p16INK4a promoter mutations are frequent in primary sclerosing cholangitis (PSC) and PSC-associated cholangiocarcinoma

Review article: current management of primary sclerosing cholangitis

The management of primary sclerosing cholangitis (PSC) is hindered by incomplete understanding of the pathogenesis of the disease and the lack of good prognostic models. Few large randomized controlled trials of drug therapy have been published. Best practice in the management of PSC is currently based therefore on careful interpretation of the available evidence, close observation of individual patients and clinical experience of the disease. Drug therapy is useful for alleviating symptoms. Ursodeoxycholic acid may slow progression of the disease and reduce the frequency of complications. Consensus is emerging on the issues of screening for the malignant complications of PSC and the indications for liver transplantation are becoming broader and encompassing the earliest stages of cholangiocarcinoma. In view of the rarity of the disease in the general population, large international collaborations to study PSC are necessary to provide clearer answers in areas of uncertainty, and these are now beginning to emerge.

Frequent p16ink4a inactivation is an early and frequent event of intraductal papillary neoplasm of the liver arising in hepatolithiasis

Intraductal papillary neoplasm of the liver (IPNL) is a precursor lesion of intrahepatic cholangiocarcinoma (ICC) arising in hepatolithiasis. In this study, 98 foci of IPNL identified in 39 surgically resected hepatolithiatic livers were investigated for expression of p16INK4a, cyclin D1, p21WAF1/CIP1, p53, mouse double-minute 2 (MDM2), and pRb. In addition, methylation-specific polymerase chain reaction (MSP) for p16 INK4a promoter region was performed in these foci. Nonneoplastic bile ducts from 11 hepatolithiatic livers, 5 histologically normal livers, and 9 cases of nonpapillary conventional ICC were used as controls. Decreased expression of p16INK4A was seen in IPNL group 1 with mild dysplasia and continued along the progression of IPNL to ICC. The expression of cyclin D1, p21WAF1/CIP1,and pRb gradually increased along the progression of IPNL to ICC and became significantly high in IPNL of group 3 (carcinoma in situ). The expression of p53 and MDM2 was increased in IPNL group 3 and group 4 with evident invasive carcinoma. MSP revealed that 54.6% of 44 IPNL foci harbored p16INK4a promoter hypermethylation, and such foci were significantly correlated with decreased expression of p16INK4a protein. Ki-67 labeling index exhibited a stepwise increase from IPNL group 1 to group 4. We conclude that p16INK4a inactivation, due mainly to its promoter hypermethylation, is a frequent and early event of IPNL and may be responsible for genetic and epigenetic alterations of other cell cycle regulators in IPNL.

Cholangiocarcinoma: molecular targeting strategies for chemoprevention and therapy

Cholangiocarcinomas are devastating cancers that are increasing in both their worldwide incidence and mortality rates. The challenges posed by these often lethal biliary tract cancers are daunting, with conventional treatment options being limited and the only hope for long-term survival being that of complete surgical resection of the tumor. Unfortunately, the vast majority of patients with cholangiocarcinoma typically seek treatment with advanced disease, and often these patients are deemed poor candidates for curative surgery. Moreover, conventional chemotherapy and radiation therapy have not been shown to be effective in prolonging long-term survival, and although photodynamic therapy combined with stenting has been reported to be effective as a palliative treatment, it is not curative. Thus, there is a real need to develop novel chemopreventive and adjuvant therapeutic strategies for cholangiocarcinoma based on exploiting select molecular targets that would impact in a significant way on clinical outcome. This review focuses on potential preventive targets in cholangiocarcinogenesis, such as inducible nitric oxide synthase, cyclooxygenase-2, and altered bile acid signaling pathways. In addition, molecular alterations related to dysregulation of cholangiocarcinoma cell growth and survival, aberrant gene expression, invasion and metastasis, and tumor microenvironment are described in the context of various clinical and pathological presentations. Moreover, an emphasis is placed on the importance of critical signaling pathways and postulated interactions, including those of ErbB-2, hepatocyte growth factor/Met, interleukin-6/glycoprotein130, cyclooxygenase-2, vascular endothelial growth factor, transforming growth factor-beta, MUC1 and MUC4, beta-catenin, telomerase, and Fas pathways as potential molecular therapeutic targets in cholangiocarcinoma.

