Topics in Anti-Cancer Research: Volume 8

Novel Drugs for Multiple Myeloma

Pawel Robak, Tadeusz Robak*

Department of Hematology Medical University of Lodz, Copernicus Memorial Hospital Ul. Ciolkowskiego 2, Lodz 93-510, Poland

Abstract

Multiple Myeloma (MM) is a complex disease considered incurable in the majority of patients; however, several new treatments have been developed over the last decade, including third generation immunomodulatory drugs (pomalidomide), second generation proteasome inhibitors (carfilzomib and ixazomib), a histone deacetylase inhibitor (panobinostat) and monoclonal antibodies (elotuzumab and daratumumab). In addition, some new agents with unique mechanisms of action are in the process of development. Of these, isatuximab, oprozomib, filanesib (ARRY-520), dinaciclib, venetoclax, selinexor, melflufen and LGH-447 are the most promising, demonstrating preclinical single-agent activity against MM. In this chapter, we present the current status of newer and investigational anti-myeloma agents, and outline future directions for clinical use. We also summarize recent developments in the treatment of MM patients, obtained through a thorough literature review of all WO, EP and US patents filed in 2010-2018, using PubMed and http://ep.espacenet.com/ as sources. The development of novel drugs will hopefully lead to therapies with more potent effects.

Keywords: Afuresertib, bortezomib, citarinostat, daratumumab, elotuzumab, filanesib, ixazomib, isatuximab, lenalidomide, melflufen, nivolumab, oprozomib, panobinostat, pembrolizumab, pomalidomide, ricolinostat, selinexor, trametinib, venetoclax, vorinostat.

* Corresponding author Tadeusz Robak: Department of Hematology Medical University of Lodz Copernicus Memorial Hospital Ul. Ciolkowskiego 2, Lodz 93-510, Poland; Tel: +48 42 689-51-91; Fax: + 48 42 689-51-92;

E-mail: robaktad@csk.umed.lodz.pl

1. INTRODUCTION

Multiple Myeloma (MM) is characterized by the malignant proliferation of plasma cells, resulting in bone lesions, hypercalcemia, infections, anemia and production of monoclonal immunoglobulin [1]. It is the second most common adult hematologic malignancy, accounting for 1.3% of all malignancies and 15% of hematological neoplasms with an annual incidence of 4.5 to six cases per 100 000 people [2]. Approximately 86 000 new cases of MM occur annually worldwide [3]. In the United States, it was estimated that 30 280 new cases and 12

590 attributable deaths occurred in 2017 [4], and its incidence has increased over the last decade, bringing with it considerable clinical, social and economic impact [5]. The median age at diagnosis is believed to be 72 years, with a mortality of 4.1/100 000/year [6].

Recent ESMO guidelines specify that a diagnosis of MM requires the presence of ≥ 10% clonal bone marrow plasma cells or biopsy-proven bony or extramedullary plasmacytoma, together with the occurrence of at least one of the following myeloma-defining events: hypercalcaemia, anaemia, bone lesions, ≥ 60% clonal Bone Marrow (BM) plasma cells or serum-free light chain ratio ≥ 100 [7]. The disease progresses from a premalignant stage called Monoclonal Gammopathy of Undetermined Significance (MGUS). MGUS is defined as a plasma cell-proliferative disorder characterized by plasma cell content of less than 10% in the BM, M-protein in serum < 30g/L, with no end organ damage and no evidence of other B-cell lymphoproliferative disorder [8]. MGUS is a common disorder in older people, accounting for 3.2% of Caucasian individuals aged over 50 years [9] and 5.3% of those aged 70 years or more. This disorder precedes the development of MM with a rate of MM transformation of 1% per year [10-12]. Symptomatic MM is characterized by neoplastic proliferation of a single clone of plasma cells producing M-protein, inducing end-organ damage, including bone lesions, anemia, renal insufficiency, and hypercalcemia (CRAB symptoms) [7, 8, 13]. MM remains an incurable disease with a median Overall Survival (OS) of six to 10 years depending on the age at diagnosis [6, 7].

