Myo-Inositol as an essential growth factor for normal and malignant human cells in tissue culture.

myo-Inositol (also called meso-inositol) is generally considered a member of the B vitamin complex and is required for growth by a number of yeasts (1) and fungi (2). An exogenous inositol requirement has, however, not been demonstrated in any bacterial species, and, although deficiency symptoms have been produced in animals, evidence for its vitamin function in man remains inconclusive. Inositol deficiency has been found to produce alopecia in rats (3, 4) and mice (5) and decreased growth in mice, rats, cotton rats, and hamsters (3, 6, 7). Several investigators have, however, been unable to confirm this growth-promoting effect (8, 9) and the role of inositol in the production or cure of experimental alopecia has also been questioned (9, 10). An interrelationship between inositol and a number of other vitamins in the production of deficiency symptoms (6, 11) is a complicating factor. A lipotropic effect in rats, independent of that of choline, has been reported by several investigators (12). Although a similar lipotropic effect has been found in man (13), there has been no demonstration of a deficiency syndrome resulting from lack of inositol. In the light of these results, it is of interest that myo-inositol has proved essential for the survival and growth of every cultured human cell examined, whether normal or malignant, as well as of a mouse sarcoma. With every one of eighteen cultured human strains, growth ceased in inositoldeficient media, there was cytopathogenic evidence of cell injury, and the cells eventually died. The quantitative aspects of that requirement and the degree to which myo-inositol could be replaced by its isomers and by related compounds are described here.