Effect of pH on plating efficiency, serum reguirement, and incorporation of radioactive precursors into human cells

Comparison of the optimal culture conditions for cell growth and tissue plasminogen activator production by human embryo lung cells on microcarriers

Optimization of culture conditions such as the dissolved O2 (DO) concentration, temperature and pH was attempted regarding both cell growth and the production of tissue plasminogen activator (TPA) in a microcarrier cell culture of human embryo lung cells. The growth rate was suppressed at a DO concentration below 30% saturation. From the pH range 7.2-7.6, both the specific growth rate and maximal cell concentration decreased. At a lower temperature than 37 degrees C, although both the specific growth rate and the maximal cell concentration decreased, the cell concentration was maintained for a longer time during the production period, high TPA productivity being maintained. As the optimal conditions for culture growth, a DO concentration of 30% saturation or over, temperature of 37 degrees C and pH of 7.4 are recommended. However, for TPA production after cell culture growth, the DO concentration should be in the range 20-30% O2 saturation, and the temperature and pH should be lowered to 33 degrees C and 6.8, respectively.

Keynote address: the influence of microenvironmental factors on the activity of radiation and drugs

The inherent radio- and chemosensitivity of tumor cells clearly affects their response to treatment. Accumulating evidence, however, suggests that the biochemical and physiological status of the cell during treatment is at least as important. In this review, a critique of the current evidence for, and extent of, microenvironmental heterogeneity in tumors is presented, emphasizing human tumor cells in situ. The expected consequences of those changes on cellular response to radiation and chemotherapy is then briefly reviewed. Finally, the continuing interest in developing new therapeutic strategies for which the tumor microenvironment is an asset (as opposed to a liability) is discussed in the context of the dynamic nature of tumors, and the complexity of adequately analyzing combination treatments.

Changes in antigen expression on human FME melanoma cells after exposure to hypoxia and acidic pH, alone or in combination

Quantitative changes in the expression of two tumour-associated surface antigens on human FME melanoma cells were studied by flow cytometry after exposure to hypoxia and acidic pH, either alone or in combination. The expression of the p250 antigen recognized by the monoclonal antibody (MAb) 9.2.27 was reduced immediately after exposure to hypoxia. The magnitude and duration of the reduction increased with increasing exposure time. Twelve to 16 hr after the end of a 6-hr exposure to hypoxia the antigen expression reached the normal level, followed by a temporary increase above this level. The p97a antigen recognized by the 4.1 MAb underwent similar changes after exposure to hypoxia for 6 hr. After exposure to hypoxia in acidic environment, the magnitude and duration of the reduction in the expression of the p250 antigen increased with increasing acidity. The enhancement in antigen expression above the normal level was less after hypoxia at acidic pH than after hypoxia at physiological pH. The combined treatment had an additive effect on the expression of the melanoma-associated antigen but did not enhance hypoxia-induced cell killing. The observed changes in antigen expression might be of importance if hypoxic tumour cells are subjected to MAbs conjugated to radioisotopes or cytotoxic agents for diagnostic or therapeutic purposes.

Dependence of misonidazole binding on factors associated with hypoxic metabolism

The binding of misonidazole (MISO) to macromolecules in hypoxic cells is believed to require metabolic reduction. Several factors in the cells' environment, such as pH, glucose, lactate and MISO concentration could affect the capacity of metabolic reduction. Modulation of the binding of MISO by these factors was studied by exposing exponential EMT6/Ro cells to MISO under extremely hypoxic conditions. No binding was observed under aerobic conditions. There was no difference in the binding of 0.02 mM MISO at varying concentrations of glucose from 0.015 mM to 5 mM. Thus, for diagnostic purposes with concentrations of MISO lower than 0.02 mM, little effect of glucose concentration is expected. However, with 5 mM MISO, the binding of MISO increased with increasing glucose concentration (3-fold increase after 2 hours incubation in 5 mM glucose relative to 0.015 mM glucose). At intermediate MISO concentrations (0.1 mM to 5 mM); the higher the MISO concentration, the greater was the increase in binding due to 5 mM glucose. There was no detectable effect of lactate (0, 3 and 10 mM) at pH 7.2 on the binding of MISO either in 0.015 mM or 5 mM glucose. However, a decrease of pH (from 7.2 to 6.5) decreased the binding of MISO in 5 mM glucose but not in 0.015 mM glucose. These data indicated that the binding of MISO is a multi-step process, which involves the concentrations of both glucose (probably via reducing equivalents) and MISO.

