PET Imaging of Innate Immune Activation Using 11C Radiotracers Targeting GPR84

Chronic innate immune activation is a key hallmark of many neurological diseases and is known to result in the upregulation of GPR84 in myeloid cells (macrophages, microglia, and monocytes). As such, GPR84 can potentially serve as a sensor of proinflammatory innate immune responses. To assess the utility of GPR84 as an imaging biomarker, we synthesized 11C-MGX-10S and 11C-MGX-11Svia carbon-11 alkylation for use as positron emission tomography (PET) tracers targeting this receptor. In vitro experiments demonstrated significantly higher binding of both radiotracers to hGPR84-HEK293 cells than that of parental control HEK293 cells. Co-incubation with the GPR84 antagonist GLPG1205 reduced the binding of both radiotracers by >90%, demonstrating their high specificity for GPR84 in vitro. In vivo assessment of each radiotracer via PET imaging of healthy mice illustrated the superior brain uptake and pharmacokinetics of 11C-MGX-10S compared to 11C-MGX-11S. Subsequent use of 11C-MGX-10S to image a well-established mouse model of systemic and neuro-inflammation revealed a high PET signal in affected tissues, including the brain, liver, lung, and spleen. In vivo specificity of 11C-MGX-10S for GPR84 was confirmed by the administration of GLPG1205 followed by radiotracer injection. When compared with 11C-DPA-713-an existing radiotracer used to image innate immune activation in clinical research studies-11C-MGX-10S has multiple advantages, including its higher binding signal in inflamed tissues in the CNS and periphery and low background signal in healthy saline-treated subjects. The pronounced uptake of 11C-MGX-10S during inflammation, its high specificity for GPR84, and suitable pharmacokinetics strongly support further investigation of 11C-MGX-10S for imaging GPR84-positive myeloid cells associated with innate immune activation in animal models of inflammatory diseases and human neuropathology.

Clinical Radiosynthesis and Translation of [18F]OP-801: A Novel Radiotracer for Imaging Reactive Microglia and Macrophages

Positron emission tomography (PET) is a powerful tool for studying neuroinflammatory diseases; however, current PET biomarkers of neuroinflammation possess significant limitations. We recently reported a promising dendrimer PET tracer ([18F]OP-801), which is selectively taken up by reactive microglia and macrophages. Here, we describe further important characterization of [18F]OP-801 in addition to optimization and validation of a two-step clinical radiosynthesis. [18F]OP-801 was found to be stable in human plasma for 90 min post incubation, and human dose estimates were calculated for 24 organs of interest; kidneys and urinary bladder wall without bladder voiding were identified as receiving the highest absorbed dose. Following optimization detailed herein, automated radiosynthesis and quality control (QC) analyses of [18F]OP-801 were performed in triplicate in suitable radiochemical yield (6.89 ± 2.23% decay corrected), specific activity (37.49 ± 15.49 GBq/mg), and radiochemical purity for clinical imaging. Importantly, imaging mice with tracer (prepared using optimized methods) 24 h following the intraperitoneal injection of liposaccharide resulted in the robust brain PET signal. Cumulatively, these data enable clinical translation of [18F]OP-801 for imaging reactive microglia and macrophages in humans. Data from three validation runs of the clinical manufacturing and QC were submitted to the Food and Drug Administration (FDA) as part of a Drug Master File (DMF). Subsequent FDA approval to proceed was obtained, and a phase 1/2 clinical trial (NCT05395624) for first-in-human imaging in healthy controls and patients with amyotrophic lateral sclerosis is underway.

