Independent associations of short- and long-term air pollution exposure with COVID-19 mortality among Californians

The growing literature demonstrating air pollution associations on COVID-19 mortality contains studies predominantly examining long-term exposure, with few on short-term exposure, and rarely both together to estimate independent associations. Because mechanisms by which air pollution may impact COVID-19 mortality risk function over timescales ranging from years to days, and given correlation among exposure time windows, consideration of both short- and long-term exposure is of importance. We assessed the independent associations between COVID-19 mortality rates with short- and long-term air pollution exposure by modeling both concurrently. Using California death certificate data COVID-19-related deaths were identified, and decedent residential information used to assess short- (4-week mean) and long-term (6-year mean) exposure to particulate matter <2.5µm (PM_2.5), nitrogen dioxide (NO₂), and ozone (O₃). Negative binomial mixed models were fitted on weekly census tract COVID-19 mortality adjusting for potential confounders with random effects for county and census tract and an offset for population. Data were evaluated separately for two time periods March 16, 2020-October 18, 2020 and October 19, 2020-April 25, 2021, representing the Spring/Summer surges and Winter surge. Independent positive associations with COVID-19 mortality were observed for short- and long-term PM_2.5 in both study periods, with strongest associations observed in the first study period: COVID-19 mortality rate ratio for a 2-μg/m³ increase in long-term PM_2.5 was 1.13 (95%CI:1.09,1.17) and for a 4.7-μg/m³ increase in short-term PM_2.5 was 1.05 (95%CI:1.02,1.08). Statistically significant positive associations were seen for both short- and long-term NO₂ in study period 1, but short-term NO₂ was not statistically significant in study period 2. Results for long-term O₃ indicate positive associations, however, only marginal significance is achieved in study period 1. These findings support an adverse effect of long-term PM_2.5 and NO₂ exposure on COVID-19 mortality risk, independent of short-term exposure, and a possible independent effect of short-term PM_2.5.

Long-term air pollution and COVID-19 mortality rates in California: Findings from the Spring/Summer and Winter surges of COVID-19

A growing number of studies report associations between air pollution and COVID-19 mortality. Most were ecological studies at the county or regional level which disregard important local variability and relied on data from only the first few months of the pandemic. Using COVID-19 deaths identified from death certificates in California, we evaluated whether long-term ambient air pollution was related to weekly COVID-19 mortality at the census tract-level during the first ∼12 months of the pandemic. Weekly COVID-19 mortality for each census tract was calculated based on geocoded death certificate data. Annual average concentrations of ambient particulate matter <2.5 μm (PM_2.5) and <10 μm (PM₁₀), nitrogen dioxide (NO₂), and ozone (O₃) over 2014-2019 were assessed for all census tracts using inverse distance-squared weighting based on data from the ambient air quality monitoring system. Negative binomial mixed models related weekly census tract COVID-19 mortality counts to a natural cubic spline for calendar week. We included adjustments for potential confounders (census tract demographic and socioeconomic factors), random effects for census tract and county, and an offset for census tract population. Data were analyzed as two study periods: Spring/Summer (March 16-October 18, 2020) and Winter (October 19, 2020-March 7, 2021). Mean (standard deviation) concentrations were 10.3 (2.1) μg/m³ for PM_2.5, 25.5 (7.1) μg/m³ for PM₁₀, 11.3 (4.0) ppb for NO₂, and 42.8 (6.9) ppb for O₃. For Spring/Summer, adjusted rate ratios per standard deviation increase were 1.13 (95% confidence interval: 1.09, 1.17) for PM_2.5, 1.16 (1.11, 1.21) for PM₁₀, 1.06 (1.02, 1.10) for NO₂, and 1.09 (1.04, 1.14) for O₃. Associations were replicated in Winter, although they were attenuated for PM_2.5 and PM₁₀. Study findings support a relation between long-term ambient air pollution exposure and COVID-19 mortality. Communities with historically high pollution levels might be at higher risk of COVID-19 mortality.

Programmed death-ligand 1 expression in rectal cancer

Background

Colorectal cancer (CRC) is the fourth most common cause of death worldwide. Approximately 30 % of all CRC occurs in the rectum. Improvements in survival rates were achieved thanks to multimodal therapy, combining surgery and chemoradiation. Nevertheless, the prognosis of patients suffering from rectal cancer (RC) remains poor. Programmed cell death protein 1 (PD-1) and its ligand programmed death ligand 1 (PD-L1) regulate tumor immune response. The aim of this study was to analyze the expression of PD-L1 in RC pre- and post-neoadjuvant therapy and evaluate PD-L1 as a biomarker and potential target for therapy.

Methods

In all, 29 patients with RC treated at the Medical University Vienna who received preoperative chemoradiation were retrospectively enrolled in this study. Expression of PD-L1 was investigated by immunohistochemistry with two different anti-PD-L1 antibodies.

Results

No PD-L1 expression on cancer cells could be observed in all 29 cases in the specimens before chemoradiation as well as in the surgical specimens after neoadjuvant therapy. In one of the two staining methods performed, five (17.24 %) post-chemoradiation cases showed faint lymphohistiocytic staining.

Conclusion

No expression of PD-L1 in RC cells before and after chemoradiation was found in our collective of 29 patients. Further investigations to evaluate the role of PD-L1 as a potential therapeutic target in RC are urgently needed.

Up-regulation of 12(S)-lipoxygenase induces a migratory phenotype in colorectal cancer cells

12(S)-Lipoxygenase (LOX) and its product 12(S)-hydroxyeicosatetraenic (HETE) acid have been implicated in angiogenesis and tumour invasion in several tumour types while their role in colorectal cancer progression has not yet been studied. We have analysed 12(S)-LOX expression in colorectal tumours and found gene expression up-regulated in colorectal cancer specimens for which the pathology report described involvement of inflammation. Using cell line models exposed to 12(S)-HETE or over-expressing 12(S)-LOX malignant cell growth as well as tumour cell migration was found to be stimulated. Specifically, Caco2 and SW480 cells over-expressing 12(S)-LOX formed fewer colonies from sparse cultures, but migrated better in filter-migration assays. SW480 LOX cells also had higher anchorage-independent growth capacity and a higher tendency to metastasise in vivo. Knock-down or inhibition of 12(S)-LOX inhibited cell migration and anchorage-independent growth in both 12(S)-LOX transfectants and SW620 cells that express high endogenous levels of 12(S)-LOX. On the cell surface E-cadherin and integrin-β1 expression were down-regulated in a 12(S)-LOX-dependent manner disturbing cell-cell interactions. The results demonstrate that 12(S)-LOX expression in inflammatory areas of colorectal tumours has the capacity to induce an invasive phenotype in colorectal cancer cells and could be targeted for therapy.

Fibroblast growth factor receptor 3-IIIc mediates colorectal cancer growth and migration

Background:

Deregulation of fibroblast growth factor receptor 3 (FGFR3) is involved in several malignancies. Its role in colorectal cancer has not been assessed before.

Methods:

Expression of FGFR3 in human colorectal tumour specimens was analysed using splice variant-specific real-time reverse transcriptase PCR assays. To analyse the impact of FGFR3-IIIc expression on tumour cell biology, colon cancer cell models overexpressing wild-type (WT-3b and WT3c) or dominant-negative FGFR3 variants (KD3c and KD3b) were generated by either plasmid transfection or adenoviral transduction.

