NMR structural analysis of MC1R-targeted rhenium(I) metallopeptides and biological evaluation of 99mTc(I) congeners

The melanocortin receptor 1 (MC1R) is a specific molecular target for detection and therapy of melanoma, as it is overexpressed in human melanomas. The design of novel peptide-based MC1R-specific probes for imaging or targeted radionuclide therapy is being actively pursued. Aiming to visualize melanoma in vivo by single photon emission computed tomography (SPECT) imaging using 99mTc(CO) 3-labeled cyclic melanocyte stimulating hormone analogues, we have designed the novel cyclic peptides c[S-NO 2-C 6H-CO-His-DPhe-Arg-Trp-Cys]-Lys-NH 2 (1) and c[NH-NO 2-C 6H 3-CO-His-DPhe-Arg-Trp-Lys]-Lys-NH 2 (2) and their corresponding conjugates c[S-NO 2-C 6H 3-CO-His-DPhe-Arg-Trp-Cys]-Lys(pz)-NH 2 (L1) and c[NH-NO 2-C 6H 3-CO-His-DPhe-Arg-Trp-Lys]- Lys(pz)-NH 2 (L2), which incorporate a pyrazolyl-diamine chelating unit (pz). Upon reaction with adequate organometallic precursors, we prepared the metalated peptides c[S-NO 2-C 6H 3-CO-His- DPhe-Arg-Trp-Cys]-Lys(pz-M(CO) 3)-NH 2 (M = Re (Re1), Tc (Tc1)) and c[NH-NO 2-C 6H 3-CO-His-DPhe-Arg-Trp- Lys]-Lys(pz-M(CO) 3)-NH 2 (M = Re (Re2), Tc (Tc2)). Competitive binding affinity assays demonstrated that metalation of L1 and L2 did not lead to a significant decrease of binding affinity toward MC1R, as concluded by comparing the IC 50 values of Re1 (IC 50 = 690 ± 250 nM) and Re2 (IC 50 = 176 ± 5 nM) to those of the nonmetalated conjugates L1 (IC 50 = 430 ± 100 nM) and L2 (IC 50 = 179 ± 39 nM). Furthermore, the potency of the alkylamine-bridged peptide derivatives is superior to that of the alkylthioaryl-bridged derivatives. NMR structural analysis performed for 1, L1, and Re1 has shown that the peptide moiety displayed an atypical β-turn conformation in solution. The three-dimensional structural features of the peptide moiety were also conserved upon conjugation to the chelator and, most importantly, after metalation. Despite presenting a significant cell internalization degree and moderate retention in murine melanoma cells, the radiopeptides Tc1 and Tc2 displayed poor tumor-targeting properties in a B16F1 melanoma-bearing mouse model. © 2012 American Chemical Society.Peer Reviewe

Respostas morfológicas e produtivas do capim-marandu adubado com doses combinadas de nitrogênio e enxofre Morphological and productive responses of marandugrass to combined rates of nitrogen and sulphur

Avaliaram-se os efeitos de combinações de doses de nitrogênio com doses de enxofre nas respostas morfológicas e produtivas de Brachiaria brizantha cv. Marandu cultivada em solução nutritiva, utilizando-se sílica como substrato, em um experimento em casa de vegetação no período da primavera. Utilizou-se o esquema fatorial 5² fracionado, com 13 combinações para nitrogênio e enxofre na solução nutritiva, em mg L-1: 14 e 3,2; 14 e 32; 14 e 80; 126 e 12,8; 126 e 64; 210 e 3,2; 210 e 32; 210 e 80; 336 e 12,8; 336 e 64; 462 e 3,2; 462 e 32; e 462 e 80, as quais foram distribuídas segundo o delineamento estatístico de blocos ao acaso, com quatro repetições. As avaliações foram realizadas em dois estádios de crescimento das plantas. Os resultados demonstraram que o fornecimento de enxofre é fundamental quando se aplica o nitrogênio. Para a maximização do número de perfilhos e de folhas, da produção de massa seca de folhas, de colmos+bainhas e da parte aérea, da área foliar e da taxa de aparecimento de folhas do capim-marandu, a combinação deve ser, no mínimo, de 358 mg L-1 para nitrogênio com 56 mg L-1 de enxofre. A taxa máxima de aparecimento de folhas para o capim-marandu ocorreu na dose de enxofre de 42 mg L-1.<br>This experiment was carried out in a greenhouse during the spring to study combinations of nitrogen and sulphur rates on Brachiaria brizantha cv. Marandu growing in nutrient solution and using ground quartz as substrate. It was set in a fractionated 5² factorial arrangement, with five rates of nitrogen and five rates of sulphur. The resulting 13 combinations were, in mg L-1: 14 and 3.2, 14 and 32, 14 and 80, 126 and 12.8, 126 and 64, 210 and 3.2, 210 and 32, 210 and 80, 336 and 12.8, 336 and 64, 462 and 3.2, 462 and 32, and 462 and 80. The experimental units were set in randomized blocks design, with four replications. Plants had two growth periods. The results showed that high availability of sulphur is required when nitrogen is supplied for total tiller number, leaf number, leaf dry matter yield, stems plus sheaths and plant tops, leaf area and leaf appearance rate. In order to maximize these variables for the marandugrass, it is necessary the minimum combination of 358 mg L-1 of nitrogen with 56 mg L-1 of sulphur. The highest leaf appearance rate for marandugrass occurred in the sulphur rate of 42 mg L-1