Abstract 1136: Targeting DHX9 inhibition as a novel therapeutic modality in microsatellite instable colorectal cancer

DHX9 is a multifunctional DEAH-box ATP-independent RNA helicase which has been reported to play important roles in replication, transcription, translation, RNA splicing and RNA processing which contribute to DHX9’s role in maintenance of genomic stability. Functionally, DHX9’s role involves binding to as well as unwinding and/or resolving double-stranded and single-stranded DNA/RNA, DNA/RNA hybrids (R-loops), circular RNA and DNA/RNA G quadraplexes. Overexpression of DHX9 is evident in multiple cancer types, including colorectal cancer (CRC) and lung cancer. In addition, microsatellite instable (MSI) tumors exhibiting defective mismatch repair (dMMR) show a strong dependence on DHX9, making this helicase an attractive target for oncology drug discovery.

Here we describe data supporting targeting DHX9 in MSI CRC as a novel therapeutic, and the first identification of potent and selective in vitro and in vivo small molecule inhibitors of DHX9. We demonstrate that DHX9 inhibition in MSI CRC, delivered either through siRNA knockdown or compound treatment, leads to an increase in RNA/DNA secondary structures such as R-loops and circRNA (i.e. circBRIP1) inducing replication stress. Cell lines that are dMMR (i.e. MSI) are unable to resolve this replication stress, resulting in prevention of DNA replication in S phase and later onset of apoptosis. We were able to confirm this selective dependency in a panel of 20 CRC cell lines; anti-proliferative effects mediated by DHX9 inhibition were dependent on cell line dMMR status in a 10-day proliferation assay. Furthermore, compound 1, an orally bioavailable DHX9 inhibitor was used to investigate in vivo efficacy in MSI CRC (LS411N) and MSS CRC (SW480) xenograft models. Compound 1 was well tolerated across the 28-day treatment period with robust and durable tumor regression (TGI = 105 %) observed in the LS411N tumor xenograft model only. In addition, following cessation of treatment, minimal tumor regrowth was observed in a 28-day post treatment window. Tumor and plasma concentrations of compound 1 and changes in pharmacodynamic markers of DHX9 inhibition, such as circBRIP1 mRNA, were measured and resulting PK and PD data were highly correlated. Together, these preclinical data validate DHX9 as a tractable new target with potential utility as a novel treatment for patients with MSI CRC.

Citation Format: Jennifer Castro, Matthew H. Daniels, Chuang Lu, David Brennan, Deepali Gotur, Young-Tae Lee, Kevin Knockenhauer, April Case, Jie Wu, Shane M. Buker, Julie Liu, Brian A. Sparling, E. Allen Sickmier, Stephen J. Blakemore, P. Ann Boriack-Sjodin, Kenneth W. Duncan, Scott Ribich, Robert A. Copeland. Targeting DHX9 inhibition as a novel therapeutic modality in microsatellite instable colorectal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1136.

Abstract A65: Development of a CD137 receptor occupancy assay to support the Phase I/II study of BT7480, a Bicycle® tumor-targeted immune cell agonist ® (Bicycle TICA™)

Bicycles are fully synthetic constrained peptides with antibody-like affinities that target selectively, readily penetrate tumor tissue, have relatively short half-lives, and can be chemically linked together to generate multifunctional molecules. BT7480 is a Bicycle TICA™ being developed as a first-in-class CD137 therapeutic for the treatment of human cancers associated with Nectin-4 expression and is currently being investigated in an ongoing Phase I/II clinical trial. Monitoring target engagement for a given therapeutic can be a key factor in recommending the Phase II dose. While flow cytometry-based receptor occupancy (RO) assays are commonly used to monitor target engagement in the clinic, a CD137-specific RO assay presents several important challenges that have historically hampered monitoring RO in the clinic including the dynamic expression of CD137 on unstimulated and stimulated T cells, the low frequency of CD137+ cells in human blood and limited reagents to confidently detect CD137+ cells in the presence of CD137-targeting drugs. To address these challenges, a fit-for-purpose 14-plex flow cytometry panel was developed that incorporates a fluorescently labelled CD137-specific binding Bicycle®. This Bicycle® was shown to directly compete with a Bicycle TICA™ for binding to CD137, but not with a fluorescently labelled anti-CD137 antibody, thereby enabling simultaneous detection of various CD137+ immune cell types as well as receptor occupancy by BT7480 in a single blood sample. Panel performance was tested across blood-based sample matrices routinely used in the clinic including EDTA and Cyto-Chex® blood collection tubes and Cell Preparation Tubes (CPT) (n=3 each). CPT were selected as the optimal sample matrix based on sample viability and highest detection of CD137 antibody+ and CD137 Bicycle®+ cells. Ex vivo RO assessments in anti-CD3 stimulated and unstimulated healthy human blood demonstrated dose-dependent detection of BT7480-occupied CD137, as well as the detection of >1000 CD137+ cells with sample viability >70% (n=5 each). The optimized method and dose-dependent detection of CD137+ cells and BT7480-occupied CD137 were further verified in unstimulated lung cancer patient whole blood samples (n≥5). Results from this study represent the first report of a clinic-ready CD137 RO assay and the first flow cytometry assay using fluorescently labelled Bicycle® reagents and demonstrate the utility of the Bicycle® CD137 RO assay to monitor target engagement in the BT7480 first-in-human clinical trial.

Citation Format: Heather Cohen, Cara Bray, Drasti Kanakia, Johanna Lahdenranta, Punit Upadhyaya, Kristen Hurov, Julia Kristensson, Chintan Jobaliya, Greg Bannish, Adam Cotty, Kevin McDonnell, Sandra Hirschberg, Sebastien Hazard, Dominic Smethurst, Nicholas Keen, Stephen J Blakemore. Development of a CD137 receptor occupancy assay to support the Phase I/II study of BT7480, a Bicycle® tumor-targeted immune cell agonist ® (Bicycle TICA™) [abstract]. In: Proceedings of the AACR Special Conference: Tumor Immunology and Immunotherapy; 2022 Oct 21-24; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2022;10(12 Suppl):Abstract nr A65.

Abstract 333: Activity of the erythropoietin-producing hepatocellular A2 receptor (EphA2) targeting Bicycle® Toxin Conjugate (BTC™) BCY6033 in EGFR inhibitor resistant non-small lung cancer (NSCLC) patient derived xenografts

Introduction: EphA2 regulates cell migration, adhesion, proliferation and differentiation, and is overexpressed in human cancers which have been shown to correlate with tumor progression. BCY6033 contains a bicyclic peptide targeting EphA2, linked to the cytotoxin Monomethyl auristatin E via a molecular spacer and cleavable linker designed to target EphA2 expressing tumors. BCY6033 is analogous to BT5528, a BTC™ currently in phase I/II clinical trial in patients with advanced malignancies associated with EphA2 expression. Recent literature indicate that tumor EphA2 expression may be up regulated in EGFR mutant lung models following 1st, 2nd and possibly 3rd generation EGFR inhibitors. Here we report on EphA2 expression in well characterized and clinically annotated patient derived xenografts (PDX) of NSCLC including EGFR mutant NSCLC derived either from erlotinib or osimertinib resistant patients. In vivo activity of BCY6033 is presented in two EphA2 expressing PDX models.

Experimental procedures: In vivo, an initial tolerability study was conducted with once weekly administration of BCY6033 by intravenous injection in NSG mice. The activity of BCY6033 was evaluated in EphA2 expressing EGFR mutant PDX models, DFCI-161 and DFCI-220 in NSG mice. A TMA was constructed containing FFPE derived from 69 PDX models (NSCLC n=61, SCLC-transformed n=5, de novo SCLC n=3). Of the 69 models, 35 were EGFR mutant. The TMA was subsequently stained via immunohistochemistry (IHC) using an α-EphA2 (R&D Systems) primary antibody. Tumor membranous H-score was assigned by a pathologist and a score of ≥50 was considered positive.

Results: Of the 69 PDXs, 16 were determined to be EphA2 positive. No correlation with genotype or clinical history was observed with EphA2 expression. EphA2 IHC was repeated on at least 5 different tumors for 5 PDX models with fast and robust in vivo growth latency. Two models, DFCI-161 and DFCI-220 with the most reproducible EphA2 staining were selected. Treatment with BCY6033 showed that a dose of 3 mg/kg once weekly administered intravenously was well tolerated in female NSG mice. BCY6033 treatment led to significant tumor growth inhibition with >80% tumor regressions in both DFCI-161 and DFCI-220 PDX models. Re-challenge of tumor out-growth showed that they retain sensitivity to BCY6033 treatment.

Conclusion: BCY6033 is a potentially promising drug effective against EphA2 expressing PDX models. Future studies and clinical trials will seek to determine the efficacy of BT5528 in EphA2 expressing tumors.

Citation Format: Kenneth Ngo, Elena V. Ivanova, Tyler J. Teceno, Carly Campbell, Johanna Lahdenranta, Stephen J. Blakemore, Gavin Bennett, Pasi A. Jänne, Cloud P. Paweletz, Prafulla C. Gokhale. Activity of the erythropoietin-producing hepatocellular A2 receptor (EphA2) targeting Bicycle® Toxin Conjugate (BTC™) BCY6033 in EGFR inhibitor resistant non-small lung cancer (NSCLC) patient derived xenografts [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 333.

