Second-generation Proteasome Inhibitor Research Articles

Inhibitors for the Immuno‐ and Constitutive Proteasome: Current and Future Trends in Drug Development

Proteolytic degradation is an essential cellular process which is primarily carried out by the 20S proteasome core particle (CP), a protease of 720 kDa and 28 individual subunits. As a result of its central functional role, the proteasome represents an attractive drug target that has been extensively investigated during the last decade and validated by the approval of bortezomib by the US Food and Drug Administration (FDA). Currently, several optimized second-generation proteasome inhibitors are being explored as anticancer drugs in clinical trials, and most of them target both constitutive proteasomes (cCPs) and immunoproteasomes (iCPs). However, selective inhibition of the iCPs, a distinct class of proteasomes predominantly expressed in immune cells, appears to be a promising therapeutic rationale for the treatment of autoimmune disorders. Although a few selective agents have already been identified, the recently determined crystal structure of the iCP will further promote the development and optimization of iCP-selective compounds.

Imaging Features of Extramedullary, Relapsed, and Refractory Multiple Myeloma involving the Liver Across Treatment With Cyclophosphamide, Lenalidomide, Bortezomib, and Dexamethasone

A 55-year-old white woman presented in June 2003 with stage IIIA Durie-Salmon immunoglobulin (Ig) G κ multiple myeloma (MM) and was initially treated with thalidomide and dexamethasone followed by cyclophosphamide, with concurrent bisphosphonate (zoledronic acid), and intensified by autologous stem-cell transplant (ASCT) after high-dose melphalan conditioning. She remained in complete remission until December 2008, when she experienced relapse with occipital plasmacytoma and symptomatic extramedullary disease (EMD) arising from her skeleton. She was treated with an experimental second-generation proteasome inhibitor (NPI-0052, 0.7 mg/m2 administered intravenously [IV]), combined with low-dose weekly oral dexamethasone. She had evidence of clinical response (disease stabilization and symptomatic improvement). Treatment was completed after 6 months, and she declined maintenance options other than bisphosphonate.

InactivatingPSMB5Mutations and P-Glycoprotein (Multidrug Resistance-Associated Protein/ATP-Binding Cassette B1) Mediate Resistance to Proteasome Inhibitors: Ex Vivo Efficacy of (Immuno)Proteasome Inhibitors in Mononuclear Blood Cells from Patients with Rheumatoid Arthritis

Bortezomib (BTZ), a registered proteasome inhibitor (PI) for multiple myeloma, has also been proposed as a potential antirheumatic agent. Its reported side effects, however, make it unappealing for long-term administration, and resistance may also develop. To overcome this, second-generation PIs became available. Here, we investigated whether a novel class of peptide epoxyketone-based PIs, including carfilzomib, N-((S)-3-methoxy-1-(((S)-3-methoxy-1-(((S)-1-((R)-2-methyloxiran-2-yl)-1-oxo-3-phenylpropan-2-yl)amino)-1-oxopropan-2-yl)amino)-1-oxopropan-2-yl)-2-methylthiazole-5-carboxamide (ONX0912), and (S)-3-(4-methoxyphenyl)-N-((S)-1-((S)-2-methyloxiran-2-yl)-1-oxo-3-phenylpropan-2-yl)-2-((S)-2-(2-morpholinoacetamido)propanamido)propanamide (ONX0914), might escape two established BTZ-resistance mechanisms: 1) mutations in the proteasome β5 subunit (PSMB5) targeted by these PIs, and 2) drug efflux mediated by ATP-binding cassette transporters. THP1 myeloid sublines with acquired resistance to BTZ (54- to 235-fold) caused by mutations in the PSMB5 gene displayed marked cross-resistance but less pronounced cross-resistance to carfilzomib (9- to 32-fold), ONX0912 (39- to 62-fold), and ONX0914 (27- to 97-fold). As for ATP-binding cassette transporter-mediated efflux, lymphoid CEM/VLB cells with P-glycoprotein (Pgp)/multidrug resistance 1 overexpression exhibited substantial resistance to carfilzomib (114-fold), ONX0912 (23-fold), and ONX0914 (162-fold), whereas less resistance to BTZ (4.5-fold) was observed. Consistently, β5 subunit-associated chymotrypsin-like proteasome activity was significantly less inhibited in these CEM/VLB cells. Ex vivo analysis of peripheral blood mononuclear cells from therapy-naive patients with rheumatoid arthritis revealed that, although basal Pgp levels were low, P-glycoprotein expression compromised the inhibitory effect of carfilzomib and ONX0914. However, the use of P121 (reversin 121), a Pgp transport inhibitor, restored parental cell inhibitory levels in both CEM/VLB cells and peripheral blood mononuclear cells. These results indicate that the pharmacologic activity of these PIs may be hindered by drug resistance mechanisms involving PSMB5 mutations and PI extrusion via Pgp.