Antigen-Dependent Inducible T-Cell Reporter System for PET Imaging of Breast Cancer and Glioblastoma

For the past several decades, chimeric antigen receptor T-cell therapies have shown promise in the treatment of cancers. These treatments would greatly benefit from companion imaging biomarkers to follow the trafficking of T cells in vivo. Methods: Using synthetic biology, we engineered T cells with a chimeric receptor synthetic intramembrane proteolysis receptor (SNIPR) that induces overexpression of an exogenous reporter gene cassette on recognition of specific tumor markers. We then applied a SNIPR-based PET reporter system to 2 cancer-relevant antigens, human epidermal growth factor receptor 2 (HER2) and epidermal growth factor receptor variant III (EGFRvIII), commonly expressed in breast and glial tumors, respectively. Results: Antigen-specific reporter induction of the SNIPR PET T cells was confirmed in vitro using green fluorescent protein fluorescence, luciferase luminescence, and the HSV-TK PET reporter with 9-(4-18F-fluoro-3-[hydroxymethyl]butyl)guanine ([18F]FHBG). T cells associated with their target antigens were successfully imaged using PET in dual-xenograft HER2+/HER2- and EGFRvIII+/EGFRvIII- animal models, with more than 10-fold higher [18F]FHBG signals seen in antigen-expressing tumors versus the corresponding controls. Conclusion: The main innovation found in this work was PET detection of T cells via specific antigen-induced signals, in contrast to reporter systems relying on constitutive gene expression.

Radiosynthesis and initial preclinical evaluation of [11C]AZD1283 as a potential P2Y12R PET radiotracer

INTRO

Chronic neuroinflammation and microglial dysfunction are key features of many neurological diseases, including Alzheimer's Disease and multiple sclerosis. While there is unfortunately a dearth of highly selective molecular imaging biomarkers/probes for studying microglia in vivo, P2Y12R has emerged as an attractive candidate PET biomarker being explored for this purpose. Importantly, P2Y12R is selectively expressed on microglia in the CNS and undergoes dynamic changes in expression according to inflammatory context (e.g., toxic versus beneficial/healing states), thus having the potential to reveal functional information about microglia in living subjects. Herein, we identified a high affinity, small molecule P2Y12R antagonist (AZD1283) to radiolabel and assess as a candidate radiotracer through in vitro assays and in vivo positron emission tomography (PET) imaging of both wild-type and total knockout mice and a non-human primate.

METHODS

First, we evaluated the metabolic stability and passive permeability of non-radioactive AZD1283 in vitro. Next, we radiolabeled [11C]AZD1283 with radioactive precursor [11C]NH4CN and determined stability in formulation and human plasma. Finally, we investigated the in vivo stability and kinetics of [11C]AZD1283 via dynamic PET imaging of naïve wild-type mice, P2Y12R knockout mouse, and a rhesus macaque.

RESULTS

We determined the half-life of AZD1283 in mouse and human liver microsomes to be 37 and > 160 min, respectively, and predicted passive CNS uptake with a small amount of active efflux, using a Caco-2 assay. Our radiolabeling efforts afforded [11C]AZD1283 in an activity of 12.69 ± 10.64 mCi with high chemical and radiochemical purity (>99%) and molar activity of 1142.84 ± 504.73 mCi/μmol (average of n = 3). Of note, we found [11C]AZD1283 to be highly stable in vitro, with >99% intact tracer present after 90 min of incubation in formulation and 60 min of incubation in human serum. PET imaging revealed negligible brain signal in healthy wild-type mice (n = 3) and a P2Y12 knockout mouse (0.55 ± 0.37%ID/g at 5 min post injection). Strikingly, high signal was detected in the liver of all mice within the first 20 min of administration (peak uptake = 58.28 ± 18.75%ID/g at 5 min post injection) and persisted for the remaining duration of the scan. Ex vivo gamma counting of mouse tissues at 60 min post-injection mirrored in vivo data with a mean %ID/g of 0.9% ± 0.40, 0.02% ± 0.01, and 106 ± 29.70% in the blood, brain, and liver, respectively (n = 4). High performance liquid chromatography (HPLC) analysis of murine blood and liver metabolite samples revealed a single radioactive peak (relative area under peak: 100%), representing intact tracer. Finally, PET imaging of a rhesus macaque also revealed negligible CNS uptake/binding in monkey brain (peak uptake = 0.37 Standard Uptake Values (SUV)).

