Novel Deleterious Dihydropyrimidine Dehydrogenase Variants May Contribute to 5-Fluorouracil Sensitivity in an East African Population

Clinical studies have identified specific genetic variants in dihydropyrimidine dehydrogenase (DPD; DPYD gene) as predictors of severe adverse toxicity to the commonly used chemotherapeutic 5-fluorouracil (5-FU); however, these studies have focused on European and European-American populations. Our laboratory recently demonstrated that additional variants in non-European haplotypes are predictive of 5-FU toxicity. The objective of this study was to identify potential risk variants in an understudied East African population relevant to our institution's catchment area. The DPYD protein-coding region was sequenced in 588 individuals of Somali or Kenyan ancestry living in central/southeast Minnesota. Twelve novel nonsynonymous variants were identified, seven of which significantly decreased DPD activity in vitro. The commonly reported toxicity-associated variants, *2A, D949V, and I560S, were not detected in any individuals. Overall, this study demonstrates a critical limitation in our knowledge of pharmacogenetic predictors of 5-FU toxicity, which has been based on clinical studies conducted in populations of limited diversity.

Clinical Pharmacogenetics Implementation Consortium guidelines for dihydropyrimidine dehydrogenase genotype and fluoropyrimidine dosing

The fluoropyrimidines are the mainstay chemotherapeutic agents for the treatment of many types of cancers. Detoxifying metabolism of fluoropyrimidines requires dihydropyrimidine dehydrogenase (DPD, encoded by the DPYD gene), and reduced or absent activity of this enzyme can result in severe, and sometimes fatal, toxicity. We summarize evidence from the published literature supporting this association and provide dosing recommendations for fluoropyrimidines based on DPYD genotype (updates at http://www.pharmgkb.org).

Epigenetic mechanisms of protein tyrosine phosphatase 6 suppression in diffuse large B-cell lymphoma: implications for epigenetic therapy

Protein tyrosine phosphatases such as PTPN6 can be downregulated in various neoplasms. PTPN6 expression by immunohistochemistry in 40 diffuse large B-cell lymphoma (DLBCL) tumors was lost or suppressed in 53% (21/40). To elucidate the molecular mechanisms of PTPN6 suppression, we performed a comprehensive epigenetic analysis of PTPN6 promoter 2 (P2). None of the DLBCL primary tumors (0/37) had PTPN6 hypermethylation on the CpG1 island using methylation-specific PCR, pyrosequencing, and high-resolution melting assays. However, hypermethylation in 57% (21/37) of cases was found in a novel CpG island (CpG2) in P2. PTPN6 gene suppression was reversed by 5-aza-deoxycytidine (5-Aza), a DNA methyltransferase inhibitor, and the histone deacetylase inhibitor (HDACi) LBH589. LBH589 and 5-Aza in combination inhibited DLBCL survival and PTPN6 hypermethylation at CpG2. The role of histone modifications was investigated with a chromatin-immunoprecipitation assay demonstrating that PTPN6 P2 is associated with silencing histone marks H3K27me3 and H3K9me3 in DLBCL cells but not normal B cells. 3-Deazaneplanocin A, a histone methyltransferase inhibitor, decreased the H3K27me3 mark, whereas HDACi LBH589 increased the H3K9Ac mark within P2 resulting in re-expression of PTPN6. These studies have uncovered novel epigenetic mechanisms of PTPN6 suppression and suggest that PTPN6 may be a potential target of epigenetic therapy in DLBCL.

Prognostic significance of thymidylate synthase, dihydropyrimidine dehydrogenase and thymidine phosphorylase protein expression in colorectal cancer patients treated with or without 5-fluorouracil-based chemotherapy

BACKGROUND

Low tumour expression levels of thymidylate synthase (TS), dihydropyrimidine dehydrogenase (DPD) and thymidine phosphorylase (TP) have been linked with improved outcome for colorectal cancer (CRC) patients treated with 5-fluorouracil (5-FU). It is unclear whether this occurs because such tumours have better prognosis or they are more sensitive to 5-FU treatment.

