Structural principles of peptide-centric chimeric antigen receptor recognition guide therapeutic expansion

Peptide-centric chimeric antigen receptors (PC-CARs) recognize oncoprotein epitopes displayed by cell-surface human leukocyte antigens (HLAs) and offer a promising strategy for targeted cancer therapy. We have previously developed a PC-CAR targeting a neuroblastoma-associated PHOX2B peptide, leading to robust tumor cell lysis restricted by two common HLA allotypes. Here, we determine the 2.1-angstrom crystal structure of the PC-CAR-PHOX2B-HLA-A*24:02-β2m complex, which reveals the basis for antigen-specific recognition through interactions with CAR complementarity-determining regions (CDRs). This PC-CAR adopts a diagonal docking mode, where interactions with both conserved and polymorphic HLA framework residues permit recognition of multiple HLA allotypes from the A9 serological cross-reactive group, covering a combined global population frequency of up to 46.7%. Biochemical binding assays, molecular dynamics simulations, and structural and functional analyses demonstrate that high-affinity PC-CAR recognition of cross-reactive pHLAs necessitates the presentation of a specific peptide backbone, where subtle structural adaptations of the peptide are critical for high-affinity complex formation, and CAR T cell killing. Our results provide a molecular blueprint for engineering CARs with optimal recognition of tumor-associated antigens in the context of different HLAs, while minimizing cross-reactivity with self-epitopes.

Targeting of intracellular oncoproteins with peptide-centric CARs

The majority of oncogenic drivers are intracellular proteins, constraining their immunotherapeutic targeting to mutated peptides (neoantigens) presented by individual human leukocyte antigen (HLA) allotypes1. However, most cancers have a modest mutational burden that is insufficient for generating responses using neoantigen-based therapies2,3. Neuroblastoma is a paediatric cancer that harbours few mutations and is instead driven by epigenetically deregulated transcriptional networks4. Here we show that the neuroblastoma immunopeptidome is enriched with peptides derived from proteins essential for tumorigenesis. We focused on targeting the unmutated peptide QYNPIRTTF discovered on HLA-A*24:02, which is derived from the neuroblastoma-dependency gene and master transcriptional regulator PHOX2B. To target QYNPIRTTF, we developed peptide-centric chimeric antigen receptors (PC-CARs) through a counter panning strategy using predicted potentially cross-reactive peptides. We further proposed that PC-CARs can recognize peptides on additional HLA allotypes when presenting a similar overall molecular surface. Informed by our computational modelling results, we show that PHOX2B PC-CARs also recognize QYNPIRTTF presented by HLA-A*23:01, the most common non-A2 allele in people with African ancestry. Finally, we demonstrate potent and specific killing of neuroblastoma cells expressing these HLAs in vitro and complete tumour regression in mice. These data suggest that PC-CARs have the potential to expand the pool of immunotherapeutic targets to include non-immunogenic intracellular oncoproteins and allow targeting through additional HLA allotypes in a clinical setting.

Structural principles of peptide-centric Chimeric Antigen Receptor recognition guide therapeutic expansion

Peptide-Centric Chimeric Antigen Receptors (PC-CARs), which recognize oncoprotein epitopes displayed by human leukocyte antigens (HLAs) on the cell surface, offer a promising strategy for targeted cancer therapy ¹ . We have previously developed a PC-CAR targeting a neuroblastoma- associated PHOX2B peptide, leading to robust tumor cell lysis restricted by two common HLA allotypes ² . Here, we determine the 2.1 Å structure of the PC-CAR:PHOX2B/HLA-A*24:02/β2m complex, which reveals the basis for antigen-specific recognition through interactions with CAR complementarity-determining regions (CDRs). The PC-CAR adopts a diagonal docking mode, where interactions with both conserved and polymorphic HLA framework residues permit recognition of multiple HLA allotypes from the A9 serological cross-reactivity group, covering a combined American population frequency of up to 25.2%. Comprehensive characterization using biochemical binding assays, molecular dynamics simulations, and structural and functional analyses demonstrate that high-affinity PC-CAR recognition of cross-reactive pHLAs necessitates the presentation of a specific peptide backbone, where subtle structural adaptations of the peptide are critical for high-affinity complex formation and CAR-T cell killing. Our results provide a molecular blueprint for engineering CARs with optimal recognition of tumor-associated antigens in the context of different HLAs, while minimizing cross-reactivity with self-epitopes.