CONCLUSION

Despite our initial encouraging liver microsome and Caco-2 monolayer data, in addition to the observed high stability of [11C]AZD1283 in formulation and human serum, in vivo brain uptake was negligible and rapid accumulation was observed in the liver of both naïve wildtype and P2Y12R knockout mice. Liver signal appeared to be independent of both metabolism and P2Y12R expression due to the confirmation of intact tracer in this tissue for both wildtype and P2Y12R knockout mice. In Rhesus Macaque, negligible uptake of [11C]AZD1283 brain indicates a lack of potential for translation or its further investigation in vivo. P2Y12R is an extremely promising potential PET biomarker, and the data presented here suggests encouraging metabolic stability for this scaffold; however, the mechanism of liver uptake in mice should be elucidated prior to further analogue development.

Glyco-nanotechnology: A biomedical perspective

Glycans govern cellular signaling through glycan-protein and glycan-glycan crosstalk. Disruption in the crosstalk initiates 'rogue' signaling and pathology. Nanomaterials supply platforms for multivalent displays of glycans, mediate 'rogue' signal correction, and provide disease treatment modalities (therapeutics). The decorated glycans also target overexpressed lectins on unhealthy cells and direct metal nanoparticles such as gold, iron oxide, and quantum dots to the site of infection. The nanoparticles inform us about the state of the disease (diagnosis) through their distinct optical, magnetic, and electronic properties. Glyco-nanoparticles can sense disease biomarkers, report changes in protein-glycan interactions, and safeguard quality control (analysis). Here we review the current state of glyco-nanotechnology focusing on diagnosis, therapeutics, and analysis of human diseases. We highlight how glyco-nanotechnology could aid in improving diagnostic methods for the detection of disease biomarkers with magnetic resonance imaging (MRI) and fluorescence imaging (FLI), enhance therapeutics such as anti-adhesive treatment of cancer and vaccines against pneumonia, and advance analysis such as the rapid detection of pharmaceutical heparin contaminant and recombinant SARS-COV-2 spike protein. We illustrate these progressions and outline future potentials of glyco-nanotechnology in advancing human health.

Synthesis and Screening of α-Xylosides in Human Glioblastoma Cells

Glycosaminoglycans (GAGs) such as heparan sulfate and chondroitin sulfate decorate all mammalian cell surfaces. These mucopolysaccharides act as coreceptors for extracellular ligands, regulating cell signaling, growth, proliferation, and adhesion. In glioblastoma, the most common type of primary malignant brain tumor, dysregulated GAG biosynthesis results in altered chain length, sulfation patterns, and the ratio of contributing monosaccharides. These events contribute to the loss of normal cellular function, initiating and sustaining malignant growth. Disruption of the aberrant cell surface GAGs with small molecule inhibitors of GAG biosynthetic enzymes is a potential therapeutic approach to blocking the rogue signaling and proliferation in glioma, including glioblastoma. Previously, 4-azido-xylose-α-UDP sugar inhibited both xylosyltransferase (XYLT-1) and β-1,4-galactosyltransferase-7 (β-GALT-7)-the first and second enzymes of GAG biosynthesis-when microinjected into a cell. In another study, 4-deoxy-4-fluoro-β-xylosides inhibited β-GALT-7 at 1 mM concentration in vitro. In this work, we seek to solve the enduring problem of drug delivery to human glioma cells at low concentrations. We developed a library of hydrophobic, presumed prodrugs 4-deoxy-4-fluoro-2,3-dibenzoyl-(α- or β-) xylosides and their corresponding hydrophilic inhibitors of XYLT-1 and β-GALT-7 enzymes. The prodrugs were designed to be activatable by carboxylesterase enzymes overexpressed in glioblastoma. Using a colorimetric MTT assay in human glioblastoma cell lines, we identified a prodrug-drug pair (4-nitrophenyl-α-xylosides) as lead drug candidates. The candidates arrest U251 cell growth at an IC50 = 380 nM (prodrug), 122 μM (drug), and U87 cells at IC50 = 10.57 μM (prodrug). Molecular docking studies were consistent with preferred binding of the α- versus β-nitro xyloside conformer to XYLT-1 and β-GALT-7 enzymes.

