Carfilzomib: in relapsed, or relapsed and refractory, multiple myeloma

The proteasome inhibitor carfilzomib exerts anti-inflammatory and antithrombotic effects on the endothelium

BACKGROUND

Carfilzomib (CFZ) is a second-generation proteasome inhibitor used to treat multiple myeloma. Potent inhibition of the proteasome results in chronic proteotoxic endoplasmic reticulum (ER) stress, leading to apoptosis. While CFZ has improved survival rates in multiple myeloma, it is associated with an increased risk of cardiovascular adverse effects. While this has been putatively linked to cardiotoxicity, CFZ could potentially also exhibit adverse effects on the endothelium.

OBJECTIVES

To investigate the effects of CFZ on the endothelium.

METHODS

Human umbilical vein endothelial cells (HUVECs) were treated with CFZ, and expression of relevant markers of ER stress, inflammation, and thrombosis was measured and functionally assessed.

RESULTS

CFZ failed to induce ER stress in HUVECs but induced the expression of Kruppel-like factor 4, endothelial nitric oxide synthase, tissue plasminogen activator, and thrombomodulin and reduced tumor necrosis factor alpha (TNFα)-mediated intercellular adhesion molecule 1 and tissue factor expression, suggesting a potential protective effect on the endothelium. Consistent with these observations, CFZ reduced leukocyte adhesion under shear stress and reduced factor Xa generation and fibrin clot formation on the endothelium following TNFα treatment and inhibited von Willebrand factor (VWF) and angiopoietin-2 exocytosis from Weibel-Palade bodies. Subsequently, CFZ inhibited the formation of VWF-platelet strings, and moreover, media derived from myeloma cell lines induced VWF release, a process also inhibited by CFZ.

CONCLUSION

These data demonstrate that CFZ is unable to induce ER stress in confluent resting endothelial cells and can conversely attenuate the prothrombotic effects of TNFα on the endothelium. This study suggests that CFZ does not negatively alter HUVECs, and proteasome inhibition of the endothelium may offer a potential way to prevent thrombosis.

Lysosomal dysfunction in Schwann cells is involved in bortezomib-induced peripheral neurotoxicity

Bortezomib (BTZ) is a proteasome inhibitor serves as a first-line drug for multiple myeloma treatment. BTZ-induced peripheral neuropathy (BIPN) is the most common adverse effect of BTZ with an incidence as high as 40-60%. However, the pathological mechanisms underlying BIPN remain largely unclear. BTZ leads to dramatic Schwann cell demyelination in sciatic nerves. Previous studies implied that myelin debris was predominantly degraded via autophagy-lysosome pathway in Schwann cells. However, the association of autophagy with BIPN has not been made. Mice were treated with BTZ (2 mg/kg, i.v.) on Day1 and Day4 each week for continuous 4 weeks. BTZ-treated mice showed enhanced mechanical hyperalgesia, decreased tail nerve conduction and sciatic nerve demyelination. Unexpectedly, BTZ led to the accumulation of autophagic vesicles, LC3-II and p62 in the sciatic nerve. Moreover, BTZ blocked autophagic flux in RSC96 Schwann cells as determined by mcherry-GFP-LC3 assay, suggesting BTZ may impair lysosomal function rather than inducing autophagy in Schwann cells. BTZ significantly reduced the lysosomal activity in Schwann cells as determined by reduced LysoTracker Red and DQ-Red-BSA staining and increased the level of immature Cathepsin B (CTSB). Remarkably, lysosomal activators PP242 and Torin1, significantly reversed the blockage of autophagic flux by BTZ. We further verified that Torin1 rescued the demyelination, nerve conduction and reduced the mechanical hyperalgesia in BIPN mice. Additionally, Torin1 did not compromise the efficacy of BTZ in suppressing multiple myeloma RPMI8226 cell. Taken together, we identified that lysosomal dysfunction in Schwann cells caused by BTZ is involved in the BIPN pathology. Improved lysosomal function in Schwann cells can be a promising strategy for BIPN treatment.

