A drug-like molecule engages nuclear hormone receptor DAF-12/FXR to regulate mitophagy and extend lifespan

Autophagy-lysosomal function is crucial for maintaining healthy lifespan and preventing age-related diseases. The transcription factor TFEB plays a key role in regulating this pathway. Decreased TFEB expression is associated with various age-related disorders, making it a promising therapeutic target. In this study, we screened a natural product library and discovered mitophagy-inducing coumarin (MIC), a benzocoumarin compound that enhances TFEB expression and lysosomal function. MIC robustly increases the lifespan of Caenorhabditis elegans in an HLH-30/TFEB-dependent and mitophagy-dependent manner involving DCT-1/BNIP3 while also preventing mitochondrial dysfunction in mammalian cells. Mechanistically, MIC acts by inhibiting ligand-induced activation of the nuclear hormone receptor DAF-12/FXR, which, in turn, induces mitophagy and extends lifespan. In conclusion, our study uncovers MIC as a promising drug-like molecule that enhances mitochondrial function and extends lifespan by targeting DAF-12/FXR. Furthermore, we discovered DAF-12/FXR as a previously unknown upstream regulator of HLH-30/TFEB and mitophagy.

Improving radiotherapy in immunosuppressive microenvironments by targeting complement receptor C5aR1

An immunosuppressive microenvironment causes poor tumor T cell infiltration and is associated with reduced patient overall survival in colorectal cancer. How to improve treatment responses in these tumors is still a challenge. Using an integrated screening approach to identify cancer-specific vulnerabilities, we identified complement receptor C5aR1 as a druggable target, which when inhibited improved radiotherapy, even in tumors displaying immunosuppressive features and poor CD8+ T cell infiltration. While C5aR1 is well-known for its role in the immune compartment, we found that C5aR1 is also robustly expressed on malignant epithelial cells, highlighting potential tumor cell-specific functions. C5aR1 targeting resulted in increased NF-κB-dependent apoptosis specifically in tumors and not normal tissues, indicating that, in malignant cells, C5aR1 primarily regulated cell fate. Collectively, these data revealed that increased complement gene expression is part of the stress response mounted by irradiated tumors and that targeting C5aR1 could improve radiotherapy, even in tumors displaying immunosuppressive features.

Galectin-1 Mediates Chronic STING Activation in Tumors to Promote Metastasis through MDSC Recruitment

The immune system plays a crucial role in the regulation of metastasis. Tumor cells systemically change immune functions to facilitate metastatic progression. Through this study, we deciphered how tumoral galectin-1 (Gal1) expression shapes the systemic immune environment to promote metastasis in head and neck cancer (HNC). In multiple preclinical models of HNC and lung cancer in immunogenic mice, Gal1 fostered the establishment of a premetastatic niche through polymorphonuclear myeloid-derived suppressor cells (PMN-MDSC), which altered the local microenvironment to support metastatic spread. RNA sequencing of MDSCs from premetastatic lungs in these models demonstrated the role of PMN-MDSCs in collagen and extracellular matrix remodeling in the premetastatic compartment. Gal1 promoted MDSC accumulation in the premetastatic niche through the NF-κB signaling axis, triggering enhanced CXCL2-mediated MDSC migration. Mechanistically, Gal1 sustained NF-κB activation in tumor cells by enhancing stimulator of interferon gene (STING) protein stability, leading to prolonged inflammation-driven MDSC expansion. These findings suggest an unexpected protumoral role of STING activation in metastatic progression and establish Gal1 as an endogenous-positive regulator of STING in advanced-stage cancers.

SIGNIFICANCE

Galectin-1 increases STING stability in cancer cells that activates NF-κB signaling and CXCL2 expression to promote MDSC trafficking, which stimulates the generation of a premetastatic niche and facilitates metastatic progression.

Clinical and research updates on the VISTA immune checkpoint: immuno-oncology themes and highlights

Immune checkpoints limit the activation of the immune system and serve an important homeostatic function but can also restrict immune responses against tumors. Inhibition of specific immune checkpoint proteins such as the B7:CD28 family members programmed cell death protein-1 (PD-1) and cytotoxic T-lymphocyte antigen-4 (CTLA-4) has transformed the treatment of various cancers by promoting the anti-tumor activation of immune cells. In contrast to these effects, the V-domain immunoglobulin suppressor of T-cell activation (VISTA) regulates the steady state of the resting immune system and promotes homeostasis by mechanisms distinct from PD-1 and CTLA-4. The effects of VISTA blockade have been shown to include a decrease in myeloid suppression coupled with proinflammatory changes by mechanisms that are separate and distinct from other immune checkpoint proteins; in some preclinical studies these immune effects appear synergistic. Given the potential benefits of VISTA blockade in the context of cancer therapy, the second Annual VISTA Symposium was convened virtually on September 23, 2022, to review new research from investigators and immuno-oncology experts. Discussions in the meeting extended the knowledge of VISTA biology and the effects of VISTA inhibition, particularly on cells of the myeloid lineage and resting T cells, as three candidate anti-VISTA antibodies are in, or nearing, clinical development.

