Nitroso (circles) urea (squares), CCNU and BCNU are highly lipid-soluble alkylating agents that allow for penetration of the blood–brain barrier (BBB) and , as such, are used in several types of brain cancer, including glioma, glioblastoma multiforme, medulloblastoma, and astrocytoma among other indications. Nitrosoureas, particularly carmustine, can cause a progressive decline in cognitive function, development of seizures, and coma. Streptozocin is a naturally occurring compound that is similar to glucose and is transported into the cell by the glucose transport protein GLUT2. Streptozocin is particularly toxic to the insulin-producing beta cells of the pancreas; hence, it is used for the treatment of pancreatic neuroendocrine tumors. Streptozocin can cause hyperglycemia/glucose intolerance, severe pain at injection site, and transaminitis.