Emerging treatments for multiple myeloma: beyond immunomodulatory drugs and bortezomib

Synergistic Apoptotic Effects of Bortezomib and Methylstat on Multiple Myeloma Cells

BACKGROUND

In this study, we aimed to determine synergistic apoptotic and cytotoxic effects of methylstat and bortezomib on U266 and ARH77 multiple myeloma (MM) cells.

METHODS

Cytotoxic effects of the drugs were demonstrated by MTT cell proliferation assay while apoptotic effects were examined by loss of mitochondrial membrane potential (MMP) by JC-1 MMP detection kit, changes in caspase-3 enzyme activity and Annexin-V apoptosis assay by flow cytometry. Expression levels of apoptotic and antiapoptotic genes were examined by qRT-PCR.

RESULTS

Our results showed that combination of methylstat and bortezomib have synergistic antiproliferative effect on MM cells as compared to either agent alone. These results were also confirmed by showing synergistic apoptotic effects determined by increased loss of mitochondrial membrane potential and increased caspase-3 enzyme activity and relocation of phosphotidyleserine on the cell membrane by Annexin-V/PI double staining. Combination of bortezomib with methylstat arrested cells at the S phase of the cell cycle. Methylstat treatment caused upregulation of FASLG, NGFR, TNF, TNFRS10B and TNFRS1B apoptotic genes and downregulation of AKT1, AVEN, BAG1 BCL2L2 and RELA antiapoptotic genes in a dose and time dependent manner.

CONCLUSION

In conclusion, our data suggested that bortezomib in combination with methylstat decreased cell proliferation and induced apoptosis significantly in U266 and ARH77 cells. When supported with in vivo analyses, methylstat might be considered as a potential new agent for the treatment of MM.

Analysis of determinants for in vitro resistance to the small molecule deubiquitinase inhibitor b-AP15

BACKGROUND

b-AP15/VLX1570 are small molecule inhibitors of the ubiquitin specific peptidase 14 (USP14) and ubiquitin carboxyl-terminal hydrolase 5 (UCHL5) deubiquitinases (DUBs) of the 19S proteasome. b-AP15/VLX1570 have been shown to be cytotoxic to cells resistant to bortezomib, raising the possibility that this class of drugs can be used as a second-line therapy for treatment-resistant multiple myeloma. Limited information is available with regard to potential resistance mechanisms to b-AP15/VLX1570.

RESULTS

We found that b-AP15-induced cell death is cell-cycle dependent and that non-cycling tumor cells may evade b-AP15-induced cell death. Such non-cycling cells may re-enter the proliferative state to form colonies of drug-sensitive cells. Long-term selection of cells with b-AP15 resulted in limited drug resistance (~2-fold) that could be reversed by buthionine sulphoximine, implying altered glutathione (GSH) metabolism as a resistance mechanism. In contrast, drug uptake and overexpression of drug efflux transporters were found not to be associated with b-AP15 resistance.

CONCLUSIONS

The proteasome DUB inhibitors b-AP15/VLX1570 are cell cycle-active. The slow and incomplete development of resistance towards these compounds is an attractive feature in view of future clinical use.

Elotuzumab in combination with lenalidomide and dexamethasone in patients with relapsed multiple myeloma: final phase 2 results from the randomised, open-label, phase 1b-2 dose-escalation study

BACKGROUND

Elotuzumab, an immunostimulatory monoclonal antibody targeting signalling lymphocytic activation molecule (SLAM) family member 7 (SLAMF7), selectively kills SLAMF7-expressing myeloma cells through direct activation and engagement of the innate immune system, and thus might have clinical benefit in the treatment of myeloma. In phase 1 of this phase 1b-2 study, 82% of patients with relapsed multiple myeloma who were given elotuzumab plus lenalidomide and dexamethasone achieved an overall response. Here we report the final phase 2 results.

METHODS

We did this randomised, multicentre, open-label, dose-escalation study (1703) at 17 hospitals in the USA, Canada, France, and Germany. Patients aged at least 18 years with confirmed, relapsed multiple myeloma, Eastern Cooperative Oncology Group performance status 0-2, and one to three previous therapies but no previous lenalidomide were eligible for phase 2. We randomly assigned patients (1:1) to either 10 mg/kg or 20 mg/kg intravenous elotuzumab plus oral lenalidomide (25 mg) and dexamethasone (40 mg). We stratified patients on the basis of the number of previous therapies (one versus two or three), and status of previous treatment with immunomodulatory drugs (yes or no), and used permuted block randomisation with a block size of four. Treatment was given in 28-day cycles until disease progression or unacceptable toxic effects occurred (elotuzumab was given on days 1, 8, 15, and 22 for cycles 1 to 2 and days 1 and 15 for subsequent cycles; lenalidomide was given on days 1-21 and dexamethasone once per week). The primary endpoint was the proportion of patients who achieved an objective response according to International Myeloma Working Group criteria. Primary analyses were done in the intention-to-treat population, and safety was analysed in all patients who received at least one dose of study drugs. This study is registered with ClinicalTrials.gov, number NCT00742560.

FINDINGS

Between Jan 4, 2010, and Dec 21, 2010, we recruited and randomly assigned 73 patients to elotuzumab (36 to 10 mg/kg, 37 to 20 mg/kg). At data cutoff (Jan 16, 2014), 13 patients remained on treatment (six on 10 mg/kg, seven on 20 mg/kg). 61 (84%) patients achieved an objective response (33 [92%] with 10 mg/kg, 28 [76%] with 20 mg/kg); 31 (42%) a very good partial response (17 [47%] with 10 mg/kg, 14 [38%] with 20 mg/kg); and 20 (27%) a partial response (10 [28%] with 10 mg/kg, 10 [27%] with 20 mg/kg). The most common treatment-emergent adverse events of any grade were diarrhoea (48 [66%]), muscle spasms (45 [62%]), and fatigue (41 [56%]). 57 (78%) patients had grade 3-4 events, the most common of which were lymphopenia (15 [21%]) and neutropenia (14 [19%]). Three deaths occurred, none related to the study drugs.

INTERPRETATION

Elotuzumab combined with lenalidomide and dexamethasone in patients with relapsed multiple myeloma showed acceptable safety and efficacy that seems better than that previously noted with lenalidomide and dexamethasone only. Phase 3 trials are in progress.

FUNDING

Bristol-Myers Squibb, AbbVie Biotherapeutics.

