PEG coating helps M13 spot cancer biomarker

Researchers in the US have wrapped bacteriophage with the polymer PEG (polyethylene glycol) to make a structure that detects PSMA, a molecular flag for prostate cancer. Their system could save lives by spotting aggressive forms of the disease at an earlier stage.

A polymer coating allows the bacteriophage to specifically target cancer cells

Bacteriophage are harmless to humans, and their surfaces can be easily modified to grab onto cancer biomarkers, which can be indirectly quantified by measuring the levels of enzymes attached to these biomarkers with an ELISA (enzyme-linked immunosorbent assay). However, non-specific adhesion between cell surface receptors and phage can lead to a reduced signal-to-noise ratio and therefore make it difficult to distinguish cancer cells.

Greg Weiss and Kritika Mohan at the University of California have overcome this issue by wrapping PEG around the phage M13. This creates a hydration sphere around the phage and limits non-specific cell adhesion, allowing them to distinguish PSMA-positive from PSMA-negative cells.

Metastatic cancer is commonly detected using expensive or invasive techniques such as PET (positron emission tomography), MRI (magnetic resonance imaging), CT (computerised tomography) and biopsies. This research could be a step towards a cheap biosensor that recognises cancer at the molecular level. ‘Eventually, the system would be developed as a blood test to detect cells metastasising from the primary tumour site,’ says Weiss, who estimates that such a device would cost between $10 (£6.45) and $5, and would give a readout within minutes.

Deepa Bedi, an expert in cancer nanomedicine from Tuskegee University in the US, says ‘this study shows the effectiveness of chemical modification of phage to reduce non-specific adhesion.’  The researchers are currently working on improving the sensitivity of the system by further modifying the phage, but stress that ‘this study describes the first steps towards early and efficient detection of metastasis-associated cells for earlier detection and favourable prognosis.’