Ribosome subunit attrition and activation of the p53-MDM4 axis dominate the response of MLL-rearranged cancer cells to WDR5 WIN site inhibition

The chromatin-associated protein WD Repeat Domain 5 (WDR5) is a promising target for cancer drug discovery, with most efforts blocking an arginine-binding cavity on the protein called the 'WIN' site that tethers WDR5 to chromatin. WIN site inhibitors (WINi) are active against multiple cancer cell types in vitro, the most notable of which are those derived from MLL-rearranged (MLLr) leukemias. Peptidomimetic WINi were originally proposed to inhibit MLLr cells via dysregulation of genes connected to hematopoietic stem cell expansion. Our discovery and interrogation of small-molecule WINi, however, revealed that they act in MLLr cell lines to suppress ribosome protein gene (RPG) transcription, induce nucleolar stress, and activate p53. Because there is no precedent for an anticancer strategy that specifically targets RPG expression, we took an integrated multi-omics approach to further interrogate the mechanism of action of WINi in human MLLr cancer cells. We show that WINi induce depletion of the stock of ribosomes, accompanied by a broad yet modest translational choke and changes in alternative mRNA splicing that inactivate the p53 antagonist MDM4. We also show that WINi are synergistic with agents including venetoclax and BET-bromodomain inhibitors. Together, these studies reinforce the concept that WINi are a novel type of ribosome-directed anticancer therapy and provide a resource to support their clinical implementation in MLLr leukemias and other malignancies.

Ribosome subunit attrition and activation of the p53-MDM4 axis dominate the response of MLL-rearranged cancer cells to WDR5 WIN site inhibition

The chromatin-associated protein WD Repeat Domain 5 (WDR5) is a promising target for cancer drug discovery, with most efforts blocking an arginine-binding cavity on the protein called the "WIN" site that tethers WDR5 to chromatin. WIN site inhibitors (WINi) are active against multiple cancer cell types in vitro, the most notable of which are those derived from MLL-rearranged (MLLr) leukemias. Peptidomimetic WINi were originally proposed to inhibit MLLr cells via dysregulation of genes connected to hematopoietic stem cell expansion. Our discovery and interrogation of small molecule WIN site inhibitors, however, revealed that they act in MLLr cell lines to suppress ribosome protein gene (RPG) transcription, induce nucleolar stress, and activate p53. Because there is no precedent for an anti-cancer strategy that specifically targets RPG expression, we took an integrated multi-omics approach to further interrogate the mechanism of action of WINi in MLLr cancer cells. We show that WINi induce depletion of the stock of ribosomes, accompanied by a broad yet modest translational choke and changes in alternative mRNA splicing that inactivate the p53 antagonist MDM4. We also show that WINi are synergistic with agents including venetoclax and BET-bromodomain inhibitors. Together, these studies reinforce the concept that WINi are a novel type of ribosome-directed anti-cancer therapy and provide a resource to support their clinical implementation in MLLr leukemias and other malignancies.

Granular cell tumor of the biliary tree in a pediatric patient

Granular cell tumor of the biliary tree is a rare benign tumor that occurs most commonly in young African-American girls. Granular cell tumor rarely is included in the differential diagnosis of biliary obstruction, yet complete surgical excision is curative. The authors report a case of granular cell tumor of the biliary tree in a pediatric patient that required a pancreaticoduodenectomy for cure.

The type I serine/threonine kinase receptor ActRIA (ALK2) is required for gastrulation of the mouse embryo

ActRIA (or ALK2), one of the type I receptors of the transforming growth factor-beta (TGF-beta) superfamily, can bind both activin and bone morphogenetic proteins (BMPs) in conjunction with the activin and BMP type II receptors, respectively. In mice, ActRIA is expressed primarily in the extraembryonic visceral endoderm before gastrulation and later in both embryonic and extraembryonic cells during gastrulation. To elucidate its function in mouse development, we disrupted the transmembrane domain of ActRIA by gene targeting. We showed that embryos homozygous for the mutation were arrested at the early gastrulation stage, displaying abnormal visceral endoderm morphology and severe disruption of mesoderm formation. To determine in which germ layer ActRIA functions during gastrulation, we performed reciprocal chimera analyses. (1) Homozygous mutant ES cells injected into wild-type blastocysts were able to contribute to all three definitive germ layers in chimeric embryos. However, a high contribution of mutant ES cells in chimeras disrupted normal development at the early somite stage. (2) Consistent with ActRIA expression in the extraembryonic cells, wild-type ES cells failed to rescue the gastrulation defect in chimeras in which the extraembryonic ectoderm and visceral endoderm were derived from homozygous mutant blastocysts. Furthermore, expression of HNF4, a key visceral endoderm-specific transcription regulatory factor, was significantly reduced in the mutant embryos. Together, our results indicate that ActRIA in extraembryonic cells plays a major role in early gastrulation, whereas ActRIA function is also required in embryonic tissues during later development in mice.

Muscle and nerve biopsy in the evaluation of neuromuscular disorders: the surgeon's perspective

BACKGROUND/PURPOSE

A muscle biopsy frequently is requested by the neurologist evaluating a child with neuromuscular symptoms. However, there are no reports discussing the preoperative evaluation for, and diagnostic yield of, this procedure. The authors reviewed our experience over a 10-year period to obtain these data.

METHODS

The records of 153 patients who underwent muscle biopsy were reviewed with particular attention to the cardiology evaluation, the pathology report, and any resultant change in diagnosis and treatment of the child.

