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.

Stabilization of c-KIT G-Quadruplex DNA Structures by the RNA Polymerase I Inhibitors BMH-21 and BA-41.

The stabilization of G-quadruplex DNA structures by small molecules with affinity to oncogene promoters has emerged as a promising anticancer strategy, due to a potential role in gene expression regulation. We explored the ability of BMH-21 (1) and its analogue BA-41 (2) to bind the G-quadruplex structure present in the c-KIT promoter by biophysical methods and molecular modeling. We provide evidence that both compounds interact with the c-KIT 21-mer sequence. The stable monomeric intramolecular parallel G-quadruplex obtained by the mutation of positions 12 and 21 allowed the precise determination of the binding mode by NMR and molecular dynamics studies. Both compounds form a complex characterized by one ligand molecule positioned over the tetrad at the 3'-end, stabilized by an extensive network of π-π interactions. The binding constants (Kb) obtained with fluorescence are similar for both complexes (around 106 M-1). Compound BA-41 (2) showed significant antiproliferative activity against a human lymphoma cell line, SU-DHL4, known to express substantial levels of c-KIT. However, the partial inhibition of c-KIT expression by Western blot analysis suggested that the interaction of compound 2 with the c-KIT promoter is not the primary event and that multiple effects provide a contribution as determinants of biological activity.

Immunotherapy-based combinations: an update.

PURPOSE OF REVIEW: The advent of immunotherapy significantly improved clinical outcomes in cancer patients, although immune checkpoint blockade (ICB) still lack of efficacy in a consistent proportion of treated patients. The purpose of this article is to review the most innovative and clinically promising ICB-based combinations designed to improve the efficacy of cancer immunotherapy. RECENT FINDINGS: First-line combinatorial treatment with ipilimumab and nivolumab has recently shown to be superior to the standard of care in a subset of metastatic nonsmall cell lung cancer (NSCLC) and renal cell carcinoma (RCC). The combination of programmed cell death protein 1 (PD-1)/PD-L1 blockade with antiangiogenics has demonstrated a consistent clinical efficacy, especially for the combination of bevacizumab and atezolizumab as first-line therapy in metastatic RCC. The sequential combination of definitive chemoradiotherapy followed by durvalumab maintenance in advanced, unresectable NSCLC became the new standard of care, while the addition of pembrolizumab to first-line chemotherapy in metastatic NSCLC significantly improves overall survival. Despite promising results for the combination of ICBs with v-raf murine sarcoma viral oncogene homolog B/MAPK/ERK kinase inhibitors or epidermal growth factor receptor inhibitors, especially in melanoma and NSCLC, safety concerns slowed down the development of such strategies. SUMMARY: Immunotherapy-based combinations are becoming the standard of care for cancer treatment, in particularly for advanced melanoma, NSCLC and RCC.

A phase II multicenter study of the anti-CD19 antibody drug conjugate coltuximab ravtansine (SAR3419) in patients with relapsed or refractory diffuse large B-cell lymphoma previously treated with rituximab-based immunotherapy.

This phase II, single-arm, multicenter study examined the efficacy and safety of coltuximab ravtansine (an anti-CD19 antibody drug conjugate) in 61 patients with histologically documented (de novo or transformed) relapsed or refractory diffuse large B-cell lymphoma who had previously received rituximab-containing immuno-chemotherapy. Patients had received a median of 2.0 (range 0-9) prior treatment regimens for diffuse large B-cell lymphoma and almost half (45.9%) had bulky disease (≥1 lesion >5 cm) at trial entry. Patients received coltuximab ravtansine (55 mg/m2) in 4 weekly and 4 biweekly administrations until disease progression or unacceptable toxicity. Forty-one patients were eligible for inclusion in the per protocol population. Overall response rate (International Working Group criteria) in the per protocol population, the primary end point, was 18/41 [43.9%; 90% confidence interval (CI:) 30.6-57.9%]. Median duration of response, progression-free survival, and overall survival (all treated patients) were 4.7 (range 0.0-8.8) months, 4.4 (90%CI: 3.02-5.78) months, and 9.2 (90%CI: 6.57-12.09) months, respectively. Common non-hematologic adverse events included asthenia/fatigue (30%), nausea (23%), and diarrhea (20%). Grade 3-4 adverse events were reported in 23 patients (38%), the most frequent being hepatotoxicity (3%) and abdominal pain (3%). Eye disorders occurred in 15 patients (25%); all were grade 1-2 and none required a dose modification. Coltuximab ravtansine monotherapy was well tolerated and resulted in moderate clinical responses in pre-treated patients with relapsed/refractory diffuse large B-cell lymphoma. (Registered at: clinicaltrials.gov identifier: 01472887).

