Jeremy A. Ross

Phase I First-in-Human Study of Venetoclax in Patients With Relapsed or Refractory Non-Hodgkin Lymphoma

Purpose B-cell leukemia/lymphoma-2 (BCL-2) overexpression is common in many non-Hodgkin lymphoma (NHL) subtypes. A phase I trial in patients with NHL was conducted to determine safety, pharmacokinetics, and efficacy of venetoclax, a selective, potent, orally bioavailable BCL-2 inhibitor. Patients and Methods A total of 106 patients with relapsed or refractory NHL received venetoclax once daily until progressive disease or unacceptable toxicity at target doses from 200 to 1,200 mg in dose-escalation and safety expansion cohorts. Treatment commenced with a 3-week dose ramp-up period for most patients in dose-escalation cohorts and for all patients in safety expansion. Results NHL subtypes included mantle cell lymphoma (MCL; n = 28), follicular lymphoma (FL; n = 29), diffuse large B-cell lymphoma (DLBCL; n = 34), DLBCL arising from chronic lymphocytic leukemia (Richter transformation; n = 7), Waldenström macroglobulinemia (n = 4), and marginal zone lymphoma (n = 3). Venetoclax was generally well tolerated. Clinical tumor lysis syndrome was not observed, whereas laboratory tumor lysis syndrome was documented in three patients. Treatment-emergent adverse events were reported in 103 patients (97%), a majority of which were grade 1 to 2 in severity. Grade 3 to 4 events were reported in 59 patients (56%), and the most common were hematologic, including anemia (15%), neutropenia (11%), and thrombocytopenia (9%). Overall response rate was 44% (MCL, 75%; FL, 38%; DLBCL, 18%). Estimated median progression-free survival was 6 months (MCL, 14 months; FL, 11 months; DLBCL, 1 month). Conclusion Selective targeting of BCL-2 with venetoclax was well tolerated, and single-agent activity varied among NHL subtypes. We determined 1,200 mg to be the recommended single-agent dose for future studies in FL and DLBCL, with 800 mg being sufficient to consistently achieve durable response in MCL. Additional investigations including combination therapy to augment response rates and durability are ongoing.

The PHB1/2 Phosphocomplex Is Required for Mitochondrial Homeostasis and Survival of Human T Cells

Many immune pathologies are the result of aberrant regulation of T lymphocytes. A functional proteomics approach utilizing two-dimensional gel electrophoresis coupled with mass spectrometry was employed to identify differentially expressed proteins in response to T cell activation. Two members of the prohibitin family of proteins, Phb1 and Phb2, were determined to be up-regulated 4–5-fold upon activation of primary human T cells. Furthermore, their expression was dependent upon CD3 and CD28 signaling pathways that synergistically led to the up-regulation (13–15-fold) of Phb1 and Phb2 mRNA levels as early as 48 h after activation. Additionally, orthophosphate labeling coupled with phosphoamino acid analysis identified Phb1 to be serine and Phb2 serine and tyrosine phosphorylated. Tyrosine phosphorylation of Phb2 was mapped to Tyr248 using mass spectrometry and confirmed by mutagenesis and phosphospecific antibodies. In contrast to previous reports of Phb1 and Phb2 being nuclear localized, subcellular fractionation, immunofluorescent, and electron microscopy revealed both proteins to localize to the mitochondrial inner membrane of human T cells. Accordingly, small interfering RNA-mediated knockdown of Phbs in Kit225 cells resulted in disruption of mitochondrial membrane potential. Additionally, Phb1 and Phb2 protein levels were up-regulated 2.5-fold during cytokine deprivation-mediated apoptosis of Kit225 cells, suggesting this complex plays a protective role in human T cells. Taken together, Phb1 and Phb2 are novel phosphoproteins up-regulated during T cell activation that function to maintain mitochondrial integrity and thus represent previously unrecognized therapeutic targets for regulating T cell activation, differentiation, viability, and function.

