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Avidin Preferentially Localizes to Bladder Tumor Tissue Compared to Normal Urothelium

Avidin appears to accumulate more in tumour tissue compared to normal urothelium, suggesting that high-energy beta emitting radionuclides associated with biotin, with which avidin binds, could be useful in treating bladder cancer.

Avidin is a 66 kD highly glycosylated and positively charged protein that shows extremely high affinity for biotin. Animal models of intraperitoneal tumours have shown that both the glycosylation and positive charge of avidin contribute to its tumour localization.

Marco Chinol, MD, with the European Institute of Oncology, Milan, Italy, and colleagues wanted to determine whether native avidin, made radioactive through the binding with technetium-99m labelled biotin (99mTc-biotin), selectively accumulated in superficial tumour tissues following intravesical administration.

They studied 15 patients with transitional cell bladder cancer in whom radiolabelled avidin was administered intravesically. Biopsies were obtained from normal and tumour tissues before transurethral resection and the radioactivity in the samples was measured.

Increased accumulation of radiolabelled avidin was observed in tumour tissue compared to normal bladder tissue. In some cases, tumour uptake was much higher than that of normal tissue.

Three patients instilled with a deglycosylated neutral form of avidin, who served as controls, showed no significant uptake in either tumour or normal urothelium and no difference in relative uptake.

They note that previous observations have indicated that the accumulation of radioactivity is greater in larger neoplasms and this "was generally confirmed in our series." According to the researchers, the case presenting the smallest lesion (0.2 cm in diameter) showed one of the lowest ratios of uptake, while the case with the largest neoplasm (8 cm in diameter) showed the highest quotient of uptake.

"The instillation of radiolabelled avidin directly or in two-step approach (first avidin and then radiolabelled biotin) warrant further investigations in order to explore the possibility to treat superficial bladder neoplasms locally with suitable therapeutic radionuclides with minimal risk of systemic toxicity for the patient," the authors conclude.


Eur Urol 2003;44:5:556-559. "Localization of avidin in superficial bladder cancer: a potentially new approach for radionuclide therapy"

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