Dimitris Stellas

A Critical Role for HSP90 in Cancer Cell Invasion Involves Interaction with the Extracellular Domain of HER-2

HSP90 is a ubiquitously expressed molecular chaperone that controls the folding, assembly, intracellular disposition, and proteolytic turnover of many proteins, most of which are involved in signal transduction processes. Recently, a surface form of HSP90 has been identified and associated with cell migration events. In this paper, we explore the interaction of surface HSP90 with HER-2, a receptor-like glycoprotein and member of the ErbB family of receptor tyrosine kinases that play central roles in cellular proliferation, differentiation, and migration as well as in cancer progress. The involvement of HSP90 in the regulation of HER-2 has been attributed so far to receptor stabilization via interaction with its cytoplasmic kinase domain. Here we present evidence, using glutathione S-transferase pull-down and transfection assays, for a novel interaction between surface HSP90 and the extracellular domain of HER-2. Specific disruption of this interaction using mAb 4C5, a function-blocking monoclonal antibody against HSP90, inhibits cell invasion accompanied by altered actin dynamics in human breast cancer cells under ligand stimulation conditions with heregulin. Additionally, disruption of surface HSP90/HER-2 interaction leads to inhibition of heregulin-induced HER-2-HER-3 heterodimer formation, reduced HER-2 phosphorylation, and impaired downstream kinase signaling. Interestingly, this disruption does not affect HER-2 internalization. Our data suggest that surface HSP90 is involved in heregulin-induced HER-2 activation and signaling, leading to cytoskeletal rearrangement, essential for cell invasion.

VEGF Signals through ATF6 and PERK to Promote Endothelial Cell Survival and Angiogenesis in the Absence of ER Stress

Accumulation of unfolded proteins in the endoplasmic reticulum (ER) initiates IRE1α, ATF6, and PERK cascades, leading to a transcriptional/translational response known as unfolded protein response (UPR). Here we show that VEGF activates UPR mediators through a PLCγ-mediated crosstalk with the mTORC1 complex without accumulation of unfolded proteins in the ER. Activation of ATF6 and PERK contributes to the survival effect of VEGF on endothelial cells (ECs) by positively regulating mTORC2-mediated phosphorylation of AKT on Ser473, which is required for full activity of AKT. Low levels of CHOP allow ECs to evade the proapoptotic effect of this UPR product. Depletion of PLCγ, ATF6, or eIF2α dramatically inhibited VEGF-induced vascularization in mouse Matrigel plugs, suggesting that the ER and the UPR machinery constitute components of the VEGF signaling circuit that regulates EC survival and angiogenesis, extending their role beyond adaptation to ER stress.

Monoclonal Antibody 4C5 Immunostains Human Melanomas and Inhibits Melanoma Cell Invasion and Metastasis

Purpose: Tumor cell metastasis constitutes a major problem in the treatment of cancer. Because the cure rate of metastatic tumors is very low, new therapeutic approaches are needed. Heat shock protein 90 (HSP90) is a molecular chaperone that is recognized as a new target for the treatment of cancer. Here, we examine the value of a monoclonal antibody (mAb) against HSP90, mAb 4C5, as a potential marker in malignant melanomas. Moreover, we investigate the possibility to use mAb 4C5 as an inhibitor of melanoma cell invasion and metastasis. Experimental Design: Paraffin blocks of formalin-fixed human melanoma tumor tissues were used to prepare tissue microarrays. The B16 F10 melanoma cell line was used in all the in vitro experiments. To assess melanoma cell invasion, the wound-healing assay and the Matrigel invasion assay were applied. To evaluate the effect of mAb 4C5 on tumor metastasis, we used an experimental model of metastatic melanoma. Results: Immunohistochemical studies done on a panel of malignant melanomas showed positive immunostaining with mAb 4C5 in all cases. mAb 4C5 inhibits B16 F10 cell invasion by binding to surface HSP90 because it is not internalized. mAb 4C5 significantly inhibits melanoma metastasis in C57BL/6 mice inoculated with B16 F10 cells. Conclusions: mAb 4C5 could be potentially used as a novel specific marker for malignant melanomas. mAb 4C5 inhibits melanoma cell invasion in vitro by binding to cell surface HSP90 expressed on B16 F10 melanoma cells. Finally, this antibody significantly inhibits melanoma metastasis, thus rendering it a potential therapeutic agent for the treatment of cancer metastasis.

