ALBERT

Description: The first two authors contributed equally to this work Identifying pharmacologic strategies to inhibit the activation of NF-κB and its target genes has been a major research pursuit. To date, no direct inhibitors of the NF-κB subunits have been explored in the clinic. Based on the constitutive activation of NF-κB in diffuse large B-cell lymphoma (DLBCL), we used this disease model to develop drugs targeting NF-κB. Using a fluorescence-based high throughput screening (HTC) approach, a unique N-quinoline-benzenesulfonamide (NQBS) scaffold was identified as potential small molecule inhibitor of the NF-κB pathway. A confocal microscopy based HTC assay performed in human umbilical vein endothelial cells (HUVEC) identified hit compounds that contained a unique NQBS core structure. The assay screened for compounds that inhibited nuclear translocation of NF-κB subunits in TNFα-induced HUVEC cells. To date over 100 NQBS analogs have been synthesized with varying potency and cytotoxicity in inhibiting growth of DLBCL lines (OCI-Ly10, RIVA, HBL-1 and OCI-Ly3). Cytotoxicity assays demonstrated that the most potent compounds exhibit IC50s in the 0.5 to 1.5 µM range. These most potent NQBS analogs identified as CU-O42 CU-O47 and CU-O75 were also able to induce apoptosis and caspase activation. Apoptosis was preceded by exclusion of the NF-κB proteins from the nucleus. To analyze the localization of NF-κB proteins within the cell compartments before and after the treatment with CU-O42, CU-O47 and CU-O75, we used confocal microscopy, electromobility shift (EMSA) and ELISA assays. Control cells tested positive for p50/p65 both within the cytoplasm and the nucleus. Following treatment with CU-O42 NF-κB was sequestered within the cytoplasm of the cell which occurred as early as 3h after exposure. In addition, all three analogs reduced the nuclear levels of NF-κB in a concentration-dependent manner when measured by EMSA and ELISA. Furthermore, CU-O47 and CU-O75 were able to inhibit TNFα induced luciferase expression in a HEK293T cell model where luciferase is controlled by an NF-κB promoter. A KINOMEscan platform (examining the activity of over 450 different kinases) showed that no NQBS analog screened (CU-O42 and CU-O75) inhibited any of the kinases in the assay. In addition, a proteasome inhibition assay tested negative for trypsin-like and chromotrypsin-like protease activity (CU-O42, CU-O47 and CU-O75). Stabilization of the inactive trimer of p50, p65 and IκBα was hypothesized as a potential mechanism of action of CU-O42 and CU-O75 through Internal Coordinate Mechanics (ICM) software. This binding hypothesis was further corroborated by cellular thermal shift assays (CETSA) with an increase of the IκBα melting temperatures (2.5-3°C) in whole cell lysates following rapid (30min) exposure to CU-O42 and CU-O75. Using a genome-wide regulatory network perturbation analysis (DeMAND) based on the RNA-Seq data collected from OCI-Ly10 cells treated with CU-O75, we identified IκBα as one of the potential targets of the compounds. Gene set enrichment analysis demonstrated NF-κB target gene downregulation using IC20 of CU-O75 at 24h (p=0.045). In vivo experiments were conducted in two models: (1) xenografts with human DLBCL cell lines of both ABC and GC subtype; and (2) myc cherry luciferase mouse model where mice spontaneously develop aggressive lymphomas. In both models, CU-O42 was able to inhibit tumor growth. Interestingly, in the xenograft model, malignant cell growth was inhibited in both ABC (HBL-1) and GC (OCI-Ly1) cells when compared to controls (p=0.01 and p=0.02). However, overall survival of mice with ABC xenografts treated with CU-042 significantly exceeded the survival of mice with GC xenografts (p

Description: Key Points A novel PI3Kδ inhibitor TGR-1202 synergizes with proteasome inhibitor carfilzomib by silencing c-Myc in preclinical models of lymphoma. The unique activity of TGR-1202 as a single agent and in combination with carfilzomib is driven by an unexpected activity targeting CK1ε.

