The novel proteasome inhibitor carfilzomib induces cell cycle arrest,apoptosis and potentiates the anti‐tumour activity of chemotherapy in rituximab‐resistant lymphoma

Targeting the proteasome system with bortezomib (BTZ) results in anti‐tumour activity and potentiates the effects of chemotherapy/biological agents in multiple myeloma and B‐cell lymphoma. Carfilzomib (CFZ) is a more selective proteasome inhibitor that is structurally distinct from BTZ. In an attempt to characterize its biological activity, we evaluated CFZ in several lymphoma pre‐clinical models. Rituximab‐sensitive cell lines (RSCL), rituximab‐resistant cell lines (RRCL), and primary tumour cells derived from B‐cell lymphoma patients were exposed to CFZ or BTZ. Cell viability and changes in cell cycle were determined. Western blots were performed to detect PARP‐cleavage and/or changes in Bcl‐2 (BCL2) family members. CFZ was 10 times more active than BTZ and exhibited dose‐ and time‐dependent cytotoxicity. CFZ exposure induced apoptosis by upregulation of Bak (BAK1) and subsequent PARP cleavage in RSCL and RRCL; it was also partially caspase‐dependent. CFZ induced G2/M phase cell cycle arrest in RSCL. CFZ demonstrated the ability to overcome resistance to chemotherapy in RRCL and potentiated the anti‐tumour activity of chemotherapy agents. Our data suggest that CFZ is able to overcome resistance to chemotherapeutic agents, upregulate pro‐apoptotic proteins to promote apoptosis, and induce G2/M cell cycle arrest in lymphoma cells. Our pre‐clinical data supports future clinical evaluation of CFZ in B‐cell lymphoma.     

Ofatumumab demonstrates activity against rituximab-sensitive and -resistant cell lines, lymphoma xenografts and primary tumour cells from patients with B-cell lymphoma

Ofatumumab is a new monoclonal antibody (mAb) targeting a novel membrane‐proximal epitope on CD20. To better define ofatumumab’s activity, we conducted pre‐clinical studies in rituximab‐sensitive cell lines (RSCL), rituximab‐resistant cell lines (RRCL), ofatumumab‐exposed cell lines (OECLs), primary lymphoma cells, and a lymphoma xenograft model. RRCL and OECL were generated by repeated exposure of sensitive cells to escalating doses of rituximab or ofatumumab ± human serum. Antibody‐dependent cellular cytotoxicity (ADCC) and complement‐mediated cytotoxicity (CMC) assays were performed to assess cellular sensitivity to rituximab or ofatumumab. Ofatumumab elicited a higher rate of CMC in RSCL, RRCL and primary tumour cells. The chronic exposure of lymphoma cells to ofatumumab resulted in rituximab resistance but less ofatumumab resistance. In an in vivo severe combined immunodeficiency mouse model of human lymphoma, ofatumumab prolonged median survival compared to rituximab. While rituximab CMC diminished with CD20 down‐regulation in RRCL passages, ofatumumab activity in vitro diminished to a lesser degree. Our data suggest that ofatumumab is more potent than rituximab in rituximab‐sensitive or rituximab‐resistant models and has the potential to decrease the development of biological resistance in patients with repeated exposure to anti‐CD20 mAbs.     

Distinct cellular and therapeutic effects of obatoclax in rituximab-sensitive and -resistant lymphomas

Bcl-2 proteins represent a rheostat that controls cellular viability. Obatoclax, a BH3-mimetic, has been designed to specifically target and counteract anti-apoptotic Bcl-2 proteins. We evaluated the biological effects of obatoclax on the anti-tumour activity of rituximab and chemotherapy agents. Obatoclax induced cell death of rituximab/chemotherapy-sensitive (RSCL), -resistant cell lines (RRCL) and primary tumour-cells derived from patients with B-cell lymphomas (N=39). Obatoclax also enhanced the activity of rituximab and had synergistic activity when combined with chemotherapy agents. The ability of Obatoclax to induce PARP cleavage varied between patient samples and was not observed in some RRCL. Inhibition of caspase activity did not affect obatoclax activity, suggesting the existence of caspase-independent death pathways. Autophagy was detected by LC3 conversion and/or electron microscopy in RRCL and in patient-derived tumour cells. Moreover, obatoclax activity was inhibited by Beclin-1 knockdown. In summary, obatoclax is an active Bcl-2 inhibitor that potentiates the activity of chemotherapy agents and, to a lesser degree, rituximab. Defining the molecular events triggered by obatoclax is necessary to further its clinical development and identify potential biomarkers that are predictive of response.     