Pharmacogenomics of bortezomib test-dosing identifies hyperexpression of proteasome genes, especially PSMD4, as novel high-risk feature in myeloma treated with Total Therapy 3

AbstractGene expression profiling (GEP) of purified plasma cells 48 hours after thalidomide and dexamethasone test doses showed these agents' mechanisms of action and provided prognostic information for untreated myeloma patients on Total Therapy 2 (TT2). Bortezomib was added in Total Therapy 3 (TT3), and 48 hours after bortezomib GEP analysis identified 80 highly survival-discriminatory genes in a training set of 142 TT3A patients that were validated in 128 patients receiving TT3B. The 80-gene GEP model (GEP80) also distinguished outcomes when applied at baseline in both TT3 and TT2 protocols. In context of our validated 70-gene model (GEP70), the GEP80 model identified 9% of patients with a grave prognosis among those with GEP70-defined low-risk disease and 41% of patients with favorable prognosis among those with GEP70-defined high-risk disease. PMSD4 was 1 of 3 genes common to both models. Residing on chromosome 1q21, PSMD4 expression is highly sensitive to copy number. Both higher PSMD4 expression levels and higher 1q21 copy numbers affected clinical outcome adversely. GEP80 baseline-defined high risk, high lactate dehydrogenase, and low albumin were the only independent adverse variables surviving multivariate survival model. We are investigating whether second-generation proteasome inhibitors (eg, carfilzomib) can overcome resistance associated with high PSMD4 levels.

Impaired bortezomib binding to mutant β5 subunit of the proteasome is the underlying basis for bortezomib resistance in leukemia cells

Proteasome inhibition is a novel treatment for several hematological malignancies. However, resistance to the proteasome inhibitor bortezomib (BTZ, Velcade) is an emerging clinical impediment. Mutations in the β5 subunit of the proteasome, the primary target of BTZ, have been associated with drug resistance. However, the exact mechanism by which these mutations contribute to BTZ resistance, is still largely unknown. Toward this end, we here developed BTZ-resistant multiple myeloma (8226) and acute lymphoblastic leukemia (CCRF-CEM) cell line models by exposure to stepwise increasing concentrations of BTZ. Characterization of the various BTZ-resistant cells revealed upregulation of mutant β5 subunit of the proteasome. These newly identified β5-subunit mutations, along with previously described mutations, formed a mutation cluster region in the BTZ-binding pocket of the β5 subunit, that of the S1 specificity pocket in particular. Moreover, we provide the first evidence that the mechanism underlying BTZ resistance in these tumor cells is impaired binding of BTZ to the mutant β5 subunit of the proteasome. We propose that proteasome subunit overexpression is an essential compensatory mechanism for the impaired catalytic activity of these mutant proteasomes. Our findings further suggest that second-generation proteasome inhibitors that target the α7 subunit of the proteasome can overcome this drug resistance modality.

Experimental approaches in the treatment of multiple myeloma.