Description: Introduction: c-Myc is a master transcription factor and one of the most frequently altered genes across a vast array of human cancers including diffuse large B-cell lymphoma (DLBCL), and is thus an attractive therapeutic target . However, no direct inhibitor of c-Myc has been successfully developed for the treatment of any cancer. The c-Myc protein has a short half-life of less than 30 minutes , and the complex secondary structures in the 5' untranslated region (UTR) of MYC mRNA make its translation highly dependent on the eukaryotic translation initiation factor 4F (eIF4F) . eIF4F exists as a complex comprised of the eIF4E, eIF4A, and eIF4G subunits. eIF4E can be sequestered by 4E-BP1, which acts as a "brake" for initiation of mRNA translation . Hyper-phosphorylation of 4E-BP1, caused by upstream signals such as mTORC1, leads to release of eIF4E from 4E-BP1, assembly of the eIF4F complex, and robust mRNA translation. Surprisingly, neither FDA approved mTORC1 inhibitors nor the investigational mTORC1/mTORC2 inhibitor MLN0128 has demonstrated adequate activity in aggressive lymphoma. The therapeutic effects of mTOR inhibition in c-Myc driven aggressive lymphoma remain poorly understood. Recognizing phosphoinositide 3-kinase (PI3K) and the proteasome pathway are both involved in activating mTOR, we hypothesized that co-targeting the PI3K and proteasome pathways might synergistically inhibit translation of c-Myc. Since both PI3K and proteasome are proven drug targets in blood cancer, such co-targeting strategy may be expeditiously studied in clinical trials for c-Myc driven aggressive lymphoma. Methods: Cytotoxicity was studied in lymphoma cell lines and primary lymphoma cells using Cell TiterGlo (Promega®). The Bliss additivism model was used to determine the expected inhibition of cell growth and the excess over Bliss (EOB) values. EOB values above 0 indicate synergy, with higher values indicating higher levels of synergy. Expression of c-Myc was investigated at the translation and transcription levels, using a combination of Western blot, qPCR, and a bi-cistronic luciferase reporter we developed to study cap dependent translation. Gene expression profiling (GEP) studies were conducted using RNAseq, and analyzed by the Fisher t-test and running enrichment score (RES) between different treatment groups. Mechanisms of synergy were determined through interrogating the effects of small molecule inhibitors and shRNA targeting regulators of various regulators of 4E-BP1. Structural studies of TGR-1202 were performed by in silico docking, and validated by synthesis of novel analogs of TGR-1202. Activity of TGR-1202 on CK1 epsilon was studied by kinome profiling (Reaction Biology®), cell free kinase assay of CK1e (Promega®), and cell based assay of CK1e autophosphorylation. Results: We found that a novel PI3K delta isoform inhibitor TGR-1202, but not the approved PI3Kd inhibitor idelalisib, was highly synergistic with the proteasome inhibitor carfilzomib in lymphoma, leukemia, and myeloma cell lines and primary lymphoma and leukemia cells (Figure 1). TGR-1202 and carfilzomib (TC) synergistically inhibited phosphorylation of eIF4E-binding protein 1 (4E-BP1), leading to suppression of c-Myc translation and silencing of c-Myc dependent transcription (Figure 2). Furthermore, the synergistic cytotoxicity of TC was rescued by overexpression of eIF4E or c-Myc. TGR-1202, but not other PI3Kd inhibitors, was active against casein kinase-1 (CK1) epsilon (Figure 3). Targeting CK1e using a selective chemical inhibitor or shRNA complements the effects of idelalisib, as a single agent or in combination with carfilzomib, in repressing phosphorylation of 4E-BP1 and the protein level of c-Myc. Conclusion: These results suggest that TGR-1202 is a first-in-class dual PI3Kd/CK1e inhibitor, which may in part explain the preliminary clinical activity of TGR-1202 in aggressive lymphoma not found with idelalisib. Targeting CK1e should become an integral part of therapeutic strategies targeting translation of oncogenes such as c-Myc. Disclosures Lentzsch: BMS: Consultancy; Foundation One: Consultancy; Celgene: Consultancy, Honoraria. O'Connor:Seattle Genetics: Research Funding; Mundipharma: Membership on an entity's Board of Directors or advisory committees; Seattle Genetics: Research Funding; Spectrum: Research Funding; Spectrum: Research Funding; Mundipharma: Membership on an entity's Board of Directors or advisory committees; TG Therapeutics: Research Funding; TG Therapeutics: Research Funding; Bristol Myers Squibb: Research Funding; Bristol Myers Squibb: Research Funding; Celgene: Research Funding; Celgene: Research Funding.