Heparan Sulfate Synthesized by Ext1 Regulates Receptor Tyrosine Kinase Signaling and Promotes Resistance to EGFR Inhibitors in GBM

Signaling from multiple receptor tyrosine kinases (RTK) contributes to therapeutic resistance in glioblastoma (GBM). Heparan sulfate (HS), present on cell surfaces and in the extracellular matrix, regulates cell signaling via several mechanisms. To investigate the role for HS in promoting RTK signaling in GBM, we generated neural progenitor cells deficient for HS by knockout of the essential HS-biosynthetic enzyme Ext1, and studied tumor initiation and progression. HS-null cells had decreased proliferation, invasion, and reduced activation of multiple RTKs compared with control. In vivo tumor establishment was significantly decreased, and rate of tumor growth reduced with HS-deficient cells implanted in an HS-poor microenvironment. To investigate if HS regulates RTK activation through platelet-derived growth factor receptor α (PDGFRα) signaling, we removed cell surface HS in patient-derived GBM lines and identified reduced cell surface PDGF-BB ligand. Reduced ligand levels were associated with decreased phosphorylation of PDGFRα, suggesting HS promotes ligand-receptor interaction. Using human GBM tumorspheres and a murine GBM model, we show that ligand-mediated signaling can partially rescue cells from targeted RTK inhibition and that this effect is regulated by HS. Indeed, tumor cells deficient for HS had increased sensitivity to EGFR inhibition in vitro and in vivo. IMPLICATIONS: Our study shows that HS expressed on tumor cells and in the tumor microenvironment regulates ligand-mediated signaling, promoting tumor cell proliferation and invasion, and these factors contribute to decreased tumor cell response to targeted RTK inhibition.

Arabinofuranose-derived positron-emission tomography radiotracers for detection of pathogenic microorganisms

PURPOSE

Detection of bacteria-specific metabolism via positron emission tomography (PET) is an emerging strategy to image human pathogens, with dramatic implications for clinical practice. In silico and in vitro screening tools have recently been applied to this problem, with several monosaccharides including l-arabinose showing rapid accumulation in Escherichia coli and other organisms. Our goal for this study was to evaluate several synthetically viable arabinofuranose-derived ¹⁸ F analogs for their incorporation into pathogenic bacteria.

PROCEDURES

We synthesized four radiolabeled arabinofuranose-derived sugars: 2-deoxy-2-[¹⁸ F]fluoro-arabinofuranoses (d-2-¹⁸ F-AF and l-2-¹⁸ F-AF) and 5-deoxy-5-[¹⁸ F]fluoro-arabinofuranoses (d-5-¹⁸ F-AF and l-5-¹⁸ F-AF). The arabinofuranoses were synthesized from ¹⁸ F^- via triflated, peracetylated precursors analogous to the most common radiosynthesis of 2-deoxy-2-[¹⁸ F]fluoro-d-glucose ([¹⁸ F]FDG). These radiotracers were screened for their uptake into E. coli and Staphylococcus aureus. Subsequently, the sensitivity of d-2-¹⁸ F-AF and l-2-¹⁸ F-AF to key human pathogens was investigated in vitro.

RESULTS

All ¹⁸ F radiotracer targets were synthesized in high radiochemical purity. In the screening study, d-2-¹⁸ F-AF and l-2-¹⁸ F-AF showed greater accumulation in E. coli than in S. aureus. When evaluated in a panel of pathologic microorganisms, both d-2-¹⁸ F-AF and l-2-¹⁸ F-AF demonstrated sensitivity to most gram-positive and gram-negative bacteria.