Myeloma therapy has undergone significant advances in recent years resulting in a marked improvement in survival. Knowledge of the active pathways involved in myeloma pathogenesis has led to the discovery of novel agents and greatly expanded the potential armamentarium available for treatment. This better understanding of the disease and resistance mechanisms has resulted in new agent classes that are being evaluated in preclinical and early clinical studies. In addition, dosing for existing agents is being optimized, and they are being given in new combinations. In this article, we review experimental agents that are showing promise in multiple myeloma treatment. New biological agents in clinical trials hold the promise of efficacy through novel mechanisms of action, with a significant reduction of dose-limiting toxicities compared with classic cytotoxic chemotherapeutics. Second-generation proteasome inhibitors and immunomodulatory agents are furthest along in clinical development, and histone deacetylase inhibitors, heat shock protein 90 inhibitors, Akt inhibitors and monoclonal antibodies are some of the other agents entering later-phase clinical trials. We also review developments in targeting the myeloma stem cell as an exciting new treatment direction.

Molecular Targeted Approaches in Mantle Cell Lymphoma

Mantle cell lymphoma (MCL) is a malignancy of mature B cells characterized by the translocation t(11;14) that leads to aberrant expression of cyclin D1. Response to first-line chemotherapy is good, but most patients relapse, resulting in a median survival of 5 to 7 years. The important PI3K/AKT/mTOR pathway can be targeted with small molecules. mTOR inhibitors have clinical activity and temsirolimus has been approved in Europe. Second-generation mTOR inhibitors and the PI3K inhibitor CAL-101 offer additional means to target the pathway. Promising results with the BTK inhibitor PCI-32765 suggest that B-cell receptor signaling could play a role. For unknown reasons, MCL appears to be particularly sensitive to disruption of protein homeostasis. The proteasome inhibitor bortezomib achieves responses in up to 50% of relapsed patients. Much work has been done in elucidating the mechanism of its cytotoxicity, its incorporation into combination therapies, and the development of second-generation proteasome inhibitors. Deacetylase and HSP90 inhibitors are also promising classes of drugs that can synergize with proteasome inhibitors. Finally, BH3 mimetics are emerging as tools to sensitize tumor cells to chemotherapy. Participation in clinical trials offers patients an immediate chance to benefit from these advances and is essential to maintain the momentum of progress.

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.

First-in-human, phase I dose-escalation study of investigational drug MLN9708, a second-generation proteasome inhibitor, in advanced nonhematologic malignancies.

3071 Background: The investigational drug MLN9708 has shown antitumor efficacy in a wide range of tumor xenografts. It dissociates from the proteasome faster and has greater tissue penetration than...

Activation of EGFR by proteasome inhibition requires HB-EGF in pancreatic cancer cells

Resistance to drug treatments underlies the high lethality of pancreatic ductal adenocarcinoma. Along with others, we have recently identified that proteasome inhibition is a promising therapeutic option in this highly refractory disease. The pleiotropic effects of proteasome inhibition include the activation of apoptotic signaling pathways and also antiapoptotic signaling pathways such as EGFR, AKT and the MAP kinases that reduce the apoptotic potential of this class of drug. In this study, we sought to determine the mechanism behind the activation of EGFR in response to proteasome inhibition in pancreatic cancer cells. We found that the second-generation proteasome inhibitor NPI-0052 induced the mRNA transcription of several EGFR family ligands (EGF, HB-EGF and epiregulin), however only increases in HB-EGF were detected at the protein level. Using both pharmacological inhibitors and lentiviral-mediated shRNA knockdown of EGFR ligand expression, we discovered that ligand cleavage by MMP/ADAMs and HB-EGF expression is required for activation of EGFR in response to proteasome inhibition. Furthermore, we discover that induction of HB-EGF is dependent on reactive oxygen species and p38-MAPK signaling but not ERK and that the transcription factor SP-1 is involved in NPI-0052-induced HB-EGF transcription. Together, these results indicate that stress signaling leading to induction of HB-EGF expression and increases in MMP/ADAM-dependent HB-EGF cleavage are responsible for proteasome inhibitor-induced activation of EGFR in pancreatic cancer cells.

