Fatty acid synthase as a new therapeutic target for HER2-positive gastric cancer

PURPOSE

Trastuzumab is an HER2-specific agent approved as the gold-standard therapy for advanced HER2-positive (HER2+) gastric cancer (GC), but the high rate and rapid appearance of resistance limit its clinical efficacy, resulting in the need to identify new vulnerabilities. Defining the drivers influencing HER2+ cancer stem cell (CSC) maintenance/survival could represent a clinically useful strategy to counteract tumor growth and therapy resistance. Accumulating evidence show that targeting crucial metabolic hubs, as the fatty acid synthase (FASN), may be clinically relevant.

METHODS

FASN protein and transcript expression were examined by WB and FACS and by qRT-PCR and GEP analyses, respectively, in trastuzumab-sensitive and trastuzumab-resistant HER2+ GC cell lines cultured in adherent (2D) or gastrosphere promoting (3D) conditions. Molecular data were analyzed in silico in public HER2+ GC datasets. The effectiveness of the FASN inhibitor TVB3166 to overcome anti-HER2 therapy resistance was tested in vitro in gastrospheres forming efficiency bioassays and in vivo in mice bearing trastuzumab-resistant GC cells.

RESULTS

We compared the transcriptome profiles of HER2+ GC cells cultured in 2D versus 3D conditions finding a significant enrichment of FASN in 3D cultures. FASN upregulation significantly correlated with high stemness score and poor prognosis in HER2+ GC cases. TVB3166 treatment significantly decreased GCSCs in all cell targets. HER2 and FASN cotargeting significantly decreased the capability to form gastrospheres versus monotherapy and reduced the in vivo growth of trastuzumab-resistant GC cells.

CONCLUSION

Our findings indicate that cotargeting HER2 and FASN increase the benefit of anti-HER2 therapy representing a new opportunity for metabolically combating trastuzumab-resistant HER2+ GC.

HER2 Copy Number and Resistance Mechanisms in Patients with HER2-positive Advanced Gastric Cancer Receiving Initial Trastuzumab-based Therapy in JACOB Trial

PURPOSE

In JACOB trial, pertuzumab added to trastuzumab-chemotherapy did not significantly improve survival of patients with HER2-positive metastatic gastric cancer, despite 3.3 months increase versus placebo. HER2 copy-number variation (CNV) and AMNESIA panel encompassing primary resistance alterations (KRAS/PIK3CA/MET mutations, KRAS/EGFR/MET amplifications) may improve patients' selection for HER2 inhibition.

EXPERIMENTAL DESIGN

In a post hoc analysis of JACOB on 327 samples successfully sequenced by next-generation sequencing (NGS; Oncomine Focus DNA), HER2 CNV, HER2 expression by IHC, and AMNESIA were correlated with overall response rate (ORR), progression-free survival (PFS), and overall survival (OS) by univariable/multivariable models.

RESULTS

Median HER2 CNV was 4.7 (interquartile range, 2.2-16.9). HER2 CNV-high versus low using the median as cutoff was associated with longer median PFS (10.5 vs. 6.4 months; HR = 0.48; 95% confidence interval: 0.38-0.62; P < 0.001) and OS (20.3 vs. 13.0 months; HR = 0.54; 0.42-0.72; P < 0.001). Combining HER2 CNV and IHC improved discriminative ability, with better outcomes restricted to HER2-high/HER2 3+ subgroup. AMNESIA positivity was found in 51 (16%), with unadjusted HR = 1.35 (0.98-1.86) for PFS; 1.43 (1.00-2.03) for OS.In multivariable models, only HER2 CNV status remained significant for PFS (P < 0.001) and OS (P = 0.004). Higher ORR was significantly associated with IHC 3+ [61% vs. 34% in 2+; OR = 3.11 (1.89-5.17)] and HER2-high [59% vs. 43% in HER2-low; OR = 1.84 (1.16-2.94)], with highest OR in the top CNV quartile. These biomarkers were not associated with treatment effect of pertuzumab.

CONCLUSIONS

HER2 CNV-high assessed by NGS may be associated with better ORR, PFS, and OS in a JACOB subgroup, especially if combined with HER2 3+. The negative prognostic role of AMNESIA requires further clinical validation.

Predictive Role of CD36 Expression in HER2-Positive Breast Cancer Patients Receiving Neoadjuvant Trastuzumab

BACKGROUND

Despite huge efforts to identify biomarkers associated with long-term clinical outcomes in patients with early-stage HER2-positive breast cancer (HER2+ BC) treated with (neo)adjuvant anti-HER2 therapy, no reliable predictors have been identified so far. Fatty acid uptake, a process mediated by the transmembrane transporter CD36, has recently emerged as a potential determinant of resistance to anti-HER2 treatments in preclinical HER2+ BC models.

METHODS

Here, we investigated the association between baseline intratumor CD36 gene expression and event-free survival in 180 patients enrolled in the phase III trial Neoadjuvant Lapatinib and/or Trastuzumab Treatment Optimization (NeoALTTO), which randomly assigned stage II-III HER2+ BC patients to receive neoadjuvant lapatinib, trastuzumab, or lapatinib-trastuzumab in combination with chemotherapy. To this aim, we selected NeoALTTO trial patients for whom pretreatment whole transcriptomic data were available. The main study results were validated in an independent cohort of patients enrolled in the neoadjuvant phase II trial NeoSphere.

RESULTS

In 180 NeoALTTO patients, high intratumor CD36 expression was independently associated with worse event-free survival in patients treated with trastuzumab-based therapy (hazard ratio [HR] = 1.72, 95% confidence interval [CI] = 1.20 to 2.46), but not with lapatinib-based (HR = 1.02, 95% CI = 0.68 to 1.53) or trastuzumab-lapatinib-based (HR = 1.08, 95% CI = 0.60 to 1.94) therapy. Among 331 NeoSphere patients evaluated, high CD36 expression was independently associated with worse patient disease-free survival in both the whole study cohort (HR = 1.197, 95% CI = 1.002 to 1.428) and patients receiving trastuzumab-based neoadjuvant therapy (HR = 1.282, 95% CI = 1.049 to 1.568).

CONCLUSIONS

High CD36 expression predicts worse clinical outcomes in early-stage HER2+ BC treated with trastuzumab-based neoadjuvant therapy.

BCL6 and the Notch pathway: a signaling axis leading to a novel druggable biotarget in triple negative breast cancer

BACKGROUND

The transcriptional repressor B-cell lymphoma 6 (BCL6) is dysregulated in several neoplasms, but its role in triple negative breast cancer (TNBC), a highly aggressive subtype which lacks effective treatment, is unclear. The presence of intratumoral cancer stem cells (CSCs) is a main cause of tumor relapse. The Notch signaling pathway is crucial for regulating CSC self-renewal and promoting breast cancer (BC) development and resistance to anticancer therapies. Here, we investigated signaling cascades of BCL6 in the CSC compartment of TNBCs, and the mechanisms that govern its activity, mainly through Notch signaling.

METHODS

Gene expression, somatic copy number alterations and clinical data from the Cancer Genome Atlas and METABRIC were accessed through the Xena and cbioportal browsers. Public transcriptome profiles from TNBC datasets were retrieved from the Gene Expression Omnibus. Mammosphere formation efficiency was calculated after BCL6 knockdown via transient siRNA transfection, stable silencing or pharmacological inhibition. The effects exhibited via BCL6 inhibition in putative TNBC stem-like cells were evaluated by immunofluorescence and qRT-PCR analyses. Chromatin immunoprecipitation experiments were performed to validate a putative BCL6 responsive element located in the first intron of the Numb gene and to define the circuit of corepressors engaged by BCL6 following its inhibition. Immunoprecipitation assays were carried out to investigate a novel interaction at the basis of BCL6 control of CSC activity in TNBC.

RESULTS

In silico analyses of benchmarked public datasets revealed a significant enrichment of BCL6 in cancer stemness related pathways, particularly of Notch signaling in TNBC. In vitro stable inhibition of BCL6 significantly reduced tumor cell growth and, accordingly, we found that the mammosphere formation efficiency of BCL6 silenced cells was significantly impaired by pharmacological inhibition of Notch signaling. BCL6 was found to be expressed at significantly higher levels in TNBC mammospheres than in their adherent counterparts, and loss of BCL6 function significantly decreased mammosphere formation with preferential targeting of CD44-positive versus ALDH-positive stem-like cells. Functional interplay between BCL6 and the chromatin remodeling factor EZH2 triggered the BCL6/Notch stemness signaling axis via inhibition of Numb transcription.

CONCLUSIONS

Our results may be instrumental for the prospective design of combination treatment strategies that selectively target novel TNBC-associated biomarker(s) whose activity is implicated in the regulation of cancer stemness (such as BCL6) and molecules in developmentally conserved signaling pathways (such as Notch) to achieve long-lasting tumor control and improve patient outcomes.

