Selective inhibition of the polypeptide chain elongation in eukaryotic cells

Inhibition of the CDK2 and Cyclin A complex leads to autophagic degradation of CDK2 in cancer cells

Cyclin-dependent kinase 2 (CDK2) complex is significantly over-activated in many cancers. While it makes CDK2 an attractive target for cancer therapy, most inhibitors against CDK2 are ATP competitors that are either nonspecific or highly toxic, and typically fail clinical trials. One alternative approach is to develop non-ATP competitive inhibitors; they disrupt interactions between CDK2 and either its partners or substrates, resulting in specific inhibition of CDK2 activities. In this report, we identify two potential druggable pockets located in the protein-protein interaction interface (PPI) between CDK2 and Cyclin A. To target the potential druggable pockets, we perform a LIVS in silico screening of a library containing 1925 FDA approved drugs. Using this approach, homoharringtonine (HHT) shows high affinity to the PPI and strongly disrupts the interaction between CDK2 and cyclins. Further, we demonstrate that HHT induces autophagic degradation of the CDK2 protein via tripartite motif 21 (Trim21) in cancer cells, which is confirmed in a leukemia mouse model and in human primary leukemia cells. These results thus identify an autophagic degradation mechanism of CDK2 protein and provide a potential avenue towards treating CDK2-dependent cancers.

CDK2 can drive the proliferation of cancer cells. Here, the authors screened for a non-ATP competitive inhibitor of the CDK2/cylinA complex and find that Homoharringtonine can disrupt the complex and promote the degradation of CDK2.

Attenuation of cytosolic translation by RNA oxidation is involved in singlet oxygen-mediated transcriptomic responses

Singlet oxygen (¹ O₂ ) production is associated with stress signalling. Here, using Arabidopsis as a model system, we study the effects of the accumulation of 8-hydroxyguanosine (8-oxoG), a major product of ¹ O₂ -mediated RNA oxidation. We show that 8-oxoG can accumulate in vivo when ¹ O₂ is produced in the cytoplasm. Conditions for such production include the application of RB in the light, dark-to-light transitions in the flu mutant, or subjecting plants to combined dehydration/light exposure. Transcriptomes of these treatments displayed a significant overlap with transcripts stimulated by the cytosolic 80S ribosomal translation inhibitors, cycloheximide and homoharringtonine. We demonstrate that 8-oxoG accumulation correlates with a decrease in RNA translatability, resulting in the rapid decrease of the levels of labile gene repressor elements such as IAA1 and JAZ1 in a proteasome-dependent manner. Indeed, genes regulated by the labile repressors of the jasmonic acid signalling pathway were induced by cycloheximide, RB or dehydration/light treatment independently of the hormone. The results suggest that ¹ O₂ , by oxidizing RNA, attenuated cellular translatability and caused specific genes to be released from the repression of their cognate short half-life repressors. The findings here describe a novel means of gene regulation via the direct interaction of ¹ O₂ with RNA.

Anti-varicella-zoster virus activity of cephalotaxine esters in vitro

Harringtonine (HT) and homoharringtonine (HHT), alkaloid esters isolated from the genus Cephalotaxus, exhibit antitumor activity. A semisynthetic HHT has been approved for treatment of chronic myelogenous leukemia. In addition to antileukemic activity, HT and HHT are reported to possess potent antiviral activity. In this study, we investigated the effects of HT and HHT on replication of varicella-zoster virus (VZV) in vitro. HT and HHT, but not their biologically inactive parental alkaloid cephalotaxine (CET), significantly inhibited replication of recombinant VZV-pOka luciferase. Furthermore, HT and HHT, but not CET, strongly induced down-regulation of VZV lytic genes and exerted potent antiviral effects against a VZV clinical isolate. The collective data support the utility of HT and HHT as effective antiviral candidates for treatment of VZV-associated diseases.

Ester alkaloids from Cephalotaxus interfere with the 2'3'-cGAMP-induced type I interferon pathway in vitro

Dysregulated activation of the cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) pathway by self-DNA contributes to interferonopathy and promotes autoimmune diseases. To identify potential suppressors of STING-induced type I interferon (IFN) induction, ethanol extracts of medicinal plants were screened for inhibitory activity against IFN-ß promoter activation. Notably, 70% ethanol extract of Cephalotaxus koreana specifically down-regulated STING-induced, but not TBK1- or IRF3-induced, IFN-ß promoter activity. The compounds exerting inhibitory activity specifically against STING-mediated IFN-ß promoter activation were identified as ester alkaloids isolated from the genus, Cephalotaxus, homoharringtonine and harringtonine. Furthermore, these two compounds inhibited 2’3’-cGAMP-induced IFN-stimulated gene expression and interaction between STING and TBK1. These suppressive effects were not observed with cephalotaxine devoid of the ester side-chain. Our data support the potential utility of homoharringtonine and harringtonine to treat STING-associated interferonopathy and autoimmune diseases.

