Kinetic analysis of hyaluronidase activity using a bioactive MRI contrast agent

Enhancing hyaluronidase enzyme activity: Insights from advancement in bovine and ovine testicular hyaluronidase purification

This essay investigates the use of an affinity resin named Capto lentil lectin for the purification of bovine and ovine testicular hyaluronidase. Hyaluronidase, an enzyme that degrades hyaluronic acid, is used widely in medical fields like dermatology, orthopedics, and ophthalmology. The research highlights the importance of optimizing the purification process to increase enzyme activity and purity. A new purification method is proposed, which begins with ammonium sulfate precipitation, followed by Blue Sepharose and Capto Lentil Lectin chromatography. This novel approach significantly increases the yield, purity, and activity of the enzyme. This study paves the way for further research into improving the purification process. The study further discusses challenges in identifying hyaluronidase bands using SDS-PAGE and highlights the necessity of using Western blotting for precise results.

MRI Contrast Agents in Glycobiology

Molecular recognition involving glycoprotein-mediated interactions is ubiquitous in both normal and pathological natural processes. Therefore, visualization of these interactions and the extent of expression of the sugars is a challenge in medical diagnosis, monitoring of therapy, and drug design. Here, we review the literature on the development and validation of probes for magnetic resonance imaging using carbohydrates either as targeting vectors or as a target. Lectins are important targeting vectors for carbohydrate end groups, whereas selectins, the asialoglycoprotein receptor, sialic acid end groups, hyaluronic acid, and glycated serum and hemoglobin are interesting carbohydrate targets.

The Labeling, Visualization, and Quantification of Hyaluronan Distribution in Tumor-Bearing Mouse Using PET and MR Imaging

PURPOSE

Hyaluronan (HA) based biomaterials are widely used as tissue scaffolds, drug formulations, as well as targeting ligands and imaging probes for diagnosis and drug delivery. However, because of the presence of abundant endogenous HA presented in various tissues in vivo, the pharmacokinetic behavior and biodistribution patterns of exogenously administered HAs have not been well characterized.

METHODS

The HA backbone was modified with Diethylenetriamine (DTPA) to enable the chelation of gadolinium (Gd) and aluminum (Al) ions. Series of PET and MR imaging were taken after the injection of HA-DTPA-Gd and HA-DTPA-Al¹⁸F while using¹⁸F-FDG and Magnevist(DTPA-Gd) as controls. The Tomographic images were analyzed and quantified to reveal the distribution and locations of HA in tumor-bearing mice.

RESULTS

The labeled HAs had good stability in plasma. They retained binding affinity towards CD44s on tumor cell surface. The injected HAs distributed widely in various organs, but were found to be cleared quickly except inside tumor tissues where the signals were higher and persisted longer.

CONCLUSION

Medical imaging tools, including MR and PET, can be highly valuable for examining biomaterial distribution non-invasively. The HA tumor accumulation properties may be explored for the development of active targeting drug carriers and molecular probes.

Chemistry of MRI Contrast Agents: Current Challenges and New Frontiers

Tens of millions of contrast-enhanced magnetic resonance imaging (MRI) exams are performed annually around the world. The contrast agents, which improve diagnostic accuracy, are almost exclusively small, hydrophilic gadolinium(III) based chelates. In recent years concerns have arisen surrounding the long-term safety of these compounds, and this has spurred research into alternatives. There has also been a push to develop new molecularly targeted contrast agents or agents that can sense pathological changes in the local environment. This comprehensive review describes the state of the art of clinically approved contrast agents, their mechanism of action, and factors influencing their safety. From there we describe different mechanisms of generating MR image contrast such as relaxation, chemical exchange saturation transfer, and direct detection and the types of molecules that are effective for these purposes. Next we describe efforts to make safer contrast agents either by increasing relaxivity, increasing resistance to metal ion release, or by moving to gadolinium(III)-free alternatives. Finally we survey approaches to make contrast agents more specific for pathology either by direct biochemical targeting or by the design of responsive or activatable contrast agents.

