Does colon cancer ever metastasize to bone first? a temporal analysis of colorectal cancer progression.

BACKGROUND: It is well recognized that colorectal cancer does not frequently metastasize to bone. The aim of this retrospective study was to establish whether colorectal cancer ever bypasses other organs and metastasizes directly to bone and whether the presence of lung lesions is superior to liver as a better predictor of the likelihood and timing of bone metastasis. METHODS: We performed a retrospective analysis on patients with a clinical diagnosis of colon cancer referred for staging using whole-body 18F-FDG PET and CT or PET/CT. We combined PET and CT reports from 252 individuals with information concerning patient history, other imaging modalities, and treatments to analyze disease progression. RESULTS: No patient had isolated osseous metastasis at the time of diagnosis, and none developed isolated bone metastasis without other organ involvement during our survey period. It took significantly longer for colorectal cancer patients to develop metastasis to the lungs (23.3 months) or to bone (21.2 months) than to the liver (9.8 months). Conclusion: Metastasis only to bone without other organ involvement in colorectal cancer patients is extremely rare, perhaps more rare than we previously thought. Our findings suggest that resistant metastasis to the lungs predicts potential disease progression to bone in the colorectal cancer population better than liver metastasis does.

Effects of butyrate on the colon cancer cell phenotype-chemosensitization and upregulation of proteins implicated in cancer progression

Colon cancer is the second leading cause of cancer mortality in the U.S. Surgery is the only truly effective human colon cancer (HCC) therapy due to marked intrinsic drug resistance. The inefficacy of therapies developed for metastatic HCC suggests that advances in colon cancer chemoprevention and chemotherapy will be needed to reduce HCC mortality. The dietary fiber metabolite butyrate (NaB) is a candidate cancer chemopreventive agent that inhibits growth, promotes differentiation and stimulates apoptosis of HCC cells. Epidemiological and experimental studies suggest that dietary fiber protects against the development of HCC, however, recent large prospective trials have not found significant protection. ^ The first central hypothesis of this dissertation project is that the diversity of phenotypic changes induced by NaB in HCC cells includes molecular alterations that oppose its chemopreventive action and thereby limit its efficacy. We investigated the effect of NaB on the expression/activity of epidermal growth factor receptor (EGFR) and cyclooxygenase-2 (COX-2) in HCC HT29 cells. NaB treatment induced a 13-fold increase in EGFR expression in concert with its chemopreventive action in vitro, i.e., induction of growth suppression and G1 arrest, apoptosis and a differentiated phenotype. NaB-induced EGFR was active based on multiple lines of evidence. The EGFR was: (1) heavily phosphorylated at Tyrosine (P-Tyr); (2) associated with the cytoskeleton; (3) localized at the cell surface, and activated in response to EGF; and (4) NaB treatment of the cells induced activation of the EGFR effector Erk1/2. NaB treatment also induced a 7-fold increase in COX-2 expression. The NaB-induced COX-2 was active based on significantly increased PGE2 production. ^ The second central hypothesis is that NaB treatment would render HCC cells more chemosensitive to chemotherapy agents based on the increased apoptotic index induced by NaB. NaB treatment chemosensitized HT29 cells to 5-FU and doxorubicin, despite increases in the expression of P-glycoprotein and a related drug resistance protein (MRP). ^ These results raise the intriguing possibility that the chemopreventive effects of fiber may require concomitant treatment with EGFR and/or COX-2 inhibitors. Similarly, NaB may be a rational drug to combine with existing chemotherapeutic agents for the management of advanced HCC patients. ^

EXPRESSION OF TUMOR ASSOCIATED ANTIGENS ON HUMAN COLON CARCINOMA CELLS (HUMAN COLON CANCER, MONOCLONAL ANTIBODY)

