Singapore cancer patients implanted with Psivida's Biosilicon

Two patients in Singapore General Hospital suffering from inoperable liver tumours have become the first cancer patients in the world to be treated with an experimental in situ radiation therapy developed by Perth nano-biotech company Psivida (ASX:PSD).

Doctors injected a suspension of Psivida's proprietary product BrachySil directly into the patients' liver tumours.

The BrachySil therapy employs 20-micron microparticles of pSivida's BioSilicon, a very pure form of silicon treated to make it extremely porous.

Where BioSilicon is formulated to accommodate drug molecules within its nanoporous structure, for slow-release implants, the silicon in BrachySil is doped with phosphorus atoms during synthesis.

The material is then irradiated to convert a proportion of the phosphorus atoms to radioisotope 32P. There is no effect on the silicon matrix.

The 32P radioisotope has a half-life of 14 days, and undergoes beta decay -- both desirable properties for a therapeutic radioisotope.

The emitted beta particles penetrate living tissues to a depth of only 8mm. When the BrachySil microparticles are injected directly into the tumour beyond this depth, the restricted killing radius limits the damage to the cancerous cells, leaving healthy tissues untouched.

With its 14-day half-life, the 32P radioisotope delivers sustained radiotherapy from within the tumour for many weeks, compared with mere days for rival isotopes.

Psivida investor relations manager Josh Mann said trials in small and large animal models of cancer confirmed that BrachySil had a very limited, spherical kill range that produced excellent tumour regression.

Oncologists at Singapore General Hospital, one of Singapore's leading cancer treatment centres, will administer the experimental BrachySil therapy to as many as 10 volunteers with inoperable, primary liver tumours over the next few weeks.

The company expects results to be available by late October. MD Gavin Rezos said the trial was an important milestone for the company, which has been working towards its first human clinical trial for two years.