Mechanism of inert inflammation in an immune checkpoint blockade-resistant tumor subtype bearing transcription elongation defects

The clinical response to immune checkpoint blockade (ICB) correlates with tumor-infiltrating cytolytic T lymphocytes (CTLs) prior to treatment. However, many of these inflamed tumors resist ICB through unknown mechanisms. We show that tumors with transcription elongation deficiencies (TEdef+), which we previously reported as being resistant to ICB in mouse models and the clinic, have high baseline CTLs. We show that high baseline CTLs in TEdef+ tumors result from aberrant activation of the nucleic acid sensing-TBK1-CCL5/CXCL9 signaling cascade, which results in an immunosuppressive microenvironment with elevated regulatory T cells and exhausted CTLs. ICB therapy of TEdef+ tumors fail to increase CTL infiltration and suppress tumor growth in both experimental and clinical settings, suggesting that TEdef+, along with surrogate markers of tumor immunogenicity such as tumor mutational burden and CTLs, should be considered in the decision process for patient immunotherapy indication.

Targeting of Cdc42 GTPase in regulatory T cells unleashes antitumor T-cell immunity

BACKGROUND

Cancer immunotherapy has taken center stage in cancer treatment. However, the current immunotherapies only benefit a small proportion of patients with cancer, necessitating better understanding of the mechanisms of tumor immune evasion and improved cancer immunotherapy strategies. Regulatory T (Treg) cells play an important role in maintaining immune tolerance through inhibiting effector T-cell function. In the tumor microenvironment, Treg cells are used by tumor cells to counteract effector T cell-mediated tumor suppression. Targeting Treg cells may thus unleash the antitumor activity of effector T cells. While systemic depletion of Treg cells can cause excessive effector T-cell responses and subsequent autoimmune diseases, controlled targeting of Treg cells may benefit patients with cancer.

METHODS

Treg cells from Treg cell-specific heterozygous Cdc42 knockout mice, C57BL/6 mice treated with a Cdc42 inhibitor CASIN, and control mice were examined for their homeostasis and stability by flow cytometry. The autoimmune responses in Treg cell-specific heterozygous Cdc42 knockout mice, CASIN-treated C57BL/6 mice, and control mice were assessed by H&E staining and ELISA. Antitumor T-cell immunity in Treg cell-specific heterozygous Cdc42 knockout mice, CASIN-treated C57BL/6 mice, humanized NSGS mice, and control mice was assessed by challenging the mice with MC38 mouse colon cancer cells, KPC mouse pancreatic cancer cells, or HCT116 human colon cancer cells.

RESULTS

Treg cell-specific heterozygous deletion or pharmacological targeting of Cdc42 with CASIN does not affect Treg cell numbers but induces Treg cell instability, leading to antitumor T-cell immunity without detectable autoimmune reactions. Cdc42 targeting causes an additive effect on immune checkpoint inhibitor anti-programmed cell death protein-1 antibody-induced T-cell response against mouse and human tumors. Mechanistically, Cdc42 targeting induces Treg cell instability and unleashes antitumor T-cell immunity through carbonic anhydrase I-mediated pH changes.

CONCLUSIONS

Rational targeting of Cdc42 in Treg cells holds therapeutic promises in cancer immunotherapy.

Tumors bearing defective transcription elongation are immune hot but resistant to immune checkpoint inhibitors

Tumors infiltrated with abundant T lymphocytes are generally thought to respond to immune checkpoint inhibitors (ICI). However, a significant proportion of immune hot tumors are resistant to ICI. The immune nature of such tumors is poorly understood. We recently reported a tumor type that is defective in transcription elongation (TEdef) and irresponsive to ICI in several clinical cohorts. Here, we show that TEdef tumors are unexpectedly infiltrated with cytotoxic T cells (CTLs) in patients and in animal models. Mechanistically, T cell infiltration is facilitated by cytoplasmic DNA/double strand RNA-nucleic acid sensing-TBK1-ccl5/cxcl/9/10 signaling cascade. However, single-cell RNA sequencing combined with flow cytometry reveals that CTLs in TEdef tumors are exhausted. Furthermore, immune suppressive regulatory T cells are enriched in TEdef tumors. ICI treatment of TEdef tumors in mice and human patients fails to further induce T cell infiltration. This study reveals a mechanism underlying inert inflammation and ICI resistance of TEdef tumors. We suggest that TEdef, alongside the surrogate markers of tumor mutational burden and CTLs, should be assessed in immunotherapy-candidate patients.

Supported by 5R01CA234038-03

Graded RhoA GTPase Expression in Treg Cells Distinguishes Tumor Immunity From Autoimmunity

RhoA of the Rho GTPase family is prenylated at its C-terminus. Prenylation of RhoA has been shown to control T helper 17 (Th17) cell-mediated colitis. By characterizing T cell-specific RhoA conditional knockout mice, we have recently shown that RhoA is required for Th2 and Th17 cell differentiation and Th2/Th17 cell-mediated allergic airway inflammation. It remains unclear whether RhoA plays a cell-intrinsic role in regulatory T (Treg) cells that suppress effector T cells such as Th2/Th17 cells to maintain immune tolerance and to promote tumor immune evasion. Here we have generated Treg cell-specific RhoA-deficient mice. We found that homozygous RhoA deletion in Treg cells led to early, fatal systemic inflammatory disorders. The autoimmune responses came from an increase in activated CD4⁺ and CD8⁺ T cells and in effector T cells including Th17, Th1 and Th2 cells. The immune activation was due to impaired Treg cell homeostasis and increased Treg cell plasticity. Interestingly, heterozygous RhoA deletion in Treg cells did not affect Treg cell homeostasis nor cause systemic autoimmunity but induced Treg cell plasticity and an increase in effector T cells. Importantly, heterozygous RhoA deletion significantly inhibited tumor growth, which was associated with tumor-infiltrating Treg cell plasticity and increased tumor-infiltrating effector T cells. Collectively, our findings suggest that graded RhoA expression in Treg cells distinguishes tumor immunity from autoimmunity and that rational targeting of RhoA in Treg cells may trigger anti-tumor T cell immunity without causing autoimmune responses.