Evaluation of the Proteasome Inhibitor MLN9708 in Preclinical Models of Human Cancer

The proteasome was validated as an oncology target following the clinical success of VELCADE (bortezomib) for injection for the treatment of multiple myeloma and recurring mantle cell lymphoma. Consequently, several groups are pursuing the development of additional small-molecule proteasome inhibitors for both hematologic and solid tumor indications. Here, we describe MLN9708, a selective, orally bioavailable, second-generation proteasome inhibitor that is in phase I clinical development. MLN9708 has a shorter proteasome dissociation half-life and improved pharmacokinetics, pharmacodynamics, and antitumor activity compared with bortezomib. MLN9708 has a larger blood volume distribution at steady state, and analysis of 20S proteasome inhibition and markers of the unfolded protein response confirmed that MLN9708 has greater pharmacodynamic effects in tissues than bortezomib. MLN9708 showed activity in both solid tumor and hematologic preclinical xenograft models, and we found a correlation between greater pharmacodynamic responses and improved antitumor activity. Moreover, antitumor activity was shown via multiple dosing routes, including oral gavage. Taken together, these data support the clinical development of MLN9708 for both hematologic and solid tumor indications.

Building on bortezomib: second-generation proteasome inhibitors as anti-cancer therapy

Inhibition of the proteasome (a highly abundant enzymatic complex responsible for intracellular protein turnover) is an effective anti-cancer therapeutic approach, as demonstrated by the first-in-class agent bortezomib. Various new proteasome inhibitors are now in development, including peptide boronic acid analogs MLN9708 and CEP-18770, peptide epoxyketones carfilzomib and PR-047, and NPI-0052, a beta-lactone compound. All are potent inhibitors of proteasome activity in vitro but show differences in enzyme binding kinetics, which might affect their pharmacology and result in different efficacy and safety profiles. Here, we review the second-generation proteasome inhibitors and assess the potential pharmacologic impact of their different chemical properties.

Drug discovery and assay development in the ubiquitin–proteasome system

The observation that tumour cells are more sensitive to pharmacological inhibition of the proteasome than normal cells has led to the development of the proteasome inhibitor bortezomib. To date, this is the only proteasome inhibitor that has been approved for clinical use. The clinical success of bortezomib, combined with the occurrence of adverse effects and the development of clinical resistance against this compound, has initiated the development of a broad range of second-generation proteasome inhibitors as well as of assays that can be used to establish a relationship between the extent and type of proteasome inhibition and the effectiveness of a particular drug. In the present paper, we discuss new strategies that may be used in the future to overcome drug resistance and to broaden the use of proteasome inhibitors for the treatment of both cancer and infectious and autoimmune disease.

Abstract B40: Development of a pharmacodynamic assay for the second-generation proteasome inhibitor MLN9708 in clinical trials of multiple myeloma

