Acidic environment leads to ROS-induced MAPK signaling in cancer cells

Cutaneous pH landscape as a facilitator of melanoma initiation and progression

Melanoma incidence is on the rise and currently causes the majority of skin cancer-related deaths. Yet, therapies for metastatic melanoma are still insufficient so that new concepts are essential. Malignant transformation of melanocytes and melanoma progression are intimately linked to the cutaneous pH landscape and its dysregulation in tumour lesions. The pH landscape of normal skin is characterized by a large pH gradient of up to 3 pH units between surface and dermis. The Na⁺ /H⁺ exchanger NHE1 is one of the major contributors of acidity in superficial skin layers. It is also activated by the most frequent mutation in melanoma, BRAF^{V 600E} , thereby causing pH dysregulation during melanoma initiation. Melanoma progression is supported by an extracellular acidification and/or NHE1 activity which promote the escape of single melanoma cells from the primary tumour, migration and metastatic spreading. We propose that viewing melanoma against the background of the acid-base physiology of the skin provides a better understanding of the pathophysiology of this disease and allows the development of novel therapeutic concepts.

Selective inhibition of carbonic anhydrase-IX by sulphonamide derivatives induces pH and reactive oxygen species-mediated apoptosis in cervical cancer HeLa cells

Selective inhibition with sulphonamides of carbonic anhydrase (CA) IX reduces cell proliferation and induces apoptosis in human cancer cells. The effect on CA IX expression of seven previously synthesised sulphonamide inhibitors, with high affinity for CA IX, as well as their effect on the proliferation/apoptosis of cancer/normal cell lines was investigated. Two normal and three human cancer cell lines were used. Treatment resulted in dose- and time-dependent inhibition of the growth of various cancer cell lines. One compound showed remarkably high toxicity towards CA IX-positive HeLa cells. The mechanisms of apoptosis induction were determined with Annexin-V and AO/EB staining, cleaved caspases (caspase-3, caspase-8, caspase-9) and cleaved PARP activation, reactive oxygen species production (ROS), mitochondrial membrane potential (MMP), intracellular pH (pHi), extracellular pH (pHe), lactate level and cell cycle analysis. The autophagy induction mechanisms were also investigated. The modulation of apoptotic and autophagic genes (Bax, Bcl-2, caspase-3, caspase-8, caspase-9, caspase-12, Beclin and LC3) was measured using real time PCR. The positive staining using γ-H2AX and AO/EB dye, showed increased cleaved caspase-3, caspase-8, caspase-9, increased ROS production, MMP and enhanced mRNA expression of apoptotic genes, suggesting that anticancer effects are also exerted through its apoptosis-inducing properties. Our results show that such sulphonamides might have the potential as new leads for detailed investigations against CA IX-positive cervical cancers.

Cathepsins: Proteases that are vital for survival but can also be fatal

The state of enzymes in the human body determines the normal physiology or pathology, so all the six classes of enzymes are crucial. Proteases, the hydrolases, can be of several types based on the nucleophilic amino acid or the metal cofactor needed for their activity. Cathepsins are proteases with serine, cysteine, or aspartic acid residues as the nucleophiles, which are vital for digestion, coagulation, immune response, adipogenesis, hormone liberation, peptide synthesis, among a litany of other functions. But inflammatory state radically affects their normal roles. Released from the lysosomes, they degrade extracellular matrix proteins such as collagen and elastin, mediating parasite infection, autoimmune diseases, tumor metastasis, cardiovascular issues, and neural degeneration, among other health hazards. Over the years, the different types and isoforms of cathepsin, their optimal pH and functions have been studied, yet much information is still elusive. By taming and harnessing cathepsins, by inhibitors and judicious lifestyle, a gamut of malignancies can be resolved. This review discusses these aspects, which can be of clinical relevance.

Alkalinization with potassium bicarbonate improves glutathione status and protein kinetics in young volunteers during 21-day bed rest

BACKGROUND & AIMS

Physical inactivity is associated with lean body mass wasting, oxidative stress and pro-inflammatory changes of cell membrane lipids. Alkalinization may potentially counteract these alterations. We evaluated the effects of potassium bicarbonate supplementation on protein kinetics, glutathione status and pro- and anti-inflammatory polyunsaturated fatty acids (PUFA) in erythrocyte membranes in humans, during experimental bed rest.

METHODS

Healthy, young, male volunteers were investigated at the end of two 21-day bed rest periods, one with, and the other without, daily potassium bicarbonate supplementation (90 mmol × d^-1), according to a cross-over design. Oxidative stress in erythrocytes was evaluated by determining the ratio between reduced (GSH) and oxidized glutathione (GSSG). Glutathione turnover and phenylalanine kinetics, a marker of whole body protein metabolism, were determined by stable isotope infusions. Erythrocyte membranes PUFA composition was analyzed by gas-chromatography.

RESULTS

At the end of the two study periods, urinary pH was 10 ± 3% greater in subjects receiving potassium bicarbonate supplementation (7.23 ± 0.15 vs. 6.68 ± 0.11, p < 0.001). Alkalinization increased total glutathione concentrations by 5 ± 2% (p < 0.05) and decreased its rate of clearance by 38 ± 13% (p < 0.05), without significantly changing GSH-to-GSSG ratio. After alkalinization, net protein balance in the postabsorptive state improved significantly by 17 ± 5% (p < 0.05) as well as the sum of n-3 PUFA and the n-3-to-n-6 PUFA ratio in erythrocyte membranes (p < 0.05).

CONCLUSIONS

Alkalinization during long-term inactivity is associated with improved glutathione status, anti-inflammatory lipid pattern in cell membranes and reduction in protein catabolism at whole body level. This study suggests that, in clinical conditions characterized by inactivity, oxidative stress and inflammation, alkalinization could be a useful adjuvant therapeutic strategy.

The effect of mast cells on the biological characteristics of prostate cancer cells

Aim of the study

To investigate the effects of mast cells on the proliferation, invasion, and metastasis of prostate cancer cells.

Material and methods

The mast cell P815 and prostate cancer LNCaP cells were chosen using a Transwell chamber to construct a two-cell cocultured in vitro model to observe the migration of mast cells to prostate cancer cells.

Results

In the migration experiment, the migration rate of mast cells from the experimental group (%) was 10.167 ±0.833, the mast cell migration rate (%) of the control group was 0.833 ±0.208, and the difference was statistically significant (p < 0.05). The MTT test showed that the OD value of cells in each group over time increased gradually, and 24 h after LNCaP cells were cocultured with different concentrations of mast cells, the OD value was significantly higher than that of the control group (p < 0.05). QRT-PCR and western blot results showed that, compared with the control group, E-cad expression from the experimental group was significantly weakened; N-cad and vimentin expression increased (p < 0.05), and c-kit and SCF expression from experimental group were significantly higher than that of the control group (p < 0.05). After the addition of c-kit neutralising antibodies, compared with the control group, the mast cell migration rate of experimental group decreased significantly and prostate cancer cell proliferation significantly decreased (p < 0.05).

Conclusions

Mast cells could promote the proliferation of prostate cancer cells and the occurrence of epithelial mesenchymal transition (EMT), which could promote the invasion and metastasis of prostate cancer cells.