STAT3 : An Important Regulator of Multiple Cytokine Functions

Maintaining T cell homeostasis is critical for normal immune response. Three sequential signals activate T cells, with signal 3 delivered by multiple cytokines that regulate cell proliferation, differentiation, and survival/death. Cytokines binding to their receptors engages two key molecular families, namely, Janus tyrosine kinases (Jaks) and signal transducers and activators of transcription (Stats). Among Stats, Stat3 is involved in the generation of T helper 17 (Th17) cells, regulation of dendritic cells, and acute inflammatory response. These aspects of Stat3 function are important for transplantation. We discuss Stat3s role in innate and adaptive immunity as well as its potential for therapeutic intervention.

Phosphoproteomic analysis of the human pathogen Trypanosoma cruzi at the epimastigote stage

Trypanosoma cruzi is the etiologic agent of Chagas disease, which affects millions of people in Latin America and has become a public health concern in the United States and areas of Europe. The possibility that kinase inhibitors represent novel anti‐parasitic agents is currently being explored. However, fundamental understanding of the cell‐signaling networks requires the detailed analysis of the involved phosphorylated proteins. Here, we have performed a comprehensive MS‐based phosphorylation mapping of phosphoproteins from T. cruzi epimastigote forms. Our LC‐MS/MS, dual‐stage fragmentation, and multistage activation analysis has identified 237 phosphopeptides from 119 distinct proteins. Furthermore, 220 phosphorylation sites were unambiguously mapped: 148 on serine, 57 on threonine, and 8 on tyrosine. In addition, immunoprecipitation and Western blotting analysis confirmed the presence of at least seven tyrosine‐phosphorylated proteins in T. cruzi. The identified phosphoproteins were subjected to Gene Ontology, InterPro, and BLAST analysis, and categorized based on their role in cell structure, motility, transportation, metabolism, pathogenesis, DNA/RNA/protein turnover, and signaling. Taken together, our phosphoproteomic data provide new insights into the molecular mechanisms governed by protein kinases and phosphatases in T. cruzi. We discuss the potential roles of the identified phosphoproteins in parasite physiology and drug development.

Searching in Mother Nature for Anti-Cancer Activity: Anti-Proliferative and Pro-Apoptotic Effect Elicited by Green Barley on Leukemia/Lymphoma Cells

Green barley extract (GB) was investigated for possible anti-cancer activity by examining its anti-proliferative and pro-apoptotic properties on human leukemia/lymphoma cell lines. Our results indicate that GB exhibits selective anti-proliferative activity on a panel of leukemia/lymphoma cells in comparison to non-cancerous cells. Specifically, GB disrupted the cell-cycle progression within BJAB cells, as manifested by G2/M phase arrest and DNA fragmentation, and induced apoptosis, as evidenced by phosphatidylserine (PS) translocation to the outer cytoplasmic membrane in two B-lineage leukemia/lymphoma cell lines. The pro-apoptotic effect of GB was found to be independent of mitochondrial depolarization, thus implicating extrinsic cell death pathways to exert its cytotoxicity. Indeed, GB elicited an increase of TNF-α production, caspase-8 and caspase-3 activation, and PARP-1 cleavage within pre-B acute lymphoblastic leukemia Nalm-6 cells. Moreover, caspase-8 and caspase-3 activation and PARP-1 cleavage were strongly inhibited/blocked by the addition of the specific caspase inhibitors Z-VAD-FMK and Ac-DEVD-CHO. Furthermore, intracellular signaling analyses determined that GB treatment enhanced constitutive activation of Lck and Src tyrosine kinases in Nalm-6 cells. Taken together, these findings indicate that GB induced preferential anti-proliferative and pro-apoptotic signals within B-lineage leukemia/lymphoma cells, as determined by the following biochemical hallmarks of apoptosis: PS externalization, enhanced release of TNF-α, caspase-8 and caspase-3 activation, PARP-1 cleavage and DNA fragmentation Our observations reveal that GB has potential as an anti-leukemia/lymphoma agent alone or in combination with standard cancer therapies and thus warrants further evaluation in vivo to support these findings.