Omacetaxine Mepesuccinate for Chronic Myeloid Leukemia

Omacetaxine mepesuccinate is approved by the Food and Drug Administration in the United States for the treatment of chronic myeloid leukemia in chronic or accelerated phase resistant to two or more tyrosine kinase inhibitors. This review summarizes the mode of action, pharmacokinetics, efficacy and safety of omacetaxine mepesuccinate. Omacetaxine mepesuccinate has activity in chronic myeloid leukemia, especially in the chronic phase, regardless of the presence of ABL1 kinase domain mutations. Omacetaxine mepesuccinate has distinct but manageable adverse events profile. Omacetaxine mepesuccinate is a treatment option for a subset of patients with refractory chronic myeloid leukemia.

Final analysis of the efficacy and safety of omacetaxine mepesuccinate in patients with chronic- or accelerated-phase chronic myeloid leukemia: Results with 24 months of follow-up

BACKGROUND

Omacetaxine, a protein synthesis inhibitor, is indicated in the United States for the treatment of patients with chronic-phase (CP) or accelerated-phase (AP) chronic myeloid leukemia (CML) with resistance and/or intolerance to 2 or more tyrosine kinase inhibitors.

METHODS

The final analysis, with 24 months of follow-up, included additional efficacy and safety analyses to assess the benefit of long-term omacetaxine administration (1.25 mg/m(2) twice daily for 14 days every 28 days followed by 7 days every 28 days) in CP-CML and AP-CML patients receiving >3 cycles.

RESULTS

Eighteen percent of CP-CML patients achieved a major cytogenetic response (MCyR) with a median duration of 12.5 months (95% confidence interval [CI], 3.5 months to not reached [NR]); responses were maintained for ≥12 months in 3 of 14 responders, and the median overall survival (OS) was 40.3 months (95% CI, 23.8 months to NR). Among patients with AP-CML, 14% achieved or maintained a major hematologic response for a median of 4.7 months (95% CI, 3.6 months to NR); MCyR was not achieved, and the median OS was 14.3 months (95% CI, 6.7-18.7 months). In patients with CP-CML and patients with AP-CML who received >3 cycles of treatment (n = 50 and n = 14, respectively), the median OS was 49.3 months (95% CI, 23.8 months to NR) and 24.6 months (95% CI, 12-37.2 months), respectively. Grade 3 or higher hematologic toxicities were the major side effects (79% and 73% for CP-CML and AP-CML, respectively), with discontinuation due to toxicity in 10% of CP patients and in 5% of AP patients.

CONCLUSIONS

These results suggest that the long-term administration of omacetaxine is feasible with dose adjustments to manage toxicities and that omacetaxine provides a durable benefit for some patients.

Foreign body granulomas after the use of dermal fillers: pathophysiology, clinical appearance, histologic features, and treatment

A foreign body granuloma is a non-allergic chronic inflammatory reaction that is mainly composed of multinucleated giant cells. Foreign body granulomas may occur after the administration of any dermal filler. Factors such as the volume of the injection, impurities present in the fillers, and the physical properties of fillers affect granuloma formation. The formation of granulomas involves five phases: protein adsorption, macrophage adhesion, macrophage fusion, and crosstalk. The clinical and pathologic features of granulomas vary depending on the type of filler that causes them. Foreign body granulomas can be treated effectively with intralesional corticosteroid injections. Surgical excisions of granulomas tend to be incomplete because granulomas have ill-defined borders and moreover, surgical excisions may leave scars and deformities.

Omacetaxine mepesuccinate in the treatment of intractable chronic myeloid leukemia

In a significant proportion of patients with chronic myeloid leukemia, resistance to BCR-ABL tyrosine kinase inhibitors develops due to acquisition of BCR-ABL kinase domain mutations and insensitivity of leukemia stem cells to tyrosine kinase inhibitors. Omacetaxine mepesuccinate (formerly called homoharringtonine) is a natural alkaloid that inhibits protein synthesis and induces cell death. Omacetaxine mepesuccinate has been recently approved by the US Food and Drug Administration to treat patients with chronic myeloid leukemia who failed to respond to multiple tyrosine kinase inhibitors and/or acquired the BCR-ABL-T315I mutation. In this review, we discuss the use and effectiveness of omacetaxine mepesuccinate in the treatment of chronic myeloid leukemia, with coverage of its pharmacology, mode of action, and pharmacokinetics. We believe that omacetaxine mepesuccinate will be beneficial to many patients with chronic myeloid leukemia who do not respond well to tyrosine kinase inhibitors.

Synthesis, pharmacophores, and mechanism study of pyridin-2(1H)-one derivatives as regulators of translation initiation factor 3A

Twenty-seven 1,5-disubstituted-pyridin-2(1H)-one derivatives were synthesized and evaluated for their anti-cancer and anti-fibrosis activity by A549 and NIH3T3 cell viability assays, respectively. To study the selectivity between the cancer and fibrosis cell lines, pharmacophore models (F1-F4) were built in advance for compounds with pyridin-2(1H)-one scaffold, which revealed the relationship between the occupation of the aromatic sub-site F4 and potent anti-cancer activity. The relationship between structure and anti-cancer activity for all target compounds is also reported herein: 1-Phenyl-5-((m-tolylamino)methyl)pyridine-2(1H)-one (22) displayed both potency and selectivity (IC50=0.13 mM) toward the A549 cell line through the inhibition of translation initiation, especially by eIF3a suppression, and can be treated as a lead for the design of novel eIF3a regulators and anti-lung cancer agents.

