Amgen’s Multiple Myeloma Drug Shows Promise in Phase 3 Trial
The drug maker is seeing great signs in the development of treatment for multiple myeloma, a bone marrow cancer. The results from its Phase 3 of Kyprolis’ clinical trial shows that patients can live almost nine months longer without worsening symptoms. According to Amgen, about 70,000 people in the U.S. are living with the disease and 24,000 new cases are diagnosed every year. With the good clinical trial result, Amgen plans to begin regulatory submissions around the world next year. Dr. Pablo Cagnoni, president of Amgen’s subsidiary Onyx Pharmaceuticals said, “The results demonstrate that Kyprolis can significantly extend the time patients live without their disease progressing. The ability of novel therapies to produce deep and durable responses may, one day, transform this uniformly fatal disease to one that is chronic and manageable.” Male patients over the age of 65 have the highest risk of developing it.
Carfilzomib (marketed under the trade name Kyprolis, Onyx Pharmaceuticals, Inc.) is an anti-cancer drug acting as a selectiveproteasome inhibitor. Chemically, it is a tetrapeptide epoxyketone and an analog of epoxomicin.
The U.S. Food and Drug Administration (FDA) approved it on 20 July 2012 for use in patients with multiple myeloma who have received at least two prior therapies, including treatment with bortezomib and an immunomodulatory therapy and have demonstrated disease progression on or within 60 days of completion of the last therapy. Approval is based on response rate. Clinical benefit, such as improvement in survival or symptoms, has not been verified.
The abbreviation CFZ is common for referring to carfilzomib, but abbreviating drug names is not best practice in medicine.
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. Craig Crews, Raymond Deshaies from Caltech, Phil Whitcome, the former CEO of Neurogen and Larry Lasky, a venture capitalist, founded Proteolix, and along with other researchers and scientists, advanced YU101. The scientists at Proteolix invented a new, distinct compound that had potential use as a drug in humans, known as carfilzomib. Proteolix advanced carfilzomib 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 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. It costs approximately $10,000 per 28-day cycle, making it the most expensive FDA-approved drug for multiple myeloma.
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.
A single-arm, Phase II trial (003-A1) of carfilzomib in patients with relapsed and refractory multiple myeloma showed that single-agent carfilzomib demonstrated a clinical benefit rate of 36 percent in the 266 patients evaluated and had an overall response rate of 22.9 percent and median duration of response of 7.8 months. The FDA approval of carfilzomib was based on results of the 003-A1 trial.
In a Phase II trial (004), 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 included a bortezomib-treated cohort. Results were reported separately. This study also found prolonged carfilzomib treatment was tolerable, with approximately 22 percent of patients continuing treatment beyond one year. The 004 trial was a smaller study originally designed to investigate the impact of carfilzomib treatment in relationship to bortezomib treatment in less heavily pretreated (1-3 prior regimens) patients.
A Phase II trial (005), which assessed the safety, pharmacokinetics, pharmacodynamics and efﬁcacy of carﬁlzomib, in patients with multiple myeloma and varyi ng degrees of renal impairment, where nearly 50 percent of patients were refractory to both bortezomib and lenalidomide, demonstrated that pharmacokinetics and safety were not influenced by the degree of baseline renal impairment. Carﬁlzomib was tolerable and demonstrated efficacy.
In another Phase II trial (006) of patients with relapsed and/or refractory multiple myeloma, carfilzomib in combination with lenalidomide and dexamethasone demonstrated an overall response rate of 69 percent.
A Phase II trial (007) for multiple myeloma and solid tumors showed promising results.
In Phase II trials of carfilzomib, the most common grade 3 or higher treatment-emergent adverse events were thrombocytopenia, anemia, lymphoenia, neutropenia, pneumonia, fatigue and hyponatremia.
In a frontline Phase I/II 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 percent very good partial response.
A phase III confirmatory clinical trial, known as the ASPIRE trial, comparing carfilzomib, lenalidomide and dexamethasone versus lenalidomide and dexamethasone in patients with relapsed multiple myeloma is ongoing. It is no longer recruiting and should report in 2014.
The initial enthusiasm following the discovery of a pharmacologically active natural product is often fleeting due to the poor prospects for its ultimate clinical application. Despite this, the ever-changing landscape of modern biology has a constant need for molecular probes that can aid in our understanding of biological processes. After its initial discovery by Bristol-Myers Squibb as a microbial anti-tumor natural product, epoxomicin was deemed unfit for development due to its peptide structure and potentially labile epoxyketone pharmacophore. Despite its drawbacks, epoxomicin’s pharmacophore was found to provide unprecedented selectivity for the proteasome. Epoxomicin also served as a scaffold for the generation of a synthetic tetrapeptide epoxyketone with improved activity, YU-101, which became the parent lead compound of carfilzomib (Kyprolis™), the recently approved therapeutic agent for multiple myeloma. In this era of rational drug design and high-throughput screening, the prospects for turning an active natural product into an approved therapy are often slim. However, by understanding the journey that began with the discovery of epoxomicin and ended with the successful use of carfilzomib in the clinic, we may find new insights into the keys for success in natural product-based drug discovery.
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