Thermotolerance and intracellular pH in two Chinese hamster cell lines adapted to growth at low pH

Wahl, Michael J.; Coss, Ronald A.; Bobyock, Suzanne B.; Leeper, Dennis B.; Owen, Charles S.

doi:10.1002/(sici)1097-4652(199602)166:2<438::aid-jcp22>3.0.co;2-5

Cited by 20 publications

(21 citation statements)

References 30 publications

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“…Most significantly, this report demonstrates that quercetin inhibits thermotolerance that occurs in cells adapted to growth at low pH. Previous results have shown that OvCa cells grown at pH 7.3 (7.3 G) or 6.7 (6.7 G) develop thermotolerance by 3-4 h during continuous heating at 428C (see figure 3) 4,5 . When cells are grown at pH 7.3 or 6.7, thermotolerance is maintained up to 8 h at 428C at a survival level between 10-20%.…”

Section: Discussionsupporting

confidence: 57%

“…However, after 6-8 h the surviving fraction stabilized at $1%, indicating the emergence of thermotolerance. In the absence of quercetin, thermotolerance was Quercetin-induced thermosensitization 511 fully developed by 4 h at 428C when cells were either at 7.3 G or 6.7 G (figure 1) 4 . By contrast, cells adapted to growth at low pH and exposed to quercetin plus hyperthermia completely lost the ability to develop thermotolerance as indicated by the loss of a plateau in surviving fraction beyond 4 h of heating (figure 2).…”

Section: Effect Of Quercetin On Response To Hyperthermiamentioning

confidence: 99%

“…By contrast, cells adapted to growth at low pH and exposed to quercetin plus hyperthermia completely lost the ability to develop thermotolerance as indicated by the loss of a plateau in surviving fraction beyond 4 h of heating (figure 2). Cells acutely acidified from pH 7.3 to 6.7 have a greatly reduced ability to develop thermotolerance during exposure to 428-hyperthermia (figure 1) 4 . Cells growing at pH 6.7 exhibited quercetin-induced heat sensitivity similar to that of cells acutely acidified from pH 7.3 to 6.7.…”

Section: Effect Of Quercetin On Response To Hyperthermiamentioning

confidence: 99%

“…Previous work has shown that Chinese hamster ovarian carcinoma cells (OvCa) adapted to growth at low pH show an ability to acquire resistance to heat-induced cell killing during prolonged heating at 428C. In contrast, cells grown at pH e 7.3 and acutely acidified from pH e 7.3 to 6.7 immediately before heating are markedly sensitized to 428-induced cytotoxicity and fail to develop thermotolerance during heating 4,5 . The acquired thermal resistance phenotype of low pH adapted cells occurs by 4 days in culture at pH e 6.7.…”

Section: Introductionmentioning

confidence: 99%

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Quercetin sensitizes cells in a tumour-like low pH environment to hyperthermia

Wachsberger

Burd

Bhala

et al. 2003

International Journal of Hyperthermia

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Quercetin has been shown to act as a hyperthermia sensitizer by inhibiting the synthesis of heat shock protein 70 (HSP70) in a variety of tumour cell lines. It is most effective under conditions of low pH. This study was designed to test the hypothesis that quercetin suppresses thermotolerance development in cells adapted to growth at low pH and renders them as responsive as acutely acidified cells to hyperthermia-induced cytotoxicity. Chinese hamster ovarian carcinoma cells (OvCa) were exposed to 42 degrees C hyperthermia and/or quercetin (50-200 mm) at their growth pH of either 7.3 or 6.7 or after acute acidification from 7.3 to 6.7. Thermotolerance development was measured by colony survival. HSP70 synthesis and total protein synthesis were measured by radioactive precursor pulse labelling techniques. Quercetin, in a concentration-dependent manner, reduced the rate of total protein synthesis and increased cytotoxicity equally after acute acidification to pH 6.7 or growth at pH 6.7 at 37 degrees C, and to a greater extent than it did in cells at pH 7.3. At 42 degrees C, 100 mm quercetin inhibited total protein synthesis, HSP70 synthesis and thermotolerance development to a similar extent in cells grown at pH 6.7 or acutely acidified to pH 6.7. In contrast, quercetin reduced but did not completely inhibit HSP70 synthesis and thermotolerance development in cells grown and heated at pH 7.3. These results support the hypothesis that quercetin can specifically reduce thermotolerance development in tumour cells adapted to growth at pHe 6.7 so that they respond similarly to acutely acidified cells. Since many tumours are adapted to growth at low pH and may resist a wide variety of therapeutic modalities, inhibition of thermotolerance expression by quercetin may not only enhance the response to hyperthermia but the response to commonly used therapies such as chemotherapy and radiation.

