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Biomedical subjects

Michael Blank

Publications and source records attributed to Michael Blank.

11 recordsLinked to original sources
PubMed2006

Condensin I recruitment and uneven chromatin condensation precede mitotic cell death in response to DNA damage.

Mitotic cell death (MCD) is a prominent but poorly defined form of death that stems from aberrant mitosis. One of the early steps in MCD is premature mitosis and uneven chromatin condensation (UCC). The mechanism underlying this phenomenon is currently unknown. In this study, we show that DNA damage in cells with a compromised p53-mediated G2/M checkpoint triggers the unscheduled activation of cyclin-dependent kinase 1 (Cdk1), activation and chromatin loading of the condensin I complex, and UCC followed by the appearance of multimicronucleated cells, which is evidence of MCD. We demonstrate that these processes engage some of the players of normal mitotic chromatin packaging but not those that drive the apoptotic chromatin condensation. Our findings establish a link between the induction of DNA damage and mitotic abnormalities (UCC) through the unscheduled activation of Cdk1 and recruitment of condensin I. These results demonstrate a clear distinction between the mechanisms that drive MCD-associated and apoptosis-related chromatin condensation and provide mechanistic insights and new readouts for a major cell death process in treated tumors.

Adenosine Triphosphatases↗
PubMed2005

Aptamers--basic research, drug development, and clinical applications.

Since its discovery in the early 1990s, aptamer technology has progressed tremendously. Automated selection procedures now allow rapid identification of DNA and RNA sequences that can target a broad range of extra- and intracellular proteins with nanomolar affinities and high specificities. The unique binding properties of nucleic acids, which are amenable to various modifications, make aptamers perfectly suitable for different areas of biotechnology. Moreover, the approval of an aptamer for vascular endothelial growth factor by the US Food and Drug Administration highlights the potential of aptamers for therapeutic applications. This review summarizes recent developments and demonstrates that aptamers are valuable tools for diagnostics, purification processes, target validation, drug discovery, and even therapeutic approaches.

Animals↗
PubMed2005

Anti-angiogenic activities of hypericin in vivo: potential for ophthalmologic applications.

Hypericin, a perihydroxylated dianthraquinone is shown here to be a highly potent inhibitor of angiogenesis in several ocular models examined in rat eyes. Extensive angiogenesis induced in the cornea and iris by intra-ocular administration of FGF-2 was effectively inhibited by a minimum of four dose regimens of hypericin (2 mg/kg) administered via the intraperitoneal route at 48 h intervals. Maximal inhibition was achieved when animal treatment with hypericin was initiated 48 h prior to inoculation of FGF-2. The molecular basis for the hypericin-mediated inhibition of angiogenesis in the anterior eye compartment appears to involve several sites in the cascade leading to angiogenesis. We show that the activating phosphorylation of extracellular signal-regulated MAP kinases (ERK1/2) is inhibited by hypericin in human retinal pigment epithelial cells and in EA.hy926 cells, an endothelial hybridoma expressing endothelial cell properties. ERK1/2 activity is required for the transactivation of hypoxia-inducible factor 1 alpha (HIF-1alpha) and in VEGF-induced blood vessel sprouting. MT1-MMP activity in human microvascular endothelial cells was also inhibited. The findings identify hypericin as a potentially useful agent in the treatment of ophthalmic neovascularization pathogeneses.

Angiogenesis Inducing Agents↗
PubMed2005

Aptamers as tools for target validation.

Synthetic nucleic acid ligands, called aptamers, bind to protein targets with high specificity and affinity. They are very potent inhibitors of protein function and their application can greatly enhance the process of target validation and drug development. An important benefit of this technology is the recent development of rapidly identifying these sophisticated ligands for almost any target molecule in multi-parallel, automated workstations. The aptamer technology is thus well-suited to addressing the growing demand for high-throughput analysis and functional validation of potential drug targets. Numerous examples have shown the potency of aptamers in inhibiting the function of proteins in cell culture and in vivo models. The technology is complementary to genetic knockout or siRNA approaches as it provides highly valuable information at the proteomic level. In addition, the aptamer technology has recently been extended to developing aptamer drugs and identifying functionally equivalent small molecule leads.

