Hagit Grimberg

Molecular imaging of cell death in vivo by a novel small molecule probe

Apoptosis has a role in many medical disorders, therefore assessment of apoptosis in vivo can be highly useful for diagnosis, follow-up and evaluation of treatment efficacy. ApoSense is a novel technology, comprising low molecular-weight probes, specifically designed for imaging of cell death in vivo. In the current study we present targeting and imaging of cell death both in vitro and in vivo, utilizing NST-732, a member of the ApoSense family, comprising a fluorophore and a fluorine atom, for both fluorescent and future positron emission tomography (PET) studies using an 18F label, respectively. In vitro, NST-732 manifested selective and rapid accumulation within various cell types undergoing apoptosis. Its uptake was blocked by caspase inhibition, and occurred from the early stages of the apoptotic process, in parallel to binding of Annexin-V, caspase activation and alterations in mitochondrial membrane potential. In vivo, NST-732 manifested selective uptake into cells undergoing cell-death in several clinically-relevant models in rodents: (i) Cell-death induced in lymphoma by irradiation; (ii) Renal ischemia/reperfusion; (iii) Cerebral stroke. Uptake of NST-732 was well-correlated with histopathological assessment of cell-death. NST-732 therefore represents a novel class of small-molecule detectors of apoptosis, with potential useful applications in imaging of the cell death process both in vitro and in vivo.

ApoSense: a novel technology for functional molecular imaging of cell death in models of acute renal tubular necrosis

PurposeAcute renal tubular necrosis (ATN), a common cause of acute renal failure, is a dynamic, rapidly evolving clinical condition associated with apoptotic and necrotic tubular cell death. Its early identification is critical, but current detection methods relying upon clinical assessment, such as kidney biopsy and functional assays, are insufficient. We have developed a family of small molecule compounds, ApoSense, that is capable, upon systemic administration, of selectively targeting and accumulating within apoptotic/necrotic cells and is suitable for attachment of different markers for clinical imaging. The purpose of this study was to test the applicability of these molecules as a diagnostic imaging agent for the detection of renal tubular cell injury following renal ischemia.MethodsUsing both fluorescent and radiolabeled derivatives of one of the ApoSense compounds, didansyl cystine, we evaluated cell death in three experimental, clinically relevant animal models of ATN: renal ischemia/reperfusion, radiocontrast-induced distal tubular necrosis, and cecal ligature and perforation-induced sepsis.ResultsApoSense showed high sensitivity and specificity in targeting injured renal tubular epithelial cells in vivo in all three models used. Uptake of ApoSense in the ischemic kidney was higher than in the non-ischemic one, and the specificity of ApoSense targeting was demonstrated by its localization to regions of apoptotic/necrotic cell death, detected morphologically and by TUNEL staining.ConclusionApoSense technology should have significant clinical utility for real-time, noninvasive detection of renal parenchymal damage of various types and evaluation of its distribution and magnitude; it may facilitate the assessment of efficacy of therapeutic interventions in a broad spectrum of disease states.

Molecular Imaging of Neurovascular Cell Death in Experimental Cerebral Stroke by PET

Clinical molecular imaging of apoptosis is a highly desirable yet unmet challenge. Here we provide the first report on 18F-labeled 5-fluoropentyl-2-methyl-malonic acid (18F-ML-10), a small-molecule, 18F-labeled PET tracer for the imaging of apoptosis in vivo; this report includes descriptions of the synthesis, radiolabeling, and biodistribution of this novel apoptosis marker. We also describe the use of 18F-ML-10 for small-animal PET of neurovascular cell death in experimental cerebral stroke in mice. Methods: 18F-ML-10 was synthesized by nucleophilic substitution from the respective mesylate precursor, and its biodistribution was assessed in healthy rats. Permanent occlusion of the middle cerebral artery (MCA) was induced in mice, and small-animal PET was performed 24 h later. Results: Efficient radiolabeling of ML-10 with 18F was achieved. Biodistribution studies with 18F-ML-10 revealed rapid clearance from blood (half-life of 23 min), a lack of binding to healthy tissues, and rapid elimination through the kidneys. No significant tracer metabolism in vivo was observed. Clear images of distinct regions of increased uptake, selectively in the ischemic MCA territory, were obtained in the in vivo small-animal PET studies. Uptake measurements ex vivo revealed 2-fold-higher uptake in the affected hemisphere and 6- to 10-fold-higher uptake in the region of interest of the infarct. The cerebral uptake of 18F-ML-10 was well correlated with histologic evidence of cell death. The tracer was retained in the stroke area but was cleared from blood and from intact brain areas. Conclusion: 18F-ML-10 is useful for noninvasive PET of neurovascular histopathology in ischemic cerebral stroke in vivo. Such an assessment may assist in characterization of the extent of stroke-related cerebral damage and in the monitoring of disease course and effect of treatment.

Monitoring of chemotherapy-induced cell death in melanoma tumors by N,N'-Didansyl-L-cystine.

Early assessment of the efficacy of anticancer agents is a highly desirable and an unmet need in clinical oncology. Clinical imaging of cell-death may be useful in addressing this need, as induction of tumor cell-death is the primary mechanism of action of most anticancer drugs. In this study, we examined the performance of N,N′-Didansyl-L-cystine (DDC), a member of the ApoSense family of novel small molecule detectors of cell-death, as a potential tool for monitoring cell-death in cancer models. Detection of cell-death by DDC was examined in fluorescent studies on B16 melanoma cells both in vitro and ex vivo following its in vivo administration. In vitro, DDC manifested selective uptake and accumulation within apoptotic cells that was highly correlated with Annexin-V binding, changes in mitochondrial membrane potential, and caspase activation. Uptake was not ATP-dependent, and was inducible by calcium mobilization. In vivo, DDC selectively targeted cells undergoing cell-death in melanoma tumors, while not binding to viable tumor cells. Chemotherapy caused marked tumor cell-death, evidenced by increased DDC uptake, which occurred before a detectable change in tumor size and was associated with increased animal survival. These data confirm the usefulness of imaging of cell-death by DDC as a tool for early monitoring of tumor response to anti-cancer therapy.

Corrigendum to “Novel molecular imaging of cell death in experimental cerebral stroke” [Brain Res. 1144 (2007) 156–164]

Department of Neurology, Rabin Medical Center, Petah-Tiqva, IsraelThe last author, Ilan Ziv discovered an error in his affiliation information. The correct affiliation information should be listed as,“Aposense Ltd, Petach-Tiqva; and the Sackler School of Medicine, Tel-Aviv University, Tel-Aviv; and the Department of Neurology,Rabin Medical Center, Petach-Tiqva, Israel”.