CONCLUSIONS

Arabinofuranose-derived ¹⁸ F PET radiotracers can be synthesized with high radiochemical purity. Our study showed absence of bacterial accumulation for 5-substitued analogs, a finding that may have mechanistic implications for related tracers. Both d-2-¹⁸ F-AF and l-2-¹⁸ F-AF showed sensitivity to most gram-negative and gram-positive organisms. Future in vivo studies will evaluate the diagnostic accuracy of these radiotracers in animal models of infection.

Visualizing antithrombin-binding 3-O-sulfated heparan sulfate motifs on cell surfaces

To map the cellular topography of the rare 3-O-sulfated structural motif of heparan sulfate (HS), we constructed quantum dot-based probes for antithrombin and FGF2, which reveal widely different distribution of the targeted HS motifs.

Cancers With Bad and Good Survival Among Male Population of Northeast India

Background: The northeast region of India has an overall high incidence, mortality and lower survival rate of cancer in the country, an annual expected of around 40,000 were diagnosed with cancer every year in this region. Mortality rate due to cancer in northeastern India is increasing mainly because of difficulties in accessing the facilities for cancer diagnosis and treatment, socioeconomic conditions, lack of awareness, taboo, misconception and wide disparity in both diagnosis and treatment of cancers among the eight different states (regions) within northeast India. Furthermore, affordability of cancer care remains a major challenge in this part of India for effective cancer control. Aim: This study was conducted with a vision to provide an idea about the cancer survival pattern of 45 million of people living in the northeastern region of India with correlation to time at diagnosis and treatment competition status. Methods: All the cases registered with a history of cancer in between 2010-2014 calendar years. Five year observed survival was calculated based on all the followed up until 2017. Three categories were made for treatment-wise survival analysis, 1) those that have completed cancer treatment 2) those that did not completed treatment 3) those who have not taken any cancer directed treatment. The 5-year survival rates were generated by using the SPSS V19 software. Kaplan-Meier method was used to generate the statistics. Results: The five years overall survival for all cancers in men is 24.3% with earlier stage at diagnosis has a better survival (Stage I, 52.1%) than later stage (Stage IV, 18.8%) at diagnosis. Completed course of cancer directed treatment found to be playing a significant role in enhancing the survival among the patients. The five-year survival for completed cancer directed treatment is 27.5% followed by 12.5% for incomplete and 8.5% for those with no cancer directed treatment group. Inequality in survival was observed among different sites of cancer, as some cancers harm younger people more than others. The five year observed survival for all sites was ranges from 0% to 75.8%. Cancer of liver (0%), pancreas (0%), lung (2.4%), gallbladder (7.9%) and stomach (10.3%) is found as more lethal than other cancers as the five years survival was in-between the range 0%-10%. Cancer of Hodgkin lymphoma (75.8%) has the highest five year cancer survival rate followed by testis (60.1%), breast-male (55.3%), penis (49.7%) and skin cancer (49.1%). The prostate cancer (19.0%) rate is very low compared with other global parts of the world where it reaches around 100% in many countries. Advances in early detection and treatment can enhance the survival rate in these regions. Conclusion: The 5-year survival showed an increasing survival with decreasing in stage at the time of diagnosis and decreasing in number of decline treatment percentage among northeastern population.

Epidemiology of gynecological cancers in Kamrup Urban District cancer registry

BACKGROUND

Cancers of the female reproductive system - namely cancer of the cervix, corpus uteri, ovarian, vulvar, vaginal, fallopian tube cancers and choriocarcinoma are an important cause of cancer morbidity and mortality among women worldwide. It is estimated to be the third most common group of malignancies in women. The comprehensive global cancer statistics from the International Agency for Research on Cancer indicate that gynaecological cancers accounted for 20% of the 14.1 million estimated new cancer cases and 8.2 million cancer deaths among women in the world in 2012. The estimation of cancer burden is necessary to set up priorities for disease control. Gynaecological cancers have increased in India and are estimated to be around 182,602 by the year 2020 constituting about 30% of the total cancers among women in India. Among these, cancer of the uterine cervix followed by ovary and corpus uteri are the major contributors.

