Sodium citrate inhibits the proliferation of human gastric adenocarcinoma epithelia cells

3D Bioprinting of Prevascularized Full-Thickness Gelatin-Alginate Structures with Embedded Co-Cultures

The use of bioprinting allows the creation of complex three-dimensional cell laden grafts with spatial placements of different cell lines. However, a major challenge is insufficient nutrient transfer, especially with the increased size of the graft causing necrosis and reduced proliferation. A possibility to improve nutrient support is the integration of tubular structures for reducing diffusion paths. In this study the influence of prevascularization in full-thickness grafts on cell growth with a variation of cultivation style and cellular composition was investigated. To perform this, the rheological properties of the used gelatin-alginate hydrogel as well as possibilities to improve growth conditions in the hydrogel were assessed. Prevascularized grafts were manufactured using a pneumatic extrusion-based bioprinter with a coaxial extrusion tool. The prevascularized grafts were statically and dynamically cultured with a monoculture of HepG2 cells. Additionally, a co-culture of HepG2 cells, fibroblasts and HUVEC-TERT2 was created while HUVEC-TERT2s were concentrically placed around the hollow channels. A static culture of prevascularized grafts showed short-term improvements in cell proliferation compared to avascular grafts, while a perfusion-based culture showed improvements in mid-term cultivation times. The cultivation of the co-culture indicated the formation of vascular structures from the hollow channels toward avascular areas. According to these results, the integration of prevascular structures show beneficial effects for the in vitro cultivation of bioprinted grafts for which its impact can be increased in larger grafts.

Understanding the Central Role of Citrate in the Metabolism of Cancer Cells and Tumors: An Update

Citrate plays a central role in cancer cells’ metabolism and regulation. Derived from mitochondrial synthesis and/or carboxylation of α-ketoglutarate, it is cleaved by ATP-citrate lyase into acetyl-CoA and oxaloacetate. The rapid turnover of these molecules in proliferative cancer cells maintains a low-level of citrate, precluding its retro-inhibition on glycolytic enzymes. In cancer cells relying on glycolysis, this regulation helps sustain the Warburg effect. In those relying on an oxidative metabolism, fatty acid β-oxidation sustains a high production of citrate, which is still rapidly converted into acetyl-CoA and oxaloacetate, this latter molecule sustaining nucleotide synthesis and gluconeogenesis. Therefore, citrate levels are rarely high in cancer cells. Resistance of cancer cells to targeted therapies, such as tyrosine kinase inhibitors (TKIs), is frequently sustained by aerobic glycolysis and its key oncogenic drivers, such as Ras and its downstream effectors MAPK/ERK and PI3K/Akt. Remarkably, in preclinical cancer models, the administration of high doses of citrate showed various anti-cancer effects, such as the inhibition of glycolysis, the promotion of cytotoxic drugs sensibility and apoptosis, the neutralization of extracellular acidity, and the inhibition of tumors growth and of key signalling pathways (in particular, the IGF-1R/AKT pathway). Therefore, these preclinical results support the testing of the citrate strategy in clinical trials to counteract key oncogenic drivers sustaining cancer development and resistance to anti-cancer therapies.

The functional roles of TCA cycle metabolites in cancer

The tricarboxylic acid cycle (TCA cycle) has been known for decades as a hub for generating cellular energy and precursors for biosynthetic pathways. Several cancers harbor mutations that affect the integrity of this cycle, mostly at the levels of isocitrate dehydrogenase (IDH), succinate dehydrogenase (SDH), and fumarate hydratase (FH). This results in dysregulation in the production of TCA cycle metabolites and is probably implicated in cancer initiation. By modulating cellular activities, including metabolism and signaling, TCA cycle intermediates are able to impact the processes of cancer development and progression. In this review, we discuss the functional roles of the TCA cycle intermediates in suppressing or promoting the progression of cancers. A further understanding of TCA metabolites' roles and molecular mechanisms in oncogenesis would prompt developing novel metabolite-based cancer therapy in the future.