Preclinical anti‐myeloma activity of the novel HDAC‐inhibitor JNJ‐26481585

Pharmacological inhibitors of histone deacetylases (HDACs) are currently being developed and tested as anti‐cancer agents and may be useful to enhance the therapeutic efficiency of established anti‐myeloma treatments. This study preclinically evaluated the effects of the ‘second generation’ pan‐HDAC inhibitor JNJ‐26481585 on human multiple myeloma (MM) cells from established cell lines and primary MM samples (n = 42). Molecular responses in both groups of MM cells included histone acetylation, a shift in Bcl2‐family members towards proapoptotic bias, attenuation of growth and survival pathway activity and Hsp72 induction. Mcl‐1 depletion and Hsp72 induction were the most reliable features observed in JNJ‐26481585‐treated primary MM samples. The drug alone effectively induced myeloma cell death at low nanomolar concentrations. In vitro combination of JNJ‐26481585 with anti‐myeloma therapeutic agents generally resulted In effects close to additivity. In view of the favourable activity of this novel HDAC‐inhibitor towards primary myeloma cells further evaluation in a clinical setting is warranted.     

Anti‐leukemic activity of valproic acid and imatinib mesylate on human Ph+ ALL and CML cells in vitro

The armamentarium of anti‐leukemic drugs has increased substantially since anti‐leukemic activities were recently found for a variety of non‐classical cytostatic drugs, among them the histone deacetylase (HDAC) inhibitor valproic acid (VPA). This study investigated the effect of VPA on proliferation and apoptosis of human Philadelphia chromosome‐positive (Ph+) acute lymphatic (ALL) and chronic myeloid leukemia (CML) cells and on colony formation of human chronic‐phase CML progenitor cells. Strong anti‐proliferative and pro‐apoptotic effects of VPA were observed on human ALL and CML cell lines at concentrations achievable in vivo. These effects were most pronounced in ALL cell lines as well as in primary ALL cells. Notably, VPA revealed enhanced activity with imatinib mesylate, nilotinib, the farnesyl transferase inhibitor SCH66336, interferon‐alpha and cytosine arabinoside. VPA inhibited the growth of colony‐forming cells from 12 Ph+ chronic‐phase CML patients but also of those from normal healthy controls in a dose‐dependent fashion. HDAC‐inhibiting activity of VPA was confirmed on ALL and CML cells. In conclusion, VPA, whether alone or in combination with other non‐classical anti‐leukemic compounds, exerts significant anti‐leukemic effects on human ALL and CML cells.     

Activity of lenalidomide in mantle cell lymphoma can be explained by NK cell‐mediated cytotoxicity

Lenalidomide is an immunomodulatory agent that has demonstrated clinical benefit for patients with relapsed or refractory mantle cell lymphoma (MCL); however, despite this observed clinical activity, the mechanism of action (MOA) of lenalidomide has not been characterized in this setting. We investigated the MOA of lenalidomide in clinical samples from patients enrolled in the CC‐5013‐MCL‐002 trial (NCT00875667) comparing single‐agent lenalidomide versus investigator's choice single‐agent therapy and validated our findings in pre‐clinical models of MCL. Our results revealed a significant increase in natural killer (NK) cells relative to total lymphocytes in lenalidomide responders compared to non‐responders that was associated with a trend towards prolonged progression‐free survival and overall survival. Clinical response to lenalidomide was independent of baseline tumour microenvironment expression of its molecular target, cereblon, as well as genetic mutations reported to impact clinical response to the Bruton tyrosine kinase inhibitor ibrutinib. Preclinical experiments revealed lenalidomide enhanced NK cell‐mediated cytotoxicity against MCL cells via increased lytic immunological synapse formation and secretion of granzyme B. In contrast, lenalidomide exhibited minimal direct cytotoxic effects against MCL cells. Taken together, these data provide the first insight into the clinical activity of lenalidomide against MCL, revealing a predominately immune‐mediated MOA.     

