New liposome-radionuclide-chelate combination for tumor targeting and rapid healthy tissue clearance

Radionuclide imaging and therapy are promising methods for controlling systemic cancers; however, their clinical application has been limited by excessive radionuclide accumulation in healthy tissues. To minimize radionuclide accumulation in non-cancerous tissues while ensuring sufficient build up in tumors, we aimed to develop a method that controlled the in vivo dynamics of radionuclides post-administration. To this end, we describe a novel strategy that combines liposomes, a potent carrier system for drug delivery, with unique radionuclide-ligand complexes based on 111In-ethylenedicysteine. Conventional 111In-ligand-complexes-carrying liposomes delivered substantial amounts of radionuclides to tumors; however, they also accumulated in the liver and spleen. In contrast, 111In-ethylenedicysteine-carrying liposomes greatly reduced non-specific accumulation, while being retained selectively at high doses within tumors. Liposomes were rapidly broken down in the liver, releasing encapsulated 111In-ligand complexes. Among the chelates used, only 111In-ethylenedicysteine could escape from the liver and be excreted in the urine. Instead, most liposomes remained intact in tumors, retaining the radionuclide-ligand complexes within them. Therefore, high tumor accumulation was obtained regardless of the type of 111In-ligand complexes in the liposomes. In vivo single photon emission computed tomography/computed tomography imaging with 111In-ethylenedicysteine-carrying liposomes accurately revealed tumor-selective radionuclide retention with little background. Hence, our new strategy could greatly enhance tumor-to-healthy tissue ratios, improve diagnostic imaging, boost therapeutic efficacy, reduce toxicity to healthy tissues, and facilitate radionuclide imaging and therapy.

Novel method for screening functional antibody with comprehensive analysis of its immunoliposome

Development of monoclonal antibody is critical for targeted drug delivery because its characteristics determine improved therapeutic efficacy and reduced side-effect. Antibody therapeutics target surface molecules; hence, internalization is desired for drug delivery. As an antibody–drug conjugate, a critical parameter is drug-to-antibody ratio wherein the quantity of drugs attached to the antibody influences the antibody structure, stability, and efficacy. Here, we established a cell-based immunotoxin screening system to facilitate the isolation of functional antibodies with internalization capacities, and discovered an anti-human CD71 monoclonal antibody. To overcome the limitation of drug-to-antibody ratio, we employed the encapsulation capacity of liposome, and developed anti-CD71 antibody-conjugated liposome that demonstrated antigen–antibody dependent cellular uptake when its synthesis was optimized. Furthermore, anti-CD71 antibody-conjugated liposome encapsulating doxorubicin demonstrated antigen–antibody dependent cytotoxicity. In summary, this study demonstrates the powerful pipeline to discover novel functional antibodies, and the optimal method to synthesize immunoliposomes. This versatile technology offers a rapid and direct approach to generate antibodies suitable for drug delivery modalities.

Functional Characterization of VEGF- and FGF-induced Tumor Blood Vessel Models in Human Cancer Xenografts

BACKGROUND/AIM

Tumor angiogenesis induced by vascular endothelial growth factor (VEGF) and/or fibroblast growth factor (FGF) plays an important role in tumor growth, metastasis, and drug resistance. However, the characteristics of tumor vessels derived from these angiogenic factors have not been fully explored.

MATERIALS AND METHODS

To functionally examine tumor vessels, we developed in vivo VEGF- and FGF-induced tumor blood vessel models. We performed immunohistochemistry and Hoechst perfusion assay to elucidate histopathological differences between the derived tumor vessels. To kinetically understand tumor perfusion, we employed radiolabeled PEGylated liposomes.

RESULTS

While tumor vessel density was substantially increased by enhanced expression levels of VEGF and FGF, permeability of VEGF-driven tumor vessels was significantly higher than that of FGF-driven ones, the latter demonstrating an increased number of pericyte-covered vessels. Accordingly, we observed an increased tumor retention of the PEGylated liposomes in the VEGF-driven tumor.

CONCLUSION

Our in vivo models of tumor vessel demonstrate the frequency of pericyte coverage and tumor perfusion levels as major functional differences between VEGF- and FGF-driven tumor vessels.

