PCI Biotech light-directed drug delivery system slows growth of invasive tumours

Norwegian firm PCI Biotech's light-activated drug delivery system is able significantly to slow the growth of an invasive tumour in mice, according to a new study. Researchers say the study provides evidence of the clinical potential of photochemical internalisation (PCI) in treating human cancer.

The study is claimed to be the first to trial the PCI process on an aggressive tumour resembling that of human soft tissue sarcoma (STS). Currently, up to half of all patients newly diagnosed with STS die within five years, with recurrence of tumours after surgery being an important problem. The research indicates that PCI could help to slow or eliminate recurrence of disease, by enhancing the delivery of drugs to the tumours.

Researchers at the Norwegian Radium Hospital used a model where the tumours grow invasively into the leg muscles of mice to produce a more accurate model of human STS. The mice were treated with different combinations of drug and light therapy while researchers measured how fast the tumours grew.

When PCI was combined with the cytotoxic drug bleomycin, the tumours took 27 days to reach the end point of 1,000mm3 compared with six days without treatment, seven days with bleomycin treatment only and 10 days when an ordinary photodynamic therapy was used. According to the researchers, PCI produced better treatment effects than photodynamic therapy because it was more effective at the periphery of the tumour, where a rim of treatment-resistant tumour cells remains after PDT treatment. In addition previous studies have suggested that PCI has better efficacy in deeper tissue layers.

Drug molecules such as bleomycin are initially taken up by the cell in enclosed compartments or vesicles called endosomes. Unlike other photodynamic approaches, the PCI system uses photosensitisers that localise to the membranes of these vesicles and, when activated by light, cause them to burst. This releases the drug molecules inside the cell, enhancing the effect of the drug.

The study, by Dr Ole-Jacob Norum and colleagues, has been published in the journal Photochemistry and Photobiology.

Dr Anders Hogset, chief scientific officer of PCI Biotech, said: "The subsistence of a rim of treatment-resistant cells in the tumour periphery is a well-known problem, both after photodynamic therapy and in other cancer treatment modalities. The demonstration in this study that the PCI technology can also target such cells further substantiates the clinical usefulness of the PCI technology."