Molecular basis of HNPCC: mutations of MMR genes

Evolving DNA repair synthetic lethality targets in cancer

DNA damage signaling response and repair (DDR) is a critical defense mechanism against genomic instability. Impaired DNA repair capacity is an important risk factor for cancer development. On the other hand, up-regulation of DDR mechanisms is a feature of cancer chemotherapy and radiotherapy resistance. Advances in our understanding of DDR and its complex role in cancer has led to several translational DNA repair-targeted investigations culminating in clinically viable precision oncology strategy using poly(ADP-ribose) polymerase (PARP) inhibitors in breast, ovarian, pancreatic, and prostate cancers. While PARP directed synthetic lethality has improved outcomes for many patients, the lack of sustained clinical response and the development of resistance pose significant clinical challenges. Therefore, the search for additional DDR-directed drug targets and novel synthetic lethality approaches is highly desirable and is an area of intense preclinical and clinical investigation. Here, we provide an overview of the mammalian DNA repair pathways and then focus on current state of PARP inhibitors (PARPi) and other emerging DNA repair inhibitors for synthetic lethality in cancer.

An update on the CNS manifestations of brain tumor polyposis syndromes

Cancer predisposition syndromes are associated with an increased risk of developing primary malignancies. Here we discuss those which are associated with an increased risk of tumors of the central nervous system (CNS) and gastrointestinal (GI) tract. These can be grouped into those in which the CNS tumors predominate versus those in which the GI cancers predominate. The former include constitutional mismatch repair deficiency (CMMRD) syndrome, Li-Fraumeni syndrome (LFS), and Cowden syndrome (CS) while the latter include familial adenomatosis polyposis 1 (FAP1), Lynch syndrome and polymerase proofreading-associated polyposis syndrome (PPAP). Tumor specificity does exist as medulloblastoma occur in FAP, LFS and CMMRD while glioma are most commonly seen in all replication repair-deficient genes and LFS. Choroid plexus carcinoma is strictly observed in LFS while Cowden syndrome patients develop Lhermitte Duclos disease or meningioma. In each syndrome, specific types of low-grade and high-grade gastrointestinal cancers can occur, but these will be discussed elsewhere. Underlying cancer predisposition syndromes are important to consider when faced with brain tumors, particularly in the pediatric and young adult age groups, as identification of an underlying germ line mutation may change the upfront management of the patient and has implications for future cancer surveillance for both the patient and potentially affected family members. Considerations of family history, presence of skin lesions and consanguinity provide valuable information in identifying patients at potential increased risk.

Significance of mismatch repair genes hMLH1 and hMSH2 expression in gastric cancer

AIM: To investigate the role of mismatch repair genes human mutL homolog 1 (hMLH1) and human mutL homolog 2 (hMSH2) in the carcinogenesis of gastric cancer.

METHODS: A total of 40 gastric cancer patients who underwent surgical resection at our hospital were included in the study, of which 33 were pathologically diagnosed as adenocarcinoma, and 7 as mucinous adenocarcinoma. All the patients did not underwent preoperative chemotherapy or immunotherapy. The gastric cancer specimens, matched cancer-adjacent tissue specimens, and 20 chronic gastritis mucosa specimens (10 diagnosed as chronic superficial gastritis by gastroscopic biopsy, and 10 as chronic atrophic gastritis) were collected. The expression of hMLH1 and hMSH2 proteins in these specimens was detected by Western blot.

RESULTS: The positive rate of hMSH2 expression in cancer tissue was significantly higher than those in cancer-adjacent tissue and gastritis mucosa tissue (0.28 ± 0.10 vs 0.23 ± 0.07 and 0.11 ± 0.10, respectively; both P < 0.01). The positive rate of hMLH1 expression in cancer tissue was significantly lower than those in cancer-adjacent tissue and gastritis mucosa tissue (0.22 ± 0.06 vs 0.28 ± 0.07, 0.26 ± 0.06, both P < 0.01). The positive rates of hMLH1 and hMSH2 expression were not correlated with various clinicopathological parameters in gastric cancer.

CONCLUSION: High hMSH2 expression and low hMLH1 expression may be potential markers for prediction of the development of gastric cancer.