2. PATHOGENESIS OF MULTIPLE MYELOMA

Multiple Myeloma (MM) develops from an accumulation of terminally-differentiated monoclonal plasma cells in the Bone Marrow (BM). MM tumor cells originate in the BM, but they are able to migrate into the peripheral blood and other tissues. MM is a multifocal disease characterized by spatial genomic heterogeneity, with several genetically-distinct malignant sub-clones [14]. Both the interaction between MM cells and host factors, and the BM microenvironment itself, play important roles in the molecular evolution of the disease and the generation of treatment-resistant cells; they also influence disease progression, with the possible development of relapsed or refractory MM [15]. The MM BM microenvironment is composed of osteoblasts, osteoclasts, BM stromal cells, an immunosuppressive milieu of cytokines, Myeloid-Derived Suppressor Cells (MDSC) and regulatory T cells. Interactions with the adhesion molecules on the surface of MM cells and the ECM components of the BM allow malignant plasma cells to disseminate throughout the BM microenvironment, during which, they receive multiple signals that maintain their survival and influence drug-induced apoptosis [16, 17]. MM plasma cells are typically found in the BM, where their growth, survival and potential drug resistance are fostered by the cellular and extracellular components of the microenvironment [18]. In this environment, MM cells adhere to BM cells with the aid of the VLA-4/ VCAM-1 integrin system [19].

The activation of the nuclear factor κB (NF-κB) family of transcription factors is typically dysregulated in MM cells; this results in greater stimulation of the cells due to the overexpression of several tumor-promoting cytokines, including Tumor Necrosis Factor (TNF), IL-1, IL-6 and BAFF [20]. This signaling can also stimulate the expression of pro-survival factors, including cFLIP, cIAP2, Bcl-xL and Bcl-2, which stimulate the growth of MM cells and protect them from the action of apoptosis-inducing chemotherapeutic agents. NF-κB signaling has also been implicated in the elevated expression of adhesion molecules such as ICAM1, which are produced by tumor cells in a NF-κB-dependent fashion. Elevated secretion of cytokines, mainly Vascular Endothelial Growth Factor (VEGF) and Fibroblast Growth Factor-2 (FGF-2) results in increased angiogenesis in the BM [21], accompanied by elevated interleukin-6 (IL-6) secretion by BM endothelial cells; thus hastening MM progression and weakening survival [22, 23].

Osteolysis is commonly observed in MM due to the activation of osteoclast progenitors, the initiation of osteoclastic bone resorption and the suppression of osteoblasts. This complex process is induced by the interaction between MM cells and the bone microenvironment via several intercellular signaling cascades, the key ones being RANK/RANKL/OPG, Notch and Wnt. Osteocytes play an important role in osteolysis through the production and secretion of various agents including Receptor Activator of NF-κB Ligand (RANKL), sclerostin and Dickkopf-1 (DKK-1) [24]. However, neoplastic plasma cells alter the BM microenvironment by stimulating the apoptosis of osteocytes, thus creating a premetastatic niche for further expansion of MM cells [25]. Osteoclast formation in the BM is stimulated by the adherence of MM cells via the action of the osteoclastogenic Vascular Cell Adhesion Molecule 1 (VCAM-1) and α4β1 integrin; together with RANKL, these factors are known to induce osteolysis [26]. These osteoclast-activation and bone reabsorption activities are also supported by the Interleukin- (IL-1β) and TNF-β produced by neoplastic plasma cells [27].

Cases of MM are typified by an upregulation of proteasome activity, and hence a disruption in the balance between the synthesis and degradation of proteins in the neoplastic plasma cells. As a result, excessive degradation occurs of the tumor suppressor p53 and the inhibitor of NF-κB in the Ubiquitin-Proteasome (UPS) pathway, leading to abnormalities in key cellular processes such as regulation of cell cycle progression, apoptosis, antigen presentation and transcription [28].

