Exelixis is reinitiating clinical development of the tyrosine kinase inhibitor XL999 in patients with non-small cell lung cancer after suspending new patient enrollment in ongoing trials in November due to cardiovascular adverse events, the company reported April 24.

The South San Francisco biotech will initiate a new Phase I clinical trial evaluating the compound in NSCLC patients who have failed at least one prior therapy after reviewing the trial protocol with FDA, the firm said.

The dose-escalation study will start patients at 0.4 mg/kg dosed weekly and patients will be monitored for potential cardiovascular events.

"Results from this Phase I clinical trial could provide Exelixis with the opportunity to move directly into a late-stage clinical trial if XL999 demonstrates anti-tumor activity with an acceptable side-effect profile in this well-defined NSCLC patient population," Exelixis said.

The firm is reinitiating the clinical program in NSCLC based on efficacy from a previous Phase II trial of XL999 in the same population. In that nine-patient trial, two patients treated with the therapy had partial responses and one had prolonged stable disease.

Exelixis, however, will not reinitiate Phase I and II clinical trials in acute myeloid leukemia and ovarian cancer, programs that were put on partial clinical hold in December based on CV events.

"Given acceptance by the FDA of the new clinical trial protocol for XL999 in patients with NSCLC, the XL999 development program will now focus on this indication," the firm said.

Exelixis announced in November that it was halting new patient enrollment in trials involving the compound due to the adverse side effects (¹ Also see "Despite Enrollment Suspension, Exelixis Optimistic On XL999" - Pink Sheet, 3 November, 2006.).

XL999 is one of 12 agents the company is developing under an agreement with GlaxoSmithKline, whereby GSK has the option to choose up to three compounds at proof of concept to further develop. Exelixis will retain the right to the others; milestone payments to Exelixis could reach $275 million.

-Jessica Merrill (j.merrill@elsevier.com)

Exelixis Will Proceed With Development Of XL999 In NSCLC Based On Efficacy Data

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