Biomedical subjects

Mikhail V Blagosklonny

Publications and source records attributed to Mikhail V Blagosklonny.

At least 19 recordsLinked to original sources

PubMed2006

Aging and immortality: quasi-programmed senescence and its pharmacologic inhibition.

While ruling out programmed aging, evolutionary theory predicts a quasi-program for aging, a continuation of the developmental program that is not turned off, is constantly on, becoming hyper-functional and damaging, causing diseases of aging. Could it be switched off pharmacologically? This would require identification of a molecular target involved in cell senescence, organism aging and diseases of aging. Notably, cell senescence is associated with activation of the TOR (target of rapamycin) nutrient- and mitogen-sensing pathway, which promotes cell growth, even though cell cycle is blocked. Is TOR involved in organism aging? In fact, in yeast (where the cell is the organism), caloric restriction, rapamycin and mutations that inhibit TOR all slow down aging. In animals from worms to mammals caloric restrictions, life-extending agents, and numerous mutations that increase longevity all converge on the TOR pathway. And, in humans, cell hypertrophy, hyper-function and hyperplasia, typically associated with activation of TOR, contribute to diseases of aging. Theoretical and clinical considerations suggest that rapamycin may be effective against atherosclerosis, hypertension and hyper-coagulation (thus, preventing myocardial infarction and stroke), osteoporosis, cancer, autoimmune diseases and arthritis, obesity, diabetes, macula-degeneration, Alzheimer's and Parkinson's diseases. Finally, I discuss that extended life span will reveal new causes for aging (e.g., ROS, 'wear and tear', Hayflick limit, stem cell exhaustion) that play a limited role now, when quasi-programmed senescence kills us first.

Aging↗

PubMed2006

Cytostatic activity of paclitaxel in coronary artery smooth muscle cells is mediated through transient mitotic arrest followed by permanent post-mitotic arrest: comparison with cancer cells.

The anti-cancer agent paclitaxel (PTX) is an effective anti-restenosis agent on drug eluting stents, primarily due to growth inhibition of coronary artery smooth muscle cells (CASMC) across a wide dose range. In this study, we compared the effects of PTX on CASMC to apoptotic-prone HL60 leukemia cells and apoptotic-reluctant A549 lung cancer cells to assess cell survival mechanisms. In comparison to HL60 and A549 cells, CASMC had a shorter mitotic arrest and a lower mitotic index. While CASMC and A549 cells did not become apoptotic and displayed a multi-nucleated phenotype, HL60 cells showed prolonged mitotic arrest followed by apoptosis. CASMC exiting mitosis were arrested in G1 as MN tetraploid cells, with decreased levels of cyclin B1 and PCNA. CASMC remained metabolically active, becoming permanently arrested as evidenced by increased levels of beta-galactosidase activity. These cells did not demonstrate elevated levels of inflammatory markers. Our findings suggest that a weak mitotic checkpoint or inhibited apoptotic cascade, or a combination of both, determine cell survival following PTX treatment. These in vitro findings suggest a mechanism for the cytostatic activity of PTX in CASMC for the inhibition of restenosis.

Apoptosis↗

PubMed2006

Prolonged mitosis versus tetraploid checkpoint: how p53 measures the duration of mitosis.

Degradation of p53 requires transcription, and therefore inhibitors of transcription cause p53 accumulation. When transcription resumes, the p53 that accumulated in turn induces p21. During mitosis, chromosomes are condensed, the nuclear envelope is dissolved and transcription is absent. If a cell stays in mitosis too long, (e.g. mitotic arrest caused by Taxol or nocodazole), then p53 accumulates. This explains how p53 can measure mitotic time and perhaps represents the most fundamental function of p53.

Antineoplastic Agents↗

PubMed2006

Cell senescence: hypertrophic arrest beyond the restriction point.

Withdrawal of mitogens (growth factors) arrests normal cells in G0 (quiescence). All other stresses and factors arrest cell cycle beyond the restriction point in G1 and G2 (non-G0 arrest), in the presence of mitogenic stimulation. Strong mitogenic stimuli by themselves cause non-G0 arrest. Unlike G0, arrest beyond restriction point is characterized by both high levels of cyclins and CDK inhibitors, activated mitogenic pathways with a secondary GF resistance, and continuous mass growth (cell hypertrophy). Prolonged hypertrophic arrest culminates in cell senescence. This review discusses that quiescence and senescence are two opposite, mutually exclusive conditions and that cell senescence can be reversed and prevented.

