as the effects of core-shell mass ratio and stirring, were discussed. Specifically, a dynamic circulation simulation microchannel system was designed and manufactured based on 3D printing technology. In this simulation system, the release rate of microcapsules is accelerated and the trend changes, with its behavior aligning with the Boltzmann model. The study demonstrates the advantages of self-assembled inorganic-organic drug-loaded microcapsules in terms of controllable fabrication and ease of functional modification, and shows the potential of 3D printed cyclic microchannel systems in terms of operability and simulation fidelity in drug and physiological analysis.

Ingenol mebutate inhibits the growth of pancreatic cancer cells in vitro via STING with an efficacy comparable to that of clinically used anticancer agents

Pancreatic cancer is associated with a poor prognosis; thus, there is an urgent need to develop new and effective treatments. Ingenol mebutate (IM), which is isolated from the latex of Euphorbia peplus, was recently shown to be effective against pancreatic cancer cell lines; however, its mechanism of action has not been fully elucidated. In this study, we focused on the less drug-sensitive pancreatic cancer cell line Panc-1 and compared IM to commercially available anticancer drugs using cell survival assays. In addition, we aimed to identify novel biomolecules that may be involved in the mechanism of action of IM using RNA sequencing, western blotting, and inhibition assays. The IC50 values after 72 h of exposure to IM and SN-38, drugs to which the Panc-1 cells are most sensitive among the tested anticancer agents, were 43.1 ± 16.8 nM and 165 ± 37 nM, respectively. IM showed a cytostatic effect equal to or greater than that of the clinically used pancreatic cancer therapeutic drugs. RNA sequencing and protein expression analysis revealed that expression of stimulator of interferon genes (STING) increased at low IM concentration, whereas cell viability decreased. Co-exposure of IM and STING inhibitor, H-151, to Panc-1 or MIA PaCa-2 cell lines canceled the growth-inhibitory effects of IM alone. In conclusion, IM may have an efficacy comparable to that of existing pancreatic cancer therapeutic agents on the less drug-sensitive Panc-1 cell line and the immune-related molecule STING plays a role in the mechanism of action of IM.

Discovery of lead natural products for developing pan-SARS-CoV-2 therapeutics

The COVID-19 pandemic, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), remains a global public health crisis. The reduced efficacy of therapeutic monoclonal antibodies against emerging SARS-CoV-2 variants of concern (VOCs), such as omicron BA.5 subvariants, has underlined the need to explore a novel spectrum of antivirals that are effective against existing and evolving SARS-CoV-2 VOCs. To address the need for novel therapeutic options, we applied cell-based high-content screening to a library of natural products (NPs) obtained from plants, fungi, bacteria, and marine sponges, which represent a considerable diversity of chemical scaffolds. The antiviral effect of 373 NPs was evaluated using the mNeonGreen (mNG) reporter SARS-CoV-2 virus in a lung epithelial cell line (Calu-3). The screening identified 26 NPs with half-maximal effective concentrations (EC50) below 50 μM against mNG-SARS-CoV-2; 16 of these had EC50 values below 10 μM and three NPs (holyrine A, alotaketal C, and bafilomycin D) had EC50 values in the nanomolar range. We demonstrated the pan-SARS-CoV-2 activity of these three lead antivirals against SARS-CoV-2 highly transmissible Omicron subvariants (BA.5, BA.2 and BA.1) and highly pathogenic Delta VOCs in human Calu-3 lung cells. Notably, holyrine A, alotaketal C, and bafilomycin D, are potent nanomolar inhibitors of SARS-CoV-2 Omicron subvariants BA.5 and BA.2. The pan-SARS-CoV-2 activity of alotaketal C [protein kinase C (PKC) activator] and bafilomycin D (V-ATPase inhibitor) suggest that these two NPs are acting as host-directed antivirals (HDAs). Future research should explore whether PKC regulation impacts human susceptibility to and the severity of SARS-CoV-2 infection, and it should confirm the important role of human V-ATPase in the VOC lifecycle. Interestingly, we observed a synergistic action of bafilomycin D and N-0385 (a highly potent inhibitor of human TMPRSS2 protease) against Omicron subvariant BA.2 in human Calu-3 lung cells, which suggests that these two highly potent HDAs are targeting two different mechanisms of SARS-CoV-2 entry. Overall, our study provides insight into the potential of NPs with highly diverse chemical structures as valuable inspirational starting points for developing pan-SARS-CoV-2 therapeutics and for unravelling potential host factors and pathways regulating SARS-CoV-2 VOC infection including emerging omicron BA.5 subvariants.

Immunothrombotic Mechanisms Induced by Ingenol Mebutate Lead to Rapid Necrosis and Clearance of Anogenital Warts

Ingenol mebutate (IM) is highly effective in the treatment of human papillomavirus (HPV)-induced anogenital warts (AGW) leading to fast ablation within hours. However, the exact mode of action is still largely unknown. We performed dermoscopy, in vivo confocal microscopy (CLM), histology, immunohistochemistry, and immunofluorescence to gain insights in mechanisms of IM treatment in AGW. In addition, we used in vitro assays (ELISA, HPV-transfection models) to further investigate in vivo findings. IM treatment leads to a strong recruitment of neutrophils with thrombosis of small skin vessels within 8 h, in a sense of immunothrombosis. In vivo and in vitro analyses showed that IM supports a prothrombotic environment by endothelial cell activation and von Willebrand factor (VWF) secretion, in addition to induction of neutrophil extracellular traps (NETosis). IM superinduces CXCL8/IL-8 expression in HPV-E6/E7 transfected HaCaT cells when compared to non-infected keratinocytes. Rapid ablation of warts after IM treatment can be well explained by the observed immunothrombosis. This new mechanism has so far only been observed in HPV-induced lesions and is completely different from the mechanisms we see in the treatment of transformed keratinocytes in actinic keratosis. Our initial findings indicate an HPV-specific effect, which could be also of interest for the treatment of other HPV-induced lesions. Larger studies are now needed to further investigate the potential of IM in different HPV tumors.

High-content phenotyping of Parkinson's disease patient stem cell-derived midbrain dopaminergic neurons using machine learning classification

Combining multiple Parkinson's disease (PD) relevant cellular phenotypes might increase the accuracy of midbrain dopaminergic neuron (mDAN) in vitro models. We differentiated patient-derived induced pluripotent stem cells (iPSCs) with a LRRK2 G2019S mutation, isogenic control, and genetically unrelated iPSCs into mDANs. Using automated fluorescence microscopy in 384-well-plate format, we identified elevated levels of α-synuclein (αSyn) and serine 129 phosphorylation, reduced dendritic complexity, and mitochondrial dysfunction. Next, we measured additional image-based phenotypes and used machine learning (ML) to accurately classify mDANs according to their genotype. Additionally, we show that chemical compound treatments, targeting LRRK2 kinase activity or αSyn levels, are detectable when using ML classification based on multiple image-based phenotypes. We validated our approach using a second isogenic patient-derived SNCA gene triplication mDAN model which overexpresses αSyn. This phenotyping and classification strategy improves the practical exploitability of mDANs for disease modeling and the identification of novel LRRK2-associated drug targets.