PATIENTS AND METHODS

Associations between TS, DPD and TP levels, determined by tissue microarrays and immunohistochemistry, and survival was evaluated in 945 CRC patients according to treatment status.

RESULTS

Low TS and DPD expression associated with worse prognosis in stage II [hazard ratio (HR) = 1.69, 95% confidence interval (CI) (1.09-2.63) and HR = 1.92 (95% CI 1.23-2.94), respectively] and stage III CRC patients treated by surgery alone [HR = 1.39 (95% CI 0.92-2.13) and HR = 1.49 (95% CI 1.02-2.17), respectively]. Low TS, DPD and TP associated with trends for better outcome in stage III patients treated with 5-FU [HR = 0.81 (95% CI 0.49-1.33), HR = 0.70 (95% CI 0.42-1.15) and HR = 0.66 (95% CI 0.39-1.12), respectively].

CONCLUSION

Low TS and DPD expression are prognostic for worse outcome in CRC patients treated by surgery alone, whereas low TS, DPD and TP expression are prognostic for better outcome in patients treated with 5-FU chemotherapy. These results provide indirect evidence that low TS, DPD and TP protein expression are predictive of good response to 5-FU chemotherapy.

Prognostication of pancreatic adenocarcinoma by expression of thymidine phosphorylase (TP) and its correlation with survival

4606

Background: Preclinical studies have indicated that TP is one of the most useful markers of tumor response to capecitabine; with elevated TP expression resulting in higher intratumor levels of 5-FU. TP level in the tumor may be associated directly with survival and may be up-regulated by XRT. Methods: Twenty patients (pts) who had newly diagnosed locally advanced pancreatic cancer, age ≥ 19 years, ECOG PS 0–2, and adequate organ function received 50.4 Gy XRT with capecitabine 1,600 mg/m2 M-F x 6 wks determined from our phase I study (JCO, Dec 2005). Following capecitabine-XRT, stable and responding pts received capecitabine 2,000mg/m2 x 14 days every 3 wks till progression. Restaging was performed every 9 wks. Tumor specimens were procured with EUS-FNA prior and week 2 after starting capecitabine-XRT to evaluate TP mRNA levels by RT-PCR. Results: TP levels were elevated post-XRT when compared to pre-XRT TP (p= 0.01). Each of the 20 pts had at least one observation of TP. Mean TP level of each pt was obtained by averaging the pre-XRT and post-XRT TP levels. If one value was missing, then the other value was used for the mean TP level. Mean TP level was significantly associated with survival using the Cox proportional hazards model (p= 0.0072). Pts were separated into two groups - those with high baseline TP level and those with lower TP level with a cut off value of 213.85 using median of mean TP level. It was observed that group with higher TP levels had better survival as compared to the group with lower TP levels. However, the survival curves of these two groups crossed over after 18 months. Conclusions: Our study suggests that the higher the TP level in tumor post-XRT, the better the survival. This is most probably due to a higher accumulation of 5-FU in tumor due to up-regulation of TP. Possible explanation for the two groups crossing over after 18 months may include heterogeneity in TP due to a difference in pharmacogenomics or idiosyncratic drug toxicity profile of capecitabine. Further studies of long-term effects of treatment with a larger number of pts are needed to study exact effects of capecitabine and XRT, and to evaluate the differential role of TP with survival.

[Table: see text]

Elucidating the mechanisms responsible for the previous failure of phase III clinical trials with eniluracil (EU) and development of a novel scheduling approach to optimize the efficacy of EU/5-fluorouracil (5-FU) combination therapy

