Lighting up tumours

INDIAN scientists have developed indigenous radioactive compounds for easier detection of cancerous and other tumours. Whereas radioactive elements conventionally used to detect cancer had to be often imported, making them expensive, the new radiopharmaceuticals -- radiation-emitting chemical compounds that illuminate specific organs -- are based on technetium-99, a radioactive element available in plenty on the country's west coast. The scientists have also developed several kits to prepare these radiopharmaceuticals quickly, making life easier for the radiologist.

Developed by scientists at the Delhi-based Institute of nuclear medicine and Allied Sciences (INMAS), a Defence Research and Development Organisation laboratory, the new chemicals can replace gallium-67 and indium-111, which have to be imported. Besides being expensive, these elements are sometimes not selective in that they may show up in several organs, or they may be unstable within the body. U P S Chauhan and his colleagues at INMAS' department of radiopharmaceuticals overcame these problems by linking the radioactive elements with an appropriate biological molecule that has the ability to attach itself specifically to the target organs.

Chauhan's team utilised the idea that human immunoglobulin G (hIgG), a key protein of the immune system, binds to inflamed tissue. They chemically modified hIgG, and labelled it with technetium-99 in such a way that its ability to recognise different types of inflammed tissue was unaffected.

To find out whether an organ harbours a tumour, the radioactive material -- or radiopharmaceuticals -- are injected into that organ and the radiations emitted are scanned using a detector, giving an image of the organ. The radiopharmaceuticals developed by INMAS scientists have been successfully tested in rabbits and in humans and found to be specific to particular tissues, and effective in generating clear images of the affected organs such as the liver and kidneys. The tests were carried out at the Bangalore-based National Institute of Mental Health and Neurosciences and at the All India Institute of Medical Sciences in Delhi.

The INMAS team has also developed a kit for producing this radiopharmaceutical quickly, when required for imaging. According to Chauhan, this kit needs no special storage or transport because its contents are freeze-dried, and has a shelf life of about 6 months.

The INMAS team has also developed a kit that can visualise the human lymphatic system that is involved in the body's self-defence. The radiopharmaceutical used in this case is made up of technetium-99 and dextran, a polymer of glucose. Another glucose-based radiopharmaceutical, glucoheptonate, has been developed to image brain tumours.