Immunohistochemical analysis reveals high frequency of PMS2 defects in colorectal cancer

BACKGROUND & AIMS: Germline mutations in the DNA mismatch repair (MMR) genes MSH2, MSH6, or MLH1 predispose to colorectal cancer (CRC) with an autosomal dominant inheritance pattern. The protein encoded by PMS2 is also essential for MMR; however, alterations in this gene have been documented only in extremely rare cases. We addressed this unexpected finding by analyzing a large series of CRCs. METHODS: Expression of MSH2, MSH6, MLH1, and PMS2 was studied by immunohistochemistry in 1048 unselected, consecutive CRCs. Where absence of MMR proteins was detected, microsatellite instability and cytosine methylation of the respective gene promoter were analyzed. The DNA of patients presenting with PMS2-deficient cancers was examined for germline and somatic alterations in the PMS2 gene. RESULTS: An aberrant pattern of MMR protein expression was detected in 13.2% of CRCs. Loss of expression of MSH2, MSH6, or MLH1 was found in 1.4%, 0.5%, and 9.8%, respectively. PMS2 deficiency accompanied by microsatellite instability was found in 16 cases (1.5%) with a weak family history of cancer. The PMS2 promoter was not hypermethylated in these cases. Despite interference of the PMS2 pseudogenes, we identified several heterozygous germline mutations in the PMS2 gene. CONCLUSIONS: PMS2 defects account for a small but significant proportion of CRCs and for a substantial fraction of tumors with microsatellite instability. However, the penetrance of heterozygous germline mutations in PMS2 is considerably lower than that of mutations in other MMR genes. The possible underlying causes of this unorthodox inheritance pattern are discussed.     

New therapeutic strategies in neuroblastoma: combined targeting of a novel tyrosine kinase inhibitor and liposomal siRNAs against ALK

Many different aberrations in the Anaplastic Lymphoma Kinase (ALK) were found to be oncogenic drivers in several cancers including neuroblastoma (NB), therefore ALK is now considered a critical player in NB oncogenesis and a promising therapeutic target. The ALK-inhibitor crizotinib has a limited activity against the various ALK mutations identified in NB patients.We tested: the activity of the novel ALK-inhibitor X-396 administered alone or in combination with Targeted Liposomes carrying ALK-siRNAs (TL[ALK-siRNA]) that are active irrespective of ALK gene mutational status; the pharmacokinetic profiles and the biodistribution of X-396; the efficacy of X-396 versus crizotinib treatment in NB xenografts; whether the combination of X-396 with the TL[ALK-siRNA] could promote long-term survival in NB mouse models.X-396 revealed good bioavailability, moderate half-life, high mean plasma and tumor concentrations. X-396 was more effective than crizotinib in inhibiting in vitro cell proliferation of NB cells and in reducing tumor volume in subcutaneous NB models in a dose-dependent manner.In orthotopic NB xenografts, X-396 significantly increased life span independently of the ALK mutation status. In combination studies, all effects were significantly improved in the mice treated with TL[ALK-siRNA] and X-396 compared to mice receiving the single agents.Our findings provide a rational basis to design innovative molecular-based treatment combinations for clinical application in ALK-driven NB tumors.     

Endothelin-1 (1-31) is an intermediate in the production of endothelin-1 after big endothelin-1 administration in vivo

The precursor of endothelin-1, big endothelin-1, can be hydrolyzed by chymase to generate endothelin-1 (1-31) in vitro. In the present study, we explored the processes involved in the production of endothelin-1 (1-31) as well as its pharmacodynamic characteristics in the rabbit in vivo. Endothelin-1 (1-31) (1 nmol/kg, injected into the left cardiac ventricle) induced a monophasic increase of mean arterial blood pressure similarly to big endothelin-1 (1-38), whereas endothelin-1 induces a biphasic response. Phosphoramidon, a dual neutral endopeptidase and endothelin-converting enzyme inhibitor, blocked both pressor responses to endothelin-1 (1-31) and big endothelin-1 but not those afforded by endothelin-1. Thiorphan, a neutral endopeptidase inhibitor, markedly inhibited the response to endothelin-1 (1-31) but only weakly reduced that of big endothelin-1. In contrast, CGS 35066, an endothelin-converting enzyme inhibitor, was significantly more efficient against the pressor response to big endothelin-1 than to endothelin-1 (1-31). Furthermore, injection of big endothelin-1 concomitantly with phosphoramidon induced an increase in endothelin-1 (1-31) plasma levels. Finally, intracardiac-administered endothelin-1 (1-31) induced an increase of endothelin-1 plasma levels, which are markedly reduced by phosphoramidon and thiorphan but not by CGS 35066. Our results thus demonstrate that endothelin-1 (1-31) is an alternate intermediate in the production of endothelin-1 after big endothelin-1 administration in the rabbit in vivo.