Adding more than one contrast agent to nanoparticles can enable accurate detection of even the smallest cancerous tumours.
Genetic mutations bring about alterations in the making of certain molecules that can cause uncontrolled cell division and lead to tumour formation. Cancers can be benign or malignant. Benign tumours remain at the spot of origin. Malignant tumours migrate or metastasize to various parts of the body and can disrupt the function of many organs. Cancer therapeutics and diagnostics aim to nip it in the bud by detecting and treating the tumour at the earliest.
Some of the early detection techniques include tissue biopsies, liquid biopsies, imaging techniques like positron emission tomography (PET), magnetic resonance imaging (MRI), computed tomography (CT) and ultrasound. However, these techniques do not provide a clear picture of the cancer type and stage at such an early level, making it difficult to come up with the right therapeutic strategies.
In cancer diagnostics, nanoparticles have made imaging of cancer and identification possible. Their small size, chemical inertness, good biocompatibility and high atomic number makes it easy to synthesize, handle and inject into the body without causing any severe side effects. The nanoparticles (10-300 nanometers in size) have a core containing the detecting material enclosed in a shell (nanoshells). The shell nullifies the chemotoxic effects of the detecting materials. The nanoshell cores can have iron oxides (detectable under MRI), gold and rare earth oxides (optical imaging), or radiolabeled substances (detected by PET).
Researchers at KTH Royal Institute of Technology have previously developed nanoshells having either Molybdenum (Mo), Ruthenium (Ru) and Rhodium (Rh) at the core and can be detected by X-Ray Fluorescence Computed Tomography (XFCT). They wanted to further enhance the sensitivity of detection by creating a dual bioimaging model. The use of multiple imaging contrast agents increases the possibility of the diseased areas to show up in scans. In a paper published in ACS publications, they conjugated a fluorophore Cy5.5 to the nanoshells to increase its detectability.
The scientists first coated the nanoshells with Silicon Oxide (SiO₂). SiO₂ has high biocompatibility, can carry other molecules, be easily modified and inhibit the toxic effects associated with Mo, Rh and Ru of the core. The coated SiO₂ increased the size of the nanoparticle to around 100 nm and is now suitable for biomedical applications.
The researchers then added Cy5.5 fluorophore onto these SiO₂ coated nanoparticles. Cy5.5 is a non-toxic near-infrared fluorophore having an emission spectrum between 685 nm and 703 nm and can penetrate deep into tissues in vivo. Cy5.5 gives an emission spectrum to the nanoparticles as they do not have any emission spectrum on their own. SiO₂ also enhances the photostability and penetration ability of Cy5.5.
The researchers wanted to test the toxicity of these nanoparticles in macrophages. They exposed the cells to both the ionic forms and the nanoparticle forms of Mo, Ru and Rh. The ionic forms negatively impacted the macrophage viability within 12 hours. However, due to the inert nature of the nanoparticles, these macrophages were not harmed. They observed that the uptake of these nanoparticles was time-dependent and it peaked at 24 hours. These nanoparticles were degraded in the lysosomes after 72 hours.
The Cy5.5 made it easy to detect the nanoparticles through confocal microscopy allowing for real-time cell analysis. When the scientists injected all the three nanoparticles within three separate spherical sample holders into a dead mouse, they were able to simultaneously spot all of them under XFCT. Since these spherical sample holders were only a few millimetres in size, this technique can enable the detection of multiple tumours of very small size in real time.
Future in vivo imaging studies are necessary to establish the potential of these targeted nanoparticles for preclinical and bioimaging studies. The presence of multiple contrast agents and dual mode of imaging can enable the accurate detection of even the smallest of tumours. Combining the power of XFCT and optical imaging can make these nanoparticles a powerful imaging tool.