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A. Al Outa et al.
that both dAbl42 and Drosophila Src43 play important roles in Drosophila eye development; therefore it is possible that upon human BCR-ABL1 expression in Drosophila eyes, the dAbl signaling pathway is activated which in its turn acti- vates Drosophila Src members and amplifies BCR-ABL1 mediated effects. Interestingly, Src is one of the kinases inhibited by dasatinib and ponatinib but not imatinib and nilotinib, therefore, this might possibly explain the more robust rescuing effect seen by dasatinib and ponatinib. Dasatinib demonstrated target specificity in vivo whereby BCR-ABL1p210/T315I flies fed on dasatinib showed the expect- ed resistance to treatment. BCR-ABL1p210/T315I resistance to imatinib and nilotinib was also confirmed as there was no rescue of ommatidial development. In contrary to what was expected, ponatinib was not successful in rescuing progeny expressing BCR-ABL1p210/T315I. While this phenom- enon is hard to explain we would like to focus on the fact that the eye defect area was significantly larger upon BCR- ABL1p210/T315I expression compared to the area upon BCR- ABL1p210 expression. Noting this significant increase in the average posterior eye defect area, we hypothesize that the phenotype was still very severe to allow for any drug reversal. Moreover, noting that the choice of the dose was limited by DMSO toxicity, the ponatinib dose used may not have been high enough to reverse the defect. On the other hand, we tried to test ponatinib to rescue the unpub- lished lethality phenotype of BCR-ABL1p210/T315I flies; inter- estingly feeding ponatinib to BCR-ABL1p210/T315I expressing
flies rescued larval lethality and allowed development to the pupal stage which suggests that the drug’s response is tissue dependent. Feeding ponatinib or dasatinib to BCR- ABL1p210 expressing flies resulted in the rescue of pupal lethality and enclosure of adult flies (unpublished data).
We propose an in vivo model for BCR-ABL1 driven trans- formation where we show the efficacy of the current potent treatments in reversing a very subtle phenotype in a specific location in the posterior end of the adult com- pound eye. This system could be used to assess the effi- cacy of novel compounds by performing high throughput library testing in vivo. We believe that a Drosophila CML model to screen for potential compounds is required in this field especially as the currently used TKI do not target CML stem cells and hence are not curative.
Acknowledgements
MS and RN are funded by the National Council for Scientific Research-Lebanon (CNRS-L). AA is the recipient of CNRS- L/AUB Doctoral Scholarship award. We thank KAS Central Research Science Laboratory (CRSL) at the American University of Beirut (AUB) for their technical help in scanning electron microscopy imaging. The expert assistance from the DTS basic research core facilities at AUB is appreciated. We would like to thank Mr. Abdel Rahman Itani and Ms. Shireen Badini for their help in coding and scoring scanning electron microscopy images.
We acknowledge the Bloomington Drosophila Stock Center (NIH P40OD018537) for providing fly stocks.
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