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Supplementary Figures 1-11, Supplementary Tables 1-2 from Chromatin Structure Predicts Epigenetic Therapy Responsiveness in Sarcoma

Background: Human Papillomavirus 16 (HPV16) is the most common etiologic agent of HPV-associated cancers. Treatment options are limited for patients with HPV16+ recurrent or metastatic cancers. HPV16 E7 and E6 oncogenes constitute attractive immunotherapeutic targets. HB-201 and HB-202 are live-attenuated replicating vectors based on LCMV and PICV arenaviruses, respectively, that express the same non-oncogenic HPV16 E7E6 fusion protein for induction of tumor specific T cell responses. Methods: A Phase I/II open labelled clinical trial of HB-201 single vector therapy and HB-202/HB-201 alternating two-vector therapy in patients with treatment-refractory HPV16+ cancers is currently ongoing (NCT04180215). To assess circulating E6/E7 specific T cell responses, IFN-γ enzyme-linked immunospot (ELISpot) and intracellular cytokine staining were performed on pre- and post-treatment peripheral blood mononuclear cells (PBMCs). Evaluation of T cell infiltration and PD-L1 status in tumor bed was performed on paired tissue biopsies from a subset of patients by multiplex immunofluorescence. Results: Single vector therapy (HB-201) and alternating two-vector therapy (HB-202/HB-201) rapidly induce high E6/E7 specific T cell levels, reaching up to ~40% of the circulating CD8+ T cell pool. Alternating two-vector therapy seems to maintain E6/E7 specific T cell responses better in continuous dosing compared to single vector therapy. Furthermore, we demonstrate tumor tissue T cell infiltration in more than 50% of patient samples analyzed. Currently, in depth sequencing of paired biopsies is underway to characterize the tumor microenvironment in response to HB-201 and HB-202/HB-201 treatment. Conclusion: In this updated dataset, we show that HB-201 and HB-202/HB-201, rapidly induce unprecedented E6/E7 specific T cell levels in circulation following a single dose. Furthermore, these data are seen in conjunction with a pronounced increase of post-treatment CD8+ T cells in tumor, suggesting E6/E7 specific T cell infiltration. Our arenavirus vectors expressing the E7E6 fusion antigen demonstrate an attractive and safe therapy for patients with treatment refractory HPV16+ cancers. The ability of replicating arenavirus vectors to incorporate a broad range of antigens and the potent T cell inducing capacity provide a strong rationale to apply this novel therapy to other cancers. Citation Format: Donna Edwards, Michael Schwendinger, Kia Katchar, Katia Schlienger, Klaus Orlinger, Igor Matushansky, Henning Lauterbach. HB-201 and HB-202, an arenavirus-based immunotherapy, induces tumor T cell infiltration in patients with HNSCC and other HPV16+ tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3284.

T cells play a central role in immune responses against cancer. Within the tumor, however, T cells are exposed to a plethora of inactivating factors causing various degrees of dysfunction, changes in metabolism and a generally reduced cellular fitness, eventually leading to tumor progression. To prevent or delay the onset of exhaustion and instead augment effector functions and persistence of functional T cells, costimulatory factors and cytokines are needed. Targeting 4-1BB (CD137), a member of the tumor necrosis factor receptor superfamily, has been shown to represent a promising strategy for inducing an activating signal in CD8+ T cells, resulting in increased pro-inflammatory cytokine secretion, cytotoxic function, and survival. Engineered arenavirus vectors based on lymphocytic choriomeningitis virus (LCMV) or Pichinde virus (PICV) have been shown previously to induce massive infiltration of tumor antigen specific CD8+ T cells into the tumor in several preclinical cancer models. To investigate whether enhanced co-stimulation via 4-1BB further improves T cell responses and/or tumor control, combination therapies with replicating LCMV based vectors (artLCMV) and 4-1BB agonists were explored. A single intravenous treatment of artLCMV encoding the tumor associated antigens (TAA) gp70 or Trp2 in B16.F10 tumor bearing mice induced TAA specific CD8+ T cells in both the periphery and the tumor, resulting in tumor growth delay and some complete responses. Combining artLCMV with agonistic anti-4-1BB significantly improved tumor control and increased the number of complete responders. Analysis of tumor infiltrating lymphocytes revealed higher absolute numbers of TAA specific CD8+ T cells in the combination group compared to the artLCMV alone group. Analyses of the TAA specific cells revealed that more cells expressed granzyme B, Ki67 and Bcl-XL when co-stimulated with anti-4-1BB compared to the group treated with artLCMV alone. Importantly, encoding 4-1BBL in addition to a TAA in artLCMV revealed similar outcomes as just summarized for the combination with agonistic antibodies. Overall, these experiments confirmed the strong antigenicity and T cell inducing capacity of the engineered arenavirus platform, leading to efficient tumor control in a stringent mouse model. Combination with 4-1BB agonists, either in form of antibodies or encoded within the vector genome, was shown to further augment TAA-specific T cell responses within the tumor, leading to better tumor growth control and a higher rate of complete responders. Citation Format: Judith Strauss, Marilies Scheinost, Theresa Kleissner, Diana Reckendorfer, Kimberly Pojar, Mohamed Habbeddine, Sarah Ahmadi-Erber, Daniela Deutschmann, Sarah Schmidt, Josipa Raguz, Igor Matushansky, Christoph Lampert, Klaus K. Orlinger, Henning Lauterbach. Evaluation of a cancer immunotherapy with engineered arenavirus vectors and 4-1BB agonists in a preclinical tumor model [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 4198.

Cytotoxic CD8+ T cells are paramount for effective cancer immunotherapy. We engineered two distantly related arenaviruses, lymphocytic choriomeningitis virus (LCMV) and Pichinde virus (PICV), encoding the same non-oncogenic HPV16 E7E6 fusion protein to effectively mount and maintain tumor specific CD8+ T cell responses. The designated vectors, HB-201 (LCMV) and HB-202 (PICV), are currently in an ongoing Phase I/II open labelled clinical trial of HB-201 single vector therapy and HB-202/HB-201 alternating two-vector therapy in patients with treatment-refractory HPV16+ cancers (NCT04180215). To characterize the immunogenic properties of both vectors, we designed a comprehensive set of preclinical and translational experiments utilizing human PBMCs, artificial APCs and HPV16 E6 and E7 specific reporter T cells. This was done in conjunction with a preclinical model for HPV16 associated cancer (TC-1). HB-201 (LCMV) and HB-202 (PICV) surrogate vectors encoding GFP readily infected human monocytes, plasmacytoid dendritic, and conventional dendritic cells. In addition, HB-201 and HB-202 vectors successfully induced antigen presentation of E7 and E6 epitopes as evidenced by TCR reporter cells. Innate immune cell activation and cytokine responses to HB-202 were slightly lower compared to HB-201, findings which are consistent with different memory profiles of E7 specific CD8+ T cells in non-tumor bearing mice. In a therapeutic setting of the TC-1 tumor model, both vectors were comparably effective, showing major infiltration of CD8+ T cells into the tumor microenvironment, tumor growth delay and a significantly prolonged survival already after a single administration. In this data set we have confirmed the strong immunogenicity of the engineered arenavirus platform leading to efficient tumor control in a relevant mouse model for HPV16+ cancers, which further supports the clinical development of our novel arenavirus platform. Citation Format: Josipa Raguz, Theresa Kleissner, Sandra Rosskopf, Mohamed Habbeddine, Katharina Lechner, Valentin Just, Donna Edwards, Igor Matushansky, Christoph Lampert, Klaus K. Orlinger, Henning Lauterbach. In vitro and in vivo characterization of non-oncolytic engineered arenavirus vectors for cancer immunotherapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2048.

