Abstract 1159: Hexamethylene bisacetamide (HMBA) inhibits the induction of alkaline phosphatase by butyrate in some bladder and colon cancer cell lines

Induction of alkaline phosphatase in colon cancer cells by inhibitors of histone deacetylase activity has been widely used to monitor the induction of differentiation. We have previously identified three human bladder cancer cell lines in which alkaline phosphatase activity can be induced by inhibitors of histone deacetylase (5637, HT1197 and HT1376 cells). In earlier work it was observed that some bromodomain inhibitors inhibit growth and induction of alkaline phosphatase in these cells. After a recent report that HMBA acts as a bromodomain inhibitor, the effects of HMBA on growth and induction of alkaline phosphatase were investigated in two colon cancer cell lines (Caco-2 and HT29) and in 5637, HT1197 and HT1376 bladder cancer cells. Growth was monitored by staining with sulforhodamine B. Incubation with 2 mM butyrate for 72 hours caused induction of alkaline phosphatase in the five cell lines. In some cell lines there was inhibition of growth and of the induction of alkaline phosphatase activity by 2 mM HMBA. Increasing the HMBA concentration to 5 mM caused significant growth inhibition in all five cell lines and significant inhibition of induction of alkaline phosphatase activity by 2 mM butyrate in the 5637, Caco-2 and HT1376 cells, whether expressed as total activity or activity per unit protein. Although the effect of HMBA on induction of alkaline phosphatase in HT29 cells was not statistically significant there is evidence in the literature for inhibition with longer incubation times. The most marked effects on enzyme induction were seen with the HT1376 bladder cancer cells and this distinction was in line with previous studies on the combined effects of butyrate and the well-established bromodomain inhibitor, JQ1. HMBA has been found by several investigators to be an effective inducer of differentiation in erythroleukemia cells as judged by hemoglobin production. The lack of induction of alkaline phosphatase by HMBA as a single agent in any of the cell lines investigated in the present work suggests that different mechanisms of induction of differentiation operate in erythroleukemia cells than in bladder and colon cancer cells.

Citation Format: Michael A. Lea. Hexamethylene bisacetamide (HMBA) inhibits the induction of alkaline phosphatase by butyrate in some bladder and colon cancer cell lines [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1159.

Abstract 227: Maltose enhanced the growth of bladder and colon cancer cells unlike some other disaccharides: Cellobiose, isomaltose, lactose, and sucrose

The addiction of most cancer cells to the metabolism of glucose is well known. The metabolism by cancer cells of other saccharides is less well characterized. We have studied the impact on growth of human bladder and colon cancer cells of mono- and disaccharides. The standard RPMI 1640 medium contains 2 mg glucose per ml. Substitution for glucose by other monosaccharides (fructose, galactose and mannose) resulted in similar growth in some cell lines but greatly diminished growth in others. For the Caco-2 and HT29 colon cancer cells, co-incubation with 2-deoxyglucose was more inhibitory for growth with fructose than with glucose as substrate. There was a similar situation with some bladder cancer cell lines (5637, HT1197 and RT4) whereas with other bladder cancer cells (HT1376, T24 and UM-UC-3) 2-deoxyglucose caused greater inhibition with glucose. In those cell lines in which alkaline phosphatase activity could be induced after incubation with butyrate (Caco-2, HT29, 5637, HT1197 and HT1376), induction by butyrate was observed with any of the monosaccharides. Similarly with the disaccharides lactose, maltose and trehalose there was induction of alkaline phosphatase by butyrate. In the course of this work it was apparent that maltose could enhance growth to an extent that was sometimes not significantly different to that seen with glucose and was not seen with cellobiose, isomaltose, lactose or sucrose. HT29 cells were the only cell line to have a substantial increased growth with trehalose. The increased growth with maltose was inhibited by 2-deoxyglucose. In conclusion, maltose increased growth of bladder and colon cancer cells without a period of adaptation.

Citation Format: Michael A. Lea, Charles desBordes. Maltose enhanced the growth of bladder and colon cancer cells unlike some other disaccharides: Cellobiose, isomaltose, lactose, and sucrose [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 227.

Abstract 4734: Response of bladder and colon cancer cells to combined treatment with bromodomain and histone deacetylase inhibitors

Since bromodomains of proteins bind acetylated histone lysine side chains while histone deacetylase inhibitors increase the level of histone acetylation, it seemed possible that bromodomain inhibitors might counteract some cellular responses to the action of histone deacetylase inhibitors. We have examined this possibility in bladder and colon cancer cells treated with combinations of bromodomain and histone deacetyalase inhibitors. Actions on growth and on the induction of alkaline phosphatase activity by histone deacetylase inhibitors were investigated. Compounds studied were the bromodomain inhibitors JQ1, I-BET763, olinone and RVX208 and the histone deacetylase inhibitors butyrate, RGFP966 and valproate. The cells studied were ones in which alkaline phosphatase activity is induced by histone deacetylase inhibitors. They were bladder cancer lines 5637, HT1197 and HT1376 and colon cancer lines Caco-2 and HT29. The combination that most clearly showed decreased induction of alkaline phosphatase activity by a bromodomain inhibitor was butyrate plus JQ1. If this action represents blocking combination of bromodomain-containing transcription factors with acetylated histones one might anticipate that inhibitory effects of histone deacetylase inhibitors on growth might be mitigated by combination with bromodomain inhibitors. However, the tendency was for additive effects on growth inhibition in accord with some data in the literature. Of the bromodomain inhibitors that were studied, JQ1 was the most effective as a growth inhibitor and olinone was the least effective. The mechanism for additive effects of bromodomain and histone deacetylase inhibitors on growth remains to be defined but antagonistic effects on cell differentiation appear possible.

Citation Format: Michael A. Lea, Niyati Patel, Charles desBordes. Response of bladder and colon cancer cells to combined treatment with bromodomain and histone deacetylase inhibitors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4734.

Effects of Biguanides on Growth and Glycolysis of Bladder and Colon Cancer Cells

Background/ Aim: There is evidence that inhibitory effects of biguanides on oxidative phosphorylation require uptake of biguanides into the mitochondria. In this study the action of two biguanides that enter the mitochondria (buformin and phenformin) were compared with the action of two biguanides with poor uptake (phenyl biguanide and proguanil).

MATERIALS AND METHODS

Effects on growth, glucose uptake and medium acidification were studied with two human colon cancer cells and seven bladder cancer cell lines.

RESULTS

Growth inhibition was greatest with proguanil followed by phenformin, buformin and phenylbiguanide. In contrast, increased glucose uptake and acidification of the medium was observed with buformin and phenformin, with no change or less acidification of the medium with phenyl biguanide and proguanil.

CONCLUSION

The effect of biguanides on glucose metabolism requires mitochondrial uptake while the mechanism for growth inhibition by biguanides remains to be defined.

