Synthesis of 1,4-azaphosphinine nucleosides and evaluation as inhibitors of human cytidine deaminase and APOBEC3A.

Nucleoside and polynucleotide cytidine deaminases (CDAs), such as CDA and APOBEC3, share a similar mechanism of cytosine to uracil conversion. In 1984, phosphapyrimidine riboside was characterised as the most potent inhibitor of human CDA, but the quick degradation in water limited the applicability as a potential therapeutic. To improve stability in water, we synthesised derivatives of phosphapyrimidine nucleoside having a CH2 group instead of the N3 atom in the nucleobase. A charge-neutral phosphinamide and a negatively charged phosphinic acid derivative had excellent stability in water at pH 7.4, but only the charge-neutral compound inhibited human CDA, similar to previously described 2'-deoxyzebularine (Ki = 8.0 ± 1.9 and 10.7 ± 0.5 µM, respectively). However, under basic conditions, the charge-neutral phosphinamide was unstable, which prevented the incorporation into DNA using conventional DNA chemistry. In contrast, the negatively charged phosphinic acid derivative was incorporated into DNA instead of the target 2'-deoxycytidine using an automated DNA synthesiser, but no inhibition of APOBEC3A was observed for modified DNAs. Although this shows that the negative charge is poorly accommodated in the active site of CDA and APOBEC3, the synthetic route reported here provides opportunities for the synthesis of other derivatives of phosphapyrimidine riboside for potential development of more potent CDA and APOBEC3 inhibitors.

Clinical profile and outcomes of childhood dilated cardiomyopathy - A single-center three-decade experience.

Introduction and Aims: Dilated cardiomyopathy (DCM) is an important cause of heart failure (HF) among children. Research on pediatric DCM remains surprisingly scarce. The primary objective of the study was to evaluate the clinical profile and outcomes of pediatric DCM and the secondary objective was to study the predictors of outcome. Methods and Results: We enrolled all patients with cardiomyopathy who presented to us between 1990 and 2020 and were younger than 18 years. During the 30-year study period, we identified 233 cases of pediatric cardiomyopathy. One hundred and nineteen (51%) cases had DCM. This retrospective cohort was analyzed to study their outcome and the possible predictors of outcome. Nearly, 8% presented in the neonatal period, and 37% in infancy. The most common mode of presentation was dyspnea on exertion (71%). Ninety-three patients presented in heart failure (78%). The median left ventricular dimension z-score in diastole was 4.3 (range 2.5-9.06). The median left ventricle (LV) ejection fraction was 31%. Seventy-two percent of this cohort were on angiotensin-converting-enzyme inhibitors, 40% on aldosterone antagonists, and 47% on beta-blockers. One-third had syndromic, metabolic, genetic, or any secondary cause identified. Twenty-seven patients satisfied the three-tiered clinical classification for the diagnosis of probable acute myocarditis. Over a mean follow-up of 3.29 years, 27% were lost to follow-up. Among the remaining patients who were on follow-up (n = 86), 39 (45%) died, 31 (36%) recovered, and 16 (18%) had persistent LV dysfunction. Heart Failure was the most common cause of death. Eight patients in this cohort (4.2%) had thromboembolic phenomena. Nine had sustained ventricular arrhythmias and six had atrial/junctional arrhythmias. Among the various risk factors studied, only infantile onset had a significant relationship with death or ventricular arrhythmias (P value- 0.05). The 5-year survival rate of DCM patients was 59%. Conclusion: A reasonably good percentage of our population showed recovery of the left ventricular function (36%). Only infantile onset had a significant relationship with death or ventricular arrhythmias. The outcome in our DCM cohort is similar to other population cohorts.

Structure-guided inhibition of the cancer DNA-mutating enzyme APOBEC3A.