Human colon cancer cells, LS180 and 174T, exhibit monoclonal antibody (mAb) 1083-17-1A and 5E113 defined tumor associated antigens. By radioimmunoassay, LS180 cells expressed the highest amount of mAb1083 defined antigens among the cell lines tested. Another mAb, 5E113, competed with mAb1083 for binding to LS180 cells, suggesting that both mAbs might bind onto identical (or adjacent) epitopes. By Scatchard analysis, about one million copies of the epitopes were present on LS180 colon cancer cells. The affinity of mAb1083 binding to the cells was 2.97 x 10('10) M('-1); the Sipsian heteroclonality value of mAb1083 was 0.9, thus approximating a single clone of reactive antibody. The qualitative studies showed that the epitopes were probably not carbohydrate because of their sensitivity to proteinases and not to mixed glucosidases and neuraminidase. The tunicamycin homologue B(,2) inhibited the incoporation of ('3)H-labeled galactose but not uptake of ('35)S-labeled methionine, nor expression of monoclonal antibody defined antigens providing further evidence to exclude the possibility of carbohydrate epitopes. There was evidence that the epitope might be partially masked in its "native" conformation, since short exposure or low dose treatment with proteases increased mAbs binding. The best detergent for antigen extraction, as detected by dot blotting and competitive inhibition assays, was octylglucoside at 30 mM concentration. Three methods, immunoprecipitation, Western blotting and photoaffinity labeling, were used to determine the molecular nature of the antigens. These results demonstrated that the antibody bound both 43 K daltons (KD) and 22 KD proteins.^ An in vitro cell-mediated immune approach was also used to attempt identifying function for the antigens. The strategy was to use mAbs to block cytotoxic effector cell killing. However, instead of blocking, the mAb1083 and 5E113 showed strong antibody-dependent cell-mediated cytotoxicities (ADCCs) in the in vitro xenoimmune assay system. In addition, cytotoxic T lymphocytes (CTLs), natural killer cells, and K cell activity were found. Since even the F(ab')2 fragment of mAbs did not inhibit the cytolytic effect, the mAbs defined antigens may not be major target molecules for CTLs. In summary, two molecular species of tumor antigen(s) were identified by mAbs to be present on colon tumor cell lines, LS180 and LS174T. (Abstract shortened with permission of author.) ^

beta-catenin interacts with and inhibits NF-kappaB in colon cancer

The β-catenin pathway plays an important role in the progression of colon cancer as well as many other cancer types. Almost all colorectal tumors show an upregulation of β-catenin activity either through mutations in the β-catenin regulator APC or through mutations in β-catenin itself. Upregulation of β-catenin leads to the transcription of many target genes involved in tumorigenesis. NF-κB is a transcription factor which activates many target genes, including both anti-apoptotic and pro-apoptotic molecules. Recently, it has been shown that GSK-3β, a negative regulator of β-catenin, is involved in the activation of NF-κB. However, the mechanism of this regulation of NF-κB by GSK-3β is unclear. As GSK-3β inhibits β-catenin we hypothesized that β-catenin may be responsible for the regulation of NF-κB by GSK-3β; i.e. β-catenin may inhibit NF-κB activity. In this study we show that β-catenin physically interacts with NF-κB leading to the inhibition of NF-κB transcriptional and DNA-binding activities. We also show that in colon cancer cells with high β-catenin expression there is a suppressed NF-κB activity and depletion of β-catenin increases NF-κB activity. Similarly, in colon cancer cells that have a low level of β-catenin NF-κB activity is high and introduction of β-catenin reduces NF-κB activity. Importantly, we show that this suppression of NF-κB by β-catenin leads to a reduction of NF-κB target gene Fas expression. Also Fas-mediated apoptosis is reduced in β-catenin overexpressing cells, which can be reversed upon depletion of β-catenin. Introduction of the NF-κB subunit p65 can restore Fas expression indicating that the effect of β-catenin on Fas is through NF-κB. Furthermore, β-catenin expression was found to inversely correlate with Fas expression in human colon and breast primary tumor tissues. As Fas downregulation is important for tumors to evade immune surveillance, β-catenin inhibition of NF-κB and Fas downregulation likely plays and important role for colon cancer progression. Additionally, we found that phosphoinositide 3-kinase plays a role in the regulation of β-catenin inhibition of NF-κB through the disruption of the β-catenin/NF-κB complex. This study provides a link between two important signal transduction pathways as well as another mechanism of β-catenin oncogenesis. ^

High-resolution microarray analysis of chromosome 20q in human colon cancer metastasis model systems