Designing a broad-spectrum integrative approach for cancer prevention and treatment

Targeted therapies and the consequent adoption of "personalized" oncology have achieved notable successes in some cancers; however, significant problems remain with this approach. Many targeted therapies are highly toxic, costs are extremely high, and most patients experience relapse after a few disease-free months. Relapses arise from genetic heterogeneity in tumors, which harbor therapy-resistant immortalized cells that have adopted alternate and compensatory pathways (i.e., pathways that are not reliant upon the same mechanisms as those which have been targeted). To address these limitations, an international task force of 180 scientists was assembled to explore the concept of a low-toxicity "broad-spectrum" therapeutic approach that could simultaneously target many key pathways and mechanisms. Using cancer hallmark phenotypes and the tumor microenvironment to account for the various aspects of relevant cancer biology, interdisciplinary teams reviewed each hallmark area and nominated a wide range of high-priority targets (74 in total) that could be modified to improve patient outcomes. For these targets, corresponding low-toxicity therapeutic approaches were then suggested, many of which were phytochemicals. Proposed actions on each target and all of the approaches were further reviewed for known effects on other hallmark areas and the tumor microenvironment. Potential contrary or procarcinogenic effects were found for 3.9% of the relationships between targets and hallmarks, and mixed evidence of complementary and contrary relationships was found for 7.1%. Approximately 67% of the relationships revealed potentially complementary effects, and the remainder had no known relationship. Among the approaches, 1.1% had contrary, 2.8% had mixed and 62.1% had complementary relationships. These results suggest that a broad-spectrum approach should be feasible from a safety standpoint. This novel approach has potential to be relatively inexpensive, it should help us address stages and types of cancer that lack conventional treatment, and it may reduce relapse risks. A proposed agenda for future research is offered.

Abstract 32: Inhibition of cancer cell growth by combined treatment with lactate dehydrogenase (LDHA) inhibitors and either phenformin or inhibitors of 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 3 (PFKFB3)

The tendency for enhanced glycolysis in cancer cells presents a target for chemotherapy. In previous studies we observed that proliferation of colon and bladder cancer cells can be inhibited by treatment with either phenformin or an inhibitor of PFKFB3 namely 3-(3-pyridinyl)-1-(4-pyridinyl)-2-propen-1-one (3PO). In the present work we have examined the action of two inhibitors that are effective at lower concentrations than 3PO, namely 1-(3-pyridinyl)-3-(2-quinolinyl)-2-propen-1-one (PQP) and 1-(4-pyridinyl)-3-(2-quinolinyl)-2-propen-1-one (PFK15). The LDHA inhibitors that we chose to study in increasing order of IC50s were methyl 1-hydroxy-6-phenyl-4-(trifluoromethyl)-1H-indole-2-carboxylate (NHI-2) < isosafrole < oxamate. A synergistic anti-cancer effect of phenformin and oxamate has been reported. In the present work with colon and bladder cancer cells, additive but not synergistic growth inhibitory effects were seen with the LDHA inhibitors of which NHI-2 was effective at the lowest concentrations. Growth inhibition with PQP and PFK15 was compared in colon (Caco-2 and HT29) and bladder cancer cells (5637, HT1376, RT4, SW780, T24, TCCSUP and UM-UC-3). Apart from RT4 cells where the effects were similar, the effects were somewhat greater with PFK15 than with PQP and for both compounds the actions were seen at lower concentrations than in previous studies with 3PO. Actions on medium acidification and glucose uptake are more readily observed in the most rapidly growing cell lines. Effects of phenformin on medium pH and glucose concentration were decreased by the PFKFB3 and LDHA inhibitors that were examined. In accord with our previous studies on inhibitors of glycolysis, the increased medium acidification and glucose uptake caused by phenformin could be blocked by combined treatment with PFKFB3 or LDHA inhibitors. At the same time additive growth inhibitory effects were observed. The results supported the concept that combined treatment with phenformin and inhibitors of glycolysis can cause additive inhibition of cell proliferation while mitigating the lactic acidosis caused by phenformin as a single agent.

Citation Format: Michael A. Lea, Yolanda Guzman, Charles desBordes. Inhibition of cancer cell growth by combined treatment with lactate dehydrogenase (LDHA) inhibitors and either phenformin or inhibitors of 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 3 (PFKFB3). [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 32.

Inhibition of Growth by Combined Treatment with Inhibitors of Lactate Dehydrogenase and either Phenformin or Inhibitors of 6-Phosphofructo-2-kinase/Fructose-2,6-bisphosphatase 3

Enhanced glycolysis in cancer cells presents a target for chemotherapy. Previous studies have indicated that proliferation of cancer cells can be inhibited by treatment with phenformin and with an inhibitor of 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase 3 (PFKFB) namely 3-(3-pyridinyl)-1-(4-pyridinyl)-2-propen-1-one (3PO). In the present work, the action of two inhibitors that are effective at lower concentrations than 3PO, namely 1-(3-pyridinyl)-3-(2-quinolinyl)-2-propen-1-one (PQP) and 1-(4-pyridinyl)-3-(2-quinolinyl)-2-propen-1-one (PFK15) were investigated. The inhibitors of lactate dehydrogenase (LDHA) studied in order of half-maximal inhibitory concentrations were methyl 1-hydroxy-6-phenyl-4-(trifluoromethyl)-1H-indole-2-carboxylate (NHI-2) < isosafrole < oxamate. In colonic and bladder cancer cells, additive growth inhibitory effects were seen with the LDHA inhibitors, of which NHI-2 was effective at the lowest concentrations. Growth inhibition was generally greater with PFK15 than with PQP. The increased acidification of the culture medium and glucose uptake caused by phenformin was blocked by combined treatment with PFKFB3 or LDHA inhibitors. The results suggest that combined treatment with phenformin and inhibitors of glycolysis can cause additive inhibition of cell proliferation and may mitigate lactic acidosis caused by phenformin when used as a single agent.

Inhibition of Growth of Bladder Cancer Cells by 3-(3-Pyridinyl)-1-(4-pyridinyl)-2-propen-1-one in Combination with Other Compounds Affecting Glucose Metabolism

In seven out of eight human bladder cell lines that were examined herein, growth was more dependent on the presence in the incubation medium of glucose rather than glutamine. The exception was the slowly growing RT4 cells that were more glutamine-dependent. Growth of all the cell lines was reduced by an inhibitor of 6-phosphofructo-2-kinase/2,6-bisphosphatase 3, namely 3-(3-pyridinyl)-1-(4-pyridinyl)-2-propen-1-one (3PO). Growth was also reduced by three compounds that reduce the conversion of glucose to lactate: namely 2-deoxyglucose, butyrate and dichloroacetate. Additive effects were seen when these molecules were combined with 3PO. Treatment of bladder cancer cells with phenformin resulted in growth inhibition that was frequently accompanied by increased glucose uptake and acidification of the medium that was blocked by co-incubation with 3PO. The actions of 3PO suggest that inhibitors of PFKB3 merit further investigation in the treatment of bladder cancer and they may be useful agents in combination with other drugs that inhibit cancer cell proliferation.

