Jason Ruth

MTAP deletion confers enhanced dependency on the PRMT5 arginine methyltransferase in cancer cells

Tumors put in a vulnerable position Cancer cells often display alterations in metabolism that help fuel their growth. Such metabolic “rewiring” may also work against the cancer cells, however, by creating new vulnerabilities that can be exploited therapeutically. A variety of human tumors show changes in methionine metabolism caused by loss of the gene coding for 5-methylthioadenosine phosphorylase (MTAP). Mavrakis et al. and Kryukov et al. found that the loss of MTAP renders cancer cell lines sensitive to growth inhibition by compounds that suppress the activity of a specific arginine methyltransferase called PRMT5. Conceivably, drugs that inhibit PRMT5 activity could be developed into a tailored therapy for MTAP-deficient tumors. Science, this issue pp. 1208 and 1214 Tumors cope with a genomic change by rewiring their metabolism, but this makes them more susceptible to certain drugs. The discovery of cancer dependencies has the potential to inform therapeutic strategies and to identify putative drug targets. Integrating data from comprehensive genomic profiling of cancer cell lines and from functional characterization of cancer cell dependencies, we discovered that loss of the enzyme methylthioadenosine phosphorylase (MTAP) confers a selective dependence on protein arginine methyltransferase 5 (PRMT5) and its binding partner WDR77. MTAP is frequently lost due to its proximity to the commonly deleted tumor suppressor gene, CDKN2A. We observed increased intracellular concentrations of methylthioadenosine (MTA, the metabolite cleaved by MTAP) in cells harboring MTAP deletions. Furthermore, MTA specifically inhibited PRMT5 enzymatic activity. Administration of either MTA or a small-molecule PRMT5 inhibitor showed a modest preferential impairment of cell viability for MTAP-null cancer cell lines compared with isogenic MTAP-expressing counterparts. Together, our findings reveal PRMT5 as a potential vulnerability across multiple cancer lineages augmented by a common “passenger” genomic alteration.

Par-4 Downregulation Promotes Breast Cancer Recurrence by Preventing Multinucleation following Targeted Therapy

Most deaths from breast cancer result from tumor recurrence, but mechanisms underlying tumor relapse are largely unknown. We now report that Par-4 is downregulated during tumor recurrence and that Par-4 downregulation is necessary and sufficient to promote recurrence. Tumor cells with low Par-4 expression survive therapy by evading a program of Par-4-dependent multinucleation and apoptosis that is otherwise engaged following treatment. Low Par-4 expression is associated with poor response to neoadjuvant chemotherapy and an increased risk of relapse in patients with breast cancer, and Par-4 is downregulated in residual tumor cells that survive neoadjuvant chemotherapy. Our findings identify Par-4-induced multinucleation as a mechanism of cell death in oncogene-addicted cells and establish Par-4 as a negative regulator of breast cancer recurrence.

The collaborative network approach: a new framework to accelerate Castleman's disease and other rare disease research