PKC agonism restricts innate immune suppression, promotes antigen cross-presentation and synergizes with agonistic CD40 antibody therapy to activate CD8+ T cells in breast cancer

Myeloid-derived suppressor cells (MDSCs) are an immature innate cell population that expands in pathological conditions such as cancer and suppresses T cells via production of immunosuppressive factors. Conversely, efficient cytotoxic T cell priming is dependent on the ability of antigen-presenting cells (APCs) to cross-present tumor antigens to CD8⁺ T cells, a process that requires a specific subtype of dendritic cells (DCs) called conventional DC1 (cDC1) which are often dysfunctional in cancer. One way to activate cDC1 is ligation of CD40 which is abundantly expressed by myeloid cells and its agonism leads to myeloid cell activation. Thus, targeting MDSCs while simultaneously expanding cross-presenting DCs represents a promising strategy that, when combined with agonistic CD40, may result in long-lasting protective immunity. In this study, we investigated the effect of PKC agonists PEP005 and prostratin on MDSC expansion, differentiation, and recruitment to the tumor microenvironment. Our findings demonstrate that PKC agonists decreased MDSC expansion from hematopoietic progenitors and induced M-MDSC differentiation to an APC-like phenotype that expresses cDC1-related markers via activation of the p38 mitogen-activated protein kinase (MAPK) pathway. Simultaneously, PKC agonists favored cDC1 expansion at the expense of cDC2 and plasmacytoid DCs (pDC). Functionally, PKC agonists blunted MDSC suppressive activity and enhanced MDSC cross-priming capacity both in vitro and in vivo. Finally, combination of PKC agonism with agonistic CD40 mAb resulted in a marked reduction in tumor growth with a significant increase in intratumoral activated CD8⁺ T cells and tissue-resident memory CD8⁺ T cells in a syngeneic breast cancer mouse model. In sum, this work proposes a novel promising strategy to simultaneously target MDSCs and promote APC function that may have highly impactful clinical relevance in cancer patients.

Natural Plant Compounds: Does Caffeine, Dipotassium Glycyrrhizinate, Curcumin, and Euphol Play Roles as Antitumoral Compounds in Glioblastoma Cell Lines?

Many plant-derived compounds are shown to be promising antitumor therapeutic agents by enhancing apoptosis-related pathways and cell cycle impairment in tumor cells, including glioblastoma (GBM) cell lines. We aimed to review four natural plant compounds effective in GBM cell lines as caffeine, dipotassium glycyrrhizinate (DPG), curcumin, and euphol. Furthermore, antitumoral effect of these plant compounds on GBM cell lines through microRNAs (miRs) modulation was investigated. However, only DPG and curcumin were found as effective on miR modulation. Caffeine arrests GBM cell cycle in G0/G1 phase by cyclin-dependent kinases (CDK) complex inhibition and by decreasing BCL-2 and increasing FOXO1 expression levels causing greater apoptotic activity. Caffeine can also directly inhibit IP3R3, p38 phosphorylation, and rho-associated protein kinase (ROCK), decreasing cell invasion and migration capacity or indirectly by inhibiting the tissue inhibitor metalloproteinase-1 (TIMP-1) and integrins β1 and β3, leading to lower matrix metalloproteinases, MMP-2 and MMP-9. DPG presents antitumoral effect in GBM cells related to nuclear factor kappa B (NF-κB) pathway suppression by IRAK2 and TRAF6-mediating miR-16 and miR-146a, respectively. More recently, it was observed that DPG upregulated miR-4443 and miR-3620, responsible for post-transcriptional inhibition of the NF-κB pathway by CD209 and TNC modulation, respectively leading to lower MMP-9 and migration capacity. Curcumin is able to increase miR-223-3p, miR-133a-3p, miR-181a-5p, miR-34a-5p, miR-30c-5p, and miR-1290 expression leading to serine or threonine kinase (AKT) pathway impairment and also it decreases miR-27a-5p, miR-221-3p, miR-21-5p, miR-125b-5p, and miR-151-3p expression causing p53-BCL2 pathway inhibition and consequently, cellular apoptosis. Interestingly, lower expression of miR-27a by curcumin action enhanced the C/EBP homologous protein(CHOP) expression, leading to paraptosis. Curcumin can inhibit miR-21 expression and consequently activate apoptosis through caspase 3 and death receptor (DR) 4 and 5 activation. Autophagy is controlled by the LC-3 protein that interacts with Atg family for the LC3-II formation and autophagy activation. Euphol can enhance LC3-II levels directly in GBM cells or inhibits tumor invasion and migration through PDK1 modulation.

Discovery of a novel megakaryopoiesis enhancer, ingenol, promoting thrombopoiesis through PI3K-Akt signaling independent of thrombopoietin

Thrombocytopenia, a most common complication of radiotherapy and chemotherapy, is an important cause of morbidity and mortality in cancer patients. However, there are still no approved agents for the treatment of radiation- and chemotherapy-induced thrombocytopenia (RIT and CIT, respectively). In this study, a drug screening model for predicting compounds with activity in promoting megakaryocyte (MK) differentiation and platelet production was established based on machine learning (ML), and a natural product ingenol was predicted as a potential active compound. Then, in vitro experiments showed that ingenol significantly promoted MK differentiation in K562 and HEL cells. Furthermore, a RIT mice model and c-MPL knock-out (c-MPL^-/-) mice constructed by CRISPR/Cas9 technology were used to assess the therapeutic action of ingenol on thrombocytopenia. The results showed that ingenol accelerated megakaryopoiesis and thrombopoiesis both in RIT mice and c-MPL^-/- mice. Next, RNA-sequencing (RNA-seq) was carried out to analyze the gene expression profile induced by ingenol during MK differentiation. Finally, through experimental verifications, we demonstrated that the activation of PI3K/Akt signaling pathway was involved in ingenol-induced MK differentiation. Blocking PI3K/Akt signaling pathway abolished the promotion of ingenol on MK differentiation. Nevertheless, inhibition of TPO/c-MPL signaling pathway could not suppress ingenol-induced MK differentiation. In conclusion, our study builds a drug screening model to discover active compounds against thrombocytopenia, reveals the critical roles of ingenol in promoting MK differentiation and platelet production, and provides a promising avenue for the treatment of RIT.

Total synthesis and biological evaluation of oscillatoxins D, E, and F

Oscillatoxins (OTXs) and aplysiatoxins are biosynthetically related polyketides produced by marine cyanobacteria. We previously developed a synthetic route to phenolic O-methyl analogs of OTX-D and 30-methyl-OTX-D during collective synthesis of these natural products. According to our synthetic strategy, we achieved total synthesis of OTX-D, 30-methyl-OTX-D, OTX-E, and OTX-F by deprotecting the O-methyl group in an earlier intermediate, and determined their biological activities. Although OTX-D and 30-methyl-OTX-D have been reported to show antileukemic activity against L1210 cell line, we found that their cytotoxicity in vitro against this cell line is relatively weak (IC50: 29-52 µm). In contrast, OTX-F demonstrated cell line-selective antiproliferative activity against DMS-114 lung cancer cells, which implies that OTXs target as yet unknown target molecules as part of this unique activity.

Putative role of natural products as Protein Kinase C modulator in different disease conditions

INTRODUCTION

Protein kinase C (PKC) is a promising drug target for various therapeutic areas. Natural products derived from plants, animals, microorganisms, and marine organisms have been used by humans as medicine from prehistoric times. Recently, several compounds derived from plants have been found to modulate PKC activities through competitive binding with ATP binding site, and other allosteric regions of PKC. As a result fresh race has been started in academia and pharmaceutical companies to develop an effective naturally derived small-molecule inhibitor to target PKC activities. Herein, in this review, we have discussed several natural products and their derivatives, which are reported to have an impact on PKC signaling cascade.