Ricolinostat (ACY‐1215) induced inhibition of aggresome formation accelerates carfilzomib‐induced multiple myeloma cell death

Proteasome inhibition induces the accumulation of aggregated misfolded/ubiquitinated proteins in the aggresome; conversely, histone deacetylase 6 (HDAC6) inhibition blocks aggresome formation. Although this rationale has been the basis of proteasome inhibitor (PI) and HDAC6 inhibitor combination studies, the role of disruption of aggresome formation by HDAC6 inhibition has not yet been studied in multiple myeloma (MM). The present study aimed to evaluate the impact of carfilzomib (CFZ) in combination with a selective HDAC6 inhibitor (ricolinostat) in MM cells with respect to the aggresome‐proteolysis pathway. We observed that combination treatment of CFZ with ricolinostat triggered synergistic anti‐MM effects, even in bortezomib‐resistant cells. Immunofluorescent staining showed that CFZ increased the accumulation of ubiquitinated proteins and protein aggregates in the cytoplasm, as well as the engulfment of aggregated ubiquitinated proteins by autophagosomes, which was blocked by ricolinostat. Electron microscopy imaging showed increased autophagy triggered by CFZ, which was inhibited by the addition of ACY‐1215. Finally, an in vivo mouse xenograft study confirmed a decrease in tumour volume, associated with apoptosis, following treatment with CFZ in combination with ricolinostat. Our results suggest that ricolinostat inhibits aggresome formation, caused by CFZ‐induced inhibition of the proteasome pathway, resulting in enhanced apoptosis in MM cells.     

Downregulation of BCL2 by AT‐101 enhances the antileukaemic effect of lenalidomide both by an immune dependant and independent manner

Over‐expression of anti‐apoptotic BCL2 has been reported in chronic lymphocytic leukaemia (CLL), but targeting BCL2 alone did not yield appreciable clinical results. However, it was demonstrated that BCL2 inhibitors enhanced the clinical efficacy of chemo and immunotherapeutics. Lenalidomide, an immunomodulator, is clinically effective in CLL and can enhance the anti‐CLL effects of CD20 targeting monoclonal antibody, rituximab. Here, we investigated the mechanism of immune‐directed killing of lenalidomide in CLL and evaluated if concurrent targeting of CD20 and BCL2 can enhance this effect. In vitro treatment with lenalidomide enhanced the antibody‐mediated cellular cytotoxicity (ADCC) directed by rituximab in autologous leukaemic cells. Furthermore, peripheral blood mononuclear cells obtained from patients after treatment with lenalidomide and rituximab showed increased ADCC in vitro versus control (pre‐treatment sample). This effect was further enhanced with pre‐treatment of tumour cells with AT‐101 (a BH3 mimetic that functions as BCL2 antagonist). Our data suggest that AT‐101 in combination with lenalidomide can potentially be an effective therapeutic regimen for CLL.     

Characterization of ibrutinib‐sensitive and ‐resistant mantle lymphoma cells

Ibrutinib inhibits Bruton tyrosine kinase (BTK), a key component of early B‐cell receptor (BCR) signalling pathways. A multicentre phase 2 trial of ibrutinib in patients with relapsed/refractory mantle cell lymphoma (MCL) demonstrated a remarkable response rate. However, approximately one‐third of patients have primary resistance to the drug while other patients appear to lose response and develop secondary resistance. Understanding the molecular mechanisms underlying ibrutinib sensitivity is of paramount importance. In this study, we investigated cell lines and primary MCL cells that display differential sensitivity to ibrutinib. We found that the primary cells display a higher BTK activity than normal B cells and MCL cells show differential sensitivity to BTK inhibition. Genetic knockdown of BTK inhibits the growth, survival and proliferation of ibrutinib‐sensitive but not resistant MCL cell lines, suggesting that ibrutinib acts through BTK to produce its anti‐tumour activities. Interestingly, inhibition of ERK1/2 and AKT, but not BTK phosphorylation per se, correlates well with cellular response to BTK inhibition in cell lines as well as in primary tumours. Our study suggests that, to prevent primary resistance or to overcome secondary resistance to BTK inhibition, a combinatory strategy that targets multiple components or multiple pathways may represent the most effective approach.     