Cross-HLA targeting of intracellular oncoproteins with peptide-centric CARs

The majority of oncogenic drivers are intracellular proteins, thus constraining their immunotherapeutic targeting to mutated peptides (neoantigens) presented by individual human leukocyte antigen (HLA) allotypes1. However, most cancers have a modest mutational burden that is insufficient to generate responses using neoantigen-based therapies2,3. Neuroblastoma is a paediatric cancer that harbours few mutations and is instead driven by epigenetically deregulated transcriptional networks4. Here we show that the neuroblastoma immunopeptidome is enriched with peptides derived from proteins that are essential for tumourigenesis and focus on targeting the unmutated peptide QYNPIRTTF, discovered on HLA-A*24:02, which is derived from the neuroblastoma dependency gene and master transcriptional regulator PHOX2B. To target QYNPIRTTF, we developed peptide-centric chimeric antigen receptors (CARs) using a counter-panning strategy with predicted potentially cross-reactive peptides. We further hypothesized that peptide-centric CARs could recognize peptides on additional HLA allotypes when presented in a similar manner. Informed by computational modelling, we showed that PHOX2B peptide-centric CARs also recognize QYNPIRTTF presented by HLA-A*23:01 and the highly divergent HLA-B*14:02. Finally, we demonstrated potent and specific killing of neuroblastoma cells expressing these HLAs in vitro and complete tumour regression in mice. These data suggest that peptide-centric CARs have the potential to vastly expand the pool of immunotherapeutic targets to include non-immunogenic intracellular oncoproteins and widen the population of patients who would benefit from such therapy by breaking conventional HLA restriction.

Abstract 1493: Discovery and CAR T targeting of lineage-restricted neuroblastoma oncoproteins

Background: The MHC presents a snapshot of the intracellular proteome for surveillance by T cells, including peptides from mutated proteins (neoantigens) and nonmutated but aberrantly expressed proteins. Though peptides derived from nonmutated oncoproteins may be presented on MHC, self-antigens are not normally immunogenic to native T cells. Neuroblastoma presents a unique combination of challenges in identifying and targeting tumor-specific antigens: low mutational burden and low MHC expression.

Methods and Results: Using an immunogenomic and immunopeptidomics approach in 16 human neuroblastoma samples, we identified 265 novel antigens presented on MHC and prioritized 6 (including the PHOX2B master regulator) as lead preclinical candidates based on: 1) binding affinity to common HLA alleles, 2) extent of differential gene expression, 3) lack of MHC presentation in healthy tissue, 4) biological relevance to neuroblastoma, and 5) recurrence across multiple tumors. We validated PHOX2B binding to the predicted HLA allele A24 using crystallography of the refolded peptide-MHC (pMHC) complex, and confirmed the peptide sequence using LC/MS/MS of the synthetic peptide. Upon antigen validation, we engineered CAR receptors to induce immunogenicity to self-antigens. Phage display libraries were used to pan for tumor-specific scFv's, using predicted cross-reactive pMHCs as decoys, generating candidate scFv's that were cloned into CAR constructs. We developed an algorithm to predict cross-reactivity against normal tissue pMHCs and screened CARs for cross-reactivity, prioritizing constructs with high tumor antigen affinity and low cross-reactivity. Lead CARs demonstrate complete elimination of tumor cells in less than 24 hours using 1:1 E:T ratios in neuroblastoma cells, and not in other cancer lines expressing HLA-A24 but not PHOX2B, demonstrating highly specific and potent killing. Robust CAR killing was induced by pulsing HLA-A24+/PHOX2B- melanoma cells with PHOX2B peptide but not with potential cross-reactive peptides. Finally, two lead CAR constructs induced complete regression of established neuroblastoma HLA-A24+ SKNAS xenografts, with additional murine trials ongoing.

