Cell-Cell and Cell-Stromal Interactions in Differentiation Therapy

摘要

Differentiation and proliferation of tumor cells can be modulated by direct cell contact and by diffusable macromolecules produced by stromal cells. The expression of specific functions of stromal, as well as epithelial cells can be influenced by specific inducers that can modulate synthesis and secretion of growth factors, extracellular matrix molecules and cell surface molecules. The end result of such alterations of stromal cell function is a decrease in proliferation and/or increase in differentiative properties of the tumor cell. The important factors in normal prostate gland differentiation are not well defined, whereas a variety of molecules have been defined in mammary gland and hematopoetic growth and differentiation. It is important to recognize that the induction of differentiation in epithelial systems does not automatically signify an alteration in tumorigenesis, much less prove the importance of cell-cell interactions in differentiation of epithelial tumors. Although there are reports of regression of tumors in strong embryonic fields or in regenerating fields and isolated reports of non-neural epithelial tumors converting to benign growth when placed in heterotypic cellular interactions, what is desperately needed is convincing evidence in well-documented model systems that specific induction of differentiated function in epithelial tumors occurs and that the phenomenon operates under the same fundamental laws that regulate cell differentiation in normal development. Until such results can be demonstrated and accepted widely, the concept of differentiation therapy will only be applicable to specialized cases like hematopoetic tumors and teratocarcinomas. To simply demonstrate that an inducer generates a differentiated response in a tumor cell population is not sufficient to argue that growth and tumorigenicity will be compromised.