Targeting gamma secretase: has progress moved up a Notch?
Authors: E.E. Ileana Dumbrava, G.B. Mills, T.A. Yap
Journal: Annals of Oncology (2018)

Notch signaling is a highly conserved pathway with critical roles in cell–cell communication, embryogenesis and homeostasis in tissues of adult organisms [1.Andersson E.R. Sandberg R. Lendahl U. Notch signaling: simplicity in design, versatility in function.Development. 2011; 138: 3593-3612Crossref PubMed Scopus (688) Google Scholar]. In cancer, Notch dysregulation is involved in wide ranging aspects of tumor biology, including oncogenesis and cancer progression, angiogenesis and in shaping tumor immunity [2.Phng L.-K. Gerhardt H. Angiogenesis: a team effort coordinated by Notch.Dev Cell. 2009; 16: 196-208Abstract Full Text Full Text PDF PubMed Scopus (610) Google Scholar, 3.Hossain F. Majumder S. Ucar D.A. et al.Notch signaling in myeloid cells as a regulator of tumor immune responses.Front Immunol. 2018; 9: 1288.Crossref PubMed Scopus (35) Google Scholar, 4.Ranganathan P. Weaver K.L. Capobianco A.J. Notch signalling in solid tumours: a little bit of everything but not all the time.Nat Rev Cancer. 2011; 11: 338-351Crossref PubMed Scopus (627) Google Scholar]. Activating mutations in NOTCH1 have been described in T-cell acute lymphoblastic leukemia, B-cell chronic lymphocytic leukemia and non-small-cell lung cancer [5.Weng A.P. Ferrando A.A. Lee W. et al.Activating mutations of NOTCH1 in human T cell acute lymphoblastic leukemia.Science. 2004; 306: 269-271Crossref PubMed Scopus (2237) Google Scholar, 6.Rossi A. Di Maio M. Chiodini P. et al.Carboplatin- or cisplatin-based chemotherapy in first-line treatment of small-cell lung cancer: the COCIS meta-analysis of individual patient data.J Clin Oncol. 2012; 30: 1692-1698Crossref PubMed Scopus (337) Google Scholar, 7.Ntziachristos P. Lim J.S. Sage J. Aifantis I. From fly wings to targeted cancer therapies: a centennial for Notch signaling.Cancer Cell. 2014; 25: 318-334Abstract Full Text Full Text PDF PubMed Scopus (264) Google Scholar, 8.Westhoff B. Colaluca I.N. D'Ario G. et al.Alterations of the Notch pathway in lung cancer.Proc Natl Acad Sci USA. 2009; 106: 22293-22298Crossref PubMed Scopus (323) Google Scholar], while loss of function mutations in NOTCH receptors have been observed in acute myelogenous leukemia (AML), and squamous cell carcinomas [9.Kannan S. Sutphin R.M. Hall M.G. et al.Notch activation inhibits AML growth and survival: a potential therapeutic approach.J Exp Med. 2013; 210: 321-337Crossref PubMed Scopus (121) Google Scholar, 10.Wang N.J. Sanborn Z. Arnett K.L. et al.Loss-of-function mutations in Notch receptors in cutaneous and lung squamous cell carcinoma.Proc Natl Acad Sci USA. 2011; 108: 17761-17766Crossref PubMed Scopus (331) Google Scholar, 11.Zhang M. Biswas S. Qin X. et al.Does Notch play a tumor suppressor role across diverse squamous cell carcinomas?.Cancer Med. 2016; 5: 2048-2060Crossref PubMed Scopus (31) Google Scholar], suggesting that Notch signaling is complex, with NOTCH possibly acting as an oncogene or tumor suppressor depending on context or tumor and/or cell type. The activation of the Notch pathway may also be influenced by key oncogenic mechanisms, such as copy number alterations, epigenetic changes and cross-talk with other signaling pathways [12.Bhagat T.D. Zou Y. Huang S. et al.Notch pathway is activated via genetic and epigenetic alterations and is a therapeutic target in clear cell renal cancer.J Biol Chem. 2017; 292: 837-846Abstract Full Text Full Text PDF PubMed Scopus (33) Google Scholar, 13.Camps J. Pitt J.J. Emons G. et al.Genetic amplification of the NOTCH modulator LNX2 upregulates the WNT/β-catenin pathway in colorectal cancer.Cancer Res. 2013; 73: 2003Crossref PubMed Scopus (61) Google Scholar, 14.Chen J. Imanaka N. Chen J. Griffin J.D. Hypoxia potentiates Notch signaling in breast cancer leading to decreased E-cadherin expression and increased cell migration and invasion.Br J Cancer. 2010; 102: 351-360Crossref PubMed Scopus (273) Google Scholar]. Genomically matched targeted therapies have been shown to lead to improved survival and clinical outcomes in molecularly selected patients, justifying the continued development of such antitumor agents [15.Massard C. Michiels S. Ferté C. et al.High-throughput genomics and clinical outcome in hard-to-treat advanced cancers: results of the MOSCATO 01 Trial.Cancer Discov. 