A Murine Cell Line Based Model of Chronic CDK9 Inhibition to Study Widespread Non-Genetic Transcriptional Elongation Defects (TEdeff) in Cancers

We have previously reported that a subset of cancers is defined by global transcriptional deregulations with widespread deficiencies in mRNA transcription elongation (TE)-we call such cancers as TE^deff. Notably, TE^deff cancers are characterized by spurious transcription and faulty mRNA processing in a large set of genes, such as interferon/JAK/STAT and TNF/NF-κB pathways, leading to their suppression. The TE^deff subtype of tumors in renal cell carcinoma and metastatic melanoma patients significantly correlate with poor response and outcome in immunotherapy. Given the importance of investigating TE^deff cancers-as it portends a significant roadblock against immunotherapy-the goal of this protocol is to establish an in vitro TE^deff mouse model to study these widespread, non-genetic transcriptional abnormalities in cancers and gain new insights, novel uses for existing drugs, or find new strategies against such cancers. We detail the use of chronic flavopiridol mediated CDK9 inhibition to abrogate phosphorylation of serine 2 residue on the C-terminal repeat domain (CTD) of RNA polymerase II (RNA Pol II), suppressing the release of RNA Pol II into productive transcription elongation. Given that TE^deff cancers are not classified under any specific somatic mutation, a pharmacological model is advantageous, and best mimics the widespread transcriptional and epigenetic defects observed in them. The use of an optimized sublethal dose of flavopiridol is the only efficacious strategy in creating a generalizable model of non-genetic widespread disruption in transcription elongation and mRNA processing defects, closely mimicking the clinically observed TE^deff characteristics. Therefore, this model of TE^deff can be leveraged to dissect, cell-autonomous factors enabling them in resisting immune-mediated cell attack.

Suppression of tumor antigen presentation during aneuploid tumor evolution contributes to immune evasion

Anti-tumor immune responses impede tumor formation, and cancers have evolved many mechanisms of immune evasion. Confirming earlier findings, we show that human tumors with high chromosomal instability (CIN+) are significantly less immunogenic, as judged by tumor lymphocyte infiltration, compared to those with more stable genomes (CIN-). This finding is paradoxical, as genomic instability is expected to evoke an innate immune response. Importantly, CIN+ tumors and cell lines exhibited suppressed expression of proteins involved in MHC class I antigen presentation at least partly due to DNA hypermethylation of the corresponding genes. Using a mouse model of the in vivo evolution of aneuploid tumors, we found that the induction of chromosomal instability in tumor cells is highly immunogenic due to the activation of the STING/TBK1 pathway and consequent increased interferon signaling and antigen presentation. However, tumors evolving under immune pressure suppress the STING/TBK1 and antigen presentation pathways and evade anti-tumor immune responses. In contrast, CIN+ tumors that develop under low immune pressure in both humans and mice retain efficient MHC class I antigen presentation and immunogenicity. Altogether, this study identifies an important mechanism of immune evasion in chromosomally unstable tumors.

Abstract B083: Defective transcription elongation in a subset of cancers confers immunotherapy resistance

Immunogenicity of most cancer types is a result of either neoantigenic mutational load, which stokes up an adaptive immune response, or due to oncogenic stress pathways, which elicit an innate antitumor response. There have been exponential gains made in recent times using numerous strategies to reactivate the host antitumor immunity including the development of immune checkpoint inhibitors. Nonetheless, the promise of a cure and durable response in select patients does not refute the low response rates in advanced cases, most of which also relapse. These observations shore up the possibility of other mechanisms beyond the inactivation of local lymphocyte infiltrates that might also play in tumor cell evasion of antitumor immune response. Through comprehensive computational and follow-up experimental validations, we have found that a subset of cancers (~15-20% of all cancers) are characterized by severe defects in almost the entire epigenetic and transcriptional apparatus. These defects result in genome-wide deregulation of histone modifications, mRNA transcription elongation, and mRNA processing and nuclear export, especially in the long genes which we term as Transcriptional Elongation Deficient: TEdef. As such, cancer cells with TEdef suppressed the expression of the pathways enriched for long genes, such as proinflammatory signaling pathways (FasL response, TNF/NF-kB signaling, interferon signaling) at both mRNA and protein levels, and had diminished response to interferon and TNF stimuli. Remarkably, in renal cell carcinoma and metastatic melanoma patients in four cohorts, the TEdef phenotype significantly correlated with poor response and unfavorable outcome to immunotherapy, but not to chemo- or targeted therapy. Importantly, forced induction of TEdef in tumor cells impaired the expression of, and signaling through, the proinflammatory pathways, and imposed a resistance to the innate and adaptive antitumor immune responses and to immune checkpoint inhibitor therapy in vivo. Tumor lymphocyte infiltration (TIL) and somatic neoepitope load (SNL) are some of the best markers of immunotherapy response in the clinic. However, TEdef tumors were characterized by a higher rate of immune cell infiltration, but paradoxically, less immune-mediated local tumor cell lysis, further supporting the notion that TEdef is a tumor cell-autonomous mechanism of immune resistance. As such, combining TIL or SNL with TEdef had superior power in predicting the progression-free and overall survival of melanoma patients treated with the anti-CTLA4 and anti-PD-1 therapy. Overall, TEdef is a novel epigenetic mechanism of resistance to antitumor immune attack, which warrants its assessment in cancer patients undergoing immunotherapy.