Results:

Although FGFR3 mRNA expression is downregulated in colorectal cancer, alterations mainly affected the FGFR3-IIIb splice variant, resulting in an increased IIIc/IIIb ratio predominantly in a subgroup of advanced tumours. Overexpression of WT3c increased proliferation, survival and colony formation in all colon cancer cell models tested, whereas WT3b had little activity. In addition, it conferred sensitivity to autocrine FGF18-mediated growth and migration signals in SW480 cells with low endogenous FGFR3-IIIc expression. Disruption of FGFR3-IIIc-dependent signalling by dominant-negative FGFR3-IIIc or small interfering RNA-mediated FGFR3-IIIc knockdown resulted in inhibition of cell growth and induction of apoptosis, which could not be observed when FGFR3-IIIb was blocked. In addition, KD3c expression blocked colony formation and migration and distinctly attenuated tumour growth in SCID mouse xenograft models.

Conclusion:

Our data show that FGFR3-IIIc exerts oncogenic functions by mediating FGF18 effects in colorectal cancer and may constitute a promising new target for therapeutic interventions.

Targeting of Hsp32 in solid tumors and leukemias: a novel approach to optimize anticancer therapy

Heat shock protein 32 (Hsp32), also known as heme oxygenase-1 (HO-1), is a stress-related anti-apoptotic molecule, that has been implicated in enhanced survival of neoplastic cells and in drug-resistance. We here show that Hsp32 is expressed in most solid tumors and hematopoietic neoplasms and may be employed as a new therapeutic target as evidenced by experiments using specific siRNA and a Hsp32-targeting pharmacologic inhibitor. This Hsp-32 targeting drug, SMA-ZnPP, was found to inhibit the proliferation of neoplastic cells with IC(50) values ranging between 1 and 50 microM. In addition, SMA-ZnPP induced apoptosis in all neoplastic cells examined. Furthermore, SMA-ZnPP was found to synergize with other targeted and conventional drugs in producing growth-inhibition. Resulting synergistic effects were observed in all tumor and leukemia cells examined. Interestingly, several of the drug partners, when applied as single agents, induced the expression of Hsp32 in neoplastic cells, suggesting that synergistic effects resulted from SMA-ZnPP-induced ablation of a Hsp32-mediated survival-pathway that is otherwise used by tumor cells to escape drug-induced apoptosis. Together, Hsp32 is an important survival factor and target in solid tumors and hematopoietic neoplasms, and may be used to optimize anticancer therapy by combining conventional or targeted drugs with Hsp32-inhibitors. Based on these data, it seems desirable to explore the value of Hsp32-targeting drugs as anti-cancer agents in clinical trials.

FGF5 as an oncogenic factor in human glioblastoma multiforme: autocrine and paracrine activities

Fibroblast growth factor 5 (FGF5) is widely expressed in embryonic but scarcely in adult tissues. Here we report simultaneous overexpression of FGF5 and its predominant high-affinity receptor (FGFR1 IIIc) in astrocytic brain tumour specimens (N=49) and cell cultures (N=49). The levels of both ligand and receptor increased with enhanced malignancy in vivo and in vitro. Furthermore, secreted FGF5 protein was generally present in the supernatants of glioblastoma (GBM) cells. siRNA-mediated FGF5 downmodulation reduced moderately but significantly GBM cell proliferation while recombinant FGF5 (rFGF5) increased this parameter preferentially in cell lines with low endogenous expression levels. Apoptosis induction by prolonged serum starvation was significantly prevented by rFGF5. Moreover, tumour cell migration was distinctly stimulated by rFGF5 but attenuated by FGF5 siRNA. Blockade of FGFR1-mediated signals by pharmacological FGFR inhibitors or a dominant-negative FGFR1 IIIc protein inhibited GBM cell proliferation and/or induced apoptotic cell death. Moreover, rFGF5 and supernatants of highly FGF5-positive GBM cell lines specifically stimulated proliferation, migration and tube formation of human umbilical vein endothelial cells. In summary, we demonstrate for the first time that FGF5 contributes to the malignant progression of human astrocytic brain tumours by both autocrine and paracrine effects.

CD44-positive colorectal adenoma cells express the potential stem cell markers musashi antigen (msi1) and ephrin B2 receptor (EphB2)

The majority of colorectal adenomas contain a mutation in the APC gene activating the wnt pathway. As wnt signalling preserves stem cell functions, it would be expected that stem cells would be enriched in adenomas. We have shown expression of the wnt target gene CD44, which may characterize the expanded stem cell compartment, in colorectal tumours. To investigate this possibility, we performed an immunohistological survey of CD44 expression in relation to the proliferation marker Ki67 and apoptosis in colorectal tumour tissue, and have isolated a CD44-positive subpopulation of the human colorectal adenoma cell line LT97 for cell biological analysis. In tissues, CD44 expression was not related to Ki67, but was associated with lower apoptosis in the CD44-positive areas. CD44-positive and -negative populations isolated from LT97 cultures were identical in their Ki-ras and p53 status but differed in their growth and survival characteristics. While CD44-positive cells attached and grew to reconstitute the original culture, the CD44-negative cells rapidly underwent apoptosis and were unable to resume growth. In comparison to unsorted growing LT97 cells, the CD44-positive cells had shifted beta-catenin into the nucleus and expressed beta-catenin target genes, such as ephrin B receptor (ephB2) and musashi antigen (msi1). By contrast, CD44-negative cultures contained no cells with nuclear beta-catenin. In summary, the CD44-positive cells accumulating in colorectal tumours have increased survival capacity both in vivo and in vitro. They also express markers typical of colorectal progenitor cells, msi1 and ephB2, in the premalignant progenitor population.

Prostaglandin E(2) stimulates progression-related gene expression in early colorectal adenoma cells

Upregulation of cyclooxygenase-2 (COX-2) and prostaglandin-dependent vascularisation in small adenomatous polyps is an essential part of colon carcinogenesis. To study the underlying cellular mechanisms, LT97 and Caco2 human colorectal tumour cells not expressing endogenous COX-2 were exposed to 1 μM prostaglandin E₂ (PGE₂) in their medium. At 30 min after addition, expression of c-fos was stimulated 5-fold and 1.3-fold, respectively, depending on the activation of both extracellular signal-regulated kinase and p38. The amount of c-jun in nuclear extracts was increased 20% in LT97 cells. Expression of COX-2 was upregulated 1.7-fold in LT97 cells and 1.5-fold in Caco2 2 h after prostaglandin (PG) addition by a p38-mediated pathway. The known PGE₂ target gene vascular endothelial growth factor (VEGF) was not modulated. Effects of sustained PGE₂ production were studied in VACO235 cells that have high endogenous COX-2 and in LT97 cells infected with an adenovirus expressing COX-2. Prostaglandin E₂ secretion into the medium was 1–2 nM and 250 pM, respectively. Expression of both VEGF and c-fos was high in VACO235 cells. In LT97 cells, COX-2 upregulated c-fos expression and c-jun content in nuclear extracts 1.7- and 1.2-fold, respectively, in a PG-dependent way. This shows that exogenous PGE₂ as well as COX-2 overexpression affect signalling and gene expression in a way that enhances tumour progression.

Heterocyclic complexes of ruthenium(III) induce apoptosis in colorectal carcinoma cells

PURPOSE

The ruthenium complex salt indazolium trans-[tetrachlorobisindazole-ruthenate(III)] (KP1019) and the analogous sodium salt KP1339 are effective tumor-inhibiting drugs in experimental therapy of autochthonous colorectal carcinomas in rats. This paper examines the cell biological mechanisms underlying their antineoplastic effects.

METHODS

Colorectal tumor cell lines were used to analyze uptake of the ruthenium(III) complexes into the cells and the mechanism as well as the efficacy of their cytotoxic effects.