DCB-3503, a tylophorine analog, inhibits protein synthesis through a novel mechanism

Background

DCB-3503, a tylophorine analog, inhibits the growth of PANC-1 (human pancreatic ductal cancer cell line) and HepG2 (human hepatocellular cancer cell line) tumor xenografts in nude mice. The inhibition of growth leads to cancer cell differentiation instead of cell death. However, the mechanisms of action of tylophorine analogs is unknown.

Methodology/Principal Findings

In this study, we show that DCB-3503 suppresses the expression of pro-oncogenic or pro-survival proteins with short half-lives, including cyclin D1, survivin, β-catenin, p53, and p21, without decreasing their mRNA levels. Proteasome inhibitor reversed the inhibitory effect of DCB-3503 on expression of these proteins. DCB-3503 inhibited the incorporation of radiolabeled amino acid and thymidine, and to a much lesser degree of uridine, in a panel of cell lines. The mechanism of inhibition of protein synthesis is different from that of cycloheximide (CHX) as assayed in cell culture and HeLa in vitro translation system. Furthermore, in contrast to rapamycin, DCB-3503 does not affect protein synthesis through the mTOR pathway. DCB-3503 treatment shifts the sedimentation profiles of ribosomes and mRNAs towards the polysomal fractions while diminishing monosome abundance, indicative of the inhibition of the elongation step of protein synthesis. Preferential down regulation of several studied proteins under these conditions is likely due to the relative short half-lives of these proteins.

Conclusion/Significance

The inhibitory effect of DCB-3503 on translation is apparently distinct from any of the current anticancer compounds targeting protein synthesis. Translation inhibitors with novel mechanism could complement current chemotherapeutic agents for the treatment of human cancers and suppress the occurrence of drug resistance.

Altering chemosensitivity by modulating translation elongation

Background

The process of translation occurs at a nexus point downstream of a number of signal pathways and developmental processes. Modeling activation of the PTEN/AKT/mTOR pathway in the Eμ-Myc mouse is a valuable tool to study tumor genotype/chemosensitivity relationships in vivo. In this model, blocking translation initiation with silvestrol, an inhibitor of the ribosome recruitment step has been showed to modulate the sensitivity of the tumors to the effect of standard chemotherapy. However, inhibitors of translation elongation have been tested as potential anti-cancer therapeutic agents in vitro, but have not been extensively tested in genetically well-defined mouse tumor models or for potential synergy with standard of care agents.

Methodology/Principal Findings

Here, we chose four structurally different chemical inhibitors of translation elongation: homoharringtonine, bruceantin, didemnin B and cycloheximide, and tested their ability to alter the chemoresistance of Eμ-myc lymphomas harbouring lesions in Pten, Tsc2, Bcl-2, or eIF4E. We show that in some genetic settings, translation elongation inhibitors are able to synergize with doxorubicin by reinstating an apoptotic program in tumor cells. We attribute this effect to a reduction in levels of pro-oncogenic or pro-survival proteins having short half-lives, like Mcl-1, cyclin D1 or c-Myc. Using lymphomas cells grown ex vivo we reproduced the synergy observed in mice between chemotherapy and elongation inhibition and show that this is reversed by blocking protein degradation with a proteasome inhibitor.

Conclusion/Significance

Our results indicate that depleting short-lived pro-survival factors by inhibiting their synthesis could achieve a therapeutic response in tumors harboring PTEN/AKT/mTOR pathway mutations.

Homoharringtonine: a new treatment option for myeloid leukemia

HHT, one of the alkaloids from a Chinese natural plant, Cephalotaxus, has shown its potential in leukemia treatment. This compound demonstrated strong growth-inhibiting activities in vitro and in animal experiments, and obtained encouraging results in some clonal proliferative disease such as in chronic myeloid leukemia (CML) and in polycythemia vera. Evidences also confirmed HHT as an apoptosis inducer in tumor cell lines and fresh cells from cancer patients. The CR rate reported with HHT-based regimen in acute nonlymphocytic leukemia showed no statistic differences from that with DNR-based regimen, although the case number was limited. While used in clinical trial, the drug often cause noticeably cardiovascular disturbances if be given rapidly by intravenous infusion. Myelosuppression is the common complication in HHT-based chemotherapy. Although with the anti-growth activity in vitro and praisable achievement in acute and chronic myeloid leukemia treatment, the drug shows no beneficial effect in lymphocytic leukemia and solid tumors. The underlying mechanism for the discrepancy of efficacy keeps unknown. This review will present with the preclinical research data including the action mechanism, pharmacokinetics and drug resistance of HHT as well as the result from the clinical trial with HHT in China and the United States.