Size optimization of carfilzomib nanocrystals for systemic delivery to solid tumors

Carfilzomib (CFZ) is a second-generation proteasome inhibitor effective in blood cancer therapy. However, CFZ has shown limited efficacy in solid tumor therapy due to the short half-life and poor tumor distribution. Albumin-coated nanocrystal (NC) formulation was shown to improve the circulation stability of CFZ, but its antitumor efficacy remained suboptimal. We hypothesize that NC size reduction is critical to the formulation safety and efficacy as the small size would decrease the distribution in the reticuloendothelial system (RES) and selectively increase the uptake by tumor cells. We controlled the size of CFZ-NCs by varying the production parameters in the crystallization-in-medium method and compared the size-reduced CFZ-NCs (z-average of 168 nm, NC₁₆₈) with a larger counterpart (z-average of 325 nm, NC₃₂₅) as well as the commercial CFZ formulation (CFZ-CD). Both CFZ-NCs showed similar or higher cytotoxicity than CFZ-CD against breast cancer cells. NC₁₆₈ showed greater uptake by cancer cells, less uptake by macrophages and lower immune cell toxicity than NC₃₂₅ or CFZ-CD. NC₁₆₈, but not NC₃₂₅, showed a similar safety profile to CFZ-CD in vivo. The biodistribution and antitumor efficacy of CFZ-NCs in mice were also size-dependent. NC₁₆₈ showed greater antitumor efficacy and tumor accumulation but lower RES accumulation than NC₃₂₅ in 4T1 breast cancer model. These results support that NC formulation with an optimal particle size can improve the therapeutic efficacy of CFZ in solid tumors.

A new combination strategy to enhance apoptosis in cancer cells by using nanoparticles as biocompatible drug delivery carriers

Some experimental and clinical studies have been conducted for the usage of chemotherapeutic drugs encapsulated into nanoparticles (NPs). However, no study has been conducted so far on the co-encapsulation of doxorubicin (Dox) and epoxomicin (Epo) into NPs as biocompatible drug delivery carriers. Therefore, we investigated if co-encapsulation of doxorubicin (Dox) and/or epoxomicin (Epo) into NPs enhance their anticancer efficiency and prevent drug resistance and toxicity to normal cells. We synthesized Dox and/or Epo loaded poly (lactic-co-glycolic acid) (PLGA) NPs using a multiple emulsion solvent evaporation technique and characterized them in terms of their particle size and stability, surface, molecular, thermal, encapsulation efficiency and in vitro release properties. We studied the effects of drug encapsulated NPs on cellular accumulation, intracellular drug levels, oxidative stress status, cellular viability, drug resistance, 20S proteasome activity, cytosolic Nuclear Factor Kappa B (NF-κB-p65), and apoptosis in breast cancer and normal cells. Our results proved that the nanoparticles we synthesized were thermally stable possessing higher encapsulation efficiency and particle stability. Thermal, morphological and molecular analyses demonstrated the presence of Dox and/or Epo within NPs, indicating that they were successfully loaded. Cell line assays proved that Dox and Epo loaded NPs were less cytotoxic to single-layer normal HUVECs than free Dox and Epo, suggesting that the NPs would be biocompatible drug delivery carriers. The apoptotic index of free Dox and Epo increased 50% through their encapsulation into NPs, proving combination strategy to enhance apoptosis in breast cancer cells. Our results demonstrated that the co-encapsulation of Dox and Epo within NPs would be a promising treatment strategy to overcome multidrug resistance and toxicity to normal tissues that can be studied in further in vivo and clinical studies in breast cancer.

Natural product scaffolds as inspiration for the design and synthesis of 20S human proteasome inhibitors

The 20S proteasome is a valuable target for the treatment of a number of diseases including cancer, neurodegenerative disease, and parasitic infection. In an effort to discover novel inhibitors of the 20S proteasome, many reseaarchers have looked to natural products as potential leads for drug discovery. The following review discusses the efforts made in the field to isolate and identify natural products as inhibitors of the proteasome. In addition, we describe some of the modifications made to natural products in order to discover more potent and selective inhibitors for potential disease treatment.

Ternary Polypeptide Nanoparticles with Improved Encapsulation, Sustained Release, and Enhanced In Vitro Efficacy of Carfilzomib

PURPOSE

To develop a new nanoparticle formulation for a proteasome inhibitor Carfilzomib (CFZ) to improve its stability and efficacy for future in vivo applications.

