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Novel, cysteine-modified chelation strategy for the incorporation of [M(I)(CO)(3)](+) (M = Re, (99m)Tc) in an ?-MSH peptide.

ABSTRACT: Engineering peptide-based targeting agents with residues for site-specific and stable complexation of radionuclides is a highly desirable strategy for producing diagnostic and therapeutic agents for cancer and other diseases. In this report, a model N-S-N(Py) ligand (3) and a cysteine-derived ?-melanocyte stimulating hormone (?-MSH) peptide (6) were used as novel demonstrations of a widely applicable chelation strategy for incorporation of the [M(I)(CO)(3)](+) (M = Re, (99m)Tc) core into peptide-based molecules for radiopharmaceutical applications. The structural details of the core ligand-metal complexes as model systems were demonstrated by full chemical characterization of fac-[Re(I)(CO)(3)(N,S,N(Py)-3)](+) (4) and comparative high-performance liquid chromatography (HPLC) analysis between 4 and [(99m)Tc(I)(CO)(3)(N,S,N(Py)-3)](+) (4a). The ?-MSH analogue bearing the N-S-N(Py) chelate on a modified cysteine residue (6) was generated and complexed with [M(I)(CO)(3)](+) to confirm the chelation strategy's utility when applied in a peptide-based targeting agent. Characterization of the Re(I)(CO)(3)-6 peptide conjugate (7) confirmed the efficient incorporation of the metal center, and the (99m)Tc(I)(CO)(3)-6 analogue (7a) was explored as a potential single photon emission computed tomography (SPECT) compound for imaging the melanocortin 1 receptor (MC1R) in melanoma. Peptide 7a showed excellent radiolabeling yields and in vitro stability during amino acid challenge and serum stability assays. In vitro B16F10 melanoma cell uptake of 7a reached a modest value of 2.3 ± 0.08% of applied activity at 2 h at 37 °C, while this uptake was significantly reduced by coincubation with a nonlabeled ?-MSH analogue, NAPamide (3.2 ?M) (P < 0.05). In vivo SPECT/X-ray computed tomography (SPECT/CT) imaging and biodistribution of 7a were evaluated in a B16F10 melanoma xenografted mouse model. SPECT/CT imaging clearly visualized the tumor at 1 h post injection (p.i.) with high tumor-to-background contrast. Blocking studies with coinjected NAPamide (10 mg per kg of mouse body weight) confirmed the in vivo specificity of 7a for MC1R-positive tumors. Biodistribution results with 7a yielded a moderate tumor uptake of 1.20 ± 0.09 percentage of the injected radioactive dose per gram of tissue (% ID/g) at 1 h p.i. Relatively high uptake of 7a was also seen in the kidneys and liver at 1 h p.i. (6.55 ± 0.36% ID/g and 4.44 ± 0.17% ID/g, respectively), although reduced kidney uptake was seen at 4 h p.i. (3.20 ± 0.48% ID/g). These results demonstrate the utility of the novel [M(I)(CO)(3)](+) chelation strategy when applied in a targeting peptide.

SUBMITTER: Jiang H

PROVIDER: S-EPMC3525672 | biostudies-literature | 2012 Nov

REPOSITORIES: biostudies-literature

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Novel, cysteine-modified chelation strategy for the incorporation of [M(I)(CO)(3)](+) (M = Re, (99m)Tc) in an α-MSH peptide.

Jiang Han H Kasten Benjamin B BB Liu Hongguang H Qi Shibo S Liu Yang Y Tian Mei M Barnes Charles L CL Zhang Hong H Cheng Zhen Z Benny Paul D PD

Bioconjugate chemistry 20121108 11

Engineering peptide-based targeting agents with residues for site-specific and stable complexation of radionuclides is a highly desirable strategy for producing diagnostic and therapeutic agents for cancer and other diseases. In this report, a model N-S-N(Py) ligand (3) and a cysteine-derived α-melanocyte stimulating hormone (α-MSH) peptide (6) were used as novel demonstrations of a widely applicable chelation strategy for incorporation of the [M(I)(CO)(3)](+) (M = Re, (99m)Tc) core into peptide ...[more]

