Biodistribution of radiolabeled adenosylcobalamin in patients diagnosed with various malignancies

Objective: To study the biodistribution of a vitamin B-12 analog, indium In 111-labeled diethylenetriamine-pentaacetate adenosylcobalamin (In 111 DAC), in patients recently diagnosed as having primary or recurrent malignancy. Patients and Methods: Thirty patients (14 women and 16 men) with radiographically or clinically diagnosed breast, lung, colon, sarcomatous, thyroid, or central nervous system malignancies were studied prior to definitive surgery or biopsy. A maximum of 650 mu Ci (2.2 mu g) of In 111 DAC was administered intravenously, Vitamin B-12 and folate levels were determined prior to injection. Serum clearance and urinary and stool excretion of the tracer were measured. Images were routinely obtained at 0.5, 3 to 5, and 20 to 24 hours after injection. Biodistribution of In 111 DAC was determined by computer analysis of regions of interest. Results: Serum T-1/2 clearance was 7 minutes. Average urinary and stool excretion of the injected dose over 24 hours was 26.1% and 0.4%, respectively. The greatest fecal uptake of In 111 DAC occurred in the liver and spleen, followed by the nasal cavity and salivary and lacrimal glands, The average tumor uptake of the injected dose was 2% at 30 minutes and 1.5% at 24 hours. High-grade primary and metastatic breast, lung, colon, thyroid, and sarcomatous malignancies were all imaged at 3 to 5 hours after injection. Central nervous system tumors and advanced metastatic prostate cancer were best identified at 24 hours. Mammographically occult, palpable, and nonpalpable breast cancers were delineated by In 111 DAC, Low-grade malignancies as well as early skeletal metastatic disease were not effectively imaged by the vitamin B-12 tracer. Patients with elevated baseline vitamin B-12 or those concurrently taking corticosteroids appeared to have optimal visualization of their malignancies. Conclusion: Vitamin B-12 mag be a useful vehicle for delivering diagnostic and therapeutic agents to various ma lignancies. Further evaluation of cobalamin analogs and their interaction with transport proteins and cellular receptors within malignant tissue and infection is warranted.