Conclusion: Neuroblastomas present a unique ligandome, including a significant number of antigens derived from lineage-restricted oncoproteins. We demonstrate proof-of-concept using scFv-based CARs to target the previously undruggable PHOX2B transcription factor in in vitro and in vivo studies. These data provide a basis for targeting non-immunogenic lineage-restricted oncoproteins using CAR T cells in neuroblastoma and other human cancers.

Citation Format: Mark Yarmarkovich, John M. Warrington, Quinlen F. Marshall, Helena Shen, Wei Li, Matt Beasley, Moreno Di Marco, Stefan Stevanovic, Nikolaos G. Sgourakis, Dimiter Dimitrov, Peter Smith, John M. Maris. Discovery and CAR T targeting of lineage-restricted neuroblastoma oncoproteins [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1493.

Abstract PO-049: SARS-CoV-2 multiepitope vaccine constructs designed to drive long-term immunity in the majority of the population

The current SARS-CoV-2 pandemic has precipitated an urgent need for a safe and effective vaccine to be developed and deployed in a highly accelerated timeframe as compared to standard vaccine development processes. Upfront selection of epitopes most likely to induce a safe and effective immune response can accelerate these efforts. Optimally designed vaccines maximize immunogenicity towards regions of proteins that contribute most to protective immunity, while minimizing the antigenic load contributed by unnecessary protein domains that may result in autoimmunity, reactogenicity, or enhanced infectivity. Adopting tools developed for population-scale characterization of HLA presentation of tumor antigens and cross-reactivity of TCRs with tumor self-antigens, we have generated an immunogenicity map of SARS-CoV-2 to inform vaccine design based on analyses across five parameters: 1) stimulation of CD4 and CD8 T cells; 2) immunogenicity across the majority of human HLA alleles; 3) targeting both evolutionarily conserved regions, as well as newly divergent regions of the virus that increase infectivity; 4) targeting linear and conformational B-cell epitopes; and 5) targeting viral regions with the highest degree of dissimilarity to the self-immunopeptidome such as to maximize safety and immunogenicity. Using these analyses, we have generated 11 SARS-CoV-2 vaccine constructs optimized for long-term immunity across the majority of the population. These constructs contain combinations of epitopes selected from our analysis such as to drive affinity-enhanced memory response in combination with current spike protein vaccine strategies, for use as T-cell vaccines, and a stand-alone vaccine designed to drive memory B- and T-cell responses in the majority of the population. Epitopes were optimized using our immunogenicity algorithm to minimize immunogenicity across the junctions between epitopes and cloned into pVAX vectors, using signal peptides targeting the lysosome, ER, and cytoplasmic secretion, such as to promote presentation to CD4, CD8, and B cells, respectively. Finally, we describe methods for identifying immunodominant epitopes arising from vaccination using barcoded, multiplexed tetramers. Vaccine constructs are currently undergoing testing in transgenic mice expressing human HLA-A2. We expect that these constructs will help drive long-term immunity across the population, targeting conserved regions across multiple coronaviruses.

Citation Format: Mark Yarmarkovich, John M. Warrington, Alvin Farrel, John M. Maris. SARS-CoV-2 multiepitope vaccine constructs designed to drive long-term immunity in the majority of the population [abstract]. In: Proceedings of the AACR Virtual Meeting: COVID-19 and Cancer; 2020 Jul 20-22. Philadelphia (PA): AACR; Clin Cancer Res 2020;26(18_Suppl):Abstract nr PO-049.

Identification of SARS-CoV-2 Vaccine Epitopes Predicted to Induce Long-Term Population-Scale Immunity

Here we propose a SARS-CoV-2 vaccine design concept based on identification of highly conserved regions of the viral genome and newly acquired adaptations, both predicted to generate epitopes presented on major histocompatibility complex (MHC) class I and II across the vast majority of the population. We further prioritize genomic regions that generate highly dissimilar peptides from the human proteome and are also predicted to produce B cell epitopes. We propose sixty-five 33-mer peptide sequences, a subset of which can be tested using DNA or mRNA delivery strategies. These include peptides that are contained within evolutionarily divergent regions of the spike protein reported to increase infectivity through increased binding to the ACE2 receptor and within a newly evolved furin cleavage site thought to increase membrane fusion. Validation and implementation of this vaccine concept could specifically target specific vulnerabilities of SARS-CoV-2 and should engage a robust adaptive immune response in the vast majority of the population.

