Plexxikon Announces Preliminary PLX4032 Phase 2 Data Confirming Substantial Response Rate in Metastatic Melanoma Patients

Berkeley, CA and Sydney, Australia — November 5, 2010

Plexxikon today announced positive preliminary data from a pivotal Phase 2 clinical trial of PLX4032 (RG7204) in metastatic melanoma, showing significant tumor shrinkage in the majority of patients. These results support previously reported positive data. Data are being presented at the seventh annual International Melanoma Research Congress of the Society for Melanoma Research (SMR) in Sydney, Australia, by Dr. Jeffrey Sosman, Director of the Melanoma Program at the Vanderbilt-Ingram Cancer Center. PLX4032 is a novel, oral drug that targets a key oncogenic driver in melanoma and other cancers.

The Phase 2 (BRIM2) trial is a single-arm study of previously treated metastatic melanoma patients with the BRAF V600 mutation. Primary endpoints for this study are best overall response rate assessed by an independent review committee (IRC) using RECIST criteria, and secondary endpoints are best overall response rate assessed by clinical investigators, duration of response, progression-free survival, overall survival and safety.  In pivotal studies, independent review committees are used to review and confirm CT scans, including a second follow-up scan and tumor assessments, allowing a patient’s response to be characterized as “confirmed.” 

Results Confirm Robust PLX4032 Activity

The open-label, multi-center study enrolled 132 patients. As of September 27, 2010, data showed a confirmed response rate of 52 percent, including:

  • 3 confirmed complete responses (CR) (no evidence of disease)
  • 66 confirmed partial responses (PR) (tumor shrinkage of at least 30 percent)

In addition, 39 patients had stable disease. The median progression-free survival (PFS) was 6.2 months, compared to historical PFS of less than two months. The median duration of response was 6.8 months. Median overall survival has not yet been reached.

The unconfirmed response rate in the Phase 2 study was 68 percent, further indicating these data are consistent with the data previously reported from the Phase 1 extension study.

The most common drug-related adverse events were rash, photosensitivity, hair loss and joint pain. These were predominantly mild or moderate in severity. Twenty-six percent of patients developed cutaneous squamous cell carcinoma, which was typically managed without treatment interruption.

“These remarkable data provide hope for melanoma patients with the BRAF mutation, who are in dire need of new treatment options for this devastating disease. We are working with the FDA and global health authorities to gather the necessary data to make this treatment available as quickly as possible to these patients,” said K. Peter Hirth, PhD, CEO of Plexxikon. “Plexxikon’s ability to make highly selective kinase inhibitors has been key to achieving this success. We are excited about exploring the use of PLX4032 in other BRAF-mutant cancers, as well as in combinations with other agents, to potentially enhance this targeted drug’s therapeutic potential.”

“PLX4032 represents a true paradigm shift in the treatment of melanoma and a real breakthrough in melanoma research,” said Dr. Jeffrey Sosman, from Vanderbilt, and the principal investigator for the Phase 2 trial. “For the first time, we have the possibility of offering a true personalized medicine targeted to melanoma patients who may benefit most from the treatment.”

PLX4032 also is currently being tested in a randomized, controlled Phase 3 (BRIM 3) trial.  Enrollment is ongoing in this trial, with approximately 680 previously untreated mutation-positive, metastatic melanoma patients targeted.

Combination trials with PLX4032 are planned, including a trial to begin in the first quarter of 2011 that will combine PLX4032 and an oral, small molecule MEK inhibitor (RG7420/GDC-0973) in melanoma patients with the BRAF mutation. In addition, trials in other BRAF mutant cancers are being planned, including for adjuvant melanoma, thyroid and colorectal cancer.

Data Reflect Earlier Results Reported in NEJM

Results from a PLX4032 Phase 1 extension study in mutation-positive melanoma patients were reported in the August 26, 2010 issue of the New England Journal of Medicine, demonstrating an initial response rate of 81 percent. The confirmed response rate, determined by an investigator assessment for this study, was 59 percent.

About PLX4032 (RG7204)—A Personalized Medicine for Cancer Treatment

PLX4032 is a novel, oral small molecule for melanoma and other cancers harboring the BRAF mutation. Plexxikon utilized its structure-guided chemistry platform to discover PLX4032, and initiated clinical development in 2006. PLX4032 is being co-developed under a 2006 license and collaboration agreement between Plexxikon and Roche. A DNA-based companion diagnostic to identify patients whose tumors carry the BRAF V600 mutation is being co-developed by Plexxikon and Roche Molecular Systems, Inc. in parallel with the therapeutic development of PLX4032. 

Additional information about PLX4032 clinical trials is available at the Roche Clinical Trials Registry (http://www.roche-trials.com), at genentechclinicaltrials@druginfo.com, by visiting www.clinicaltrials.gov, or by contacting the Genentech clinical trial call center at 888-662-6728. 

About Melanoma

Melanoma is the most serious type of skin cancer and is growing at a rate of about five to six percent annually. More than 70,000 people in the U.S. and 160,000 people worldwide are diagnosed with melanoma each year. It is one of the deadliest cancers, with a five-year survival rate of less than 15 percent for people with advanced (Stage IV) melanoma. Historically, the median progression-free survival for a patient with metastatic melanoma is less than 60 days, and the median overall survival for these patients is approximately eight months.

Risk factors for melanoma include a positive family history of melanoma, prior melanoma, multiple clinically atypical moles or dysplastic nevi, inherited genetic mutations, fair skin and sun exposure. However, melanoma can occur in any ethnic group and also in areas of the body without substantial exposure to the sun.

About Plexxikon

Plexxikon is a leader in the structure-guided discovery and development of novel small molecule pharmaceuticals to treat human disease.  The company’s lead compound, PLX4032, is in late-stage clinical trials for the treatment of melanoma. The company is developing a portfolio of clinical and preclinical stage compounds to address significant unmet medical needs in cardio-renal disease, CNS disorders, autoimmune and neuro-inflammatory diseases, and oncology.   Plexxikon’s proprietary Scaffold-Based Drug Discovery™ platform integrates multiple state-of-the-art technologies, including structural screening as a key component that provides a significant competitive advantage over other drug discovery approaches. For more information, please visit www.plexxikon.com.

Contacts:

Kathleen Sereda Glaub
President
Plexxikon Inc.
+1 (510) 647-4009
kglaub@plexxikon.com  


For Plexxikon
Susan Kinkead
+1 (415) 751-3611
susan@kinkeadcomm.com

or

Jennifer Cook Williams
+1 (360) 668-3701
jennifer@cwcomm.org