3. NOVEL DRUGS FOR MULTIPLE MYELOMA

In recent years, several new drugs with different mechanisms of action have transformed our approach to the treatment of patients with relapsed/refractory MM [29]. These include third-generation Immunomodulatory Drugs (IMiDs) (pomalidomide), second generation Proteasome Inhibitors (PIs) (carfilzomib and ixazomib), a histone deacetylase inhibitor (panobinostat) and monoclonal antibodies (mAbs) (elotuzumab and daratumumab). Schematic presentation of newer drugs for MM and their targets is displayed in Fig. (1).

Recently, the US Food and Drug Administration (FDA) and European Medicines Agency (EMA) have approved pomalidomide, carfilzomib, panobinostat, elotuzumab, ixazomib and daratumumab for the treatment of patients with refractory/relapsed MM.

4. PROTEASOME INHIBITORS

Three proteasome inhibitors (bortezomib, carfilzomib and ixazomib) were currently approved for the treatment of MM and several new drugs from this group are undergoing clinical trials (Fig. 2). Proteasome Inhibitors (PIs) induce the Unfolded Protein Response (UPR) and, ultimately, cell apoptosis via proteasomal inhibition. The UPR mechanism is relatively more sensitive to PIs in MM cells, resulting in the synthesis of higher levels of monoclonal proteins. PIs induce cell death through various mechanisms, including the inhibition of NF-κB activity, activation of p53, accumulation of misfolded proteins, activation of c-Jun N-terminal kinase and stabilization of cell cycle inhibitors [30-32]. These drugs may prevent NF-κB dependent upregulation of the FA/BRCA DNA repair pathway and increase the cytotoxic effect of alkylating drugs [33]. Several novel PIs with improved pharmacodynamic or pharmacokinetic properties, such as marizomib, delanzomib or oprozomib, are currently under investigation in clinical trials [34].

4.1. Bortezomib

Bortezomib (Velcade®, Millennium/Takeda, Janssen) is a first-in-class selective, reversible inhibitor of the 26S proteasome which plays a role in the degradation of many intracellular proteins [35-37]. Bortezomib exerts its antiproliferative and antitumor activity by inhibiting the proteasomal degradation of several regulatory ubiquitinated proteins; however, it demonstrates high proteasomal selectivity and does not inhibit other proteases [38, 39]. It exerts substantial anti-myeloma activity in previously-untreated and relapsed/refractory MM patients either when used as a single drug or in combination with other anti-cancer agents. Several clinical trials have found it to possess clinical activity in newly-diagnosed and relapsed/refractory MM patients, as well as in maintenance therapy [40].

Bortezomib was the first proteasome inhibitor approved by the FDA fast-track route in 2003 for the treatment of relapsed and/or refractory MM patients progressing after two prior therapies [41, 42]. In 2008, the FDA approved injected bortezomib for the treatment of previously-untreated MM. In 2012, subcutaneous administration of bortezomib was approved by the FDA and EMA for all approved indications. In 2014, the FDA approved bortezomib for the retreatment of adult patients with MM whose disease had previously responded to bortezomib therapy but had relapsed at least six months after completion [43].

Although bortezomib can be administered both intravenously and subcutaneously [44], the subcutaneous route is now recommended based on the results of the large randomized Phase III trial (MMY-3021 trial) including 222 relapsed MM patients [44]. This non-inferiority trial found that subcutaneous bortezomib induced similar Overall Response (OR) rate, time to progression, and one-year Overall Survival (OS) scores as intravenous administration. In addition, subcutaneous administration was found to be associated with greater tolerability and lower peripheral neuropathy than intravenous administration. Subcutaneous bortezomib is also more convenient for patients, and this method of administration is now recommended. Importantly, renal insufficiency does not influence the safety and efficacy of bortezomib [45], and impairments in hepatic function do not significantly influence its pharmacodynamic properties [46].

