Investigation of cell cycle arrest effects of actinomycin D at G1 phase using proteomic methods in B104-1-1 cells

Suppressing proteasome activity enhances sensitivity to actinomycin D in diffuse anaplastic Wilms tumor

Wilms tumor is the most common pediatric kidney cancer, and diffuse anaplastic Wilms tumor is the most chemoresistant subtype. Here, we explore how Wilms tumor cells evade the chemotherapy actinomycin D, which inhibits ribosomal RNA biogenesis. Using ribosome profiling, protein arrays, and a genome-wide knockout screen, we describe how actinomycin D disrupts protein homeostasis and blocks cell-cycle progression. When ribosomal capacity is limited by actinomycin D treatment, anaplastic Wilms tumor cells preferentially translate proteasome components. Next, we find that the proteasome inhibitor bortezomib sensitizes cells to actinomycin D treatment in vitro and prolongs survival in xenograft models. Lastly, increased levels of proteasome components are associated with anaplastic histology and worse prognosis in Wilms tumor patients. In sum, maintaining protein homeostasis is critical for Wilms tumor proliferation, and it can be therapeutically disrupted by blocking protein synthesis or turnover.

NMNAT1 Is a Survival Factor in Actinomycin D-Induced Osteosarcoma Cell Death

Osteosarcoma is a frequent and extremely aggressive type of pediatric cancer. New therapeutic approaches are needed to improve the overall survival of osteosarcoma patients. Our previous results suggest that NMNAT1, a key enzyme in nuclear NAD+ synthesis, facilitates the survival of cisplatin-treated osteosarcoma cells. A high-throughput cytotoxicity screening was performed to identify novel pathways or compounds linked to the cancer-promoting role of NMNAT1. Nine compounds caused higher toxicity in the NMNAT1 KO U2OS cells compared to their wild type counterparts, and actinomycin D (ActD) was the most potent. ActD-treatment of NMNAT1 KO cells increased caspase activity and secondary necrosis. The reduced NAD+ content in NMNAT1 KO cells was further decreased by ActD, which partially inhibited NAD+-dependent enzymes, including the DNA nick sensor enzyme PARP1 and the NAD+-dependent deacetylase SIRT1. Impaired PARP1 activity increased DNA damage in ActD-treated NMNAT1 knockout cells, while SIRT1 impairment increased acetylation of the p53 protein, causing the upregulation of pro-apoptotic proteins (NOXA, BAX). Proliferation was decreased through both PARP- and SIRT-dependent pathways. On the one hand, PARP inhibitors sensitized wild type but not NMNAT1 KO cells to ActD-induced anti-clonogenic effects; on the other hand, over-acetylated p53 induced the expression of the anti-proliferative p21 protein leading to cell cycle arrest. Based on our results, NMNAT1 acts as a survival factor in ActD-treated osteosarcoma cells. By inhibiting both PARP1- and SIRT1-dependent cellular pathways, NMNAT1 inhibition can be a promising new tool in osteosarcoma chemotherapy.

Improved functional oocyte enucleation by actinomycin D for bovine somatic cell nuclear transfer

Somatic cell nuclear transfer (SCNT) allows animal cloning but remains technically challenging. This study investigated limitations to functional oocyte enucleation by actinomycin D (AD) as a means of making SCNT easier to perform. Denuding oocytes or inhibiting transcription before AD treatment revealed that the toxicity of this compound during bovine oocyte maturation is mediated by cumulus cells. Exposure of denuded oocytes to higher concentrations of AD (5-20μgmL-1 ) and stepwise reductions of the incubation period (from 14.0 to 0.25h) led to complete inhibition of parthenogenetic development. Bovine SCNT using this improved AD enucleation protocol (NT(AD)) restored cleavage rates compared with rates in the parthenogenetic and SCNT controls (P(CTL) and NT(CTL) respectively). However, NT(AD) was associated with increased caspase-3 activity in cleavage stage embryos and did not recover blastocyst rates. The removal of AD-treated oocyte spindle before reconstruction (NT(AD+SR)) improved embryo development and reduced caspase-3 activity to levels similar to those in the P(CTL) and NT(CTL) groups. Furthermore, mid-term pregnancies were achieved using NT(AD+SR) blastocysts. In conclusion, improvements in AD functional enucleation for bovine SCNT circumvents most cellular roadblocks to early embryonic development and future investigations must focus on restoring blastocyst formation.

