Effects of thermochemotherapy [1-hexylcarbamoyl-5-fluorouracil (HCFU) combined with hyperthermia]: a basic study on the most effective timing and sequence in vivo

1-Hexylcarbamoyl-5-fluorouracil (HCFU) is known to be hydrolyzed to 5-fluorouracil (5-FU) by heating. We have previously reported the enhancement of the antitumor effects of HCFU when combined with hyperthermia (1). This study aimed at determining the most effective timing schedule for HCFU combined with hyperthermia for clinical application. On the third, 6th, 9th, 12th and 15th day after transplantation, HCFU (80 mg/kg) was administered and hyperthermia induced. The antitumor effect was evaluated by the measurement of tumor volume. 5-FU concentration in the tumor tissue was analyzed on the 12th day after transplantation after administering 150 mg/kg HCFU, with or without hyperthermia (43.5 degrees C, 45 min). 5-FU concentration in serum and other tissues (kidney, liver and submandibular gland) were also analyzed. The concentration was measured by a high performance liquid chromatograph (HPLC) following Mori et al 's method (2). An enhanced antitumor effect and a significant increase in 5-FU concentration in tumor tissue were observed in post-heated groups of mice as compared with pre-heated groups and groups given HCFU alone. The results showed that HCFU given 1 to 2 hours prior to hyperthermia was the most effective treatment.

Enhancement of antitumor effects of new analogue of platinum, cis-diammine (glycolato) platinum (254-S) combined with hyperthermia in vivo

Cis-diammine (glycolato) platinum (254-S) is a second generation platinum complex with reduced nephrotoxicity. In this study the antitumor effect of 254-S combined with hyperthermia in vivo in mice was studied. On the 6th day after inoculation of the Ehrlich ascites tumour cells, 254-S (15mg/kg) was administered intraperitoneally (i.p.) and hyperthermia was induced by using a circulating water bath at 42.5 degrees C for 45 min. The antitumour effect was evaluated by relative tumour volume. Furthermore, platinum concentration in tumour tissue was determined by using atomic absorption spectrophotometry. The most effective condition was found to be the combination of 254-S with hyperthermia. A significantly higher concentration of platinum in the tumour tissue was observed when treatment with 254-S was combined with hyperthermia, than with treatment using 254-S alone. Our study suggested that the accumulation of 254-S in the tumour tissue, and its retention at a high concentration within the tumour tissue long term was one of the reasons for the enhancement of antitumour effect of 254-S treatment when combined with hyperthermia.

Antitumor effect of carboplatin combined with hyperthermia on Ehrlich-ascites tumor in vivo

We examined the optimal timing for the enhancement of antitumor effects of CDDP analogues, cis- diammine-1,1- cyclobutane dicarboxylate platinum (II); CBDCA combined with hyperthermia against the CD-1 mice bearing Ehrlich ascites tumor (EAT) cells in vivo. The prolonged tumor doubling time was observed when two modalities were combined. The longest tumor doubling time was obtained by simultaneous administration of CBDCA combined with hyperthermia. The findings indicated that the most effective condition was the simultaneous combination of CBDCA with hyperthermia. An increase in intratumoral platinum concentration was observed by the treatment of CBDCA simultaneous combined with hyperthermia.

Antitumour effect of irradiation followed by hyperglycemia and hyperthermia: the dependence on tumour size and blood flow

