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Abstract Background Adhesion of cancer cells to extracellular matrix laminin through the integrin superfamily reportedly induces drug resistance. Heterodimers of integrin α6 (CD49f) with integrin β1 (CD29) or β4 (CD104) are major functional receptors for laminin. Higher CD49f expression is reportedly associated with a poorer response to induction therapy in childhood B‐cell precursor acute lymphoblastic leukemia (BCP‐ALL). Moreover, a xenograft mouse model transplanted with primary BCP‐ALL cells revealed that neutralized antibody against CD49f improved survival after chemotherapy. Aims Considering the poor outcomes in Philadelphia chromosome (Ph)‐positive ALL treated with conventional chemotherapy without tyrosine kinase inhibitors, we sought to investigate an involvement of the laminin adhesion. Methods and results Ph‐positive ALL cell lines expressed the highest levels of CD49f among the BCP‐ALL cell lines with representative translocations, while CD29 and CD104 were ubiquitously expressed in BCP‐ALL cell lines. The association of Ph‐positive ALL with high levels of CD49f gene expression was also confirmed in two databases of childhood ALL cohorts. Ph‐positive ALL cell lines attached to laminin and their laminin‐binding properties were disrupted by blocking antibodies against CD49f and CD29 but not CD104. The cell surface expression of CD49f, but not CD29 and CD104, was downregulated by imatinib treatment in Ph‐positive ALL cell lines, but not in their T315I‐acquired sublines. Consistently, the laminin‐binding properties were disrupted by the imatinib pre‐treatment in the Ph‐positive ALL cell line, but not in its T315I‐acquired subline. Conclusion BCR::ABL1 plays an essential role in the laminin adhesion of Ph‐positive ALL cells through upregulation of CD49f.
Takahashi et al. (Mon,) studied this question.