Control of CREB expression in tumors: from molecular mechanisms and signal transduction pathways to therapeutic target

The cyclic AMP response element binding (CREB) protein has pleiotropic activities in physiologic processes. Due to its central position downstream of many growth signaling pathways CREB has the ability to influence cell survival, growth and differentiation of normal, but also of tumor cells suggesting an oncogenic potential of CREB. Indeed, increased CREB expression and activation is associated with tumor progression, chemotherapy resistance and reduced patients' survival. We summarize here the different cellular functions of CREB in tumors of distinct histology as well as its use as potential prognostic marker. In addition, the underlying molecular mechanisms to achieve constitutive activation of CREB including structural alterations, such as gene amplification and chromosomal translocation, and deregulation, which could occur at the transcriptional, post-transcriptional and post-translational level, will be described. Since downregulation of CREB by different strategies resulted in inhibition of cell proliferation, invasion and induction of apoptosis, the role of CREB as a promising target for cancer therapy will be also discussed.

Extracellular acidification induces ROS- and mPTP-mediated death in HEK293 cells

The extracellular pH (pHe) is a key determinant of the cellular (micro)environment and needs to be maintained within strict boundaries to allow normal cell function. Here we used HEK293 cells to study the effects of pHe acidification (24 h), induced by mitochondrial inhibitors (rotenone, antimycin A) and/or extracellular HCl addition. Lowering pHe from 7.2 to 5.8 reduced cell viability by 70% and was paralleled by a decrease in cytosolic pH (pHc), hyperpolarization of the mitochondrial membrane potential (Δψ), increased levels of hydroethidine-oxidizing ROS and stimulation of protein carbonylation. Co-treatment with the antioxidant α-tocopherol, the mitochondrial permeability transition pore (mPTP) desensitizer cyclosporin A and Necrostatin-1, a combined inhibitor of Receptor-interacting serine/threonine-protein kinase 1 (RIPK1) and Indoleamine 2,3-dioxygenase (IDO), prevented acidification-induced cell death. In contrast, the caspase inhibitor zVAD.fmk and the ferroptosis inhibitor Ferrostatin-1 were ineffective. We conclude that extracellular acidification induces necroptotic cell death in HEK293 cells and that the latter involves intracellular acidification, mitochondrial functional impairment, increased ROS levels, mPTP opening and protein carbonylation. These findings suggest that acidosis of the extracellular environment (as observed in mitochondrial disorders, ischemia, acute inflammation and cancer) can induce cell death via a ROS- and mPTP opening-mediated pathogenic mechanism.

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Extracellular acidification induces mitochondrial dysfunction.

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Extracellular acidification increases intracellular ROS levels.

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Extracellular acidification stimulates protein carbonylation.

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Extracellular acidification induces mPTP opening- and ROS-dependent cell death.

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Acidosis-induced oxidative stress likely contributes to various pathologies.

Tumor Acidosis and Hypoxia Differently Modulate the Inflammatory Program: Measurements In Vitro and In Vivo

Inflammatory mediators produced by the tumor cells are of importance for immune response but also for malignant progression. The aim of the study was to analyze the expression of monocyte chemoattractant protein-1, interleukin-6 (IL-6), tumor necrosis factor-α, inducible isoform of nitric oxide synthase (iNOS), cyclooxygenase-2, and osteopontin in vitro in two different tumor cell lines under hypoxia (pO₂ ≈ 1.5 mmHg) and/or acidosis (pH = 6.6) for up to 24 hours since hypoxia and acidosis are common characteristics of solid tumors. Additionally, the same tumor cell lines implanted in vivo were made hypoxic and acidotic artificially for 24 hours, after which the cytokine expression was measured. Finally, the activation of ERK1/2 and p38 by acidosis/hypoxia and their impact on cytokine expression were studied. The results indicate that acidosis and hypoxia have fundamentally different (often opposing) effects on cytokine expression. In addition, these effects were tumor cell line specific. When combining hypoxia and acidosis, the overall changes reflect an additive effect of both conditions alone, indicating that hypoxia and acidosis act by independent mechanisms. The in vivo changes corresponded well with the results obtained in the isolated tumor cells. Only iNOS expression was downregulated in vivo but increased in cell culture. For IL-6 expression, the acidosis-induced changes were dependent on ERK1/2 activation. In conclusion, it was demonstrated that the environmental pO₂ and pH strongly affect the expression of inflammatory mediators in tumor cells. In vivo, most of the inflammatory mediators were downregulated, which could limit the activation of immune cells and by this foster the immune escape of tumors.

Impact of the Tumor Microenvironment on the Expression of Inflammatory Mediators in Cancer Cells

Hypoxia and extracellular acidosis are common features of solid malignant tumors. The aim of the study was to analyze whether these pathophysiological parameters affect the expression of inflammatory mediators in tumor cells. Therefore the mRNA expression of MCP-1 (monocyte chemotactic protein 1), iNOS and osteopontin was measured under hypoxic (pO2 1 mmHg) and acidotic (pH 6.6) conditions by qPCR in AT1 R-3327 prostate cancer cells. In addition, the underlying signaling cascades were analyzed by using inhibitors of the p38 and ERK1/2 MAP kinase pathways.Hypoxia led to a significant decrease of the expression of MCP-1 and osteopontin over the complete observation period of 24 h, whereas the iNOS expression after an initial reduction slightly increased. Acidotic conditions for up to 6 h increased the iNOS expression significantly which was functional as indicated by an elevated level of nitrate/nitrite formation by 30 %. Acidosis had almost no impact on the MCP-1 expression of tumor cells, whereas the osteopontin level tended to increase leading to a significantly elevated level after 24 h at pH 6.6. Inhibiting the p38 and ERK1/2 under control conditions revealed that the MAPKs play a significant role for the regulation of the expression of inflammatory mediators. MCP-1 expression could be lowered by inhibiting ERK1/2 whereas iNOS expression was dependent on both p38 and ERK1/2 MAPK. These results indicate that the adverse tumor microenvironment affects the expression of inflammatory mediators by tumors cells and may therefore modulate the immune response within the tumor tissue.

Cancer metabolism: New insights into classic characteristics

Initial studies of cancer metabolism in the early 1920s found that cancer cells were phenotypically characterized by aerobic glycolysis, in that these cells favor glucose uptake and lactate production, even in the presence of oxygen. This property, called the Warburg effect, is considered a hallmark of cancer. The mechanism by which these cells acquire aerobic glycolysis has been uncovered. Acidic extracellular fluid, secreted by cancer cells, induces a malignant phenotype, including invasion and metastasis. Cancer cells survival depends on a critical balance of redox status, which is regulated by amino acid metabolism. Glutamine is extremely important for oxidative phosphorylation and redox regulation. Cells highly dependent on glutamine and that cannot survive with glutamine are called glutamine-addicted cells. Metabolic reprogramming has been observed in cancer stem cells, which have the property of self-renewal and are resistant to chemotherapy and radiotherapy. These findings suggest that studies of cancer metabolism can reveal methods of preventing cancer recurrence and metastasis.

