Measurement of pH in tissue has shown that the microenvironment in tumors is generally more acidic than in normal tissues. Major mechanisms which lead to tumor acidity probably include the production of lactic acid and hydrolysis of ATP in hypoxic regions of tumors. Further reduction in pH may be achieved in some tumors by administration of glucose (+/- insulin) and by drugs such as hydralazine which modify the relative blood flow to tumors and normal tissues. Cells have evolved mechanisms for regulating their intracellular pH. The amiloride-sensitive Na+/H+ antiport and the DIDS-sensitive Na+-dependent HCO3-/Cl- exchanger appear to be the major mechanisms for regulating pHi under conditions of acid loading, although additional mechanisms may contribute to acid extrusion. Mitogen-induced initiation of proliferation in some cells is preceded by cytoplasmic alkalinization, usually triggered by stimulation of Na+/H+ exchange; proliferation of other cells can be induced without prior alkalinization. Mutant cells which lack Na+/H+ exchange activity have reduced or absent ability to generate solid tumors; a plausible explanation is the failure of such mutant cells to withstand acidic conditions that are generated during tumor growth. Studies in tissue culture have demonstrated that the combination of hypoxia and acid pHe is toxic to mammalian cells, whereas short exposures to either factor alone are not very toxic. This interaction may contribute to cell death and necrosis in solid tumors. Acidic pH may influence the outcome of tumor therapy. There are rather small effects of pHe on the response of cells to ionizing radiation but acute exposure to acid pHe causes a marked increase in response to hyperthermia; this effect is decreased in cells that are adapted to low pHe. Acidity may have varying effects on the response of cells to conventional anticancer drugs. Ionophores such as nigericin or CCCP cause acid loading of cells in culture and are toxic only at low pHc; this toxicity is enhanced by agents such as amiloride or DIDS which impair mechanisms involved in regulation of pHi. It is suggested that acid conditions in tumors might allow the development of new and relatively specific types of therapy which are directed against mechanisms which regulate pHi under acid conditions.

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Acid pH in Tumors and Its Potential for Therapeutic Exploitation

Flavonoids, a class of natural products of high pharmacological potency

5. Cyanine-Based pHi Indicators 2717 5.1. Design of pH-Sensitive Cyanine Dyes 2717 5.2. Near-Neutral Cyanine-Based pH Indicators 2718 5.3. Acidic Cyanine-Based pH Indicators 2719 6. Miscellaneous Small Molecule pHi Indicators 2719 6.1. Various Indicators for Near-Neutral pH Values 2719 6.1.1. Europium Complex 2719 6.1.2. Fluorene Derivative 2719 6.1.3. 1,4-Dihydroxyphthalonitrile (1,4-DHPN) 2720 6.1.4. 8-Hydroxypyrene-1,3,6-trisulfonic acid (HPTS) 2720

Fluorescent indicators for intracellular pH.

Tumors contain oxygenated and hypoxic regions, so the tumor cell population is heterogeneous. Hypoxic tumor cells primarily use glucose for glycolytic energy production and release lactic acid, creating a lactate gradient that mirrors the oxygen gradient in the tumor. By contrast, oxygenated tumor cells have been thought to primarily use glucose for oxidative energy production. Although lactate is generally considered a waste product, we now show that it is a prominent substrate that fuels the oxidative metabolism of oxygenated tumor cells. There is therefore a symbiosis in which glycolytic and oxidative tumor cells mutually regulate their access to energy metabolites. We identified monocarboxylate transporter 1 (MCT1) as the prominent path for lactate uptake by a human cervix squamous carcinoma cell line that preferentially utilized lactate for oxidative metabolism. Inhibiting MCT1 with alpha-cyano-4-hydroxycinnamate (CHC) or siRNA in these cells induced a switch from lactate-fueled respiration to glycolysis. A similar switch from lactate-fueled respiration to glycolysis by oxygenated tumor cells in both a mouse model of lung carcinoma and xenotransplanted human colorectal adenocarcinoma cells was observed after administration of CHC. This retarded tumor growth, as the hypoxic/glycolytic tumor cells died from glucose starvation, and rendered the remaining cells sensitive to irradiation. As MCT1 was found to be expressed by an array of primary human tumors, we suggest that MCT1 inhibition has clinical antitumor potential.