RESULTS

KP1019 and KP1339 are efficiently taken up into the cells: 100 microM ruthenium(III) complex in the growth medium led to the uptake of 120-160 ng ruthenium per 10(6) cells within 30 min. Uptake of KP418 was tenfold lower correlating with its lower cytotoxic efficiency. KP1019 and KP1339 induced apoptosis in SW480 and HT29 cells predominantly by the intrinsic mitochondrial pathway as indicated by loss of mitochondrial membrane potential. Correspondingly sensitivity of the cells paralleled expression of bcl(2) while it was only slightly affected by mutations in Ki-ras.

CONCLUSIONS

Our data demonstrate that trans-[tetrachlorobisindazole-ruthenate(III)] complex salts are promising candidate drugs in the second-line treatment of colorectal cancers resistant to other cytostatic drugs and has been introduced into phase I clinical trials.

Intrinsic and acquired forms of resistance against the anticancer ruthenium compound KP1019 [indazolium trans-[tetrachlorobis(1H-indazole)ruthenate (III)] (FFC14A)

KP1019 [indazolium trans-[tetrachlorobis(1H-indazole)ruthenate (III)] (FFC14A) is a metal complex with promising anticancer activity. Since chemoresistance is a major obstacle in chemotherapy, this study investigated the influence of several drug resistance mechanisms on the anticancer activity of KP1019. Here we demonstrate that the cytotoxic effects of KP1019 are neither substantially hampered by overexpression of the drug resistance proteins multidrug resistance-related protein 1, breast cancer resistance protein, and lung resistance protein nor the transferrin receptor and only marginally by the cellular p53 status. In contrast, P-glycoprotein overexpression weakly but significantly (up to 2-fold) reduced KP1019 activity. P-glycoprotein-related resistance was based on reduced intracellular KP1019 accumulation and reversible by known P-glycoprotein modulators. KP1019 dose dependently inhibited ATPase activity of P-glycoprotein with a K(i) of approximately 31 microM. Furthermore, it potently blocked P-glycoprotein-mediated rhodamine 123 efflux under serum-free conditions (EC(50), approximately 8 microM), however, with reduced activity at increased serum concentrations (EC(50) at 10% serum, approximately 35 microM). Moreover, P-glycoprotein-mediated daunomycin resistance could only be marginally restored by KP1019 in serum-containing medium, also indicating an influence of serum proteins on the interaction between KP1019 and P-glycoprotein. Acquired KP1019 resistance was investigated by selecting KB-3-1 cells against KP1019 for more than 1 year. Only an approximately 2-fold KP1019 resistance could be induced, which unexpectedly was not due to overexpression of P-glycoprotein or other efflux pumps. Accordingly, KP1019-resistant cells did not display reduced drug accumulation. Their unique cross-resistance pattern confirmed an ABC transporter-independent resistance phenotype. In summary, the likeliness of acquiring insensitivity to KP1019 during therapy is expected to be low, and resistance should not be based on overexpression of drug efflux transporters.

Naturally occurring lignans efficiently induce apoptosis in colorectal tumor cells

Plant-derived lignans caused cell loss by apoptosis in colorectal adenoma and carcinoma cells. Nordihydroguaiaretic acid (NDGA), commonly used for the inhibition of lipoxygenase isoenzymes, showed the strongest growth inhibition with an IC50 of 1.9+/-0.5 microg followed by epiashantin (IC50=9.8+/-4.5 microM) and arctigenin (IC50=16.5+/-8.5 microM). The lignans caused a time- and dose-dependent loss of mitochondrial membrane potential (MMP), down regulation of the anti-apoptotic protein bcl(xl) and an increase of the apoptotic index. The time interval until loss of MMP and down modulation of bcl(xl) became evident correlated with the efficiency of growth inhibition by NDGA, epiashantin and yangambin. Bcl2 and caspase 3 were not involved. NDGA also induced a shift of the culture population to the G2/M phase of the cell cycle. With respect to these results, naturally occurring lignans could be useful in the therapy and chemoprevention of colorectal tumors.

Cells obtained from colorectal microadenomas mirror early premalignant growth patterns in vitro

LT97, a permanent cell line consisting of epithelial cells with an early premalignant genotype was established from small colorectal polyps. LT97 cells have lost both alleles of the APC tumour suppressor gene. In addition, they carry a mutated Ki-ras oncogene, while TP53 is normal. LT97 growth characteristics are thus representative of early adenomas. They had to be passaged as multicellular aggregates indicating a dependency of survival on cell-cell contact and in accordance with their premalignant genotype were not capable of growth in soft agar. LT97 cells did express both the EGF-receptor and small amounts of TGF(alpha) establishing an autocrine growth or survival pathway. However, in spite of autocrine TGF(alpha) production, growth was strongly dependent on exogenous growth factors--mainly EGF, insulin and HGF. Inhibition of the EGF-receptor kinase induced apoptosis at an IC(50) concentration of 4 micromolar indicating that TGF(alpha) activated survival pathways in the early adenoma cell.

Cells obtained from colorectal microadenomas mirror early premalignant growth patterns in vitro

LT97, a permanent cell line consisting of epithelial cells with an early premalignant genotype was established from small colorectal polyps. LT97 cells have lost both alleles of the APC tumour suppressor gene. In addition, they carry a mutated Ki-ras oncogene, while TP53 is normal. LT97 growth characteristics are thus representative of early adenomas. They had to be passaged as multicellular aggregates indicating a dependency of survival on cell-cell contact and in accordance with their premalignant genotype were not capable of growth in soft agar. LT97 cells did express both the EGF-receptor and small amounts of TGF(alpha) establishing an autocrine growth or survival pathway. However, in spite of autocrine TGF(alpha) production, growth was strongly dependent on exogenous growth factors--mainly EGF, insulin and HGF. Inhibition of the EGF-receptor kinase induced apoptosis at an IC(50) concentration of 4 micromolar indicating that TGF(alpha) activated survival pathways in the early adenoma cell.

In vitro models for the identification and characterization of tumor-promoting and protective factors for colon carcinogenesis

The present review aims to give a short overview of the existing cell culture models and their characteristics. While both the induction and the prevention of tumors can only be unequivocally demonstrated in vivo, in vitro models of colorectal cell growth are essential tools for the identification of candidate compounds and for the analysis of underlying mechanisms. Unfortunately normal and premalignant colorectal epithelial cells that represent the target cells of tumor promoters like desoxycholic acid or 1,2-diglyceride and could be used to investigate their cell biological effects are difficult to obtain. Cell line studies have mostly used carcinoma cell lines or rat small intestinal epithelial cells. Some normal immortalized cell lines have been established but are not widely used, and premalignant adenoma cell lines are extremely rare. However, those that do exist are useful both in mechanistic studies of cell growth and for the analysis of tumor promoters and chemoprotectors of colorectal carcinogenesis.

Tissue localization of TGFalpha and apoptosis are inversely related in colorectal tumors

Expression of TGFalpha and the EGF receptor was studied in relation to apoptosis in human colorectal mucosa and premalignant and malignant tumors. In normal mucosa the proteins colocalized both in the proliferation compartment and at the luminal pole of the crypts in cells committed to undergo apoptosis. While staining for the EGF receptor was increased in premalignant and malignant lesions, TGFalpha was undetectable in aberrant crypt foci as well as large areas of adenomas. Incidence of apoptosis (AI) was high in these areas ranging from 8.83-24.59. Adenomas did, however, contain islands of high TGFalpha expression where AI was decreased to a range of 0.76-4.00 (decreased at P=0.0027). In carcinomas TGFalpha expression was increased above both normal and adenoma levels corresponding to the decrease in apoptosis in the malignant tumors. Tissue localization of TGFalpha and AI were still inversely related ( P=0.022), but interpatient variability was much larger than for adenomas. The data indicate that TGFalpha is the main survival factor in premalignant tumor cells of the colon, while additional factors moderate its effect in carcinomas. This suggests the possibility of targeting the EGF receptor pathway not only for treatment but also for the reversal of adenoma growth and the prevention of malignant colorectal tumors.

