Susanne E. Korsse

The long and winding road to rational treatment of cancer associated with LKB1/AMPK/TSC/mTORC1 signaling

The liver kinase B1 (LKB1)/adenosine mono-phosphate-activated protein kinase (AMPK)/tuberous sclerosis complex (TSC)/mammalian target of rapamycin (mTOR) complex (mTORC1) cassette constitutes a canonical signaling pathway that integrates information on the metabolic and nutrient status and translates this into regulation of cell growth. Alterations in this pathway are associated with a wide variety of cancers and hereditary hamartoma syndromes, diseases in which hyperactivation of mTORC1 has been described. Specific mTORC1 inhibitors have been developed for clinical use, and these drugs have been anticipated to provide efficient treatment for these diseases. In the present review, we provide an overview of the metabolic LKB1/AMPK/TSC/mTORC1 pathway, describe how its aberrant signaling associates with cancer development, and indicate the difficulties encountered when biochemical data are extrapolated to provide avenues for rational treatment of disease when targeting this signaling pathway. A careful examination of preclinical and clinical studies performed with rapamycin or derivatives thereof shows that although results are encouraging, we are only half way in the long and winding road to design rationale treatment targeted at the LKB1/AMPK/TSC/mTORC1 pathway. Inherited cancer syndromes associated with this pathway such as the Peutz–Jeghers syndrome and TSC, provide perfect models to study the relationship between genetics and disease phenotype, and to delineate the complexities that underlie translation of biochemical and genetical information to clinical management, and thus provide important clues for devising novel rational medicine for cancerous diseases in general.

Targeting LKB1 signaling in cancer.

The serine/threonine kinase LKB1 is a master kinase involved in cellular responses such as energy metabolism, cell polarity and cell growth. LKB1 regulates these crucial cellular responses mainly via AMPK/mTOR signaling. Germ-line mutations in LKB1 are associated with the predisposition of the Peutz-Jeghers syndrome in which patients develop gastrointestinal hamartomas and have an enormously increased risk for developing gastrointestinal, breast and gynecological cancers. In addition, somatic inactivation of LKB1 has been associated with sporadic cancers such as lung cancer. The exact mechanisms of LKB1-mediated tumor suppression remain so far unidentified; however, the inability to activate AMPK and the resulting mTOR hyperactivation has been detected in PJS-associated lesions. Therefore, targeting LKB1 in cancer is now mainly focusing on the activation of AMPK and inactivation of mTOR. Preclinical in vitro and in vivo studies show encouraging results regarding these approaches, which have even progressed to the initiation of a few clinical trials. In this review, we describe the functions, regulation and downstream signaling of LKB1, and its role in hereditary and sporadic cancers. In addition, we provide an overview of several AMPK activators, mTOR inhibitors and additional mechanisms to target LKB1 signaling, and describe the effect of these compounds on cancer cells. Overall, we will explain the current strategies attempting to find a way of treating LKB1-associated cancer.

Pancreatic cancer risk in Peutz-Jeghers syndrome patients: a large cohort study and implications for surveillance

Background Although Peutz-Jeghers syndrome (PJS) is known to be associated with pancreatic cancer (PC), estimates of this risk differ widely. This hampers counselling of patients and implementation of surveillance strategies. We therefore aimed to determine the PC risk in a large cohort of Dutch PJS patients. Methods PJS was defined by diagnostic criteria recommended by the WHO, a proven LKB1 mutation, or both. All patients with a presumptive diagnosis of pancreatic, ampullary or distal bile duct cancer were identified. Cases were reviewed clinically, radiologically and immunohistochemically. Cumulative PC risks were calculated by Kaplan-Meier analysis and relative risks by Poisson regression analysis. Results We included 144 PJS patients (49% male) from 61 families (5640 person years follow-up). Seven (5%) patients developed PC at a median age of 54 years. Four patients (3%) were diagnosed with distal bile duct (n=2) or ampullary cancer (n=2) at a median age of 55 years. The cumulative risk for PC was 26% (95% CI 4% to 47%) at age 70 years and relative risk was 76 (95% CI 36 to 160; p<0.001). The cumulative risk for pancreatico-biliary cancer was 32% (95% CI 11% to 52%) at age 70 years, with a relative risk of 96 (95% CI 53 to 174; p<0.001). Conclusions PJS patients have a highly increased risk for pancreatico-biliary cancer. Therefore, patients are eligible for surveillance within well defined research programmes to establish the benefit of such surveillance.

Identification of molecular alterations in gastrointestinal carcinomas and dysplastic hamartomas in Peutz-Jeghers syndrome

