A new study by members of the Cumming School of Medicine (CSM) at the University of Calgary finds niacin, commonly called vitamin B3, combined with chemotherapy can help immune cells attack glioblastoma (a type of brain tumour), dramatically slowing progression of the disease, in mice.
The results published in Science Translational Medicine found the lifespan of mice with glioblastoma that received combination therapy tripled, increasing to 150 days from 40 days.
“It is a remarkable result. While it’s not a cure, it’s a promising step forward against this incurable disease,” says Dr. Wee Yong, PhD, the principal investigator on the study and a professor in the departments of Clinical Neurosciences and Oncology at the CSM and member of the Hotchkiss Brain Institute and Arnie Charbonneau Cancer Institute.
“The brain tumour stem cells for glioblastoma have been very resistant to treatment, so instead of targeting those cells we targeted the immune system to help the body to attack and destroy the stem cells.”
Glioblastoma is the most aggressive form of brain cancer.
Even with treatment, chemotherapy and radiation, most people die within 14 to 16 months of being diagnosed. One of the reasons this cancer is so deadly is because it hijacks the immune system, suppressing it and reprogramming immune cells to work for the tumour.
In the study, the researchers found that niacin therapy alone extended survival and that the combination therapy with temozolomide (a chemotherapy drug commonly used against glioblastoma) markedly prolonged survival by stimulating and re-educating immune cells to stop helping the cancer and instead, destroy it.
“We were able to help immune cells do what they’re supposed to do, attack and kill cancer cells,” says Dr. Susobhan Sarkar, PhD, first author on the study.
“We screened 1,040 compounds and found niacin had the properties needed to activate immune cells, specifically myeloid cells, and inhibit the growth of brain tumour initiating stem cells.”
Slide showing brain tumour stem cells fail to grow when confronted with niacin-treated immune cells. The image is credited to Wee Yong.
The study is supported by Alberta Innovates in collaboration with the Alberta Cancer Foundation and the HBI through a translational research grant donated by the Ronald and Irene Ward Foundation and the Canadian Institutes of Health Research (CIHR).
The CIHR has already provided funding to move this research forward to a clinical trial.
“We are very fortunate to have the support of the CIHR,” says Yong. “We still require approvals from Health Canada and ethics.
It’s extremely important to follow strict protocols and conduct a clinical trial first, even though this treatment involves two well-known, existing therapies.
It’s important people don’t rush out and try adding niacin on their own, as we need to confirm dosage, delivery and length of time for optimum clinical results.”
Yong will be working with Dr. Gloria Roldan Urgoiti, MD, an oncologist and Dr. Paula de Robles, MD, a neuro-oncologist at Tom Baker Cancer Centre, on the clinical trial.
Glioblastomas (GBMs) are the most malignant and common form of primary tumors that arise in the adult central nervous system (CNS). They are deadly tumors with a median survival of 14.6 months despite aggressive surgery, chemotherapy with temozolomide, and radiation (1).
The prognosis for GBMs remains dismal, in part, because their stem-like cells, brain tumor–initiating cells (BTICs), are relatively resistant to chemoradiotherapy (2–4), in contrast to their more differentiated progenies.
Further, BTICs account for glioma recurrence during temozolomide treatment in mice (2). Thus, there is an unmet need to develop therapeutics targeting BTICs.
An additional feature that contributes to the deadly nature of GBM is the tumors’ efficient exploitation of their microenvironment, including of immune cells that infiltrate the tumor (3–12).
The inflammatory infiltrate is dominated by peripherally derived macrophages and CNS-intrinsic microglia. These cells are histologically indistinguishable from each other and are collectively termed macrophages/microglia.
The macrophages/microglia and circulating monocytes that become macrophages in tissues (collectively referred to here as myeloid cells) may initially attempt to control tumor growth but are ultimately subverted by BTICs and their progenies to assume an immunosuppressive phenotype and to promote GBM growth (8, 12, 13).
Hence, medications that disable the tumor-promoting macrophages/microglia or those that reactivate the tumor-fighting properties of compromised circulating monocytes, in addition to tumor-infiltrating macrophages/microglia, are highly desired for GBMs.
There is immense interest in improving the prognosis of GBM by targeting monocytes, macrophages, and microglia. Approaches include deleting these populations by targeting their survival factor, colony-stimulating factor-1 (14, 15); reducing their chemotaxis into tumor (16–18); using them as vehicles for drug delivery (19); depleting the number of immunosuppressive cells (16, 20) or increasing the amount of proinflammatory cells (21–23); blocking immunosuppression by these cells (24); reprogramming or converting the immunosuppressive cells into proinflammatory types (25–28); or using pharmacological activators to produce stimulated phenotypes that curb tumor growth (21, 22, 24).
