Ccr20th Anniversary Commentary

CCR 20th Anniversary Commentary 20th Anniversary Commentary

CCR 20th Anniversary Commentary: In the Beginning, There Was PS-341 Beverly A. Teicher1 and Kenneth C. Anderson2

Proteasome inhibitors have a 20-year history in cancer ther- proteasome inhibitors with publication of reports on bortezo- apy. The first proteasome inhibitor, bortezomib, a breakthrough mib, carfilzomib, and the oral proteasome inhibitor ixazomib treatment for multiple myeloma, moved rapidly through devel- (MLN9708). Clin Cancer Res; 21(5); 939–41. 2015 AACR. opment from the bench in 1994 to first FDA approval in 2003. See related article by Teicher et al., Clin Cancer Res 1999;5(9) Clinical Cancer Research has chronicled the development of September 1999;2638–45

The incorporation of the first-in-class proteasome inhibitor, CFU-GM from the same mice. PS-341 increased the tumor cell bortezomib, to the antimyeloma armamentarium can be consid- killing of radiotherapy, cyclophosphamide, and cisplatin in mice ered one of the major milestones in the treatment of patients with bearing the EMT-6 tumor. In the tumor-growth delay assay, PS-341 myeloma, greatly improving the response rates and overall sur- had antitumor activity against both primary and metastatic Lewis vival in both first-line and relapsed/refractory settings. lung carcinoma. In combination regimens with 5-fluorouracil, The regulation of protein activities by proactive synthesis and cisplatin, paclitaxel, and doxorubicin, PS-341 produced additive degradation is vital to cellular metabolic integrity and prolifera- tumor-growth delays against the subcutaneous tumor and was tion. The proteasome, a large, multimeric protease complex, has a highly effective against disease metastatic to the lungs (2). central role in cellular protein regulation through catabolism of a In 1995, PS-341, along with several analogues, was submitted to wide variety of proteins, resulting in the activation of certain the NCI-60 cell line screen and was found to have potent, wide- pathways and the blocking of others (1). The proteasome degrades ranging activity in solid and liquid tumor cell lines. A good proteins that have been conjugated to multiple units of the correlation was established between proteasome inhibition and polypeptide ubiquitin; this is the ubiquitin–proteasome pathway. cell line response among tested compounds. PS-341 produced a In 1993, Alfred Goldberg, the discoverer of the proteasome, unique pattern in the COMPARE analysis, suggesting that PS-341 along with his colleagues founded the company MyoGenetics to had a novel mechanism of action. PS-341 had antitumor activity in develop proteasome inhibitors to treat muscle-wasting conditions. several human solid tumor xenografts (3). In 1996, increased Julian Adams, a medicinal chemist, was recruited to head the nuclear factor kB(NF-kB) activity was associated with increased company (Fig. 1). Because proteasome inhibitors were quite toxic, tumor cell survival, adhesion of tumor to bone marrow, and IL6 a new therapeutic focus was needed. The lead compound, MG-341, secretion in the bone marrow milieu in multiple myeloma. The selectively inhibited the chymotryptic activity of the 20S protea- function of NF-kB is inhibited through binding to its inhibitor, IKB. some. In 1994, the anticancer activity of the boronic acid dipeptide Release of activated NF-kB follows proteasome-mediated degrada- proteasome inhibitor MG-341 was examined in vitro and in vivo at tion of IKB after phosphorylation and conjugation with ubiquitin. the Dana-Farber Cancer Institute. Publication of the results was Myeloma cells have increased IKB phosphorylation and increased held up for several years, during which time MyoGenetics became NF-kB activity compared with normal hematopoietic cells. PS-341 ProScript and MG-341 became PS-341. PS-341 was a potent blocked nuclear translocation of NF-kB and demonstrated antitu- cytotoxic agent toward MCF-7 human breast carcinoma cells in mor activity against chemoresistant and chemosensitive myeloma culture, producing an IC90 of 0.05 mmol/L on 24-hour exposure. In cells alone and in models of the bone marrow microenvironment the EMT-6 tumor cell survival assay, PS-341 was potently cytotoxic in both in vitro and in vivo murine xenograft models of human when administered to mice. PS-341 was also toxic to bone marrow myeloma. Moreover, the sensitivity of chemoresistant myeloma cells to chemotherapeutic agents was markedly increased when these agents were combined with PS-341 (4). 1Division of Cancer Treatment and Diagnosis, National Cancer Insti- ProScript was acquired by Millennium Pharmaceuticals in tute, Rockville, Maryland. 2Dana-Farber Cancer Institute, Harvard 1999. Critical to enabling the development of PS-341 was the Medical School, Boston, Massachusetts. development of a suitable formulation that produced a stable Corresponding Author: Beverly A. Teicher, National Cancer Institute, National composition that released the boronic acid compound in aqueous Institutes of Health, 9609 Medical Center Drive, RM 4-W602, MSC 9735, media (5). The formulation and preclinical safety testing of PS- Bethesda, MD 20892. Phone: 240-276-5972; Fax: 240-276-7895; E-mail: 341 in the formulation was carried out by the Developmental [email protected] or [email protected] Therapeutics Program of the National Cancer Institute. Several doi: 10.1158/1078-0432.CCR-14-2549 phase I clinical trials were conducted with bortezomib with varied 2015 American Association for Cancer Research. dosing schedules and patient groups. In 2002, a breakthrough

