Mantle cell lymphoma in relapse: the role of emerging new drugs

Bcl-2 Family Members Bcl-xL and Bax Cooperatively Contribute to Bortezomib Resistance in Mantle Cell Lymphoma

Mantle cell lymphoma (MCL) is an aggressive non-Hodgkin lymphoma with poor prognosis, due to the inevitable development of drug resistance. Despite being the first-in-class proteasome inhibitor for relapsed/refractory MCL, resistance to bortezomib (BTZ) in MCL patients remains a major hurdle of effective therapy, and relapse following BTZ is frequent. Understanding the mechanisms underlying BTZ resistance is, therefore, important for improving the clinical outcome and developing novel therapeutic strategies. Here, we established de novo BTZ-resistant human MCL-derived cells with the highest resistance index of 300-fold compared to parental cells. We provided compelling evidence that both Bcl-xL and Bax are key mediators in determining BTZ sensitivity in MCL cells. Overexpression of antiapoptotic Bcl-xL and depletion of proapoptotic Bax cooperatively protected MCL cells against BTZ-induced apoptosis, causing acquired BTZ resistance, likely by tilting the balance of Bcl-2 family proteins toward antiapoptotic signaling. Bioinformatics analyses suggested that high BCL2L1 (encoded Bcl-xL) and low BAX were, in part, associated with poor prognosis of MCL patients, e.g., when combined with low OGT, which regulates cellular O-GlcNAcylation. Our findings support recent strategies in small molecule drug discovery co-targeting antiapoptotic Bcl-2 family proteins using BH3 mimetics and Bax using Bax activators to overcome cancer drug resistance.

Resistance to the Proteasome Inhibitors: Lessons from Multiple Myeloma and Mantle Cell Lymphoma

Since its introduction in the clinics in early 2000s, the proteasome inhibitor bortezomib (BTZ) significantly improved the prognosis of patients with multiple myeloma (MM) and mantle cell lymphoma (MCL), two of the most challenging B cell malignancies in western countries. However, relapses following BTZ therapy are frequent, while primary resistance to this agent remains a major limitation for further development of its therapeutic potential. In the present chapter, we recapitulate the molecular mechanisms associated with intrinsic and acquired resistance to BTZ learning from MM and MCL experience, including mutations of crucial genes and activation of prosurvival signalling pathways inherent to malignant B cells. We also outline the preclinical and clinical evaluations of some potential druggable targets associated to BTZ resistance, considering the most meaningful findings of the past 10 years. Although our understanding of BTZ resistance is far from being completed, recent discoveries are contributing to develop new approaches to treat relapsed MM and MCL patients.

Deciphering the Elevated Lipid via CD36 in Mantle Cell Lymphoma with Bortezomib Resistance Using Synchrotron-Based Fourier Transform Infrared Spectroscopy of Single Cells

Despite overall progress in improving cancer treatments, the complete response of mantle cell lymphoma (MCL) is still limited due to the inevitable development of drug resistance. More than half of patients did not attain response to bortezomib (BTZ), the approved treatment for relapsed or refractory MCL. Understanding how MCL cells acquire BTZ resistance at the molecular level may be a key to the long-term management of MCL patients and new therapeutic strategies. We established a series of de novo BTZ-resistant human MCL-derived cells with approximately 15- to 60-fold less sensitivity than those of parental cells. Using gene expression profiling, we discovered that putative cancer-related genes involved in drug resistance and cell survival tested were mostly downregulated, likely due to global DNA hypermethylation. Significant information on dysregulated lipid metabolism was obtained from synchrotron-based Fourier transform infrared (FTIR) spectroscopy of single cells. We demonstrated for the first time an upregulation of CD36 in highly BTZ-resistant cells in accordance with an increase in their lipid accumulation. Ectopic expression of CD36 causes an increase in lipid droplets and renders BTZ resistance to various human MCL cells. By contrast, inhibition of CD36 by neutralizing antibody strongly enhances BTZ sensitivity, particularly in CD36-overexpressing cells and de novo BTZ-resistant cells. Together, our findings highlight the potential application of CD36 inhibition for BTZ sensitization and suggest the use of FTIR spectroscopy as a promising technique in cancer research.