Abstract 1169: Growth regulation of bladder cancer cells by compounds that affect glucose metabolism

The observation that cancer cells tend to exhibit enhanced rates of glycolysis presents a target for therapeutic regulation of cancer cell growth by molecules that regulate glucose metabolism. We have extended our earlier studies on colon cancer cells with an examination in bladder cancer cells of the action of an established inhibitor of PFKFB3, namely 3-(3-pyridinyl)-1-(4-pyridinyl)-2-propen-1-one (3PO) as a single agent and in combination with other molecules that affect glycolysis and proliferation. 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 3 (PFKFB-3) is an enzyme regulating glycolysis in many tumor cells. Cell growth was monitored by staining with sulforhodamine B. Of the 8 cell lines examined, growth was most rapid in the T24 and UM-UC-3 bladder cancer cells. The slowest growth was seen with RT4, TCCSUP and HT1197 cells while intermediate growth rates were observed with 5637, HT1376, and SW780 cells. Glucose uptake from the medium and acidification of the medium over a 72-hour incubation tended to correlate with growth rate. Thus the greatest changes were seen with the T24 and UM-UC-3 cell lines and the least change was seen with RT4 and TCCSUP cells. Growth was inhibited when glutamine was omitted from the medium but growth was blocked in the absence of glucose except for RT4 cells in which growth was inhibited more in the absence of glutamine. Treatment with 10 μM 3PO as a single agent for 72 hours caused average growth inhibition in the range of 25-50% without apparent relationship to the control growth rates of the cell lines. Additive inhibitory effects on growth were observed when cells were coincubated with 3PO and either 1 mM 2-deoxyglucose, 50 μM phenformin or 1 mM butyrate. In addition to being growth inhibitory, butyrate also caused significant induction of alkaline phosphatase activity in some cell lines. When cells were incubated with phenformin as a single agent, there was generally an increased acidification of the medium that was diminished by coincubation with 3PO. In conclusion, 3PO was an inhibitor of proliferation of human bladder cancer cells and may be a useful agent in combination with other drugs that inhibit bladder cancer cell proliferation.

Citation Format: Michael A. Lea, Charles desBordes. Growth regulation of bladder cancer cells by compounds that affect glucose metabolism. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1169. doi:10.1158/1538-7445.AM2015-1169

Growth inhibition of colon cancer cells by compounds affecting AMPK activity

AIM: To determine if other molecules reported to modulate AMP-dependent protein kinase (AMPK) activity would have effects resembling those of metformin and phenformin on colon cancer cell proliferation and metabolism.

METHODS: Studies were performed with four human colon cancer cell lines, Caco-2, HCT116, HT29 and SW1116. The compounds that were studied included A-769662, 5-aminoimidazole-4-carboxamide-1-ribofuranoside, butyrate, (-)-epigallocatechin gallate (EGCG), KU-55933, quercetin, resveratrol and salicylates. The parameters that were measured were cell proliferation and viability, glucose uptake, lactate production and acidification of the incubation medium.

RESULTS: Investigations with several molecules that have been reported to be associated with AMPK activation (A-769662, 5-aminoimidazole-4-carboxamide-1-b-D-ribofuranoside, EGCG, KU-55933, quercetin, resveratrol and salicylates) or AMPK inhibition (compound C) failed to reveal increased medium acidification and increased glucose uptake in colon cancer cells as previously established with metformin and phenformin. The only exception was 5-aminosalicylic acid with which there were apparently lower glucose levels in the medium after incubation for 72 h. Further study in the absence of cells revealed that the effect was an artifact due to inhibition of the enzyme-linked glucose assay. The compounds were studied at concentrations that inhibited cell proliferation.

CONCLUSION: It was concluded that treatment with several agents that can affect AMPK activity resulted in the inhibition of the proliferation of colon cancer cells under conditions in which glucose metabolism is not enhanced, in contrast to the effect of biguanides.

Abstract 1855: Regulation of proliferation of colon cancer cells by compounds affecting glycolysis including 3-bromopyruvate, 2-deoxyglucose and biguanides

In earlier work we found that incubation of colon cancer cells with 2-deoxyglucose had an additive inhibitory effect on proliferation with the biguanides, metformin and phenformin, and blocked the acidification of the medium caused by incubation of cells with biguanides. In the present work, studies were performed with Caco-2, HCT116, HT29 and SW1116 colon cancer cells. Metabolism of glucose and acidification of the medium was greater with the more rapidly proliferating cells being greatest with HCT116 cells and least with SW1116 cells. We have seen that, as with 2-deoxyglucose, 3-bromopyruvate can also prevent the lowering of medium pH caused by biguanide treatment. . Inhibition of glucose metabolism paralleled the decrease in acidification of the medium. 3-bromopyruvate inhibited colon cancer cell proliferation. Additive effects with metformin and 3-bromopyruvate were not observed in any of the four colon cancer cell lines but some additive effects were seen with phenformin and 3-bromopyruvate. An additive effect was more notable in combined treatment with 3-bromopyruvate and 2-deoxyglucose. Induction of alkaline phosphatase activity serves as a marker of differentiation in colon cancer cells. The induction of alkaline phosphatase activity by butyrate was not consistently affected by combination with other agents that modified glucose metabolism. The drug combinations that were examined inhibited proliferation in wild type and P53 null HCT116 cells and affected colon cancer lines with different growth rates. Although metformin and phenformin increase glucose metabolism by colon cancer cells while 3-bromopyruvate and 2-deoxyglucose inhibit glucose metabolism, all these compounds have potential inhibitory action on the proliferation of colon cancer cells.

Citation Format: Michael A. Lea, Mehreen Qureshi, Michael Buxhoeveden, Nicolette Gengel, Jessica Kleinschmit, Charles desBordes. Regulation of proliferation of colon cancer cells by compounds affecting glycolysis including 3-bromopyruvate, 2-deoxyglucose and biguanides. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1855. doi:10.1158/1538-7445.AM2013-1855

Regulation of the proliferation of colon cancer cells by compounds that affect glycolysis, including 3-bromopyruvate, 2-deoxyglucose and biguanides

In previous studies performed by our group, we observed that 2-deoxyglucose blocked the acidification of the medium used for culture of colon cancer cells caused by incubation with biguanides and it had an additive inhibitory effect on growth. In the present work, we found that 3-bromopyruvate can also prevent the lowering of pH caused by biguanide treatment. 3-Bromopyruvate inhibited colonic cancer cell proliferation, but the effect was not always additive to that of biguanides and an additive effect was more notable in combined treatment with 3-bromopyruvate and 2-deoxyglucose. The induction of alkaline phosphatase activity by butyrate was not consistently affected by combination with other agents that modified glucose metabolism. The drug combinations that were examined inhibited proliferation of wild-type and p53-null cells and affected colonic cancer lines with different growth rates.

Abstract 4069: 2-deoxyglucose and compound C reversed acidification but enhanced growth inhibition in colon cancer cells treated with metformin and phenformin

A report that effects of butyrate on some cells may be mediated by activation of AMP-dependent kinase (AMPK) prompted us to examine if other AMPK activators can induce differentiation and inhibit proliferation of colon cancer cells in a manner similar to butyrate. Using induction of alkaline phosphatase as a marker, we observed that compound C, an AMPK inhibitor, could decrease the differentiating effect of butyrate or valproate on SW1116 and Caco-2 colon cancer cells. On the other hand, A769662, an activator of AMPK did not increase alkaline phosphatase activity and decreased the induction seen with butyrate. Metformin was observed to be less effective than butyrate in the induction of alkaline phosphatase but was more effective as a growth inhibitor. Phenformin was found to be a more potent growth inhibitor than metformin and both compounds cause acidification of the medium when incubated with colon cancer cells. pH changes were monitored with a pH electrode and by the decrease in absorbance of phenol red at 560 nm. Coincubation with compound C decreased the acidification caused by the biguanides. Combined incubation of 2-deoxyglucose with either of the biguanides prevented the acidification of the medium but enhanced the growth inhibitory effects. Growth inhibitory effects of biguanides appeared less with a tetrazolium reduction assay than with thymidine incorporation but supported the conclusion that combination with 2-deoxyglucose could increase growth inhibition caused by biguanides.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4069. doi:10.1158/1538-7445.AM2011-4069

Addition of 2-deoxyglucose enhances growth inhibition but reverses acidification in colon cancer cells treated with phenformin

A report that effects of butyrate on some cells may be mediated by activation of AMP-activated protein kinase (AMPK) prompted this study which examines if other AMPK activators can induce differentiation and inhibit proliferation of colon cancer cells in a manner similar to butyrate. Using induction of alkaline phosphatase as a marker, it was observed that compound C, an AMPK inhibitor, is able to reduce the differentiating effect of butyrate on SW1116 and Caco-2 colon cancer cells. Metformin was observed to be less effective than butyrate in the induction of alkaline phosphatase but was more effective as a growth inhibitor. Phenformin was found to be a more potent growth inhibitor than metformin and both compounds cause acidification of the medium when incubated with colon cancer cells. Combined incubation of 2-deoxyglucose with either of the biguanides prevented the acidification of the medium but enhanced the growth inhibitory effects.