METHODS

All information presented in this review article regarding the regulation of PKC by natural products has been acquired by a systematic search of various electronic databases, including ScienceDirect, Scopus, Google Scholar, Web of science, ResearchGate, and PubMed. The keywords PKC, natural products, curcumin, rottlerin, quercetin, ellagic acid, epigallocatechin-3 gallate, ingenol 3 angelate, resveratrol, protocatechuic acid, tannic acid, PKC modulators from marine organism, bryostatin, staurosporine, midostaurin, sangivamycin, and other relevant key words were explored.

RESULTS

The natural products and their derivatives including curcumin, rottlerin, quercetin, ellagic acid, epigallocatechin-3 gallate, ingenol 3 angelate, resveratrol, bryostatin, staurosporine, and midostaurin play a major role in the management of PKC activity during various disease progression.

CONCLUSION

Based on the comprehensive literature survey, it could be concluded that various natural products can regulate PKC activity during disease progression. However, extensive research is needed to circumvent the challenge of isoform specific regulation of PKC by natural products.

Rebound increases in chemokines by CXCR2 antagonist in breast cancer can be prevented by PKCδ and PKCε activators

Activation of CXCR2 by chemokines such as CXCL1 and CXCL2 increases aggressiveness of breast cancer, inducing chemoresistance, hence CXCR2 antagonists are in clinical trials. We previously reported that inhibition of CXCR2 increases MIP-2 (CXCL2), which may inhibit anti-tumoral effects of CXCR2 antagonists. This seems to be due to inhibition of protein kinase C (PKC) by CXCR2 antagonist since specific inhibitor of PKC also enhances MIP-2 secretion. We here examined whether CXCR2 inhibitor also increases KC (CXCL1) secretion, ligand for CXCR2 involved in metastasis and PKC activators can prevent increases in chemokine secretion. We used SB 225002, which is a specific CXCR2 antagonist. The effects of PKC activators that have documented anti-tumoral effects and activates multiple isozymes of PKC such as Ingenol-3-angelate (I3A) and bryostatin-1 were examined here. In addition, FR236924, PKCε selective and 7α-acetoxy-6β-benzoyloxy-12-O-benzoylroyleanone (Roy-Bz), PKCδ selective activators were also tested. The effects of activators were determined using brain metastatic (4TBM) and heart metastatic (4THM) subset of 4T1 breast carcinoma cells because these aggressive carcinoma cells with cancer stem cell features secrete high levels of KC and MIP-2. Inhibition of CXCR-2 activity increased KC (CXCL1) secretion. PKC activators prevented SB225002-induced increases in KC and MIP-2 secretion. Different activators/modulators induce differential changes in basal and SB225002-induced chemokine secretion as well as cell proliferation and the activators that act on PKCδ and/or PKCε such as bryostatin 1, FR236924 and Roy-Bz are the most effective. These activators alone also decrease cell proliferation or chemokine secretion or both. Given the role of KC and MIP-2 in drug resistance including chemotherapeutics, activators of PKCε and PKCδ may prevent emerging of resistance to CXCR2 inhibitors as well as other chemotherapeutics.

Targeting Cutaneous T-Cell Lymphoma Cells by Ingenol Mebutate (PEP005) Correlates with PKCδ Activation, ROS Induction as Well as Downregulation of XIAP and c-FLIP

New therapeutic strategies are needed for cutaneous T-cell lymphoma (CTCL), and the plant extract ingenol mebutate (PEP005) may be considered. PEP005 has been approved for actinic keratosis, and proapoptotic activities were described in different cancer cells. Here, we aimed to investigate its efficacy in four CTCL cell lines and its mode of action. While HuT-78 and HH responded with induced apoptosis as well as with loss of cell viability and cell proliferation, MyLa and SeAx remained resistant. Interestingly, both sensitive and resistant cells showed caspase-8 activation and enhanced levels of reactive oxygen species (ROS), while final caspase-3 activation was restricted to sensitive cells. Apoptosis induction was prevented by the caspase inhibitor QVD-Oph as well as by the antioxidant vitamin E. Caspase activation by PEP005 may be explained to some extent by the downregulation of the caspase antagonistic proteins c-FLIP and XIAP in sensitive cells, whereas both proteins were strongly expressed in resistant cells. Finally, PEP005 resulted in the activation of proapoptotic PKCδ, and the PKC inhibitor bisindolylmaleimide I reduced apoptosis, caspase-3 processing and ROS production, as well as restored cell viability. In conclusion, PKCδ appeared as a central player in apoptosis regulation in CTCL cells, also suggesting its therapeutic targeting.

A Therapeutic Strategy to Combat HIV-1 Latently Infected Cells With a Combination of Latency-Reversing Agents Containing DAG-Lactone PKC Activators

Advances in antiviral therapy have dramatically improved the therapeutic effects on HIV type 1 (HIV-1) infection. However, even with potent combined antiretroviral therapy, HIV-1 latently infected cells cannot be fully eradicated. Latency-reversing agents (LRAs) are considered a potential tool for eliminating such cells; however, recent in vitro and in vivo studies have raised serious concerns regarding the efficacy and safety of the "shock and kill" strategy using LRAs. In the present study, we examined the activity and safety of a panel of protein kinase C (PKC) activators with a diacylglycerol (DAG)-lactone structure that mimics DAG, an endogenous ligand for PKC isozymes. YSE028, a DAG-lactone derivative, reversed HIV-1 latency in vitro when tested using HIV-1 latently infected cells (e.g., ACH2 and J-Lat cells) and primary cells from HIV-1-infected individuals. The activity of YSE028 in reversing HIV-1 latency was synergistically enhanced when combined with JQ1, a bromodomain and extra-terminal inhibitor LRA. DAG-lactone PKC activators also induced caspase-mediated apoptosis, specifically in HIV-1 latently infected cells. In addition, these DAG-lactone PKC activators showed minimal toxicity in vitro and in vivo. These data suggest that DAG-lactone PKC activators may serve as potential candidates for combination therapy against HIV-1 latently infected cells, especially when combined with other LRAs with a different mechanism, to minimize side effects and achieve maximum efficacy in various reservoir cells of the whole body.

Functional proteomic analysis reveals roles for PKCδ in regulation of cell survival and cell death: Implications for cancer pathogenesis and therapy

Protein Kinase C-δ (PKCδ), regulates a broad group of biological functions and disease processes, including well-defined roles in immune function, cell survival and apoptosis. PKCδ primarily regulates apoptosis in normal tissues and non-transformed cells, and genetic disruption of the PRKCD gene in mice is protective in many diseases and tissue damage models. However pro-survival/pro-proliferative functions have also been described in some transformed cells and in mouse models of cancer. Recent evidence suggests that the contribution of PKCδ to specific cancers may depend in part on the oncogenic context of the tumor, consistent with its paradoxical role in cell survival and cell death. Here we will discuss what is currently known about biological functions of PKCδ and potential paradigms for PKCδ function in cancer. To further understand mechanisms of regulation by PKCδ, and to gain insight into the plasticity of PKCδ signaling, we have used functional proteomics to identify pathways that are dependent on PKCδ. Understanding how these distinct functions of PKCδ are regulated will be critical for the logical design of therapeutics to target this pathway.