Targeting the PI3K/Akt/mTOR signaling pathway by pterostilbene attenuates mantle cell lymphoma progression

Mantle cell lymphoma (MCL) is an aggressive and mostly incurable B-cell malignancy with frequent relapses after an initial response to standard chemotherapy. Therefore, novel therapies are urgently required to improve MCL clinical outcomes. In this study, MCL cell lines were treated with pterostilbene (PTE), a non-toxic natural phenolic compound primarily found in blueberries. The antitumor activity of PTE was examined by using the Cell Counting Kit-8, apoptosis assays, cell cycle analysis, JC-1 mitochondrial membrane potential assay, western blot analysis, and tumor xenograft models. PTE treatment induced a dose-dependent inhibition of cell proliferation, including the induction of cell apoptosis and cell cycle arrest at the G0/G1 phase. Moreover, the PI3K/Akt/mTOR pathway was downregulated after PTE treatment, which might account for the anti-MCL effects of PTE. Synergistic cytotoxicity was also observed, both in MCL cells and in xenograft mouse models, when PTE was administered in combination with bortezomib (BTZ). The antitumor effects of PTE shown in our study provide an innovative option for MCL patients with poor responses to standardized therapy. It is noteworthy that the treatment combining PTE with BTZ warrants clinical investigation, which may offer an alternative and effective MCL treatment in the future.

Inhibition of Lyn is a promising treatment for mantle cell lymphoma with bortezomib resistance

Although proteasome inhibition with bortezomib (BTZ) is a validated treatment for relapsed or refractory mantle cell lymphoma (MCL), many patients show resistance to BTZ. However, the molecular mechanism of BTZ resistance in MCL has not been elucidated. In the present study, we investigated BTZ-resistant MCL cells in vitro and in vivo. We demonstrate that BTZ-resistant MCL cells showed highly increased expression of the B-cell receptor (BCR) components CD79A and CD19. Activation of the BCR signaling pathway enhanced the activity of Src family kinases (SFKs), especially Lyn, and downstream kinases PI3K/AKT/mTOR in BTZ-resistant MCL cells. Depletion of CD79A and Lyn significantly reduced several kinase activities involved in PI3K signaling, leading to inhibition of proliferation. In addition, the SFKs inhibitor dasatinib inhibited the proliferation of BTZ-resistant cells, preventing the binding of CD19 with Lyn and PI3K p85. We also verified our findings with the mouse xenograft tumor model. Dasatinib treatment significantly decreased tumor size in the mouse bearing BTZ-resistant MCL cells, but not in the mouse bearing BTZ-sensitive MCL cells. Collectively, our data show that overexpression of the BCR and its activated signaling confers BTZ resistance in MCL cells. Thus, targeting BCR signaling with dasatinib could be a novel therapeutic approach for patients with MCL that has relapsed or is refractory to treatment with BTZ.

Inhibitors of SCF-Skp2/Cks1 E3 ligase block estrogen-induced growth stimulation and degradation of nuclear p27kip1: therapeutic potential for endometrial cancer

In many human cancers, the tumor suppressor, p27(kip1) (p27), a cyclin-dependent kinase inhibitor critical to cell cycle arrest, undergoes perpetual ubiquitin-mediated proteasomal degradation by the E3 ligase complex SCF-Skp2/Cks1 and/or cytoplasmic mislocalization. Lack of nuclear p27 causes aberrant cell cycle progression, and cytoplasmic p27 mediates cell migration/metastasis. We previously showed that mitogenic 17-β-estradiol (E2) induces degradation of p27 by the E3 ligase Skp1-Cullin1-F-Box- S phase kinase-associated protein2/cyclin dependent kinase regulatory subunit 1 in primary endometrial epithelial cells and endometrial carcinoma (ECA) cell lines, suggesting a pathogenic mechanism for type I ECA, an E2-induced cancer. The current studies show that treatment of endometrial carcinoma cells-1 (ECC-1) with small molecule inhibitors of Skp2/Cks1 E3 ligase activity (Skp2E3LIs) stabilizes p27 in the nucleus, decreases p27 in the cytoplasm, and prevents E2-induced proliferation and degradation of p27 in endometrial carcinoma cells-1 and primary ECA cells. Furthermore, Skp2E3LIs increase p27 half-life by 6 hours, inhibit cell proliferation (IC50, 14.3μM), block retinoblastoma protein (pRB) phosphorylation, induce G1 phase block, and are not cytotoxic. Similarly, using super resolution fluorescence localization microscopy and quantification, Skp2E3LIs increase p27 protein in the nucleus by 1.8-fold. In vivo, injection of Skp2E3LIs significantly increases nuclear p27 and reduces proliferation of endometrial epithelial cells by 42%-62% in ovariectomized E2-primed mice. Skp2E3LIs are specific inhibitors of proteolytic degradation that pharmacologically target the binding interaction between the E3 ligase, SCF-Skp2/Cks1, and p27 to stabilize nuclear p27 and prevent cell cycle progression. These targeted inhibitors have the potential to be an important therapeutic advance over general proteasome inhibitors for cancers characterized by SCF-Skp2/Cks1-mediated destruction of nuclear p27.

