706 Conditional cytokine therapeutics for tumor-selective biological activity: preclinical characterization of a dual-masked IFN-a2b

Background

Cytokines have been shown to elicit broad anti-tumor activity in preclinical models. These results have translated into the approval for clinical use of IFN-alpha and IL-2 before the checkpoint therapy era. However, to date, the clinical success of cytokines has been limited by systemic toxicity and poor exposure. CytomX Therapeutics has developed a new class of antibodies called Probody® therapeutics (Pb-Tx), designed to widen the therapeutic window by minimizing binding to targets in healthy tissue while being preferentially activated in the tumor microenvironment (TME) by tumor-associated proteases. CytomX has applied the Pb-Tx platform across multiple modalities including traditional antibodies, antibody-drug conjugates and T-cell engaging bispecifics and has advanced multiple programs into clinical studies. Here we have expanded the Pb-Tx platform with a conditionally activated cytokine version of IFN-α2b that has the potential to improve the therapeutic index of IFN-alpha therapy and allow systemic delivery.

Methods

We engineered an IFN-α2b with a dual masking strategy using a cleavable Fc domain at one end of IFN-a2b, and a cleavable affinity peptide mask at the other end. The construct was optimized to both maximize cleavability and minimize IFN-a2b toxicity. All animal experiments were reviewed and approved by CytomX's Institutional Animal Care and Use Committee (IACUC Protocol AP303).

Results

The optimized IFN-a2b conditionally activated cytokine strongly reduced IFN-a2b activity in vitro (5,000X) in its dual-masked form. Its activity was fully restored upon protease activation. Transcriptional profiling of in vitro treated PBMC confirmed reduction of interferon-mediated activities of the masked molecule. In vitro studies with dissociated tumors indicated its ability to activate tumor immune infiltrate, that could be further enhanced by concomitant PD-L1 blockade. In mouse xenograft studies, conditionally activated IFN-a2b cytokines induced complete regression at doses as low as 0.1mpk (activity comparable to peginterferon). Surrogate conditionally activated IFN-a2b molecules were also highly potent in syngeneic mice in vivo efficacy studies. Finally, we established an in vivo safety model in hamster which has been shown to be sensitive to IFN-a-mediated toxicity in the liver and bone marrow. In hamster, we showed that conditionally activated IFN-a2b cytokines are well tolerated up to 15mpk and have reduced systemic IFN-a2b mediated toxicity as compared to the unmasked cytokine.

Conclusions

Taken together these preclinical data further support the development of conditionally activated IFN-a2b with the potential to improve the therapeutic index of IFN-a therapy and to enable single agent and combination treatment in multiple clinical settings.

Ethics Approval

All animal experiments were reviewed and approved by CytomX's Institutional Animal Care and Use Committee (IACUC Protocol AP303).

Abstract 3202: A probody drug conjugate targeting CD166 (ALCAM) enhances preclinical antitumor activity of a probody therapeutic targeting PD-1

Immune checkpoint blockade therapies have been shown to induce potent and durable anti-tumor immunity in many cancer types. Nevertheless, not all patients benefit from immunotherapy, and immune-related adverse events remain a problem. Recently, it has been demonstrated that Antibody Drug Conjugates (ADCs) are not only capable of killing cancer cells but also can act to induce the immunogenic cell death of tumor cells as well as directly activate dendritic cells. These results provided a rationale to combine ADCs with immunotherapy to enhance the potential of immune checkpoint blockade therapies in a broader population of patients.

CytomX Therapeutics has developed a new class of antibodies called Probody™ therapeutics, designed to widen the therapeutic window by minimizing binding to target in healthy tissue while being specifically activated in the tumor microenvironment (TME) by tumor-associated proteases. Probody technology has been evaluated in preclinical studies in several antibody formats, with efficacy and increased safety windows observed for Probody therapeutics targeting the PD-1 pathway, Probody drug conjugates (PDCs) targeting highly expressed tumor antigens, and T-cell engaging bispecific Probody therapeutics. Here we extend our evaluation of the Probody platform to the combination of CX-2009, an investigational PDC targeting human CD166, with an investigational Probody therapeutic targeting PD-1.

