One signal that is overactivated in a wide range of tumour types is the production of a phospholipid, phosphatidylinositol (3,4,5) trisphosphate, by phosphatidylinositol 3-kinase (PI3K) This lipid and the protein kinase that is activated by it — AKT — trigger a cascade of responses, from cell growth and proliferation to survival and motility, that drive tumour progression Small-molecule therapeutics that block PI3K signalling might deal a severe blow to cancer cells by blocking many aspects of the tumour-cell phenotype

The phosphatidylinositol 3-Kinase AKT pathway in human cancer.

PTEN is among the most frequently inactivated tumour suppressor genes in sporadic cancer. PTEN has dual protein and lipid phosphatase activity, and its tumour suppressor activity is dependent on its lipid phosphatase activity, which negatively regulates the PI3K-AKT-mTOR pathway. Germline mutations in PTEN have been described in a variety of rare syndromes that are collectively known as the PTEN hamartoma tumour syndromes (PHTS). Cowden syndrome is the best-described syndrome within PHTS, with approximately 80% of patients having germline PTEN mutations. Patients with Cowden syndrome have an increased incidence of cancers of the breast, thyroid and endometrium, which correspond to sporadic tumour types that commonly exhibit somatic PTEN inactivation. Pten deletion in mice leads to Cowden syndrome-like phenotypes, and tissue-specific Pten deletion has provided clues to the role of PTEN mutation and loss in specific tumour types. Studying PTEN in the continuum of rare syndromes, common cancers and mouse models provides insight into the role of PTEN in tumorigenesis and will inform targeted drug development.

/pdf/pten-loss-in-the-continuum-of-common-cancers-rare-syndromes-13zshfdjpg.pdf

PTEN loss in the continuum of common cancers, rare syndromes and mouse models

Purpose This phase I dose-escalation study investigated the maximum-tolerated dose (MTD), safety, preliminary activity, pharmacokinetics (PK), and pharmacodynamics of BKM120, a potent and highly specific oral pan-Class I PI3K inhibitor. Patients and Methods Thirty-five patients with advanced solid tumors received daily BKM120 12.5 to 150 mg. Dose escalation was guided by a Bayesian logistic regression model with overdose control. Assessments included archival tumor molecular status, response by Response Evaluation Criteria in Solid Tumors (RECIST), positron emission tomography tracer uptake ([18F]fluorodeoxyglucose positron emission tomography [FDG-PET]), fasting plasma C-peptide, and phosphorylated ribosomal protein S6 (pS6) in skin biopsies. Results Overall, treatment was well tolerated. Dose-limiting toxicities were grade 2 mood alteration (80 mg), grade 3 epigastralgia, grade 3 rash, grade 2 and grade 3 mood alteration (100 mg), and two grade 4 hyperglycemia (150 mg). The MTD was 100 mg/d. Frequent tr...

Phase I, dose-escalation study of BKM120, an oral pan-class I PI3K inhibitor, in patients with advanced solid tumors

The PTEN (phosphatase and tensin homologue deleted on chromosome 10) tumour suppressor is a PI (phosphoinositide) 3-phosphatase that can inhibit cellular proliferation, survival and growth by inactivating PI 3-kinase-dependent signalling. It also suppresses cellular motility through mechanisms that may be partially independent of phosphatase activity. PTEN is one of the most commonly lost tumour suppressors in human cancer, and its deregulation is also implicated in several other diseases. Here we discuss recent developments in our understanding of how the cellular activity of PTEN is regulated, and the closely related question of how this activity is lost in tumours. Cellular PTEN function appears to be regulated by controlling both the expression of the enzyme and also its activity through mechanisms including oxidation and phosphorylation-based control of non-substrate membrane binding. Therefore mutation of PTEN in tumours disrupts not only the catalytic function of PTEN, but also its regulatory aspects. However, although mutation of PTEN is uncommon in many human tumour types, loss of PTEN expression seems to be more frequent. It is currently unclear how these tumours lose PTEN expression in the absence of mutation, and while some data implicate other potential tumour suppressors and oncogenes in this process, this area seems likely to be a key focus of future research.

/pdf/pten-function-how-normal-cells-control-it-and-tumour-cells-3idta1g3ps.pdf

PTEN function: how normal cells control it and tumour cells lose it

PTEN is a potent tumour suppressor, and its loss of function is frequently observed in both heritable and sporadic cancers. PTEN has phosphatase-dependent and phosphatase-independent (scaffold) activities in the cell and governs a variety of biological processes, including maintenance of genomic stability, cell survival, migration, proliferation and metabolism. Even a subtle decrease in PTEN levels and activity results in cancer susceptibility and favours tumour progression. Regulation of PTEN has therefore emerged as a subject of intense research in tumour biology. Recent discoveries, including the existence of distinct PTEN isoforms and the ability of PTEN to form dimers, have brought to light new modes of PTEN function and regulation. These milestone findings have in turn opened new therapeutic avenues for cancer prevention and treatment through restoration of PTEN tumour suppressor activity.

The functions and regulation of the PTEN tumour suppressor: new modes and prospects

Loss of heterozygosity and mutations in the PTEN (MMAC1) tumor suppressor gene are frequent in endometrial carcinoma. Promoter hypermethylation has recently been identified as an alternative mechanism of tumor suppressor gene inactivation in cancer, but its importance in the PTEN gene in endometrial carcinoma is unknown. The purpose of our study was to assess the frequency of promoter methylation of the PTEN gene and to determine its correlation with clinicopathologic variables in a prospective and population-based series of endometrial carcinomas with complete follow-up. Presence of PTEN promoter methylation was seen in 26 of 138 patients (19%). Methylation was significantly associated with metastatic disease (p = 0.01) and a microsatellite unstable phenotype (p = 0.006). In conclusion, we find that PTEN promoter methylation is relatively frequent in endometrial carcinoma. Its association with metastatic disease and microsatellite instability implicates its importance in the development of this tumor type.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/1097-0215%2820010101%2991%3A1%3C22%3A%3AAID-IJC1002%3E3.0.CO%3B2-S

PTEN methylation is associated with advanced stage and microsatellite instability in endometrial carcinoma.

The replication error repair (RER) phenotype has been reported in 9-43% of sporadic endometrial carcinomas, but there are conflicting data about its effect on prognosis in this disease. This study was performed to establish the frequency of the RER phenotype and to determine its effect on prognosis in a population-based series of 259 endometrial carcinomas with long-term follow-up. Five mononucleotide and dinucleotide microsatellite markers on different chromosomes were analyzed, and tumors exhibiting microsatellite instability at two or more loci were classified as RER+. A total of 116 of 259 tumors (45%) were RER+. The 5-year survival rate for the RER- group was 76.2% compared with 79.6% for RER+ cases (P = 0.6). The 5-year recurrence-free survival rate among the 228 patients surgically treated for cure was 80.6% in the RER- group compared with 83.6% in the RER+ group (P = 0.6). The analysis indicates that the RER phenotype is common in endometrial carcinomas, but there is no association with prognosis in this large population-based series of endometrial carcinomas.

https://cancerres.aacrjournals.org/content/canres/60/6/1750.full.pdf

Helga B. Salvesen

Papers

PTEN methylation is associated with advanced stage and microsatellite instability in endometrial carcinoma.

Frequency and prognostic impact of microsatellite instability in a large population-based study of endometrial carcinomas.