Front‐line management of non‐Hodgkin lymphoma in Australia. Part 1: follicular lymphoma

Outcomes with follicular lymphoma (FL) have improved in the modern era and median survival is now beyond 15 years. Therapeutic decisions need to consider this increased survival as well as recent clinical trial data and emerging treatments. In this context, we present here current approaches to front‐line management of FL in Australia. Treatment choices depend on the disease stage, tumour burden, the patient's age, symptoms, comorbidities and preferences. Only about 10–15% of patients with FL are diagnosed with early stage disease. For patients with low‐grade, early stage disease, radiotherapy (RT) is recommended. The addition of chemotherapy has been shown to increase progression‐free survival (PFS) but without demonstrated overall survival advantage. For patients with low‐tumour‐burden, advanced‐stage FL, immediate treatment may not be required and we recommend considering active monitoring. For stage III/IV disease that is symptomatic and/or with high tumour burden, established first‐line treatment is chemotherapy in combination with rituximab, often followed by rituximab maintenance. The listing of bendamustine and now obinutuzumab on the Pharmaceutical Benefits Scheme has expanded the first‐line treatment options in Australia to include bendamustine in combination with rituximab (without rituximab maintenance permitted) or with obinutuzumab plus 2 years obintuzumab maintenance. In the FL subgroup of the Study group indolent Lymphomas (StiL) trial, therapy with bendamustine plus rituximab significantly increased PFS compared with rituximab in combination with cyclophosphamide, doxorubicin, vincristine and prednisolone, without rituximab maintenance. Initial tolerability may be more favourable with bendamustine in combination with anti‐CD20 antibody therapy than other therapies overall, but clinical vigilance is still required because of concerns of late infectious toxicities associated with prolonged T‐cell depletion.     

Treatment of Epstein Barr virus‐induced haemophagocytic lymphohistiocytosis with rituximab‐containing chemo‐immunotherapeutic regimens

Haemophagocytic lymphohistiocytosis (HLH) is a life threatening complication of Epstein–Barr virus (EBV) infection. The anti‐CD20 antibody rituximab depletes B cells, leading to improved outcomes for patients with EBV‐associated B‐lymphoproliferative disorders. To gather data on the use of rituximab in EBV‐HLH, we performed a retrospective investigation involving 42 EBV‐HLH patients who had received treatment with rituximab‐containing regimens. On average, patients received 3 rituximab infusions (range 1–10) at a median dose of 375 mg/m². In all patients, rituximab was administered with other HLH‐directed medications, including steroids, etoposide and/or ciclosporin. Rituximab‐containing regimens appeared well tolerated and improved clinical status in 43% of patients. Examination of laboratory data obtained prior to and within 2–4 weeks after the first rituximab dose revealed significant reductions in EBV load (median load pre‐rituximab: 114 200 copies/ml, median post‐rituximab: 225 copies/ml, P = 0·0001) and serum ferritin levels (median ferritin pre‐rituximab: 4260 μg/l, median post‐rituximab: 1149 μg/l, P = 0·001). Thus, when combined with conventional HLH‐directed therapies, rituximab improves symptoms, reduces viral load and diminishes inflammation. These data support the incorporation of rituximab into future prospective clinical trials for patients with EBV‐HLH.     

Preclinical evaluation of the BET bromodomain inhibitor BAY 1238097 for the treatment of lymphoma

The epigenome is often deregulated in cancer and treatment with inhibitors of bromodomain and extra‐terminal proteins, the readers of epigenetic acetylation marks, represents a novel therapeutic approach. Here, we have characterized the anti‐tumour activity of the novel bromodomain and extra‐terminal (BET) inhibitor BAY 1238097 in preclinical lymphoma models. BAY 1238097 showed anti‐proliferative activity in a large panel of lymphoma‐derived cell lines, with a median 50% inhibitory concentration between 70 and 208 nmol/l. The compound showed strong anti‐tumour efficacy in vivo as a single agent in two diffuse large B cell lymphoma models. Gene expression profiling showed BAY 1238097 targeted the NFKB/TLR/JAK/STAT signalling pathways, MYC and E2F1‐regulated genes, cell cycle regulation and chromatin structure. The gene expression profiling signatures also highly overlapped with the signatures obtained with other BET Bromodomain inhibitors and partially overlapped with HDAC‐inhibitors, mTOR inhibitors and demethylating agents. Notably, BAY 1238097 presented in vitro synergism with EZH2, mTOR and BTK inhibitors. In conclusion, the BET inhibitor BAY 1238097 presented promising anti‐lymphoma preclinical activity in vitro and in vivo, mediated by the interference with biological processes driving the lymphoma cells. Our data also indicate the use of combination schemes targeting EZH2, mTOR and BTK alongside BET bromodomains.     

