Modeling chronic myeloid leukemia in drosophila melanogaster : insights on pathogenesis and therapeutic approaches

Abstract

Background: Chronic myeloid leukemia (CML) is caused by a balanced chromosomal translocation resulting in the formation of BCR-ABL1 fusion gene encoding a constitutively active BCR-ABL1 tyrosine kinase, which activates a myriad of signal transduction pathways leading to malignant transformation. Although tyrosine kinase inhibitors (TKIs) have revolutionized CML therapy and became the standard treatment of CML; they are non-curative and some mutations have proven elusive particularly the T315I mutation. The fruit fly Drosophila melanogaster is an established efficient in vivo model to study human diseases including cancer. The targeted expression of chimeric human-fly and full human BCR-ABL1 in Drosophila eyes has been shown to result in detrimental effects. Hence, a well-established fruit fly CML model is crucial for getting better insights on the disease pathogenesis and alternative therapeutic approaches. Methods: In this study, we generated transgenic fly lines carrying the full human BCR-ABL1p210 and the first and second generation TKI resistant BCR-ABL1p210-T315I fusion oncogenes using Phi-C31 mediated site-specific transgenesis. The binary GAL4-UAS system was used for spatial and temporal control over transgene expression in different Drosophila tissues including eyes, hemocytes, wings, imaginal discs and ubiquitous expression. For analysis of eye phenotypes, flies were fixed, critically point dried, gold-coated and visualized using scanning electron microscope (SEM). A grading scale that describes the different levels of severity of the eye phenotype was used for quantification. For drug studies, TKIs (imatinib, nilotinib, dasatinib and ponatinib) were mixed with fly food and larvae were allowed to feed on the mixture. Eclosing adult flies were monitored for changes in ommatidial architecture in the posterior end of the eye which showed a unique defect upon BCR-ABL1 expression. One researcher coded the SEM images and another researcher was blinded to the data and used Image J to measure the area of the po