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.

[Peutz-Jeghers syndrome]. / Het syndroom van Peutz-Jeghers.

Peutz-Jeghers syndrome is a rare, autosomal dominant inherited disorder, which is characterized by mucocutaneous pigmentations, gastrointestinal polyposis and an increased risk of cancer. It is caused by germline mutations in the LKB1 tumour suppressor gene, as a result of which hamartomatous polyps can develop already at an early age, which may cause various complications, including abdominal pain, anaemia, and acute intestinal obstruction. Patients have an increased risk of developing cancer, in the gastroinstestinal tract and in other organs. As a result of the risk of complications related to the hamartomatous polyps and the increased risk of cancer, the medical management mainly consists of surveillance. Upper and lower endoscopies are recommended for surveillance, the small bowel should be investigated with magnetic resonance imaging and regular inspection of the pancreas with imaging techniques is recommended. Women are advised to seek regular breast- and gynaecological screening from an early age. The pathogenesis of hamartomas and carcinomas is unclear. More insight into the molecular background might lead to targeted medicinal therapies for patients with this syndrome.

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.

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.