Potentials of PKC in Cancer Progression and Anticancer Drug Development

PKC is a family of serine-threonine kinases which play crucial roles in the regulation of important signal transduction pathways in mammalian cell-biology. These enzymes are themselves regulated by various molecules that can serve as ligands to the regulatory domains and translocate PKC to membrane for activity. The role of PKC in the modulation of both proliferative and apoptotic signaling in cancer has become a subject of immense interest after it was discovered that PKC regulates a myriad of enzymes and transcription factors involved in carcinogenic signaling. Therefore, PKC has served as an attractive target for the development of newer generation of anti-cancer drugs. The following review discusses the potential of PKC to be regarded as a target for anti-cancer therapy. We also review all the molecules that have been discovered so far to be regulators/activators/inhibitors of PKC and also how far these molecules can be considered as potential candidates for anti-cancer drug development based on PKC.

Semi-Synthetic Ingenol Derivative from Euphorbia tirucalli Inhibits Protein Kinase C Isotypes and Promotes Autophagy and S-phase Arrest on Glioma Cell Lines

The identification of signaling pathways that are involved in gliomagenesis is crucial for targeted therapy design. In this study we assessed the biological and therapeutic effect of ingenol-3-dodecanoate (IngC) on glioma. IngC exhibited dose-time-dependent cytotoxic effects on large panel of glioma cell lines (adult, pediatric cancer cells, and primary cultures), as well as, effectively reduced colonies formation. Nevertheless, it was not been able to attenuate cell migration, invasion, and promote apoptotic effects when administered alone. IngC exposure promoted S-phase arrest associated with p21CIP/WAF1 overexpression and regulated a broad range of signaling effectors related to survival and cell cycle regulation. Moreover, IngC led glioma cells to autophagy by LC3B-II accumulation and exhibited increased cytotoxic sensitivity when combined to a specific autophagic inhibitor, bafilomycin A1. In comparison with temozolomide, IngC showed a mean increase of 106-fold in efficacy, with no synergistic effect when they were both combined. When compared with a known compound of the same class, namely ingenol-3-angelate (I3A, Picato^®), IngC showed a mean 9.46-fold higher efficacy. Furthermore, IngC acted as a potent inhibitor of protein kinase C (PKC) activity, an emerging therapeutic target in glioma cells, showing differential actions against various PKC isotypes. These findings identify IngC as a promising lead compound for the development of new cancer therapy and they may guide the search for additional PKC inhibitors.

Medically Useful Plant Terpenoids: Biosynthesis, Occurrence, and Mechanism of Action

Specialized plant terpenoids have found fortuitous uses in medicine due to their evolutionary and biochemical selection for biological activity in animals. However, these highly functionalized natural products are produced through complex biosynthetic pathways for which we have a complete understanding in only a few cases. Here we review some of the most effective and promising plant terpenoids that are currently used in medicine and medical research and provide updates on their biosynthesis, natural occurrence, and mechanism of action in the body. This includes pharmacologically useful plastidic terpenoids such as p-menthane monoterpenoids, cannabinoids, paclitaxel (taxol®), and ingenol mebutate which are derived from the 2-C-methyl-d-erythritol-4-phosphate (MEP) pathway, as well as cytosolic terpenoids such as thapsigargin and artemisinin produced through the mevalonate (MVA) pathway. We further provide a review of the MEP and MVA precursor pathways which supply the carbon skeletons for the downstream transformations yielding these medically significant natural products.

Tumor suppressive role for kinases phosphorylating p53 in DNA damage-induced apoptosis

Tumor suppressor p53 plays an important role in cancer prevention. Under normal conditions, p53 is maintained at a low level. However, in response to various cellular stresses, p53 is stabilized and activated, which, in turn, initiates DNA repair, cell-cycle arrest, senescence and apoptosis. Post-translational modifications of p53 including phosphorylation, ubiquitination, and acetylation at multiple sites are important to regulate its activation and subsequent transcriptional gene expression. Particularly, phosphorylation of p53 plays a critical role in modulating its activation to induce apoptosis in cancer cells. In this context, previous studies show that several serine/threonine kinases regulate p53 phosphorylation and downstream gene expression. The molecular basis by which p53 and its kinases induce apoptosis for cancer prevention has been extensively studied. However, the relationship between p53 phosphorylation and its kinases and how the activity of kinases is controlled are still largely unclear; hence, they need to be investigated. In this review, we discuss various roles for p53 phosphorylation and its responsible kinases to induce apoptosis and a new therapeutic approach in a broad range of cancers.

Ingenol mebutate induces a tumor cell-directed inflammatory response and antimicrobial peptides thereby promoting rapid tumor destruction and wound healing

BACKGROUND

Ingenol mebutat (IM)-gel is effective for the topical treatment of epithelial tumors, including actinic keratoses (AKs) or anogenital warts (AGW). AK patients treated with IM develop intensified inflammatory reactions on sights of prior clinical visible or palpable AKs as compared to the surrounding actinically damaged skin, suggesting the induction of a tumor cell-directed inflammation. AGW patients treated with IM develop even stronger inflammatory reactions with large erosions, suggesting a directed inflammatory response against HPV-infected keratinocytes. Of note, even widespread erosions heal very fast without any superinfections. Here, we set out to elucidate underlying molecular and cellular mechanisms of these clinical observations.

METHODS

The effects of IM (10-9-10-5 M) on the expression and translation of a comprehensive set of chemokines (CXCL1, CXCL8, CXCL9, CXCL10, CXCL11, CXCL14, CCL2, CCL5, CCL20, CCL27) and antimicrobial peptides (AMP) (HBD1, HBD2, HBD3, LL37, RNase7) were analyzed in primary human epithelial keratinocytes (HEK) and a set of epithelial cancer cell lines by RT-qPCR and ELISA in vitro. To study the possible effects of different concentrations of IM on migratory, respectively wound healing responses, an in vitro scratch assay was conducted on HEK.

RESULTS

Ingenol mebutat significantly and dose-dependently induced the expression of proinflammatory chemokines (CXCL8, CCL2) and AMP (RNase7, HBD3) in HEK and epithelial cancer cell lines. A significantly stronger induction of CXCL8 and CCL2 was observed in our tested tumor cells as compared to HEK. We did not observe any significant effect of IM on HEK migration, respectively wound healing responses in vitro for any tested concentration (10-9, 10-8, 10-6 M) except 10-7 M, which induced a significant inhibition.

CONCLUSIONS

Our data suggest that tumor cells are more susceptible to IM as compared to differentiated HEK. This is evident by a stronger IM-mediated induction of proinflammatory chemokines in tumor cells, which may result in a tumor cell-directed inflammatory response and rapid tumor destruction. In addition, IM induces AMP in keratinocytes and seems not to severely interfere with keratinocyte migration, which contributes to a fast and uncomplicated wound healing. Surprising is a selective inhibition of keratinocyte migration by IM at the concentration of 10-7 M pointing to very dose depending biological effects, induced by IM.

Dangerous plants in dermatology: Legal and controlled

The plant and mushroom kingdoms have species used for intoxication, inebriation, or recreation. Some of these species are toxic. Given that many of these plants or substances are illegal and have histories of abuse, much of the research regarding therapeutic application is based on basic science, animal studies, and traditional use. This review examines Cannabis, Euphorbia, Ricinus, Podophyllum, Veratrum, mushrooms, and nightshades, along with resveratrol and cocaine as they relate to dermatology.