Decursin inhibits EGFR-ERK1/2 signaling axis in advanced human prostate carcinoma cells

We have shown that decursin, a coumarin compound, induces cell cycle arrest and apoptosis in human prostate cancer cells (PCa); however, its molecular mechanisms are largely unexplored. We studied the mechanisms associated with its anticancer activity in advanced human prostate carcinoma cells. We found that decursin inhibited epidermal growth factor receptor (EGFR) signaling by inhibiting its activating phosphorylation at tyrosine 1068 residue in DU145 and 22Rv1 cells. This inhibition of EGFR was associated with the downregulation of ERK1/2 phosphorylation. Both EGFR and ERK1/2 are known to be deregulated/activated in many human malignancies. Consistent with our earlier study, decursin (25-100 µM) treatment for 24-72 h inhibited DU145 cell proliferation by 49%-87% (p < 0.001) which was associated with strong G1 phase arrest and cell death. It also decreased (p < 0.001) the number of surviving colonies. Decursin moderately increased the expression of Rb-related proteins p107 and p130 but decreased the levels of E2F family transcription factors including E2F-3, E2F-4 and E2F-5. Further, decursin strongly inhibited the growth of androgen-dependent prostate carcinoma 22Rv1 cells from 61% to 79% (p < 0.001) and arrested these cells at G1 phase via induction of cyclin-dependent kinase inhibitor p27/Kip1 and downregulation of CDK2 and CDK4 protein expression. Additionally, EGFR inhibitor erlotinib- and EGF ligand-modulated EGFR activation validated EGFR signaling as a target of decursin-mediated cell growth inhibition and cytotoxicity. Decursin decreased EGF ligand-induced phosphorylation of EGFR (Y-1068) as well as activation of its downstream mediator, ERK1/2. Furthermore, inhibitory targeting of EGFR-ERK1/2 axis by combinatorial treatment of decursin and erlotinib further sensitized DU145 cells for the decursin-induced growth inhibition and cell death. Overall, these findings strongly suggest that anticancer efficacy of decursin against human PCa involves inhibitory targeting of EGFR-ERK1/2 signaling axis, a pathway constitutively active in advanced PCa.

Abstract 66: Galectin-1 mediated chronic tumoral-STING activation promotes metastasisthrough MDSC recruitment

Tumor cells alter the immune microenvironment to facilitate metastatic progression. Galectin-1 (Gal1) is a known modulator of tumor growth and progression in multiple cancer types including head and neck cancer (HNC). However, its contribution to the regulation of metastasis is poorly understood. Through this study we report a previously unknown role for Gal1 in modulating the STING pathway to regulate metastasis. The cGAS-STING pathway has paradoxical roles in cancer depending on the kinetics and strength of its induction, with chronic STING activation being linked to immune suppression and tumor progression while acute activation being associated with immune activation. However, little is known about the pathways that promote chronic STING activation. Using HNC and lung cancer models, we show that Gal-1 enhances STING protein stability, leading to sustained NF-κΒ activation and heightened chemokine-driven recruitment of myeloid derived suppressor cells (MDSCs). We show that Gal1-STING connection fosters the establishment of pre-metastatic niche through polymorphonuclear MDSCs (PMN-MDSCs), which modify the local lung microenvironment to support metastatic spread. Notably, RNA sequencing of MDSCs isolated from pre-metastatic lungs indicate the role of PMN-MDSCs in remodeling collagen and the extracellular matrix in the pre-metastatic compartment. Our findings reveal an unexpected role of STING activation in metastatic progression of HNC and lung cancer models and establish Gal1 as an endogenous positive regulator of STING.

Citation Format: Dhanya K. Nambiar, Vignesh Vignesh Viswanathan, Hongbin Cao, Weiruo Zhang, Li Guan, Manish Chamoli, Brittany Holmes, Christina Kong, Rachel Hildebrand, Amanda Koong, Rie Eyben, Amato Giaccia, Lingyin Li, Edgar Engleman, Quynh Thu Le. Galectin-1 mediated chronic tumoral-STING activation promotes metastasisthrough MDSC recruitment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 66.

NFE2L2 Mutations Enhance Radioresistance in Head and Neck Cancer by Modulating Intratumoral Myeloid Cells

Radiotherapy (RT) is one of the primary treatments of head and neck squamous cell carcinoma (HNSCC), which has a high-risk of locoregional failure (LRF). Presently, there is no reliable predictive biomarker of radioresistance in HNSCC. Here, we found that mutations in NFE2L2, which encodes Nrf2, are associated with a significantly higher rate of LRF in patients with oral cavity cancer treated with surgery and adjuvant (chemo)radiotherapy but not in those treated with surgery alone. Somatic mutation of NFE2L2 led to Nrf2 activation and radioresistance in HNSCC cells. Tumors harboring mutant Nrf2E79Q were substantially more radioresistant than tumors with wild-type Nrf2 in immunocompetent mice, whereas the difference was diminished in immunocompromised mice. Nrf2E79Q enhanced radioresistance through increased recruitment of intratumoral polymorphonuclear myeloid-derived suppressor cells (PMN-MDSC) and reduction of M1-polarized macrophages. Treatment with the glutaminase inhibitor CB-839 overcame the radioresistance induced by Nrf2E79Q or Nrf2E79K. RT increased expression of PMN-MDSC-attracting chemokines, including CXCL1, CXLC3, and CSF3, in Nrf2E79Q-expressing tumors via the TLR4, which could be reversed by CB-839. This study provides insights into the impact of NFE2L2 mutations on radioresistance and suggests that CB-839 can increase radiosensitivity by switching intratumoral myeloid cells to an antitumor phenotype, supporting clinical testing of CB-839 with RT in HNSCC with NFE2L2 mutations.

SIGNIFICANCE

NFE2L2 mutations are predictive biomarkers of radioresistance in head and neck cancer and confer sensitivity to glutaminase inhibitors to overcome radioresistance.

The Combination of Radiotherapy and Complement C3a Inhibition Potentiates Natural Killer cell Functions Against Pancreatic Cancer

Pancreatic cancer is one of the deadliest cancers, against which current immunotherapy strategies are not effective. Herein, we analyzed the immune cell composition of the tumor microenvironment of pancreatic cancer samples in The Cancer Genome Atlas and found that the presence of intratumoral NK cells correlates with survival. Subsequent analysis also indicated that NK cell exclusion from the microenvironment is found in a high percentage of clinical pancreatic cancers and in preclinical models of pancreatic cancer. Mechanistically, NK cell exclusion is regulated in part by complement C3a and its receptor signaling. Inhibition of the C3a receptor enhances NK cell infiltration in syngeneic mouse models of pancreatic cancer resulting in tumor growth delay. However, tumor growth inhibition mediated by NK cells is not sufficient alone for complete tumor regression, but is potentiated when combined with radiation therapy. Our findings indicate that although C3a inhibition is a promising approach to enhance NK cell-based immunotherapy against pancreatic cancer, its combination with radiation therapy hold greater therapeutic benefit.