Abstract The ubiquitin-proteasome system processes the majority of cellular proteins and is the principal pathway by which cells regulate protein homeostasis. The successful development of VELCADE® (bortezomib) for Injection for multiple myeloma and previously treated mantle cell lymphoma has validated the proteasome as a therapeutic target for the treatment of malignancies. MLN9708 is a second-generation reversible proteasome inhibitor developed to achieve greater oral bioavailability, improved pharmacokinetics and greater antitumor activity than bortezomib. MLN9708 is currently in human clinical development for both hematological and non-hematological malignancies. MLN9708 immediately hydrolyzes to the biologically active form MLN2238 upon exposure to aqueous solutions or plasma, and MLN2238 was used for all preclinical studies described below. In vitro, MLN2238 inhibited 20S proteasome activity, preferentially binding the 20S 5 site with an IC50 of 3.4 nM and demonstrated potent activity against cultured cancer cells in cell viability assays. In vivo, MLN2238 achieved exposures that resulted in significant blood and tumor proteasome inhibition in xenograft-bearing mice and had increased plasma and tumor exposure compared to bortezomib when dosed at their respective maximum tolerated doses (MTD). MLN2238 also elicited a stronger pharmacodynamic (PD) response than bortezomib in xenograft tumors, as measured by tumor 20S 5 site-specific activity and expression levels of GADD34 and ATF-3, two genes involved in the unfolded protein response (UPR) pathway shown to be upregulated in response to proteasome inhibition. Here we describe the development of an ATF-3 IHC assay suitable for use in bone marrow samples isolated from multiple myeloma patients enrolled in Phase I trials of MLN9708. Using both quantitativeWestern blotting and IHC assays, we demonstrated that treatment of cultured myeloma cell lines with MLN2238 results in a dose-dependent increase in ATF-3 levels. Antibody specificity was confirmed by IHC analysis of HCT-116 cells following knockdown of ATF-3 by siRNA. An ATF-3 PD response is detectable by IHC in several xenograft models and in selected normal tissues from mice dosed with MLN2238. The elevation in ATF-3 is delayed by several hours compared to 20S proteasome inhibition in cells and tissues, consistent with it being a downstream effect of proteasome inhibition. To test the use of the ATF-3 IHC assay on clinical samples from multiple myeloma patients, we developed a dual staining assay with CD38, a marker expressed on multiple myeloma cells. We show baseline staining of ATF-3 and CD38 in formalin-fixed paraffin embedded bone marrow aspirates and biopsies from patients who have not received MLN9708. This assay has potential for use in evaluating the levels of CD38 and ATF-3 in pre- and post-treatment bone marrow samples from patients treated with MLN9708. Citation Information: Mol Cancer Ther 2009;8(12 Suppl):B40.

Antitumor Activity of MLN9708, a Second-Generation Proteasome Inhibitor, in Preclinical Models of Lymphoma.