In the last three years, several generic equivalents of Velcade have become available. In 2015, the European Commission granted marketing authorisation for Bortezomib Accord (Accord Healthcare Ltd.), and in 2016, the EMA approved generic Bortezomib Hospira and Bortezomib Sun [SUN Pharmaceutical Industries B.V.)]. Generic bortezomib has a lower price and is more widely used, even in lower-income countries [47].

Bortezomib is highly effective in previously untreated MM patients, including high-risk patient subgroups. The drug is also effective in older patients with comorbidities, renal insufficiency and poor-risk cytogenetics including t(4;14) translocation or del(17p) [48, 49]. Based on the results of the current Phase 3 trials, three-drug combinations including bortezomib and dexamethasone have become the standard induction regimens in previously-untreated patients prior to Autologous Stem Cell Transplantation (ASCT) [7, 50, 51]. In certain circumstances, bortezomib - dexamethasone can be effective in older patients who may be unsuitable for ASCT. Bortezomib can also be combined with bendamustine - doxorubicin or bendamustine - dexamethasone in previously-untreated and relapsed/refractory MM patients [52, 53]. Consolidation and maintenance therapy with bortezomib following Autologous Stem Cell Transplantation (ASCT) is associated with increased Progression Free Survival (PFS) and an overall improvement in OS, especially in patients with the high-risk disease [54]. A recent study indicates that bortezomib consolidation therapy is effective in delaying disease progression and improving the quality of responses in newly-diagnosed patients following ASCT, regardless of prior bortezomib exposure, and that it is generally well tolerated [55, 56].

4.2. Carfilzomib

Carfilzomib (Kyprolis, Onyx, Amgen) is a new-generation irreversible proteasome inhibitor with significant activity in relapsed or refractory MM, even in patients pretreated with bortezomib or immunomodulatory drugs. Carfilzomib has greater activity and was found to induce longer PFS than bortezomib in patients with relapsed MM. Carfilzomib was approved by the FDA in 2012 for the treatment of relapsed and refractory MM on the basis of the PX-171-003-A1 Phase 2 Study of carfilzomib in relapsed and refractory MM [57]. Subsequently, its high activity in MM patients has been confirmed in two Phase 3 trials: the ASPIRE Phase 3 study compared carfilzomib, lenalidomide and dexamethasone with lenalidomide and dexamethasone in patients with relapsed MM [58] and the ENDEAVOR Phase 3 study compared carfilzomib and dexamethasone with bortezomib and dexamethasone in relapsed MM patients [59]. Both the trials indicated that the carfilzomib combinations were more effective than those used in the control arms. In the EMN011 trial, carfilzomib was combined with pomalidomide and dexamethasone (KPD) in MM patients refractory to bortezomib and lenalidomide [60]. All the patients received four cycles of KPD; however, those who had not previously received ASCT received high dose melphalan (200mg/m²) before ASCT, followed by consolidation with four additional cycles of KPD and pomalidomide - dexamethasone maintenance until progression. An 87% OR rate was observed, including 31% CR. At a median follow-up of 16.3 months, median PFS was 18 months

4.3. Ixazomib

Ixazomib (MLN9708; Ninlaro, Millennium/Takeda Oncology) is an oral proteasome inhibitor with high therapeutic activity in MM [61]. It was selected from boron-containing proteasome inhibitors based on a physicochemical profile distinct from bortezomib (Fig. 1) [62]. The drug can be administered intravenously and orally. Ixazomib combined with lenalidomide and dexamethasone offered improved PFS and duration of response in patients with relapsed and/or relapsed/refractory MM in comparison with those treated with lenalidomide and dexamethasone alone [63].

Based on the results of the large Phase III TOURMALINE MM1 trial, ixazomib has been approved for use in combination with lenalidomide and dexamethasone for the treatment of MM patients who have received at least one prior course of therapy [63].