HER2 Signaling and Breast Cancer Stem Cells: The Bridge behind HER2-Positive Breast Cancer Aggressiveness and Therapy Refractoriness

Simple Summary

Breast cancer (BC) is not a single disease, but a group of different tumors, and altered HER2 expression defines a particularly aggressive subtype. Although HER2 pharmacological inhibition has dramatically improved the prognosis of HER2-positive BC patients, there is still an urgent need for improved knowledge of HER2 biology and mechanisms underlying HER2-driven aggressiveness and drug susceptibility. Emerging data suggest that the clinical efficacy of molecularly targeted therapies is related to their ability to target breast cancer stem cells (BCSCs), a population that is not only self-sustaining and able to differentiate into distinct lineages, but also contributes to tumor growth, aggressiveness, metastasis and treatment resistance. The aim of this review is to provide an overview of how the full-length HER2 receptor, the d16HER2 splice variant and the truncated p95HER2 variants are involved in the regulation and maintenance of BCSCs.

Abstract

HER2 overexpression/amplification occurs in 15–20% of breast cancers (BCs) and identifies a highly aggressive BC subtype. Recent clinical progress has increased the cure rates of limited-stage HER2-positive BC and significantly prolonged overall survival in patients with advanced disease; however, drug resistance and tumor recurrence remain major concerns. Therefore, there is an urgent need to increase knowledge regarding HER2 biology and implement available treatments. Cancer stem cells (CSCs) represent a subset of malignant cells capable of unlimited self-renewal and differentiation and are mainly considered to contribute to tumor onset, aggressiveness, metastasis, and treatment resistance. Seminal studies have highlighted the key role of altered HER2 signaling in the maintenance/enrichment of breast CSCs (BCSCs) and elucidated its bidirectional communication with stemness-related pathways, such as the Notch and Wingless/β-catenin cascades. d16HER2, a splice variant of full-length HER2 mRNA, has been identified as one of the most oncogenic HER2 isoform significantly implicated in tumorigenesis, epithelial-mesenchymal transition (EMT)/stemness and the response to targeted therapy. In addition, expression of a heterogeneous collection of HER2 truncated carboxy-terminal fragments (CTFs), collectively known as p95HER2, identifies a peculiar subgroup of HER2-positive BC with poor prognosis, with the p95HER2 variants being able to regulate CSC features. This review provides a comprehensive overview of the current evidence regarding HER2-/d16HER2-/p95HER2-positive BCSCs in the context of the signaling pathways governing their properties and describes the future prospects for targeting these components to achieve long-lasting tumor control.

Targeting lipid metabolism is an emerging strategy to enhance the efficacy of anti-HER2 therapies in HER2-positive breast cancer

De novo or acquired resistance of cancer cells to currently available Human Epidermal Growth Factor Receptor 2 (HER2) inhibitors represents a clinical challenge. Several resistance mechanisms have been identified in recent years, with lipid metabolism reprogramming, a well-established hallmark of cancer, representing the last frontier of preclinical and clinical research in this field. Fatty Acid Synthase (FASN), the key enzyme required for fatty acids (FAs) biosynthesis, is frequently overexpressed/activated in HER2-positive (HER2+) breast cancer (BC), and it crucially sustains HER2+ BC cell growth, proliferation and survival. After the synthesis of new, selective and well tolerated FASN inhibitors, clinical trials have been initiated to test if these compounds are able to re-sensitize cancer cells with acquired resistance to HER2 inhibition. More recently, the upregulation of FA uptake by cancer cells has emerged as a potentially new and targetable mechanism of resistance to anti-HER2 therapies in HER2+ BC, thus opening a new era in the field of targeting metabolic reprogramming in clinical setting. Here, we review the available preclinical and clinical evidence supporting the inhibition of FA biosynthesis and uptake in combination with anti-HER2 therapies in patients with HER2+ BC, and we discuss ongoing clinical trials that are investigating these combination approaches.

Hormone receptor status influences the impact of body mass index and hyperglycemia on the risk of tumor relapse in early-stage HER2-positive breast cancer patients

Background:

High body mass index (BMI) has been associated with worse clinical outcomes in patients with early-stage breast cancer (BC), and its negative effects could be mediated by hyperglycemia/diabetes. However, the prognostic impact of high BMI in early-stage HER2-positive (HER2+) BC patients remains controversial.

Methods:

We conducted a retrospective study to investigate the impact of baseline BMI or glycemia on relapse-free survival (RFS) and overall survival (OS) in patients with surgically resected, stage I–III HER2+ BC treated with standard-of-care, trastuzumab-containing adjuvant biochemotherapy. The optimal BMI and glycemia cut-off values for RFS were identified through maximally selected rank statistics. Cox regression models were used to assess the impact of BMI, glycemia and other relevant variables on clinical outcomes.

Results:

Among 505 patients included in the study, a BMI cut-off of 27.77 kg/m² was identified as the best threshold to discriminate between patients with low BMI (n = 390; 77.2%) or high BMI (n = 115; 22.8%). At multivariable analysis, higher BMI was associated with significantly worse RFS [hazard ratio 2.26; 95% confidence interval (CI): 1.08–4.74, p = 0.031] and worse OS (hazard ratio 2.25, 95% CI 1.03–4.94, p = 0.043) in the whole patient population. The negative impact of high BMI was only observed in patients with hormone receptor (HR)-negative/HER2+ BC (hazard ratio 2.29; 95% CI: 1.01–5.20; p = 0.047), but not in patients with HR-positive (HR+)/HER2+ BC (hazard ratio 1.36; 95% CI: 0.61–3.07, p = 0.452). By contrast, hyperglycemia (⩾109 mg/dl) at baseline was associated with a trend toward significantly worse RFS at multivariable analysis only in patients with HR+/HER2+ BC (hazard ratio 2.52; 95% CI: 0.89–7.1; p = 0.080).

Conclusions:

High BMI is associated with worse clinical outcomes in early-stage HR−/HER2+ BC patients treated with trastuzumab-containing adjuvant biochemotherapy, while baseline hyperglycemia could be a predictor of worse RFS in HR+/HER2+ BC patients. Prospective studies are needed to investigate if modifying patient BMI/glycemia during treatment can improve clinical outcomes.

Impact of Baseline and On-Treatment Glycemia on Everolimus-Exemestane Efficacy in Patients with Hormone Receptor-Positive Advanced Breast Cancer (EVERMET)

PURPOSE

The mTOR complex C1 (mTORC1) inhibitor everolimus in combination with the aromatase inhibitor exemestane is an effective treatment for patients with hormone receptor-positive (HR⁺), HER2-negative (HER2^-), advanced breast cancer (HR⁺/HER2^- aBC). However, everolimus can cause hyperglycemia and hyperinsulinemia, which could reactivate the PI3K/protein kinase B (AKT)/mTORC1 pathway and induce tumor resistance to everolimus.

EXPERIMENTAL DESIGN

We conducted a multicenter, retrospective, Italian study to investigate the impact of baseline and on-treatment (i.e., during first 3 months of therapy) blood glucose levels on progression-free survival (PFS) in patients with HR⁺/HER2^- aBC treated with everolimus-exemestane.

RESULTS

We evaluated 809 patients with HR⁺/HER2^- aBC treated with everolimus-exemestane as any line of therapy for advanced disease. When evaluated as dichotomous variables, baseline and on-treatment glycemia were not significantly associated with PFS. However, when blood glucose concentration was evaluated as a continuous variable, a multivariable model accounting for clinically relevant patient- and tumor-related variables revealed that both baseline and on-treatment glycemia are associated with PFS, and this association is largely attributable to their interaction. In particular, patients who are normoglycemic at baseline and experience on-treatment diabetes have lower PFS compared with patients who are already hyperglycemic at baseline and experience diabetes during everolimus-exemestane therapy (median PFS, 6.34 vs. 10.32 months; HR, 1.76; 95% confidence interval, 1.15-2.69; P = 0.008).

CONCLUSIONS

The impact of on-treatment glycemia on the efficacy of everolimus-exemestane therapy in patients with HR⁺/HER2^- aBC depends on baseline glycemia. This study lays the foundations for investigating novel therapeutic approaches to target the glucose/insulin axis in combination with PI3K/AKT/mTORC1 inhibitors in patients with HR⁺/HER2^- aBC.

Cancer Stem Cells: Devil or Savior-Looking behind the Scenes of Immunotherapy Failure

Although the introduction of immunotherapy has tremendously improved the prognosis of patients with metastatic cancers of different histological origins, some tumors fail to respond or develop resistance. Broadening the clinical efficacy of currently available immunotherapy strategies requires an improved understanding of the biological mechanisms underlying cancer immune escape. Globally, tumor cells evade immune attack using two main strategies: avoiding recognition by immune cells and instigating an immunosuppressive tumor microenvironment. Emerging data suggest that the clinical efficacy of chemotherapy or molecularly targeted therapy is related to the ability of these therapies to target cancer stem cells (CSCs). However, little is known about the role of CSCs in mediating tumor resistance to immunotherapy. Due to their immunomodulating features and plasticity, CSCs can be especially proficient at evading immune surveillance, thus potentially representing the most prominent malignant cell component implicated in primary or acquired resistance to immunotherapy. The identification of immunomodulatory properties of CSCs that include mechanisms that regulate their interactions with immune cells, such as bidirectional release of particular cytokines/chemokines, fusion of CSCs with fusogenic stromal cells, and cell-to-cell communication exerted by extracellular vesicles, may significantly improve the efficacy of current immunotherapy strategies. The purpose of this review is to discuss the current scientific evidence linking CSC biological, immunological, and epigenetic features to tumor resistance to immunotherapy.