Ingenol-3-Angelate Suppresses Growth of Melanoma Cells and Skin Tumor Development by Downregulation of NF-κB-Cox2 Signaling

BACKGROUND A recent focus in skin cancer prevention intervenes though modulating molecular links between inflammation and cell growth signaling, such as NF-κB. This study elucidates the effect of a non-tumor promoting phorbol ester, ingenol-3-angelate (I3A), on the growth of human melanoma cells and on the 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced skin inflammation and 7,12-Dimethylbenz(a)anthracene (DMBA)-induced skin carcinoma in mice. MATERIAL AND METHODS Cell viability was assessed by MTT assay, cell proliferation by clonogenic assay, apoptosis and cell cycle arrest was analyzed by flow cytometry, protein expression was studied by IHC and Western blotting, and gene expression by qPCR. RESULTS I3A suppressed the survival and proliferation of human melanoma cells with estimated IC50 values around 38 and 46 μM for A2058 and HT144 cell, respectively. I3A activated the protein levels of PKCδ and PKCε, which induced apoptosis by activating caspase-9 and caspace-3 followed by lowering of mitochondrial membrane potential and enhancing DNA fragmentation. I3A induced G1 phase cell cycle arrest as well as G2/M phase arrest in both cell lines. I3A inhibited the levels of NFκB p65 protein as well as phosphorylation of p65 and its nuclear translocation. I3A suppressed the gene expression of NF-κB, COX-2 and iNOS. I3A inhibited TPA-induced inflammation and epidermal hyperplasia in female ICR mice by downregulating NF-κB and iNOS. I3A suppressed the growth of skin tumor in DMBA-induced mice in dose-dependent manner. CONCLUSIONS The mechanism of I3A induces apoptosis in human melanoma cells and suppresses skin inflammation and carcinoma via downregulation of NF-κB-iNOS-COX-2 signaling.

A Computational Investigation of the Uncatalysed and Water-Catalysed Acyl Rearrangements in Ingenol Esters

Ingenol esters have been identified as potent anticancer and HIV latency reversing agents. Ingenol-3-angelate was recently approved as a topical treatment for precancerous actinic keratosis skin lesions. It was found, however, that ingenol esters can undergo a series of acyl rearrangements, which may affect their biological potency and the shelf-life of drug formulations. We use double-hybrid density functional theory to explore the mechanisms for the uncatalysed and water-catalysed acyl migrations in a model ingenol ester. The uncatalysed reaction may proceed either via a concerted mechanism or via a stepwise mechanism that involves a chiral orthoester intermediate. We find that the stepwise pathway is kinetically preferred by a significant amount of ΔΔH‡298 = 44.5 kJ mol−1. The uncatalysed 3-O-acyl to 5-O-acyl and 5-O-acyl to 20-O-acyl stepwise rearrangements involve cyclisation and ring-opening steps, both concomitant with a proton transfer. We find that the ring-opening step is the rate-determining step for both rearrangements, with reaction barrier heights of ΔH‡298 = 251.6 and 177.1 kJ mol−1 respectively. The proton transfers in the cyclisation and ring-opening steps may be catalysed by a water molecule. The water catalyst reduces the reaction barrier heights of these steps by over 90 kJ mol−1.

Chemical Proteomics Identifies SLC25A20 as a Functional Target of the Ingenol Class of Actinic Keratosis Drugs

The diterpenoid ester ingenol mebutate (IngMeb) is the active ingredient in the topical drug Picato, a first-in-class treatment for the precancerous skin condition actinic keratosis. IngMeb is proposed to exert its therapeutic effects through a dual mode of action involving (i) induction of cell death that is associated with mitochondrial dysfunction followed by (ii) stimulation of a local inflammatory response, at least partially driven by protein kinase C (PKC) activation. Although this therapeutic model has been well characterized, the complete set of molecular targets responsible for mediating IngMeb activity remains ill-defined. Here, we have synthesized a photoreactive, clickable analogue of IngMeb and used this probe in quantitative proteomic experiments to map several protein targets of IngMeb in human cancer cell lines and primary human keratinocytes. Prominent among these targets was the mitochondrial carnitine-acylcarnitine translocase SLC25A20, which we show is inhibited in cells by IngMeb and the more stable analogue ingenol disoxate (IngDsx), but not by the canonical PKC agonist 12-O-tetradecanoylphorbol-13-acetate (TPA). SLC25A20 blockade by IngMeb and IngDsx leads to a buildup of cellular acylcarnitines and blockade of fatty acid oxidation (FAO), pointing to a possible mechanism for IngMeb-mediated perturbations in mitochondrial function.

Protein Kinases C-Mediated Regulations of Drug Transporter Activity, Localization and Expression

Drug transporters are now recognized as major actors in pharmacokinetics, involved notably in drug–drug interactions and drug adverse effects. Factors that govern their activity, localization and expression are therefore important to consider. In the present review, the implications of protein kinases C (PKCs) in transporter regulations are summarized and discussed. Both solute carrier (SLC) and ATP-binding cassette (ABC) drug transporters can be regulated by PKCs-related signaling pathways. PKCs thus target activity, membrane localization and/or expression level of major influx and efflux drug transporters, in various normal and pathological types of cells and tissues, often in a PKC isoform-specific manner. PKCs are notably implicated in membrane insertion of bile acid transporters in liver and, in this way, are thought to contribute to cholestatic or choleretic effects of endogenous compounds or drugs. The exact clinical relevance of PKCs-related regulation of drug transporters in terms of drug resistance, pharmacokinetics, drug–drug interactions and drug toxicity remains however to be precisely determined. This issue is likely important to consider in the context of the development of new drugs targeting PKCs-mediated signaling pathways, for treating notably cancers, diabetes or psychiatric disorders.

In vitro effects of the small-molecule protein kinase C agonists on HIV latency reactivation

The persistence of latently HIV-infected cellular reservoirs represents the major obstacle to virus eradication in patients under antiretroviral therapy (ART). Cure strategies to eliminate these reservoirs are thus needed to reactivate proviral gene expression in latently infected cells. In this study, we tested optimal concentrations of PKC agonist candidates (PEP005/Ingenol-3-angelate, prostratin, bryostatin-1, and JQ1) to reactivate HIV latency in vitro, and examined their effects on cell survival, activation and epigenetic histone methylation after treatment alone or in combination in cell line and isolated CD4 T cells from SIV-infected macaques. The results showed that PKC agonists increased cell activation with different degrees of latency reactivation, concomitant with reduced levels of histone methylation. With increasing concentrations, prostratin and byrostain-1 treatment rapidly reduced cell survival and cell activation. The PKC agonist combinations, or in combination with JQ1, led to modest levels of synergistic reactivation of HIV. Remarkably, PEP005 treatment alone caused marked reactivation of HIV latency, similar to PMA stimulation. These findings suggested that PEP005 alone, as indicated its lower cytotoxicity and lower effective dose inducing maximal reactivation, might be a candidate for effectively reactivating HIV latency as part of a therapeutic strategy for HIV infection.

Repeated Treatments with Ingenol Mebutate Prevents Progression of UV-Induced Photodamage in Hairless Mice

Background and Aim

Ingenol mebutate (IngMeb) is an effective treatment for actinic keratosis. In this study, we hypothesized that repeated treatments with IngMeb may prevent progression of UV-induced photodamage, and that concurrent application of a corticosteroid may reduce IngMeb-induced local skin responses (LSR).