2557

Background: Irreversible inhibition of dihydropyrimidine dehydrogenase (DPD) by EU blocks 5-FU catabolism allowing for oral 5-FU administration with complete bioavailability. Unfortunately, phase III trials with co-administered EU/5-FU showed inferiority vs. 5-FU/leucovorin, and were discontinued. We recently reported that competitive inhibition of human uridine phosphorylase (UP) and thymidine phosphorylase (TP) 5-FU-anabolic enzymes by EU is an important mechanism potentially responsible for clinical failure of the combined EU/5- FU regimen. We hypothesize that EU inhibition of UP and TP is transient, while that of DPD is prolonged, allowing for novel schedule dependent optimization of EU/5-FU dosing regimens with improved efficacy. Methods: In this phase I study, five patients received a single oral dose (2 mg, 5 mg or 10 mg) of EU 12–14 hours prior to scheduled resection of primary/metastatic colorectal cancer. Dosage was as follows: Two patients received the 2 mg dose, one patient received the 5 mg dose and two patients received the 10 mg dose. Matched normal and tumor tissue biopsies were immediately snap frozen and subsequently UP, TP and DPD activity was measured in vitro via HPLC detection of [6- 14C]-5-FU catabolites/anabolites. Peripheral blood mononuclear cell (PBMC) DPD activity was determined at baseline prior to EU administration, 30 min prior to surgery (Day 1), and on Days 2, 5 and 14 following EU administration. Results: At 12–14 hours following EU administration, there was an absence of inhibition of UP and TP, while DPD was significantly inhibited in matched tumor and normal tissue. Importantly, PBMC DPD activity was significantly inhibited by EU on Day 1 (12–14 hours after EU administration) and Day 2 (36 hours after EU administration) at 0 ± 0% and 17 ± 11% (mean ± SD) of baseline, respectively. Conclusions: These data demonstrate a differential recovery time of EU mediated inhibition of UP and TP compared to DPD, which permits future schedule dependent optimization of EU/5-FU therapy.

No significant financial relationships to disclose.

The 2-13C-5-fluorouracil breath test (FUBT) as a novel, rapid method for assessment of dihydropyrimidine dehydrogenase (DPD) activity in cancer patients: Initial characterization and comparison to the 2-13C-uracil breath test (UraBT)

2551

Background: The UraBT is currently in development as a phenotypic test to screen for DPD deficiency. Following an oral dose of 2-13C-uracil, the UraBT shows a significant relationship between breath 13CO2 metabolite formation and plasma 2-13C-uracil and 2-13C-dihydrouracil pharmacokinetics. We herein describe a novel, potentially more clinically relevant test in which a small oral dose of 2-13C-5-fluorouracil (5-FU) is administered, followed by assessment of breath 13CO2 metabolite formation as previously described for the UraBT. We hypothesize that the FUBT can rapidly assess interindividual variability in 5-FU catabolism and predisposition to 5-FU toxicity. Methods: Over two sessions separated by a seven day washout, a single dose (6mg/kg, p.o.) of 2-13C-uracil or 2-13C-5-FU was administered to patients with stage III-IV colorectal cancer (n = 4). Subsequent to drug administration, in each session, 13CO2 catabolite formation was quantified in the breath over eight hours. In a separate investigation over two sessions separated by a seven day washout, a single dose (3mg/kg, p.o.) of 2-13C-uracil or 213C-5-FU was administered to colorectal cancer patients with previously documented severe (n=2) or moderate (n=2) 5-FU dose-related hematological/gastrointestinal toxicity. Following drug administration 13CO2 catabolite formation was quantified over eight hours. 13CO2 concentration was expressed as Delta Over Baseline (DOB) in all sessions. Results: Compared to the UraBT, the FUBT showed an increased Cmax (50.7 ± 6.6 DOB/mg vs. 36.8 ± 7.8 DOB/mg; mean ± SD) and decreased Tmax (25 ± 4 min vs. 45 ± 6 min) for 13CO2 formation (p<0.05). The FUBT was able to distinguish patients with previously reported severe and moderate 5- FU toxicity, with 13CO2 Cmax values of 35.5 ± 9.5 DOB/mg (mean ± SD) and 59.8 ± 7.3 DOB/mg, respectively. Importantly, FUBT Cmax values positively correlated with DPD activity (rs=1.00, p<0.01). Conclusions: These data lend support to further development of the FUBT as a rapid and informative test to assess DPD activity and to predict susceptibility to severe dose-related 5-FU toxicity. [CA116964]

No significant financial relationships to disclose.

Dose dependent inhibition of uridine phosphorylase (UP) by eniluracil (EU): Was the clinical inferiority of the EU/5-fluorouracil (5-FU) phase III trials due to an unrecognized inhibition of 5-FU anabolism?