PMID: 23110503

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Project description:The copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) click reaction was used to incorporate alkyne-functionalized dipicolylamine (DPA) ligands (1 and 3) for fac-[M(I)(CO)3](+) (M = Re/(99m)Tc) complexation into an ?-melanocyte stimulating hormone (?-MSH) peptide analogue. A novel DPA ligand with carboxylate substitutions on the pyridyl rings (3) was designed to increase the hydrophilicity and to decrease in vivo hepatobiliary retention of fac-[(99m)Tc(I)(CO)3](+) complexes used in single photon emission computed tomography (SPECT) imaging studies with targeting biomolecules. The fac-[Re(I)(CO)3(3)] complex (4) was used for chemical characterization and X-ray crystal analysis prior to radiolabeling studies between 3 and fac-[(99m)Tc(I)(OH2)3(CO)3](+). The corresponding (99m)Tc complex (4a) was obtained in high radiochemical yields, was stable in vitro for 24 h during amino acid challenge and serum stability assays, and showed increased hydrophilicity by log P analysis compared to an analogous complex with nonfunctionalized pyridine rings (2a). An ?-MSH peptide functionalized with an azide was labeled with fac-[M(I)(CO)3](+) using both click, then chelate (CuAAC reaction with 1 or 3 followed by metal complexation) and chelate, then click (metal complexation of 1 and 3 followed by CuAAC with the peptide) strategies to assess the effects of CuAAC conditions on fac-[M(I)(CO)3](+) complexation within a peptide framework. The peptides from the click, then chelate strategy had different HPLC tR's and in vitro stabilities compared to those from the chelate, then click strategy, suggesting nonspecific coordination of fac-[M(I)(CO)3](+) using this synthetic route. The fac-[M(I)(CO)3](+)-complexed peptides from the chelate, then click strategy showed >90% stability during in vitro challenge conditions for 6 h, demonstrated high affinity and specificity for the melanocortin 1 receptor (MC1R) in IC50 analyses, and led to moderately high uptake in B16F10 melanoma cells. Log P analysis of the (99m)Tc-labeled peptides confirmed the enhanced hydrophilicity of the peptide bearing the novel, carboxylate-functionalized DPA chelate (10a') compared to the peptide with the unmodified DPA chelate (9a'). In vivo biodistribution analysis of 9a' and 10a' showed moderate tumor uptake in a B16F10 melanoma xenograft mouse model with enhanced renal uptake and surprising intestinal uptake for 10a' compared to predominantly hepatic accumulation for 9a'. These results, coupled with the versatility of CuAAC, suggests this novel, hydrophilic chelate can be incorporated into numerous biomolecules containing azides for generating targeted fac-[M(I)(CO)3](+) complexes in future studies.

Project description:PurposeSentinel lymph node (SLN) biopsy has proven to reliably stage the clinically negative neck in early-stage oral squamous cell carcinoma (OSCC). [99mTc]Tc-tilmanocept may be of benefit in OSCC with complex lymphatic drainage patterns and close spatial relation to SLNs.MethodsA prospective within-patient evaluation study was designed to compare [99mTc]Tc-tilmanocept with [99mTc]Tc-nanocolloid for SLN detection. A total of 20 patients with early-stage OSCC were included, who underwent lymphoscintigraphy with both tracers. Both lymphoscintigraphic images of each patient were evaluated for SLN detection and radiotracer distribution at 2-4 h post-injection.ResultsThe injection site's remaining radioactivity was significantly lower for [99mTc]Tc-tilmanocept (29.9%), compared with [99mTc]Tc-nanocolloid (60.9%; p < 0.001). Radioactive uptake in SLNs was significantly lower for [99mTc]Tc-tilmanocept (1.95%) compared with [99mTc]Tc-nanocolloid (3.16%; p = 0.010). No significant difference was seen in SLN to injection site ratio in radioactivity between [99mTc]Tc-tilmanocept (0.066) and [99mTc]Tc-nanocolloid (0.054; p = 0.232). A median of 3.0 and 2.5 SLNs were identified with [99mTc]Tc-tilmanocept and [99mTc]Tc-nanocolloid, respectively (p = 0.297). Radioactive uptake in higher echelon nodes was not significantly different between [99mTc]Tc-tilmanocept (0.57%) and [99mTc]Tc-nanocolloid (0.86%) (p = 0.052). A median of 2.0 and 2.5 higher echelon nodes was identified with [99mTc]Tc-tilmanocept and [99mTc]Tc-nanocolloid, respectively (p = 0.083).Conclusion[99mTc]Tc-tilmanocept had a higher injection site clearance, but at the same time a lower uptake in the SLN, resulting in an SLN to injection site ratio, which was not significantly different from [99mTc]Tc-nanocolloid. The relatively low-radioactive uptake in SLNs of [99mTc]Tc-tilmanocept may limit intraoperative detection of SLNs, but can be overcome by a higher injection dose.

