Experimental therapies for chronic pain

Chronic pain, an underestimated but complex medical and social phenomenon, is often resistant to currently used analgesic drugs. The effect of these substances is frequently self-limiting, with increasing level of unwanted side effects caused by increased doses. Moreover, most pharmacological therapies for pain are administered systemically, either via the enteral or the parenteral route, and exert their effects on a multitude of organs and structures in the body regardless of their involvement in chronic pain pathways. Unlike pharmacological agents, biological pain therapies provide a means to target single molecules or specific types of neural cells in spatially limited areas in the central nervous system. Biological therapies utilize externally administered natural or synthetic agents acting at specific receptors on the spinal or supraspinal level, or virus or cell vectors allowing the expression and secretion of such agents in small compartments. By targeting a particular receptor or other specific protein involved in signal transmission, biological approaches to the treatment of chronic pain may provide greater analgesic efficacy without the limitations associated with current pharmacological therapies. This review summarizes published data on the most important of the currently known targets for biological therapy of chronic pain, and focuses on therapeutic approaches for modulation of these targets and on results from preclinical and clinical trials. Biological therapies for chronic pain hold great promise and are rapidly developing, but currently still are in a very early stage and therefore deemed experimental and not suitable for routine clinical use.