Citation Format: Vishnu Modur. Defective transcription elongation in a subset of cancers confers immunotherapy resistance [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr B083.

Abstract A50: Modeling and targeting of oncogenic proteotoxic stress in drug-resistant breast cancer

ERBB2/HER2-positive breast cancers are associated with poor prognosis, and resistance to HER2-targeted therapy (trastuzumab and lapatinib) presents a significant clinical hurdle. There are no treatment options for metastatic HER2+ BCs that have progressed on HER2-targeted therapy. At present, most of the research on therapeutic strategies in therapy-refractory Her2+ BCs focuses on resensitizing tumor cells to HER2-targeting agents. We have shown that targeting of nononcogenic vulnerabilities, specifically adaptive proteotoxic stress response, is a promising therapeutic approach in this subset of BCs (Singh N. et al, HER2-mTOR signaling-driven breast cancer cells require ER-associated degradation to survive. Science Signaling 2015). We showed that Her2+ BCs have specific dependence on the endoplasmic reticulum (ER)-associated degradation (ERAD) pathway to suppress the hyperactive Her2/mTOR pathway-driven proteotoxic stress. Here, we explore the kinetics of protein homeostatic changes during the course of Her2-targeted drug therapy, and identify optimal therapeutic windows for the targeting of ERAD in the therapy-refractory Her2+ BCs.

Using an integrated systems approach, we have modeled the dynamics of signaling and protein homeostasis changes in Her2+ cells during remission, resistance, and relapse phases of Her2-targeted therapy. We found that the resistance and relapse phases of anti-Her2 drug (lapatinib and trastuzumab) treatment are associated with Her2-independent acquisition of mTOR signaling, as previously reported. However, these signaling pathway changes also resulted in heightened proteotoxic burden on the ER due to increased protein synthesis rates, which was further exacerbated upon the release of cells from anti-Her2 treatment. Accordingly, cells in the relapse phase, and even more so upon further drug withdrawal, showed significantly heightened sensitivity to the inhibition of ERAD. This study reveals the kinetics of protein homeostasis associated with the signaling pathway changes during acquired resistance to anti-Her2 therapy, and suggests optimal therapeutic windows for the targeting of ERAD in therapy-refractory Her2+ BCs.

Citation Format: Navneet Singh, Vishnu Modur, Belal Muhammad, Kakajan Komurov. Modeling and targeting of oncogenic proteotoxic stress in drug-resistant breast cancer [abstract]. In: Proceedings of the AACR Special Conference: Advances in Breast Cancer Research; 2017 Oct 7-10; Hollywood, CA. Philadelphia (PA): AACR; Mol Cancer Res 2018;16(8_Suppl):Abstract nr A50.

Characterization of immortalized human mammary epithelial cell line HMEC 2.6

Primary human mammary epithelial cells have a limited life span which makes it difficult to study them in vitro for most purposes. To overcome this problem, we have developed a cell line that was immortalized using defined genetic elements, and we have characterized this immortalized non-tumorigenic human mammary epithelial cell line to establish it as a potential model system. human mammary epithelial cells were obtained from a healthy individual undergoing reduction mammoplasty at SIU School of Medicine. The cells were transduced with CDK4R24C followed by transduction with human telomerase reverse transcriptase. Post all manipulation, the cells displayed a normal cell cycle phase distribution and were near diploid in nature, which was confirmed by flow cytometry and karyotyping. In vitro studies showed that the cells were anchorage dependent and were non-invasive in nature. The cell line expressed basal epithelial markers such as cytokeratin 7, CD10, and p63 and was negative for the expression of estrogen receptor and progesterone receptor. Upon G-band karyotyping, the cell line displayed the presence of a few cytogenic abnormalities, including trisomy 20 and trisomy 7, which are also commonly present in other immortalized mammary cell lines. Furthermore, the benign nature of these cells was confirmed by multiple in vitro and in vivo experiments. Therefore, we think that this cell line could serve as a good model to understand the molecular mechanisms involved in the development and progression of breast cancer and to also assess the effect of novel therapeutics on human mammary epithelial cells.

Abstract B33: Loss of transcriptional fidelity in cancers confers immunotherapy resistance

