Michael Sebag

Daratumumab monotherapy in patients with treatment-refractory multiple myeloma (SIRIUS): an open-label, randomised, phase 2 trial.

BACKGROUND New treatment options are needed for patients with multiple myeloma that is refractory to proteasome inhibitors and immunomodulatory drugs. We assessed daratumumab, a novel CD38-targeted monoclonal antibody, in patients with refractory multiple myeloma. METHODS In this open-label, multicentre, phase 2 trial done in Canada, Spain, and the USA, patients (age ≥18 years) with multiple myeloma who were previously treated with at least three lines of therapy (including proteasome inhibitors and immunomodulatory drugs), or were refractory to both proteasome inhibitors and immunomodulatory drugs, were randomly allocated in a 1:1 ratio to receive intravenous daratumumab 8 mg/kg or 16 mg/kg in part 1 stage 1 of the study, to decide the dose for further assessment in part 2. Patients received 8 mg/kg every 4 weeks, or 16 mg/kg per week for 8 weeks (cycles 1 and 2), then every 2 weeks for 16 weeks (cycles 3-6), and then every 4 weeks thereafter (cycle 7 and higher). The allocation schedule was computer-generated and randomisation, with permuted blocks, was done centrally with an interactive web response system. In part 1 stage 2 and part 2, patients received 16 mg/kg dosed as in part 1 stage 1. The primary endpoint was overall response rate (partial response [PR] + very good PR + complete response [CR] + stringent CR). All patients who received at least one dose of daratumumab were included in the analysis. The trial is registered with ClinicalTrials.gov, number NCT01985126. FINDINGS The study is ongoing. In part 1 stage 1 of the study, 18 patients were randomly allocated to the 8 mg/kg group and 16 to the 16 mg/kg group. Findings are reported for the 106 patients who received daratumumab 16 mg/kg in parts 1 and 2. Patients received a median of five previous lines of therapy (range 2-14). 85 (80%) patients had previously received autologous stem cell transplantation, 101 (95%) were refractory to the most recent proteasome inhibitors and immunomodulatory drugs used, and 103 (97%) were refractory to the last line of therapy. Overall responses were noted in 31 patients (29.2%, 95% CI 20.8-38.9)-three (2.8%, 0.6-8.0) had a stringent CR, ten (9.4%, 4.6-16.7) had a very good PR, and 18 (17.0%, 10.4-25.5) had a PR. The median time to first response was 1.0 month (range 0.9-5.6). Median duration of response was 7.4 months (95% CI 5.5-not estimable) and progression-free survival was 3.7 months (95% CI 2.8-4.6). The 12-month overall survival was 64.8% (95% CI 51.2-75.5) and, at a subsequent cutoff, median overall survival was 17.5 months (95% CI 13.7-not estimable). Daratumumab was well tolerated; fatigue (42 [40%] patients) and anaemia (35 [33%]) of any grade were the most common adverse events. No drug-related adverse events led to treatment discontinuation. INTERPRETATION Daratumumab monotherapy showed encouraging efficacy in heavily pretreated and refractory patients with multiple myeloma, with a favourable safety profile in this population of patients. FUNDING Janssen Research & Development.

An open-label, single-arm, phase 2 (PX-171-004) study of single-agent carfilzomib in bortezomib-naive patients with relapsed and/or refractory multiple myeloma

Carfilzomib is a selective proteasome inhibitor that binds irreversibly to its target. In phase 1 studies, carfilzomib elicited promising responses and an acceptable toxicity profile in patients with relapsed and/or refractory multiple myeloma (R/R MM). In the present phase 2, multicenter, open-label study, 129 bortezomib-naive patients with R/R MM (median of 2 prior therapies) were separated into Cohort 1, scheduled to receive intravenous carfilzomib 20 mg/m(2) for all treatment cycles, and Cohort 2, scheduled to receive 20 mg/m(2) for cycle 1 and then 27 mg/m(2) for all subsequent cycles. The primary end point was an overall response rate (≥ partial response) of 42.4% in Cohort 1 and 52.2% in Cohort 2. The clinical benefit response (overall response rate + minimal response) was 59.3% and 64.2% in Cohorts 1 and 2, respectively. Median duration of response was 13.1 months and not reached, and median time to progression was 8.3 months and not reached, respectively. The most common treatment-emergent adverse events were fatigue (62.0%) and nausea (48.8%). Single-agent carfilzomib elicited a low incidence of peripheral neuropathy-17.1% overall (1 grade 3; no grade 4)-in these pretreated bortezomib-naive patients. The results of the present study support the use of carfilzomib in R/R MM patients. This trial is registered at www.clinicaltrials.gov as NCT00530816.

