e15654 Background: Fimepinostat (F), a small molecule dual inhibitor of PI3K α, β, and δ isoforms and Class I and II histone deacetylases (HDACs), is currently under investigation for the treatment of aggressive hematological cancers. Preclinical studies demonstrated that F both decreases transcription of myc and MYC-targeted genes (via HDAC inhibition) and increases destruction of MYC protein (via PI3K inhibition). This study sought to identify differences in transcript-level signatures of gene networks in pre-treatment tumor samples associated with future clinical response to F. Methods: Among 105 patients (pts) with relapsed or refractory (R/R) diffuse large B-cell lymphoma (DLBCL) treated in phase 1/2 clinical trials of F (± rituximab), 33 pts had pre-treatment tumor biopsy samples available for molecular testing. All pts had measurable disease at baseline and had at least 1 post-baseline tumor assessment. To be included in the analysis set, pts must have been on study for ≥42 days. RNA libraries were created and sequenced on the Illumina HiSeq platform. Gene Set Enrichment Analysis (GSEA; Subramanian et al., 2005) was used to study changes in transcript expression patterns that correlate with responder (complete/partial response) or non-responder (progressive disease) pt populations. ~20,000 genes were rank-ordered by log2-fold change and tested against the MSigDB (Liberzon et al., 2011) collection of gene expression signatures. Results: > 1500 Gene Sets with False Discovery Rate (FDR) < = 0.05 and Normalized Enrichment Score (NES) > 1.3 for genes upregulated in the F-responder population were identified. These Gene Sets represent transcriptional activity associated with well characterized biological pathways or gene expression signatures determined empirically. The top 20 signatures by NES were associated with general transcription functions (E2F, RNA polymerase), chromosomal structure (meiotic recombination, telomere maintenance) and specifically, MYC transcription targets (NES: 2.7; FDR q-val: 0). Additional signatures consistent with PI3K (GSK3b) and HDAC activity in the responder population were also identified, as would be expected for a dual inhibitor of PI3Ks and HDACs. Conclusions: GSEA analysis of genes upregulated in the F-treated responder DLBCL pts are consistent with preclinical data showing that F functions to suppress MYC in tumor cells. F is currently undergoing active clinical study in combination with venetoclax for the treatment of R/R DLBCL or high grade B-cell lymphoma (HGBL): NCT01742988.
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