Therapeutic Effects of an Anti-Myc Drug on Mouse Pancreatic Cancer

BACKGROUND Pancreatic ductal adenocarcinoma (PDA) is frequently driven by oncogenic KRAS(KRAS*) mutations. We developed a mouse model of KRAS*-induced PDA and, based on genetic results demonstrating that KRAS* tumorigenicity depends on Myc activity, we evaluated the therapeutic potential of an orally administered anti-Myc drug. METHODS We tested the efficacy of Mycro3, a small-molecule inhibitor of Myc-Max dimerization, in the treatment of mouse PDA (n = 9) and also of xenografts of human pancreatic cancer cell lines (NOD/SCID mice, n = 3-12). Tumor responses to the drug were evaluated by PET/CT imaging, and histological, immunohistochemical, molecular and microarray analyses. The Students t test was used for differences between groups. All statistical tests were two-sided. RESULTS Transgenic overexpression of KRAS* in the pancreas resulted in pancreatic intraepithelial neoplasia in two-week old mice, which developed invasive PDA a week later and became moribund at one month. However, this aggressive form of pancreatic tumorigenesis was effectively prevented by genetic ablation of Myc specifically in the pancreas. We then treated moribund, PDA-bearing mice daily with the Mycro3 Myc-inhibitor. The mice survived until killed at two months. PET/CT image analysis (n = 5) demonstrated marked shrinkage of PDA, while immunohistochemical analyses showed an increase in cancer cell apoptosis and reduction in cell proliferation (treated/untreated proliferation index ratio: 0.29, P < .001, n = 3, each group). Tumor growth was also drastically attenuated in Mycro3-treated NOD/SCID mice (n = 12) carrying orthotopic or heterotopic xenografts of human pancreatic cancer cells (eg, mean tumor weight ± SD of treated heterotopic xenografts vs vehicle-treated controls: 15.2±5.8 mg vs 230.2±43.9 mg, P < .001). CONCLUSION These results provide strong justification for eventual clinical evaluation of anti-Myc drugs as potential chemotherapeutic agents for the treatment of PDA.

Inhibiting matrix metalloproteinases, an old story with new potentials for cancer treatment.

Five decades of extensive research have passed since the description for the first time of the existence of an enzyme, which had the ability to degrade collagen during the metamorphosis of tadpoles. In fact, during these years, a large family of enzymes possessing the unique ability of degrading the extra cellular matrix (ECM) has been discovered. These enzymes are widely known as Matrix Metalloproteinases (MMPs) and it is noteworthy that many members of this family are directly linked to several human diseases such as arthritis and cancer. Moreover, due to the critical role of certain members of MMPs in cancer invasion and metastasis, great efforts have been made in order to find new inhibitory compounds against these MMPs. In this work we attempt to summarize the current status of the intervention strategies against MMPs, using inhibitory compounds that could block the activation of MMPs directly or indirectly. Furthermore we will try to shed light towards new potential strategies of MMP inhibitors using monoclonal antibodies.