To evaluate the anti-tumor activity of PDC CX-2009 in a syngeneic mouse model, human CD166 was overexpressed on the surface of the CT-26 murine colon carcinoma cell line. The combination treatment of CX-2009 with a surrogate mouse anti-PD-1 Probody molecule significantly inhibited tumor growth in human CD166 positive CT-26 tumor-bearing mice as compared to CX-2009 or anti-PD-1 Probody molecule alone. Tumor rejection is partially dependent on CD8+ T cells as illustrated by the evidence of a CD8+ memory T cell response in a re-challenge assay, and a reduced activity of CX-2009 alone or in combination with a mouse anti-PD-1 Probody molecule after CD8+ T cell depletion. The immunogenic potential of CX-2009 was further evaluated in multiple in vitro assays using human cancer cells and human PBMCs. In contrast to its cytotoxic activity towards CD166+ tumor cells, CX-2009 spares T cells and may enhance T cell priming.

These preclinical data demonstrate the potential utility of a combination of PDC CX-2009 with a Probody therapeutic targeting the PD-1 pathway. Generally, these data highlight the potential to combine ADCs or PDCs with immune checkpoint blockade therapies.

PROBODY is a trademark of CytomX Therapeutics, Inc.

Citation Format: Erwan Le Scolan, Tiffany Tse, Michael Krimm, Will Garner, Hikmat Assi, Jennifer Razo, Laurie Wong, Kenneth Wong, Victoria Singson, Jennifer Leong, Linnea Diep, Jennifer Richardson, Siew Schleyer, Dylan Daniel, Marcia Belvin, Michael Kavanaugh. A probody drug conjugate targeting CD166 (ALCAM) enhances preclinical antitumor activity of a probody therapeutic targeting PD-1 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3202.

Inhaled TLR9 Agonist Renders Lung Tumors Permissive to PD-1 Blockade by Promoting Optimal CD4+ and CD8+ T-cell Interplay

Currently approved inhibitors of the PD-1/PD-L1 pathway represent a major advance for the treatment of lung cancers, yet they are ineffective in a majority of patients due to lack of preexisting T-cell reactivity. Here, we show that a TLR9 agonist delivered by inhalation is able to prime T-cell responses against poorly immunogenic lung tumors and to complement the effects of PD-1 blockade. Inhaled TLR9 agonist causes profound remodeling in tumor-bearing lungs, leading to the formation of tertiary lymphoid structures adjacent to the tumors, CD8⁺ T-cell infiltration into the tumors, dendritic cell expansion, and antibody production. Inhalation of TLR9 agonist also increased the pool of functional PD-1^lowT-bet^high effector CD8⁺ T cells in tumor-bearing lungs. Effector CD8⁺ T cells generated by inhaled TLR9 agonist treatment were licensed by PD-1 blockade to become highly functional CTLs, leading to a durable rejection of both lung tumors and tumor lesions outside the lungs. CD4⁺ T cells activated in response to inhaled TLR9 play a critical role in this process by controlling the proliferation, preventing exhaustion, and guiding the differentiation of optimally functional CTLs. This study characterizes a strategy to apply localized TLR9 stimulation to a tumor type not accessible for direct injection, a strategy that may expand the therapeutic potential of PD-1 blockade in non-small cell lung cancer.Significance: These findings demonstrate that local delivery of a toll-like receptor 9 agonist can change the immune content of an entire organ and enhance the efficacy of immune checkpoint inhibition.Graphical Abstract: http://cancerres.aacrjournals.org/content/canres/78/17/4943/F1.large.jpg Cancer Res; 78(17); 4943-56. ©2018 AACR.