Abstract 1976: Development of a CD137 receptor occupancy assay to support the phase I/II study of BT7480, a Bicycle tumor-targeted immune cell agonist™ (Bicycle TICA®)

Bicycles are fully synthetic constrained peptides with antibody-like affinities that target selectively, readily penetrate tumor tissue, have relatively short half-lives, and can be chemically linked together to generate multifunctional molecules. BT7480 is a Bicycle TICA® being developed as a first-in-class CD137 therapeutic for the treatment of human cancers associated with Nectin-4 expression which is currently being investigated in an ongoing phase I/II clinical trial. Monitoring target engagement for a given therapeutic can be a key factor in recommending the phase II dose. While flow cytometry-based receptor occupancy (RO) assays are commonly used to monitor target engagement in the clinic, a CD137-specific RO assay presents several important challenges that have historically hampered monitoring RO in the clinic including the dynamic expression of CD137 on unstimulated and stimulated T cells, the low frequency of CD137+ cells in human blood and limited reagents to confidently detect CD137+ cells in the presence of CD137-targeting drugs. To address these challenges, a fit-for-purpose 14-plex flow cytometry panel was developed that incorporates a fluorescently labelled CD137-specific binding Bicycle®. This CD137 Bicycle® was shown to directly compete with BT7480 for binding to CD137, but not with fluorescently labelled anti-CD137 antibody, thereby enabling simultaneous detection of various CD137+ immune cell types as well as receptor occupancy by BT7480 in a single blood sample. Panel performance was tested across blood-based sample matrices routinely used in the clinic including EDTA and Cyto-Chex® blood collection tubes and Cell Preparation Tubes (CPT) (n=3 each). CPT were selected as the optimal sample matrix based on sample viability and highest detection of CD137 antibody+ and CD137 Bicycle® + cells. Ex vivo RO assessments in anti-CD3 stimulated and unstimulated healthy human blood, demonstrated dose-dependent detection of CD137 RO by BT7480 and the detection of >1000 CD137+ cells with sample viability >70% (n=5 each). The optimized method and dose-dependent detection of CD137+ cells and RO by BT7480 was further verified in unstimulated lung cancer patient whole blood samples (n=5). Results from this study represent the first report of a clinic-ready CD137 RO assay and the first flow cytometry assay using fluorescently labelled Bicycle® reagents and demonstrate the utility of the Bicycle® CD137 RO assay to monitor target engagement in the BT7480 first-in-human clinical trial.

Citation Format: Heather Cohen, Drasti Kanakia, Johanna Lahdenranta, Punit Upadhyaya, Kristen Hurov, Julia Kristensson, Chintan Jobaliya, Greg Bannish, Adam Cotty, Kevin McDonnell, Sandra Hirschberg, Phil Brandish, Sebastien Hazard, Dominic Smethurst, Nicholas Keen, Stephen J. Blakemore. Development of a CD137 receptor occupancy assay to support the phase I/II study of BT7480, a Bicycle tumor-targeted immune cell agonist™ (Bicycle TICA®) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1976.

Abstract 391: Molecular-based enrichment strategy for Nectin-4 targeted Bicycle toxin conjugate BT8009

Introduction: BT8009 consists of a bicyclic peptide targeting the tumor antigen Nectin-4, linked to the cytotoxin monomethyl auristatin E (MMAE) via a molecular spacer and cleavable linker. BT8009 is currently being investigated in a Phase 1/2 clinical trial (BT8009-100, NCT04561362) in relapsed and/or refractory solid tumor patients. Nectin-4 positive tumor tissue will be a requirement for enrolment eligibility (with the exception of bladder cancer) starting in dose escalation level 3. Nectin-4 positivity will be determined by IHC on tumor tissue, requiring either tumor membrane or tumor cytoplasmic H-score ≥ 100.

Methods: Nectin-4 is not included on commercial NGS panels or routinely screened by IHC. Therefore, the work reported here aimed to identify a routinely measured molecular surrogate of tumor Nectin-4 protein expression (i.e. somatic mutation or gene amplification) that could potentially increase patient screening frequency, yield, and likelihood of response to BT8009. Here we demonstrate that Nectin-4 copy number is associated with Nectin-4 mRNA expression in 9 cancer indications in TCGA including breast, bladder, and lung cancer. In addition, across >30 cancer indications in TCGA, copy number of Nectin-4 is highly correlated with SDHC copy number (these two genes are ~225 kb apart on 1q23), which is included on multiple commercially available NGS panels. Taken together, these results suggest that the existence of an SDHC amplification could be used as an enrichment tool to identify patients with Nectin-4 positive tumors. To test this hypothesis, we obtained 100 TNBC human tumor samples and generated data to determine Nectin-4 and SDHC copy number as well as Nectin-4 protein expression status by IHC.

Results: SDHC and Nectin-4 copy number were observed to be highly positively correlated (Spearman's Rho=0.93). Furthermore, all (N = 22) TNBC tumors with a Nectin-4 copy number ≥ 3 were identified as positive for Nectin-4 protein expression and were at or above the H-score threshold required for enrolment to BT8009-100. In contrast, within the subset of tumors that were diploid for Nectin-4/SDHC (n=30), there were both Nectin-4 positive and negative tumors. This suggests that the presence of SDHC/Nectin-4 amplification can be used to increase the probability of identifying Nectin-4 expressing tumors.

Conclusions: We demonstrate the potential utility of using pre-existing patient NGS data with SDHC amplifications to increase the frequency of identifying patients with high Nectin-4 expressing tumors via IHC. The use of this strategy is ongoing at all current sites enrolling patients to BT8009-100.

Citation Format: Tara Gelb, Sean Santos, Amy Dickson, Carly Campbell, Mike Rigby, Andrew J. Mckenzie, Dan Rozelle, Stephen J. Blakemore. Molecular-based enrichment strategy for Nectin-4 targeted Bicycle toxin conjugate BT8009 [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 391.

Abstract 1724: Microinjection of Nectin-4/CD137 tumor-targeted immune cell agonist (TICA™) activates the local tumor microenvironment

A new generation of both systemic and targeted CD137 agonists are entering clinical development following agonistic anti-CD137 (4-1BB) antibody development nearly a decade ago. However, each of these molecules rely on biologic agents with potentially suboptimal properties for CD137 agonism due to their relatively large size and long circulating half-lives which may limit their tissue penetration, cause sustained agonism resulting in overstimulation and activation-induced lymphocyte cell death. Fully synthetic constrained bicyclic peptides (Bicycles™) with antibody-like affinities and target selectivity are uniquely suited to circumvent limitations of other targeted CD137 agonistic therapeutics. BT7480 and BCY11864 are tumor targeted immune cell agonists (TICA) designed to deliver a highly potent CD137 agonist to Nectin-4 overexpressing tumors with a flexible dosing schedule maximizing anti-tumor activity while circumventing the need for continuous systemic exposure. The Comparative In Vivo Oncology (CIVO) platform has been developed to enable in situ investigation of multiple microdosed drugs simultaneously in human tumors with safety and feasibility of this platform recently demonstrated in patients with soft tissue sarcomas. CIVO percutaneously injects drug microdoses directly into tumor tissue as trackable columns where tissue can be analyzed after resection for the effect of the drug treatment in the tumor. Here we report on an evaluation of the feasibility of using the CIVO -platform to demonstrate the mechanism of action of our tumor target-dependent CD137 agonist TICAs. Both BT7480 and BCY11864 demonstrate extremely potent Nectin-4-dependent CD137 agonism in primary human PBMC/tumor cell co-culture assays. Systemic administration of BT7480 in Nectin-4 expressing tumors in immunocompetent mice leads to profound reprogramming of the tumor immune microenvironment including a rapid increase in T cell chemotactic cytokine transcripts and macrophage gene signatures followed by an increase in cytotoxic cell gene signature and increase in intratumoral CD8+ T cells. CIVO was used to demonstrate the in vivo mechanism of action of a Nectin-4/CD137 TICA. Micro-injection of BCY11864 into Nectin-4 expressing tumors in immunocompetent mice led to dose dependent induction of immune activation markers in the tumor microenvironment and activation of the tumor resident cytotoxic T cells was evident 24 hours after BCY11864 micro-injection. Akin to our findings with transcriptional profiling of the tumor response to BT7480, BCY11864 activity was shown not to be limited to T cells but also included other CD137 positive cell populations such as myeloid and NK cells. We hypothesize that tumor targeted CD137 agonism may lead to initial myeloid cell response that enhances the cytotoxic T cell recruitment and activation in the tumor tissue.

Citation Format: Johanna Lahdenranta, Stephen J. Blakemore, Kristen Hurov, Marc O. Grenley, Punit Upadhyaya, Carly Campbell, Elizabeth Repash, Eric Haines, Philip E. Brandish, Richard A. Klinghoffer, Nicholas Keen. Microinjection of Nectin-4/CD137 tumor-targeted immune cell agonist (TICA™) activates the local tumor microenvironment [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 1724.