2058

Background: Eniluracil (EU) is an irreversible inactivator of dihydropyrimidine dehydrogenase (DPD). EU inhibits DPD dependent 5-fluorouracil (5-FU) catabolism, allowing for oral 5-FU administration with essentially complete bioavailability. Although earlier murine studies suggested an increased antitumor effect when EU was administered before 5-FU, clinical studies used co-administered EU and 5-FU (ratio: 10 EU:1 5-FU) (b.i.d.). These phase III trials demonstrated inferiority compared to a regimen of 5-FU/leukovorin, leading to discontinuation of EU development. We hypothesize that the clinical failure of this EU/5-FU schedule may have resulted from competitive inhibition of 5-FU anabolic (ANA) activation by EU. In this study we examined whether EU could competitively inhibit uridine phosphorylase (UP) or orotate phosphoribosyl transferase (OPRT), the primary ANA enzymes of 5-FU. Methods: The cytoplasmic fraction of human embryonic kidney cells (HEK-293) was used as the source of UP and OPRT. Reverse phase HPLC with radioactivity detection was used to quantify [2-14C]-uracil formation from [2-14C]-uridine (UP activity) and to quantify [6-14C]-FUMP formation from [6-14C]-5-FU (OPRT activity). For UP activity, reaction mixtures consisted of increasing concentrations of EU in phosphate buffer containing 150 μM [2-14C]-uridine. For OPRT activity, reaction mixtures consisted of increasing concentrations of EU in phosphate buffer containing 5 μM [6-14C]-FU and 100 μM benzylacyclouridine (UP inhibitor). Reactions were initiated with addition of UP/OPRT enzyme source and allowed to proceed for 30 min at 37°C. Results: EU displayed dose-dependent competitive inhibition of UP activity (IC50 = 0.375 mM). In particular, the EU/5-FU ratio of 2.5:1 produced approximately 50% inhibition of UP activity. In contrast, EU did not inhibit OPRT activity. Conclusions: This study demonstrates that EU competitively inhibits UP, an important enzyme in 5-FU ANA activation, and suggests that changing the dose ratio and/or increasing the interval between EU and 5-FU administration may be useful in optimizing 5-FU antitumor efficacy.

[Table: see text]

Prognostic and predictive significance of 5-fluorouracil metabolic enzymes in colorectal cancer

2021

Background: Low levels of the 5-Fluorouracil (5-FU) metabolic enzymes, thymidylate synthase (TS), dihydropyrimdine dehydrogenase (DPD) and thymidine phosphorylase (TP) are linked to improved survival in colorectal cancer (CRC) patients receiving 5-FU chemotherapy. However, whether they are prognostic (related to tumor biology) or predictive (drug sensitivity) indicators is not clarified. This study aimed to (1) discriminate the prognostic and predictive significance of TS, DPD and TP and (2) ascertain the clinical and molecular subtype associations of the proteins in a large sample series. Methods: Tissue arrays containing sections from 956 stage 2/3 CRC cases were stained immunohistochemically for TS, DPD and TP. Associations with clinical and molecular characteristics and survival according to treatment status were assessed by Kruskall-Wallis and Kaplan-Meier analysis. Results: Low TS levels were associated with late stage, proximal tumor location and absence of microsatellite instability, low DPD with younger age and late stage and low TP with proximal tumor location. Low levels of all three enzymes associated with absence of tumor infiltrating lymphocytes. There were no associations with gender, grade or ras and p53 mutation. In stage 2 patients treated by surgery alone, those with low DPD levels had a worse survival than those with high levels (p<0.01). Stage 3 patients treated with chemotherapy had a better survival than those without in subgroups of patients with low TS (p=0.05), DPD (p<0.01) and TP (p=0.03) but not high levels of the proteins. Conclusions: Our results suggest the improved outcome of 5FU-treated patients with low tumor TS, DPD and TP levels may be due primarily to a benefit from adjuvant treatment rather than a favorable prognosis. TS, DPD and TP levels may be useful indicators for identifying CRC patients likely to benefit from 5-FU treatment.

