Alpelisib Challenge Test (ACT)

The goal of this study is to test a potentially easier method for measuring how much insulin a person is capable of producing than the current gold-standard method, the "hyperglycemic clamp." Participants will come in for a two-day (overnight) visit in which they will first undergo a "hyperglycemic clamp," in which they receive an intravenous (into the vein) infusion of glucose (sugar) in order to measure the maximum amount of insulin their body produces in response. They will then consume a series of three standardized meals throughout the rest of the day. At 23:00, they will take a single dose of alpelisib, a drug that interferes within insulin's actions in the body. Then, the following morning, they will undergo a "Mixed Meal Tolerance Test" in which they consume a standardized liquid nutritional beverage and have blood drawn periodically before and during the test.