A Nanolaser Created for Diagnosing and Preventing Melanoma Metastasis

American scientists have developed a laser-based device capable of accurately detecting circulating cancer cells in the blood and immediately destroying them. If further testing confirms its effectiveness, oncologists will have a unique tool for non-invasive cancer diagnosis and preventing its spread throughout the body. Its application could save tens of thousands of lives.

Almost all types of malignant tumors have a tendency to metastasize. This term refers to the process by which cancer cells detach from the primary tumor and form secondary sites – metastases – in other parts of the body. This is made possible by the natural ability of malignant cells to acquire the properties of other cell types. This "plasticity" allows them to transform from cells anchored in the overall tumor mass into free cells that can move within the body and invade other tissues.

Typically, the appearance of secondary tumor sites indicates that the disease has reached a dangerous stage III or IV and now poses an even greater threat to life. To date, metastases are the leading cause of cancer death – nearly 90% of cancer patients die from them. Therefore, scientists around the world continue to seek ways to destroy wandering cancer cells before they can settle in other organs and form new tumor sites.

Researchers from the University of Arkansas have come closest to solving this problem. They developed a nanolaser device to detect circulating malignant cells in the blood and destroy them. The experimental device, dubbed the cytophone, operates on the well-known photoacoustic effect, which works as follows. When a pulse of light of a certain wavelength hits a material, it heats up and expands slightly – resulting in sound waves that can be detected.

The researchers note that this mechanism is best exemplified in melanoma – the most aggressive form of skin cancer. The new device affects the blood with light pulses through the skin's surface. Healthy cells absorb this energy in minimal amounts, while melanoma cells – due to the presence of the pigment melanin – absorb light waves much more actively. Under the influence of heat, they expand, creating sound waves that are captured by a special ultrasound transducer.

Next, software comes into play, which, thanks to specially developed algorithms, processes the signals received from the transducer instantaneously and notifies the specialist of the detection of cancer cells in the bloodstream.

Initial Trials

Recently, the first phase of clinical trials of the new technology on humans took place. A total of 28 individuals undergoing or having undergone treatment for melanoma and 19 healthy volunteers were registered for participation. As a result, the cytophone was able to detect circulating tumor cells in the blood of 27 out of 28 participants in the experimental group, taking between one and sixty minutes to do so. In the control group, the device did not detect the presence of cancer, thus passing the false positive test.

Researchers were surprised that the new technology was capable of recognizing and capturing malignant cells even when melanoma was not visible on the skin – either because it had not yet manifested external signs or because it had already been surgically removed by that time.

But even more surprising to the scientists was another fact. Despite the fact that the conducted trials aimed to test the diagnostic capabilities of the cytophone, it also demonstrated the ability to effectively destroy wandering tumor cells in the blood immediately after their detection. "When melanin absorbs thermal energy released due to laser exposure, the water around it inside the cell begins to evaporate as it heats up. Bubbles of steam form, which, expanding and bursting, mechanically damage the cancer cell, leading to its death," the researchers explain.

They emphasize that in six participants from the "melanoma" group, the device destroyed most of the detected cancer cells, and in one case, nearly 100%. No side effects were recorded during the trials, and healthy blood cells remained unharmed after exposure to the nanolaser. This is because the laser light is scattered on the skin's surface, meaning it is not sufficiently focused on individual cells to damage them.

The scientists note that they used the cytophone in a low-power mode. However, even at low energy levels, the nanolaser was able to destroy a large number of cancer cells. Accordingly, in further trials, which plan to use higher power levels, the device may demonstrate even greater effectiveness.

"Our technology has enormous potential in preventing cancer metastasis," the researchers say. "With it, doctors will be able to obtain a fast, highly accurate, non-invasive method for detecting circulating tumor cells in the blood and destroying them before they can form new cancer sites." Additionally, the device could be used to track dynamics and assess the effectiveness of ongoing treatment: if the concentration of individual malignant cells in the blood decreases, it means the therapy is working.

Phenomenal Accuracy

The author of the technology states that he conceived it ten years ago. Throughout this time, he tested the safety of the device in preclinical studies on animals, and only then approached the U.S. Food and Drug Administration for permission to begin human trials.

To date, the cytophone is the only non-invasive method for detecting circulating tumor cells in the blood. Its advantages over other similar technologies are evident. First and foremost, it has phenomenally high diagnostic accuracy. All similar systems require a blood sample from the patient, which is then analyzed in a laboratory. Considering that blood is usually taken in a volume of about 8 ml, with a low concentration of cancer cells, the analysis simply will not show them. The new device, however, is capable of detecting one pathological cell in a liter of blood, and not in laboratory conditions, but by directly scanning the bloodstream.

Currently, the creators are preparing for the next phase of trials, which will involve a much larger number of participants. This time, the researchers plan to focus on the therapeutic capabilities of the cytophone and assess its compatibility with other methods used to combat metastases. They hypothesize that the use of the nanolaser will enhance the action of anti-tumor drugs used in melanoma treatment.

In the future, the developers intend to expand the device's capabilities so that it can recognize and kill circulating cells not only of melanoma but also of other types of cancer. Given that they do not contain melanin, researchers will likely need to use special markers – such as gold nanoparticles – which, like melanin, will cause heating of tumor cells.