2017; 7: 586-595Crossref PubMed Scopus (419) Google Scholar]. There are different strategies in targeting the Notch signaling pathway, including the development of monoclonal antibodies against the NOTCH transmembrane receptors (NOTCH 1–4) or gamma-secretase complex proteolytic activity (γ-secretase) inhibitors that prevent the release of the Notch intracellular domain (NICD) and thus its translocation to the nucleus where it mediates its main activity. This inhibits the DNA-binding protein CSL (CBF1–Suppressor of Hairless–LAG1) and the co-activator MAML1 (Mastermind-like transcriptional co-activator 1), thus blocking the transcription of target genes that regulate cell proliferation and survival, which normally occur during Notch pathway activation [16.Kopan R. Ilagan M.X.G. The canonical Notch signaling pathway: unfolding the activation mechanism.Cell. 2009; 137: 216-233Abstract Full Text Full Text PDF PubMed Scopus (2553) Google Scholar] (Figure 1). In the original article by Massard and co-investigators published in Annals of Oncology, the results of a phase I multicenter trial of LY3039478—a potent orally bioavailable γ-secretase inhibitor—are reported [17.Massard C. Azaro A. Soria J.-C. et al.First-in-human study of LY3039478, an oral notch signaling inhibitor in advanced or metastatic cancer.Ann Oncol. 2018; 29: 1911-1917Abstract Full Text Full Text PDF PubMed Scopus (78) Google Scholar]. LY3039478 is one of the most potent γ-secretase inhibitors, which demonstrated monotherapy activity and acceptable toxicity in animal model systems, justifying its transition to the clinic [18.Bender M.H. Gao H. Capen A.R. et al.Abstract 1131: novel inhibitor of Notch signaling for the treatment of cancer.Cancer Res. 2013; 73: 1131Google Scholar]. The primary objectives were to determine (part A, dose escalation) and confirm (part B, dose expansion) the recommended phase II dose, while secondary objectives included the evaluation of safety, tolerability, pharmacokinetics, pharmacodynamics and preliminary antitumor activity of LY3039478. A total of 110 patients were enrolled in 8 centers globally, with the majority of patients heavily pre-treated at least 4 lines of prior systemic therapies. The most frequent tumor types enrolled were colorectal, ovarian, breast and adenoid cystic carcinomas. During dose escalation (part A), 55 patients were treated with increasing doses of LY3039478, ranging from 2.5 to 100 mg TIW of LY3039478 in 28-day cycles. The dose expansion phase (part B) initially included 25 patients who received a dose of 75 mg TIW, but this dose was subsequently decreased to 50 mg TIW to improve the gastrointestinal tolerance of LY3039478; an additional 50 patients then received LY3039478 at 50 mg TIW. Although three of five dose-limiting toxicities (DLTs) comprised grade 4 thrombocytopenia, the investigators reported that these were likely to be confounded by the patients' underlying clinical conditions; no other grade 3–4 thrombocytopenia adverse events were observed in the study. Other DLTs comprised grade 3 nausea and grade 3 colitis, with goblet cell hyperplasia and reversible mucoid enteropathy affecting the small and large intestine, which has previously been described with Notch inhibitors [19.Searfoss G.H. Jordan W.H. Calligaro D.O. et al.Adipsin, a biomarker of gastrointestinal toxicity mediated by a functional γ-secretase inhibitor.J Biol Chem. 2003; 278: 46107-46116Abstract Full Text Full Text PDF PubMed Scopus (323) Google Scholar]. The most common treatment-related adverse events were grade 1–2 diarrhea, nausea/vomiting, fatigue and anorexia. Pharmacodynamic studies indicated target modulation, albeit in skin which may not accurately reflect the tumor ecosystem, with the inhibition of several Notch-regulated genes, such as hairy and enhancer of split-1 (HES1), cyclin-D1 (CCND1) and Notch-regulated ankyrin repeat (NRARP) at doses of 45–100 mg of LY3039478 TIW. Importantly, LY3039478 at optimal doses altered plasma Aβ by 80%, which is indicative of γ-secretase inhibition. However, whether an 80% change in Aβ is sufficient to indicate interdiction of functional NICD signaling has not yet been resolved. Indeed, LY3039478 only demonstrated modest clinical benefit rates (defined as RECIST complete and partial responses and/or RECIST stable disease) of 11% during dose escalation and 9% in dose expansion. This was despite mandating that patients during dose expansion harbored NOTCH 1–4 alterations (mutations or amplifications), Notch overexpression or FBXW7 mutations. This may potentially be due to context dependency between different tumor types, or the lack of variant interpretation of the true actionability of each of the NOTCH alterations. Furthermore, it may also indicate that inhibition of the Notch pathway to 20% of baseline levels is insufficient to induce cell death, or that bypass mechanisms are readily engaged in human tumors. One patient with ER/PR+ and HER2 1+ breast cancer harboring an FBXW7 mutation did have an RECIST partial response lasting 9.5 months, potentially highlighting the importance of FBXW7 in the regulation of Notch signaling, as suggested in preclinical