Endocytotic uptake of HPMA-based polymers by different cancer cells: impact of extracellular acidosis and hypoxia

Background

Polymeric nanoparticles allow to selectively transport chemotherapeutic drugs to the tumor tissue. These nanocarriers have to be taken up into the cells to release the drug. In addition, tumors often show pathological metabolic characteristics (hypoxia and acidosis) which might affect the polymer endocytosis.

Materials and methods

Six different N-(2-hydroxypropyl)methacrylamide (HPMA)-based polymer structures (homopolymer as well as random and block copolymers with lauryl methacrylate containing hydrophobic side chains) varying in molecular weight and size were analyzed in two different tumor models. The cellular uptake of fluorescence-labeled polymers was measured under hypoxic (pO₂ ≈1.5 mmHg) and acidic (pH 6.6) conditions. By using specific inhibitors, different endocytotic routes (macropinocytosis and clathrin-mediated, dynamin-dependent, cholesterol-dependent endocytosis) were analyzed separately.

Results

The current results revealed that the polymer uptake depends on the molecular structure, molecular weight and tumor line used. In AT1 cells, the uptake of random copolymer was five times stronger than the homopolymer, whereas in Walker-256 cells, the uptake of all polymers was much stronger, but this was independent of the molecular structure and size. Acidosis increased the uptake of random copolymer in AT1 cells but reduced the intracellular accumulation of homopolymer and block copolymer. Hypoxia reduced the uptake of all polymers in Walker-256 cells. Hydrophilic polymers (homopolymer and block copolymer) were taken up by all endocytotic routes studied, whereas the more lipophilic random copolymer seemed to be taken up preferentially by cholesterol- and dynamin-dependent endocytosis.

Conclusion

The study indicates that numerous parameters of the polymer (structure, size) and of the tumor (perfusion, vascular permeability, pH, pO₂) modulate drug delivery, which makes it difficult to select the appropriate polymer for the individual patient.

Inhibition of Carbonic Anhydrase IX by Ureidosulfonamide Inhibitor U104 Reduces Prostate Cancer Cell Growth, But Does Not Modulate Daunorubicin or Cisplatin Cytotoxicity

Carbonic anhydrase (CA) IX has emerged as a promising target for cancer therapy. It is highly upregulated in hypoxic regions and mediates pH regulation critical for tumor cell survival as well as extracellular acidification of the tumor microenvironment, which promotes tumor aggressiveness via various mechanisms, such as augmenting metastatic potential. Therefore, the aim of this study was to analyze the complex interdependency between CA IX and the tumor microenvironment in prostate tumor cells with regard to potential therapeutic implications. CA IX was upregulated by hypoxia as well as acidosis in prostate cancer cells. This induction did not modulate intracellular pH but led to extracellular acidification. Pharmacological inhibition of CA IX activity by U104 (SLC-0111) resulted in a reduction in tumor cell growth and an increase in apoptotic cell death. Intracellular pH was reduced under normoxic and even more so under hypoxic conditions when CA IX level was high. However, although intracellular pH regulation was disturbed, targeting CA IX in combination with daunorubicin or cisplatin did not intensify apoptotic tumor cell death. Hence, targeting CA IX in prostate cancer cells can lead to intracellular pH dysregulation and, consequently, can reduce cellular growth and elevate apoptotic cell death. Attenuation of extracellular acidification by blocking CA IX might additionally impede tumor progression and metastasis. However, no beneficial effect was seen when targeting CA IX in combination with chemotherapeutic drugs.

The iron-dependent mitochondrial superoxide dismutase SODA promotes Leishmania virulence

Leishmaniasis is one of the leading globally neglected diseases, affecting millions of people worldwide. Leishmania infection depends on the ability of insect-transmitted metacyclic promastigotes to invade mammalian hosts, differentiate into amastigotes, and replicate inside macrophages. To counter the hostile oxidative environment inside macrophages, these protozoans contain anti-oxidant systems that include iron-dependent superoxide dismutases (SODs) in mitochondria and glycosomes. Increasing evidence suggests that in addition to this protective role, Leishmania mitochondrial SOD may also initiate H₂O₂-mediated redox signaling that regulates gene expression and metabolic changes associated with differentiation into virulent forms. To investigate this hypothesis, we examined the specific role of SODA, the mitochondrial SOD isoform in Leishmania amazonensis Our inability to generate L. amazonensis SODA null mutants and the lethal phenotype observed following RNAi-mediated silencing of the Trypanosoma brucei SODA ortholog suggests that SODA is essential for trypanosomatid survival. L. amazonensis metacyclic promastigotes lacking one SODA allele failed to replicate in macrophages and were severely attenuated in their ability to generate cutaneous lesions in mice. Reduced expression of SODA also resulted in mitochondrial oxidative damage and failure of SODA/ΔsodA promastigotes to differentiate into axenic amastigotes. SODA expression above a critical threshold was also required for the development of metacyclic promastigotes, as SODA/ΔsodA cultures were strongly depleted in this infective form and more susceptible to reactive oxygen species (ROS)-induced stress. Collectively, our data suggest that SODA promotes Leishmania virulence by protecting the parasites against mitochondrion-generated oxidative stress and by initiating ROS-mediated signaling mechanisms required for the differentiation of infective forms.

Stressor-driven extracellular acidosis as tumor inducer via aberrant enzyme activation: A review on the mechanisms and possible prophylaxis

When the extracellular pH of human body vacillates in either direction, tissue homeostasis is compromised. Fluctuations in acidity have been linked to a wide variety of pathological conditions, including bone loss, cancer, allergies, and auto-immune diseases. Stress conditions affect oxygen tension, and the resultant hypoxia modulates the expression and/or activity of membrane-tethered transporters/pumps, transcription factors, enzymes and intercellular junctions. These modifications provoke erratic gene expression, aberrant tissue remodeling and oncogenesis. While the physiological optimization of pH in tissues is practically challenging, it is at least theoretically achievable and can be considered as a possible therapy to resolve a broad array of diseases.

Unraveling the cytotoxicity and metabolic pathways of binary natural deep eutectic solvent systems

In this study, the anticancer potential and cytotoxicity of natural deep eutectic solvents (NADESs) were assessed using HelaS3, PC3, A375, AGS, MCF-7, and WRL-68 hepatic cell lines. NADESs were prepared from choline chloride, fructose, or glucose and compared with an N,N-diethyl ethanolammonium chloride:triethylene glycol DES. The NADESs (98 ≤ EC50 ≥ 516 mM) were less toxic than the DES (34 ≤ EC50 ≥ 120 mM). The EC50 values of the NADESs were significantly higher than those of the aqueous solutions of their individual components but were similar to those of the aqueous solutions of combinations of their chief elements. Due to the uniqueness of these results, the possibility that NADESs could be synthesized intracellularly to counterbalance the cytotoxicity of their excess principal constituents must be entertained. However, further research is needed to explore this avenue. NADESs exerted cytotoxicity by increasing membrane porosity and redox stress. In vivo, they were more destructive than the DES and induced liver failure. The potential of these mixtures was evidenced by their anticancer activity and intracellular processing. This infers that they can serve as tools for increasing our understanding of cell physiology and metabolism. It is likely that we only have begun to comprehend the nature of NADESs.