Most cancers are immunogenic, either due to neo-antigenic mutational load that makes them susceptible to rejection by the adaptive immune system, or due to oncogenic stress pathways that makes them vulnerable to innate anti-tumor responses. The therapeutic strategies to reactivate the host anti-tumor immunity have a great promise for cancer therapy. However, despite the unprecedented promise of a cure and durable disease management in select patients, the response rates are still low in advanced cases, most of which also relapse. These findings reflect the multitude of mechanisms of tumor cell evasion of anti-tumor immunity, and that mechanisms beyond inactivation of local lymphocyte infiltrates might also play a role. Through comprehensive computational and follow-up experimental validations, we have found that a subset of cancers (~15-20% of all cancers) is characterized by severe defects in almost the entire epigenetic and transcriptional apparatus, resulting in genome-wide deregulation of histone modifications, mRNA transcription elongation, splicing and processing (Loss of Transcriptional Fidelity: LTF). LTF impaired the transcription of long genes in the genome at both mRNA and protein levels; and the pathways that are primarily regulated by long genes, such as immune-related (FasL response, TNF/NF-kB signaling, interferon signaling), MAP kinase and tyrosine kinase signaling pathways, were significantly suppressed in LTF+ (i.e. those with LTF) tumors. We validated the LTF phenotype and associated epigenetic and transcriptional defects in some cancer cell lines, and showed that severe loss of transcriptional fidelity can confer resistance to pro-inflammatory anti-tumor mechanisms in vitro, and suppress immune-mediated tumor rejection in vivo. As such, we found that LTF predicted poor response to immunotherapeutic, but not to chemo- or targeted therapy, agents in the clinic, including immune checkpoint inhibitors, in 3 different cohorts. Therefore, LTF is a previously unknown global phenotype in cancer cells that confers cell-autonomous resistance to anti-tumor immune attacks. Tumor lymphocyte infiltration is one of the best markers of immunotherapy response in the clinic. However, LTF+ tumors were characterized by a higher rate of immune cell infiltration, but paradoxically, less immune-mediated local tumor cell lysis, further supporting the notion that LTF is a tumor cell-autonomous mechanism of immune resistance. As such, combining tumor lymphocyte infiltration with LTF had superior power in predicting the progression-free and overall survival of melanoma patients treated with the anti-CTLA4 antibody ipilimumab. This study uncovers a major phenotype in cancers that dictates global transcriptional and signaling state in the cell, and response to immunotherapeutic agents in the clinic. Further, this study warrants assessment of markers of LTF in immunotherapy-candidate patients, especially given that LTF+ kidney cancer patients had significantly better response to targeted therapy agents.

Citation Format: Navneet Singh, Vishnu Modur, Vakul Mohanty, Kwangmin Choi, Edith M. Janssen, Lisa Privette-Vinnedge, Gang Huang, Kakajan Komurov. Loss of transcriptional fidelity in cancers confers immunotherapy resistance. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2016 Oct 20-23; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2017;5(3 Suppl):Abstract nr B33.

Abstract 585: Elevated levels of CD24 in head and neck squamous carcinoma cells: A potential marker for unfavorable cisplatin response

Introduction: Head and neck cancers are usually detected in their later stages of progression, resulting in a 5-year survival rate of only 30-50%. Chemotherapy is a treatment of choice for locally advanced head and neck squamous cellular carcinoma (HNSCC), and unfortunately, only a subset of HNSCC responds favorably to cisplatin treatment. Currently, there are no predictive markers of a tumor's response to cisplatin therapy. Therefore, to investigate the extremely low rates of durable remission in HNSCC, we employed a method of screening membrane bound surface stem cell markers as a means to possibly identify a group of cells that are inherently resistant to high doses of cisplatin treatment.

Methods: Flow cytometry, MTT assay, QPCR, CD24 RNA interference, western blot, orosphere formation assay and IHC

Results: Three UM-SCC cell lines were taken that had variable degrees of sensitivity to cisplatin, but all the lines formed a pronounced cisplatin resistant tail in a dose response curve. In an effort to screen for the fraction of cells that formed the cisplatin resistant tail, we observed that these three UM-SCC lines that expressed similar amounts of membrane bound CD44 had variable levels of membrane bound CD24 initially; however, all showed higher levels of CD24 with increased cisplatin dosage. Levels of CD24 peaked at the super high doses of cisplatin that had resulted in a cisplatin resistant tail. To further our study on the relationship between CD24 and cisplatin resistance, UM-SCC-10B and UM-SCC-10B/pt15s, a cisplatin sensitive-resistant pair from the larynx that express high amounts of CD24 in normal conditions, were selected. Upon confirmation of CD24 up-regulation at a clinically relevant dose of cisplatin [10uM], a lentiviral vector construct containing a CD24 siRNA was introduced into the model pair. The knockdown of CD24 resulted in increased sensitivity to cisplatin, and it diminished the cisplatin resistant tail in a dose response curve. Also, CD24 knockdown lines had significantly lower cisplatin IC-50 values. Upon treating the CD24 high UM-SCC-10B and UM-SCC-10B/pt15s with a combination of monoclonal CD24 antibody and cisplatin, higher cisplatin sensitivity was achieved. This was followed by screening of CD24 expression in head and neck tumor tissue samples from patients that had undergone cisplatin treatment. The tissue screening further confirmed the correlation between CD24 overexpression and unfavorable cisplatin treatment response.

Conclusion: Our work thus far, indicates that higher expression of CD24 in head and neck tumors result in a cisplatin resistant population that may well be the cause of unfavorable response to cisplatin treatment. Overall, CD24 has the potential to be a valuable predictor of response to cisplatin in HNSCC patients as well as a therapeutic target.

Citation Format: Vishnu Modur. Elevated levels of CD24 in head and neck squamous carcinoma cells: A potential marker for unfavorable cisplatin response. [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 585. doi:10.1158/1538-7445.AM2015-585

HPV and CSC in HNSCC cisplatin resistance

Cisplatin (DNA intercalator), a standard chemotherapy drug often used to treat head and neck squamous cellular carcinoma (HNSCC) has very low response rates in recurrent disease of HNSCC, this is a major clinical problem today. However, a valuable window to look in to the underlying molecular aspects of a favorable and unfavorable cisplatin response is offered by a distinct disease entity in HNSCC - HPV+ OPSCC. It responds far more favorably to cisplatin than non-HPV driven HNSCC. Another intriguing aspect of head and neck cancer biology is the emergence of the CD44+ cancer stem cell - the tumor initiating population that in all likelihood is the root cause of therapeutic resistance. The critical question is, are there any differences between the CD44+ CSC population of an HPV+ OPSCC and a non-HPV HNSCC? In this regard, the inverse relation between EGFR levels and HPV status in OPSCC may be a common thread that connects the better response rates of HPV+ OPSCC with the contribution of CD44+ stem cells of HNSCC to chemoresistance.