A SARS-CoV-2 Vaccination Strategy Focused on Population-Scale Immunity

Here we propose a vaccination strategy for SARS-CoV-2 based on identification of both highly conserved regions of the virus and newly acquired adaptations that are presented by MHC class I and II across the vast majority of the population, are highly dissimilar from the human proteome, and are predicted B cell epitopes. We present 65 peptide sequences that we expect to result in a safe and effective vaccine which can be rapidly tested in DNA, mRNA, or synthetic peptide constructs. These include epitopes that are contained within evolutionarily divergent regions of the spike protein reported to increase infectivity through increased binding to the ACE2 receptor, and within a novel furin cleavage site thought to increase membrane fusion. This vaccination strategy specifically targets unique vulnerabilities of SARS-CoV-2 and should engage a robust adaptive immune response in the vast majority of the human population.

A SARS-CoV-2 Vaccination Strategy Focused on Population-Scale Immunity

Here we propose a vaccination strategy for SARS-CoV-2 based on identification of both highly conserved regions of the virus and newly acquired adaptations that are presented by MHC class I and II across the vast majority of the population, are highly dissimilar from the human proteome, and are predicted B cell epitopes. We present 65 peptide sequences that we expect to result in a safe and effective vaccine which can be rapidly tested in DNA, mRNA, or synthetic peptide constructs. These include epitopes that are contained within evolutionarily divergent regions of the spike protein reported to increase infectivity through increased binding to the ACE2 receptor, and within a novel furin cleavage site thought to increase membrane fusion. This vaccination strategy specifically targets unique vulnerabilities of SARS-CoV-2 and should engage a robust adaptive immune response in the vast majority of the human population.

Immunogenicity and Immune Silence in Human Cancer

Despite recent advances in cancer immunotherapy, the process of immunoediting early in tumorigenesis remains obscure. Here, we employ a mathematical model that utilizes the Cancer Genome Atlas (TCGA) data to elucidate the contribution of individual mutations and HLA alleles to the immunoediting process. We find that common cancer mutations including BRAF-V600E and KRAS-G12D are predicted to bind none of the common HLA alleles, and are thus “immunogenically silent” in the human population. We identify regions of proteins that are not presented by HLA at a population scale, coinciding with frequently mutated hotspots in cancer, and other protein regions broadly presented across the population in which few mutations occur. We also find that 9/29 common HLA alleles contribute disproportionately to the immunoediting of early oncogenic mutations. These data provide insights into immune evasion of common driver mutations and a molecular basis for the association of particular HLA genotypes with cancer susceptibility.

When Cold Is Hot: Immune Checkpoint Inhibition Therapy for Rhabdoid Tumors

Carcinogen-induced cancers typically have high mutation burdens and an inflamed microenvironment and thus are poised to respond to immune checkpoint inhibitors (ICIs). However, cancers with loss-of-function mutations in the SWI/SNF complex have few additional mutations yet also have an inflamed immunophenotype and should respond to ICI therapy.

High Throughput pMHC-I Multimer Library Production Using Chaperone-Mediated Peptide Exchange

The development of pMHC-multimer technologies has been indispensable for the characterisation of T cell responses to individual viral and tumor peptide antigens. Given the large variety of T cell receptors expressed in polyclonal repertoires, peptide exchange technologies are becoming increasingly important in providing a high throughput means of generating pMHC-multimer libraries, containing a wide range of antigens to probe such repertoires. Here we present a simple method for the isolation of empty MHC-I molecules which can be readily used for high throughput multimer library preparation. We utilise the chaperone TAPBPR, which binds MHC-I molecules and stabilises them in a peptide-receptive conformation, to isolate empty MHC-I molecules through the combination of placeholder peptides and small molecule competitors. We demonstrate that empty H-2Dd:TAPBPR and HLA-A*02:01:TAPBPR complexes can be stored long term and subsequently loaded with peptides of choice in a high throughput fashion to afford pMHC-multimer libraries. The resulting pMHC-multimers show equivalent flow cytometric properties to multimers made from MHC-I molecules refolded in vitro with synthetic peptides and are significantly improved relative to multimers prepared using peptide exchange of conditional ligands. Using this simple system to generate a library of oligonucleotide-labeled pMHC-multimers, combined with our recently described multi-modal cellular indexing technology (ECCITE-seq), we can identify distinct T cell receptor sequences present in polyclonal repertoires, together with their antigen specificities.