METHODS

CFZ-loaded ternary polypeptide nanoparticles (CFZ/tPNPs) were prepared by using heptakis(6-amino-6-deoxy)-β-cyclodextrin(hepta-hydrochloride) (HaβCD) and azido-poly(ethylene glycol)-block-poly(L-glutamic acid sodium salt) (N₃-PEG-PLE). The process involved ternary (hydrophobic/ionic/supramolecular) interactions in three steps: 1) CFZ was entrapped in the cavity of HaβCD by hydrophobic interaction, 2) the drug-cyclodextrin inclusion complexes were mixed with N₃-PEG-PLE to form polyion complex nanoparticles, and 3) the nanoparticles were modified with fluorescent dyes (AFDye 647) for imaging and/or epithelial cell adhesion molecule (EpCAM) antibodies for cancer cell targeting. CFZ/tPNPs were characterized for particle size, surface charge, drug release, stability, intracellular uptake, proteasome inhibition, and in vitro cytotoxicity.

RESULTS

tPNPs maintained an average particle size of 50 nm after CFZ entrapment, EpCAM conjugation, and freeze drying. tPNPs achieved high aqueous solubility of CFZ (>1 mg/mL), sustained drug release (t_1/2 = 6.46 h), and EpCAM-mediated cell targeting, which resulted in increased intracellular drug accumulation, prolonged proteasome inhibition, and enhanced cytotoxicity of CFZ in drug-resistant DLD-1 colorectal cancer cells.

CONCLUSIONS

tPNPs improved stability and efficacy of CFZ in vitro, and these results potentiate effective cancer treatment using CFZ/tPNPs in future vivo studies.

Carfilzomib, lenalidomide, and dexamethasone in patients with relapsed multiple myeloma categorised by age: secondary analysis from the phase 3 ASPIRE study

A primary analysis of the ASPIRE study found that the addition of carfilzomib to lenalidomide and dexamethasone (carfilzomib group) significantly improved progression-free survival (PFS) compared with lenalidomide and dexamethasone alone (control group) in patients with relapsed multiple myeloma (RMM). This post hoc analysis examined outcomes from ASPIRE in patients categorised by age. In the carfilzomib group, 103/396 patients were ≥70 years old, and in the control group, 115/396 patients were ≥70 years old. Median PFS for patients <70 years old was 28·6 months for the carfilzomib group versus 17·6 months for the control group [hazard ratio (HR), 0·701]. Median PFS for patients ≥70 years old was 23·8 months for the carfilzomib group versus 16·0 months for the control group (HR, 0·753). For patients <70 years the overall response rate (ORR) was 86·0% (carfilzomib group) and 66·9% (control group); for patients ≥70 years old the ORR was 90·3% (carfilzomib group) and 66·1% (control group). Within the carfilzomib group, grade ≥3 cardiovascular adverse events occurred more frequently among patients ≥70 years old compared with patients <70 years old. Carfilzomib-lenalidomide-dexamethasone has a favourable benefit-risk profile for patients with RMM, including elderly patients ≥70 years old.

TRIAL REGISTRATION

clinicaltrials.gov identifier: NCT01080391.

Analysis of Real-World Data on Overall Survival in Multiple Myeloma Patients With ≥3 Prior Lines of Therapy Including a Proteasome Inhibitor (PI) and an Immunomodulatory Drug (IMiD), or Double Refractory to a PI and an IMiD

BACKGROUND

This retrospective study evaluated the treatment patterns in and overall survival (OS) of multiple myeloma (MM) patients who were refractory to a proteasome inhibitor (PI) and an immunomodulatory drug (IMiD) or who had received three or more prior lines of therapy (LOTs) including a PI and an IMiD.

METHODS

Electronic health records in the IMS LifeLink and OPTUM databases were screened for indexing periods of 2000-2014 and 2007-2014, respectively. Patients who were refractory to both a PI and an IMiD (criterion 1) or who received three or more prior LOTs (including a PI and an IMiD) and showed disease progression within 60 days of their most recent regimen (criterion 2) comprised the eligible population. Median OS from time of last LOT was assessed for the full cohort, cohorts meeting criteria 1 and 2, and clinically important subgroups.

RESULTS

Of 3,929 and 3,837 patients with MM diagnoses evaluated in the IMS LifeLink and OPTUM databases, 500 and 162 met the eligibility criteria, respectively. Similar median OS was observed for eligible patients in the IMS LifeLink and OPTUM databases (7.9 vs. 7.9 months; p = .5358). In subgroup analyses of the IMS LifeLink data set, median OS was longer in patients <65 years of age than it was for those ≥65 years at eligibility (9.5 vs 6.7 months; p < .01) and in patients with good or unreported versus poor performance status at last claim (7.8 or 8.8 vs. 2.9 months; p < .0001).

