Tabriz University of Medical Sciences BioImpacts 2228-5652 12 5 2022 09 01 The oncolytic activity of Clostridium novyi nontoxic spores in breast cancer 405 414 10.34172/bi.2021.25 EN Fatemeh Abedi Jafari https://orcid.org/0000-0002-7261-674X Asghar Abdoli https://orcid.org/0000-0002-1605-4471 Reza Pilehchian Neda Soleimani Seyed Masoud Hosseini Journal Article 10.34172/bi.2021.25 2020 04 02 2021 01 12 Introduction: Hypoxia context is highly specific for tumors and represents a unique niche which is not found elsewhere in the body. Clostridium novyi is an obligate anaerobic bacterium. It has a potential to treat tumors. The aim of this study was to produce the C. novyi nontoxic spores and to investigate its oncolytic effect on breast cancer in mice model. Methods: Primarily, the lethal toxin gene in C. novyi type B was removed. Colonies were isolated using PCR testing. To assure the removal of alpha-toxin, plasmid extraction and in vivo assay were conducted. Next, to treat breast cancer model in different sizes of tumors, a single dose of spores of C. novyi nontoxic was tested. Results: The results denoted that C. novyi nontoxic lost lethal toxin and a­­ppeared to be safe. For smaller than 1000 mm3 tumors, a single dose of C. novyi nontoxic was able to cure 100% of mice bearing breast tumors. Hence the mice remained free of tumor relapse. Tumors larger than 1000 mm3 were not cured by a single dose­ of C. novyi nontoxic treatment. Conclusion: The experiment concluded that the C. novyi nontoxic might be a suitable and safe candidate, a novel therapeutic approach to encounter such hypoxic regions in the center of tumors. Research also showed that bacteriolytic therapy by C. novyi nontoxic could lead to regression in small tumor.