Identification and Characterization of 1,25-Dihydroxyvitamin D3-responsive Repressor Sequences in the Rat Parathyroid Hormone-related Peptide Gene

Parathyroid hormone-related peptide (PTHRP) gene transcription is suppressed by 1,25-dihydroxyvitamin D3 (1,25(OH)2D3), the active metabolite of vitamin D3. In the present report, we examined 1,25(OH)2D3-mediated repression of PTHRP expression by transfection of PTHRP promoter/reporter constructs in normal human keratinocytes and by DNA binding. We localized an element conferring 1,25(OH)2D3-mediated repression in vivo to a 47-base pair (bp) region located −1121 to −1075 from the transcriptional start site. Mobility shift analysis revealed that this vitamin D response element (VDRE) forms DNA-protein complexes. The addition of a monoclonal antibody that recognizes the DNA binding region of the vitamin D receptor (VDR) attenuated binding of the receptor to the 47-bp sequence, whereas the addition of monoclonal antibody raised against the retinoid X receptor (RXR) further retarded the mobility of the protein-DNA complex. Consequently, the PTHRP promoter element binds a VDR·RXR heterodimer. Examination of this VDRE revealed complete sequence homology with a half-site of the human and rat osteocalcin VDRE (GGGTGA). Furthermore, mutation analysis suggests that a 16-bp domain consisting of an almost perfect repeat separated by a 3-base pair “spacer” GAG is responsible for the DNA-protein interaction within this 47-bp sequence. Our results therefore indicate the existence of an inhibitory VDRE within the PTHRP promoter that is similar in sequence composition and cellular factor requirement to classical up-regulatory VDREs.

Design and Synthesis of Active Site Inhibitors of the Human Farnesyl Pyrophosphate Synthase: Apoptosis and Inhibition of ERK Phosphorylation in Multiple Myeloma Cells

Human farnesyl pyrophosphate synthase (hFPPS) controls intracellular levels of FPP and post-translational prenylation of small GTPase proteins, which are essential for cell signaling and cell proliferation. Clinical investigations provide evidence that N-BP inhibitors of hFPPS are disease modifying agents that improve survival of multiple myeloma (MM) patients via mechanisms unrelated to their skeletal effects. A new series of N-BPs was designed that interact with a larger portion of the GPP subpocket, as compared to the current therapeutic drugs, and rigidify the (364)KRRK(367) tail of hFPPS in the closed conformation in the absence of IPP. An analogue of this series was used to demonstrate inhibition of the intended biological target, resulting in apoptosis and down-regulation of ERK phosphorylation in human MM cell lines.

Thienopyrimidine Bisphosphonate (ThPBP) Inhibitors of the Human Farnesyl Pyrophosphate Synthase: Optimization and Characterization of the Mode of Inhibition.

Human farnesyl pyrophosphate synthase (hFPPS) controls the post-translational prenylation of small GTPase proteins that are essential for cell signaling, cell proliferation, and osteoclast-mediated bone resorption. Inhibition of hFPPS is a clinically validated mechanism for the treatment of lytic bone diseases, including osteoporosis and cancer related bone metastases. A new series of thienopyrimidine-based bisphosphonates (ThP-BPs) were identified that inhibit hFPPS with low nanomolar potency. Crystallographic evidence revealed binding of ThP-BP inhibitors in the allylic subpocket of hFPPS. Simultaneous binding of inorganic pyrophosphate in the IPP subpocket leads to conformational closing of the active site cavity. The ThP-BP analogues are significantly less hydrophilic yet exhibit higher affinity for the bone mineral hydroxyapatite than the current N-BP drug risedronic acid. The antiproliferation properties of a potent ThB-BP analogue was assessed in a multiple myeloma cell line and found to be equipotent to the best current N-BP drugs. Consequently, these compounds represent a new structural class of hFPPS inhibitors and a novel scaffold for the development of human therapeutics.

Translation initiation factor eIF4F modifies the dexamethasone response in multiple myeloma

Significance Multiple myeloma (MM) is a cancer that develops in the bone marrow and remains incurable to this day. It is a cancer type that shows hallmarks of deregulated protein synthesis control. To uncover new vulnerabilities in this disease, we performed a focused RNAi screen to identify components of the translation apparatus that, when depleted, would sensitize tumor cells to dexamethasone (DEX), a component of frontline therapy in this cancer. We found that suppression of eukaryotic initiation factor 4F, a heterotrimeric complex required for cap-dependent translation initiation, is a modifier of the DEX response in MM. Our efforts uncover a previously unidentified vulnerability in MM that should be explored clinically. Enhanced protein synthesis capacity is associated with increased tumor cell survival, proliferation, and resistance to chemotherapy. Cancers like multiple myeloma (MM), which display elevated activity in key translation regulatory nodes, such as the PI3K/mammalian target of rapamycin and MYC-eukaryotic initiation factor (eIF) 4E pathways, are predicted to be particularly sensitive to therapeutic strategies that target this process. To identify novel vulnerabilities in MM, we undertook a focused RNAi screen in which components of the translation apparatus were targeted. Our screen was designed to identify synthetic lethal relationships between translation factors or regulators and dexamethasone (DEX), a corticosteroid used as frontline therapy in this disease. We find that suppression of all three subunits of the eIF4F cap-binding complex synergizes with DEX in MM to induce cell death. Using a suite of small molecules that target various activities of eIF4F, we observed that cell survival and DEX resistance are attenuated upon eIF4F inhibition in MM cell lines and primary human samples. Levels of MYC and myeloid cell leukemia 1, two known eIF4F-responsive transcripts and key survival factors in MM, were reduced upon eIF4F inhibition, and their independent suppression also synergized with DEX. Inhibition of eIF4F in MM exerts pleotropic effects unraveling a unique therapeutic opportunity.

