Apoptosis Imaging: Anti-Cancer Agents in Medicinal Chemistry
ABSTRACT There is a rapid expansion in the number of new anti-cancer drugs with remarkably different mechanisms of action that can augment traditional chemotherapy. As these agents are often used in combination with traditional chemotherapy testing the effects of these novel agents has proven difficult requiring large sample sizes to detect relatively small differences in patient survival. Despite the wide variety of mechanisms, most new drugs are thought to ultimately induce apoptosis of tumor cells or their supportive vasculature. Imaging agents that can non-invasively monitor apoptosis in response to these new drugs could therefore help streamline the drug development process. They may also help guide oncologists to identify those patients that could best benefit from a given therapeutic regimen, dose, or duration of drug. In this article we will outline the existing imaging agents and modalities that are currently undergoing clinical testing and those that could be rapidly translated into humans.
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- "Though PS exposure on the outer leaflet of the cell membrane has been a well-studied death phenotype, the molecular link between apoptosis and PS externalization is still unclear . Detailed information on the intracellular changes and proteins involved so far are described elsewhere [27,28,29,30,31]. "
ABSTRACT: Evaluation of efficacy of anti-cancer therapy is currently performed by anatomical imaging (e.g., MRI, CT). Structural changes, if present, become apparent 1-2 months after start of therapy. Cancer patients thus bear the risk to receive an ineffective treatment, whilst clinical trials take a long time to prove therapy response. Both patient and pharmaceutical industry could therefore profit from an early assessment of efficacy of therapy. Diagnostic methods providing information on a functional level, rather than a structural, could present the solution. Recent technological advances in molecular imaging enable in vivo imaging of biological processes. Since most anti-cancer therapies combat tumors by inducing apoptosis, imaging of apoptosis could offer an early assessment of efficacy of therapy. This review focuses on principles of and clinical experience with molecular imaging of apoptosis using Annexin A5, a widely accepted marker for apoptosis detection in vitro and in vivo in animal models. 99mTc-HYNIC-Annexin A5 in combination with SPECT has been probed in clinical studies to assess efficacy of chemo- and radiotherapy within 1-4 days after start of therapy. Annexin A5-based functional imaging of apoptosis shows promise to offer a personalized medicine approach, now primarily used in genome-based medicine, applicable to all cancer patients.Cancers 05/2013; 5(2):550-68. DOI:10.3390/cancers5020550
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ABSTRACT: Noninvasive detection and in vivo imaging of apoptosis plays a critical role in the development of therapeutics in many different fields including cancer. We have developed an apoptosis biosensor by fusing green fluorescent protein (GFP) to the N-terminus of the naturally secreted Gaussia luciferase separated by a caspase-3 cleavage peptide consisting of aspartic acid (D), glutamic acid (E), valine (V), and aspartic acid (D) or DEVD. We showed that this fusion is retained in the cytoplasm of cells in an inactive form. Upon apoptosis, the DEVD peptide is cleaved in response to caspase-3 activation, freeing ssGluc, which can now enter the secretory pathway where it is folded properly and is released from the cells and can be detected in the conditioned medium in culture or in blood of live animals ex vivo over time. Because Gluc is secreted from cells via conventional pathway through the endoplasmic reticulum (ER), Golgi and vesicles, we showed that the presence of Gluc in these compartments in response to apoptosis can be visualized in vivo using bioluminescence imaging. This reporter provides a valuable tool for imaging and real-time monitoring of apoptosis and is compatible with high-throughput functional screening application in cultured cells and animal models.Molecular Therapy 02/2011; 19(6):1090-6. DOI:10.1038/mt.2011.17 · 6.23 Impact Factor
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ABSTRACT: Metabolic biotinylation of intracellular and secreted proteins as well as surface receptors in mammalian cells provides a versatile way to monitor gene expression; to purify and target viral vectors; to monitor cell and tumor distribution in real time in vivo; to label cells for isolation; and to tag proteins for purification, localization, and trafficking. Here, we show that metabolic biotinylation of proteins fused to the bacterial biotin acceptor peptides (BAP) varies among different mammalian cell types and can be enhanced by over 10-fold upon overexpression of the bacterial biotin ligase directed to the same cellular compartment as the fusion protein. We also show that in vivo imaging of metabolically biotinylated cell surface receptors using streptavidin conjugates is significantly enhanced upon coexpression of bacterial biotin ligase in the secretory pathway. These findings have practical applications in designing more efficient targeting and imaging strategies.Analytical Chemistry 02/2011; 83(3):994-9. DOI:10.1021/ac102758m · 5.64 Impact Factor