One in three people will develop cancer in their lifetime, and 25% will die from that cancer. In order to combat the disease, more than 50% of cancer patients will receive radiation therapy (RT). (American Cancer Society, Cancer Facts and Figures 2013, Atlanta: American Cancer Society; 2013.) The application of nanotechnology to RT holds the potential to radically improve the results of this widely-used therapy.
RT, or radiotherapy, has been used to treat cancer since the discovery of X-rays in 1895. In the early days of RT, crudely built cathode-ray tubes were used to direct beams of radiation but modern technology has advanced to megavoltage linear accelerators, electron radiation, heavy ion radiation (e.g. protons and carbon ions) and image-guided RT. Furthermore, diagnostic imaging of tumours has progressed with the use of three and four-dimensional computed tomographic (CT) simulators and magnetic resonance (MR) simulators.
The ideal RT treatment scheme is to optimise the therapeutic dosage to the tumour cells whilst minimising the damage to the normal tissue. However, although several advents have greatly improved the use of RT, it remains limited by what radiobiologists call the “the four R’s of RT”. Briefly, the four R’s – Repair, Repopulation, Reassortment, and Reoxygenation – describe the mechanisms cancerous cells use to survive and continue growing in spite of RT.
Nanotechnology holds the potential to combat these limitations and could change the way RT is used in the diagnosis, treatment and prevention of cancer.
Radiosensitivity is defined as the response cancer cells have to RT. Highly radiosensitive cancer cells can be rapidly killed with a modest dose of radiation. Nanomedicine aims to increase radiosensitisation and radioprotection by means of increasing the dosage of radiation delivered to tumours. In addition, nanoparticles targeted specifically to cancer cells have been developed to overcome the radioresistance exhibited by some cancers such as malignant melanomas, renal cell cancer and glioblastomas (brain tumours).
Professor Kobus Slabbert, a radiobiologist from iThemba LABS (Laboratory for Accelerator Based Sciences) in the Western Cape, explains as follows: “Several mechanisms have been researched, including the use of electron dense high atomic (Z) elements (such as metallic nanoparticles, e.g. gold and hafnium) or quantum dots (semi-conductor crystals), to enhance the attenuation and local radiation dosage from X-rays within cancer cells. This will induce the release of free radicals over a short distance – sparing normal tissue whilst causing irreparable double stranded breaks in the DNA of the targeted cells.”
Nanomedicine is engaged in the designing of carriers (such as liposomes, dendrimers, polymeric nanoparticles, etc.) which involve the encapsulation and controlled release of radiosensitising drugs. Furthermore, targeted nanoparticles for cancer treatment are highly sought-after for metastatic cancers due to their inability to be treated with conventional RT; meaning that, very soon, RT as we know it will be forever changed.
Writer: Janske Nel
Reviewed by: Prof Kobus Slabbert and Prof Sabelo Mhlanga