Antitumor effects of eribulin depend on modulation of the tumor microenvironment by vascular remodeling in mouse models

We previously reported that eribulin mesylate (eribulin), a tubulin‐binding drug (TBD), could remodel tumor vasculature (i.e. increase tumor vessels and perfusion) in human breast cancer xenograft models. However, the role of this vascular remodeling in antitumor effects is not fully understood. Here, we investigated the effects of eribulin‐induced vascular remodeling on antitumor activities in multiple human cancer xenograft models. Microvessel densities (MVD) were evaluated by immunohistochemistry (CD31 staining), and antitumor effects were examined in 10 human cancer xenograft models. Eribulin significantly increased MVD compared to the controls in six out of 10 models with a correlation between enhanced MVD levels and antitumor effects (R² = 0.54). Because of increased MVD, we next used radiolabeled liposomes to examine whether eribulin treatment would result in increased tumoral accumulation levels of these macromolecules and, indeed, we found that eribulin, unlike vinorelbine (another TBD) enhanced them. As eribulin increased accumulation of radiolabeled liposomes, we postulated that this treatment might enhance the antitumor effect of Doxil (a liposomal anticancer agent) and facilitate recruitment of immune cells into the tumor. As expected, eribulin enhanced antitumor activity of Doxil in a post‐erlotinib treatment H1650 (PE‐H1650) xenograft model. Furthermore, infiltrating CD11b‐positive immune cells were significantly increased in multiple eribulin‐treated xenografted tumors, and natural killer (NK) cell depletion reduced the antitumor effects of eribulin. These findings suggest a contribution of the immune cells for antitumor activities of eribulin. Taken together, our results suggest that vascular remodeling induced by eribulin acts as a microenvironment modulator and, consequently, this alteration enhanced the antitumor effects of eribulin.

Abstract 5927: Eribulin modulates tumor microenvironment through vascular remodeling for antitumor effect in multiple mouse xenograft models

Eribulin mesilate (Eribulin), a first-in-class halichondrin B-based microtubule dynamics inhibitor, has been reported to remodel tumor vasculature (i.e., improvement of tumor vessels and perfusion) in human breast cancer xenograft models; however, the role of this vascular remodeling in anti-tumor effects is not fully understood. Here, we investigated the effects of eribulin-induced vascular remodeling on anti-tumor activities in multiple human cancer xenograft models. Microvessel densities (MVDs) were evaluated by immunohistochemistry (CD31 staining), and anti-tumor effects were examined in 10 human cancer xenograft models treated with eribulin. Eribulin treatment significantly increased MVDs compared to the corresponding control groups in 7 out of 10 models with a correlation between enhanced MVD levels and anti-tumor effects (R2=0.55). Because of observed increases in MVDs, we next utilized 111In-labeled PEGylated liposomes to examine if eribulin treatment would result in increased tumoral accumulation levels of such liposomes, and indeed, we found that eribulin, unlike vinorelbine another tubulin inhibitor, enhanced them. Since eribulin treatment increased accumulation of 111In-labeled PEGylated liposomes, we postulated that this treatment might enhance anti-tumor effect of Doxil (a liposomal anti-cancer agent). As expected, eribulin enhanced anti-tumor activity of Doxil in the PE-H1650 xenograft model. Then, we evaluated whether eribulin facilitated the recruitment of immune cells into the tumor. Infiltrating CD11b-positive immune cells were significantly increased in the multiple eribulin-treated xenografted tumors, and natural killer (NK) cell depletion reduced anti-tumor effects of eribulin. Collectively, these findings suggested a contribution of the immune cells for anti-tumor activities of eribulin. Taken together, our results obtained from multiple human cancer xenograft models suggested that vascular remodeling induced by eribulin therapy would act as a microenvironment modulator, and contributed to show anti-tumor effects of eribulin.

Citation Format: Ken Ito, Shusei Hamamichi, Takanori Abe, Tsuyoshi Akagi, Hiroshi Shirota, Satoshi Kawano, Makoto Asano, Osamu Asano, Akira Yokoi, Junji Matsui, Izumi O. Umeda, Hirofumi Fujii. Eribulin modulates tumor microenvironment through vascular remodeling for antitumor effect in multiple mouse xenograft models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5927. doi:10.1158/1538-7445.AM2017-5927

Radiolabeled liposome imaging determines an indication for liposomal anticancer agent in ovarian cancer mouse xenograft models

