A CHEMOTHERAPY drug has been tweaked by chemists so that it is activated only
by light. This could enable doctors to target the toxic cancer treatment
directly at tumours, leaving healthy tissues unscathed.
The drug is cisplatin, an important treatment for testicular and ovarian
cancers. It binds to DNA in tumour cells, preventing the genetic code from
giving its orders and disrupting cell division. But the drug also affects DNA in
other rapidly dividing cells, so it is highly toxic to healthy tissues.
Ordinary cisplatin contains platinum in the form Pt(II), which makes ionic
bonds with two chloride ions. The new cisplatin molecule, developed by Peter
Sadler of Edinburgh University, contains Pt(IV), which makes four ionic bonds,
two with iodide ions instead of chloride. Pt(IV) can鈥檛 bind to DNA, so it can鈥檛
disrupt cell division. But when exposed to blue laser light, it reverts to the
active form Pt(II) that is able to latch onto DNA. So by giving a patient the
new drug and then illuminating tumour cells with lasers, it should be possible
to kill tumours without damaging other tissues (Angewandte Chemie
International Edition, vol 38, p 1460).
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鈥淭he idea is to get compounds that aren鈥檛 toxic on their own but can be
activated in selected cells,鈥� says Sadler. Pharmacologists at Greifswald
University in Germany have already shown that the new treatment can kill cancer
cells in the test tube. Human trials are 鈥渟ome way down the line鈥�, says Sadler.
He hopes to alter the compound so that it is activated by red light, which
penetrates skin better than blue.
