Quantification of in vivo Photofrin uptake by human pituitary adenoma tissue

Abstract

Object. Photofrin is widely distributed in the body after intravenous injection. This study was designed to quantify the preferential uptake of Photofrin by pituitary adenoma tissue for intraoperative photodynamic therapy. Methods. Eight patients (seven men) with recurrent pituitary adenomas who had undergone previous surgery and radiation therapy were recruited for a Phase I/II feasibility study of the application of photodynamic therapy to pituitary tumors. Photofrin was administered intravenously at a dose of 2 mg/kg body weight 48 hours before repeated transsphenoidal hypophysectomy was performed. At the time of the operation, pituitary adenoma tissue, muscle, fat, skin, and plasma were obtained for measurement of Photofrin content by fluorometric assay. The mean Photofrin level in pituitary adenoma tissue was 6.87 ng/mg (95% confidence interval [CI] 3.99–9.75), which was significantly higher than the uptake by skeletal muscle (2.24 ng/mg, 95% CI 1.28–3.2; p = 0.008), or fat (2.54 ng/mg, 95% CI 0.66–4.42; p = 0.007). Nevertheless, the mean drug concentration in pituitary adenoma tissue was not significantly different from the level in plasma (7.65 µg/ml, 95% CI 5.38–9.90; p = 0.558). Skin specimens were available in four patients, and these showed a mean uptake of 2.19 ng/mg. Conclusions. Photofrin is preferentially retained by pituitary adenoma tissue to levels both adequate for intraoperative photodynamic therapy and approximately 50% higher than those reported for gliomas.