Kenta Masuda

Application of MicroRNA in Diagnosis and Treatment of Ovarian Cancer

Ovarian cancer has a poor prognosis because early detection is difficult and recurrent ovarian cancer is usually drug-resistant. The morbidity and mortality of ovarian cancer are high worldwide and new methods of diagnosis and therapy are needed. MicroRNAs (miRNAs) are posttranscriptional regulators of gene expression that are involved in carcinogenesis, metastasis, and invasion. Thus, miRNAs are likely to be useful as diagnostic and prognostic biomarkers and for cancer therapy. Many miRNAs have altered expression in ovarian cancer compared to normal ovarian tissues and these changes may be useful for diagnosis and treatment. For example, deficiencies of enzymes including Dicer and Drosha that are required for miRNA biogenesis may be adverse prognostic factors; miRNAs such as miR-214 and miR-31, which are involved in drug resistance, and the miR-200 family, which is implicated in metastasis, may serve as biomarkers; and transfection of downregulated miRNAs and inhibition of upregulated miRNAs may be effective for treatment of ovarian cancer. Chemotherapy targeting epigenetic mechanisms associated with miRNAs may also be effective to reverse gene silencing.

ARID1A gene mutation in ovarian and endometrial cancers (Review)

The AT-rich interacting domain-containing protein 1A gene (ARID1A) encodes ARID1A, a member of the SWI/SNF chromatin remodeling complex. Mutation of ARID1A induces changes in expression of multiple genes (CDKN1A, SMAD3, MLH1 and PIK3IP1) via chromatin remodeling dysfunction, contributes to carcinogenesis, and has been shown to cause transformation of cells in association with the PI3K/AKT pathway. Information on ARID1A has emerged from comprehensive genome-wide analyses with next-generation sequencers. ARID1A mutations have been found in various types of cancer and occur at high frequency in endometriosis-associated ovarian cancer, including clear cell adenocarcinoma and endometrioid adenocarcinoma, and also occur at endometrial cancer especially in endometrioid adenocarcinoma. It has also been suggested that ARID1A mutation occurs at the early stage of canceration from endometriosis to endometriosis-associated carcinoma in ovarian cancer and also from atypical endo-metrial hyperplasia to endometrioid adenocarcinoma in endometrial cancer. Therefore, development of a screening method that can detect mutations of ARID1A and activation of the PI3K/AKT pathway might enable early diagnosis of endometriosis-associated ovarian cancers and endometrial cancers. Important results may also emerge from a current clinical trial examining a multidrug regimen of temsirolimus, a small molecule inhibitor of the PI3K/AKT pathway, for treatment of advanced ovarian clear cell adenocarcinoma with ARID1A mutation and PI3K/AKT pathway activation. Also administration of sorafenib, a multikinase inhibitor, can inhibit cancer proliferation with PIK3CA mutation and resistance to mTOR inhibitors and GSK126, a molecular-targeted drug can inhibit proliferation of ARID1A-mutated ovarian clear cell adenocarcinoma cells by targeting and inhibiting EZH2. Further studies are needed to determine the mechanism of chromatin remodeling dysregulation initiated by ARID1A mutation, to develop methods for early diagnosis, to investigate new cancer therapy targeting ARID1A, and to examine the involvement of ARID1A mutations in development, survival and progression of cancer cells.

Carcinogenic mechanisms of endometrial cancer: Involvement of genetics and epigenetics

Endometrial cancer is increasing worldwide and the number of patients with this disease is likely to continue to grow, including younger patients. Many endometrial cancers show estrogen‐dependent proliferation, but the carcinogenic mechanisms are unknown or not completely explained beyond mutations of single oncogenes and tumor suppressor genes. Possible carcinogenic mechanisms include imbalance between endometrial proliferation by unopposed estrogen and the mismatch repair (MMR) system; hypermethylation of the MMR gene hMLH1; mutation of PTEN, β‐catenin and K‐ras genes in type I endometrial cancer and of HER‐2/neu and p53 genes in type II endometrial cancer; hypermethylation of SPRY2, RASSF1A, RSK4, CHFR and CDH1; and methylation of tumor suppressor microRNAs, including miR‐124, miR‐126, miR‐137, miR‐491, miR‐129‐2 and miR‐152. Thus, it is likely that the carcinogenic mechanisms of endometrial cancer involve both genetic and epigenetic changes. Mutations and methylation of MMR genes induce various oncogenic changes that cause carcinogenesis, and both MMR mutation in germ cells and methylation patterns may be inherited over generations and cause familial tumorigenesis. Determination of the detailed carcinogenic mechanisms will be useful for prevention and diagnosis of endometrial cancer, risk assessment, and development of new treatment strategies targeting MMR genes.