CONCLUSION

The findings of this survival analysis suggest that outcomes for these patients remain poor despite the availability of newer agents.

IMPLICATIONS FOR PRACTICE

This real-world retrospective study of electronic health records examines the survival outcomes of patients with multiple myeloma who are heavily pretreated or highly refractory to currently approved treatments, including recently approved proteasome inhibitors and immunomodulatory drugs. This survival analysis showed that outcomes for these patients remain poor despite the availability of newer agents, with median overall survival of approximately 8 months. These findings highlight a critical need to develop novel therapies for these patients and also serve as a reference point against which emerging agents for heavily pretreated or highly refractory disease may be evaluated.

Identifying the Minimal Enzymes Required for Biosynthesis of Epoxyketone Proteasome Inhibitors

Epoxyketone proteasome inhibitors have attracted much interest due to their potential as anticancer drugs. Although the biosynthetic gene clusters for several peptidyl epoxyketone natural products have recently been identified, the enzymatic logic involved in the formation of the terminal epoxyketone pharmacophore has been relatively unexplored. Here, we report the identification of the minimal set of enzymes from the eponemycin gene cluster necessary for the biosynthesis of novel metabolites containing a terminal epoxyketone pharmacophore in Escherichia coli, a versatile and fast-growing heterologous host. This set of enzymes includes a non-ribosomal peptide synthetase (NRPS), a polyketide synthase (PKS), and an acyl-CoA dehydrogenase (ACAD) homologue. In addition to the in vivo functional reconstitution of these enzymes in E. coli, in vitro studies of the eponemycin NRPS and (13) C-labeled precursor feeding experiments were performed to advance the mechanistic understanding of terminal epoxyketone formation.

David and Goliath: chemical perturbation of eukaryotes by bacteria

Environmental microbes produce biologically active small molecules that have been mined extensively as antibiotics and a smaller number of drugs that act on eukaryotic cells. It is known that there are additional bioactives to be discovered from this source. While the discovery of new antibiotics is challenged by the frequent discovery of known compounds, we contend that the eukaryote-active compounds may be less saturated. Indeed, despite there being far fewer eukaryotic-active natural products these molecules interact with a far richer diversity of molecular and cellular targets.

DNA damage-induced ubiquitylation of proteasome controls its proteolytic activity

Stability of proteins is largely controlled by post-translational covalent modifications. Among those, ubiquitylation plays a central role as it marks the proteins for proteasome-dependent degradation. Proteolytic activities of proteasomes are critical for execution of various cellular processes, including DNA damage signaling and repair. However, very little is known about the regulation of proteasomal activity in cells during genotoxic stress. Here we investigated post-translational modifications of the 20S proteasomal subunits upon DNA damage induced by doxorubicin. Using mass-spectrometry, we found novel sites of phosphorylation and ubiquitylation in multiple proteasome subunits upon doxorubicin treatment. Ectopic co-expression of proteasome subunits and tagged ubiquitin confirmed the presence of ubiquitylated forms of PSMA5, PSMA1, PSMA3 and PSMB5 in cells. Moreover, we demonstrated that ubiquitylation in vitro inhibited chymotrypsin-like and caspase-like activities of proteasomes. In vivo, doxorubicin increased the activity of proteasomes, paralleling with attenuation of the overall level of proteasome ubiquitylation. Collectively, our results suggest a novel mechanism whereby the proteolytic activities of proteasomes are dynamically regulated by ubiquitylation upon DNA damage.

Genetic basis for the biosynthesis of the pharmaceutically important class of epoxyketone proteasome inhibitors

The epoxyketone proteasome inhibitors are an established class of therapeutic agents for the treatment of cancer. Their unique α',β'-epoxyketone pharmacophore allows binding to the catalytic β-subunits of the proteasome with extraordinary specificity. Here, we report the characterization of the first gene clusters for the biosynthesis of natural peptidyl-epoxyketones. The clusters for epoxomicin, the lead compound for the anticancer drug Kyprolis, and for eponemycin were identified in the actinobacterial producer strains ATCC 53904 and Streptomyces hygroscopicus ATCC 53709, respectively, using a modified protocol for Ion Torrent PGM genome sequencing. Both gene clusters code for a hybrid nonribosomal peptide synthetase/polyketide synthase multifunctional enzyme complex and homologous redox enzymes. Epoxomicin and eponemycin were heterologously produced in Streptomyces albus J1046 via whole pathway expression. Moreover, we employed mass spectral molecular networking for a new comparative metabolomics approach in a heterologous system and discovered a number of putative epoxyketone derivatives. With this study, we have definitively linked epoxyketone proteasome inhibitors and their biosynthesis genes for the first time in any organism, which will now allow for their detailed biochemical investigation.

