Oncologists have an array of treatment options for their patients with cancer. However, some of those treatments are painful and have very difficult side effects. But scientists are investigating new methods that may be easier to withstand. These include heat and gold nanoparticles. Let’s take a deeper look at this process.
Hyperthermia as cancer treatment
Hyperthermia, also known as overheating, is a therapy that uses heat to kill cancer cells. Currently, it’s best used alongside other therapies such as chemotherapy or radiation therapy.
It has challenges. It’s crucial to target the heat in the right place. This is where gold can help. Research shows that gold nanoparticles can be used to heat and kill cancer cells with very good precision and few side effects. It is called photothermal therapy and shows potential for being an effective treatment against cancer.
Severe fever and cancer
In the 19th century, some doctors noticed that certain cancer patients who suffered from high fevers found their cancer symptoms decreased. Some patients experienced complete tumor regression.
One surgeon, Dr. William Coley investigated this further in 1891 by injecting S. pyogenes into a patient’s inoperable tumor to see if the infection would help shrink it. The patient’s body temperature rose to 105 degrees. Days after the fever began, his tumor started to shrink. After two weeks, the tumor had been eliminated. Coley spent years perfecting bacterial injections to treat tumors. These formulations became known as Coley’s toxins. This treatment appeared to work best on bone cancers and soft-tissue sarcomas.
The FDA removed Coley’s toxins from its list of approved drugs in 1962. This treatment method is currently illegal in the United States. Chemotherapy, radiotherapy, and surgery currently prevail as the approved treatments.
Still, researchers continued to investigate hyperthermia and how it reduces tumors.
What we know about heat and cancer
In general, tumors are more acidic than regular tissues and have areas with inadequate oxygen supplies. These two characteristics can make tumors resistant to radiation and chemotherapy, but more vulnerable to heat stress. Scientists have found that hyperthermia causes cell apoptosis by causing irreparable mitochondrial damage. Hyperthermia can also trigger cell necrosis by damaging the cell membrane and denaturing proteins. Hyperthermia can initiate both of these cell death pathways in a single tumor simultaneously.
In addition, heat stress makes tumors more susceptible to radiation, thus making that treatment more effective. Research also indicates that heat stress makes tumors more vulnerable to chemotherapy.
The challenge is to target the heat to the right spot. Current methods are invasive, and the heat may not be distributed uniformly. This is where gold nanoparticles can help.
Gold nanoparticles
It is crucial to target specific areas without heating the healthy tissue that surrounds the tumor. Nanoparticles help with this process. Using nanoparticles and near-infrared light to generate heat in a tumor is minimally invasive, more uniform, and much more precise in targeting the tumor on a cellular level.
Getting nanoparticles into tumors
A tumor is not healthy, normal tissue, so the blood vessels that feed the tumor aren’t normal or healthy either. And in a tumor, lymphatic vessels are compressed, causing poor lymphatic drainage out of the tumor.
The leaky blood vessels and poor lymphatic drainage cause an effect that allows the nanoparticles to move from the bloodstream into the tumor and accumulate there.
Gold nanoparticles work well for photothermal therapy, which typically uses infrared light to heat tissues. This form of light can penetrate deep into the body. That’s where gold becomes essential. Gold is fairly biocompatible as it is an inert metal. Gold nanoparticles can absorb light energy and heat up to above 113 degrees Fahrenheit.
Near-infrared (NIR) light in the range of 800 to 1200 nanometers can be directed into the body, where it hits the nanoparticles, which then heat up. Depending on size and shape, gold nanoparticles can absorb different frequencies of light and can be designed for maximum absorption of NIR light.
The size of the gold nanoparticles matter. In general, smaller metallic nanoparticles more efficiently convert light energy to heat energy than larger metallic nanoparticles do.
There are two methods for inducing hyperthermia in a tumor.
First, the gold nanoparticles can be heated to high temperatures (higher than 113 degrees Fahrenheit) for several minutes. This leads to cell death through thermal ablation.
A second method creates mild hyperthermia (107.6 to 109.4 degrees Fahrenheit) within the tumor. This triggers cellular damage and makes the tumor blood vessels more leaky. This method allows for other therapies such as chemotherapy to be used at the same time.
Photothermal therapy with other cancer treatments
Because the blood vessels that feed the tumor aren’t healthy, there may be areas of a tumor that don’t have a good blood supply, which results in hypoxia. The nanoparticles may not accumulate in these regions since the blood supply is deficient, which means photothermal therapy alone may not destroy all the cancer cells in the tumor.
Research shows that surviving tumor cells exposed to heat can quickly become resistant to thermal stress, resulting in the recurrence and spread of cancer. This is why combining photothermal therapy with other treatments is crucial.
Final thoughts
The National Cancer Institute notes that hyperthermia has been used to treat the following types of advanced cancers: appendix cancer, bladder cancer, brain cancer, breast cancer, cervical cancer, esophageal cancer, head and neck cancer, liver cancer, lung cancer, melanoma, mesothelioma, sarcoma, and rectal cancer.
Photothermal therapy used in combination with other cancer therapies has great potential in treating primary tumors or metastatic cancer for several different types of cancer. Several clinical trials are looking at gold nanoparticles in photothermal therapy, and early results appear promising. However, these studies are in their early phases.
As researchers and clinicians perfect treatment with photothermal therapy, it may become a promising option for those patients with cancer.