Animals↗
PubMed2005

Competitive quenching: a possible novel approach in protecting RPE cells from damage during PDT.

PURPOSE: The purpose of this study is to demonstrate feasibility of using our novel concept, termed competitive quenching, for protecting the choroidal extravascular compartment and retinal pigment epithelium (RPE) from verteporfin (VP)-induced phototoxicity using hypericin. Furthermore, we aim to achieve partitioning of the quencher, hypericin, in the extravascular space and VP within the microvascular compartment of the chorio-retinal complex in vivo. METHODS: We protect RPE cells from damage inflicted by photoactivated VP by introducing hypericin into these cells prior to photosensitization to quench the photosensitizing activity of VP. Cell protection levels were measured by MTT and Hemacolor viability assays. Wavelength range used for VP photoexcitation (700 +/- 40 nm) excludes the absorption range of hypericin, preventing the latter from photoactivation. Pharmacokinetic conditions, in which hypericin spreads throughout the choroidal and retinal extravascular space while VP is confined to the vasculature, are delineated using double-fluorescence imaging. RESULTS: Cell viability increased 3- to 5-fold when 10-20 microM hypericin were present in RPE cells during photosensitization with 0.1-0.5 microM VP. VP fluorescence intensity was unchanged by the presence of hypericin in the cells. Hypericin administered intravenously to rats was confined to the choroidal vasculature after 15 min to 2 hr. Subsequently, hypericin partitioned to the choroidal and retinal extravascular space. VP administered at this time was confined to the microvasculature. CONCLUSIONS: RPE and choroid may potentially be protected by compartmentalizing hypericin to the extravascular compartment while VP administered shortly before photosensitization is confined to the microvasculature. Adverse photodynamic therapy (PDT) damage to choroidal tissues adjacent to neovasculature targeted for photoablation have the potential of being prevented by competitive quenching with hypericin.

Animals↗
PubMed2004

Antimetastatic activity of the photodynamic agent hypericin in the dark.

A unique property of the photodynamic signal transduction inhibitor hypericin (HY) is high functionality in the dark, which has been shown to result in portfolio of anticancer activities both in vitro and in vivo. Here we show that treatment with HY significantly reduces growth rate of metastases in 2 murine models: breast adenocarcinoma (DA3) and squamous cell carcinoma (SQ2). Focus on metastases was achieved by resection of primary tumors at stages in which micrometastases exist in lungs. Long-term animal survival in DA3 tumor-excised groups increased from 15.6% in controls to 34.5% following supplementary treatment with HY. In mice bearing SQ2 tumor metastases, therapy with HY increased animal survival from 17.7% in controls to 46.1%. Using Laser-induced fluorescence and multipixel spectral image analyses, we demonstrate that HY has a high tendency to accumulate in primary and metastatic tumors; HY content in lungs bearing metastases was approximately 2-fold higher than in the lungs of healthy animals. The tendency of HY to preferentially concentrate in lung metastases, combined with its potent antiproliferative activities, may render HY as a useful supplementary modality in the treatment of metastatic cancer irrespective of photoactivation.

Animals↗
PubMed2003

Enhanced ubiquitinylation of heat shock protein 90 as a potential mechanism for mitotic cell death in cancer cells induced with hypericin.

A unique property of the photodynamic signal transduction inhibitor hypericin is functionality in the dark. We show in tumor cells that hypericin targets the heat shock protein (Hsp) 90 chaperone but not Hsp70 (Hsc70) to enhanced ubiquitinylation. As a consequence Hsp90 chaperone functionality is abrogated and the client proteins, mutant p53, Cdk4, Raf-1, and Plk, are displaced from complexes with Hsp90, destabilized, and degraded via a proteasome-independent pathway. Decline in Raf-1 prevents downstream activation of extracellular signal-regulated kinase 1/2 kinases, the Ras/Raf pathway is inhibited, and tumor cell proliferation is arrested. The cells exhibit multiple aberrations including retardation at G(2)-M, increased cell volume, and multinucleation, all of which are hallmarks of mitotic cell death. The studies demonstrate that ubiquitinylation of Hsp90 inactivates the chaperone, destabilizes the plethora of client proteins, and creates deficiencies in multiple unrelated cellular functions. This combination constitutes a mechanism by which hypericin generates mitotic cell death in cancer cells.

