Use of planaria for evaluation of complex mixture toxicity.
The goal of this research is to develop an invertebrate model for evaluating the potential of extracts from complex environmental matrices (derived from known locations of toxicity) for their potential to induce solid tumors in planaria. Planaria are flatworms (Platyhelminthes) that were once widely used for toxicity testing but were largely abandoned as molecular biology tools became more important in toxicology. Before their decline in popularity, there were a handful of scattered reports that these simple animals, unlike other invertebrates, were capable of forming solid tumors when exposed to human carcinogens. This unusual characteristic is presumably related to their well-known exaggerated capability of regeneration which in turn is associated with an abundance of stem cells distributed throughout their somatic tissues. In the mid 1980s, the planaria model of tumorigenesis was definitively described by researchers at Colorado State University in a pair of publications in the Journal of Experimental Zoology (Neoplastic Transformation in the Planarian: I. Carcinogenesis and Histopathology. 1986 F. Hall, M. Morita and J. Best. J. Exp. Zool. 240:211-227 and Neoplastic Transformation in the Planarian: II. Ultrastructure and Malignant Reticuloma. 1986 F. Hall, M. Morita and J. Best. J. Exp. Zool. 240:229-244.). This work was followed by that of Dr. David Schaeffer at the University of Illinois School of Veterinary Medicine. Recently, planaria have returned to the forefront of biological research due to the discovery of a diploid species (Schmidtea mediterranea) that has both sexual and asexual strains and a wide range of molecular tools have been developed for this species including the mapping of the its genome. Development of an invertebrate assay for tumorigenesis could provide alternatives to much more costly and time-consuming rodent models as well as facilitate the identification of genotoxic components of complex mixtures through bioassay-driven fractionation studies.