Acidic cellular microenvironment modifies carcinogen-induced DNA damage and repair

Chronic inflammation creates an acidic microenvironment, which plays an important role in cancer development. To investigate how low pH changes the cellular response to the carcinogen benzo[a]pyrene (B[a]P), we incubated human pulmonary epithelial cells (A549 and BEAS-2B) with nontoxic doses of B[a]P using culturing media of various pH’s (extracellular pH (pH_e) of 7.8, 7.0, 6.5, 6.0 and 5.5) for 6, 24 and 48 h. In most incubations (pH_e 7.0–6.5), the pH in the medium returned to the physiological pH 7.8 after 48 h, but at the lowest pH (pH_e < 6.0), this recovery was incomplete. Similar changes were observed for the intracellular pH (pH_i). We observed that acidic conditions delayed B[a]P metabolism and at t = 48 h, and the concentration of unmetabolized extracellular B[a]P and B[a]P-7,8-diol was significantly higher in acidic samples than under normal physiological conditions (pH_e 7.8) for both cell lines. Cytochrome P450 (CYP1A1/CYP1B1) expression and its activity (ethoxyresorufin-O-deethylase activity) were repressed at low pH_e after 6 and 24 h, but were significantly higher at t = 48 h. In addition, a DNA repair assay showed that the incision activity was ~80% inhibited for 6 h at low pH_e and concomitant exposure to B[a]P. However, at t = 48 h, the incision activity recovered to more than 100% of the initial activity observed at neutral pH_e. After 48 h, higher B[a]P-DNA adduct levels and γ-H2AX foci were observed at low pH samples than at pH_e 7.8. In conclusion, acidic pH delayed the metabolism of B[a]P and inhibited DNA repair, ultimately leading to increased B[a]P-induced DNA damage.

ERK-mediated NF-κB activation through ASIC1 in response to acidosis

Acidic microenvironment is a common feature of solid tumors. We have previously shown that neuron specific acid-sensing ion channel 1 (ASIC1) is expressed in breast cancer, and it is responsible for acidosis-induced cellular signaling through AKT, leading to nuclear factor-κB (NF-κB) activation, and cell invasion and metastasis. However, AKT is frequently activated in cancer. Thus, a key question is whether ASIC1-mediated cell signaling still takes place in the cancer cells carrying constitutively active AKT. In the present study, we show that among four prostate cancer cell lines tested, 22Rv1 cells express the highest level of phosphorylated AKT that is not impacted by acidosis. However, acidosis can still induce NF-κB activation during which extracellular signal-regulated kinase (ERK) serves as an alternative pathway for ASIC-mediated cell signaling. Inhibition of ERK by chemical inhibitors or small interfering RNAs suppresses the acidosis-induced NF-κB activity through regulation of the inhibitory subunit IκBα phosphorylation. Furthermore, suppression of ASIC1-mediated generation of reactive oxygen species (ROS) by ROS scavengers, such as glutathione or N-acetyl-cysteine causes a decrease in ERK phosphorylation and degradation of IκBα. Finally, ASIC1 is upregulated in a subset of prostate cancer cases and ASIC1 knockout by CRISPR/Cas9 significantly suppresses cell invasion, and castration resistance both in vitro and in vivo. Together, these results support the significance of ASIC1-ROS-ERK-IκBα-NF-κB axis in prostate tumorigenesis, especially in the constitutively active AKT background.

Turning the gun on cancer: Utilizing lysosomal P-glycoprotein as a new strategy to overcome multi-drug resistance

Oxidative stress plays a role in the development of drug resistance in cancer cells. Cancer cells must constantly and rapidly adapt to changes in the tumor microenvironment, due to alterations in the availability of nutrients, such as glucose, oxygen and key transition metals (e.g., iron and copper). This nutrient flux is typically a consequence of rapid growth, poor vascularization and necrosis. It has been demonstrated that stress factors, such as hypoxia and glucose deprivation up-regulate master transcription factors, namely hypoxia inducible factor-1α (HIF-1α), which transcriptionally regulate the multi-drug resistance (MDR), transmembrane drug efflux transporter, P-glycoprotein (Pgp). Interestingly, in addition to the established role of plasma membrane Pgp in MDR, a new paradigm of intracellular resistance has emerged that is premised on the ability of lysosomal Pgp to transport cytotoxic agents into this organelle. This mechanism is enabled by the topological inversion of Pgp via endocytosis resulting in the transporter actively pumping agents into the lysosome. In this way, classical Pgp substrates, such as doxorubicin (DOX), can be actively transported into this organelle. Within the lysosome, DOX becomes protonated upon acidification of the lysosomal lumen, causing its accumulation. This mechanism efficiently traps DOX, preventing its cytotoxic interaction with nuclear DNA. This review discusses these effects and highlights a novel mechanism by which redox-active and protonatable Pgp substrates can utilize lysosomal Pgp to gain access to this compartment, resulting in catastrophic lysosomal membrane permeabilization and cell death. Hence, a key MDR mechanism that utilizes Pgp (the "gun") to sequester protonatable drug substrates safely within lysosomes can be "turned on" MDR cancer cells to destroy them from within.

Doxorubicin loaded large-pore mesoporous hydroxyapatite coated superparamagnetic Fe3O4 nanoparticles for cancer treatment

In the present study, a series of multifunctional drug delivery systems based on mesostructured hydroxyapatite coating and superparamagnetic nanoparticles with pH-responsive characters was prepared. The structure of each new synthesized nanoscale composite was fully characterized by XRD, FTIR, TEM, VSM and BET. The results showed a good ordered mesostructure having large pores, high pore volume, high surface area, and varied super paramagnetic properties. The mesoporous hydroxyapatite coated super paramagnetic Fe3O4 nanoparticles were applied as a drug delivery carrier loaded with doxorubicin (DOX) as a model drug. The storage/release properties of the developed nonocarriers in phosphate buffer saline (PBS) were studied in two certain pHs: pH=7.4 (the human blood pH) and pH=5.5 (pH of cancer cells). The large pores in the synthesized mesoporous acted as an excellent carrier for DOX molecules with a loading efficiency of ≈93% which is much higher than that of the conventional hydroxyapatite particles. When the pH of the release medium (PBS) was changed from 7.4 to 5.5, the drug release increased significantly from 10% of the adsorbed drug to about 70%. DOX-loaded mesostructure hydroxyapatite reduced the viability of SKBR3 and T47D cells by 54.7 and 57.3%, respectively, which were very similar to 56.8 and 60.4% reduction resulted from free DOX incubation. This new drug delivery system which benefits from both super paramagnetic properties and pH-responsive performances may serve as a suitable platform for developing new biocompatible drug carriers and could have a good potential use in targeted cancer therapy.

Role of the tumor microenvironment in tumor progression and the clinical applications (Review)

Oncogene activation and tumor-suppressor gene inactivation are considered as the main causes driving the transformation of normal somatic cells into malignant tumor cells. Cancer cells are the driving force of tumor development and progression. Yet, cancer cells are unable to accomplish this alone. The tumor microenvironment is also considered to play an active role rather than simply acting as a by-stander in tumor progression. Through different pathways, tumor cells efficiently recruit stromal cells, which in turn, provide tumor cell growth signals, intermediate metabolites, and provide a suitable environment for tumor progression as well as metastasis. Through reciprocal communication, cancer cells and the microenvironment act in collusion leading to high proliferation and metastatic capability. Understanding the role of the tumor microenvironment in tumor progression provides us with novel approaches through which to target the tumor microenvironment for efficient anticancer treatment. In this review, we summarize the mechanisms involved in the recruitment of stromal cells by tumor cells to the primary tumor site and highlight the role of the tumor microenvironment in the regulation of tumor progression. We further discuss the potential approaches for cancer therapy.