Carbon nanotube-delivered iC9 suicide gene therapy for killing breast cancer cells in vitro

AIM

To induce a safe death to MCF-7 human breast cancer cell line through gene therapy based on iC9 suicide gene.

MATERIALS & METHODS

To induce apoptosis to MCF-7 cell line, iC9 gene was transfected using pyridine-functionalized multi-walled carbon nanotubes. Then, to enhance chemotherapy, iC9 suicide gene therapy was performed alongside.

RESULTS

The results show that the MCF-7 cells were efficiently eliminated in a high percentage by this approach. Furthermore, the suicide gene by itself/in combination with the chemotherapeutic drugs managed to pass the cell cycle arrests.

CONCLUSION

We introduced an in vitro treatment approach based on suicide gene therapy and the first step was taken toward the enhancement of chemotherapy, although more investigation is required.

Cytotoxic conjugates of betulinic acid and substituted triazoles prepared by Huisgen Cycloaddition from 30-azidoderivatives

In this work, we describe synthesis of conjugates of betulinic acid with substituted triazoles prepared via Huisgen 1,3-cycloaddition. All compounds contain free 28-COOH group. Allylic bromination of protected betulinic acid by NBS gave corresponding 30-bromoderivatives, their substitution with sodium azides produced 30-azidoderivatives and these azides were subjected to CuI catalysed Huisgen 1,3-cycloaddition to give the final conjugates. Reactions had moderate to high yields. All new compounds were tested for their in vitro cytotoxic activities on eight cancer and two non-cancer cell lines. The most active compounds were conjugates of 3β-O-acetylbetulinic acid and among them, conjugate with triazole substituted by benzaldehyde 9b was the best with IC50 of 3.3 μM and therapeutic index of 9.1. Five compounds in this study had IC50 below 10 μM and inhibited DNA and RNA synthesis and caused block in G0/G1 cell cycle phase which is highly similar to actinomycin D. It is unusual that here prepared 3β-O-acetates were more active than compounds with the free 3-OH group and this suggests that this set may have common mechanism of action that is different from the mechanism of action of previously known 3β-O-acetoxybetulinic acid derivatives. Benzaldehyde type conjugate 9b is the best candidate for further drug development.

Identification and characterization of molecular targets of natural products by mass spectrometry

Natural products, and their derivatives and mimics, have contributed to the development of important therapeutics to combat diseases such as infections and cancers over the past decades. The value of natural products to modern drug discovery is still considerable. However, its development is hampered by a lack of a mechanistic understanding of their molecular action, as opposed to the emerging molecule-targeted therapeutics that are tailored to a specific protein target(s). Recent advances in the mass spectrometry-based proteomic approaches have the potential to offer unprecedented insights into the molecular action of natural products. Chemical proteomics is established as an invaluable tool for the identification of protein targets of natural products. Small-molecule affinity selection combined with mass spectrometry is a successful strategy to "fish" cellular targets from the entire proteome. Mass spectrometry-based profiling of protein expression is also routinely employed to elucidate molecular pathways involved in the therapeutic and possible toxicological responses upon treatment with natural products. In addition, mass spectrometry is increasingly utilized to probe structural aspects of natural products-protein interactions. Limited proteolysis, photoaffinity labeling, and hydrogen/deuterium exchange in conjunction with mass spectrometry are sensitive and high-throughput strategies that provide low-resolution structural information of non-covalent natural product-protein complexes. In this review, we provide an overview on the applications of mass spectrometry-based techniques in the identification and characterization of natural product-protein interactions, and we describe how these applications might revolutionize natural product-based drug discovery.