The combination of bortezomib with enzastaurin or lenalidomide enhances cytotoxicity in follicular and mantle cell lymphoma cell lines

We analyzed the combination of a proteasome inhibitor (bortezomib) with enzastaurin (PKC/AKT-inhibitor) or lenalidomide (immunomodulatory agent) for the inhibition of proliferation and induction of apoptosis in B-cell lymphoma cell lines and primary malignant cells. The effects of bortezomib, enzastaurin or lenalidomide, alone or in combinations, on cell viability and apoptosis were evaluated using the Cell Proliferation Kit and flow cytometry analysis. The interaction between drugs was examined by the Chou-Talalay method. Cell cycle analysis was performed by flow cytometry. The PI3K/AKT, PKC and MAPK/ERK signaling pathways were analyzed using western blot. Bortezomib with either enzastaurin or lenalidomide synergistically induced anti-proliferative and pro-apoptotic effects in B-cell lymphoma cells, even in the presence of the bone marrow microenvironment. The direct cytotoxicity is mediated by signaling events involving the PI3K/AKT, PKC and MAPK/ERK pathways leading to cell death. The significant increase of apoptosis was mediated by an increased ratio of pro-apoptotic proteins (Bax, Bad and Bim) to anti-apoptotic proteins (Bcl-2, Bcl-xL and Mcl-1), triggering the cleavage of caspases -3, -9, -8 and PARP. Further evaluation of the combination of bortezomib with enzastaurin or lenalidomide for the treatment of B-cell lymphoma is warranted, with the goal to improve the quality of life and survival of patients.

Extramedullary progression of multiple myeloma despite concomitant medullary response to multiple combination therapies and autologous transplant: a case report

INTRODUCTION

Extramedullary myeloma that occurs during the clinical course of multiple myeloma is rare but is an independent poor prognostic factor with mortality of 73% and median survival of 12 months despite aggressive therapies including novel agents. The clinicopathological aspects, biology and management of extramedullary myelomas are poorly understood. Our case highlights the pathobiological aspects of this important but rare entity, and the repercussions of modern therapies.

CASE PRESENTATION

A 60-year-old Caucasian man initially presented with an anterior rib fracture. Subsequent workup revealed stage IIIB immunoglobulin G lambda multiple myeloma. A bone marrow biopsy showed sheets of plasma cells, harboring unfavorable cytogenetics including deletion of 17p and t(4;14). He achieved near complete remission and resolution of karyotypic abnormalities with three cycles of induction doxorubicin, thalidomide, and dexamethasone (clinical trial). This was followed by high-dose melphalan and autologous stem cell transplant. He relapsed 1 year later. His bone marrow at that time showed only a few scattered polyclonal plasma cells. He received three cycles of bortezomib and tanespimycin (clinical trial) and achieved very good partial response. He again relapsed 1 year later with multiple large peripheral soft tissue masses and lymph nodes. Biopsies of the peripheral lesions were consistent with extramedullary myeloma, but repeat bone marrow biopsy continued to show no evidence of intramedullary disease.

CONCLUSIONS

This is one of the few cases reported that illustrates the differential response of extramedullary compared to intramedullary myeloma to multiple standard combination therapies including novel therapeutics and transplant, resulting in a very short survival. Several mechanisms for intra-to-extra medullary migration and hence the differential treatment response have been hypothesized. Physicians should be aware of this problem during treatment with immunomodulatory drugs and proteasome inhibitors not only in relapsed but also in front-line setting. In such cases, there is a potential role for evolving targeted therapeutics as we continue to better understand the tumor biology.

In vivo murine model of acquired resistance in myeloma reveals differential mechanisms for lenalidomide and pomalidomide in combination with dexamethasone

The development of resistance to therapy is unavoidable in the history of multiple myeloma patients. Therefore, the study of its characteristics and mechanisms is critical in the search for novel therapeutic approaches to overcome it. This effort is hampered by the absence of appropriate preclinical models, especially those mimicking acquired resistance. Here we present an in vivo model of acquired resistance based on the continuous treatment of mice bearing subcutaneous MM1S plasmacytomas. Xenografts acquired resistance to two generations of immunomodulatory drugs (IMiDs; lenalidomide and pomalidomide) in combination with dexamethasone, that was reversible after a wash-out period. Furthermore, lenalidomide-dexamethasone (LD) or pomalidomide-dexamethasone (PD) did not display cross-resistance, which could be due to the differential requirements of the key target Cereblon and its substrates Aiolos and Ikaros observed in cells resistant to each combination. Differential gene expression profiles of LD and PD could also explain the absence of cross-resistance. Onset of resistance to both combinations was accompanied by upregulation of the mitogen-activated protein kinase/extracellular signal-regulated kinase (ERK) kinase (MEK)/ERK pathway and addition of selumetinib, a small-molecule MEK inhibitor, could resensitize resistant cells. Our results provide insights into the mechanisms of acquired resistance to LD and PD combinations and offer possible therapeutic approaches to addressing IMiD resistance in the clinic.

Small molecule MIRA-1 induces in vitro and in vivo anti-myeloma activity and synergizes with current anti-myeloma agents

Background:

Small molecule MIRA-1 induced mutant p53-dependent apoptosis in several types of solid tumours. However, anti-tumour activity of MIRA-1 in haematological malignancies including multiple myeloma (MM) is unknown. In this study, we evaluated the effect of MIRA-1 in MM.

Methods:

We examined the anti-tumour activity of MIRA-1 alone or in combination with current anti-myeloma agents in a panel of MM cell lines, primary MM samples, and in a mouse xenograft model of MM.

Results:

MIRA-1 treatment resulted in the inhibition of viability, colony formation, and migration and increase in apoptosis of MM cells irrespective of p53 status accompanied by upregulation of Puma and Bax and downregulation of Mcl-1 and c-Myc. Genetic knockdown of p53 did not abrogate apoptotic response of MIRA-1. MIRA-1 triggered activation of PERK and IRE-α leading to splicing of XBP1 indicating an association of endoplasmic reticulum stress response. Furthermore, combined treatment of MIRA-1 with dexamethasone, doxorubicin or velcade displayed synergistic response in MM cells. Importantly, MIRA-1 alone or in combination with dexamethasone retarded tumour growth and prolonged survival without showing any untoward toxicity in the mice bearing MM tumour.

Conclusions:

Our data provide the preclinical framework for clinical evaluation of MIRA-1 as a novel therapeutic agent to improve patient outcome in MM.

Protein kinase CK2 inhibition down modulates the NF-κB and STAT3 survival pathways, enhances the cellular proteotoxic stress and synergistically boosts the cytotoxic effect of bortezomib on multiple myeloma and mantle cell lymphoma cells

CK2 is a pivotal pro-survival protein kinase in multiple myeloma that may likely impinge on bortezomib-regulated cellular pathways. In the present study, we investigated CK2 expression in multiple myeloma and mantle cell lymphoma, two bortezomib-responsive B cell tumors, as well as its involvement in bortezomib-induced cytotoxicity and signaling cascades potentially mediating bortezomib resistance. In both tumors, CK2 expression correlated with that of its activated targets NF-κB and STAT3 transcription factors. Bortezomib-induced proliferation arrest and apoptosis were significantly amplified by the simultaneous inhibition of CK2 with two inhibitors (CX-4945 and K27) in multiple myeloma and mantle cell lymphoma cell lines, in a model of multiple myeloma bone marrow microenvironment and in cells isolated from patients. CK2 inhibition empowered bortezomib-triggered mitochondrial-dependent cell death. Phosphorylation of NF-κB p65 on Ser529 (a CK2 target site) and rise of the levels of the endoplasmic reticulum stress kinase/endoribonuclease Ire1α were markedly reduced upon CK2 inhibition, as were STAT3 phospho Ser727 levels. On the contrary, CK2 inhibition increased phospho Ser51 eIF2α levels and enhanced the bortezomib-dependent accumulation of poly-ubiquitylated proteins and of the proteotoxic stress-associated chaperone Hsp70. Our data suggest that CK2 over expression in multiple myeloma and mantle cell lymphoma cells might sustain survival signaling cascades and can antagonize bortezomib-induced apoptosis at different levels. CK2 inhibitors could be useful in bortezomib-based combination therapies.

