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Cysteine cathepsins: their role in tumor progression and recent trends in the development of imaging probes.

Löser R, Pietzsch J - Front Chem (2015)

Bottom Line: The considerable progress in this field over the last two decades has also raised interest in the visualization of these enzymes in their native context, especially with regard to tumor imaging.After a short introduction to structure and general functions of human cysteine cathepsins, we highlight their importance for drug discovery and development and provide a critical update on the current state of knowledge toward their involvement in tumor progression, with a special emphasis on their role in therapy response.In accordance with a radiopharmaceutical point of view, the main focus of this review article will be the discussion of recently developed fluorescence and radiotracer-based imaging agents together with related molecular probes.

View Article: PubMed Central - PubMed

Affiliation: Department of Radiopharmaceutical and Chemical Biology, Institute of Radiopharmaceutical Cancer Research, Helmholtz-Zentrum Dresden-Rossendorf Dresden, Germany ; Department of Chemistry and Food Chemistry, Technische Universität Dresden Dresden, Germany.

ABSTRACT
Papain-like cysteine proteases bear an enormous potential as drug discovery targets for both infectious and systemic human diseases. The considerable progress in this field over the last two decades has also raised interest in the visualization of these enzymes in their native context, especially with regard to tumor imaging. After a short introduction to structure and general functions of human cysteine cathepsins, we highlight their importance for drug discovery and development and provide a critical update on the current state of knowledge toward their involvement in tumor progression, with a special emphasis on their role in therapy response. In accordance with a radiopharmaceutical point of view, the main focus of this review article will be the discussion of recently developed fluorescence and radiotracer-based imaging agents together with related molecular probes.

No MeSH data available.


Related in: MedlinePlus

Polymeric/particulate fluorescent probes for cathepsin B. Due to its complexity and size, probe 24 is only schematically represented.
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Figure 9: Polymeric/particulate fluorescent probes for cathepsin B. Due to its complexity and size, probe 24 is only schematically represented.

Mentions: The development of imaging probes is not restricted to compounds of low molecular weight and a few polymeric and particulate probes for the in vivo detection of cathepsin B have been described. Among the first macromolecular probes for this purpose is a poly-L-lysine-based polymer, whose amino groups were partially functionalized with Cy5.5. The spatial proximity of the fluorophores led to internal fluorescence quenching and unmodified lysines served as recognition sites for cathepsin B-catalyzed cleavage, resulting in enhanced fluorescence. In vivo, probe activation within a mouse model of human breast cancer correlated with the tumor-associated cathepsin B activity (Bremer et al., 2002). In a different approach, a nanoparticle consisting of O6-hydroxyethylchitosane (chitosane = deacetylchitin) has been functionalized with the heptapeptidic cathepsin B recognition sequence GRR↓GKGG to a substitution degree of 21 peptide chains per 1 molecule of chitosane-based nanoparticle (Figure 9, compound 23) (Ryu et al., 2011). The particles exhibited a molecular weight of 345 kDa and a spherical shape with a diameter of 280 nm. The hexapeptide was equipped with Cy5.5 at the N-terminus and BHQ-3 at the side chain of Lys as fluorescence emitter and quencher, respectively. Exposure of the nanoprobe to 1.5 nM of cathepsin B resulted in an approximately 15-fold increase in fluorescence, while no significant dequenching was observed with cathepsin L, the aspartic protease cathepsin D or cathepsin B in the presence of Z-Phe-Lys-FMK (1b) as inhibitor. The uptake of the cathepsin B-responsive nanoparticle in SCC7 murine squamous cell carcinoma was accompanied by increasing red fluorescence, which colocalized with the green fluorescence for immunohistochemical detection of cellular cathepsin B. The cell-associated Cy5.5 fluorescence signal could be blocked by treatment with 1b and the particulate probe resulted in stronger NIR fluorescence than the isolated, soluble quenched peptide. The in vivo evaluation of the nanoprobe 23 was performed in mice bearing SCC7 tumors. The tumor-associated fluorescence increased up to 6 h p.i. Regarding the influence of inhibitor treatment and the comparison with the non-particulate probe the results obtained in cellulo could be confirmed. The fluorescence in non-target organs was more than twice as low as in the tumor. In a further study, this probe was re-evaluated in mice bearing tumors derived from HT29 human colorectal carcinoma cells (Ryu et al., 2014). Intravenous injection of the nanoprobe into these animals resulted in NIR fluorescence signals that were 17-fold higher than in the control animal where the tumor-associated cathepsin B activity has been blocked by intratumoral injection of 1b. Furthermore, the probe's capability to image the metastasis-associated cathepsin B activity in three different mouse models of metastatic tumors was evaluated. The first model concerned metastasis to the liver of 4T1-luc2 cells injected into spleen. Liver metastases were detectable 10–14 days after tumor cell injection into the spleen by luciferase-based bioluminescence imaging. Systemic administration of the cathepsin B-responsive nanoparticle resulted in a NIR fluorescence that matched the bioluminescence signal, while only minimal fluorescence was detectable upon injecting the probe into normal mice. The increased expression of cathepsin B in liver metastases has been confirmed by Western blot analysis. Similar results were obtained when murine red-fluorescent-protein-expressing RFP-B16F10 melanoma cells or highly malignant HT1080 cells were injected into the tail vein and into the peritoneum, respectively. The former experiment models the process of metastasis to the lung and the latter that of peritoneal metastasis. The uptake of the cathepsin B-responsive nanoprobe has been investigated in all these four tumor cell lines by fluorescence microscopy. A strong cell-associated Cy5.5-derived fluorescence was observable for the tumor cells, whereas only faint signals were detectable for the cathepsin B-negative NIH3T3 mouse embryo fibroblasts.