Abstract 1197: A multi tumor survey of Nectin-4 expression to guide BT8009 indication selection

Introduction: Bicycles® are a novel class of fully synthetic, short, constrained peptides. BT8009 consists of a bicyclic peptide targeting the tumor antigen Nectin-4, linked to the cytotoxin monomethyl auristatin E (MMAE) via a molecular spacer and cleavable linker. Nectin-4 is a validated tumor target and is highly expressed in a wide range of tumors. A Phase I/II dose escalation/expansion study, BT8009-100 (NCT04561362), enrolling patients with advanced solid tumors associated with Nectin-4 expression is ongoing in the US. Here we report the analysis of tumor tissue microarrays (TMAs) stained with a Nectin-4 immunohistochemistry (IHC) assay to support patient selection for the BT8009-100 study. Methods: We developed a clinical grade Nectin-4 IHC assay on the Leica platform using a proprietary rabbit monoclonal α-Nectin-4 primary antibody (Abcam, Burlingame, CA) and the BOND Polymer Refine detection kit. TMAs of cancer types reported to have high Nectin-4 expression, including esophageal, pancreatic, bladder, head & neck, stomach, non-small cell lung, breast, and ovarian cancer, were stained and manually scored for Nectin-4 levels, with the tumor microenvironment evaluated in a subset of samples. Nectin-4 H-scores (stain intensity on a scale of 0-3 x percent positive tumor cells) were generated by a pathologist independently for tumor cell membrane and tumor cytoplasm. H-scores ≥ 100 in the tumor membrane or cytoplasm were considered positive. Results: In all indications tested, a greater degree of Nectin-4 positivity was observed in the tumor cytoplasm as compared to tumor membrane. Breast and bladder cancer had the greatest frequency of Nectin-4 positivity. Subtype analysis in breast cancer identified enrichment of Nectin-4 expression in hormone receptor negative and human epidermal growth factor receptor 2 positive tumors.

Conclusion: The frequency of Nectin-4 expression as measured by IHC across multiple tumor types may guide clinical strategy for the BT8009 program.

TableIndicationTotal cores (n)Percent Tumor Membrane PositivePercent Tumor Cytoplasm PositivePercent Tumor Membrane or Cytoplasm PositiveBreast225164957Bladder142274256Esophagus14073032Head & Neck69102532Lung15731717Ovarian8921315Pancreas96123Stomach131022

Citation Format: Carly T. Campbell, Robert Smale, Michael Rigby, Shawn Watson, Amy Dickson, Tara Gelb, Heather Cohen, Pierre Lee, Josette William Ragheb, Stephen J. Blakemore. A multi tumor survey of Nectin-4 expression to guide BT8009 indication selection [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 1197.

Susceptibility to prosocial and antisocial influence in adolescence

Introduction

Adolescents are particularly susceptible to social influence and previous studies have shown that this susceptibility decreases with age. The current study used a cross-sectional experimental paradigm to investigate the effect of age and puberty on susceptibility to both prosocial and antisocial influence.

Methods

Participants (N = 520) aged 11–18 from London and Cambridge (United Kingdom) rated how likely they would be to engage in a prosocial (e.g. “help a classmate with their work”) or antisocial (e.g. “make fun of a classmate”) act. They were then shown the average rating (in fact fictitious) that other adolescents had given to the same question, and were then asked to rate the same behaviour again.

Results

Both prosocial and antisocial influence decreased linearly with age, with younger adolescents being more socially influenced when other adolescents’ ratings were more prosocial and less antisocial than their own initial rating. Both antisocial and prosocial influence significantly decreased across puberty for boys but not girls (independent of age).

Conclusions

These findings suggest that social influence declines with increasing maturity across adolescence. However, the exact relationship between social influence and maturity is dependent on the nature of the social influence and gender. Understanding when adolescents are most susceptible to different types of social influence, and how this might influence their social behaviour, has important implications for understanding adolescent social development.

Neural correlates of social influence on risk perception during development

Studies have shown that adolescents are more likely than adults to take risks in the presence of peers than when alone, and that young adolescents' risk perception is more influenced by other teenagers than by adults. The current fMRI study investigated the effect of social influence on risk perception in female adolescents (aged 12-14) and adults (aged 23-29). Participants rated the riskiness of everyday situations and were then informed about the (alleged) risk ratings of a social influence group (teenagers or adults), before rating each situation again. The results showed that adolescents adjusted their ratings to conform with others more than adults did, and both age groups were influenced more by adults than by teenagers. When there was a conflict between the participants' own risk ratings and the ratings of the social influence group, activation was increased in the posterior medial frontal cortex, dorsal cingulate cortex and inferior frontal gyrus in both age groups. In addition, there was greater activation during no-conflict situations in the right middle frontal gyrus and bilateral parietal cortex in adults compared with adolescents. These results suggest that there are behavioral and neural differences between adolescents and adults in conflict and no-conflict social situations.

Abstract A047: MT1-MMP Immunohistochemistry (IHC) analysis of tumor microarrays (TMAs) using a novel scoring system guides patient selection for BT1718 expansion cohorts

Introduction: BT1718 is a targeted Bicycle peptide-conjugate designed to deliver the anti-tubulin agent, DM1 to tumors expressing membrane type 1-matrix metalloprotease (MT1-MMP; MMP14; MT1). In vivo preclinical studies demonstrated that anti-tumor activity of BT1718 is dependent on the level of tumor MT1-MMP expression. In patient tumors MT1-MMP expression has been reported in tumor and stromal cells, both of which may contribute to the potential for anti-tumor effects following BT1718 dosing. BT1718 is currently being investigated in a Phase 1/2 clinical trial, which includes both dose escalation (ongoing) and dose expansion cohorts enrolling patients with advanced solid tumors that have exhausted standard therapeutic options. The dose expansion cohorts will enroll patients with tumors expressing high levels of MT1-MMP following establishment of the recommended Phase 2 dose. Here we describe the analysis of TMAs stained using a clinical grade MT1-MMP IHC assay to guide which patient populations to include in BT1718 dose expansion cohorts. Methods: A clinical grade MT1-MMP IHC assay was developed on the Ventana platform using a Millipore MT1-MMP primary antibody (MAB3328) at 1:6000 and detected using Optiview chemistry. Cancer indications reported in the literature with high MT1-MMP expression including ovarian, bladder, triple negative breast, esophageal, and NSCLC were stained and MT1-MMP expression levels estimated by consensus review of two pathologists using an H-score scale (staining intensity*percent positivity). H-scores (0-300) were derived separately for tumor membrane (TM), cytoplasm (TC), and stroma (TS) for each case. Results: MT1-MMP expression in TM/TS, but not TC is likely to yield the greatest potential for BT1718 binding and subsequent anti-tumor activity. Therefore, analyses of TM/TS H-scores were used to identify BT1718 dose expansion cohorts. Histograms were generated separately for TM and TS H-scores with a bin-width of 50. The distribution of MT1-MMP staining in TM and TS was different (Table 1) with H-score between 0-49 being the most frequently populated TM bin, regardless of indication. In contrast, TS scores were typically higher (e.g. H-score=100-149), with the clearest example being ovarian cancer (89% of cases TM 0-49 & only 20% of cases TS 0-49). In addition, within NSCLC, tumor subtype analysis demonstrated that cases of squamous histology appeared enriched for higher TM H-scores (TM≥150=36%) compared to adenocarcinoma cases (TM≥150=2%). Moreover, various TM and/or TS H-score boundaries were modelled with the aim of delivering a proposed cut-off for recruiting patients with high MT1-MMP expression to the expansion cohorts, the results of this modelling will be presented. Table 1: Distribution of MT1-MMP TM and TS H-scores across multiple indications p>

Citation Format: Tara Gelb, Chris Bacon, Philip Sloan, Mike Rigby, Stephanie Guerrera, Fiona Kelly, Stefan Symeonides, Stephen J Blakemore. MT1-MMP Immunohistochemistry (IHC) analysis of tumor microarrays (TMAs) using a novel scoring system guides patient selection for BT1718 expansion cohorts [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr A047. doi:10.1158/1535-7163.TARG-19-A047

PI3Kδ inhibition elicits anti-leukemic effects through Bim-dependent apoptosis

PI3Kδ plays pivotal roles in the maintenance, proliferation and survival of malignant B-lymphocytes. Although not curative, PI3Kδ inhibitors (PI3Kδi) demonstrate impressive clinical efficacy and, alongside other signaling inhibitors, are revolutionizing the treatment of hematological malignancies. However, only limited in vivo data are available regarding their mechanism of action. With the rising number of novel treatments, the challenge is to identify combinations that deliver curative regimes. A deeper understanding of the molecular mechanism is required to guide these selections. Currently, immunomodulation, inhibition of B-cell receptor signaling, chemokine/cytokine signaling and apoptosis represent potential therapeutic mechanisms for PI3Kδi. Here we characterize the molecular mechanisms responsible for PI3Kδi-induced apoptosis in an in vivo model of chronic lymphocytic leukemia (CLL). In vitro, PI3Kδi-induced substantive apoptosis and disrupted microenvironment-derived signaling in murine (Eμ-Tcl1) and human (CLL) leukemia cells. Furthermore, PI3Kδi imparted significant therapeutic responses in Eμ-Tcl1-bearing animals and enhanced anti-CD20 monoclonal antibody therapy. Responses correlated with upregulation of the pro-apoptotic BH3-only protein Bim. Accordingly, Bim-/- Eμ-Tcl1 Tg leukemias demonstrated resistance to PI3Kδi-induced apoptosis were refractory to PI3Kδi in vivo and failed to display combination efficacy with anti-CD20 monoclonal antibody therapy. Therefore, Bim-dependent apoptosis represents a key in vivo therapeutic mechanism for PI3Kδi, both alone and in combination therapy regimes.