Abstract P3-02-01: Fatty acid uptake as a potentially new resistance mechanism to anti-HER2 treatments in HER2-positive breast cancer

Background: Although anti-HER2 treatments, including the monoclonal antibodies trastuzumab (T) and pertuzumab (P) and the tyrosine kinase inhibitor lapatinib (L), have remarkably improved the prognosis of patients with HER2-positive breast cancer (HER2+ BC), acquired resistance to these compounds remains a major clinical issue. HER2-mediated signaling induces fatty acid (FA) de novo biosynthesis, and ongoing clinical trials are investigating FA synthase enzyme (FASN) inhibitors in combination with anti-HER2 treatments. We hypothesized that by inhibiting FA biosynthesis, HER2 inhibitors make HER2+ BC cells dependent on extracellular FA uptake, which could contribute to resistance to anti-HER2 treatments. Methods: In tumor biopsy specimens from HER2+ BC patients treated with preoperative T-containing chemotherapy (ChT), we performed quantitative real time PCR (qRT-PCR) to measure expression levels of the lipoprotein lipase (LPL) enzyme and the FA transporter CD36, two key players in the uptake of extracellular FAs. The same analyses were also performed in surgical tumor specimens from patients failing to achieve pathologic complete response (pCR), and paired Wilcoxon test was used to compare CD36 expression levels of pre- versus post-treatment tumors. In MDA-MB-361, HCC1954 and BT474 HER2+ BC cell lines, we investigated the association between baseline CD36 expression and cells’ sensitivity to L, or their ability to uptake the docosahexanoic acid (DHA) from culture media. Finally, we assessed the antiproliferative effect of combining L with the CD36 inhibitor Sulfo N-Succinimidoyl Oleate (SSO). Results: 82 patients with stage II-III HER2+ BC were treated with preoperative ChT plus T at Fondazione IRCCS Istituto Nazionale dei Tumori between January 2013 and December 2017. As expected, achieving pCR was associated with better relapse-free survival (RFS) and overall survival (OS). Baseline LPL and CD36 expression did not correlate with pCR probability (p=0.15 and 0.1, respectively), nor with RFS (p=0.28 and 0.7, respectively) or OS (p=0.42 and 0.35, respectively). On the other hand, in 20 patients failing to achieve pCR, we found significantly increased LPL (p=0.00096) and a trend towards increased CD36 (p=0.12) expression in post-treatment surgical specimens. In a parallel cohort of 17 stage II-III HER2+ BC patients enrolled in a prospective study, LPL and CD36 expression was significantly increased 21 days after the first administration of single-agent T (p=0.0002 and p&lt;0.0001, respectively). In keeping with our working hypothesis, cell susceptibility to L was inversely associated with CD36 expression or DHA uptake, with L-sensitive BT474 cells displaying the lowest CD36 expression and DHA uptake from culture media. Consistent with analyses on tumor specimens from patients, treatment with L increased CD36 gene expression and protein levels in L-resistant HCC1954 cells, but not in L-sensitive BT474 ones. Finally, SSO showed additive antiproliferative effects in combination with L in HCC1954, but not in BT474 cells. Conclusions: This is the first study to show that pharmacological inhibition of HER2 induces short- and long-term upregulation of LPL/CD36 expression in HER2+ BC cell lines and tumor specimens, and that CD36 inhibition sensitizes intrinsically resistant HER2+ BC cells to L. Prospective clinical studies are required to validate the role of enhanced FA uptake as a potential mechanism of resistance to anti-HER2 treatments in HER2+ BC.

Citation Format: Claudio Vernieri, Lorenzo Castagnoli, Francesca Ligorio, Antonino Belfiore, Elena Fasano, Paola A. Corsetto, Simona Faraci, Marta Brambilla, Francesca Corti, Tiziana Triulzi, Daniele Generali, Andrea Vingiani, Angela M. Rizzo, Giulia V. Bianchi, Giuseppe Capri, Elda Tagliabue, Filippo de Braud, Giancarlo Pruneri, Serenella M. Pupa. Fatty acid uptake as a potentially new resistance mechanism to anti-HER2 treatments in HER2-positive breast cancer [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P3-02-01.

Abstract P1-07-02: Withdrawn

This abstract was withdrawn by the authors.

Citation Format: Di Nicola M, Volpari T, Fucà G, Romero Cordoba S, De Santis F, Rondinone O, Faraci S, Ferris F, Puricelli C, Castagnoli L, Marullo R, Cerchietti L, Pupa S. Withdrawn [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P1-07-02.

Impact of systemic and tumor lipid metabolism on everolimus efficacy in advanced pancreatic neuroendocrine tumors (pNETs)

The mTOR inhibitor everolimus is effective against advanced pancreatic neuroendocrine tumors (pNETs). However, it can cause metabolic adverse events, such as hyperglycemia, hypertriglyceridemia and hypercholesterolemia. In this work we aimed at evaluating the impact of systemic and tumor lipid metabolism on everolimus efficacy. We carried out a monocentric, retrospective study to correlate plasma triglyceride and cholesterol levels with the progression free survival (PFS) of advanced pNET patients treated with everolimus. In formalin fixed, paraffin embedded (FFPE) tumor specimens, we also assessed by mRNA quantification and immunohistochemistry the expression of acetyl-CoA carboxylase 1 (ACC1) and fatty acid synthase (FASN), two enzymes crucially involved in fatty acid biosynthesis, and we analyzed their impact on PFS. We evaluated 58 consecutive pNET patients who started everolimus between December 2006 and January 2015. Patients with higher plasma triglycerides during the first 3 months of treatment had an increased risk of disease progression (aHR 3.08, 95% CIs 1.15-8.21; p = 0.025). In 23 FFPE tumor specimens amenable for IHC evaluations, we found a positive correlation between ACC1 and FASN at both mRNA (r = 0.87, p = 0.00045) and protein (r = 0.68, p = 0.0004) level. Patients with higher ACC1 protein expression in metastatic lesions had significantly lower PFS when compared to patients with lower ACC1 levels (5.5 vs. 36 months; aHR 4.49, 95% CIs 1.08-18.72; p = 0.039). In conclusion, systemic and tumor lipid metabolism are associated with the PFS of everolimus-treated patients with advanced pNETs; based on these findings, dietary and pharmacological interventions targeting lipid metabolism could improve everolimus efficacy in this patient population.

Innovative therapy, monoclonal antibodies, and beyond: Highlights from the eighth annual meeting

The eighth annual conference of "Innovative therapy, monoclonal antibodies, and beyond" was held in Milan on Jan. 26, 2018, and hosted by Fondazione IRCCS-Istituto Nazionale dei Tumori (Fondazione IRCCS INT). The conference was divided into two main scientific sessions, of i) pre-clinical assays and novel biotargets, and ii) clinical translation, as well as a third session of presentations from young investigators, which focused on recent achievements within Fondazione IRCCS INT on immunotherapy and targeted therapies. Presentations in the first session addressed the issue of cancer immunotherapy activity with respect to tumor heterogeneity, with key topics addressing: 1) tumor heterogeneity and targeted therapy, with the definition of the evolutionary Index as an indicator of tumor heterogeneity in both space and time; 2) the analysis of cancer evolution, with the introduction of the TRACERx Consortium-a multi-million pound UK research project focused on non-small cell lung cancer (NSCLC); 3) the use of anti-estrogen agents to boost immune recognition of breast cancer cells; and 4) the high degree of functional plasticity within the NK cell repertoire, including the expansion of adaptive NK cells following viral challenges. The second session addressed: 1) the effectiveness of radiotherapy to enhance the proportion of patients responsive to immune-checkpoint blockers (ICBs); 2) the use of MDSC scores in selecting melanoma patients with high probability to be responsive to ICBs; and 3) the relevance of the gut microbiome as a predictive factor, and the potential of its perturbation in increasing the immune response rate to ICBs. Overall, a picture emerged of tumor heterogeneity as the main limitation that impairs the effectiveness of anti-cancer therapies. Thus, the choice of a specific therapy based on reproducible and selective predictive biomarkers is an urgent unmet clinical need that should be addressed in order to increase the proportion of long-term responding patients and to improve the sustainability of novel drugs.

Intratumor lactate levels reflect HER2 addiction status in HER2-positive breast cancer

Despite different molecular tumor profiles indicate that human epidermal growth factor receptor 2 (HER2) messenger RNA (mRNA) levels mirror HER2 addiction and trastuzumab benefit in HER2-positive breast cancer (BC), the identification of noninvasive clinical predictors of trastuzumab sensitivity remains an unmet clinical need. In the current study, we investigated whether intratumor lactate levels reflect HER2 addiction and, in turn, trastuzumab susceptibility. Accordingly, the gene expression profiles of transgenic murine BC cell lines expressing the human d16HER2 variant (HER2-addicted) or human full-length HER2 (WTHER2; HER2-nonaddicted) revealed a significant enrichment of glycolysis-related gene pathways in HER2-addicted cells. We studied the metabolic content of 22 human HER2-positive BC by quantitative nuclear magnetic resonance spectroscopy and found that those cases with higher lactate levels were characterized by higher HER2 transcript levels. Moreover, gene expression analyses of HER2-positive BC samples from a TCGA data set revealed a significant enrichment in glycolysis-related pathways in high/HER2-addicted tumors. These data were confirmed by metabolic analyses of human HER2-positive BC cell lines with high or low HER2 transcript levels, which revealed significantly more active glycolytic metabolism in high HER2 transcript than in low HER2 transcript cells. Overall, our results provide evidence for noninvasive intratumor lactate detection as a potential metabolic biomarker of HER2 addiction and trastuzumab response suggesting the possibility to use in vivo imaging to assess lactate levels and, in turn, select HER2-positive BC patients who are more likely to benefit from anti-HER2 treatments.