First Y-type actinomycins from Streptomyces with divergent structure-activity relationships for antibacterial and cytotoxic properties

Streptomyces sp. strain Gö-GS12 was found to produce five novel actinomycins Y(1)-Y(5) (). Their amino acid pattern discloses them as members of a new family of this important class of antibiotics. Compounds differ from Z-type actinomycins in their beta-peptidolactone rings which here contain trans-4-hydroxyproline (Hyp) or 4-oxoproline (OPro) amino acids, and from the X-congeners by containing methylalanine (MeAla). Within the new Y-type actinomycins variations are not only in the rare chlorinated or hydroxylated threonine residue. Furthermore, the beta-ring can undergo rearrangement by a two-fold acyl shift (compounds and ) or show a unique additional ring closure with the chromophore (compound ), resulting in metabolites with yet unknown structural motifs, altered conformations and distinct bioactivities. The strongest bioactivity was found for the chlorine containing actinomycin Y(1) (), the most surprising for Y(5) () with cytotoxic and antibacterial effects losing their coherence, which has been observed for the first time here.

Grb2 signaling in cell motility and cancer

BACKGROUND

Metastasis is the primary cause of death in most human cancers, and understanding the molecular mechanisms underpinning this multistep process is fundamental to identifying novel molecular targets and developing more effective therapies.

OBJECTIVE/METHODS

Here we review the role of growth factor receptor-bound protein 2 (Grb2) in cancer and specifically in metastasis-related processes, and summarize the development of anticancer therapeutics selectively targeting this adapter protein.

RESULTS/CONCLUSION

Grb2 is a key molecule in intracellular signal transduction, linking activated cell surface receptors to downstream targets by binding to specific phosphotyrosine-containing and proline-rich sequence motifs. Grb2 signaling is critical for cell cycle progression and actin-based cell motility, and, consequently, more complex processes such as epithelial morphogenesis, angiogenesis and vasculogenesis. These functions make Grb2 a therapeutic target for strategies designed to prevent the spread of solid tumors through local invasion and metastasis.

The cytotoxicity of a Grb2-SH3 inhibitor in Bcr-Abl positive K562 cells

Chronic myelogenous leukemia (CML) is characterized by the presence of Bcr-Abl oncoprotein. Gleevec has been designed to treat many CML patients by specifically targeting Bcr-Abl, but resistance to it is already apparent in many cases. In CML cells, Bcr-Abl activates several signaling pathways, including the Ras-dependent pathway, in which growth factor receptor binding 2 (Grb2) acts as an adaptor protein. A specific Grb2-SH3 inhibitor (denoted as peptidimer-c) that disrupts Grb2-Sos complex was designed and synthesized in our laboratory. In this study, we investigated the effect and the molecular mechanism of this inhibitor. Peptidimer-c was shown to bind to Grb2 in K562 cells, a cell line over-expressing Bcr-Abl oncoprotein. It caused cytotoxicity in the cells, and inhibited their ability of colony formation in the semi-solid medium. It was shown to induce apoptosis of K562 cells in a dose-dependent mode, the apoptotic effect of peptidimer-c being associated with caspase-3 activation. The effect of peptidimer-c on growth inhibition was also shown to be accompanied by S-phase arrest of cell cycle mediated by down-regulation of cyclin A and Cdk2, as well as phospho-Cdk2. The above results indicated that peptidimer-c may be another potential therapeutic agent for CML, which can induce S-phase arrest in the Bcr-Abl positive K562.

A novel histone deacetylase pathway regulates mitosis by modulating Aurora B kinase activity

Histone deacetylase (HDAC) inhibitors perturb the cell cycle and have great potential as anti-cancer agents, but their mechanism of action is not well established. HDACs classically function as repressors of gene expression, tethered to sequence-specific transcription factors. Here we report that HDAC3 is a critical, transcription-independent regulator of mitosis. HDAC3 forms a complex with A-Kinase-Anchoring Proteins AKAP95 and HA95, which are targeted to mitotic chromosomes. Deacetylation of H3 in mitosis requires AKAP95/HA95 and HDAC3 and provides a hypoacetylated H3 tail that is the preferred substrate for Aurora B kinase. Phosphorylation of H3S10 by Aurora B leads to dissociation of HP1 proteins from methylated H3K9 residues on mitotic heterochromatin. This transcription-independent pathway, involving interdependent changes in histone modification and protein association, is required for normal progression through mitosis and is an unexpected target of HDAC inhibitors, a class of drugs currently in clinical trials for treating cancer.