Aging↗

PubMed2005

Why therapeutic response may not prolong the life of a cancer patient: selection for oncogenic resistance.

Most cancers do not respond to chemotherapy. Disappointedly, even objective clinical responses to anticancer therapy often do not translate into improvements in overall survival. To explain the response-survival paradox, it has been pointed out that effective therapy is ineffective against cancer stem cells, which replenish the tumor (causing relapse). In contrast, I discuss that, according to this scenario, patient survival will be prolonged at least by the duration of remission. Furthermore, stem-cell-based relapses will be sensitive to the initial therapy, and in theory cancer could be controlled indefinitely. To explain the paradox, I discuss that effective therapy selects for resistance among proliferating cancer cells. Importantly, mechanisms of resistance can be divided into nononcogenic (e.g., drug transporters and mutation in drug-targets) and oncogenic (e.g., apoptosis avoidance and cell cycle dysregulation). Oncogenic resistance is associated with highly aggressive cancer phenotype and, therefore, there is no increase in overall survival. I further suggest that (a) therapeutic response is a prerequisite for successful therapy, (b) resistance can be exploited for therapeutic advantage, (c) each response can be translated into increased survival, and (e) in slow growing tumors, cancer can be stopped without tumor shrinkage. Therapy will control cancer if it can selectively suppress proliferating cancer cells and will improve survival as long as acquired resistance can be exploited.

Cell Proliferation↗

PubMed2005

How Avastin potentiates chemotherapeutic drugs: action and reaction in antiangiogenic therapy.

At first glance, the antiangiogenic drug Avastin (bevacizumab) must paradoxically normalize angiogenesis, in order to potentiate chemotherapy. However, this may be only a part of the story. Here I discuss that the synergy between Avastin and chemotherapy is also consistent with the classic notion that antiangiogenic therapy actually inhibits angiogenesis. It has been previously predicted that inhibition of angiogenesis (action) will induce a reactive resistance (reaction), which is mediated by the HIF-1/VEGF pathway in cancer cells, thus allowing both endothelial and cancer cells to resist therapy. Therefore, inhibitors of the reactive resistance are needed to potentiate anti-angiogenic therapy. In the combination of chemotherapy plus Avastin, it is chemotherapy that is the principal antiangiogenic agent. This role of chemotherapy requires that something should be added to block the reaction. And this is exactly what Avastin does (by blocking VEGF). While chemotherapy inhibits angiogenesis, Avastin abrogates the reactive resistance, sensitizing both endothelial and cancer cells to therapy.

Angiogenesis Inhibitors↗

PubMed2005

Teratogens as anti-cancer drugs.

Most anticancer drugs are teratogens, merely because they target vital cellular functions. Conversely, some plants produce agents that intentionally target embryonic signaling pathways, precisely to cause birth defects if pregnant animals eat such plants. Cyclopamine, a teratogen produced by a flowering plant, inhibits the Hh/Gli pathway, causing developmental defects such as cyclopia (one eye in the middle of the face). In theory, selective teratogens may suppress cancer cells that reactivate embryonic pathways, while sparing most normal cells. I discuss the potential (and limits) of teratogens in cancer therapy, linking diverse topics from morning sickness of pregnancy, embryonic pathways and poisonous plants to the mechanism of action of anticancer teratogens and their combinations with less selective cytotoxic agents.

Animals↗

PubMed2005

Depletion of mutant p53 and cytotoxicity of histone deacetylase inhibitors.

Mutant p53 is a cancer-specific target for pharmacologic intervention. We show that histone deacetylase inhibitors such as FR901228 and trichostatin A completely depleted mutant p53 in cancer cell lines. This depletion was preceded by induction of p53-regulated transcription. In cells with mutant p53 pretreated with histone deacetylase inhibitors, DNA damage further enhanced the p53 trans-function. Furthermore, histone deacetylase inhibitors were preferentially cytotoxic to cells with mutant p53 rather than to cells lacking wild-type p53. We suggest that, by either restoring or mimicking p53 trans-functions, histone deacetylase inhibitors initiate degradation of mutant p53. Because mutant p53 is highly expressed, a sudden restoration of p53-like functions is highly cytotoxic to cells with mutant p53. In a broader perspective, this shows how selectivity may be achieved by targeting a non-cancer-specific target, such as histone deacetylases, in the presence of a cancer-specific alteration, such as mutant p53.

