Abstract
Parasporins (PSs) are a group of nonhemolytic crystal proteins synthesized by Bacillus thuringiensis (Bt) and are known for their cytotoxic activity against various cancer cell lines. In this study, the cytotoxicity of 6 parasporin-positive Bt isolates from the soil of cherry gardens in Türkiye was investigated. First, the pH of the solubilization buffer and proteinase K concentration were optimized. After that, parasporal proteins of Bt isolates were solubilized in a buffer at pH 11.5 and digested with 150 µg/ml proteinase K. The MTT assay was carried out to determine the cytotoxic effects of active parasporal proteins from different Bt isolates on human uterine cervix cancer (HeLa), human lung cancer (A549), human breast cancer (MCF-7), prostate cancer (PC-3), lymphoma (Burkitt), and healthy human embryonic kidney (HEK-293) cell lines. The Bt 5.4 isolate was selected for further analysis because it significantly reduced the viability of all the cancer cell lines but did not affect the viability of the HEK-293 cells. Inverted microscope analysis revealed that parasporal proteins caused morphological changes in both A549 and PC3 cell lines. Flow cytometry analysis indicated that the parasporal protein (20 µg/ml) of Bt 5.4 induced 71% and 31% apoptotic cell death in A549 and PC-3 cells, respectively. Similarly, caspase-3 activity was 7.5-fold and 2.5-fold greater in parasporin-treated A549 and PC-3 cells than in untreated cells. In addition, cell cycle analysis via propidium iodide (PI) revealed cell cycle arrest in the G1 phase in both cancer cell lines. Moreover, a moderate synergistic effect of cisplatin and parasporal protein was observed in A549 cells. Finally, ELISA revealed that the secretion of vascular endothelial growth factor (VEGF) was significantly lower in A549 and PC-3 cells after 24 h of treatment with parasporal protein than in untreated cells, demonstrating that parasporal protein has an antiangiogenic effect. In conclusion, these findings indicate the anticancer potential of parasporal proteins and suggest that the Bt 5.4 isolate is a promising source for the development of novel and targeted cancer therapeutics. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12896-025-01084-z.