The V599E BRAF mutation is uncommon in biliary tract cancers

Activating point mutations of the BRAF oncogene have been identified in several solid tumors, most commonly in cutaneous melanomas and papillary carcinomas of the thyroid. A specific point mutation--V599E--accounts for the overwhelming majority of these mutational events. We explored the frequency of the V599E BRAF mutation in biliary tract cancers. In all, 62 archival biliary tract cancers, including 15 gallbladder cancers, 15 extrahepatic, and 10 intrahepatic cholangiocarcinomas from the United States, and 22 gallbladder carcinomas from Chile were analyzed for the V599E mutation of the BRAF gene using three distinct methods: direct sequencing, a primer extension method (Mutector assay), and the highly sensitive quantitative Gap Ligase Chain Reaction. The common V599E mutation was not identified in any of the 62 biliary cancer samples using these three methods of detection. The V599E somatic mutation of the BRAF gene is absent in biliary tract cancers, at least in the two geographic populations (United States and Chile) examined. Activation of the RAS/RAF/MAP kinase pathway in biliary tract cancers is likely to be secondary to oncogenic RAS mutations, or due to mutations of the BRAF gene at nucleotide positions not explored in the current study.

A review and update on cholangiocarcinoma

Cholangiocarcinoma is a malignant neoplasm arising from the biliary epithelium that was first described by Durand-Fardel in 1840. Today, it continues to defy diagnosis and treatment. It is difficult to diagnose in part because of its relative rarity, and because it is clinically silent until it becomes advanced disease with obstructive symptoms. The worldwide incidence of cholangiocarcinoma has risen over the past three decades. There is marked geographic variability in the prevalence of this disease, due in large part to regional environmental risk factors. Surgical resection remains the only curative treatment, and high priorities are improving diagnostic methods, and clinical staging for resection once the disease is suspected. A recent trend towards aggressive surgical management has improved outcomes. Chemotherapy, palliative stenting, and radiation are reserved for patients who are not resectable, those with recurrence after surgery, and those who decline surgical intervention. Recent trials using combination systemic chemotherapy and neoadjuvant chemoradiation are promising, but require further study. Over the past five years, several important studies have yielded new insights into the molecular mechanisms of cholangiocarcinoma tumorigenesis. In this review we discuss epidemiology, etiologic factors, molecular pathogenesis, diagnosis, staging, and treatment of cholangiocarcinoma. Particular focus is on recent studies into the cellular and molecular pathogenesis of the disease, recent chemotherapy trials, and newer methods of staging and screening for this devastating malignancy.

Diagnosis and treatment of cholangiocarcinoma

Cholangiocarcinoma presents a formidable diagnostic and treatment challenge. The majority of patients present with unresectable disease and have a survival of less than 12 months following diagnosis. Progress has been made by the appropriate selection of patients for treatment options including resection, with the routine use of more aggressive resections in order to achieve margin-negative resections. This has resulted in longer survival times for these patients. Neoadjuvant and adjuvant therapies have, for the most part, not improved survival in patients with this tumor, and new strategies are needed to improve this line of therapy. The prognosis for unresectable patients is poor, and palliative measures should be aimed at increasing quality of life first and increasing survival second.

Implication of the INK4a/ARF locus in gastroenteropancreatic neuroendocrine tumorigenesis

The INK4a/ARF locus on chromosome 9p21 is one of the important defenses against tumor development and engages both the Rb and the p53 tumor suppressor pathways through its capacity to encode two distinct proteins, p16(INK4a) and p14(ARF). Despite controversial reports, the body of present data suggests that tumor suppressors p16(INK4a) and p14(ARF) are targets of in-activation in GEP-NETs. Moreover, tumor type-specific aberrant p16(INK4a) silencing appears to be associated with advanced tumor stage and may function as a predictor of patients' outcome after surgical resection. Since conventional histological and biochemical assessment are limited with respect to predicting GEP-NET behavior or outcome, methylation profiles including INK4a/ARF might offer a tool to refine future diagnosis and therapeutic management of GEP-NET patients.