RESULTS

All 153 specimens contained adequate tissue for complete histological analysis. Preoperative cardiology consults were obtained in 82% of the children, with abnormalities found in 9%. Severe cardiac dysfunction was found in three children, all of whom had a previously diagnosed cardiomyopathy or dysrhythmia. No pathological abnormality was found in 41% of the muscle biopsy specimens, and nonspecific pathological findings were described in 23%. A specific diagnosis was made in 36%. Only 19% of the children had their treatment changed by the results of the muscle biopsy.

CONCLUSIONS

Muscle biopsies can be performed safely without routine preoperative cardiac evaluation. A specific diagnosis, however, may be made in less than half of the patients with a change in therapy available for even fewer.

Infantile intestinal leiomyosarcoma: surgical resection (without adjuvant therapy) for cure

A 7-week-old boy presented with a 6-week history of failure to thrive, acute intestinal obstruction, and an apparently irreducible intussusception (noted on contrast enema). He underwent abdominal exploration, during which a cecal mass was identified and resected. The mass proved to be a leiomyosarcoma. Histologically, it was an intermediate-grade malignancy with a predicted 5-year survival rate of 16% to 23% based on data from the adult experience. Three years after resection and without having received adjuvant therapy, he is healthy and free of disease. A review of the literature showed that in infants these tumors are predominantly colonic, compared with the predilection for small intestinal lesions found in the older pediatric and adult populations. Infantile intestinal leiomyosarcomata are rare malignancies that do well if complete surgical excision of the disease can be accomplished. The histological prognostic indicators proposed for intestinal leiomyosarcomas in the adult population cannot be extrapolated to infants because when they occur in infants, they appear to be less aggressive, and these patients do well without adjuvant therapy.

Left ventricular failure complicating severe pediatric burn injuries

PURPOSE

Despite improvements in the overall survival rates for critically burned children, failed resuscitation may account for 54% of deaths following burn injuries. Clinical and experimental studies have implicated failure of the right side of the heart in adults, biventricular failure in elderly patients, and inadequate resuscitation as causes of refractory burn shock. This retrospective study of resuscitation at a tertiary pediatric burn center showed that myocardial depression is a complicating factor in the treatment of the pediatric burn victim.

METHODS

From 1989 to 1992, 28 critically burned children (> or = 60% total burn surface area) were resuscitated primarily at our center (admission within 24 hours of injury). Twenty-seven children had central lines, nine of whom underwent pulmonary artery catheterization for intensive hemodynamic monitoring because standard resuscitative therapy had failed. The average amount of fluid received at 8 and 24 hours after injury was within 10% of the calculated volume based on the Parkland formula.

RESULTS

Indexes of a failing rescue attempt included respiratory distress (PaO2/FlO2 < or = 200), central venous pressure of greater than 10 mm Hg, and urine output of less than 1 mL/kg/h. Filling pressures were found to be normal or elevated in all children, indicating adequate volume replacement. Evaluation of cardiac function was performed using a thermodilution technique and showed that 100% of the study group had depressed left ventricular function, with an average left ventricular stroke work index (LVSWI) of 19.9 g.m/m2 (normal, 44 to 68 g.m/m2), whereas only 38% had concomitant right ventricular failure. This left-sided dysfunction persisted throughout the acute resuscitation period but was improved after appropriate modification of fluid resuscitation and initiation of vasopressors (average final LVSWI, 38.0 g.m/m2). There were no complications from placement of the Swan-Ganz catheters in this group.

CONCLUSION

Cardiogenic failure is a major determinant of a failing pediatric burn resuscitation, and, contrary to the adult burn patient, the myocardial depression is predominantly left-sided. Information from pulmonary artery catheters can help direct therapy by providing indications for vasopressors and modifying fluid resuscitation.

Mortality and respiratory failure in a pediatric burn population

A 9-year retrospective review of 1,242 admissions to a tertiary burn center identified 137 patients who were intubated and ventilated for a critical airway or pulmonary problem. These patients varied in age from 2 months to 18 years with an average total body surface area (TBSA) burn of 55%. We evaluated this group for evidence of respiratory failure (ARF) as defined by the respiratory failure index (RFI) (PaO2/FIO2 < or = 300). While only 23% of admissions to the burn center were related to flame burns, these injuries accounted for 82% of children who had ARF. Forty-two percent of these intubated children had abnormalities on their admission chest x-ray and 61% of this cohort developed evidence of ARF as defined by the RFI. The development of sepsis along with ARF regardless of TBSA involvement doubles the mortality of ARF alone. Early burn wound excision and grafting is critically important to prevent the late complication of sepsis. We carefully monitor ventilator settings to insure low peak inspiratory pressures, allowing relative hypercapnia and avoiding hyperoxia. Despite an increased number of admissions and critically injured children, we have not seen an increase in morbidity and have had a 53% reduction in mortality in the last 2 years with these techniques. We believe this management offers the best outcome for the pediatric burn victim and would recommend this strategy to other centers dealing with these severely injured children.

Affective illness and S-adenosyl methionine: a preliminary report

S-Adenosyl methionine may well have an antidepressant action beyond a placebo effect but this is virtually confined to endogenous depression. This should be subjected to further study. Our own double-blind placebo-controlled study is still incomplete. The indications are that SAM specifically affects folate, dopamine, and serotonin metabolism as well as activating and switching brain mechanisms. This suggests exciting prospects for further investigations. SAM is a nontoxic physiological metabolite virtually free of side effects.