Preclinical research suggests that light-triggered, chemotherapy-loaded nanoparticles could treat multiple myeloma (MM) and other malignancies.
Researchers showed that light emitted as part of traditional cancer-imaging techniques could also trigger a light-sensitive chemotherapy drug.
When this drug was packaged into nanoparticles that target lit-up cancer cells, the drug produced toxic free radicals that killed the cancer cells.
Researchers found this technique to be effective in mice with MM and aggressive, metastatic breast cancer.
“Our study shows that this phototherapeutic technology is particularly suited to attacking small tumors that spread to different parts of the body, including deep in the bone marrow,” said Samuel Achilefu, PhD, of Washington University in St. Louis, Missouri.
Dr Achilefu and his colleagues described the technology in Nature Communications.
The technology harnesses the chemotherapy drug titanocene. When used alone, titanocene did not work well in clinical trials, even at relatively high doses. However, when it is exposed to the radiation emitted by visible light, titanocene produces reactive particles that are toxic to cells, even at low doses.
Dr Achilefu and his colleagues packaged low doses of titanocene inside nanoparticles targeted to proteins on the surface of cancer cells. Specifically, the team used nanomicelles targeting VLA-4, “an attractive target for precision imaging and therapy” in MM, according to the researchers.
When these nanomicelles made contact with MM cells, their membranes fused together, releasing titanocene into the cells.
The researchers then delivered the imaging agent fluorodeoxyglucose (FDG). MM cells took up the FDG at high rates, causing the cells to glow in a positron emission tomography scan. This glow also triggered the titanocene, releasing free radicals and killing the MM cells.
This treatment strategy was used on mice with MM once a week for 4 weeks. In the weeks following, the treated mice had significantly smaller tumors and survived longer than control mice. Fifty percent of treated mice survived at least 90 days, and 50% of control mice survived 62 days.
This strategy also produced an anti-tumor effect in mice with breast cancer, although, in these experiments, the researchers used human serum albumin nanoparticles.
The effect in breast cancer was less pronounced than in MM. The researchers said this was likely due to the extreme aggressiveness of the breast cancer cell line used.
The team also found that certain MM cells were resistant to this treatment technique.
“This is an opportunity to learn because it’s similar to what is seen in patients—some of the cells become dormant but don’t die after treatment,” Dr Achilefu said. “When we looked closer at the cells that were resistant to our phototherapy, we saw that the surface protein we are targeting was not there.”
Specifically, the resistant cells had downregulated expression of CD49d, and the researchers believe this may have impaired the binding of nanomicelles to the MM cells.
“So next, we want to find out if we can pinpoint another surface protein to target and kill these resistant cells along with the myeloma cells that did respond to the original therapy, which could lead to complete remission,” Dr Achilefu said.
Furthermore, Dr Achilefu envisions that, one day, doctors might be able to use this technology to prevent cancer from recurring.
“We are interested in exploring whether this is something a patient in remission could take once a year for prevention,” Dr Achilefu said. “The toxicity appears to be low, so we imagine an outpatient procedure that could involve zapping any cancerous cells, making cancer a chronic condition that could be controlled long-term.”
Dr Achilefu and his colleagues believe this phototherapeutic technology is less toxic than standard radiation and chemotherapy because the titanocene and FDG are targeted to the same place at the same time only in cancer cells.
The body rids itself of titanocene through the liver, while FDG is cleared through the kidneys. The fact that these components are disposed of separately minimizes damage to other organs. When separated, the components are not toxic, according to the researchers.