Liposomal anticancer agents can effectively deliver drugs to tumor lesions, but their therapeutic effects are enhanced in only limited number of patients. Appropriate biomarkers to identify responder patients to these liposomal agents will improve their treatment efficacies. We carried out pharmacological and histopathological analyses of mouse xenograft models bearing human ovarian cancers (Caov‐3, SK‐OV‐3, KURAMOCHI, and TOV‐112D) to correlate the therapeutic effects of doxorubicin‐encapsulated liposome (Doxil^®) and histological characteristics linked to the enhanced permeability and retention effect. We next generated ¹¹¹In‐encapsulated liposomes to examine their capacities to determine indications for Doxil^® treatment by single‐photon emission computed tomography (SPECT)/CT imaging. Antitumor activities of Doxil^® were drastically enhanced in Caov‐3, moderately in SK‐OV‐3, and minimally in KURAMOCHI and TOV‐112D when compared to doxorubicin. Microvessel density and vascular perfusion were high in Caov‐3 and SK‐OV‐3, indicating a close relation with the enhanced antitumor effects. Next, ¹¹¹In‐encapsulated liposomes were given i.v. to the animals. Their tumor accumulation and area under the curve values over 72 h were high in Caov‐3, relatively high in SK‐OV‐3, and low in two other tumors. Importantly, as both Doxil^® effects and liposomal accumulation varied in the SK‐OV‐3 group, we individually obtained SPECT/CT images of SK‐OV‐3‐bearing mouse (n = 11) before Doxil^® treatment. Clear correlation between liposomal tumor accumulation and effects of Doxil^® was confirmed (R² = 0.73). Taken together, our experiments definitely verified that enhanced therapeutic effects through liposomal formulations of anticancer agents depend on tumor accumulation of liposomes. Tumor accumulation of the radiolabeled liposomes evaluated by SPECT/CT imaging is applicable to appropriately determine indications for liposomal antitumor agents.

Novel Indocyanine Green-Phytate Colloid Technique for Sentinel Node Detection in Head and Neck: Mouse Study

OBJECTIVE

Sentinel node navigation surgery using real-time, near-infrared imaging with indocyanine green is becoming popular by allowing head and neck surgeons to avoid unnecessary neck dissection. The major drawback of this method is its quick migration through the lymphatics, limiting the diagnostic time window and undesirable detection of downstream nodes. We resolved this problem by mixing indocyanine green (ICG) with phytate colloid to retard its migration and demonstrated its feasibility in a nude mouse study.

STUDY DESIGN

Experimental prospective animal study.

SETTINGS

Animal laboratory.

SUBJECTS AND METHODS

Indocyanine green at 3 concentrations was tested to determine the optimal concentration for sentinel lymph node detection in a mouse model. Effect of indocyanine green with phytate colloid mixture solutions was also analyzed. Indocyanine green or mixture solution at different mixing ratios were injected into the tongue of nude mice and near-infrared fluorescence images were captured sequentially for up to 48 hours. The brightness of fluorescence in the sentinel lymph node and lymph nodes further downstream were assessed.

RESULTS

Indocyanine green concentration >50 μg/mL did not improve sentinel lymph node detection. The addition of phytate colloid to indocyanine green extended the period when sentinel lymph node was detectable. Second echelon lymph nodes were not imaged in mice injected with the mixture, while these were visualized in mice injected with indocyanine green alone.

CONCLUSION

This novel technique of ICG-phytate colloid mixture allows prolonged diagnostic time window, prevention of downstream subsequent nodes detection, and improved accuracy for the detection of true sentinel lymph nodes.

Abstract 145: Development of Radiolabeled Liposomes for Atherosclerotic Plaque Imaging

Objectives

Molecular imaging enables non-invasive in vivo detection of vulnerable plaques. Macrophage infiltration is characteristics for atherosclerotic vulnerable plaques, and many apoptotic cells are seen in this region. Also, it is known that macrophages recognize phosphatidylserine (PS) that is exposed on the cell surface during apoptosis to phagocytize these cells. In this study, we prepared radiolabeled phosphatidylserine liposomes for detection of vulnerable plaques.

