Bulletin Autumn‧Winter 1999

The climbing plant Trichosanthes Kirilowii Prof. Tam's technology is based on a v e ry simple rationale. Protein molecules w i t h a molecular we i ght less t han 60,000 daltons are quickly got rid of by our kidneys. Hence, interferon, like trichosanthin and t h e ir predecessor p e n i c i l l i n, a l l w i t h molecular we i gh ts of o n ly about 20,000 d a l t o n s, passes q u i c k l y t h r o u g h o u r kidneys. (Incidentally this explains w h y i n the olden days, du r i ng wartime, penicillin was recycled f r om patients' urine.) The wa y to lengthen the molecules' time i n the b o d y a nd s ub s equen t ly t he ir c u r a t i ve effects is to make them heavier. To increase the molecular weight of interferon, PEG, a harmless polyethylene glycol, is attached to interferon molecules. But here's where it becomes tricky. PEG can be attached to any part of the molecular c o n f i g u r a t i on and it w o u l d extend half-life. Howe v er if it is attached too close to sites whe re the drug's activity takes place, it w o u l d hinder the activity of the drug. If, say, half-life is q u a d r u p l ed b ut d r ug activity is reduced b y f our times, the wh o le purpose w o u l d be defeated. So the aim is to f i nd the right sites to a t t ach PEG so t h at h a l f - l i fe is increased and r educ t i on i n d r ug activity mi n imi zed. The p r e d i c t i on of p o t e n t i al sites is d o ne u s i ng a s pe c i al f o r m u l a o n the computer. W i t h trichosanthin. Prof. Tam a n d t he o t her researchers f o u n d t w o o p t i mal sites amo ng the i n i t i al seven to n i n e p o s s i b le ones. The se are n o w undergoing clinical trials. W i t h interferon, they have n ow identified five possible sites. The testing of one site takes about half a year, d u r i ng w h i c h ma ny complications may occur such as cross-linkage of interferon molecules and other unforeseen problems. But things are looking promising and the success of these endeavours w i l l b r i ng enormous benefits to H o ng Ko ng and the rest of the So u th Ch i na r e g i on wh e re hepatitis is prevalent. Hepatitis, like all diseases, makes no class a nd n a t i o n al boundaries. Treatments and cures should likewise be equally accessible to all. If the project succeeds, the costs of p r o d u c i ng interferon w i l l be reduced b y at least half to two-thirds, w h i ch means that it w i l l be affordable to more, its side-effects w i l l be mi n imi zed as fewer doses w i l l be required, and fewer people w i l l die unnecessarily f r om sclerosis and liver cancer. The project is also exemplary of the University's contribution to H o ng Kong's biotechnology field, and i n line w i t h the p o l i c y of t he H K S AR g o v e r nme nt to encourage innovation and technology. •