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Section: Discussionsupporting

confidence: 57%

Section: Effect Of Quercetin On Response To Hyperthermiamentioning

confidence: 99%

Section: Effect Of Quercetin On Response To Hyperthermiamentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Quercetin sensitizes cells in a tumour-like low pH environment to hyperthermia

Wachsberger

Burd

Bhala

et al. 2003

International Journal of Hyperthermia

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“…However, cells explanted from rodent tumours are not sensitized to hyperthermia in vitro by low pH 15 . Several laboratories, including our own, have reported that growth of rodent cells in an acidic environment confers resistance to hyperthermic sensitization by low pH [16][17][18][19][20] .…”

Section: Introductionmentioning

confidence: 99%

Acute extracellular acidification reduces intracellular pH, 42°C-induction of heat shock proteins and clonal survival of human melanoma cells grown at pH 6.7

Coss

Storck

Wachsberger

et al. 2004

International Journal of Hyperthermia

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Two human melanoma cell lines, SK-Mel-28 and DB-1, were used for in vitro studies of the mechanisms underlying heat resistance of human tumour cells adapted to growth in acidic environments. Adaptation to growth at low pH was characterized by resistance to 42 degrees C cytotoxicity and accompanied by an increase in endogenous levels of Hsp70 and/or Hsp27. Acute extracellular acidification to levels below pH 6.5 was required to sensitize the melanoma cells to 42 degrees C. Furthermore, cells grown at low pH were more resistant to sensitization by acute acidification than cells grown at pH 7.3. The intracellular pH (pHi) of cells grown at pH 6.7 was less than the pHi of cells grown at pH 7.3 both before and after acute acidification. A pHi threshold existed for melanoma cells growing at pH 7.3 below which they became sensitized to 42 degrees C. This pHi threshold differed between the SK-Mel-28 and DB-1 cells. In contrast, a pHi threshold for heat sensitization did not exist for cells growing at pH 6.7: any reduction in pHi before heating resulted in increased cell killing. Since cells grown at low pH lack a pHi threshold for heat sensitization, they are sensitized more to 42 degrees C per unit decrease in pHi than cells grown at pH 7.3. Acute acidification abrogated the 42 degrees C-induction of Hsp70 and Hsp27 in the melanoma cells. The pHi thresholds for abrogation of these HSPs are slightly higher than or comparable with the thresholds for cytoxicity for each cell line grown at pH 7.3, but abrogation occurred over a narrower range of pHi compared with cytotoxicity. Abrogation of heat-induced expression of these HSPs correlates with cytotoxicity in both cell lines with the exception of Hsp27 expression in SK-Mel-28 cells. In conclusion, strategies that reduce pHi in melanoma cells growing at low pH, such as in acidotic regions of tumours, could selectively sensitize them to hyperthermia because they lack a pHi threshold for heat sensitization.

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Altered proton extrusion in cells adapted to growth at low extracellular pH

et al. 1997

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Intracellular pH (pHi) homeostasis is crucial to cell survival. Cells that are chronically exposed to a low pH environment must adapt their hydrogen ion extrusion mechanisms to maintain their pHi in the physiologic range. An important component of the adaptation to growth at low pH is the upregulation of pHi relative to the extracellular pH (pHe). To test the ability of low pHe adapted cells to respond to a pHi lowering challenge, a fluorescence assay was used that directly monitors proton removal as the rate of change of pHi during recovery from cytosolic acidification. Two cell lines of Chinese hamster origin (ovarian carcinoma and ovary fibroblastoid cells) were compared, both of which showed altered proton extrusion after adaptation to growth at low pHe = 6.70. In the ovarian carcinoma (OvCa) cell line, the pattern was consistent with an upregulation by means of an increase in the number of functional proton transporters in the plasma membrane. In the ovary fibroblastoid (CHO-10B) cell line, pHi was consistently elevated in adapted cells as compared with cells grown at normal pHe = 7.30 without an increase in maximum extrusion rate. This upregulation was consistent with a shift in the activating pHi of proton transporters without an increase in the number of transporters, i.e., a change in substrate affinity of the transporter. In OvCa cells, recovery from acidification could be blocked by amiloride, an inhibitor of Na+/ H+ exchange. In contrast, a more modest effect of amiloride on CHO cells was observed but a complete inhibition was seen with the Cl-/HCO(-3)exchange inhibitor 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS). These data indicate that the two cell lines rely to different degrees on the two major pathways for pH regulation during recovery from cytosolic acidification.

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Thermotolerance and intracellular pH in two Chinese hamster cell lines adapted to growth at low pH

Cited by 20 publications

References 30 publications

Quercetin sensitizes cells in a tumour-like low pH environment to hyperthermia

Quercetin sensitizes cells in a tumour-like low pH environment to hyperthermia

Acute extracellular acidification reduces intracellular pH, 42°C-induction of heat shock proteins and clonal survival of human melanoma cells grown at pH 6.7

Altered proton extrusion in cells adapted to growth at low extracellular pH

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