Abstract 4696: Development of an inhaled TLR9 agonist for the immunotherapy of lung cancer

CpG-oligonucleotides (CpG-ODN) stimulate innate immune responses through Toll-like receptor-9 (TLR9). Intratumoral (IT) administration of CpG-ODN has been shown to be safe and clinically effective in humans and in multiple animal species. An important feature of local administration of a CpG-ODN is the ability to stimulate immune responses that control the growth of distant, uninjected tumors. Such treatment is especially effective when combined with a complementary mode of immunotherapy, such as anti-PD-1 or radiation. However, repeated IT injection is not practical for many tumor types, including most lung cancers. In mild asthmatic patients and healthy subjects, CpG-ODN have demonstrated safety and pharmacologic activity when delivered by inhalation directly to the lungs. Thus, inhaled CpG presents an alternative to IT injection for primary lung cancers and for other tumor types with prominent lung metastases. In the 4T1 mouse model of metastatic breast cancer, treatment of mice with a CpG-ODN administered intranasally led to a marked reduction in the number of lung metastases. This reduction was accompanied by infiltration of tumors with activated CD8+ and CD4+ T cells and the formation of highly organized tertiary lymphoid structures. These changes are similar to those observed after IT injection of solid tumors growing subcutaneously, and are consistent with changes observed in human tumors responsive to immunotherapy. In the 4T1 model, intranasal CpG-ODN strongly synergized with systemic anti-PD-1 treatment and induced complete clearance of lung tumors, as well as metastases in tissues not exposed to the CpG-ODN, including liver, pancreas and bone. This generation of systemic immunity resulted in long-term survival in the majority of mice. Immune cell subset depletion studies implicate both CD8 and CD4 T cells in the rejection of lung tumors treated with inhaled CpG-ODN plus anti-PD1. Dynavax has developed a CpG-ODN, DV281, that is optimized for aerosol delivery and plans to initiate clinical studies in NSCLC patients in 2017.

Citation Format: Marilena Gallotta, Hikmat Assi, Robert L. Coffman, Cristiana Guiducci. Development of an inhaled TLR9 agonist for the immunotherapy of lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4696. doi:10.1158/1538-7445.AM2017-4696

Abstract 3195: STAT3 inhibition using shRNA inhibits GBM proliferation, cell migration, anchorage-independent growth of mouse, rat, and human stem-like cells in vitro; and it induces long term survival and anti-GBM immunity in vivo

The purpose of this study was to elucidate the role of Signal Transducers and Activators of Transcription 3 (STAT3) signaling on the tumor microenvironment in the most commonly occurring and aggressive primary brain tumor, Glioblastoma Multiforme (GBM), including preclinical testing of inhibition of STAT3 expression in vivo in syngeneic and patient derived xenograft (PDX) models of GBM. GBM is genetically heterogeneous, but always overexpresses genes that are vital to cell cycle regulation, cell growth and proliferation, cell invasion, and angiogenesis. STAT proteins are transcription factors associated with gene regulation and expression signatures that are implicated in several survival pathways that enable human GBMs to grow in the brain parenchyma. In addition, STAT3 has been identified as a central mechanism in tumor-induced immunosuppression in GBM and other cancers. We studied the effects of STAT3 inhibition via shRNA down-regulation in vivo and in vitro using patient derived primary glioma cells (HF2303 & MGG8) in conjunction with other glioma lines from humans, mice, and rats (U251, GL26, and CNS-1, respectively). In this study, we found that GBM cells harboring down-regulated STAT3 signaling exhibit delayed proliferation, increased apoptosis, and anchorage independence. In vivo, STAT3 inhibition resulted in increased survival rates when tumor cells were treated with the STAT3 shRNA both pre- and post-GBM implantation (syngeneic GBM model). Our data demonstrate that STAT3 has a profound influence on the GBM microenvironment, which prevents the host from clearing the tumor. Down-regulating this signaling pathway using gene therapeutic strategies allows for infiltration of immune cells, decreased invasion, and a decrease in GBM cells’ proliferation that leads to the tumor elimination in ∼83% of the animals, this was associated with the development of an effective anti-tumor immunity that prevents tumor recurrence. Given the phenotype of STAT3 inhibition in in vitro assays and its success in in vivo GBM models, inhibition of STAT3 expression using shRNA and gene therapy technologies constitutes an attractive strategy for preclinical development as a potent therapeutic target for GBM.