Emerging roles for hyaluronidase in cancer metastasis and therapy

Hyaluronidases are a family of five human enzymes that have been differentially implicated in the progression of many solid tumor types, both clinically and in functional studies. Advances in the past 5 years have clarified many apparent contradictions: (1) by demonstrating that specific hyaluronidases have alternative substrates to hyaluronan (HA) or do not exhibit any enzymatic activity, (2) that high-molecular weight HA polymers elicit signaling effects that are opposite those of the hyaluronidase-digested HA oligomers, and (3) that it is actually the combined overexpression of HA synthesizing enzymes with hyaluronidases that confers tumorigenic potential. This review examines the literature supporting these conclusions and discusses novel mechanisms by which hyaluronidases impact invasive tumor cell processes. In addition, a detailed structural and functional comparison of the hyaluronidases is presented with insights into substrate selectivity and potential for therapeutic targeting. Finally, technological advances in targeting hyaluronidase for tumor imaging and cancer therapy are summarized.

Detecting enzyme activities with exogenous MRI contrast agents

This review focuses on exogenous magnetic resonance imaging (MRI) contrast agents that are responsive to enzyme activity. Enzymes can catalyze a change in water access, rotational tumbling time, the proximity of a (19)F-labeled ligand, the aggregation state, the proton chemical-exchange rate between the agent and water, or the chemical shift of (19)F, (31)P, (13)C or a labile (1)H of an agent, all of which can be used to detect enzyme activity. The variety of agents attests to the creativity in developing enzyme-responsive MRI contrast agents.

Imaging aspects of the tumor stroma with therapeutic implications

Cancer cells rely on extensive support from the stroma in order to survive, proliferate and invade. The tumor stroma is thus an important potential target for anti-cancer therapy. Typical changes in the stroma include a shift from the quiescence promoting-antiangiogenic extracellular matrix to a provisional matrix that promotes invasion and angiogenesis. These changes in the extracellular matrix are induced by changes in the secretion of extracellular matrix proteins and glucose amino glycans, extravasation of plasma proteins from hyperpermeable vessels and release of matrix modifying enzymes resulting in cleavage and cross-linking of matrix macromolecules. These in turn alter the rigidity of the matrix and the exposure and release of cytokines. Changes in matrix rigidity and vessel permeability affect drug delivery and mediate resistance to cytotoxic therapy. These stroma changes are brought about not only by the cancer cells, but also through the action of many cell types that are recruited by tumors including immune cells, fibroblasts and endothelial cells. Within the tumor, these normal host cells are activated resulting in loss of inhibitory and induction of cancer promoting activities. Key to the development of stroma-targeted therapies, selective biomarkers were developed for specific imaging of key aspects of the tumor stroma.

Peritoneal adhesion and angiogenesis in ovarian carcinoma are inversely regulated by hyaluronan: the role of gonadotropins

Ovarian carcinoma is the leading cause of death among gynecologic cancers. Although transformation of the outer ovarian epithelium was linked with ovulation, the disease is significantly more prevalent and severe in postmenopausal women. We postulated that menopause could augment ovarian cancer progression through the effects of gonadotropins on multifocal seeding to the mesothelial layer lining the peritoneum. This seeding is mediated by integrins as well as by CD44 interaction with hyaluronan (HA). Here, we report the effect of gonadotropins on HA synthesis and degradation and on peritoneal adhesion. A significant concentration- and time-dependent induction in expression levels of HA synthases (HASs) and hyaluronidases (Hyals) was observed in vitro on stimulation of human epithelial ovarian carcinoma cells by gonadotropins. Hormonal regulation of HA-mediated adhesion was manifested in vivo as well, by fluorescence microscopy of stained MLS multicellular tumor spheroids. The number of spheroids adhered to the mesothelium of ovariectomized CD-1 nude mice 9.5 hours after intraperitoneal insertion was significantly higher than in nonovariectomized mice. Inhibition of HA synthesis by 6-diazo-5-oxo-1-norleucine (DON) both in spheroids and ovariectomized mice significantly reduced the number of adhered spheroids. Thus, the change in the hormonal environment during menopause assists in HA-dependent adherence of ovarian cancer spheroids onto the peritoneum. However, HA is antiangiogenic and it can significantly suppress tumor progression. Accordingly, angiogenesis of the adhered spheroids was significantly elevated in DON-treated tumors. These results can explain the selective pressure that can lead to simultaneously increased tumor expression of both HASs and Hyals.