Mechanisms of Pinometostat (EPZ-5676) Treatment-Emergent Resistance in MLL-Rearranged Leukemia

DOT1L is a protein methyltransferase involved in the development and maintenance of MLL-rearranged (MLL-r) leukemia through its ectopic methylation of histones associated with well-characterized leukemic genes. Pinometostat (EPZ-5676), a selective inhibitor of DOT1L, is in clinical development in relapsed/refractory acute leukemia patients harboring rearrangements of the MLL gene. The observation of responses and subsequent relapses in the adult trial treating MLL-r patients motivated preclinical investigations into potential mechanisms of pinometostat treatment-emergent resistance (TER) in cell lines confirmed to have MLL-r. TER was achieved in five MLL-r cell lines, KOPN-8, MOLM-13, MV4-11, NOMO-1, and SEM. Two of the cell lines, KOPN-8 and NOMO-1, were thoroughly characterized to understand the mechanisms involved in pinometostat resistance. Unlike many other targeted therapies, resistance does not appear to be achieved through drug-induced selection of mutations of the target itself. Instead, we identified both drug efflux transporter dependent and independent mechanisms of resistance to pinometostat. In KOPN-8 TER cells, increased expression of the drug efflux transporter ABCB1 (P-glycoprotein, MDR1) was the primary mechanism of drug resistance. In contrast, resistance in NOMO-1 cells occurs through a mechanism other than upregulation of a specific efflux pump. RNA-seq analysis performed on both parental and resistant KOPN-8 and NOMO-1 cell lines supported two unique candidate pathway mechanisms that may explain the pinometostat resistance observed in these cell lines. These results are the first demonstration of TER models of the DOT1L inhibitor pinometostat and may provide useful tools for investigating clinical resistance. Mol Cancer Ther; 16(8); 1669-79. ©2017 AACR.

EGR2 mutations define a new clinically aggressive subgroup of chronic lymphocytic leukemia

Recurrent mutations within EGR2 were recently reported in advanced-stage chronic lymphocytic leukemia (CLL) patients and associated with a worse outcome. To study their prognostic impact, 2403 CLL patients were examined for mutations in the EGR2 hotspot region including a screening (n=1283) and two validation cohorts (UK CLL4 trial patients, n=366; CLL Research Consortium (CRC) patients, n=490). Targeted deep-sequencing of 27 known/postulated CLL driver genes was also performed in 38 EGR2-mutated patients to assess concurrent mutations. EGR2 mutations were detected in 91/2403 (3.8%) investigated cases, and associated with younger age at diagnosis, advanced clinical stage, high CD38 expression and unmutated IGHV genes. EGR2-mutated patients frequently carried ATM lesions (42%), TP53 aberrations (18%) and NOTCH1/FBXW7 mutations (16%). EGR2 mutations independently predicted shorter time-to-first-treatment (TTFT) and overall survival (OS) in the screening cohort; they were confirmed associated with reduced TTFT and OS in the CRC cohort and independently predicted short OS from randomization in the UK CLL4 cohort. A particularly dismal outcome was observed among EGR2-mutated patients who also carried TP53 aberrations. In summary, EGR2 mutations were independently associated with an unfavorable prognosis, comparable to CLL patients carrying TP53 aberrations, suggesting that EGR2-mutated patients represent a new patient subgroup with very poor outcome.

Abstract 312: Evidence of EZH2 dependent and independent mechanisms of tazemetostat treatment emergent resistance in models of diffuse large B cell lymphoma

Tazemetostat is a small molecule inhibitor of the histone methyltransferase EZH2 and is currently in phase 2 clinical trials including relapsed refractory Non-Hodgkin Lymphomas (RR-NHL) Diffuse Large B Cell Lymphoma and Follicular Lymphoma. In the phase 1 clinical trial RR-NHL patients demonstrated positive clinical activity with a favorable safety profile. Acquired mutations in the D1 domain (I109K, Y111D, Y111L) and the SET domain (Y661D) of EZH2 have recently been reported as a mechanism of resistance to non-tazemetostat small molecule EZH2 inhibition. Given the clinical activity observed in the phase 1 tazemetostat clinical trial and these reports of pre-clinical EZH2 inhibitor induced resistance we embarked on investigations of the potential of tazemetostat to induce resistance in NHL cell lines. An EZH2 Y641F mutant DLBCL cell line WSU-DLCL2 was exposed to 1 μM tazemetostat, a dose which is 100 fold greater than the naïve line's 11 day growth IC50. After 8 weeks, growth of the tazemetostat treated cells matched that of the control cells. Subsequent increases in dose of tazemetostat up to 10 μM did not yield any changes in growth rate of the treated cells. EZH2 wild-type PMBCL cell line U2940 was exposed to a step wise increase in tazemetostat concentration for 7 weeks and finally maintained at the naïve cell line 11 day proliferation IC50 of 10 μM, with minimal effects on cell growth. Tazemetostat resistant cell lines were screened for acquired EZH2 mutations using a full coding next generation sequencing assay, with a mean depth of 17,126 across all positions. Sequencing results showed the resistant U2940 had gained mutations in EZH2 similar to those previously identified, a heterozygous Y661N mutation and a low frequency mutation of Y111H, consistent with a subclonal mutation. These acquired mutations have been reported to interfere with the binding of EZH2 inhibitors, which supports the minimal reduction of H3K27me3 as measured by ELISA in the resistant U2940 after treatment with tazemetostat. In contrast, after induction of tazemetostat resistance WSU-DLCL2 retained equipotent sensitivity to reduction of H3K27me3 by ELISA. Correspondingly, sequencing of EZH2 in the resistant WSU-DLCL2 line did not identify any additional mutations. These findings suggest continued target engagement with tazemetostat in the resistant WSU-DLCL2, and that a novel bypass mechanism may be engaged to confer resistance. In an attempt to identify the mechanism of resistance in the WSU-DLCL2 line, whole exome sequencing and RNA sequencing has been performed. Detailed mutational, gene expression and pathway analysis will be performed on these data to investigate mechanisms of treatment emergent resistance to tazemetostat. Understanding these mechanisms may guide hypotheses for rational combinations and provide direction for future preclinical and potentially clinical studies.

Citation Format: Carly T. Campbell, Jeff S. Jasper, Scott R. Daigle, Scott A. Ribich, Heike Keilhack, Jesse S. Smith, Peter T. Ho, Stephen J. Blakemore. Evidence of EZH2 dependent and independent mechanisms of tazemetostat treatment emergent resistance in models of diffuse large B cell lymphoma. [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 312.

Abstract 137: Development and application of a 62-gene panel for assessment of somatic sequence and structural variants in tumor DNA derived from non-Hodgkin lymphoma patients treated in a phase 1 clinical trial with the EZH2 inhibitor tazemetostat

Tazemetostat is a small molecule inhibitor of the histone methyltransferase EZH2 and is currently in phase 2 clinical trials in relapsed refractory Non-Hodgkin's Lymphomas (RR-NHL) including diffuse large B cell and follicular lymphoma. We report the development and application of a NHL targeted sequencing panel designed to identify molecular variants, including specific somatic sequence mutations (single base and insertion/deletion), amplifications and translocations in both tumor and cell free circulating tumor DNA (ctDNA). Analysis of somatic alterations in both tissue and ctDNA collected pre-dose enables determination of molecular variants that may correspond with clinical activity, while longitudinal analysis of ctDNA sampled on therapy could help monitor patients for minimal residual disease and emergence of acquired resistance. In collaboration with Personal Genome Diagnostics (PGDx) a panel of 62 NHL specific genes was designed to selectively analyze regions of the genome previously identified as somatically altered in NHL. DNA derived from matched tumor tissue and plasma were screened utilizing this panel using the Illumina HiSeq 2500 platform with 100 bp paired-end reads. Average target coverage for the tissue panel was 1,250-fold while coverage for the ctDNA was approximately 20,000-fold and 3,700-fold for sequence mutations and structural alterations, respectively. Data were analyzed using PGDx's validated cancer genome analysis algorithms that allow for reliable identification of mutations with high sensitivity and specificity. Validation of both the tumor and ctDNA panels was performed using tumor and plasma specimens previously characterized for sequence mutations, amplifications, translocations, and microsatellite instability. For archive tumor, analyses of cell line specimens with an experimental tumor purity of 20-100% using 50-100ng of DNA yielded sensitivity and specificity of 100% for detection of 358 previously characterized sequence mutations and structural variants. Similar ctDNA analyses using fragmented cell line and plasma derived DNA with an experimental tumor purity of 0.10%-25.0% using 9-167ng of DNA yielded a sensitivity of 100% for detection of over 100 genetic variants. Following successful validation of the panel we proceeded to sequence tumor tissue from 11 patients and ctDNA from 16 NHL patients enrolled in the tazemetostat phase 1 clinical trial. Tumor tissue from these patient samples had been previously sequenced using a smaller 39 gene panel. We observed high concordance with 100% of variants detected within the shared gene set of 33 genes between the historic data and our new 62 gene panel. We will report the landscape and concordance of genetic alterations identified through next-generation sequencing analyses of tumor and cell-free DNA.

Citation Format: Scott R. Daigle, Samuel Angiuoli, Sian Jones, Scott Ribich, Heike Keilhack, Mark Sausen, Peter T. Ho, Stephen J. Blakemore. Development and application of a 62-gene panel for assessment of somatic sequence and structural variants in tumor DNA derived from non-Hodgkin lymphoma patients treated in a phase 1 clinical trial with the EZH2 inhibitor tazemetostat. [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 137.