No significant financial relationships to disclose.

Dihydropyrimidine dehydrogenase deficiency (DPD) in GI malignancies: Experience of 4 years

2056

Background: 5-Fluorouracil (5-FU) is an integral part of treatment of GI malignancies. While normal DPD enzyme activity is rate limiting in 5-FU catabolism, its deficiency could increase concentrations of bioavailable 5-FU anabolic products leading to 5-FU related toxicity syndrome. With DPD deficiency, 5-FU is discontinued. Data regarding safety of capecitabine (CAP) in this population is scarce. Methods: Patients were tested for DPD deficiency after excessive toxicities from 5-FU and CAP at UAB between 2001 and 2005. DPD activity was evaluated by PBMC radio assay, genotyping of DPYD gene by DHPLC, or 2-13C uracil breath test (UraBT). Results: Of 23 patients with GI malignancies (small intestine, gastric, pancreatic, HCC, and colorectal) evaluated, 7 (30%) were DPD deficient. Among these 7 patients, DPD activity ranged from 0.064 - 0.18 nmol/min/mg. Age ranged from 51–75 years, M:F ratio = 1.3:1, and ethnicities included Caucasian (71%), African-American (14%) and South-Asian (14%). Four were treated with 5-FU/LV (2 Roswell; 2 Mayo); 2 CAP (1800mg/m2); and 2 high dose bolus 5-FU (1400mg/m2) + PN401 (tri-acetyluridine). Toxicities included mucositis (71%), diarrhea (43%), nausea (29%), memory loss/altered mental status (43%), cytopenias (43%), hypotension (14%), respiratory distress (14%), acute renal failure (14%), and severe skin rashes (43%). Re-challenge with CAP in 1 patient after the Mayo regimen caused grade 3 HFS only on dorsal surfaces of hands. One patient on PN401 had a grade 3 facial rash as the worst toxicity. Genotypic analysis of the DPYD gene in the second on PN401, who had severe leucopenia, demonstrated a heterozygous mutation (IVS14+1 G>A, DPYP*2A). UraBT in 2 patients revealed 1 to be DPD-deficient (DOB50 of 112.8; PDR of 49.4%) and borderline normal values (DOB50 of 130.9; PDR of 52.5%) in a second patient. There were 2 toxicity-related deaths (28%): 1 on CAP and 1 on 5-FU + PN401. Conclusions: DPD deficiency was observed in several ethnicities. Patients with CAP toxicities should also be tested for DPD deficiency. Role of PN401 in rescuing 5-FU toxicity in DPD deficiency is not clear. Screening patients for DPD deficiency prior to administration of 5-FU or CAP, using UraBT, could potentially lower risk of toxicity. Future studies should validate this technique.

[Table: see text]

Molecular basis of altered uracil catabolism in individuals with 5-FU toxicity and normal DPD enzyme activity

3070

Background: Dihydropyrimidine dehydrogenase (DPD) deficiency accounts for approximately 43% of grade 3–4 toxicity to 5-Fluorouracil (5-FU). However, a significant number of patients with normal DPD enzyme activity remain with unexplained molecular basis of 5-FU toxicity. It has been suggested by the few cases previously reported that deficiency of dihydropyrimidinase (DHP)enzyme encoded by the DPYS gene and/or beta-ureidopropionase enzyme, encoded by the BUP-1 gene, could also be implicated in 5-FU toxicity. Methods: This study included 40 volunteers with known 13C-UraBT and DPD enzyme activity, 25 cancer patients with 5-FU toxicity despite normal DPD enzyme activity, and 25 liver biopsies from cancer patients with different grades of toxicity. All samples were analyzed for molecular defects in the DPYS and BUP-1 genes, using DHPLC and RT-PCR techniques. Results: Molecular analysis of the DPYS gene revealed the presence of two non-conservative amino acid changes, one frame-shift mutation that leads to a stop codon and premature termination of the DHP protein, five silent mutations, nine intronic sequence variations, two sequence variations in the 5’UTR and one in the non-coding region of exon 10. Molecular analysis of the BUP-1 gene revealed the presence of two non-conservative amino acid changes, one of which (314C>A: A85E) has already been reported to abolish enzyme activity; six silent mutations, four intronic sequence variations, one polymorphism in the 5’upstream sequence, and one sequence variation in each of the 5’UTR and the 3’UTR. Conclusions: The molecular basis of 5-FU toxicity is not limited to DPD deficiency; since molecular defects in genes downstream of DPD can potentially also impair 5-FU catabolism. Genetic testing for molecular defects in DPYS and BUP-1 may predict patients at risk of developing 5-FU toxicity despite having normal DPD enzyme activity. Assessing the integrity of the entire uracil catabolic pathway might be crucial to avoid toxicity in a significant group of patients receiving 5-FU or a related drug (CA62164).