Recently identified and potential targets for colon cancer treatment

The systemic therapy for colorectal cancer has advanced from essentially a single, partially effective agent, 5-fluorouracil, to a combination of cytotoxics and antibodies offering increased survival. In addition to damage of DNA through agents, such as oxaliplatin and irinotecan, and inhibition of DNA replication, a promising approach involves modifying the control of gene expression, including epigenetic control. Modulation of invasion and metastasis should become increasingly important. Inhibition of growth-factor signaling with small-molecule drugs and antibodies can be a part of this effort. Further progress in the control of gene expression in colon cancer may be achieved with miRNAs and RNA interference if technical problems can be overcome. A number of genetic changes in colorectal cancer progression have been identified and offer targets for future therapy.

Inhibition of growth and induction of alkaline phosphatase in colon cancer cells by flavonols and flavonol glycosides

We observed previously that quercetin can increase the activity of the differentiation markers alkaline phosphatase and dipeptidyl peptidase in Caco-2 colon cancer cells. In the present work, we compared the effects of quercetin on cell proliferation and differentiation with the action of related flavonols and quercetin glycosides. Relative to the action of quercetin, effects on growth and enzyme activities did not always follow parallel trends but quercetin 3-glucoside was notably more potent in both respects while quercetin rutinoside was less active. Of the compounds examined, baicalein and myricetin caused the greatest production of hydrogen peroxide when incubated with the medium. Flavonols can have pro-oxidant effects, but our data suggested that this action was not the sole determinant of growth inhibitory or differentiating effects on Caco-2 cells. Our data indicated that effects of quercetin on colon cancer cell lines can be greatly affected by glycoside modification.

Abstract 567: Inhibition of growth and induction of differentiation by apigenin, baicalein and quercetin in colon cancer cells

There is considerable data to support the concept that polyphenolic molecules that occur in fruits and vegetables may have beneficial effects as cancer chemopreventive agents. We have shown previously that these polyphenolic molecules can induce enzyme markers of differentiation either alone, or in combination with histone deacetylase (HDAC) inhibitors. These data raise the question whether the induction of enzyme markers for differentiation are due to the anti- or pro-oxidant properties of polyphenols. We have compared the action of three flavonol molecules, apigenin, baicalein, and quercetin on four cell lines derived from human colon cells (Caco-2, SW1116, HT-29, and NCM460). The three polyphenols caused increases in alkaline phosphatase activity but no increase or decrease in aminopeptidase activity in Caco-2 cells. There was no induction of differentiation in the other cell lines by the three polyphenols. Since production of hydrogen peroxide has been reported when some polyphenolic compounds are incubated with serum-containing medium, we examined this phenomenon with the three polyphenols. Production of hydrogen peroxide was greater with baicalein than with quercetin or apigenin. When Caco-2 cells were incubated with hydrogen peroxide, there was some increase in alkaline phosphatase, but the concentrations required were higher than for the polyphenols and the magnitude of the effect was less. Further studies were performed with baicalein because that molecule had resulted in greater production of hydrogen peroxide. To test the significance of the hydrogen peroxide formation, we added catalase, but this addition did not prevent the increase in alkaline phosphatase or the decrease in protein synthesis in Caco-2 cells after incubation with baicalein. In addition, we wanted to determine the potential of the three polyphenols in combination with butyrate to increase the activity of alkaline phosphatase in Caco-2 cells. Synergistic effects were seen for the increase in alkaline phosphatase activity in Caco-2 cells for baicalein and quercetin, but not with apigenin. In conclusion, Caco-2 human colon cancer cells are notably sensitive to growth inhibitory and differentiating effects of apigenin, baicalein, and quercetin. It was evident that these polyphenols can have pro-oxidant effects, but our data suggested that this action was not the sole determinant of growth inhibitory or differentiating effects on colon cancer cells.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 567.

Inhibition of growth and induction of differentiation markers by polyphenolic molecules and histone deacetylase inhibitors in colon cancer cells

Previously we found that a fruit-derived polyphenol fraction caused an inhibition of proliferation and an induction of differentiation markers in Caco-2 human colon cancer cells. In the present work, we sought to determine if individual polyphenols would exert similar actions. Proliferation was inhibited by several polyphenolic molecules including gallic acid, ellagic acid, quercetin and resveratrol. In Caco-2 cells, growth inhibition was accompanied by increased specific activities of two differentiation markers, alkaline phosphatase and dipeptidyl peptidase, but not of aminopeptidase. Increased enzyme activities were not seen in HT29 and SW1116 colon cancer cells. In Caco-2 cells there were additive effects of butyrate or valproate and polyphenolic molecules. Histone acetylation was not greatly affected by the polyphenols. Cycloheximide inhibited protein synthesis in the 3 cell types examined but paradoxically, in Caco-2 cells it caused increased specific activities of alkaline phosphatase and dipeptidyl peptidase. Several plant polyphenols can inhibit the growth of colon cancer cells but increased specific activity of some differentiation markers seen in Caco-2 cells did not appear to be a general phenomenon in colon cancer cells.

Inhibition of growth and induction of differentiation of colon cancer cells by peach and plum phenolic compounds

The action of extracts from anthocyanin-enriched plums and peaches on growth and differentiation was studied with human colon cancer cells. Growth inhibitory effects were observed in Caco-2, SW1116, HT29 and NCM460 cells. In Caco-2 cells but not in the other cells studied there was evidence for increased differentiation as judged by increased activity of alkaline phosphatase and dipeptidyl peptidase. A differentiating effect on Caco-2 cells was not seen with cyanidin or cyanidin-3-glucoside but the action of the fruit extracts was additive with the action of butyrate and with the MEK1/2 inhibitor U0126. Fractionation using C18 indicated activity resided within a fraction containing anthocyanins but further fractionation using LH-20 suggested that most of the activity was in a fraction containing polyphenols other than anthocyanins. It was concluded that several peach and plum phenolic molecules can influence growth and differentiation in human colon cancer cells.