Methods

PS liposomes and control liposomes (phosphatidylcholine (PC) liposomes) were prepared by lipid film hydration. The prepared sizes were 100 nm and 200 nm (PS100, PS200, PC100, and PC200 liposomes). The liposomes were radiolabeled by encapsulating 111 In-NTA using active-loading method. The 111 In-liposomes were incubated with mouse peritoneum macrophages for 2hr and uptake level was investigated. For biodistribution study, 111 In-liposomes were intravenously injected to ddY mice. Also, the 111 In-liposomes were injected to apoE -/- mice, and the aortas were harvested for autoradiography and Oil-Red O staining. For SPECT imaging, WHHL rabbits were used.

Results

The in vitro uptake levels to macrophages were 60.5, 14.7, 32.0, 14.4 %dose/mg protein, for 111 In-PS100, 111 In-PC100, 111 In-PS200, 111 In-PC200, respectively. The liver uptake was high in all liposomes, and blood clearance was faster in PS liposomes than PC liposomes. The in vivo distributions of 111 In-labeled PS liposomes to atherosclerotic regions were well matched with Oil-Red O staining in apoE -/- mouse. Target-to-non-target ratio was highest in 111 In-PS200. The aorta was successfully visualized by SPECT at 48hr after the 111 In-labeled PS liposome injection.

Conclusions

By in vitro uptake study, it is revealed that macrophage targeting was accomplished by PS. Also, atherosclerotic region was successfully detected by 111 In-PS200 in apoE-/- mice and WHHL rabbits in vivo .

In vivo SPECT imaging with 111In-DOTA-c(RGDfK) to detect early pancreatic cancer in a hamster pancreatic carcinogenesis model

Early detection of pancreatic cancer is key to overcoming its poor prognosis. α(v)β(3)-integrin is often overexpressed in pancreatic tumor cells, whereas it is scarcely expressed in normal pancreatic cells. In this study, we investigated the usefulness of SPECT imaging with (111)In-1,4,7,10-tetraazacylododecane-N,N',N″,N'''-tetraacetic acid-cyclo-(Arg-Gly-Asp-d-Phe-Lys) [(111)In-DOTA-c(RGDfK)], an imaging probe of α(v)β(3)-integrin, for the early detection of pancreatic cancer in a hamster pancreatic carcinogenesis model.

METHODS

Hamsters were subcutaneously injected with the pancreatic duct carcinogen N-nitrosobis(2-oxopropyl)amine to induce pancreatic cancer. N-nitrosobis(2-oxopropyl)amine-treated hamsters underwent in vivo SPECT with (111)In-DOTA-c(RGDfK). After imaging, the tumor-to-normal pancreatic tissue radioactivity ratios in excised pancreatic samples were measured with autoradiography (ARG) and compared with the immunopathologic findings for α(v)β(3)-integrin. In a mouse model in which inflammation was induced with turpentine, the uptake of (111)In-DOTA-c(RGDfK) in inflammatory regions was evaluated with ARG and compared with that of (18)F-FDG.

RESULTS

(111)In-DOTA-c(RGDfK) was clearly visualized in pancreatic cancer lesions as small as 3 mm in diameter. ARG analysis revealed high tumor-to-normal pancreatic tissue radioactivity ratios (4.6 ± 1.0 [mean ± SD] in adenocarcinoma and 3.3 ± 1.4 in atypical hyperplasia). The uptake of (111)In-DOTA-c(RGDfK) strongly correlated with α(v)β(3)-integrin expression. In the inflammatory model, inflammation-to-muscle ratios for (18)F-FDG and (111)In-DOTA-c(RGDfK) were 8.37 ± 4.37 and 1.98 ± 0.60, respectively. These results imply that (111)In-DOTA-c(RGDfK) has a lower rate of false-positive tumor detection than (18)F-FDG.

CONCLUSION

Our findings suggest that SPECT with (111)In-DOTA-c(RGDfK) has great potential for the early and accurate detection of pancreatic cancer.