Abstract 2719: Use of abiraterone against a luminal androgen receptor breast cancer cell line

Background: Data from this pre-clinical model suggests that the LAR TNBC subtype is unique and may respond to novel hormonal agents such as bicalutamide or abiraterone. The LAR subtype represents 11 % of all TNBC (which represent 20% of all breast cancers). Thus, positive studies of abiraterone could potentially extend the application of abiraterone to an additional 2% of all breast cancer patients, who could be treated in the metastatic, neoadjuvant, and adjuvant setting (for five years) with hormonal maintenance therapy. We, therefore, conducted studies of abiraterone on LAR TNBC cell line, MDA-MB-453. .

Methods: i). Cell proliferation- Cell proliferation will be done by plating 500,000 cells in triplicate Petri dishes and measuring cell number over a six day period between parent cells and cellstreated with the following varying concentrations of abiraterone: 100 ng/ml, 250 ng/ml, and 400 ng/ml. ii).Cell cycle effects- Cells were incubated for 24 hours with abiraterone and then lifted from the plate with trypsin/EDTA (0.5%/0.1%) and fixed overnight in 80% ethanol. This was followed by staining in PBS with 10 ug/ml of propidium iodide for twenty minutes at room temperature. Flow cytometry was performed in our facility, and data was obtained on the percentage of the cell population in various points of the cell cycle. iii). Apoptosis and necrosis assay (Annexin-V-PI assay)- Cells were harvested at 72 hours post-seeding and incubation with abiraterone and washed with ice-cold PBS, followed by staining with 1ug/ml of PI and 5ul of Alexa Fluor® 488 annexin V in 100ul of annexin binding buffer (10 mM Hepes/NaOH, pH 7.4, 140 mM NaCl, 2.5 mM CaCl2). After the incubation at room temperature for 15 minutes, 400ul of ice-cold annexin binding buffer was added and stained cells were analyzed by Becton-Dickinson FACSCalibur Flow Cytometer.

Results: Abiraterone caused a significant impact on cell proliferation and promoted apoptosis in the MDA-MB-453 population. Cell cycle effects were also noted with abiraterone treatment.

Conclusion: Abiraterone has activity against MDA-MB-453, a breast cancer cell line known to express luminal androgen receptor. The results suggest that further studies may be warranted with this agent against this unique subtype of breast cancer.

Citation Format: Krishna A. Rao, Vishnu Modur, Sumana Ghosh. Use of abiraterone against a luminal androgen receptor breast cancer cell line. [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 2719. doi:10.1158/1538-7445.AM2014-2719

Abstract 3860: Cisplatin-induced CD24 upregulation in CD44+ stem-like head and neck squamous carcinoma cells: a potential marker for unfavorable cisplatin response

Introduction: Head and neck cancers are usually detected in its later stages of progression, resulting in a 5-year survival rate of only 30-50%. Chemotherapy is the treatment of choice for locally advanced head and neck squamous cellular carcinoma (HNSCC), and unfortunately, only a subset of HNSCC responds favorably to cisplatin treatment. Currently, there are no predictive markers of a tumor's response to cisplatin therapy. Therefore, to investigate the extremely low rates of cisplatin response in HNSCC, we employed a method of screening membrane bound surface stem cell markers as a means to possibly identify a group of cells that are inherently resistant to high doses of cisplatin treatment.

Methodology: Expression of membrane bound CD24 was measured by flow cytometry. Tumor cell viability in response to cisplatin was measured by MTT assay. QPCR was performed using a standard thermocycler program and data was normalized to β-Actin. CD24 RNA interference was done through lentiviral transduction with Puromycin and GFP based selection. Standard Western blot procedures were used to check STAT3 and p-STAT3 expression. Ororsphere formation assay was performed in low attachment dishes with stem cell specific media

Results: Four UM-SCC cell lines were taken that had variable degrees of sensitivity to cisplatin, but all the lines formed a pronounced cisplatin resistant tail in a dose response curve. In an effort to screen for the fraction of cells that formed the cisplatin resistant tail, we observed that these four UM-SCC lines that expressed similar amounts of membrane bound CD44 had variable levels of membrane bound CD24. Levels of CD24 peaked at super high doses of cisplatin that had resulted in a cisplatin resistant tail. To further our study, UM-SCC-10B and UM-SCC-10B/pt15s, a cisplatin sensitive-resistant pair from the larynx that express high amounts of CD24 in normal conditions, were selected. Upon confirmation of CD24 up-regulation at a clinically relevant dose of cisplatin [10uM], a lentiviral vector construct containing a CD24 siRNA was introduced into the model pair. The knockdown of CD24 resulted in increased sensitivity to cisplatin, and it eliminated the cisplatin resistant tail in a dose response curve. It also showed reduced phosphorylation levels of STAT3. Interestingly, the lone CSC marker in HNSCC, CD44, by itself did not select for a cisplatin resistant population.

Conclusion: Our work thus far, indicates that up-regulation of CD24 and the resulting phosphorylation of STAT3 upon cisplatin exposure is a phenomenon that leads to cisplatin resistance, and it could be a crucial EGFR independent STAT3 activating mechanism that needs to be explored further. In case a similar relationship in clinical specimens corroborates these in vitro findings, CD24 has the potential to be a valuable predictor of response to cisplatin in HNSCC patients as well as a therapeutic target.