Induction of differentiation of colon cancer cells by combined inhibition of kinases and histone deacetylase

The MAP kinase pathway inhibitor U0126 in combination with butyrate promotes differentiation in some colon cancer cell lines. We examined several inhibitors of histone deacetylase (HDAC) in combination with U0126 and other protein kinase inhibitors to see if these effects are general properties of HDAC inhibitors or butyrate alone. Alkaline phosphatase and peptidase activities were examined as markers for cellular differentiation in the human colon cancer cell lines Caco-2 and HT29 and the minimally transformed NCM460. Several HDAC inhibitors caused greater increases of alkaline phosphatase in the cancer cells than in NCM460, in which butyrate was the only HDAC inhibitor that caused a consistent increase. Unlike the JNK and PKC inhibitors examined, the MEK 1/2 inhibitor U0126 induced alkaline phosphatase activity in Caco-2 as a single agent and caused additive effects with HDAC inhibitors. The PI-3 kinase inhibitor LY294002 had little effect alone but enhanced the response of most HDAC inhibitors as did the raf inhibitor GW5074. In addition to butyrate, several HDAC inhibitors can induce differentiation in colon cancer cells and the responses may be enhanced by U0126, GW5074 and LY294002.

Inhibition of cell proliferation by potential peroxisome proliferator-activated receptor (PPAR) gamma agonists and antagonists

This study was initiated to determine if potential PPAR gamma antagonists could block the inhibition of cell proliferation caused by 4-phenylbutyrate. The action of 4-phenylbutyrate differed from other PPAR gamma ligands examined in that it induces histone acetylation. Proliferation of DS19 mouse erythroleukemia cells was inhibited by PPAR gamma agonists (4-phenylbutyrate, rosiglitazone, ciglitazone and GW1929) and by potential PPAR gamma antagonists: BADGE (Biphenol A diglycidyl ether), GW9662, PD068235 and diclofenac. Combined incubations tended to exhibit additive inhibitory effects. Potential PPAR gamma agonists and antagonists inhibited the incorporation of thymidine into DNA of human prostate (PC3), colon (Caco-2) and breast (T47D) cancer cells but also affected NIH3T3 cells that have little or no expression of PPAR gamma. Lipid accumulation in T47D cells was seen after incubation with 4-phenylbutyrate and both potential PPAR gamma agonists and antagonists. The extent to which the effects of 4-phenylbutyrate on cell proliferation are mediated through PPAR gamma or induction of histone acetylation remains an open question. We conclude that potential PPAR gamma antagonists may fail to reverse the growth inhibitory effect of PPAR gamma ligands and may themselves act as growth inhibitory agents.

Induction of histone acetylation and inhibition of growth by phenyl alkanoic acids and structurally related molecules

PURPOSE

A structure-activity study was undertaken to determine the influence of side chain length of phenyl alkanoic acids and the degree of unsaturation of phenyl alkenoic acids on the induction of histone acetylation and inhibition of cancer cell proliferation.

MATERIALS AND METHODS

Studies on cell proliferation were performed with DS19 mouse erythroleukemic cells, PC-3 human prostate cancer cells and Caco-2 human colon cancer cells. Actions on histone deacetylase and the induction of histone acetylation were compared for 4-phenylbutyrate and structurally related molecules.

RESULTS

Increasing inhibition of cell proliferation by phenyl alkanoic acids together with a decrease in cells in S phase and an increase in apoptotic cells was observed with increased chain length between four and ten carbons. Introduction of double bonds into the side chain was associated with increased growth inhibition. In contrast, 4-phenylbutyrate was a more potent inhibitor of histone deacetylase and inducer of histone acetylation than the other phenyl alkanoic acids examined.

CONCLUSIONS

In comparison with the action of 4-phenylbutyrate, actions other than inhibition of histone deacetylase appear to be more important for growth inhibition by longer chain phenyl alkanoic and phenyl alkenoic acids.

Induction of histone acetylation and inhibition of growth of mouse erythroleukemia cells by S-allylmercaptocysteine

Growth-inhibitory effects on DS19 mouse erythroleukemia cells were seen in the micromolar concentration range with allicin and S-allylmercaptocysteine and in the millimolar range with allyl butyrate, allyl phenyl sulfone, and S-allyl cysteine. Increased acetylation of histones was induced by incubation of cells with the allyl compounds at concentrations similar to those that resulted in the inhibition of cell proliferation. The induction of histone acetylation by S-allylmercaptocysteine was also observed in Caco-2 human colon cancer cells and T47D human breast cancer cells. In contrast to the effect on histone acetylation, there was a decrease in the incorporation of phosphate into histones when DS19 cells were incubated with 25 microM S-allylmercaptocysteine. Histone deacetylase activity was inhibited by allyl butyrate, but there was little or no effect with the allyl sulfur compounds examined in this study. A similar degree of downregulation of histone deacetylase and histone acetyltransferase was observed when DS19 cells were incubated with S-allylmercaptocysteine or allyl isothiocyanate. The induction of histone acetylation by S-allylmercaptocysteine was not blocked by a proteasome inhibitor. The mechanism by which S-allylmercaptocysteine induces histone acetylation remains to be characterized. It may be related in part to metabolism to allyl mercaptan, which is a more effective inhibitor of histone deacetylase.

Exposure to a deuterated analogue of phenylbutyrate retards S-phase progression in HT-29 colon cancer cells

Differentiation agents that induce neoplastic cells to regain a normal phenotype and/or cause growth arrest without significantly affecting normal cells represent an attractive option for cancer treatment. Analogues of short chain fatty acids, such as phenylbutyrate (PB), have been studied as clinically relevant agents. In an attempt to improve its pharmacokinetic profile, structural modifications of PB and other fatty acids have been studied. We hypothesize that strategic isotopic modification of PB would result in a longer half-life and thus translate into a more potent differentiation agent for clinical use. Using a colon cancer model, we demonstrated that 2,2,3,3-tetradeuterated PB (D4PB) significantly increased induction of apoptosis and inhibition of cell proliferation as compared with PB and butyrate. Difference in potency could not be explained by the effect of D4PB on the expression of specific regulatory proteins of the apoptotic cascade or from the inhibitory effect of D4PB on histone deacetylase activity. Interestingly, exposure of HT-29 colon cancer cells to D4PB resulted in a slowing of S transit, in contrast to butyrate and PB, which induced a G2/M cell cycle block. This difference in cell cycle effect may explain the differences seen in the potency of the phenotypic changes seen with treatment with D4PB. Further studies are needed to elucidate the mechanisms underlying effects of D4PB on the cell cycle.

Induction of histone acetylation in rat liver and hepatoma by organosulfur compounds including diallyl disulfide

In previous studies, diallyl disulfide induced histone acetylation and differentiation in DS19 mouse erythroleukemic cells. In the present work the potential induction of histone acetylation in tumor-bearing rats was examined. Increased acetylation of histones in liver and Morris hepatoma 7777 was induced by treatment of rats with diallyl disulfide (200 mg/kg body weight), allyl mercaptan (100 mg/kg body weight) and butanethiol (100 mg/kg body weight). The level of histone acetylation was greater in liver than in the hepatoma and the response to the organosulfur compounds tended to be less in the tumor. The data suggested that compounds in garlic or their metabolites may increase the acetylation of core nucleosomal histones and thereby favor cell differentiation.