Role of transforming growth factor alpha and prostaglandins in preferential growth of preneoplastic rat hepatocytes

The role of transforming growth factor alpha (TGFalpha) and prostaglandins (PGs) in the preferential growth of preneoplastic liver cells was studied. Rats received the genotoxic hepatocarcinogen N-nitrosomorpholine (NNM); placental glutathione S-transferase (GSTp) was used as a marker to identify preneoplastic foci. Preneoplastic foci expressing TGFalpha (TGFalpha(+)) grew more rapidly than TGFalpha negative (TGFalpha(-)) ones. Almost all tumours studied were positive for TGFalpha. The key enzymes of prostaglandin synthesis, cyclooxygenase I (Cox-1) and II (Cox-2), were present in all unaltered and preneoplastic cells and tended to decrease in the later stages of hepatocarcinogenesis. Immunostaining revealed that cultures of hepatocytes, isolated from NNM-treated livers by collagenase perfusion, contained 1-2% GSTp-positive (GSTp(+)) and 9% TGFalpha(+) hepatocytes; 0.6% of the cells were GSTp(+)/TGFalpha(+). Cox-1 and Cox-2 were present in all cells. DNA replication was almost exclusively associated with expression of TGFalpha. GSTp(+) hepatocytes showed a 3- to 4-fold higher probability of TGFalpha expression and of DNA synthesis than GSTp-negative (GSTp(-)) cells. PGE(2) or PGF(2alpha) increased expression of TGFalpha and DNA replication in GSTp(-) cells but not in GSTp(+) cells. PGA(2) and PGJ(2) decreased DNA synthesis in TGFalpha(+) cells without an obvious effect on the intracellular levels of TGFalpha. The Cox-2 inhibitor SC236 suppressed DNA replication preferentially in GSTp(+) cells; this inhibition was reversed by PGE(2)/F(2alpha). Indomethacin had no effect. These results suggest the following conclusions. (i) Growth regulation of preneoplastic GSTp(+) cells in culture exhibits distinct differences from GSTp(-) cells and elevated expression of TGFalpha contributes to their growth advantage. (ii) TGFalpha renders preneoplastic hepatocytes sensitive to suppression of DNA synthesis by PGA(2)/J(2). (iii) SC236, a Cox-2 inhibitor, may have preventive value in hepatocarcinogenesis.

Growth inhibition and induction of apoptosis in colorectal tumor cells by cyclooxygenase inhibitors

Non-steroidal anti-inflammatory drugs (NSAIDs) inhibit colorectal carcinogenesis and prevent or revert the growth of premalignant colonic polyps. They inhibit cyclooxygenase (COX) but recent data indicate that this is not the only or even the most important mechanism of inhibition in colorectal tumor cells. We have used colonic carcinoma and adenoma cell lines to study the effects of the NSAID sulindac sulfide, its COX-inactive metabolite, sulindac sulfone, and the isoenzyme-specific inhibitors SC58125, SC236 and SC58560 on tumor cell growth in relation to COX-2 expression and prostaglandin production. To establish the role of COX-2 in NSAID action, we constructed clones expressing different levels of COX-2 from SW480 cells. All five compounds inhibited DNA synthesis and/or induced apoptosis, each with a characteristic pattern. ID(50)s were very similar in all the cell lines and were independent of COX expression, except for the COX-1 inhibitor SC58560, which was least effective in HT29/HI1, the cell line expressing the highest level of COX-1 (ID(50) 70 microM; in other cells lines the ID(50) was 15 microM). For all other compounds ID(50) concentrations varied less than two-fold: 25-40, 40-90 and 150 microM for SC236, sulindac sulfide and sulindac sulfone, respectively. SC58125 was the weakest inhibitor, never causing >50% cell loss. All compounds modulated expression of Bcl-2 and Bak and activated caspase 3. Overexpression of COX-2 in SW480 cells protected them against induction of apoptosis by sulindac sulfide. The effect was restricted to clones producing high levels of prostaglandin E(2). In summary, our data indicate that both COX-dependent and COX-independent mechanisms are involved in NSAID-induced growth in colorectal tumor cells. The concentrations necessary to inhibit growth were higher than serum concentrations that can be obtained in vivo, indicating that the therapeutic effect of NSAIDs cannot be explained by a direct effect of NSAIDs on the epithelial cells alone. For therapeutic purposes, compounds using different targets could be used to minimize side effects while optimizing therapeutic effect.

Lipopolysaccharide causes atrophy of Peyer's patches and an increased expression of CD28 and B7 costimulatory ligands

Intestinal mucosal dysfunction appears to contribute to infectious complications in critically ill patients. The current study was undertaken to investigate whether endotoxin affects lymphocyte subpopulations and the expression of costimulatory signals in Peyer's patches (PP). Female Balb/c mice were given an intraperitoneal injection of 25 microg LPS and sacrified 24 h or 72 h later to determine total cell yield, lymphocyte subpopulations (B-cells, total T-cells, CD4+- and CD8+-cells), the costimulatory molecules CD28, B7.1 (CD80) and B7.2 (CD86) and the percentage of apoptotic cells in PP and in the spleen as well as small intestinal IgA concentration. Lipopolysaccharide (LPS) challenge caused a significant decrease of total cell yield in PP at both time-points (-50+/-28% and -43+/-25%, respectively; P < 0.001). This decrease was significant for all measured lymphocyte subpopulations. In contrast, total cell yield was increased (P < 0.001) in the spleen 24 h (+52+/-13%) and 72 h (+130+/-22%) after LPS. The decrease of lymphocyte numbers in the PP was accompanied by an increased percentage of lymphocytes expressing costimulatory molecules. In this respect, an increased percentage of CD40+CD80+, CD40+CD86+, and of CD4+CD28+ could be demonstrated after LPS administration. In the spleen, the percentage of CD4+CD28+ was also elevated after LPS bolus, however, the percentage of CD40+CD80+ was reduced, and that of CD40+CD86+ was unaltered. The influence of LPS on apoptosis of lymphocytes was time-dependent. The percentage of apoptotic cells 24 h after LPS was increased in PP (P < 0.01), but was unchanged in the spleen. Seventy-two hours after LPS injection, the percentage of apoptotic cells returned to normal in PP. Luminal IgA levels remained unchanged after LPS challenge. In conclusion, our data show that LPS causes atrophy of PP which seems to be counterregulated by an enhanced expression of costimulatory molecules.