Amomum tsao-ko fruit extract suppresses lipopolysaccharide-induced inducible nitric oxide synthase by inducing heme oxygenase-1 in macrophages and in septic mice

Amomum tsao-ko Crevost et Lemarié (Zingiberaceae) has traditionally been used to treat inflammatory and infectious diseases, such as throat infections, malaria, abdominal pain and diarrhoea. This study was designed to assess the anti-inflammatory effects and the molecular mechanisms of the methanol extract of A. tsao-ko (AOM) in lipopolysaccharide (LPS)-induced RAW 264.7 macrophages and in a murine model of sepsis. In LPS-induced RAW 264.7 macrophages, AOM reduced the production of nitric oxide (NO) by inhibiting inducible nitric oxide synthase (iNOS) expression, and increased heme oxygenase-1 (HO-1) expression at the protein and mRNA levels. Pretreatment with SnPP (a selective inhibitor of HO-1) and silencing HO-1 using siRNA prevented the AOM-mediated inhibition of NO production and iNOS expression. Furthermore, AOM increased the expression and nuclear accumulation of NF-E2-related factor 2 (Nrf2), which enhanced Nrf2 binding to antioxidant response element (ARE). In addition, AOM induced the phosphorylation of extracellular regulated kinase (ERK) and c-Jun N-terminal kinase (JNK) and generated reactive oxygen species (ROS). Furthermore, pretreatment with N-acetyl-l-cysteine (NAC; a ROS scavenger) diminished the AOM-induced phosphorylation of ERK and JNK and AOM-induced HO-1 expression, suggesting that ERK and JNK are downstream mediators of ROS during the AOM-induced signalling of HO-1 expression. In LPS-induced endotoxaemic mice, pretreatment with AOM reduced NO serum levels and liver iNOS expression and increased HO-1 expression and survival rates. These results indicate that AOM strongly inhibits LPS-induced NO production by activating the ROS/MAPKs/Nrf2-mediated HO-1 signalling pathway, and supports its pharmacological effects on inflammatory diseases.

Efficient alachlor degradation by the filamentous fungus Paecilomyces marquandii with simultaneous oxidative stress reduction

The acceleration of alachlor degradation by Paecilomyces marquandii under controlled and optimized conditions of fungal cultivation in liquid batches was observed (by ca. 20% in comparison to the flask cultures). Acidic environment and oxygen limitation resulted in deterioration of herbicide elimination. Efficient xenobiotic degradation did not correlate with free radicals formation, but some conditions of bioreactor cultivation such as neutral pH and oxygen enriched atmosphere (pO2⩾30%) caused a decrease in the reactive oxygen species (ROS) accumulation in mycelia. The changes in the glutathione (GSH) and ascorbic acid (AA) levels, also in the dismutase (SOD) and catalase (CAT) activities showed active response of the tested fungus against alachlor induced oxidative stress. These results will contribute to the improvement of chloroacetanilides elimination by fungi and extend the knowledge concerning oxidative stress induction and fungal cellular defense.

Acidosis differently modulates the inflammatory program in monocytes and macrophages

Inflammation, ischemia or the microenvironment of solid tumors is often accompanied by a reduction of extracellular pH (acidosis) that stresses the cells and acts on cellular signaling and transcription. The effect of acidosis on the expression of various inflammatory markers, on functional parameters (migration, phagocytic activity) and on signaling pathways involved was studied in monocytic cells and macrophages. In monocytic cell lines acidosis led to a reduction in expression of most of the inflammatory mediators, namely IL-1ß, IL-6, TNF-α, MCP-1, COX-2 and osteopontin. In primary human monocytes MCP-1 and TNF-α were reduced but COX-2 and IL-6 were increased. In RAW264.7 macrophage cell line IL-1ß, COX-2 and iNOS expression was increased, whereas MCP-1 was reduced similar to the effect in monocytic cells. For primary human monocyte-derived macrophages the regulation of inflammatory markers by acidosis depended on activation state, except for the acidosis-induced downregulation of MCP-1 and TNF-α. Acidosis affected functional immune cell behavior when looking at phagocytic activity which was increased in a time-dependent manner, but cellular motility was not changed. Neither ERK1/2 nor CREB signaling was stimulated by the reduction of extracellular pH. However, p38 was activated by acidosis in RAW264.7 cells and this activation was critical for the induction of IL-1ß, COX-2 and iNOS expression. In conclusion, acidosis may impede the recruitment of immune cells, but fosters inflammation when macrophages are present by increasing the level of COX-2 and iNOS and by functionally forcing up the phagocytic activity.

Acidosis promotes invasiveness of breast cancer cells through ROS-AKT-NF-κB pathway

It is well known that acidic microenvironment promotes tumorigenesis, however, the underlying mechanism remains largely unknown. In the present study, we show that acidosis promotes invasiveness of breast cancer cells through a series of signaling events. First, our study indicates that NF-κB is a key factor for acidosis-induced cell invasion. Acidosis activates NF-κB without affecting STAT3 activity; knockdown of NF-κB p65 abrogates the acidosis-induced invasion activity. Next, we show that the activation of NF-κB is mediated through phosphorylation and degradation of IκBα; and phosphorylation and nuclear translocation of p65. Upstream to NF-κB signaling, AKT is activated under acidic conditions. Moreover, acidosis induces generation of reactive oxygen species (ROS) which can be suppressed by ROS scavengers, reversing the acidosis-induced activation of AKT and NF-κB, and invasiveness. As a negative regulator of AKT, PTEN is oxidized and inactivated by the acidosis-induced ROS. Finally, inhibition of NADPH oxidase (NOX) suppresses acidosis-induced ROS production, suggesting involvement of NOX in acidosis-induced signaling cascade. Of considerable interest, acidosis-induced ROS production and activation of AKT and NF-κB can be only detected in cancer cells, but not in non-malignant cells. Together, these results demonstrate a cancer specific acidosis-induced signaling cascade in breast cancer cells, leading to cell invasion.

Acidosis-Induced Changes in Proteome Patterns of the Prostate Cancer-Derived Tumor Cell Line AT-1

Under various pathological conditions, such as inflammation, ischemia and in solid tumors, physiological parameters (local oxygen tension or extracellular pH) show distinct tissue abnormalities (hypoxia and acidosis). For tumors, the prevailing microenvironment exerts a strong influence on the phenotype with respect to proliferation, invasion, and metastasis formation and therefore influences prognosis. In this study, we investigate the impact of extracellular metabolic acidosis (pH 7.4 versus 6.6) on the proteome patterns of a prostate cancer-derived tumor cell type (AT-1) using isobaric labeling and LC-MS/MS analysis. In total, 2710 proteins were identified and quantified across four biological replicates, of which seven were significantly affected with changes >50% and used for validation. Glucose transporter 1 and farnesyl pyrophosphatase were found to be down-regulated after 48 h of acidic treatment, and metallothionein 2A was reduced after 24 h and returned to control values after 48 h. After 24 and 48 h at pH 6.6, glutathione S transferase A3 and NAD(P)H dehydrogenase 1, cellular retinoic acid-binding protein 2, and Na-bicarbonate transporter 3 levels were found to be increased. The changes in protein levels were confirmed by transcriptome and functional analyses. In addition to the experimental in-depth investigation of proteins with changes >50%, functional profiling (statistical enrichment analysis) including proteins with changes >20% revealed that acidosis upregulates GSH metabolic processes, citric acid cycle, and respiratory electron transport. Metabolism of lipids and cholesterol biosynthesis were downregulated. Our data comprise the first comprehensive report on acidosis-induced changes in proteome patterns of a tumor cell line.

