Chapter 4: Molecular biology in medicine.

Rational Drug Design 2

Rational drug design When our immune system fights off the flu it develops a memory of it, the next time we encounter the same strain we may not even develop symptoms before it is fought off. The problem is that new strains are constantly appearing, so the process must be repeated time and time again. Two surface proteins on influenza virus: Haemagglutinin is active in gaining entry to a cell. Neuraminidase allows the exit of new virus particles from a cell, freeing them to infect other cells. 3

Rational drug design Neuraminidase is an enzyme that varies in structure from strain to strain. Examination of strains of the virus from past years demonstrated that although most of the molecule changed dramatically, one small part remained constant. Fortunately, this non-variable part is the active site of the enzyme. 4

Using the active site If a drug was to be designed to inhibit the active site of neuraminidase, the molecular structure of the site had to be worked out. This was done by computer modelling so that the active site’s exact shape and the spatial arrangements of the atoms surrounding it became known. Computer representation of the anti-flu drug in the active site of neuraminidase. 5

Designing the drug Photo: CDC Once the detailed structure of the active site was known a molecule could be designed to fit and bind to the active site, Then an anti-flu drug was created! This technique, in which the active site of a molecule is determined and a second molecule (the drug) is constructed to fit into that active site to inhibit the activity of the first molecule, is called rational drug design. 6

How does it work? 7

Developing Vaccines 8

Contains whole, nonvirulent microorganisms Types of Vaccine There are two basic types of vaccine: subunit vaccines and whole-agent vaccines. Recombinant vaccines Toxoids Conjugated vaccines Acellular vaccines Attenuated (weakened) Inactivated (killed) ie. just antigen Subunit Vaccine Contains some part or product of micro-organisms that can produce an immune response Whole-Agent Vaccine Contains whole, nonvirulent microorganisms 9

Case study: Malaria

Malaria There are a number of strains, all carried by the Anopheles mosquito 1/3 of the world’s population is at risk. Every year there are 4 million new cases and 2 million deaths Involves a very complex life cycle Illness mainly due to: Capillaries becoming blocked by “sticky protein” on red blood cells Release of the toxin GPL Healthy blood cells being overtaken by the parasite Only Plasmodium Faliciparum curable as in other strains parasites lay dormant in gut Resistance Mosquitoes becoming resistant to DDT Plasmodium becoming resistant to Chloroquine

Developing Vaccines MALARIA Developing a vaccine is difficult due to Malarial DNA constantly changing and therefore its recognizable protein coat aswell. A potential vaccine could pre-expose people to a microscopic quantity of the GPL toxin Another option is to create an inhibitor to block the receptor site on the “sticky protein” so that it is unable to bind to tissue and block capillaries MEASELS Still a major cause of death in developing countries due to unavailability of vaccine and difficulty in storing it Current trials have spliced Measles antigen into a strain of lettuce Lettuce is freeze-dried in to powder and then packaged in to tablets Cheap and does not require refrigeration

Manufacturing Biological Molecules 13

Manufacturing biological molecules Insulin: produced by the pancreas, a hormone that controls the level of glucose in the blood by controlling its uptake from the blood by cells… A deficiency of this hormone results in an abnormally high level of glucose in the blood - diabetes. Because the amino acid sequence of the active molecule of insulin is known, a piece of DNA carrying the instructions (code) for insulin can be built and inserted into a plasmid vector. 14

Manufacturing biological molecules 15

Manufacturing biological molecules Application for manufactured molecules Insulin (for diabetics) Growth hormone Factor VIII (blood clotting agent missing in hemophiliacs) Advantages Can be produced in very large quantities If viral antigen can be copied, can be produced using no materials of human biological origin – minimises risk of associated disease Eg. in the past haemophiliacs receiving transfusions of Factor VIII from blood risked HIV Eg. patients receiving growth hormone from cadavers risked the brain disease CJD

Nanoparticles 17

Manufacturing biological molecules Very small human-made particle (0.1-100 nM in diameter) Being used to deliver drugs directly to the cells requiring them In cancer trials with mice, survival chances increased by 30% Made up of 3 parts Fluorescent stain – to follow progress Methotrexate – a drug that destroys cancerous cells Folic Acid – a vitamin required by rapidly reproducing cells