The subunit stoichiometry of heteromeric glycine-gated channels (GlyRs) determines fundamental properties of these key inhibitory neurotransmitter receptors; however the ratio of α1 to β-subunits per receptor remains controversial. We used single molecule imaging and stepwise photobleaching in Xenopus oocytes to directly determine the subunit stoichiometry of a glycine receptor to be 3α1:2β. This approach allowed us to determine the receptor stoichiometry in mixed populations consisting of both heteromeric and homomeric channels, additionally revealing the quantitative proportions for the two populations.

Cys-loop ligand-gated ion channels (LGICs) mediate fast ionotropic neurotransmission. They are proven drug targets in nematodes and arthropods, but are poorly characterized in flatworms. In this study, we characterized the anion-selective, non-acetylcholine-gated Cys-loop LGICs from Schistosoma mansoni. Full-length cDNAs were obtained for SmGluCl-1 (Smp_096480), SmGluCl-2 (Smp_015630) and SmGluCl-3 (Smp_104890). A partial cDNA was retrieved for SmGluCl-4 (Smp_099500/Smp_176730). Phylogenetic analyses suggest that SmGluCl-1, SmGluCl-2, SmGluCl-3 and SmGluCl-4 belong to a novel clade of flatworm glutamate-gated chloride channels (GluCl) that includes putative genes from trematodes and cestodes. The flatworm GluCl clade was distinct from the nematode-arthropod and mollusc GluCl clades, and from all GABA receptors. We found no evidence of GABA receptors in S. mansoni. SmGluCl-1, SmGluCl-2 and SmGluCl-3 subunits were characterized by two-electrode voltage clamp (TEVC) in Xenopus oocytes, and shown to encode Cl−-permeable channels gated by glutamate. SmGluCl-2 and SmGluCl-3 produced functional homomers, while SmGluCl-1 formed heteromers with SmGluCl-2. Concentration-response relationships revealed that the sensitivity of SmGluCl receptors to L-glutamate is among the highest reported for GluCl receptors, with EC50 values of 7–26 µM. Chloride selectivity was confirmed by current-voltage (I/V) relationships. SmGluCl receptors are insensitive to 1 µM ivermectin (IVM), indicating that they do not belong to the highly IVM-sensitive GluClα subtype group. SmGluCl receptors are also insensitive to 10 µM meclonazepam, a schistosomicidal benzodiazepine. These results provide the first molecular evidence showing the contribution of GluCl receptors to L-glutamate signaling in S. mansoni, an unprecedented finding in parasitic flatworms. Further work is needed to elucidate the roles of GluCl receptors in schistosomes and to explore their potential as drug targets.

Helminth parasites rely on fast-synaptic transmission in their neuromusculature to experience the outside world and respond to it. Acetylcholine plays a pivotal role in this and its receptors are targeted by a wide variety of both natural and synthetic compounds used in human health and for the control of parasitic disease. The model, Caenorhabditis elegans is characterized by a large number of acetylcholine receptor subunit genes, a feature shared across the nematodes. This dynamic family is characterized by both gene duplication and loss between species. The pentameric levamisole-sensitive acetylcholine receptor has been characterized from C. elegans, comprised of five different subunits. More recently, cognate receptors have been reconstituted from multiple parasitic nematodes that are found to vary in subunit composition. In order to understand the implications of receptor composition change and the origins of potentially novel drug targets, we investigated a specific example of subunit duplication based on analysis of genome data for 25 species from the 50 helminth genome initiative. We found multiple independent duplications of the unc-29, acetylcholine receptor subunit, where codon substitution rate analysis identified positive, directional selection acting on amino acid positions associated with subunit assembly. Characterization of four gene copies from a model parasitic nematode, Haemonchus contortus, demonstrated that each copy has acquired unique functional characteristics based on phenotype rescue of transgenic C. elegans and electrophysiology of receptors reconstituted in Xenopus oocytes. We found evidence that a specific incompatibility has evolved for two subunits co-expressed in muscle. We demonstrated that functional divergence of acetylcholine receptors, driven by directional selection, can occur more rapidly than previously thought and may be mediated by alteration of receptor assembly. This phenomenon is common among the clade V parasitic nematodes and this work provides a foundation for understanding the broader context of changing anthelmintic drug targets across the parasitic nematodes.

