Combinatory Treatment of Canavanine and Arginine Deprivation Efficiently Targets Human Glioblastoma Cells via Pleiotropic Mechanisms

Therapeutic potential of arginine deprivation therapy for gliomas: a systematic review of the existing literature

Background

Arginine deprivation therapy (ADT) hinders glioma cells' access to nutrients by reducing peripheral blood arginine, showing great efficacy in various studies, which suggests it as a potentially promising treatment for glioma. The aim of this systematic review was to explore the mechanism of ADT for gliomas, the therapeutic effect based on existing research, and possible combination therapies.

Methods

We performed a systematic literature review of PubMed, ScienceDirect and Web of Science databases according to PRISMA guidelines, searching for articles on the efficacy of ADT in glioma.

Results

We identified 17 studies among 786 search results, among which ADT therapy mainly based on Arginine free condition, Arginine Deiminase and Arginase, including three completed clinical trials. ADT therapy has shown promising results in vivo and in vitro, with its safety confirmed in clinical trials. In the early phase of treatment, glioblastoma (GBM) cells develop protective mechanisms of stress and autophagy, which eventually evolve into caspase dependent apoptosis or senescence, respectively. The immunosuppressive microenvironment is also altered by arginine depletion, such as the transformation of microglia into a pro-inflammatory phenotype and the activation of T-cells. Thus, ADT therapy demonstrates glioma-killing effect in the presence of a combination of mechanisms. In combination with various conventional therapies and investigational drugs such as radiotherapy, temozolomide (TMZ), cyclin-dependent kinase inhibitors (CDK) inhibitors and autophagy inducers, ADT therapy has been shown to be more effective. However, the phenomenon of drug resistance due to re-expression of ASS1 rather than stem cell remains to be investigated.

Conclusion

Despite the paucity of studies in the literature, the available data demonstrate the therapeutic potential of arginine deprivation therapy for glioma and encourage further research, especially the exploration of its combination therapies and the extrapolation of what we know about the effects and mechanisms of ADT from other tumors to glioma.

Canavanine Content Quantification in Processed Bitter Vetch (Vicia ervilia) and Its Application as Flour in Breads: An Analysis of Nutritional and Sensory Attributes

Bitter vetch (Vicia ervilia Willd.) is a traditional Mediterranean-West Asian legume, mainly used as livestock feed because of its toxic non-proteinogenic amino acid, canavanine. However, historical sources suggest its past human consumption. Currently, bitter vetch is a minor crop confined to marginal soils in semi-arid regions, presenting a potential alternative protein source amid projected climate changes. This study evaluated the nutritional and sensory attributes of bitter vetch seeds processed through various household methods. Germination and cooking significantly reduced the canavanine content by 28% and 60%, respectively. Incorporating bitter vetch flour (BVF) into wheat bread enhanced protein and fiber contents without substantially altering carbohydrate and lipid levels, and the baking process reduced the canavanine content by 40%. Bitter vetch flour enriched the bread with iron and calcium, contributing significantly to their daily nutritional intakes. Sensory evaluations indicated positive reception for bread with 12% BVF, achieving a balance between nutritional enhancement and consumer acceptance. This study identifies bitter vetch seeds as a valuable resource for improving bread formulations with corrected gluten contents and enhanced protein quality, as measured using protein-digestibility-corrected amino acid score (PDCAAS) values. With strategic processing and formulation adjustments, bitter vetch has the potential to re-emerge as a feasible high-protein grain crop, promoting sustainable farming.

Synthetic lethality between toxic amino acids, RTG-target genes and chaperones in Saccharomyces cerevisiae

The toxicity of non-proteinogenic amino acids has been known for decades. Numerous reports describe their antimicrobial/anticancer potential. However, these molecules are often toxic to the host as well; thus, a synthetic lethality approach that reduces the dose of these toxins while maintaining toxicity can be beneficial. Here we investigate synthetic lethality between toxic amino acids, the retrograde pathway, and molecular chaperones. In Saccharomyces cerevisiae, mitochondrial retrograde (RTG) pathway activation induces transcription of RTG-target genes to replenish alpha-ketoglutarate and its downstream product glutamate; both metabolites are required for arginine and lysine biosynthesis. We previously reported that tolerance of canavanine, a toxic arginine derivative, requires an intact RTG pathway, and low-dose canavanine exposure reduces the expression of RTG-target genes. Here we show that only a few of the examined chaperone mutants are sensitive to sublethal doses of canavanine. To predict synthetic lethality potential between RTG-target genes and chaperones, we measured the expression of RTG-target genes in canavanine-sensitive and canavanine-tolerant chaperone mutants. Most RTG-target genes were induced in all chaperone mutants starved for arginine; the same trend was not observed under lysine starvation. Canavanine exposure under arginine starvation attenuated and even reversed RTG-target-gene expression in the tested chaperone mutants. Importantly, under nearly all tested genetic and pharmacological conditions, the expression of IDH1 and/or IDH2 was induced. In agreement, idh1 and idh2 mutants are sensitive to canavanine and thialysine and show synthetic growth inhibition with chaperone mutants. Overall, we show that inhibiting molecular chaperones, RTG-target genes, or both can sensitize cells to low doses of toxic amino acids.