Autophagic and apoptotic types of programmed cell death exhibit different fates of cytoskeletal filaments

Programmed cell death comprises several subtypes, as revealed by electron microscopy. Apoptosis or type I programmed cell death is characterized by condensation of cytoplasm and preservation of organelles, essentially without autophagic degradation. Autophagic cell death or type II programmed cell death exhibits extensive autophagic degradation of Golgi apparatus, polyribosomes and endoplasmatic reticulum, which precedes nuclear destruction. In the present study, we analysed the fate of cytokeratin and F-actin during autophagic cell death in the human mammary carcinoma cell line MCF-7 because recent studies suggest that an intact cytoskeleton is necessary for autophagocytosis. Programmed cell death was induced by 10(-)(6) M tamoxifen. For quantitative light microscopic analysis, autophagic vacuoles were visualized by monodansyl cadaverin, which stains autophagic vacuoles as distinct dot-like structures. In control cultures, the number of monodansylcadaverin-positive cells did not exceed 2%. Tamoxifen induced a dramatic increase 2–4 days after treatment to a maximum of 60% monodansylcadaverin-positive cells between days 5 and 7. Cell death, as indicated by nuclear condensation, increased more gradually to about 18% of all cells on day 7. In cells with pyknotic nuclei cytokeratin appeared disassembled but retained its immunoreactivity; actin was still polymerized to filaments, as demonstrated by its reaction with phalloidin. Western blot analysis showed no significant cleavage of the monomeric cytokeratin fraction. For comparison, apoptotic or type I cell death was studied using the human colon cancer cell HT29/HI1 treated with the tyrosine kinase inhibitor tyrphostin A25 as a model. Cleavage of cytokeratin was already detectable in early morphological stages of apoptosis. F-actin was found to depolymerize; its globular form could be detected by antibodies; western blot analysis revealed no products of proteolytic cleavage. In conclusion, in our model of apoptosis, early stages are associated with depolymerization of actin and degradation of intermediate filaments. In contrast, during autophagic cell death intermediate and microfilaments are redistributed, but largely preserved, even beyond the stage of nuclear collapse. The present data support the concept that autophagic cell death is a separate entity of programmed cell death that is distinctly different from apoptosis.

Protein-kinase-C iso-enzymes support DNA synthesis and cell survival in colorectal-tumor cells

Protein-kinase-C signalling has been blocked in colorectal tumor cells by kinase inhibitors, by TPA down-regulation or by exposure to anti-sense oligonucleotides. This resulted in growth inhibition in all cell lines used. The kinase inhibitors H7 and calphostin induced apoptosis, demonstrated by the appearance of cells with characteristically condensed chromatin and the induction of stand-breaks in the DNA. A cell-death-inducing concentration of 15 microgram/ml H7 down-regulated the bcl-2 levels after 9 hr, while bak levels were not affected. Gö6976,-an inhibitor of Ca(++)-dependent PKC iso-enzymes, was not active in growth inhibition or induction of apoptosis. Analysis of DNA synthesis in inhibitor-treated cultures indicated that H7 caused strong inhibition in all cell lines, while the more specific inhibitor calphostin was effective only in VACO235 adenoma cells. When down-regulation by TPA or anti-sense oligonucleotides was used to block PKC, effects on cell numbers were smaller and delayed. However, induction of apoptosis was significantly increased in SW480 carcinoma cells 4 days after exposure to anti-epsilon and anti-zeta oligonucleotides in SW480 and T84 carcinoma cells. Apoptosis was preceeded by loss of PKC protein and of bcl-2 from day 1 after addition of the oligonucleotides. In VACO235 adenoma cells, no induction of apoptosis could be observed when anti-epsilon and anti-zeta oligonucleotides were used. On the other hand, the adenoma cells were more responsive to anti-alpha and anti-beta oligonucleotides, which strongly inhibited DNA-synthesis 3 days after addition to the culture medium. Our results indicate that the Ca(++)-dependent PKCs alpha and beta are involved in proliferation signals, while the Ca(++)-independent PKCs epsilon and zeta are involved in survival pathways of colorectal tumor cells.

The hemoregulatory peptide pEEDCK may inhibit stem cell proliferation via hydropathic binding to antisense sequence motifs in interleukin-11 and other growth factors

In undisturbed bone marrow, most hemopoietic stem cells are nonproliferating despite the presence of multiple growth factors. Endogenous inhibitory factors are responsible for maintenance of this quiescence. Previously we sequenced and synthesized the inhibitory pentapeptide pGlu-Glu-Asp-Cys-Lys (pEEDCK), which originally derives from granulocytes, and investigated the role of this peptide in stem cell quiescence. To provide some mechanistic insight, in the present work we studied the structural relationship of this peptide to specific growth-factor-derived sequence motifs. In the murine system in vivo as well as in long-term bone marrow, antiserum to pEEDCK produced a significant stimulation of formation of colony-forming units-granulocyte/macrophage. Binding of peptides to proteins often takes place at hydropathically complementary sites. Therefore, we searched for peptides corresponding to the complementary sequence to pEEDCK. We identified antisense sequences in the genes of various cytokines and cytokine receptors including interleukin-11. The corresponding peptide Val-Leu-Leu-Thre-Arg (VLLTR) and several other peptides hydropathically complementary to pEEDCK were synthesized. We found that pEEDCK binds specifically to these peptides as well as to complete interleukin-11. Dissociation constants were in the 10 microM range. The peptide hydropathically corresponding to pEEDCK (VLLTR) was found to stimulate colony-forming units-granulocyte/macrophage formation. Our data suggest that pEEDCK could exert a coordinating function in the hemopoietic cytokine network by binding to multiple regulatory proteins and modulating their activity.

Quercetin-induced apoptosis in colorectal tumor cells: possible role of EGF receptor signaling

Flavonoids are among the best candidates for mediating the protective effect of diets rich in fruits and vegetables with respect to colorectal cancer. To gain additional information about their growth effects on colorectal tumors and their cellular mechanisms of action, a series of related flavonoids was added to cultures of colonic tumor cells. Most compounds induced growth inhibition and cell loss at concentrations of 1-100 microM, relative effectivity being quercetin > apigenin > fisetin > robinetin and kaempferol. Myricetin was only slightly effective. Quercetin was the strongest inducer of apoptosis in a process that was reversible until 10 hours by flavonoid removal and until 24 hours by fetal calf serum. Cells were preferentially retained in the S phase. On the cellular level, quercetin sensitivity was correlated with epidermal growth factor (EGF) receptor levels, rapid growth, and poor differentiation, indicating the possibility of targeting those cells most harmful for the organism. The flavonoid transiently inhibited EGF receptor phosphorylation but had only little effect on other signaling molecules. Even after recovery of receptor phosphorylation, cells remained resistant to EGF stimulation. In summary, the data indicate that inhibition of EGF receptor kinase is an integral part of quercetin-induced growth inhibition, but additional mechanisms also contribute to the overall effect.

Inhibition of epidermal-growth-factor-receptor-dependent signalling by tyrphostins A25 and AG1478 blocks growth and induces apoptosis in colorectal tumor cells in vitro

Growth effects of tyrphostins A25 and AG1478 on colorectal tumor cells were studied to explore therapeutic potential. Cell number, DNA synthesis and apoptotic index were measured as growth parameters and cell-death-associated proteins Bcl-2 and Bak and protein phosphorylation were analyzed. Both tyrphostins inhibited DNA synthesis and induced apoptosis in tumor cell cultures with different patterns of activity. A25 displayed strong selectivity for the cell lines expressing high levels of epidermal growth factor (EGF), HT29/HI1 and SW480. Inhibition of DNA synthesis was efficient in all cells except T84, and the apoptotic index increased two- to fivefold. By contrast, AG1478 was highly effective in all cell lines. In addition, it caused cell loss in VACO235 adenoma cells at concentrations lower than those necessary to inhibit BrdU incorporation, reflecting preferential retention of cells actively synthesizing DNA. Induction of apoptosis was more efficient with AG1478 than with A25 (tenfold in VACO235). Insulin-like growth factor (IGF1) did not rescue cells exposed to A25 or to high concentrations of AG1478, but was effective with suboptimal amounts of AG1478. Both compounds inhibited phosphorylation of the EGF receptor as well as additional proteins. AG1478 induced expression of Bak and down-regulated Bcl-2. In summary, tyrphostins may provide alternatives for colorectal tumor treatment. Their broader range of activities and the lower susceptibility to interactions with IGF1 can be an advantage over receptor antibodies.