New compounds are needed to treat parasitic nematode infections in humans, livestock and plants. Small molecule anthelmintics are the primary means of nematode parasite control in animals; however, widespread resistance to the currently available drug classes means control will be impossible without the introduction of new compounds. Adverse environmental effects associated with nematocides used to control plant parasitic species are also motivating the search for safer, more effective compounds. Discovery of new anthelmintic drugs in particular has been a serious challenge due to the difficulty of obtaining and culturing target parasites for high-throughput screens and the lack of functional genomic techniques to validate potential drug targets in these pathogens. We present here a novel strategy for target validation that employs the free-living nematode Caenorhabditis elegans to demonstrate the value of new ligand-gated ion channels as targets for anthelmintic discovery. Many successful anthelmintics, including ivermectin, levamisole and monepantel, are agonists of pentameric ligand-gated ion channels, suggesting that the unexploited pentameric ion channels encoded in parasite genomes may be suitable drug targets. We validated five members of the nematode-specific family of acetylcholine-gated chloride channels as targets of agonists with anthelmintic properties by ectopically expressing an ivermectin-gated chloride channel, AVR-15, in tissues that endogenously express the acetylcholine-gated chloride channels and using the effects of ivermectin to predict the effects of an acetylcholine-gated chloride channel agonist. In principle, our strategy can be applied to validate any ion channel as a putative anti-parasitic drug target.

To determine causes of apoptotic resistance, we analyzed 124 primary B cell NHL samples using BH3 profiling, a technique that measures the mitochondrial permeabilization upon exposure to synthetic BH3 peptides. Our cohort included samples from chronic lymphocytic leukemia (CLL), follicular lymphoma (FL), diffuse large B-cell lymphoma (DLBCL), high-grade B cell lymphoma with translocations in MYC and BCL2 (HGBL-DH), mantle cell lymphoma (MCL) and marginal zone lymphoma (MZL). While a large number of our samples displayed appropriate responses to apoptosis-inducing peptides, pro-apoptotic functional defects, implicating BAX, BAK, BIM or BID, were seen in 32.4% of high-grade NHLs (12/37) and in 3.4% of low-grade NHLs (3/87, p < 0.0001). The inhibition of single anti-apoptotic proteins induced apoptosis in only a few samples, however, the dual inhibition of BCL2 and MCL1 was effective in 83% of samples, indicating MCL1 was the most common cause of lack of response to the BCL2 inhibitor, venetoclax. We then profiled Toledo and OCI-Ly8 high-grade lymphoma cell lines to determine which drugs could reduce MCL1 expression and potentiate venetoclax responses. Doxorubicin and vincristine decreased levels of MCL1 and increased venetoclax-induced apoptosis (all p < 0.05). Overall, in primary NHLs expressing BCL2 that have no defects in pro-apoptotic signaling, a poor response to venetoclax is primarily due to the presence of MCL1, which may be overcome by combining venetoclax with doxorubicin and vincristine-based chemotherapy or with other anti-microtubule inhibitors.

Relapse occurs in 10-40% of Burkitt lymphoma (BL) patients that have completed intensive chemotherapy regimens and is typically fatal. While treatment-naive BL has been characterized, the genomic landscape of BL at the time of relapse (rBL) has never been reported. Here, we present a genomic characterization of two rBL patients. The diagnostic samples had mutations common in BL, including MYC and CCND3. Additional mutations were detected at relapse, affecting important pathways such as NFκB (IKBKB) and MEK/ERK (NRAS) signaling, glutamine metabolism (SIRT4), and RNA processing (ZFP36L2). Genes implicated in drug resistance were also mutated at relapse (TP53, BAX, ALDH3A1, APAF1, FANCI). This concurrent genomic profiling of samples obtained at diagnosis and relapse has revealed mutations not previously reported in this disease. The patient-derived cell lines will be made available and, along with their detailed genetics, will be a valuable resource to examine the role of specific mutations in therapeutic resistance.