Novel treatment for mantle cell lymphoma including therapy-resistant tumor by NF-κB and mTOR dual-targeting approach

Mantle cell lymphoma (MCL) is one of the most aggressive B-cell non-Hodgkin lymphomas with a median survival of approximately five years. Currently, there is no curative therapy available for refractory MCL because of relapse from therapy-resistant tumor cells. The NF-κB and mTOR pathways are constitutively active in refractory MCL leading to increased proliferation and survival. Targeting these pathways is an ideal strategy to improve therapy for refractory MCL. Therefore, we investigated the in vitro and in vivo antilymphoma activity and associated molecular mechanism of action of a novel compound, 13-197, a quinoxaline analog that specifically perturbs IκB kinase (IKK) β, a key regulator of the NF-κB pathway. 13-197 decreased the proliferation and induced apoptosis in MCL cells including therapy-resistant cells compared with control cells. Furthermore, we observed downregulation of IκBα phosphorylation and inhibition of NF-κB nuclear translocation by 13-197 in MCL cells. In addition, NF-κB-regulated genes such as cyclin D1, Bcl-XL, and Mcl-1 were downregulated in 13-197-treated cells. In addition, 13-197 inhibited the phosphorylation of S6K and 4E-BP1, the downstream molecules of mTOR pathway that are also activated in refractory MCL. Further, 13-197 reduced the tumor burden in vivo in the kidney, liver, and lungs of therapy-resistant MCL-bearing nonobese diabetic severe-combined immunodeficient (NOD/SCID) mice compared with vehicle-treated mice; indeed, 13-197 significantly increased the survival of MCL-transplanted mice. Together, results suggest that 13-197 as a single agent disrupts the NF-κB and mTOR pathways leading to suppression of proliferation and increased apoptosis in malignant MCL cells including reduction in tumor burden in mice.

Sorafenib inhibits cell migration and stroma-mediated bortezomib resistance by interfering B-cell receptor signaling and protein translation in mantle cell lymphoma

PURPOSE

We evaluated the antitumoral properties of the multikinase inhibitor sorafenib in mantle cell lymphoma (MCL), an aggressive B lymphoma for which current therapies have shown limited efficacy.

EXPERIMENTAL DESIGN

Sensitivity to sorafenib was analyzed in MCL cell lines and primary samples in the context of BCR and microenvironment simulation. Sorafenib signaling was characterized by quantitative PCR, Western blotting, immunofluorescence, and protein immunoprecipitation. Migration analysis included flow cytometric counting, actin polymerization assays, and siRNA-mediated knockdown of focal adhesion kinase (FAK). In vivo antitumor effect of sorafenib and bortezomib was analyzed in an MCL xenograft mouse model.

RESULTS

Sorafenib rapidly dephosphorylates the BCR-associated kinases, Syk and Lyn, as well as FAK, an Src target involved in focal adhesion. In this line, sorafenib displays strong synergy with the Syk inhibitor, R406. Sorafenib also blocks Mcl-1 and cyclin D1 translation, which promotes an imbalance between pro- and antiapoptotic proteins and facilitates Bax release from cyclin D1, leading to the induction of mitochondrial apoptosis and caspase-dependent and -independent mechanisms. Moreover, sorafenib inhibits MCL cell migration and CXCL12-induced actin polymerization. FAK knockdown partially prevents this inhibitory effect, indicating that FAK is a relevant target of sorafenib. Furthermore, sorafenib enhances the antitumoral activity of bortezomib in an MCL xenograft mouse model as well as overcomes stroma-mediated bortezomib resistance in MCL cells.

CONCLUSION

We show for the first time that sorafenib interferes with BCR signaling, protein translation and modulates the microenvironment prosurvival signals in MCL, suggesting that sorafenib, alone or in combination with bortezomib, may represent a promising approach to treat patients with MCL.