Cross-Cohort Analysis Identifies a TEAD4-MYCN Positive Feedback Loop as the Core Regulatory Element of High-Risk Neuroblastoma

High-risk neuroblastomas show a paucity of recurrent somatic mutations at diagnosis. As a result, the molecular basis for this aggressive phenotype remains elusive. Recent progress in regulatory network analysis helped us elucidate disease-driving mechanisms downstream of genomic alterations, including recurrent chromosomal alterations. Our analysis identified three molecular subtypes of high-risk neuroblastomas, consistent with chromosomal alterations, and identified subtype-specific master regulator proteins that were conserved across independent cohorts. A 10-protein transcriptional module-centered around a TEAD4-MYCN positive feedback loop-emerged as the regulatory driver of the high-risk subtype associated with MYCN amplification. Silencing of either gene collapsed MYCN-amplified (MYCNAmp) neuroblastoma transcriptional hallmarks and abrogated viability in vitro and in vivo Consistently, TEAD4 emerged as a robust prognostic marker of poor survival, with activity independent of the canonical Hippo pathway transcriptional coactivators YAP and TAZ. These results suggest novel therapeutic strategies for the large subset of MYCN-deregulated neuroblastomas.Significance: Despite progress in understanding of neuroblastoma genetics, little progress has been made toward personalized treatment. Here, we present a framework to determine the downstream effectors of the genetic alterations sustaining neuroblastoma subtypes, which can be easily extended to other tumor types. We show the critical effect of disrupting a 10-protein module centered around a YAP/TAZ-independent TEAD4-MYCN positive feedback loop in MYCNAmp neuroblastomas, nominating TEAD4 as a novel candidate for therapeutic intervention. Cancer Discov; 8(5); 582-99. ©2018 AACR.This article is highlighted in the In This Issue feature, p. 517.

A Recurrent Mutation in Anaplastic Lymphoma Kinase with Distinct Neoepitope Conformations

The identification of recurrent human leukocyte antigen (HLA) neoepitopes driving T cell responses against tumors poses a significant bottleneck in the development of approaches for precision cancer therapeutics. Here, we employ a bioinformatics method, Prediction of T Cell Epitopes for Cancer Therapy, to analyze sequencing data from neuroblastoma patients and identify a recurrent anaplastic lymphoma kinase mutation (ALK R1275Q) that leads to two high affinity neoepitopes when expressed in complex with common HLA alleles. Analysis of the X-ray structures of the two peptides bound to HLA-B*15:01 reveals drastically different conformations with measurable changes in the stability of the protein complexes, while the self-epitope is excluded from binding due to steric hindrance in the MHC groove. To evaluate the range of HLA alleles that could display the ALK neoepitopes, we used structure-based Rosetta comparative modeling calculations, which accurately predict several additional high affinity interactions and compare our results with commonly used prediction tools. Subsequent determination of the X-ray structure of an HLA-A*01:01 bound neoepitope validates atomic features seen in our Rosetta models with respect to key residues relevant for MHC stability and T cell receptor recognition. Finally, MHC tetramer staining of peripheral blood mononuclear cells from HLA-matched donors shows that the two neoepitopes are recognized by CD8+ T cells. This work provides a rational approach toward high-throughput identification and further optimization of putative neoantigen/HLA targets with desired recognition features for cancer immunotherapy.

Abstract 5824: MHC class I immunogenicity and novel tumor antigen discovery in neuroblastoma

Background: Neuroblastoma is a childhood tumor characterized by relatively few somatic mutations and low MHC expression, which has thus far largely precluded it from investigation using adoptive immunotherapy.

