mTOR inhibition amplifies the anti-lymphoma effect of PI3Kß/d blockage in diffuse large B-cell lymphoma

Diffuse large B-cell lymphoma (DLBCL) is a heterogeneous diagnostic category that can be stratified in molecular subtypes based on gene expression profiles and genetic alterations. As roughly one-third of DLBCL patients do not sustainably respond to the current standard chemo-immunotherapy, novel treatment options targeting oncogenic pathways might improve their outcome. Chronic B-cell receptor signaling or PTEN deficiency drive the constitutive activation of the phosphoinositide 3-kinase (PI3K). Since pan-PI3K inhibitors cause severe side effects, we investigated the anti-lymphoma efficacy of the specific PI3Kß/d inhibitor AZD8186. We identified a subset of DLBCL models within activated B cell-like (ABC) and germinal center B cell-like (GCB) DLBCL that were sensitive to AZD8186 treatment. On the molecular level, PI3Kß/d inhibition decreased the pro-survival nuclear factor kappa-B (NF-?B) and activator protein 1 (AP-1) activity or led to downregulation of the oncogenic transcription factor MYC. In AZD8186-resistant models, we detected a feedback activation of the PI3K/AKT/mTOR pathway following PI3Kß/d inhibition. The combined treatment with AZD8186 and the mTOR inhibitor AZD2014 overcame resistance to PI3Kß/d inhibition and completely prevented outgrowth of lymphoma cells in vivo in cell line- and patient-derived xenograft mouse models. Collectively, our study reveals that subsets of DLBCLs are addicted to PI3Kß/d signaling and thus identifies a previously unappreciated role of the PI3Kß isoform in DLBCL survival. Furthermore, our data demonstrate that combined targeting of PI3Kß/d and mTOR is effective in all major DLBCL subtypes supporting the evaluation of this strategy in a clinical trial setting. Overall design: For gene expression profiling, we performed RNA-sequencing of two AZD8186-sensitive ABC DLBCL cell lines (OCI-Ly10 and TMD8) and two sensitive GCB DBLCL cell lines (HT and K422) after 6, 12 (not TMD8), 18, and 24 hours of AZD8186 treatment, compared to untreated controls. Each time point was measured once, resulting in 30 samples in total. Statistics were computed over all time points and the two cell lines of the same DLBCL subtype.