Srinivas Chiguru

New frontiers and developing applications in 19F NMR

1.1 Overview 19F NMR is gaining interest as a tool for diverse physiological and pharmaceutical investigations as evidenced by new reporter molecules and detection strategies. The relatively high sensitivity of 19F and lack of interfering background signal in the body have enabled the observation of exogenously administered agents and their metabolites. The 19F nucleus exhibits a large chemical shift range (~300 ppm), which is exquisitely sensitive to the electronic microenvironment, and many reporter molecules have been developed. In addition to chemical shift studies, relaxation processes (R1 and R2), and chemical exchange have also been tailored to be responsive to a parameter of interest such as pO2, pH, metal ion concentrations, transgene/enzyme activity or hypoxia. Recent emphasis has been on enhancing signal sensitivity and developing novel response mechanisms to sense environmental parameters. This review focuses on quantitative tissue oximetry, detection of ions including pH, and detection of enzyme activity. Fluorine NMR has been widely exploited for laboratory investigations and is garnering developing use in pre-clinical applications for small animals in vivo.

Use of Fc-Engineered Antibodies as Clearing Agents to Increase Contrast During PET

Despite promise for the use of antibodies as molecular imaging agents in PET, their long in vivo half-lives result in poor contrast and radiation damage to normal tissue. This study describes an approach to overcome these limitations. Methods: Mice bearing human epidermal growth factor receptor type 2 (HER2)–overexpressing tumors were injected with radiolabeled (124I, 125I) HER2-specific antibody (pertuzumab). Pertuzumab injection was followed 8 h later by the delivery of an engineered, antibody-based inhibitor of the receptor, FcRn. Biodistribution analyses and PET were performed at 24 and 48 h after pertuzumab injection. Results: The delivery of the engineered, antibody-based FcRn inhibitor (or Abdeg, for antibody that enhances IgG degradation) results in improved tumor-to-blood ratios, reduced systemic exposure to radiolabel, and increased contrast during PET. Conclusion: Abdegs have considerable potential as agents to stringently regulate antibody dynamics in vivo, resulting in increased contrast during molecular imaging with PET.

A new F-18 labeled PET agent for imaging Alzheimer's plaques

Amyloid plaques and neurofibrillary tangles are hallmarks of Alzheimer’s disease (AD). Advances in development of imaging agents have focused on targeting amyloid plaques. Notable success has been the development of C‐11 labeled PIB (Pittsburgh Compound) and a number of studies have demonstrated the utility of this agent. However, the short half life of C‐11 (t1/2: 20 min), is a limitation, thus has prompted the development of F‐18 labeled agents. Most of these agents are derivatives of amyloid binding dyes; Congo red and Thioflavin. Some of these agents are in clinical trials with encouraging results. We have been exploring new class of agents based on 8‐hydroxy quinoline, a weak metal chelator, targeting elevated levels of metals in plaques. Iodine‐123 labeled clioquinol showed affinity for amyloid plaques however, it had limited brain uptake and was not successful in imaging in intact animals and humans. We have been successful in synthesizing F‐18 labeled 8‐hydroxy quinoline. Small animal PET/CT imagi...

Targeting phosphatidylserine with calcium-dependent protein-drug conjugates for the treatment of cancer

In response to cellular stress, phosphatidylserine is exposed on the outer membrane leaflet of tumor blood vessels and cancer cells, motivating the development of phosphatidylserine-specific therapies. The generation of drug-conjugated phosphatidylserine-targeting agents represents an unexplored therapeutic approach, for which antitumor effects are critically dependent on efficient internalization and lysosomal delivery of the cytotoxic drug. In the current study, we have generated phosphatidylserine-targeting agents by fusing phosphatidylserine-binding domains to a human IgG1-derived Fc fragment. The tumor localization and pharmacokinetics of several phosphatidylserine-specific Fc fusions have been analyzed in mice and demonstrate that Fc-Syt1, a fusion containing the synaptotagmin 1 C2A domain, effectively targets tumor tissue. Conjugation of Fc-Syt1 to the cytotoxic drug monomethyl auristatin E results in a protein–drug conjugate (PDC) that is internalized into target cells and, due to the Ca2+ dependence of phosphatidylserine binding, dissociates from phosphatidylserine in early endosomes. The released PDC is efficiently delivered to lysosomes and has potent antitumor effects in mouse xenograft tumor models. Interestingly, although an engineered, tetravalent Fc-Syt1 fusion shows increased binding to target cells, this higher avidity variant demonstrates reduced persistence and therapeutic effects compared with bivalent Fc-Syt1. Collectively, these studies show that finely tuned, Ca2+-switched phosphatidylserine-targeting agents can be therapeutically efficacious. Mol Cancer Ther; 17(1); 169–82. ©2017 AACR.

Assessment of disease progression in Alzheimer's transgenic mice by PET imaging with F-18 quinoline

Michael O’Neill, Christian Czech, Ozmen Laurence, Jill Richardson, Gianluigi Forloni, Giovanni Frisoni, Laboratory of Epidemiology and Neuroimaging, IRCCS Fatebenefratelli, Brescia, Italy, Brescia, Italy; Mario Negri Institute for Pharmacological Research, Milano, Italy; Laboratory of Epidemiology and Neuroimaging, IRCCS Fatebenefratelli, Brescia, Italy; Mario Negri Institute for Pharmacological Research, Ranica(BG), Italy; Mario Negri Institute for Pharmacological Research, Milan, Italy; Eli Lilly, Lilly Research Centre, Surrey, United Kingdom; CNS Research, Hoffmann-La Roche AG, Basel, Switzerland; GlaxoSmithKline, Stevenage, United Kingdom; IRCCS Fatebenefratelli, Brescia, Italy.