Practical approaches to the use of lenalidomide in multiple myeloma: a canadian consensus.

In Canada, lenalidomide combined with dexamethasone (Len/Dex) is approved for use in relapsed or refractory multiple myeloma (RRMM). Our expert panel sought to provide an up-to-date practical guide on the use of lenalidomide in the managing RRMM within the Canadian clinical setting, including management of common adverse events (AEs). The panel concluded that safe, effective administration of Len/Dex treatment involves the following steps: (1) lenalidomide dose adjustment based on creatinine clearance and the extent of neutropenia or thrombocytopenia, (2) dexamethasone administered at 20–40 mg/week, and (3) continuation of treatment until disease progression or until toxicity persists despite dose reduction. Based on available evidence, the following precautions should reduce the risk of common Len/Dex AEs: (1) all patients treated with Len/Dex should receive thromboprophylaxis, (2) erythropoiesis-stimulating agents (ESAs) should be used cautiously, and (3) females of child-bearing potential and males in contact with such females must use multiple contraception methods. Finally, while Len/Dex can be administered irrespective of prior therapy and in all prognostic subsets, patients with chromosomal deletion 17(p13) have less favorable outcomes with all treatments, including Len/Dex. New directions for the use of lenalidomide in RRMM are also considered.

A Covalent Cysteine‐Targeting Kinase Inhibitor of Ire1 Permits Allosteric Control of Endoribonuclease Activity

The unfolded protein response (UPR) initiated by the transmembrane kinase/ribonuclease Ire1 has been implicated in a variety of diseases. Ire1, with its unique position in the UPR, is an ideal target for the development of therapies; however, the identification of specific kinase inhibitors is challenging. Recently, the development of covalent inhibitors has gained great momentum because of the irreversible deactivation of the target. We identified and determined the mechanism of action of the Ire1‐inhibitory compound UPRM8. MS analysis revealed that UPRM8 inhibition occurs by covalent adduct formation at a conserved cysteine at the regulatory DFG+2 position in the Ire1 kinase activation loop. Mutational analysis of the target cysteine residue identified both UPRM8‐resistant and catalytically inactive Ire1 mutants. We describe a novel covalent inhibition mechanism of UPRM8, which can serve as a lead for the rational design and optimization of inhibitors of human Ire1.

CCR1 blockade and myeloma bone disease.

In this issue of Blood, Dairaghi and colleagues demonstrate the efficacy of a potent and orally bioavailable inhibitor of CCR1, one of the receptors for the chemokine CCL3/MIP-1, in a mouse model of multiple myeloma (MM) and MM bone disease. They show CCX721 to be a highly selective and efficient inhibitor of CCR1 and in turn a suppressor of osteoclastic activity, osteolytic lesions, and disease burden in a preclinical MM model.

Unraveling the Prenylation–Cancer Paradox in Multiple Myeloma with Novel Geranylgeranyl Pyrophosphate Synthase (GGPPS) Inhibitors

Post-translational prenylation of the small GTP-binding proteins (GTPases) is vital to a plethora of biological processes, including cellular proliferation. We have identified a new class of thienopyrimidine-based bisphosphonate (ThP-BP) inhibitors of the human geranylgeranyl pyrophosphate synthase (hGGPPS) that block protein prenylation in multiple myeloma (MM) cells leading to cellular apoptosis. These inhibitors are also effective in blocking the proliferation of other types of cancer cells. We confirmed intracellular target engagement, demonstrated the mechanism of action leading to apoptosis, and determined a direct correlation between apoptosis and intracellular inhibition of hGGPPS. Administration of a ThP-BP inhibitor to a MM mouse model confirmed in vivo downregulation of Rap1A geranylgeranylation and reduction of monoclonal immunoglobulins (M-protein, a biomarker of disease burden) in the serum. These results provide the first proof-of-principle that hGGPPS is a valuable therapeutic target in oncology and more specifically for the treatment of multiple myeloma.