Amplification of human chromosome 20q DNA is the most frequently occurring chromosomal abnormality detected in sporadic colorectal carcinomas and shows significant correlation with liver metastases. Through comprehensive high-resolution microarray comparative genomic hybridization and microarray gene expression profiling, we have characterized chromosome 20q amplicon genes associated with human colorectal cancer metastasis in two in vitro metastasis model systems. The results revealed increasing complexity of the 20q genomic profile from the primary tumor-derived cell lines to the lymph node and liver metastasis derived cell lines. Expression analysis of chromosome 20q revealed a subset of over expressed genes residing within the regions of genomic copy number gain in all the tumor cell lines, suggesting these are Chromosome 20q copy number responsive genes. Bases on their preferential expression levels in the model system cell lines and known biological function, four of the over expressed genes mapping to the common intervals of genomic copy gain were considered the most promising candidate colorectal metastasis-associated genes. Validation of genomic copy number and expression array data was carried out on these genes, with one gene, DNMT3B, standing out as expressed at a relatively higher levels in the metastasis-derived cell lines compared with their primary-derived counterparts in both the models systems analyzed. The data provide evidence for the role of chromosome 20q genes with low copy gain and elevated expression in the clonal evolution of metastatic cells and suggests that such genes may serve as early biomarkers of metastatic potential. The data also support the utility of the combined microarray comparative genomic hybridization and expression array analysis for identifying copy number responsive genes in areas of low DNA copy gain in cancer cells. ^

Oncologic outcomes in diabetic patients with colon cancer

Type II diabetes mellitus is a growing problem worldwide and although its association with increased cardiovascular morbidity and mortality is well known, its role in the development of cancer is now being further elucidated. Recently, there has been increasing evidence that not only are diabetics more susceptible towards development of particular types of cancer, but also have worse oncologic outcomes. This retrospective chart review investigates whether diabetics with colon cancer have a poorer prognosis than their nondiabetic counterparts. Patients with high risk Stage II and Stage III colon cancer who were diagnosed and/or treated at The University of Texas M.D. Anderson Cancer Center from 1/1/2000 till 12/1/2004 were included in our study. We carried out a survival analysis using Kaplan-Meier method and multivariable analysis to assess differences in outcomes of the two population groups. We found that the decreased overall survival in diabetics did not reach statistical significance but this could be due to a lower event rate in our study. Larger studies are required to investigate this further. ^

Adherence to adjuvant chemotherapy and post-treatment surveillance in a large community-based cohort of patients with colon cancer

The objective of this dissertation was to determine the initiation and completion rates of adjuvant chemotherapy, its toxicity and the compliance rates of post-treatment surveillance for elderly patients with colon cancer using the linked Surveillance, Epidemiology, and End Results – Medicare database.^ The first study assessed the initiation and completion rate of 5-fluorouracil-based adjuvant chemotherapy and its relationship with patient characteristics. Of the 12,265 patients diagnosed with stage III colon adenocarcinoma in 1991-2005, 64.4% received adjuvant chemotherapy within 3-months after tumor resection and 40% of them completed the treatment. Age, marital status, and comorbidity score were significant predictors for chemotherapy initiation and completion.^ The second study estimated the incidence rate of toxicity-related endpoints among stage III colon adenocarcinoma patients treated with chemotherapy in 1991-2005. Of the 12,099 patients, 63.9% underwent chemotherapy and had volume depletion disorder (3-month cumulative incidence rate [CIR]=9.1%), agranulocytosis (CIR=3.4%), diarrhea (CIR=2.4%), nausea and vomiting (CIR=2.3%). Cox regression analysis confirmed such association (HR=2.76; 95% CI=2.42-3.15). The risk of ischemic heart diseases was slightly associated with chemotherapy (HR=1.08), but significantly among patients aged <75 with no comorbidity (HR=1.70). ^ The third study determined the adherence rate of follow-up cares among patients diagnosed with stage I-III colon adenocarcinoma in 2000 - June 2002. We identified 7,348 patients with a median follow-up of 59 months. The adherence rate was 83.9% for office visits, 29.4% for CEA tests, and 74.3% for colonoscopy. Overall, 25.2% met the recommended post-treatment care. Younger age at diagnosis, white race, married, advanced stage, fewer comorbidities, and chemotherapy use were significantly associated with guideline adherence.^ In conclusions, not all colon cancer patients received chemotherapy. Receiving chemotherapy was associated with increased risk of developing gastrointestinal, hematological and cardiac toxicities. Patients were more likely to comply with the schedule for office visits and colonoscopy but failed in CEA tests. ^