Despite technological advances and substantial investments of time and funding, many challenges exist for rare disease research and drug development. Basic disease mechanisms are often poorly understood, selection of suitable research participants can be diffi cult, and endpoints for clinical trial registration might not be established. Progress is further impeded by limited collaboration and data coordination, misaligned incentives, funding decisions made in isolation from community consensus, and inter-institutional barriers to tissue sharing. Although frequently used, off -label treatments are infrequently tracked, and thus valuable opportunities to build on observations are lost. One coauthor (DCF) comments, “Despite being a physician, I didn’t fully understand the barriers that slowed down life-saving progress until I was dying from a rare illness. I received my last rites in 2010 while battling idiopathic multicentric Castleman’s disease and found that [the disease] had no Food and Drug Administration [FDA]-approved therapies, a poorly understood model of pathogenesis, and a 65% 5-year survival rate”. After surviving three life-threatening episodes, DCF began to assess how non-profi t research funding was allocated for rare diseases, for which 95% of conditions do not have an FDA-approved therapy. Disease research organisations (DROs) make important contributions by funding research. However, the framework through which many (but not all) DROs traditionally distribute funding can present challenges (fi gure). DROs typically fundraise fi rst and then invite researchers to apply through a request for proposals (RFP) to use the funding for their specifi c purposes. In parallel, these organisations often provide patients with supportive resources and facilitate referrals to experts, who collect and store clinical data and biomaterials at their respective institutions. This model can in some cases result in organisations funding studies targeted at questions proposed by a small selection of researchers with requisite tissue samples rather than the studies that may have the highest impact on the fi eld, which might require collaboration and sample sharing. A more effi cient, collaborative, and consensus-driven framework than exists at present is needed to fully harness the opportunities aff orded by technological advances for the approximately 7000 rare diseases and 350 million individuals affl icted globally. One such neglected rare condition is Castleman’s disease, which describes a heterogeneous group of lymphoproliferative disorders straddling the fi elds of immunology, oncology, and virology. Castleman’s disease ranges from a single region of enlarged lymph nodes (unicentric Castleman’s disease) to multicentric lymphadenopathy with systemic infl ammation and multiple organ system dysfunction (multicentric Castleman’s disease) caused by immune activation and proinfl ammatory hypercytokinaemia, often including interleukin 6. Multicentric Castleman’s disease is either caused by human herpesvirus 8 (HHV8) infection, which is called HHV8-associated multicentric Castleman’s disease, or is idiopathic in HHV8-negative patients and called idiopathic multicentric Castleman’s disease. The absence of a unique international classifi cation of disease (ICD) code for Castleman’s disease has made epidemiological studies diffi cult. The estimated incidence of all forms of Castleman’s disease is 6500–7700 individuals of all ages every year in the USA or about 2·2 per 100 000.

SPSB1 Promotes Breast Cancer Recurrence by Potentiating c-MET Signaling

UNLABELLED Breast cancer mortality is principally due to tumor recurrence; however, the molecular mechanisms underlying this process are poorly understood. We now demonstrate that the suppressor of cytokine signaling protein SPSB1 is spontaneously upregulated during mammary tumor recurrence and is both necessary and sufficient to promote tumor recurrence in genetically engineered mouse models. The recurrence-promoting effects of SPSB1 result from its ability to protect cells from apoptosis induced by HER2/neu pathway inhibition or chemotherapy. This, in turn, is attributable to SPSB1 potentiation of c-MET signaling, such that preexisting SPSB1-overexpressing tumor cells are selected for following HER2/neu downregulation. Consistent with this, SPSB1 expression is positively correlated with c-MET activity in human breast cancers and with an increased risk of relapse in patients with breast cancer in a manner that is dependent upon c-MET activity. Our findings define a novel pathway that contributes to breast cancer recurrence and provide the first evidence implicating SPSB proteins in cancer. SIGNIFICANCE The principal cause of death from breast cancer is recurrence. This study identifies SPSB1 as a critical mediator of breast cancer recurrence, suggests activation of the SPSB1-c-MET pathway as an important mechanism of therapeutic resistance in breast cancers, and emphasizes that pharmacologic targets for recurrence may be unique to this stage of tumor progression.

International, evidence-based consensus treatment guidelines for idiopathic multicentric Castleman disease

Castleman disease (CD) describes a group of heterogeneous hematologic disorders with characteristic histopathological features. CD can present with unicentric or multicentric (MCD) regions of lymph node enlargement. Some cases of MCD are caused by human herpesvirus-8 (HHV-8), whereas others are HHV-8-negative/idiopathic (iMCD). Treatment of iMCD is challenging, and outcomes can be poor because no uniform treatment guidelines exist, few systematic studies have been conducted, and no agreed upon response criteria have been described. The purpose of this paper is to establish consensus, evidence-based treatment guidelines based on the severity of iMCD to improve outcomes. An international Working Group of 42 experts from 10 countries was convened by the Castleman Disease Collaborative Network to establish consensus guidelines for the management of iMCD based on published literature, review of treatment effectiveness for 344 cases, and expert opinion. The anti-interleukin-6 monoclonal antibody siltuximab (or tocilizumab, if siltuximab is not available) with or without corticosteroids is the preferred first-line therapy for iMCD. In the most severe cases, adjuvant combination chemotherapy is recommended. Additional agents are recommended, tailored by disease severity, as second- and third-line therapies for treatment failures. Response criteria were formulated to facilitate the evaluation of treatment failure or success. These guidelines should help treating physicians to stratify patients based on disease severity in order to select the best available therapeutic option. An international registry for patients with CD (ACCELERATE, #NCT02817997) was established in October 2016 to collect patient outcomes to increase the evidence base for selection of therapies in the future.

