X-linked inhibitor of apoptosis protein represents a promising therapeutic target for relapsed/refractory ALL

Acute lymphoblastic leukemia (ALL) represents the most frequent malignancy in children, and relapse/refractory (r/r) disease is difficult to treat, both in children and adults. In search for novel treatment options against r/r ALL, we studied inhibitor of apoptosis proteins (IAP) and Smac mimetics (SM). SM-sensitized r/r ALL cells towards conventional chemotherapy, even upon resistance against SM alone. The combination of SM and chemotherapy-induced cell death via caspases and PARP, but independent from cIAP-1/2, RIPK1, TNFα or NF-κB. Instead, XIAP was identified to mediate SM effects. Molecular manipulation of XIAP in vivo using microRNA-30 flanked shRNA expression in cell lines and patient-derived xenograft (PDX) models of r/r ALL mimicked SM effects and intermediate XIAP knockdown-sensitized r/r ALL cells towards chemotherapy-induced apoptosis. Interestingly, upon strong XIAP knockdown, PDX r/r ALL cells were outcompeted in vivo, even in the absence of chemotherapy. Our results indicate a yet unknown essential function of XIAP in r/r ALL and reveal XIAP as a promising therapeutic target for r/r ALL.

Abstract 1540: Creating faithful genetic zebrafish models of pediatric high grade gliomas and MPNSTs

Pediatric high-grade gliomas (HGGs) are the leading cause of cancer-related death in children. Despite a slight improvement of patient prognosis over the past decades pediatric HGGs remain largely incurable. Thus, new experimental models are needed to understand the mechanisms of the disease and find more effective treatment options. We previously reported a model of HGGs and malignant peripheral nerve sheath tumors (MPNSTs) which is based on the combined deficiencies in the tumor suppressor genes tp53 and nf1. However, HGG penetrance is very low in this line and most fish develop MPNSTs starting at about 3 months of age. On top of the existing model we used CRISPR/Cas9 to incorporate knock-out mutations in the tumor suppressor genes atrx or suz12 which are described to be involved in pediatric HGG biology. Heterozygous atrx loss-of-function (lof) did not impact tumor onset or penetrance of neither HGGs nor MPNSTs. Since a total loss of atrx was lethal in development, we re-injected effective atrx targeting gRNAs and Cas9 mRNA into the atrx+/- line to create a mosaic atrx-/- genotype. Surprisingly, despite a high mutation efficiency of the remaining atrx allele the re-injection strategy still did not alter tumor onset and penetrance in that model. This suggests that loss of atrx is only effective in HGGs in cooperation with additional hits other than tp53 and nf1. In contrast, loss of suz12 cooperated well with the tp53/nf1-deficient background. As nf1, suz12 is duplicated in zebrafish (suz12a and suz12b) resulting in 4 alleles of each gene per cell. When at least 2 out of 4 alleles of either suz12a or suz12b were lost, MPNST onset was accelerated. This effect was much stronger in tp53-/-, nf1a+/-, nf1b-/- fish (5-7 weeks) compared to tp53-/-, nf1a+/+, nf1b-/- siblings (3-4 weeks). This indicates that the tumor supporting effect of suz12 lof increases the more nf1 levels decrease. However, HGG onset still remained unchanged. We hypothesize that efficient onset of HGGs in our model requires the presence of an activated oncogene. Specific missense mutations in H3F3A are reported to be implicated in HGG progression in children and young adults. Thus, we overexpressed zebrafish h3f3a-K27M or -G34R mutant sequences in the tp53/nf1/atrx/suz12-deficient line and are currently investigating possible changes in tumor biology. Our zebrafish models of pediatric HGGs and MPNSTs will be useful to dissect the mechanisms underlying the cooperation among driver mutations and for small molecule screens to identify specific inhibitors of cell growth and survival in these malignancies.