Histone deacetylases are dysregulated in rheumatoid arthritis and a novel histone deacetylase 3–selective inhibitor reduces interleukin‐6 production by peripheral blood mononuclear cells from rheumatoid arthritis patients

Objective

To characterize the role of histone deacetylase (HDAC) activity in rheumatoid arthritis (RA) and to evaluate the effects of MI192, a novel HDAC‐3–selective inhibitor, compared with the established nonselective HDAC inhibitor trichostatin A (TSA), on proinflammatory cytokine production.

Methods

Activity of HDAC and histone acetyltransferase was measured in peripheral blood mononuclear cells (PBMCs) from RA patients by spectrophotometric assay, prior to and after 12 weeks of etanercept therapy. The effects of HDAC inhibitor treatment on cytokine production in both RA and healthy PBMCs were assessed by enzyme‐linked immunosorbent assay.

Results

RA PBMCs exhibited significantly increased HDAC activity (P = 0.007) compared to PBMCs from healthy individuals, and the increase was unaltered after 12 weeks of etanercept therapy. TSA was a potent inhibitor of tumor necrosis factor (TNF) and interleukin‐6 (IL‐6) production in both RA and healthy PBMCs and of interferon‐γ (IFNγ) production in healthy PBMCs; IFNγ was not produced by RA PBMCs. MI192 inhibited TNF production at high concentrations and dose‐dependently inhibited IL‐6 in RA PBMCs but not healthy PBMCs, across a dose range of 10 μM–5 nM.

Conclusion

HDAC activity is dysregulated in RA PBMCs and is a potential target for therapeutic intervention, as it is not affected by conventional anti‐TNF treatment with etanercept. Both the selective and the nonselective HDAC inhibitors (MI192 and TSA, respectively) were found to regulate cytokine production from PBMCs, but their effects were cell type and compound specific. HDAC inhibitors have potential in the treatment of RA, and HDAC‐selective inhibition may improve the therapeutic margin of safety; however, further clinical characterization and evaluation for adverse effects is needed.

     

Identification of an ABCB1 (P‐glycoprotein)‐positive carfilzomib‐resistant myeloma subpopulation by the pluripotent stem cell fluorescent dye CDy1

Multiple myeloma (MM) is characterized by the malignant expansion of differentiated plasma cells. Although many chemotherapeutic agents display cytotoxic activity toward MM cells, patients inevitably succumb to their disease because the tumor cells become resistant to the anticancer drugs. The cancer stem cell hypothesis postulates that a small subpopulation of chemotherapy‐resistant cancer cells is responsible for propagation of the tumor. Herein we report that efflux of the pluripotent stem cell dye CDy1 identifies a subpopulation in MM cell lines characterized by increased expression of P‐glycoprotein, a member of the ABC (ATP‐binding cassette) superfamily of transporters encoded by ABCB1. We also demonstrate that ABCB1‐overexpressing MM cells are resistant to the second‐generation proteasome inhibitor carfilzomib that recently received accelerated approval for the treatment of therapy‐refractive MM by the U.S. Food and Drug Administration. Moreover, increased resistance to carfilzomib in sensitive MM cells following drug selection was associated with upregulation of ABCB1 cell‐surface expression which correlated with increased transporter activity as measured by CDy1 efflux. We further show that chemosensitization of MM cells to carfilzomib could be achieved in vitro by cotreatment with vismodegib, a hedgehog pathway antagonist which is currently in MM clinical trials. CDy1 efflux may therefore be a useful assay to determine whether high expression of ABCB1 is predictive of poor clinical responses in MM patients treated with carfilzomib. Our data also suggest that inclusion of vismodegib might be a potential strategy to reverse ABCB1‐mediated drug resistance should it occur. Am. J. Hematol. 88:265–272, 2013. © 2013 Wiley Periodicals, Inc.     

