One of the most important areas in nanomedicine today is to develop drug carriers for treating diseases like cancer. Scientists have made considerable progress over the last 20 years in identifying specific cancer markers and developing the appropriate targeting molecules. Polymer capsules are promising in this respect because their surfaces can be modified, or functionalized, with a wide range of cancer-targeting molecules.

The new capsules, developed by Frank Caruso of the University of Melbourne and colleagues, are prepared by layer-by-layer assembly. The researchers start by sequentially depositing multilayers of thiolated poly(methacrylic acid), or PMASH, and poly(N-vinyl pyrrolidone), or PVPON, on silica particles through hydrogen bonding. Following assembly, the PMASH multilayers are stabilized by oxidizing the thiol groups to form disulphide bonds. Next, the silica templates are dissolved and the PVPON is released from the multilayers, resulting in the single component disulphide-bonded PMASH capsules.

These "hydrogel" polymer capsules are then conjugated with cancer-specific monoclonal antibodies using a heterotelechelic linker, poly(N-vinyl pyrrolidone) containing thiol and amine end groups.

Versatile approach

"The functionalization approach we report here is versatile," Caruso told, "so it is an easy matter to modify these capsules with a range of macromolecules to suit specific biomedical applications."

The researchers tested the polymer capsules on human colorectal cancer cells, which have an antigen called A33 and an epidermal growth factor receptor (EGFR) on their surface. They found that the capsules bound in greater numbers to these cancer cells when compared with capsules that had not been functionalized. The results suggest that these capsules can specifically interact with biological cells through antibody/antigen reactions, says Caruso.

"Our future research is aimed at engineering the chemical and physical properties of the capsules so that the constructs can accumulate and internalize into tumours," revealed Caruso.

The work was reported in ACS Nano.