Targeted Arginine Metabolism Therapy: A Dilemma in Glioma Treatment

Efforts in the treatment of glioma which is the most common primary malignant tumor of the central nervous system, have not shown satisfactory results despite a comprehensive treatment model that combines various treatment methods, including immunotherapy. Cellular metabolism is a determinant of the viability and function of cancer cells as well as immune cells, and the interplay of immune regulation and metabolic reprogramming in tumors has become an active area of research in recent years. From the perspective of metabolism and immunity in the glioma microenvironment, we elaborated on arginine metabolic reprogramming in glioma cells, which leads to a decrease in arginine levels in the tumor microenvironment. Reduced arginine availability significantly inhibits the proliferation, activation, and function of T cells, thereby promoting the establishment of an immunosuppressive microenvironment. Therefore, replenishment of arginine levels to enhance the anti-tumor activity of T cells is a promising strategy for the treatment of glioma. However, due to the lack of expression of argininosuccinate synthase, gliomas are unable to synthesize arginine; thus, they are highly dependent on the availability of arginine in the extracellular environment. This metabolic weakness of glioma has been utilized by researchers to develop arginine deprivation therapy, which ‘starves’ tumor cells by consuming large amounts of arginine in circulation. Although it has shown good results, this treatment modality that targets arginine metabolism in glioma is controversial. Exploiting a suitable strategy that can not only enhance the antitumor immune response, but also “starve” tumor cells by regulating arginine metabolism to cure glioma will be promising.

Characterization of canavanine-resistance of cat1 and vhc1 deletions and a dominant any1 mutation in fission yeast

Positive and counter-selectable markers have been successfully integrated as a part of numerous genetic assays in many model organisms. In this study, we investigate the mechanism of resistance to arginine analog canavanine and its applicability for genetic selection in Schizosaccharomyces pombe. Deletion of both the arginine permease gene cat1 and SPBC18H10.16/vhc1 (formerly mistakenly called can1) provides strong drug resistance, while the single SPBC18H10.16/vhc1 deletion does not have an impact on canavanine resistance. Surprisingly, the widely used can1-1 allele does not encode for a defective arginine permease but rather corresponds to the any1-523C>T allele. The strong canavanine-resistance conferred by this allele arises from an inability to deposit basic amino acid transporters on the cellular membrane. any1-523C>T leads to reduced post-translational modifications of Any1 regulated by the Tor2 kinase. We also demonstrate that any1-523C>T is a dominate allele. Our results uncover the mechanisms of canavanine-resistance in fission yeast and open the opportunity of using cat1, vhc1 and any1 mutant alleles in genetic assays.

Molecular and Cellular Mechanisms of Glioblastoma

Glioblastoma is the most malignant primary brain tumor [...].

Polyphenolic Compounds of Crataegus Berry, Leaf, and Flower Extracts Affect Viability and Invasive Potential of Human Glioblastoma Cells

Crataegus contains numerous health-promoting compounds that are also proposed to have anti-cancer properties. Herein, we aimed at a contemporaneous evaluation of the effects of polyphenol-rich extracts of berries, leaves, and flowers of six Crataegus species on the viability and invasive potential on the highly aggressive human glioblastoma U87MG cell line. The treatment with the extracts evoked cytotoxic effects, with the strongest in the berry extracts. All extracts not only promoted the apoptosis-related cleavage of poly (ADP-ribose) polymerase 1 (PARP1) but also substantially inhibited the activity of pro-survival kinases, focal adhesion kinase (FAK), and protein kinase B (PKB; also known as Akt), thus indicating the suppression of proliferative and invasive potentials of the examined glioblastoma cells. The qualitative and quantitative characterization of the extracts’ content was also performed and revealed that amongst 37 polyphenolic compounds identified in the examined Crataegus extracts, the majority (29) was detected in berries; the leaf and flower extracts, exerting milder cytotoxic effects, contained only 14 and 13 compounds, respectively. The highest polyphenol content was found in the berries of C. laevigata x rhipidophylla x monogyna, in which flavan-3-ols and phenolic acids predominated. Our results demonstrated that a high content of polyphenolic compounds correlated with the extract cytotoxicity, and especially berries were a valuable source of compounds with anti-cancer potential. This might be a promising option for the development of an effective therapeutic strategy against highly malignant glioblastomas in the future.