Off-Target drug effects resulting in altered gene expression events with epigenetic and "Quasi-Epigenetic" origins

This review synthesizes examples of pharmacological agents who have off-target effects of an epigenetic nature. We expand upon the paradigm of epigenetics to include "quasi-epigenetic" mechanisms. Quasi-epigenetics includes mechanisms of drugs acting upstream of epigenetic machinery or may themselves impact transcription factor regulation on a more global scale. We explore these avenues with four examples of conventional pharmaceuticals and their unintended, but not necessarily adverse, biological effects. The quasi-epigenetic drugs identified in this review include the use of beta-lactam antibiotics to alter glutamate receptor activity and the action of cyclosporine on multiple transcription factors. In addition, we report on more canonical epigenome changes associated with pharmacological agents such as lithium impacting autophagy of aberrant proteins, and opioid drugs whose chronic use increases the expression of genes associated with addictive phenotypes. By expanding our appreciation of transcriptomic regulation and the effects these drugs have on the epigenome, it is possible to enhance therapeutic applications by exploiting off-target effects and even repurposing established pharmaceuticals. That is, exploration of "pharmacoepigenetic" mechanisms can expand the breadth of the useful activity of a drug beyond the traditional drug targets such as receptors and enzymes.