STAT5 regulation of BCL10 parallels constitutive NFκB activation in lymphoid tumor cells

BackgroundSignal Transducer and Activator of Transcription 5 A and B (STAT5) are key survival factors in cells of the lymphoid lineage. Identification of novel, tissue-specific STAT5 regulated genes would advance the ability to combat diseases due to aberrant STAT5 signaling. In the present work a library of human STAT5 bound genomic elements was created and validated.ResultsOf several STAT5 responsive genomic regulatory elements identified, one was located within the first intron of the human BCL10 gene. Chromatin immuno-precipitation reactions confirmed constitutive in vivo STAT5 binding to this intronic fragment in various human lymphoid tumor cell lines. Interestingly, non-phosphorylated STAT5 was found in the nuclei of Kit225 and YT cells in the absence of cytokine stimulation that paralleled constitutive NFκB activation. Inhibition of the hyperactive JAK3/STAT5 pathway in MT-2 cells via the Mannich-base, NC1153, diminished the constitutive in vivo occupancy of BCL10-SBR by STAT5, reduced NFκB activity and BCL10 protein expression in a dose dependent manner. Moreover, depletion of STAT5 via selective antisense oligonucleotide treatment similarly resulted in decreased BCL10 mRNA and protein expression, cellular viability and impaired NFκB activity independent of IL-2.ConclusionThese results suggest that the NFκB regulator BCL10 is an IL-2-independent STAT5 target gene. These findings proffer a model in which un-activated STAT5 can regulate pathways critical for lymphoid cell survival and inhibitors that disrupt STAT5 function independent of tyrosine phosphorylation may be therapeutically effective in treating certain leukemias/lymphomas.

Promising efficacy and acceptable safety of venetoclax plus bortezomib and dexamethasone in relapsed/refractory MM

The antiapoptotic proteins BCL-2 and myeloid cell leukemia sequence 1 (MCL-1) promote multiple myeloma (MM) cell survival. Venetoclax is a selective, orally bioavailable small-molecule BCL-2 inhibitor; bortezomib can indirectly inhibit MCL-1. In preclinical studies, venetoclax enhanced bortezomib activity, suggesting that cotargeting of BCL-2 and MCL-1 could be an effective treatment strategy in myeloma. This phase 1b trial studied patients with relapsed/refractory MM receiving daily venetoclax (50-1200 mg per designated dose cohort; 800 mg in safety expansion) in combination with bortezomib and dexamethasone. A total of 66 patients were enrolled (54 in the dose-escalation cohorts and 12 in the safety expansion). Patients had received a median of 3 prior therapies (range, 1-13); 26 (39%) were refractory to prior bortezomib and 35 (53%) to lenalidomide; 39 (59%) had prior stem cell transplant. The combination was generally well tolerated, and common adverse events included mild gastrointestinal toxicities (diarrhea [46%], constipation [41%], and nausea [38%]) and grade 3/4 cytopenias (thrombocytopenia [29%] and anemia [15%]). The overall response rate (ORR) was 67% (44/66); 42% achieved very good partial response or better (≥VGPR). Median time to progression and duration of response were 9.5 and 9.7 months, respectively. ORR of 97% and ≥VGPR 73% were seen in patients not refractory to bortezomib who had 1 to 3 prior therapies. Patients with high BCL2 expression had a higher ORR (94% [17/18]) than patients with low BCL2 expression (59% [16/27]). This novel combination of venetoclax with bortezomib and dexamethasone has an acceptable safety profile and promising efficacy in patients with relapsed/refractory MM. This trial was registered at www.clinicaltrials.gov as #NCT01794507.

Regulation of T cell homeostasis by JAKs and STATs.

Regulation of T cell homeostasis is critical for maintaining normal immune function. An imbalance in T cell proliferation can result in disorders ranging from cancer and autoimmunity to immunodeficiencies. Full activation of T cells requires three sequential signals, where signal 3, which is delivered by multiple cytokines, regulates proliferation, differentiation, and survival/death. Signaling from cytokines through their receptors is primarily delivered by two molecular families, namely Janus tyrosine kinases (JAKs) and signal transducers and activators of transcription (STATs). Invaluable knowledge about JAKs and STATs has arisen from studies of mice made genetically deficient in these molecules, analyses of tumor models, and studies of expression patterns by proteomics/genomics, which all have begun to define the role of JAKs and STATs in survival versus apoptosis. These findings also have suggested ways in which JAKs and STATs may be manipulated for therapeutic intervention in lymphoid-derived diseases. This review seeks to focus on the role of JAK tyrosine kinases and STAT transcription factors in mediating the lymphocyte life cycle and how they might be manipulated for therapeutic applications.