No significant financial relationships to disclose.

Upregulation of thymidine phosphorylase (TP) by radiation (XRT): Phase II study of capecitabine (CAP) with XRT in pts with locally advanced (LA) pancreatic cancer

14001

Background: Preliminary studies have shown that XRT unregulates TP, the main enzyme responsible for activity of CAP. The objectives of this phase II study were to further evaluate effect of XRT on TP, DPD, and TNF-alpha as well as response and efficacy of CAP with concurrent XRT in pts with LA pancreatic cancer. Methods: Pts received 50.4 Gy XRT with CAP at 1600 mg/m2 M-F × 6 wks determined from our phase I study (JCO, Dec 2005). Following CAP-XRT, stable and responding pts on CT scan were treated with CAP 2000mg/m2 × 14 days q 3 wks till progression. Restaging was performed every 9 wks. Tumor specimens were procured with EUS-FNA 1 wk prior and 2 wks after CAP-XRT to evaluate TP, DPD, and TNF-alpha mRNA levels by RT-PCR. A sample size of 20 was selected (mean 1 vs. S with mean 0=13.5; alpha = 0.05; power = .99; t-test). Results: 19 pts (median age: 67; M/F: 7/12) were enrolled at UAB between March 2004 and June 2005. 4 pts (21%) had confirmed partial responses and 13 (68%) had stable disease. 2 pts underwent surgery (Ro in 1; extensive fibrosis in 1). Six-month survival rate was 89%. We have not met enough deaths to estimate median survival. Grade 3 and 4 toxicities included: nausea/vomiting (5%), thrombosis (5%), hyperbilirubinemia (5%), and grade 3 GI bleeding (5%). No hematological toxicities except grade 1 thrombocytopenia (5%) and grade 1 anemia (10%). All pts completed full CAP-XRT with 3 dose reductions (by 20%). Pts received mean of 5.4 cycles (range: 3–15) of CAP alone with a total of 104 cycles with dose reductions in 7 cycles (by 25%). TP was elevated during wk 2 when compared to pre-XRT TP (P = .005) but DPD was not (P = .13) nor was TNF-alpha (P = .37). No correlation between TP and TNF-alpha was noticed. No association between TP/DPD ratio and efficacy of CAP was identified. Tumor TP expression was higher (183.16) in pt with GI bleeding. Conclusions: This Phase II study further confirms our Phase I results that CAP-XRT is an effective, tolerable, and an easy alternative to infusional 5-FU regimen for pts with LA pancreatic cancer. Also TP upregulation by XRT was statistically significant. While these results support use of CAP-XRT in pancreatic cancer, there appears to be additional genes (other than TP, DPD) associated with response to CAP and CAP-XRT.

[Table: see text]

Retroviral transduction of human dihydropyrimidine dehydrogenase cDNA confers resistance to 5-fluorouracil in murine hematopoietic progenitor cells and human CD34+-enriched peripheral blood progenitor cells

