ODP551 Halting ErbB-2 Isoforms Retrograde Transport to the Nucleus as a New Theragnostic Approach for Triple Negative Breast Cancer

Triple negative breast cancer (TNBC) is clinically defined by the absence of estrogen and progesterone receptors and the lack of membrane overexpression or gene amplification of the receptor tyrosine kinase ErbB-2/HER2. Due to its heterogeneity, clinical biomarkers and targeted therapies for this disease remain elusive, and chemotherapy has been the standard of care for TNBC. ErbB-2 is classically located at the membrane of BC cells, where it triggers signaling cascades and promotes oncogenesis. We previously demonstrated that ErbB-2 is also localized in the nucleus (NErbB-2) of TNBC cells, from where it drives growth (1). We also discovered that TNBC expresses both wild-type ErbB-2 (WTErbB-2) and alternative ErbB-2 isoform c (ErbB-2c) (1). ErbB-2 migrates to the nucleus via retrograde transport. Here, we revealed that Retro-2, an inhibitor of retrograde transport that protects cells form the deleterious effects of toxins and viruses, evicts both WTErbB-2 and ErbB-2c from the nucleus of BC cells. Using BC models from several molecular subtypes, as well as normal breast cells, we demonstrated that Retro-2 specifically halts the proliferation of cells expressing NErbB-2. Moreover, Retro-2 decreased the expression of genes induced by NErbB-2 (i. e. cyclin D1 and Erk5) and promoted cell cycle arrest at G0/G1 phase and apoptosis. In addition to R2 growth inhibitory activity in vitro, we here also demonstrated that its optimized cyclic derivative Retro-2.1 (in particular the (S)-enantiomer) showed improved efficacy both to evict ErbB-2 isoforms from the nucleus and to inhibit proliferation in vitro. Importantly, Retro-2 eviction of both ErbB-2 isoforms from the nucleus resulted in a striking growth abrogation in multiple TNBC preclinical models, including xenografts and tumor explants). Our mechanistic studies demonstrated that Retro-2 induces a differential accumulation of WTErbB-2 at the early endosomes and plasma membrane, and of ErbB-2c at the Golgi, shedding light both on Retro-2 action on endogenous protein cargoes undergoing retrograde transport and on the biology of ErbB-2 splicing variants. Compelling evidence demonstrated that mRNAs 5' and 3' untranslated regions (UTRs) mediate post-transcriptional regulation of gene expression and determine protein levels and fate. While both T1 and T3 have different 5' but the same 3' UTRs sequences, our in silico studies showed that T1 and T3 RNA secondary structures vary in the region containing both their 5' and 3' UTRs. These findings suggest that T3 secondary structure impacts in its cell specific localization. Together, our present discoveries identify R2 as a precision oncology tool to target NErbB-2 retrograde transport. This novel theragnostic approach could greatly improve the outcome of TNBC patients. (1) Chervo MF et al, Oncogene 2020: 39: 6245-62.

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Comprehensive Identification of Pathogenic Gene Variants in Patients With Neuroendocrine Disorders

PURPOSE

Congenital hypopituitarism (CH) can present in isolation or with other birth defects. Mutations in multiple genes can cause CH, and the use of a genetic screening panel could establish the prevalence of mutations in known and candidate genes for this disorder. It could also increase the proportion of patients that receive a genetic diagnosis.

METHODS

We conducted target panel genetic screening using single-molecule molecular inversion probes sequencing to assess the frequency of mutations in known hypopituitarism genes and new candidates in Argentina. We captured genomic deoxyribonucleic acid from 170 pediatric patients with CH, either alone or with other abnormalities. We performed promoter activation assays to test the functional effects of patient variants in LHX3 and LHX4.

RESULTS

We found variants classified as pathogenic, likely pathogenic, or with uncertain significance in 15.3% of cases. These variants were identified in known CH causative genes (LHX3, LHX4, GLI2, OTX2, HESX1), in less frequently reported genes (FOXA2, BMP4, FGFR1, PROKR2, PNPLA6) and in new candidate genes (BMP2, HMGA2, HNF1A, NKX2-1).