Synthesis and evaluation of a novel (99m)Tc-labeled bioreductive probe for tumor hypoxia imaging

Tumor hypoxia is closely associated with the malignant progression and/or the high metastatic ability of tumors and often induces resistance to chemo- and/or radiotherapy. Thus, the detection and evaluation of hypoxia is important for the optimization of cancer therapy. We designed a novel (99m)Tc-labeled probe for tumor hypoxia imaging that utilizes bioreductive reactions in hypoxic cells. This probe, which contains a 4-nitrobenzyl ester group, is reduced in hypoxic cells to produce a corresponding carboxylate anion that cannot penetrate cell membranes because of its hydrophilicity and negative charge; therefore, it is expected to be trapped inside hypoxic cells. Based on this unique strategy, we synthesized the Technetium-99m ((99m)Tc)-labeled probe (99m)Tc-SD32. The uptake of (99m)Tc-SD32 in tumor cells was investigated under normoxic and hypoxic conditions. (99m)Tc-SD32 showed sufficient accumulation and good retention in hypoxic cells. In addition, we demonstrated that (99m)Tc-SD32 was subjected to bioreduction in hypoxic cells and was trapped as the corresponding carboxylate anion. These results indicated that (99m)Tc-SD32 would be a promising agent for in vivo hypoxia imaging.

High resolution SPECT imaging for visualization of intratumoral heterogeneity using a SPECT/CT scanner dedicated for small animal imaging

OBJECTIVES

Tumor interiors are never homogeneous and in vivo visualization of intratumoral heterogeneity would be an innovation that contributes to improved cancer therapy. But, conventional nuclear medicine tests have failed to visualize heterogeneity in vivo because of limited spatial resolution. Recently developed single photon emission computed tomographic (SPECT) scanners dedicated for small animal imaging are of interest due to their excellent spatial resolution of <1 mm, but few studies have focused on the evaluation of intratumoral heterogeneity. We investigated the optimal conditions related to high resolution imaging of heterogeneous tumor interiors using a small animal SPECT scanner.

METHODS

The conditions related to SPECT/CT visualization of heterogeneous tumor interiors were investigated using phantoms with (111)In and simulations of actual small animal imaging. The optimal conditions obtained were validated by in vivo imaging of sarcoma 180-bearing mice.

RESULTS

Larger number of counts must be obtained within limited acquisition time to visualize tumor heterogeneity in vivo in animal imaging, compared to cases that simply detect tumors. At an acquisition time of 30 min, better image quality was obtained with pinhole apertures diameter of 1.4 mm than of 1.0 mm. The obtained best spatial resolution was 1.3 mm, it was acceptable for our purpose, though a little worse than the best possible performance of the scanner (1.0 mm). Additionally, the reconstruction parameters, such as noise suppression, voxel size, and iteration/subset number, needed to be optimized under the limited conditions and were different from those found under the ideal condition. The minimal radioactivity concentration for visualization of heterogeneous tumor interiors was estimated to be as high as 0.2-0.5 MBq/mL. Liposomes containing (111)In met this requirement and were administered to tumor-bearing mice. SPECT imaging successfully showed heterogeneous (111)In distribution within the tumors in vivo with good spatial resolution. A threshold of 0.2 MBq/g for clear visualization of tumor heterogeneity was validated. Autoradiograms obtained ex vivo of excised tumors confirmed that the in vivo SPECT images accurately depicted the heterogeneous intratumoral accumulation of liposomes.

CONCLUSION

Intratumoral heterogeneity was successfully visualized under the optimized conditions using a SPECT/CT scanner.

Segmental acquisition method for stationary objects in (18)F-fluorodeoxyglucose positron emission tomography tests

PURPOSE

We investigated whether images of stationary objects obtained by segmental acquisition with positron emission tomography using 2-deoxy-2-[(18)F]-fluoro-D: -glucose (FDG-PET) are of a quality equivalent to those obtained by conventional continuous acquisition.

MATERIALS AND METHODS

Phantoms filled with FDG and mid-abdominal regions of 18 patients who underwent FDG-PET tests were imaged by both continuous and segmental acquisition methods. The total acquisition time was set to 3 min; in the segmental acquisition mode, imaging for 15 s was repeated 12 times. Segmental images (SIs) obtained by superimposition of the reconstructed images were compared quantitatively and visually with continuous images (CIs).

RESULTS

In all the phantom and clinical studies, SIs were never worse than CIs. The variances of the background counts of SIs were 9.8% and 13.0% less those of CIs in phantom and clinical studies, respectively. Visual assessments showed that SIs provided better detection of hot areas and superior image quality when compared to CIs.

CONCLUSION

For stationary objects, the quality of images obtained by the segmental method is equivalent to that of images obtained conventionally by continuous acquisition. Moreover, under some conditions SIs provide better results than CIs.