Severe 5-fluorouracil (5-FU) toxicity has been reported among patients lacking dihydropyrimidine dehydrogenase (DPD) enzymatic activity. DPD is the principal enzyme involved in the degradation of 5-FU to 5'-6'-dihydrofluorouracil, which is further metabolized to fluoro-beta-alanine. We demonstrate here that overexpression of human DPD confers resistance to 5-FU in NIH3T3 cells, mouse bone marrow cells, and in human CD34+-enriched hematopoietic progenitor cells. An SFG-based dicistronic retroviral vector containing human DPD cDNA, an internal ribosomal entry site (IRES), and the neomycin phosphotransferase (Neo) gene was constructed (SFG-DPD-IRES-Neo). Transduced NIH3T3 cells demonstrated a 2-fold (ED50) increase in resistance to a 4-hour exposure of 5-FU in comparison to nontransduced cells. Expression of DPD was confirmed by Northern and Western blot analyses, and DPD enzyme activity was detectable only in transduced cells. Infection of mouse bone marrow cells with this retroviral construct resulted in an increased number of 5-FU-resistant CFU-GM colonies, compared to mock-transduced bone marrow in both 4-hour and 12- to 14-day exposures. Infection of human CD34+-enriched cells with this construct and incubation with 5-FU (10(-6) M) for 14 days also resulted in an increased number of 5-FU-resistant colonies. Retroviral transduction of human hematopoietic progenitor cells with a cDNA-expressing human DPD conferred resistance to 5-FU in NIH3T3 cells, mouse bone marrow cells, and human CD34+-enriched cells. These results encourage the use of this gene as a method to protect patients from 5-FU myelotoxicity.

Role of matrix metalloproteinases in colorectal carcinogenesis

OBJECTIVE

To measure coexpression of matrix metalloproteinase (MMP)-2, MMP-7, and MMP-9 genes by real-time quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR) in benign and malignant phases of colorectal carcinogenesis.

SUMMARY BACKGROUND DATA

Matrix metalloproteinases degrade and remodel the extracellular matrix and have been implicated in facilitating carcinoma cells to invade and metastasize. MMP-2, MMP-7, and MMP-9 have been shown to be overexpressed in various carcinomas; however, simultaneous examination of these enzymes in human normal mucosa, adenoma, and carcinoma has not been performed to date.

METHODS

Between January 1, 1998, and June 15, 2000, 40 patients underwent colectomy and harvest and snap-freezing of normal mucosa, adenoma, and carcinoma. Five patients had adenoma and carcinoma in the same specimen; 35 had either adenoma (n = 6) or carcinoma (n = 29). Taqman qRT-PCR methodology was used to measure MMP gene copy number and normalized to beta-actin RNA expression.

RESULTS

The mean age was 62 +/- 4 years, with 22 men and 18 women. One fifth of the adenomas exhibited severe dysplasia. MMP-7 gene expression was significantly increased in adenomas (43 times normal mucosa) but did not increase further in carcinomas (50 times normal mucosa). MMP-2 and MMP-9 were not different in adenomas (1.8 and 1.4 times normal mucosa, respectively) but were elevated in carcinomas (2.2 and 1.8 times normal mucosa, respectively). There was no correlation between size or dysplasia in adenomas or AJCC stage in carcinomas and MMP gene expression.

CONCLUSIONS

Overexpression of MMP-7 is an early event in the adenoma-to-carcinoma pathway, and expression does not appear to increase further in carcinomas. MMP-2 and MMP-9 appear to be primarily overexpressed in carcinomas. This may be one mechanism by which adenoma cells gain the ability to invade and carcinoma cells to metastasize.

Current status of oral chemotherapy for colorectal cancer

The treatment of advanced colorectal cancer over the past 4 decades has required the use of intravenous chemotherapy, most typically fluorouracil (5-FU). The possibility of providing an alternative to intravenous delivery while at the same time improving the quality of life of patients who require fluorouracil for advanced or adjuvant therapy has provided the stimulus for the development of oral fluoropyrimidine drugs. Five oral fluoropyrimidine drugs have recently entered clinical trials in the United States. These include capecitabine (Xeloda), UFT (uracil and tegafur) or UFT/leucovorin (Orzel), eniluracil (ethynyluracil), S-1, and BOF A-2. At least two of these drugs have demonstrated survival equivalent to the standard intravenous fluorouracil and leucovorin regimens used to treat advanced colorectal cancer. This, together with less severe toxicity and potential increased quality of life, should lead to approval of one or more of these oral agents in the near future. Based on both patient and physician acceptance of oral fluoropyrimidines, other oral drugs from classes other than fluoropyrimidines will likely be developed in the near future.

