Tese
Avaliação das atividades antimicrobiana e citotóxica de peptídeos derivados do veneno do anuro Pithecopus megacephalus e da peçonha da aranha Lycosa erythrognatha
Fecha
2019-10-28Autor
Joaquim Teixeira de Avelar Júnior
Institución
Resumen
Bioactive peptides are a vast class of molecules with diverse biopharmaceutical
potentials, including antimicrobial activity over a broad organism classes such as
bacteria, fungi, protozoa and viruses. Several of these peptides have also shown
antitumoral activity.
In this thesis we focused on Pithecopus megacephalus frog secretion, as well as the
peptide LyeTx I-Des-His, a synthetic variation of LyeTx I, a peptide purified from the
venom of the spider Lycosa erythrognatha, with the objective to find bioactive peptides
mainly against cancer cells, more specifically of the triple negative type. The
fractionation of the P. megacephala secretion showed a rich variability on peptides and
14 of them were sequenced. From this set, three peptides were synthesized and tested
against bacteria, fungi and three cancer cell lines (MDA-MB-231, MCF-7, both from
breast cancer and HCT-116 from colorectal cancer) and one non-cancer cell line (HEK-
293), as a control. The results suggested an increase on proliferative activity of two
peptides over cancer cells, without apparent activity on HEK-293 cells. In a second part
of this work, we proposed to test LyeTx I-Des-His combined with cisplatin, in three
different molar proportions. The proportion peptide:cisplatin, (P:C) 1:1, in the IC50 dose,
showed synergistic effect as well as a selectivity index value, greater than cisplatin
isolated treatment. When investigating the possible cell death mechanisms involved, we
observed several indications of autophagic cell death process. This mechanism was
supported by the following results: cells treated with P:C combinations arrested in
G2/M cell cycle phase, cells were marked in red with the pH sensitive dye acridine
orange and when pretreated with an autophagy inhibitor (Bafilomycin A1) this
coloration was reversed. In addition, western blot experiments indicated a possible
reduction of P21 expression and of AKT phosphorylation. The decreasing of AKT
phosphorylation could be indicative of autophagy, as already described. However, other
studies are necessary to better clarify the involved pathways on these activities of the
drugs. In addition, toxicity studies are essential in a possible validation of LyeTx I-DesHis as a therapeutic drug candidate These findings demonstrated that the peptide LyeTx
I-Des-His seems a good candidate to be combined with some well-established drugs,
improving the combat to cancer cells, by inducing other death cascades.