Methods

Hairless mice (n = 60; 3 groups of 20 mice) were irradiated with solar simulated ultraviolet radiation (UVR) throughout the study. Five single treatments with IngMeb were given at 4-week intervals (Days 21, 49, 77, 105, and 133). Clobetasol propionate (CP) was applied once daily for 5 days prior to each IngMeb application, as well as 6 h and 1 day post treatment. One week after IngMeb treatment No. 1, 3, and 5 (Days 28, 84, and 140), biopsies from four mice in each group were collected for histological evaluation of UV-damage on a standardized UV-damage scale (0–12). LSR (0–24) were assessed once daily (Days 1–7) after each IngMeb treatment.

Results

IngMeb prevented progression of photodamage in terms of keratosis grade, epidermal hypertrophy, dysplasia, and dermal actinic damage with a lower composite UV-damage score on day 140 (UVR 10.25 vs. UVR+IngMeb 6.00, p = 0.002) compared to UVR alone. IngMeb induced LSR, including erythema, flaking, crusting, bleeding, vesiculation, and ulceration. Concurrent CP increased LSR (max LSR Tx 1–5: UVR+IngMeb+CP 3.6–5.5 vs. UVR+IngMeb 2.6–4.3) and provided better prevention of photodamage compared to IngMeb alone (Day 140: UVR+IngMeb 6.00 vs. UVR+IngMeb+CP 3.00 p < 0.001).

Conclusion

Repeated field-directed treatments with IngMeb prevent progression of cutaneous photodamage in hairless mice, while CP cannot be used to alleviate IngMeb-induced LSR. The findings suggest that IngMeb may potentially serve as a prophylactic treatment for UV-induced tumors.

Protein kinase C controls lysosome biogenesis independently of mTORC1

Lysosomes respond to environmental cues by controlling their own biogenesis, but the underlying mechanisms are poorly understood. Here we describe a protein kinase C (PKC)-dependent and mTORC1-independent mechanism for regulating lysosome biogenesis, which provides insights into previously reported effects of PKC on lysosomes. By identifying lysosome-inducing compounds we show that PKC couples activation of the TFEB transcription factor with inactivation of the ZKSCAN3 transcriptional repressor through two parallel signalling cascades. Activated PKC inactivates GSK3β, leading to reduced phosphorylation, nuclear translocation and activation of TFEB, while PKC activates JNK and p38 MAPK, which phosphorylate ZKSCAN3, leading to its inactivation by translocation out of the nucleus. PKC activation may therefore mediate lysosomal adaptation to many extracellular cues. PKC activators facilitate clearance of aggregated proteins and lipid droplets in cell models and ameliorate amyloid β plaque formation in APP/PS1 mouse brains. Thus, PKC activators are viable treatment options for lysosome-related disorders.

Tumor-Preferential Induction of Immune Responses and Epidermal Cell Death in Actinic Keratoses by Ingenol Mebutate

The rapid and strong clinical efficacy of the first-in-class, ingenol mebutate, against actinic keratosis (AK) has resulted in its recent approval. We conducted the first comprehensive analysis of the cellular and molecular mode of action of topical ingenol mebutate 0.05% gel in both AK and uninvolved skin of 26 patients in a phase I, single-center, open-label, within-patient comparison. As early as 1 day after application, ingenol mebutate induced profound epidermal cell death, along with a strong infiltrate of CD4⁺ and CD8⁺ T-cells, neutrophils, and macrophages. Endothelial ICAM-1 activation became evident after 2 days. The reaction pattern was significantly more pronounced in AK compared with uninvolved skin, suggesting a tumor-preferential mode of action. Extensive molecular analyses and transcriptomic profiling of mRNAs and microRNAs demonstrated alterations in gene clusters functionally associated with epidermal development, inflammation, innate immunity, and response to wounding. Ingenol mebutate reveals a unique mode of action linking directly to anti-tumoral effects.

Trial Registration: ClinicalTrials.gov NCT01387711

Synthesis and Cytotoxicity against K562 Cells of 3-O-Angeloyl-20-O-acetyl Ingenol, a Derivative of Ingenol Mebutate

Ingenol mebutate possesses significant cytotoxicity and is clinically used to treat actinic keratosis. However, ingenol mebutate undergoes acyl migration which affects its bioactivity. Compound 3-O-angeloyl-20-O-acetyl ingenol (AAI, also known as 20-O-acetyl-ingenol-3-angelate or PEP008) is a synthetic derivative of ingenol mebutate. In this work, we report the AAI synthesis details and demonstrate AAI has higher cytotoxicity than ingenol mebutate in a chronic myeloid leukemia K562 cell line. Our data indicate that the increased activity of AAI originates from the improved intracellular stability of AAI rather than the increased binding affinity between AAI and the target protein protein kinase Cδ (PKCδ). AAI inhibits cell proliferation, induces G2/M phase arrest, disrupts the mitochondrial membrane potential, and stimulates apoptosis, as well as necrosis in K562 cells. Similar to ingenol mebutate, AAI activates PKCδ and extracellular signal regulated kinase (ERK), and inactivates protein kinase B (AKT). Furthermore, AAI also inhibits JAK/STAT3 pathway. Altogether, our studies show that ingenol derivative AAI is cytotoxic to K562 cells and modulates PKCδ/ERK, JAK/STAT3, and AKT signaling pathways. Our work suggests that AAI may be a new candidate of chemotherapeutic agent.

Ingenol Disoxate: A Novel 4-Isoxazolecarboxylate Ester of Ingenol with Improved Properties for Treatment of Actinic Keratosis and Other Non-Melanoma Skin Cancers

Introduction

Ingenol mebutate gel (Picato^®, LEO Pharma A/S) is approved for the field treatment of actinic keratosis and is characterized by high sustained clearance of actinic lesions. The inherent propensity of ingenol mebutate towards chemical rearrangement necessitates refrigeration of the final product. We sought to identify novel ingenol derivatives with enhanced chemical stability and similar or improved in vitro potency and in vivo efficacy.

Methods

A number of ingenol esters were synthesized with full regiocontrol from ingenol. Chemical stability was determined in aqueous buffer at physiological pH and hydroalcoholic gel at lower pH. Acute cytotoxicity was determined in HeLa or HSC-5 cells. Keratinocyte proliferation, viability and caspase 3/7 activation was measured in primary epidermal keratinocytes. Relative gene expression levels were determined by real-time quantitative PCR. Evaluation of in vivo tumor ablating potential was performed in the murine B16 melanoma mouse model and in the UV-induced skin carcinogenesis model in hairless SKH-1 mice following topical treatment for two consecutive days with test compounds formulated at 0.1% in a hydroalcoholic gel.

Results

This work resulted in the identification of ingenol disoxate (LEO 43204) displaying increased stability in a clinically relevant formulation and in aqueous buffer with minimal pH-dependent acyl migration degradation. Ingenol disoxate exhibited a significantly higher cytotoxic potency relative to ingenol mebutate. Likewise, cell growth arrest in normal human keratinocyte was more potently induced by ingenol disoxate, which was accompanied by protein kinase C dependent transcription of markers of keratinocyte differentiation. Most notably, ingenol disoxate possessed a superior antitumor effect in a B16 mouse melanoma model and significantly increased median survival time relative to ingenol mebutate. A significant effect on tumor ablation was also observed in a murine model of ultraviolet irradiation-induced skin carcinogenesis.

