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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

Cysteine-cathepsin targeting radiotracers labeled with I-125.
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Figure 10: Cysteine-cathepsin targeting radiotracers labeled with I-125.

Mentions: The development of radiotracers which target cysteine cathepsins started three decades ago with a tetrapeptide-derived chloromethylketone-based inhibitor labeled with iodine-125 ([125I]25a, Figure 10). Iodine-125 is one of four biomedically relevant iodine radioisotopes (Wilbur, 1992; Mier and Eisenhut, 2011). It stabilizes by electron capture, where a proton combines with an electron of the inner shells, usually the K-shell. The formed electron gap is filled under the emission of X-ray photons. While iodine-125-based radiotracers are typically employed for in vitro investigations, this radionuclide also offers the possibility of small-animal SPECT imaging. Radioiodination of biologically relevant compounds is very often achieved by reacting a hydroxyphenyl moiety with an iodine−+1 species which is generated from radioactive iodide and a mild oxidizing agent such as iodogen. This principle has been used to introduce iodine-125 into compounds [125I]25, [125I]26 and [125I]28–33 (Figure 10), which are all irreversible inhibitors that covalently target different cysteine proteases. Compounds [125I]25a and b seem to be the first described radiotracers to target cysteine cathepsins (Docherty et al., 1983, 1984). They have been used to identify a protease of 31.5 kDa of the granule fraction of rat Langerhans islets as cathepsin B by immunoprecipatation and SDS-PAGE. It is known that peptide-derived chloromethylketones can also interact covalently with the active site of serine proteases and Docherty et al. (1983) demonstrated the reactivity of [125I]25a toward trypsin. Therefore, doubts in the selectivity and the high intrinsic reactivity of this radiotracer motivated Mason et al. (1989b) to prepare [125I]26a as a 125I-labeled diazoketone. The specific activity of [125I]26a was determined to be 222 MBq/μmol. Deiodo-26a has been shown to be an effective inactivator of cathepsins L and B with selectivity over calpain, a cytosolic Ca2+-dependent cysteine protease. Iodination to non-radioactive 26a even improves the inhibitory properties (Crawford et al., 1988). The radiotracer [125I]26a has been used to identify cathepsin L and B in Kirsten-virus-transformed NIH3T3 cells by SDS-PAGE. Electrophoretic separation of trichloroacetic acid precipitates derived from extracts of cells that were incubated with [125I]26a indicated the presence of one active cathepsin B species of 33–35 kDa and two active forms of cathepsin L of 30 and 23 kDa. For comparison, immunoprecipitates of labeled proteins obtained by pulse-chase incubation with [35S]methionine were separated by SDS-PAGE. This resulted in the detection of a 39 and a 36 kDa species which have been assigned to the intracellular precursors of cathepsin B and L, respectively. Radiotracer [125I]26a was furthermore applied to investigate the presence of active cathepsins B and L in homogenates of human post mortem tissues of heart and skeletal muscle, brain, kidney, pancreas, and spleen (Mason et al., 1989a). Hence, [125I]26a represents an early example of an ABP. Further investigations by Mason et al. led to the development of radiotracer [125I]26b, in which the Z group of [125I]26a has been replaced by Fmoc and a second iodo-substituent has been attached ortho to the hydroxyl group in the tyrosine side chain (Xing et al., 1998). Notably, the non-radioactive reference compound 26b showed an inhibitory potential toward cathepsin B that was 15-fold higher than that of its deiodinated counterpart and more than twice as strong compared to the corresponding monoiodinated derivative. Considering inhibition of cathepsin L, the influence of iodination was inverse compared to cathepsin B, while inhibition of cathepsin L by 26b was still faster than that of cathepsin B. 26b was devoid of inhibitory potency toward cathepsin S. Radioiodination of deiodo-26b in the presence of non-radioactive sodium iodide resulted in the formation of [125I]26b. Thus, [125I]26b represents a carrier-added radiotracer in contrast to non-carrier-added [125I]26a. This is reflected by the specific activity of [125I]25b, which is with 8.3 MBq/μmol considerably lower than that of [125I]26a. Incubation of [125I]26b with a panel of human breast tumor cells and subsequent cell lysis and electrophoretic protein separation by SDS-PAGE showed that these cells contain up to four different molecular species of cathepsin L and two different forms of cathepsin B. The knowledge of the radiotracer's specific activity enabled the calculation of quantitative amounts of the different cathepsin B and L species in these cells in pmol/mg of cellular protein. Interestingly, these studies have revealed that higher levels of active cathepsins B and L are expressed in invasive breast tumor cells (MDA-MB-231, MDA-MB-435S and HS-578T), compared with those that are not invasive (MCF7 and SK-BR-3).


