Background/Aim: Antimony is a chemical element used in the therapy of parasitic diseases with a promising anticancer potential. The aim of this study was to evaluate in vitro activity of free or liposomal vesicle-packed antimony trioxide (AT or LAT) in the t(15;17)(q22;q21) translocationpositive acute promyelocytic leukemia (APL) cell line NB4. Materials and Methods: Cytotoxicity was analysed with trypan blue exclusion, the MTT assay and neutral red exclusion assay; cell proliferation with PicoGreen ® ; and reactive oxygen species (ROS) production with DCFDA. Results: Liposomal particles did not change the pH of the cell culture medium and entered the cells. Both formulations resulted in a time-and concentration-dependent cytotoxicity and production of ROS. LAT showed higher toxicity at lower concentrations compared to AT. Conclusion: LAT may be used to decrease drug dosage and maintain high anti-tumoral effects on APL cells.Cancer is a multifactorial disease, and therefore its treatment needs to address different targets to achieve better results. New therapeutic strategies are investigated and repositioning of drugs is a promising alternative. Antimony is used in the therapy of leishmaniasis and schistosomiasis. The main serious adverse effects are associated to cardiotoxicity in about 9% of the patients and pancreatitis, more commonly seen in co-infections (HIV and visceral leishmaniasis) (1). Reactive oxygen species (ROS) production and oxidative stress damage are the main mechanisms of cell damage caused by antimony (2). Studies have shown that autophagy induced by antimony is triggered by the production of ROS and not by the activation of the mTOR pathway (3). In the present study, we used liposomes, which have low biological impact (4). Nanoparticles can improve drug delivery and efficiency at a lower dosage, reducing toxic effects, which is highly needed in cancer treatment (5). Therefore, we compared the effects of free antimony trioxide (AT) and AT encapsulated in liposomes (LAT) on the acute promyelocytic leukemia (APL) cell line NB4.APL is caused by the fusion protein PML/RARA and was the first leukemia treated with the specific molecular targeting drug all-trans-retinoic acid (ATRA) (6). Despite the high efficiency of the treatment, 5 to 20% of the patients develop the ATRA syndrome, a life-threatening condition associated with organ infiltration by myeloid cells, cytokine production, high expression of CD13 in leukemic cells, and hyperleukocytosis, leading to endothelial inflammation and bleeding in the affected organs (6). Arsenic Trioxide (ATO) is an efficient drug for APL treatment, and in association with ATRA, decreases relapse in about 90% of cases ( 7), but its use is limited by the risk of toxicity and potential carcinogenicity (8).The free antimony trioxide (Sb 2 O 3 ) shows chemical structure and mechanistic properties similar to ATO against 6061

Antimonials are used as chemotherapy for leishmaniasis, but have limited results due to their toxicity and broad resistance already acquired by the parasites. Nanotechnology offers an alternative to reduce these effects through the use of biocompatible nanocarriers, which can be vectorized to the target site. In addition, the redirection of molecules, already developed for the treatment of other pathologies, has the advantage of being already approved for therapy by regulatory agencies. The present study addresses the production of liposomal vesicles containing antimony trioxide (LC Sb2O3), as well as the evaluation of activity against tumor and bacterial cells. We produce liposomes in order of nanometric size, polydispersity index (PDI <0.3), pH value close to physiological (7.2), and zeta potential (anionic). Cytotoxicity was evaluated in 24 and 72 hours, in the HepG2, T98G, and U87MG tumor cell lines, by the method (3-4.5 dimethylthiazole-2.5 diphenyltetrazolium bromide) (MTT). The minimum inhibitory concentration (MIC) was tested on three bacterial strains (American Type Culture Collection – ATCC-Escherichia coli ATCC 35218, Staphylococcus aureus ATCC 29213 and Enterococcus faecalis ATCC 29212) and mandatory (Staphylococcus aureus and Klebsiella pneumoniae). The liposomes were more cytotoxic than Sb2O3 in the free form, for all tested cell lines. This effect was stronger after 72 hours incubation. Antimony trioxide in both free and liposomal forms showed low antibacterial activity. Based on our results, we suggest that liposomes containing antimony trioxide have the potential for the repositioning of drugs addressing anticancer therapy.