Although tremendous growth and success have been seen in the realm of oncology during the last decade, cancer remains a commonly fatal malady that accounts for millions of global deaths annually. It was reported that 9.6 million people died from cancer in 2018 and the number of cancer-related deaths would be increased up to approximately 30 million a year by 2030 (CA, 2018; The Lancet, 2018).
Limitations of Conventional Therapies
Current clinically prevailing treatments for cancer rely on surgery, radiation and chemotherapy, which are all seriously dissatisfactory due to their limited therapeutic potential. Specifically, surgery and radiation can be applied only in certain circumstances where tumor cells can be seen on imaging scans to avoid damaging to healthy tissues. Chemotherapy, as a current mainstay cancer treatment, has been extensively exploited in clinic thanks to its inherent simpleness and convenience. However, the problem consists in its low efficiency in drug delivery, nonspecific drug distribution and associated underlying side effects such as hair loss, weakness and immune-depression as the chemical agents could be toxic to normal cells as well as malignant tumors. Innovative strategies are urgently demanded to break through those limitations of current methods and achieve more efficient and radical cure for cancer.
Cancer Nanotechnology Coming to the Rescue
Recently, researchers are putting a lot of effort in creating drugs exploiting nanotechnology, which involves the control of extremely tiny biological particles such as atoms and molecules, to create new materials with a variety of functional properties, including many that could be exceptionally beneficial for cancer treatment. The first cancer nanomedicine, Doxil, was approved by the U.S. Food and Drug Administration (FDA) in 1995, since then a dramatically growing number of nanoparticles have been reported as drug carriers or therapeutic agents, capable of performing early diagnosis, curing with minimal side effects, and evaluating the efficacy of the treatments in a non-invasive way, etc.
Nanotechnology in Cancer Treatment
Nano Rocket Launchers: Nanoparticles as Drug Carriers
Some novel chemotherapeutic agents such as calcium phosphate and citrate have been under investigation for a few years. Unlike indiscriminate attacks seen from typical agents in traditional chemotherapeutics, calcium phosphate and citrate only kill cancerous cells they are delivered into, thus avoiding off-tumor toxicity. Nevertheless, calcium phosphate and citrate are also involved in the regulation of many cellular signaling pathways. So here comes the pivotal problem: how to transport them into targeted cancer cells without disrupting normal cellular signals?
A solution from nanotechnology was reported last month. Researchers from Ludwig Maximilian University of Munich encapsulated calcium phosphate and citrate in a lipid layer, creating nanoparticles capable of bypassing regulatory controls (Chem, 2020). Those nanoparticles remained intact until they were taken up by cancer cells where the lipid layer was broken down and large amounts of calcium and citrate inside were released into the cytoplasm. Notably, a second membrane coat was observed covering those nanoparticles before cell uptake. The membrane was exclusively ruptured in cancer cells and allowed compounds leaking only there rather than in healthy ones, giving a highly selective toxicity to the nanoparticles.
However, the underlying molecular mechanisms behind this selective rupture remain unknown and demand further exploration.
The lipid-based nanoparticle enters into and releases toxic compounds in a cancer cell. (Credit: Constantin von Schirnding, et al.)
The vast majority of work to date in the realm of cancer nanotechnology has focused on spherical liposomes as those involved in the previously mentioned study, however, an increasing number of inorganic materials (such as silica) has also been seen to be used for drug delivery in recent years. For instance, researchers from Houston Methodist Research Institute once used tiny silica beads to precisely transport chemotherapy drugs into fibroblasts surrounding and nourishing cancer cells, showing the potential of silica nanoparticles in improving drug delivery with reduced side effects (NIH Director’s Blog, 2014).