Colorectal Carcinogenesis: Connecting K-RAS-Induced Transformation and CREB Activity In Vitro and In Vivo

Oncogenic transformation is often associated with an increased expression of the cAMP response element binding (CREB) transcription factor controlling the expression of genes involved in cell proliferation, cell cycle, apoptosis, and tumor development, but a link between K-RAS(V12)-induced transformation and CREB has not yet been determined. Therefore, the constitutive and/or inhibitor-regulated mRNA and protein expression of CREB and signal transduction components and growth properties of parental fibroblasts, K-RAS(V12)-transformed counterparts, shCREB K-RAS(V12) transfectants and human colon carcinoma cells were determined. Increased CREB transcript and protein levels accompanied by an enhanced CREB activity was detected in K-RAS(V12)-transformed murine fibroblasts and K-RAS(V12)-mutated human tumor cells, which is dependent on the MAPK/MEK, PI3K, and/or PKC signal transduction. Immunohistochemical (IHC) staining of colorectal carcinoma lesions and murine tumors, with known KRAS gene mutation status, using antibodies specific for CREB and phospho-CREB, revealed a mechanistic link between CREB expression and K-RAS(V12)-mutated colorectal carcinoma lesions when compared with control tissues. Silencing of CREB by shRNA and/or treatment with a CREB inhibitor (KG-501) reverted the neoplastic phenotype of K-RAS(V12) transformants as demonstrated by a more fibroblast-like morphology, enhanced apoptosis sensitivity, increased doubling time, decreased migration, invasion and anchorage-independent growth, reduced tumorigenesis, and enhanced immunogenicity in vivo. The impaired shCREB-mediated invasion of K-RAS(V12) transformants was accompanied by a transcriptional downregulation of different matrix metalloproteinases (MMP) coupled with their reduced enzymatic activity.

IMPLICATIONS

CREB plays a key role in the K-RAS(V12)-mediated neoplastic phenotype and represents a suitable therapeutic target for murine and human K-RAS(V12)-induced tumors.

Novel Paraoxonase 2-Dependent Mechanism Mediating the Biological Effects of the Pseudomonas aeruginosa Quorum-Sensing Molecule N-(3-Oxo-Dodecanoyl)-L-Homoserine Lactone

Pseudomonas aeruginosa produces N-(3-oxo-dodecanoyl)-L-homoserine lactone (3OC12), a crucial signaling molecule that elicits diverse biological responses in host cells thought to subvert immune defenses. The mechanism mediating many of these responses remains unknown. The intracellular lactonase paraoxonase 2 (PON2) hydrolyzes and inactivates 3OC12 and is therefore considered a component of host cells that attenuates 3OC12-mediated responses. Here, we demonstrate in cell lines and in primary human bronchial epithelial cells that 3OC12 is rapidly hydrolyzed intracellularly by PON2 to 3OC12 acid, which becomes trapped and accumulates within the cells. Subcellularly, 3OC12 acid accumulated within the mitochondria, a compartment where PON2 is localized. Treatment with 3OC12 caused a rapid PON2-dependent cytosolic and mitochondrial pH decrease, calcium release, and phosphorylation of stress signaling kinases. The results indicate a novel, PON2-dependent intracellular acidification mechanism by which 3OC12 can mediate its biological effects. Thus, PON2 is a central regulator of host cell responses to 3OC12, acting to decrease the availability of 3OC12 for receptor-mediated effects and acting to promote effects, such as calcium release and stress signaling, via intracellular acidification.

Tumor microenvironment promotes dicarboxylic acid carrier-mediated transport of succinate to fuel prostate cancer mitochondria

Prostate cancer cells reprogram their metabolism, so that they support their elevated oxidative phosphorylation and promote a cancer friendly microenvironment. This work aimed to explore the mechanisms that cancer cells employ for fueling themselves with energy rich metabolites available in interstitial fluids. The mitochondria oxidative phosphorylation in metastatic prostate cancer DU145 cells and normal prostate epithelial PrEC cells were studied by high-resolution respirometry. An important finding was that prostate cancer cells at acidic pH 6.8 are capable of consuming exogenous succinate, while physiological pH 7.4 was not favorable for this process. Using specific inhibitors, it was demonstrated that succinate is transported in cancer cells by the mechanism of plasma membrane Na(+)-dependent dycarboxylic acid transporter NaDC3 (SLC13A3 gene). Although the level of expression of SLC13A3 was not significantly altered when maintaining cells in the medium with lower pH, the respirometric activity of cells under acidic condition was elevated in the presence of succinate. In contrast, normal prostate cells while expressing NaDC3 mRNA do not produce NaDC3 protein. The mechanism of succinate influx via NaDC3 in metastatic prostate cancer cells could yield a novel target for anti-cancer therapy and has the potential to be used for imaging-based diagnostics to detect non-glycolytic tumors.

Low pH increases the yield of exosome isolation

Exosomes are the extracellular vesicles secreted by various cells. Exosomes mediate intercellular communication by delivering a variety of molecules between cells. Cancer cell derived exosomes seem to be related with tumor progression and metastasis. Tumor microenvironment is thought to be acidic and this low pH controls exosome physiology, leading to tumor progression. Despite the importance of microenvironmental pH on exosome, most of exosome studies have been performed without regard to pH. Therefore, the difference of exosome stability and yield of isolation by different pH need to be studied. In this research, we investigated the yield of total exosomal protein and RNA after incubation in acidic, neutral and alkaline conditioned medium. Representative exosome markers were investigated by western blot after incubation of exosomes in different pH. As a result, the concentrations of exosomal protein and nucleic acid were significantly increased after incubation in the acidic medium compared with neutral medium. The higher levels of exosome markers including CD9, CD63 and HSP70 were observed after incubation in an acidic environment. On the other hand, no exosomal protein, exosomal RNA and exosome markers have been detected after incubation in an alkaline condition. In summary, our results indicate that the acidic condition is the favorable environment for existence and isolation of exosomes.

