Biodistribution of [64Cu]Cu2+ and variance of metallothionein during tumor treatment by copper

Insights into Trace Metal Metabolism in Health and Disease from PET: "PET Metallomics"

Essential trace metals such as copper, zinc, iron, and manganese perform critical functions in cellular and physiologic processes including catalytic, regulatory, and signaling roles. Disturbed metal homeostasis is associated with the pathogenesis of diseases such as dementia, cancer, and inherited metabolic abnormalities. Intracellular pathways involving essential metals have been extensively studied but whole-body fluxes and transport between different compartments remain poorly understood. The growing availability of PET scanners and positron-emitting isotopes of key essential metals, particularly 64Cu, 63Zn, and 52Mn, provide new tools with which to study these processes in vivo. This review highlights opportunities that now present themselves, exemplified by studies of copper metabolism that are in the vanguard of a new research front in molecular imaging: "PET metallomics."

Reduced 64Cu uptake and tumor growth inhibition by knockdown of human copper transporter 1 in xenograft mouse model of prostate cancer

Copper is an element required for cell proliferation and angiogenesis. Human prostate cancer xenografts with increased (64)Cu radioactivity were visualized previously by PET using (64)CuCl2 as a radiotracer ((64)CuCl2 PET). This study aimed to determine whether the increased tumor (64)Cu radioactivity was due to increased cellular uptake of (64)Cu mediated by human copper transporter 1 (hCtr1) or simply due to nonspecific binding of ionic (64)CuCl2 to tumor tissue. In addition, the functional role of hCtr1 in proliferation of prostate cancer cells and tumor growth was also assessed.

METHODS

A lentiviral vector encoding short-hairpin RNA specific for hCtr1 (Lenti-hCtr1-shRNA) was constructed for RNA interference-mediated knockdown of hCtr1 expression in prostate cancer cells. The degree of hCtr1 knockdown was determined by Western blot, and the effect of hCtr1 knockdown on copper uptake and proliferation were examined in vitro by cellular (64)Cu uptake and cell proliferation assays. The effects of hCtr1 knockdown on tumor uptake of (64)Cu were determined by PET quantification and tissue radioactivity assay. The effects of hCtr1 knockdown on tumor growth were assessed by PET/CT and tumor size measurement with a caliper.

RESULTS

RNA interference-mediated knockdown of hCtr1 was associated with the reduced cellular uptake of (64)Cu and the suppression of prostate cancer cell proliferation in vitro. At 24 h after intravenous injection of the tracer (64)CuCl2, the (64)Cu uptake by the tumors with knockdown of hCtr1 (4.02 ± 0.31 percentage injected dose per gram [%ID/g] in Lenti-hCtr1-shRNA-PC-3 and 2.30 ± 0.59 %ID/g in Lenti-hCtr1-shRNA-DU-145) was significantly lower than the (64)Cu uptake by the control tumors without knockdown of hCtr1 (7.21 ± 1.48 %ID/g in Lenti-SCR-shRNA-PC-3 and 5.57 ± 1.20 %ID/g in Lenti-SCR-shRNA-DU-145, P < 0.001) by PET quantification. Moreover, the volumes of prostate cancer xenograft tumors with knockdown of hCtr1 (179 ± 111 mm(3) for Lenti-hCtr1-shRNA-PC-3 or 39 ± 22 mm(3) for Lenti-hCtr1-shRNA-DU-145) were significantly smaller than those without knockdown of hCtr1 (536 ± 191 mm(3) for Lenti- SCR-shRNA-PC-3 or 208 ± 104 mm(3) for Lenti-SCR-shRNA-DU-145, P < 0.01).

CONCLUSION

Overall, data indicated that hCtr1 is a promising theranostic target, which can be further developed for metabolic imaging of prostate cancer using (64)CuCl2 PET/CT and personalized cancer therapy targeting copper metabolism.

In vitro and in vivo evaluation of ⁶⁴Cu-radiolabeled KCCYSL peptides for targeting epidermal growth factor receptor-2 in breast carcinomas