Animals↗
PubMed2002

Effect of geographic migration on SMI prevalence estimates.

The prevalence of serious mental illness (SMI) varies by the socioeconomic characteristics of communities. This variation is presumed to be due to the differential incidence of disorders caused by adverse social factors (social causation) and differential geographic migration (social selection and drift). The objective of this study was to measure the geographic migration patterns of adults treated for SMI. A sample of 11,725 adults with three or more psychiatric hospital admissions between July 1978 and November 1992 was drawn from inpatient records. At least one third migrated to different counties between first and last admission. Migration rates were higher for Whites than for African Americans and higher for unmarried than for married patients. There were no significant differences in migration rates by gender or mental disorder. Patient migration did not parallel shifts in the general population. Patient migration was generally toward medium-size, low-income urban counties with relatively declining general populations, and movement was away from both the most rural and the largest urban counties. Public needs assessments and resource allocation policies may understate the need in communities with net SMI out-migration and overstate endemic need where there is net in-migration. In the long term, these same policies may induce migration through resource allocation decisions.

Adolescent↗
PubMed2002

Wavelength-dependent properties of photodynamic therapy using hypericin in vitro and in an animal model.

Wavelength effects in photodynamic therapy (PDT) with hypericin (HY) were examined in a C26 colon carcinoma model both in vitro and in vivo. Irradiation of HY-sensitized cells in vitro with either 550 or 590 nm caused the loss of cell viability in a drug- and light-dose-dependent manner. The calculated ratio of HY-based PDT (HY-PDT) efficiencies at these two wavelengths was found to correlate with the numerical ratio of absorbed photons at each wavelength. In vivo irradiation of C26-derived tumors, 6 h after intraperitoneal administration of HY (5 mg/kg), caused extensive vascular damage and tumor necrosis. The depth of tumor necrosis (d) was more pronounced at 590 than at 550 nm and increased when the light dose was raised from 60 to 120 J/cm2. The maximal depths of tumor necrosis (at 120 J/cm2) were 7.5+/-1.5 mm at 550 nm and 9.9+/-0.8 mm at 590 nm. Both values are rather high in view of the limited penetration of green-yellow light into the tissue. Moreover, the depth ratio, d590/d550 = 1.3 (P < 0.001), is smaller than expected considering the 2.2-fold lower HY absorbance and the 1.7-fold lower tissue penetration of radiation at 550 than at 590 nm. This finding indicates that in vivo the depth at which HY-PDT elicits tumor necrosis is not only determined by photophysical considerations (light penetration, number of absorbed photons) but is also influenced significantly by other mechanisms such as vascular effects. Therefore, despite the relatively short-wavelength peaks of absorption, our observations suggest that HY is an effective photodynamic agent that can be useful in the treatment of tumors with depths in the range of 1 cm.

Animals↗
PubMedDate not supplied

Nucleic acid aptamers in human viral disease.

Nucleic acid aptamers are short, single-stranded oligonucleotides or their modified analogues which avidly and specifically interact with targeted ligands through their 3-dimensional structure. Aptamers can be selected out of a large combinatorial oligonucleotide library through an in vitro evolution process termed SELEX. Since 1990, a wide variety of aptamers targeted to ligands ranging from small molecules to complex mixtures have been isolated. Most selected aptamers have shown high specificity to and affinity for their ligands and are potential detection and/or diagnostic reagents. Furthermore, some aptamers specifically inhibit biological functions of targeted proteins, resulting in potent therapeutic candidates in disease models. Some recent advances to increase the stability of aptamers, extend their in vivo circulation time and their in vivo expression have pushed aptamers closer to therapeutic applications. This review presents recent developments in the field of aptamer research and focuses on their applications to human viral diseases, particularly HIV induced diseases.

HIV Infections↗