CONCLUSION

In this work, we report the prevalence of mutations in known CH genes in Argentina and provide evidence for new candidate genes. We show that CH is a genetically heterogeneous disease with high phenotypic variation and incomplete penetrance, and our results support the need for further gene discovery for CH. Identifying population-specific pathogenic variants will improve the capacity of genetic data to predict eventual clinical outcomes.

Abstract P6-20-14: Neutralizing soluble tumor necrosis factor alpha overcomes trastuzumab-resistant breast cancer immune evasion by downregulating mucin 4, improving NK cell function and decreasing myeloid-derived suppressor cells in tumor microenvironment

Background: Novel strategies aimed to overcome trastuzumab (Tz) resistance of HER2+ breast cancer (BC) are needed. Recently, we demonstrated a novel immune evasion strategy used by BC where tumor necrosis factor alpha (TNF) induces upregulation of the transmembrane glycoprotein mucin 4 (MUC4) via NF-kB activation to impair Tz binding that prevents antibody mediated killing of BC cells. Etanercept, a non-selective inhibitor of soluble and transmembrane TNF (sTNF, tmTNF), downregulated MUC4 expression and sensitized de novo Tz-resistant BC xenografts to Tz. Moreover, we showed that MUC4 expression is an independent predictor of poor disease-free survival in patients treated with Tz in the adjuvant setting (Clin Cancer Res 2017, 23:636). Etanercept is immunosuppressive due to off-target effects on tmTNF while selective inhibition of sTNF improves the immune response to the tumor (Cancer Immunol Res 2016, 4:441). Because of the immunosuppressive properties of etanercept, we wanted study if the dominant negative-TNF protein XPro1595 (DN-TNF; also known as INB03) that neutralizes sTNF without affecting tmTNF is able to downregulate MUC4 to inhibit Tz-resistant tumor growth and improve innate antitumor immune response.

Methods: To assess the effect of DN-TNF on Tz-resistant HER2+ tumor growth, JIMT-1 cells were s.c. injected in nude mice. When tumors were established, animals were treated with IgG, DN-TNF, Tz or DN-TNF+Tz, i.p. twice a week for one month. Innate immune response was determined by flow cytometry analysis of NK cells activation and degranulation and myeloid-derived suppressor cells (MDSC) subtypes in tumor microenvironment (TME) and in spleen. Tz-dependent NK cells degranulation was assessed in splenocytes using HER2+, Tz-sensitive cell line BT-474 as the target. MUC4 and phospho NF-kB expression was determined by Western blot.

Results: Treatment with Tz or DN-TNF had no impact on JIMT-1 tumor growth. However, co-treatment with DN-TNF and Tz resulted in significantly less growth. At day 21st, tumor volume was 75mm3 in DN-TNF+Tz vs 300mm3 control groups. DN-TNF+Tz treatment showed a decrease in myeloid cell infiltration and MDSC phenotype was enriched in the granulocytic-MDSC vs monocytic-MDSC suggesting a less immunosuppressive TME. DN-TNF+Tz administration significantly increased activation and degranulation of tumor infiltrating NK cells. In addition, spleen NK cells from these animals exhibited enhanced Tz-dependent degranulation vs control groups. MUC4 expression was downregulated in tumors treated with DN-TNF and NF-kB phosphorylation was inhibited (all comparisons p<0.05).

Conclusion: These results suggest that targeting sTNF together with Tz treatment improves antitumor immune response reducing tumor burden. Activated NK cells can more effectively attack the tumor due to a less suppressive TME and decreased MUC4 expression enhancing Tz binding in Tz-resistant HER2+ BC. Patients with increased levels of TNF expressing MUC4 in their tumors could be eligible for a combined therapy with DN-TNF and Tz to overcome/avoid resistance to therapy. These results can be translated quickly into the clinic.

Citation Format: Schillaci R, Bruni S, De Martino M, Mercogliano MF, Inurrigarro G, Frahm I, Proietti CJ, Elizalde PV. Neutralizing soluble tumor necrosis factor alpha overcomes trastuzumab-resistant breast cancer immune evasion by downregulating mucin 4, improving NK cell function and decreasing myeloid-derived suppressor cells in tumor microenvironment [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 P6-20-14.