The normally antiviral enzyme APOBEC3A is an endogenous mutagen in human cancer. Its single-stranded DNA C-to-U editing activity results in multiple mutagenic outcomes including signature single-base substitution mutations (isolated and clustered), DNA breakage, and larger-scale chromosomal aberrations. APOBEC3A inhibitors may therefore comprise a unique class of anti-cancer agents that work by blocking mutagenesis, slowing tumor evolvability, and preventing detrimental outcomes such as drug resistance and metastasis. Here we reveal the structural basis of competitive inhibition of wildtype APOBEC3A by hairpin DNA bearing 2'-deoxy-5-fluorozebularine in place of the cytidine in the TC substrate motif that is part of a 3-nucleotide loop. In addition, the structural basis of APOBEC3A's preference for YTCD motifs (Y = T, C; D = A, G, T) is explained. The nuclease-resistant phosphorothioated derivatives of these inhibitors have nanomolar potency in vitro and block APOBEC3A activity in human cells. These inhibitors may be useful probes for studying APOBEC3A activity in cellular systems and leading toward, potentially as conjuvants, next-generation, combinatorial anti-mutator and anti-cancer therapies.

Clinical profile and outcomes of pediatric hypertrophic cardiomyopathy in a South Indian tertiary care cardiac center: a three decade experience.

INTRODUCTION: Although much research has been done on adult hypertrophic cardiomyopathy, data on pediatric hypertrophic cardiomyopathy is still limited. METHODS AND RESULTS: The study enrolled all patients with cardiomyopathy who presented to us between 1990 to 2020 and were younger than 18 yrs. During the thirty-year study period, we identified 233 cases of pediatric cardiomyopathy. Sixty-three cases (27%) had hypertrophic cardiomyopathy. Out of the 63 HCM cases, 12% presented in the neonatal period and 37% presented in the first year of life. The median age of presentation was 7 yrs (Range 0.1-18 yrs). Sixteen patients had proven syndromic, metabolic, or genetic disease (25%). LV outflow obstruction was present in 30 patients (47%). Noonan syndrome was present in 9 of the 63 patients (14%). Dyspnea on exertion was the most common mode of presentation. Cardiac MRI was done in 28 patients, out of which 17 had late gadolinium enhancement (LGE). Mid myocardial enhancement was the most common pattern. Four patients had LGE of more than 15%. Over a mean follow-up period of 5.6 years (0.1-30 years), twenty-one were lost to follow-up (33%). Among the patients whose outcome was known, eleven died (26%), and thirty-one (73%) were alive. The 5-year survival rate of HCM patients was 82%, and the 10-year survival rate was 78%. Seven died of sudden cardiac death, three from heart failure, and one from ventricular arrhythmias. Sustained ventricular arrhythmias were seen in three patients and atrial arrhythmias in two. First-degree AV block was seen in 10 patients (15%) and bundle branch blocks (BBB) in five (8%). Eight patients required ICD or transplant (12.7%). Two patients underwent ICD for primary prevention, and one underwent PPI for distal AV conduction disease. Among the various clinical, echocardiographic, and radiological risk factors studied, only consanguinity showed a trend towards higher events of death or ventricular arrhythmias (P-value 0.08). CONCLUSION: More than one-third of our HCM cohort presented in infancy. LV outflow tract obstruction is common (47%). Mid myocardial enhancement was the most common pattern of late gadolinium enhancement. SCD was the most common cause of death. The outcome in our HCM cohort is good and similar to other population cohorts. Only Consanguinity showed a trend towards higher events of death or ventricular arrhythmias.

Seven-membered ring nucleobases as inhibitors of human cytidine deaminase and APOBEC3A.