Epigenetics and genetics in endometrial cancer: new carcinogenic mechanisms and relationship with clinical practice

Endometrial cancer is the seventh most common cancer worldwide among females. An increased incidence and a younger age of patients are also predicted to occur, and therefore elucidation of the pathological mechanisms is important. However, several aspects of the mechanism of carcinogenesis in the endometrium remain unclear. Associations with genetic mutations of cancer-related genes have been shown, but these do not provide a complete explanation. Therefore, epigenetic mechanisms have been examined. Silencing of genes by DNA hypermethylation, hereditary epimutation of DNA mismatch repair genes and regulation of gene expression by miRNAs may underlie carcinogenesis in endometrial cancer. New therapies include targeting epigenetic changes using histone deacetylase inhibitors. Some cases of endometrial cancer may also be hereditary. Thus, patients with Lynch syndrome which is a hereditary disease, have a higher risk for developing endometrial cancer than the general population. Identification of such disease-related genes may contribute to early detection and prevention of endometrial cancer.

Epimutation and cancer: a new carcinogenic mechanism of Lynch syndrome (Review)

Epimutation is defined as abnormal transcriptional repression of active genes and/or abnormal activation of usually repressed genes caused by errors in epigenetic gene repression. Epimutation arises in somatic cells and the germline, and constitutional epimutation may also occur. Epimutation is the first step of tumorigenesis and can be a direct cause of carcinogenesis. Cancers associated with epimutation include Lynch syndrome (hereditary non-polyposis colorectal cancer, HNPCC), chronic lymphocytic leukemia, breast cancer and ovarian cancer. Epimutation has been shown for many tumor suppressor genes, including RB, VHL, hMLH1, APC and BRCA1, in sporadic cancers. Methylation has recently been shown in DNA from normal tissues and peripheral blood in cases of sporadic colorectal cancer and many studies show constitutive epimutation in cancers. Epimutation of DNA mismatch repair (MMR) genes (BRCA1, hMLH1 and hMSH2) involved in development familial cancers has also been found. These results have led to a focus on epimutation as a novel oncogenic mechanism.

Hereditary gynecological tumors associated with Peutz-Jeghers syndrome (Review)

Peutz-Jeghers syndrome (PJS) is an autosomal dominant disease that is characterized by gastrointestinal hamartomatous polyposis and mucocutaneous melanin spots. The tumor suppressor gene, STK11/LKB1, which is located on chromosome 19p13.3, has been reported to be responsible for this condition. PJS is complicated by benign and malignant tumors of various organs and complications from rare diseases, including sex cord tumor with annular tubules (SCTAT) and minimal deviation adenocarcinoma (MDA), which have also recently attracted attention in the field of gynecology. Among the total MDA cases, 10% are complications of PJS, and mutations in the STK11 gene are closely associated with the development and prognosis of MDA. Furthermore, a new type of uterine cervical tumor, lobular endocervical glandular hyperplasia (LEGH), has been identified and has been predicted to be a precancerous lesion of MDA. The first case of LEGH induced by a germline STK11 mutation has also been described. A high risk of endometrial cancer in PJS has also been reported. These developments suggest that PJS is an important syndrome of hereditary gynecological tumors that requires further study.