Broad targeting of angiogenesis for cancer prevention and therapy

Deregulation of angiogenesis – the growth of new blood vessels from an existing vasculature – is a main driving force in many severe human diseases including cancer. As such, tumor angiogenesis is important for delivering oxygen and nutrients to growing tumors, and therefore considered an essential pathologic feature of cancer, while also playing a key role in enabling other aspects of tumor pathology such as metabolic deregulation and tumor dissemination/metastasis. Recently, inhibition of tumor angiogenesis has become a clinical anti-cancer strategy in line with chemotherapy, radiotherapy and surgery, which underscore the critical importance of the angiogenic switch during early tumor development. Unfortunately the clinically approved anti-angiogenic drugs in use today are only effective in a subset of the patients, and many who initially respond develop resistance over time. Also, some of the anti-angiogenic drugs are toxic and it would be of great importance to identify alternative compounds, which could overcome these drawbacks and limitations of the currently available therapy. Finding “the most important target” may, however, prove a very challenging approach as the tumor environment is highly diverse, consisting of many different cell types, all of which may contribute to tumor angiogenesis. Furthermore, the tumor cells themselves are genetically unstable, leading to a progressive increase in the number of different angiogenic factors produced as the cancer progresses to advanced stages. As an alternative approach to targeted therapy, options to broadly interfere with angiogenic signals by a mixture of non-toxic natural compound with pleiotropic actions were viewed by this team as an opportunity to develop a complementary anti-angiogenesis treatment option. As a part of the “Halifax Project” within the “Getting to know cancer” framework, we have here, based on a thorough review of the literature, identified 10 important aspects of tumor angiogenesis and the pathological tumor vasculature which would be well suited as targets for anti-angiogenic therapy: (1) endothelial cell migration/tip cell formation, (2) structural abnormalities of tumor vessels, (3) hypoxia, (4) lymphangiogenesis, (5) elevated interstitial fluid pressure, (6) poor perfusion, (7) disrupted circadian rhythms, (8) tumor promoting inflammation, (9) tumor promoting fibroblasts and (10) tumor cell metabolism/acidosis. Following this analysis, we scrutinized the available literature on broadly acting anti-angiogenic natural products, with a focus on finding qualitative information on phytochemicals which could inhibit these targets and came up with 10 prototypical phytochemical compounds: (1) oleanolic acid, (2) tripterine, (3) silibinin, (4) curcumin, (5) epigallocatechin-gallate, (6) kaempferol, (7) melatonin, (8) enterolactone, (9) withaferin A and (10) resveratrol. We suggest that these plant-derived compounds could be combined to constitute a broader acting and more effective inhibitory cocktail at doses that would not be likely to cause excessive toxicity. All the targets and phytochemical approaches were further cross-validated against their effects on other essential tumorigenic pathways (based on the “hallmarks” of cancer) in order to discover possible synergies or potentially harmful interactions, and were found to generally also have positive involvement in/effects on these other aspects of tumor biology. The aim is that this discussion could lead to the selection of combinations of such anti-angiogenic compounds which could be used in potent anti-tumor cocktails, for enhanced therapeutic efficacy, reduced toxicity and circumvention of single-agent anti-angiogenic resistance, as well as for possible use in primary or secondary cancer prevention strategies.

Acidic environment activates inflammatory programs in fibroblasts via a cAMP-MAPK pathway

The tissue micromilieu in disorders (inflammation, ischemia, tumor) often shows pronounced metabolic acidosis that may alter signaling and transcriptional activity in resident cells which can be of special importance for omnipresent fibroblasts. In the present study we investigated the impact of metabolic acidosis on rat fibroblasts with special emphasis on their role in inflammation by regulation of TNF-α, MCP-1, COX-2 and iNOS expression and the signaling pathways involved. Extracellular acidosis led to an enhanced expression of TNF-α, COX-2 and iNOS in parallel to an activation of p38 and ERK1/2 kinases that was not observed by sole intracellular acidosis. Accordingly, the protein amounts of TNF-α and COX-2 as well as the production of nitrate and nitrite were elevated. Acidosis-induced expression of COX-2 and iNOS depended on p38 kinase, but not on ERK1/2. In contrast acidosis-induced TNF-α expression was independent of both kinases. Although GPR4, GPR68 and GPR132 are expressed in fibroblasts, the involvement of these potential candidate pH sensors could be ruled out since no acidosis-induced elevation in intracellular cAMP or free calcium content was observed. Furthermore our data show that MAPK activation by an acidic micromilieu depends on Ser/Thr phosphatase activity, but not on the production of reactive oxygen species and is sensitive to cAMP antagonism by Rp-cAMPS. In conclusion, our results show that an acidic microenvironment induces a differential transcriptional program of pathological relevant genes in fibroblasts via the cAMP-phosphatase-MAPK pathway and thereby generates a parainflammatory situation that can result in tissue remodeling.

Bicarbonate transport inhibitor SITS modulates pH homeostasis triggering apoptosis of Dalton's lymphoma: implication of novel molecular mechanisms

Bicarbonate transporter (BCT) plays a crucial role in maintaining pH homeostasis of tumor cells by import of HCO3(-). This helps the tumor cells in manifesting extracellular tumor acidosis, accompanied by a relative intracellular alkalinization, which in turn promotes tumor progression. Therefore, blocking BCT-mediated HCO3(-) transport is envisaged as a promising anticancer therapeutic approach. Thus, using a murine model of a T cell lymphoma, designated as Dalton's lymphoma (DL), in the present in vitro investigation the antitumor consequences of blocking BCT function by its inhibitor 4-acetamido-4-isothiocyanostilbene-2,2-disulfonate (SITS) were explored. Treatment of DL cells with SITS resulted in an increase in the extracellular pH, associated with a decline in DL cell survival and augmented induction of apoptosis. BCT inhibition also elevated the expression of cytochrome c, caspase-9, caspase-3, Bax, reactive oxygen species, and nitric oxide along with inhibition of HSP-70 and Bcl2, which regulate tumor cell survival and apoptosis. SITS-treated DL cells displayed upregulated production of IFN-γ and IL-6 along with a decline of IL-10. Treatment of DL cells with SITS also inhibited the expression of fatty acid synthase, which is crucial for membrane biogenesis in neoplastic cells. The expression of lactate transporter MCT-1 and multidrug resistance regulating protein MRP-1 got inhibited along with hampered uptake of glucose and lactate production in SITS-treated DL cells. Thus, the declined tumor cell survival following inhibition of BCT could be the consequence of interplay of several inter-connected regulatory molecular events. The outcome of this study indicates the potential of BCT inhibition as a novel therapeutic approach for treatment of hematological malignancies.

Working with "H2S": facts and apparent artifacts

Hydrogen sulfide (H2S) is an important signaling molecule with physiological endpoints similar to those of nitric oxide (NO). Growing interest in its physiological roles and pharmacological potential has led to large sets of contradictory data. The principle cause of these discrepancies can be the common neglect of some of the basic H2S chemistry. This study investigates how the experimental outcome when working with H2S depends on its source and dose and the methodology employed. We show that commercially available NaHS should be avoided and that traces of metal ions should be removed because these can reduce intramolecular disulfides and change protein structure. Furthermore, high H2S concentrations may lead to a complete inhibition of cell respiration, mitochondrial membrane potential depolarization and superoxide generation, which should be considered when discussing the biological effects observed upon treatment with high concentrations of H2S. In addition, we provide chemical evidence that H2S can directly react with superoxide. H2S is also capable of reducing cytochrome c(3+) with the concomitant formation of superoxide. H2S does not directly react with nitrite but with NO electrodes that detect H2S. In addition, H2S interferes with the Griess reaction and should therefore be removed from the solution by Cd(2+) or Zn(2+) precipitation prior to nitrite quantification. 2-Phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide (PTIO) is reduced by H2S, and its use should be avoided in combination with H2S. All these constraints must be taken into account when working with H2S to ensure valid data.

