Mouse studies conducted by researchers in Finland, Sweden and Switzerland have shown how the most aggressive form of brain cancer, glioblastoma, can be stopped dead by an antihistamine drug that triggers a form of cell death caused by leaky lysosomes. Led by Pirjo Laakkonen, PhD, at the University of Helsinki, the studies demonstrated an association between fatty acid binding protein-derived growth inhibitor (MDGI) and a poorer prognosis in patients.
MDGI transports fatty acids into cells, and the team’s studies found that blocking the MDGI gene in glioblastoma cell lines disrupted the transport of fatty acids into cells and their incorporation into lysosomal membranes, which compromised the composition and integrity of the lysosomal membrane, resulting in permeabilization of the lysosomal membrane (LMP). LMP is an intracellular cell death pathway triggered when the contents of the lysosome infiltrate the cell. The team’s subsequent studies in cell lines and in live mice found that treatment with clemastine, an older type of antihistamine that can cross the blood-brain barrier, effectively mirrored the effects of MDGI, triggering PML and causing the death of glioblastoma cells without harming healthy cells. .
The researchers say their findings could help scientists develop new treatments for glioblastoma. “Our research demonstrates that MDGI is a key factor in regulating and maintaining lysosomal membrane structure,” commented Laakkonen. “This is the first gene found to regulate membrane stability … Our results demonstrate that antihistamines and other drugs that increase lysosomal membrane permeability can be considered as an ameliorative therapy for patients with glioblastoma alongside established treatments. “
The results are reported in EMBO Molecular Medicine, in an article entitled “Vulnerability of invasive glioblastoma cells to lysosomal membrane destabilization. “
Glioblastoma is the most common, aggressive, and fatal form of glioma with a “dismal” prognosis, the authors noted. Current surgical approaches cannot remove all of the tumor, and the remaining multidrug-resistant cells and cancer stem cells spread the tumor and cause a relapse, even after radiation therapy and chemotherapy. âMost likely, different approaches are needed to eradicate the invasive cells and cells that reside in the tumor mass,â the team said.
Their work had previously identified MDGI as a glioma biomarker of invasive gliomas, and linked increased expression of the protein to a more severe grade of glioma. Also known as the heart-type fatty acid binding protein (FABP3), MDGI is a fatty acid binding protein (FABP) that is involved in the absorption of fatty acids, and in particular the absorption of fatty acids. polyunsaturated fatty acids (PUFAs) in glioma cells.
The analyzes recently reported by the lower grade glioma team confirmed a link between increased expression of MDGI and lower patient survival. “… both MDGI expression and high tumor grade are independently associated with poor overall survival, increasing the risk of death by a factor of two,” commented the authors. They also found that significantly more MDGI was expressed in glioblastomas than in lower grade gliomas.
Through other experiments, researchers have shown that MDGI is essential for the survival of glioma cells. Glioma cells designed to overexpress MDGI also grew more aggressively and invasively than unmodified tumor cells after implantation in experimental mice. Conversely, the silence of the MDGI gene significantly reduced the viability of the patient-derived glioma cells and blocked cell proliferation. Human glioblastoma cells lacking in MDGI were also unable to form tumors when transplanted into mice. “These results demonstrate a dose-dependent effect of MDGI silencing on the growth and viability of glioblastoma cells.”
The team’s studies of cell lines indicated that blocking MDGI prevented the transport of fatty acids – and in particular linoleic acid – into cells for incorporation into lysosomal membranes. Linoleic acid is an essential PUFA, which cells cannot be made from scratch, and therefore must be obtained from food and imported into cells. Without MDGI, glioma cells could not access enough linoleic acid, which then lacked lysosomal membranes. “Our lipid analyzes show that MDGI silencing alters the trafficking of polyunsaturated fatty acids (FAs) into cells, resulting in significant alterations in the lipid composition of lysosomal membranes.” Without the correct fatty acid composition, lysosomal membranes become more permeable and the enzymes and other components they contain escape into the cell cytoplasm, causing cell death.
Previous work had suggested that certain classes of antihistamines could trigger PML, so the team performed a series of tests to assess clemastine, a first-generation cationic amphiphilic (CAD) antihistamine, both on glioblastoma cells. in culture and on the growth of human glioblastoma xenografts. in experimental mice. Encouragingly, the drug did kill tumor cells grown in the lab at doses that were not harmful to any other cell type tested. “We observed a dramatic loss in the viability of glioblastoma cells which was associated with loss of lysosomal membrane integrity at doses which did not affect the proliferation or viability of many normal cells in vitro,” reported writes the investigators.
Treatment with clemastine also blocked tumor growth and increased survival in tumor-bearing mice. “When we evaluated the preclinical efficacy of clemastine, the survival of animals with intracranial glioblastoma xenografts was significantly prolonged compared to controls due to eradication of invasive glioma cells.” Interestingly, the authors pointed out, an earlier study had shown that the use of antihistamines CAD was linked to significantly reduced all-cause mortality in cancer patients compared to non-CAD antihistamines.
“Our study demonstrates the crucial role of MDGI in the survival of glioma cells, by binding this fatty acid binding protein to maintaining the integrity of the lysosomal membrane,” they concluded. “This unexpected fragility of infiltrating cells aggressive towards PML offers new opportunities for clinical interventions, such as the repositioning of an established antihistamine drug, to eradicate inoperable, invasive and chemo-resistant glioma cells from the maintenance of disease progression and recurrenceâ¦ More broadly, PML inducing agents should be considered as a possible new treatment option for gliomas. “