Fig. (1))

Schematic presentation of newer drugs for multiple myeloma and their targets. Abbreviatins: BMSC - bone marrow stromal cell; CRBN - cereblon; XPO-1- nuclear export protein exportin- 1 ; SLAMF 7 - SLAM Family Member 7.

4.4. Marizomib

Marizomib (Salinosporamide A, NPI-0052; Triphase ResearchKasaba Hobi, Mysore) is a second-generation beta-lactone-gamma-lactam proteasome inhibitor that inhibits the three proteolytic activities of the 20S proteasome with a specificity distinct from that of bortezomib or carfilzomib [64]. The drug is in clinical development for the treatment of relapsed and refractory MM. The findings of a Phase 1 study indicate that six of 68 tested patients achieved minimal response or better, including five Partial Responses (PR) [65]. The most common Adverse Events (AE) were fatigue, headache, nausea, diarrhea, dizziness and vomiting. The optimal use of marizomib in patients presenting central nervous system AE is described in its patent form [66]. Another study including 14 patients at marizomib, pomalidomide and dexamethasone found six (54%) of 11 evaluable patients to achieve a Partial Response (PR), two (12%) a minimal response and three (27%) Stable Disease (SD) [67].

4.5. Oprazomib

Oprozomib (ONX -0912, Amgen Inc.) is another oral, irreversible PI with a mechanism of action similar to that of marizomib. In a Phase 1b/2 single-agent study performed in 106 patients, PR or better was achieved in 27% of carfilzomib-refractory patients, 33% of carfilzomib-sensitive patients and in 25% of bortezomib-refractory patients [68].

Another Phase 1b/2 study examined the use of oprozomib in combination with dexamethasone in 29 patients with the refractory/relapsed disease [69]. PR was observed in 41.7% of 12 patients receiving oprozomib in doses starting at 210mg per day given on day 1, 2, 8 and 9 of a 14-day cycle; however, no responses were seen when the drug was given on days 1 to 5 of a 14-day cycle. Oprazomib was also tested in combination with pomalidomide and dexamethasone in 31 patients with relapsed/refractory MM [70]. Of 17 patients treated with oprazomib at a dose of 210mg per day on day 1, 2, 8, 9, 15, 16, 22 and 23 of 28-day cycles with subsequent escalations, ten (59%) displayed a PR or better. The combination of oprozomib, pomalidomide and dexamethasone was well tolerated with no major side effects.

4.6. Delanzomib

Delanzomib (CEP-18770, Cephalon, Inc.) is a novel orally-active PI that lowers the activity of NF-κB. It was found to possess a favorable safety profile, with a lack of neurotoxicity [71, 72]. However, a single-agent multicenter Phase 1/2 study of delanzomib in patients with relapsed/refractory MM found that of the patients who received the MTD, 26 (55%) displayed stable disease and four (9%) PR. Median Time to Progression (TTP) was 2.5 months. Due to these disappointing results, further development of delanzomib for MM was discontinued.

4.7. Agents Under Investigation

There are several new proteasome inhibitors currently under investigation, both used alone and in combination with other agents [73-75]. Selected recent patents involving novel proteasome inhibitors which may be potentially useful in MM are listed in Table 1 [76-80]. Novel spiro- and cyclic bis-benzylidine PIs U pl09 and UP 119 have been developed recently with potential use in MM [73]. Further progress in the treatment of MM has also been made by the combination of proteasome inhibitors with existing therapies [74, 75]. In particular, proteasome-targeting analogs of rapamycin and rapamycin, such as secorapamycin, which are active in bortezomib-resistant cells, have been developed; significantly, secorapamycin acts synergistically in vitro with other proteasome inhibitors, including the clinically-approved bortezomib and carfilzomib [76]. Moreover, it has been reported recently that roneparstat, a modified heparin derivative, can increase the antimyeloma activity