EXELIXIS REPORTS DATA FROM ONGOING PHASE 1 STUDY OF XL019 TO TREAT MYELOFIBROSIS – UPDATE

12/10/2007 2:06:40 PM Monday afternoon, Exelixis, Inc. (EXEL), a developer of therapies for the treatment of cancer and other serious diseases, announced data from an ongoing Phase 1 trial of XL019 to treat patients with myelofibrosis, a myeloproliferative disorder, or MPD.

The primary objective of the trial is to determine the safety and tolerability of XL019 when administered orally once daily for 21 days in 28-day cycles. Secondary objectives include evaluation of the pharmacokinetics and pharmacodynamics of XL019, and to evaluate response using the International Working Group for myelofibrosis consensus response criteria.

XL019 is an investigational small molecule that selectively inhibits the tyrosine kinase JAK2, one of four JAK family members activated in response to cytokines and hematopoietic growth factors. JAK2 is inappropriately activated in the majority of MPD patients and is deregulated in a number of solid tumors, including certain subtypes of lymphoma.

The preliminary results of the study indicates reduction in spleen size of 33% to 100% in five of six patients evaluated, reduction in erythropoietin-independent colony formation of up to 39% and up to 100% in two patients evaluated, relief of constitutional symptoms and reduction in the number of cells with the JAK2 V617F mutation.

The results also showed correlation between XL019 exposure and decreases in phosphorylation of STAT, a marker for JAK activity and XL019 was generally well tolerated with no evidence of myelosuppression.

Michael Morrissey, president of research and development at Exelixis stated, “The strong linkage of JAK2 to MPDs provides a potentially quick route to market, with potential for additional opportunities in larger commercial indications. We are planning to initiate pivotal trials of XL019 in myelofibrosis patients in 2008.”

EXEL’s shares are currently trading at $8.66, up 19 cents or 2.15% from its previous closing of $8.85.