Infection with human papillomavirus (HPV) is associated with a variety of cancer types and limited therapy options. Therapeutic cancer vaccines targeting the HPV16 oncoproteins E6 and E7 have recently been extensively explored as a promising immunotherapy approach to drive durable antitumor T cell immunity and induce effective tumor control. With the goal to achieve potent and lasting antitumor T cell responses, we generated a novel lymphocytic choriomeningitis virus (LCMV)-based vaccine, TT1-E7E6, targeting HPV16 E6 and E7. This replication-competent vector was stably attenuated using a three-segmented viral genome packaging strategy. Compared to wild-type LCMV, TT1-E7E6 demonstrated significantly reduced viremia and CNS immunopathology. Intravenous vaccination of mice with TT1-E7E6 induced robust expansion of HPV16-specific CD8+ T cells producing IFN-γ, TNF-α and IL-2. In the HPV16 E6 and E7-expressing TC-1 tumor model, mice immunized with TT1-E7E6 showed significantly delayed tumor growth or complete tumor clearance accompanied with prolonged survival. Tumor control by TT1-E7E6 was also achieved in established large-sized tumors in this model. Furthermore, a combination of TT1-E7E6 with anti-PD-1 therapy led to enhanced antitumor efficacy with complete tumor regression in the majority of tumor-bearing mice that were resistant to anti-PD-1 treatment alone. TT1-E7E6 vector itself did not exhibit oncolytic properties in TC-1 cells, while the antitumor effect was associated with the accumulation of HPV16-specific CD8+ T cells with reduced PD-1 expression in the tumor tissues. Together, our results suggest that TT1-E7E6 is a promising therapeutic vaccine for HPV-positive cancers.

Background: Human Papillomavirus 16 (HPV16) is linked to most HPV-associated cancers such as cervical, head and neck, vaginal and anal cancers. Treatment options are limited for patients with HPV16+ recurrent or metastatic cancers. The generation and maintenance of the HPV16+ malignant state requires the stable expression of HPV16-specific E7 and E6 oncogenes, which therefore constitute attractive targets for immunotherapy. HB-201 and HB-202 are both replicating live-attenuated vectors based on arenaviruses LCMV and PICV, respectively, expressing the same non-oncogenic HPV16 E7E6 fusion protein for induction of tumor specific T-cell responses. In preclinical models, administration of HB-201 alone and sequential administration of HB-202 followed by HB-201 was safe and demonstrated potent immunogenicity by induction of E7 and E6 -specific CD8+ T cell responses and efficient tumor control of HPV+ TC-1 tumors. Methods: A first-in-human, Phase I/II open-labelled clinical trial of HB-201 single vector therapy and HB-201 & HB-202 two-vector therapy in patients with treatment-refractory HPV16+ cancers is currently ongoing (NCT04180215). Here, we present first immunogenicity results from the dose escalation phase I of this study. The phase I of the trial is designed to evaluate different dose levels and dosing schedules of HB-201 as a single-vector therapy or as an alternating two-vector therapy together with HB-202. Peripheral blood mononuclear cells (PBMCs) were collected before and after treatment from all patients. PBMCs from a subset of patients were examined for HPV16-specific T cell responses measured by IFN-γ enzyme-linked immunospot. Paired tissue biopsy and serum samples were also collected and being currently evaluated for histology and pharmacokinetics. Results: We demonstrated induction of a directly ex vivo (i.e. no expansion) detectable HPV16-specific T-cell response in PBMCs from patients receiving a single dose of HB-201 or HB-202. Additional exploratory analysis will be available at the time of the meeting. Conclusion: These preliminary data demonstrate for the first time with arenavirus vectors, the induction of HPV16-specific T cells in cancer patients following a single injection of HB-201 or HB-202. Arenavirus vectors expressing E7E6 may constitute a new potential therapy for patients with treatment refractory HPV16+ cancers. Clinical data will be presented in an upcoming scientific meeting. Additional schedules, alternating two-vector therapy with HB-201/HB-202, and combination with anti-PD-1 mAbs are being explored in additional cohorts. Citation Format: Kia Katchar, Michael Schwendinger, Diane DaSilva, Henning Lauterbach, Klaus Orlinger, Xiaoping Qing, Daniel Pinschewer, Igor Matushansky. Preliminary analysis of immunogenicity of HB-201 and HB-202, an arenavirus-based cancer immunotherapy, in patients with advanced HPV16-positive cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr LB049.

2502 Background: Human papillomavirus 16 (HPV16) is linked to several cancer types. Treatment options are limited for patients with HPV16 positive (HPV16+) recurrent or metastatic cancers. Generation and maintenance of HPV16+ malignant state require stable expression of HPV16-specific E7 and E6 oncoproteins, also a source of immunogenic neoantigens. HB-201 and HB-202 are replicating live-attenuated vectors based on lymphocytic choriomeningitis virus and Pichinde virus, respectively, which express the same non-oncogenic HPV16 E7E6 fusion protein to induce tumor-specific T-cell responses. This is a first-in-human phase 1/2 study of HB-201 monotherapy and HB-201 & HB-202 alternating 2-vector therapy. Dose escalation is ongoing with a 3+3 design. Methods: Phase 1 is assessing different regimens and dose levels of HB-201 monotherapy and HB-201 & HB-202 alternating 2-vector therapy given intravenously (IV) with or without an initial intratumoral administration. The patient population includes HPV16+ head and neck squamous cell carcinoma (HNSCC) and other HPV16+ cancers. Safety, tolerability, and preliminary antitumor activity by Response Evaluation Criteria in Solid Tumors (RECIST) 1.1 or immune RECIST are assessed. Results: As of Jan 2021, 25 patients with a median of 3 prior anticancer treatments have been enrolled. All had HPV16+ confirmed genotype; the most common primary site was oropharynx (72%). No dose-limiting toxicities were reported. Treatment-emergent adverse events (TEAEs) occurred in 21 patients (84%), were generally mild or moderate, with events related to study drug reported in 14 patients (56%). TEAEs reported in >10% of patients regardless of causality included fatigue, pyrexia, nausea, decreased appetite, anemia, arthralgia, chills, constipation, diarrhea, hypertension, influenza-like illness, pneumonia, and vomiting. Serious TEAEs developed in 6 patients (24%), including 1 with grade 5 hemorrhagic shock deemed unrelated to study drug. Grade 3 fatigue was the only serious or grade ≥3 TEAE assessed as related to study drug. TEAEs caused no treatment discontinuation. There were 18 patients evaluable for efficacy. For the 16 patients on HB-201 monotherapy, assessment of target lesions showed 2 partial responses (including 1 patient with an unconfirmed immune CR) and 6 patients had stable disease (SD). For the 2 patients on HB-201 & HB-202 alternating therapy, both had SD. So far, the longest duration of response was 4.8 months (144 days) and the maximum decrease in tumor diameter was 60%, both seen in HNSCC patients receiving HB-201 IV. Conclusions: HB-201 monotherapy and HB-201 & HB-202 2-vector alternating therapy were generally well-tolerated and showed preliminary antitumor activity as monotherapy in heavily pre-treated patients with HPV16+ HNSCC and other solid tumors. Clinical trial information: NCT04180215.