Abstract A068: Targeting glioblastoma stem cells through a MET inhibitor

Background: Glioblastoma (GBM) is the most common and aggressive human brain cancer with high relapse rate, lacking any targeted therapy. The current therapy consisting of surgery in combination with radiotherapy and the DNA-alkylating agent temozolomide has led to median survival increase. Nevertheless, many patients, after early treatment response, experience drug resistance and tumor progression. Recent advances identified cancer stem cell subpopulation as the cause of treatment failure, suggesting that the direct targeting of this cell subset may represent an innovative approach to improve the therapy efficacy. Based on studies indicating the role of the tyrosine kinase receptor MET in GBM stem cells, we examined the effects of the rational combination of radiotherapy with a MET inhibitor against stem-like cells from a human GBM cell line. Methods: Stem-like cells from U87MG cell line were sorted using PKH-67-labeling method for isolating slow-dividing cells (PKH67+), and analyzed for cell proliferation index by WST assay, clonogenic potential, and expression of stemness-related transcription factors by RT-PCR. Effects by the MET inhibitor alone and in combination with radiotherapy (IR) were evaluated on cell proliferation by Trypan Blue exclusion test, on apoptosis, cell cycle progression, GFAP protein expression by flow cytometry and on neurosphere-forming efficiency. The mechanisms underlying the effects induced by the combined treatment were dissected by biochemical and RT-PCR assays. Results: The PKH-67+ cells recapitulated the functional properties of stem-like cells, as slower cell proliferation index, higher clonogenic capacity, and expression of stemness-transcription factors than the negative counterpart. They also displayed a marked radioresistance dependent on MET signalling activation and characterized by the enrichment in stem-like cells as indicated by the upregulation of stemness-related transcription factor expression Nanog and Sox2, and enhanced susceptibility to MET inhibitor. The single-agent therapy with the inhibitor induced cell proliferation inhibition with an early cell cycle arrest in G2/M phase and a late cytotoxic effect. The drug alone negatively affected the neurosphere-forming efficiency and the clonogenic capacity. Following IR, the daily treatment with the inhibitor of MET significantly caused time-dependent cell proliferation inhibition, associated with an increased percentage of apoptotic cells and cells positive for GFAP, a glial differentiation marker, as compared to single-agent treatments. The biochemical analysis confirmed that MET inhibition remarkably impaired the radioresistance, and parallelly reduced the content of stem-like cells, as indicated either by the negative regulation of Nanog and Sox2 genes or the positive regulation of GFAP. Conclusions: Our results provide evidence that targeting MET with a specific inhibitor might interfere with MET-mediated radiotherapy resistance, thus sensitizing the GBM-stem-like cells to radiation, depleting the pool, and parallelly inducing their reprogramming towards more differentiated subtype.

Citation Format: Anna Rossini, Evelyn Oliva Savoia, Eleonora Cicoria, Lorenzo Castagnoli, Serenella Pupa, Filippo de Braud, Massimo Di Nicola. Targeting glioblastoma stem cells through a MET inhibitor [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr A068.

c-MYC G-quadruplex binding by the RNA polymerase I inhibitor BMH-21 and analogues revealed by a combined NMR and biochemical Approach

BACKGROUND

Pyridoquinazolinecarboxamides have been reported as RNA polymerase I inhibitors and represent a novel class of potential antitumor agents. BMH-21, was reported to intercalate with GC-rich rDNA, resulting in nucleolar stress as a primary mechanism of cytotoxicity.

METHODS

The interaction of BMH-21 and analogues with DNA G-quadruplex structures was studied by NMR and molecular modelling. The cellular response was investigated in a panel of human tumor cell lines and protein expression was examined by Western Blot analysis.

RESULTS AND CONCLUSIONS

We explored the ability of BMH-21 and its analogue 2 to bind to G-quadruplex present in the c-MYC promoter, by NMR and molecular modelling studies. We provide evidence that both compounds are not typical DNA intercalators but are effective binders of the tested G-quadruplex. The interaction with c-MYC G-quadruplex was reflected in down-regulation of c-Myc expression in human tumor cells. The inhibitory effect was almost complete in lymphoma cells SUDHL4 characterized by overexpression of c-Myc protein. This downregulation reflected an early and persistent modulation of cMyc mRNA. Given the relevance of c-MYC in regulation of ribosome biogenesis, it is conceivable that the inhibition of c-MYC contributes to the perturbation of nuclear functions and RNA polymerase I activity. Similar experiments with CX-5461, another RNA polymerase I transcription inhibitor, indicate the same behaviour in G-quadruplex stabilization.

GENERAL SIGNIFICANCE

Our results support the hypothesis that BMH-21 and analogue compounds share the same mechanism, i.e. G-quadruplex binding as a primary event of a cascade leading to inhibition of RNA polymerase I and apoptosis.

Biomarkers of Primary Resistance to Trastuzumab in HER2-Positive Metastatic Gastric Cancer Patients: the AMNESIA Case-Control Study

Purpose: Refining the selection of HER2-positive metastatic gastric cancer patient candidates for trastuzumab is a challenge of precision oncology. Preclinical studies have suggested several genomic mechanisms of primary resistance, leading to activation of tyrosine kinase receptors other than HER2 or downstream signaling pathways.Experimental Design: We carried out this multicenter, prospective, case-control study to demonstrate the negative predictive impact of a panel of candidate genomic alterations (AMNESIA panel), including EGFR/MET/KRAS/PI3K/PTEN mutations and EGFR/MET/KRAS amplifications. Hypothesizing a prevalence of candidate alterations of 30% and 0% in resistant and sensitive HER2-positive patients, respectively, 20 patients per group were needed.Results: AMNESIA panel alterations were significantly more frequent in resistant (11 of 20, 55%) as compared with sensitive (0% of 17) patients (P < 0.001), and in HER2 IHC 2⁺ (7 of 13, 53.8%) than 3⁺ (4 of 24, 16.7%) tumors (P = 0.028). Patients with tumors bearing no candidate alterations had a significantly longer median progression-free [5.2 vs. 2.6 months; HR, 0.34; 95% confidence interval (CI), 0.07-0.48; P = 0.001] and overall survival (16.1 vs. 7.6 months; HR, 0.38; 95% CI, 0.09-0.75; P = 0.015). The predictive accuracy of the AMNESIA panel and HER2 IHC was 76% and 65%, respectively. The predictive accuracy of the combined evaluation of the AMNESIA panel and HER2 IHC was 84%.Conclusions: Our panel of candidate genomic alterations may be clinically useful to predict primary resistance to trastuzumab in patients with HER2-positive metastatic gastric cancer and should be further validated with the aim of molecularly stratifying HER2-addicted cancers for the development of novel treatment strategies. Clin Cancer Res; 24(5); 1082-9. ©2017 AACR.

Abstract 5428: Lactate production as a potential marker of HER2-addiction and Trastuzumab susceptibility

Background: Although the introduction of the HER2-specific humanized monoclonal antibody Trastuzumab (T) in clinical practice revolutionized the treatment of HER2-positive breast cancer (BC), about half of the T-treated patients do not benefit or become refractory after its administration. Despite different molecular tumor profiles significantly associated with T benefit were reported, the identification of a non invasive clinical approach to select patients responsive or not to T is still a clinical unmet task. We recently reported that mammary cancer cell lines derived from spontaneous nodules arisen in mice transgenic for the human d16HER2 splice variant (HER2-addicted) were significantly enriched in genes involved in glycolysis pathway versus those developed in mice transgenic for the human full-length HER2-positive (WTHER2) (HER2-non addicted) (1,2). Accordingly, the aim of our study was to define whether tumor lactate levels could reflect HER2 addiction and, in turn, T susceptibility.

Methods: The metabolite content in murine and human HER2-positive cell lines and specimens was determined by quantitative Nuclear Magnetic Resonance (NMR) spectroscopy. The optical metabolic imaging that quantifies the levels of the anaerobic glycolysis-related metabolite nicotinamide adenine dinucleotide (NADH) and the aerobic metabolite flavin adenine dinucleotide (FAD) was represented by Optical redox ratio (NADH/FAD). The extracellular levels of lactate were calculated by blood gas analyzer.

Results: The metabolic profile of HER2-addicted (MI6, MI7) versus -non-addicted (WTHER2_1, WTHER2_2) murine tumor cells revealed higher intracellular levels of metabolites associated to glycolysis in MI6 and MI7 cells versus WTHER2-positive cells. In keeping, also the evaluation of the metabolic profile of human HER2-positive BC cell lines classified as addicted (SKBR3 and BT474) or not (MDAMB453 and MDAMB361) to HER2-signaling (3) confirmed significant higher intracellular and extracellular levels of lactate in HER2-addicted versus -non-addicted cells. The extracellular levels of NADH and NADH/FAD ratio further sustained a significantly higher activity of an anaerobic metabolism in HER2-addicted cells. Noteworthy, the metabolic profile of 27 HER2-positive BC cases treated with T, classified as HER2-addicted or not on the basis of the activation status of d16HER2 (1), provided further evidence of significantly higher levels of lactate in tumors HER2-addicted.