Active cell death (apoptosis) and cellular proliferation as indicators of exposure to carcinogens

An excess of cell multiplication over cell death is a crucial characteristic of preneoplastic and neoplastic cell populations. In many tumours, the rates of both cell birth and cell death are increased over those in the tissue of origin. Cell death may occur through active mechanisms: cellular suicide or active or programmed cell death, often referred to as apoptosis. The term 'apoptosis' was originally used on morphological grounds for a type of cell death characterized by condensation and fragmentation of cytoplasm and chromatin; however, other types of active cell death exist, in which cytoplasmic degradation by lysosomal, autophagic or proteasomal mechanisms may dominate, e.g. in some experimental mammary tumours and mammary tumour cell lines. Morphological and biochemical differences between the types of programmed cell death should be considered when selecting markers for identification and quantification of cell death. There is still a paucity of specific, efficient methods to assay active cell death, and unequivocal differentiation from degenerative necrosis, especially in tumours, may be difficult or impossible. Active cell death is regulated by a complex network of survival factors and death signals. Many mitogens of exogenous or endogenous origin not only stimulate cell birth but at the same time may inhibit cell death, i.e. increase survival. Endogenous factors also exist which induce active cell death; these include transforming growth factor beta1, CD95 or Fas ligand and tumour necrosis factor. Signal pathways leading to birth or death of cells appear to be interconnected to allow for the fine tuning of cell numbers in tissues. Active cell death can be triggered in two principal ways: by toxic chemicals or injury leading to damage of DNA or of other important cellular targets, and activation or inactivation of receptors by growth-regulating signal factors in the organism. Increases in cell proliferation or in cell survival induced by a chemical do not necessarily lead to cancer, but may indicate carcinogenic potential. Chemicals can affect the balance between replication and death of cells in a number of ways. Firstly, genotoxic carcinogens induce genetic damage which subsequently leads to activation of the suicide machinery, involving genes such as p53. As a result, cells with promutational lesions and mutations are eliminated, thereby providing protection from potentially initiated cells. Secondly, toxic doses of genotoxic or nongenotoxic agents induce acute or chronic injury, leading to cell death and subsequent regenerative proliferation. Thirdly, nongenotoxic carcinogens which are primary mitogens may increase the birth and/or inhibit the death of cells by direct interference with growth signalling pathways. This group of agents includes several trophic hormones; e.g. oestradiol stimulates both the replication and survival of mammary tumour cells. As demonstrated in the rat liver model, preneoplastic and neoplastic cells may be over-responsive to mitogenic or survival signals and thereby undergo selective growth. Conversely, preneoplastic clones and even malignant tumours may still depend on the survival effect of mitogens and regress upon withdrawal of the agent. This indicates that the mitogenic action of the agent is reversible and underlines the principal difference between genotoxic and nongenotoxic carcinogens. In conclusion, studies on cell proliferation and cell death are useful as adjuncts to carcinogenicity assays, and the results may facilitate the interpretation of effects. In conjunction with other biological data, this information may provide an indication of potential carcinogenicity.

Effect of anthraquinone-laxatives on the proliferation and urokinase secretion of normal, premalignant and malignant colonic epithelial cells

Even though 1,8-dihydroxyanthraquinone (DHA)-laxatives have been implicated in colon carcinogenesis, the available information is still inconclusive. The aim of this study was to demonstrate the effect of the DHA-laxatives, danthrone, rhein, aloe-emodin and sennidine, on colorectal tumour cells. In SW480 carcinoma cultures, dose-dependent induction of urokinase secretion into the medium was the predominant effect. Simultaneously, cell numbers were decreased by DHA-aglycones, but not by sennoside or the biphenylic laxative bisacodyl. DNA synthesis was not similarly reduced: 0.4-4 microM danthrone and sennidine even stimulated 5-bromo-2'-desoxyuridine (BrdU) uptake into DNA. When uptake was normalised to cell number, danthrone and sennidine doubled BrdU uptake/10(6) cells, 18 microM rhein and 0.7 microM aloe-emodin induced increases of 37 and 50%, respectively. This may at least partially be due to selective resistance of S-phase cells to DHA-caused cell loss. In VACO235 adenoma cells, sennidine and aloe-emodin did not affect urokinase secretion, but stimulated growth. Both cell numbers and DNA synthesis were increased. In contrast to SW480 carcinoma cells, VACO235 cells were also sensitive to sennoside and bisacodyl. No effects of DHA were observed in normal colorectal epithelial cells. The biological effects were preceeded by specific phosphorylation of cellular proteins with molecular weights of 110, 78, 63, 57 kDa, indicating the specific induction of a cellular signalling cascade by the laxatives.

Survival of normal colonic epithelial cells from both rats and humans is prolonged by coculture with rat embryo colonic fibroblasts

Primary cultures of normal colonic epithelial cells from both humans (HCEC) and rats (RCEC) have been established using coculture with colon fibroblasts isolated from rat term embryos. While no other factors we have analyzed had any effect on the survival of epithelial cells, which is normally 3-4 days, coculture with viable fibroblasts extended this period to at least 2 weeks. The effects depended on early passages and low seeding densities of the fibroblasts and on direct cell-cell contact. We have obtained cultures of epithelial cells expressing keratin, laminin, and uvomorulin, displaying a polygonal, epithelial morphology and forming microvilli. DNA synthesis as measured by BrdU uptake into DNA varied widely between colonies of the same culture depending on cell morphology: flat colonies of RCECs contained 5.7% +/- 0.56% BrdU-positive cells, while the proportion in dense three-dimensional colonies reached 50.3% +/- 2.6%. In HCECs the growth fraction was lower, but showed the same distribution between classes of colonies. In the presence of rat embryonic colon fibroblasts, growth factors exerted survival activity on colonic epithelial cells. Consecutive addition of insulin and epidermal growth factor/fibroblast growth factor (EGF/FGF) increased colony number (15.0 +/- 1.0 and 23.0 +/- 2.0 colonies/well respectively; p < or = 0.05 increased above control) and size (1022 +/- 155 and 1207 +/- 158 cells/colony respectively; p < or = 0.05 increased above control) compared to serum-free control medium and basic MEM without growth factors. BrdU labeling index was not increased, however: EGF/FGF actually decreased BrdU labeling from 33.2% +/- 3.9% in controls to 21.3% +/- 3.8% in the EGF/FGF group (p < or = 0.05) owing to the high proportion of flat colonies consisting of resting cells. The newly established culture model can now be used to investigate growth control mechanisms in colonic mucosa and the effects of toxic and/or tumor-promoting substances on these mechanisms.

Apoptosis in human colorectal tumours: ultrastructure and quantitative studies on tissue localization and association with bak expression

Apoptotic cell death in human tumours has been demonstrated by electron and light microscopy. In adenomas, fragmented and apoptotic nuclei and signs of phagocytosis have been observed close to the basement membrane. In carcinomas the characteristic structures were apoptotic bodies with small fragments of chromatin. DNA fragmentation was shown by in situ end-labelling. Quantitative assessment of apoptosis and proliferation revealed a high apoptotic index (AI) in all types of adenoma (tubular: 1.77+/-0.35%, tubulovillous: 2.38+/-0.41%; villous: 3.3+/-0.39%) as well as loss of compartmentalization of proliferating and dying cells. In carcinomas a shift towards proliferation was evident, as shown by lower AIs than in adenomas (0.9+/-0.68% and 1.1+/-0.12% for moderately and poorly differentiated tumours), higher Ki67 indices (38.32+/-2.23% and 57+/-3.89%, respectively) and higher mitosis (0.9+/-0.56% and 1.21+/-0.17%, respectively). However, apoptosis was observed in all tumours and is available as a target for therapeutic intervention. Expression of the apoptosis related proteins bcl-2 and bak also reflected loss of compartmentalization. While bcl-2 did not show a consistent relationship to AI in tumour specimens, bak was positively correlated with apoptosis in 4 of 8 adenomas and 4 of 7 carcinomas, suggesting a role for this protein in the induction of apoptosis in a subset of tumours.