Abstract 5383: DOT1L inhibitor EPZ-5676 synergizes with cytarabine and azacitidine in preclinical models of MLL-rearranged leukemia

EPZ-5676 is a small molecule inhibitor of the histone methyltransferase DOT1L currently in clinical development and represents a first in class novel therapeutic agent for the treatment of MLL-rearranged (MLL-r) leukemia. In preclinical studies, EPZ-5676 selectively inhibited intracellular histone H3K79 methylation, downstream target gene expression and demonstrated complete tumor regression in a MLL-r leukemia xenograft model. We previously reported synergistic and durable anti-proliferative activity when EPZ-5676 was combined with current AML standard of care drugs, cytarabine and daunorubicin in MLL-r leukemia models MOLM-13 (MLL-AF9) and MV4-11 (MLL-AF4). Combination benefit was also observed when MLL-r cells were treated with cytarabine, prior to co-treatment with EPZ-5676. Additionally, both cytarabine and the DNA methyltransferase inhibitor azacitidine, displayed synergistic anti-leukemic activity in MLL-r rearranged cells in a 7 day co-treatment model (7 days of continuous treatment with EPZ-5676 and second agent; see Klaus et al, JPET, 2014). In this report we discuss results of investigating additional treatment schedules using EPZ-5676 in combination with azacitidine in MLL-r cells. Cells were pretreated with azacitidine at nanomolar concentrations known to reverse promoter DNA-hypermethylation and alter the chromatin state (Tsai et al., Cancer Cell, 2012). We found treating MV4-11 and MOLM-13 cells once daily for three consecutive days followed by sequential treatment with EPZ-5676 elicited a synergistic anti-proliferative effect using the Chou-Talalay method (Chou, Pharmacol Rev., 2006). Results of studies to investigate the mechanism of this synergistic cell killing, including evaluation of differentiation markers and Annexin V staining will be reported. To determine if combinations of EPZ-5676 with cytarabine or azacitidine were tolerable and efficacious in vivo, nude rats implanted subcutaneously with MV4-11 tumors were treated using a range of doses and schedules. Azacitidine and cytarabine were delivered by intraperitoneal injection once daily for 14 days at their respective maximum tolerated doses of 2 and 200 mg/kg. Dosing at the established MTD, these agents inhibited the subcutaneous MV4-11 tumor growth by 50% compared to vehicle controls. Efficacy results from the EPZ-5676 combination studies with cytarabine or azacitidine will be presented. In summary, our results indicate that EPZ-5676 in combination with cytarabine or azacitidine revealed a synergistic effect, regardless of the treatment schedule used in preclinical models of MLL-r leukemia. Tolerable in vivo rat combination doses for EPZ-5676 with both cytarabine and azacitidine have been determined in support of potential future assessment of these combinations in MLL-r leukemia patients.

Citation Format: Christine R. Klaus, Scott R. Daigle, Vivek Chopra, Jeffrey A. Keats, Carly T. Campbell, Dorothy Iwanowicz, Edward J. Olhava, Margaret P. Scott, Roy M. Pollock, Robert A. Copeland, Jesse J. Smith, Jorge DiMartino, Stephen J. Blakemore, Alejandra Raimondi. DOT1L inhibitor EPZ-5676 synergizes with cytarabine and azacitidine in preclinical models of MLL-rearranged leukemia. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5383. doi:10.1158/1538-7445.AM2015-5383

Abstract 2701: Characterization of acquired EPZ-5676 resistance in cell line models of MLL rearranged leukemia

DOT1L inhibitor EPZ-5676 is currently under Phase 1 clinical trial investigation in relapsed/refractory patients with acute leukemia, including those with an MLL-rearrangement (MLL-r). Early clinical results, including complete remissions, support ongoing clinical development and preclinical investigation into mechanisms precipitating EPZ-5676 treatment induced resistance. MLL-r cell lines KOPN-8 (MLL-ENL) and NOMO-1 (MLL-AF9) were exposed to an EPZ-5676 concentration above the pre-determined 14 day proliferation assay IC90. Initial treatment of the cell lines led to the expected inhibition of H3K79 dimethylation (H3K79me2) and MLL-r target genes HOXA9 and MEIS1 as outlined in previous work (Daigle et al, Cancer Cell 2011). Resistance to EPZ-5676 in both cell lines emerged following three weeks of continued treatment with EPZ-5676 and was defined by increased growth rates in the presence of inhibitor. Mechanisms of resistance for both cell lines were investigated using RNASeq and ChIPSeq on parental and resistant cell line pools. Our analysis identified common characteristics between the resistant cell lines, but mechanisms by which they became resistant differed. Global H3K79me2 inhibition was maintained in both refractory cell lines, yet ChIP-seq analysis of resistant pools identified specific loci with H3K79me2 recovery in KOPN-8 cells. In resistant KOPN-8 cells recovery of H3K79me2 was concentrated at the HOXA locus and other MLL-r target genes (e.g. MEIS1 and RUNX2), with the remainder of actively transcribed genes maintaining H3K79me2 inhibition at levels observed in parental cells. In contrast, resistant NOMO-1 cells did not recover H3K79me2 at any actively transcribed genes, including those of the MLL-r signature. Only resistant KOPN-8 cells regained expression of the MLL-r target genes HOXA9 and MEIS1. Of note both resistant NOMO-1 and KOPN-8 cell lines had 8 and 40 fold upregulation of the ABCB1 (MDR1, P-gp) tranporter respectively when compared to a matched control cell line. To explore the role of drug efflux transporter ABCB1 on resistance, we treated cells with Valspodar, a known inhibitor of ABCB1. Following treatment with 1 μM Valspodar, KOPN-8 cells showed decreased cell growth similar to the naïve control cell line. Supporting the presence of an alternative resistance mechanism in NOMO-1 cells in addition to MDR1 upregulation, NOMO-1 cells remained resistant upon Valspodar treatment. Detailed gene expression and pathway analysis will be presented supporting mechanisms of treatment emergent resistance to EPZ-5676. In summary, we have identified two mechanisms of EPZ-5676 resistance in MLL-r cell lines, one mechanism dependent on and the other independent of ABCB1. Further refinement of these mechanisms will aid in providing hypotheses for testing mechanisms of EPZ-5676 treatment emergent resistance in patients and may support designing future rational clinical combinations.

Citation Format: Scott R. Daigle, Carly T. Campbell, Nigel J. Waters, Edward J. Olhava, Robert A. Copeland, Stephen J. Blakemore, Roy M. Pollock, Jesse J. Smith. Characterization of acquired EPZ-5676 resistance in cell line models of MLL rearranged leukemia. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2701. doi:10.1158/1538-7445.AM2015-2701

Abstract A45: Investigation of efficacy of the NAE inhibitor MLN4924 across large-scale cell line panels reveals potentially sensitive cancer indications and candidate predictive biomarkers

MLN4924 is an investigational inhibitor of NAE (Nedd8 Activating Enzyme). NAE mediates NEDD8 conjugation and thus regulates the cullin-RING ligase (CRL) proteasomal degradation pathway. MLN4924 is currently being tested in Phase 1 clinical trials of patients with hematological or solid tumors. To support future clinical development and identify potential biomarkers of tumor sensitivity or resistance, two large cancer cell line panels (Panel 1, N=653; Panel 2, N=240) were treated with MLN4924 and cell viability data (IC50, EC50, and POC - Percentage of Control) were generated. These data were used to correlate sensitivity/resistance with the cell line's tumor histology and with underlying genetic data for the specific cell lines. Overlapping cell lines from the two panels (114) showed consistent growth inhibition effects (Spearman Correlation coefficient = 0.72). Using Fisher's exact test and POC cutoffs at 25% and 50% quartiles on viability data, we identified bladder cancer and head and neck cancer lines as associated with MLN4924 sensitivity in both panels. Using median percentage of control values as cutoff, we applied Fisher's exact test to evaluate associations of individual mutations in the cell lines to MLN4924 sensitivity or resistance. Examples of mutations linked to sensitivity include KDM6A (p-value = 0.02, Panel 1; p-value = 0.06, Panel 2). APC mutation is associated with resistance to MLN4924 (p-value = 5.75 × 10−5, Panel 1; p-value = 0.04, Panel 2).

Combining cell viability and baseline gene expression data from cell line Panel 2, a PLSR predictive model was developed, identifying a gene signature (102 genes) for MLN4924 sensitivity and resistance. A median cutoff of PLSR scores was applied to separate predicted sensitive/resistant cell lines. Consistent with previous association of cell viability with histology, PLSR analysis of gene expression predicted that bladder cancer cell lines are particularly sensitive to MLN4924. Two pathway analysis approaches were applied to identify MLN4924 sensitivity related pathways using either whole genome information (GSEA) or the PLSR gene signature list. The two approaches consistently indicated an over-representation of signaling pathways including cell cycle, development hedgehog signaling and ErbB signaling. The over-represented cell cycle pathway is in good agreement with previous MLN4924 mechanism of action studies. In particular, this finding was independently validated via a whole genome siRNA screen that also identified the cell cycle pathway as associated with tumor sensitivity. The consistent observations from two large cell line panels and a siRNA screen support the utility of these approaches for clarifying sensitive and resistant tumor cell types and also potentially identifying candidate biomarkers.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr A45.