Project description:BACKGROUND:Molecular breast imaging (MBI) performed with 99mTc sestamibi has been shown to be a valuable technique for the detection of breast cancer. Alternative radiotracers such as 99mTc maraciclatide may offer improved uptake in breast lesions. The purpose of this study was to compare relative performance of 99mTc sestamibi and 99mTc maraciclatide in patients with suspected breast cancer, using a high-resolution dedicated gamma camera for MBI. Women with breast lesions suspicious for malignancy were recruited to undergo two MBI examinations-one with 99mTc sestamibi and one with 99mTc maraciclatide. A radiologist interpreted MBI studies in a randomized, blinded fashion to assign an assessment score (1-5) and measured lesion size. Lesion-to-background (L/B) ratio was measured with region-of-interest analysis. RESULTS:Among 39 analyzable patients, 21 malignant tumors were identified in 21 patients. Eighteen of 21 tumors (86%) were seen on 99mTc sestamibi MBI and 19 of 21 (90%) were seen on 99mTc maraciclatide MBI (p?=?1). Tumor extent measured with both radiopharmaceuticals correlated strongly with pathologic size (99mTc sestamibi, r?=?0.84; 99mTc maraciclatide, r?=?0.81). The L/B ratio in detected breast cancers was similar for the two radiopharmaceuticals: 1.55?±?0.36 (mean?±?S.D.) for 99mTc sestamibi and 1.62?±?0.37 (mean?±?S.D.) for 99mTc maraciclatide (p?=?0.53). No correlation was found between the L/B ratio and molecular subtype for 99mTc sestamibi (r s ?=?0.12, p?=?0.63) or 99mTc maraciclatide (r s ?=?-0.12, p?=?0.64). Of 20 benign lesions, 10 (50%) were seen on 99mTc sestamibi and 9 of 20 (45%) were seen on 99mTc maraciclatide images (p?=?0.1). The average L/B ratio for benign lesions was 1.34?±0.40 (mean?±S.D.) for 99mTc sestamibi and 1.41?±0.52 (mean?±S.D.) for 99mTc maraciclatide (p?=?0.75). Overall diagnostic performance was similar for both radiopharmaceuticals. AUC from ROC analysis was 0.83 for 99mTc sestamibi and 0.87 for 99mTc maraciclatide (p?=?0.64). CONCLUSIONS:99mTc maraciclatide offered comparable lesion uptake to 99mTc sestamibi, in both malignant and benign lesions. There was good correlation between lesion extent and uptake measured from both radiopharmaceuticals. 99mTc maraciclatide offered a marginal (but not significant) improvement in sensitivity over 99mTc sestamibi. Our findings did not support an association between the uptake of either radiopharmaceutical and tumor molecular subtype. TRIAL REGISTRATION:ClinicalTrials.gov, NCT00888589.

Project description:ObjectiveTo investigate the value of integrin ?v?3 targeted imaging with 99mTc-HYNIC-PEG4-E[PEG4-c(RGDfk)]2 (99mTc-3P-RGD2) as a radiotracer in dectecting osteolytic bone metastases.MethodsThis is a retrospective study involving a cohort of 69 consecutive patients including 59 with lung cancer and 10 with other cancers. Patients were required to receive whole body scan (WBS) and regional SPECT/CT imaging with 99mTc-3P-RGD2 (RGD imaging) and 99mTc-MDP (MDP imaging) as a radiotracer successively within days. Final diagnosis was based on comprehensive assessment of all available data including case history, CT, MRI, SPECT/CT, PET/CT, histopathology and 6-12 months follow-up. Visual observation and semiquantitative analysis (T/N: tracer uptake ratio of osteolytic metastases to normal bone) of 99mTc-3P-RGD2 or 99mTc-MDP imaging were performed and their detective values for osteolytic metastases were compared.ResultsA total of 131 osteolytic metastatic lesions were retrospectively studied. Osteolytic metastases mainly presented as "hot region", occasionally as "cool or normal region" on RGD imaging. The detection sensitivity of RGD WBS for osteolytic metastases was significantly higher than that of 99mTc-MDP WBS (80.9% vs. 46.6%, p<0.01). The sensitivity increased to 96.2% (126/131) when combining with SPECT/CT. 99mTc-3P-RGD2 imaging also promoted the detection of unknown primary tumor, lymph node metastases and offered information for clinical staging. T/N of 99mTc-3P-RGD2 in lung adenocarcinoma osteolytic metastases showed no statistical difference compared with that in squamous-cell carcinoma (6.84±3.46 vs. 7.33±3.22, t = 0.39, p = 0.71). Whereas, it was higher in osteolytic metastases from lung cancer than that from thyroid cancer (7.05±3.01 vs. 4.11±2.67, p = 0.03).Conclusion99mTc-3P-RGD2 peptide imaging showed great potential for detection of osteolytic bone metastasis due to high expression level of integrin ?v?3 on osteoclast and most tumor cells.

Dataset Information

Novel, cysteine-modified chelation strategy for the incorporation of [M(I)(CO)(3)](+) (M = Re, (99m)Tc) in an ?-MSH peptide.

Publications

Novel, cysteine-modified chelation strategy for the incorporation of [M(I)(CO)(3)](+) (M = Re, (99m)Tc) in an α-MSH peptide.

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