Engineering probiotic yeast for efficient sulforaphane delivery

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Project Summary / Abstract for WS00393217 Principal Investigator: Charles Denby, PhD (BFS) Engineering probiotic yeast for efficient sulforaphane delivery Consumption of cruciferous vegetables such as broccoli, brussels sprouts, and cauliflower has been shown to reduce the risk of developing multiple forms of cancer. Recent research has suggested that these health benefits result in part from the biochemical activity of isothiocyanates, a class of natural products found in these vegetables. Sulforaphane (SFN), one such isothiocyanate produced in abundance by crucifers like broccoli and kale, has shown especially impressive potential as a chemo-preventative and cancer therapeutic in in vitro and animal model studies. It has been challenging to rigorously assess the health benefits of SFN in humans, however. These challenges result from SFN’s inherent instability, as well as the varying effects that different food preparation methods and personal microbiome compositions have on SFN bioavailability. In this STTR, we propose to engineer a probiotic yeast that will biosynthesize SFN from within the human gastrointestinal tract. This probiotic yeast will provide a consistent and direct source of SFN that readily diffuses into the bloodstream, and is not dependent on specific microbiome compositions, food preparation methods, or drug regimens. Given the impressive body of research detailing the potential for SFN to treat prostate cancer in cell culture and animal models, we will develop this probiotic for potential use as a prostate cancer therapeutic. The probiotic microbe we will use as a host for our engineering efforts is the safe, and genetically tractable probiotic yeast, S. boulardii. The engineered S. boulardii strain will provide a means to directly assess the health benefits of SFN in prostate cancer therapy, while also providing a mechanism to efficiently deliver SFN for cancer therapeutic and preventative purposes. Phase I experiments will develop a S. boulardii strain that secretes a highly active myrosinase enzyme that is able to perform the terminal step in SFN biosynthesis. To achieve this goal, we will screen libraries of myrosinases, secretion signals, and yeast promoters to identify the genetic components that most effectively produce SFN under gastrointestinal conditions. To establish a proof-of-principle and motivate further research, Phase I will seek to engineer S. boulardii for production of 200 µmoles SFN per day, as small clinical trials that administered this quantity have shown encouraging results. In Phase II research, we will further engineer S. boulardii such that it contains the entire SFN biosynthesis pathway and produces SFN from fermentable sugars. Resultant strains will be tested in prostate cancer mouse models for safety and cancer-preventive properties. This project is directly in line with the NCI mission, as it will advance our understanding of a promising cancer therapeutic molecule, while also providing a direct means of delivering this potential therapeutic for cancer therapy and prevention.