pH and the effect of NH4Cl on human gingival fibroblasts

pH variations in the range from 6.9 to 7.9 modified the growth rate of human gingival fibroblasts in culture, a pH optimum being found at 7.6-7.8. A pH dependent growth inhibition by ammonia was evident, being particularly prominent in the presence of 2 mM NH4Cl. At this concentration an effect ranging from a complete cessation of growth at pH 8.0 to an indication of a slight stimulatory effect at pH 7.2 was found. Concomitant with this amplification of the growth inhibitory effect, a state of unbalanced growth in the sense of an increased cellular protein content was induced by ammonia upon increasing the pH of the medium. The incorporation of 14C-proline into the total protein fraction decreased rapidly, particularly in the control cultures, with pH; an inhibition by ammonia being found at pH 7.0 and 7.5 with no effect at pH 7.1. Except for part of the inhibition by ammonia, changes in specific activity of 14C-proline in the cellular amino acid pool could ac count for these pH effects. Ammonia reduced the proportion of radiolabeled protein recovered as collagen both from the cells and medium at the lower pHs, whereas the only significant effect on noncollagen protein was an increased fraction being secreted at pH 7.1 in the presence of 10 mM NH4Cl.

The relevance of tumour pH to the treatment of malignant disease

The wide range of tumour pH values that have been determined in human tumours is shown in Fig. 4. It can be seen that tumour pH values may be very low, or may fall in the same range as the values found in normal tissues. This means that pH-mediated modification of therapeutic effectiveness will be patient specific, rather than a general phenomenon. That the pH of the cellular environment might influence the effectiveness of various therapeutic agents is not a new idea. The data published in this field to date concerning such effects have been discussed extensively and are summarized in Table IV. Here we can see that low pH leads to decreased cell survival following treatment with hyperthermia, radiotherapy combined with hyperthermia, radiosensitizers and various chemotherapeutic agents. Conversely, low pH affords some protection against radiation and some drugs. Most of these data were, of necessity, derived from in vitro studies. In vivo studies are in most cases not feasible due to the difficulty of isolating the effect of one selected factor. Low tumour pH is, in vivo, generally assumed to be closely interlinked with tissue hypoxia and low blood-flow levels, each of which may individually influence the experimental outcome. Moreover, most of the aforementioned in vitro studies were conducted under well-oxygenated conditions. As previously mentioned, euoxic cells can, under certain conditions, maintain a pH gradient over the cell membrane. This collapses with the onset of hypoxia, leading to intracellular acidification. Low oxygen levels have been shown to be characteristic of many tumours. Within these limitations it is thus evident that tumour pH values could have far-reaching consequences for therapy. If the in vitro findings should prove to be relevant to the clinical situation various applications are possible. Pre-selection of patients less likely to respond to certain (toxic) chemotherapeutic agents, or conversely selection of agents that are more likely to be effective in the pH range of the tumour to be treated are two examples. Alternatively, the exploitation of low tumour pH values is a possibility. Agents that form or release toxic derivatives in areas of low pH, e.g., pH-sensitive liposomes, will work selectively in such areas. Tumour selective therapy may also be possible in patients with higher tumour pH values if the tumour pH can be lowered. This has been achieved experimentally by the administration of hyperthermia at temperatures above 42 degrees C, or by the administration of glucose.(ABSTRACT TRUNCATED AT 400 WORDS)

Stimulation of glycosaminoglycan production and lysosomal activity of human synovial cells in culture by low environmental pH

Glycosaminoglycan production, acid hydrolase activity, proliferation, and morphology were examined in human synovial cells subjected to low environmental pH. The amount and the molecular size of newly synthesised glycosaminoglycan (GAG) were increased without significant change in the rate of cell proliferation. Lowered pH produced an increase in the size of cytoplasmic organelles. Some of these possessed ultrastructural features of lysosomes, but others were clearly nonlysosomal and were of uncertain identity. Intracellular activity of the lysosomal acid hydrolase N-acetyl-beta-glucosaminidase (NAG) was not altered by low pH, but a marked increase occurred in extracellular NAG activity, indicating enhanced release.