Induction of histone acetylation in mouse erythroleukemia cells by some organosulfur compounds including allyl isothiocyanate

In previous studies we observed that some allyl sulfides can cause increased acetylation of histones and differentiation in DS19 mouse erythroleukemia cells. In the present work we observed increased acetylation of histones with allyl isothiocyanate and butanethiol but not with butyl sulfide or butyl disulfide. Increased acetylation of histones was established by change in electrophoretic mobility, incorporation of [3H]acetate or immunoblotting. Histone deacetylase in nuclei of DS19 cells was inhibited 74% by 0.5 mM allyl mercaptan and 43% by 0.5 mM butanethiol but was not significantly affected by 0.5 mM allyl isothiocyanate. There was some degree of reversibility in the effect of allyl isothiocyanate when the cells were incubated for 15 hr in fresh medium. The data suggested that allyl isothiocyanate may stimulate histone acetylation rather than inhibit histone deacetylation. Addition of allyl isothiocyanate, however, had very little or no additional effect on the induction of histone acetylation caused by trichostatin A. Histone acetyltransferase activity determined in cell homogenates was not increased by preincubation of cells with allyl isothiocyanate or inclusion of allyl isothiocyanate in the assay medium. It was concluded that treatment of mouse erythroleukemia cells with allyl isothiocyanate can cause increased acetylation of histones but the mechanism for this effect requires further elucidation.

Metabolic limits on dive duration and swimming speed in the southern elephant seal Mirounga leonina

The ability of air-breathing marine predators to forage successfully depends on their ability to remain submerged. This is in turn related to their total O(2) stores and the rate at which these stores are used up while submerged. Body size was positively related to dive duration in a sample of 34 adult female southern elephant seals from Macquarie Island. However, there was no relationship between body size and dive depth. This indicates that smaller seals, with smaller total O(2) stores, make shorter dives than larger individuals but operate at similar depths, resulting in less time being spent at depth. Nine adult female elephant seals were also equipped with velocity time depth recorders. In eight of these seals, a plot of swimming speed against dive duration revealed a cloud of points with a clear upper boundary. This boundary could be described using regression analysis and gave a significant negative relationship in most cases. These results indicate that metabolic rate varies with activity levels, as indicated by swimming speed, and that there are quantifiable limits to the distance that a seal can travel on a dive of a given swimming speed. However, the seals rarely dive to these physiological limits, and the majority of their dives are well within their aerobic capacity. Elephant seals therefore appear to dive in a way that ensures that they have a reserve of O(2) available.

Increased acetylation of histones induced by diallyl disulfide and structurally related molecules

In previous studies, diallyl disulfide induced differentiation in DS19 mouse erythroleukemic cells. A mechanism mediated by increased histone acetylation was investigated. Diallyl disulfide caused increased acetylation of H4 and H3 histones in DS19 cells and K562 human leukemic cells. Diallyl disulfide was more effective than diallyl monosulfide and diallyl sulfone. Acetylation was also induced in rat hepatoma and human breast cancer cells by diallyl disulfide or its metabolite, allyl mercaptan. Allyl mercaptan was a more potent inhibitor of histone deacetylase than diallyl disulfide. Differentiation in erythroleukemic cells by diallyl disulfide and allyl mercaptan may be mediated through induction of histone acetylation.

Induction of histone acetylation and growth regulation in eryrthroleukemia cells by 4-phenylbutyrate and structural analogs

The objective of this investigation was to study the relationship between histone acetylation and growth inhibition by 4-phenylbutyrate and structural analogs. Inhibition of growth of DS19 mouse erythroleukemia cells and K562 human leukemic cells by 4-phenylbutyrate did not appear to be mediated by glutamine depletion. Vanadate blocked differentiation of DS19 cells but did not affect the hyperacetylation of histones. 2-phenylbutyrate was a more effective inhibitor of cell proliferation than 3-phenylbutyrate but was less effective as an inducer of histone acetylation. 4-Phenylbutyrate was a more effective inhibitor of histone deacetylase and inducer of histone acetylation than the structural analogs examined including 2- and 3-phenylbutyrate, cinnamate, methoxycinnamate, 2-phenoxybutyrate and phenoxyacetate.

Induction of reporter gene expression by inhibitors of histone deacetylase

The relationship between histone acetylation and induction of gene expression was studied in Ros 17/2.8 rat osteosarcoma cells transfected with the pCH110 plasmid. This plasmid is commonly used in cotransfections as a measure of transfection efficiency. Cells were incubated for 48 hours with sodium butyrate, phenylbutyrate, 3-bromopropionate or trichostatin A. There was an approximate relationship between the extent of beta-galactosidase induction and the degree of histone hyperacetylation. Trichostatin A was the most effective agent followed by sodium butyrate and then phenylbutyrate. The toxicity of 3-bromopropionate made it difficult to compare its action with the other agents. Phenylbutyrate was less effective than sodium butyrate in causing induction of gene expression and histone hyperacetylation but this action may be a factor in the growth-inhibitory and differentiating activity of phenylbutyrate which has also been attributed to glutamine depletion.

Differential expression of cytochrome P4502E1 (CYP2E1) in Morris hepatomas and livers of tumor bearing rats

The objective of this investigation was to determine if the decrease of cytochrome P4502E1 (CYP2E1) in hepatomas is related to the tumor growth rate. There was a significant correlation between N-nitrosodimethylamine (NDMA) demethylase activities and CYP2E1 protein levels in rat liver and hepatomas. The levels of NDMA demethylase activities and CYP2E1 protein content were lower in hepatomas than in the corresponding host livers. NDMA demethylase activities and CYP2E1 protein levels were greater in hepatomas of slow and intermediate growth rate than in fast growing hepatomas. A similar trend was also observed with CYP2E1 mRNA levels. The results demonstrated an inverse relationship between growth rate of rat hepatomas and the expression of CYP2E1.

Heart rate, swimming speed, and estimated oxygen consumption of a free-ranging southern elephant seal

Heart rate, swimming speed, and diving behaviour were recorded simultaneously for an adult female southern elephant seal during her postbreeding period at sea with a Wildlife Computers heart-rate time depth recorder and a velocity time depth recorder. The errors associated with data storage versus real-time data collection of these data were analysed and indicated that for events of short duration (i.e., less than 10 min or 20 sampling intervals) serious biases occur. A simple model for estimating oxygen consumption based on the estimated oxygen stores of the seal and the assumption that most, if not all, dives were aerobic produced a mean diving metabolic rate of 3.64 mL O2 kg-1, which is only 47% of the field metabolic rate estimated from allometric models. Mechanisms for reducing oxygen consumption while diving include cardiac adjustments, indicated by reductions in heart rate on all dives, and the maintenance of swimming speed at near the minimum cost of transport for most of the submerged time. Heart rate during diving was below the resting heart rate while ashore in all dives, and there was a negative relationship between the duration of a dive and the mean heart rate during that dive for dives longer than 13 min. Mean heart rates declined from 40 beats min-1 for dives of 13 min to 14 beats min-1 for dives of 37 min. Mean swimming speed per dive was 2.1 m s-1, but this also varied with dive duration. There were slight but significant increases in mean swimming speeds with increasing dive depth and duration. Both ascent and descent speeds were also higher on longer dives.

Organosulfur compounds and cancer

There is evidence that organosulfur compounds can inhibit the induction and growth of cancer. Several organosulfur compounds are dietary constituents and Allium species are a rich source of such molecules. Some but not all epidemiological studies have suggested that consumption of garlic can decrease cancer incidence. There is substantial evidence that constituents of garlic including diallyl sulfides can inhibit the induction of cancer in experimental animals. Effects on both tumor initiation and promotion have been documented. Some effects may be mediated by modulation of carcinogen metabolism involving altered ratios of phase I and phase II drug metabolizing enzymes. 59,60 Inhibitory actions on the growth of tumor cells have been documented and, for some tumor cells, differentiating effects of diallyl sulfides can occur. A definitive mechanism of action has not been established and evidence exists for effects at several sites in carcinogen metabolism and regulation of tumor growth. It is not always clear that laboratory studies can be extrapolated to reasonable levels of consumption by humans of garlic or other Allium species.

