Parasporin, a novel protein with a unique cytocidal activity, was first discovered from Non-Insecticidal Bacillus thuringiensis by Mizuki et al.. The term parasporin is defined as "Bacillus thuringiensis and related bacterial parasporal proteins that are non-hemolytic but capable of preferentially killing cancer cells".
The whole idea came from the view that, it has been well established that Non-insecticidal B. thuringiensis strains are more widely distributed than insecticidal ones, and which raises a question whether such non-insecticidal inclusions have any biological activity which is as yet undiscovered. And astoundingly on the road to find the answer a strong cytocidal protein has been discovered which have activities against human cancer cells. The proteins were heterogeneous in cytotoxicity spectra
b. Parasporin, a Human Leukemic Cell-Recognizing Parasporal Protein of Bacillus thuringiensis,
EIICHI MIZUKI et. al., 2000, CLINICAL AND DIAGNOSTIC LABORATORY