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

Löser R, Pietzsch J - Front Chem (2015)

Cysteine-cathepsin targeting radiotracers labeled with I-125.
© Copyright Policy
Related In: Results  -  Collection

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

Figure 10: Cysteine-cathepsin targeting radiotracers labeled with I-125.
Mentions: The development of radiotracers which target cysteine cathepsins started three decades ago with a tetrapeptide-derived chloromethylketone-based inhibitor labeled with iodine-125 ([125I]25a, Figure 10). Iodine-125 is one of four biomedically relevant iodine radioisotopes (Wilbur, 1992; Mier and Eisenhut, 2011). It stabilizes by electron capture, where a proton combines with an electron of the inner shells, usually the K-shell. The formed electron gap is filled under the emission of X-ray photons. While iodine-125-based radiotracers are typically employed for in vitro investigations, this radionuclide also offers the possibility of small-animal SPECT imaging. Radioiodination of biologically relevant compounds is very often achieved by reacting a hydroxyphenyl moiety with an iodine−+1 species which is generated from radioactive iodide and a mild oxidizing agent such as iodogen. This principle has been used to introduce iodine-125 into compounds [125I]25, [125I]26 and [125I]28–33 (Figure 10), which are all irreversible inhibitors that covalently target different cysteine proteases. Compounds [125I]25a and b seem to be the first described radiotracers to target cysteine cathepsins (Docherty et al., 1983, 1984). They have been used to identify a protease of 31.5 kDa of the granule fraction of rat Langerhans islets as cathepsin B by immunoprecipatation and SDS-PAGE. It is known that peptide-derived chloromethylketones can also interact covalently with the active site of serine proteases and Docherty et al. (1983) demonstrated the reactivity of [125I]25a toward trypsin. Therefore, doubts in the selectivity and the high intrinsic reactivity of this radiotracer motivated Mason et al. (1989b) to prepare [125I]26a as a 125I-labeled diazoketone. The specific activity of [125I]26a was determined to be 222 MBq/μmol. Deiodo-26a has been shown to be an effective inactivator of cathepsins L and B with selectivity over calpain, a cytosolic Ca2+-dependent cysteine protease. Iodination to non-radioactive 26a even improves the inhibitory properties (Crawford et al., 1988). The radiotracer [125I]26a has been used to identify cathepsin L and B in Kirsten-virus-transformed NIH3T3 cells by SDS-PAGE. Electrophoretic separation of trichloroacetic acid precipitates derived from extracts of cells that were incubated with [125I]26a indicated the presence of one active cathepsin B species of 33–35 kDa and two active forms of cathepsin L of 30 and 23 kDa. For comparison, immunoprecipitates of labeled proteins obtained by pulse-chase incubation with [35S]methionine were separated by SDS-PAGE. This resulted in the detection of a 39 and a 36 kDa species which have been assigned to the intracellular precursors of cathepsin B and L, respectively. Radiotracer [125I]26a was furthermore applied to investigate the presence of active cathepsins B and L in homogenates of human post mortem tissues of heart and skeletal muscle, brain, kidney, pancreas, and spleen (Mason et al., 1989a). Hence, [125I]26a represents an early example of an ABP. Further investigations by Mason et al. led to the development of radiotracer [125I]26b, in which the Z group of [125I]26a has been replaced by Fmoc and a second iodo-substituent has been attached ortho to the hydroxyl group in the tyrosine side chain (Xing et al., 1998). Notably, the non-radioactive reference compound 26b showed an inhibitory potential toward cathepsin B that was 15-fold higher than that of its deiodinated counterpart and more than twice as strong compared to the corresponding monoiodinated derivative. Considering inhibition of cathepsin L, the influence of iodination was inverse compared to cathepsin B, while inhibition of cathepsin L by 26b was still faster than that of cathepsin B. 26b was devoid of inhibitory potency toward cathepsin S. Radioiodination of deiodo-26b in the presence of non-radioactive sodium iodide resulted in the formation of [125I]26b. Thus, [125I]26b represents a carrier-added radiotracer in contrast to non-carrier-added [125I]26a. This is reflected by the specific activity of [125I]25b, which is with 8.3 MBq/μmol considerably lower than that of [125I]26a. Incubation of [125I]26b with a panel of human breast tumor cells and subsequent cell lysis and electrophoretic protein separation by SDS-PAGE showed that these cells contain up to four different molecular species of cathepsin L and two different forms of cathepsin B. The knowledge of the radiotracer's specific activity enabled the calculation of quantitative amounts of the different cathepsin B and L species in these cells in pmol/mg of cellular protein. Interestingly, these studies have revealed that higher levels of active cathepsins B and L are expressed in invasive breast tumor cells (MDA-MB-231, MDA-MB-435S and HS-578T), compared with those that are not invasive (MCF7 and SK-BR-3).

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