Plasma proteomics identifies a ‘chemokine storm’ in idiopathic multicentric Castleman disease

Human Herpesvirus‐8 (HHV‐8)‐negative/idiopathic multicentric Castleman disease (iMCD) is a poorly understood disease involving polyclonal lymphoproliferation with dysmorphic germinal centers, constitutional symptoms, and multi‐organ failure. Patients can experience thrombocytopenia, anasarca, reticulin fibrosis, renal dysfunction, organomegaly, and normal immunoglobulin levels, – iMCD‐TAFRO. Others experience thrombocytosis, milder effusions, and hypergammaglobulinemia, –iMCD‐Not Otherwise Specified (iMCD‐NOS). Though the etiology is unknown in both subtypes, iMCD symptoms and disease progression are believed to be driven by a cytokine storm, often including interleukin‐6 (IL‐6). However, approximately two‐thirds of patients do not respond to anti‐IL‐6 therapy; alternative drivers and signaling pathways are not known for anti‐IL‐6 nonresponders. To identify potential mediators of iMCD pathogenesis, we quantified 1129 proteins in 13 plasma samples from six iMCD patients during flare and remission. The acute phase reactant NPS‐PLA2 was the only significantly increased protein (P = .017); chemokines and complement were significantly enriched pathways. Chemokines represented the greatest proportion of upregulated cytokines, suggesting that iMCD involves a chemokine storm. The chemokine CXCL13, which is essential in homing B cells to germinal centers, was the most upregulated cytokine across all patients (log2 fold‐change = 3.22). Expression of CXCL13 was also significantly increased in iMCD lymph node germinal centers compared to controls in a stromal meshwork pattern. We observed distinct proteomic profiles between the two iMCD‐TAFRO patients, who both failed anti‐IL‐6‐therapy, and the four iMCD‐NOS patients, in whom all three treated with anti‐IL‐6‐therapy responded, suggesting that differing mechanisms may exist. This study reveals proteomic differences between flare and remission and the potential to molecularly define iMCD subgroups.

Abstract 4985: Cellular dormancy in residual disease following oncogene inhibition

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA Tumor recurrence is the primary cause of cancer-related mortality. Recurrent tumors arise from residual cancer cells surviving treatment of the primary tumor. It remains unclear whether residual tumor cells are quiescent, or whether they are proliferative but tumor recurrence is limited by a countervailing level of cell death, due to insufficient vascularization or an inhospitable microenvironment. Using inducible models for HER2/neu and Wnt1 mammary tumorigenesis, we found that residual tumor cells surviving oncogene inhibition are quiescent, and reside in a desmoplastic and well-vascularized microenvironment. We confirmed these results by performing gene expression analysis on residual tumor cells, primary tumor cells, recurrent tumor cells, and stromal cells. Gene ontology analysis identified dramatic downregulation of gene clusters associated with proliferation in dormant residual tumor cells compared to all other cell types. Genes we identified as up- or downregulated in dormant residual disease were identified in other models of dormancy, suggesting generalizable mechanisms underpinning dormancy in different contexts. Dormancy-specific changes in additional genes further suggest a role for both EMT and stem cell-related signaling in dormant residual disease which survives targeted therapy. Finally, we demonstrated quiescent residual disease in a xenograft model of breast cancer treated with clinically relevant targeted therapies. In summation, these results suggest both that residual disease may exhibit cellular dormancy following targeted therapy, and that some mechanisms regulating cellular quiescence may be similar across different contexts. Citation Format: Jason Ruth, Dhruv Pant, Blaine Keister, Christopher Sterner, Lewis Chodosh. Cellular dormancy in residual disease following oncogene inhibition. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4985. doi:10.1158/1538-7445.AM2014-4985