New proteasome inhibitors in myeloma

Proteasome inhibition has a validated role in cancer therapy since the successful introduction of bortezomib for the treatment of multiple myeloma (MM) and mantle cell lymphoma, leading to the development of second-generation proteasome inhibitors (PI) for MM patients in whom currently approved therapies have failed. Five PIs have reached clinical evaluation, with the goals of improving efficacy and limiting toxicity, including peripheral neuropathy (PN). Carfilzomib, an epoxyketone with specific chymothrypsin-like activity, acts as an irreversible inhibitor and was recently FDA approved for the response benefit seen in relapsed and refractory MM patients previously treated with bortezomib, thalidomide and lenalidomide. ONX-0912 is now under evaluation as an oral form with similar activity. The boronate peptides MLN9708 and CEP-18770 are orally bioactive bortezomib analogs with prolonged activity and greater tissue penetration. NPI-0052 (marizomib) is a unique, beta-lactone non-selective PI that has been shown to potently overcome bortezomib resistance in vitro. All of these second-generation PIs demonstrate encouraging anti-MM activity and appear to reduce the incidence of PN, with clinical trials ongoing.

Marine-derived angiogenesis inhibitors for cancer therapy

Angiogenesis inhibitors have been successfully used for cancer therapy in the clinic. Many marine-derived natural products and their analogues have been reported to show antiangiogenic activities. Compared with the drugs in the clinic, these agents display interesting characteristics, including diverse sources, unique chemical structures, special modes of action, and distinct activity and toxicity profiles. This review will first provide an overview of the current marine-derived angiogenesis inhibitors based on their primary targets and/or mechanisms of action. Then, the marine-derived antiangiogenic protein kinase inhibitors will be focused on. And finally, the clinical trials of the marine-derived antiangiogenic agents will be discussed, with special emphasis on their application potentials, problems and possible coping strategies in their future development as anticancer drugs.

Perifosine and sorafenib combination induces mitochondrial cell death and antitumor effects in NOD/SCID mice with Hodgkin lymphoma cell line xenografts

The effects of the Akt inhibitor perifosine and the RAF/MEK/ERK inhibitor sorafenib were investigated using two CD30(+)Hodgkin lymphoma cell lines (L-540 and HDLM-2) and the CD30(-)HD-MyZ histiocytic cell line. The combined perifosine/sorafenib treatment significantly inhibited mitogen-activated protein kinase and Akt phosphorylation in two of the three cell lines. Profiling of the responsive cell lines revealed that perifosine/sorafenib decreased the amplitude of transcriptional signatures that are associated with the cell cycle, DNA replication and cell death. Tribbles homolog 3 (TRIB3) was identified as the main mediator of the in vitro and in vivo antitumor activity of perifosine/sorafenib. Combined treatment compared with single agents significantly suppressed cell growth (40-80%, P<0.001), induced severe mitochondrial dysfunction and necroptotic cell death (up to 70%, P<0.0001) in a synergistic manner. Furthermore, in vivo xenograft studies demonstrated a significant reduction in tumor burden (P<0.0001), an increased survival time (81 vs 45 days, P<0.0001), an increased apoptosis (2- to 2.5-fold, P<0.0001) and necrosis (2- to 8-fold, P<0.0001) in perifosine/sorafenib-treated animals compared with mice receiving single agents. These data provide a rationale for clinical trials using perifosine/sorafenib combination.

Novel players in multiple myeloma pathogenesis: role of protein kinases CK2 and GSK3

Multiple myeloma (MM) is an incurable plasma cell malignancy, which causes a significant morbidity due to organ damage and bone tissue destruction. In recent years, novel drugs have become available for MM therapy thanks to a more deepened knowledge of this disease's pathogenesis. The perspective of employing targeted therapies has considerably changed the expectations on the clinical outcome for patients affected by this malignancy and among the targetable molecules identified for MM therapy are several protein kinases, which have been proven to play relevant roles in supporting malignant plasma cell growth by regulating critical signaling cascades and by sustaining oncogenic mechanisms. Protein kinase CK2 (formerly known as casein kinase 2) and GSK3 (glycogen synthase kinase 3) are two multifaceted serine-threonine kinases whose task in the pathogenesis of malignant cell growth is increasingly emerging both in solid and blood tumors. In hematologic malignancies, CK2 and GSK3 have been shown to play an oncogenic function in chronic and acute leukemias as well as in MM. They have been demonstrated to act by impinging on pivotal signaling pathways that control malignant clone growth. We will herein briefly review the more recent advancements on the role of these two kinases in regulating the NF-κB, STAT3 and endoplasmic reticulum (ER) stress/unfolded protein response (UPR) signaling in MM and discuss the rationale of using small selective inhibitors as a therapeutic strategy to hamper the growth of malignant plasma cells or to improve the MM-associated bone disease.

Novel anticancer agents for multiple myeloma: a review of the evidence for their therapeutic and economic value

Recent advances in oncology treatment have improved patient outcomes at the expense of increasing healthcare costs. The indication multiple myeloma is especially characterized by a recent and continuing flood of expensive novel agents. A review encompassing all elements necessary to perform an economic evaluation of novel agents for multiple myeloma was conducted for thalidomide, bortezomib and lenalidomide. Improvements in efficacy have led to a switch from conventional therapy to novel agents as standard therapy. Incremental cost-effectiveness ratios for novel agents alone or in combination with conventional agents were generally regarded to be within acceptable ranges. Conflicting results were reported for the incremental cost-effectiveness of bortezomib versus lenalidomide, as unresolved questions remain regarding their comparative effectiveness. Future economic evaluations will require an assessment of the cost-effectiveness of these agents in terms of sequence within the treatment paradigm and in combination with one another.

Protein kinase CK2 protects multiple myeloma cells from ER stress-induced apoptosis and from the cytotoxic effect of HSP90 inhibition through regulation of the unfolded protein response

PURPOSE

Protein kinase CK2 promotes multiple myeloma cell growth by regulating critical signaling pathways. CK2 also modulates proper HSP90-dependent client protein folding and maturation by phosphorylating its co-chaperone CDC37. Because the endoplasmic reticulum (ER) stress/unfolded protein response (UPR) is central in myeloma pathogenesis, we tested the hypothesis that the CK2/CDC37/HSP90 axis could be involved in UPR in myeloma cells.