The APOBEC3 (APOBEC3A-H) enzyme family as a part of the human innate immune system deaminates cytosine to uracil in single-stranded DNA (ssDNA) and thereby prevents the spread of pathogenic genetic information. However, APOBEC3-induced mutagenesis promotes viral and cancer evolution, thus enabling the progression of diseases and development of drug resistance. Therefore, APOBEC3 inhibition offers a possibility to complement existing antiviral and anticancer therapies and prevent the emergence of drug resistance, thus making such therapies effective for longer periods of time. Here, we synthesised nucleosides containing seven-membered nucleobases based on azepinone and compared their inhibitory potential against human cytidine deaminase (hCDA) and APOBEC3A with previously described 2'-deoxyzebularine (dZ) and 5-fluoro-2'-deoxyzebularine (FdZ). The nanomolar inhibitor of wild-type APOBEC3A was obtained by the incorporation of 1,3,4,7-tetrahydro-2H-1,3-diazepin-2-one in the TTC loop of a DNA hairpin instead of the target 2'-deoxycytidine providing a Ki of 290 ± 40 nM, which is only slightly weaker than the Ki of the FdZ-containing inhibitor (117 ± 15 nM). A less potent but notably different inhibition of human cytidine deaminase (CDA) and engineered C-terminal domain of APOBEC3B was observed for 2'-deoxyribosides of the S and R isomers of hexahydro-5-hydroxy-azepin-2-one: the S-isomer was more active than the R-isomer. The S-isomer shows resemblance in the position of the OH-group observed recently for the hydrated dZ and FdZ in the crystal structures with APOBEC3G and APOBEC3A, respectively. This shows that 7-membered ring analogues of pyrimidine nucleosides can serve as a platform for further development of modified ssDNAs as powerful A3 inhibitors.

Structure-guided inhibition of the cancer DNA-mutating enzyme APOBEC3A.

The normally antiviral enzyme APOBEC3A1-4 is an endogenous mutagen in many different human cancers5-7, where it becomes hijacked to fuel tumor evolvability. APOBEC3A's single-stranded DNA C-to-U editing activity1,8 results in multiple mutagenic outcomes including signature single-base substitution mutations (isolated and clustered), DNA breakage, and larger-scale chromosomal aberrations5-7. Transgenic expression in mice demonstrates its tumorigenic potential9. APOBEC3A inhibitors may therefore comprise a novel class of anti-cancer agents that work by blocking mutagenesis, preventing tumor evolvability, and lessening detrimental outcomes such as drug resistance and metastasis. Here we reveal the structural basis of competitive inhibition of wildtype APOBEC3A by hairpin DNA bearing 2'-deoxy-5-fluorozebularine in place of the cytidine in the TC recognition motif that is part of a three-nucleotide loop. The nuclease-resistant phosphorothioated derivatives of these inhibitors maintain nanomolar in vitro potency against APOBEC3A, localize to the cell nucleus, and block APOBEC3A activity in human cells. These results combine to suggest roles for these inhibitors to study A3A activity in living cells, potentially as conjuvants, leading toward next-generation, combinatorial anti-mutator and anti-cancer therapies.

Safety of drug-eluting stents for stenting patent arterial duct in neonates.

OBJECTIVES: The primary objective was to evaluate the trend of blood sirolimus concentrations in neonates following ductal stenting. The long-term outcomes and incidence of infections were also evaluated. METHODS: Prospective open-label observational study in a tertiary referral centre over a 1-year period. Serum sirolimus levels were estimated at 1 hour and 24hrs post-stent insertion followed by 7 days in neonates who underwent ductal stenting. The trend in sirolimus levels, incidence of infections, complications and outcomes following ductal stenting were studied. RESULTS: Seven neonates with duct-dependent pulmonary circulation underwent ductal stenting at median age of 8.5 days and weight of 2.83kg. The average stent size was 3.5±0.4 mm, and average stent length was 16.3±5.1 mm. The mean sirolimus concentrations at 1 hour, 24 hours and 7 days were 41.3±6.9ng/ml, 15.4±7.1ng/ml and 3.1±0.85ng/ml respectively. Levels fell below therapeutic range for all patients by 7 days. Three patients had sepsis or necrotising enterocolitis, but responded well to antibiotics; 1 patient had aspiration related sudden death. There were no further events at a mean follow-up of 207 days, and 4 patients underwent elective surgery at 238 ± 81 days after ductal stenting. CONCLUSIONS: This study demonstrates applicability of drug-eluting stents for ductal stenting in newborns. Drug-eluting stents with abluminal drug delivery are associated with high sirolimus levels in initial hours but rapidly taper to negligible levels within a week of implantation. Neonates with high pre-procedure likelihood of infection developed sepsis but responded well to conservative management. The patency of drug-eluting ductal stents is preserved over long-term follow-up.