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.

HSPH1 inhibition downregulates Bcl-6 and c-Myc and hampers the growth of human aggressive B-cell non-Hodgkin lymphoma.

We have shown that human B-cell non-Hodgkin lymphomas (B-NHLs) express heat shock protein (HSP)H1/105 in function of their aggressiveness. Here, we now clarify its role as a functional B-NHL target by testing the hypothesis that it promotes the stabilization of key lymphoma oncoproteins. HSPH1 silencing in 4 models of aggressive B-NHLs was paralleled by Bcl-6 and c-Myc downregulation. In vitro and in vivo analysis of HSPH1-silenced Namalwa cells showed that this effect was associated with a significant growth delay and the loss of tumorigenicity when 10(4) cells were injected into mice. Interestingly, we found that HSPH1 physically interacts with c-Myc and Bcl-6 in both Namalwa cells and primary aggressive B-NHLs. Accordingly, expression of HSPH1 and either c-Myc or Bcl-6 positively correlated in these diseases. Our study indicates that HSPH1 concurrently favors the expression of 2 key lymphoma oncoproteins, thus confirming its candidacy as a valuable therapeutic target of aggressive B-NHLs.

Improved outcome of patients with relapsed/refractory Hodgkin lymphoma with a new fotemustine-based high-dose chemotherapy regimen.

High-dose chemotherapy (HDT) with autologous stem cell transplantation is the standard of care for relapsed/refractory (RR) Hodgkin lymphoma (HL). Given that HDT may cure a sizeable proportion of patients refractory to first salvage, development of newer conditioning regimens remains a priority. We present the results of a novel HDT regimen in which carmustine was substituted by a third-generation chloroethylnitrosourea, fotemustine, with improved pharmacokinetics and safety (FEAM; fotemustine, etoposide, cytarabine, melphalan) in 122 patients with RR-HL accrued into a prospective registry-based study. Application of FEAM resulted in a 2-year progression-free survival (PFS) of 73·8% [95% confidence interval (CI), 0·64-0·81] with median PFS, overall survival and time to progression yet to be reached. The 2-year risk of progression adjusted for the competitive risk of death was 19·4% (95% CI, 0·12-0·27) for the entire patient population. Most previously established independent risk factors, except for fluorodeoxyglucose ((18) (F) FDG)-uptake, were unable to predict for disease progression and survival after FEAM. Although 32% of patients had (18) (F) FDG-positrin emission tomography-positive lesions before HDT, the 2-year risk of progression adjusted for competitive risk of death was 19·4% (95% CI; 0·12-0·27). No unusual acute toxicities or early/late pulmonary adverse events were registered. FEAM emerges as an ideal HDT regimen for RR-HL patients typically pre-exposed to lung-damaging treatments.

Thrombopoietin receptor agonists for preparing adult patients with immune thrombocytopenia to splenectomy: results of a retrospective, observational GIMEMA study.

In patients with immune thrombocytopenia (ITP) refractory to corticosteroids and intravenous immunoglobulins (IVIG), splenectomy may result at higher risk of peri-operative complications and, for this reason, potentially contraindicated. The thrombopoietin receptor agonists (TPO-RAs) romiplostim and eltrombopag have shown high therapeutic activity in primary ITP, but data of efficacy and safety regarding their use in preparation for splenectomy are missing. Thirty-one adult patients, median age 50 years, with corticosteroids and/or IVIG refractory persistent and chronic ITP who were treated with TPO-RAs (romiplostim= 24; eltrombopag= 7) with the aim to increase platelet count and allow a safer execution of splenectomy were retrospectively evaluated. Twenty-four patients (77%) responded to the use of TPO-RAs with a median platelet count that increased from 11 × 10(9) /L before starting TPO-RAs to 114 × 10(9) /L pre-splenectomy, but a concomitant treatment with corticosteroids and/or IVIG was required in 19 patients. Twenty-nine patients underwent splenectomy while two patients who responded to TPO-RAs subsequently refused surgery. Post-splenectomy complications were characterized by two Grade 3 thrombotic events (1 portal vein thrombosis in the patient with previous history of HCV hepatitis and 1 pulmonary embolism), with a platelet count at the time of thrombosis of 260 and 167 × 10(9) /L, respectively and one Grade 3 infectious event. TPO-RAs may represent a therapeutic option to improve platelet count and reduce the risk of peri-operative complications in ITP candidates to splenectomy. An increased risk of post-splenectomy thromboembolic events cannot be ruled out and thromboprophylaxis with low-molecular weight heparin is generally recommended.