Mantle cell lymphoma: 2015 update on diagnosis,risk‐stratification,and clinical management

Disease Overview : Mantle cell lymphoma (MCL) is a non‐Hodgkin lymphoma characterized by involvement of the lymph nodes, spleen, blood and bone marrow with a short remission duration to standard therapies and a median overall survival (OS) of 4‐5 years. Diagnosis : Diagnosis is based on lymph node, bone marrow, or tissue morphology of centrocytic lymphocytes, small cell type, or blastoid variant cells. A chromosomal translocation t (11:14) is the molecular hallmark of MCL, resulting in the overexpression of cyclin D1. Cyclin D1 is detected by immunohistochemistry in 98% of cases. The absence of SOX‐11 or a low Ki‐67 may correlate with a more indolent form of MCL. The differential diagnosis of MCL includes small lymphocytic lymphoma, marginal zone lymphoma, and follicular lymphoma. Risk Stratification : The MCL International Prognostic Index (MIPI) is the prognostic model most often used and incorporates ECOG performance status, age, leukocyte count, and lactic dehydrogenase. A modification of the MIPI also adds the Ki‐67 proliferative index if available. The median OS for the low‐risk group was not reached (5‐year OS of 60%). The median OS for the intermediate risk group was 51 months and 29 months for the high risk group. Risk‐Adapted Therapy : For selected indolent, low MIPI MCL patients, initial observation may be appropriate therapy. For younger patients with intermediate or high risk MIPI MCL, aggressive therapy with a cytotoxic regimen ± autologous stem cell transplantation should be considered. For older MCL patients with intermediate or high risk MIPI, combination chemotherapy with R‐CHOP, R‐Bendamustine, or a clinical trial should be considered. In addition, rituximab maintenance therapy may prolong the progression‐free survival. At the time of relapse, agents directed at activated pathways in MCL cells such as bortezomib (NFkB inhibitor), lenalidamide (anti‐angiogenesis) and Ibruitinib (Bruton's Tyrosine Kinase [BTK] inhibitor) have demonstrated excellent clinical activity in MCL patients. Autologous or allogeneic stem cell transplantation can also be considered in young patients. Clinical trials with novel agents are always a consideration for MCL patients. Am. J. Hematol. 90:740–745, 2015. © 2015 Wiley Periodicals, Inc.     

The Bruton tyrosine kinase (BTK) inhibitor PCI‐32765 synergistically increases proteasome inhibitor activity in diffuse large‐B cell lymphoma (DLBCL) and mantle cell lymphoma (MCL) cells sensitive or resistant to bortezomib

Interactions between the Bruton tyrosine kinase (BTK) inhibitor PCI‐32765 and the proteasome inhibitor (bortezomib) were examined in diffuse large‐B cell lymphoma (DLBCL) and mantle cell lymphoma (MCL) cells, including those highly resistant to bortezomib. Co‐administration of PCI‐32765/bortezomib synergistically increased mitochondrial injury and apoptosis in germinal centre‐ or activated B‐cell‐like‐DLBCL cells and in MCL cells. These events were accompanied by marked AKT and nuclear factor (NF)‐κB (NFKB1) inactivation, down‐regulation of Mcl‐1 (MCL1), Bcl‐xL (BCL2L1), and XIAP, and enhanced DNA damage (e.g., γH2A.X formation) and endoplasmic reticulum (ER) stress. Similar interactions were observed in highly bortezomib‐resistant DLBCL and MCL cells, and in primary DLBCL cells. In contrast, PCI‐32765/bortezomib regimens displayed minimal toxicity toward normal CD34⁺ bone marrow cells. Transfection of DLBCL cells with a constitutively active AKT construct attenuated AKT inactivation and significantly diminished cell death, whereas expression of an NF‐κB “super‐repressor” (IκBα_ser34/36) increased both PCI‐32765 and bortezomib lethality. Moreover, cells in which the ER stress response was disabled by a dominant‐negative eIF2α construct were resistant to this regimen. Finally, combined exposure to PCI‐32765 and bortezomib resulted in more pronounced and sustained reactive oxygen species (ROS) generation, and ROS scavengers significantly diminished lethality. Given promising early clinical results for PCI‐32765 in DLBCL and MCL, a strategy combining BTK/proteasome inhibitor warrants attention in these malignancies.     

