Cyanobacteria are an important source of structurally bioactive metabolites, with cytotoxic, antiviral, anticancer,
antimitotic, antimicrobial, specific enzyme inhibition and immunosuppressive activities. This study focused on the antitumor
and antimicrobial activities of intra and extracellular cyanobacterial extracts. A total of 411 cyanobacterial strains
were screened for antimicrobial activity using a subset of pathogenic bacteria as target. The in vitro antitumor assays were
performed with extracts of 24 strains tested against two murine cancer cell lines (colon carcinoma CT-26 and lung cancer
3LL). Intracellular extracts inhibited 49 and 35% of Gram-negative and Gram-positive pathogenic bacterial growth, respectively.
Furthermore, the methanolic intracellular extract of Cylindrospermopsis raciborskii CYP011K and Nostoc sp.
CENA69 showed inhibitory activity against the cancer cell lines. The extracellular extract from Fischerella sp. CENA213
and M. aeruginosa NPJB-1 exhibited inhibitory activity against 3LL lung cancer cells at 0.8 µg ml-1 and Oxynema sp.
CENA135, Cyanobium sp. CENA154, M. aeruginosa NPJB-1 and M. aeruginosa NPLJ-4 presented inhibitory activity
against CT26 colon cancer cells at 0.8 µg ml-1. Other extracts were able to inhibit 3LL cell-growth at higher concentrations
(20 µg ml-1) such as Nostoc sp. CENA67, Cyanobium sp. CENA154 and M. aeruginosa NPLJ-4, while CT26 cells
were inhibited at the same concentration by Nostoc sp. CENA67 and Fischerella sp. CENA213. These extracts presented
very low inhibitory activity on human peripheral blood lymphocytes. The results showed that some cyanobacterial strains
are a rich source of natural products with potential for pharmacological and biotechnological applications.