/pdf/targeting-lactate-fueled-respiration-selectively-kills-3m61rjbps3.pdf

Targeting lactate-fueled respiration selectively kills hypoxic tumor cells in mice

Present methods for measuring or buffering intracellular free calcium concentrations are almost entirely limited to robust and well anchored cells which can tolerate insertion of ion-selective microelectrodes or microinjection of calcium indicators or buffers into one cell at a time. A very few types of small cells can be loaded with buffers or indicators during controlled lysis, but such procedures grossly perturb membrane integrity and soluble cytoplasmic constituents. Liposome fusion releases only trace quantities of the trapped solute into the cytoplasm and incorporates foreign lipid into the target cell membranes. I now describe a simple technique which loads Ca2+-selective chelators into the cytoplasm of intact cells in suspension and avoids the disadvantages of previous methods. The chelators are made temporarily membrane permeable by masking their four carboxylates with special esterifying groups which then hydrolyse inside the cells, regenerating and trapping the original chelators. The method is demonstrated on red cells, mast cells and lymphocytes.

A non-disruptive technique for loading calcium buffers and indicators into cells.

Intracellular pH measurements in Ehrlich ascites tumor cells utilizing spectroscopic probes generated in situ.

Bioflavonoids are potent inhibitors of lactate transport in Ehrlich ascites tumor cells. The most effective bioflavonoids have four to five hydroxyl groups. Sugar substitution at carbon three, or reduction of the double bond between carbons two and three, decreases their inhibitory activity. Quercetin, the most extensively studied of these compounds, inhibits lactate efflux by 50% at 0.1 micrograms/mg of protein. On addition of quercetin to glycolyzing Ehrlich ascites tumor cells, lactate accumulates inside the cell and the intracellular pH drops. Total lactate production is also inhibited. Nigericin prevents the internal acidification that occurs in the presence of quercetin and also reduces the inhibition of glycolysis. Thus, it appears that inhibition of lactate efflux can affect glycolysis through a lowering of the intracellular pH. The inhibitory effect of quercetin on glycolysis can be explained by its effect on lactate efflux and its previously reported effect on the Na+--K+ ATPase [Suolinna, E.--M., et al. (1974) J. Natl. Cancer Inst. 53, 1515].

Inhibition of lactate transport and glycolysis in Ehrlich ascites tumor cells by bioflavonoids.

Computational Prediction of the Just-Suspended Speed, N, in Stirred Vessels Using the Lattice Boltzmann Method (LBM) Coupled with a Novel Mathematical Approach

Abstract A physics-based approach for modeling convective gas-liquid mass transfer across free surfaces in lab-scale agitated vessels is presented. This approach, which combines numerical modeling with semi-empirical turbulence theory, is validated across multiple operating scales and conditions. The findings show that, regardless of the mechanical action driving motion, free surface mass transfer rate in lab-scale systems is consistent with empirical relationships. The role and importance of free surface convective mass transfer in lab scale devices is also discussed. The computational approach is shown to be practical within the context of industrial analysis and design timescales.

Modeling free surface gas transfer in agitated lab-scale bioreactors

https://sti.srs.gov/fulltext/SRNL-STI-2022-00325.pdf

John A. Thomas

Papers

Intracellular pH measurements in Ehrlich ascites tumor cells utilizing spectroscopic probes generated in situ.

Inhibition of lactate transport and glycolysis in Ehrlich ascites tumor cells by bioflavonoids.

Computational Prediction of the Just-Suspended Speed, N, in Stirred Vessels Using the Lattice Boltzmann Method (LBM) Coupled with a Novel Mathematical Approach

Modeling free surface gas transfer in agitated lab-scale bioreactors

Blending and Cavern Formation within Non-Newtonian Fluids in Stirred Tanks: Application to Nuclear Waste Fluid Processing