MiR-16 mediates trastuzumab and lapatinib response in ErbB-2-positive breast and gastric cancer via its novel targets CCNJ and FUBP1

ErbB-2 amplification/overexpression accounts for an aggressive breast cancer (BC) subtype (ErbB-2-positive). Enhanced ErbB-2 expression was also found in gastric cancer (GC) and has been correlated with poor clinical outcome. The ErbB-2-targeted therapies trastuzumab (TZ), a monoclonal antibody, and lapatinib, a tyrosine kinase inhibitor, have proved highly beneficial. However, resistance to such therapies remains a major clinical challenge. We here revealed a novel mechanism underlying the antiproliferative effects of both agents in ErbB-2-positive BC and GC. TZ and lapatinib ability to block extracellular signal-regulated kinases 1/2 and phosphatidylinositol-3 kinase (PI3K)/AKT in sensitive cells inhibits c-Myc activation, which results in upregulation of miR-16. Forced expression of miR-16 inhibited in vitro proliferation in BC and GC cells, both sensitive and resistant to TZ and lapatinib, as well as in a preclinical BC model resistant to these agents. This reveals miR-16 role as tumor suppressor in ErbB-2-positive BC and GC. Using genome-wide expression studies and miRNA target prediction algorithms, we identified cyclin J and far upstream element-binding protein 1 (FUBP1) as novel miR-16 targets, which mediate miR-16 antiproliferative effects. Supporting the clinical relevance of our results, we found that high levels of miR-16 and low or null FUBP1 expression correlate with TZ response in ErbB-2-positive primary BCs. These findings highlight a potential role of miR-16 and FUBP1 as biomarkers of sensitivity to TZ therapy. Furthermore, we revealed miR-16 as an innovative therapeutic agent for TZ- and lapatinib-resistant ErbB-2-positive BC and GC.

Stat3 regulates ErbB-2 expression and co-opts ErbB-2 nuclear function to induce miR-21 expression, PDCD4 downregulation and breast cancer metastasis

Membrane overexpression of the receptor tyrosine kinase ErbB-2 (MErbB-2) accounts for a clinically aggressive breast cancer (BC) subtype (ErbB-2-positive) with increased incidence of metastases. We and others demonstrated that nuclear ErbB-2 (NErbB-2) also plays a key role in BC and is a poor prognostic factor in ErbB-2-positive tumors. The signal transducer and activator of transcription 3 (Stat3), another player in BC, has been recognized as a downstream mediator of MErbB-2 action in BC metastasis. Here, we revealed an unanticipated novel direction of the ErbB-2 and Stat3 interaction underlying BC metastasis. We found that Stat3 binds to its response elements (GAS) at the ErbB-2 promoter to upregulate ErbB-2 transcription in metastatic, ErbB-2-positive BC. We validated these results in several BC subtypes displaying metastatic and non-metastatic ability, highlighting Stat3 general role as upstream regulator of ErbB-2 expression in BC. Moreover, we showed that Stat3 co-opts NErbB-2 function by recruiting ErbB-2 as its coactivator at the GAS sites in the promoter of microRNA-21 (miR-21), a metastasis-promoting microRNA (miRNA). Using an ErbB-2 nuclear localization domain mutant and a constitutively activated ErbB-2 variant, we found that NErbB-2 role as a Stat3 coactivator and also its direct role as transcription factor upregulate miR-21 in BC. This reveals a novel function of NErbB-2 as a regulator of miRNAs expression. Increased levels of miR-21, in turn, downregulate the expression of the metastasis-suppressor protein programmed cell death 4 (PDCD4), a validated miR-21 target. Using an in vivo model of metastatic ErbB-2-postive BC, in which we silenced Stat3 and reconstituted ErbB-2 or miR-21 expression, we showed that both are downstream mediators of Stat3-driven metastasis. Supporting the clinical relevance of our results, we found an inverse correlation between ErbB-2/Stat3 nuclear co-expression and PDCD4 expression in ErbB-2-positive primary invasive BCs. Our findings identify Stat3 and NErbB-2 as novel therapeutic targets to inhibit ErbB-2-positive BC metastasis.