NEW YORKTwo large phase III trials using tirapazamine
(investigational, also known as tirazone) in triplet regimens for
non-small-cell lung cancer (NSCLC) are rapidly accruing patients, according to
a report presented at the Chemotherapy Foundation Symposium XIX (abstract 60).
A novel drug that targets hypoxic tumor cells, tirapazamine is being tried
in conjunction with cisplatin (Platinol) and vinorelbine (Navelbine) in an
international trial, reported Joseph A. Treat, MD, vice chairman, Fox Chase
Temple University Cancer Center. In a US trial, it is being combined with
paclitaxel (Taxol) and carboplatin (Paraplatin).
The International Tirazone Triple Trial (i3T), Dr. Treat said, may finish
slightly ahead of schedule early in 2002, having accrued 575 of the projected
800 patients by the end of October at 100 sites in 13 countries. Under the
protocol, all patients receive cisplatin every 4 weeks at 100 mg/m² and vinorelbine 25
mg/m² weekly. In one arm, patients also receive 330 mg/m² of tirapazamine every 4 weeks.
The Southwest Oncology Group has accrued 175 of the projected 500 patients
for its trial comparing a standard pacli-taxel-carboplatin regimen with one
that adds tirapazamine, Dr. Treat said. In this trial, the tirapazamine dose
starts at 260 mg/m² but may be escalated to 330 mg/m² for patients who tolerate the lower amount. The carboplatin dose is AUC
6, and the paclitaxel dose is 225 mg/m².
Preclinical trials in mice, Dr. Treat said, showed that tirapazamine given
as a single agent produced relatively little cell kill or antitumor activity.
These studies also showed that the synergistic effect of tirapazamine with
platinum agents is induced only if the drug is given either 2 hours before or
after the platinum.
"This is a schedule-dependent drug, at least in the preclinical
models," Dr. Treat said, "and we have taken this time reference into
account in the clinic."
Tumor-cell hypoxia confers resistance to chemotherapy and radiation, he
noted. "Tirapazamine is novel," he said, "in that it very
selectively goes after these hypoxic cells, and prior exposure of cells to the
agent sensitizes the kill by cisplatin." Preclinical studies, he added,
showed a synergistic effect of tirapazamine with cisplatin, paclitaxel,
gemcitabine (Gemzar), and radiation therapy.