Conclusions: Overall, even if a dysregulated glucose metabolism is a tumor hallmark, our results provide relevant in vitro and in vivo evidences of the potential future non-invasive lactate detection as a possible biomarker of HER2-addiction and T-responsiveness.

Supported by the Italian Ministry of Health and AIRC.

References:

1) Castagnoli L et Al, Cancer Res 2014

2) Castagnoli L et Al ,Oncogene 2016

3) Shiu KK et Al, Oncogene 2014

Citation Format: Lorenzo Castagnoli, Egidio Iorio, Ada Koschorke, Cristina Ghirelli, Gianmauro Palombelli, Debora Giani, Matteo Dugo, Daniele Morelli, Rossella Canese, Elda Tagliabue, Serenella M. Pupa. Lactate production as a potential marker of HER2-addiction and Trastuzumab susceptibility [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 5428. doi:10.1158/1538-7445.AM2017-5428

Pathobiological implications of the d16HER2 splice variant for stemness and aggressiveness of HER2-positive breast cancer

We have previously shown that the d16HER2 splice variant is linked to HER2-positive breast cancer (BC) tumorigenesis, progression and response to Trastuzumab. However, the mechanisms by which d16HER2 contributes to HER2-driven aggressiveness and targeted therapy susceptibility remain uncertain. Here, we report that the d16HER2-positive mammary tumor cell lines MI6 and MI7, derived from spontaneous lesions of d16HER2 transgenic (tg) mice and resembling the aggressive features of primary lesions, are enriched in the expression of Wnt, Notch and epithelial–mesenchymal transition pathways related genes compared with full-length wild-type (WT) HER2-positive cells (WTHER2_1 and WTHER2_2) derived from spontaneous tumors arising in WTHER2 tg mice. MI6 cells exhibited increased resistance to anoikis and significantly higher mammosphere-forming efficiency (MFE) and self-renewal capability than the WTHER2-positive counterpart. Furthermore, d16HER2-positive tumor cells expressed a higher fraction of CD29^High/CD24⁺/SCA1^Low cells and displayed greater in vivo tumor engraftment in serial dilution conditions than WTHER2_1 cells. Accordingly, NOTCH inhibitors impaired mammosphere formation only in MI6 cells. A comparative analysis of stemness-related features driven by d16HER2 and WTHER2 in ad hoc engineered human BC cells (MCF7 and T47D) revealed a higher MFE and aldehyde dehydrogenase-positive staining in d16HER2- vs WTHER2-infected cells, sustaining consistent BC-initiating cell enrichment in the human setting. Moreover, marked CD44 expression was found in MCF7_d16 and T47D_d16 cells vs their WTHER2 and Mock counterparts. Clinically, BC cases from two distinct HER2-positive cohorts characterized by high levels of expression of the activated-d16HER2 metagene were significantly enriched in the Notch family and signal transducer genes vs those with low levels of the metagene.

Abstract 3826: Phenethyl isothiocyanate hampers growth and progression of HER2-positive breast cancers

Background: Almost 90% of all breast cancers (BCs) express a splice variant of HER2 lacking exon 16 (d16HER2), which promotes the generation of stable and active d16HER2 homodimers on the tumor cell surface. Comparison of the tumorigenic potential of human d16HER2 and the full-length HER2 (WTHER2) in transgenic mice revealed a significantly shorter latency period and a higher incidence of tumors in the d16HER2 line, suggesting enrichment of this variant in HER2+ BC stem cells. Based on reports that cruciferous vegetable-derived compounds such as isothiocyanates (ITCs) mediate strong anti-tumorigenic effects on numerous oncotypes and target BC stem cells, we tested the effect of the phenethyl ITC (PEITC), alone or together with Trastuzumab (T), which reportedly targets HER2+ BC stem cells, on d16HER2-positive tumor growth and progression in transgenic mice.

Methods: The percentage of tumor cells expressing high levels of CD29 and CD24 and low levels of SCA-1 (CD29high/CD24+/SCA-1low) murine stem cell markers was evaluated by multiparametric flow cytometry in cell models derived from spontaneous d16HER2 and WTHER2 transgenic lesions. Mammosphere forming efficiency (MFE%) was calculated in d16HER2- and WTHER2-positive tumor cells. The therapeutic activity of PEITC, T and their combination was assessed in vitro based on their ability to decrease the MFE% and the expression of stem cell markers in d16HER2- vs. WTHER2-positive tumor cells, and in vivo in d16HER2 transgenic mice. Analyses by western blot, histology/immunohistochemistry and magnetic resonance spectroscopy (MRS) are ongoing to assess apoptosis, necrosis and metabolomic profiles of treated tumors vs. controls.

Results: d16HER2 tumor cells showed a significantly higher MFE% and higher expression of stem cell markers than did WTHER2 tumor cells. PEITC and T significantly reduced MFE% as compared to controls (p = 0.0342 and p = 0.0083, respectively), and their combination exerted significantly stronger inhibition than T (p = 0.001) or PEITC (p = 0.0003) alone only in d16HER2 cells. The percentage of tumor cells expressing CD29high/CD24+/SCA-1low in d16HER2 tumor cells after treatment with T, PEITC or both was also reduced. Whereas PEITC monotherapy did not significantly reduce mammary tumor incidence compared to controls, while T effectively suppressed d16HER2-driven tumor growth (p = 0.0002), the combination of PEITC and T significantly heightened the impairment of mammary lesion development compared to T alone (p = 0.0046). Ex vivo metabolomic analyses by MRS of d16HER2-positive murine and human BC cell lines showed an increase in glycolytic pathway as compared to the respective WTHER2 cells.

Conclusions: Our results provide in vivo evidence that the combination of T and PEITC mediates a significantly greater anti-tumor effect than either alone, most likely targeting BC stem cells.

Supported by the Italian Ministry of Health and AIRC.

Citation Format: Ada Koschorke, Lorenzo Castagnoli, Gaia C. Ghedini, Tiziana Triulzi, Claudia Chiodoni, Rossella Canese, Egidio Iorio, Manuela Iezzi, Patrizia Nanni, Elda Tagliabue, Serenella M. Pupa. Phenethyl isothiocyanate hampers growth and progression of HER2-positive breast cancers. [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 3826.

Abstract 2314: d16HER2 splice variant regulates the activity of HER2-positive breast cancer-initiating cells

The transmembrane tyrosine kinase receptor HER2, overexpressed in ∼20% of human breast cancers (BCs), identifies an aggressive tumor subtype and is reportedly an important regulator of breast cancer-initiating cell activity (BCIC). We found that ∼90% of HER2+ BC patients constitutively express a splice isoform of wild-type HER2 (WTHER2) gene characterized by the lack of exon 16 (d16HER2), a deletion that promotes the generation of a particularly aggressive HER2 isoform and that forms stable and constitutively activated d16HER2 homodimers. Our comparison of the tumorigenic potential of the human d16HER2 and WTHER2 genes in the corresponding transgenic mouse models revealed a significantly shorter tumor latency period (p&lt; 0.001) and a higher tumor incidence in the d16HER2 mice (p&lt;0.001), suggesting a role for this variant in HER2-driven activation of BCICs. In this context, our preliminary analyses of HER2-positive primary mammary tumor cell lines MI6 and MI7 derived from spontaneous transgenic d16HER2 mice showed a significantly higher mammosphere-forming efficiency and higher levels of stem cell marker transcripts, including CD44, Wnt, Notch and Bmi1, compared to transgenic mouse WTHER2 tumor cells (WTHER2_1 and WTHER2_2). Mammospheres generated from human HER2-overexpressing breast cancer cell lines BT474 and MDA-MB-361, which also express the d16HER2 variant, exhibited an increase in the relative abundance of d16HER2 mRNA compared with that in the same parental cells cultured in adhesion conditions, as indicated by qPCR analyses. Experiments in mice injected into the mammary fat pad with the d16HER2- and WTHER2-positive cell lines at different serial dilutions indicate a consistently higher “stemness potential” of MI6 and MI7 cells compared to WTHER2_1 and WTHER2_2 cells, strongly suggesting that the d16HER2 variant plays a greater role than WTHER2 in regulating BCICs of HER2-driven mammary tumors.