Abstract PO-048: VISTA immune-checkpoint blunts radiotherapy induced anti-tumor immune response

Radiotherapy (RT) is the primary treatment of many solid neoplasms including head and neck cancer (HNC). Itis well accepted that the tumoricidal effects of RT can be significantly influenced by the immune system. Induction of cell death by radiation can elicit an anti-tumor immune response; however, it could also promote pathways of immunosuppression, which in turn can stimulate local tumor recurrence and/or distant metastases. A mechanism by which RT or chemoradiation (CRT) contributes to immunosuppression is by expansion of myeloid derived suppressive cells (MDSCs). MDSCs are a heterogeneous population of immature myeloid cells, which undergo significant expansion during cancer development and progression. Although MDSCs have been linked to inferior prognosis and treatment failure, the mechanisms by which they contribute to treatment RT failure are not well understood. Through this study we investigated the role of VISTA (V-domain Ig Suppressor of T cell Activation) immune-checkpoint on MDSCs in regulating RT response in vivo. Using syngeneic mouse models of HNC (MOC2 [HPV-] & MEERL [HPV+]), we show that both single fraction/fractionated irradiation regimens significantly increase polymorphonuclear (PMN)-MDSCs in both the tumor and the blood post-RT. We see a similar increase in PMN-MDSCs in HNC patient blood samples (12/16) at mid treatment time point (3-4 weeks after starting RT). Further analyses of immune cells reveal a significant induction of the inhibitory immune-checkpoint VISTA on PMN-MDSCs post-RT. VISTA is a multifaceted negative checkpoint protein that is expressed on most hematopoietic cells, especially on myeloid lineage. VISTA is known to contribute to the overall T cell-suppressive function. We find that irradiation of bone marrow derived-MDSCs or patient PBMC derived PMN-MDSCs leads to upregulation of VISTA surface expression as early as 24 hours after RT. Additionally, the VISTAhi MDSCs have significantly elevated levels of the immunosuppressive cytokine IL-10. We then seek to study the impact of inhibiting VISTA on RT induced immune response and tumor control in a HNC model. The combination of anti-VISTA antibody and fractionated RT (3Gy X 5) leads to a significant decrease in tumor volume compared to either RT alone or anti-VISTA antibody alone. Therapeutic blocking of VISTA checkpoint along with radiation also lead to a reduction in metastatic seeding in the lung in these mice compared to RT alone group. These findings are associated with a decrease of PMN-MDSCs in both tumor and the lungs and an increase in CD4+ T cells and dendritic cells in the tumor of the anti-VISTA antibody + RT group compared to RT alone group. These results underline the role of VISTA in compromising the anti-tumor effects of RT and suggest that targeting VISTA may enhance RT efficacy in HNC patients.

Citation Format: Dhanya K. Nambiar, Nishant Mehta, Sainiteesh Maddineni, Hongbin Cao, Vignesh Viswanathan, Tia Cheunkarndee, Jennifer R. Cochran, Quynh Thu Le. VISTA immune-checkpoint blunts radiotherapy induced anti-tumor immune response [abstract]. In: Proceedings of the AACR Virtual Special Conference on Radiation Science and Medicine; 2021 Mar 2-3. Philadelphia (PA): AACR; Clin Cancer Res 2021;27(8_Suppl):Abstract nr PO-048.

Y box binding protein 1 inhibition as a targeted therapy for ovarian cancer

Y box binding protein 1 (YB-1) is a multifunctional protein associated with tumor progression and the emergence of treatment resistance (TR). Here, we report an azopodophyllotoxin small molecule, SU056, that potently inhibits tumor growth and progression via YB-1 inhibition. This YB-1 inhibitor inhibits cell proliferation, resistance to apoptosis in ovarian cancer (OC) cells, and arrests in the G1 phase. Inhibitor treatment leads to enrichment of proteins associated with apoptosis and RNA degradation pathways while downregulating spliceosome pathway. In vivo, SU056 independently restrains OC progression and exerts a synergistic effect with paclitaxel to further reduce disease progression with no observable liver toxicity. Moreover, in vitro mechanistic studies showed delayed disease progression via inhibition of drug efflux and multidrug resistance 1, and significantly lower neurotoxicity as compared with etoposide. These data suggest that YB-1 inhibition may be an effective strategy to reduce OC progression, antagonize TR, and decrease patient mortality.

Novel Aza-podophyllotoxin derivative induces oxidative phosphorylation and cell death via AMPK activation in triple-negative breast cancer

BACKGROUND

To circumvent Warburg effect, several clinical trials for different cancers are utilising a combinatorial approach using metabolic reprogramming and chemotherapeutic agents including metformin. The majority of these metabolic interventions work via indirectly activating AMP-activated protein kinase (AMPK) to alter cellular metabolism in favour of oxidative phosphorylation over aerobic glycolysis. The effect of these drugs is dependent on glycaemic and insulin conditions.  Therefore, development of small molecules, which can activate AMPK, irrespective of the energy state, may be a better approach for triple-negative breast cancer (TNBC) treatment.

METHODS

Therapeutic effect of SU212 on TNBC cells was examined using in vitro and in vivo models.

RESULTS

We developed and characterised the efficacy of novel AMPK activator (SU212) that selectively induces oxidative phosphorylation and decreases glycolysis in TNBC cells, while not affecting these pathways in normal cells.   SU212 accomplished this metabolic reprogramming by activating AMPK independent of energy stress and irrespective of the glycaemic/insulin state. This leads to mitotic phase arrest and apoptosis in TNBC cells. In vivo, SU212 inhibits tumour growth, cancer progression and metastasis.