Microbial natural products: molecular blueprints for antitumor drugs

Microbes from two of the three domains of life, the Prokarya, and Eukarya, continue to serve as rich sources of structurally complex chemical scaffolds that have proven to be essential for the development of anticancer therapeutics. This review describes only a handful of exemplary natural products and their derivatives as well as those that have served as elegant blueprints for the development of novel synthetic structures that are either currently in use or in clinical or preclinical trials together with some of their earlier analogs in some cases whose failure to proceed aided in the derivation of later compounds. In every case, a microbe has been either identified as the producer of secondary metabolites or speculated to be involved in the production via symbiotic associations. Finally, rapidly evolving next-generation sequencing technologies have led to the increasing availability of microbial genomes. Relevant examples of genome mining and genetic manipulation are discussed, demonstrating that we have only barely scratched the surface with regards to harnessing the potential of microbes as sources of new pharmaceutical leads/agents or biological probes.

From epoxomicin to carfilzomib: chemistry, biology, and medical outcomes

The initial enthusiasm following the discovery of a pharmacologically active natural product is often fleeting due to the poor prospects for its ultimate clinical application. Despite this, the ever-changing landscape of modern biology has a constant need for molecular probes that can aid in our understanding of biological processes. After its initial discovery by Bristol-Myers Squibb as a microbial anti-tumor natural product, epoxomicin was deemed unfit for development due to its peptide structure and potentially labile epoxyketone pharmacophore. Despite its drawbacks, epoxomicin's pharmacophore was found to provide unprecedented selectivity for the proteasome. Epoxomicin also served as a scaffold for the generation of a synthetic tetrapeptide epoxyketone with improved activity, YU-101, which became the parent lead compound of carfilzomib (Kyprolis™), the recently approved therapeutic agent for multiple myeloma. In this era of rational drug design and high-throughput screening, the prospects for turning an active natural product into an approved therapy are often slim. However, by understanding the journey that began with the discovery of epoxomicin and ended with the successful use of carfilzomib in the clinic, we may find new insights into the keys for success in natural product-based drug discovery.

Flipping the switch from g1 to s phase with e3 ubiquitin ligases

The cell cycle ensures genome maintenance by coordinating the processes of DNA replication and chromosome segregation. Of particular importance is the irreversible transition from the G1 phase of the cell cycle to S phase. This transition marks the switch from preparing chromosomes for replication ("origin licensing") to active DNA synthesis ("origin firing"). Ubiquitin-mediated proteolysis is essential for restricting DNA replication to only once per cell cycle and is the major mechanism regulating the G1 to S phase transition. Although some changes in protein levels are attributable to regulated mRNA abundance, protein degradation elicits very rapid changes in protein abundance and is critical for the sharp and irreversible transition from one cell cycle stage to the next. Not surprisingly, regulation of the G1-to-S phase transition is perturbed in most cancer cells, and deregulation of key molecular events in G1 and S phase drives not only cell proliferation but also genome instability. In this review we focus on the mechanisms by which E3 ubiquitin ligases control the irreversible transition from G1 to S phase in mammalian cells.

Cell cycle-regulated protein abundance changes in synchronously proliferating HeLa cells include regulation of pre-mRNA splicing proteins

Cell proliferation involves dramatic changes in DNA metabolism and cell division, and control of DNA replication, mitosis, and cytokinesis have received the greatest attention in the cell cycle field. To catalogue a wider range of cell cycle-regulated processes, we employed quantitative proteomics of synchronized HeLa cells. We quantified changes in protein abundance as cells actively progress from G1 to S phase and from S to G2 phase. We also describe a cohort of proteins whose abundance changes in response to pharmacological inhibition of the proteasome. Our analysis reveals not only the expected changes in proteins required for DNA replication and mitosis but also cell cycle-associated changes in proteins required for biological processes not known to be cell-cycle regulated. For example, many pre-mRNA alternative splicing proteins are down-regulated in S phase. Comparison of this dataset to several other proteomic datasets sheds light on global mechanisms of cell cycle phase transitions and underscores the importance of both phosphorylation and ubiquitination in cell cycle changes.