Endogenous Opioid Systems, Stress, and Cancer

Abstract

Opium’s importance in both medicinal and social contexts dates back thousands of years (Blum, 1970; Terry and Pellens, 1928). Interest in opiates and opiate-like compounds (heretofore collectively referred to as “opioids”) had been maintained throughout the years. A major breakthrough in our understanding of opioids came with the discovery of opioid receptors in 1973 by groups led by Simon (Simon et al., 1973), Snyder (Pert and Snyder, 1973), and Terenius (1973), along with the equally elegant finding of endogenous opioids by Hughes, Kosterlitz and colleagues (Hughes, 1975; Hughes et al., 1975) in 1975. Discovery of opioid receptors and the endogenous opioids (collectively referred to as “endogenous opioid systems”) stands as a landmark of scientific achievement. Needless to say, this has stimulated intense research activity which has already culminated in important information as to the mechanisms and functions of opioids. One such exciting insight has been the discovery in 1983 that endogenous opioid systems are related to growth of both normal and abnormal cells and tissues (Zagon and McLaughlin, 1983a, b, c, d). This has led to a fascinating story concerning the fundamental nature of growth (Zagon and McLaughlin, 1984a, b, c; 1985a, b). The major purpose of this chapter is to review the evidence relating endogenous opioid systems to cancer. Since some aspects of stress may be associated with the endogenous opioid systems, and ACTH and some endogenous opioids share the same precursor (pro-opiomelanocortin), we have also included relevant information on the topic of stress and cancer in an attempt to provide perspective to the entire field of endogenous opioid systems and tumor biology.