CONCLUSIONS

SU212 directly activates AMPK in TNBC cells, but does not hamper glucose metabolism in normal cells. Our study provides compelling preclinical data for further development of SU212 for the treatment of TNBC.

The role of Glial cell derived neurotrophic factor in head and neck cancer

Glial cell-derived neurotrophic factor (GDNF) is reported to promote the survival of neurons and salivary gland regeneration after radiation damage. This study investigated the effect of GDNF on cell migration, growth, and response to radiation in preclinical models of head and neck squamous cell carcinoma (HNSCC) and correlated GDNF expression to treatment outcomes in HNSCC patients. Our ultimate goal is to determine whether systemic administration of GDNF at high dose is safe for the management of hyposalivation or xerostomia in HNSCC patients. Three HPV-positive and three HPV-negative cell lines were examined for cell migration, growth, and clonogenic survival in vitro and tumor growth assay in vivo. Immunohistochemical staining of GDNF, its receptors GFRα1 and its co-receptor RET was performed on two independent HNSCC tissue microarrays (TMA) and correlated to treatment outcomes. Results showed that GDNF only enhanced cell migration in two HPV-positive cells at supra-physiologic doses, but not in HPV-negative cells. GDNF did not increase cell survival in the tested cell lines post-irradiation. Likewise, GDNF treatment affected neither tumor growth in vitro nor response to radiation in xenografts in two HPV-positive and two HPV-negative HNSCC models. High stromal expression of GDNF protein was associated with worse overall survival in HPV-negative HNSCC on multivariate analysis in a combined cohort of patients from Stanford University (n = 82) and Washington University (n = 189); however, the association between GDNF gene expression and worse survival was not confirmed in a separate group of HPV-negative HNSCC patients identified from the Cancer Genome Atlas (TCGA) database. Based on these data, we do not believe that GNDF is a safe systemic treatment to prevent or treat xerostomia in HNSCC and a local delivery approach such as intraglandular injection needs to be explored.

Galectin-1-driven T cell exclusion in the tumor endothelium promotes immunotherapy resistance

Immune checkpoint inhibitors (ICIs), although promising, have variable benefit in head and neck cancer (HNC). We noted that tumor galectin-1 (Gal1) levels were inversely correlated with treatment response and survival in patients with HNC who were treated with ICIs. Using multiple HNC mouse models, we show that tumor-secreted Gal1 mediates immune evasion by preventing T cell migration into the tumor. Mechanistically, Gal1 reprograms the tumor endothelium to upregulate cell-surface programmed death ligand 1 (PD-L1) and galectin-9. Using genetic and pharmacological approaches, we show that Gal1 blockade increases intratumoral T cell infiltration, leading to a better response to anti-PD1 therapy with or without radiotherapy. Our study reveals the function of Gal1 in transforming the tumor endothelium into an immune-suppressive barrier and that its inhibition synergizes with ICIs.

The Immune Subtypes and Landscape of Squamous Cell Carcinoma

PURPOSE

To identify immune subtypes and investigate the immune landscape of squamous cell carcinomas (SCC), which share common etiology and histologic features.

EXPERIMENTAL DESIGN

Based on the immune gene expression profiles of 1,368 patients with SCC in the Cancer Genome Atlas (TCGA), we used consensus clustering to identify robust clusters of patients and assessed their reproducibility in an independent pan-SCC cohort of 938 patients. We further applied graph structure learning-based dimensionality reduction to the immune profiles to visualize the distribution of individual patients.

RESULTS

We identified and independently validated six reproducible immune subtypes associated with distinct molecular characteristics and clinical outcomes. An immune-cold subtype had the least amount of lymphocyte infiltration and a high level of aneuploidy, and these patients had the worst prognosis. By contrast, an immune-hot subtype demonstrated the highest infiltration of CD8⁺ T cells, activated NK cells, and elevated IFNγ response. Accordingly, these patients had the best prognosis. A third subtype was dominated by M2-polarized macrophages with potent immune-suppressive factors such as TGFβ signaling and reactive stroma, and these patients had relatively inferior prognosis. Other subtypes showed more diverse immunologic features with intermediate prognoses. Finally, our analysis revealed a complex immune landscape consisting of both discrete clusters and continuous spectrum.

CONCLUSIONS

This study provides a conceptual framework to understand the tumor immune microenvironment of SCCs. Future work is needed to evaluate its relevance in the design of combination treatment strategies and guiding optimal selection of patients for immunotherapy.

Abstract 4068: Galectin-1 intensifies immunosuppression in head and neck cancer by boosting myeloid-derived suppressive cell (MDSC) expansion

Head and neck squamous cell carcinoma (HNSCC), with more than 450,000 newly diagnosed cases annually, is the 6th most common cancer worldwide. Recent literature shows that tumor induced suppression of the host immune system is critical to HNSCC progression and metastases. Tumor secreted factors directly influence the expansion of myeloid-derived suppressor cells (MDSCs), which are considered important contributors for tumor to escape from immune surveillance. The presence of expanded MDSCs peripherally and within the tumor microenvironment is associated with metastasis and recurrence after definitive treatment in HNSCC patients. In this study, we evaluated at the role of tumor secreted Galectin-1 in recruitment of MDSCs in HNSCC. We utilized HPV-negative as well as HPV-positive HNSCC models to test the effect of Galectin-1 knockout (KO) in the tumor microenvironment. CRISPR/Cas9 knock out Galectin-1 in MOC2 and MEERL models resulted in a ~50% reduction in the tumor growth. We further analyzed the tumor microenvironment of these tumors for MDSC recruitment. Both MOC2 and MEERL tumors showed highly inflammatory phenotype, with significant presence of MDSCs (&gt;70% of CD45+ cells were of myeloid origin). Knocking out Galectin-1 led to a significant decrease in CD11b+Gr1+ MDSCs in both MOC2 and MEERL tumors. We also observed high level of MDSCs in both the spleen and the peripheral blood of mice bearing Galectin-1 wildtype (WT) tumors in both models. In contrast, knocking out Galectin-1 from the tumor reduced systemic MDSCs levels. To investigate how Galectin-1 modulates MDSC levels, we compared the secreted cytokine profiles between MOC2 WT and Galectin-1 KO tumors. Galectin-1 null cells secreted significantly lower levels of monocyte and macrophage recruiting chemokines: CCL5, CXCL1, and G-CSF. Analysis of the gene expression signatures of MOC-2 WT and KO tumor cells revealed critical signaling pathways differences, including down-regulation of PI3K-AKT pathway in KO-tumors. In conclusion, the present study reveals that tumor derived Galectin-1 can stimulate the recruitment of MDSCs, thereby potentiating an inflammatory tumor microenvironment which supports HNSCC progression. (Acknowledgements: BMS for Anti-Gal1 Abs. Dr R. Uppaluri, for MOC-2 oral cancer cells, Dr. W. Spanos for MEERL cells)