EXPERIMENTAL DESIGN

We analyzed CK2 activity upon ER stress, the effects of its inactivation on the UPR pathways and on ER stress-induced apoptosis. The consequences of CK2 plus HSP90 inhibition on myeloma cell growth in vitro and in vivo and CK2 regulation of HSP90-triggered UPR were determined.

RESULTS

CK2 partly localized to the ER and ER stress triggered its kinase activity. CK2 inhibition reduced the levels of the ER stress sensors IRE1α and BIP/GRP78, increased phosphorylation of PERK and EIF2α, and enhanced ER stress-induced apoptosis. Simultaneous inactivation of CK2 and HSP90 resulted in a synergic anti-myeloma effect (combination index = 0.291) and in much stronger alterations of the UPR pathways as compared with the single inhibition of the two molecules. Cytotoxicity from HSP90 and CK2 targeting was present in a myeloma microenvironment model, on plasma cells from patients with myeloma and in an in vivo mouse xenograft model. Mechanistically, CK2 inhibition led to a reduction of IRE1α/HSP90/CDC37 complexes in multiple myeloma cells.

CONCLUSIONS

Our results place CK2 as a novel regulator of the ER stress/UPR cascades and HSP90 function in myeloma cells and offer the groundwork to design novel combination treatments for this disease.

Preclinical activity, pharmacodynamic, and pharmacokinetic properties of a selective HDAC6 inhibitor, ACY-1215, in combination with bortezomib in multiple myeloma

Histone deacetylase (HDAC) enzymatic activity has been linked to the transcription of DNA in cancers including multiple myeloma (MM). Therefore, HDAC inhibitors used alone and in combination are being actively studied as novel therapies in MM. In the present study, we investigated the preclinical activity of ACY-1215, an HDAC6-selective inhibitor, alone and in combination with bortezomib in MM. Low doses of ACY-1215 combined with bortezomib triggered synergistic anti-MM activity, resulting in protracted endoplasmic reticulum stress and apoptosis via activation of caspase-3, caspase-8, and caspase-9 and poly (ADP) ribosome polymerase. In vivo, the anti-MM activity of ACY-1215 in combination with bortezomib was confirmed using 2 different xenograft SCID mouse models: human MM injected subcutaneously (the plasmacytoma model) and luciferase-expressing human MM injected intravenously (the disseminated MM model). Tumor growth was significantly delayed and overall survival was significantly prolonged in animals treated with the combination therapy. Pharmacokinetic data showed peak plasma levels of ACY-1215 at 4 hours after treatment coincident with an increase in acetylated α-tubulin, a marker of HDAC6 inhibition, by immunohistochemistry and Western blot analysis. These studies provide preclinical rationale for acetylated α-tubulin use as a pharmacodynamic biomarker in future clinical trials.

The pan-histone deacetylase inhibitor CR2408 disrupts cell cycle progression, diminishes proliferation and causes apoptosis in multiple myeloma cells

In view of the fact that histone deacetylases (HDACs) are promising targets for myeloma therapy, we investigated the effects of the HDAC inhibitor CR2408 on multiple myeloma (MM) cells in vitro. CR2408 is a direct pan-HDAC inhibitor and inhibits all known 11 HDACs with a 50% inhibitory concentration (IC(50) ) of 12 nmol/l (HDAC 6) to 520 nmol/l (HDAC 8). Correspondingly, CR2408 induces hyperacetylation of histone H4, inhibits cell growth and strongly induces apoptosis (IC(50) =0.1-0.5 μmol/l) in MM cell lines and primary MM cells. CR2408 leads to fragmentation of cells and induces an accumulation in the subG1 phase accompanied with moderately decreased levels of cyclin D1 and cdk4 and strongly decreased levels of cdc25a, pRb and p53. Interruption of the cell cycle is reflected by inhibition of cell proliferation and is accompanied by decreased phosphorylation of 4E-BP1 and p70S6k. Treatment with CR2408 results in increased protein levels of Bim and pJNK and downregulation of Bad and Bcl-xL and activation of Caspases 3, 8 and 9. Furthermore, as HDAC inhibitors have shown synergism with other drugs, these effects were investigated and synergism was observed for combinations of CR2408 with doxorubicin and bortezomib. In conclusion, we have identified potent anti-myeloma activity for this novel HDAC inhibitor that gives further insights into the biological sequelae of HDAC inhibition in MM.

Perifosine plus bortezomib and dexamethasone in patients with relapsed/refractory multiple myeloma previously treated with bortezomib: results of a multicenter phase I/II trial

PURPOSE

Novel agents have improved patient outcome in relapsed or relapsed/refractory multiple myeloma (MM). Preclinical data show that the novel signal transduction modulator, perifosine, enhances the cytotoxicity of dexamethasone and bortezomib. Clinical data suggest that perifosine in combination with dexamethasone has activity in relapsed or relapsed/refractory MM.

PATIENTS AND METHODS

In a phase I/II study, perifosine in combination with bortezomib with or without dexamethasone was prospectively evaluated in 84 patients with relapsed or relapsed/refractory MM. All were heavily pretreated and bortezomib exposed; 73% were refractory to bortezomib, and 51% were refractory to bortezomib and dexamethasone. The dose selected for the phase II study was perifosine 50 mg/d plus bortezomib 1.3 mg/m(2), with the addition of low-dose dexamethasone at 20 mg if progression occurred on perifosine plus bortezomib alone.

RESULTS

An overall response rate (ORR; defined as minimal response or better) of 41% was demonstrated with this combination in 73 evaluable patients, including an ORR of 65% in bortezomib-relapsed patients and 32% in bortezomib-refractory patients. Therapy was generally well tolerated; toxicities, including gastrointestinal adverse effects and fatigue, proved manageable. No treatment-related mortality was seen. Median progression-free survival was 6.4 months, with a median overall survival of 25 months (22.5 months in bortezomib-refractory patients).

CONCLUSION

Perifosine-bortezomib ± dexamethasone demonstrated encouraging activity in heavily pretreated bortezomib-exposed patients with advanced MM. A phase III trial is underway comparing perifosine-bortezomib plus dexamethasone with bortezomib-dexamethasone in patients with relapsed/refractory MM previously treated with bortezomib.

