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D Rotin

Publications and source records attributed to D Rotin.

47 records · Page 3Linked to original sources
PubMed1989

Acid pH in tumors and its potential for therapeutic exploitation.

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.

Animals↗
PubMed1989

Requirement of the Na+/H+ exchanger for tumor growth.

The Na+/H+ exchanger is involved in a variety of cellular processes, including regulation of intracellular pH and possibly the control of cell growth and proliferation. To study the role of the Na+/H+ exchanger in tumor growth, human sodium proton exchanger-deficient (HSPD) mutants were derived from the human bladder carcinoma cell line MGH-U1 (EJ) by the proton suicide selection technique (J. Pouyssegur et al., Proc. Natl. Acad. Sci. USA, 81: 4833-4837, 1984). The HSPD cells were approximately 40% larger and contained approximately 70% more DNA than the parental cells. They were unable to grow in vitro in the absence of bicarbonate at pH less than 7.0, whereas the parental cells grew well at pH greater than or equal to 6.6. This difference in acid sensitivity was abolished in the presence of bicarbonate. In contrast to the parental MGH-U1 cells, the Na+/H+-deficient HSPD cells either failed to grow tumors, or showed severely retarded tumor growth when implanted into immune-deprived mice. This difference in tumor growth was not attributed to differences in cell size and DNA content, because Na+/H+ exchange-competent large cells (HLC), derived during the same proton suicide selection process as the HSPD cells, grew tumors at a rate close to that of the parental cells. Cells derived from the few tumors which grew after implantation of HSPD mutant cells were revertants which had regained Na+/H+ activity. HSPD cells also failed to form spheroids in culture, and the only spheroid formed consisted of revertant cells which had regained both Na+/H+ exchange activity and tumorigenic capacity. These results suggest that the Na+/H+ exchanger is important for tumor growth.

Animals↗
PubMed1989

Impaired cell volume regulation in Na(+)-H+ exchange-deficient mutants.

To elucidate the mechanism of regulatory volume increase (RVI) in Chinese hamster ovary cells, Na(+)-H+ exchange-deficient mutants, called AP-1, were derived from WT-5 cells, a wildtype subclone. The absence of functional antiports in AP-1 cells was established through measurements of intracellular pH (pHi) and Na+ uptake. Cells exposed to hypotonic medium initially swelled but regained near-normal volume within minutes. When isotonicity was then restored, WT-5 cells shrank immediately and then carried out RVI, which was inhibited by 0.1 mM amiloride. This amiloride-sensitive RVI was absent in the AP-1 mutants, suggesting involvement of Na(+)-H+ exchange. In some cell types, RVI is mediated by Na(+)-K(+)-2Cl- cotransport. Bumetanide-sensitive 86Rb+ (K+) influx was detectable in both WT-5 and AP-1 cells, suggesting the presence of Na(+)-K(+)-2Cl- cotransport. Bumetanide-sensitive influx was stimulated by osmotic shrinking in WT-5 cells, and only slightly in AP-1 cells. However, Na(+)-K(+)-2Cl- cotransport did not contribute to volume regulation, since bumetanide (50 microM) failed to inhibit RVI in osmotically shrunken WT-5 cells. The inability of cotransport to induce a volume gain in WT-5 cells was attributable to the simultaneous stimulation of Na(+)-K(+)-2Cl- efflux. The rate of efflux was similar in magnitude to the corresponding influx rate so that net Na(+)-K(+)-2Cl- cotransport was negligible. These results show that RVI in osmotically shrunken Chinese hamster ovary cells is mediated by the Na(+)-H+ antiport and that, although stimulated, Na(+)-K(+)-2Cl- cotransport does not contribute to anisosmotic volume regulation.

Animals↗
PubMed1987

Cytotoxicity of compounds that interfere with the regulation of intracellular pH: a potential new class of anticancer drugs.

The extracellular pH (pHe) in many solid tumors is often lower than in normal tissues. Cells may survive conditions of acid pHe because antiports in their membrane exchange Na+ for H+, or HCO3- for Cl-, and thus regulate the intracellular pH (pHi). We have therefore assessed the effects of drugs which interfere with regulation of pHi on survival of Chinese hamster ovary and human bladder cancer MGH-U1 cells in tissue culture. Nigericin, an ionophore which acidifies the cytoplasm when cells are placed in medium at low pHe, was not toxic at pHe 6.5 or above but became very toxic as pHe was reduced below this value. Amiloride and 4,4'-diisothiocyanostilbene 2,2-disulfonic acid, inhibitors of the Na+/H+ and HCO3-/Cl- exchangers, respectively, decreased pHi in the presence of nigericin at low pHe. These drugs showed little or no toxicity in the pHe range of 6.0-7.0 but added greatly to the toxicity of nigericin. A combination of all three drugs led to toxicity in the pHe range of 6.5-6.8, well within the measured range of tumor pH, but not at pHe 7.0 or above. A combination of low pH and hypoxia, two conditions likely to be found in regions distant from tumor blood vessels, caused cell mortality in the absence of drugs, and this effect was increased by nigericin used alone or in combination with amiloride and 4,4'-diisothiocyanostilbene 2,2-disulfonic acid. These drugs may be regarded as prototypes for potential new anticancer agents that might achieve selective killing of tumor cells by interfering with the regulation of intracellular pH.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1986

Influence of hypoxia and an acidic environment on the metabolism and viability of cultured cells: potential implications for cell death in tumors.