Acetylation↗

PubMed2005

Accumulation of hypoxia-inducible factor-1alpha is limited by transcription-dependent depletion.

In the presence of oxygen and iron, hypoxia-inducible factor (HIF-1alpha) is rapidly degraded via the prolyl hydroxylases (PHD)/VHL pathways. Given striking similarities between p53 and HIF-1alpha regulation, we previously suggested that HIF-1 transcriptionally initiates its own degradation and therefore inhibitors of transcription must induce HIF-1alpha. Under normoxia, while inducing p53, inhibitors of transcription did not induce HIF-1alpha. Under hypoxia or low iron (DFX), inhibitors of transcription dramatically super-induced HIF-1alpha. Removal of inhibitors resulted in outburst of the HIF-1-dependent transcription followed by depletion of HIF-1alpha. Although hypoxia/DFX induced PHD3, we excluded the PHD/VHL pathway in the regulation of HIF-1alpha under hypoxia/DFX. The transcription-dependent degradation of HIF-1alpha under hypoxia occurs via the proteasome and is accelerated by protein acetylation. Thus, HIF-1alpha is regulated by two distinct mechanisms. Under normoxia, HIF-1alpha is degraded via the classic PHD/VHL pathway, is expressed at low levels and therefore does not activate the feedback loop. But under hypoxia, HIF-1alpha accumulates and transcriptionally activates its own degradation that is independent from the PHD/VHL pathway.

Cell Hypoxia↗

PubMed2005

Molecular theory of cancer.

The mutation theory of cancer was always confronted by alternative (vitalistic) theories, which insist that cancer (like life itself) cannot be reduced to molecular interactions. In fact, the most fundamental feature of the somatic mutation theory of cancer is that it is a molecular theory, meaning that all the complexity of cancer on any level (e.g., tissue) can be explained on the molecular level. To emphasize the essence of mutation theory, cancer-causing mutation can be defined as any (a) molecular event that is (b) somatically inheritable and (c) selectable (e.g., provides selective advantage in restrictive/carcinogenic conditions). Here I review molecular (somatic mutation) theory and its alternatives and discuss that molecular interactions can completely explain complex tissue phenomena such as benign tumors and stroma initiated tumorigenesis. In addition, molecular theory predicts extragenetic somatic hereditary in cancer (e.g., posttranslational protein modifications that initiate and are supported by positive feedback loops) and also explains the relationship between selection for resistance, hallmarks of cancer and genetic instability. From molecules to cells to the organism, this review discusses how somatically heritable molecular alterations (genetic, epigenetic and extragenetic) alter translation of cellular signals, resulting in resistance to growth inhibition and apoptosis, that is manifested as secondary hallmarks of cancer (metastasis, angiogenesis and immortality) and, finally, as the amazing ability of some cancer cells such as canine transmissible sarcoma to 'live in a wild' like unicellular mammalian species.

Genes, Tumor Suppressor↗

PubMed2005

Selective killing of adriamycin-resistant (G2 checkpoint-deficient and MRP1-expressing) cancer cells by docetaxel.

Chemotherapy of cancer is limited by toxicity to normal cells. Drug resistance further limits the therapy. Here, we investigated selective killing of drug-resistant cancer cells by antagonistic drug combinations, which can spare (because of drug antagonism) normal cells. We used paired cell lines that are resistant to Adriamycin due to either expression of MRP1 or lack of G2 checkpoints. The goal was to selectively kill Adriamycin-resistant cancer cells with Docetaxel (Taxotere), while protecting parental (Adriamycin-sensitive) cells, using cytostatic concentrations of Adriamycin. Taxotere kills cells in mitosis. Therefore, by arresting parental cells in G2, 20 to 40 ng/mL of Adriamycin prevented cell death caused by Taxotere. Also, Adriamycin prevented the effects of Taxotere in normal human lymphocytes. In contrast, Taxotere selectively killed MRP1-expressing leukemia cells, which did not undergo G2 arrest in the presence of Adriamycin. Also, in the presence of Adriamycin, HCT116-p21-/- cancer cells with a defective G2 checkpoint entered mitosis and were selectively killed by Taxotere. Finally, 20 ng/mL of Adriamycin protected normal FDC-P1 hematopoietic cells from Taxotere. Whereas parental cells were protected by Adriamycin, the mitogen-activated protein/extracellular signal-regulated kinase inhibitor PD90598 potentiated the cytotoxic effect of Taxotere selectively in Raf-1-transformed FDC-P1 leukemia cells. We propose a therapeutic strategy to prevent normal cells from entering mitosis while increasing apoptosis selectively in mitotic cancer cells.