Abstract 4325: The requisites for in vivo clear visualization of intratumoral heterogeneity by a SPECT/CT scanner dedicated for small animal imaging

Objectives: Although even conventional nuclear medicine tests could successfully detect tumor masses in vivo, they did not always visualize heterogeneous interiors of tumor masses. The clear visualization of intratumoral heterogeneity in vivo will give us additional information about the choice of cancer therapy. Recently developed single photon emission computed tomography (SPECT) scanners dedicated for small animal imaging show excellent spatial resolution (&lt; 1 mm) and they are expected to visualize intratumoral heterogeneity in vivo even for mouse tumors. But, little studies have revealed the requisites for this purpose. In this study, we considered the conditions to image intratumoral heterogeneity in vivo.

Materials and Methods: A small animal SPECT/CT scanner with four detectors equipped with 9-pinhole collimators (1.0 mm or 1.4 mm of pinholes, Bioscan, Washington, D.C.) was used. First, phantom experiments with 111In of similar radioactivity that is commonly used in mouse imaging studies were performed to evaluate the optimal conditions to obtain best spatial resolution and concentration linearity. Then, mouse tumors were imaged. 111In-labeled liposomes with high specific activity and high concentration were injected to Sarcoma180 bearing ddY mice. In vivo SPECT images and ex vivo autoradiograms were compared and the radioactivity distribution in tumors and other tissues was measured.

Results: In phantom experiments with 111In, the best spatial resolution under the current experimental conditions simulating in vivo small animal imaging was 1.1 mm (1.4 mmϕ, 5 MBq/mL, 120 min of total acquisition), although they greatly depended on total acquisition counts or total radioactivity. The good linearity between the concentration and SPECT values was obtained under the condition of 0.5-1.5 MBq/mL. 111In-labeled liposomes (15-20 MBq/mouse) were strongly accumulated in the tumor (1-2 MBq/g, 10-15% of injected dose/g), predominantly in the marginal regions of tumors. And, SPECT clearly visualized this heterogeneous intratumoral localization in vivo with good spatial resolution with the acquisition time of 60 min at 24h after the injection. The threshold to clearly visualize the tumor heterogeneity was about 0.5 MBq/g. Ex vivo autoradiograms of excised tumors demonstrated that the small animal SPECT scanner could successfully image the heterogeneous intratumoral accumulation of liposomes.

Conclusion: The SPECT/CT scanner dedicated for small animal imaging successfully visualized the tumor heterogeneity in vivo using radioactive probes with rather high specific radioactivity and high concentration.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4325.

5-S-GAD, a novel radical scavenging compound, prevents lens opacity development

The ability of N-beta-alanyl-5-S-glutathionyl-3,4-dihydroxyphenylalanine (5-S-GAD)-a novel catechol derivative isolated from an insect as an antibacterial substance-to scavenge free radicals and prevent cataract progression was examined. 5-S-GAD scavenged 1,1-diphenylpicrylhydrazyl (DPPH) and superoxide anions (O(2)(*)(-)), and inhibited lipid peroxidation. It also significantly inhibited the onset of glucocorticoid-induced lens opacification in chick embryos. These effects of 5-S-GAD were stronger than those of N-acetylcarnosine and TEMPOL, which are reported to be effective radical scavengers in the prevention of cataract progression. 5-S-GAD clearly delayed the maturation of cataracts induced by diamide in cultured lenses of rats. Daily instillation of 5-S-GAD retarded the development of lens opacity in galactose-fed rats. Biochemical analysis of the lenses revealed that 20-kDa proteins, presumably consisting of alpha-crystallin, were the most susceptible to oxidative stress, which leads to the carbonylation of the side chains of these proteins. alpha-Crystallin carbonylation induced by diamide or galactose was notably inhibited by 5-S-GAD in a dose-dependent manner. Our results show that 5-S-GAD prevents acute lens opacification in these short-term experimental models, possibly in part by virtue of its antioxidative property, and 5-S-GAD is expected to have long-term pharmaceutical effects.