Defective synaptic connectivity and axonal neuropathology in a human iPSC-based model of familial Parkinson’s disease

Significance Parkinson’s disease (PD) is an incurable neurodegenerative disorder characterized by motor and nonmotor deficits, including cognitive decline and dementia. The protein αSyn is strongly associated with PD pathogenesis, whereas αSyn mutations, such as p.A53T, cause familial forms of PD. Animal models are crucial for understanding PD pathogenesis, but there are limitations in the extent to which these models reproduce faithfully the human disease. Cell-reprogramming technologies allow the generation of human neurons from patients with PD, but it has proven difficult to identify cellular pathologies in induced pluripotent stem cell–derived neurons. In this study, we created a robust p.A53T patient–derived model of PD that captures disease-related phenotypes under basal conditions, thus providing a unique system for studies of disease mechanisms and development of therapeutics. α-Synuclein (αSyn) is the major gene linked to sporadic Parkinson’s disease (PD), whereas the G209A (p.A53T) αSyn mutation causes a familial form of PD characterized by early onset and a generally severe phenotype, including nonmotor manifestations. Here we generated de novo induced pluripotent stem cells (iPSCs) from patients harboring the p.A53T mutation and developed a robust model that captures PD pathogenic processes under basal conditions. iPSC-derived mutant neurons displayed novel disease-relevant phenotypes, including protein aggregation, compromised neuritic outgrowth, and contorted or fragmented axons with swollen varicosities containing αSyn and Tau. The identified neuropathological features closely resembled those in brains of p.A53T patients. Small molecules targeting αSyn reverted the degenerative phenotype under both basal and induced stress conditions, indicating a treatment strategy for PD and other synucleinopathies. Furthermore, mutant neurons showed disrupted synaptic connectivity and widespread transcriptional alterations in genes involved in synaptic signaling, a number of which have been previously linked to mental disorders, raising intriguing implications for potentially converging disease mechanisms.

Two novel compounds of vanadium and molybdenum with carnitine exhibiting potential pharmacological use

The reaction of sodium orthovanadate with carnitine hydrochloride molecule results in the precipitation of decavanadate compound of carnitine whereas the reaction of metallic molybdenum with hydrogen peroxide and carnitine results in the peroxo-molybdenum complex of carnitine. The decavanadate compound as well as the molybdenum complex of carnitine have been characterized by means of elemental analysis, IR, electronic spectra, (1)H NMR, 2D-COSY-NMR (=correlation spectroscopy) and thermo-gravimetric analysis (TGA). In addition decavanadate compound of carnitine was fully characterized by X-ray crystallography. The analytical data were in good agreement with the empirical formulae of both, decavanadate compound and molybdenum complex. The two compounds were also evaluated for cell toxicity and their anticancer activity by the MTT(3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide)-based assay method, using primary cells and tumor cell lines of both human and murine origins and the results show that compound 1 shows an increased biological activity in comparison with compound 2. Moreover using confocal microscopy and antibodies against cleaved caspase 3 we further analyzed the cell toxicity and we conclude that the apoptotic pathway is triggered efficiently with tumor specificity by compound 1 and not by compound 2.

Chimeric lipid/block copolymer nanovesicles: Physico-chemical and bio-compatibility evaluation

Chimeric systems are mixed nanovectors composed by different in nature materials and exhibit new functionalities and properties. The particular chimeric nanovectors, formed by the co-assembly of low and high molecular weight amphiphiles, have the potential to be utilized as drug delivery platforms. We have utilized two lipids, l-α-phosphatidylcholine, hydrogenated (Soy)(HSPC) and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), and a poly(oligoethylene glycol acrylate)-b-poly(lauryl acrylate) (POEGA-PLA) block copolymer, at different molar ratios, in aqueous media. Light scattering, differential scanning calorimetry (DSC) and imaging techniques (cryo-TEM, AFM) were employed in order to elucidate the structure and properties of the nanostructures, as well as the cooperativity between the components. DSC experiments showed considerable interaction of the block copolymer with the lipid bilayers and suggested an inhomogeneous distribution of the copolymer chains and lateral phase separation of the components. Vesicle formation was observed in most cases by cryo-TEM with a chimeric membrane exhibiting kinks, in accordance with DSC data. A series of biocompatibility experiments indicated good in vitro biological stability and low cytotoxicity in vivo of the novel nanocarriers. Finally, ibuprofen (IBU) was used as model drug in order to study the loading and the release properties of the prepared chimeric lipid/block copolymer vesicles.