Disruption of IkappaB kinase (IKK)-mediated RelA serine 536 phosphorylation sensitizes human multiple myeloma cells to histone deacetylase (HDAC) inhibitors

Post-translational modifications of RelA play an important role in regulation of NF-κB activation. We previously demonstrated that in malignant hematopoietic cells, histone deacetylase inhibitors (HDACIs) induced RelA hyperacetylation and NF-κB activation, attenuating lethality. We now present evidence that IκB kinase (IKK) β-mediated RelA Ser-536 phosphorylation plays a significant functional role in promoting RelA acetylation, inducing NF-κB activation, and limiting HDACI lethality in human multiple myeloma (MM) cells. Immunoblot profiling revealed that although basal RelA phosphorylation varied in MM cells, Ser-536 phosphorylation correlated with IKK activity. Exposure to the pan-HDACIs vorinostat or LBH-589 induced phosphorylation of IKKα/β (Ser-180/Ser-181) and RelA (Ser-536) in MM cells, including cells expressing an IκBα "super-repressor," accompanied by increased RelA nuclear translocation, acetylation, DNA binding, and transactivation activity. These events were substantially blocked by either pan-IKK or IKKβ-selective inhibitors, resulting in marked apoptosis. Consistent with these events, inhibitory peptides targeting either the NF-κB essential modulator (NEMO) binding domain for IKK complex formation or RelA phosphorylation sites also significantly increased HDACI lethality. Moreover, IKKβ knockdown by shRNA prevented Ser-536 phosphorylation and significantly enhanced HDACI susceptibility. Finally, introduction of a nonphosphorylatable RelA mutant S536A, which failed to undergo acetylation in response to HDACIs, impaired NF-κB activation and increased cell death. These findings indicate that HDACIs induce Ser-536 phosphorylation of the NF-κB subunit RelA through an IKKβ-dependent mechanism, an action that is functionally involved in activation of the cytoprotective NF-κB signaling cascade primarily through facilitation of RelA acetylation rather than nuclear translocation.

In vitro effects of perifosine, bortezomib and lenalidomide against hematopoietic progenitor cells from healthy donors

The novel AKT inhibitor perifosine possesses myelopoiesis-stimulating effects in rodents. We studied the in vitro effects of the novel agents perifosine, bortezomib and lenalidomide in addition to adriamycin against normal human hematopoietic progenitor cells (HPC) using different clonogenic and non-clonogenic assays. All agents inhibited colony-forming unit (CFU) formation, perifosine inhibiting mainly CFU-granulocyte/macrophage formation and the other agents burst-forming unit-erythroid formation. Perifosine combined with lenalidomide or adriamycin tended to act antagonistically in suppressing CFU formation. Despite their inhibition of CFU formation, perifosine, bortezomib and lenalidomide induced only slight or moderate cytotoxicity in CD34(+) selected HPC, as assessed using different assays such as flow cytometry-based detection of activated caspases and immunohistochemistry studies (e.g., Ki-67 staining). In contrast to its myelopoiesis-stimulating effects in rodents, perifosine--like bortezomib and lenalidomide--suppresses the clonogenic potential of HPC from healthy donors in vitro and thus probably plays no role in preventing neutropenia or in shorting its duration after intensive chemotherapy. However, all these novel agents typically induce only slight or moderate suppression of the clonogenic potential or loss of viability of normal HPC at clinically achievable plasma concentrations, assuming that hematoxicity is manageable and functional HPC can be collected after treatment with these compounds.

Targeting NF-κB and HIF-1 pathways for the treatment of cancer: part I

The process of chronic inflammation is a common link which connects different kinds of environmental pollutants and infections with tumorigenesis. Transcription factor NF-κB is a common final target for many inflammatory and cell proliferation pathways, independent of the source of stimuli (e.g., cytokines, growth factors, environmental carcinogens, radiation, hypoxia, bacteria, and viruses). Over-activation of NF-κB has been confirmed in many tumors, resulting in worse prognosis for patient survival. Therefore, inhibition of cellular pathways for NF-κB activation is nowadays considered as a promising anti-cancer therapy and is extensively studied in clinical trials, or even has been adopted as an approved therapy in some kinds of cancer.

Future directions of next-generation novel therapies, combination approaches, and the development of personalized medicine in myeloma

Despite tangible progress in recent years, substantial therapeutic challenges remain in multiple myeloma (MM), particularly for patients at high risk for early relapse or death and for those with advanced multi-drug resistant disease and refractoriness to currently available combination regimens. Addressing these challenges requires identification of novel classes of anti-MM agents, their incorporation into safe and more effective combination regimens, and development of efficient algorithms to select the most appropriate therapeutic options for the clinical and molecular features of individual patients at a given time during their disease. Ideally, these goals can be facilitated by preclinical identification of the "driver" molecular lesions on which different myeloma subtypes exquisitely depend, and by informative preclinical models simulating the clinical setting(s) in which trials will be conducted. Large prospective studies of patients treated uniformly with contemporary clinical regimens are essential, but there is also a major need for flexibility in studying new regimens in the future. Long-term patient follow-up and integrated annotation of clinical (safety and efficacy) and correlative (molecular, biochemical, etc) data are also critical. Novel molecular profiling techniques will likely identify more clinically and biologically discrete subsets of patients with recurrent, even if infrequent, lesions. This molecular heterogeneity, combined with the increasing numbers of candidate therapeutic targets and respective investigational agents, may pose formidable challenges for the development and implementation of personalized medicine in MM. This review discusses these challenges, as well as potential strategies to address them, with the aim of making significant improvement in the clinical outcome of patients with MM.

Proteostasis: a new therapeutic paradigm for pulmonary disease

Among lung pathologies, α1AT, chronic obstructive pulmonary disease (COPD), emphysema, and asthma are diseases triggered by local environmental stress in the airway that we refer to herein collectively as airway stress diseases (ASDs). A deficiency of α-1-antitrypsin (α1AT) is an inherited genetic disorder that is a consequence of the misfolding of α1AT during protein synthesis in liver hepatocytes, reducing secretion to the plasma and delivery to the lung. Deficiency of α1AT in the lung triggers a similar pathological phenotype to other ASDs. Moreover, the loss of α1AT in the lung is a well-known environmental risk factor for COPD/emphysema. To date there are no effective therapeutic approaches to address ASDs, which reflects a general lack of understanding of their cellular basis. Herein, we propose that ASDs are disorders of proteostasis. That is, they are initiated and propagated by a common theme-a challenge to protein folding capacity maintained by the proteostasis network (PN) (see Balch et al., Science 2008;319:916-919). The PN is a network of chaperones and degradative components that generates and manages protein folding pathways responsible for normal human physiology. In ASD, we suggest that the PN system fails to respond to the increased burden of unfolded proteins due to genetic and environmental stresses, thus triggering pulmonary pathophysiology. We introduce the enabling concept of proteostasis regulators (PRs), small molecules that regulate signaling pathways that control the composition and activity of PN components, as a new and general approach for therapeutic management of ASDs.