Citation Format: Nathan T. VanderVeen, Nicholas Raja, Elizabeth Yi, James Curtin, Peter Chockley, Hikmat Assi, Jonathan Savakus, Tom Mikkelsen, Samuel Rabkin, Pedro R. Lowenstein, Maria G. Castro. STAT3 inhibition using shRNA inhibits GBM proliferation, cell migration, anchorage-independent growth of mouse, rat, and human stem-like cells in vitro; and it induces long term survival and anti-GBM immunity in vivo. [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 3195. doi:10.1158/1538-7445.AM2015-3195

Abstract 457: Depletion of glioma infiltrating myeloid derived suppressor cells promotes anti-tumor T cell responses

MDSCs represent a population of immature myeloid cells at various stages of differentiation that have the potential to inhibit anti-tumor T cell immunity. We demonstrate the accumulation of MDSCs in GL26 and M7-induced glioma (GBM) bearing mice. Absolute numbers of Ly-6G+ (Gr-1high) MDSCs showed a 200 fold increase within the tumor microenvironment (TME) 28 days post-tumor implantation. The numbers of Ly-6C+ (Gr-1low) MDSCs also showed a similar trend within the TME. While this massive influx of MDSCs was noted within intracranial tumors, MDSC levels did not increase in the dLNs, spleen or bone marrow (BM) of intracranial tumor bearing mice. MDSC numbers were significantly elevated in the blood of GL26 and M7 intracranial tumor bearing mice at 28 days. While both Gr-1high and Gr-1low MDSCs isolated from the TME of GL26 intracranial tumor bearing mice inhibited antigen-specific T cell proliferation, Gr-1low MDSC were found to be more efficient. Gr-1high or Gr-1low MDSCs from the bone marrow of intracranial tumor bearing mice failed to suppress antigen-specific T cell proliferation suggesting that TME derived factors may activate MDSCs to exert their immune-suppressive properties. In vivo, depletion of Gr-1+ cells enhanced the median survival of GBM bearing mice. Furthermore, when combined with Ad-TK + Ad-FLT3L immune-gene therapy, Gr-1+ depletion significantly enhanced the frequency of tumor-specific T cells within the TME and spleen and increased IFN-γ production by splenic T cells. Our data therefore indicates that inhibiting the accumulation of MDSCs with in the GBM TME promotes the generation of robust anti-tumor immunity. Preliminary experiments to determine the mechanism of MDSC trafficking to the TME point towards the receptor CXCR2 and its ligand CXCL1. Microarray analysis of glioma cell lines showed elevated levels of CXCL1 mRNA. Additionally a culture of primary mixed glial cells also produced CXCL1 when stimulated with GBM cell lysates. SB225002, a CXCR2 inhibitor suppressed the migration of MDSCs towards GBM cells in an in vitro migration assay. Overall, our data suggests that strategies that inhibit MDSC recruitment to the GBM TME and/or block their activity could enhance the T cell mediated tumor clearance and provide survival benefit.

Work supported by grants from NIH-NINDS

Citation Format: Neha Kamran, Youping Li, Mariela Moreno-Ayala, Hikmat Assi, Marianela Candolfi, Marta Dzaman, Pedro Lowenstein, Maria Castro. Depletion of glioma infiltrating myeloid derived suppressor cells promotes anti-tumor T cell responses. [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 457. doi:10.1158/1538-7445.AM2015-457

Severe gastrointestinal hemorrhage during targeted therapy for advanced breast carcinoma

The introduction of targeted agents has improved survival for patients with a number of types of cancer, including several breast cancer subtypes. However, these agents are not without toxicities, and the fact that many patients are now on targeted therapy for extended periods of time has presented new challenges for the management of adverse effects. Everolimus is an inhibitor of mtor (the mammalian target of rapamycin) that is used as targeted therapy for advanced, hormone receptor-positive, her2-negative breast cancer in postmenopausal women in combination with exemestane, after treatment failure with letrozole or anastrozole. Minor hemorrhagic events are relatively common with targeted agents, but life-threatening hemorrhages, although uncommon, can also occur. We report a case of life-threatening gastrointestinal bleeding in a 48-year-old woman being treated with everolimus for advanced infiltrating ductal carcinoma of the breast. The bleeding was successfully treated with 13 sessions of endoscopic hemostasis using argon plasma coagulation.

