Initial in vivo testing of TPO-receptor agonist eltrombopag in osteosarcoma patient-derived xenograft models by the pediatric preclinical testing consortium.

Eltrombopag is a small molecule, thrombopoietin receptor agonist approved for the treatment of patients with aplastic anemia and chronic immune thrombocytopenia. It is also a polyvalent cation chelator and inhibits leukemia cell proliferation via reduction of intracellular iron. The in vivo efficacy of eltrombopag was tested against a panel of six Pediatric Preclinical Testing Consortium osteosarcoma xenografts at doses of 5 mg/kg/day (moderate dose) and 50 mg/kg/day (high dose). Eltrombopag, at moderate doses, failed to significantly improve event-free survival (EFS) in 6/6 models. At high doses, eltrombopag significantly prolonged EFS in 2/2 models, though the effect size was small. All models tested demonstrated progressive disease. While eltrombopag did not meaningfully inhibit osteosarcoma growth, it also did not stimulate tumor growth, suggesting it may be safely investigated as a supportive care agent to enhance platelet recovery post chemotherapy.

Evaluation of Eribulin Combined with Irinotecan for Treatment of Pediatric Cancer Xenografts.

PURPOSE: Vincristine combined with camptothecin derivatives showed synergy in preclinical pediatric cancer models, and the combinations are effective in treatment of childhood solid tumors. We determined whether the synergy between vincristine and irinotecan extends to eribulin, another microtubule inhibitor. EXPERIMENTAL DESIGN: Vincristine or eribulin, alone or combined with irinotecan, was studied in 12 xenograft models. Tumor regression and time to event were used to assess antitumor activity. Pharmacodynamic studies and RNA sequencing (RNA-seq) were conducted 24 and 144 hours after single-agent or combination treatment. Effects on vascular development were studied in Matrigel plugs implanted in mice. The interaction between binary combinations was examined in vitro. RESULTS: Eribulin combined with irinotecan was more effective than vincristine-irinotecan in 6 of 12 models. Pharmacodynamic markers induced by eribulin (phospho-histone H3) and irinotecan (γ-H2A.X) were abrogated in combination-treated tumors. The predominant RNA-seq signature in combination-treated tumors was activation of the TP53 pathway with increased nuclear TP53. Massive apoptosis was observed 24 hours only after treatment with the eribulin combination. In vitro, neither combination showed interaction using combination index analysis. Eribulin alone and the combination caused alterations in developing vasculature. CONCLUSIONS: The eribulin combination is very active in these xenograft models, but not synergistic in vitro. The combination reduced pharmacodynamic markers indicative of single-agent mechanisms but in tumors, dramatically activated the TP53 pathway. Although a mechanism for in vivo synergy requires further study, it is possible that eribulin-induced inhibition of microtubule dynamics enhances irinotecan-induced nuclear accumulation of TP53, leading to rapid cell death.

A gene catalogue of the euchromatic male-specific region of the horse Y chromosome: comparison with human and other mammals.

Studies of the Y chromosome in primates, rodents and carnivores provide compelling evidence that the male specific region of Y (MSY) contains functional genes, many of which have specialized roles in spermatogenesis and male-fertility. Little similarity, however, has been found between the gene content and sequence of MSY in different species. This hinders the discovery of species-specific male fertility genes and limits our understanding about MSY evolution in mammals. Here, a detailed MSY gene catalogue was developed for the horse--an odd-toed ungulate. Using direct cDNA selection from horse testis, and sequence analysis of Y-specific BAC clones, 37 horse MSY genes/transcripts were identified. The genes were mapped to the MSY BAC contig map, characterized for copy number, analyzed for transcriptional profiles by RT-PCR, examined for the presence of ORFs, and compared to other mammalian orthologs. We demonstrate that the horse MSY harbors 20 X-degenerate genes with known orthologs in other eutherian species. The remaining 17 genes are acquired or novel and have so far been identified only in the horse or donkey Y chromosomes. Notably, 3 transcripts were found in the heterochromatic part of the Y. We show that despite substantial differences between the sequence, gene content and organization of horse and other mammalian Y chromosomes, the functions of MSY genes are predominantly related to testis and spermatogenesis. Altogether, 10 multicopy genes with testis-specific expression were identified in the horse MSY, and considered likely candidate genes for stallion fertility. The findings establish an important foundation for the study of Y-linked genetic factors governing fertility in stallions, and improve our knowledge about the evolutionary processes that have shaped Y chromosomes in different mammalian lineages.