The interrelationship of three tumour parameters-volume, blood flow and growth delay-was evaluated after irradiation alone or combined with hyperglycemia (HG) and hyperthermia (HT). The experiments were performed on Ehrlich carcinoma tumours 5, 7 or 9 days after intramuscular implantation when they reached a mean volume of approximately 0.17, 0.46 or 0.90 cm3, respectively. Tumours were irradiated at a dose of 12.5 Gy. In groups of trimodality therapy, induction of HG (5i.p. injections of glucose during a 2-h period, total dose of glucose 10.4 g/kg) was started immediately after irradiation, and HT (water bath, 43 degrees C, 30 min) was given 3 h later. Regardless of the method of therapy, blood flow in the central part of each tumour was measured 4 and 7 h after irradiation by 133Xe clearance technique. It was shown that if tumours were treated by irradiation alone, both tumour blood flow and growth delay declined with increasing tumour volume. There was no correlation between individual values of tumour blood flow intensity and growth delay within each size group, and only all the data pooled together showed a significant direct relationship between these two parameters. In contrast, for radiotherapy with HG and HT, the antitumour effect increased with tumour volume. Blood flow was strongly inhibited by radio-modifiers; the larger tumours, the lower levels of perfusion were observed. There was a pronounced trend of increased tumour growth delay with decreased blood flow for tumours of the same volume, and these parameters were highly correlated if all individual data were analysed together regardless of tumour size. It was concluded that postirradiation blood flow inhibition plays a significant role in the tumouricidal effect of irradiation with HG and HT. The monitoring of tumour perfusion may be useful for the prediction of the effectiveness of such postirradiation modification, which is especially attractive in radiotherapy of large advanced tumours.

Endogenous production of tumor necrosis factor alpha in combination with hyperthermia for the treatment of mice bearing Ehrlich ascites tumor

Multiple hyperthermia was found to exert an additive antitumor effect when combined with the in vivo production of tumor necrosis factor alpha (TNF-alpha) in mice bearing Ehrlich ascites tumor (EAT). TNF-alpha was produced in EAT-bearing mice by priming the animals with zymosan and subsequently challenging with lipopolysaccharide (LPS). Mice were pretreated with sulindac and D-mannoheptulose to alleviate the toxic side effects of LPS. While the ability of these tumor-bearing mice to produce TNF-alpha remained unchanged under hyperthermia, the EAT cell number was suppressed in the combined-treatment group compared with groups treated with TNF-alpha or hyperthermia alone. In the same comparison, the life span of EAT-bearing mice in the combined-treatment group was prolonged.

Cisplatin sensitivity and thermochemosensitisation in thermotolerant cDDP-sensitive and -resistant cell lines

Development of thermotolerance is an important phenomenon that must be considered when thermochemotherapy with multiple heat treatments is used clinically. To study the effect of thermotolerance on cellular cisplatin (cDDP) sensitivity at 37 degrees C and 43 degrees C in cell lines with different cDDP sensitivities, two Ehrlich ascites tumour cell lines (one with high cDDP sensitivity and one with in vitro acquired cDDP resistance) were used. The results indicate that in both cell lines the state of thermotolerance per se did not affect the cDDP sensitivity at 37 degrees C. Thus, general elevations in 'all' heat shock protein levels as found in thermotolerant cells apparently do not influence cDDP sensitivity to a considerable extent. The sensitising effect of a (second) heat treatment given simultaneously with a cDDP treatment was less in thermotolerant cells. Thermal enhancement ratios (TERs) at the 10% survival level for heat doses of 43 degrees C for 30 min or 43 degrees C for 60 min were reduced by a factor of 1.6 and 2.1 in cDDP-resistant and -sensitive thermotolerant cells respectively, as compared with control cells. Thus, protection against heat damage in thermotolerant cells seems to be paralleled by diminished thermal chemosensitisation. Although the effect of thermotolerance on the cDDP-sensitising effect was less pronounced in the resistant cells, a modifying effect on the resistance factor was not achieved.

