Cyclic Dipeptides in the Induction of Maturation for Cancer Therapy

Studies have suggested a possible form of therapy based on the use of maturation‐inducing compounds to induce differentiation of neoplastic cells and stimulate faster recovery of the normal cell population. The study of the effects of nine cyclic dipeptides on biochemical markers of differentiation implicated their potential to induce differentiation. Studies were undertaken to determine the specificity of these agents for HT‐29 cell cultures as well as the identification of the signal transduction pathways affected by these agents inducing the differential gene expression observed in the cells. The cyclic dipeptides studied showed a high degree of specificity, having no significant effect on Caco‐2 cells (P > 0.05), representing the normal gastrointestinal mucosa. All inducers administered were shown to affect the total energy state of HT‐29 cells, an effect which increased the probability of HT‐29 cell differentiation. Results indicated that those agents which induced differential gene expression acted at different steps in the isolated signal transduction pathway. Cyclo(Trp‐Trp) and cyclo(Phe‐Pro) induced a high degree of acetylation of histones (P < 0.05), while the remaining cyclic dipeptides induced a high degree of phosphorylation of histones (P < 0.05) (cyclo(Trp‐Trp) induced a moderate degree of histone phosphorylation). The results from histone phosphorylation and acetylation and cyclic AMP responsive element binding protein phosphorylation studies suggest that the cyclic dipeptides activate a chromatin switch, which leads to the increase in accessibility of lineage‐specific genes for transcription.