The unprecedented success of checkpoint blockade therapies clearly demonstrates the power of the immune system to fight cancer. Yet, only a minority of cancer patients respond with long-term control of the tumor or even cure, necessitating the development of other treatment modalities. Hookipa Pharma developed a novel attenuated, replication-competent viral vector platform (TheraT) that induces powerful cytotoxic T lymphocyte responses against foreign and self-antigens. In a preclinical model for human papilloma virus 16 (HPV16) associated cancer (TC-1), we evaluated immunogenicity and efficacy upon systemic and intratumoral application of TheraT vectors based on the arenaviruses lymphocytic choriomeningitis virus (LCMV) and pichinde virus (PICV). Both HB-201 (LCMV) and HB-202 (PICV) product candidates encode a non-oncogenic but highly antigenic E6/E7 fusion protein from HPV16. Independent of the route of administration, single administration of HB-201 or HB-202 induced potent peripheral E7-specific CD8+ T cell responses and led to efficient tumor growth control. Survival of TheraT treated animals was significantly longer compared to buffer treated animals. Similarly, single systemic as well as intratumoral application of HB-201 or HB-202 induced major infiltration of CD8+ T cells into the tumor microenvironment. Combination of intravenous HB-201 and anti-PD1 was well tolerated but did not further enhance efficacy in this model, implicating the presence of other immune evasion factors. In conclusion, replication-attenuated TheraT is safe, highly immunogenic and shows excellent therapeutic efficacy after single intravenous and intratumoral application. These data underline the potential and versatility of this novel vector platform. Mechanistic studies in various mouse tumor models are underway. Phase 1/2 clinical trial initiation of HB-201 monotherapy is planned for end of 2019 and preparations for an IND filing for a combination trial of HB-201 and HB-202 in H1 2020 have been initiated. Citation Format: Josipa Raguz, Sarah Schmidt, Theresa Kleisner, Manuel Zerbs, Goran Bekic, Sonja Feher, Daniel Oeler, Felix Stemeseder, Ursula Berka, Bettina Kiefmann, Sophie Schulha, Igor Matushansky, Henning Lauterbach, Klaus Orlinger. TheraT - a highly versatile arenavirus based vector platform for intravenous and intratumoral cancer immunotherapy [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4058.

TPS3171 Background: Human Papillomavirus 16 (HPV16) is linked to several cancer types; treatment options are limited for patients with HPV16+ recurrent or metastatic cancers. The generation and maintenance of the HPV16+ malignant state requires the stable expression of HPV16-specific E7 and E6 oncogenes, which can also serve as immunogenic tumor-associated antigens. HB-201 is a replication-competent live-attenuated vector based on the arenavirus LCMV encoding a non-oncogenic E7 and E6 fusion protein. In preclinical models, both intravenously (IV) and intratumorally (IT) administered HB-201 demonstrate potent immunogenicity by induction of HPV16-specific cytotoxic T cells and associated efficacy. Methods: This is a first in human, Phase I/II study of HB-201 monotherapy or in combination with PD-1 immune checkpoint inhibitor (anti-PD-1) in HPV16+ confirmed recurrent/metastatic cancers. Phase I consists of 2 treatment groups, each conducted with a 3+3 dose escalation design. Group 1 is enrolling patients with HPV16+ head and neck squamous cell carcinoma who will receive HB-201 IV only. Group 2 is enrolling HPV16+ cancer patients with a safely accessible tumor site who will receive HB-201 IT for the first dose, followed by HB-201 IV for subsequent doses (IT-IV). HB-201 will be administered every 21 days. The Phase II component will be conducted with the recommended Phase II doses (RP2Ds) defined in Phase I and will consist of 3 groups: Group A (HB-201 IV only), Group B (HB-201 IV plus anti-PD-1), and Group C (HB-201 IT-IV). Key eligibility criteria include age > 18, ECOG performance status 0-1, confirmed HPV16+ recurrent or metastatic cancer, disease progression from at least 1 systemic standard of care therapy, and measurable disease per RECIST v1.1. The Phase I primary objective is to determine RP2Ds for IV and IT HB-201. The Phase II primary objective is to assess antitumor activity. Secondary endpoints for both phases include safety, tolerability, overall survival, progression-free survival, and duration of response. Exploratory objectives include characterization of immunogenicity of HB-201 and biomarkers associated with immune or antitumor response. Enrollment to Groups 1 and 2 began in December 2019. Clinical trial information: NCT04180215 .

e14303 Background: Active immunization against cancer requires the induction of exquisitely potent tumor-specific CD8+ T cell (CTL) responses, which can be repeatedly boosted and reactivated. Hookipa Pharma engineered a replication-attenuated viral vector platform (TheraT) based on the arenavirus lymphocytic choriomeningitis virus (LCMV), which meets these aforementioned criteria. Here, we present a preclinical data package of Hookipa´s lead immunotherapy product HB-201, targeting HPV16-driven cancer. Methods: TheraT-E7E6 encodes a highly immunogenic, non-oncogenic version of the human papilloma virus 16 (HPV16) oncoproteins E7 and E6. Results: Attenuation and safety of TheraT-E7E6 were demonstrated by i) rapid viral clearance after systemic administration of the vector and ii) reduced neurovirulence in mice.TheraT-E7E6 can be administered intravenously as systemic therapy or intratumorally as local therapy with an abscopal-like effect. Treatment was shown to induce substantial CD8+ T cell expansion and high frequencies of E7- and E6-specific CTL responses with a balanced effector / central memory profile. These responses were boosted and reactivated upon TheraT-E7E6 re-administration. TheraT-E7E6 eradicated palpable tumors in a syngeneic mouse TC-1 tumor model of HPV-driven cancer. Even in mice with large tumors (~300mm3) TheraT-E7E6 afforded significant tumor control and improved survival, with high frequencies of E7-specific CTLs persisting for several weeks. Animals which cleared the tumor after TheraT therapy were long term protected from tumor re-challenge. Furthermore, TheraT is efficacious in checkpoint inhibitory refractory models and can also synergize in combination with checkpoint inhibitors (CPIs). Conclusions: In conclusion, replication-attenuated TheraT-E7E6 is safe, highly immunogenic and shows excellent therapeutic efficacy as mono- or combination therapy in a preclinical model of HPV-induced cancer. Clinical trials for the treatment of HPV16+ cancers will be initiated in 2019.