Enhanced inhibitory effects of hyperthermia combined with ascorbic acid on DNA synthesis in Ehrlich ascites tumor cells grown at a low cell density

Effects of hyperthermia and cell densities on inhibitory activity of ascorbic acid on DNA synthesis in Ehrlich ascites tumor cells were studied. When cells at a low density of 5 x 10(3)/ml were treated with 75 microM ascorbic acid for 1 h, DNA synthesis was inhibited after treatment at 37 degrees C and the inhibition was significantly enhanced at 42 degrees C. At a cell density as high as 1 x 10(5)/ml, however, inhibition did not occur at 37 degrees C or 42 degrees C. In contrast, dehydroascorbic acid was inactive even at a low cell density under similar conditions. Inhibitory effects of ascorbic acid on DNA synthesis were also markedly enhanced by treatment at 40 degrees C. DNA synthesis was not inhibited in the absence of the drug. Furthermore, mice transplanted with cells treated with a combination of 75 microM ascorbic acid and hyperthermia at 42 degrees C, considerably prolonged their survival time in comparison with untreated cells. Addition of ascorbic acid to hyperthermia is suggested to be an advantageous treatment for cancer.

Elimination of Ehrlich tumours by ATP-induced growth inhibition, glutathione depletion and X-rays

ATP-induced tumour growth inhibition is accompanied by a selective decrease in the content of the tripeptide glutathione (GSH) within the cancer cells in vivo. Depletion of cellular GSH sensitizes tumours to chemotherapy and radiation, but the usefulness of this depletion depends on whether the levels of GSH can be reduced in the tumour relative to normal tissues. We report here that administration of ATP in combination with diethylmaleate and X-rays leads to complete regression of 95% of Ehrlich ascites tumours in mice. This shows that an aggressive tumour can be eliminated by using a therapy based on modulation of GSH levels in cancer cells.

Non-immunologically-mediated cytotoxicity of Lactobacillus casei and its derivative peptidoglycan against tumor cell lines

Lactobacillus casei, which shows antitumoral activity mediated by the stimulation of cellular defence mechanisms, and its peptidoglycan were tested for their ability to inhibit in vitro the viability of various murine (Yac-1, P815, Ehrlich ascites tumor, mammary carcinoma) and human (K562, KB) tumor cell lines through primary cytotoxic activity. Treatment of these tumor line with L. casei or its peptidoglycan at different doses and for different times demonstrated a decrease in viability by 25-30%. This cytotoxic activity was revealed by 51Cr release, succinate dehydrogenase (SDH) activity, ATP assays and morphological alterations in the treated tumor cells. Immunoenzymatic assays (ELISA) showed a precise ratio of binding between Ehrlich ascites or YAC-1 cell membranes and peptidoglycan. This binding is discussed with regard to the structure of the peptidoglycan molecule. The results suggest that L. casei and its derivative peptidoglycan have both a stimulating activity in normal cells and an inhibiting activity in tumor cells, as has been found for other immunomodulatory complexes.

The immunostimulating activities of anti-tumor polysaccharides from Pseudostellaria heterophylla

We have previously shown that a mitogenic fraction (PH-I) separated from Pseudostellaria heterophylla exhibits both immunomodulatory and anti-tumor activities. In the present study, PH-I was further purified by gel filtration chromatography and the resulting three fractions (PH-I A, PH-I B and PH-I C) were assessed for their anti-tumor activity in vivo. It was found that fraction PH-I C from P. heterophylla could markedly suppress the growth of EAT cells in vivo. Mechanistic studies have shown that i.p. injection of PH-I C into mice could enhance the phagocytic activity of thioglycollate-elicited peritoneal macrophages. Moreover, PH-I C showed a potent activating effect on the cytotoxic activity of natural killer (NK) cells and alloreactive cytotoxic T cells (Tc) as well as increased the MurIL-2-induced lymphokine activated killer cell (LAK) activity in vitro. In addition, PH-I C could increase the number of tumor infiltrating lymphocytes (TILs) in the tumor site of WEHI-164-bearing mice. Finally, i.v. injection of PH-I C significantly elevated the levels of IFN-gamma and IL-4 in sera of EAT-bearing mice.