Adult weight gain and risk of colon cancer in men

Previous research supports the hypothesis that a "rich" diet (i.e., high in fat and low in fiber) increases the risk of colon cancer. Previous research also supports the hypothesis that physical inactivity increases the risk of colon cancer, perhaps because physical inactivity decreases gut motility, thereby increasing tee time that carcinogens are in contact with the intestinal mucosa. Habitual physical inactivity, combined with rich diet, ordinarily results in chronic energy imbalance and gain in weight, except when energy balance is modified by disease or factors such as cigarette smoking. Cigarette smokers typically stay lean because of effects of smoking on the resting metabolic rate as well as on efficiency of caloric intake and storage. Therefore, if physical inactivity and rich diet do increase the risk of colon cancer, then weight gain during young adulthood should be positively associated with incidence of colon cancer during later life, especially in nonsmokers.^ This hypothesis was investigated in a cohort of 2,059 randomly selected middle-aged men who were employed at the Western Electric Company in Chicago and were free of clinically diagnosed cancer at initial examination in 1958. Body mass index (BMI) in middle age was calculated from measured height and weight at the initial examination. BMI at age 20 was estimated from weight at age 20 as recalled at the initial examination and height as measured at the initial examination. Change in BMI between age 20 and middle age was estimated by subtracting the BMI at 20 from the BMI in middle age. Forty-nine incident cases of colon cancer were detected during 25 years (43,326 person-years) at risk. When stratified by level of change in BMI from age 20 to middle age ($\le$1.9, 2.0-3.9, 4.0-5.9, $\ge$6.0 kg/m$\sp2$), age-adjusted relative hazards of colon cancer in never-smokers were 1.00, 1.22, 2.31, and 5.01, respectively (p for trend = 0.008); corresponding values in ever-smokers were 1.00, 0.95, 0.77, and 0.87, These associations did not change appreciably after further adjustment for BMI at age 20, subscapular-triceps skinfold ratio, cigarette smoking, consumption of alcohol, energy, fat, and calcium.^ We also investigated the hypothesis that the risk of colon cancer was higher in men who were lean at age 20 and became fat by middle age (lean-to-fat) than in men who were fat at age 20 and stayed fat in middle-age (fat-to-fat). "Lean" was defined as BMI $<$24 kg/m$\sp2$ at age 20 and as BMI $<$27.0 kg/m$\sp2$ in middle age. Among never-smokers, in comparison to men who were lean at age 20 and in middle age (lean-to-lean), the age-adjusted relative hazard of colon cancer was 1.43 in the fat-to-fat group (95% confidence interval (CI) 0.37-5.52) and 3.36 in the lean-to-fat group (95% CI 1.21-9.37). This investigation provides new results on the magnitude of risk of colon cancer associated with weight gain during adulthood (from age 20 to middle age). This relation was obscured or underestimated in previous studies due to effect-modification by cigarette smoking. Finally, the result supports the idea that a life-style characterized by chronic energy imbalance during young adulthood increases risk of colon cancer. ^

Geographic variation in the utilization and survival associated with oxaliplatin chemotherapy in patients with stage III colon cancer

Background: Overall objectives of this dissertation are to examine the geographic variation and socio-demographic disparities (by age, race and gender) in the utilization and survival of newly FDA-approved chemotherapy agents (Oxaliplatin-containing regimens) as well as to determine the cost-effectiveness of Oxaliplatin in a large nationwide and population-based cohort of Medicare patients with resected stage-III colon cancer. Methods: A retrospective cohort of 7,654 Medicare patients was identified from the Surveillance, Epidemiology and End Results – Medicare linked database. Multiple logistic regression was performed to examine the relationship between receipt of Oxaliplatin-containing chemotherapy and geographic regions while adjusting for other patient characteristics. Cox proportional hazard model was used to estimate the effect of Oxaliplatin-containing chemotherapy on the survival variation across regions using 2004-2005 data. Propensity score adjustments were also made to control for potential bias related to non-random allocation of the treatment group. We used Kaplan-Meier sample average estimator to calculate the cost of disease after cancer-specific surgery to death, loss-to follow-up or censorship. Results: Only 51% of the stage-III patients received adjuvant chemotherapy within three to six months of colon-cancer specific surgery. Patients in the rural regions were approximately 30% less likely to receive Oxaliplatin chemotherapy than those residing in a big metro region (OR=0.69, p=0.033). The hazard ratio for patients residing in metro region was comparable to those residing in big metro region (HR: 1.05, 95% CI: 0.49-2.28). Patients who received Oxalipaltin chemotherapy were 33% less likely to die than those received 5-FU only chemotherapy (adjusted HR=0.67, 95% CI: 0.41-1.11). KMSA-adjusted mean payments were almost 2.5 times higher in the Oxaliplatin-containing group compared to 5-FU only group ($45,378 versus $17,856). When compared to no chemotherapy group, ICER of 5-FU based regimen was $12,767 per LYG, and ICER of Oxaliplatin-chemotherapy was $60,863 per LYG. Oxaliplatin was found economically dominated by 5-FU only chemotherapy in this study population. Conclusion: Chemotherapy use varies across geographic regions. We also observed considerable survival differences across geographic regions; the difference remained even after adjusting for socio-demographic characteristics. The cost-effectiveness of Oxaliplatin in Medicare patients may be over-estimated in the clinical trials. Our study found 5-FU only chemotherapy cost-effective in adjuvant settings in patients with stage-III colon cancer.^