Active immunization against cancer requires the induction of exquisitely potent tumor-specific CD8+ T-cell (CTL) responses, which can be repeatedly boosted and reactivated. Hookipa Pharma engineered a replication-attenuated viral vector platform (TheraT®) based on the arenavirus lymphocytic choriomeningitis virus (LCMV), which meets these aforementioned criteria. Here, we present a preclinical data package of Hookipa´s lead immunotherapy product HB-201, targeting HPV16-driven head and neck cancer. It encodes a non-oncogenic version of the human papilloma virus 16 (HPV16) oncoproteins E7 and E6 (TheraT®-E7E6). Attenuation and safety of TheraT®-E7E6 were demonstrated by i) rapid viral clearance after systemic administration of the vector and ii) reduced neurovirulence in mice. TheraT®-E7E6 treatment was shown to induce substantial CD8+ T-cell expansion and high frequencies of E7- and E6-specific CTL responses with a balanced effector / central memory profile. These responses were boosted and reactivated upon TheraT®-E7E6 re-administration. TheraT®-E7E6 eradicated palpable TC-1 tumors, a syngeneic mouse tumor model of HPV-driven cancer. Even in mice with large tumors (~300mm3), TheraT®-E7E6 afforded significant tumor control and improved survival, with high frequencies of E7-specific CTLs persisting for several weeks. Furthermore, the efficacy of TheraT®-E7E6 can be potentiated in combination therapies, e.g., with PD-1 checkpoint inhibitors. In conclusion, replication-attenuated TheraT®-E7E6 is safe, highly immunogenic and shows excellent therapeutic efficacy as mono- or combination therapy in a preclinical model of HPV-induced cancer. Clinical trials for the treatment of HPV16+ cancers will be initiated in 2019. Citation Format: Sarah Schmidt, Ahmed ElGazzar, Weldy V. Bonilla, Mindaugas Pauzuolis, Andrea Reiter, Theresa Kleissner, Daniel Oeler, Felix Stemeseder, Ursula Berka, Bettina Kiefmann, Sophie Schulha, Igor Matushansky, Doron Merkler, Daniel Pinschewer, Klaus Orlinger. Live-attenuated LCMV-based vector for active immunotherapy of HPV16+ cancer [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 B131.

Adjuvant chemotherapy for soft tissue sarcoma (STS) remains controversial while improvement in survival has never been conclusively demonstrated for metastatic STS. We identified individuals in SEER-Medicare with resected or metastatic STS, 1991-2007. Of 2,382 patients with resected STS, 106 (4.5%) received chemotherapy. High tumor grade, larger tumor size, and malignant fibrous histiocytoma subtype were associated with chemotherapy receipt. Of 365 patients with metastatic STS, 118 (32.4%) received chemotherapy. Younger age, fewer comorbidities, and being married were associated with chemotherapy receipt. Consistent with clinical trials, we found minimal use of chemotherapy. Clinical factors were associated with chemotherapy receipt in nonmetastatic STS.

Genetic and epigenetic events within a cell which promote a block in normal development or differentiation coupled with unregulated proliferation are hallmarks of neoplastic transformation. Differentiation therapy involves the use of agents with the ability to induce differentiation in cells that have lost this ability, i.e. cancer cells. The promise of differentiation-based therapy as a viable treatment modality is perhaps best characterized by the addition of retinoids in the treatment of acute promyelocytic leukemia (APML) revolutionizing the management of APML and dramatically improving survival. However, interest and application of differentiation-based therapy for the treatment of solid malignancies have lagged due to deficiencies in our understanding of differentiation pathways in solid malignancies. Over the past decade, a differentiation-based developmental model for solid tumors has emerged providing insights into the biology of various solid tumors as well as identification of targetable pathways capable of re-activating blocked terminal differentiation programs. Furthermore, a variety of agents including retinoids, histone deacetylase inhibitors (HDACI), PPARγ agonists, and others, currently in use for a variety of malignancies, have been shown to induce differentiation in solid tumors. Herein we discuss the relevancy of differentiation-based therapies in solid tumors, using soft tissue sarcomas (STS) as a biologic and clinical model, and review the preclinical data to support its role as a promising modality of therapy for the treatment of solid tumors.

Alveolar rhabdomyosarcomas (ARMS) are characterised by a PAX3/7-FKHR translocation, which is presumed to promote a differentiation arrest in the myogenic lineage, in which setting secondary genetic events occur, resulting in sarcomagenesis. The aim of this study was to identify the mechanism by which PAX3/7-FKHR expression results in a myogenic differentiation block, as discrete from the secondary genetic events that complete the sarcomagenic process.We performed a novel differential gene expression analysis comparing normal mesenchymal stem cells with previously generated non-tumorigenic mesenchymal stem cells expressing the PAX7-FKHR fusion gene, as well as with a known tumorigenic, PAX7-FKHR-expressing ARMS cell line, CW9019.This novel analysis uncovered the upregulation of the NF-kappaB pathway as a function of PAX3/7-FKHR expression, but distinct from the secondary sarcomagenic process; thus implicating NF-kappaB as a mediator of the PAX3/7-FKHR differentiation block. We further show that NF-kappaB activity is upregulated in PAX7-FKHR cells when compared to parental MSCs due to upregulation of the PI3K/AKT pathway. In addition we show that NF-kappaB inhibits myogenesis via activation of cyclinD1/ cdk4 complexes, which sequester MyoD1, a key myogenic transcription factor.Our results highlight the importance of the NF-kappaB pathway in myogenesis and sarcomagenesis and suggest that this pathway may be one of the potential therapeutic targets in the treatment of ARMS.

To formally explore the potential therapeutic effect of histone deacetylase inhibitors (HDACI) and DNA-methyltransferase inhibitors (DNA-MI) on sarcomas, we treated a large sarcoma cell line panel with five different HDACIs in the absence and presence of the DNA-MI decitabine. We observed that the IC50 value of each HDACI was consistent for all cell lines whereas decitabine as a single agent showed no growth inhibition at standard doses. Combination HDACI/DNA-MI therapy showed a preferential synergism for specific sarcoma cell lines. Subsequently, we identified and validated (in vitro and in vivo) a two-gene set signature (high CUGBP2; low RHOJ) that associated with the synergistic phenotype. We further uncover that the epigenetic synergism leading to specific upregulation of CDKI p21 in specific cell lines is a function of the differences in the degree of baseline chromatin modification. Finally, we show that these chromatin and gene expression patterns are similarly present in the majority of high-grade primary sarcomas. Our results provide the first demonstration of a gene set that can predict responsiveness to HDACI/DNA-MI and links this responsiveness mechanistically to the baseline chromatin structure. Mol Cancer Ther; 10(2); 313–24. ©2011 AACR.

To expand the available tools for investigating human sarcomas, we characterized the primary properties of 22 common, uncommon, and newly characterized sarcoma cell lines representing eight different histological subtypes. Throughout the characterization process we noticed that in vitro markers and assays are poor indicators of tumorigenicity and that generated xenografts often bear little resemblance to the original histopathology. In vitro properties examined included morphology, proliferation rate, cell cycle characteristics, invasiveness, and immunohistochemical expression of p53 and phospho-AKT. In vivo properties examined included days to tumor formation in NOD/SCID mice, xenograft morphology in several locations and immunohistochemical expression of Ki67, p53 and phospho-AKT. We believe that such an in depth comparison of a large cohort of sarcoma cell lines will be useful in both designing and interpreting experiments aimed at elucidating both the molecular biology and efficacy of therapeutic agents in sarcomas. However, that data generated also suggests a small set of sarcoma cell lines may be inappropriate for generalizations regarding biological behavior of specific sarcoma subtypes. Integration of functional genomics or other more sophisticated assays of cell lines may help bridge the differences in vitro and in vivo.