studies [20.Matsumoto A. Onoyama I. Sunabori T. et al.Fbxw7-dependent degradation of Notch is required for control of "stemness" and neuronal-glial differentiation in neural stem cells.J Biol Chem. 2011; 286: 13754-13764Abstract Full Text Full Text PDF PubMed Scopus (83) Google Scholar]. However, other patients with FBXW7 mutations were treated on trial without response, possibly because of co-alterations and activation of other pathways. Although no objective RECIST responses were observed in patients with adenoid cystic carcinoma, where activation of the Notch pathway was previously described as a key dysregulated pathway [21.Ho A.S. Kannan K. Roy D.M. et al.The mutational landscape of adenoid cystic carcinoma.Nat Genet. 2013; 45: 791-798Crossref PubMed Scopus (317) Google Scholar], three patients demonstrated durable stable disease of at least 8 months and one patient with positive NOTCH1 expression had an unconfirmed metabolic partial response. Given the important roles of Notch signaling in cancer initiation and progression, several clinical phase I–II trials with γ-secretase inhibitors have been conducted. However, the clinical development of the majority of these agents has been hampered by narrow therapeutic indices, with limited antitumor activity and serious gastrointestinal toxicities observed. Nonetheless, anecdotal clinical responses have been observed in patients with anaplastic astrocytoma, desmoid tumors, colorectal cancers with neuroendocrine features, and papillary thyroid cancers in early phase clinical trials [22.Tolcher A.W. Messersmith W.A. Mikulski S.M. et al.Phase I study of RO4929097, a gamma secretase inhibitor of Notch signaling, in patients with refractory metastatic or locally advanced solid tumors.J Clin Oncol. 2012; 30: 2348-2353Crossref PubMed Scopus (192) Google Scholar, 23.Krop I. Demuth T. Guthrie T. et al.Phase I pharmacologic and pharmacodynamic study of the gamma secretase (Notch) inhibitor MK-0752 in adult patients with advanced solid tumors.JCO. 2012; 30: 2307-2313Crossref PubMed Scopus (235) Google Scholar, 24.Kummar S. O'Sullivan Coyne G. Do K.T. et al.Clinical activity of the γ-secretase inhibitor PF-03084014 in adults with desmoid tumors (aggressive fibromatosis).JCO. 2017; 35: 1561-1569Crossref PubMed Scopus (103) Google Scholar]. Understanding when NICD is modified and how these modifications influence its activity will be important for the future development of γ-secretase inhibitors in rationally selected patients. The limited clinical activity as single agent with γ-secretase inhibitors might also be explained by resistance mechanisms simultaneously blocking apoptosis and inducing cytoprotective autophagy, resulting in increased cancer cell survival [25.Timme C.R. Gruidl M. Yeatman T.J. Gamma-secretase inhibition attenuates oxaliplatin-induced apoptosis through increased Mcl-1 and/or Bcl-xL in human colon cancer cells.Apoptosis. 2013; 18: 1163-1174Crossref PubMed Scopus (32) Google Scholar]. This may be overcome through rational combinations with chemotherapy and other molecularly targeted agents. However, a major challenge will be the management of gastrointestinal toxicities that may be exacerbated by many of these drug combinations. A phase I clinical trial with LY3039478 in combination with the CDK4/6 inhibitor abemaciclib, Hedgehog inhibitor taladegib or chemotherapy is currently ongoing (NCT02784795). Notch signaling has also been shown to be a key player in shaping the immune microenvironment by increasing pro-tumoral monocytes and macrophages in breast cancer [26.Shen Q. Cohen B. Zheng W. et al.Notch shapes the innate immunophenotype in breast cancer.Cancer Discov. 2017; 7: 1320-1335Crossref PubMed Scopus (74) Google Scholar] and decreasing cytotoxic T cells in pancreatic adenocarcinoma [27.Balli D. Rech A.J. Stanger B.Z. Vonderheide R.H. Immune cytolytic activity stratifies molecular subsets of human pancreatic cancer.Clin Cancer Res. 2017; 23: 3129-3138Crossref PubMed Scopus (143) Google Scholar], thus providing the rationale for possible combination studies with immunotherapy. Furthermore, γ-secretase inhibition increases the recognition of multiple myeloma by B-cell maturation antigen (BCMA)-chimeric antigen receptor (CAR) T cells and a combination study with BCMA-specific CAR-T cells plus LY3039478 is currently ongoing in patients with refractory or relapsed multiple myeloma (NCT03502577). Overall, the study by Massard et al. has demonstrated limited antitumor activity of LY3039478 monotherapy in a heterogeneous unselected population, but with manageable gastrointestinal toxicity. Notch inhibitor strategies using rational drug combinations in molecularly selected patients are thus now urgently required in order to advance the field up a few notches. None declared.