Citation Format: Vishnu Modur. Cisplatin-induced CD24 upregulation in CD44+ stem-like head and neck squamous carcinoma cells: a potential marker for unfavorable cisplatin response. [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 3860. doi:10.1158/1538-7445.AM2014-3860

Abstract 232: Cancer stem cells and cisplatin

Introduction:

Cisplatin is an important chemotherapeutic agent, which has resulted in higher overall response rates when combined with 5-FU or taxane combinations in treating squamous cellular carcinoma of the head and neck. However, HNSCC tumor response rates to cisplatin range from 20-30%, a major clinical hurdle today. To address this issue thoroughly, we investigated the resistance to cisplatin in HNSCC under the purview of the cancer stem cell hypothesis, using the widely studied CSC marker combinations of, CD44+ 24- and ALDH-Hi. In order to get a broader perspective on this issue, we worked on multiple HNSCC tumor cell lines with varying degrees of cisplatin resistance, arising from tumors of the pharynx, larynx, tongue, tonsils, alveolus, hypopharynx and supraglottis.

Methods:

Seven HNSCC cell lines were analyzed for their CSC percentage through FACS, utilizing CD44+ 24- and ALDH-Hi marker systems. Cisplatin IC-50 for each of these seven cell lines was then determined by plotting percent viability vs. drug concentration curves. The remaining viable cells after cisplatin treatment were then analyzed through FACS for their CD44+ 24- and ALDH-Hi percentages in order to compare with the CSC percentage in the untreated HNSCC lines.

Results:

There was a wide variation in the percentages of CD44+24- and ALDH-Hi cells across these seven HNSCC lines. An inverse correlation between the initial percentages of CD44+24- and ALDH-Hi cells and the corresponding cisplatin IC-50 values was seen. HNSCC cell lines that had lower IC-50 values for cisplatin displayed greater cell viability at higher concentrations of cisplatin. This was evident by a long tail in the sigmoidal dose response curve. The number of viable cells at the end of cisplatin treatment had a linear relationship with the overall percentage of CSCs in the control untreated cell lines.

Conclusion:

Our results suggest that the resistance offered by the CD44+24- and ALDH1-Hi cells is apparent only once the initial 50% loss of cells occurs. This in vitro biphasic decline in percent viable cells clearly indicates that HNSCC cisplatin resistance is a twofold problem. The bulk of non-cancer stem cells within a tumor can acquire resistance to cisplatin via multiple molecular pathways, but this is only a front line cover of resistance to the resistance offered by the cancer stem cells.

Citation Format: Vishnu Modur. Cancer stem cells and cisplatin. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 232. doi:10.1158/1538-7445.AM2013-232

Abstract 5169: Roles of lipogenesis in cancer stem-like cells at early stage of breast cancer

Ductal carcinoma in situ (DCIS) is considered an early stage of breast cancer and it is the precursor of invasive breast carcinoma. However, the transition from normal breast epithelial cells to DCIS is still not clearly elucidated. In order to determine the role of lipogenesis in normal to DCIS transition, we investigated the roles of SREBP1, a major transcription regulator of lipogenesis and its downstream lipogenic genes such as ACLY, ACC1 and FAS, by isolating cancer stem-like cells (CSCs) from DCIS.com cell line which forms typical DCIS lesions in animals by using the well-established cell surface markers, CD24−/CD44+/ESA+. We found that lipid synthesis was significantly upregulated in CSCs from DCIS.com in contrast to the corresponding population from normal breast epithelial cells (MCF10A). Furthermore, we found that this elevation of lipogenesis is indeed caused by the overexpression of SREBP1 which co-ordinately induces the overexpression of the downstream lipogenic genes. The CSCs obtained from DCIS.com were also found to be more tumorigenic than the parental cells as shown by the limiting dilution analysis. To determine the role of elevated level of SREBP1 and lipogenesis in the transition of normal breast epithelial cells to DCIS phenotype, we overexpressed SREBP1 in MCF10A and examined the transforming properties. Our in vitro data showed that MCF10A-SREBP1 cells indeed expressed a significantly higher level of SREBP1 and other lipogenic genes and this elevated level of lipogenesis resulted in the increased cell proliferation, increased mammospheres forming ability and enhanced cellular growth in 3D culture. These data suggest that increased lipogenesis in breast CSCs plays critical roles in DCIS formation. We also examined the effects of Resveratrol on CSCs from DCIS.com. Resveratrol significantly reduced the total lipid content by inhibiting SREBP1 and in turn other lipogenic genes and induced a series of pro-apoptotic genes such as DAPK2 and BNIP3 causing the death of CSCs from DCIS. The mammosphere forming ability of CSCs from DCIS was also blocked by Resveratrol. We also observed that Resveratrol indeed significantly suppressed the formation of DCIS by inhibiting lipogenesis and by upregulating DAPK2 and BNIP3 in our animal model of human DCIS. Collectively, our results indicate that lipogenic genes ACLY, ACC-1, FAS and SREBP1 are significantly up regulated in early stage of breast tumorigenesis and they confer proliferative and growth advantages to these cells. Lipogenesis targeting effect of Resveratrol on CSCs from DCIS provides us with a strong rationale to use this agent for chemo-prevention against DCIS.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 5169. doi:1538-7445.AM2012-5169

Hyaluronan synthase HAS2 promotes tumor progression in bone by stimulating the interaction of breast cancer stem-like cells with macrophages and stromal cells

The molecular mechanisms that operate within the organ microenvironment to support metastatic progression remain unclear. Here, we report that upregulation of hyaluronan synthase 2 (HAS2) occurs in highly metastatic breast cancer stem-like cells (CSC) defined by CD44(+)/CD24(-)/ESA(+) phenotype, where it plays a critical role in the generation of a prometastatic microenvironment in breast cancer. HAS2 was critical for the interaction of CSCs with tumor-associated macrophages (TAM), leading to enhanced secretion of platelet-derived growth factor-BB from TAMs, which then activated stromal cells and enhanced CSC self-renewal. Loss of HAS2 in CSCs or treatment with 4-methylumbelliferone, an inhibitor of HAS, which blocks hyaluronan production, drastically reduced the incidence and growth of metastatic lesions in vitro or in vivo, respectively. Taken together, our findings show a critical role of HAS2 in the development of a prometastatic microenvironment and suggest that HAS2 inhibitors can act as antimetastatic agents that disrupt a paracrine growth factor loop within this microenvironment.