Hypoxia and an acidic environment are known to occur in regions of solid tumors and might be involved in the causation of necrosis. The viability and energy metabolism of cells in tissue culture were therefore investigated under hypoxic and/or acidic conditions. Acute exposure of Chinese hamster ovary (CHO) cells or human bladder cancer MGH-U1 cells to hypoxia plus low pH (6.5 to 6.0) was cytotoxic in a time- and pH-dependent manner; surviving fraction was reduced to approximately 10(-4) following a 6-h exposure to hypoxia at pH 6.0. There was no effect on viability when aerobic CHO cells were exposed for 6 h at pH 6.0, or when either cell line was rendered hypoxic for 6 h at pH 7.0; MGH-U1 cells showed slight sensitivity to acidic pH in air. Decrease in viability of CHO cells incubated under acid conditions was observed over the range of oxygen concentrations from 0.2 to 0.05%, similar to the range which causes change in cellular sensitivity to radiation. Glucose consumption and lactate production by both cell lines were inhibited at low pH under both aerobic and hypoxic conditions. Cellular adenosine triphosphate (ATP) levels and the energy charge [(ATP + 1/2 adenosine diphosphate)/(adenosine monophosphate + adenosine diphosphate + ATP)] of CHO cells were reduced by about 85 and 25%, respectively, after a 6-h exposure to hypoxia at pH 6.0 but were not influenced by hypoxia or acid pH alone. Inhibition of glycolysis by incubation of CHO cells under hypoxic conditions in the absence of glucose (at pH 7.0) led to a larger fall in cellular ATP and energy charge, but cell survival fell to only approximately 10(-2) at 6 h. These results demonstrate that hypoxia and an acid environment interact to cause marked toxicity. A decrease in energy charge of the cells may contribute to loss of viability, but additional mechanisms appear to be involved.

Adenosine Triphosphate↗
PubMed1984

The effect of the drug lonidamine on Chinese hamster ovary cells in vitro and on experimental tumors.

Hypoxic cells in solid tumors are known to be resistant to radiation, and may also be resistant to some anti-cancer drugs. Biochemical properties of hypoxic cells, such as their dependence on anaerobic glycolysis leading to production of lactate and low pH might have potential for inhibition by drugs with selective activity against hypoxic cells. Such drugs might improve the Therapeutic Index when used with radiation or some conventional anti-cancer drugs. Preliminary studies have shown that the combination of hypoxia and low pH (pH 6.5-6.0) was cytotoxic to Chinese Hamster Ovary (CHO) cells incubated in vitro for up to 6 hours, although neither factor alone reduced plating efficiency. Lonidamine, an inhibitor of mitochondrially-bound hexokinase and lactate transport, was cytotoxic to CHO cells at low pH, but had no effect at physiological pH under aerobic or hypoxic conditions. Lonidamine has also been tested for in vivo effects against three murine tumors: the KHT fibrosarcoma, 16/C mammary carcinoma and the Lewis Lung Tumor. The drug was tested either alone, or with radiation or Adriamycin to kill aerobic cells, and/or with glucose and insulin to lower intra-tumor pH. No major therapeutic effects have been demonstrated.

Animals↗
PubMed1983

The possible role of juvenile hormone esterase in the regulation of juvenile hormone titre in the female cockroach Diploptera punctata.

Juvenile hormone (JH) degradation in vitro and in vivo was studied in the viviparous cockroach Diploptera punctata. In vitro studies with juvenile hormone esterase (JHE) and "general" or l-naphthyl acetate esterase (NAcE) revealed that diethyl-p-nitrophenylphosphate (paraoxon) inhibited both JHE and NAcE activity, but the latter was more sensitive and was completely inhibited at 0.1 mM. NAcE activity was resistant to inhibition with Triton X-100, whereas JHE activity in haemolymph of adult females was inhibited 100% at Triton X-100 concentration of 0.25%. Eighty percent inhibition of JHE activity in vivo was observed following injection of 0.2 microL Triton X-100. In contrast to the previously observed dose-dependant increase in JHE activity. NAcE activity did not increase following treatment of allatectomized females with the JH analogue ethyl-2E,4E-3,7,11-trimethyl-2,4-dodecadienoate (hydroprene). Hydroprene was not catabolized in haemolymph of D. punctata in vitro. The half-life of C16 JH (JH III) in the haemolymph, in vivo, was 1.65 h for day 5 females and 2 h for day 6 females.

Animals↗