Hes1 expression and CYLD repression are essential events downstream of Notch1 in T-cell leukemia

Notch activation is a current event in T Acute Lymphoblastic Leukemia (T-ALL) but the downstream elements that are able to support Notch-dependent leukemias are not well characterized. We have recently shown that the Notch-Hes1-CYLD-NFkB axis is crucial in the maintenance of T-ALL, but detailed evaluation of the contribution of each one of these elements is still missing. Here we use a Notch1-induced leukemia in vivo model to study the effect of silencing the Notch-target gene, Hes1, or over-expressing the Hes1-target, CYLD. We here show that both strategies completely abolish the ability of constitutive active Notch1 to generate T-ALL.

Outcome and toxicity in the modern era of new drugs for multiple myeloma: a reappraisal for comparison with future investigational trials

The introduction of new drugs such as thalidomide, lenalidomide, and bortezomib has led to novel treatment strategies and significantly improved the outcome of patients with multiple myeloma (MM). The enhanced knowledge of myeloma pathogenesis has allowed the identification of new therapeutic targets and many clinical trials are either planned or in progress to evaluate these more selective drugs in the near future. The results of these studies, however, will have to be compared with the results of existing novel therapies for the treatment of MM in order to define whether new protocols do not duplicate current new standards and constitute a real improvement. We reviewed the results of a series of phase I, II, III studies with thalidomide, lenalidomide, and bortezomib combinations for newly diagnosed MM in order to define a reasonable standard in terms of activity, efficacy, and toxicity and to have a potentially useful starting point for comparisons with future investigational trials. Three-drug regimens appear to double the complete remission (CR) rate (20%), though regimens containing 4 drugs triple the CR rate (30%), compared with those containing only 2 agents (10%). These improvements in the depth and quality of response translate into a progressive increase in the progression-free survival rate at 2 years (from approximately 54%-62% to 75%, respectively). Conversely, by using additional agents, a marked increase in hematologic toxicity has been described (8%, 28%, and 28% respectively), whereas nonhematologic toxicity appears to be similar (26%, 24%, and 27%, respectively). These results suggest that new trials in the future will constitute significant progress if they can improve on the current relatively favorable efficacy/toxicity ratio. Nonetheless, exciting new combinations in development do hold promise and results from these studies are eagerly awaited.

Smoldering (asymptomatic) multiple myeloma: revisiting the clinical dilemma and looking into the future

Recent studies show that multiple myeloma (MM) is consistently preceded by an asymptomatic precursor state. Smoldering MM (SMM) is a MM precursor defined by an M-protein concentration >or= 3 g/dL and/or >or= 10% bone marrow plasma cells, in the absence of end-organ damage. Compared with individuals diagnosed with monoclonal gammopathy of undetermined significance (MGUS), patients with SMM have a much higher annual risk of developing MM. However, based on clinical observations, the natural history of SMM varies greatly, from stable MGUS-like disease to highly progressive disease. Using conventional clinical markers, SMM patients can be stratified into 3 risk groups. Importantly, because of considerable molecular heterogeneity, we currently lack reliable markers to predict prognosis for individual SMM patients. Furthermore, until recently, potent drugs with reasonable toxicity profiles have not been available for the development of early MM treatment strategies. Consequently, current clinical guidelines emphasize the application of close clinical monitoring followed by treatment when the patient develops symptomatic MM. This review focuses on novel biomarkers, molecular profiles, and microenvironmental interactions of interest in myelomagenesis. We also discuss how the integration of novel biologic markers and clinical monitoring of SMM could facilitate the development of early treatment strategies for high-risk SMM patients in the future.

Development of early treatment strategies for high-risk myeloma precursor disease in the future

Smoldering myeloma (SMM) is a precursor state of multiple myeloma. It is defined by an M-protein concentration ≥3 g/dL and/or ≥10% clonal bone marrow plasma cells, in the absence of end-organ damage. Based on clinical observations, the natural history of SMM varies greatly, from stable, monoclonal gammopathy of undetermined significance (MGUS)-like disease to highly progressive disease. Using conventional clinical markers, SMM patients can be stratified into clinical risk groups. However, due to considerable molecular heterogeneity, we currently lack reliable markers to predict prognosis for individual SMM patients. Based on the International Myeloma Working Group 2010 guidelines, patients diagnosed with MGUS and SMM should not be treated outside of clinical trials. Overall, treatment trials for MGUS patients are complicated, as these individuals are relatively healthy and the majority has a low life-time risk of progression, especially when other causes of death are taken into account. In contrast to MGUS, early treatment strategies for SMM are particularly attractive, as the rate of progression to multiple myeloma is substantially higher. Until recently, potent drugs with reasonable toxicity profiles have not been available for the development of early multiple myeloma treatment strategies. This review discusses how the integration of novel biological markers and clinical monitoring of SMM could facilitate the development of early treatment strategies for high-risk SMM patients in the future.

Novel therapeutic strategies in multiple myeloma: role of the heat shock protein inhibitors

Despite advances in understanding the molecular pathogenesis of multiple myeloma and promising new therapies, almost all patients eventually relapse with resistant disease. There is therefore a strong rationale for combining novel therapies that target intrinsic molecular pathways mediating multiple myeloma cell resistance. One such protein family is the heat shock proteins (HSP), especially the HSP90 family. Heat shock protein inhibitors have been identified as promising cancer treatments as, while they only inhibit a single biologic function, the chaperone-protein association, their effect is widespread as it results in the destruction of numerous client proteins. This article reviews the preclinical and clinical data, which support the testing of HSP90 inhibitors as cancer drugs and update the reader on the current status of the ongoing clinical trials of HSP90 inhibitors in multiple myeloma.

The DAC system and associations with multiple myeloma

Despite the clear progress achieved in recent years in the treatment of MM, most patients eventually relapse and therefore novel therapeutic options are still necessary for these patients. In this regard, several drugs that target specific mechanisms of the tumor cells are currently being explored in the preclinical and clinical setting. This manuscripts offers a review of the rationale and current status of the antimyeloma activity of one of the most relevant examples of these targeted drugs: deacetylase inhibitors (DACi). Several studies have demonstrated the prooncogenic activity of deacetylases (DACs) through the targeting not only of histones but also of non histone proteins relevant to tumor progression, such as p53, E2F family members, Bcl-6, Hsp90, HIF-1α or Nur77. This fact together with the DACs overexpression present in several tumors, has prompted the development of some DACi with potential antitumor effect. This situation is also evident in the case of MM as two mechanisms of DACi, the inhibition of the epigenetic inactivation of p53 and the blockade of the unfolded protein response, through the inhibition of the aggressome formation (by targeting DAC6) and the inactivation of the chaperone system (by acetylating HSP-90), provides the rationale for the exploration of the potential antimyeloma activity of these compounds. Several DACi with different chemical structure and different selectivity for targeting the DAC families have been tested in MM. Their preclinical activity in monotherapy has been quite exciting and has been described to be mediated by various mechanisms: the induction of apoptosis and cell cycle arrest mainly by the upregulation of p21; the interferece with the interaction between plasma cells and the microenvironment, by reducing the expression and signalling of several cytokines or by inhibiting angiogenesis. Finally they also have a role in protecting murine models from myeloma bone disease. Neverteless, the clinical activity in monotherapy of these drugs in relapsed/refractory MM patients has been very modest. This has prompted the development of combinations such as the one with bortezomib or lenalidomide and dexamethasone, which have already been taken into the clinics with positive preliminary results.