KAI1 gene is engaged in NDRG1 gene-mediated metastasis suppression through the ATF3-NFkappaB complex in human prostate cancer

NDRG1 and KAI1 belong to metastasis suppressor genes, which impede the dissemination of tumor cells from primary tumors to distant organs. Previously, we identified the metastasis promoting transcription factor, ATF3, as a downstream target of NDRG1. Further analysis revealed that the KAI1 promoter contained a consensus binding motif of ATF3, suggesting a possibility that NDRG1 suppresses metastasis through inhibition of ATF3 expression followed by activation of the KAI1 gene. In this report, we found that ectopic expression of NDRG1 was able to augment endogenous KAI1 gene expression in prostate cancer cell lines, whereas silencing NDRG1 was accompanied with significant decrease in KAI1 expression in vitro and in vivo. In addition, our results of ChIP analysis indicate that ATF3 indeed bound to the promoter of the KAI1 gene. Importantly, our promoter-based analysis revealed that ATF3 modulated KAI1 transcription through cooperation with other endogenous transcription factor as co-activator (ATF3-JunB) or co-repressor (ATF3-NFκB). Moreover, loss of KAI1 expression significantly abrogated NDRG1-mediated metastatic suppression in vitro as well as in a spontaneous metastasis animal model, indicating that KA11 is a functional downstream target of the NDRG1 pathway. Our result of immunohistochemical analysis showed that loss of NDRG1 and KAI1 occurs in parallel as prostate cancer progresses. We also found that a combined expression status of these two genes serves as a strong independent prognostic marker to predict metastasis-free survival of prostate cancer patients. Taken together, our result revealed a novel regulatory network of two metastasis suppressor genes, NDRG1 and KAI1, which together concerted metastasis-suppressive activities through an intrinsic transcriptional cascade.

Elevated serum M-CSF level predicts reduced survival in metastatic breast cancer patients

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Background: Macrophage colony stimulating factor (M-CSF) and its receptor (CSF-1R, the c-fms oncogene protein product) have been reported to be expressed in a variety of cancers, including breast cancer. The M-CSF produced by breast cancer cells and surrounding stromal cells increases osteoclast formation and maturation and enhances the expression of stromal RANK ligand, both of which increase osteolytic bone degradation. In this study we evaluated the predictive and prognostic potential of circulating M-CSF in metastatic breast cancer patients treated with hormone therapy. Methods: Using an M-CSF ELISA (R&D Systems, Minneapolis, MN), M-CSF concentration was determined in pretreatment sera from 204 metastatic breast cancer patients enrolled in a phase III 2nd-line hormone therapy trial of fadrozole vs. megace, and also in sera from 25 post-menopausal control female subjects. Results: The serum M-CSF level from the 25 healthy post-menopausal female control subjects had a mean ± SD of 835.6 ± 276.1 pg/ml (range 319.0 - 1,465.8 pg/ml). The upper limit of normal was defined as the 95th percentile of the serum M-CSF level from the female control group (1277 pg/ml). Pretreatment serum M-CSF levels from the metastatic breast cancer patients ranged from 82.2 - 3,019.8 pg/ml, and were found elevated above the upper limit of normal in 15 of 204 patients (7.35 %). Patients with elevated pretreatment serum M- CSF did not have a significantly different objective response rate, clinical benefit rate, or time to progression to hormone therapy; but these patients did have significantly reduced overall survival (median survival 10.0 months) compared to patients with normal serum M-CSF levels (median survival 24.3 months)(p = 0.007). In multivariate analysis with serum HER-2/neu included as a covariate, elevated serum M-CSF level remained a significant independent variable for reduced survival (p= 0.032). Conclusions: Pretreatment serum M-CSF levels were elevated in 7 % of metastatic breast cancer patients compared to healthy female control subjects, and these patients had significantly reduced overall survival. Serum M-CSF deserves further study to determine its predictive and prognostic biomarker potential in breast cancer patients.

No significant financial relationships to disclose.

Fluid flow activates a regulator of translation, p70/p85 S6 kinase, in human endothelial cells

Cellular phenotype is determined not only by genetic transcription but also by subsequent translation of mRNA into protein. Extracellular signals trigger intracellular pathways that distinctly activate translation. The 70/85-kDa S6 kinase (pp70(S6k)) is a central enzyme in the signal-dependent control of translation, but its regulation in endothelial cells is largely unknown. Here we show that fluid flow (in the absence of an exogenous mitogen) as well as humoral agonists activate endothelial pp70(S6k). Rapamycin, an inhibitor of the mammalian target of rapamycin (mTOR), and wortmannin, a phosphatidylinositol 3-kinase inhibitor, blocked flow-induced pp70(S6k) activation; FK-506, a rapamycin analog with minimal mTOR inhibitory activity, and PD-98059, an inhibitor of the flow-sensitive mitogen-activated protein kinase pathway, had no effect. Synthesis of Bcl-3, a protein whose translation is controlled by an mTOR-dependent pathway, was induced by flow and inhibited by rapamycin and wortmannin. Transcriptional blockade did not abolish the flow-induced upregulation of Bcl-3. Fluid forces may therefore modify endothelial phenotype by specifically regulating translation of certain mRNA transcripts into protein.

