Cancer risk in MLH1, MSH2 and MSH6 mutation carriers; different risk profiles may influence clinical management

Background: Lynch syndrome (LS) is associated with a high risk for colorectal cancer (CRC) and extracolonic malignancies, such as endometrial carcinoma (EC). The risk is dependent of the affected mismatch repair gene. The aim of the present study was to calculate the cumulative risk of LS related cancers in proven MLH1, MSH2 and MSH6 mutation carriers.Methods: The studypopulation consisted out of 67 proven LS families. Clinical information including mutation status and tumour diagnosis was collected. Cumulative risks were calculated and compared using Kaplan Meier survival analysis.Results: MSH6 mutation carriers, both males and females had the lowest risk for developing CRC at age 70 years, 54% and 30% respectively and the age of onset was delayed by 3-5 years in males. With respect to endometrial carcinoma, female MSH6 mutation carriers had the highest risk at age 70 years (61%) compared to MLH1 (25%) and MSH2 (49%). Also, the age of EC onset was delayed by 5-10 years in comparison with MLH1 and MSH2.Conclusions: Although the cumulative lifetime risk of LS related cancer is similar, MLH1, MSH2 and MSH6 mutations seem to cause distinguishable cancer risk profiles. Female MSH6 mutation carriers have a lower CRC risk and a higher risk for developing endometrial carcinoma. As a consequence, surveillance colonoscopy starting at age 30 years instead of 20-25 years is more suitable. Also, prophylactic hysterectomy may be more indicated in female MSH6 mutation carriers compared to MLH1 and MSH2 mutation carriers

Mutations of Cys-17 and Ala-271 in the Human Histamine H₂ Receptor Determine the Species Selectivity of Guanidine-Type Agonists and Increase Constitutive Activity

In a steady-state GTPase activity assay, N-[3-(1H-imidazol-4-yl)propyl)]guanidines and N(G)-acylated derivatives are more potent and efficacious at fusion proteins of guinea pig (gpH₂R-GsαS) than human (hH₂R-GsαS) histamine H₂ receptor, coupled to the short splice variant of Gsα, GsαS. Whereas Ala-271 (hH₂R) and Asp-271 (gpH₂R) in transmembrane domain 7 were identified to determine the potency differences of guanidine-type agonists, the molecular basis for the efficacy differences remains to be elucidated. A homology model of the gpH₂R suggested that an H-bond between Tyr-17 and Asp-271 stabilizes an active receptor conformation of the gpH₂R. In the present study, we generated a mutant hH₂R-GsαS with Cys-173Tyr- 17/Ala-2713Asp-271 exchanges (hH₂R3gpH₂R) that exhibited an enhanced level of constitutive GTPase activity and adenylyl cyclase activity compared with wild-type hH₂R-GsαS and gpH₂R-GsαS. Potencies and efficacies of guanidines and N(G)-acylguanidines were increased at this mutant receptor compared with hH₂R-GsαS, but they were still lower than at gpH₂R-GsαS, suggesting that aside from Tyr-17 and Asp-271 additional amino acids contribute to the distinct pharmacological profiles of both species isoforms. Another hH₂R-GsαS mutant with a Cys-173Tyr-17 exchange showed inefficient coupling to GsαS as revealed by reduced agonist-stimulated GTPase and basal adenylyl cyclase activities. Collectively, our present pharmacological study confirms the existence of an H-bond between Tyr-17 and Asp-271 favoring the stabilization of an active receptor conformation. Distinct potencies and efficacies of agonists and inverse agonists further support the concept of ligand-specific conformations in wild-type and mutant H₂R-GsαS fusion proteins

Constitutive Activity and Ligand Selectivity of Human, Guinea Pig, Rat, and Canine Histamine H₂ Receptors

Previous studies revealed pharmacological differences between human and guinea pig histamine H₂ receptors (H₂Rs) with respect to the interaction with guanidine-type agonists. Because H₂R species variants are structurally very similar, comparative studies are suited to relate different properties of H₂R species isoforms to few molecular determinants. Therefore, we systematically compared H₂Rs of human (h), guinea pig (gp), rat (r), and canine (c). Fusion proteins of hH₂R, gpH₂R, rH₂R, and cH₂R, respectively, and the short splice variant of Gsα, GsαS, were expressed in Sf9 insect cells. In the membrane steady-state GTPase activity assay, cH₂R-GsαS but neither gpH₂R-GsαS nor rH₂R-GsαS showed the hallmarks of increased constitutive activity compared with hH₂R-GsαS, i.e., increased efficacies of partial agonists, increased potencies of agonists with the extent of potency increase being correlated with the corresponding efficacies at hH₂R-GsαS, increased inverse agonist efficacies, and decreased potencies of antagonists. Furthermore, in membranes expressing nonfused H₂Rs without or together with mammalian GsαS or H₂R-Gsα fusion proteins, the highest basal and GTP-dependent increases in adenylyl cyclase activity were observed for cH₂R. An example of ligand selectivity is given by metiamide, acting as an inverse agonist at hH₂R-GsαS, gpH₂R-GsαS, and rH₂R-GsαS in the GTPase assay in contrast to being a weak partial agonist with decreased potency at cH₂R-GsαS. In conclusion, the cH₂R exhibits increased constitutive activity compared with hH₂R, gpH₂R, and rH₂R, and there is evidence for ligand-specific conformations in H₂R species isoforms

