Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:4.6.1.2 (guanylate cyclase)
 8,497 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In vitro competitive binding studies of In-DOTA-NCS-6-Ahx-Phe(19)-ST[1-19] vs. 125I-Tyr(5)-6-Ahx-Phe(19)-ST[1-19] with guanylate cyclase -C (GC-C) receptors on human colon cancer LS-180 cells revealed an IC(50) value of 7.7 +/- 0.1.6 nM. The in vitro cellular residualization studies of the 111In-DOTA-NCS-ST peptide and GC-C receptor mediated stimulated cGMP production with LS-180 cells demonstrates that this peptide selectively binds to LS-180 cells in an agonistic fashion. In vivo biodistribution studies in LS-180 tumor bearing SCID mice demonstrates that the 111In-DOTA-NCS-ST peptide targets the tumor with a specific uptake of 0.94 +/- 0.31%ID/g at 1 hr p.i. and approximately 23% was retained by the tumor at 4 hrs p.i. The radioactivity cleared rapidly from the blood stream with 84.5 +/- 3.4%ID at 1h p.i. found in the urine. High activity in urine and kidney, and minimal activity in liver and intestines, demonstrates preferential clearance of the radioactivity through the renal/urinary pathway. The specific in vitro and in vivo accumulation of the radioactivity by LS-180 human colonic cancer cells highlights the potential of radiometallated-DOTA-ST analogs as diagnostic/therapeutic radiopharmaceuticals.
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PMID:In vivo evaluation of an 111In-labeled ST-peptide analog for specific-targeting of human colon cancers. 1171 9

New human Escherichia coli heat-stable peptide (ST(h)) analogues containing a DOTA chelating group were synthesized by sequential and selective formation of disulfides bonds in the peptide. This synthetic approach utilizes three orthogonal thiol-protecting groups, Trt, Acm, and t-Bu, to form three disulfide bonds by successive reactions using 2-PDS, iodine, and silyl chloride-sulfoxide systems. The DOTA-ST(h) conjugates exhibiting high guanylin/guanylate cyclase-C (GC-C) receptor binding affinities were obtained with >98% purity. In vitro competitive binding assays, employing T-84 human colon cancer cells, demonstrated the IC(50) values of <2 nM for GC-C receptor binding suggesting that the new synthetic ST(h) analogues are biologically active. In vitro stability studies of the (111)In-DOTA-Phe(19)-ST(h) conjugate incubated in human serum at 37 degrees C under 5% CO(2) atmosphere revealed that this conjugate is extremely stable with no observable decomposition at 24 h postincubation. HPLC analysis of mouse urine at 1 h pi of the (111)In-DOTA-Phe(19)-ST(h) conjugate showed only about 15% decomposition suggesting that the (111)In-DOTA-Phe(19)-ST(h) conjugate is highly stable, even under in vivo conditions. In vivo pharmacokinetic studies of the (111)In-DOTA-Phe(19)-ST(h) conjugate in T-84 human colon cancer derived xenografts in SCID mice conducted at 1 h pi showed an initial tumor uptake of 2.04 +/- 0.30% ID/g at 1 h pi with efficient clearance from the blood pool (0.23 +/- 0.14% ID/g, 1 h pi) by excretion mainly through the renal/urinary pathway (95.8 +/- 0.2% ID, 1 h pi). High tumor/blood, tumor/muscle, and tumor/liver ratios of approximately 9:1, 68:1, and 26:1, respectively, were achieved at 1 h pi The specific in vitro and in vivo uptake of the radioactivity by human colonic cancer cells highlights the potential of radiometalated-DOTA-ST(h) conjugates as diagnostic/therapeutic radiopharmaceuticals.
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PMID:Chemical synthesis of Escherichia coli ST(h) analogues by regioselective disulfide bond formation: biological evaluation of an (111)In-DOTA-Phe(19)-ST(h) analogue for specific targeting of human colon cancers. 1190 59