Inhibition of glucocorticoid-induced cataracts in chick embryos by RU486: A model for studies on the role of glucocorticoids in development

Cataract formation can be induced by glucocorticoid treatment of developing chick embryos. We show here that this response can be blocked very effectively by use of the antiglucocorticoid RU486. When dexamethasone (0.02 micromol/egg) was administered from day 13 to 16 chick embryos, their lenses (over 80%) became cataract (GC-induced cataract; stage IV-V) within 48 hrs. These GC-induced cataract formations were prevented by administration of RU486 (0.2 micromol/egg) on day 9. However, RU486 also inhibited hatching even though the embryos showed normal growth and appearance. In control embryos, more than 90% live chicks (39/42 chicks) were hatched on day 22. Chick embryos treated with RU486 on day 9 appeared to grow normally until 21, but could not hatch. When chick embryos were treated with RU486 (0.2 micromol/egg) on day 15, more than 80% live embryos (34/42 chicks) were hatched on day 23 with normal appearance, which was one day delay comparing to the control. These observations indicate that endogenous glucocorticoids are involved in the ability to hatch and that RU486 is able to block the actions of endogenous glucocorticoids. Thus, RU486 should be a very useful tool for studies on other biochemical and physiological aspects of chick embryo development that are under glucocorticoid control.

Predominant phosphatase in the ocular lens regulated by physiological concentrations of magnesium and calcium

A magnesium-dependent phosphatase with a molecular weight of about 55 kDa was found in the lens of chicken embryo, mouse, rabbit and bovine. It appears to be unique to the lens and, when activated by magnesium, accounts for the majority of the phosphatase activity in the lens. Phosphatases in the lens were separated by using high-resolution gel permeation column chromatography, and phosphatase activity was determined with p-nitrophenyl phosphate (pNPP) as a substrate. The 55-kDa phosphatase showed very low basal activity, but the activity was increased concentration-dependently by magnesium ion (Mg(2+)), and at 1 mM Mg(2+), this enzyme accounted for over 50% of the total phosphatase activity in the lens. Calcium potently inhibited the magnesium-activated phosphatase activity in a dose-dependent (IC(50); about 50 microM), uncompetitive manner. The phosphatase activity was high in the acidic pH range, with an optimum pH value of 5.5. The characteristics of the lens Mg(2+)-dependent phosphatase, such as substrate specificity and sensitivity to various phosphatase inhibitors, showed little similarity to those of any reported phosphatase. The Mg(2+) and Ca(2+) concentrations that were found to be effective in this study are similar to physiological concentrations in the lens; therefore it is likely that these ions physiologically regulate the 55-kDa phosphatase activity in the lens.

18 kDa protein tyrosine phosphatase in the ocular lens

Protein tyrosyl phosphorylation and dephosphorylation play essential roles in regulating cellular events such as proliferation and differentiation, and their involvement in the lens development and transparency is also suggested. The level of tyrosine phosphorylation in a given protein is regulated by the opposing actions of protein-tyrosine kinases (Tyr kinases) and protein-tyrosine phosphatases (TyrPases). Recent studies have revealed that some Tyr kinases, such as platelet-derived growth factor receptor and fibroblast growth factor receptor, are present in the lens, however, little is known about TyrPases in the lens. In this study, we found a 18 kDa protein tyrosine phosphatase (18 kDa TyrPase) predominantly present in the ocular lens of various animals. We purified the phosphatase from the lens of chick embryo and characterized its activity.Phosphatase activity was determined in chick embryo, mouse, rabbit and bovine lenses using p -nitrophenyl phosphate (p NPP) as substrate. All lenses examined dephosphorylated p NPP under acidic conditions, and a large portion of the activity resided in a low molecular weight protein, ca. 18 kDa, following high-resolution gel permeation column chromatography. The brain and liver showed high dephosphorylation activities, but most of their activity was present in high molecular weight fractions, unlike that in the lens. The 18 kDa phosphatase was purified from the lens of 17 day old chick embryos to near-homogeneity with two-step rapid chromatography. This phosphatase showed strict substrate specificity for phosphotyrosine and phosphotyrosyl peptides, suggesting that it was a kind of protein tyrosine phosphatases (TyrPases). Several known inhibitors of TyrPases, such as SH blockers, vanadate and phenylarsine oxide, strongly inhibited the enzyme activity. The molecular weight, substrate specificity, and responses to various inhibitors and activators coincide well with those reported for the low molecular weight protein tyrosine phosphatase (LMW-TyrPase), belonging to the TyrPase superfamily. These results suggest that the 18 kDa phosphatase found in the lens is a LMW-TyrPase. The 18 kDa TyrPase is the predominant phosphatase in the ocular lens. It may be involved in regulation of lens cell proliferation, differentiation and/or lens transparency.