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1995: Myogenetics 2006: FDA approves 2010: phase III 2013: oral MLN9708 2001: preclinical becomes bortezomib for refractory of carﬁlzomib in myeloma phase III results in CCR ProScript mantle cell lymphoma myeloma (ongoing) (ongoing)

2003: FDA approves 2009: Onyx 2012: MLN9708 2014: MLN9708 1994: Teicher lab 1999: initial bortezomib for Pharmaceuticals myeloma phase I active against explores MG-341 anticancer third-line therapy acquires Proteolix results at ASH myeloma bone in cancer models activity in CCR in myeloma (carﬁlzomib) Annual Meeting disease in CCR

1990 1995 2000 2005 2010 2015

1993: Myogenetics 1999: Millennium 2003: 2008: FDA 2010: Onyx 2012: FDA founded Pharmaceuticals proteasome in approves reports approves Kyprolis acquires ProScript myeloma in CCR bortezomib for positive for third-line ﬁrst-line treatment phase II treatment in myeloma in myeloma in myeloma

1995: PS-341 2002: phase I 2005: FDA approves 2009: 2011: MLN9708 2014: FDA submitted to results include 9 bortezomib for carﬁlzomib active in approves Velcade NCI-60 screen multiple myeloma second-line treatment phase I myeloma in mantle cell responders in myeloma in CCR models in CCR lymphoma

Figure 1. Timeline highlighting the discovery and development of proteasome inhibitor anticancer agents and the role of Clinical Cancer Research (CCR) in communicating these important ﬁndings.

phase I clinical trial of bortezomib in patients with refractory to progression was increased by a factor of 2 to 4 with bortezomib hematologic malignancies was reported. Patients received borte- compared with the last therapy patients received before entering zomib twice weekly for 4 weeks at escalating doses, followed by a the study. Responses were associated with increased hemoglobin 2-week rest period. Twenty-seven patients received 293 doses of levels and decreased transfusion requirements, improved quality bortezomib, including 24 complete cycles. Dose-limiting toxici- of life, and improved levels of normal immunoglobulins. ties attributed to bortezomib included thrombocytopenia, hypo- Although this trial was uncontrolled, several methods were used natremia, hypokalemia, fatigue, and malaise. In pharmacody- to reduce bias in assessing the response to therapy. Each patient namic studies, bortezomib induced 20S proteasome inhibition in was used as his or her own control in the assessment of the time to a time- and dose-dependent manner. Among 9 fully assessable progression of disease relative to that with the last therapy patients with heavily pretreated plasma cell malignancy complet- received before enrollment, and a landmark analysis was per- ing one cycle of therapy, there was one complete response and a formed to demonstrate an association between a response to reduction in paraprotein levels and/or marrow plasmacytosis in 8 bortezomib alone and survival. In addition, the median duration other patients. In addition, one patient with mantle cell lymphoma of survival among patients without a response (8 months) was and another with follicular lymphoma had shrinkage of nodal within the range (6–9 months) that was expected on the basis of disease. Bortezomib showed activity against refractory multiple the literature. Response to bortezomib did not correlate with most myeloma and possibly non–Hodgkin lymphoma in this study (6). of the standard myeloma prognostic factors, including the dele- This phase I clinical trial, along with preclinical evidence of tion of chromosome 13, which predicts a poor outcome with antimyeloma activity, provided the rationale for a multicenter, conventional therapy. An international, randomized, multicenter open-label, nonrandomized phase II study of bortezomib for the phase III trial comparing bortezomib with high-dose dexameth- treatment of relapsed, refractory myeloma. The phase II trial asone in patients with relapsed multiple myeloma was initiated reported in 2003 enrolled 202 patients. Of 193 patients who (7). In 2003, bortezomib was approved for the treatment of could be evaluated, 92% had been treated with three or more of refractory multiple myeloma, and in 2005 bortezomib was the major classes of agents for myeloma, and in 91%, the mye- approved for treatment of patients with multiple myeloma who loma was refractory to the therapy received most recently. The had received at least one prior therapy. On June 23, 2008, the FDA overall rate of response to bortezomib was 35%, and those with a approved bortezomib for use in patients with multiple myeloma response included 7 patients in whom myeloma protein became as an initial treatment. In 2006, bortezomib was approved for undetectable and 12 in whom myeloma protein was detectable treatment of relapsed or refractory mantle cell lymphoma, and in only by immunoﬁxation. The median overall survival was 16 2014 it was approved for previously untreated patients with months, with a median duration of response of 12 months. Time mantle cell lymphoma.