Diagnosis and treatment of cholangiocarcinoma

Epidemiologic studies have demonstrated increasing mortality rates from intrahepatic cholangiocarcinoma during the past decades. Primary sclerosing cholangitis is the most important predisposing condition to the development of cholangiocarcinoma. Improvements in noninvasive diagnostic techniques have led to decreased use of invasive procedures. Magnetic resonance imaging (MRI) has the potential to depict parenchymal, ductal, and vascular tumor involvement. However, diagnosis can be difficult, and often ultrasonography, MRI, CT, and invasive cholangiography are complementary investigations. Genetic aberrations in brush cytology specimens should be explored further in prospective studies. Endoscopic ultrasonography, intraductal ultrasonography, and positron emission tomography are interesting techniques that are under evaluation. Radical surgery with negative histologic margins is the only curative option in cholangiocarcinoma. With more aggressive surgical approaches, including partial hepatectomy, 3-year survival rates of 35% to 50% can be achieved. Liver transplantation for unresectable cholangiocarcinoma was shown to be feasible in pilot studies of highly selected patients.

Progression of gene hypermethylation in gallstone disease leading to gallbladder cancer

BACKGROUND

Aberrant methylation of tumor-suppressor genes is associated with a loss of gene function that can afford selective growth advantages to sporadic neoplastic cells arising during gallbladder inflammation.

METHODS

Fifty-four gallbladder neoplasms were selected from tumor banks in the United States and Chile. Each of the neoplasms was subjected to methylation-specific polymerase chain reaction to detect promoter methylation associated with six candidate tumor-suppressor genes (p16, APC, methylguanine methyltransferase, hMLH1, retinoic acid receptor beta-2, and p73) implicated in multiple human cancer types.

RESULTS

Aberrant methylation of any of the six candidate tumor-suppressor genes was detected in 72% of the gallbladder neoplasms, 28% of the cases of chronic cholecystitis, and in only 1 of the 15 normal gallbladder controls. The four most commonly methylated genes in the gallbladder cancers were p16 (56%), p73 (28%), APC (27%), and hMLH1 (14%). Significant differences in gene methylation were discovered between US gallbladder cancers and those from Chile, where gallbladder cancer is one of the leading causes of cancer-related deaths. APC methylation was present in 42% of the US cases but in only 14% of the Chilean tumors (P =.028). p73 methylation was common among the Chilean cancers (40%) compared with those from the United States (13%; P =.034).

CONCLUSIONS

The acquisition of hypermethylation at multiple tumor-suppressor gene-promoter sites may contribute to tumor formation and progression within the chronically inflamed gallbladder. The apparent differences in methylation patterns among the Chilean and US gallbladder cases may indicate a unique biology associated with this cancer in different parts of the world.

p16 INK4a gene promoter variation and differential binding of a repressor, the ras-responsive zinc-finger transcription factor, RREB

BALB/c mice are susceptible to the development of pristane-induced plasma cell tumors, and have a rare allelic variant in the coding region of the p16(INK4a) (p16) tumor suppressor gene that produces a protein with impaired activity. We have now found that the BALB/c p16 promoter has an allelic variant that may also compromise p16 activity. Following pristane treatment, BALB/c p16 mRNA levels in B cells were lower than that in DBA/2 or C.D2-Pctr1, a resistant BALB/c congenic strain that harbors DBA/2 chromatin surrounding the p16 locus. Four sequence variants were found between BALB/c and DBA/2 in the p16 promoter region. In reporter assays, the DBA promoter was at least four times more active in driving luciferase expression than the BALB/c promoter. Most of the difference in activity was localized to a single nucleotide deletion in BALB/c. This deletion created a consensus binding site for RREB, a ras-responsive transcriptional element with zinc-finger binding motifs. Transient transfections with RREB confirmed that the p16 promoter can be downregulated by RREB, in a Ras- or Mek-dependent manner, and that the BALB/c promoter is more sensitive than DBA/2 to regulation by RREB. BALB/c mice have both regulatory and coding region defects that may contribute to the impairment of p16 gene function.