Cysteine cathepsins: their role in tumor progression and recent trends in the development of imaging probes.

Löser R, Pietzsch J - Front Chem (2015)

Polymeric/particulate fluorescent probes for cathepsin B. Due to its complexity and size, probe 24 is only schematically represented.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4477214&req=5

Figure 9: Polymeric/particulate fluorescent probes for cathepsin B. Due to its complexity and size, probe 24 is only schematically represented.
Mentions: The development of imaging probes is not restricted to compounds of low molecular weight and a few polymeric and particulate probes for the in vivo detection of cathepsin B have been described. Among the first macromolecular probes for this purpose is a poly-L-lysine-based polymer, whose amino groups were partially functionalized with Cy5.5. The spatial proximity of the fluorophores led to internal fluorescence quenching and unmodified lysines served as recognition sites for cathepsin B-catalyzed cleavage, resulting in enhanced fluorescence. In vivo, probe activation within a mouse model of human breast cancer correlated with the tumor-associated cathepsin B activity (Bremer et al., 2002). In a different approach, a nanoparticle consisting of O6-hydroxyethylchitosane (chitosane = deacetylchitin) has been functionalized with the heptapeptidic cathepsin B recognition sequence GRR↓GKGG to a substitution degree of 21 peptide chains per 1 molecule of chitosane-based nanoparticle (Figure 9, compound 23) (Ryu et al., 2011). The particles exhibited a molecular weight of 345 kDa and a spherical shape with a diameter of 280 nm. The hexapeptide was equipped with Cy5.5 at the N-terminus and BHQ-3 at the side chain of Lys as fluorescence emitter and quencher, respectively. Exposure of the nanoprobe to 1.5 nM of cathepsin B resulted in an approximately 15-fold increase in fluorescence, while no significant dequenching was observed with cathepsin L, the aspartic protease cathepsin D or cathepsin B in the presence of Z-Phe-Lys-FMK (1b) as inhibitor. The uptake of the cathepsin B-responsive nanoparticle in SCC7 murine squamous cell carcinoma was accompanied by increasing red fluorescence, which colocalized with the green fluorescence for immunohistochemical detection of cellular cathepsin B. The cell-associated Cy5.5 fluorescence signal could be blocked by treatment with 1b and the particulate probe resulted in stronger NIR fluorescence than the isolated, soluble quenched peptide. The in vivo evaluation of the nanoprobe 23 was performed in mice bearing SCC7 tumors. The tumor-associated fluorescence increased up to 6 h p.i. Regarding the influence of inhibitor treatment and the comparison with the non-particulate probe the results obtained in cellulo could be confirmed. The fluorescence in non-target organs was more than twice as low as in the tumor. In a further study, this probe was re-evaluated in mice bearing tumors derived from HT29 human colorectal carcinoma cells (Ryu et al., 2014). Intravenous injection of the nanoprobe into these animals resulted in NIR fluorescence signals that were 17-fold higher than in the control animal where the tumor-associated cathepsin B activity has been blocked by intratumoral injection of 1b. Furthermore, the probe's capability to image the metastasis-associated cathepsin B activity in three different mouse models of metastatic tumors was evaluated. The first model concerned metastasis to the liver of 4T1-luc2 cells injected into spleen. Liver metastases were detectable 10–14 days after tumor cell injection into the spleen by luciferase-based bioluminescence imaging. Systemic administration of the cathepsin B-responsive nanoparticle resulted in a NIR fluorescence that matched the bioluminescence signal, while only minimal fluorescence was detectable upon injecting the probe into normal mice. The increased expression of cathepsin B in liver metastases has been confirmed by Western blot analysis. Similar results were obtained when murine red-fluorescent-protein-expressing RFP-B16F10 melanoma cells or highly malignant HT1080 cells were injected into the tail vein and into the peritoneum, respectively. The former experiment models the process of metastasis to the lung and the latter that of peritoneal metastasis. The uptake of the cathepsin B-responsive nanoprobe has been investigated in all these four tumor cell lines by fluorescence microscopy. A strong cell-associated Cy5.5-derived fluorescence was observable for the tumor cells, whereas only faint signals were detectable for the cathepsin B-negative NIH3T3 mouse embryo fibroblasts.

Bottom Line: The considerable progress in this field over the last two decades has also raised interest in the visualization of these enzymes in their native context, especially with regard to tumor imaging.After a short introduction to structure and general functions of human cysteine cathepsins, we highlight their importance for drug discovery and development and provide a critical update on the current state of knowledge toward their involvement in tumor progression, with a special emphasis on their role in therapy response.In accordance with a radiopharmaceutical point of view, the main focus of this review article will be the discussion of recently developed fluorescence and radiotracer-based imaging agents together with related molecular probes.

View Article: PubMed Central - PubMed

Affiliation: Department of Radiopharmaceutical and Chemical Biology, Institute of Radiopharmaceutical Cancer Research, Helmholtz-Zentrum Dresden-Rossendorf Dresden, Germany ; Department of Chemistry and Food Chemistry, Technische Universität Dresden Dresden, Germany.

ABSTRACT
Papain-like cysteine proteases bear an enormous potential as drug discovery targets for both infectious and systemic human diseases. The considerable progress in this field over the last two decades has also raised interest in the visualization of these enzymes in their native context, especially with regard to tumor imaging. After a short introduction to structure and general functions of human cysteine cathepsins, we highlight their importance for drug discovery and development and provide a critical update on the current state of knowledge toward their involvement in tumor progression, with a special emphasis on their role in therapy response. In accordance with a radiopharmaceutical point of view, the main focus of this review article will be the discussion of recently developed fluorescence and radiotracer-based imaging agents together with related molecular probes.

No MeSH data available.


Related in: MedlinePlus