Genome instability quantified in constitutive tissues as well as putatively stable tumor tissue in hereditary non -polyposis colon cancer patients by small pool PCR

Microsatellite instability (MSI) is a hallmark of the mutator phenotype associated with Hereditary Non-Polyposis Colon Cancer (HNPCC). The MSI-High (MSI-H) HNPCC population has been well characterized, but the microsatellite low and stable (MSI-L/MSS) HNPCC population is much less understood. We hypothesize there are significant levels of MSI in HNPCC DNA classified as MSI-L/MSS, but no single variant allele makes up a sufficient population in the tumor DNA to be detected by standard analysis. Finding variants would suggest there is a mutator phenotype for the MSI-L/MSS HNPCC population that is distinct from the MSI-H HNPCC populations. This study quantified and compared MSI in HNPCC patients previously shown to be MSI-H, MSI-L/MSS and an MSI-H older, sporadic colorectal cancer patient. Small-pool Polymerase Chain Reactions (SP-PCRs) were conducted where the DNAs from each sample and controls are diluted into multiple pools, each containing approximately single genome equivalents. At least 100 alleles/sample were studied at six microsatellite loci. Mutant fragments were identified, quantified, and compared using Poisson statistics. Most of the variants were small deletions or insertions, with more mutants being deletions, as has been previously described in yeast and transgenic mice. SP-PCR, where most of the pools contained only 3 or less fragments, enabled identification of variants too infrequent to be detected by large pool PCR. Mutant fragments in positive control MSI-H tumor samples ranged from 0.26 to 0.68 in at least 4 of the 6 loci tested and were consistent with their MSI-H status. In the so called MSS tumors and constitutive tissues (normal colon tissue, and PBLs) of all the HNPCC patients, low, but significant levels of MSI were seen in at least two of the loci studied. This phenomenon was not seen in the sporadic MSI constitutive tissues nor the normal controls and suggests haploinsufficiency, gain-of-function, or a dominant/negative basis of the instability in HNPCC patients carrying germline mutations for tumor suppressor genes. A different frequency and spectrum of mutant fragments suggests a different genetic basis (other than a major mutation in MLH1 or MSH2) for disease in MSI-L and MSS HNPCC patients. ^

HIV-related malignancies: A community-based study using a linkage of cancer registry and HIV registry data