Complete inhibition of extranodal dissemination of lymphoma by edelfosine-loaded lipid nanoparticles

Background: Lipid nanoparticles (LNs) made of synthetic lipids Compritol® 888 ATO and Precirol® ATO 5 were developed with an average size of 110.4 ± 2.1 and 103.1 ± 2.9 nm, and an encapsulation efficiency above 85% for both type of lipids. These LNs decrease the hemolytic toxicity of the drug by 90%. Materials & methods: Pharmacokinetic and biodistribution profiles of the drug were studied after intravenous and oral administration of edelfosine-containing LNs. Results: This provided an increase in relative oral bioavailability of 1500% after a single oral administration of drug-loaded LNs, maintaining edelfosine plasma levels over 7 days in contrast to a single oral administration of edelfosine solution, which presented a relative oral bioavailability of 10%. Moreover, edelfosine-loaded LNs showed a high accumulation of the drug in lymph nodes and resulted in slower tumor growth than the free drug in a murine lymphoma xenograft model, as well as potent extranodal dissemination inhibition.

Original submitted 5 April 2011; Revised submitted 5 July 2011

Dual-targeting immunotherapy of lymphoma: potent cytotoxicity of anti-CD20/CD74 bispecific antibodies in mantle cell and other lymphomas

We describe the use of novel bispecific hexavalent Abs (HexAbs) to enhance anticancer immunotherapy. Two bispecific HexAbs [IgG-(Fab)4 constructed from veltuzumab (anti-CD20 IgG) and milatuzumab (anti-CD74 IgG)] show enhanced cytotoxicity in mantle cell lymphoma (MCL) and other lymphoma/leukemia cell lines, as well as patient tumor samples, without a crosslinking Ab, compared with their parental mAb counterparts, alone or in combination. The bispecific HexAbs have different properties from and are more potent than their parental mAbs in vitro. The juxtaposition of CD20 and CD74 on MCL cells by the HexAbs resulted in homotypic adhesion and triggered intracellular changes that include loss of mitochondrial transmembrane potential, production of reactive oxygen species, rapid and sustained phosphorylation of ERKs and JNK, down-regulation of pAkt and Bcl-xL, actin reorganization, and lysosomal membrane permeabilization, culminating in cell death. They also displayed different potencies in depleting lymphoma cells and normal B cells from whole blood ex vivo and significantly extended the survival of nude mice bearing MCL xenografts in a dose-dependent manner, thus indicating stability and antitumor activity in vivo. Such bispecific HexAbs may constitute a new class of therapeutic agents for improved cancer immunotherapy, as shown here for MCL and other CD20+/CD74+ malignancies.

The mitochondrial ATP-dependent Lon protease: a novel target in lymphoma death mediated by the synthetic triterpenoid CDDO and its derivatives

Synthetic triterpenoids are multitarget compounds exhibiting promise as preventative and therapeutic agents for cancer. Their proposed mechanism of action is by forming Michael adducts with reactive nucleophilic groups on target proteins. Our previous work demonstrates that the 2-cyano-3,12-dioxooleana-1,9-dien-28-oic acid (CDDO) and its derivatives promote B-lymphoid cell apoptosis through a mitochondria-mediated pathway linked to mitochondrial protein aggregation. As one function of the Lon protease is to eliminate abnormal mitochondrial proteins, we hypothesized that CDDO-induced protein aggregation and lymphoma apoptosis occur by inactivating this enzyme. Here, we show that CDDO and its derivatives directly and selectively inhibit Lon. CDDO blocks Lon-mediated proteolysis in biochemical and cellular assays, but does not inhibit the 20S proteasome. Furthermore, a biotinylated-CDDO conjugate modifies mitochondrial Lon. A striking common phenotype of CDDO-treated lymphoma cells and Lon-knockdown cells is the accumulation of electron-dense aggregates within mitochondria. We also show that Lon protein levels are substantially elevated in malignant lymphoma cells, compared with resting or activated B cells. Finally, we demonstrate that Lon knockdown leads to lymphoma cell death. Together, these findings suggest that Lon inhibition plays a contributory role in CDDO-induced lymphoma cell death, and support the concept that mitochondrial Lon is a novel anticancer drug target.