In vitro cytotoxicity of the novel antimyeloma agents perifosine, bortezomib and lenalidomide against different cell lines

The novel AKT inhibitor perifosine, a synthetic alkylphospholipid, is currently being investigated in clinical trials for the treatment of different hematological and oncological malignancies. The in vitro cytotoxicity of perifosine, bortezomib and lenalidomide against 6 cell lines derived from hematological malignancies was investigated using trypan blue staining, flow cytometry-based detection of activated caspases, Annexin V assays, immunohistochemistry studies (KI-67 and caspase-3 staining) and the immature-myeloid-information (IMI) technique. Perifosine and bortezomib induced concentration- and time-dependent cytotoxicity in all cell lines tested. Perifosine together with bortezomib largely exerted additive or synergistic effects with combination indices ranging from 1.13 to 0.22 for combined efficacies of 25% to 75% after 24-hour incubation. Lenalidomide-triggered cytotoxicity was low in all cell lines tested with any assay (less than 10% compared to the negative control). Finally, perifosine, but not bortezomib or lenalidomide, significantly increased the number of cells detected in the IMI channel. Perifosine and bortezomib- but not lenalidomide- trigger substantial cytotoxicity by caspase activation and mainly act additively or synergistically. The IMI technique might be a useful tool for studying cytotoxicity of agents like perifosine that interact mainly with the cellular membrane.

Schwann cell autophagy induced by SAHA, 17-AAG, or clonazepam can reduce bortezomib-induced peripheral neuropathy

BACKGROUND

The proteasome inhibitor bortezomib has improved the survival of patients with multiple myeloma but bortezomib-induced peripheral neuropathy (BiPN) has emerged as a serious potential complication of this therapy. Animal studies suggest that bortezomib predominantly causes pathological changes in Schwann cells. A tractable system to evaluate combination drugs for use with bortezomib is essential to enable continuing clinical benefit from this drug.

METHODS

Rat schwannoma cells were pretreated with vincristine (VCR), histone deacetylase inhibitors, anticonvulsants, or a heat-shock protein 90 (HSP90) inhibitor. To then monitor aggresome formation as a result of proteasome inhibition and the activation of chaperone-mediated autophagy (CMA), we performed double-labelling immunofluorescent analyses of a cellular aggregation-prone protein marker.

RESULTS

Aggresome formation was interrupted by VCR, whereas combination treatments with bortezomib involving suberoylanilide hydroxamic acid, 17-allylamino-17-demethoxy-geldanamycin, or clonazepam appear to facilitate the disposal of unfolded proteins via CMA, inducing HSP70 and lysosome-associated membrane protein type 2A (LAMP-2A).

CONCLUSIONS

This schwannoma model can be used to test BiPN-reducing drugs. The present data suggest that aggresome formation in Schwann cells is a possible mechanism of BiPN, and drugs that induce HSP70 or LAMP-2A have the potential to alleviate this complication. Combination clinical trials are warranted to confirm the relevance of these observations.

A defucosylated anti-CD317 antibody exhibited enhanced antibody-dependent cellular cytotoxicity against primary myeloma cells in the presence of effectors from patients

The humanized monoclonal antibody (mAb) against CD317 antigen (anti-HM1.24 antibody; AHM), which is highly expressed on multiple myeloma (MM), induces antibody-dependent cellular cytotoxicity (ADCC). However, the antitumor activity of AHM in the clinical setting has not been clearly demonstrated. In this study, we produced defucosylated AHM and evaluated its potency for clinical application by performing autologous ADCC assays against primary MM cells from patients. Defucosylated AHM that was produced in rat myeloma YB2/0 cells expressing a low level of fucosyltransferase (FUT8) showed significant ADCC activity against three out of six primary MM cells in the presence of autologous PBMC, whereas conventional AHM did not. The results indicate that the potency of AHM to induce ADCC against primary MM cells was insufficient, but was significantly augmented by defucosylation. To generate more homogenous defucosylated monoclonal antibodies (mAb) for fermentation, we disrupted the GFT gene that encodes a GDP-fucose transporter in a CHO/DXB11 cell line by sequential homologous recombination. Analysis of the N-linked oligosaccharide in the defucosylated AHM produced by the established GFT(-/-)CHO cell line showed that a majority (93.4%) of the oligosaccharide was fucose free. The GFT(-/-) cells stably produced defucosylated mAb over passages. These results demonstrate that GTF(-/-)CHO-produced defucosylated AHM (GFTKO-AHM) will be a promising new therapeutic antibody against MM in the clinical setting.

Development of target-specific treatments in multiple myeloma

In the last decade, the novel agents lenalidomide, bortezomib, and thalidomide have dramatically improved outcomes for patients with multiple myeloma (MM). A number of new therapies with precise targets involved in MM cell growth and replication are now in development and have the potential for further improvements. Second-generation proteasome inhibitors and thalidomide derivatives may offer increased efficacy and safety. Investigational therapies with rationally selected targets in MM include inhibitors of histone deacetylase, heat shock protein 90, mammalian target of rapamycin, BCL2, Akt, mitogen-activated protein kinase, and telomerase. In addition, monoclonal antibodies directed against several targets have been developed and many are showing promise in initial clinical trials in MM. Interest in the ancient remedy of arsenic trioxide has been revived because of its proapoptotic effects on mitochondria, despite its established toxicities. In general, combination regimens are proving the most efficacious, which is to be expected given the multiple overlapping pathways responsible for MM growth and progression.

Protein kinase networks regulating glucocorticoid-induced apoptosis of hematopoietic cancer cells: fundamental aspects and practical considerations

Glucocorticoids (GCs) are integral components in the treatment protocols of acute lymphoblastic leukemia, multiple myeloma, and non-Hodgkin lymphoma owing to their ability to induce apoptosis of these malignant cells. Resistance to GC therapy is associated with poor prognosis. Although they have been used in clinics for decades, the signal transduction pathways involved in GC-induced apoptosis have only partly been resolved. Accumulating evidence shows that this cell death process is mediated by a communication between nuclear GR affecting gene transcription of pro-apoptotic genes such as Bim, mitochondrial GR affecting the physiology of the mitochondria, and the protein kinase glycogen synthase kinase-3 (GSK3), which interacts with Bim following exposure to GCs. Prevention of Bim up-regulation, mitochondrial GR translocation, and/or GSK3 activation are common causes leading to GC therapy failure. Various protein kinases positively regulating the pro-survival Src-PI3K-Akt-mTOR and Raf-Ras-MEK-ERK signal cascades have been shown to be activated in malignant leukemic cells and antagonize GC-induced apoptosis by inhibiting GSK3 activation and Bim expression. Targeting these protein kinases has proven effective in sensitizing GR-positive malignant lymphoid cells to GC-induced apoptosis. Thus, intervening with the pro-survival kinase network in GC-resistant cells should be a good means of improving GC therapy of hematopoietic malignancies.