Antineoplastic Agents, Phytogenic↗

PubMed2005

Complementation of two mutant p53: implications for loss of heterozygosity in cancer.

Remarkably, a cancer cell rarely possesses two mutant p53 proteins. Instead, mutation of one allele is usually associated with loss of the second p53 allele. Why do not two mutant p53 co-exist? We hypothesize that two different p53 may complement each other, when expressed at equal levels. By titrating trans-deficient and DNA-binding-deficient p53 in cells with mutant p53 and by co-transfecting distinct mutant p53 in p53-null cells, we demonstrated activation of p53-dependent transcription. We suggest that, due to complementation of two mutant p53, cancer cells need to delete the second p53 allele rather than mutate it.

Cell Line, Tumor↗

PubMed2005

Kinase-addiction and bi-phasic sensitivity-resistance of Bcr-Abl- and Raf-1-expressing cells to imatinib and geldanamycin.

By activating anti-apoptotic factors (e.g., Hsp70, Raf-1, Bcl-xL), Bcr-Abl blocks apoptotic pathways at multiple levels, thus rendering leukemia cells resistant to chemotherapeutic agents such as doxorubicin (DOX). In Bcr-Abl-transfected HL60 (HL/Bcr-Abl) cells, procaspase-9 was increased and partially processed. The Bcr-Abl inhibitor imatinib (Gleevec, STI-571) released the apoptotic stream. Also, HL/Bcr-Abl cells were hyper-sensitive to geldanamycin (GA), which depletes Bcr-Abl and Raf-1. Raf-1 and Bcr-Abl-transfected FDC-P1 hematopoietic cells were selectively sensitive to GA and imatinib, respectively. Remarkably, cell clones with high levels of Bcr-Abl that could not be depleted by GA were relatively resistant to both GA and imatinib. GA and flavopiridol sensitized such resistant cells to imatinib. These data suggest bi-phasic sensitivity to mechanism-based therapeutic agents. Although Bcr-Abl renders cells hyper-sensitive, an excess of Bcr-Abl results in resistance (due to the remaining activity). We discuss therapeutic approaches to overcome bi-phasic resistance to mechanisms-based agents.

Antineoplastic Agents↗

PubMed2005

How cancer could be cured by 2015.

As announced by Andrew von Eschenbach, the NCI has set the goal of eliminating suffering and death due to cancer by 2015. Supporting this prediction, I discuss that cancer might be controlled and even cured by combining three potential therapeutic strategies aimed at (i) cancer-specific targets, (ii) universally-vital targets with selective protection of normal cells (the selective combinations) and (iii) tissue-specific targets. Although (i) targeting cancer-specific pathways (e.g., by imatinib and gefitinib) is probable, it alone will not be sufficient to control cancer. This strategy is limited to oncogene (kinase)-dependent cancers and is further limited by therapy-induced resistance and tumor progression. Thus, targeting cancer-specific pathways needs to be complemented by two divergent therapeutic strategies: (ii) selective combinations and (iii) tissue-selective therapy. With selective protection of normal cells (based on cell cycle and apoptosis manipulation), combinations of selective and chemotherapeutic drugs can be effective in most common cancers. Alternatively, tissue-selective therapy can suppress cancer cells in a tissue-selective manner, sparing other tissues. While alone, each therapeutic strategy may cause drug resistance and even tumor progression; these obstacles can be overcome and even exploited by using all three strategies in sequence. And finally, these strategies will benefit from molecular diagnostics and can be used for chemoprevention.

Antineoplastic Agents↗

PubMed2005

Overcoming limitations of natural anticancer drugs by combining with artificial agents.