Epidermal growth factor receptor-2 (EGFR-2) has been implicated in the pathogenesis of breast and other carcinomas. In this report, we tested the ability of a bacteriophage selected peptide KCCYSL, radiolabeled with ⁶⁴Cu, to image EGFR-2 expressing breast tumors in vivo by positron emission tomography (PET). We evaluated and compared the in vivo tissue distribution and imaging properties of ⁶⁴Cu-X-(Gly-Ser-Gly)-KCCYSL peptide (X = 1,4,7,10, tetraazacyclododecane-N,N',N'',N'''-tetracetic acid, [DOTA] 1,4,8,11-tetraazabicyclo[6.6.2]hexadecane-4,11-diacetic acid [CB-TE2A], and 1,4,7-triazacyclononane-1,4,7-triacetic acid [NOTA] chelators) in a human breast cancer xenograft mouse model using dual modality PET and computed tomography (CT). The synthesized peptides DO3A-GSG-KCCYSL, CB-TE2A-GSG-KCCYSL, and NO2A-GSG-KCCYSL were purified, radiolabeled with ⁶⁴Cu, and evaluated for human breast cancer cell (MDA-MB-435) binding, 50% inhibitory concentration, and serum stability. In vivo pharmacokinetic and small animal PET/CT imaging studies were performed using SCID mice bearing MDA-MB-435 xenografts. The radiolabeled peptides bound with an 50% inhibitory concentration of 42.0 ± 10.2 nM (DO3A), 31 ± 7.9 nM (CB-TE2A), and 44.2 ± 6.6 nM (NO2A) to cultured MDA-MB-435 cells. All of the radiolabeled peptides were stable in vitro. The tumor uptake of DO3A, CB-TE2A, and NO2A peptides were 0.73 ± 0.15 percent injected dose per gram (%ID/g), 0.64 ± 0.08%ID/g, and 0.52 ± 0.04%ID/g, respectively at 1 hour. Liver uptake for the ⁶⁴Cu-DO3A-peptide (1.68 ± 0.42%ID/g) was more than that of the ⁶⁴Cu-CB-TE2A-peptide (0.52 ± 0.02% ID/g) and ⁶⁴Cu-NO2A-peptide (0.48 ± 0.05%ID/g) at 2 hours. PET/CT studies revealed successful tumor uptake of ⁶⁴Cu-peptides at 2 hours postinjection. In vivo kidney retention was observed with all of the radiolabeled peptides. The optimization of bifunctional chelators improves the pharmacokinetic properties of the ⁶⁴Cu-labeled GSG-KCCYSL peptide, which enables the selection of a suitable peptide homolog as a PET imaging agent for EGFR-2 expressing breast carcinomas.

Nitroimidazole conjugates of bis(thiosemicarbazonato)64Cu(II) - Potential combination agents for the PET imaging of hypoxia

Combination agents comprising two different pharmacophores with the same biological target have the potential to show additive or synergistic activity. Bis(thiosemicarbazonato)copper(II) complexes (e.g. (64)Cu-ATSM) and nitroimidazoles (e.g. (18)F-MISO) are classes of tracer used for the delineation of tumor hypoxia by positron emission tomography (PET). Three nitroimidazole-bis(thiosemicarbazonato)copper(II) conjugates were produced in order to investigate their potential as combination hypoxia imaging agents. Two were derived from the known bifunctional bis(thiosemicarbazone) H(2)ATSM/A and the third from the new precursor diacetyl-2-(4-N-methyl-3-thiosemicarbazone)-3-(4-N-ethylamino-3-thiosemicarbazone) - H(2)ATSM/en. Oxygen-dependent uptake studies were performed using the (64)Cu radiolabelled complexes in EMT6 carcinoma cells. All the complexes displayed appreciable hypoxia selectivity, with the nitroimidazole conjugates displaying greater selectivity than a simple propyl derivative used as a control. Participation of the nitroimidazole group in the trapping mechanism is indicated by the increased hypoxic uptake of the 2- vs. the 4-substituted (64)Cu-ATSM/A derivatives. The 2-nitroimidazole derivative of (64)Cu-ATSM/en demonstrated superior hypoxia selectivity to (64)Cu-ATSM over the range of oxygen concentrations tested. Biodistribution of the radiolabelled 2-nitroimidazole conjugates was carried out in EMT6 tumor-bearing mice. The complexes showed significantly different uptake trends in comparison to each other and previously studied Cu-ATSM derivatives. Uptake of the Cu-ATSM/en conjugate in non-target organs was considerably lower than for derivatives based on Cu-ATSM/A.

Solution equilibria of copper(II) complexation with N,N′-(2,2′-azanediylbis(ethane-2,1-diyl))dipicolinamide: A bio-distribution and dermal absorption study

The protonation equilibria of a pentadentate ligand, N,N'-(2,2'-azanediylbis(ethane-2,1-diyl))dipicolinamide ([H(2)(5555)-N]) and the complexation of this ligand with Cu(II) Ca(II), Zn(II) and Ni(II) have been studied by pH-potentiometry, (1)H NMR spectroscopy and UV-vis spectrophotometry. (1)H NMR detected the protonation of the pyridyl groups and formation of Cu[H(2)(5555)-N]H species at low pH, while amide group deprotonation at higher pH resulted in the formation of Cu[H(2)(5555)-N]H(-1) and Cu[H(2)(5555)-N]H(-2) species in solution. Potentiometric detection of protonated species was limited by the acidic nature of the pyridyl nitrogen donors. From UV-vis spectroscopy it is suggested that the amide nitrogens are coordinated. This conclusion is supported by Molecular Mechanics calculations. Water-octanol partition coefficients for the Cu(II)-[H(2)(5555)-N] system indicated that although the Cu[H(2)(5555)-N]H(-1) species is largely hydrophilic, approximately 54% of the complex goes into the organic phase. This percentage is able to promote dermal absorption of copper with a calculated penetration rate of 1.92x10(-1)cmh(-1). This was confirmed by dermal absorption studies which illustrate the role of hydrophobicity in promoting percutaneous drug administration.