Background. Increased incidence of cancer is documented in immunosuppressed transplant patients. Likewise, as survival increases for persons infected with the Human Immunodeficiency Virus (HIV), we expect their incidence of cancer to increase. The objective of this study was to examine the current gender specific spectrum of cancer in an HIV infected cohort (especially malignancies not currently associated with Acquired Immunodeficiency Syndrome (AIDS)) in relation to the general population.^ Methods. Cancer incidence data was collected for residents of Harris County, Texas who were diagnosed with a malignancy between 1975 and 1994. This data was linked to HIV/AIDS registry data to identify malignancies in an HIV infected cohort of 14,986 persons. A standardized incidence ratio (SIR) analysis was used to compare incidence of cancer in this cohort to that in the general population. Risk factors such as mode of HIV infection, age, race and gender, were evaluated for contribution to the development of cancer within the HIV cohort, using Cox regression techniques.^ Findings. Of those in the HIV infected cohort, 2289 persons (15%) were identified as having one or more malignancies. The linkage identified 29.5% of these malignancies (males 28.7% females 60.9%). HIV infected men and women had incidences of cancer that were 16.7 (16.1, 17.3) and 2.9 (2.3, 3.7) times that expected for the general population of Harris County, Texas, adjusting for age. Significant SIR's were observed for the AIDS-defining malignancies of Kaposi's sarcoma, non-Hodgkin's lymphoma, primary lymphoma of the brain and cancer of the cervix. Additionally, significant SIR's for non-melanotic skin cancer in males, 6.9 (4.8, 9.5) and colon cancer in females, 4.0 (1.1, 10.2) were detected. Among the HIV infected cohort, race/ethnicity of White (relative risk 2.4 with 95% confidence intervals 2.0, 2.8) or Spanish Surname, 2.2 (1.9, 2.7) and an infection route of male to male sex, with, 3.0 (1.9, 4.9) or without, 3.4 (2.1, 5.5) intravenous drug use, increased the risk of having a diagnosis of an incident cancer.^ Interpretation. There appears to be an increased risk of developing cancer if infected with the HIV. In addition to the malignancies routinely associated with HIV infection, there appears to be an increased risk of being diagnosed with non-melanotic skin cancer in males and colon cancer in females. ^

IN VITRO INDUCTION OF XENOIMMUNE RESPONSES TO LIPOSOMES CONTAINING HUMAN COLON TUMOR ANTIGENS

Liposomes prepared with human LS174T colon tumor cell membranes induce specific primary and secondary xenogeneic immune responses in BALB/c splenocytes in vitro. The multilamellar vesicular liposomes were prepared by adding sonicated membrane fragments in 8 mM CaCl(,2) to a dried lipid film. Cytoxic splenocytes generated in vivo exhibited specificity for the LS174T cell; liposomes elicited higher levels of cytotoxicity than did membranes (P < 0.01). Secondary blastogenic responses elicited in in vivo-primed spleen cells by liposomes also produced a significantly greater (P < 0.005) response than membranes. Subsequently, in vitro induction of primary blastogenic and cytotoxic responses by liposomes were accomplished and revealed similar kinetics to that of whole LS174T cell immunogens. Specificity of the in vitro-primed spleen cells was clearly demonstrated (P < 0.01) on a variety of human tumor cells using both the primed lymphocyte and cell-mediated cytotoxicity assays. The results of competitive inhibition tests with autologous lymphoblasts demonstrated that 30% of the cytotoxic activity was directed against lymphocyte antigens.^ The adjuvant effect of liposomes was shown to be mediated primarily by tumor antigens exposed on the outer surface of liposomes. Trypsinization of the liposomes which eliminated 96% of the surface protein reduced the ability of liposomes to induce cytotoxic splenocytes. The generation of cytolytic activity with liposomes of increasing protein concentration showed that while 10 (mu)g protein was threshold, 100 (mu)g protein induced maximal responses. In addition, membrane fluidity studies revealed that rigid liposomes were significantly (P < 0.05) more efficacious than fluid liposomes in inducing cytotoxicity.^ The induction of the primary response required the presence of nonadherent splenocytes bearing the Thy-1, Lyt-1, and Lyt-2 surface markers. The role of a Lyt-123 subpopulation was suggested by the inability of both the Lyt-1 and Lyt-2 depleted populations to completely restore the cytolytic levels to normal. In addition, the interaction of I-A('+) spleen adherent cells with liposomes for at least 8 hours was required to generate maximal cytotoxic activity. The phenotype of the cytotoxic effector was Thy-1('+), Lyt-2('+), and I-A('d-).^ Incorporation of tumor antigens into liposomes has thus enabled primary immunization in vitro to human colon cancer antigens and may afford an adaptable means to evaluate and to select specific immune responses, as well as to identify colon tumor-specific determinants.^

Role of cytochrome P450 in DNA damage produced by treatment of colon cells with 1,2-dimethylhydrazine