Methods: We characterized MHC-presented antigens in 8 patient derived xenograft (PDX) tumors using LC/MS/MS immunopeptidomics. We developed a method to identify antigens derived from differentially expressed proteins by combining RNA-seq data from 153 neuroblastoma and 1641 healthy tissues, and ligandomic data from 190 healthy tissues. We also performed functional characterization on the ability HLA-A2 neuroblastoma lines to elicit a T-cell response using CEF1 antigen-specific T-cell hyrbidoma when challenged with flu virus, and performed bioinformatic analysis of the TME.

Results: From 8 PDX tumors, we identified a total of 14119 MHC-presented antigens. Interestingly, we observed antigens from all tumors which stained negative for MHC by IHC, suggesting that antigens can be identified from tumors below the detection limits of the standard staining protocols. We first searched the ligandome dataset for all possible neoantigens of 8-14aa arising from known mutations. Not having found any mutated neoantigens, we developed a method to search for tumor antigens derived neuroblastoma-specific proteins. We discovered 83 MHC ligands that derive from neuroblastoma-specific proteins, which we expect to be promising targets for adoptive T-cell therapy. We also found a number of recurrent antigens across tumor samples, suggesting that the proteins from which these antigens derive could be used in HLA-agnostic tumors vaccines.

To test whether the MHC expression in neuroblastoma is sufficient to induce a T-cell response, we characterized the ability of neuroblastoma cells to elicit a CD8 response to CEF1 antigen. We demonstrate that despite low MHC expression in all lines tested, 4/7 lines are able to induce a robust T-cell response to flu antigen greater than HLA-A2 melanoma cells (>20pg/mL IL-2 release in all responsive lines).

We also characterized immune activity in patient tumors using Granzyme A (GZMA) and Perforin (PRF1) as surrogates for T-cell activity. We observed a strong correlation between known T-cell-recruiting cytokines (particularly CXCL5/9/10) and GZMA/PRF1 (p=2.51x10-35), providing further evidence that T-cells are active in the tumor microenvironment despite low MHC expression on tumor cells.

Conclusions: We identify neuroblastoma-specific MHC class I antigens in each of the 8 PDX tumors we tested, yielding a total of 83 novel antigens. We conclude that neuroblastoma tumors harbor promising tumor-specific targets for immunotherapy despite low rates of somatic mutation and low MHC expression, and that at least a subset of these tumors are able to induce a robust response using antigen-specific T-cell hybridomas. We also describe methods of identifying tumor-specific MHC antigens in other tumors with low mutational burden.

Note: This abstract was not presented at the meeting.

Citation Format: Mark Yarmarkovich, Moreno Di Marco, Olivia Padovan, Jenna Lobby, Laurence Eisenlohr, Dimitrios Monos, Stefan Stevanovic, John M. Maris. MHC class I immunogenicity and novel tumor antigen discovery in neuroblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5824. doi:10.1158/1538-7445.AM2017-5824

Abstract 4384: Selective cross-cohort discovery of transcriptional mechanisms presiding over high-risk neuroblastoma subtype state maintenance

BACKGROUND: Neuroblastoma (NBL) is the most common extracranial solid tumor in children. High-risk NBLs progress to metastatic disease and have 5-year survival of only ∼40%, despite intensive multimodal therapy. This malignancy is characterized by significant heterogeneity, both clinical and molecular, which is still poorly understood.

Rather than focusing on its initiating genetic events, which are highly idiosyncratic, we focused on the core regulatory machinery responsible for implementation and maintenance of tumor state. This approach led to elucidating three molecularly distinct subtypes of high-risk NBLs, as well as the core regulatory machinery responsible for their implementation and stability, including canalization and integration of mutational events and regulation of the genetic programs that represent the hallmarks of this disease.

METHODS: We dissected large-scale gene expression profiling data available from TARGET and NRC Consortium by clustering algorithm and established three subtypes of high-risk NBL, followed by identification of master regulators (MR)s of each subtype by Master Regulator Inference algorithm (Lefebvre, C. et al, 2010). We performed extensive experimental validation of MRs by both in-vitro and in-vivo RNAi mediated screening, using cell viability as readout. We then used a variety of experimental assays to elucidate the modular logic controlling disease state and to identify novel NBL subtype specific dependencies.