Abstract A38: Development and implementation of immunohistochemistry (IHC)-based pharmacodynamic (PD) biomarkers demonstrate NAE pathway inhibition in MLN4924 solid tumor clinical trials

MLN4924 is an investigational small molecule NEDD8 activating enzyme (NAE) inhibitor with antitumor activity in preclinical models of several tumor types that is currently in Phase I clinical development in both hematological and solid tumors. NAE is an essential controller of the NEDD8 conjugation pathway that is required for cullin-RING ligase (CRL) activity. MLN4924 forms a covalent adduct with NAE, inhibiting enzyme activity and thus preventing ubiquitination and proteasomal degradation of CRL substrate proteins. CRL substrates have important roles in cell-cycle progression, DNA replication (CDT1), oxidative stress response (NRF-2), and survival signaling; interfering with their degradation ultimately leads to apoptosis. MLN4924 is the first NAE inhibitor to enter clinical development and evidence of target inhibition and/or downstream pathway modulation were key objectives of the Phase I studies. Here we describe the development, validation and clinical implementation of IHC PD assays for MLN4924 that quantify levels of CRL substrates CDT1 and NRF-2 and demonstrate MLN-4924 NEDD8 adduct formation in both skin and solid tumors.

Pre-clinical solid tumor xenograft models were treated with increasing doses of MLN4924. Tumors were collected at multiple post-dose time points (30 minutes to 48 hours) to develop clinical assays and establish the biopsy schedule. Levels of stabilized substrates CDT1 and NRF-2, and presence of MLN4924-NEDD8 adduct were measured by quantitative and semi-quantitative IHC, respectively. Slides were scanned as whole slide images using an Aperio XTscan scope and analyzed for a percent positive pixel count using Metamorph imaging software. Western blotting of xenograft material showed decreased cullin neddylation while IHC showed an increase of CRL substrates CDT1 and NRF-2. Regulation of all PD markers was dose and time dependent. Substrate levels were most robust in the highest dose groups and peaked between 2–8 hours after dosing, returning to base line levels by 24 hours. The MLN4924-NEDD8 adduct was observed in xenograft tumors within 30 minutes of treatment indicating that MLN4924 rapidly distributed to the tumor tissue and persisted up to 24 hours. These data supported the selection of a 3–6 hr window for post-dose biopsy sampling in the clinical studies.

IHC assays were successfully adapted to clinical trial fine needle tumor biopsies and skin punch biopsies. In phase I studies levels of CDT1, NRF-2 and MLN4924-NEDD8 adduct in skin and tumor were compared in biopsies obtained at screening and 3–6 hours after the second day of dosing. CDT1 and NRF-2 IHC staining was quantified exclusively in regions of tumor or skin epidermal area. Elevations in CDT1 and NRF-2 substrate levels were observed in skin and tumor biopsies. Greater than 50% of all skin (n=38) and tumor biopsies (n=16) demonstrated a robust PD response suggesting target engagement. IHC analysis of MLN4924-NEDD8 adduct showed that drug was present in 100% of the post dose tumor biopsies.

These data demonstrate evidence of inhibition of NAE activity and downstream pathway modulation by MLN4924 in skin and multiple tumor types.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr A38.

Abstract B5: Sequence analysis of HSP90-encoding genes in breast tumor tissue identifies a novel 9 bp deletion in HSP90AB1

The 90 kDa heat-shock protein (HSP90) functions as a ubiquitous cellular chaperone in cells, and is required for the function and stability of many client proteins such as ERBB2, EGFR, BCR-ABL, MET, androgen and estrogen receptors, BRAF and HIF-1α.1 There are four primary genes that encode for HSP90 in humans: HSP90AA1 and HSP90AB1 (cytosolic), HSP90B1 (endoplasmic reticulum) and TRAP1 (mitochondrial). Increased HSP90 expression has been associated with poor prognosis in cancer, and inhibiting HSP90 can lead to degradation of many oncogenic client proteins via the proteasome pathway.1

HSP90 has been the subject of intense drug discovery activities, with several therapeutics under clinical investigation.2 However, the data on single nucleotide polymorphisms (SNPs) and potential somatic mutations within the HSP90-encoding genes in tumor tissue is limited. Target allelic variation can alter drug binding and therapeutic response, as demonstrated by Iressa™'s reported specific efficacy in EGFR-mutant non-small cell lung cancer patients.3 Therefore, it is critical to understand target allelic variance as part of a drug development program.

To facilitate drug development efforts around HSP90, we investigated allelic variation within the coding regions of HSP90AA1 (second isoform) and HSP90AB1 genes in 49 formalin-fixed paraffin- embedded human breast tumor samples. Sample SNP data were compared to control data from the NCBI Entrez SNP database. We observed four synonymous changes within HSP90AA1, and two synonymous changes within HSP90AB1. Intriguingly, we also observed a heterozygous 9-base deletion in exon 1 of HSP90AB1 within one breast tumor patient sample. This deletion results in an alanine>valine substitution at amino acid 22 and a loss of amino acid 23-25 (glutamine, leucine, methionine). The deleted region includes one turn of a 3-turn alpha helix, located within the N-terminal domain structure of the HSP90AB1 protein. Full details of HSP90 allelic variance within breast tumor tissue, and a discussion of the potential functional significance of the deletion, will be provided.

References:

1. Pearl LH, Prodromou C, Workman P. The HSP90 molecular chaperone: an open and shut case for treatment. Biochem J. 2008;410:439-53.

2. Hahn JS. The HSP90 chaperone machinery: From structure to drug development. BMB Reports. 2009;42(10):623-30.

3. Sequist LV, Bell DW, Lynch TJ, Haber DA. Molecular predictors of response to epidermal growth factor receptor antagonists in non- small-cell lung cancer. J Clin Oncol. 2007;25(5):587-95.

Citation Information: Clin Cancer Res 2010;16(14 Suppl):B5.

Causal reasoning identifies mechanisms of sensitivity for a novel AKT kinase inhibitor, GSK690693

Background

Inappropriate activation of AKT signaling is a relatively common occurrence in human tumors, and can be caused by activation of components of, or by loss or decreased activity of inhibitors of, this signaling pathway. A novel, pan AKT kinase inhibitor, GSK690693, was developed in order to interfere with the inappropriate AKT signaling seen in these human malignancies. Causal network modeling is a systematic computational analysis that identifies upstream changes in gene regulation that can serve as explanations for observed changes in gene expression. In this study, causal network modeling is employed to elucidate mechanisms of action of GSK690693 that contribute to its observed biological effects. The mechanism of action of GSK690693 was evaluated in multiple human tumor cell lines from different tissues in 2-D cultures and xenografts using RNA expression and phosphoproteomics data. Understanding the molecular mechanism of action of novel targeted agents can enhance our understanding of various biological processes regulated by the intended target and facilitate their clinical development.

Results

Causal network modeling on transcriptomic and proteomic data identified molecular networks that are comprised of activated or inhibited mechanisms that could explain observed changes in the sensitive cell lines treated with GSK690693. Four networks common to all cell lines and xenografts tested were identified linking GSK690693 inhibition of AKT kinase activity to decreased proliferation. These networks included increased RB1 activity, decreased MYC activity, decreased TFRC activity, and increased FOXO1/FOXO3 activity.

Conclusion

AKT is involved in regulating both cell proliferation and apoptotic pathways; however, the primary effect with GSK690693 appears to be anti-proliferative in the cell lines and xenografts evaluated. Furthermore, these results indicate that anti-proliferative responses to GSK690693 in either 2-D culture or xenograft models may share common mechanisms within and across sensitive cell lines.

The detection of intentional contingencies in simple animations in patients with delusions of persecution

BACKGROUND

It has been proposed that delusions of persecution are caused by the tendency to over-attribute malevolent intentions to other people's actions. One aspect of intention attribution is detecting contingencies between an agent's actions and intentions. Here, we used simplified stimuli to test the hypothesis that patients with persecutory delusions over-attribute contingency to agents' movements.

METHOD

Short animations were presented to three groups of subjects: (1) schizophrenic patients; (2) patients with affective disorders; and (3) normal control subjects. Patients were divided on the basis of the presence or absence of delusions of persecution. Participants watched four types of film featuring two shapes. In half the films one shape's movement was contingent on the other shape. Contingency was either 'intentional': one shape moved when it 'saw' another shape; or 'mechanical': one shape was launched by the other shape. Subjects were asked to rate the strength of the relationship between the movement of the shapes.

RESULTS

Normal control subjects and patients without delusions of persecution rated the relationship between the movement of the shapes as stronger in both mechanical and intentional contingent conditions than in non-contingent conditions. In contrast, there was no significant difference between the ratings of patients with delusions of persecution for the conditions in which movement was animate. Patients with delusions of persecution perceived contingency when there was none in the animate non-contingent condition.

CONCLUSIONS

The results suggest that delusions of persecution may be associated with the over-attribution of contingency to the actions of agents.

An interference effect of observed biological movement on action

It has been proposed that actions are intrinsically linked to perception and that imagining, observing, preparing, or in any way representing an action excites the motor programs used to execute that same action. There is neurophysiological evidence that certain brain regions involved in executing actions are activated by the mere observation of action (the so-called "mirror system;" ). However, it is unknown whether this mirror system causes interference between observed and simultaneously executed movements. In this study we test the hypothesis that, because of the overlap between action observation and execution, observed actions should interfere with incongruous executed actions. Subjects made arm movements while observing either a robot or another human making the same or qualitatively different arm movements. Variance in the executed movement was measured as an index of interference to the movement. The results demonstrate that observing another human making incongruent movements has a significant interference effect on executed movements. However, we found no evidence that this interference effect occurred when subjects observed a robotic arm making incongruent movements. These results suggest that the simultaneous activation of the overlapping neural networks that process movement observation and execution infers a measurable cost to motor control.

