Residual mitral regurgitation impact on outcomes after mitraclip therapy: five-year follow-up from the GRASP registry

Funding Acknowledgements

Type of funding sources: None.

Background – Although percutaneous mitral valve repair is an attractive alternative treatment option for patients with severe mitral regurgitation (MR) at high surgical risk, residual MR is commonly observed after the procedure and little is known about its impact on outcomes after MitraClip therapy, expecially in patients with severe left ventricular (LV) impairment.

Purpose – The aim of this prospective, observational study was to evaluate the impact of residual MR (MR ≤1+ vs. MR >1+) on long-term outcomes of mitral valve repair with the MitraClip System in high surgical risk patients presenting with moderate-to-severe or severe MR and with severe reduction of LV ejection fraction (EF).

Methods – Patients enrolled in the prospective Getting Reduction of Mitral Insufficiency by Percutaneous Clip Implantation (GRASP) with functional MR and EF ≤30% who were eligible at almost five-year follow-up were included in the present analysis.  The primary endpoint was death at 5-year follow-up.  Also echocardiographic parameters at baseline and 5-year follow-up and rehospitalization rates were assessed.

Results – A total of 139 patients were included: 92 (66.2%) with post-procedural residual MR ≤1+ and 47 (33.8%) with residual MR > 1+ (41 patients with residual MR 2+, 5 with residual MR 3+, 1 with residual MR 4+).  Comparable clinical and echocardiographic baseline characteristics were observed between the two groups except for NYHA functional class IV and implanted pace-maker (more frequent in patients with residual MR >1+) and previous myocardial infarction (more frequent  in patients with residual MR ≤1+). At 5-year follow-up, no significant differences were reported in the primary endpoint (49.6% in patients with residual MR ≤ 1+ vs. 65.3% in patients with residual MR > 1+, p 0.203) and in cardiac death (37.8% in patients with residual MR ≤ 1+ vs. 42.6% in patients with residual MR > 1+, p 0.921). Cox regression analysis identified residual MR > 1+ as an independent predictor of re-hospitalization (HR 0.51, 95% CI 0.28-0.92, p =0.026). At 5-year follow-up,  a significant reduction in left ventricular end-systolic volume was  observed in patients with residual MR ≤ 1+.

Conclusions – At 5-year follow no significant differences in survival emerged in patients with severe  LV dysfunction undergoing MitraClip therapy regardless residual MR. Nevertheless residual MR > 1+ emerged as an indipendent predictor of re-hospitalization.

Synthesis and Pharmacological Evaluation of 4-Iminothiazolidinones for Inhibition of PI3 Kinase

The thiazolidinedione, compound 1, has previously shown pan-inhibition of the phosphoinositide 3-kinase (PI3K) class I isoforms. We hypothesized the derivatization of the thiazolidinedione core of compound 1 could introduce isoform selectivity. We report the synthesis, characterization, and inhibitory activity of a novel series of 4-iminothiazolidin-2-ones for inhibition of the class I PI3K isoforms. Their synthesis was successfully achieved by multiple pathways described in this paper. Initial in vitro data of 28 analogues demonstrated poor inhibition of all class I PI3K isoforms. However, we identified an alternate target, the phosphodiesterases, and present preliminary screening results showing improved inhibitory activity.

CYT997: a novel orally active tubulin polymerization inhibitor with potent cytotoxic and vascular disrupting activity in vitro and in vivo

CYT997 is a wholly synthetic compound that possesses highly potent cytotoxic activity in vitro through inhibition of microtubule polymerization. CYT997 blocks the cell cycle at the G(2)-M boundary, and Western blot analysis indicates an increase in phosphorylated Bcl-2, along with increased expression of cyclin B1. Caspase-3 activation is also observed in cells treated with CYT997 along with the generation of poly(ADP-ribose) polymerase. The compound possesses favorable pharmacokinetic properties, is orally bioavailable, and is efficacious per os in a range of in vivo cancer models, including some refractory to paclitaxel treatment. CYT997 exhibits vascular disrupting activity as measured in vitro by effects on the permeability of human umbilical vein endothelial cell monolayers, and in vivo by effects on tumor blood flow. CYT997 possesses a useful combination of pharmacologic and pharmacokinetic properties and has considerable potential as a novel anticancer agent.

Dissecting isoform selectivity of PI3K inhibitors: the role of non-conserved residues in the catalytic pocket

The last few years have seen the identification of numerous small molecules that selectively inhibit specific class I isoforms of PI3K (phosphoinositide 3-kinase), yet little has been revealed about the molecular basis for the observed selectivities. Using site-directed mutagenesis, we have investigated one of the areas postulated as being critical to the observed selectivity. The residues Thr(886) and Lys(890) of the PI3Kgamma isoform project towards the ATP-binding pocket at the entrance to the catalytic site, but are not conserved. We have made reciprocal mutations between those residues in the beta isoform (Glu(858) and Asp(862)) and those in the alpha isoform (His(855) and Gln(859)) and evaluated the potency of a range of reported PI3K inhibitors. The results show that the potencies of beta-selective inhibitors TGX221 and TGX286 are unaffected by this change. In contrast, close analogues of these compounds, particularly the alpha-isoform-selective compound (III), are markedly influenced by the point mutations. The collected data suggests two distinct binding poses for these inhibitor classes, one of which is associated with potent PI3Kbeta activity and is not associated with the mutated residues, and a second that, in accord with earlier hypotheses, does involve this pair of non-conserved amino acids at the catalytic site entrance and contributes to the alpha-isoform-selectivity of the compounds studied.

Identification of a unique filamin A binding region within the cytoplasmic domain of glycoprotein Ibalpha

Binding of the platelet GPIb/V/IX (glycoprotein Ib/V/IX) receptor to von Willebrand factor is critical for platelet adhesion and aggregation under conditions of rapid blood flow. The adhesive function of GPIbalpha is regulated by its anchorage to the membrane skeleton through a specific interaction with filamin A. In the present study, we examined the amino acid residues within the cytoplasmic tail of GPIbalpha, which are critical for association with filamin A, using a series of 25-mer synthetic peptides that mimic the cytoplasmic tail sequences of wild-type and mutant forms of GPIbalpha. Peptide binding studies of purified human filamin A have demonstrated a major role for the conserved hydrophobic stretch L567FLWV571 in mediating this interaction. Progressive alanine substitutions of triple, double and single amino acid residues within the Pro561-Arg572 region suggested an important role for Trp570 and Phe568 in promoting GPIbalpha binding to filamin A. The importance of these two residues in promoting filamin A binding to GPIbalpha in vivo was confirmed from the study of Chinese-hamster ovary cells expressing GPIbalpha Trp570-->Ala and Phe568-->Ala substitutions. Phenotypic analysis of these cell lines in flow-based adhesion studies revealed a critical role for these residues in maintaining receptor anchorage to the membrane skeleton and in maintaining cell adhesion to a von Willebrand factor matrix under high-shear conditions. These studies demonstrate a novel filamin A binding motif in the cytoplasmic tail of GPIbalpha, which is critically dependent on both Trp570 and Phe568.