Alveolar rhabdomyosarcoma (ARMS) is a pediatric sarcoma that typically occurs in older children predominantly arising in the trunk and extremities, and exhibits a worse prognosis than other types of rhabdomyosarcomas. Most ARMS tumors have t(2; 13) or t(1; 13) translocations, involving PAX3-FKHR and PAX7-FKHR fusion genes, respectively. These genetic events result in a molecular gain of function of the fusion protein which is proposed, in a yet unspecified mechanism, to perturb the differentiation of muscle progenitor cells. While a significant amount of work has been done characterizing PAX-FKHR fusion proteins in ARMS and elucidating their involvement in the sarcomagenic process, their relationship to normal skeletal muscle differentiation remains unestablished. In this manuscript we will explore a potential role for mesenchymal stem cells as the cell of origin of ARMS, and the possibility that PAX-FKHR fusion genes may commit these cells to a myogenic lineage while inhibiting terminal differentiation, thus contributing to ARMS formation. We will also review the structure and function of alternate transcripts of PAX3, PAX7, FKHR and the fusion genes PAX3-FKHR and PAX7-FKHR, and discuss the role of these genes and their downstream targets in development of ARMS. Additionally, we will review transgenic mouse models and their ability to mimic the formation of ARMS.

Malignant fibrous histiocytoma (MFH), now termed high-grade undifferentiated pleomorphic sarcoma, is a commonly diagnosed mesenchymal tumor, yet both the underlying molecular mechanisms of tumorigenesis and cell of origin remain unidentified. We present evidence demonstrating that human mesenchymal stem cells (hMSCs) are the progenitors of MFH. DKK1, a Wnt inhibitor and mediator of hMSC proliferation, is overexpressed in MFH. Using recombinant proteins, antibody depletion, and siRNA knockdown strategies of specific Wnt elements, we show that DKK1 inhibits hMSC commitment to differentiation via Wnt2/beta-catenin canonical signaling and that Wnt5a/JNK noncanonical signaling regulates a viability checkpoint independent of Dkk1. Finally, we illustrate that hMSCs can be transformed via inhibition of Wnt signaling to form MFH-like tumors in nude mice, and conversely, MFH cells in which Wnt signaling is appropriately reestablished can differentiate along mature connective tissue lineages. Our results provide mechanistic insights regarding the cell of origin of MFH, establish what we believe is a novel tumor suppressor role for Wnt signaling, and identify a potential therapeutic differentiation strategy for sarcomas.

Some tumor cells can be stimulated to differentiate and undergo terminal cell division and loss of tumorigenicity. The in vitro differentiation of murine erythroleukemia (MEL) cells is a dramatic example of tumor-cell reprogramming. We found that reentry of MEL cells into terminal differentiation is accompanied by an early transient decline in the activity of cyclin-dependant kinase (CDK) 2, followed by a decline of CDK6. Later, as cells undergo terminal arrest, CDK2 and CDK4 activities decline. By analyzing stable MEL-cell transfectants containing vectors directing inducible expression of specific CDK inhibitors, we show that only inhibitors that block the combination of CDK2 and CDK6 trigger differentiation. Inhibiting CDK2 and CDK4 does not cause differentiation. Importantly, we also show that reprogramming through inhibition of CDKs is restricted to G 1 phase of the cell cycle. The results imply that abrogation of normal cell-cycle controls in tumor cells contributes to their inability to differentiate fully and that restoration of such controls in G 1 can lead to resumption of differentiation and terminal cell division. The results also indicate that CDK4 and CDK6 are functionally distinct and support our hypothesis that the two CDKs regulate cell division at different stages of erythroid maturation.

Progression through the mammalian cell cycle is regulated by cyclins, cyclin- dependent kinases (CDKs), and cyclin-dependent kinase inhibitors (CKIs). The function of these proteins in the irreversible growth arrest associated with terminally differentiated cells is largely unknown. The function of Cip/Kip proteins p21Cip1and p27Kip1 during erythropoietin-induced terminal differentiation of primary erythroblasts isolated from the spleens of mice infected with the anemia-inducing strain of Friend virus was investigated. Both p21Cip1 and p27Kip1 proteins were induced during erythroid differentiation, but only p27Kip1 associated with the principal G1CDKs—cdk4, cdk6, and cdk2. The kinetics of binding of p27Kip1 to CDK complexes was distinct in that p27Kip1 associated primarily with cdk4 (and, to a lesser extent, cdk6) early in differentiation, followed by subsequent association with cdk2. Binding of p27Kip1 to cdk4 had no apparent inhibitory effect on cdk4 kinase activity, whereas inhibition of cdk2 kinase activity was associated with p27Kip1binding, accumulation of hypo-phosphorylated retinoblastoma protein, and G1 growth arrest. Inhibition of cdk4 kinase activity late in differentiation resulted from events other than p27Kip1 binding or loss of cyclin D from the complex. The data demonstrate that p27Kip1 differentially regulates the activity of cdk4 and cdk2 during terminal erythroid differentiation and suggests a switching mechanism whereby cdk4 functions to sequester p27Kip1 until a specified time in differentiation when cdk2 kinase activity is targeted by p27Kip1 to elicit G1 growth arrest. Further, the data imply that p21Cip1 may have a function independent of growth arrest during erythroid differentiation.

Progression through the mammalian cell cycle is regulated by cyclins, cyclin- dependent kinases (CDKs), and cyclin-dependent kinase inhibitors (CKIs). The function of these proteins in the irreversible growth arrest associated with terminally differentiated cells is largely unknown. The function of Cip/Kip proteins p21Cip1and p27Kip1 during erythropoietin-induced terminal differentiation of primary erythroblasts isolated from the spleens of mice infected with the anemia-inducing strain of Friend virus was investigated. Both p21Cip1 and p27Kip1 proteins were induced during erythroid differentiation, but only p27Kip1 associated with the principal G1CDKs—cdk4, cdk6, and cdk2. The kinetics of binding of p27Kip1 to CDK complexes was distinct in that p27Kip1 associated primarily with cdk4 (and, to a lesser extent, cdk6) early in differentiation, followed by subsequent association with cdk2. Binding of p27Kip1 to cdk4 had no apparent inhibitory effect on cdk4 kinase activity, whereas inhibition of cdk2 kinase activity was associated with p27Kip1binding, accumulation of hypo-phosphorylated retinoblastoma protein, and G1 growth arrest. Inhibition of cdk4 kinase activity late in differentiation resulted from events other than p27Kip1 binding or loss of cyclin D from the complex. The data demonstrate that p27Kip1 differentially regulates the activity of cdk4 and cdk2 during terminal erythroid differentiation and suggests a switching mechanism whereby cdk4 functions to sequester p27Kip1 until a specified time in differentiation when cdk2 kinase activity is targeted by p27Kip1 to elicit G1 growth arrest. Further, the data imply that p21Cip1 may have a function independent of growth arrest during erythroid differentiation.