Acidic priming enhances metastatic potential of cancer cells

Metabolic acidosis is a common feature of tumor microenvironment and may affect the phenotype of tumor cells, including invasive capacity and formation of metastases. We tested whether previous exposure to an acidic environment alters metastatic potential of two rat carcinoma cell lines in the animal model. In addition, we determined the effect of an acidic environment on motility and invasive capacity of AT-1 prostate carcinoma cells in culture. Exposure of tumor cells to an acidic environment (pH 6.6, 5 % CO2, 6 h) prior to tail vein injection in rats enhanced formation of lung metastases significantly. In culture, acidosis increased cellular motility of AT-1 cells. When the tumor cells were transferred back to pH 7.4, enhanced motility persisted for at least 3 h but vanished after longer periods (24 h), therefore presenting a "short-term memory effect." Although acidosis augmented phosphorylation of ERK1/2 and p38, and inhibition of ERK1/2 phosphorylation or of p38 kinase activity reduced basal motility at pH 7.4, acidosis-induced increase in motility was not dependent on ERK1/2 or p38 kinase. Src family kinases were not involved either. By contrast, scavenging reactive oxygen species (ROS), known to be increased in AT-1 cells under acidic conditions, blunted acidosis-induced motility increase. Our data indicate that tumor cells may acquire enhanced motility in an acidic micromilieu, at least in part due to enhanced ROS formation. Because enhanced motility persists for at least 3 h after leaving the acidic environment, this may promote metastasis formation, as observed in our in vivo model.

Repair of oxidative DNA damage and cancer: recent progress in DNA base excision repair

SIGNIFICANCE

Reactive oxygen species (ROS) are generated by exogenous and environmental genotoxins, but also arise from mitochondria as byproducts of respiration in the body. ROS generate DNA damage of which pathological consequence, including cancer is well established. Research efforts are intense to understand the mechanism of DNA base excision repair, the primary mechanism to protect cells from genotoxicity caused by ROS.

RECENT ADVANCES

In addition to the notion that oxidative DNA damage causes transformation of cells, recent studies have revealed how the mitochondrial deficiencies and ROS generation alter cell growth during the cancer transformation.

CRITICAL ISSUES

The emphasis of this review is to highlight the importance of the cellular response to oxidative DNA damage during carcinogenesis. Oxidative DNA damage, including 7,8-dihydro-8-oxoguanine, play an important role during the cellular transformation. It is also becoming apparent that the unusual activity and subcellular distribution of apurinic/apyrimidinic endonuclease 1, an essential DNA repair factor/redox sensor, affect cancer malignancy by increasing cellular resistance to oxidative stress and by positively influencing cell proliferation.

FUTURE DIRECTIONS

Technological advancement in cancer cell biology and genetics has enabled us to monitor the detailed DNA repair activities in the microenvironment. Precise understanding of the intracellular activities of DNA repair proteins for oxidative DNA damage should provide help in understanding how mitochondria, ROS, DNA damage, and repair influence cancer transformation.

Proton concentrations can be a major contributor to the modification of osteoclast and osteoblast differentiation, working independently of extracellular bicarbonate ions

We established a system to separately analyze the role of protons and bicarbonate ions in vitro in which the pH of the medium was controlled by HEPES at various concentrations of sodium bicarbonate (NaHCO3) in the absence of carbon dioxide (CO2). Using this system, we demonstrated that acidosis promoted osteoclast formation independently of extracellular NaHCO3 in a short-term culture. Protons and bicarbonate ions acted on osteoclast differentiation with opposite effects, the former positively and the latter negatively. The HEPES-based system maintained pH in the absence of extracellular NaHCO3 without CO2. Therefore, we could demonstrate that osteoblast differentiation was promoted at higher pH in a long-term culture system without NaHCO3 in which ALP activity and nodule mineralization were enhanced. This finding indicates that protons negatively control osteoblast differentiation independently of extracellular bicarbonate ions. However, the difference in the concentration of NaHCO3 did not have any influence on nodule mineralization. The opposite effects of protons, the promotion of osteoclast formation and the inhibition of osteoblast differentiation, were suppressed in the presence of 5 mM N-acetyl cysteine, a reagent activating the scavenging of reactive oxygen species (ROS), implying that ROS act on both systems, the promotion of large osteoclast formation and the deterioration of osteoblast formation under acidosis.

Endocytosis and cancer

Endocytosis entails selective packaging of cell-surface proteins, such as receptors for cytokines and adhesion components, in cytoplasmic vesicles (endosomes). The series of sorting events that determines the fate of internalized proteins, either degradation in lysosomes or recycling back to the plasma membrane, relies on intrinsic sequence motifs, posttranslational modifications (e.g., phosphorylation and ubiquitination), and transient assemblies of both Rab GTPases and phosphoinositide-binding proteins. This multicomponent process is enhanced and skewed in cancer cells; we review mechanisms enabling both major drivers of cancer, p53 and Ras, to bias recycling of integrins and receptor tyrosine kinases (RTKs). Likewise, cadherins and other junctional proteins of cancer cells are constantly removed from the cell surface, thereby disrupting tissue polarity and instigating motile phenotypes. Mutant forms of RTKs able to evade Cbl-mediated ubiquitination, along with overexpression of the wild-type forms and a variety of defective feedback regulatory loops, are frequently detected in tumors. Finally, we describe pharmacological attempts to harness the peculiar endocytic system of cancer, in favor of effective patient treatment.

The role of a Schiff base scaffold, N-(2-hydroxy acetophenone) glycinate-in overcoming multidrug resistance in cancer

Drug resistance is a problem that hinders the numerous successes of chemotherapeutic intervention of cancer and continues to be a major obstacle for cures. Till date, several attempts have been made to develop suitable multidrug resistance (MDR) reversing agents. But, throughout the clinical development of MDR reversing agents, patients repeatedly suffer from toxicities. So far, some anticancer activity of Schiff bases which are the condensation products of carbonyl compounds and primary amines and their metal complexes has been described. But, overcoming multidrug resistance, by the use of such small molecules still remain unexplored. Under this backdrop, in search of less toxic and more effective MDR reversing agents our laboratory has developed the different metal chelates of Schiff base N-(2-hydroxy acetophenone)glycinate (NG) which is structurally similar to azatyrosine [L-β-(5-hydroxy-2-pyridyl)-alanine] that inhibits tumor formation by deactivating the c-Raf-1 kinase and c-Ha-ras signalling pathway. A decade-long research proposes possible strategies to overcome MDR by exploiting the chemical nature of such metal chelates. In this review we have catalogued the success of metal chelates of NG to overcome MDR in cancer. The review depict that the problem of MDR can be circumvent by synchronized activation of immunogenic cell death pathways that utilize the components of a host's immune system to kill cancer cells in combination with other conventional strategies. The current wealth of preclinical information promises better understanding of the cellular processes underlying MDR reversing activity of metal derivatives of NG and thus exposes several cellular targets for rational designing of new generation of Schiff base metal chelates as MDR reversing agents.