Normal pulmonary venous drainage in the setting of total anomalous pulmonary venous connection.

Total anomalous pulmonary venous connection (TAPVC) and anomalous pulmonary venous drainage are not synonymous. This has been described in the setting of right isomerism (bilateral right sidedness) where the pulmonary veins are connected anomalously but drain normally to the left-sided morphological right atrium. We describe another situation in right isomerism where normal pulmonary venous drainage is present in the setting of TAPVC.

Influence of age at surgery on left ventricular strain in patients with anomalous origin of left coronary artery from pulmonary artery.

OBJECTIVES: Myocardial strain abnormalities are described after surgical repair of anomalous left coronary artery from pulmonary artery (ALCAPA) even after recovery of ventricular function. The factors that predispose to the presence of these strain abnormalities in the presence of normal ventricular function are unknown. The aim of this study was to find out whether the age at repair influences the presence of global and regional strain abnormalities on follow-up. METHODS: Repaired ALCAPA patients from a single centre (n = 40) with good ventricular ejection fraction on follow-up were recruited. Baseline and follow-up data were collected from electronic records. Global and regional myocardial strain assessment was done by speckle tracking echocardiography prospectively. The association between age at repair and strain abnormalities on follow-up was analysed. RESULTS: The patients who presented earlier had significantly worse ventricular function pre-operatively compared to older patients (P < 0.0005). Global longitudinal strain was abnormal in 40% of patients with normal ventricular ejection fraction on follow-up. Presence of longitudinal strain abnormalities was more in patients who underwent repair at older age than in those who were repaired earlier (P < 0.0005). The probability of having normal longitudinal strain on follow-up was 81.6% if surgery was done before 7.8 months of age. If operated before 6 months, the odds of having normal myocardial strain was 11 times higher. Regional strain abnormalities of varying severity were present in all patients in the left and in some patients in the right coronary artery territories. CONCLUSIONS: Older age at ALCAPA repair is associated with increased incidence of myocardial strain abnormalities. Regional strain abnormalities were found in both left and right coronary artery territories.

Design, Synthesis, and Evaluation of a Cross-Linked Oligonucleotide as the First Nanomolar Inhibitor of APOBEC3A.

Drug resistance is a major problem associated with anticancer chemo- and immunotherapies. Recent advances in the understanding of resistance mechanisms have revealed that enzymes of the APOBEC3 (A3) family contribute to the development of drug resistance in multiple cancers. A3 enzymes are polynucleotide cytidine deaminases that convert cytosine to uracil (C→U) in single-stranded DNA (ssDNA) and in this way protect humans against viruses and mobile retroelements. On the other hand, cancer cells use A3s, especially A3A and A3B, to mutate human DNA, and thus by increasing rates of evolution, cancer cells escape adaptive immune responses and resist drugs. However, as A3A and A3B are non-essential for primary metabolism, their inhibition opens up a strategy to augment existing anticancer therapies and suppress cancer evolution. To test our hypothesis that pre-shaped ssDNA mimicking the U-shape observed in ssDNA-A3 complexes can provide a better binder to A3 enzymes, a Cu(I)-catalyzed azide-alkyne cycloaddition was used to cross-link two distant modified nucleobases in ssDNA. The resultant cytosine-containing substrate, where the cytosine sits at the apex of the loop, was deaminated faster by the engineered C-terminal domain of A3B than a standard, linear substrate. The cross-linked ssDNA was converted into an A3 inhibitor by replacing the 2'-deoxycytidine in the preferred TCA substrate motif by 2'-deoxyzebularine, a known inhibitor of single nucleoside cytidine deaminases. This strategy yielded the first nanomolar inhibitor of engineered A3BCTD and wild-type A3A (Ki = 690 ± 140 and 360 ± 120 nM, respectively), providing a platform for further development of powerful A3 inhibitors.