Initial in vitro and in vivo assessment of Au@DTDTPA-RGD nanoparticles for Gd-MRI and 68Ga-PET dual modality imaging

Gadolinium chelate coated gold nanoparticles (Au@DTDTPA) can be applied as contrast agents for both in vivo X-ray and magnetic resonance imaging. In this work, our aim was to radiolabel and evaluate this gold nanoparticle with Ga-68, in order to produce a dual modality PET/MRI imaging probe. For a typical preparation of 68Ga-labeled nanoparticles, the Au@DTDTPA nanoparticles (Au@DTDTPA/Au@DTDTPA-RGD) were mixed with ammonium acetate buffer, pH 5 and 40 MBq of 68Ga eluate. The mixture was then incubated for 45 min at 65 AaC. Radiochemical purity was determined by ITLC. In vitro stability of both radiolabeled species was assessed in saline and serum. In vitro cell binding experiments were performed on integrin ανβ3 receptor-positive U87MG cancer cells. Non-specific Au@DTDTPA was used for comparison. Ex vivo biodistribution studies and in vivo PET and MRI imaging studies in U87MG tumor-bearing SCID mice followed. The Au@DTDTPA nanoparticles were labeled with Gallium-68 at high radiochemical yield (>95%) and were stable at RT, and in the presence of serum, for up to 3 h. The cell binding assay on U87MG glioma cells proved that 68Ga-cRGD-Au@DTDTPA had specific recognition for these cells. Biodistribution studies in U87MG tumor-bearing SCID mice showed that the tumor to muscle ratio increased from 1 to 2 h p.i. (3,71 ± 0.22 and 4,69 ± 0.09 respectively), showing a clear differentiation between the affected and the non-affected tissue. The acquired PET and MRI images were in accordance to the ex vivo biodistribution results. The preliminary results of this study warrant the need for further development of Au@DTDTPA nanoparticles radiolabeled with Ga-68, as possible dual-modality PET/MRI imaging agents.

Targeting highly expressed extracellular HSP90 in breast cancer stem cells inhibits tumor growth in vitro and in vivo.

ABSTRACT Breast cancer stem cells (BCSC) have been identified in breast carcinoma as CD44+/CD24−/low cells, which display tumorigenic activity and have the ability to self-renew, differentiate and metastasize. Previous studies showed that extracellular HSP90 (eHSP90) participates in the invasion and metastatic processes of various cancers including breast cancer. Here, we show for the first time that eHSP90 is over-expressed in mammosphere cultures that are derived from the MDA-MB-231, MDA-MB-453 and MCF-7 breast cancer cell lines. These mammospheres are highly enriched in cells of the CD44+/CD24−/low BCSC phenotype and additionally show high expression of the BCSC markers CD49f and Sox2. Thus our results indicate that eHSP90 represents a potential novel BCSC marker. Moreover, we present evidence that eHSP90 is functionally involved in BCSC activity in vitro and in vivo. Selective neutralization of eHSP90, using the monoclonal antibody mAb 4C5, has the capacity to inhibit stem cell activity in vitro because the formation of mammosphere-derived colonies is dramatically reduced in its presence. In vivo, the treatment of mice with mAb4C5 using a prophylactic protocol, significantly inhibited the primary growth of MDA-MB-231 and mammosphere-derived tumors. More importantly, administration of this antibody in a therapeutic protocol caused a statistically significant regression of established tumors derived from MDA-MB-231 originating mammospheres. Tumor regression was even greater when mAb 4C5 was administered in combination with paclitaxel. Overall, our findings implicate eHSP90 as a potential novel BCSC biomarker. Moreover they show that eHSP90 participates in BCSC-derived primary tumor growth. Finally, we provide additional support for the possible therapeutic value of mAb4C5 in the treatment of breast cancer.