Enhancement of doxorubicin-induced cytotoxicity by hyperthermia in Ehrlich ascites cells

Hyperthermia (HPT) at 43 degrees C for 30 min increased the cytotoxic activity of doxorubicin against the growth of Ehrlich ascites carcinoma cells. There was more delay in tumor growth with 89% inhibition in the tumor volume and 90% increase in the survival of the tumor-bearing animals compared to control group. Combination of HPT with doxorubicin showed a more pronounced inhibitory effect on tumor content of DNA, RNA, protein, cholesterol, total lipid and acid phosphatase activity. HPT did not significantly affect the doxorubicin uptake into tumor cells, but it has some inhibitory effect on some vital components. Along with other results, our data suggest the benefit of using HPT to enhance the cytotoxic activity of doxorubicin with a consequent reduction of doxorubicin dose and hence a decrease of its serious side effects.

Antitumor activity of an immobilized peroxidase system against murine Ehrlich ascites is mediated by the immune system

Earlier studies have shown that a mixture of glucose oxidase and a peroxidase exerts a tumoricidal effect on rats bearing Novikoff hepatomas when the enzyme mixture is injected intraperitoneally. The enzyme mixture was shown to be nontoxic when injected into healthy animals at levels up to 600 times the therapeutic dose. In the present study, we have evaluated the possibility that the host immune defense system may be involved in the antitumor activity of the peroxidase system, using the murine Ehrlich ascites tumor as the target. The results revealed that the antitumor activity of the peroxidase system is absent in tumor-bearing animals whose immune system has been compromised by whole body gamma-irradiation or by an induced selenium deficiency. The peroxidase system was also found to be inactive in tumor-bearing mice whose immune system was suppressed by the administration of cyclosporin A as well as in athymic (nu/nu) mice. These results indicate that T lymphocytes may directly or indirectly be involved in the in vivo antitumor activity of the peroxidase system. This could explain the observed high selectivity toward tumor cells by the enzyme system in vivo and its lack of toxicity in healthy animals.

Sensitizing for cis-diamminedichloroplatinum(II) action by hyperthermia in resistant cells

cDDP-resistant Ehrlich ascites tumour (EAT) cells (ER cells) were tested for cellular content of total glutathione, heat sensitivity, cDDP sensitivity and synergistic effects of a combined treatment of heat and chemotherapy. In comparison with the non-resistant EAT cells (EN) the ER cells had an elevated level of glutathione. Treatment with D,L-buthionine-(S,R)-sulphoximine (BSO), resulting in almost complete depletion of cellular glutathione, did not cause drug sensitization. The ER cells were somewhat less heat sensitive compared with the EN cells. Heat chemosensitization was observed for the EN cells as well as for the ER cells. At 43 degrees C (but not at 42 degrees C) the thermal enhancement ratio (TER) for cDDP toxicity was significantly higher in the ER cells. The total number of cells killed by the combined treatment was less in the ER cells than in the EN cells. After analysing existing literature, combined with the current results, it is concluded that although cDDP-resistant cells can often considerably be chemosensitized by hyperthermia, in most cases the difference in cDDP sensitivity cannot be overcome totally. In those situations where cDDP-resistant cells are more sensitive to heat and also show a high TER, especially at clinically relevant temperatures, hyperthermia as added modality is indicated for clinical treatment.

Immune response developing in tumorous organism as a result of immunotherapy. Chance of recovery?

S-allylgutimine has immunostimulant and tumor cell inhibitory activities. This complex action may be a result of the stimulation of IL-2 production. The effectiveness of immunotherapy depends on the uncoupling of IL-2 downregulation. This principle can be widely used with those immunological diseases where IL-2 level is decreased through downregulation. The Kokonov reaction, which was used originally to indicate tumors, is presumably a marker of immunoreactivity. According to one hypothesis no specific antigen can be found on the surface of neoplastic cells but another type, 'weak antigen' appears, which originates from the alteration of a cell surface glycoprotein beta 1-6 saccharide chain branching that is directly related to the increased immune reactivity. The inhibition of downregulation enhances the elimination of neoplastic cells whose membrane surface glycoproteins are altered.