Pluripotent cells can be derived from various types of somatic cells by nuclear reprogramming using defined transcription factors. It is, however, unclear whether human cancer cells can be similarly reprogrammed and subsequently terminally differentiated with abrogation of tumorigenicity. Here, using sarcomas we show that human-derived complex karyotype solid tumors: (1) can be reprogrammed into a pluripotent-like state as defined by all in vitro criteria used to define pluripotent stem cells generated from somatic cells; (2) can be terminally differentiated into mature connective tissue and red blood cells; and (3) terminal differentiation is accompanied with loss of both proliferation and tumorigenicity. We go on to perform the first global DNA promoter methylation and gene expression analyses comparing human cancers to their reprogrammed counterparts and report that reprogramming/differentiation results in significant epigenetic remodeling of oncogenes and tumor suppressors, while not significantly altering the differentiation status of the reprogrammed cancer cells, in essence dedifferentiating them to a state slightly before the mesenchymal stem cell differentiation stage. Our data demonstrate that direct nuclear reprogramming can restore terminal differentiation potential to human-derived cancer cells, with simultaneous loss of tumorigenicity, without the need to revert to an embryonic state. We anticipate that our models would serve as a starting point to more fully assess how nuclear reprogramming overcomes the multitude of genetic and epigenetic aberrancies inherent in human cancers to restore normal terminal differentiation pathways. Finally, these findings suggest that nuclear reprogramming may be a broadly applicable therapeutic strategy for the treatment of cancer.

Congenital limb reduction defects occurring in isolation of other developmental abnormalities continue to be an important medical problem in which little progress has been made. Herein we generated transgenic mice expressing Dkk1 in an appendicular mesodermal pattern. Prx1-Dkk1 mice recapitulate a full spectrum of human congenital limb reduction defects, without other developmental issues, and have normal life-spans. Importantly, a close examination of the inheritance pattern suggests that there is a significant degree of incomplete penetrance as progeny of phenotypically positive or phenotypically negative, but genotypically positive Prx1-Dkk1 mice, consistently give rise to both phenotypically positive mice and phenotypically normal-appearing mice. Thus, this heterogeneous phenotype is reproducible with each generation regardless of the phenotype of the parents. We further go on to identify that mesenchymal stem cells from Prx1-Dkk1 mice have limited proliferative ability, but normal differentiation potential, which may explain the mechanism for the limb reduction defects observed. We believe Prx1-Dkk1 mice may prove useful in the future to study the mechanisms underlying the development of congenital limb reduction defects.

Sarcomas are malignant solid tumors of mesenchymal origin which consist of 10-15% of all pediatric malignancies and associated with significantly high mortality rates despite current therapies. Oncogenic fusion genes, resulting from non-random chromosomal translocations, characterize a subset of sarcomas including rhabdomyosarcoma, the Ewing's sarcoma family of tumors, and synovial sarcoma. As investigators gain further insight into the role that fusion genes play in the development and progression of sarcomas, we are slowly uncovering novel molecules and pathways that are proving to be essential for the growth and maintenance of sarcomas and other malignancies. MicroRNAs (miRs) have been implicated in a diversity of human diseases including cancer. Only recently, has miR deregulation been shown to be an important component of sarcomagenesis. This review summarizes the recent discoveries tying miR deregulation to sarcoma biology and will discuss the potential and feasibility of miRs as novel therapeutic adjuncts to current therapies. The methodological approaches utilized in the study of miR biology and development of miR-based treatment regimens can serve as a paradigm for future investigations in other translocation-associated solid tumors.

An increasing body of evidence suggests that cancer cells acquire "stem-like" epigenetic and signaling characteristics during the tumorigenic process, including global DNA hypo-methylation, gene-specific DNA hyper-methylation, and small RNA deregulation. RNAs have been known to be epigenetic regulators, both in stem cells and in differentiated cells. A novel class of small RNAs, called piwi-interacting RNAs (piRNAs), maintains genome integrity by epigenetically silencing transposons via DNA methylation, especially in germline stem cells. piRNAs interact exclusively with the Piwi family of proteins. The human Piwi ortholog, Hiwi, has been found to be aberrantly expressed in a variety of human cancers and in some, its expression correlates with poor clinical prognosis. However, there has been little investigation into the potential role that Piwi and piRNAs might play in contributing to the "stem-like" epigenetic state of a cancer. This review will highlight the current evidence supporting the importance of Piwi and piRNAs in the epigenetics of cancer and provide a potential model for the role of Piwi and piRNAs in tumorigenesis.

The mainstay of treatment for adults with soft-tissue sarcomas is wide surgical excision. Half of all patients with adequate local control of high-grade sarcomas develop distant metastases and, despite additional treatment, ultimately die from their disease. This daunting reality has resulted in a three-decade research effort to assess the efficacy of adjuvant therapy for adult soft-tissue sarcomas. The multitude of histopathological subtypes, each with its own biology and clinical behavior, and the rarity of adult soft-tissue sarcomas as a whole greatly complicate such an assessment. This Perspectives article examines data that support or refute the use of adjuvant chemotherapy in the treatment of soft-tissue sarcomas.

The essence and origin of malignant fibrous histiocytoma (MFH) have been debated for now close to five decades. Originally characterized as a morphologically unique soft tissue sarcoma subtype in 1963 of unclear etiology with a following decade and a half of research only to conclude that “the issue of histogenesis [of MFH] is largely unresolvable”; it is “now regarded as synonymous with [high grade] undifferentiated pleomorphic sarcoma [HGUPS] and essentially represents a diagnosis of exclusion”. Yet despite this apparent lack of progress, the first decade of the 21st century has seen some significant progress in terms of defining the origins of MFH. Perhaps more importantly these origins might also pave the way for novel therapies. This manuscript will highlight MFH’s troubled history, discuss recent advances, comment as to what the coming years may promise, and what further needs to be done to make sure that progress continues.

Sarcomas are the mesenchymal-derived malignant tumors of connective tissues (e.g., fat, bone, and cartilage) presumed to arise from aberrant development or differentiation of mesenchymal stem cells (MSCs). Appropriate control of stem cell maintenance versus differentiation allows for normal connective tissue development. Current theories suggest that loss of this control-through accumulation of genetic lesions in MSCs at various points in the differentiation process -leads to development of sarcomas, including undifferentiated, high grade sarcoma tumors [1]. The initiation of stem cell differentiation is highly associated with alteration of gene expression, which depends on chromatin remodeling [2, 3]. Epigenetic chromatin modifying agents have been shown to induce cancer cell differentiation and are currently being used clinically to treat cancer. This review will focus on the importance of epigenetic chromatin remodeling in the context of mesenchymal stem cells, sarcoma tumorigenesis and differentiation therapy.