Supported by Minister of Health and AIRC

Citation Format: Lorenzo Castagnoli, Ada Koschorke, Gaia C. Ghedini, Lorenzo Galvani, Valentina Ciravolo, Cristina Ghirelli, Arianna Palladini, Alessia Lamolinara, Manuela Iezzi, Pier Luigi Lollini, Tiziana Triulzi, Patrizia Nanni, Elda Tagliabue, Serenella M. Pupa. d16HER2 splice variant regulates the activity of HER2-positive breast cancer-initiating cells. [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 2314. doi:10.1158/1538-7445.AM2015-2314

Abstract 2637: Role of d16HER2 splice variant in HER2-positive breast cancer

Almost 90% of human primary breast cancers (BCs) express 4-9% of total wild-type (WT) HER2 as a splice variant lacking exon 16 (d16HER2). Consequent in-frame activating deletion of 2 cysteine residues causes an imbalanced conformation resulting in receptor constitutive homodimerization, enhanced signaling activity, transformation and altered trastuzumab (T) binding. We recently produced a human d16HER2 transgenic (tg) mouse characterized by a rapid multifocal mammary tumors onset and the expression of active d16HER2 dimers on tumor cells, whose downstream signaling was found coupled to multiple activated nodes that include Src kinase. In order to dissect d16HER2 role in the aggressiveness and in the susceptibility to anti-HER2 therapy, we focused on the generation of stable d16HER2-expressing mammary tumor cell lines to be used in different bioassays. An immunomagnetic purification procedure was applied to generate primary homogeneously d16HER2-expressing cell cultures. These purified tumor cell lines were analyzed by flow cytometry and immunofluorescence and their migration/invasion ability was assessed through Boyden chamber test. d16HER2 downstream signaling was evaluated by western blot and T, Lapatinib (L) and Dasatinib (D) drugs sensitivity was measured with WST-1 and soft-agar bioassays. As controls, we compared in vitro d16HER2-models oncogenic features to those of the human BC BT474, which also co-expresses a low amount of d16HER2 transcript (4%), and to a murine mammary carcinoma cell line (wtHER2), derived from a primary mammary tumor developed in human WT HER2 tg mice. We found that d16HER2 in vitro models expressed high levels of stable homodimers combined with the recruitment of activated Src, STAT3, MAPK and Akt, as in vivo primary mammary tumors. Both in bidimensional (2D) and matrigel-cultured tumor cells, we confirmed the T lower binding capability for d16HER2 than other anti-HER2 MAbs directed to different extracellular domain epitopes. d16HER2 tumor cells had an enhanced migratory and invasive capacity compared to wtHER2 and BT474 cells and, notably, were completely resistant to T treatment and less responsive to L. In virtue of a highly activated Src kinase expression in d16HER2-positive models, we tested in 2D the therapeutic effects of D and observed that d16HER2-cells were significantly more sensitive than wtHER2 and BT474 cells. Preliminary 3D-drug susceptibility assays showed that the sensitivity of d16HER2 cells increased for all the tested drugs, if assessed in a suitable environment such as soft-agar. Our findings further indicate that the constitutive expression of d16HER2 variant identifies an aggressive tumor phenotype and confirm, at least in vitro in 2D conditions, that this isoform is resistant to T and L, whereas is sensitive to D. Further analyses are ongoing to analyze in vivo drug sensitivity of d16 in comparison to WT HER2 model.

Supported by AIRC and Ministry of Health

Citation Format: Gaia C. Ghedini, Arianna Palladini, Valentina Ciravolo, Lorenzo Castagnoli, Giulia Marzano, Roberta Zappasodi, Guido Santilli, Augusto Amici, Alessia Lamolinara, Manuela Iezzi, Patrizia Nanni, Elda Tagliabue, Serenella M. Pupa. Role of d16HER2 splice variant in HER2-positive breast cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2637. doi:10.1158/1538-7445.AM2014-2637

Abstract 916: Role of delta16HER2 splice variant in HER2-driven tumor progression and response to targeted therapy

We reported that the splice variant of human HER2 lacking exon 16 (delta16HER2) represents a highly penetrating HER2 oncogenic alteration identified in human primary breast tumor specimens and is able to influence the response to Trastuzumab. This HER2 variant forms covalent cysteine bonds that generate constitutively active homodimers, thereby activating multiple oncogenic downstream signaling pathways that we recently found to be mediated through activated Src kinase. To examine the ability of delta16HER2 to transform mammary epithelium in vivo and to monitor delta16HER2-driven tumorigenesis in live mice, we generated a FVB transgenic mouse model for the human delta16HER2 isoform. Transgenic female mice developed multifocal mammary tumors with a rapid onset starting at about 12 weeks of age and progressively thereafter, clearly pointing to the candidacy of the delta16HER2 isoform as the transforming form of the human HER2 oncoprotein. Histological and immunohistochemical analysis (IHC) of primary mammary nodules revealed a population of polygonal cells with classical epithelia-like aspects distinctly expressing HER2 and also a population of smaller spindle-shaped cells arranged in fascicles with lower levels of HER2 expression, suggesting the onset of the epithelial-to-mesenchymal transition (EMT). Consistent with these findings, FACS analysis of delta16HER2-positive tumor cells immunomagnetically purified from disaggregated transgenic primary tumors indicated the increased mean fluorescence intensity of HER2 staining with increasing tumor cell size. IHC analysis of the lung metastases that had formed in the majority of female mice revealed monomorphic and classical epithelial tumor cells homogeneously expressing high levels of delta16HER2. FACS and IHC analyses confirmed the lower binding efficacy of Trastuzumab to delta16HER2-overexpressing primary tumor cells cultured both under bidimensional (2D) and tridimensional (3D) conditions as compared to monoclonal reagents directed to different HER2 extracellular domain epitopes. Experiments in both primary and metastatic in vitro and in vivo delta16HER2-positive models are in progress to determine whether delta16HER2-driven tumor aggressiveness and Trastuzumab susceptibility depend not only on genetic changes intrinsic to the tumor cell, i.e., the EMT process, but also on extrinsic tumor surrounding microenvironment-related factors such as an imbalance between extracellular and intracellular pH, redox state and hypoxia. Preliminary FACS and IHC analyses indicate that delta16HER2-positive primary tumor cells are reactive for known epithelial markers as EpCAM, E-cadherin- and ck-18 and, a small subset of these mammary tumor cells, also stain positive for the mesenchymal differentiation markers vimentin, N-cadherin and ck14 significantly indicating an active EMT program. Supported by AIRC and Ministry of Health

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 916. doi:1538-7445.AM2012-916

The human splice variant Δ16HER2 induces rapid tumor onset in a reporter transgenic mouse

Several transgenic mice models solidly support the hypothesis that HER2 (ERBB2) overexpression or mutation promotes tumorigenesis. Recently, a HER2 splice variant lacking exon-16 (Δ16HER2) has been detected in human breast carcinomas. This alternative protein, a normal byproduct of HER2, has an increased transforming potency compared to wild-type (wt) HER2 receptors. To examine the ability of Δ16HER2 to transform mammary epithelium in vivo and to monitor Δ16HER2-driven tumorigenesis in live mice, we generated and characterized a mouse line that transgenically expresses both human Δ16HER2 and firefly luciferase under the transcriptional control of the MMTV promoter. All the transgenic females developed multifocal mammary tumors with a rapid onset and an average latency of 15.11 weeks. Immunohistochemical analysis revealed the concurrent expression of luciferase and the human Δ16HER2 oncogene only in the mammary gland and in strict correlation with tumor development. Transgenic Δ16HER2 expressed on the tumor cell plasma membrane from spontaneous mammary adenocarcinomas formed constitutively active homodimers able to activate the oncogenic signal transduction pathway mediated through Src kinase. These new transgenic animals demonstrate the ability of the human Δ16HER2 isoform to transform "per se" mammary epithelium in vivo. The high tumor incidence as well as the short latency strongly suggests that the Δ16HER2 splice variant represents the transforming form of the HER2 oncoprotein.

Multiple modification and protein interaction signals drive the Ring finger protein 11 (RNF11) E3 ligase to the endosomal compartment

Ring finger protein 11 (RNF11) is a small RING E3-ligase overexpressed in numerous human prostate, colon and invasive breast cancers. Although functional studies have implicated RNF11 in a variety of biological processes, including signal transduction and apoptosis, the molecular mechanisms underlying its function are still poorly understood. In this study we show that RNF11 is a membrane-associated E3 ligase co-localizing with markers of both the early and the recycling endosomes. Several modification and protein interaction signals in the RNF11 sequence are shown to affect its compartmentalization. Membrane binding requires two acylation motifs driving the myristoylation of Gly2 and the S-palmitoylation of Cys4. Accordingly, genetic removal of the myristoylating signal results in diffuse staining, whereas an RNF11 protein mutated in the palmitoylation signal is retained in compartments of the early secretory pathway. However, amino-terminal fusion to green fluorescent protein of a 10-residue peptide containing both acylation signals re-localizes the chimera to the plasma membrane, but it is not sufficient to direct it to the recycling compartment suggesting that additional signals contribute to the correct localization. In addition, we show that membrane anchoring through acylation is necessary for RNF11 to be post-translationally modified by the addition of several ubiquitin moieties and that loss of acylation severely impairs the in vivo ubiquitination mediated by the HECT E3-ligases Itch and Nedd4. Finally, in cells transfected with RNF11 we observe a correlation between high RNF11 expression, as in tumor cells, and a swelling of the endosomal compartment suggesting a possible role of the dysregulation of the endosome compartment in tumorigenesis.

Abstract 4785: Identification of HSP105 as a novel non-Hodgkin lymphoma (NHL) restricted antigen

We recently reported that vaccination using dendritic cells (DCs) loaded with killed autologous tumor cells in relapsed indolent NHL patients induced objective clinical responses that correlate with multifaceted immunological responses. In particular, since responders (R) showed tumor-restricted humoral immunity in autologous setting, we exploited antibody (Ab) repertoires from vaccinated patients to evaluate whether the observed antibody responses was directed to indolent NHL-shared antigens (ags).