How the brain perceives causality: an event-related fMRI study

Detection of the causal relationships between events is fundamental for understanding the world around us. We report an event-related fMRI study designed to investigate how the human brain processes the perception of mechanical causality. Subjects were presented with mechanically causal events (in which a ball collides with and causes movement of another ball) and non-causal events (in which no contact is made between the balls). There was a significantly higher level of activation of V5/MT/MST bilaterally, the superior temporal sulcus bilaterally and the left intraparietal sulcus to causal relative to non-causal events. Directing attention to the causal nature of the stimuli had no significant effect on the neural processing of the causal events. These results support theories of causality suggesting that the perception of elementary mechanical causality events is automatically processed by the visual system.

The cerebellum is involved in predicting the sensory consequences of action

We used H2(15)O PET to examine neural responses to parametrically varied degrees of discrepancy between the predicted and actual sensory consequences of movement. Subjects used their right hand to move a robotic arm. The motion of this robotic arm determined the position of a second foam-tipped robotic arm, which made contact with the subject's left palm. Using this robotic interface, computer controlled delays were introduced between the movement of the right hand and the tactile stimulation on the left. Activity in the right lateral cerebellar cortex showed a positive correlation with delay. These results suggest the cerebellum is involved in signalling the sensory discrepancy between the predicted and actual sensory consequences of movements.

Abnormalities in the awareness and control of action

Much of the functioning of the motor system occurs without awareness. Nevertheless, we are aware of some aspects of the current state of the system and we can prepare and make movements in the imagination. These mental representations of the actual and possible states of the system are based on two sources: sensory signals from skin and muscles, and the stream of motor commands that have been issued to the system. Damage to the neural substrates of the motor system can lead to abnormalities in the awareness of action as well as defects in the control of action. We provide a framework for understanding how these various abnormalities of awareness can arise. Patients with phantom limbs or with anosognosia experience the illusion that they can move their limbs. We suggest that these representations of movement are based on streams of motor commands rather than sensory signals. Patients with utilization behaviour or with delusions of control can no longer properly link their intentions to their actions. In these cases the impairment lies in the representation of intended movements. The location of the neural damage associated with these disorders suggests that representations of the current and predicted state of the motor system are in parietal cortex, while representations of intended actions are found in prefrontal and premotor cortex.

The perception of self-produced sensory stimuli in patients with auditory hallucinations and passivity experiences: evidence for a breakdown in self-monitoring

BACKGROUND

To test the hypothesis that certain psychotic symptomatology is due to a defect in self-monitoring, we investigated the ability of groups of psychiatric patients to differentiate perceptually between self-produced and externally produced tactile stimuli.

METHODS

Responses to tactile stimulation were assessed in three groups of subjects: schizophrenic patients; patients with bipolar affective disorder or depression; and normal control subjects. Within the psychiatric groups subjects were divided on the basis of the presence or absence of auditory hallucinations and/or passivity experiences. The subjects were asked to rate the perception of a tactile sensation on the palm of their left hand. The tactile stimulation was either self-produced by movement of the subject's right hand or externally produced by the experimenter.

RESULTS

Normal control subjects and those psychiatric patients with neither auditory hallucinations nor passivity phenomena experienced self-produced stimuli as less intense, tickly and pleasant than identical, externally produced tactile stimuli. In contrast, psychiatric patients with these symptoms did not show a decrease in their perceptual ratings for tactile stimuli produced by themselves as compared with those produced by the experimenter. This failure to show a difference in perception between self-produced and externally produced stimuli appears to relate to the presence of auditory hallucinations and/or passivity experiences rather than to the diagnosis of schizophrenia.

CONCLUSIONS

We propose that auditory hallucinations and passivity experiences are associated with an abnormality in the self-monitoring mechanism that normally allows us to distinguish self-produced from externally produced sensations.

Why can't you tickle yourself?

It is well known that you cannot tickle yourself. Here, we discuss the proposal that such attenuation of self-produced tactile stimulation is due to the sensory predictions made by an internal forward model of the motor system. A forward model predicts the sensory consequences of a movement based on the motor command. When a movement is self-produced, its sensory consequences can be accurately predicted, and this prediction can be used to attenuate the sensory effects of the movement. Studies are reviewed that demonstrate that as the discrepancy between predicted and actual sensory feedback increases during self-produced tactile stimulation there is a concomitant decrease in the level of sensory attenuation and an increase in tickliness. Functional neuroimaging studies have demonstrated that this sensory attenuation might be mediated by somatosensory cortex and anterior cingulate cortex: these areas are activated less by a self-produced tactile stimulus than by the same stimulus when it is externally produced. Furthermore, evidence suggests that the cerebellum might be involved in generating the prediction of the sensory consequences of movement. Finally, recent evidence suggests that this predictive mechanism is abnormal in patients with auditory hallucinations and/or passivity experiences.

Four-year PhDs in neuroscience: an assessment after four years

In 1996, as an innovation for the UK, the Wellcome Trust set up two 'American style' four-year PhD programmes in neuroscience, with an initial year of broad training followed by a three-year PhD. Here, some of the first cohort of students, who are soon to graduate and the coordinators of the programmes, give their views on this experiment in neuroscience research training.

The cerebellum contributes to somatosensory cortical activity during self-produced tactile stimulation

We used fMRI to examine neural responses when subjects experienced a tactile stimulus that was either self-produced or externally produced. The somatosensory cortex showed increased levels of activity when the stimulus was externally produced. In the cerebellum there was less activity associated with a movement that generated a tactile stimulus than with a movement that did not. This difference suggests that the cerebellum is involved in predicting the specific sensory consequences of movements and providing the signal that is used to attenuate the sensory response to self-generated stimulation. In this paper, we use regression analyses to test this hypothesis explicitly. Specifically, we predicted that activity in the cerebellum contributes to the decrease in somatosensory cortex activity during self-produced tactile stimulation. Evidence in favor of this hypothesis was obtained by demonstrating that activity in the thalamus and primary and secondary somatosensory cortices significantly regressed on activity in the cerebellum when tactile stimuli were self-produced but not when they were externally produced. This supports the proposal that the cerebellum is involved in predicting the sensory consequences of movements. In the present study, this prediction is accurate when tactile stimuli are self-produced relative to when they are externally produced, and is therefore used to attenuate the somatosensory response to the former type of tactile stimulation but not the latter.

Spatio-temporal prediction modulates the perception of self-produced stimuli

We investigated why self-produced tactile stimulation is perceived as less intense than the same stimulus produced externally. A tactile stimulus on the palm of the right hand was either externally produced, by a robot or self-produced by the subject. In the conditions in which the tactile stimulus was self-produced, subjects moved the arm of a robot with their left hand to produce the tactile stimulus on their right hand via a second robot. Subjects were asked to rate intensity of the tactile sensation and consistently rated self-produced tactile stimuli as less tickly, intense, and pleasant than externally produced tactile stimuli. Using this robotic setup we were able to manipulate the correspondence between the action of the subjects' left hand and the tactile stimulus on their right hand. First, we parametrically varied the delay between the movement of the left hand and the resultant movement of the tactile stimulus on the right hand. Second, we implemented varying degrees of trajectory perturbation and varied the direction of the tactile stimulus movement as a function of the direction of left-hand movement. The tickliness rating increased significantly with increasing delay and trajectory perturbation. This suggests that self-produced movements attenuate the resultant tactile sensation and that a necessary requirement of this attenuation is that the tactile stimulus and its causal motor command correspond in time and space. We propose that the extent to which self-produced tactile sensation is attenuated (i.e., its tickliness) is proportional to the error between the sensory feedback predicted by an internal forward model of the motor system and the actual sensory feedback produced by the movement.

CCR7 (EBI1) receptor down-regulation in asthma: differential gene expression in human CD4+ T lymphocytes

Asthma is an inflammatory disorder, and the CD4+ T lymphocyte plays a key role in mediating the inflammatory response. We used a high-density grid, hybridization-based, differential gene expression technology to analyse molecular mechanisms underlying in vivo CD4+ T-cell activation in both steroid-resistant asthma (SRA) and steroid-sensitive asthma (SSA). Hybridization of radioactively-labelled first-strand cDNAs prepared from different biological samples, to identical high-density gridded arrays of PCR amplicons derived from cDNA clone inserts immobilized on nylon membranes, was compared by phosphorimaging. Hybridization data were captured and processed using image analysis software that can identify the location and signal intensity of each hybridized cDNA. This produces a hierarchy of signals of differing intensities between the two grids, representing differential gene expression in the two different RNA samples. CCR7 (EBI1), a lymphocyte-specific G-protein-coupled receptor, was down-regulated in the CD4+ T cells of SRA and SSA non-atopic, compared to non-asthmatic non-atopic individuals. This observation is intriguing given that CCR7 and its ligand EBI1-Ligand Chemokine (ELC), may play a role in the migration and homing of normal lymphocytes. Also, TNFR2 is up-regulated in both SSA non-atopic and SRA atopic as compared to non-asthmatic controls. LAMR1 is down-regulated in CD4+ T cells of SRA compared to non-asthmatic individuals, irrespective of their atopic status. These could be general phenomena resulting from cytokine release.

Identification of two novel diurnal genes by screening of a rat brain cDNA library

While the hypothalamus is fundamental for sleep and circadian regulation, the molecular mechanism involved are poorly understood. We have used a differential gene expression technique to identify hypothalamic genes which have altered expression in rat sleep periods. Complex cDNA probes from rat hypothalami removed at Zeitgeber times 4 and 15 were hybridised to rat brain cDNA library girds. From 30 differentially expressed clones, six were further analysed and two were confirmed to exhibit increased expression at Zeitgeber time 4. A Northern blot hybridization of brain, heart, kidney, lung, testis and skin mRNA showed that both clones were brain specific. Therefore, we have identified two novel brain specific diurnally expressed hypothalamic genes. Both genes may have roles in sleep or circadian regulation.

