Photoimmunotherapy offers a new weapon in the arsenal of cancer fighting agents, suggests a study published in Nature Medicine.

Conventional photodynamic therapy (PDT) which combines a photosensitizing agent with the physical energy of non-ionizing light to kill cells, does not work for cancer therapy due to non targeted photosensitizes also being taken up by normal tissues, resulting in serious side effects. Hisataka Kobayashi and colleagues, from the National Cancer Institute, Bethesda, Maryland, US, therefore set out to design a photosensitizer that would specifically target cancer cells.

What is different about their new agent, they say, is that the monoclonal antibody (mAB) based photosensitizer is only activated by near infrared (NIR) for targeted phototherapy when bound to the target molecule on the cancer cellular membrane. The treatment couples anti tumour antibodies targeting epidermal growth factor receptors to the phthalocyanine dye, IR700 , which responds to near infra light. The dye permeates into cells where it produces reactive oxygen species intracellularly resulting in cell death.

An additional feature of the agent is that it also emits a diagnostic fluorescence that can be used to target the application of light to further minimize exposure to non relevant tissues.

To examine action of the conjugate invivo the investigators prepared a mouse xenograft tumour model. When they shone near-infrared light on mice with tumours they found that cancer cells expressing the epidermal growth factor receptor died.

The authors say that the possibility of covalently conjugating any number of different antibodies to IR700 offers a highly flexible therapeutic platform.

Reference

M Mitsunaga, M Ogawa, N Kosaka, et al. Cancer cell-selective in vivo near infrared photoimmunotherapy targeting specific membrane molecules. Nature Medicine 2011. Doi:10.1038/nm.2554