The importance of adult stem cells in the development of neoplastic diseases is becoming increasingly well appreciated. We hypothesized that sarcomas of soft tissue could be categorized by their developmental/differentiation status from stem cell to mature tissue, similar to the hematological malignancies. We conducted gene expression analyses during in vitro differentiation of human mesenchymal stem cells into adipose tissue, as a representative mature connective tissue, and identified genes whose expression changed significantly during adipogenesis. Gene clustering and distance correlation analysis allowed the assignment of a unique time point during adipogenesis that strongly correlates to each of the four major liposarcoma subtypes. Using a novel gene expression strategy, in which liposarcomas are compared to their corresponding adipocytic maturing cells, we identified a group of genes overexpressed in liposarcomas that indicate the stage of differentiation arrest, ie, sharing a similar expression profile to adipocytic cells at a corresponding stage of differentiation, and a distinct set of genes overexpressed in liposarcomas that are not found in the corresponding stage of differentiation. We propose that the latter set is enriched for candidate transformation-associated genes. Our results indicate that a degree of developmental maturity can be quantitatively assigned to solid tumors, supporting the notion that transformation of a solid tumor stem cell can occur at distinct stages of maturation.

The Wnt signal transduction pathway coordinates myriad activities, from development and differentiation to proliferation and tumorigenesis. What is perhaps most remarkable is that Wnt signaling is able to accomplish this diverse set of activities in a cell-specific and differentiation stage-dependent manner. In this review, we will highlight the diverse effect of Wnt signaling on three types of tissue stem cells and their corresponding malignancies.

Epidermal growth factor receptor (EGFR) is a validated therapeutic target for lung cancer. First and second generation EGFR inhibitors (e.g., gefitinib, erlotinib and afatinib) have revolutionized treatment paradigms of non-small cell lung cancer (NSCLC) patients with oncogenic EGFR mutations. The use of EGFR tyrosine kinase inhibitors (TKI) provides superior efficacy compared to chemotherapy in patients with EGFR L858R or exon 19 deletion tumors. However, resistance inevitably develops after 8-12 months of treatment; most commonly via a secondary T790M point mutation at the gatekeeper residue of EGFR. Furthermore, responses are hindered due to treatment intolerance in the form of rash and diarrhea that are mediated by simultaneous inhibition of wild-type (WT) EGFR at doses required for mutant EGFR suppression. To overcome these limitations, we initiated a project to identify mutant-selective EGFR inhibitors that potently inhibit both activating and T790M resistance EGFR mutations while sparing WT EGFR. In this presentation, we report our medicinal chemistry approach and optimization that led to the discovery of EGF816, a selective and potent covalent mutant-selective EGFR inhibitor with single digit nanomolar cellular target modulation on both activating and T790M resistance mutations. In addition, we will also report validated clinical efficacy data from the first patient treated with EGF816. Citation Format: Gerald Lelais, Robert Epple, Pierre-Yves Michellys, Thomas H. Marsilje, Yun Long, Matthew McNeill, Bei Chen, Wenshuo Lu, Badry Bursulaya, Michael DiDonato, Yong Jia, Shailaja Kasibhatla, Chun Li, Igor Matushansky, Steven Bender. Discovery of a potent covalent mutant-selective EGFR inhibitor - the journey from high throughput screening to EGF816. [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 2585. doi:10.1158/1538-7445.AM2015-2585

8013 Background: The emergence of T790M resistance mutations (mt) occurs in up to 50% of patients (pt) with NSCLC harboring a sensitizing EGFR mt treated with erlotinib or gefitinib. EGF816 is a co...

We analyzed the PI3K-AKT signaling cascade in a cohort of sarcomas and found a marked induction of insulin receptor substrate-2 (IRS2) and phosphorylated AKT and a concomitant upregulation of downstream effectors in most leiomyosarcomas. To determine the role of aberrant PI3K-AKT signaling in leiomyosarcoma pathogenesis, we genetically inactivated Pten in the smooth muscle cell lineage by cross-breeding Pten(loxP/loxP) mice with Tagln-cre mice. Mice carrying homozygous deletion of Pten alleles developed widespread smooth muscle cell hyperplasia and abdominal leiomyosarcomas, with a very rapid onset and elevated incidence (approximately 80%) compared to other animal models. Constitutive mTOR activation was restricted to the leiomyosarcomas, revealing the requirement for additional molecular events besides Pten loss. The rapamycin derivative everolimus substantially decelerated tumor growth on Tagln-cre/Pten(loxP/loxP) mice and prolonged their lifespan. Our data show a new and critical role for the AKT-mTOR pathway in smooth muscle transformation and leiomyosarcoma genesis, and support treatment of selected sarcomas by the targeting of this pathway with new compounds or combinations of these with conventional chemotherapy agents.

Sarcomas comprise a heterogeneous group of malignancies that are derived from mesenchymal cells, which under normal circumstances lead to the development of connective tissues such as bone, muscle, fat, and cartilage. During the past decade, insight has been gained regarding the aberrancies that occur during normal development that result in mesenchymal cells transforming into sarcomas. More recently, these insights have led to the development of successful therapies that target the specific mechanisms inherent to individual sarcomas. This overview discusses some of the aberrant molecular mechanisms shared in sarcomas and reviews several sarcoma subtypes in which the most advances have been made. Finally, the ways in which these advances in basic science are translating into and redefining clinical practice are highlighted.

PU.1 and GATA-1 are two hematopoietic specific transcription factors that play key roles in development of the myeloid and erythroid lineages, respectively. The two proteins bind to one another and inhibit each other's function in transcriptional activation and promotion of their respective differentiation programs. This mutual antagonism may be an important aspect of lineage commitment decisions. PU.1 can also act as an oncoprotein since deregulated expression of PU.1 in erythroid precursors causes erythroleukemias in mice. Studies of cultured mouse erythroleukemia cell lines indicate that one aspect of PU.1 function in erythroleukemogenesis is its ability to block erythroid differentiation by repressing GATA-1 (N. Rekhtman, F. Radparvar, T. Evans, and A. I. Skoultchi, Genes Dev. 13:1398-1411, 1999). We have investigated the mechanism of PU.1-mediated repression of GATA-1. We report here that PU.1 binds to GATA-1 on DNA. We localized the repression activity of PU.1 to a small acidic N-terminal domain that interacts with the C pocket of pRB, a well-known transcriptional corepressor. Repression of GATA-1 by PU.1 requires pRB, and pRB colocalizes with PU.1 and GATA-1 at repressed GATA-1 target genes. PU.1 and pRB also cooperate to block erythroid differentiation. Our results suggest that one of the mechanisms by which PU.1 antagonizes GATA-1 is by binding to it at GATA-1 target genes and tethering to these sites a corepressor that blocks transcriptional activity and thereby erythroid differentiation.

Oncogenic transformation usually inhibits normal cell differentiation processes. Certain chemical agents can force some tumor cells to resume their differentiation program and undergo cell cycle arrest, an approach termed differentiation therapy. Mouse erythroleukemia (MEL) cells represent an important cell culture model system for investigating the principles of differentiation therapy. MEL cells are malignant erythroblasts that are blocked from differentiating into mature erythroid cells because of inappropriate expression of the transcription factor PU.1, which binds to and represses GATA-1, a key transcriptional stimulator of red blood cell differentiation. We report here that the block to differentiation in MEL cells can be overcome by providing the cells with additional GATA-1. A conditionally active form of GATA-1 can trigger the cells to differentiate, undergo terminal cell division, and lose their tumorigenicity. We also show that the gene for the cell cycle inhibitor p21 is transcriptionally regulated by GATA-1 and is a likely downstream effector of GATA-1 that helps to promote differentiation and proliferation arrest.