Concepts of cell death and application to carcinogenesis

The occurrence of cell death as a physiologic event in multicellular organisms has been known for more than 150 yr. In 1972, the term apoptosis was introduced on morphological grounds. The hypothesis that all kinds of cell death can be categorized as either "apoptotic" or "necrotic" is not generally confirmed. Cells seem to use different pathways for suicide, as reflected by different morphology: condensation-prominent, Type I or apoptosis; autophagy-prominent, Type II; and so forth. Type II cell death was found in mammary tissue and mammary tumor cells and in a variety of other organs. For unequivocal identification of the various types of cell death, morphological, biochemical, and functional criteria may be used in combination. During tumor development in various organs of animals and humans, not only rates of cell proliferation but also rates of cell death may increase with increasing malignancy. Morphological and functional criteria (antipromotion, withdrawal of survival factors) indicate that cell death in tumors frequently is of an active nature.

Protein kinase C tissue localization in human colonic tumors suggests a role for adenoma growth control

BACKGROUND & AIMS

Protein kinase C (PKC) has been implicated as a mediator of growth control during colorectal carcinogenesis, but the mechanisms involved are still a matter of dispute. The aim of this study was to analyze PKC patterns and tissue distribution to gain further insight in PKC function during tumor development in the gut.

METHODS

PKC isoenzymes alpha, beta 1, beta 2, delta, and eta and the proliferation antigen Ki67 were analyzed in formalin-fixed normal, premalignant, and malignant specimens using immunohistochemistry.

RESULTS

In normal colonic mucosa, protein levels of all PKC isoenzymes followed an increasing gradient from the bottom to the top of the crypt, staining mainly terminally differentiated, resting cells. Atypical crypts observed in the normal mucosa adjacent to tumors expressed higher levels of Ca(2+)-dependent isoenzymes than the surrounding tissue. In tumors, the number and abundance of PKC isoenzymes was inversely related to proliferation in 7 adenomas and 9 carcinomas. Areas containing PKC-beta 1 as the only isoenzyme had the highest proliferation rates (50%-82% Ki67-positive cells).

CONCLUSIONS

The data suggest a function of PKCs, especially PKC-beta 1, in colorectal carcinogenesis and tumor growth control.

Five of six protein kinase C isoenzymes present in normal mucosa show reduced protein levels during tumor development in the human colon

Protein kinase C (PKC) isoenzyme patterns were analyzed from human colonic epithelial cells of normal, premalignant and malignant origin. PKCs alpha, beta and zeta were found predominantly in the cytosol and the subtypes delta, epsilon and neta almost exclusively in the particulate fraction. Of the isoenzymes found beta, epsilon and neta were low in abundance and could only be detected after partial purification of cellular fractions on DE52-cellulose. Only PKC beta was similar in abundance in normal mucosa, premalignant and malignant colonic epithelial cells, while all other isoenzymes were decreased in abundance in tumor cells. The loss of PKC protein in tumor cells correlated with a loss in enzyme activity, as has been described before by other groups, especially affecting the Ca(2+)-dependent isoenzymes. On the other hand, activation of PKC by phorbol ester treatment in vivo was only possible in carcinoma cells (4/4) and a subset of adenomas (3/7). Normal human colonic epithelial cells did not respond to TPA treatment with either stimulation of PKC activity or translocation of cytosolic enzymes to the particulate fraction. Instead, TPA treatment resulted in a rapid loss of protein for the isoenzymes alpha, delta and to a lesser degree also beta. We assume that this reflects qualitative differences in response between normal and tumor cells, that may be due to the differences in isoenzyme distribution.

Retinoids inhibit protein kinase C-dependent transduction of 1,2-diglyceride signals in human colonic tumor cells

1,2-Diglycerides with long-chain fatty acid residues related to nutritional fat (LCDGs) specifically affect growth and urokinase secretion in human colonic tumor cells, but not in normal mucosa. This allows them to advance and enhance carcinogenesis in the colon and rectum. SW480 colon carcinoma cells are LCDG sensitive in the same way as primary colonic tumor cells and have therefore been used as a model system to study the mechanism of LCDG action and to search for inhibitors of tumor development in the colon. Using this model system, we have shown that the effects of LCDGs are transmitted by protein kinase C and abolished by downregulation of the enzyme. Retinol, retinoic acid, and beta-carotene in nanomolar concentrations inhibit LCDG-induced growth and urokinase secretion and block stimulation of protein kinase C. Although retinol and retinoic acid at higher concentrations also display stimulatory activity, beta-carotene does not. At 100 nM, a concentration that can easily be reached in the plasma of humans, beta-carotene reduces LCDG-induced urokinase secretion about 50%. Inasmuch as beta-carotene does not have side effects due to intrinsic activities and storage effects, beta-carotene and foods rich in carotenes could be useful in the prevention of colorectal cancer.

Urokinase secretion from human colon carcinomas induced by endogenous diglycerides

Colon tumor cells are more responsive to certain growth modulators in their local environment in vivo than are normal colonocytes. Examples of this class of compounds are the fecal diglycerides (DGs)(E. Friedman et al., Cancer Res., 49: 544-548, 1989), which may act as endogenous tumor promoters. At the concentration found in vivo, fecal DGs composed of oleic, myristic, and palmitic fatty acids induced mitogenesis of all classes of benign tumor cells and of half of the resected carcinomas tested in primary culture, but induced no detectable mitogenesis of normal colonocytes. Colon tumor cells also exhibit selective responses to these endogenous modulators as measured by another biological parameter, secretion of urokinase from carcinomas than from normal colonocytes. Fecal DGs also induced a 13-fold increase in urokinase mRNA synthesis in colon carcinoma cells and induced secretion of active urokinase from each of five resected carcinomas. Colon carcinomas, at both the primary site and metastatic to the liver, secreted the Mr 55,000 form of urokinase constitutively and secreted the same form upon treatment with fecal DGs. An increase in the steady-state level of urokinase secretion by saturated-chain DGs exhibited a strong dependency on the chain length of the fatty acid residues, those of 14 and 16 carbons having the greatest activity. Thus, fecal DGs composed of oleic, myristic, and palmitic acid residues induce two biological activities selectively in colon tumor cells, each of which would enhance tumor development. Selective mitogenesis would increase adenoma and carcinoma cell number relative to normal colonocyte number, and induction of the proteolytic enzyme urokinase would aid local invasion of the carcinoma within the bowel wall.

Tyrosine phosphorylation of a Mr 63,000 protein induced by an endogenous mitogen in human colon carcinoma cells, but not in normal colonocytes

Transformation of normal human colonocytes makes them sensitive to new mitogenic signals. Long-chain diglycerides (LCDGs) found in the human colon are mitogens selective for colon tumor cells, inducing mitogenesis in premalignant cells from each of 13 adenomas and in malignant cells from two of four carcinomas, but having no mitogenic effects on normal colonocytes (E. Friedman, P. Isaksson, J. Rafter, B. Marian, S. Winawer, and H. Newmark, Cancer Res., 49:544-548, 1989). Parallel to this biological activity pattern, LCDGs induce protein phosphorylation only in adenomas and carcinomas. Immunoblotting with an anti-phosphotyrosine monoclonal antibody demonstrated that the LCDG dimyristin, at concentrations found within the body, induced a 6-fold increase of tyrosine phosphorylation of an Mr 63,000 protein found in the particulate fraction of colon carcinoma cells. Tyrosine phosphorylation was maximal 0.5 min after addition of the LCDG, then fell, but remained elevated 40% over constitutive levels for at least 6 h. The Mr 63,000 tyrosine phosphoprotein was found in each of four colon carcinoma cell lines and an adenoma, but not in normal colonocytes, suggesting that the tyrosine kinase is activated only in tumor cells. Constitutive levels of the Mr 63,000 substrate were enhanced 2-fold by incubation of cells for 20 h with sodium orthovanadate, a tyrosine phosphatase inhibitor. This result suggested that carcinoma cells continually phosphorylate and dephosphorylate this tyrosine kinase substrate during growth. Thus, the colon tumor cell mitogen, dimyristin, utilizes a signal transduction pathway, containing the Mr 63,000 tyrosine kinase substrate, which is already in use during cell growth, possibly by other mitogens or growth factors.