Agglutinins from aquatic insects--tumor cell agglutination activity

Agglutinins were identified in whole body extracts of aquatic insects by means of murine tumor cell agglutination, using sarcoma 180 ascites, Ehrlich, and MM-46 cells. Screening revealed agglutinins in 5 of 10 of the larvae tested, and in 2 of 6 of the water-dwelling adult insects; Gerris paludum insularis and Gyrinus japonicus. Only the agglutinin from adult G. paludum also agglutinated human erythrocytes. An ascites tumor was converted into a solid form in vivo after administration of G. paludum agglutinin. The observation that these aquatic insect agglutinins preferentially agglutinate tumor cells has considerable implications in terms of anti-tumor effects such as inhibition of cell proliferation and metastasis.

Effects of hyperthermia on the metabolism of 5-fluorouracil in vitro

The effects of hyperthermia (38-42 degrees C) on the metabolism of 5-fluorouracil (5-FU) were examined using Ehrlich tumour cells (E-cells) and Sarcoma-180 cells (S-180 cells) in vitro. A temperature-dependent elevation of the intracellular concentration of 5-FU was observed in both types of tumour cell after incubation with 5-FU. The levels of 5-fluorouridine (FUR) and 5-fluoro-2'-deoxyuridine (FdUR), which are active metabolites of 5-FU, increased significantly after treatment of cells with 5-FU and hyperthermia. The highest concentrations of these active metabolites were found when the cells were incubated at 39 degrees C. The levels of alpha-fluoro-beta-ureido-propionic acid (FUPA) and F-beta-alanine, which are inactive catabolic metabolites of 5-FU, also increased when the cells were incubated at 39 degrees C. The percentage inhibition of thymidilate synthetase (TS) activity remained high (about 60-70%) at 39 degrees C for 240 min. These results suggest that the optimal temperature for potentiating the intracellular metabolism of 5-FU, in terms of both activation and inactivation, is 39 degrees C in vitro.

Effect of hyperthermia and protein kinase C inhibitors on DNA synthesis and cell proliferation on Ehrlich ascites tumour cells in vitro

Effect of hyperthermia and/or protein kinase inhibitors on DNA synthesis and cell proliferation was investigated in Ehrlich ascites tumour cells in vitro. Both H-7 and H-8, potent inhibitors of protein kinase C, suppressed DNA synthesis significantly, but HA1004, an inhibitor of cAMP- and cGMP-dependent protein kinase, did not. Hyperthermia increased greatly the suppressive activity of H-7 and H-8 but not that of HA1004. H-7 also inhibited cell growth. These results suggest that the inhibition of protein kinase C enhances the suppression of DNA synthesis and the proliferation of tumour cells by hyperthermia.

In vivo production of tumor necrosis factor for the treatment of mice bearing Ehrlich ascites tumor

Tumor necrosis factor (TNF) was produced in mice bearing Ehrlich ascites tumor (EAT) by priming with zymosan and subsequently challenging with lipopolysaccharide. The optimal conditions for the in vivo production of TNF in treating EAT bearing mice were established. The endotoxin shock induced in mice during TNF production could be minimized by the combined administration of sulindac and mannoheptulose. The endogenous TNF produced could suppress proliferation of EAT cells as well as prolong the survival time of mice bearing small tumors.

Cytotoxicity of mitomycin C and carboquone combined with hyperthermia against hypoxic tumor cells in vitro

Enhancement of the cytotoxicity of mitomycin C (MMC) and carboquone (CQ) by hypoxia at elevated temperature was examined using the SDI test of mouse Sarcoma 180 and Ehrlich cells and clonogenic assay of HeLa cells. When Sarcoma 180 and Ehrlich cells were incubated at 43 degrees C for 2-10 h, the hyperthermic effect was enhanced by hypoxia. The succinate dehydrogenase activity of the cells was reduced by hyperthermia to a greater extent in the presence of hypoxia (O2:5%) than under conditions of aeration (O2:20%). When the cells were exposed to various concentrations of MMC and CQ, under hypoxia, activity of the drugs was enhanced compared to the findings under conditions of aeration. The enhancement was prominent in case of drugs and hyperthermia combined. Clonogenicity of hypoxic HeLa cells was also reduced to a greater extent with this combination than in case of aerated cells. We tentatively speculate that hyperthermo-chemotherapy using MMC and CQ has a potential to attack selectively hypoxic cells present in a solid tumor.

