Streptozotocin is approved by the U.S. Food and Drug Administration for treating metastatic cancer of the pancreatic islet cells. Since it carries a substantial risk of toxicity and rarely cures the cancer, its use is generally limited to patients whose cancer cannot be removed by surgery. In these patients, streptozotocin can reduce the tumor size and reduce symptoms. A typical dose is 500 mg/m2/day by intravenous injection, for 5 days, repeated every 4–6 weeks. Due to its high toxicity to beta cells, in scientific research, streptozotocin has also been long used for inducing insulitis and diabetes on experimental animals. Streptozotocin has also been used for modeling Alzheimer's disease through memory loss in mice.
Mechanism
Streptozotocin is a glucosamine-nitrosourea compound. As with other alkylating agents in the nitrosourea class, it is toxic to cells by causing damage to the DNA, though other mechanisms may also contribute. DNA damage induces activation of PARP which is likely more important for diabetes induction than the DNA damage itself. Streptozotocin is similar enough to glucose to be transported into the cell by the glucose transport protein GLUT2, but is not recognized by the other glucose transporters. This explains its relative toxicity to beta cells, since these cells have relatively high levels of GLUT2.
History
Streptozotocin was originally identified in the late 1950s as an antibiotic. The drug was discovered in a strain of the soil microbeStreptomyces achromogenes by scientists at the drug company Upjohn in Kalamazoo, Michigan. The soil sample in which the microbe turned up had been taken from Blue Rapids, Kansas, which can therefore be considered the birthplace of streptozotocin. Upjohn filed for patent protection for the drug in August 1958 and was granted in March 1962. Recent advancements in understanding the biosynthesis of this natural product have been made by Balskus et al. In short, the authors found the gene cluster responsible for production of Streptozotocin in Streptomyces achromogenes and identified novel function of a non-heme iron enzyme, SznF, which forms the N-N bond in the N-nitrosourea pharmacophore by oxidative rearrangement. In the mid-1960s, streptozotocin was found to be selectively toxic to the beta cells of the pancreatic islets, the cells that normally regulate blood glucose levels by producing the hormoneinsulin. This suggested the drug's use as an animal model of diabetes, and as a medical treatment for cancers of the beta cells. In the 1960s and 1970s, the National Cancer Institute investigated streptozotocin's use in cancer chemotherapy. Upjohn filed for FDA approval of streptozotocin as a treatment for pancreatic islet cell cancer in November 1976, and approval was granted in July 1982. The drug was subsequently marketed as Zanosar. Streptozotocin is now long off patent and many generic formulations are available.