Pomalidomide in combination with dexamethasone results in synergistic anti‐tumour responses in pre‐clinical models of lenalidomide‐resistant multiple myeloma

Pomalidomide is an IMiD^® immunomodulatory agent, which has shown clinically significant benefits in relapsed and/or refractory multiple myeloma (rrMM) patients when combined with dexamethasone, regardless of refractory status to lenalidomide or bortezomib. (Schey et al, 2004 ; San Miguel et al, 2013; Richardson et al, 2014; Scott, 2014 ) In this work, we present preclinical data showing that the combination of pomalidomide with dexamethasone (PomDex) demonstrates potent anti‐proliferative and pro‐apoptotic activity in both lenalidomide‐sensitive and lenalidomide‐resistant MM cell lines. PomDex also synergistically inhibited tumour growth compared with single‐agent treatment in xenografts of lenalidomide‐resistant H929 R10‐1 cells. Typical hallmarks of IMiD compound activity, including IKZF3 (Aiolos) degradation, and the downregulation of interferon regulatory factor (IRF) 4 and MYC, seen in lenalidomide‐sensitive H929 MM cell lines, were also observed in PomDex‐treated lenalidomide‐resistant H929 MM cells. Remarkably, this resulted in strong, synergistic effects on the induction of apoptosis in both lenalidomide‐sensitive and resistant MM cells. Furthermore, gene expression profiling revealed a unique differential gene expression pattern in PomDex‐treated samples, highlighted by the modulation of pro‐apoptotic pathways in lenalidomide‐resistant cells. These results provide key insights into molecular mechanisms of PomDex in the lenalidomide‐resistant setting.     

Impact of prior rituximab on outcomes of autologous stem‐cell transplantation in patients with relapsed or refractory aggressive B‐cell lymphoma: a multicentre retrospective Spanish group of lymphoma/autologous bone marrow transplant study

The use of highly effective rituximab‐containing therapy for treating diffuse large B‐cell lymphoma (DLBCL) makes it more difficult to salvage relapsed or refractory patients. Autologous stem‐cell transplantation (ASCT) is the reference treatment for these patients, but the impact of previous exposure to rituximab on the subsequent results of ASCT remains unknown. We analysed 248 patients with relapsed or refractory DLBCL or grade 3B follicular lymphoma pre‐treated with rituximab as part of first‐line therapy (R+ group) who received ASCT, in comparison with a control group of 127 patients without previous exposure to rituximab (R? group). The complete remission (CR) rates were similar in both groups. Multivariate analysis identified age‐adjusted International Prognostic Index at diagnosis, extranodal involvement and disease status at transplant, and the number of previous chemotherapy lines as independent factors with a negative influence on CR rate. Compared with R? patients, those in the R+ group had a significantly better progression‐free survival (63% vs. 48% at 5 years) and overall survival (72% vs. 61% at 5 years). This observation was independent of other prognostic factors that affected these outcomes. In conclusion, ASCT is no less effective in patients with relapsed or refractory aggressive B‐cell lymphoma pre‐treated with first‐line rituximab‐containing therapy than in rituximab‐naive patients.     

Follicular helper T‐cells: expanding roles in T‐cell lymphoma and targets for treatment

Follicular helper T‐cells (Tfh cells) are a subset of CD4⁺ T‐cells that are essential for normal production of high affinity antibodies. Tfh cells characteristically produce IL21 and IL4 and show high expression of surface markers CXCR5, ICOS, PDCD1 (PD‐1) and the chemokine CXCL13. In this review we will focus on the emerging links between Tfh cells and subtypes of T‐cell non‐Hodgkin lymphoma: angioimmunoblastic T‐cell lymphoma (AITL) and ~20% of peripheral T‐cell lymphoma not otherwise specified (PTCL‐NOS) have surface marker features of Tfh cells and share a spectrum of genetic abnormalities. The recurrent genetic abnormalities associated with AITL include mutations in epigenetic modifiers such as TET2 and DNMT3A and the motility and adhesion gene, RHOA, is mutated in up to 70% of cases. ~20% of PTCL‐NOS demonstrate RHOA mutations and have other characteristics suggesting an origin in Tfh cells. The recognition that specific genetic and surface markers are associated with malignant Tfh cells suggests that the next few years will bring major changes in diagnostic and treatment possibilities. For example, antibodies against IL21, PDCD1 and ICOS are already in clinical trials for autoimmune disease or other malignancies and antibodies against CXCL13 are in pre‐clinical development.