METHODS AND MATERIALS

Cancer is not notifiable in India, so method of collecting information on cancer was active with voluntary participation of different sources including major hospitals, diagnostic centers, state referral board and birth and death registration centers within registry area.

RESULTS

A total of 3767 (44%) cases were registered in women out of the total number of 8561 cancer cases during the period from 2010-2014. In case of gynaecological cancers a total of 661 cases of cervical, ovarian and corpus uterine cancers were registered out of the total 3767 female cancer cases (17.5%) for the year 2010-2014.The annual average crude rate in women for all sites of cancer was 117.4 per 100000 population. The corresponding AARs was 166.6.

CONCLUSIONS

Women's health issues have attained high concern in recent decades. Utmost efforts should be made to educate women in early cancer detection by creating awareness on risk factors and symptoms.

A glycan-based approach to therapeutic angiogenesis

Angiogenesis, the sprouting of new blood vessels from existing vasculature, involves multiple complex biological processes, and it is an essential step for hemostasis, tissue healing and regeneration. Angiogenesis stimulants can ameliorate human disease conditions including limb ischemia, chronic wounds, heart disease, and stroke. The current strategies to improve the bioavailability of pro-angiogenic growth factors, including VEGF and FGF2, have remained largely unsuccessful. This study demonstrates that small molecules, termed click-xylosides, can promote angiogenesis in the in vitro matrigel tube formation assay and the ex ovo chick chorioallantoic membrane assay, depending on their aglycone moieties. Xyloside treatment enhances network connectivity and cell survivability, thereby, maintaining the network structures on matrigel culture for an extended period of time. These effects were achieved via the secreted xyloside-primed glycosaminoglycans (GAG) chains that in part, act through an ERK1/2 mediated signaling pathway. Through the remodeling of GAGs in the extracellular matrix of endothelial cells, the glycan approach, involving xylosides, offers great potential to effectively promote therapeutic angiogenesis.

Synthesis and biomedical applications of xylosides

Xylosides modulate the biosynthesis of sulfated glycosaminoglycans (GAGs) in various cell types. A new class of xylosides called "click-xylosides" has been synthesized for their biostability, ease of chemical synthesis, and tunable sulfated GAG biogenesis in vitro and in vivo. These click-xylosides have several therapeutic and biomedical applications in the regulation of angiogenesis, tumor inhibition, and regeneration. This protocol focuses on the synthesis of click-xylosides, their cellular priming activities, and biomedical applications.

A hybrid soft solar cell based on the mycobacterial porin MspA linked to a sensitizer-viologen Diad

A prototype of a nano solar cell containing the mycobacterial channel protein MspA has been successfully designed. MspA, an octameric transmembrane channel protein from Mycobacterium smegmatis, is one of the most stable proteins known to date. Eight Ruthenium(II) aminophenanthroline-viologen maleimide Diads (Ru-Diads) have been successfully bound to the MspA mutant MspAA96C via cysteine-maleimide bonds. MspA is known to form double layers in which it acts as nanoscopic surfactant. The nanostructured layer that is formed by (Ru-Diad)8MspA at the TiO2 electrode is photochemically active. The resulting "protein nano solar cell" features an incident photon conversion efficiency of 1% at 400 nm. This can be regarded as a proof-of-principle that stable proteins can be successfully integrated into the design of solar cells.