Pleiotropic antitumor effects of the pan-HDAC inhibitor ITF2357 against c-Myc-overexpressing human B-cell non-Hodgkin lymphomas.

Histone deacetylases (HDAC) extensively contribute to the c-Myc oncogenic program, pointing to their inhibition as an effective strategy against c-Myc-overexpressing cancers. We, thus, studied the therapeutic activity of the new-generation pan-HDAC inhibitor ITF2357 (Givinostat®) against c-Myc-overexpressing human B-cell non-Hodgkin lymphomas (B-NHLs). ITF2357 anti-proliferative and pro-apoptotic effects were analyzed in B-NHL cell lines with c-Myc translocations (Namalwa, Raji and DOHH-2), stabilizing mutations (Raji) or post-transcriptional alterations (SU-DHL-4) in relationship to c-Myc modulation. ITF2357 significantly delayed the in vitro growth of all B-NHL cell lines by inducing G1 cell-cycle arrest, eventually followed by cell death. These events correlated with the extent of c-Myc protein, but not mRNA, downregulation, indicating the involvement of post-transcriptional mechanisms. Accordingly, c-Myc-targeting microRNAs let-7a and miR-26a were induced in all treated lymphomas and the cap-dependent translation machinery components 4E-BP1, eIF4E and eIF4G, as well as their upstream regulators, Akt and PIM kinases, were inhibited in function of the cell sensitivity to ITF2357, and, in turn, c-Myc downregulation. In vivo, ITF2357 significantly hampered the growth of Namalwa and Raji xenografts in immunodeficient mice. Noteworthy, its combination with suboptimal cyclophosphamide, achieved complete remissions in most animals and equaled or even exceeded the activity of optimal cyclophosphamide. Collectively, our findings provide the rationale for testing the clinical advantages of adding ITF2357 to current therapies for the still very ominous c-Myc-overexpressing lymphomas. They equally provide the proof-of-concept for its clinical evaluation in rational combination with the promising inhibitors of B-cell receptor and PI3K/Akt/mTOR axis currently in the process of development.

Evaluation of an every-other-day palonosetron schedule to control emesis in multiple-day high-dose chemotherapy.

AIM: Efficacy of intermittent palonosetron dosing in patients undergoing multiple-day, high-dose chemotherapy (HDC) was investigated. PATIENTS & METHODS: Fifty-eight patients received palonosetron (0.25 mg intravenous [iv.]) every other day plus daily dexamethasone (8 mg iv. twice daily) dosing. The primary end point was complete control (CC; no emesis, no rescue anti-emetics, and no more than mild nausea) in the overall acute-period (until 24 h after chemotherapy completion). RESULTS: Acute-period CC occurred in 81% and 50% of patients receiving palonosetron and ondansetron (historical control cohort), respectively. Palonosetron (odds ratio [OR]: 4.37; p = 0.001) and a longer duration of HDC regimen (OR: 3.47; p = 0.011) independently predicted a better anti-emetic outcome. CONCLUSION: Palonosetron every other day plus daily dexamethasone is an effective anti-emetic coverage in patients undergoing HDC.

Immunological characterization of a long-lasting response in a patient with metastatic triple-negative breast cancer treated with PD-1 and LAG-3 blockade.

