Avaliação pré-clínica de lipossomas pH-sensíveis de longa circulação contendo cisplatina

Abstract

cis-Diamminedichloroplatinum (II) or cisplatin (CDDP) is one of the anticancer agents most widely used in the treatment of solid tumors. However, the effectiveness of its clinical use is hampered by the induction of severe side effects and its tendency to provoke chemoresistance. To circumvent these inconveniences, drug delivery systems, such as long-circulating and pH-sensitive liposomes containing CDDP (SpHL-CDDP) have been developed. This work presents the pre-clinical evaluation of SpHL-CDDP, involving biodistribution study, antitumoral efficacy and preliminary evaluation of toxicity after administration in Ehrlich solid tumor-bearing Swiss mice. Initially, it was investigated the preparation of radiolabelled CDDP (CDDP*). The irradiation of CDDP using the TRIGA MARK I IPR R-1 and with the covering of cadmium capsule showed to be more appropriate in terms of higher specific activity (57.0 kBq.mg-1) than that bare samples (40.0 kBq.mg-1). In addition, the CDDP* did not suffer any degradation. The biodistribution study of SpHL-CDDP in Ehrlich solid tumor-bearing Swiss mice revealed a higher residence time into bloodstream than that observed with free CDDP treatment. The values of distribution volume were equal to 1807.91 and 651.60 mL/kg and those of area under the curve (AUC) were equivalent to 64.70 and 141.51 h.g/mL for free CDDP and SpHL-CDDP treatments, respectively. The prolonged circulation of SpHL-CDDP into bloodstream allowed to get value of AUC that were two times superior in the tumor region than that obtained after free CDDP administration. In addition, the determination of tissue blood partition coefficient (Kp) showed that a higher extensive distribution in the tumor after SpHL-CDDP administration than that after free CDDP injection (Kp was equal to 1.51 and 1.23, respectively). This finding can contribute to a better antitumoral efficacy of SpHL-CDDP treatment. The treatment of mice with SpHL-CDDP also demonstrated a lower affinity for renal tissue than that observed with free CDDP treatment. This relevant result may signify a reduction or absence of nephrotoxicity after SpHL-CDDP administration. The extensive uptake of CDDP by organs of the mononuclear phagocytic system (liver and spleen) was occurred after SpHL-CDDP administration. Finally, it was investigated the citotoxicity, antitumoral effect and toxicity of SpHL-CDDP in comparison with xi free CDDP. The citotoxicity and intracellular accumulation of CDDP were evaluated in the human lung cancer cell line (GLC4) and its resistant subline to CDDP (GLC4/CDDP). The free CDDP showed higher citotoxic activity than that observed to SpHL-CDDP for sensitive cells line. This fact is probably related to different uptake mechanisms of the free and the encapsulated CDDP. However, it is worth noting that the liposomal formulation exhibited the same efficacy against CDDP-sensitive and CDDP-resistant cells. This finding indicates that these liposomes were able to overcome the resistance mechanisms in vitro. After the intravenous administration of SpHL-CDDP and free CDDP formulations, the tumor volume, survival rate, and body weight variation were evaluated. After 32 days, the growth of the Ehrlich solid tumor in Swiss mice was similar for both treatments. However, the median of survival obtained with SpHL-CDDP treatment was higher than that observed for free CDDP treatment (66 and 52 days, respectively). The animals treated with free CDDP presented a significant body weight loss. This fact was not observed for SpHL-CDDP treatment. These findings show that SpHL-CDDP treatment was able to maintain the antitumoral effect of CDDP without to induce the appearance of toxicity. Thus, the SpHL-CDDP proved to be a relevant strategy for the use of CDDP in the treatment of tumors.