Conclusion

These data illustrate that the favorable in vitro and in vivo pharmacological properties driving ingenol mebutate efficacy are either preserved or improved in ingenol disoxate. In combination with improved chemical stability to potentially facilitate storage of the final product at ambient temperatures, these features support further development of ingenol disoxate as a convenient and efficacious treatment modality of non-melanoma skin cancers.

Funding

LEO Pharma A/S.

Electronic supplementary material

The online version of this article (doi:10.1007/s13555-016-0137-2) contains supplementary material, which is available to authorized users.

Protein Kinase C as Regulator of Vascular Smooth Muscle Function and Potential Target in Vascular Disorders

Vascular smooth muscle (VSM) plays an important role in maintaining vascular tone. In addition to Ca2+-dependent myosin light chain (MLC) phosphorylation, protein kinase C (PKC) is a major regulator of VSM function. PKC is a family of conventional Ca2+-dependent α, β, and γ, novel Ca2+-independent δ, ɛ, θ, and η, and atypical ξ, and ι/λ isoforms. Inactive PKC is mainly cytosolic, and upon activation it undergoes phosphorylation, maturation, and translocation to the surface membrane, the nucleus, endoplasmic reticulum, and other cell organelles; a process facilitated by scaffold proteins such as RACKs. Activated PKC phosphorylates different substrates including ion channels, pumps, and nuclear proteins. PKC also phosphorylates CPI-17 leading to inhibition of MLC phosphatase, increased MLC phosphorylation, and enhanced VSM contraction. PKC could also initiate a cascade of protein kinases leading to phosphorylation of the actin-binding proteins calponin and caldesmon, increased actin-myosin interaction, and VSM contraction. Increased PKC activity has been associated with vascular disorders including ischemia-reperfusion injury, coronary artery disease, hypertension, and diabetic vasculopathy. PKC inhibitors could test the role of PKC in different systems and could reduce PKC hyperactivity in vascular disorders. First-generation PKC inhibitors such as staurosporine and chelerythrine are not very specific. Isoform-specific PKC inhibitors such as ruboxistaurin have been tested in clinical trials. Target delivery of PKC pseudosubstrate inhibitory peptides and PKC siRNA may be useful in localized vascular disease. Further studies of PKC and its role in VSM should help design isoform-specific PKC modulators that are experimentally potent and clinically safe to target PKC in vascular disease.

Human thrombopoiesis depends on Protein kinase Cδ/protein kinase Cε functional couple

A deeper understanding of the molecular events driving megakaryocytopoiesis and thrombopoiesis is essential to regulate in vitro and in vivo platelet production for clinical applications. We previously documented the crucial role of PKCε in the regulation of human and mouse megakaryocyte maturation and platelet release. However, since several data show that different PKC isoforms fulfill complementary functions, we targeted PKCε and PKCδ, which show functional and phenotypical reciprocity, at the same time as boosting platelet production in vitro. Results show that PKCδ, contrary to PKCε, is persistently expressed during megakaryocytic differentiation, and a forced PKCδ down-modulation impairs megakaryocyte maturation and platelet production. PKCδ and PKCε work as a functional couple with opposite roles on thrombopoiesis, and the modulation of their balance strongly impacts platelet production. Indeed, we show an imbalance of PKCδ/PKCε ratio both in primary myelofibrosis and essential thrombocythemia, featured by impaired megakaryocyte differentiation and increased platelet production, respectively. Finally, we demonstrate that concurrent molecular targeting of both PKCδ and PKCε represents a strategy for in vitro platelet factories.

Natural Product Vibsanin A Induces Differentiation of Myeloid Leukemia Cells through PKC Activation

All-trans retinoic acid (ATRA)-based cell differentiation therapy has been successful in treating acute promyelocytic leukemia, a unique subtype of acute myeloid leukemia (AML). However, other subtypes of AML display resistance to ATRA-based treatment. In this study, we screened natural, plant-derived vibsane-type diterpenoids for their ability to induce differentiation of myeloid leukemia cells, discovering that vibsanin A potently induced differentiation of AML cell lines and primary blasts. The differentiation-inducing activity of vibsanin A was mediated through direct interaction with and activation of protein kinase C (PKC). Consistent with these findings, pharmacological blockade of PKC activity suppressed vibsanin A-induced differentiation. Mechanistically, vibsanin A-mediated activation of PKC led to induction of the ERK pathway and decreased c-Myc expression. In mouse xenograft models of AML, vibsanin A administration prolonged host survival and inhibited PKC-mediated inflammatory responses correlated with promotion of skin tumors in mice. Collectively, our results offer a preclinical proof of concept for vibsanin A as a myeloid differentiation-inducing compound, with potential application as an antileukemic agent. Cancer Res; 76(9); 2698-709. ©2016 AACR.

Total synthesis of natural derivatives and artificial analogs of 13-oxyingenol and their biological evaluation

Natural derivatives and artificial analogs of 13-oxyingenol were synthesized, and these analogs induced HL-60 differentiation and apoptosis.

Ingenane Diterpenoids

Despite a more recent isolation and chemical characterization when compared to phorbol, along with its chemical instability, limited distribution in Nature, and scarce availability, ingenol is the only Euphorbia diterpenoid that has undergone successful pharmaceutical development, with ingenol 3-angelate (ingenol mebutate, Picato(®)) entering the pharmaceutical market in 2012 for the treatment of actinic keratosis. The phytochemical, chemical, and biological literature on members of the ingenane class of diterpenoids is reviewed from their first isolation in 1968 through 2015, highlighting unresolved issues both common to phorboids (biogenesis, relationship between molecular targets, and in vivo activity) and specific to ingenol derivatives (two-dimensional representation, in-out stereoisomerism, versatility of binding mode to PKC, and inconsistencies in the structural elucidation of some classes of derivatives). The biogenesis of ingenol is discussed in the light of the Jakupovic proposal of a dissection between the formation of the macrocyclic Euphorbia diterpenoids and the phorboids, and the clinical development of ingenol mebutate is chronicled in the light of its "reverse-pharmacology" focus.

13-Oxyingenol dodecanoate, a cytotoxic ingenol derivative, induces mitochondrial apoptosis and caspase-dependent Akt decrease in K562 cells

13-Oxyingenol dodecanoate (13OD) is an ingenol derivative prepared from Chinese traditional medicine Euphorbia kansui without any report about its bioactivity. The present study demonstrated for the first time that 13OD displayed potent cytotoxicity against chronic myeloid leukemia K562 cells in vitro. 13OD inhibited proliferation, induced G2/M phase arrest, and exhibited potent apoptotic activity in K562 cells. In K562 cells, 13OD disrupted the mitochondrial membrane potential and induced high level of ROS, which played an indispensable role in 13OD-induced apoptosis. Further investigations on the molecular mechanisms revealed that total Akt protein level was decreased in a caspase-dependent way after treatment with 13OD; in addition, ERK was activated by 13OD, and this activation played a protective role in 13OD stimulation. Altogether, these results revealed that the cytotoxic ingenol derivative 13OD induced apoptosis with novel mechanisms for the proapoptotic function in cancer cells, and suggested that 13OD may serve as a lead template for rational drug design and for future anticancer agent development.