We previously screened a drug library of 1040 compounds and reported on those that inhibit microglia activity (29).
In that screen, we also found compounds that further increased microglial inflammatory activity elicited by lipopolysaccharide (LPS) stimulation, as measured by elevation of tumor necrosis factor–α (TNF-α). Of these, amphotericin B, an antifungal medication, had considerable antitumor activity (22), but this medication is poorly tolerated in humans. Another compound that increased TNF-α in LPS-activated microglia in our screen was niacin (vitamin B3 or nicotinic acid) (29).
Because niacin has been safely used in humans at high doses to treat atherosclerotic coronary disease and dyslipidemias (30–32), we investigated the hypotheses that niacin-stimulated myeloid cells would inhibit the growth of BTICs in culture and prolong the survival of mice with intracranial BTICs. Here, we report our findings that niacin is a promising treatment for the currently incurable GBMs.
Combination therapy with niacin and temozolomide further enhances longevity of mice with intracranial BTICs
We determined whether temozolomide, a U.S. Food and Drug Administration–approved alkylating chemotherapeutic drug used in GBM, could add to the therapeutic effects of niacin in reducing BTIC growth by mobilizing myeloid cells. Whereas temozolomide (100 μM) and Niacin-MonoCM by themselves reduced BTIC growth in culture, the most marked decrease of growth occurred when these were combined (fig. S13).
Next, we addressed whether niacin and temozolomide have combinatorial effects in mice implanted with intracranial patient-derived BTICs. We used BT048 and BT53M, which are both MGMT methylated and temozolomide sensitive (22). For the mice with BT048 implants, temozolomide (40 mg/kg) was given orally 5 days/week for 3 consecutive weeks with a break of 2 days of no injection between weeks.
This was unexpectedly toxic, resulting in six deaths in the first week of temozolomide treatment, and the mice that died were excluded from analyses. For the remaining mice, MRI detection at day 49 showed a reduction in tumor volume in the niacin but not temozolomide or combination groups (Fig. 7A).
Niacin and the combination treatment prolonged survival compared to vehicle based on Kaplan-Meier analysis (Fig. 7B), but the combination was not substantially different when compared to niacin.
MRI analyses at day 49 in asymptomatic animals showed smaller tumors in niacin or combination treatment mice compared to vehicle or temozolomide animals (Fig. 7C). A single survivor in the niacin plus temozolomide group of BT048-implanted mice receiving daily niacin treatment died after a year, indicating a marked increase in survival.
We repeated the niacin/temozolomide experiment in mice implanted with the BT53M line, where we reduced the temozolomide dose to 30 mg/kg and adjusted its interval (gap of 1 week of no treatment with temozolomide between the second and third week) to minimize its toxicity.
MRI was conducted on day 36, when one vehicle-treated mouse was manifesting signs of tumor-associated toxicity (lethargy, fluffed fur). Figure 7D shows that whereas vehicle-treated mice already had measurable tumor volume, no MRI-detectable tumor was found in the other three groups at this early time point.
Subsequent survival analyses show that temozolomide improved survival, which was exceeded in the niacin group. Notably, the combination of niacin and temozolomide markedly prolonged survival by at least fivefold compared to vehicle-treated mice; the combination also conferred a survival advantage (P = 0.002) when compared to niacin (Fig. 7E).
We repeated the BT53M implants in a different experiment for histology comparisons, focusing on vehicle and niacin treatment. In this second experiment, where 7000 instead of the usual 10,000 BT53M cells were implanted, asymptomatic mice were euthanized at 7 weeks after implantation.
Tumors detected by hematoxylin and eosin staining in vehicle mice were larger (covering the entire field in Fig. 7F) when compared to those in niacin-treated animals (tumor was confined to the center of the field).
Iba1 and iNOS (inducible nitric oxide synthase) staining, indicative of a proinflammatory macrophage/microglia population (Fig. 7F), were more evident in the niacin-treated group and corroborated by blinded rank-order analyses (Fig. 7, G and H).
Moreover, the tumors in the vehicle-treated mice showed a higher proliferation index, as detected by Ki67 staining, compared to those in niacin-treated animals (Fig. 7, F and I). Overall, these results affirm the efficacy of niacin in reducing tumor volume, prolonging survival, and adding to the therapeutic effect of temozolomide.
University of Calgary