Fecal diglycerides as selective endogenous mitogens for premalignant and malignant human colonic epithelial cells

Diglycerides (DGs) have been found in fecal extracts at concentrations which induce mitogenesis of adenoma and some carcinoma cells but not normal cells in primary culture. DGs containing stearic, oleic, palmitic, and myristic acid side chains were found in fecal extracts from each of eight subjects. Synthetic 1,2-DGs, containing the fatty acids found in endogenous fecal DGs, induced mitogenesis in cultures of premalignant cells from each of 13 adenomas, covering all histological classes, and in cultures from two of four carcinomas. The potent adenoma mitogen, dimyristin, had no mitogenic activity on cultures of normal colonic epithelial cells from seven different subjects. These results suggest DGs may act as endogenous mitogens in the development of human colon cancer. The extent of adenoma mitogenesis was correlated with the chain length of the saturated R-groups: 16 greater than 14 greater than 12 greater than 10 greater than 8 much greater than 18. DGs with oleic acid residues, C18:1, were among the most active, while substitution of even one fatty acid residue with a stearic acid residue, C18:0, reduced or eliminated mitogenic activity. Dimyristin also induced enhanced levels of urokinase secretion from carcinoma cells, in parallel to the phorbol ester tumor promoter, 12-O-tetradecanoylphorbol-13-acetate. These results imply that DGs found in the colon induce a selective growth of benign colonic tumors and some carcinomas, and may enhance the invasive capacity of carcinomas, while leaving normal cells unaffected.

Tumor-promoting phorbol esters cause a stable reduction of dermal collagen in mouse skin

Chronic treatment with the tumor-promoting phorbol esters 12-O-tetradecanoylphorbol-13-acetate (TPA) and 12-O-retinoylphorbol-13-acetate (RPA) causes permanently increased levels of active collagenolytic enzymes in the dermis and leads to a stable reduction of dermal collagen content. Non-promoting skin mitogens like the Ca-ionophore A 23187 or the 4-O-methylether of TPA, while being active stimulators of collagenolytic enzymes, do not support chronic collagen degradation throughout the experimental period. On the other hand, TPA-induced collagen degradation is not necessarily influenced by inhibition of tumor promotion. Fluocinolone acetonid (FA), an inhibitor preventing not only tumor development but also chronic inflammation and the establishment of a stationary hyperplasia, has been compared with retinoic acid (RA) which has no influence on either the inflammatory reaction or hyperplasia. While FA inhibited the dermal effects of TPA almost completely, RA at a dose that prevented tumor development by 80% had no effect whatsoever in this respect. Therefore, we conclude that both epidermal proliferation and inflammation are accompanied by collagenolytic reactions in the dermis. During chronic treatment sustained collagenolysis correlates with inflammation and/or the establishment of a stationary hyperplasia. Like these it can be regarded as a necessary but insufficient condition of tumor promotion (second stage).

Chronic 12-O-tetradecanoylphorbol-13-acetate treatment prevents restoration of collagen loss associated with its inflammatory effect on mouse skin

The extracellular matrix of the dermis is subject to severe alterations during tumor promotion with phorbol esters in mouse skin. The metabolic changes also involve general stimulation of protein synthesis and most specifically an increase of collagen synthesis. During chronic treatment with the tumor promoting phorbol esters 12-O-tetradecanoylphorbol-13-acetate (TPA) and 12-O-retinoylphorbol-13-acetate (RPA) increased protein synthesis was observed that did not occur during treatment with the non-promoting mitogens 4-O-methyl-TPA and Ca-ionophore A 23187. Relative collagen synthesis measured as the ratio of radioactivities in hydroxyproline and proline or as the proportion of total radioactivity in pepsin resistant material was elevated, too, but not sufficiently to substitute for TPA-induced collagen loss. In contrast collagen degradation caused by the non-promoting irritant A 23187 is followed by an immediate, substantial increase of collagen synthesis. When TPA treatment was discontinued after a few applications insufficient for tumor development rapid resynthesis of collagen took place. Therefore we assume that continued phorbol ester application not only caused connective tissue damage but also prevents the repair of that damage. This effect seems to be promoter specific and contributes to the disruption of dermal-epidermal interactions during tumor promotion.

Skin tumor promotion is associated with increased type V collagen content in the dermis

Tumor promotion in mouse skin depends upon establishment of hyperproliferation as well as inflammation and involves disturbance of normal communication between dermis and epidermis. As the collagenous matrix of the dermis is known to play an important role in the maintenance of normal dermal-epidermal interactions, alterations of the dermal collagen types during tumor promotion with 12-O-tetradecanoyl-phorbol-13-acetate (TPA) were investigated. In TPA-treated samples no difference between the relative content of type I and III collagen was observed, whereas the content of type V was significantly increased. When TPA treatment was discontinued before tumor development no increase of type V collagen was observed. Furthermore, treatment with the non-promoting mitogens 4-O-methyl-TPA and Ca-ionophore A 23187 did not result in any alterations of the matrix composition. These data indicate that the increase of type V collagen content is part of the disturbed tissue interactions between dermis and epidermis that facilitate tumor development.

Enhancement of collagen-degrading enzymes in the dermis after one topical application of tumor-promoting phorbol esters

The effect of tumor-promoting and non-promoting skin mitogens on the induction of matrix degradation in the dermis of mouse skin has been examined. A stimulation of active collagenolytic and proteolytic enzyme levels was observed after application of the tumor promoters 12-O-tetradecanoyl-phorbol-13-acetate (TPA) and 12-O-retinoylphorbol-13-acetate (RPA) as well as the non-promoting skin irritant Ca-ionophore A 23187, but not with the non-irritant mitogen 4-O-methyl-TPA. It therefore appears that the enhancement of collagenolytic and proteolytic enzymes after tumor promoter treatment is mainly due to the inflammation that is always caused by the promoter. However, a subfraction of collagenolytic enzymes that is not extracted from the dermis with 0.5 M NaCl but only with 5 M urea is specifically increased after treatment with TPA and RPA. This fraction is absent in A 23187- or 4-O-methyl-TPA-treated dermis. This indicates that apart from inflammation-induced matrix degradation there is also stimulation of enzymes which are directly related to tumor promotion.

Dermal collagen metabolism during tumor promotion with 12-O-tetradecanoylphorbol-13-acetate in mouse skin

Treatment of the skin with the tumor promoting phorbol ester 12-O-tetradecanoylphorbol-13-acetate leads to a reduction of the collagen content of the dermis of the mouse. The collagen degradation as well as synthesis is affected by the tumor promoter, the effect on degradation being more pronounced at the beginning of the treatment. The collagenolytic activity that can be extracted from the dermis is increased 5- to 6-fold during the first five applications and approximately 2-fold at later times. The uptake of [14C]proline in both total protein and NaCl-soluble collagen is doubled, but the increase of collagen synthesis does not restore a normal collagen content in the dermis, as it is accompanied by an elevated level of collagenolytic activity.