Safety and tolerability of ingenol mebutate in the treatment of actinic keratosis

INTRODUCTION

Ingenol mebutate is a topical therapeutic agent for the treatment of actinic keratosis (AK). It has a novel mode of action and has shown comparable efficacy to other topical field therapies. This article summarizes and provides perspective on the safety profile of ingenol mebutate from clinical studies of this agent.

AREAS COVERED

The unique mechanism of action of ingenol mebutate, the basis for a rapid clinical effect, is outlined. Safety and tolerability data, including mean composite local skin response (LSR) scores, type of LSR, and adverse events from a range of clinical studies both in healthy volunteers and patients with AK, are reviewed. The safety profile of ingenol mebutate is then compared with other agents used to treat AK lesions.

EXPERT OPINION

Ingenol mebutate has a dosing period of 2 - 3 days, which is short compared with other field therapies, and there is no evidence of systemic absorption. The fact that most of the LSRs observed are mild to moderate in intensity and transient, with a majority resolved within 2 weeks, makes for a favorable safety profile. Ingenol mebutate enhances the armamentarium available to the dermatologist for the treatment of AK.

Protein kinase C-dependent regulation of human hepatic drug transporter expression

Hepatic drug transporters are now recognized as major actors of hepatobiliary elimination of drugs. Characterization of their regulatory pathways is therefore an important issue. In this context, the present study was designed to analyze the potential regulation of human hepatic transporter expression by protein kinase C (PKC) activation. Treatment by the reference PKC activator phorbol 12-myristate 13-acetate (PMA) for 48h was shown to decrease mRNA expression of various sinusoidal transporters, including OATP1B1, OATP2B1, NTCP, OCT1 and MRP3, but to increase that of OATP1B3, whereas mRNA expression of canalicular transporters was transiently enhanced (MDR1), decreased (BSEP and MRP2) or unchanged (BCRP) in human hepatoma HepaRG cells. The profile of hepatic transporter mRNA expression changes in PMA-treated HepaRG cells was correlated to that found in PMA-exposed primary human hepatocytes and was similarly observed in response to the PKC-activating marketed drug ingenol mebutate. It was associated with concomitant repression of OATP1B1 and OATP2B1 protein expression and reduction of OATP, OCT1, NTCP and MRP2 activity. The use of chemical PKC inhibitors further suggested a contribution of novel PKCs isoforms to PMA-mediated regulations of transporter mRNA expression. PMA was finally shown to cause epithelial-mesenchymal transition (EMT) in HepaRG cells and exposure to various additional EMT inducers, i.e., hepatocyte growth factor, tumor growth factor-β1 or the HNF4α inhibitor BI6015, led to transporter expression alterations highly correlated to those triggered by PMA. Taken together, these data highlight PKC-dependent regulation of human hepatic drug transporter expression, which may be closely linked to EMT triggered by PKC activation.

Yessotoxin activates cell death pathways independent of Protein Kinase C in K-562 human leukemic cell line

Protein Kinase C (PKC) is a group of enzymes involved in pro-survival or pro-apoptotic events depending on the cellular model. Moreover, Yessotoxin (YTX) modulates its expression and activates different cell death pathways. In K-562 tumor cell line, YTX induces apoptosis and autophagy after 24 and 48 h of incubation, respectively, and the toxin carries out its action through the phosphodiesterase 4A (PDE4A). Therefore, the levels of two subtypes of PKC, conventional (cPKC) and δ isotype of novel PKC (PKCδ) were studied at these times after YTX incubation. Also their involvement in the cell death activated by the toxin and their relationship with PDE4A was checked. The expression of cPKC and PKCδ in cytosol, plasma membrane and nucleus was studied in normal and PDE4A-silenced cells. Furthermore, cell viability of normal cells, as well as cPKC-, PKCδ- and PDE4A-silenced cells was tested by Lactate Dehydrogenase (LDH) assay. As a result, PKCδ showed a key role in K-562 cell survive, since without this protein, K-562 cell decreased their viability. Furthermore, modulation of PKCs by YTX treatment was observed, however, the changes in the expression of these proteins are independent of cell death activated by the toxin. In addition, the modulation of PKCs detected is PDE4A-dependent, since the silencing of this protein change PKC expression pattern.

Digging deep into "dirty" drugs - modulation of the methylation machinery

DNA methylation and histone modification are epigenetic mechanisms that result in altered gene expression and cellular phenotype. The exact role of methylation in myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML) remains unclear. However, aberrations (e.g. loss-/gain-of-function or up-/down-regulation) in components of epigenetic transcriptional regulation in general, and of the methylation machinery in particular, have been implicated in the pathogenesis of these diseases. In addition, many of these components have been identified as therapeutic targets for patients with MDS/AML, and are also being assessed as potential biomarkers of response or resistance to hypomethylating agents (HMAs). The HMAs 5-azacitidine (AZA) and 2'-deoxy-5-azacitidine (decitabine, DAC) inhibit DNA methylation and have shown significant clinical benefits in patients with myeloid malignancies. Despite being viewed as mechanistically similar drugs, AZA and DAC have differing mechanisms of action. DAC is incorporated 100% into DNA, whereas AZA is incorporated into RNA (80-90%) as well as DNA (10-20%). As such, both drugs inhibit DNA methyltransferases (DNMTs; dependently or independently of DNA replication) resulting in the re-expression of tumor-suppressor genes; however, AZA also has an impact on mRNA and protein metabolism via its inhibition of ribonucleotide reductase, resulting in apoptosis. Herein, we first give an overview of transcriptional regulation, including DNA methylation, post-translational histone-tail modifications, the role of micro-RNA and long-range epigenetic gene silencing. We place special emphasis on epigenetic transcriptional regulation and discuss the implication of various components in the pathogenesis of MDS/AML, their potential as therapeutic targets, and their therapeutic modulation by HMAs and other substances (if known). The main focus of this review is laid on dissecting the rapidly evolving knowledge of AZA and DAC with a special focus on their differing mechanisms of action, and the effect of HMAs on transcriptional regulation.

Pharmaceuticals that contain polycyclic hydrocarbon scaffolds

This review comprehensively explores approved pharmaceutical compounds that contain polycyclic scaffolds and the properties that these skeletons convey.

Targeting TRAF3 Downstream Signaling Pathways in B cell Neoplasms

B cell neoplasms comprise >50% of blood cancers. However, many types of B cell malignancies remain incurable. Identification and validation of novel genetic risk factors and oncogenic signaling pathways are imperative for the development of new therapeutic strategies. We and others recently identified TRAF3, a cytoplasmic adaptor protein, as a novel tumor suppressor in B lymphocytes. We found that TRAF3 inactivation results in prolonged survival of mature B cells, which eventually leads to spontaneous development of B lymphomas in mice. Corroborating our findings, TRAF3 deletions and inactivating mutations frequently occur in human B cell chronic lymphocytic leukemia, splenic marginal zone lymphoma, mantle cell lymphoma, multiple myeloma, Waldenström’s macroglobulinemia, and Hodgkin lymphoma. In this context, we have been investigating TRAF3 signaling mechanisms in B cells, and are developing new therapeutic strategies to target TRAF3 downstream signaling pathways in B cell neoplasms. Here we discuss our new translational data that demonstrate the therapeutic potential of targeting TRAF3 downstream signaling pathways in B lymphoma and multiple myeloma.