Efficacy of phosphatidylinositol‐3 kinase inhibitors with diverse isoform selectivity profiles for inhibiting the survival of chronic lymphocytic leukemia cells

Pharmacological inhibition of phosphatiylinositide‐3‐kinase (PI3K)‐mediated signaling holds great promise for treating chronic lymphocytic leukemia (CLL). Therefore we assessed three structurally related PI3K inhibitors targeting the PI3K‐δ isoform for their ability to inhibit the survival of freshly isolated CLL cells. The purely PI3K‐δ‐selective inhibitor idelalisib was compared to copanlisib (BAY 80‐6946) and duvelisib (IPI‐145), with isoform target profiles that additionally include PI3K‐α or PI3K‐γ, respectively. The concentrations leading to half‐maximal reduction of the survival of CLL cells were more than ten‐fold lower for copanlisib than for idelalisib and duvelisib. At concentrations reflecting the biological availability of the different inhibitors, high levels of apoptotic response among CLL samples were attained more consistently with copanlisib than with idelalisib. Copanlisib selectively reduced the survival of CLL cells compared to T cells and to B cells from healthy donors. In addition copanlisib and duvelisib impaired the migration of CLL cells towards CXCL12 to a greater extent than equimolar idelalisib. Similarly copanlisib and duvelisib reduced the survival of CLL cells in co‐cultures with the bone marrow stroma cell line HS‐5 more strongly than idelalisib. Survival inhibition by copanlisib and idelalisib was enhanced by the monoclonal CD20 antibodies rituximab and obinutuzumab (GA101), while antibody‐dependent cellular cytotoxicity mediated by alemtuzumab and peripheral blood mononuclear cells was not substantially impaired by both PI3K inhibitors for the CLL‐derived JVM‐3 cell line as target cells. Taken together, targeting the α‐ and δ‐ p110 isoforms with copanlisib may be a useful strategy for the treatment of CLL and warrants further clinical investigation. What's new? Pharmacological inhibition of phosphatidylinositide‐3‐kinase (PI3K)‐mediated signaling holds great promise for treating chronic lymphocytic leukemia (CLL). Here, the authors assessed the PI3K‐delta‐selective inhibitor idelalisib alongside two novel PI3K‐delta inhibitors, which additionally target the PI3K‐alpha (copanlisib) or gamma (duvelisib) isoforms. They found copanlisib to inhibit the survival of CLL cells at least ten‐fold more efficiently than idelalisib and duvelisib. Survival inhibition by copanlisib was cell‐type selective, accompanied by strong reduction of chemotaxis, and efficacious in the presence of stroma cell support. Survival inhibition by copanl