Currently gliomas represent about 81% of malignant brain tumors with increased incidence in children and in adults over 45 years. A large number of type 1 neurokinin receptor (NK-1) are expressed in glioma cells, being the binding of substance P (SP) to these receptors, involved in the development and progression of this tumor type.The SP conjugated at DOTA chelator (SP-DOTA), radiolabeled, have been tested for use in the treatment of gliomas, and the lutetium-177 ( 177 Lu), due to its lower tissue range, has been the most suitable radioisotope for tumors located in critical areas brain. However, studies indicate the necessity of adding an excess of methionine to prevent the peptide SP-DOTA-177 Lu oxidation in order to increase the stability and capacity to bind to tumor cells. To overcome this challenge, there is the prospect of using a new analog of SP with a modified structure, to prevent peptide oxidation. In this context, the aim of this work was study the labeling of a new analog of SP with 177 Lu and characterize their properties in vitro and in vivo, in order to obtain a novel radiopharmaceutical with potential application in brain tumor therapy, and perform preliminary studies labeling of this new analog with yttrium-90 ( 90 Y). The new analog was obtained by replacement of the amino acid methionine (Met) by the amino acid norleucine (Nle) at position 11 of the peptide chain of SP, and these peptides were called SP(Met 11 )-DOTA and SP(Nle 11 )-DOTA respectively. After analysis of the oxidation for the two peptides, the radiolabeling parameters of the SP(Nle 11 )-DOTA with 177 LuCl3 were studied to determine the best labeling condition. The SP(Nle 11 )-DOTA was also radiolabeled with 90 Y, using standard condition, and the stability in vitro of the SP(Nle 11 )-DOTA-90 Y assessed under refrigeration (2-8 °C) and under freezing (-20° C), after radiolabeling with high activity and use of stabilizing agent. The stabilities in vitro of the SP (Nle 11 )-DOTA-177 Lu under refrigeration (2-8 °C), under freezing (-20 °C) and in human serum (37 °C) were determined after radiolabeling with high activity, with use of stabilizing agents and after dilution. The ability of in vitro binding to tumor cells (U-87 MG and M059J) and the biodistribution in vivo in healthy BALB/c mice were determined for the 177 Lu-DOTA-SP(Nle 11 ) and compared to 177 Lu-DOTA-SP(Met 11 ). The plasma protein binding and biodistribution in Nude mice with tumor model were also evaluated. The results obtained from analysis of oxidation for the two peptides confirmed the importance of adding excess methionine to prevent peptide oxidation and indicated a high stability of the DOTA-SP(Nle 11 ), during and after the radiolabeling process. The addition of 148 MBq (4 mCi) of 177 LuCl3 solution in 0.05N HCl at 10 µg DOTA-SP(Nle 11 ) diluted in 0.4 M sodium acetate buffer pH 4.5 followed by incubation at a temperature of 90 °C for 30 minutes under constant agitation to 350 rpm was defined as standard labeling condition. The freezing (-20 °C), the use of...