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Carfilzomib (CFZ) is a tetrapeptide epoxyketone and a selective proteasome inhibitor. It is an analog of epoxomicin. Unlike many other peptide drugs, Carfilzomib withstands gut passage and can be taken orally.

Discovery, early development and regulatory approval
Carfilzomib is derived from epoxomicin, a natural product that was shown by the laboratory of Craig Crews at Yale University to inhibit the proteasome. The Crews laboratory subsequently invented a more specific derivative of epoxomicin named YU101, which was licensed to Proteolix, Inc.. Scientists at Proteolix modified YU101 to create carfilzomib, which they advanced to multiple Phase 1 and 2 clinical trials, including a pivotal Phase 2 clinical trial designed to seek accelerated approval. Clinical trials for carfilzomib continue under Onyx Pharmaceuticals, which acquired Proteolix in 2009. In January 2011, the U.S. FDA granted carfilzomib fast-track status, allowing Onyx to initiate a rolling submission of its new drug application for carfilzomib. In December 2011, the FDA granted Onyx standard review designation, for its new drug application submission based on the 003-A1 study, an open-label, single-arm Phase 2b trial. The trial evaluated 266 heavily-pretreated patients with relapsed and refractory multiple myeloma who had received at least two prior therapies, including bortezomib and either thalidomide or lenalidomide. Carfilzomib was approved by the FDA for use in patients with relapsed and refractory multiple myeloma on 20 July 2012. Onyx expects to launch the drug in the U.S. on 1 August 2012. When it launches, it will cost $10,000 per 28-day cycle, making it the most expensive FDA-approved drug for multiple myeloma.

Mechanism
Carfilzomib irreversibly binds to and inhibits the chymotrypsin-like activity of the 20S proteasome, an enzyme that degrades unwanted cellular proteins. Inhibition of proteasome-mediated proteolysis results in a build-up of polyubiquinated proteins, which may cause cell cycle arrest, apoptosis, and inhibition of tumor growth.

Clinical trials
A phase 2 trial for multiple myeloma showed promising results.

A single-arm, phase 2 trial of carfilzomib in patients with relapsed and refractory multiple myeloma showed that single-agent carfilzomib had durable responses in 36 percent of the 257 patients evaluated.

In another phase 2 trial of patients with relapsed and/or refractory multiple myeloma, carfilzomib in combination with lenalidomide and dexamethasone demonstrated an overall response rate of 78 percent. Researchers found carfilzomib could be administered over a period of 14–23 months with no new or overlapping toxicities.

In a phase 2 trial, carfilzomib had a 53 percent overall response rate among patients with relapsed and/or refractory multiple myeloma who had not previously received bortezomib. This study also found prolonged carfilzomib treatment is well-tolerated with approximately 22 percent of patients continuing treatment beyond one year.

In phase 2 trials of carfilzomib, the most common grade 3 or higher treatment-emergent adverse events were thrombocytopenia, anemia, lymphoenia, neutropenia, pneumonia, fatigue and hyponatremia.

A phase 3 trial comparing carfilzomib, lenalidomide and dexamethasone versus lenalidomide and dexamethasone in patients with relapsed multiple myeloma is ongoing.

In a frontline phase 1/2 study, the combination of carfilzomib, lenalidomide, and low-dose dexamethasone was highly active and well tolerated, permitting the use of full doses for an extended time in newly-diagnosed multiple myeloma patients, with limited need for dose modification. Responses were rapid and improved over time, reaching 100% very good partial response.