Introduction: Terrestrial Actinobacteria are microorganisms well known as a prolific source of secondary metabolites with a diversity of functions, such as antibacterial and antitumor. As marine environments provide a broad spectrum of habitats, Actinobacteria can adapt and produce different metabolites that may be important for the discovery of new drugs. The Brazilian coast remains poorly studied for its biotechnological potential. Therefore, the main goal of this study was to prospect the anticâncer potential of Actinobacteria recovered from sediments collected at the Archipelago of Alcatrazes, a biodiverse Conservation Unit off the state of Sao Paulo.

Methods: Marine sediments were collected in 3 different points around the Archipelago of Alcatrazes, in depths between 9m and 13m, and stored in sterile bags at -20ºC until processing. Sediment samples were processed by two different methods, where, in M1, they were desiccated and stamped into agar Petri dishes, and, in M2, they were diluted and streaked into the agar media. Three different culture medias were used: A1 (high nutritional level), TM (low nutritional with high trace metals levels), and SwA (minimum nutritional level). The dishes were routinely checked for individual colonies, and these were transferred to fresh A1 agar dishes and repeatedly moved again until pure colonies were achieved. Afterwards, the purified strains were transferred to liquid A1 broth, incubated for 5 to 10 days at 28ºC under constant shaking, and extracted with ethyl acetate for cytotoxicity analysis. The extracts were analyzed at concentrations of 5 and 50 µg/mL against a cell line of human colorectal carcinoma - HCT-116 - using the MTT assay method. The extracts that induced over 70% cell growth inhibition at the higher concentration were considered active and analyzed in a quantitative protocol, using a range of concentrations (0.0032 – 50 μg/mL) to obtain their respective IC50.

Results: Between both isolation methods and the three medias used, 20 strains were purified, extracted and tested on the MTT qualitative assay. As a result, 13 extracts were found to be active. Of these, 9 demonstrated cytotoxic activity against HCT-116 cells on the quantitative MTT protocol. By the National Cancer Institute (NCI) guidelines, 8 of these extracts exhibited an IC50 under 20 µg/mL and their cytotoxicity was considered relevant. Among these, it is important to highlight BRB-449, with IC50 of 2.04 μg/mL. Moreover, BRB-420 and BRB-430, also showed low values of IC50, 4.46 and 4.35, respectively.

Conclusion: Within the 20 actinobacteria isolated from the sediments of the Archipelago of Alcatrazes, 65% produced bioactive extracts, while 8 of these extracts showed promising cytotoxicity and should be investigated, both chemically and pharmacologically. Nevertheless, this study demonstrates that microorganisms from the Archipelago of Alcatrazes produce relevant natural products with biomedical potentials and should be furthered studied so such bioprospective capability is fulfilled.

Financial support: INCT BioNat (CNPq/INCT Process #465637/2014-0), FAPESP (Process #2015/17177-6), CAPES, ICB – USP and PPG Bioprodutos e Bioprocessos – UNIFESP.