Overlooking evolution: a systematic analysis of cancer relapse and therapeutic resistance research

Cancer therapy selects for cancer cells resistant to treatment, a process that is fundamentally evolutionary. To what extent, however, is the evolutionary perspective employed in research on therapeutic resistance and relapse? We analyzed 6,228 papers on therapeutic resistance and/or relapse in cancers and found that the use of evolution terms in abstracts has remained at about 1% since the 1980s. However, detailed coding of 22 recent papers revealed a higher proportion of papers using evolutionary methods or evolutionary theory, although this number is still less than 10%. Despite the fact that relapse and therapeutic resistance is essentially an evolutionary process, it appears that this framework has not permeated research. This represents an unrealized opportunity for advances in research on therapeutic resistance.

Carfilzomib interacts synergistically with histone deacetylase inhibitors in mantle cell lymphoma cells in vitro and in vivo

Interactions between the proteasome inhibitor carfilzomib and the histone deacetylase (HDAC) inhibitors vorinostat and SNDX-275 were examined in mantle cell lymphoma (MCL) cells in vitro and in vivo. Coadministration of very low, marginally toxic carfilzomib concentrations (e.g., 3-4 nmol/L) with minimally lethal vorinostat or SNDX-275 concentrations induced sharp increases in mitochondrial injury and apoptosis in multiple MCL cell lines and primary MCL cells. Enhanced lethality was associated with c-jun-NH,-kinase (JNK) 1/2 activation, increased DNA damage (induction of λH2A.X), and ERK1/2 and AKT1/2 inactivation. Coadministration of carfilzomib and histone deacetylase inhibitors (HDACI) induced a marked increase in reactive oxygen species (ROS) generation and G(2)-M arrest. Significantly, the free radical scavenger tetrakis(4-benzoic acid) porphyrin (TBAP) blocked carfilzomib/HDACI-mediated ROS generation, λH2A.X formation, JNK1/2 activation, and lethality. Genetic (short hairpin RNA) knockdown of JNK1/2 significantly attenuated carfilzomib/HDACI-induced apoptosis, but did not prevent ROS generation or DNA damage. Carfilzomib/HDACI regimens were also active against bortezomib-resistant MCL cells. Finally, carfilzomib/vorinostat coadministration resulted in a pronounced reduction in tumor growth compared with single agent treatment in an MCL xenograft model associated with enhanced apoptosis, λH2A.X formation, and JNK activation. Collectively, these findings suggest that carfilzomib/HDACI regimens warrant attention in MCL.

Vorinostat-induced apoptosis in mantle cell lymphoma is mediated by acetylation of proapoptotic BH3-only gene promoters

PURPOSE

Mantle cell lymphoma (MCL) is an aggressive B-cell neoplasm with generally poor prognosis, for which current therapies have shown limited efficacy. Vorinostat is a histone deacetylase inhibitor (HDACi) that has been approved for the treatment of cutaneous T-cell lymphoma. Our purpose was to describe the molecular mechanism whereby vorinostat induces apoptosis in MCL with particular emphasis on the role of proapoptotic BH3-only proteins.

EXPERIMENTAL DESIGN

The sensitivity to vorinostat was analyzed in eight MCL cell lines and primary cells from 10 MCL patients. Determination of vorinostat mechanism of action was done by flow cytometry, immunoblotting, HDAC activity assay kit, quantitative reverse transcription PCR, chromatin immunoprecipitation, and siRNA-mediated transfection.

RESULTS

Vorinostat inhibited total histone deacetylase activity leading to selective toxicity toward tumor cells. Vorinostat-mediated cell death implied the activation of mitochondrial apoptosis, as attested by BAX and BAK conformational changes, mitochondrial depolarization, reactive oxygen species generation, and subsequent caspase-dependent cell death. This phenomenon was linked to H4 hyperacetylation on promoter regions and consequent transcriptional activation of the proapoptotic BH3-only genes BIM, BMF, and NOXA. Selective knockdown of the three corresponding proteins rescued cells from vorinostat-induced apoptosis. Moreover, vorinostat enhanced the activity of the BH3-mimetic ABT-263 in MCL cells, leading to synergistic apoptosis induction.

CONCLUSION

These results indicated that transcriptional upregulation of BH3-only proteins plays an important role in the antitumoral activity of vorinostat in MCL, and that HDACi alone or in combination with BH3-mimetizing agents may represent a promising therapeutic approach for MCL patients.