Immunohistochemistry and flow-cytometric analyses of biotinylated Immunoglobulins (Igs) from vaccinated patients’ serum samples preadsorbed on normal isolated B cells in the attempt to decrease Abs cross-reacting with normal auto-ags showed that only post-vaccine serum Ig of responders specifically reacted with higher intensity on allogeneic NHL tumors (either long term cell cultures or primary tumors from the same series) compared to matched biotinylated Igs from control samples (pre-vaccine serum from responders, pre- and post-vaccine serum from non-responders and healthy donors). In addition, only Abs contained in post-vaccine serum from R significantly inhibited NHL DOHH2 cells growth strongly suggesting the presence of therapeutic Abs in their serum samples. These findings indicate that Igs from R recognize tumor cell-surface associated molecules different from patient-specific idiotypes and support the potential expression of novel NHL-restricted ags. As a step toward identifying NHL-restricted ags as potential novel therapeutic targets, we applied a properly modified serological proteome analysis (SERPA) using as target DOHH2 cells and as probes pre- and post-vaccine Ab repertoires from our series. Proteins, fractionated using an OFFGEL IPG strip (pH 3-10), were separated on SDS-PAGE and then immunoblotted with pre- and post-vaccine Igs from R and controls. Differential hybridization analyses have revealed some potential candidate tumor-associated antigens which include heat shock protein 105 (HSP105), whose immunological role has been already proved in solid tumors. Preliminary data indicate that HSP105 is also expressed on cell membrane from different tumor B cell lines and experiments are in progress to evaluate its potential implication in tumor growth control. Partially supported by AIRC.

Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4785.

Mutations in the external loops of BK virus VP1 and urine viral load in renal transplant recipients

Polyomavirus-associated nephropathy (PVAN) is a major complication that occurs after renal transplantation and is induced by reactivation of the human polyomavirus BK (BKV). The structure of the viral capsid protein 1 (VP1) is characterized by the presence of external loops, BC, DE, EF, GH, and HI, which are involved in receptor binding. The pathogenesis of PVAN is not well understood, but viral risk factors are thought to play a crucial role in the onset of this pathology. In an attempt to better understand PVAN pathogenesis, the BKV-VP1 coding region was amplified, cloned, and sequenced from the urine of kidney transplant recipients who did, and did not, develop the pathology. Urine viral loads were determined by using real time quantitative PCR (Q-PCR). Amino acid substitutions were detected in 6/8 patients, and 6/7 controls. The BC and EF loop regions were most frequently affected by mutations, while no mutations were found within the GH and HI loops of both patients and controls. Some mutations, that were exclusively detected in the urine of PVAN patients, overlapped with previously reported mutations, although a correlation between changes in amino acids and the development of PVAN was not found. Urine viral loads were higher than that of the proposed cut-off loads for identification of patients that are at a high risk of developing PVAN (10(7) copies/ml), both in the PVAN and control groups, thus confirming that urine viral load is not a useful predictive marker for the development of PVAN.

Handgrip impairment in Charcot-Marie-Tooth disease

AIM

Charcot-Marie-Tooth disease (CMT) is a genetic neuropathy causing muscle weakening in the feet, legs and hands, with consequent impairment of ambulation and handgrip. For fast clinical evaluation and rehabilitation management of handgrip deficits, a functional classification in 4 stages or levels of clinical severity, based on the loss of handgrip types from the finest to the roughest, has been recently proposed. The aim of this study is to evaluate the prevalence of each level of handgrip impairment in a wide population of patients affected with demyelinating and axonal CMT.

METHODS

Two-hundred and forty-eight non-operated hands were examined to evaluate if and how the pinch between the pulp of the thumb and the pulp of the second or third finger was made, starting from the palm-up position with the fingers abducted or, in case of impossibility to do so, if a lateral pinch or only a grasp was possible. Following to this observation, each hand was fitted in 1 of the 4 stages described in the above-mentioned classification and then the frequency of each stage was determined.

RESULTS

As a whole, 75.4% hands were at stage 1; 9.7 were at stage 2; 10.9% at stage 3; 4% at stage 4.

CONCLUSIONS

The results of this survey reveal that, in the majority of the CMT cases, handgrip is affected mildly so that only simple recommendations to prevent further muscle and joint damage are required; however, in more than 1 out 5 cases, the handrip impairment is quite severe and requires a detailed rehabilitative program with daily exercises, and, in a small number of cases, is so severe that independence in the daily living activities is lost or very reduced.

Carl von Rokitansky and the Italian translation of the Handbuch der Pathologischen Anatomie: a linguistic and doctrinal enigma

Carl von Rokitansky was the author of a treatise that came out between 1842 and 1846 with the title Handbuch der Pathologischen Anatomie. A historical milestone in pathological anatomy, Rokitansky's work represented the first attempt to systematically classify pathological specimens. Its publication inevitably made a great impact on Vienna, at that time the major European medical centre. The Italian translation of Rokitansky's masterpiece, Trattato Completo di Anatomia Patologica, published in Venice in 1852, was carried out by Ricchetti and Fano: the former a philologist and the latter a Triestine physician who, in 1873, had worked at Simon Pertot's side, the first prosector to be assumed in Trieste. From the start, the two translators not only made no secret of the linguistic obstacles they came up against, but also how unconvincing Rokitansky's doctrines were; a scepticism emerged from their words that inevitably contributed to the realization of a translation difficult to read. Undoubtedly, Rokitansky elaborated a theory of disease containing a certain degree of unclarity and in this respect it is interesting to emphasize that even the English translation, Manual of Pathologic Anatomy (1849-1854), demonstrated similar conceptual problems. A convinced supporter of gross pathology, Rokitansky put forth a theory of disease, the so-called Krasenlehre, resting upon humoral doctrines. This new knowledge inevitably exerted a great influence over Viennese, as well as German, medicine. Rokitansky's humoral pathology survived until the 1850s, when it was attacked by young Virchow, the future, universally recognized, father of cellular pathology, who definitively extinguished speculative humoral pathology.

A two-hybrid system based on chimeric operator recognition for studying protein homo/heterodimerization in Escherichia coli

The development of a convenient and promising alternative to the various two-hybrid methods that are used to study protein-protein interactions is described. In this system, a lambdoid chimeric operator is recognized by a hybrid repressor formed by two chimeric monomers whose C-terminal domains are composed of heterologous proteins (or protein domains). Only if these proteins efficiently dimerize in vivo is a functional repressor formed able to bind the chimeric operator and shut off the synthesis of a downstream reporter gene. This new approach was tested with several interacting proteins ranging in size from less than 100 to more than 800 amino acids and, to date, no size or topology limit has been detected.

Physical interaction with Yes-associated protein enhances p73 transcriptional activity

Specific protein-protein interactions are involved in a large number of cellular processes and are mainly mediated by structurally and functionally defined domains. Here we report that the nuclear phosphoprotein p73 can engage in a physical association with the Yes-associated protein (YAP). This association occurs under physiological conditions as shown by reciprocal co-immunoprecipitation of complexes from lysates of P19 cells. The WW domain of YAP and the PPPPY motif of p73 are directly involved in the association. Furthermore, as required for ligands to group I WW domains, the terminal tyrosine (Y) of the PPPPY motif of p73 was shown to be essential for the association with YAP. Unlike p73alpha, p73beta, and p63alpha, which bind to YAP, the endogenous as well as exogenously expressed wild-type p53 (wt-p53) and the p73gamma isoform do not interact with YAP. Indeed, we documented that YAP interacts only with those members of the p53 family that have a well conserved PPXY motif, a target sequence for WW domains. Overexpression of YAP causes an increase of p73alpha transcriptional activity. Differential interaction of YAP with members of the p53 family may provide a molecular explanation for their functional divergence in signaling.

Selection of ligands by panning of domain libraries displayed on phage lambda reveals new potential partners of synaptojanin 1

One of the goals of functional genomics is the description of reliable and complete protein interaction networks. To facilitate ligand discovery from complex protein mixtures, we have developed an improved approach that is affected by a negligible fraction of false positives. We have combined a novel technique based on the display of cDNA libraries on the capsid of bacteriophage lambda and an efficient plaque assay to reveal phage displaying ligands that are enriched after only a couple of affinity purification steps. We show that the lambda display system has a unique ability to display, at high density, proteins ranging in size from a few to at least 300 amino acid residues. This characteristic permits attenuation of the size bias in the selection procedure and, at the same time, offers a sensitive plaque assay that permits us to do away with the ligand background without unduly increasing the number of selection cycles. By using a proline-rich fragment of the synaptojanin 1 protein as a bait, we have identified, in a brain cDNA display library, seven ligands all containing either SH3 or WW domains. Four of these correspond to proteins that have already been validated as physiological partners, while the remaining three are new partners, whose physiological relevance remains to be established. Two different proline-rich regions of the p21-activated protein kinase 1 (Pak1) and WAVE/SCAR2 protein retrieve from the library different proteins containing SH3 or WW domains.