Extracellular Citrate Is a Trojan Horse for Cancer Cells

The first intermediate in the mitochondrial tricarboxylic acid (TCA) cycle is citrate, which is essential and acts as a metabolic regulator for glycolysis, TCA cycle, gluconeogenesis, and fatty acid synthesis. Within the cytosol, citrate is cleaved by ATP citrate lyase (ACLY) into oxaloacetate (OAA) and acetyl-CoA; OAA can be used for neoglucogenesis or in the TCA cycle, while acetyl-CoA is the precursor of some biosynthetic processes, including the synthesis of fatty acids. Accumulating evidence suggests that citrate is involved in numerous physiological and pathophysiological processes such as inflammation, insulin secretion, neurological disorders, and cancer. Considering the crucial role of citrate to supply the acetyl-CoA pool for fatty acid synthesis and histone acetylation in tumors, in this study we evaluated the effect of citrate added to the growth medium on lipid deposition and histone H4 acetylation in hepatoma cells (HepG2). At low concentration, citrate increased both histone H4 acetylation and lipid deposition; at high concentration, citrate inhibited both, thus suggesting a crucial role of acetyl-CoA availability, which prompted us to investigate the effect of citrate on ACLY. In HepG2 cells, the expression of ACLY is correlated with histone acetylation, which, in turn, depends on citrate concentration. A decrease in H4 acetylation was also observed when citrate was added at a high concentration to immortalized human hepatic cells, whereas ACLY expression was unaffected, indicating a lack of control by histone acetylation. Considering the strong demand for acetyl-CoA but not for OAA in tumor cells, the exogenous citrate would behave like a trojan horse that carries OAA inside the cells and reduces ACLY expression and cellular metabolism. In addition, this study confirmed the already reported dual role of citrate both as a promoter of cell proliferation (at lower concentrations) and as an anticancer agent (at higher concentrations), providing useful tips on the use of citrate for the treatment of tumors.

Cross-Linkable Microgel Composite Matrix Bath for Embedded Bioprinting of Perfusable Tissue Constructs and Sculpting of Solid Objects

Tissue engineering is a rapidly growing field, which requires advanced fabrication technologies to generate cell-laden tissue analogues with a wide range of internal and external physical features including perfusable channels, cavities, custom shapes, and spatially varying material and/or cell compositions. A versatile embedded printing methodology is proposed in this work for creating custom biomedical acellular and cell-laden hydrogel constructs by utilizing a biocompatible microgel composite matrix bath. A sacrificial material is patterned within a biocompatible hydrogel precursor matrix bath using extrusion printing to create three-dimensional features; after printing, the matrix bath is cross-linked, and the sacrificial material is flushed away to create perfusable channels within the bulk composite hydrogel matrix. The composite matrix bath material consists of jammed cross-linked hydrogel microparticles (microgels) to control rheology during fabrication along with a fluid hydrogel precursor, which is cross-linked after fabrication to form the continuous phase of the composite hydrogel. For demonstration, gellan or enzymatically cross-linked gelatin microgels are utilized with a continuous gelatin hydrogel precursor solution to make the composite matrix bath herein; the composite hydrogel matrix is formed by cross-linking the continuous gelatin phase enzymatically after printing. A variety of features including discrete channels, junctions, networks, and external contours are fabricated in the proposed composite matrix bath using embedded printing. Cell-laden constructs with printed features are also evaluated; the microgel composite hydrogel matrices support cell activity, and printed channels enhance proliferation compared to solid constructs even in static culture. The proposed method can be expanded as a solid object sculpting method to sculpt external contours by printing a shell of sacrificial ink and further discarding excess composite hydrogel matrix after printing and cross-linking. While aqueous alginate solution is used as a sacrificial ink, more advanced sacrificial materials can be utilized for better printing resolution.

Effects of Long-Term Citrate Treatment in the PC3 Prostate Cancer Cell Line

Acute administration of a high level of extracellular citrate displays an anti-proliferative effect on both in vitro and in vivo models. However, the long-term effect of citrate treatment has not been investigated yet. Here, we address this question in PC3 cells, a prostate-cancer-derived cell line. Acute administration of high levels of extracellular citrate impaired cell adhesion and inhibited the proliferation of PC3 cells, but surviving cells adapted to grow in the chronic presence of 20 mM citrate. Citrate-resistant PC3 cells are significantly less glycolytic than control cells. Moreover, they overexpress short-form, citrate-insensitive phosphofructokinase 1 (PFK1) together with full-length PFK1. In addition, they show traits of mesenchymal-epithelial transition: an increase in E-cadherin and a decrease in vimentin. In comparison with PC3 cells, citrate-resistant cells display morphological changes that involve both microtubule and microfilament organization. This was accompanied by changes in homeostasis and the organization of intracellular organelles. Thus, the mitochondrial network appears fragmented, the Golgi complex is scattered, and the lysosomal compartment is enlarged. Interestingly, citrate-resistant cells produce less total ROS but accumulate more mitochondrial ROS than control cells. Consistently, in citrate-resistant cells, the autophagic pathway is upregulated, possibly sustaining their survival. In conclusion, chronic administration of citrate might select resistant cells, which could jeopardize the benefits of citrate anticancer treatment.