Abstract Medicinal opioids are essential medicines for treating pain, but exhibit addictive properties. The United States has committed significant resources to curb opioid dependence and overdose. The nal-opioids, a suite of antagonist and mixed partial agonist opioids, are an important group of pharmacotherapies used in drug- addicted patients for treating overdose, managing symptoms during detoxification, and maintenance by blocking reward responses. In pain management patients, nal-opioids are used in combination with opioids to prevent addiction and abuse, and to reduce side effects. Current production methods for nal-opioids are inefficient, expensive, and rely on the farming of a drug crop. The raw starting materials for nal-opioid synthesis are natural opiates that are extracted from opium poppy and subsequently chemically modified through a series of inefficient reaction steps. As a result of the costs associated with this process, nal-opioids command a substantially higher price than opiates that have not been chemically modified. For example, natural morphine active pharmaceutical ingredient (API) retails for ~$1,000/kg, whereas naloxone and buprenorphine cost ~$12,000/kg and ~$28,000/kg, respectively. Antheia?s technology will produce nal-opioids efficiently and at a fraction of the cost of the current production methods. The novel technology allows for total biosynthesis of nal-opioids by yeast fermentation, thereby removing the reliance on drug crop farming and changing the way these life-saving therapeutics are manufactured. Antheia will leverage its existing technology for producing opioids in yeast and extend the biosynthetic capabilities of these strains to include precursors of the nal-opioids, and ultimately the end products naloxone, naltrexone, and buprenorphine. Technoeconomic models indicate that Antheia?s unique technology will result in greater than a 10-fold reduction in the cost of producing these compounds. The objective of this Phase I SBIR project will be to develop engineered yeast strains that produce high levels of noroxymorphone, the direct precursor for the nal-opioids naloxone and naltrexone, through whole cell biocatalysis. First, a yeast strain capable of high-level oxycodone biosynthesis will be constructed by the addition and optimization of two enzymatic steps to Antheia?s existing opioid production strains. Second, two novel O-demethylase and N-demethylase enzyme activities will be developed with enzyme evolution and a high-throughput colorimetric screening assay. Finally, the O- and N-demethylase activities will be combined with the optimized oxycodone-producing strain to deliver a novel bioproduction system for noroxymorphone. This project will address major technical barriers to the microbial production of nal-opioids and support the commercial viability of this technology. By addressing much of the technical risk, this SBIR project will enable investor-funded development and scale up, and Antheia?s entry into a new product line to help combat growing opioid abuse and addiction.