Retrograde inflammatory signaling from neutrophils to endothelial cells by soluble interleukin-6 receptor alpha

Endothelial cells initiate the inflammatory response by recruiting and activating leukocytes. IL-6 is not an agonist for this, but we found soluble IL-6 receptor alpha-subunit (IL-6Ralpha), with their constitutive IL-6 synthesis, stimulated endothelial cells to synthesize E-selectin, intracellular adhesion molecule-1, vascular cellular adhesion molecule-1, IL-6, and IL-8, and to bind neutrophils. Neutrophils express significant amounts of IL-6Ralpha and upon stimulation shed it: this material activates endothelial cells through a newly constituted IL-6 receptor. Retrograde signaling from PMN activated in the extravascular compartment to surrounding endothelial cells will recruit more and a wider variety of leukocytes. The limiting signal is a soluble receptor, not a cytokine.

Oncostatin M is a proinflammatory mediator. In vivo effects correlate with endothelial cell expression of inflammatory cytokines and adhesion molecules

Oncostatin M is a member of the IL-6 family of cytokines that is primarily known for its effects on cell growth. Endothelial cells have an abundance of receptors for oncostatin M, and may be its primary target. We determined if oncostatin M induces a key endothelial cell function, initiation of the inflammatory response. We found that subcutaneous injection of oncostatin M in mice caused an acute inflammatory reaction. Oncostatin M in vitro stimulated: (a) polymorphonuclear leukocyte (PMN) transmigration through confluent monolayers of primary human endothelial cells; (b) biphasic PMN adhesion through rapid P-selectin expression, and delayed adhesion mediated by E-selectin synthesis; (c) intercellular adhesion molecule-1 and vascular cell adhesion molecule-1 accumulation; and (d) the expression of PMN activators IL-6, epithelial neutrophil activating peptide-78, growth-related cytokine alpha and growth-related cytokine beta without concomitant IL-8 synthesis. The nature of the response to oncostatin M varied with concentration, suggesting high and low affinity oncostatin M receptors independently stimulated specific responses. Immunohistochemistry showed that macrophage-like cells infiltrating human aortic aneurysms expressed oncostatin M, so it is present during a chronic inflammatory reaction. Therefore, oncostatin M, but not other IL-6 family members, fulfills Koch's postulates as an inflammatory mediator. Since its effects on endothelial cells differ significantly from established mediators like TNFalpha, it may uniquely contribute to the inflammatory cycle.

Endothelial cell inflammatory responses to tumor necrosis factor alpha. Ceramide-dependent and -independent mitogen-activated protein kinase cascades

Ceramide generation by stimulated sphingomyelinase activity has been implicated in tumor necrosis factor alpha (TNF) signaling of apoptosis and differentiation. We examined the role of ceramide in a major action of TNF: the initiation of inflammatory events. Sphingomyelinase C at high levels induced inflammatory protein expression in endothelial cells resulting in leukocyte adhesion, but the pattern of induction of adhesion molecules (E-selectin, ICAM-1, VCAM-1) and cytokines (interleukins 6 and 8) differed from that induced by TNF. TNF induced only a small increase in ceramide: using lower doses of sphingomyelinase to mimic this we found that small amounts of ceramide did not induce protein expression, but still rapidly activated Raf-1, mitogen-activated protein/extracellular regulated kinase (ERK) kinase (MEK) and ERKs. TNF additionally caused rapid p38 and JNK-1 mitogen-activated protein kinase activation and efficient NF-kappaB translocation, which could not be achieved even by high levels of ceramide. Thus activation of the ERK cascade alone is an incomplete endothelial cell stimulus, and the TNF receptor generates at least two signals: Raf-1 activation, which could be ceramide-dependent; and ceramide-independent efficient NF-kappaB translocation and activation of p38 and JNK-1 mitogen-activated kinases.

The necrotic venom of the brown recluse spider induces dysregulated endothelial cell-dependent neutrophil activation. Differential induction of GM-CSF, IL-8, and E-selectin expression

Brown recluse spider (Loxosceles reclusa) venom induces severe dermonecrotic lesions. The mechanism for this is unknown but presents an interesting paradox: necrosis is completely dependent on the victim's neutrophils, yet neutrophils are not activated by the venom. We show Loxosceles venom is a potent, but disjointed, endothelial cell agonist. It weakly induced E-selectin expression, but not intercellular adhesion molecule-1 or IL-6 expression, yet significantly stimulated release of IL-8 and large amounts of GM-CSF by 4 h. In contrast, TNF strongly induced all of these, except for GM-CSF. PMN bound to E-selectin on venom-activated endothelial cells, apparently via counterreceptors different from those that bind E-selectin on TNF alpha-activated monolayers. Notably, PMN bound venom-activated monolayers only at intercellular junctions, did not polarize, and completely failed to migrate beneath the monolayer. Despite this, bound PMN demonstrated increased intracellular Ca2+ levels and secreted primary and secondary granule markers. The latter event was suppressed by sulfones used to treat envenomation. We have defined a new endothelial cell agonist, Loxosceles venom, that differentially stimulates the inflammatory response of endothelial cells. This, in turn, leads to a dysregulated PMN response where adhesion and degranulation are completely dissociated from shape change and transmigration.