Identification of two novel diurnal genes by screening of a rat brain cDNA library

While the hypothalamus is fundamental for sleep and circadian regulation, the molecular mechanisms involved are poorly understood. We have used a differential gene expression technique to identify hypothalamic genes which have altered expression in rat sleep periods. Complex cDNA probes from rat hypothalami removed at Zeitgeber times 4 and 15 were hybridised to rat brain cDNA library girds. From 30 differentially expressed clones, six were further analysed and two were confirmed to exhibit increased expression at Zeitgeber time 4. A Northern blot hybridization of brain, heart, kidney, lung, testis and skin mRNA showed that both clones were brain specific. Therefore, we have identified two novel brain specific diurnally expressed hypothalamic genes. Both genes may have roles in sleep or circadian regulation.

Central cancellation of self-produced tickle sensation

A self-produced tactile stimulus is perceived as less ticklish than the same stimulus generated externally. We used fMRI to examine neural responses when subjects experienced a tactile stimulus that was either self-produced or externally produced. More activity was found in somatosensory cortex when the stimulus was externally produced. In the cerebellum, less activity was associated with a movement that generated a tactile stimulus than with a movement that did not. This difference suggests that the cerebellum is involved in predicting the specific sensory consequences of movements, providing the signal that is used to cancel the sensory response to self-generated stimulation.

GLUT5 expression and fructose transport in human skeletal muscle

Biochemical and immunocytochemical studies have revealed that, in addition to GLUT1 and GLUT4, human skeletal muscle also expresses the GLUT5 hexose transporter. The subcellular distribution of GLUT5 is distinct from that of GLUT4, being localised exclusively in the sarcolemmal membrane. The substrate selectivity of GLUT5 is also considered to be different to that of GLUT1 and GLUT4 in that it operates primarily as a fructose transporter. Consistent with this suggestion studies in isolated human sarcolemmal vesicles have shown that fructose transport obeys saturable kinetics with a Vmax of 477 +/- 37 pmol.mg protein-1 min-1 and a Km of 8.3 +/- 1.2 mM. Unlike glucose uptake, fructose transport in sarcolemmal vesicles was not inhibited by cytochalasin B suggesting that glucose and fructose are unlikely to share a common route of entry into human muscle. Muscle exercise, which stimulates glucose uptake through the increased translocation of GLUT4 to the plasma membrane, does not increase fructose transport or sarcolemmal GLUT5 content. In contrast, muscle inactivity, induced as a result of limb immobilisation, caused a significant reduction in muscle GLUT4 expression with no detectable effects on GLUT5. The presence of a fructose transporter in human muscle is compatible with studies showing that this tissue can utilise fructose for both glycolysis and glycogenesis. However, the full extent to which provision of fructose via GLUT5 is important in meeting the energy requirements of human muscle during both physiological and pathophysiological circumstances remains an issue requiring further investigation.

Predicting the consequences of our own actions: the role of sensorimotor context estimation

During self-generated movement it is postulated that an efference copy of the descending motor command, in conjunction with an internal model of both the motor system and environment, enables us to predict the consequences of our own actions (von Helmholtz, 1867; Sperry, 1950; von Holst, 1954; Wolpert, 1997). Such a prediction is evident in the precise anticipatory modulation of grip force seen when one hand pushes on an object gripped in the other hand (Johansson and Westling, 1984; Flanagan and Wing, 1933). Here we show that self-generation is not in itself sufficient for such a prediction. We used two robots to simulate virtual objects held in one hand and acted on by the other. Precise predictive grip force modulation of the restraining hand was highly dependent on the sensory feedback to the hand producing the load. The results show that predictive modulation requires not only that the movement is self-generated, but also that the efference copy and sensory feedback are consistent with a specific context; in this case, the manipulation of a single object. We propose a novel computational mechanism whereby the CNS uses multiple internal models, each corresponding to a different sensorimotor context, to estimate the probability that the motor system is acting within each context.

How do we predict the consequences of our actions? A functional imaging study

Humans are readily able to distinguish expected and unexpected sensory events. Whether a single mechanism underlies this ability is unknown. The most common type of expected sensory events are those generated as a consequence of self-generated actions. Using H2 15O PET, we studied brain responses to such predictable sensory events (tones) and to similar unpredictable events and especially how the processing of predictable sensory events is modified by the context of a causative self-generated action. Increases in activity when the tones were unpredictable were seen in the inferior and superior temporal lobe bilaterally, the right parahippocampal gyrus and right parietal cortex. Self-generated actions produced activity in a number of motor and premotor areas, including dorsolateral prefrontal cortex. We observed an interaction between the predictability of stimuli and self-generated actions in several areas, including the medial posterior cingulate cortex, left insula, dorsomedial thalamus, superior colliculus and right inferior temporal cortex. This modulation of activity associated with stimulus predictability in the context of self-generated actions implies that these areas may be involved in self-monitoring processes. Detection of expected stimuli and the detection of the sensory consequences of self-generated actions appear to be functionally distinct processes, and are carried out in different cortical areas. These observations support theoretical approaches to cognition that postulate the existence of a self-monitoring system.

Effects of limb immobilization on cytochrome c oxidase activity and GLUT4 and GLUT5 protein expression in human skeletal muscle

1. We investigated the effects of limb immobilization (for 1 or 6 weeks) in a long leg cast after a closed tibial fracture (n = 11). Biopsies of vastus lateralis were taken on admission and after either 1 week (n = 5) or 6 weeks (n = 6) and analysed for muscle fibre type characteristics, cytochrome c oxidase activity and the abundance of GLUT4 and GLUT5 hexose transporters. 2. After 1 week of immobilization there was a significant decrease (8%) in the cross-sectional area of type I, but not type II, muscle fibers and in the protein-DNA ratio (16%) compared with the initial biopsy. Six weeks of immobilization led to further muscle atrophy compared with the initial biopsy and a further reduction in the cross-sectional area of both type I and II fibres (29% and 36% decrease respectively) and in the protein-DNA ratio (25%). No changes were observed in the free leg after 1 week. However, at th end of the 6 week study period, the cross-sectional area of boty type I and II fibres of the free leg were increased (7% and 5%) and there was significant increase in the protein-DNA ratio (14%), indicating a net increase in muscle protein content. 3. Assay for cytochrome c oxidase activity showed significant reduction after 1 (30%) or 6 weeks (36%) of immobilization, reflecting a reduced capacity for oxidative metabolism. No significant changes in activity were observed in muscle from the free leg after 1 or 6 weeks of study. 4. The concentrations of GLUT4 and GLUT5 protein were determined by Western blot analysis. Limb immobilization induced a marked (50%) reduction in muscle GLUT4 protein concentration after 1 week that persisted for 6 weeks. A transient but significant increase (approximately twofold) in GLUT4 concentration was detected in muscle from the free leg after 1 week, but this returned to pre-imobilization values at 6 week. Unlike GLUT4, no significant changes in the abundance of the GLUT5 protein were detected in either the immobilized or free leg at the end of the 1 or 6 week periods. 5. The present findings indicate that disuse rapidly induces a selective loss of activity and abundance of some non-myofibrillar proteins in humans. The decrease in GLUT4 protein abundance and cytochrome c oxidase activity during muscle disuse is consistent with a decreased capacity for glucose uptake and with a lower oxidative potential of inactive muscle. The lack of any major changes in GLUT5 protein abundance during limb immobilization indicates that the expression of some non-myofibrillar proteins is differentially regulated in response to muscle disuse.

The GLUT5 hexose transporter is also localized to the basolateral membrane of the human jejunum

The intestine is a major site of expression of the human GLUT5 hexose transporter, which is thought to be localized exclusively to the brush border membrane (BBM) where its major role is likely to be in the absorption of fructose. In this study we present novel biochemical and morphological evidence showing that the GLUT5 transporter is also expressed in the basolateral membrane (BLM) of the human intestine. BBM and BLM were isolated by fractionation of human jejunum. BBM were enriched with alkaline phosphatase activity by over 9-fold relative to a crude jejunal homogenate and contained immunoreactive sucrase-isomaltase and GLUT5 proteins. By contrast the BBM fraction was substantially depleted of immunoreactive a1 subunits of the Na,K-ATPase and GLUT2 glucose transporters which were abundantly present in the BLM fraction. This BLM fraction was enriched by over 11-fold in potassium-stimulated phosphatase activity relative to the crude homogenate; BLM also reacted to immunological probes for GLUT5 but showed no observable reactivity with antibodies directed against sucrase-isomaltase. Quantitative immunoblotting revealed that the BBM and BLM contained near equal amounts of GLUT5 per mg of membrane protein. Immunogold localization of GLUT5 on ultrathin sections of human jejunum showed that GLUT5 was present in both apical BBM and BLM. This gold labelling was absent when antiserum was pre-incubated with the antigenic peptide corresponding to a specific C-terminal sequence of human GLUT5. Quantitative analyses of the number of gold particles per unit length of BBM and BLM indicated that the mean density of gold labelling was marginally greater in the BBM (0.399 gold particles/micrometer) than in the BLM (0.293 gold particle/micrometer). The localization of GLUT5 in the BLM of the human jejunum may suggest that it specifically participates in the transfer of fructose across the basal membrane of the enterocyte.