Heteromeric insect odorant receptors (ORs) form ligand-activated nonselective cation channels in recombinant expression systems. We performed a pharmacological characterization of Drosophila melanogaster and Bombyx mori ORs expressed in the Xenopus laevis oocyte expression system and characterized them using the 2-electrode voltage clamp. We identified amiloride derivatives as high-affinity blockers, which inhibit the ion current through the channel in a low micromolar range. For the heteromeric Drosophila Or47a + DmelOrco receptor, the potency sequence (IC(50)) is HMA [5-(N,N-hexamethylene)amiloride] (3.9 µM), MIA [5-(N-methyl-N-isobutyl)amiloride] (11.0 µM), and DMA [5-(N,N-dimethyl)amiloride] (113.3 µM). Amiloride itself is nearly ineffective. Other tested insect ORs (Drosophila Or49b + DmelOrco, B. mori BmorOr1 + BmorOrco) were blocked in a similar fashion suggesting that the amiloride derivatives were potential general blockers of all receptor combinations. Our results suggest that pyrazine derivatives of amiloride are useful probes to study the mechanism of chemosensory transduction in insects in more detail.

Introduction: Although rare, acute myeloid leukemia (AML) in children and adolescents is the most frequent treatment-related malignancy in children and adolescents. Both, chemotherapy and irradiation, but also predisposing inherited syndromes might be involved in leukemogenesis. The overall prognosis is generally poor and curative treatment requires allogeneic stem cell transplantation (alloSCT) in almost all cases. Methods: In clinical trials or registries of the AML‐BFM Study group, between 1993 and 2018 145 children and adolescents (f=70; m=75) with tAML have been enrolled. T‐AML was defined according to the WHO 2016 classification. Patients were included if the initial malignancy occurred before their 18th birthday. Thirteen patients were excluded due to the lack of data concerning the primary malignancy. Whereas between 1993 and 2003, full AML-BFM treatment with double induction and two consolidation elements prior to SCT was recommended (AML-BFM 93 / AML-BFM 98), since 2004 only double induction and direct alloSCT have been applied. AlloSCT should be performed in 1st CR but also in case of no evidence of blasts (NEL), e.g. hematological regeneration was not required. Results: The median age was 10.6 years old and ranged from 1.4 to 26.6 years. The median percentage of BM blasts was 68% (range 11 ‐ 95%), the median WBC of 10,100/ μl (range 1,100 ‐ 201,000/μl) and hemoglobin 9.6 g/dl (range 6.5‐13.1 g/dl) According to the FAB classification, FAB M4/M5 (66%) was the largest group, followed by FAB M0/M1/ M2 (25%), FAB M6/M7 (6%) and others (6%). This corresponded to genetics: t(9;11) 32% and other MLL rearranged AML ((10;11); t(11;19), t(4;11); 15%, normal (n=13; 13%), or complex karyotype (n=10; 10%). Other patients had different findings such as n‐ras (n=8; 8%), trisomy 8 (n=5; 5%), t(8;21); 1%, inv(16), 2%, monosomy 7 (n=2; 2%), WT1 (n=4;4%) or NPM1, c‐kit, CEBPαdm, FLT3‐ITD (n=1 each). Twenty-eight different primary malignancies were reported, the median interval between primary malignancy and tAML was 2.6 years (range 1.3 to 22 years). Acute lymphoblastic leukemia (n=37, 28%) was the most frequent primary malignancy, however in total tAML occurred in 47% of the patients following solid tumors (n=68; Ewing-sarcoma n=11, 8%, osteosarcoma n=12; 9%, neuroblastoma n=13, 10%, rhambomyosarcoma n=7; 5%, nephroblastoma n=5; 4%), in 40% following systemic malignancies (ALL, non-Hodgkin lymphoma n=7; 7%, Hodgkin-lymphoma (n=6, 4%) and in 13% following brain tumors (medulloblastoma n=6, 4%; others n=8, 9%).The 5yrs‐overall survival (OS) rate of the complete cohort was 28 ± 4%, increasing from 19 ± 5% (n=70 1993‐2003) to 34±7% (n=41, 2004‐2011) up to 45±9% (n=34 2012‐2018; p log rank <0.03). The OS is similar for solid tumors (28±6%) and systemic malignancies (37±6%) but inferior for patients with a previous brain tumor (6±6%; p<0.002). Early death was recorded in 20/145 patients (14%). Children with tAML, who achieved CR (47%) or at least no evidence of leukemia (NEL; 39%) had an OS 60±7% and 32±11%, respectively. By contrast, 10 out of 11 patients with persistence blasts at time of alloSCT died. Conclusions: T‐AML in pediatric patients is still associated with a poor prognosis due to poor response, increased toxicities and unfavorable genetic aberrations. T-AML following brain tumors as 1st malignancy showed the worst prognosis. The reduction to two treatment elements prior to alloSCT and proceeding to SCT without CR might contribute to the improvement of survival. Disclosures Reinhardt: BlueBirdBio: Membership on an entity's Board of Directors or advisory committees; CLS Behring: Research Funding; Novartis: Membership on an entity's Board of Directors or advisory committees; CElgene: Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen: Membership on an entity's Board of Directors or advisory committees; Roche: Research Funding.