Abstract 3724Poster Board III-660Lymphomas account for about 5% of all cases of cancer in the US. In 2009, it is estimated that 74490 Americans will be diagnosed with lymphoma, which includes approximately 8510 new cases of Hodgkin's lymphoma and 65980 new cases of non-Hodgkin's lymphoma (NHL). An estimated 20790 men and women will die from lymphoma in 2009, the majority (93.8%) of which from NHL. Standard treatment includes chemotherapy and radiation to destroy the malignant lymphoma cells; however, newer therapies are currently being explored. Bortezomib is approved for multiple myeloma and relapsed mantle cell lymphoma, and is under clinical investigation in other types of NHL and other B-cell malignancies. Similar to bortezomib, MLN9708 is a modified dipeptidyl boronic acid that is a potent, reversible and specific inhibitor of the proteasome. MLN9708 preferentially binds to and inhibits b5 enzymatic activity of the 20S catalytic core. It is currently in Phase I trials for the treatment of solid and hematologic malignancies. MLN9708 immediately hydrolyzes to MLN2238, the biologically active form, on exposure to aqueous solutions or plasma. MLN2238 was used for all preclinical studies described below. We evaluated the ability of MLN2238 to inhibit tumor growth in two preclinical models of diffuse large B-cell lymphoma (DLBCL), an aggressive lymphoma that accounts for ∼40% of lymphomas in adults. OCI-LY10 and PHTX-22L are two examples of ABC-subtype of DLBCL. The antitumor activity of MLN2238 was evaluated in CB-17 Scid female mice bearing OCI-LY10 lymphoma xenografts. Tumor inhibition was determined by calculating the treatment over control (T/C) ratio of the mean tumor volume and the percentage of tumor growth inhibition (TGI) on the last day of the study. MLN2238 administered intravenous (IV) at 18 mg/kg once weekly (QW) resulted in tumor regression in 6 of 7 animals (T/C = 0.12; TGI = 88%) and a partial response in the remaining animal (43% reduction in tumor volume). MLN2238 administered at 8 mg/kg or 4 mg/kg IV QW resulted in a T/C of 0.42 and 0.36. Proteasome activity in the tumor was inhibited 49 and 44% 1 hour after a single IV dose of MLN2238 at 14 or 7 mg/kg, respectively. The other tumor model, PHTX-22L, is a primary tumor xenograft that was derived from a tumor surgically removed from the right lymph node of a 71-year-old Caucasian male. SCID NOD female mice implanted with PHTX-22L tumor fragments were treated twice weekly (BIW) with IV doses of vehicle, MLN2238 at 4 mg/kg SC once daily (QD), MLN2238 at 14 mg/kg IV BIW or bortezomib at 0.8 mg/kg IV BIW. The strongest antitumor activity was seen in PHTX-22L tumor bearing mice treated with IV MLN2238 14 mg/kg BIW (T/C = 0.14; TGI = 86%, p < 0.001) or SC MLN2238 4 mg/kg QD (T/C = 0.15; TGI = 85%, p < 0.01). These dosing regimens significantly inhibited tumor growth compared with vehicle treatment. In the same study, bortezomib treatment IV at 0.8 mg/kg on a BIW schedule had no antitumor effect (T/C = 0.88; TGI = 12%, p = 0.86) and was not statistically different from the vehicle treated group. Proteasome activity was significantly inhibited in both blood and tumor following a single dose of MLN2238 administered IV at 14 mg/kg or SC at 4 mg/kg. Proteasome activity was inhibited greater than 50% for up to 8 hrs following the IV dose in both blood and tumor, whereas proteasome activity recovered more quickly following the SC dose. In a separate preclinical study, the antitumor activity of MLN2238 administered at lower doses and on alternate schedules was examined. SCID NOD mice bearing PHTX-22L xenografts were administered MLN2238 IV at 11 mg/kg BIW, 7 mg/kg BIW, 11 mg/kg QW or 5 mg/kg QDx2/week resulted in significant antitumor activity (T/C = 0.04, 0.08, 0.15, 0.16; TGI = 96, 92, 85, 84%, respectively). More importantly, drug treatment caused tumor regression (tumor volume at the end of the study was less than 50% of the starting tumor volume) in 8 of 10 mice in the 11 mg/kg BIW, 5/10 in the 7 mg/kg BIW, 2/8 in the 11 mg/kg QW and 1/10 in the 5 mg/kg QDx2/week treatment groups. The efficacy of MLN2238 dosed IV either at 7 mg/kg QW or 3.5 mg/kg BIW in this model was less efficacious (T/C = 0.61 and 0.64). In addition to PHTX-22L, we have access to several other primary lymphoma tumor xenograft models that we plan to evaluate for sensitivity to MLN2238 treatment. These studies demonstrate that MLN2238 is active in preclinical models of lymphoma, and that MLN2238 has antitumor activity in a model of lymphoma that is refractory to bortezomib treatment. Disclosures:Donelan:Milllennium: Employment. Bannerman:Milllennium: Employment. Bano:Milllennium: Employment. Babcock:Milllennium: Employment. Hales:Millennium Pharmaceuticals: Employment. Stringer:Milllennium: Employment. Burke:Milllennium: Employment. Danaee:Milllennium: Employment, Equity Ownership. Faron-Yowe:Milllennium: Employment. Koenig:Milllennium: Employment. Lichter:Milllennium: Employment. Kupperman:Milllennium: Employment.

Proteasome inhibitors in the treatment of multiple myeloma.

Targeting intracellular protein turnover by inhibiting the ubiquitin-proteasome pathway as a strategy for cancer therapy is a new addition to our chemotherapeutic armamentarium, and has seen its greatest successes against multiple myeloma. The first-in-class proteasome inhibitor, bortezomib, was initially approved for treatment of patients in the relapsed/refractory setting as a single agent, and was recently shown to induce even greater benefits as part of rationally designed combinations that overcome chemoresistance. Modulation of proteasome function is also a rational approach to achieve chemosensitization to other antimyeloma agents, and bortezomib has now been incorporated into the front-line setting. Bortezomib-based induction regimens are able to achieve higher overall response rates and response qualities than was the case with prior standards of care, and unlike these older approaches, maintain efficacy in patients with clinically and molecularly defined high-risk disease. Second-generation proteasome inhibitors with novel properties, such as NPI-0052 and carfilzomib, are entering the clinical arena, and showing evidence of antimyeloma activity. In this spotlight review, we provide an overview of the current state of the art use of bortezomib and other proteasome inhibitors against multiple myeloma, and highlight areas for future study that will further optimize our ability to benefit patients with this disease.

