Use of bioaffinity chromatography to prospect for anticancer substances in marine actinomycetes: XIAP and STMN1 as pharmacological targets.

The richness of natural products comes from an evolutionary optimization of their distinct biological functions, which include the regulation of endogenous defense mechanisms and interaction with other organisms, which explains their relevance for the treatment of infectious diseases and cancer. Cancer is a set of diseases that can start in any tissue or organ, characterized by the uncontrolled growth of cells that can invade other tissues and organs. There are overexpressed proteins in cancer cell lines that assist in tumor viability and survival, as are the cases of XIAP and STathmina (STMN1), used as targets in the present study. XIAP is a protein from the apoptosis inhibiting protein family and was initially identified as a protein that binds to caspases acting inhibiting apoptosis by the intrinsic and extrinsic pathway, being important in the regulation of several pathways of cell death and inflammation. STMN1 was first characterized as an 18kDa peptide overexpressed in acute leukemia and proliferative lymphocytes, being an important protein in the progression of the cell cycle, chromosomal segregation, cell mobility and survival because of its role in destabilizing microtubules. This study was developed in two fronts, one related to the isolation of new substances modulating the proteins XIAP and STMN1 from the extract of marine bacteria collected in different points of the Brazilian coast (Described in chapter 1); and a second that involved the study of a natural substance, embelin, isolated from the Embelia ribes plant, described in the literature as a modulator of XIAP (described in chapter 2). Regarding chapter 1, both proteins were produced by heterologous expression, and their protocol was standardized. The functional chromatography technique also proved to be valid for the prospecting of substances that modulate both proteins, with specific and unspecific hits for both being obtained at the end. The isolation of the active substances and their testing in leukemia cell lines was not possible, however the extracts were compared to the GNPS, AntiBase and Scifinder database. Based on this analysis, two substances were annotated, corresponding to two hits identified in the functional chromatography, burkholone, which was identified when using XIAP, and phthoxazolin A, annotated when using STMN1. However, there is no information in the literature relating to the potential interaction of these substances with the proteins studied in this work, which reinforces the importance of this strategy in the establishment of targets for cytotoxic substances. Referring to Chapter 2, embelin was studied in a combination therapy with venetoclax. Venetoclax (ABT-199) is an oral bioavailability drug that selectively inhibits BCL2 and was approved for the treatment of chronic lymphocytic leukemia. We found that the combination of venetoclax and embelin reduces the viability of acute myeloid leukemia (AML) cells by triggering apoptosis, XIAP down-regulation and DNA damage induced. Due to the low toxicity of embelin, this drug can be used in combination to reduce doses of venetoclax, which could minimize side effects with maintaining therapeutic response or even reverse resistance mechanisms in AML patients. Our findings further highlight drugs targeting IAP as a putative anticancer option for AML. (AU)