Molecular imaging and targeted therapies

Targeted therapeutic and imaging agents are becoming more prevalent, and are used to treat increasingly smaller segments of the patient population. This has lead to dramatic increases in the costs for clinical trials. Biomarkers have great potential to reduce the numbers of patients needed to test novel targeted agents by predicting or identifying non-response early-on and thus enriching the clinical trial population with patients more likely to respond. Biomarkers are characteristics that are objectively measured and evaluated as indicators of normal biological processes, pathogenic processes, or pharmacologic responses to a therapeutic intervention. Biomarkers can be used to predict response to specific therapies, predict response regardless of therapy, or to monitor response once a therapy has begun. In terms of drug development, predictive biomarkers have the greatest impact, as they can be used as inclusion criteria for patient segmentation. Prognostic markers are used routinely in clinical practice but do not provide direction for the use of targeted therapies. Imaging biomarkers have distinct advantages over those that require a biopsy sample in that they are "non-invasive" and can be monitored longitudinally at multiple time points in the same patient. This review will examine the role of functional and molecular imaging in predicting response to specific therapies; will explore the advantages and disadvantages of targeting intracellular or extracellular markers; and will discuss the attributes of useful targets and methods for target identification and validation.

Hyaluronidase activity of human Hyal1 requires active site acidic and tyrosine residues

Hyaluronidases are a family of endolytic glycoside hydrolases that cleave the beta1-4 linkage between N-acetylglucosamine and glucuronic acid in hyaluronan polymers via a substrate-assisted mechanism. In humans, turnover of hyaluronan by this enzyme family is critical for normal extracellular matrix remodeling. However, elevated expression of the Hyal1 isozyme accelerates tumor growth and metastatic progression. In this study, we used structural information, site-directed mutagenesis, and steady state enzyme kinetics to probe molecular determinants of human Hyal1 function. Mutagenesis of active site residues Glu(131) and Tyr(247) to Gln and Phe, respectively, eliminated activity at all hyaluronan concentrations (to 125 microm or 2.5 mg/ml). Conservative mutagenesis of Asp(129) and Tyr(202) significantly impaired catalysis by increases of 5- and 10-fold in apparent K(m) and reductions in V(max) of 95 and 50%, respectively. Tyr(247) and Asp(129) are required for stabilization of the catalytic nucleophile, which arises as a resonance intermediate of N-acetylglucosamine on the substrate. Glu(131) is a likely proton donor for the hydroxyl leaving group. Tyr(202) is a substrate binding determinant. General disulfide reduction had no effect on activity in solution, but enzymatic deglycosylation reduced Hyal1 activity in a time-dependent fashion. Mutagenesis identified Asn(350) glycosylation as the requisite modification. Deletion of the C-terminal epidermal growth factor-like domain, in which Asn(350) is located, also eliminated activity, irrespective of glycosylation. Collectively, these studies define key components of Hyal1 active site catalysis, and structural factors critical for stability. Such detailed understanding will allow rational design of enzyme modulators.

Design and characterization of a new irreversible responsive PARACEST MRI contrast agent that detects nitric oxide

Irreversible responsive PARAmagnetic Chemical Exchange Saturation Transfer (PARACEST) MRI contrast agents constitute a new type of agent for molecular imaging. To investigate the utility of this approach, a novel PARACEST MRI contrast agent, Yb(III)-(1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid)-orthoaminoanilide (Yb-DO3A-oAA), was developed that detects nitric oxide (NO). The agent exhibited two CEST effects at -11 ppm and +8 ppm, which were assigned to chemical exchange from amide and amine functional groups, respectively. The effects of pH, temperature, and concentration were investigated to characterize the complex and to optimize PARACEST detection. This responsive PARACEST MRI contrast agent incurred an irreversible covalent change in the presence of NO and O(2), which caused an irreversible disappearance of both PARACEST effects from MR images. The NO-dependent response of a relaxivity-based MRI contrast agent, Gd-DO3A-oAA, was investigated for comparison. This report highlights the advantages of irreversible MRI contrast agents, demonstrates that large changes in PARACEST can be used to create a highly responsive agent, and indicates challenges that must be overcome to apply this type of contrast agent to in vivo biomedical applications in molecular imaging.