Small-Angle X-ray Scattering (SAXS) Measurements of APOBEC3G Provide Structural Basis for Binding of Single-Stranded DNA and Processivity.

APOBEC3 enzymes are polynucleotide deaminases, converting cytosine to uracil on single-stranded DNA (ssDNA) and RNA as part of the innate immune response against viruses and retrotransposons. APOBEC3G is a two-domain protein that restricts HIV. Although X-ray single-crystal structures of individual catalytic domains of APOBEC3G with ssDNA as well as full-length APOBEC3G have been solved recently, there is little structural information available about ssDNA interaction with the full-length APOBEC3G or any other two-domain APOBEC3. Here, we investigated the solution-state structures of full-length APOBEC3G with and without a 40-mer modified ssDNA by small-angle X-ray scattering (SAXS), using size-exclusion chromatography (SEC) immediately prior to irradiation to effect partial separation of multi-component mixtures. To prevent cytosine deamination, the target 2'-deoxycytidine embedded in 40-mer ssDNA was replaced by 2'-deoxyzebularine, which is known to inhibit APOBEC3A, APOBEC3B and APOBEC3G when incorporated into short ssDNA oligomers. Full-length APOBEC3G without ssDNA comprised multiple multimeric species, of which tetramer was the most scattering species. The structure of the tetramer was elucidated. Dimeric interfaces significantly occlude the DNA-binding interface, whereas the tetrameric interface does not. This explains why dimers completely disappeared, and monomeric protein species became dominant, when ssDNA was added. Data analysis of the monomeric species revealed a full-length APOBEC3G-ssDNA complex that gives insight into the observed "jumping" behavior revealed in studies of enzyme processivity. This solution-state SAXS study provides the first structural model of ssDNA binding both domains of APOBEC3G and provides data to guide further structural and enzymatic work on APOBEC3-ssDNA complexes.

Left ventricular-infundibular apical septal defect: a rare entity revisited.

Apical ventricular septal defects are a heterogeneous group of septal defects that need accurate anatomic characterisation for planning appropriate management. Left ventricular-infundibular apical septal defects are defects between the left ventricular septum and the infundibular apex of the right ventricle with distinctive morphological features. We describe two illustrative examples of this septal defect with focus on their therapeutic implications and long-term outcome.

Chylotamponade in Pediatric Primary Mediastinal Large B-Cell Lymphoma.

Chylotamponade involves rapid accumulation of chyle in the pericardium elevating the pericardial pressures above normal right heart filling pressures, and is extremely rare. A 12-y-old boy presented to the emergency with complaints of facial puffiness for 1 mo and breathing difficulty for 1 wk. The neck veins were distended, and the heart sounds were muffled. A chest CT demonstrated a large anterior mediastinal mass with pleural and pericardial effusions. Echocardiography confirmed cardiac tamponade. Pericardiocentesis revealed chylopericardium. He was placed on a chyle leak diet, and the drain was removed after 48 h. Biopsy of the mediastinal mass revealed a primary mediastinal B-cell lymphoma. He was successfully managed with chemotherapy. The index case demonstrates how prompt identification and management of chylotamponade and treatment of the underlying cause can lead to good clinical outcomes.

Percutaneous Closure of Giant Aortic Pseudoaneurysm in a Child.

Although percutaneous closure of aortic pseudoaneurysms have been described in adults with good results, there are no reports in children. This case demonstrates that in selected high-risk cases where the anatomy is suitable, percutaneous closure may be feasible and safe in children.