Endoglycosidase H-sensitive glycopeptides in eleven different animal cells

We have examined the distribution of mannose-labelled glycopeptides in eleven different animal cells grown in vitro. All of the cells examined contained endoglycosidase H-sensitive species of high and low molecular weight, associated with the cell material and with the cell surface; however, the distribution between the two pools was different, suggesting a 'sorting out' of glycoproteins. Another conclusion from our studies is that the oligosaccharide processing known to occur during or after membrane glycoprotein translation is incomplete in a high percentage of mannose-containing N-linked oligosaccharides of cell surfaces. There was no consistent correlation between the relative amounts of endoglycosidase H-sensitive and -resistant glycopeptides and whether the cells were normal, virus-transformed or tumour-derived.

Hydrogen ion dynamics and cancer: an appraisal

The concentration of hydrogen ions plays a critical role in all biochemical processes, including multiple enzymatic reactions, and in the regulation of metabolism. The acid-base aspects of metabolism as applied to cancer are considered. Preliminary data are presented. The primary concept of hydrogen ion dynamics is related to prevention, development, and etiology of carcinogenicity, as well as to the regression of certain malignant malignant tumors. The present overview summarizes, in terms of H+ dynamics, many related concepts in oncologic research and associates and integrates a variety of basic and clinical observations toward better understanding of cancer cell behavior, biology, and host-tumor relationships.

Optimizing culture conditions for the production of animal cells in microcarrier culture

Cytodex 1 microcarriers have been used for the successful culture of more than 80 different types of animal cells--including primary cells, normal diploid cell strains and established or transformed cell lines. culture volumes have ranged from a few milliliters for diagnostic studies to over several hundred liters for vaccine production. Experience with this wide variety of cell types and culture volumes has enabled the identification of several parameters critical for obtaining maximum cell yields from microcarrier cultures. The most vital stage for the successful microcarrier culture of many cell types was the initial stage of the culture cycle. To achieve high cell yields, it was necessary to use culture procedures which maximized plating efficiency and final cell yield could be further increased by ensuring that the inoculation cell density exceeded a critical viable cell/microcarrier ratio. Modifications of the standard microcarrier culture procedures included reducing initial culture volume, reducing the initial stirring speed and/or supplementing the medium during the early stages of the culture cycle. Control of pH, nutrient supply, and gas tension were all critical throughout the culture cycle. Results with low-serum and serum-free media indicate that the requirement for fetal calf serum in the microcarrier culture of Vero and MRC-5 cells can be reduced or even eliminated. Large scale microcarrier culture equipment should take into account the modified culture procedures which are often required to achieve the full potential of this culture method. The design of a new flexible culture system suitable for pilot and production scale cultures is presented. This system accomodates a wide variety of culture and production procedures and through a recirculation system permits: (a) "in-line" monitoring and control of culture parameters; (b) provides an efficient gas exchange capacity which obviates the need for fermenter headspace and sparging; and (c) allows for maximal utilization of medium components and rapid harvesting of medium or cell products.

Environmental pH modulation of collagenase in normal human fibroblast cultures

Normal human skin fibroblast cultures have been used to assess the effects of relatively minor changes in environmental pH on collagenase, a major extracellular gene product. Collagenase accumulation in the culture medium, measured both as enzyme activity and immunoreactive material, was 2- to 10-fold greater at pH 7.6--8.2 than at pH 6.8--7.2. The pH-associated increase in collagenase was paralleled by an increase in general protein synthesis. Nevertheless, prototypic lysosomal and cytoplasmic enzymes changed very little under identical culturing conditions. Although substantial intracellular protein degradation occurred at all pH values, the small differences either in general protein degradation or in specific collagenase degradation in the medium were of insufficient magnitude to account for the increased accumulation of collagenase.

Studies on mannose-containing glycopeptides from a normal and an SV40 transformed human cell

The oligosaccharide moiety of cell-surface mannose-labelled glycopeptides from a normal (WI38) and an SV40 transformed cell (W118Va) have been investigated using specific glycosidases. Partially purified mannose-containing glycopeptides were separated into acidic and neutral species by high voltage paper electrophoresis. Endo-beta-N-acetylgucosaminidase D, in the presence of three exoglycosidases, released from the acidic glycopeptides of non-growing cells a product completely absent in growing cells. However, the acidic species from growing WI18 Va and WI38 were found to be similar in the products released by enzyme digestion. The neutral species from growing normal cells contained a proportion of the glycopeptides resistant to endoglycosidase D while those from the non-growing cells were almost free of these resistant species. The SV40 transformed cells were further enriched, when compared to normal cells (WI38), in these neutral resistant species. We suggest that the oligomannosyl core of the majority of the susceptible species contains three mannose residues while that of the resistant species contains between six and eight.