Effect of hyperthermia on thymidine salvage as related to DNA synthesis

The effect of increasing temperature up to 43 degrees C on thymidine (TdR) salvage, i.e. uptake of TdR, thymidine kinase (TK) activity, intracellular amount of thymidinetriphosphate (dTTP) and specific activity of 3H-dTTP and incorporation of dTTP into DNA, was studied in ascites tumour cells in vitro. While the uptake of [3H]TdR was almost unchanged up to 40.5 degrees C and 2.4 h followed by a decrease at later times and higher temperatures, TK activity declined already after 30 min in a temperature-dependent way, leading to a decrease in cellular amount of dTTP reaching almost undetectable values at 43 degrees C and 6.0 h. The specific activity of [3H]dTTP in the cell was elevated at 39 degrees C and 43 degrees C, but somewhat reduced at 40.5 degrees C. Incorporation into DNA of [3H]TdR decreased in a temperature-dependent way with increasing incubation time. After correction for specific activity of [3H]dTTP, however, the incorporation of [3H]TdR into DNA at 39 degrees C and 40.5 degrees C was unchanged up to 2.4 h and for 40.5 degrees C up to 6.0 h, while incorporation into DNA at 43 degrees C was still reduced. The overall protein synthesis was also reduced in a temperature-dependent way. We concluded that phosphorylation of TdR to dTMP was more sensitive to moderately elevated temperatures than uptake of TdR and DNA synthesis per se, caused by a reduced TK activity. The decline in TK activity was probably due to a decrease in TK polypeptide synthesis.

Antitumor action of an acidic glycoprotein (SAGP) from Streptococcus pyogenes in mice

We have shown that an acidic glycoprotein (SAGP) isolated from a cell-free extract of Streptococcus pyogenes (Su strain) prolonged the life-span of Ehrlich ascites carcinoma (EAC)-bearing mice. The present study shows that the life-span prolonging effect of SAGP in EAC-bearing mice was reduced by whole body X-irradiation before EAC inoculation. SAGP (500 micrograms protein/mouse/day X 4, i.p.) also showed a life-span prolonging effect (T/C (%) = 169) on Meth A fibrosarcoma (Meth A)-bearing mice, but the effect of SAGP was abrogated by an i.p. pretreatment of the host with carrageenan, an antimacrophage agent. The spleen cells from the Meth A-inoculated and SAGP-treated mice were found to have a considerable cytostatic activity by a 3H-thymidine incorporation assay. But the activity disappeared in the presence of carrageenan. These results suggest that the in vivo antitumor effects of SAGP are mediated through its immunomodulating action.

The effect of anti-AFP-F(ab)'2 and adriamycin conjugate on transplantable tumors in mice

Efficacy of the conjugate anti-AFP-F(ab)'2 with adriamycin, anti-AFP-F(ab)'2-adr, against transplantable tumors was studied in mice. The results showed that LD50 of anti-AFP-F(ab)'2-adr in mice was 7.43 mg/kg and that anti-AFP-F(ab)'2-adr in a dose of 1/10-1/5 LD50 could inhibit the growth of transplanted hepatocellular carcinoma. In addition, anti-AFP-F(ab)'2-adr with local application of AFP could markedly inhibit the growth of transplanted Ehrlich ascites cancer. From the above it is suggested that anti-AFP-F(ab)'2-adr can be used to treat hepatic carcinoma with satisfactory results.