Abstract 1085: Glioma-infiltrating myeloid derived suppressor cells inhibit anti-tumor T cell responses

Efficacy of immunotherapeutic approaches against glioma is limited by the immunosuppressive tumor microenvironment. Tumor derived TGF-β, IL-10 and Prostaglandin E2 along with the presence of regulatory T cells (Tregs) and tumor associated macrophages (TAMs) promote the immune escape in gliomas. Also, tumor derived factors induce the expansion of myeloid derived suppressor cells (MDSCs). MDSCs represent a heterogeneous population of myeloid cells at various stages of differentiation that have the potential to inhibit anti-tumor T cell responses. Herein we demonstrate the accumulation of MDSCs in GL26 brain tumor bearing mice. Absolute numbers of Ly-6G+ (Gr-1high) MDSCs showed a 200 fold increase within the tumor mass 28 days post-tumor implantation. In contrast, the numbers of Ly-6C+ (Gr-1low) MDSCs did not significantly change within the tumor microenvironment. While this massive influx of MDSCs was noted within intracranial tumors, the levels of Ly-6G+ or Ly-6C+ MDSCs did not increase in the tumor draining lymph nodes (dLNs), spleen, bone marrow or blood of intracranial tumor bearing mice. Mice bearing GL26 or B16-F0 tumors in the flank showed a ∼3 fold increased influx of Ly-6G+ MDSCs within the tumor mass, the spleen and circulating MDSCs. Ly-6G+ MDSCs isolated from the brain tumors and spleens of GL26 intracranial tumor bearing mice inhibited tumor antigen-specific CD8+ T cell proliferation and T cell proliferation mediated by CD3 ligation . On the other hand, Ly-6C+ MDSCs did not did not elicit inhibition of T cell proliferation. Preliminary experiments using tumor cells' conditioned media indicate that CXCR2 signaling mediates the migration of MDSCs in a transwell assay and suggest the possibility that it could mediate MDSCs' migration into the tumor microenvironment in vivo. Overall, our data shows that MDSCs accumulate within the glioma mass and inhibit tumor-specific T cell responses. Strategies that inhibit MDSC recruitment to the tumor microenvironment and/or block their activity may therefore enhance the T cell mediated tumor clearance and suppress glioma progression.

Supported by National Institutes of Health/ National Institute of Neurological Disorders & Stroke (NIH/NINDS) Grants RO1-NS074387 and RO1-NS054193

Citation Format: Neha Kamran, Hikmat Assi, Marianela Candolfi, Mariela Moreno, Youping Li, Pedro R. Lowenstein, Maria G. Castro. Glioma-infiltrating myeloid derived suppressor cells inhibit anti-tumor T cell responses. [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 1085. doi:10.1158/1538-7445.AM2014-1085

Abstract 187: Absence of S100A9 confers survival advantage in an aggressive de novo mouse model of glioblastoma multiforme

Glioblastoma multiforme (GBM) is the most common (60%) primary brain tumor in adults and constitutes a major challenge for both patients and clinicians, with a median survival of only 15-21 months when treated with surgery, radiation therapy and temozolomide. To improve patient outcome, a promising and safe avenue of adjuvant treatment is immune therapy with dendritic cell vaccines or adoptive T cell transfer. These treatments are however hindered by the immune suppressive environment induced by GBMs. Understanding the mechanisms by which GBM suppress the anti-tumor immune response is paramount in order to develop successful immune therapies.