Research into the interaction between the E. coli heat-stable enterotoxin (STh) and the guanylin receptor guanylate cyclase C (GC-C) has generated >100 synthetic analogs of the peptide, several of which have been investigated as imaging or therapeutic agents for colorectal cancers. The evidence presented here suggests that in addition to STh binding to GC-C expressing cell lines derived from human colon, STh also specifically binds to an as yet unidentified receptor expressed in high densities on the surface of cell lines derived from human breast cancers. In vitro whole-cell crosslinking studies using 125I-labeled F19-STh(1-19) demonstrate that the putative STh binding protein migrates as an approximately 120-125 kDa species by SDS-PAGE, significantly smaller than the glycosylated GC-C molecule found in the T84 human colon cancer cell line. RT-PCR using total RNA isolated from breast and colon cancer cell lines indicates that GC-C transcripts are undetectable in human breast cancer cell lines and abundant in human colon cancer cell lines. In vitro competitive binding studies using STh analogs and the estrogen receptor positive (ER+) T-47D cell line demonstrated IC50 values between 2.6 and 8.5 nM. Similar studies on the estrogen receptor negative (ER-) cell line MDA-MB-231 showed IC50's between 5.6 and 9.9 nM. Saturation binding analysis revealed receptor expression to fall between 40,000 and 120,000 sites per cell in these cell lines, receptor abundances equal to or greater than the abundance of GC-C in colorectal cancer cell lines. STh binding to these cells, although of similar affinity to STh binding to GC-C, is distinguishable from it on the basis of its ligand specificity. The characteristics of STh analogs as radiopharmaceutical agents were tested in an in vivo model utilizing T-47D human breast cancer cell xenografts in SCID mice. Clearance of STh analogs was rapid, primarily via renal excretion into the urine, with >85% ID excreted into the urine at 1 h p.i. Tumor uptake at 1 h p.i. in T-47D tumor cell xenografts was 0.67+/-0.23% ID/g, and was significantly decreased (p<0.05) upon co-administration of 4 mg/kg unlabeled STh. These results suggest that STh may find application for the imaging and treatment of breast cancer.
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PMID:In vitro and in vivo evaluation of 111In-labeled E. coli heat-stable enterotoxin analogs for specific targeting of human breast cancers. 1672 66

Analogues of the E. coli heat-stable enterotoxin (STh) are currently under study as both imaging and therapeutic agents for colorectal cancer. Studies have shown that the guanylate cyclase C (GC-C) receptor is commonly expressed in colorectal cancers. It has also been shown that STh peptides inhibit the growth of tumor cells expressing GC-C. The ability to determine GC-C status of tumor tissue using in vivo molecular imaging techniques would provide a useful tool for the optimization of GC-C-targeted therapeutics. In this work, we have compared receptor binding affinities, internalization/efflux rates, and in vivo biodistribution patterns of an STh analogue linked to N-terminal DOTA, TETA, and NOTA chelating moieties and radiolabeled with Cu-64. The peptide F(19)-STh(2-19) was N-terminally labeled with three different chelating groups via NHS ester activation and characterized by RP-HPLC, ESI-MS, and GC-C receptor binding assays. The purified conjugates were radiolabeled with Cu-64 and used for in vitro internalization/efflux, in vivo biodistribution, and in vivo PET imaging studies. In vivo experiments were carried out using SCID mice bearing T84 human colorectal cancer tumor xenografts. Incorporation of DOTA-, TETA-, and NOTA-chelators at the N-terminus of the peptide F(19)-STh(2-19) resulted in IC(50)s between 1.2 and 3.2 nM. In vivo, tumor localization was similar for all three compounds, with 1.2-1.3%ID/g at 1 h pi and 0.58-0.83%ID/g at 4 h pi. The principal difference between the three compounds related to uptake in nontarget tissues, principally kidney and liver. At 1 h pi, (64)Cu-NOTA-F(19)-STh(2-19) demonstrated significantly (p < 0.05) lower uptake in liver than (64)Cu-DOTA-F(19)-STh(2-19) (0.36 +/- 0.13 vs 1.21 +/- 0.65%ID/g) and significantly (p < 0.05) lower uptake in kidney than (64)Cu-TETA-F(19)-STh(2-19) (3.67 +/- 1.60 vs 11.36 +/- 2.85%ID/g). Use of the NOTA chelator for coordination of Cu-64 in the context of E. coli heat-stable enterotoxin analogues results in higher tumor/nontarget tissue ratios at 1 h pi than either DOTA or TETA macrocycles. Heat-stable enterotoxin-based radiopharmaceuticals such as these provide a means of noninvasively determining GC-C receptor status in colorectal cancers by PET.
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PMID:Comparative evaluation of three 64Cu-labeled E. coli heat-stable enterotoxin analogues for PET imaging of colorectal cancer. 2053 42