Citation Format: Felix Oppel, Ting Tao, Shuning He, Mark W. Zimmerman, Dong H. Ki, Nina Weichert, A Thomas Look. Creating faithful genetic zebrafish models of pediatric high grade gliomas and MPNSTs [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1540. doi:10.1158/1538-7445.AM2017-1540

Levetiracetam as a possible cause of secondary graft failure after allogenic hematopoietic stem cell transplantation

BACKGROUND

Levetiracetam is increasingly used as antiepileptic drug (AED) of choice in children as well as in adults with complex diseases due to its lack of interactions and a large spectrum of action. Secondary graft failure, i.e. loss of donor cells after initial engraftment, is a relatively uncommon but serious and life-theatening complication after pediatric hematopoietic stem cell transplantation.

METHODS AND RESULTS

We report a case of secondary graft failure after hematopoietic stem cell transplantation for treatment-related myelodysplastic syndrome during antiepileptic treatment with levetiracetam. Exclusion of all other possible etiologies left levetiracetam as the most likely cause of the imminent complete secondary graft failure after hematopoietic stem cell transplantation. Furthermore, the blood cell count improved just a few days after cessation of levetiracetam medication.

CONCLUSION

Thus, we recommend that in case of secondary graft failure after hematopoietic stem cell transplantation, all possible causes should carefully be excluded, including adverse events through new generation AED agents. Switching to different AEDs with less harming effect on bone marrow function should strongly be considered.

Evaluation of effectiveness of instruction and study habits in two consecutive clinical semesters of the medical curriculum Munich (MeCuM) reveals the need for more time for self study and higher frequency of assessment

BACKGROUND

Seven years after implementing a new curriculum an evaluation was performed to explore possibilities for improvements.

PURPOSES

To analyze students' study habits in relation to exam frequency and to evaluate effectiveness of instruction.

METHODS

Time spent on self study (TSS) and the quantity of instruction (QI) was assessed during the internal medicine and the surgical semester. Students and faculty members were asked about study habits and their evaluation of the current curriculum.

RESULTS

The TSS/QI ratio as a measure of effectiveness of instruction ranges mainly below 1.0 and rises only prior to exams. Students and teachers prefer to have multiple smaller exams over the course of the semester. Furthermore, students wish to have more time for self-guided study.

CONCLUSIONS

The TSS/QI ratio is predominantly below the aspired value of 1.0. Furthermore, the TSS/QI ratio is positively related to test frequency. We therefore propose a reduction of compulsory lessons and an increase in test frequency.

Some ABCA3 mutations elevate ER stress and initiate apoptosis of lung epithelial cells

BACKGROUND

ABCA3 transporter (ATP-binding cassette transporter of the A subfamily) is localized to the limiting membrane of lamellar bodies, organelles for assembly and storage of pulmonary surfactant in alveolar epithelial type II cells (AECII). It transports surfactant phospholipids into lamellar bodies and absence of ABCA3 function disrupts lamellar body biogenesis. Mutations of the ABCA3 gene lead to fatal neonatal surfactant deficiency and chronic interstitial lung disease (ILD) of children. ABCA3 mutations can result in either functional defects of the correctly localized ABCA3 or trafficking/folding defects where mutated ABCA3 remains in the endoplasmic reticulum (ER).

METHODS

Human alveolar epithelial A549 cells were transfected with vectors expressing wild-type ABCA3 or one of the three ABCA3 mutant forms, R43L, R280C and L101P, C-terminally tagged with YFP or hemagglutinin-tag. Localization/trafficking properties were analyzed by immunofluorescence and ABCA3 deglycosylation. Uptake of fluorescent NBD-labeled lipids into lamellar bodies was used as a functional assay. ER stress and apoptotic signaling were examined through RT-PCR based analyses of XBP1 splicing, immunoblotting or FACS analyses of stress/apoptosis proteins, Annexin V surface staining and determination of the intracellular glutathion level.

RESULTS

We demonstrate that two ABCA3 mutations, which affect ABCA3 protein trafficking/folding and lead to partial (R280C) or complete (L101P) retention of ABCA3 in the ER compartment, can elevate ER stress and susceptibility to it and induce apoptotic markers in the cultured lung epithelial A549 cells. R43L mutation, resulting in a functional defect of the properly localized ABCA3, had no effect on intracellular stress and apoptotic signaling.

CONCLUSION

Our data suggest that expression of partially or completely ER localized ABCA3 mutant proteins can increase the apoptotic cell death of the affected cells, which are factors that might contribute to the pathogenesis of genetic ILD.