DEVELOPMENT OF NOVEL PRECLINICAL MODELS OF SECONDARY RESISTANCE TO THE PI3KΔ INHIBITOR IDELALISIB IN SPLENIC MARGINAL ZONE LYMPHOMA (SMZL)

Abstract

Background: Targeting the BCR signaling is one of the main novel therapeutic approaches for lymphoma patients. Different drugs with distinct or overlapping targets are now in the clinical setting including PI3Kdelta inhibitor (i) idelalisib. A better understanding of mechanisms of action and resistance to the drug could lead to rationally designed therapies and potential strategies to prevent resistance. Hence, we generated resistant in vitro clones to idelalisib in SMZL models. Material(s) and Method(s): VL51 and Karpas1718 cells were exposed to IC90 concentration of idelalisib for several weeks until they acquired specific drug resistance (resistant). Cell lines were cultured upon the same conditions with no drug exposure (parental). Proliferation of acquired stable resistance was tested by MTT assay (72 hrs) in resistant and parental after 2 weeks of drug-free culture. IC50 values were estimated. Multi-drug resistance phenotype (MDR1 expression, realtime PCR) was discarded. Gene expression profiling (GEP) was obtained with the Illumina-HumanHT-12 Expression-BeadChips and analyzed with moderated t-test and GSEA. Result(s): VL51 cells resistant to idelalisib exhibited over tenfold increase in their IC50 versus their parental cells (12.5 vs 1.2 muM). Karpas1718 reached a sixfold increase (10 vs 1.5 muM). To assess whether the acquired resistance to idelalisib was specific for PI3Kdelta inhibition, we performed MTT assay for idelalisib, dual PI3k-mTOR I PQR309, PI3Kdelta/gamma I duvelisib and mTOR I everolimus. Resistant clones showed similar sensitivity than parental when exposed to PQR309 or everolimus. Duvelisib antitumor activity was decreased but not abolished in resistant cells.Expression profiles of resistant and parental cells were compared. Signatures related to FGFR mutations, DNA recombination and Isotype switching processes and to silencing of PIK3CA, SYK, GSK3A/B and AKT1 were enriched in the resistant clones of both cell lines. BCR and NFKB signaling gene sets were enriched in VL51 resistant clones but decreased in Karpas1718 resistant clones suggesting different mechanisms of resistance. The latter cells showed an increase in cell cycle genes and MYC targets. Consistent with the BCR genes changes, enrichment of AICDA off-targets was evident in VL51 resistant and for Karpas1718 parental clones. CD79A, CD19, CXCR4 (upregulated), CDKN2C, CDKN2A (downregulated) were among the affected genes in resistant VL51, while BIRC3, CARD11, CXCR5, CD37 (downregulated) in resistant Karpas1718. Conclusion(s): We presented two novel models, derived from SMZL, of secondary resistance to the PI3Kdelta I idelalisib. These models, apparently driven by different biologic processes, will help in clarifying mechanisms of resistance to the drug and to evaluate alternative therapeutic approaches.