Protective effect of fungal growth product (6MFA), assessed therapeutically against Ehrlich's ascites tumor in Swiss mice

6MFA is a growth product of the fungus Aspergillus ochraceus (ATCC 28706) obtained by fermentation in stationary culture. It has both interferon inducing and antiviral properties, in vivo and in vitro, with a relatively high margin of safety (9, 17, 18). Ehrlich's ascites tumor bearing Swiss albino male mice were treated with 0.5 ml of acqueous preparation of 6MFA (0.75 mg total solids) i.p. in a therapeutic regimen schedule; the sham treated mice received only PBS. 6MFA treatment produced an increase in mean survival time over the untreated controls, restricted the body weight increase due to ascites and decreased the rate of mortality. As much as 100% of survival response was obtained in the group treated with 0.5 ml of 6MFA at the rate of one inoculation per week for 5 weeks. In general a dose-dependent response was seen in the antitumor effect of 6MFA against Ehrlich's ascites tumor in Swiss mice. Delay in administration of 6MFA to tumor bearing mice affected the survival rate.

Antigen shedding vs. development of natural suppressor cells as mechanism of tumor escape in mice bearing Ehrlich tumor

C57BL/6J mice immunized with devitalized Ehrlich tumor (ET) cells produce high serum levels of IgM antibodies to ET cell-surface carbohydrates that are critical in the observed resistance against this tumor. However, this response is not found in ET-bearing mice at any stage of tumor development. Since previous studies had shown splenic natural suppressor (NS) cells in ET-bearers, their role in such IgM impairment was assessed. Here we show that tumor-bearers' spleen cells (TBSC) are unable to produce IgM in vitro in response to LPS, due to the presence of NS cells. Nevertheless, TBSC do produce IgM antibodies to ET cell-surface carbohydrates in increasing amounts as the tumor progresses. Yet these antibodies are not detected in sera of ET-bearers and are greatly decreased in immunized mice with a growing tumor. Moreover, increasing amounts of circulating carbohydrates, able to absorb most specific IgM, are found in ET-bearing sera associated with a large molecular size structure(s). These carbohydrates are also found in ET cell-culture supernatants and cell-free ascites fluid derived from this tumor, indicating their tumor origin. Taken together, our results indicate that lack of specific IgM antibodies in ET-bearing mice is not due to faulty production, but to in vivo absorption by carbohydrates shed from ET cells in increasing amounts as the tumor progresses. Thus, NS cells are unable to suppress this IgM production in vivo, despite the strong suppressor activity they show for many responses in vitro.

Enhanced inhibition of DNA synthesis and release of membrane phospholipids in tumour cells treated with a combination of acylated ascorbate and hyperthermia

Combined antitumour effects of mono- or diacyl ascorbates and heat treatment were studied in comparison with the parent compound, L-ascorbic acid (AsA). At 37 degrees C, 75 microM 6-O-palmitoyl (6P) and 6-O-stearoyl (6S) ascorbates appreciably inhibited DNA synthesis in Ehrlich ascites tumour cells. Hyperthermia at 42 degrees C for 1 h increased the inhibition. In contrast, AsA or 2,6-O-dipalmitoyl ascorbate (DP), even at concentrations as high as 100 microM, caused no inhibition at 37 degrees C or 42 degrees C. The results suggest that the inhibitory action is not caused by the fatty acid moiety itself; it is more likely to be caused by the balance in the hydrophobicity and hydrophilicity of the monoacylated AsA, a property not found in diacylated or intact AsA. Inhibition of DNA synthesis caused by exposure to 6P during hyperthermia of tumour cells was greater than before or after hyperthermia. 6P or 6S, but not AsA or DP, released phospholipids such as phosphatidylcholine and phosphatidylethanolamine from cells labelled with [14C]oleic acid, as shown by radiocurves taken from thin-layer chromatograms. Damage of the cell membrane seemed to be involved in the inhibition of DNA synthesis caused by monoacylated AsA, which is surface-active.