When cells start to grow uncontrollably and form a tumor, they are confronted and invaded by the body’s defense–the immune system. Yet our protective immune cells are often disarmed by the tumor, which renders them ineffective and stops them from killing off cancer cells. This is the case for the deadly and highly incurable brain cancer called glioblastoma. So, finding ways to reactivate these immune cells to eliminate tumors may help fight invasive and evasive cancers like glioblastoma.
Sarkar and colleagues from the University of Calgary published an article in Science Translational Medicine showing that immune cells can be reactivated by niacin (vitamin B3). The investigators showed that these immune cells exposed to niacin can inhibit the growth of human cancer cells that initiate glioblastomas. “We highlight niacin, a common vitamin that can be quickly translated into clinical application, as an immune stimulator against glioblastomas,” said the investigators in the article.
Glioblastomas are the most hostile and common form of tumors that arise in the adult central nervous system. They are deadly, with a survival of about 15 months even when patients are treated with aggressive surgery, chemotherapy, and radiation. The prognosis for glioblastomas remains dismal, in part, because their stem-like cells called brain tumor-initiating cells are relatively resistant to chemotherapy and radiation. So, there is a need to develop therapeutics targeting brain tumor-initiating cells.
An additional feature that contributes to the deadly nature of glioblastomas is the tumors’ efficient exploitation of their surroundings, including the immune cells that infiltrate the tumor. Immune cells that infiltrate tissues and tumors called macrophages and their blood circulating precursors called monocytes, collectively referred to as myeloid cells, may initially attempt to control tumor growth but are ultimately subverted by brain tumor-initiating cells and their progenies to suppress the immune system and to promote glioblastoma growth. Hence, medications that reactivate the infiltrating and fighting properties of compromised myeloid cells are highly desired for glioblastomas.
A recent study testing for compounds that affect myeloid cell activity showed that the common vitamin niacin had stimulating effects. Niacin acts as a precursor to and has the ability to increase the levels of nicotinamide adenine dinucleotide (NAD+), a molecule that plays a critical role in cellular energy generation and that can boost immune function. Niacin can elevate human NAD+ in blood and potentially in other tissues as well. Since niacin has been safely used in humans at high doses, Sarkar and colleagues investigated if niacin-stimulated myeloid cells would inhibit the growth of brain tumor-initiating cells taken from glioblastoma patients.
To do so, the investigative team from the University of Calgary implanted patient-derived glioblastoma tumor-initiating cells into the brains of mice to form brain tumors. A week after the operation, they began to treat the mice with saline or niacin for 5 weeks, and 6 weeks after the implantation, they used MRI to examine the size of the brain tumors. The MRIs showed that these mice treated with niacin had brain tumors that grew to less than half the size of the brain tumors in mice treated with saline. Also, the niacin-treated mice ended up living longer compared to saline-treated mice.
The investigators then repeated these experiments, but this time they threw the current drug standard of care for glioblastoma, temozolomide, into the mix. When they treated these mice with a combination of niacin and temozolomide, the mice survived longer than either agent alone. These experiments highlight the potential of adding niacin to the current therapeutic regimen for glioblastoma.
The investigators found that niacin-exposed monocytes attenuated the growth of brain tumor-initiating cells derived from glioblastoma patients by secreting a molecule called interferon-α14 that inhibits the growth and replication of cells that harbor its receptor, which is often found on cancer cells. Along these lines, the therapeutic effects of niacin were negated in mice harboring brain tumor-initiating cells lacking the receptor for interferon-α14, which showed that niacin’s effects depended on interferon-α14.
They then wanted to see if niacin could elicit the same effect with human myeloid cells. To do so, the investigators took myeloid cells from glioblastoma patients as well as people without glioblastomas and cultured them in petri dishes. They then took the solutions that these myeloid cells were grown in and tried to grow brain tumor-initiating cells from different glioblastoma patients.
The solutions from myeloid cells taken from healthy patients inhibited the growth of the brain tumor-initiating cells whereas the solutions from myeloid cells taken from glioblastoma patients had no effect. However, when they repeated the experiment but this time added niacin to the myeloid cells from glioblastoma patients, the investigators saw a major decrease in the growth of brain tumor-initiating cells. This shows that niacin treatment reactivated the brain tumor-initiating cell growth inhibitory ability of glioblastoma patient-derived monocytes.
Notably, niacin increased the amount of the anti-proliferation factor interferon-α14 in the solutions from glioblastoma-derived myeloid cells. When the investigators blocked the receptor for interferon-α14, niacin no longer reactivated the tumor growth-inhibiting capacity of glioblastoma patient-derived monocytes, thus supporting the involvement of interferon-α14 in niacin-induced tumor control.
These findings show that niacin is a promising treatment for the currently incurable glioblastomas. “We propose the immune-stimulatory activity of niacin, a common vitamin that could be rapidly translated into clinical use, as an adjunctive treatment for patients with glioblastoma,” said the investigators in the article. “The subverted myeloid immunity in other cancers could also be conducive for niacin intervention, but this remains to be determined in future studies.”