Clinical implications of dihydropyrimidine dehydrogenase on 5-FU pharmacology

Dihydropyrimidine dehydrogenase (DPD) is the initial rate-limiting enzyme in the catabolism of 5-fluorouracil (5-FU), accounting for catabolism of over 85% of an administered dose of 5-FU. DPD plays an important role in regulating the availability of 5-FU for anabolism. DPD also accounts for much of the variability observed with the therapeutic use of 5-FU. This includes variable 5-FU levels over 24 hours during a continuous infusion; the widely reported variability in the pharmacokinetics of 5-FU; the observed variable bioavailability that led to the recommendation that 5-FU not be administered as an oral agent; and lastly, the observed variability in both toxicity and drug response (resistance) after identical 5-FU doses. Knowledge of the DPD level, as well as the levels of other potentially important molecular markers (e.g., thymidylate synthase), may permit adjustments or modulation of the 5-FU dose that can result in an increase in the therapeutic efficacy of 5-FU.

Molecular cloning and characterization of the human dihydropyrimidine dehydrogenase promoter

Several studies have demonstrated that dihydropyrimidine dehydrogenase (EC 1.3.1.2) has a critical role in the pharmacokinetics of the anticancer agent 5-fluorouracil. We previously reported the structural organization of the human DPYD gene. In this article, we describe the molecular cloning and functional characterization of 1.2 kb of the 5' flanking region of the DPYD gene. Sequence analysis demonstrated that this region of the DPYD gene lacks the typical TATA or CCAAT boxes with several GC-rich regions containing potential cis-regulatory elements. Progressive 5' deletions of the 5' flanking region were fused to the luciferase reporter gene and transient expression measured following transfection into HeLa and 293 cells. Comparative analysis of luciferase activity revealed that a 208 bp region of the DPYD gene (-121/+86) contained equivalent transcriptional activity to the complete 1.2 kb 5' flanking region of the DPYD gene. Site-directed mutagenesis of the luciferase reporter constructs demonstrated that the -72/-23 sequence contained two regulatory regions (designated elements I and II) essential for promoter activity. Gel shift experiments demonstrated that both regulatory elements specifically bind with protein(s) from nuclear extracts of 293 cells. Competitive binding experiments with 293 nuclear extracts and radiolabeled oligonucleotides (corresponding to elements I and II) suggest that the same protein(s) bind to both regulatory elements. We conclude that constitutive expression of the DPYD gene involves a limited GC-rich region of the 5' flanking sequence of the DPYD gene which contains two regulatory elements.

Activation of protein kinase C induces nuclear translocation of RFX1 and down-regulates c-myc via an intron 1 X box in undifferentiated leukemia HL-60 cells

Treatment of human promyelocytic leukemia cells (HL-60) with phorbol 12-myristate 13-acetate (PMA) is known to decrease c-myc mRNA by blocking transcription elongation at sites near the first exon/intron border. Treatment of HL-60 cells with either PMA or bryostatin 1, which acutely activates protein kinase C (PKC), decreased the levels of myc mRNA and Myc protein. The inhibition of Myc synthesis accounted for the drop in Myc protein, because PMA treatment had no effect on Myc turnover. Treatment with PMA or bryostatin 1 increased nuclear protein binding to MIE1, a c-myc intron 1 element that defines an RFX1-binding X box. RFX1 antiserum supershifted MIE1-protein complexes. Increased MIE1 binding was independent of protein synthesis and abolished by a selective PKC inhibitor, which also prevented the effect of PMA on myc mRNA and protein levels and Myc synthesis. PMA treatment increased RFX1 in the nuclear fraction and decreased it in the cytosol without affecting total RFX1. Transfection of HL-60 cells with myc reporter gene constructs showed that the RFX1-binding X box was required for the down-regulation of reporter gene expression by PMA. These findings suggest that nuclear translocation and binding of RFX1 to the X box cause the down-regulation of myc expression, which follows acute PKC activation in undifferentiated HL-60 cells.