| dc.description.abstract | The continuous administration of cisplatin (CDDP), a chemotherapeutic agent used to treat
various types of solid tumors, is limited due to adverse reactions, such as nephrotoxicity,
hepatotoxicity, neurotoxicity, myelotoxicity, and ototoxicity. In an attempt to circumvent these
inconveniences and improve the therapeutic index of CDDP, pharmacotechnical modifications
have been proposed, such as the encapsulation of CDDP in drug delivery systems, like
liposomes. In this sense, it was proposed to develop a thermosensitive liposome of nonfunctionalized cisplatin (TSL-CDDP), functionalized with hyaluronic acid (HA) by
electrostatic interaction (TSL-CDDP-HA-1) and functionalized with HA by covalent bond
(TSL-CDDP-SA-HA-2), in order to provide an active targeting for the tumor region. Initially,
a detailed study was carried out to characterize the formulations developed, through the
association of dynamic light scattering (DLS), microcalorimetry, and low angle X-ray
scattering (SAXS) techniques. The CDDP encapsulation rate was evaluated by high
performance liquid chromatography using a diethyldithiocarbamate derivatization method.
Then, cytotoxicity against MDA-MB-231 tumor cells was evaluated, as well as in vivo toxicity
in healthy Swiss mice. The characterization results showed an average diameter less than 200
nm and a polydispersity index (PDI) suggestive of homogeneous formulations (< 0.2),
indicating the absence of vesicle aggregation even after functionalization with HA. The
efficiency of the HA-coating of liposome was attributed to values of zeta potential close to
neutrality. The DLS data showed a significant reduction in the mean diameter and Kcps (Kilo
counts per second) of the formulations evaluated at 40oC, and the coating with HA did not alter
the phase transition temperature of the formulations. CDDP encapsulation was 9.3 ± 0.7% for
TSL-CDDP-SA-HA, 16.1 ± 1.9% for TSL-CDDP-HA and 13.7 ± 0.9% for TSL -CDDP. The
profile obtained by SAXS for all the formulations studied was characteristic of a lamellar
organization independent of the evaluated temperature and presented dilation of the bilayer,
caused by disorganization in the lipid structure, confirming the conformational alteration due
to heating. However, the in vitro release profile suggested possible drug adsorption in the
phospholipid bilayer causing a diffusion rate of CDDP before reaching Tc (42oC), for TSLCDDP and TSL-CDDP-SA-HA. For TSL-CDDP-HA, the presence of the polymer may be
modulating this diffusion, generating a more controlled and slower release profile. The
biological results showed that TSL-CDDP have greater cytotoxicity when compared to free
CDDP, in addition to leading to an increase in the occurrence of senescence. The use of
hyperthermia in the groups treated with LTS-CDDP and LTS-CDDP-HA increased the
occurrence of apoptosis compared to groups without hyperthermia. In the in vivo study, greater
toxicity of the cationic formulation was observed for healthy cells, with the occurrence of
nephrotoxicity in animals treated with LTS-CDDP. While, with the use of the HA ligand, the
known adverse effects related to the use of CDDP were eliminated, since the animals treated
with this formulation did not show significant changes in hematological and biochemical tests,
as well as in histological analyzes. Thus, the proposed formulation of CDDP, thermosensitive
and containing HA by electrostatic interaction, has adequate characteristics for cancer treatment
intravenously, in association with moderate hyperthermia, and may be able to reduce CDDPrelated toxicity, representing a potential alternative for the delivery of this drug. | |