Recurrent pericardial effusion in a boy: A clue to underlying pericardial and pulmonary lymphangiectasia.

Pulmonary lymphangiectasia is a rare congenital malformation of lymphatic vessels. We report the case of a 5-year-old boy with recurrent pericardial effusion which was diagnosed to be due to pericardial and pulmonary lymphangiectasia.

Hemianomalous pulmonary venous drainage and type IIb coronary sinus septal defect - Utility of subxiphoid and right parasternal views.

A 3-year-old boy presented with history of recurrent respiratory tract infections in infancy. Clinically he had hemodynamically significant pre-tricuspid left-to-right shunt and no pulmonary hypertension. Transthoracic echocardiography delineated anomalous drainage of the left sided pulmonary veins to a dilated coronary sinus opening into the right atrium. Closer evaluation from the subxiphoid and right parasternal views led to the diagnosis of an associated type IIb coronary sinus septal defect.

A Comparative Study of Invasive Modalities for Evaluation of Pulmonary Arteriovenous Fistula after Bidirectional Glenn Shunt.

Development of pulmonary AV fistula (PAVF) after bidirectional glenn shunt (BDG) results in significant cyanosis, impaired exercise performance, and increased morbidity and mortality. We attempted to detect and quantify PAVF in post-BDG patients by saline contrast transesophageal echocardiography (TEE) and compare with pulmonary angiography and pulmonary vein oximetry. This was a prospective study done between 2017 and 2018. Twenty-five children who underwent BDG and planned for cardiac catheterization prior to Fontan completion were included in the study. All patients underwent pulmonary angiography, oximetry, and saline contrast TEE at the time of cardiac catheterization. Twenty-two patients had undergone unilateral BDG surgery and three were palliated by bilateral BDG. The mean oxygen saturation was 80 ± 5.2%. Thirteen patients (52%) had preserved antegrade pulmonary blood flow. Eighteen patients (72%) had PAVF by angiography and oximetry, while 19 (76%) had PAVF identified by contrast echocardiography. There was moderate correlation between the degree of pulmonary venous desaturation and grading of PAVF by contrast echocardiography. PAVF was predominantly located in the lower zones of the lungs. Higher grades of PAVF were not seen in patients with preserved antegrade flow after BDG. Angiographically detected PAVF showed a steady increase with increasing delay to cardiac catheterization from BDG. Significant reduction in systemic saturation was limited to advanced grades of PAVF in patients after BDG. Saline contrast TEE, pulmonary venous oximetry, and pulmonary angiography equally identified PAVF in patients after BDG. Prognostic utility of the same needs to be assessed by long-term follow-up of these subjects.

Small-Angle X-ray Scattering Models of APOBEC3B Catalytic Domain in a Complex with a Single-Stranded DNA Inhibitor.

In normal cells APOBEC3 (A3A-A3H) enzymes as part of the innate immune system deaminate cytosine to uracil on single-stranded DNA (ssDNA) to scramble DNA in order to give protection against a range of exogenous retroviruses, DNA-based parasites, and endogenous retroelements. However, some viruses and cancer cells use these enzymes, especially A3A and A3B, to escape the adaptive immune response and thereby lead to the evolution of drug resistance. We have synthesized first-in-class inhibitors featuring modified ssDNA. We present models based on small-angle X-ray scattering (SAXS) data that (1) confirm that the mode of binding of inhibitor to an active A3B C-terminal domain construct in the solution state is the same as the mode of binding substrate to inactive mutants of A3A and A3B revealed in X-ray crystal structures and (2) give insight into the disulfide-linked inactive dimer formed under the oxidizing conditions of purification.

Left ventricular noncompaction in primary systemic carnitine deficiency: A rare association.

Left ventricular noncompaction (LVNC) is a rare phenotype of dilated cardiomyopathy. We report a child with primary systemic carnitine deficiency having associated LVNC.