RESULTS: We identified unique MR protein modules for three distinct molecular subtypes of high-risk NBL, which were conserved across independent cohorts. Experimental MR validation identified a TEAD4-MYCN positive feedback loop as the key NBL state maintenance mechanisms in the MYCN amplification associated subtype. Jointly, MYCN and TEAD4 regulate 90% of inferred MR proteins and causally implement 70% of the subtype gene expression signature. Biologically, MYCN repressed differentiation and TEAD4 activated proliferation, two hallmarks of MYCN-amplified NBL. Specifically, TEAD4 was shown to induce MYCN-independent proliferation by transactivating key genes implicated in high-risk NBL pathogenesis, including cyclin-dependent kinases, cyclins, E2Fs, DNA replication factors, checkpoint kinases and ubiquitin ligases. Consistently, TEAD4 inhibition induced loss of NBL cell viability, thus providing novel therapeutic targets. TEAD4 activity was an outstanding predictor of survival, independent of outcome-related variables.

CONCLUSION: Our results show that the inference of transcriptional regulators driving distinct molecular subgroups when combined with functional analyses is valuable to uncover the regulatory modules required for sustaining the tumor subtypes. This approach can be used to successfully identify the functional bottlenecks of other cancer subtypes.

Citation Format: Presha Rajbhandari, Gonzalo Lopez, Jiyang Yu, Ruth Rodriguez-Barrueco, Mariano Alvarez, Daniel Martinez, Mark Yarmarkovich, Jo Vandesompele, Pieter Mestdagh, Jose M. Silva, Anna Lasorella, Antonio Iavarone, John M. Maris, Andrea Califano. Selective cross-cohort discovery of transcriptional mechanisms presiding over high-risk neuroblastoma subtype state maintenance. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4384.

Anomalous uptake and circulatory characteristics of the plant-based small RNA MIR2911

Inconsistent detection of plant-based dietary small RNAs in circulation has thwarted the use of dietary RNA therapeutics. Here we demonstrate mice consuming diets rich in vegetables displayed enhanced serum levels of the plant specific small RNA MIR2911. Differential centrifugation, size-exclusion chromatography, and proteinase K treatment of plant extracts suggest this RNA resides within a proteinase K-sensitive complex. Plant derived MIR2911 was more bioavailable than the synthetic RNA. Furthermore, MIR2911 exhibited unusual digestive stability compared with other synthetic plant microRNAs. The characteristics of circulating MIR2911 were also unusual as it was not associated with exosomes and fractionated as a soluble complex that was insensitive to proteinase K treatment, consistent with MIR2911 being stabilized by modifications conferred by the host. These results indicate that intrinsic stability and plant-based modifications orchestrate consumer uptake of this anomalous plant based small RNA and invite revisiting plant-based microRNA therapeutic approaches.

Influence of glycosylation pattern on the molecular properties of monoclonal antibodies

Glycosylation is an important post-translational modification during protein production in eukaryotic cells, and it is essential for protein structure, stability, half-life, and biological functions. In this study, we produced various monoclonal antibody (mAb) glycoforms from Chinese hamster ovary (CHO) cells, including the natively glycosylated antibody, the enriched G0 form, the deglycosylated form, the afucosylated form, and the high mannose form, and we compared their intrinsic properties, side-by-side, through biophysical and biochemical approaches. Spectroscopic analysis indicates no measureable secondary or tertiary structural changes after in vitro or in vivo modification of the glycosylation pattern. Thermal unfolding experiments show that the high mannose and deglycosylated forms have reduced thermal stability of the CH2 domain compared with the other tested glycoforms. We also observed that the individual domain's thermal stability could be pH dependent. Proteolysis analysis indicates that glycosylation plays an important role in stabilizing mAbs against proteases. The stability of antibody glycoforms at the storage condition (2-8 °C) and at accelerated conditions (30 and 40 °C) was evaluated, and the results indicate that glycosylation patterns do not substantially affect the storage stability of the antibody we studied.