Therapeutic strategies within the ubiquitin proteasome system

The ubiquitin-dependent proteolysis system (UPS) is the main driver of regulated protein degradation in all eukaryotic cells, and it is becoming increasingly clear that defects within this pathway drive a large number of human pathologies. Recent success in the use of proteasome inhibitors in the treatment of hematological malignancies validates the UPS as a viable therapeutic pathway, and substantial effort is now focused on the development of both second-generation proteasome inhibitors as well as novel strategies for the inhibition of upstream UPS enzymes. In this review we discuss the potential 'druggability' of key nodes within the UPS and summarize recent advances within the field.

First-in-human phase I study of the novel structure proteasome inhibitor NPI-0052

3516 Background: NPI-0052 is a second-generation proteasome inhibitor that has a novel structure with preclinical studies suggesting unique proteasome inhibition (PI), signal transduction, efficacy and toxicology profiles, and activities in a broad range of models including bortezomib (BZ) resistant models. Methods: Patients were treated with NPI-0052 IV weekly x 3 in 4-week cycles in a 3+3 design dose escalation to a Recommended Phase 2 Dose (RP2D). PI was assayed in whole blood (PWB) and in PBMCs. Up to 10 patients each (lymphoma and solid tumors) are treated at the RP2D. Results: 39 patients have been treated between 0.0125 mg/m2 to 0.8 mg/m2 for up to 12 cycles. The RP2D was 0.8 mg/m2 and has been well tolerated in this study, with the most notable drug-related adverse events being N/V, fatigue, diarrhea, dizziness, headache, decreases in hemoglobin, and insomnia. Thrombocytopenia or neuropathy did not appear to be induced by NPI-0052. Escalation was halted at 0.8 mg/m2, as DLT of transient “hallucinations” (visual imprints when eyes closed) and dizziness/unsteady gait were reported in another study at 0.9 mg/m2. PK data indicate T1/2 ∼4–10 minutes, with clearance at 3–15 L/min and Vz of 35–85L. PI (chymotrypsin-like activity) in PWB and PBMC were dose dependent (mean D1 and D15 PI in PWB at 0.8 mg/m2 was 75 and 100%) (efficacious doses of BZ have been reported to result in a range of ∼40–70% PI). PI in PBMC returned to ∼baseline within one week of each dose, while inhibition remained in PWB. Stable disease was observed in patients with cervical carcinoma (11 months; maximum response was 24%; PI increased with dose escalation), colorectal, hepatocellular, adenoid cystic, melanoma, granulosis cell and ovarian. Conclusions: NPI-0052 produces dose-dependent pharmacologic effects, with equal to greater PI seen than reported with therapeutic doses of BZ. At the RP2D toxicity is mild-to-moderate, without the toxicity profile associated with BZ. Together with preclinical data this suggests NPI-0052 may have utility in treating patients who are not candidates for BZ as well as in indications and combinations that have not supported BZ use. Additional trials have been initiated including combinations with other targeted agents. [Table: see text]

Emerging Treatments for Multiple Myeloma: Beyond Immunomodulatory Drugs and Bortezomib

The successful clinical development of thalidomide, bortezomib, and lenalidomide not only transformed the therapeutic management of multiple myeloma (MM) but also catalyzed a renewed interest in the development of additional classes of novel agents for this disease. This review focuses on a series of new therapeutics that have shown promising preclinical results, as well as encouraging safety profiles and early evidence of anti-MM activity in clinical studies, either alone or in combination with other, conventional or novel, anti-MM treatments. These agents include second-generation proteasome inhibitors and immunomodulatory agents, as well as members of other therapeutic classes, such as histone deacetylase inhibitors (HDAC), heat shock protein 90 (Hsp90) inhibitors, and the alkylphospholipid Akt inhibitor perifosine.

A191 NPI-0052: A Second-Generation Proteasome Inhibitor

A191 NPI-0052: A Second-Generation Proteasome Inhibitor