Dr P Ravi Shankar

Pokhara

The fight against disease has been waged from the dawn of human civilisation. Protozoa, bacteria, fungi, viruses and prions constantly attack us and test our defence mechanisms. We have been refining our weapons in the fight against these invaders. The invaders and human cells are barely a few microns across and some are even smaller.

Nanotechnology — the science of the very small — may open

a new dimension in man’s fight against illness, disease and

death. The word ‘nano’ comes from the Greek language and means ‘dwarf’.

Richard Feynman, a leading physicist of the 20th century of California Institute of Technology, is regarded as the first visionary in the field of nanotechnology.

The human body is composed of cells. Each cell consists of smaller structures like the nucleus, mitochondrion, ribosomes and many others. Cells are arranged to form tissues, organs and the entire human body. Today as doctors, we intervene on a large scale, at the systemic level. Nanotechnology is giving us the opportunity to treat disease at a sub-molecular level.

‘Fantastic Voyage’ a sci-fi movie from the 1960s showed nanoscale robots (nanobots) coursing through the bloodstream. ‘Inner Space’ a movie by Steven Spielberg deals with a miniaturised Martin Short inside a ‘nanobot’ coursing through the body cavity.

Dr James Baker Jr at the Center for Biologic Nanotechnology at the University of Michigan and his group have developed non-toxic emulsions that penetrate and kill infectious microorganisms ranging from the flu virus to anthrax spores. Soyabean oil is emulsified with detergents to form nanodrops 400-600 nm.

When the oil droplets come into contact with the membranes of bacteria or viruses, they fuse with the membrane, blow it apart and kill the pathogens. The tissue structure and the internal supporting framework of human cells prevent them from being disrupted by the droplets. The fact that spores (the dormant forms of bacteria) were killed was particularly encouraging.

One of the first medical applications of nanotechnology (though not strictly at the nanometre level) was tried in diabetic rats. The implant was developed by Tejal Desai at the University of Illinois. It consists of a silicon box, a 10th of a millimetre across, which contains a sponge of collagen tissue seeded with pancreatic cells. The box is porous with holes 20 nm wide. The holes let in glucose molecules and lets out insulin. The larger cells of the body’s immune system are kept out. If the cells detect too much glucose in the bloodstream, then they start releasing insulin.

‘Dendrimers’ are spherical, branching molecules looking like a bush. Take a football or volleyball and stick in twigs randomly all around the surface. Now shrink it down to nanometre size and

you get a good replica of a ‘dendrimer’. They are covered with dozens of molecular handles to which various groups may be attached. Dendrimers can act as nano-sized tool kits.

The immune system does not recognise the dendrimer as foreign and an immune response does not take place. Dendrimers do not have folding and crevices where antibodies can bind and flag down the cells of the immune system. They appear as a uniform spherical mass of amino acids. ‘Apoptosis’ or ‘programmed cell death’ happens in many tissues in the body. The advantage of ‘apoptosis’ is that only the cells marked for destruction are destroyed. The neighbouring cells are not affected. In ‘instructive apoptosis’ the cell is instructed by the immune system to commit suicide.

Certain atoms or molecules bind to receptors on the cell

surface and can bring about the cell death. Cancer cells can be killed by a nanoprobe carrying these molecules. Alternatively,

the probe can breach the cell membrane with a tube and drain the cell contents. The dendrimers can be used to create an anti-cancer nanodevice.

‘Targeting groups’ could be attached to the cancer cells. The targeting groups can be fluorescent. Inside the cell another ‘dendrimer’ confirms the cancer. Another handle may contain a ‘cytotoxin’ like cisplatin. The release of the toxin can be brought about by laser light. Something similar to the ‘smart bombs’ of today, where a laser light illuminates the target and the missile follows behind on the trail of the laser.

Nanotechnology has many applications, some already in the lab, and others still in the realm of science fiction. Dr Eric Drexler, sometimes affectionately called Mr Nano had said, “With our present technology, we are still forced to handle atoms in unruly herds. Nanotechnology will handle individual atoms and molecules with control and precision.”