Cell proliferation and differentiation are highly coordinated during normal development. Many tumor cells exhibit both uncontrolled proliferation and a block to terminal differentiation. To understand the mechanisms coordinating these two processes, we have investigated the relation between cyclin-dependent kinase (CDK) activities and the block to differentiation in murine erythroleukemia (MEL) cells. We found that CDK6 (but not CDK4) is rapidly downregulated as MEL cells are induced to re-enter erythroid differentiation and that maintenance of CDK6 (but not CDK4) activity by transfection blocks differentiation. Moreover, we found that PU.1, an Ets transcription factor that is oncogenic in erythroid cells and also can block their differentiation, controls the synthesis of CDK6 mRNA. These results suggest a mechanism for coupling proliferation and the block to differentiation in these leukemic cells through the action of an oncogenic transcription factor (PU.1) on a key cell cycle regulator (CDK6). Our findings suggest that studying the relative roles of CDK6 and CDK4 in other types of malignant cells will be important in designing approaches for cell cycle inhibition and differentiation therapy in cancer.

10560 Background: Soft tissue sarcomas are rare tumors, for which complete surgical resection offers the best chance of survival. However, two thirds of diagnosed tumors are unresectable and/or met...

Terminal differentiation of erythroid cells results in terminal cell divisions followed by irreversible cell cycle withdrawal of hemoglobinized cells. The mechanisms leading to cell cycle withdrawal were assessed in stable transfectants of murine erythroleukemia cells, in which the activities of cyclin-dependent kinases (CDKs) and CDK inhibitors (CDKIs) could be tightly regulated during differentiation. Cell cycle withdrawal of differentiating cells is mediated by induction of several CDKIs, thereby leading to inhibition of CDK2 and CDK4. Manipulation of CDK activity in differentiating cells demonstrates that the onset of cell cycle withdrawal can be either greatly accelerated or greatly delayed without affecting hemoglobin levels. Extending the proliferation of differentiating cells requires the synergistic action of CDK2 and CDK4. Importantly, CDK6 cannot substitute for CDK4 in this role, which demonstrates that the 2 cyclin D–dependent kinases are functionally different. The results show that differentiating hemoglobinized cells can be made to proliferate far beyond their normal capacity to divide.

Induced pluripotent stem cells (iPSCs) are defined as somatic cells that have been “reprogrammed” (using either the four transcriptional factors Oct4, Sox2, Klf4 and c-Myc or Oct4, Sox2, Nanog, and Lin28) to exhibit embryonic stem cell-like pluripotent differentiation properties. The generation of iPSCs was a great achievement for the field of cell transplantation and tissue engineering. More recently multiple cancer cell lines (e.g., leukemic cells, melanoma cells & gastric cancer cells) have been successfully reprogrammed to the iPSC-state, at least as defined by (1) expression of genes specific to undifferentiated embryonic stem cells; and (2) pluripotency as defined by embryoid body formation in vitro and early markers of commitment to various differentiation lineages. However, the question that remains unanswered is: can the cancer derived iPSCs complete maturation along a given lineage, be it the lineage from which it was derived (i.e., originally prematurely blocked) or an alternative lineage? If the former were demonstrated it would in essence answer the question of whether global changes in chromatin architecture or ‘epigenetics’ (which are believed to underlie the mechanism of nuclear iPSC reprogramming) can supersede the specific genetic changes (i.e., mutations) in DNA that resulted in the lineage specific differentiation block and subsequent tumorigenesis. To attempt to answer these questions we generated iPSC-cancer cells from sarcoma cell lines representing undifferentiated sarcomas, osteosarcoma cells, liposarcoma cells, and sarcomas of unknown lineage. While the original sarcoma cell lines could not be differentiated in vitro into mature connective tissue cells, their iPSC-counterparts readily differentiated into multiple mature connective tissue lineages. Furthermore, assessment of proliferation indicated that acquisition of the mature phenotype was concurrent with cessation of proliferation; and thus abrogation of tumorigenicity. We are currently (1) performing gene expression, miRNA, and global DNA promoter methylation profiling in order to assess the mechanism by which iPSC-based reprogramming of cancer cells over-rides the inherent genetic mutations in these cells and restores the capacity for terminal differentiation; and (2) extending our work to carcinomas. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 488. doi:10.1158/1538-7445.AM2011-488

9507 Background: We sought to elucidate the relationship between the human adult mesenchymal stem cell (hMSC), Wnt signaling and sarcomagenesis. Methods: In vitro hMSC differentiation, microarray gene expression analysis, distance correlation analysis, and standard molecular biology techniques were used to explore the role of Wnt in controlling the differentiation of both hMSCs and high grade undifferentiated sarcoma (HGUS; MFH, malignant fibrous histiocytoma), a common form of adult soft tissue sarcoma. Results: We determined that 1) hMSCs appear to be the progenitor cells of HGUS/MFH; 2) Dickkopf-1 (Dkk1), a specific inhibitor of Wnt signaling, is overexpressed in MFH as compared to other sarcoma subtypes and is involved in the proliferation of hMSCs; 3) in hMSCs, Dkk1 levels decline and nuclear β-catenin accumulates as hMSCs reach confluence, a prerequisite for initiation of in vitro differentiation, while in an MFH cell line Dkk1 levels do not decline and there is no nuclear β-catenin accumulation; 3) MFH cells appear to be primed for differentiation and express early markers of mesenchymal differentiation, then undergo apoptosis, if nuclear β-catenin is manipulated to enter the nucleus; 4) Wnt2 signals via the canonical β-catenin pathway and is responsible for “commitment” of hMSC and an MFH cell line to various differentiation pathways, while Wnt5a signals via the non-canonical JNK pathway in preventing apoptosis upon appropriate commitment toward differentiation. Conclusions: We identified the contribution of canonical and non-canonical Wnt signaling in the differentiation of hMSCs and showed that enhancing signaling via these pathways could be exploited as a potential target for therapy for high grade undifferentiated sarcomas. These data implicate Wnt-signaling as a mechanism of tumor suppression in early sarcomagenesis. No significant financial relationships to disclose.

In vitro differentiation of murine erythroleuekemia cells recapitulates many aspects of the erythroid terminal differentiation program, including hemoglobin synthesis and proliferation arrest. It also provides an opportunity to study the changes occurring during reprogramming of tumor cells into their normal differentiation program. This review is focused on the recent progress made in understanding the key events occurring during the reprogramming of erythroleukemia cells. We discuss the contributions of PU.1 to the block to terminal differentiation exhibited by the erythroleukemia cells as well as the role of GATA-1 in restoring normal differentiation. We also discuss the role of certain cell cycle regulators in the decision to resume normal differentiation and in the resulting terminal cell divisions and arrest.