HDAC Inhibition Induces MicroRNA-182, which Targets RAD51 and Impairs HR Repair to Sensitize Cells to Sapacitabine in Acute Myelogenous Leukemia

PURPOSE

The double-strand breaks elicited by sapacitabine, a clinically active nucleoside analogue prodrug, are repaired by RAD51 and the homologous recombination repair (HR) pathway, which could potentially limit its toxicity. We investigated the mechanism by which histone deacetylase (HDAC) inhibitors targeted RAD51 and HR to sensitize acute myelogenous leukemia (AML) cells to sapacitabine.

EXPERIMENTAL DESIGN

Chromatin immunoprecipitation identified the role of HDACs in silencing miR-182 in AML. Immunoblotting, gene expression, overexpression, or inhibition of miR-182 and luciferase assays established that miR-182 directly targeted RAD51. HR reporter assays, apoptotic assays, and colony-forming assays established that the miR-182, as well as the HDAC inhibition-mediated decreases in RAD51 inhibited HR repair and sensitized cells to sapacitabine.

RESULTS

The gene repressors, HDAC1 and HDAC2, became recruited to the promoter of miR-182 to silence its expression in AML. HDAC inhibition induced miR-182 in AML cell lines and primary AML blasts. miR-182 targeted RAD51 protein both in luciferase assays and in AML cells. Overexpression of miR-182, as well as HDAC inhibition-mediated induction of miR-182 were linked to time- and dose-dependent decreases in the levels of RAD51, an inhibition of HR, increased levels of residual damage, and decreased survival after exposure to double-strand damage-inducing agents.

CONCLUSIONS

Our findings define the mechanism by which HDAC inhibition induces miR-182 to target RAD51 and highlights a novel pharmacologic strategy that compromises the ability of AML cells to conduct HR, thereby sensitizing AML cells to DNA-damaging agents that activate HR as a repair and potential resistance mechanism. Clin Cancer Res; 22(14); 3537-49. ©2016 AACR.

Implantation of Cryopreserved Mitral Allograft into the Tricuspid Position in an Experimental Study in Sheep: Technical Aspects of Implantation and Immediate Results Evaluated by Epicardial Echocardiography

AIMS

Cryopreserved mitral allograft valve (MAV) offers theoretical advantages over conventional mechanical or biological prostheses in tricuspid position, especially in infectious endocarditis patients. MAV processing and tricuspid valve (TV) replacement in a sheep model is described.

METHODS AND RESULTS

In 20 adult sheep, MAV were harvested, processed and cryopreserved. One month later, recipient's TV were excised and the MAVs were transplanted into the tricuspid position in 13 sheep, under general anaesthesia, via a right thoracotomy, with an extracorporeal circulation (ECC) and cardioplegic heart arrest. Both MAV papillary muscles were anchored into the right ventricular wall by transmural stitches and the MAV anulus was sewn into the recipient's tricuspid anulus. After weaning from ECC, the anatomy and function of the MAV in the tricuspid position was assessed by epicardial echocardiography. The average duration of the ECC was 58 minutes (42-88), the cardioplegic heart arrest was 36 minutes (28-45). Weaning from EEC was always uneventful. Right atrial & pulmonary artery pressure measurements and epicardial echocardiography documented good function of all MAVs.

CONCLUSION

MAV remained mechanically strong enough for implantation into the tricuspid position. Reproducible technique of MAV transplantation into the tricuspid position with excellent early postoperative haemodynamic performance was developed.

[Pulmonary embolism following aorto-coronary by-pass]

The authors present a case-review of a 65 year-old female patient, hospitalized for rest dyspnoea and collaps condition, 3 weeks following her completed aorto-coronary by-pass. The symptoms were caused by a massive lung embolism. Upon the echocardiographic examination, a massive thrombus in the right-sided cardiac spaces--a rare complication of cardiosurgical procedures--was detected. The patient was treated surgically. At the present time, 4 months following the procedure, the patient is completely recovered.

One-year results from cryopreserved mitral allograft transplantation into the tricuspid position in a sheep experimental model

Mitral allografts are still used only exceptionally in the mitral or tricuspid position. The main indication remains infectious endocarditis of atrioventricular valves for its flexibility and low risk of infection. The aim of our study was to evaluate 1-year results of mitral allografts transplantation into the tricuspid position in a sheep model. Mitral allografts were processed, cryopreserved, and transplanted into the tricuspid position anatomically (Group I - 11 animals) or antianatomically (Group II - 8 animals). All survivors (4 from Group I, and 3 from Group II) were checked at 3, 6, and 12 months by echocardiography with the exception of one survivor from Group II (which was examinated only visually). Examination throughout follow-up included for mitral allograft regurgitation and annuli dilatation. At postmortem, the papillary muscles were healed and firmly anchored to the right ventricular wall in all subjects. Transventricular fixation of the papillary muscles with buttressed sutures was proven to be a stable, reproducible, and safe method for anchoring mitral allograft leaflets. There were no significant differences between the two implantation methods. Annulus support of mitral allografts might be very useful in this type of operation and could prevent annular dilatation.

[Aortic allograft (homograft) for the treatment of valvular disorders in adults with focus on treatment of infective aortic valve endocarditis]

Still after 40 years of heart valve prostheses intensive development ideal valve substitute still does not exist. Aortic allograft represents one alternative which could be used for aortic and/or pulmonary valve replacement. This type of biological heart valve prosthesis is being currently discussed from the point of view of Tissue Banking, as well as from clinical aspects--e.g. surgical implantation technique and long term results. Live issue remains particularly the aortic allograft implantation into the aortic position. The authors discuss the aortic allograft role in the aortic valve infectious endocarditis treatment, which was widespread worldwide and accepted. Aortic allograft implantation is considered as a method of choice in that particular indication, especially in prosthetic aortic valve endocarditis and in left ventricle outlet tract destruction cases. The method is considered to be more technically demanding than routine heart valve surgery (heart valve replacement by means of mechanical or commercial biological prostheses), but literary and authors own experience in that particular group of patients looks encouraging. Aortic allografts permanent supply in our country is secured.

[Midterm results aortic valve replacement with allograft]

INTRODUCTION

Aortic allograft implantation into the aortic position in adults is standard procedure with some controversary. The most popular indication is bacterial endocarditis. We would like to present our midterm results.

RESULTS

We implanted 61 allografts in 60 patients (between 10/2002 and 04/2008). Men were 46 (76.8%) and average age was 57 +/- 10.76 year. 30 days mortality was 9 people (15.0%, all with bacterial endocarditis). Late mortality 1 man (1.6%). Follow up 1-66 months, average 39.18 SD +/- 14.3 months, median 42 months.

CONCLUSION

Implantation of aortic allograft into the aortic position is standard procedure with good midterm results. Relative high early mortality is dependent on preoperative status in patiens with acute bacterial endocarditis--all early death people were people with acute bacterial endocarditis and minimally one vital organ severe dysfunction.