Citation Format: Dhanya K. Nambiar, Todd A. Aguilera, Joshua Daniel Bloomstein, Dadi Jiang, Hongbin Cao, Albert Koong, Quynh Thu Le. Galectin-1 intensifies immunosuppression in head and neck cancer by boosting myeloid-derived suppressive cell (MDSC) expansion [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4068.

Abstract LB-180: Targeting galectin-1 in combination with radiation and immune checkpoint therapy in head and neck cancers

Head and neck cancers (HNC) development shows significant changes in the immune profile, with lower systemic lymphocyte counts and reduced tumor-infiltrating lymphocytes, which inversely correlate with survival. Galectin-1 (Gal-1) is secreted at high level by cancer cells, including HNC, and contributes to tumor-immune escape and disease progression. Previously, we have shown that both hypoxia and radiotherapy (RT) can stimulate Gal-1 secretion. Immune checkpoint therapies, specifically targeting the PD1 pathway, allows T cells to be effective in shrinking tumors and lengthen survival in patients with metastatic HNC. However, these therapies work only in a small number of patients with tumors showing significant T cell infiltration. Targeting Gal-1 in HNC therefore, could be a useful therapeutic approach, as it may synergize with radiation and immunotherapy. Using the CRISPR/Cas9 deletion approach, we developed an orthotopic model of HNC with/without Gal-1 expression. We found that in both subcutaneous and orthotopic model of oral cancer, Gal-1 KO (knock-out) tumors showed marked decrease in tumor growth and nodal metastases. These differences were attributed to enhanced infiltration of CD4+ and CD8+ T cells, in the absence of Gal-1. Using a series of transendothelial migration assays in vitro and tracking adoptively transferred T cells in vivo, we show that presence of Gal-1 in the tumor microenvironment strongly suppresses T cell infiltration into tumors. We found that Gal-1 secretion led to a systemic immune suppressive response not just intra-tumorally but also in the circulating blood compartment, resulting in reduction of both CD4+ and CD8+ T cells. Concurrently, we detected higher levels of IFN-γ secretion in mice with Gal-1 KO tumors. We also observed a higher expression of PD-L1 and Gal-9 on the endothelium of WT-Gal1 compared to Gal-1 KO tumors, leading to T cell exhaustion and ineffective systemic immune response. In addition, there was noteworthy increase in the PD1+ and Tim3+ T cells in Gal-1 WT tumors compared to Gal-1 KO tumors, suggesting a role of Gal-1 in T cell anergy. Finally, we show that knocking out Gal-1 either genetically or by a blocking antibody, we could convert an anti-PD1 Ab non-responsive tumor into a responsive tumor with a significant decrease in tumor burden. In summary, our study shows Gal-1 in the tumor microenvironment could hamper immune response by impeding transendothelial T cell migration into the tumor, blocking pro-inflammatory cytokine secretions and up-regulating inhibitory immune checkpoints ligands in both tumor endothelial and T cells. Our data suggests that Gal-1 may mediate poor-response or resistance to anti-PD1 therapy and combinatorial approaches of galectin-1 inhibition with PD-1 checkpoint inhibitors may enhance therapeutic efficacy in HNC. (Acknowledgements: BMS for Anti-PD1 and Anti-Gal1 Abs. Dr R. Uppaluri, for MOC-2 oral cancer cells).

Citation Format: Dhanya K. Nambiar, Todd Aguilera, Joshua Daniel Bloomstein, Hongbin Cao, Albert Koong, Quynh Thu Le. Targeting galectin-1 in combination with radiation and immune checkpoint therapy in head and neck cancers [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 LB-180. doi:10.1158/1538-7445.AM2017-LB-180

Chemical Space Mimicry for Drug Discovery

We describe a new library generation method, Machine-based Identification of Molecules Inside Characterized Space (MIMICS), that generates sets of molecules inspired by a text-based input. MIMICS-generated libraries were found to preserve distributions of properties while simultaneously increasing structural diversity. Newly identified MIMICS-generated compounds were found to be bioactive as inhibitors of specific components of the unfolded protein response (UPR) and the VEGFR2 pathway in cell-based assays, thus confirming the applicability of this methodology toward drug design applications. Wider application of MIMICS could facilitate the efficient utilization of chemical space.