Role of CAAT/enhancer binding protein homologous protein in panobinostat-mediated potentiation of bortezomib-induced lethal endoplasmic reticulum stress in mantle cell lymphoma cells

PURPOSE

Bortezomib induces unfolded protein response (UPR) and endoplasmic reticulum stress, as well as exhibits clinical activity in patients with relapsed and refractory mantle cell lymphoma (MCL). Here, we determined the molecular basis of the improved in vitro and in vivo activity of the combination of the pan-histone deacetylase inhibitor panobinostat and bortezomib against human, cultured, and primary MCL cells.

EXPERIMENTAL DESIGN

Immunoblot analyses, reverse transcription-PCR, and immunofluorescent and electron microscopy were used to determine the effects of panobinostat on bortezomib-induced aggresome formation and endoplasmic reticulum stress in MCL cells.

RESULTS

Treatment with panobinostat induced heat shock protein 90 acetylation; depleted the levels of heat shock protein 90 client proteins, cyclin-dependent kinase 4, c-RAF, and AKT; and abrogated bortezomib-induced aggresome formation in MCL cells. Panobinostat also induced lethal UPR, associated with induction of CAAT/enhancer binding protein homologous protein (CHOP). Conversely, knockdown of CHOP attenuated panobinostat-induced cell death of MCL cells. Compared with each agent alone, cotreatment with panobinostat increased bortezomib-induced expression of CHOP and NOXA, as well as increased bortezomib-induced UPR and apoptosis of cultured and primary MCL cells. Cotreatment with panobinostat also increased bortezomib-mediated in vivo tumor growth inhibition and improved survival of mice bearing human Z138C MCL cell xenograft.

CONCLUSION

These findings suggest that increased UPR and induction of CHOP are involved in enhanced anti-MCL activity of the combination of panobinostat and bortezomib.

Erucylphosphohomocholine, the first intravenously applicable alkylphosphocholine, is cytotoxic to acute myelogenous leukemia cells through JNK- and PP2A-dependent mechanisms

Alkylphospholipids and alkylphosphocholines (APCs) are promising antitumor agents, which target the plasma membrane and affect multiple signal transduction networks. We investigated the therapeutic potential of erucylphosphohomocholine (ErPC3), the first intravenously applicable APC, in human acute myelogenous leukemia (AML) cells. ErPC3 was tested on AML cell lines, as well as AML primary cells. At short (6-12 h) incubation times, the drug blocked cells in G2/M phase of the cell cycle, whereas, at longer incubation times, it decreased survival and induced cell death by apoptosis. ErPC3 caused JNK 1/2 activation as well as ERK 1/2 dephosphorylation. Pharmacological inhibition of caspase-3 or a JNK 1/2 inhibitor peptide markedly reduced ErPC3 cytotoxicity. Protein phosphatase 2A downregulation by siRNA opposed ERK 1/2 dephosphorylation and blunted the cytotoxic effect of ErPC3. ErPC3 was cytotoxic to AML primary cells and reduced the clonogenic activity of CD34(+) leukemic cells. ErPC3 induced a significant apoptosis in the compartment (CD34(+) CD38(Low/Neg) CD123(+)) enriched in putative leukemia-initiating cells. This conclusion was supported by ErPC3 cytotoxicity on AML blasts showing high aldehyde dehydrogenase activity and on the side population of AML cell lines and blasts. These findings indicate that ErPC3 might be a promising therapeutic agent for the treatment of AML patients.

The novel inhibitor of histone deacetylase resminostat (RAS2410) inhibits proliferation and induces apoptosis in multiple myeloma (MM) cells

Inhibition of histone deacetylase (HDAC) is a promising mechanism for novel, anti-myeloma agents. We investigated the effects of the novel HDAC inhibitor resminostat on multiple myeloma (MM) cells in vitro. Resminostat is a potent inhibitor of HDACs 1, 3 and 6 [50% inhibitory concentration (IC50)=43-72 nmol/l] representing HDAC classes I and II and induces hyperacetylation of histone H4 in MM cells. Low micromolar concentrations of resminostat abrogated cell growth and strongly induced apoptosis (IC50=2.5-3 micromol/l in 3 out of 4 MM cell lines) in MM cell lines as well as primary MM cells. At 1 micromol/l, resminostat inhibited proliferation and induced G0/G1 cell cycle arrest in 3 out of 4 MM cell lines accompanied with decreased levels of cyclin D1, cdc25a, Cdk4 and pRb as well as upregulation of p21. Resminostat decreased phosphorylation of 4E-BP1 and p70S6k indicating an interference with Akt pathway signalling. Treatment with resminostat resulted in increased protein levels of Bim and Bax and decreased levels of Bcl-xL. Caspases 3, 8 and 9 were activated by resminostat. Furthermore, synergistic effects were observed for combinations of resminostat with melphalan and the proteasome inhibitors bortezomib and S-2209. In conclusion, we have identified potent anti-myeloma activity for this novel HDAC inhibitor.

Antibody-maytansinoid conjugates for the treatment of myeloma

Despite recent advances in the treatment of multiple myeloma, new agents are still needed to improve the outcome for patients. The established success of monoclonal antibodies in the treatment of some cancers has promoted interest in developing antibody-based therapies for multiple myeloma. Efforts have included the development of antibodies conjugated to potent cytotoxic moieties that combine the specificity of anti-myeloma-targeting antibodies with highly active anti-tumor compounds. Two such immunoconjugates currently in clinical development are composed of antibodies that target cell surface proteins found on multiple myeloma cells, and are coupled to cytotoxic maytansinoids. IMGN901 targets the neural cell adhesion molecule, CD56, which is expressed on the majority of myeloma cells, as well as on other cancers, while BT062 targets CD138, a primary diagnostic marker for multiple myeloma. In this review, we discuss the preclinical and early clinical data for these two promising new antibody-based anti-myeloma agents.

Update on Hsp90 inhibitors in clinical trial

Twenty-five years ago the first small molecule inhibitors of Hsp90 were identified. In the intervening years there has been dramatic progress in basic scientific understanding of the Hsp90 chaperone machinery and in the role of Hsp90 in malignancy. The first-in-class Hsp90 inhibitor 17-AAG entered into Phase I clinical trials in 1999. There are now 13 Hsp90 inhibitors in clinical trial, representing multiple drug classes, and hundreds of patients have been treated in adult oncology and pediatric oncology trials. This review will provide an overview of the clinical trial results thus far. In addition, pivotal issues in further development of Hsp90 inhibitors as anticancer drugs will be discussed.