Viruses and bacteria are common causes of pathogenic infections in humans and other organisms. Many viruses rely on the proprotein convertases produced by their host to initiate and spread infection , . Certain bacteria also rely on these proprotein 1 2 convertases, usually to activate bacterial toxins which cause disease. In addition, a number of cancers, including malignant glioma , astrocytoma , cervical cancer , and at 3 4 5 least one colon cancer cell line , also rely on furin or its substrates for malignant growth 6 and/or metastasis. Therefore, medications that inhibit certain proprotein convertases might prevent or treat such diseases. However, the most commonly used proprotein convertase inhibitors have a narrow therapeutic index, which means the dose that inhibits the enzyme is similar to the dose that causes toxicity in the patient. One example of this is dec-RVKR-cmk. Others are complex biological products that can be difficult to synthesize or expensive to produce, or too large in size to enter cells or be absorbed effectively by the body or delivered to the affected organ or system. One example of this is alpha-1-antitrypsin-Portland , , a modified form of alpha-1-antitrypsin (which is about 44 kd in size). In addition, the efficacy and toxicity of many of these substances are often unknown, and information about the long-term side effects of their use is scarce if not absent. Thus, there is a clear and unmet need to develop effective small-molecule proprotein convertase inhibitors that can better prevent or treat bacterial, viral, or neoplastic diseases that are facilitated by proprotein convertase activity. The following experiment was conducted to evaluate the effectiveness of the noble gas xenon as a furin inhibitor.