940 Clin Cancer Res; 21(5) March 1, 2015 Clinical Cancer Research

The success of bortezomib sparked further investigation of the of MLN2238 versus bortezomib showed a significantly longer proteasome as a target for anticancer therapy. Carfilzomib (PR- survival time in mice treated with MLN2238 than mice receiving 171) is a novel irreversible proteasome inhibitor of the epoxy- bortezomib. Immununostaining of tumors from MLN2238-trea- ketone class that is structurally and mechanistically distinct from ted mice showed growth inhibition, apoptosis, and decreased bortezomib. Consequently, proteasome inhibition is more sus- angiogenesis. Mechanistic studies showed that MLN2238-trig- tained with carfilzomib than with bortezomib. The epoxyketone gered apoptosis was associated with inhibition of NF-kB activa- pharmacophore of carfilzomib is highly selective for the NH2- tion. Combining MLN2238 with lenalidomide, histone deacety- terminal threonine residue that catalyzes enzymatic activity in lase inhibitor suberoylanilide hydroxamic acid, or dexametha- each of the proteolytic active sites within the proteasome. In a sone increased antimyeloma activity (9). Bortezomib slows pro- phase I trial, reported in 2009, evaluating the safety and efficacy of gression of myeloma bone disease. This beneficial impact of carfilzomib in relapsed or refractory hematologic malignancies, bortezomib on bone metabolism is not due to antimyeloma 29 patients enrolled that were relapsed or refractory after at least activity; bortezomib directly interferes with osteoclastogenesis two prior therapies. Nonhematologic toxicities included fatigue, and resorption and promotes osteoblast formation and function. nausea, febrile neutropenia, thrombocytopenia, and diarrhea in Clinical trials of orally administered MLN9708 (now in phase III) more than one third of patients. Antitumor activity was observed indicate that the agent is tolerable, with infrequent peripheral at doses 11 mg/m2, with one unconfirmed complete response neuropathy and clinical antimyeloma activity reported either (mantle cell), one partial response (multiple myeloma), and two when it is used alone or in combination with other antimyeloma minimal responses (multiple myeloma and Waldenstrom€ mac- drugs, as well as signs of additional beneficial bone effects (10, 11). roglobulinemia). This first clinical use of carfilzomib indicated Six of the nine reports highlighted in this short history of that the agent was tolerable and had clinical activity in multiple proteasome inhibitor anticancer agents were published in CCR. hematologic malignancies (8). In 2012, carfilzomib was The 20-year history of proteasome inhibitors in cancer coin- approved for the treatment of patients with myeloma who have cideswiththe20yearsofCCR. It is an honor to be part of the received at least two prior therapies, including bortezomib and an story. immunomodulatory agent. MLN9708 (ixazomib citrate), a novel orally bioactive protea- Disclosure of Potential Conflicts of Interest some inhibitor, hydrolyzes to the biologically active compound K.C. Anderson is a consultant/advisory board member for Millennium MLN2238 (ixazomib), which preferentially and reversibly inhi- Pharmaceuticals. No potential conflicts of interest were disclosed by the other bits the proteasome chymotryptic–like subunit, resulting in the author. accumulation of ubiquitinated proteins. MLN2238 had a stron- ger, more sustained proteasome inhibition in xenograft tumors, Authors' Contributions and a weaker, less sustained effect in whole blood than did Conception and design: B.A. Teicher, K.C. Anderson bortezomib. MLN2238 inhibited growth and induced apoptosis Writing, review, and/or revision of the manuscript: B.A. Teicher, in multiple myeloma cells resistant to conventional and borte- K.C. Anderson zomib therapies without affecting the viability of normal cells. In animal tumor models, MLN2238 inhibited tumor growth with Received October 2, 2014; accepted December 3, 2014; published online significantly reduced tumor recurrence. A head-to-head analysis March 2, 2015.

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Beverly A. Teicher and Kenneth C. Anderson

Clin Cancer Res 2015;21:939-941.

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