Effects of C18 fatty acid isomers on DNA synthesis in hepatoma and breast cancer cells

The influence of geometrical isomerism on the growth regulatory effects of 18 carbon unsaturated fatty acids on the incorporation of [3H]thymidine into DNA was studied in 7800NJ rat hepatoma and T47D human breast cancer cells. 9 cis, 12 cis linoleic acid was more inhibitory than the trans 9, trans 12 isomer (linolelaidic acid). The monounsaturated cis isomer, oleic acid, was also more inhibitory than the trans isomer. In contrast to published studies on the proliferation of breast cancer cells, we observed conditions in which linoleic acid was more inhibitory than conjugated linoleic acid for thymidine incorporation into DNA. Increasing the concentration of bovine serum albumin from 1 mg/ml to a physiological concentration of 38 mg/ml greatly diminished inhibitory effects and favored stimulatory effects on hepatoma and breast cancer cells. The results suggested that the growth inhibitory and stimulatory effects of C18 unsaturated fatty acids on cancer cells are influenced by geometrical isomerism and the ratio of the albumin to fatty acid concentrations.

Discordant effects of butyrate analogues on erythroleukemia cell proliferation, differentiation and histone deacetylase

Actions of butyrate and structural analogues on histone deacetylase activity were compared with effects on proliferation and differentiation of erythroleukemia cells. Proliferation was inhibited by 5 mM tert- butylacetate, phenylacetate, phenylbutyrate, 3-bromopropionate and ethyl butyrate without induction of hemoglobin synthesis. n - Butyramide was a stronger inhibitor of cell proliferation and a more effective inducer of hemoglobin synthesis than isobutyramide. The data from combination studies were compatible with butyramide and isobutyramide being weaker agonists that competed for a common site with butyrate. Butyramide and isobutyramide were weaker inhibitors of histone deacetylase than 4-phenylbutyrate and phenylacetate, which in turn were less effective than 3-bromopropionate and butyrate. Butyrate and analogues had similar inhibitory effects on histone deacetylase activity in nuclei from mouse DS19 cells and human K562 cells. Effects on histone deacetylase did not show a consistent correlation with inhibition of cell proliferation or induction of hemoglobin synthesis.

Inhibitory effect of arginine restriction on hepatoma growth

The potential effects of arginine depletion on promotion of hepatocarcinogenesis and the proliferation of hepatoma cells was investigated. A promotional effect of an arginine-free diet on tumor incidence in liver and kidney was not detected in rats and mice treated with N-nitrosodimethylamine. Inhibitory effects of an arginine-deficient diet on the growth of transplanted hepatomas were observed. Relative to the effect on body weight, the inhibition was greater in mice than rats. The inhibitory effects of an arginine-deficient diet were not correlated with the arginase activity in the tumors. Studies with hepatoma cells treated with polyethyleneglycol-modified arginase indicated that the inhibitory effects of arginine-deprivation on DNA synthesis need not be related to depletion of polyamine precursors.

Changes in the glucose-6-phosphatase complex in hepatomas

Hepatomas tend to have a decreased glucose-6-phosphatase activity. We have observed phenotypic stability for this change in Morris hepatomas transplanted in rats. To determine if this decrease is selective for translocase functions or the hydrolase activity associated with glucose-6-phosphatase, we have compared activities in liver and hepatomas with glucose-6-phosphate or mannose-6-phosphate as substrates and with intact or histone-disrupted microsomes. In five out of seven subcutaneously transplanted rat hepatoma lines, the microsomal mannose-6-phosphatase activity was lower than in preparations from liver of normal or tumor-bearing rats. With liver microsomes and with most hepatoma microsomes, preincubation with calf thymus histones caused a greater increase in mannose-6-phosphatase than in glucose-6-phosphatase activity. In studies with liver and hepatoma microsomes there were similar increases in mannose-6-phosphatase activity with total calf thymus histones and arginine-rich histones. A smaller increase was seen with lysine-rich histones. The effect of polylysine was similar to the action of lysine-rich histones. There was only a small effect with protamine at the same concentration (1 mg/ml). Rat liver or hepatoma H1 histones gave only about half the activation seen with core nucleosomal histones. Our data suggested that microsomes of rat hepatomas tend to have decreased translocase and hydrolase functions of glucose-6-phosphatase relative to activities in untransformed liver.

Inhibitory effects of tea extracts and (-)-epigallocatechin gallate on DNA synthesis and proliferation of hepatoma and erythroleukemia cells

Polyphenols extracted from green or black tea with ethyl acetate were strongly inhibitory for DNA synthesis in HTC rat hepatoma cells and DS19 mouse erythroleukemia cells at concentrations of 0.1-0.2 mg/ml. There was less inhibition with a subsequent black tea fraction extracted with butanol and with the residual water-soluble fraction. Although cell proliferation was inhibited by (-)-epigallocatechin gallate and the tea extracts, there were only marginal effects on differentiation of DS19 cells as judged by hemoglobin synthesis.

Butyramide and monobutyrin: growth inhibitory and differentiating agents

Butyramide and monobutyrin were chosen for study as neutral compounds that might exhibit some of the growth inhibitory and differentiating effects of butyrate. Inhibitory effects on DNA synthesis in hepatoma cells and on cellular proliferation in mouse erythroleukemia cells were observed. Induction of differentiation by butyramide and monobutyrin was seen in mouse erythroleukemia cells as monitored by increased synthesis of hemoglobin and H1 zero histone. Butyramide and monobutyrin were less effective inducers of hemoglobin synthesis than butyrate but their neutral character may offer an advantage in the induction of tumor cell differentiation.

Inhibitory action of orotate, 2-thioorotate and isoorotate on nucleotide metabolism and nucleic acid synthesis in hepatoma cells

1. The specificity of the action of orotate on hepatoma cells was investigated. 2. Orotic acid and its methyl ester had similar inhibitory effects on the incorporation of [3H]thymidine into DNA of hepatoma cells. 3. In contrast to previous studies in vivo, incubation of rat kidney cells with orotate caused an increase in the ratio of UTP/ATP concentrations that was similar to effects on hepatic cells. 4. Inhibitory effects of 2-thioorotate and isoorotate on metabolism were found to be less selective and required higher concentrations than with orotate.

dUTP pyrophosphatase and uracil-DNA glycosylase in rat liver and hepatomas

1. The activity of dUTP pyrophosphatase (dUTPase) was similar in rat liver and hepatomas of slow or moderate growth rate but was increased several fold in three rapidly growing hepatomas. 2. There was an approx three-fold increase in the activity of uracil-DNA glycosylase in Morris hepatoma 7800 but there was little change in activity in other hepatomas that were examined. 3. The activities of dUTPase and uracil-DNA glycosylase were not significantly affected by two diets that may be promotional for hepatocarcinogenesis, a high orotate diet and an arginine-deficient diet.