Silibinin inhibits hypoxia-induced HIF-1α-mediated signaling, angiogenesis and lipogenesis in prostate cancer cells: In vitro evidence and in vivo functional imaging and metabolomics

Hypoxia is associated with aggressive phenotype and poor prognosis in prostate cancer (PCa) patients suggesting that PCa growth and progression could be controlled via targeting hypoxia-induced signaling and biological effects. Here, we analyzed silibinin (a natural flavonoid) efficacy to target cell growth, angiogenesis, and metabolic changes in human PCa, LNCaP, and 22Rv1 cells under hypoxic condition. Silibinin treatment inhibited the proliferation, clonogenicity, and endothelial cells tube formation by hypoxic (1% O₂ ) PCa cells. Interestingly, hypoxia promoted a lipogenic phenotype in PCa cells via activating acetyl-Co A carboxylase (ACC) and fatty acid synthase (FASN) that was inhibited by silibinin treatment. Importantly, silibinin treatment strongly decreased hypoxia-induced HIF-1α expression in PCa cells together with a strong reduction in hypoxia-induced NADPH oxidase (NOX) activity. HIF-1α overexpression in LNCaP cells significantly increased the lipid accumulation and NOX activity; however, silibinin treatment reduced HIF-1α expression, lipid levels, clonogenicity, and NOX activity even in HIF-1α overexpressing LNCaP cells. In vivo, silibinin feeding (200 mg/kg body weight) to male nude mice with 22Rv1 tumors, specifically inhibited tumor vascularity (measured by dynamic contrast-enhanced MRI) resulting in tumor growth inhibition without directly inducing necrosis (as revealed by diffusion-weighted MRI). Silibinin feeding did not significantly affect tumor glucose uptake measured by FDG-PET; however, reduced the lipid synthesis measured by quantitative ¹ H-NMR metabolomics. IHC analyses of tumor tissues confirmed that silibinin feeding decreased proliferation and angiogenesis as well as reduced HIF-1α, FASN, and ACC levels. Together, these findings further support silibinin usefulness against PCa through inhibiting hypoxia-induced signaling. © 2016 Wiley Periodicals, Inc.

Hypoxia induces triglycerides accumulation in prostate cancer cells and extracellular vesicles supporting growth and invasiveness following reoxygenation

Hypoxia is an independent prognostic indicator of poor outcome in several malignancies. However, precise mechanism through which hypoxia promotes disease aggressiveness is still unclear. Here, we report that under hypoxia (1% O₂), human prostate cancer (PCA) cells, and extracellular vesicles (EVs) released by these cells, are significantly enriched in triglycerides due to the activation of lipogenesis-related enzymes and signaling molecules. This is likely a survival response to hypoxic stress as accumulated lipids could support growth following reoxygenation. Consistent with this, significantly higher proliferation was observed in hypoxic PCA cells following reoxygenation associated with rapid use of accumulated lipids. Importantly, lipid utilization inhibition by CPT1 inhibitor etomoxir and shRNA-mediated CPT1-knockdown significantly compromised hypoxic PCA cell proliferation following reoxygenation. Furthermore, COX2 inhibitor celecoxib strongly reduced growth and invasiveness following hypoxic PCA cells reoxygenation, and inhibited invasiveness induced by hypoxic PCA EVs. This establishes a role for COX2 enzymatic products in the enhanced PCA growth and invasiveness. Importantly, concentration and loading of EVs secreted by PCA cells were significantly compromised under delipidized serum condition and by lipogenesis inhibitors (fatostatin and silibinin). Overall, present study highlights the biological significance of lipid accumulation in hypoxic PCA cells and its therapeutic relevance in PCA.

Angiogenesis Assays

Neoangiogenesis constitutes one of the first steps of tumor progression beyond a critical size of tumor growth, which supplies a dormant mass of cancerous cells with the required nutrient supply and gaseous exchange through blood vessels essentially needed for their sustained and aggressive growth. In order to understand any biological process, it becomes imperative that we use models, which could mimic the actual biological system as closely as possible. Hence, finding the most appropriate model is always a vital part of any experimental design. Angiogenesis research has also been much affected due to lack of simple, reliable, and relevant models which could be easily quantitated. The angiogenesis models have been used extensively for studying the action of various molecules for agonist or antagonistic behaviour and associated mechanisms. Here, we have described two protocols or models which have been popularly utilized for studying angiogenic parameters. Rat aortic ring assay tends to bridge the gap between in vitro and in vivo models. The chorioallantoic membrane (CAM) assay is one of the most utilized in vivo model system for angiogenesis-related studies. The CAM is highly vascularized tissue of the avian embryo and serves as a good model to study the effects of various test compounds on neoangiogenesis.

Silibinin Preferentially Radiosensitizes Prostate Cancer by Inhibiting DNA Repair Signaling

Radiotherapy, a frequent mode of cancer treatment, is often restricted by dose-related toxicity and development of therapeutic resistance. To develop a novel and selective radiosensitizer, we studied the radiosensitizing effects and associated mechanisms of silibinin in prostate cancer. The radiosensitizing effect of silibinin with ionizing radiation (IR) was assessed on radioresistant prostate cancer cell lines by clonogenic, cell cycle, cell death, and DNA repair assays. Tumor xenograft growth, immunohistochemical (IHC) analysis of tumor tissues, and toxicity-related parameters were measured in vivo. Silibinin (25 μmol/L) enhanced IR (2.5-10 Gy)-caused inhibition (up to 96%, P < 0.001) of colony formation selectively in prostate cancer cells, and prolonged and enhanced IR-caused G2-M arrest, apoptosis, and ROS production. Mechanistically, silibinin inhibited IR-induced DNA repair (ATM and Chk1/2) and EGFR signaling and attenuated the levels of antiapoptotic proteins. Specifically, silibinin suppressed IR-induced nuclear translocation of EGFR and DNA-PK, an important mediator of DSB repair, leading to an increased number of γ-H2AX (ser139) foci suggesting lesser DNA repair. In vivo, silibinin strongly radiosensitized DU145 tumor xenograft inhibition (84%, P < 0.01) with higher apoptotic response (10-fold, P < 0.01) and reduced repair of DNA damage, and rescued the mice from IR-induced toxicity and hematopoietic injury. Overall, silibinin enhanced the radiotherapeutic response via suppressing IR-induced prosurvival signaling and DSB repair by inhibiting nuclear translocation of EGFR and DNA-PK. Because silibinin is already in phase II clinical trial for prostate cancer patients, the present finding has translational relevance for radioresistant prostate cancer.