Alternative bacteriophage display systems

Filamentous phage has been extensively used to implement various aspects of phage display technology. The success of these organisms as vectors to present foreign peptides and to link them to their coding sequences is a consequence of their structural and biological characteristics. Some of these properties, however, represent a limitation when one attempts to display proteins that cannot be efficiently exported through the bacterial membrane or do not fold properly in the periplasm. Thus, the desirability of developing alternative display systems was recognised recently and led to the development of a different class of display vectors that assemble their capsid in the cytoplasm and are released via cell lysis. This review describes and compares the properties of these alternative display systems.

Physical and functional interaction between p53 mutants and different isoforms of p73

p53 is the most frequently inactivated tumor suppressor gene in human cancer, whereas its homologue, p73, is rarely mutated. Similarly to p53, p73 can promote growth arrest or apoptosis when overexpressed in certain p53-null tumor cells. It has previously been shown that some human tumor-derived p53 mutants can exert gain of function activity. The molecular mechanism underlying this activity remains to be elucidated. We show here that human tumor-derived p53 mutants (p53His175 and p53Gly281) associate in vitro and in vivo with p73 alpha, beta, gamma, and delta. This association occurs under physiological conditions, as verified in T47D and SKBR3 breast cancer cell lines. The core domain of mutant p53 is sufficient for the association with p73, whereas both the specific DNA binding and the oligomerization domains of p73 are required for the association with mutant p53. Furthermore, p53His175 and p53Gly281 mutants markedly reduce the transcriptional activity of the various isoforms of p73. Thus, human tumor-derived p53 mutants can associate with p73 not only physically but also functionally. These findings define a network involving mutant p53 and the various spliced isoforms of p73 that may confer upon tumor cells a selective survival advantage.

Domain repertoires as a tool to derive protein recognition rules

Several approaches, some of which are described in this issue, have been proposed to assemble a complete protein interaction map. These are often based on high throughput methods that explore the ability of each gene product to bind any other element of the proteome of the organism. Here we propose that a large number of interactions can be inferred by revealing the rules underlying recognition specificity of a small number (a few hundreds) of families of protein recognition modules. This can be achieved through the construction and characterization of domain repertoires. A domain repertoire is assembled in a combinatorial fashion by allowing each amino acid position in the binding site of a given protein recognition domain to vary to include all the residues allowed at that position in the domain family. The repertoire is then searched by phage display techniques with any target of interest and from the primary structure of the binding site of the selected domains one derives rules that are used to infer the formation of complexes between natural proteins in the cell.

The SH3 domains of endophilin and amphiphysin bind to the proline-rich region of synaptojanin 1 at distinct sites that display an unconventional binding specificity

The proline-rich domain of synaptojanin 1, a synaptic protein with phosphatidylinositol phosphatase activity, binds to amphiphysin and to a family of recently discovered proteins known as the SH3p4/8/13, the SH3-GL, or the endophilin family. These interactions are mediated by SH3 domains and are believed to play a regulatory role in synaptic vesicle recycling. We have precisely mapped the target peptides on human synaptojanin that are recognized by the SH3 domains of endophilins and amphiphysin and proven that they are distinct. By a combination of different approaches, selection of phage displayed peptide libraries, substitution analyses of peptides synthesized on cellulose membranes, and a peptide scan spanning a 252-residue long synaptojanin fragment, we have concluded that amphiphysin binds to two sites, PIRPSR and PTIPPR, whereas endophilin has a distinct preferred binding site, PKRPPPPR. The comparison of the results obtained by phage display and substitution analysis permitted the identification of proline and arginine at positions 4 and 6 in the PIRPSR and PTIPPR target sequence as the major determinants of the recognition specificity mediated by the SH3 domain of amphiphysin 1. More complex is the structural rationalization of the preferred endophilin ligands where SH3 binding cannot be easily interpreted in the framework of the "classical" type I or type II SH3 binding models. Our results suggest that the binding repertoire of SH3 domains may be more complex than originally predicted.

Phage displayed peptide libraries

Peptide libraries may be constructed by grafting, in vitro, random DNA sequences into a carrier gene and then introducing the degenerate hybrid coding sequence into an expression organism. This review will focus on phage display, which was the first expression organism for peptide library expression to be described and which still maintains predominance in this area because of its simplicity, minimal cost, ease of manipulation, power and robustness. Using phage as the host, a repertoire of random peptides can be expressed that may be searched by a variety of screening or selection procedures. By physically associating each element of the peptide library with its coding sequence, selection for a property of a specific peptide results in the enrichment of the corresponding gene thus facilitating its cloning and amplification. This review focuses on the construction and screening of peptide libraries displayed on filamentous phage capsid and only briefly discusses the display of proteins and protein domains.

Intersectin, a novel adaptor protein with two Eps15 homology and five Src homology 3 domains

We screened a Xenopus laevis oocyte cDNA expression library with a Src homology 3 (SH3) class II peptide ligand and identified a 1270-amino acid-long protein containing two Eps15 homology (EH) domains, a central coiled-coil region, and five SH3 domains. We named this protein Intersectin, because it potentially brings together EH and SH3 domain-binding proteins into a macromolecular complex. The ligand preference of the EH domains were deduced to be asparajine-proline-phenylalanine (NPF) or cyclized NPF (CX1-2NPFXXC), depending on the type of phage-displayed combinatorial peptide library used. Screens of a mouse embryo cDNA library with the EH domains of Intersectin yielded clones for the Rev-associated binding/Rev-interacting protein (RAB/Rip) and two novel proteins, which we named Intersectin-binding proteins (Ibps) 1 and 2. All three proteins contain internal and C-terminal NPF peptide sequences, and Ibp1 and Ibp2 also contain putative clathrin-binding sites. Deletion of the C-terminal sequence, NPFL-COOH, from RAB/Rip eliminated EH domain binding, whereas fusion of the same peptide sequence to glutathione S-transferase generated strong binding to the EH domains of Intersectin. Several experiments support the conclusion that the free carboxylate group contributes to binding of the NPFL motif at the C terminus of RAB/Rip to the EH domains of Intersectin. Finally, affinity selection experiments with the SH3 domains of Intersectin identified two endocytic proteins, dynamin and synaptojanin, as potential interacting proteins. We propose that Intersectin is a component of the endocytic machinery.

Recognition specificity of individual EH domains of mammals and yeast

The Eps homology (EH) domain is a recently described protein binding module that is found, in multiple or single copies, in several proteins in species as diverse as human and yeast. In this work, we have investigated the molecular details of recognition specificity mediated by this domain family by characterizing the peptide-binding preference of 11 different EH domains from mammal and yeast proteins. Ten of the eleven EH domains could bind at least some peptides containing an Asn-Pro-Phe (NPF) motif. By contrast, the first EH domain of End3p preferentially binds peptides containing an His-Thr/Ser-Phe (HT/SF) motif. Domains that have a low affinity for the majority of NPF peptides reveal some affinity for a third class of peptides that contains two consecutive amino acids with aromatic side chains (FW or WW). This is the case for the third EH domain of Eps15 and for the two N-terminal domains of YBL47c. The consensus sequences derived from the peptides selected from phage-displayed peptide libraries allows for grouping of EH domains into families that are characterized by different NPF-context preference. Finally, comparison of the primary sequence of EH domains with similar or divergent specificity identifies a residue at position +3 following a conserved tryptophan, whose chemical characteristics modulate binding preference.

[Reconversion after Hartmann's procedure. Our experience]

An increasing number of intestinal reconversion after Hartmann have been performed in recent years, especially due to improved surgical techniques and progressively lengthened lifespan. The authors report 33 cases of intestinal recanalization of 100 interventions according to Hartmann from 1984 to 1996 (21 not neoplastic pathologies, 12 neoplasias). The variables considered included: patient age, type of disease requiring intervention according to Hartmann, oncologic characteristic of patients with neoplasia, interval between the two interventions, preoperative examinations performed, morbidity and mortality after reconversion. Furthermore, the fundamental indications for reconversion are described, in particular in patients with neoplasias (CEA, transanal echo, total body Ct, anal manometry). The low frequency of preoperative complications, zero mortality, satisfactory long-term follow-up (only one patient with neoplastic relapse) indicate that colon-rectal reconversion can also be performed in the elderly and patients with neoplasias with favorable prognosis.

Construction, exploitation and evolution of a new peptide library displayed at high density by fusion to the major coat protein of filamentous phage

The amino-terminus of the major coat protein (PVIII) of filamentous phage can be extended, up to 6-7 residues, without interfering with the phage life cycle. We have constructed a library of approximately ten millions different phage each displaying a different octapeptide joined to the amino-terminus of the 2700 copies of PVIII. Most of the resulting clones are able to produce infective particles. This molecular repertoire constituted by the periodic regular decoration of the phage filament surface, can be utilized to search elements that bind proteins or relatively small organic molecules like the textile dye Cibacron blue. By sequential growth cycles we have performed a library evolution experiment to select phage clones that have a growth advantage in the absence of any requirement for binding a specific target. The consensus of the best growers reveals a Pro rich sequence with large hydrophobic residues at position 7 and Asn at position 1 of the random peptide insert. We propose that the assembly secretion process is favoured in phages displaying this family of peptides since they fit the groove between two adjacent PVIII subunits by making advantageous molecular contacts on the phage surface.