Chiral N(G)-acylated hetarylpropylguanidine-type histamine H2 receptor agonists do not show significant stereoselectivity

A set of chiral imidazolylpropylguanidines and 2-aminothiazolylpropylguanidines bearing N(G)-3-phenyl- or N(G)-3-cyclohexylbutanoyl residues was synthesized and investigated for histamine H2 receptor (H2R) agonism (guinea pig (gp) right atrium, GTPase assay on recombinant gp and human (h) H2R) and for hH2R selectivity compared to hH1R, hH3R and hH4R. In contrast to previous studies on arpromidine derivatives, the present investigation of acylguanidine-type compounds revealed only very low eudismic ratios (1.1 – 3.2), indicating the stereochemistry of the acyl moiety to play only a minor role in this series of H2R agonists

N(G)-Acylated aminothiazolylpropylguanidines as potent and selective histamine H2 receptor agonists

The bioisosteric replacement of the guanidino group in arpromidine-like histamine H2 receptor (H2R) agonists by an acylguanidine moiety is a useful approach to obtain potent H2R agonists with improved oral bioavailability and penetration across the blood brain barrier. Unfortunately, the selectivity of such N(G)-acylated imidazolylpropyl-guanidines for the H2R is poor, in particular versus histamine H3 (H3R) and H4 receptors (H4R). This drawback appears to depend on the "privileged" imidazolylpropylguanidine structure. The 2-amino-4-methylthiazol-5-yl moiety is a bioisostere of the imidazole ring in the moderately potent H2R selective histamine analogue amthamine. This approach was successfully applied to acylguanidine-type H2R agonists. The aminothiazoles are nearly equipotent with the corresponding imidazoles as H2R agonists. Compared to histamine, the potency is increased up to 40-fold on the guinea pig right atrium and up to 125- and 280-fold, respectively, in GTPase assays at human and guinea pig H2R-GsαS fusion proteins expressed in Sf9 insect cells. Docking studies on H2R models support the hypothesis that 2-aminothiazolyl and imidazolyl derivatives interact with H2Rs as bioisosteres. In contrast to the imidazoles, the aminothiazoles are devoid of agonistic or relevant antagonistic effects on H1, H3 and H4 receptors. Moreover, unlike amthamine, the 4-methyl group does not significantly contribute to the H2R agonism of N(G)-acylated 2-amino-4-methylthiazol-5-ylpropylguanidines

Assessment of Unilateral Spatial Neglect: Scoring Star Cancellation Performance From Video Recordings-Method, Reliability, Benefits, and Normative Data

Unilateral spatial neglect, a debilitating condition affecting awareness of one side of space, is commonly assessed using cancellation tasks in which patients cross out targets distributed over a sheet. Standard scores emphasize the left–right distribution of omissions. Here, the additional value of extracting temporal as well as spatial aspects of performance from video recordings was examined. Videos from 18 patients with left neglect and 19 healthy age-matched control participants were obtained. Interrater reliability of the video analysis was high. In addition to overall differences in target detection and bias, patients significantly differed from the control group in terms of the location of first cancellation, overall slowness, greater variability in speed, systematic slowing with time on task and as a function of target location, less coherent search organization, and a sharply increased tendency to recancel targets. Considering a subset of patients whose scores, by standard criteria, were at or near the normal range indicated that these additional variables indeed increased the sensitivity of the task as well as allowed the simultaneous assessment of spatial and nonspatial aspects of the disorder

The bivalent ligand approach leads to highly potent and selective acylguanidine-type histamine H2 receptor agonists

Bivalent histamine H2 receptor (H2R) agonists were synthesized by connecting pharmacophoric 3-(2-amino-4-methylthiazol-5-yl)-, 3-(2-aminothiazol-5-yl)-, 3-(imidazol-4-yl)- or 3-(1,2,4-triazol-5-yl)-propylguanidine moieties by NG-acylation with alkanedioic acids of various chain lengths. The compounds were investigated for H2R agonism in GTPase and [35S]GTPγS binding assays at guinea pig (gp) and human (h) H2R-GsαS fusion proteins including various H2R mutants, at the isolated gp right atrium, and in GTPase assays for activity on recombinant H1, H3 and H4 receptors. The bivalent ligands are H2R partial or full agonists, up to two orders of magnitude more potent than monovalent acylguanidines and, with octanedioyl or decanedioyl spacers, up to 4000 times more potent than histamine at the gpH2R. In contrast to their imidazole analogs, the aminothiazoles are highly selective for H2R vs. other HR subtypes. Compounds with (theoretically) sufficient spacer length (20 CH2 groups) to simultaneously occupy two orthosteric binding sites in H2R dimers are nearly inactive, whereas highest potency resides in compounds with considerably shorter spacers. Thus, there is no evidence for interaction with H2R dimers. The high agonistic potency may rather result from interaction with an accessory binding site at the same receptor protomer