Combined effect of pH and sodium cyanate on the inhibition of tumor cell proliferation and metabolism by BCNU and hyperthermia

In previous studies, we have found that combined treatment with BCNU and sodium cyanate could have a greater effect on the survival of mice bearing B16 melanoma than treatment with either agent alone. With rat hepatoma and human colon cancer cells in culture, we have obtained evidence that the inhibition of cell proliferation by sodium cyanate is greater at pH 6.6 than at pH 7.4. In the present work, the effects of combination treatments on the proliferation of cancer cells were studied with cyanate, pH, BCNU, and hyperthermia. With HT29 human colon cancer cells, the inhibitory effect of BCNU (50-100 micrograms/ml) was greater when the cells were treated at pH 6.6 than at pH 7.4. The influence of pH appeared to be absent or minimal at lower or higher concentrations of BCNU. We confirmed our previous observation that the inhibition of proliferation of LS174T human colon cancer cells is greater at pH 6.6 than at pH 7.4, and we observed an inhibitory effect of BCNU (50 or 200 micrograms/ml). However, no more than additive effects were seen with combination treatment. An inhibitory effect of hyperthermia was seen for the incorporation of [3H]-leucine into protein of rat hepatoma cells (HTC) and for that of [3H]-thymidine into DNA of human colon cancer (HT29) cells. In neither case was the effect of hyperthermia significantly enhanced by treatment with sodium cyanate beyond that seen with one of the treatments alone. The data confirmed that the inhibitory effect of sodium cyanate on cell proliferation can be enhanced by a low pH but did not provide evidence for synergistic effects in combination with BCNU or hyperthermia.

Influence of inhibitors of eicosanoid metabolism on proliferation of rat hepatoma cells and on tumor-host interaction

The influence of eicosanoids on the proliferation of hepatoma (HTC) cells was studied in culture and in tumor-bearing rats. The cells in culture demonstrated a capacity to metabolize arachidonic acid to eicosanoids including thomboxane B2 and the prostaglandins E2 and F2 alpha a. An effect of these eicosanoids on cell proliferation was suggested by the decreased cell division seen with an inhibitor of cyclooxygenase, flurbiprofen. A biphasic effect on the proliferation of HTC cells was observed with increasing concentrations of prostaglandin F2 alpha. These studies were extended to tumor-bearing rats where inhibitory effects on the early stages of tumor growth were seen with flurbiprofen. Bleeding times were decreased in tumor-bearing rats but were restored to control values by treatment with flurbiprofen and an inhibitor of thromboxane synthetase, OKY 046. These drugs and a thromboxane/endoperoxide receptor antagonist, SQ 29, 548, were not observed to have statistically significant effects on isotope-labeled water distribution but they had substantial effects on the maintenance of body weight by tumor-bearing rats. The data suggested that the cachexia of tumor-bearing animals may be mediated at least in part by the action of eicosanoids.

Levels of oncogene transcripts in hepatomas of different growth rates and in liver in response to diets which cause a nucleotide imbalance

The relationship between levels of gene transcripts and tumor growth was studied in rat hepatomas showing a wide spectrum of growth rates. The level of c-myc and actin gene transcripts were generally increased in the hepatomas but were independent of the growth rate of the tumors. Oncogene expression was studied in the livers of rats on diets which cause a nucleotide imbalance in the liver and which have been reported to be promotional for hepatocarcinogenesis. The levels of c-myc transcripts were elevated three-fold with an arginine-deficient diet but were little changed with a high-orotate diet. The data suggested that levels of c-myc transcripts in rat liver cannot be related in a uniform manner to nucleotide imbalance, tumor promotion or hepatoma growth.

Inhibitory effects of orotate on precursor incorporation into nucleic acids

The influence of orotic acid on the incorporation of precursors into nucleic acids was studied in mice and rats and in isolated cells. In vivo, orotate levels were modified by two diets which are known to increase the rate of pyrimidine nucleotide synthesis in rat liver. Of these diets, a 1% orotate diet had greater inhibitory effects than an arginine-deficient diet on the incorporation of [3H]orotate into RNA of mouse kidney than mouse liver. This contrasted with the situation in the rat where there was a greater effect in the liver than the kidney. The situation in the rat was more readily interpreted than in the mouse in terms of previously established effects of these diets on ribonucleotide pool sizes. However, studies using [3H]adenosine as a precursor for incorporation into RNA suggested that even in the mouse the effects of orotate were on pool sizes rather than an inhibitory effect on RNA synthesis. The incorporation of [3H]thymidine into DNA was inhibited by orotate to a similar degree in cultured HTC hepatoma cells and a line of rat liver epithelial cells. An effect on DNA synthesis rather than solely on pool sizes was suggested by the observation that the pool size of dTTP was not increased by 5 mM orotate under conditions in which there was a four-fold increase in the level of UTP in HTC cells. An inhibitory effect of orotate on DNA synthesis was further supported by an observation of decreased incorporation of [3H]deoxyadenosine into DNA and a lower rate of cellular proliferation.

Influence of pH on the modification of thiols by carbamoylating agents and effects on glutathione levels in normal and neoplastic cells

In previous studies, we have suggested that the selective inhibitory effect of sodium cyanate (NaOCN) on hepatoma metabolism may be due to the lower pH observed in tumors relative to normal tissues. Lower pH might enhance the action of NaOCN by increasing the formation of isocyanic acid and carbamoylation of sulfhydryl groups. In the present work, studies were conducted on the effect of pH on the carbamoylation of sulfhydryl groups. The data indicated that carbamoylation of the sulfhydryl group of glutathione by NaOCN was enhanced by decreasing the pH from 7.4 to 6.6. A less pH-dependent response was observed with organic isocyanates. However, all reactions were reversible after the pH was increased by the addition of base. Kinetic studies showed that the rate of the reaction is very rapid, a maximal effect occurring within the first 10 min. Dose-dependent modifications of cellular glutathione by NaOCN and organic isocyanates were observed in human HT29 colon tumor cells, rat HTC hepatoma cells, and rat hepatocytes. The rate of carbamoylation of the glutathione sulfhydryl group in cells was similar to that of pure glutathione (GSH). The effect of buthionine sulfoxamine on GSH levels in cells was at least as great as that of sodium cyanate, but only the latter showed inhibitory effects on macromolecular synthesis; these were very rapid, pH-dependent, and reversible in tumor cells. Our results suggest that cellular sulfhydryl group(s) other than that of GSH might be involved in the effect of NaOCN on macromolecular synthesis.

Interrelationship between sodium cyanate and pH in the regulation of tumor cell division

Previous studies have suggested that the selective inhibitory effects of sodium cyanate on tumor metabolism in vivo may be related to a lower interstitial pH in tumors. In the present work, the influence of extracellular pH on the actions of sodium cyanate was studied with one rat hepatoma cell line (HTC) and two human colon tumor cell lines (HT29 and LS174T) and with rat hepatocytes to determine if the effects are accompanied by changes in intracellular pH. With some tumor cells, an inhibition of cell proliferation was observed when the cells were exposed to an acidic medium (pH 6.6). However, the LS174T line of human tumor cells divided at pH 6.6 essentially as fast as at pH 7.4. In the concentration range of 0.02-0.1 mg/ml, a greater inhibitory effect of cyanate on cell proliferation was observed at the lower pH. Intracellular pH was found to be influenced by the sodium ion concentration of the medium to a similar degree in the three tumor lines that were examined. The intracellular pH was found to be significantly affected by cyanate in rat hepatocytes and in two of the tumor cell lines (HT29 and LS174T). The data suggested that not only does extracellular pH influence the inhibitory effect of cyanate on tumor cell proliferation but also that cyanate can affect the regulation of intracellular pH in normal and neoplastic cells.