Channel blocking of MspA revisited

Porin A from Mycobacterium smegmatis (MspA) is a highly stable, octameric channel protein, which acts as the main transporter of electrolytes across the cell membrane. MspA features a narrow, negatively charged constriction zone, allowing stable binding of various analytes thereby blocking the channel. Investigation of channel blocking of mycobacterial porins is of significance in developing alternate treatment methods for tuberculosis. The concept that ruthenium(II)quaterpyridinium complexes have the capability to act as efficient channel blockers for MspA and related porins, emerged after very high binding constants were measured by high-performance liquid chromatography and steady-state luminescence studies. Consequently, the interactions between the ruthenium(II) complex RuC2 molecules and MspA, leading to RuC2@MspA assemblies, have been studied utilizing time-resolved absorption/emission, atomic force microscopy, dynamic light scattering, ζ potential measurements, and isothermal titration calorimetry. The results obtained provide evidence for the formation of clusters/large aggregates of RuC2 and MspA. The results are of interest with respect to utilizing prospective channel blockers in porins. The combination of results from conceptually different techniques shed some light onto the chemical nature of MspA-channel blocker interactions thus contributing to the development of a paradigm for channel blocking.

Maleimide-functionalized photochromic spirodihydroindolizines

Two photochromic spirodihydroindolizine/betaine systems for tethering to peptides and proteins via a maleimide function have been prepared. The absorption spectra of the betaines are in the red region of the visible spectrum and in the near-IR spectral domain, which are suitable energies of light for future in vivo applications. The half-times of cyclization have been determined for both DHI/betaine systems. The findings are consistent with a thermal barrier of varying size between the transoid and cisoid conformers of the betaines.

Developing New Strategies for the Treatment of Tuberculosis Employing Ruthnium(II)Quaterpyridyl Compexes

A series of ruthenium(II)quaterpyridyl complexes has been synthesized as prototypes for mycobacterial channel blockers. These Ru(II)complexes show distinct changes in their luminescence spectra when bound to the porin MspA from M. smegmatis, which is a non-pathogenic relative of M. tuberculosis. By using HPLC, we have determined binding constants of the Ru(II)-complexes to MspA in phosphate buffer (0.05M, pH = 6.8) ranging from 5.2 x 109 M-1 (Ru-C2) to 1.8 x 109 M-1 (Ru-C4). Our findings indicate that channel blocking is a promising treatment strategy for mycobacterial infections. It appears to be also a viable approach towards luminescent nanostructures, because MspA features extraordinary stability.Keywords: Ru(II)complexe, porin MspA, mycobacterial infection, tuberculosisDOI: 10.3126/jncs.v23i0.2091Journal of  Nepal Chemical Society, Vol. 23, 2008/2009 Page:2-10. 

MspA Porin-Gold Nanoparticle Assemblies: Enhanced Binding through a Controlled Cysteine Mutation

In this study, the interactions of two gold nanoparticles of different sizes (average diameters of 3.7 +/- 2.6 and 17 +/- 3 nm) with octameric mycobacterial porin A from Mycobacterium smegmatis (MspA) and a mutant of MspA featuring a cysteine mutation in position 126 (Q126C) are investigated. From the observation of enhanced photoluminescence quenching, it is inferred that the presence of eight cysteines in the MspA Q126C mutant significantly enhances the binding of selected small gold nanoparticles within the inner pore of MspA. The large gold nanoparticle/porin complex shows photoluminescence enhancement, which is expected since the larger nanoparticles cannot dock within the homopore of MspA due to size exclusion. In addition to the fluorescence experiments, observation of energy transfer from the small gold nanoparticles to the MspA shows the close proximity of the small gold nanoparticles with the porin. Interestingly, the energy transfer of the large nanoparticle/MspA complex is completely missing. From high-performance liquid chromatography data, the estimated binding constants for small Au@MspA, large Au@MspA, small Au@MspAcys, and large Au@MspAcys are 1.3 x 10 (9), 2.22 x 10 (10), > 10 (12) (irreversible), and 1.7 x 10 (10), respectively.