Efficacy of venetoclax as targeted therapy for relapsed/refractory t(11;14) multiple myeloma.

Venetoclax is a selective, orally bioavailable BCL-2 inhibitor that induces cell death in multiple myeloma (MM) cells, particularly in those harboring t(11;14), which express high levels of BCL-2 relative to BCL-XL and MCL-1. In this phase 1 study, patients with relapsed/refractory MM received venetoclax monotherapy. After a 2-week lead-in with weekly dose escalation, daily venetoclax was given at 300, 600, 900, or 1200 mg in dose-escalation cohorts and 1200 mg in the safety expansion. Dexamethasone could be added on progression during treatment. Sixty-six patients were enrolled (30, dose-escalation cohorts; 36, safety expansion). Patients received a median of 5 prior therapies (range, 1-15); 61% were bortezomib and lenalidomide double refractory, and 46% had t(11;14). Venetoclax was generally well tolerated. Most common adverse events included mild gastrointestinal symptoms (nausea [47%], diarrhea [36%], vomiting [21%]). Cytopenias were the most common grade 3/4 events, with thrombocytopenia (32%), neutropenia (27%), anemia (23%), and leukopenia (23%) reported. The overall response rate (ORR) was 21% (14/66), and 15% achieved very good partial response or better (≥VGPR). Most responses (12/14 [86%]) were reported in patients with t(11;14). In this group, ORR was 40%, with 27% of patients achieving ≥VGPR. Biomarker analysis confirmed that response to venetoclax correlated with higher BCL2:BCL2L1 and BCL2:MCL1 mRNA expression ratios. Venetoclax monotherapy at a daily dose up to 1200 mg has an acceptable safety profile and evidence of single-agent antimyeloma activity in patients with relapsed/refractory MM, predominantly in patients with t(11;14) abnormality and those with a favorable BCL2 family profile. Registered at www.clinicaltrials.gov: #NCT01794520.

Protein Phosphatase 2A Regulates Interleukin-2 Receptor Complex Formation and JAK3/STAT5 Activation

Reversible protein phosphorylation plays a key role in interleukin-2 (IL-2) receptor-mediated activation of Janus tyrosine kinase 3 (JAK3) and signal transducer and activator of transcription 5 (STAT5) in lymphocytes. Although the mechanisms governing IL-2-induced tyrosine phosphorylation and activation of JAK3/STAT5 have been extensively studied, the role of serine/threonine phosphorylation in controlling these effectors remains to be elucidated. Using phosphoamino acid analysis, JAK3 and STAT5 were determined to be serine and tyrosine-phosphorylated in response to IL-2 stimulation of the human natural killer-like cell line, YT. IL-2 stimulation also induced serine/threonine phosphorylation of IL-2Rβ, but not IL-2Rγ. To investigate the regulation of serine/threonine phosphorylation in IL-2 signaling, the roles of protein phosphatase 1 (PP1) and 2A (PP2A) were examined. Inhibition of phosphatase activity by calyculin A treatment of YT cells resulted in a significant induction of serine phosphorylation of JAK3 and STAT5, and serine/threonine phosphorylation of IL-2Rβ. Moreover, inhibition of PP2A, but not PP1, diminished IL-2-induced tyrosine phosphorylation of IL-2Rβ, JAK3, and STAT5, and abolished STAT5 DNA binding activity. Serine/threonine phosphorylation of IL-2Rβ by a staurosporine-sensitive kinase also blocked its association with JAK3 and IL-2Rγ in YT cells. Taken together, these data indicate that serine/threonine phosphorylation negatively regulates IL-2 signaling at multiple levels, including receptor complex formation and JAK3/STAT5 activation, and that this regulation is counteracted by PP2A. These findings also suggest that PP2A may serve as a therapeutic target for modulating JAK3/STAT5 activation in human disease.