The study of colon cancer has taken advantage of the development of a model in animals in which tumors in the colon are easily induced by chemical treatment. When 1,2-dimethylhydrazine (DMH) is injected into rats tumor growth is observed in colon in preference to other tissues. This observation led us to investigate the Cytochrome P450 system in colon and its participation in the particular “colon sensitivity” to DMH. It has been established that the Cytochrome P450 system participates in the metabolism of DMH and the methyl carbonium product of Cytochrome P450 activation of DMH is responsible for DNA damage which is considered an initial step to carcinogenesis. The Cytochrome P450 system is a reasonable place to search for an explanation of this organotropic effect of DMH and we feel that the knowledge obtained from this study can take us closer to understanding the development of colonic malignancy. In our study we used a human colon cell line (LS174T) treated with DMH. The Cytochrome P450 system in the cells was manipulated with inducers of different isoforms of Cytochrome P450. The effect of DMH on colon cells was measured by determination of O-6-methylguanine which is a DNA adduct derived from the metabolism of this chemical and is associated with development of tumors. Our results support the hypothesis that Cytochrome P450 plays an important role in the damage to cellular DNA by DMH. This damage is increased after induction of Cytochromes P450 1A1 and 2E1. The effect of inhibition of the methyltransferase and glutathione systems on protection against DMH damage in colon demonstrated the importance of the protective role of the former and the lack of effective protection of the latter system. ^

Development of colorectal cancer gene therapy

Colorectal cancer is the number two cancer killer in the United States. Although primary colorectal cancer can be resected by surgery, patients often die from metastatic disease. Liver is the most common site of metastasis for colorectal cancer. It is difficult to selectively kill metastatic colon cancer cells without damaging normal liver functions. Thus it becomes a high priority to develop a selective targeting system for the treatment of colorectal cancer liver metastasis. ^ In the current study, a gene therapy strategy that allows a therapeutic gene to selectively destroy metastatic colon cancer cells without affecting normal liver cells is developed. The APC gene is frequently mutated in colorectal cancers. These mutations activate β-catenin responsive promoters. An optimized β-catenin responsive promoter, containing TCF consensus binding sites, was engineered for this study. This TCF promoter was found to express preferentially in APC mutated/β-catenin activated colorectal cancers while maintaining a low expression level in cell lines of liver origin. A recombinant adenoviral vector AdTCF-TK, in which the TCF promoter controls expression of the herpes simplex virus thymidine kinase gene, selectively destroyed colorectal cancer cells in vitro. AdTCF-TK virus and ganciclovir treatment also inhibited the growth of solid tumour derived from the colon cancer cell line DLD-1 in nude mice. In a control experiment, the growth inhibition effect of the same virus was attenuated in a liver cancer cell line. ^ In the present study, a novel method was developed to target therapeutic gene expression to colon cancer cells at reduced liver toxicity to the patients. The same gene therapy design may also be applied to treat tumours carrying mutations in the β-catenin gene, which is a central component of the APC signal transduction pathway. In summary, the principle for a rational design of a cancer specific treatment approach is demonstrated in this study. In the future, mutations in cancer patients will be more easily identified. Using the same principle developed in this study, specific regimen can be designed to treat these patients based on the specific genetic changes found in the tumour. ^

Logistic regression models for ordinal response: A study of self-efficacy in colorectal cancer screening

The ordinal logistic regression models are used to analyze the dependant variable with multiple outcomes that can be ranked, but have been underutilized. In this study, we describe four logistic regression models for analyzing the ordinal response variable. ^ In this methodological study, the four regression models are proposed. The first model uses the multinomial logistic model. The second is adjacent-category logit model. The third is the proportional odds model and the fourth model is the continuation-ratio model. We illustrate and compare the fit of these models using data from the survey designed by the University of Texas, School of Public Health research project PCCaSO (Promoting Colon Cancer Screening in people 50 and Over), to study the patient’s confidence in the completion colorectal cancer screening (CRCS). ^ The purpose of this study is two fold: first, to provide a synthesized review of models for analyzing data with ordinal response, and second, to evaluate their usefulness in epidemiological research, with particular emphasis on model formulation, interpretation of model coefficients, and their implications. Four ordinal logistic models that are used in this study include (1) Multinomial logistic model, (2) Adjacent-category logistic model [9], (3) Continuation-ratio logistic model [10], (4) Proportional logistic model [11]. We recommend that the analyst performs (1) goodness-of-fit tests, (2) sensitivity analysis by fitting and comparing different models.^