CT-2103: emerging utility and therapy for solid tumours

CT-2103 (XYOTAX(TM), Cell Therapeutics, Inc.) is a conjugate of paclitaxel to a polyglutamate polymer. its macromolecular nature exploits enhanced permeability and retention in tumour tissues. This compound is stable and inactive in aqueous solution and undergoes predominantly intracellular metabolism at the site where active paclitaxel is released. Because it does not require a Cremophor(R) EL vehicle, it can be administered by short infusion into peripheral veins. In preclinical models, compared with the same dose of unconjugated paclitaxel in Cremophor EL-ethanol, CT-2103 yields greater than or equal to12-fold increase in area under the curve in both plasma and tumour tissue. This alteration in drug pharmacokinetics and biodistribution is attributable to the ability of macromolecules to concentrate in areas of vascular leakiness, such as tumour tissue. CT-2103 is taken up by both tumour cells and normal phagocytic cells and is transported to lysosomes, where it is released by specific proteases through enzymatic action. In syngeneic and xenogeneic tumour models, at the maximally tolerated dose, CT-2103 appears to be more active than the standard doses of paclitaxel. it has also demonstrated activity in paclitaxel-resistant tumour models. Its potential enhancement of efficacy and decrease in drug-related toxicities make this agent an attractive option for therapeutic investigation. In Phase I trials it has been relatively well-tolerated, with acceptable toxicity at doses less than or equal to 225 mg/m(2) every 3 weeks. In combination with carboplatin the maximum tolerated dose is 235 mg/m(2) and the recommended Phase II dose 210 mg/m(2). Activity has been demonstrated in both non-small cell lung carcinoma (NSCLC) and in ovarian cancer, Phase III studies are currently testing this agent versus standard paclitaxel as maintenance therapy for first-line treatment-naive ovarian cancer. In addition, CT-2103 at a dose of 210 mg/m(2) (performance status [PS] 0 - 1) or 175 mg/m(2) (PS 2) is being compared with docetaxel (75 mg/m(2)) for the second-line treatment of NSCLC. In front-line PS 2 NSCLC patients, this agent in combination with carboplatin is undergoing comparison with paclitaxel/carboplatin; in a separate effort, single agent CT-2103 is being compared with either gemcitabine or vinorelbine. These studies will determine whether the preclinical and early clinical promise of this agent can be realised in the clinical treatment of solid tumours.