During a billion years of evolution, living creatures have perfected cytotoxic agents to kill other organisms without killing themselves, thus providing us with antibiotics to kill bacteria without killing eukaryotic (e.g. human) cells. Some natural agents inhibit specifically most vital cellular structures and functions in cancer cells. However, nature was not creating antibiotics for cancer, and natural agents kill cancer cells precisely because they share targets with normal cells. To discriminate between particular cancer cells and normal cells, we can design or select artificial agents that are not necessarily lethal but are aimed either at cancer-specific targets or at dispensable and even unavailable (in cancer cells) targets. Using rational drug combinations, such selective agents can assist natural agents to eradicate cancer cells selectively.

Antineoplastic Agents, Alkylating↗

PubMed2004

The interaction of p53 with replication protein A mediates suppression of homologous recombination.

The tumor suppressor protein p53 is emerging as a central regulator of homologous recombination (HR) processes and DNA replication. P53 may downregulate HR through multiple mechanisms including the reported associations with the Rad51 and Rad54 recombinases, and the BLM and WRN helicases. Here, we investigated whether the interaction of p53 with human replication protein A (RPA) is necessary for the regulation of HR. By employing a plasmid-based HR assay in p53-null H1299 lung carcinoma cells, we studied the HR-suppressing properties of a panel of p53 mutants, which varied in their ability to interact with RPA. Both wild-type p53 and a transactivation-deficient p53 mutant (L22Q/W23S) suppressed HR and prevented RPA binding to ssDNA in vitro and in vivo. Conversely, p53 mutations that specifically disrupt the RPA-binding domain, while not compromising p53 transactivation function (D48H/D49H and W53S/F54S), did not affect HR. Suppression of HR was also not seen with missense mutations in the p53 core domain (His175 and His273), which retained the ability to interact with RPA, suggesting that the disruption of additional binding interactions of p53, for example, with Rad51 or recombination intermediates, also impacts on HR. We hypothesize that sequestration of RPA by p53 at the sites of recombination is one means by which p53 can inhibit HR processes. Our data support and extend the previously formulated 'dual model' of p53's role as guardian of the genome.

Base Sequence↗

PubMed2004

Flavopiridol, an inhibitor of transcription: implications, problems and solutions.

After a decade of exciting promises, the CDK inhibitor flavopiridol has quietly failed in most clinical trials. This review discusses that flavopiridol is a potent inhibitor of global transcription. This explains not only downregulation of numerous proteins, cell cycle arrest and apoptosis but also all pleiotropic and mysterious effects of flavopiridol. Yet, flavopiridol is not just a second actinomycin D. As an inhibitor of transcription with a unique mechanism of action, flavopiridol may have tremendous clinical potentials. This article reviews the molecular and cellular effects of flavopiridol as well as mechanisms of therapeutic and side effects, suggesting its novel clinical applications as a single agent and in drug combinations.

Apoptosis↗

PubMed2004

Paclitaxel induces primary and postmitotic G1 arrest in human arterial smooth muscle cells.

Paclitaxel (PTX), a microtubule-active drug, causes mitotic arrest leading to apoptosis in certain tumor cell lines. Here we investigated the effects of PTX on human arterial smooth muscle cell (SMC) cells. In SMC, PTX caused both (a) primary arrest in G(1) and (b) post-mitotic arrest in G(1). Post-mitotic cells were multinucleated (MN) with either 2C (near-diploid) or 4C (tetraploid) DNA content. At PTX concentrations above 12 ng/ml, MN cells had 4C DNA content consistent with the lack of cytokinesis during abortive mitosis. Treatment with 6-12 ng/ml PTX yielded MN cells with 2C DNA content. Finally, 1-6 ng/ml of PTX, the lowest concentrations that affected cell proliferation, caused G(1) arrest without multinucleation. It is important that PTX did not cause apoptosis in SMC. The absence of apoptosis could be explained by mitotic exit and G(1) arrest as well as by low constitutive levels of caspase expression and by p53 and p21 induction. Thus, following transient mitotic arrest, SMC exit mitosis to form MN cells. These post-mitotic cells were subsequently arrested in G(1) but maintained normal elongated morphology and were viable for at least 21 days. We conclude that in SMC PTX causes post-mitotic cell cycle arrest rather than cell death.

Aorta↗