In patients with advanced triple-negative breast cancer (TNBC), translational research efforts are needed to improve the clinical efficacy of immunotherapy with checkpoint inhibitors. Here, we report on the immunological characterization of an exceptional, long-lasting, tumor complete response in a patient with metastatic TNBC treated with dual PD-1 and LAG-3 blockade within the phase I/II study CLAG525X2101C (NCT02460224) The pre-treatment tumor biopsy revealed the presence of a CD3+ and CD8+ cell infiltrate, with few PD1+ cells, rare CD4+ cells, and an absence of both NK cells and LAG3 expression. Conversely, tumor cells exhibited positive staining for the three primary LAG-3 ligands (HLA-DR, FGL-1, and galectin-3), while being negative for PD-L1. In peripheral blood, baseline expression of LAG-3 and PD-1 was observed in circulating immune cells. Following treatment initiation, there was a rapid increase in proliferating granzyme-B+ NK and T cells, including CD4+ T cells, alongside a reduction in myeloid-derived suppressor cells. The role of LAG-3 expression on circulating NK cells, as well as the expression of LAG-3 ligands on tumor cells and the early modulation of circulating cytotoxic CD4+ T cells warrant further investigation as exploitable predictive biomarkers for dual PD-1 and LAG-3 blockade.Trial registration: NCT02460224. Registered 02/06/2015.

Biomarker and pharmacodynamic activity of the transforming growth factor-beta (TGFß) inhibitor SAR439459 as monotherapy and in combination with cemiplimab in a phase I clinical study in patients with advanced solid tumors.

SAR439459, a 'second-generation' human anti-transforming growth factor-beta (TGFß) monoclonal antibody, inhibits all TGFß isoforms and improves the antitumor activity of anti-programmed cell death protein-1 therapeutics. This study reports the pharmacodynamics (PD) and biomarker results from phase I/Ib first-in-human study of SAR439459 ± cemiplimab in patients with advanced solid tumors (NCT03192345). In dose-escalation phase (Part 1), SAR439459 was administered intravenously at increasing doses either every 2 weeks (Q2W) or every 3 weeks (Q3W) with cemiplimab IV at 3 mg/kg Q2W or 350 mg Q3W, respectively, in patients with advanced solid tumors. In dose-expansion phase (Part 2), patients with melanoma received SAR439459 IV Q3W at preliminary recommended phase II dose (pRP2D) of 22.5/7.5 mg/kg or at 22.5 mg/kg with cemiplimab 350 mg IV Q3W. Tumor biopsy and peripheral blood samples were collected for exploratory biomarker analyses to assess target engagement and PD, and results were correlated with patients' clinical parameters. SAR439459 ± cemiplimab showed decreased plasma and tissue TGFß, downregulation of TGFß-pathway activation signature, modulation of peripheral natural killer (NK) and T cell expansion, proliferation, and increased secretion of CXCL10. Conversion of tumor tissue samples from 'immune-excluded' to 'immune-infiltrated' phenotype in a representative patient with melanoma SAR439459 22.5 mg/kg with cemiplimab was observed. In paired tumor and plasma, active and total TGFß1 was more consistently elevated followed by TGFß2, whereas TGFß3 was only measurable (lower limit of quantitation ≥2.68 pg/mg) in tumors. SAR439459 ± cemiplimab showed expected peripheral PD effects and TGFß alteration. However, further studies are needed to identify biomarkers of response.

Serological identification of HSP105 as a novel non-Hodgkin lymphoma therapeutic target.

We reported that the clinical efficacy of dendritic cell-based vaccination is strongly associated with immunologic responses in relapsed B-cell non-Hodgkin lymphoma (B-NHL) patients. We have now investigated whether postvaccination antibodies from responders recognize novel shared NHL-restricted antigens. Immunohistochemistry and flow cytometry showed that they cross-react with allogeneic B-NHLs at significantly higher levels than their matched prevaccination samples or nonresponders' antibodies. Western blot analysis of DOHH-2 lymphoma proteome revealed a sharp band migrating at approximately 100 to 110 kDa only with postvaccine repertoires from responders. Mass spectrometry identified heat shock protein-105 (HSP105) in that molecular weight interval. Flow cytometry and immunohistochemistry disclosed HSP105 on the cell membrane and in the cytoplasm of B-NHL cell lines and 97 diagnostic specimens. A direct correlation between HSP105 expression and lymphoma aggressiveness was also apparent. Treatment of aggressive human B-NHL cell lines with an anti-HSP105 antibody had no direct effects on cell cycle or apoptosis but significantly reduced the tumor burden in xenotransplanted immunodeficient mice. In vivo antilymphoma activity of HSP105 engagement was associated with a significant local increase of Granzyme B(+) killer cells that very likely contributed to the tumor-restricted necrosis. Our study adds HSP105 to the list of nononcogenes that can be exploited as antilymphoma targets.