Background: Chronic lymphocytic leukemia (CLL) has a classic immunophenotype, consisting of light chain restriction, CD5+, CD19+, dim CD20, CD23+, CD43+, CD200+, CD10- and CD79b-. This distinguishes it from normal B cells and other lymphoproliferative disorders (LPDs). Antibodies targeting these antigens are included in two 8-color flow cytometry panels developed by the Euroflow consortium for the work up of B cell LPDs. Combining these antibodies into one 10-color panel would be more cost-effective. Furthermore, new CLL therapies can induce deep remissions, creating an increasing demand to measure minimal residual disease (MRD), defined as having over 1 residual leukemic cell per 10,000 leukocytes (10-4). The current international standardized approach for measuring MRD established by the European Research Initiative on CLL (ERIC) uses a panel of antibodies targeting CD3, CD5, CD19, CD20, CD22, CD43, CD79b and CD81. However, these antibody-fluorochrome combinations are different than those used by the Euroflow diagnostic panels. Thus laboratories considering implementing MRD testing would need to purchase antibodies for 3 different panels (2 diagnostic and 1 MRD). We expanded the Euroflow 8-color lymphocyte screening tube (LST) to include CD200 and CD23, such that CLL can be detected in one 10-color tube, at levels as low as 0.01%. The goal of this study was to determine the potential cost savings in implementing this new panel and to determine if it is sensitive enough to detect MRD. Methods: We calculated the number of samples analyzed with our modified 10-color LST tube (mLST1, obtained lyophilized) from April 2018 to March 2019 to rule out an LPD and the number of antibody aliquots saved using this approach compared to the standard 2-tube Euroflow method. We also created a version of the above-mentioned panel (mLST2) using liquid antibodies to increase the generalizability of our results, substituting CD38 with CD43 to see if this improved MRD detection (see panels below). For MRD testing, we used CLL samples from 24 different patients to produce 60 MRD samples at various concentrations of leukemic cells. Samples were prepared by spiking CLL cells into suspensions of normal leukocytes at approximate concentrations of 0.1%, 0.01% and 0.001%. Each sample was aliquoted and stained with the three panels: ERIC, mLST1 and mLST2. Data was acquired using a BD FACSCanto II or a BD FACSAria Fusion and analysed using BD FACSDiva software. CLL cells were identified based on differential expression of key markers and MRD was calculated as the number of CLL cells/total leukocytes. MRD positivity was defined as ≥ 0.01%. Agreement between the panels was assessed using the Bland-Altman plot method. We also calculated the percentage agreement between the panels in identifying MRD positivity. Results: In 1 year, mLST1 was performed on 474 samples, of these 220 had an LPD and 123 (56%) had a classic CLL phenotype, obviating the need for further testing. This resulted in the net savings of 476 antibody aliquots. For MRD assessment, differential expression of CD5 and CD20 were the most significant contributors in distinguishing CLL from normal B cells using the mLST1 and mLST2. We identified one CLL case with an atypical immunophenotype (dim CD5, bright CD20) which proved difficult to gate using a mLST panel. There was agreement in MRD results obtained with the mLST panels and the ERIC panel. For values above the limit of quantification, the 95% limit of agreement was ±0.3369 log for the ERIC vs mLST1 comparison and ±0.3485 log for the ERIC vs mLST2 comparison. Thus, variability in MRD levels between the panels was less than 2-fold the majority of the time, which we considered clinically acceptable as MRD is measured on an exponential scale. The ERIC panel and the mLST1 had 88.3% agreement in distinguishing MRD-positive versus MRD-negative samples. Agreement was 93.3% between the ERIC panel and the mLST2. Conclusions: Using a modified 10-color LST panel for both diagnosis and MRD measurement of CLL is feasible. The advantages are increased familiarity with the antibodies and potential cost savings, making MRD accessible to more cytometry laboratories. Atypical CLL cases without the usual CD5 positivity and dim CD20 are very difficult to gate using an LST panel. In these cases, the ERIC panel is clearly superior as CD22, CD79b, CD81 and CD43 can still provide separation between the malignant and normal lymphocytes. Disclosures Bazinet: BD Biosciences: Other: Provided a significant amount of the antibodies used in this project free of cost.. Wever:Teva Canada Innovation: Employment. Gimmig:BD Biosciences: Employment. Johnson:Lundbeck: Employment, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel fees, gifts, and others, Research Funding; Merck: Consultancy, Honoraria; Roche: Consultancy, Employment, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel fees, gifts, and others, Research Funding; Abbvie: Consultancy, Employment, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; BD Biosciences: Other: Provided a significant proportion of the antibodies used in this project free of cost.; BMS: Consultancy, Honoraria; Seattle Genetics: Honoraria.

The treatment of patients with relapsed or refractory lymphoid neoplasms represents a significant clinical challenge. Here, we identify the pro‐survival BCL‐2 protein family member MCL‐1 as a resistance factor for the BCL‐2 inhibitor venetoclax in non‐Hodgkin lymphoma (NHL) cell lines and primary NHL samples. Mechanistically, we show that the antibody‐drug conjugate polatuzumab vedotin promotes MCL‐1 degradation via the ubiquitin/proteasome system. This targeted MCL‐1 antagonism, when combined with venetoclax and the anti‐CD20 antibodies obinutuzumab or rituximab, results in tumor regressions in preclinical NHL models, which are sustained even off‐treatment. In a Phase Ib clinical trial (NCT02611323) of heavily pre‐treated patients with relapsed or refractory NHL, 25/33 (76%) patients with follicular lymphoma and 5/17 (29%) patients with diffuse large B‐cell lymphoma achieved complete or partial responses with an acceptable safety profile when treated with the recommended Phase II dose of polatuzumab vedotin in combination with venetoclax and an anti‐CD20 antibody.