Cytokinetics ( CYTK) said its experimental head-and-neck cancer drug ispinesib failed a clinical trial in which it was meant to reduce or eliminate tumors. The two-stage trial, involving 20 patients with squamous-cell carcinoma of the head and neck, was designed to study the drug's safety and effectiveness in patients who saw at least a partial reduction in tumor size after infusions of ispinesib. No patients saw their tumors shrink during the treatment stage of the trial, however, so no participants could advance to the second stage, the company reported. The best overall response was stabilization of the disease in five of the 19 patients evaluated. Ispinesib belongs to a class of cancer drugs known as KSP inhibitors, which work by targeting a protein that causes tumor cells to multiply. The trial was conducted in conjunction with drug giant GlaxoSmithKline ( GSK) and the National Cancer Institute. Cytokinetics shares were losing 22 cents, or 3.5%, to $6.13.