Phase II study of sorafenib in patients with relapsed or refractory lymphoma.

The safety and activity of the multikinase inhibitor sorafenib were investigated in patients with relapsed or refractory lymphoproliferative disorders who received sorafenib (400 mg) twice daily until disease progression or appearance of significant clinical toxicity. The primary endpoint was overall response rate (ORR). Biomarkers of sorafenib activity were analysed at baseline and during treatment. Thirty patients (median age, 61 years; range, 18-74) received a median of 4 months of therapy. Grade 3-4 toxicities included hand/foot skin reactions (20%), infections (12%), neutropenia (20%) and thrombocytopenia (14%). Two patients achieved complete remission (CR), and two achieved partial remission (PR) for an ORR of 13%. Stable disease (SD) and progressive disease (PD) was observed in 15 (50%) and 11 patients (37%), respectively. The median overall survival (OS) for all patients was 16 months. For patients who achieved CR, PR and SD, the median time to progression and OS was 5 and 24 months, respectively. Compared with patients with PD, responsive patients had significantly higher baseline levels of extracellular signal-regulated kinase phosphorylation and autophagy and presented a significant reduction of these parameters after 1 month of therapy. Sorafenib was well tolerated and had a clinical activity that warrants development of combination regimens.

Human CD34+ cells engineered to express membrane-bound tumor necrosis factor-related apoptosis-inducing ligand target both tumor cells and tumor vasculature.

Adenovirus-transduced CD34+ cells expressing membrane-bound tumor necrosis factor-related apoptosis-inducing ligand (CD34-TRAIL+ cells) exert potent antitumor activity. To further investigate the mechanism(s) of action of CD34-TRAIL+ cells, we analyzed their homing properties as well as antitumor and antivascular effects using a subcutaneous myeloma model in immunodeficient mice. After intravenous injection, transduced cells homed in the tumor peaking at 48 hours when 188 plus or minus 25 CD45+ cells per 10(5) tumor cells were detected. Inhibition experiments showed that tumor homing of CD34-TRAIL+ cells was largely mediated by vascular cell adhesion molecule-1 and stromal cell-derived factor-1. Both CD34-TRAIL+ cells and soluble (s)TRAIL significantly reduced tumor volume by 40% and 29%, respectively. Computer-aided analysis of TdT-mediated dUTP nick end-labeling-stained tumor sections demonstrated significantly greater effectiveness for CD34-TRAIL+ cells in increasing tumor cell apoptosis and necrosis over sTRAIL. Proteome array analysis indicated that CD34-TRAIL+ cells and sTRAIL activate similar apoptotic machinery. In vivo staining of tumor vasculature with sulfosuccinimidyl-6-(biotinamido) hexanoate-biotin revealed that CD34-TRAIL+ cells but not sTRAIL significantly damaged tumor vasculature, as shown by TdT-mediated dUTP nick end-labeling+ endothelial cells, appearance of hemorrhagic areas, and marked reduction of endothelial area. These results demonstrate that tumor homing of CD34-TRAIL+ cells induces early vascular disruption, resulting in hemorrhagic necrosis and tumor destruction.

Targeted protein degraders from an oncologist point of view: The Holy Grail of cancer therapy?

In the era of precision medicine, monoclonal antibodies and small molecule inhibitors are the mainstays of the biological therapy in patients with solid tumors. However, resistance to treatment and the "undruggability" of certain key oncogenic proteins emerged as major limitations and jeopardize the clinical benefit of modern therapeutic approaches. Targeted protein degraders are novel molecules entering the early phase of clinical development that exploit the intracellular ubiquitine-proteasome system to promote a specific degradation of target proteins. Since the peculiar mechanism of action, targeted protein degraders have the potential to limit and overcome resistance to treatment and to allow a full actionability of certain cancer drivers that are actually elusive targets. Here, we discuss the state-of-the-art and the open issues in the development of these emerging biological agents from a clinical perspective and with a focus on solid tumors.

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.