Silibinin inhibits aberrant lipid metabolism, proliferation and emergence of androgen-independence in prostate cancer cells via primarily targeting the sterol response element binding protein 1

Prostate cancer (PCA) kills thousands of men every year, demanding additional approaches to better understand and target this malignancy. Recently, critical role of aberrant lipogenesis is highlighted in prostate carcinogenesis, offering a unique opportunity to target it to reduce PCA. Here, we evaluated efficacy and associated mechanisms of silibinin in inhibiting lipid metabolism in PCA cells. At physiologically achievable levels in human, silibinin strongly reduced lipid and cholesterol accumulation specifically in human PCA cells but not in non-neoplastic prostate epithelial PWR-1E cells. Silibinin also decreased nuclear protein levels of sterol regulatory element binding protein 1 and 2 (SREBP1/2) and their target genes only in PCA cells. Mechanistically, silibinin activated AMPK, thereby increasing SREBP1 phosphorylation and inhibiting its nuclear translocation; AMPK inhibition reversed silibinin-mediated decrease in nuclear SREBP1 and lipid accumulation. Additionally, specific SREBP inhibitor fatostatin and stable overexpression of SREBP1 further confirmed the central role of SREBP1 in silibinin-mediated inhibition of PCA cell proliferation and lipid accumulation and cell cycle arrest. Importantly, silibinin also inhibited synthetic androgen R1881-induced lipid accumulation and completely abrogated the development of androgen-independent LNCaP cell clones via targeting SREBP1/2. Together, these mechanistic studies suggest that silibinin would be effective against PCA by targeting critical aberrant lipogenesis.

Abstract 3339: Silibinin improves radiotherapeutic efficacy in prostate cancer by reducing IR-induced toxicity and EMT

Radiotherapy of prostate carcinoma is well established and frequently utilized in a significant proportion of cancer patients. However, two major concerns with radiotherapy is the effect on normal tissues and development of more invasive-radioresistant population. We have previously shown that the use of a plant flavonoid, silibinin can radiosensitize prostate cancer cells preferentially in vitro, by inhibiting DNA damage repair. We extended this study further, to validate the effects of silibinin in improving the radiotherapeutic efficacy in vivo. Our results showed that, in vivo, silibinin strongly radiosensitized DU145 tumor xenograft inhibition (84%, P&lt;0.01) with higher apoptotic response (10-fold, P&lt;0.01) and reduced repair of DNA damage as evidenced by reduced Chk2 activation and enhanced pH2A.X foci in tumor tissues. Interestingly, we also observed that silibinin could rescue the mice from IR-caused hematopoietic injury and normal tissue toxicity. Studies have shown that ionizing radiation (IR) increases the vascularity and invasiveness of surviving radioresistant cancer cells. This invasive phenotype of radioresistant cells is an upshot of radiation induced pro-survival and mitogenic signaling in cancer as well as endothelial cells. In the current study, we demonstrate that silibinin can also radiosensitize endothelial cells by inhibiting expression of pro-angiogenic factors. Combining silibinin with IR not only down-regulated endothelial cell proliferation, clonogenicity and tube formation ability rather it significantly reduced migratory and invasive properties of PCa cells which were otherwise marginally affected by IR treatment alone. We have found that most of the pro-angiogenic, migratory and EMT promoting proteins were up regulated in response to IR in PCa cells. All of these invasive and EMT promoting actions of IR were markedly decreased by silibinin. Further, we found that potentiated effect was an end result of attenuation of IR activated mitogenic and pro-survival signaling, including Akt, Erk1/2 and STAT-3 by silibinin. Therefore, the study not only underlines the preferential radiosensitizing ability of silibinin in PCa, but also shows its efficacy in modulating IR-induced toxicity in normal cells and EMT in PCa cells.

Citation Format: Dhanya K. Nambiar, Paulraj Rajamani, Anil Jain, Gagan Deep, Rajesh Agarwal, Rana P. Singh. Silibinin improves radiotherapeutic efficacy in prostate cancer by reducing IR-induced toxicity and EMT. [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 3339. doi:10.1158/1538-7445.AM2015-3339

Silibinin attenuates ionizing radiation-induced pro-angiogenic response and EMT in prostate cancer cells

Radiotherapy of is well established and frequently utilized in prostate cancer (PCa) patients. However, recurrence following therapy and distant metastases are commonly encountered problems. Previous studies underline that, in addition to its therapeutic effects, ionizing radiation (IR) increases the vascularity and invasiveness of surviving radioresistant cancer cells. This invasive phenotype of radioresistant cells is an upshot of IR-induced pro-survival and mitogenic signaling in cancer as well as endothelial cells. Here, we demonstrate that a plant flavonoid, silibinin can radiosensitize endothelial cells by inhibiting expression of pro-angiogenic factors. Combining silibinin with IR not only strongly down-regulated endothelial cell proliferation, clonogenicity and tube formation ability rather it strongly (p<0.001) reduced migratory and invasive properties of PCa cells which were otherwise marginally affected by IR treatment alone. Most of the pro-angiogenic (VEGF, iNOS), migratory (MMP-2) and EMT promoting proteins (uPA, vimentin, N-cadherin) were up-regulated by IR in PCa cells. Interestingly, all of these invasive and EMT promoting actions of IR were markedly decreased by silibinin. Further, we found that potentiated effect was an end result of attenuation of IR-activated mitogenic and pro-survival signaling, including Akt, Erk1/2 and STAT-3, by silibinin.