Carcinoma of the lower uterine segment (LUS): Clinicopathological characteristics and association with Lynch syndrome

Endometrial cancer arises from the uterine body and fundus in many cases, but can also originate from the lower region of the uterine body through the upper region of the cervix. Such tumors are referred to as carcinoma of the lower uterine segment (LUS) or isthmus, and account for 3-6.3% of all cases of endometrial cancer. This relatively low incidence has permitted performance of only small-scale studies, but the clinical and pathological characteristics of carcinoma of the LUS in all these reports have differed from those of other endometrial cancers. Generally, endometrial cancer is classified into estrogen-dependent endometrioid adenocarcinoma (designated as type I), and non-endometrioid types that are less associated with estrogen and include poorly differentiated adenocarcinoma (type II). In some reports, carcinoma of the LUS has been found to have type II characteristics. Carcinoma of the LUS has also been associated with Lynch syndrome, a hereditary disease with frequent development of colorectal, endometrial, and ovarian cancers. Lynch syndrome is thought to be induced by mismatch repair gene mutation. The frequency of Lynch syndrome in cases of general endometrial cancer is 1-2%. In contrast, the frequency in patients with carcinoma of the LUS is much higher, with up to 29% of cases diagnosable with Lynch syndrome and a high frequency of hMSH2 mutation found in one study. This suggests that further investigation of the clinical and pathological characteristics of carcinoma of the LUS and the association with Lynch syndrome is required through performance of a large-scale survey.

Endometrial Cancer and Hypermethylation: Regulation of DNA and MicroRNA by Epigenetics

Endometrial cancer is the seventh most common cancer in women worldwide. Therefore elucidation of the pathogenesis and development of effective treatment for endometrial cancer are important. However, several aspects of the mechanism of carcinogenesis in the endometrium remain unclear. Associations with genetic variation and mutations of cancer-related genes have been shown, but these do not provide a complete explanation. Therefore, in recent years, epigenetic mechanisms that do not involve changes in DNA sequences have been examined. Studies aimed at detection of aberrant DNA hypermethylation in cancer cells present in microscopic amounts in vivo and application of the results to cancer diagnosis have also started. Breakdown of the DNA mismatch repair mechanism is thought to play a large role in the development of endometrial cancer, with changes in the expression of the hMLH1 gene being particularly important. Silencing of genes such as APC and CHFR, Sprouty 2, RASSF1A, GPR54, CDH1, and RSK4 by DNA hypermethylation, onset of Lynch syndrome due to hereditary epimutation of hMLH1 and hMSH2 mismatch repair genes, and regulation of gene expression by microRNAs may also underlie the carcinogenic mechanisms of endometrial cancer. Further understanding of these issues may permit development of new therapies.

MicroRNAS in endometrial cancer: recent advances and potential clinical applications.

Endometrial cancer is a common malignant gynecological tumor, but there are few biomarkers that are useful for early and accurate diagnosis and few treatments other than surgery. However, use of microRNAs (miRNAs) that induces gene downregulation in cells may permit effective and minimally invasive diagnosis and treatment. In endometrial cancer cells, expression levels of miRNAs including miR-185, miR-210 and miR-423 are upregulated and those of miR-let7e, miR-30c and miR-221 are downregulated compared to normal tissues, and these miRNAs are involved in carcinogenesis, invasion and metastasis. miRNAs with expression changes such as miR-181b, miR-324-3p and miR-518b may be used as prognostic biomarkers and transfection of miR-152 may inhibit cancer growth. However, most current studies of miRNAs are at a basic level and further work is needed to establish clinical applications targeting miRNAs.

Progestin therapy for endometrial cancer: The potential of fourth-generation progestin (Review)

Progestin preparations are made of synthetic progesterone and have often been used for hormone therapy in gynecological patients with endometriosis or endometrial cancer. Hormone therapy using progestin is considered to be one of the effective means of treatment particularly when dealing with endometrial cancer (an estrogen-dependent tumor). Numerous reports have been published concerning its efficacy in advanced or recurrent cases of atypical endometrial hyperplasia or endometrial cancer. Dienogest has been developed as a fourth-generation progestin for hormone therapy for endometriosis that can be used with high safety for long periods of time. In Japan, dienogest has been recommended as a first-line drug for endometriosis-associated pain. However, its antitumor activity has also been attracting close attention following a report that this drug suppressed the proliferation in vitro of endometrial cancer-derived cell lines which failed to respond to other progestins such as medroxyprogesterine acetate (MPA). The mechanism for antitumor activity of dienogest is considered to differ from the mechanism for antitumor activity of conventional progestin preparations used for treatment of endometrial cancer. This drug is expected to be clinically applicable as a new drug for the treatment of endometrial cancer.