Abstract :
[en] This work started as part of a Specific Targeted Research Project, ADONIS (FP-6 of the European Commission) and the aim of the project was the development of active targeting gold nanoparticles for optoacoustic imaging, from chemistry to biology. The establishment of a biosensor composed of antibody-functionalized gold nanorods is achieved on a model of tumor, in our case prostate cancer. Prostate cancer is a major public health problem in our industrialized countries, indeed it is the most frequent cancer and the second leading cause of death by cancer in men [1]. A major challenge in prostate cancer oncology is to develop more accurate, precise and less invasive tools for early stage diagnostic, including more accurate imaging assessments than those currently available. An efficient imaging technique which significantly improves the sensitivity and the specificity of the diagnostic and enables prediction of the cancer behavior would be extremely valuable to oncologists. Briefly the developed biosensor model consists of a gold nanorod – designed to convert a primary optical excitation into a detectable acoustic signal – coupled with a monoclonal antibody that targets prostate cancer cells for a specific recognition. Improved access to the target can be achieved by targeting accessible extracellular domain of a membrane protein, here the Prostate Specific Membrane Antigen (PSMA) [2]. PSMA is a transmembrane protein considered as a suitable biomarker for prostate cancer [3] and which is under intense investigation for use as an imaging and therapeutic target. PSMA is highly expressed in prostate cancers and also expressed in the tumor associated neovasculature of most solid cancers [4].
Before biological assessments the cytotoxic surfactant, essential to form rod-shaped nanoparticles, is exchanged by a mixture of two functionalized polyethylene glycol (PEG) molecules: HS-PEG-OMe for nanoparticle passivation and HS-PEG-NH2 for subsequent coupling with the antibody. The different cytotoxicity assays are achieved to establish the toxic threshold of the surfactant in order to know what CTAB concentration maybe tolerable on the cells. This argument is important during the displacement of the surfactant, based on successive centrifugations, because the whole discard of CTAB seem to be time-consuming or even
routinely unfeasible. Once this threshold drawn up, the PEGylated GNRs can be assessed on cancer cells, what seems being a common in vitro investigation. However unexpected issues came up during the experiments and had to be considered due to the properties of the nanomaterial. Nevertheless, after cytotoxicity assessment of PEGylated nanoparticles, the biosensor binding on targeted cells was assessed by fluorescence and scanning electron microscopies, two straightforward and flexible techniques. The antibody coupled to the gold nanorod is specific to the human prostate carcinoma LNCaP cell line, reported to express PSMA
which is an admitted biomarker of this cell line [5]. Finally, in order to complete the specific targeting of the biosensor, the antibody-coupled gold nanorods are injected in nude mice to evaluate their biodistribution and bioaccumulation for which inductively coupled plasma mass spectrometry (ICP/MS) is the technique of choice. Preliminary optoacoustic imaging is the ultimate step for the state-of-theart of the developed biosensor. Although the promising end results, particularly biodistribution assays, new questioning swarm and this is more and more discussed in publications due to the in vivo use of nanomaterials. Owing to their increasingly
extensive use, their nanometer sizes and their physiological contact (more or less long), controlling the interaction of nanoparticles with biological systems became a fundamental challenge of nanomedicine [6]. Therefore the protein opsonization on the gold nanorods is a tremendous study and is accomplished via mass spectrometry analyses.
