Naoaki Shintani

Kinetics of Internalization and Cytotoxicity of Transferrin‐Neocarzinostatin Conjugate in Human Leukemia Cell Line, K562

ABSTRACT Human serum transferrin was conjugated with an anticancer‐active polypeptide, neocarzinostatin, by using N‐succinimidy1‐3‐(2‐pyridyldithio)propionate. The conjugate consisted of 1.8 mol of neocarzinostatin per 1 mol of transferrin on average and retained cytotoxic activity against human tumor cells. This conjugate was capable of binding to the transferrin receptor of human myelogenous leukemia K562 cells and was internalized by endocytosis. The LD50 values of the conjugate and neocarzinostatin alone in the presence of excess native bovine transferrin were 0.20 μ/ml and 1.80 μ/ml, respectively, suggesting that the effect of the conjugate was greater than that of neocarzinostatin alone. A pulse‐chase experiment using 125I‐labeled conjugate revealed that 25% of the internalized conjugate was degraded in lysosomes and the rest was recycled back to the cell surface without degradation. About 75% of this conjugate recycled back to the cell surface in 18.3 min (3.4 min for receptor binding and 14.9 min for recycling to the cell surface through the acidosomes), while the rest was delivered from the cell surface to the lysosome in 19.6 min. This phenomenon was confirmed by chasing the radioactivity in subcellular fractions separated by Percoll density gradient centrifugation. Therefore, it was concluded that this conjugate is internalized specifically by transferrin receptors and is at least partly transferred to and accumulated in lysosomal compartments, resulting in the inhibition of cellular DNA synthesis.

A novel treatment for early gastrointestinal carcinoma by ultrasonic endoscopic mucosal stripping.

PurposeThe aim of this study was to clarify the indications for a new endoscopic mucosal resection (EMR) technique that employs a cavitational ultrasonic surgical aspirator (CUSA). Endoscopic mucosal resection has proved an effective technique for treating early mucosal gastrointestinal cancer. However, resecting a lesion larger than 2 cm en bloc requires special devices and a long processing time; and it engenders the risk of bleeding, perforation, and other complications.MethodsWe investigated application of the CUSA for detaching the mucosa from the muscularis propria of extracted porcine stomachs and then clarified the specification of an endoscopic ultrasonic scalpel for endoscopic mucosal resection by investigating characteristics of two original, handmade prototype cavitational ultrasonic surgical aspirators.ResultsUse of a cavitational ultrasonic surgical aspirator should improve the ease and safety of detaching the mucosa. A small, high-power ultrasonic cylindrical vibrator should be developed to make possible a probe-type scalpel with a piezoelectric vibrator mounted in the tip of a catheter. An ultrasonic transmission-type scalpel could lead to the development of a new endoscopic mucosal resection device for clinical use.ConclusionsThe CUSA should enable us to develop a safer, simpler, time-saving scalpel for endoscopic mucosal resection, although some resolvable technical problems remain. The CUSA might enable us to diagnose carcinoma invasion into the submucosa in aspirated specimens and then aspirate out the entire invading submucosal carcinoma.