The anti-cancer activity of alkali-solubilized protease-activated parasporal proteins produced by 78 local Bacillus thuringiensis strains and 14 reference B. thuringiensis strains was screened against five human cancer cell lines (CACO-2, Hep2, HepG2, K562, and MCF-7). Activated parasporal proteins were tested for their hemolytic activity against human erythrocytes. It was found that activated parasporal proteins of 25 local B. thuringiensis strains and 9 reference strains were non-hemolytic. Non-hemolytic parasporal proteins produced by 9 local B. thuringiensis strains were found to exhibit no to low cytotoxicity against human non-cancerous Hs27 cells. Out of them, activated parasporal proteins of two local B. thuringiensis strains (J61; B. thuringiensis serovar kumamotoensis and J72; B. thuringiensis serovar tohokuensis) were found to produce high to very high in vitro selective cytotoxicities, preferentially toxic to cancerous cells, against all cancer cell lines used in this study. This is the first observation of the anti-cancer activity from B. thuringiensis serovar kumamotoensis. Based on IC50 values, activated parasporal proteins of J61 strain produced the most significant cytotoxicity against all cancer cell lines. Furthermore, CACO-2 and MCF-7 cells were found to be the most sensitive. Thus, parasporal proteins produced by B. thuringiensis serovar kumamotoensis strain J61 and/or B. thuringiensis serovar tohokuensis strain J72 may be used as alternative or improving means for current cancer therapy.
Key words: Bacillus thuringiensis, kumamotoensis, tohokuensis, parasporal, cancer.
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