Peutz-Jeghers syndrome (PJS) is caused by mutations in the LKB1 gene. It is characterized by gastrointestinal polyposis and an increased cancer risk, mainly in the gastrointestinal tract. Mechanisms of PJS-associated carcinogenesis are unclear. We investigated the involvement of candidate genes and molecular pathways in PJS-associated gastrointestinal cancers and dysplastic hamartomas. Cases were selected from the Dutch PJS cohort. Available tissue was immunostained for phospho-S6, β-catenin, P53 and SMAD4. DNA was isolated from carcinoma tissue and dysplastic and non-dysplastic areas of hamartomas specifically. Mutation analyses were done for BRAF, KRAS and P53, and loss of heterozygosity (LOH) analyses for LKB1 and P53. Twenty-four of 144 patients (17%) developed 26 gastrointestinal malignancies at a median age of 49 years (interquartile range: 35-60). Eleven of 792 hamartomas (1.4%) of 9 patients were classified as dysplastic. LOH of LKB1 was detected in three of six (50%) carcinomas and in the dysplastic part of three of five (60%) hamartomas. Aberrant P53 expression was observed in 8 of 15 (53%) carcinomas. Six carcinomas with P53 overexpression harboured a P53 mutation, with loss of the remaining wild-type allele in four. Two hamartomas showing P53 overexpression in high-grade dysplastic foci harboured a P53 mutation with LOH. Loss of nuclear SMAD4 was observed in high-grade dysplastic foci of two of four (50%) hamartomas, in contrast to low-grade dysplastic foci (0/4) and non-dysplastic epithelium. Our findings suggest a role for mutant P53 in PJS-associated gastrointestinal carcinogenesis. Inactivation of transforming growth factor-β/bone morphogenetic protein signalling and complete loss of LKB1 might be involved in dysplastic transformation of gastrointestinal hamartomas specifically.

Small bowel endoscopy and Peutz-Jeghers syndrome

Peutz-Jeghers syndrome (PJS) is a rare, autosomal dominant inherited disease. It is clinically characterized by the development of gastrointestinal hamartomas, mainly located in the small bowel. These hamartomas are prone to complications such as intussusceptions, abdominal complaints and anaemia. Furthermore, patients are at increased risk for developing small bowel cancer. Therefore, regular surveillance of the small bowel is indicated. However, the optimal strategy for surveillance has not been determined yet. This review gives an overview of the different techniques that have been described to examine the small bowel of PJS patients. First, a number of radiologic and endoscopic imaging modalities with diagnostic value are discussed. Secondly, recently developed advanced endoscopy techniques are described that can serve both as a diagnostic and therapeutic tool in the surveillance of the small bowel. Finally, a recommendation is given how to apply these individual techniques for small bowel surveillance in a step-up approach.

Peutz-Jeghers syndrome and family planning: the attitude towards prenatal diagnosis and pre-implantation genetic diagnosis

Peutz–Jeghers syndrome (PJS) is a hereditary disorder caused by LKB1 gene mutations, and is associated with considerable morbidity and decreased life expectancy. This study was conducted to assess the attitude of PJS patients towards family planning, prenatal diagnosis (PND) and pregnancy termination, and pre-implantation genetic diagnosis (PGD). In a cross-sectional study, 61 adult PJS patients were asked to complete a questionnaire concerning genetic testing, family planning, PND and PGD. The questionnaire was completed by 52 patients (85% response rate, 44% males) with a median age of 44 (range 18–74) years. A total of 37 (71%) respondents had undergone genetic testing. In all, 24 respondents (46%, 75% males) had children. A total of 15 (29%) respondents reported that their diagnosis of PJS had influenced their decisions regarding family planning, including 10 patients (19%, 9/10 females) who did not want to have children because of their disease. Termination of pregnancy after PND in case of a foetus with PJS was considered ‘acceptable’ for 15% of the respondents, whereas 52% considered PGD acceptable. In conclusion, the diagnosis of PJS influences the decisions regarding family planning in one third of PJS patients, especially in women. Most patients have a negative attitude towards pregnancy termination after PND, while PGD in case of PJS is judged more acceptable. These results emphasise the importance of discussing aspects regarding family planning with PJS patients, including PND and PGD.

GNAS is not involved in gastrointestinal tumour formation in Peutz-Jeghers syndrome

Peutz-Jeghers syndrome (PJS), caused by germ-line mutations in LKB1, is characterized by the development of hamartomatous polyps in the gastrointestinal (GI) tract. McCune Albright syndrome (MAS), caused by somatic activating mutations in GNAS, presents with cutaneous, skeletal, and endocrine manifestations. Recently, hamartomatous GI polyps with histological features similar to those in PJS were observed in MAS patients, suggesting a role for GNAS in the pathogenesis of PJS. This study reports the first somatic GNAS mutation analysis in GI tumours of PJS patients. No mutations were observed, suggesting that GNAS is not involved in the pathogenesis of GI tumours in PJS.

Gastrointestinal diseases and their oro-dental manifestations: Part 4: Peutz-Jeghers syndrome.

Peutz-Jeghers syndrome (PJS) is a rare, autosomal dominant inherited disorder, caused by germline mutations in the LKB1 tumour suppressor gene. It is clinically characterised by distinct perioral mucocutaneous pigmentations, gastrointestinal polyposis and an increased cancer risk in adult life. Hamartomatous polyps can develop already in the first decade of life and may cause various complications, including abdominal pain, bleeding, anaemia, and acute intestinal obstruction. Furthermore, patients have an increased risk for developing cancer, both in the gastrointestinal tract as in other organs. The medical management of PJS mainly consists of surveillance and treatment of the hamartomatous polyps. Upper and lower endoscopies are recommended for surveillance and removal of PJS polyps in the stomach and the small and large intestine. Furthermore, the high risk for pancreatic cancer justifies surveillance of the pancreatic region by MRI or endoscopic ultrasound. In addition, breast and gynaecological surveillance is recommended for female patients. Although the genetic defect underlying PJS is known, the pathogenesis of hamartomas and carcinomas is unclear. More insight into the molecular background of PJS might lead to targeted therapies for patients with this syndrome.