Abstract 4114: Silibinin inhibits hypoxia-induced proliferation, angiogenesis and lipogenesis in prostate cancer cells both in vitro and in vivo

Hypoxia (low oxygen conditions) in prostate tumors is associated with aggressive phenotype and poor prognosis. Also, hypoxia is considered the first major challenge faced by growing mass of neoplastic cells, as cells in hypoxic areas are surrounded by metabolic waste, acidic pH and necrotic cells. To overcome these hostile conditions, tumor cells activate transcriptional machinery leading to neo-angiogenesis, altered metabolism and selection of resistant clones. This suggests that prostate cancer (PCa) growth and progression could be prevented via targeting hypoxia-induced signaling. Here, we analyzed silibinin effect on hypoxia-induced proliferation, angiogenesis and metabolic changes in human PCa cells both in vitro and in vivo. Silibinin inhibited LNCaP cells clone formation (exposed to 1% O2 for 48 hrs and then returned to normoxic culture conditions) by 90-100% at 25-50 µM doses. Under similar hypoxic conditions in 22Rv1 cells, silibinin inhibited the clone formation by 63-77% at 25-50 µM doses. Importantly, conditioned media collected from PCa cells under hypoxic conditions (1% O2 for 24 hrs) induced tube formation by human umbilical vein endothelial cells (HUVEC) on matrigel, whereas conditioned media from silibinin-treated hypoxic PCa cells or silibinin addition in hypoxic-conditioned media abrogated HUVEC tube formation. Interestingly, we observed higher lipid accumulation in LNCaP cells under hypoxia, which was decreased (∼70%) by silibinin. Molecular analyses showed that silibinin decreases hypoxia-induced HIF-1α expression without affecting HIF-1β in PCa cells. Furthermore, silibinin increased the level of FIH (factor inhibiting HIF) and prolyl-hydroxylase 2, involved in HIF-1α degradation. Also, silibinin decreased the level of phosphorylated mTOR and ERK1/2 in PCa cells under hypoxia, and strongly inhibited lipid synthesis via activating AMP-activated protein kinase and decreasing acetyl Co A carboxylase, fatty acid synthase, acetyl Co A synthetase, fatty-acyl Co A synthetase and lipin expression. In vivo, silibinin effect on hypoxia-induced proliferation, angiogenesis and metabolism was analyzed in 22Rv1 xenograft model. Mice with established 22Rv1 tumors were imaged at base-line as well as 6 and 15 days following silibinin administration (200 mg/kg body weight) by diffusion weighted (DWI), dynamic contrast enhanced (DCE)-MRI and 18FDG-PET. At the study end, endogenous tumor metabolites were assed by NMR and various biomarkers by IHC. In vivo results showed that silibinin feeding reduced the tumor volume (by 47%), inhibited HIF-1α signaling, decreased proliferation and angiogenesis (DCE-MRI), induced apoptotic death and modulated tumor metabolism (PET and NMR). Together, these findings further support silibinin usefulness in PCa prevention through inhibiting hypoxia-induced proliferation, angiogenesis and lipogenesis.

Citation Format: Gagan Deep, Anand M. Ramteke, Dhanya K. Nambiar, Anil K. Jain, Natalie J. Serkova, Chapla Agarwal, Rajesh Agarwal. Silibinin inhibits hypoxia-induced proliferation, angiogenesis and lipogenesis in prostate cancer cells both in vitro and in vivo. [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 4114. doi:10.1158/1538-7445.AM2014-4114

Abstract 845: Silibinin radiosensitizes prostate cancer cells by enhancing radiation-induced cell death and inhibiting nuclear EGFR-mediated DNA repair

Nearly 60% of all cancer patients undergo radiotherapy at some juncture of their treatment schedule. However, the problem of therapeutic resistance and side effects to normal dividing cells wanes the positive facets of radiotherapy. Radiosensitizing agents have met with limited success in clinical settings. Hence, development of novel radiosensitizers with a selective response is greatly desired. Herein, we analyzed the radiosensitizing effects of silibinin, a natural plant flavonoid on prostate cancer (PCa) cells in vitro. Clonogenic assay and soft agar colony formation assay revealed that silibinin (25-100µM) could significantly enhance radiation (2.5-10 Gy) induced inhibition in colony formation selectively in PCa cells. G2/M phase is the most sensitive phase for radiation-induced damage. Silibinin enhanced and prolonged radiation-induced G2/M arrest in both DU145 and PC-3 cells. Even though low doses of silibinin (25µM) alone did not induce significant cell death, it could substantially enhance radiation-induced apoptosis. This could also be due to increased and prolonged ROS production observed in combination treatment. Foremost among the pro-survival pathways activated by radiation which contributes to therapeutic resistance is the EGFR pathway. Radiation-induced activation of EGFR subdues the response, both by induction of pro-survival pathway and by activating DNA repair after its nuclear translocation. We observed that silibinin could reduce radiation-induced EGFR signaling and consequently reverse the resistance mediating mechanisms within the cell. Silibinin down regulated levels of anti-apoptotic BCl-2 and survivin, enhanced by radiation. Inhibiting DNA repair would essentially enhance therapeutic index of radiation. Hence, we examined whether silibinin can down-regulate the repair pathways activated in response to radiation. Silibinin reversed the radiation-induced activation of CHK1 and CHK2 at both mRNA and protein levels. We further analyzed its effect on radiation-induced nuclear translocation of EGFR. Our study revealed that silibinin inhibited the nuclear translocation of EGFR and subsequently also affected the nuclear localization of DNA-PK, which is known to be one of the most important mediators of DSB repair in human cells. This was further evident by the increase in the number of pH2AX (ser139) foci suggesting lesser DNA repair in these cells. Thus, we found that silibinin not only enhanced the cell death by reversing the pro-survival signaling activated by radiation; but also suppressed the repair of DSBs by inhibiting nuclear-EGFR mediated DNA-PK activation. Overall, since silibinin is already in phase II clinical trial for prostate cancer patients, the present findings indicate that a combinatorial approach involving silibinin with radiation could prove to be more effective against radioresistant PCa.

Citation Format: Dhanya K. Nambiar, Paulraj Rajamani, Rana P. Singh. Silibinin radiosensitizes prostate cancer cells by enhancing radiation-induced cell death and inhibiting nuclear EGFR-mediated DNA repair. [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 845. doi:10.1158/1538-7445.AM2014-845