The Sleeping Beauty transposase system was used to modify the genetic makeup of stem cells in the sub-ventricular zone of neonatal mice and thus induce de novo glioblastomas with several combinations of genes. The most aggressive tumors where induced when combining NRAS and SV-40 Large T antigen (NLgT) generating invasive tumors which show the histological hallmarks human GBM (WHO grade IV) with pseudo-pallisading necrosis, neovascularization and hemorrhages, rendering the mice moribund with a median survival of 30 days.

Myeloid derived suppressive cells, a heterogeneous population of immature bone marrow derived cells, are induced by cancers and other consumptive diseases and strongly inhibit adaptive and innate immune responses. We show that MDSCs isolated from de novo GBMs, inhibit antigen-specific and antigen non-specific T cell proliferation. Tumor infiltrating MDSCs highly express the pro-inflammatory secreted calcium binding protein S100A9 and its cognate receptors RAGE and TLR4. In bone marrow cultures, conditioned media from primary cell lines derived from NLgT tumors induce a marked expansion (60-70%) of myeloid derived suppressor cells (MDSCs) and enhance the expression of S100A9. Mice deficient for S100A9 with de novo NLgT tumors show an increased survival compared to wild-type animals (median survival= 47days, a 56% improvement). Analysis of tumor-infiltrating mononuclear cells in moribund NLgT wild-type and S100A9KO mice shows no significant difference in percent infiltrating MDSCs, macrophages and dendritic cells (% of CD45+), however the percent of CD8+ cytotoxic T lymphocytes is increased in S100A9 KO (16% vs. 6% p=0.0228). In addition, expression of MHCII is increased in macrophages and dendritic cells from S100A9 KO mice when compared to wild type mice.

Taken together these data suggest that the absence of S100A9 confers a survival advantage by allowing a stronger anti-tumor immune response with:(1) increased number of cytotoxic T lymphocytes and (2) increased maturation of antigen presenting cells. Experiments are currently underway to identify the detailed cellular and molecular events, which give rise to this phenotype.

This study was supported by NIH/RO1 NS057711 and NS074387.

Citation Format: Alexandra Calinescu, Hikmat Assi, Bradley Kolb, Carl Koschmann, Pedro R. Lowenstein, John Ohlfest, Maria G. Castro. Absence of S100A9 confers survival advantage in an aggressive de novo mouse model of glioblastoma multiforme. [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 187. doi:10.1158/1538-7445.AM2014-187

Lentiviral-induced high-grade gliomas in rats: the effects of PDGFB, HRAS-G12V, AKT, and IDH1-R132H

In human gliomas, the RTK/RAS/PI(3)K signaling pathway is nearly always altered. We present a model of experimental gliomagenesis that elucidates the contributions of genes involved in this pathway (PDGF-B ligand, HRAS-G12V, and AKT). We also examine the effect on gliomagenesis by the potential modifier gene, IDH1-R132H. Injections of lentiviral-encoded oncogenes induce de novo gliomas of varying penetrance, tumor progression, and histological grade depending on the specific oncogenes used. Our model mimics hallmark histological structures of high-grade glioma, such as pseudopalisades, glomeruloid microvascular proliferation, and diffuse tumor invasion. We use our model of gliomagenesis to test the efficacy of an experimental brain tumor gene therapy. Our model allowed us to test the contributions of oncogenes in the RTK/RAS/PI(3)K pathway, and their potential modification by over-expression of mutated IDH1, in glioma development and progression in rats. Our model constitutes a clinically relevant system to study gliomagenesis, the effects of modifier genes, and the efficacy of experimental therapeutics.

Adenoviral vector-mediated gene therapy for gliomas: coming of age

INTRODUCTION

Glioblastoma multiforme (GBM) is the most common primary brain tumor in adults and it carries a dismal prognosis. Adenoviral vector (Ad)-mediated gene transfer is being developed as a promising therapeutic strategy for GBM. Preclinical studies have demonstrated safety and efficacy of adenovirus administration into the brain and tumor mass in rodents and into the non-human primates' brain. Importantly, Ads have been safely administered within the tumor resection cavity in humans.

AREAS COVERED

This review gives background on GBM and Ads; we describe gene therapy strategies for GBM and discuss the value of combination approaches. Finally, we discuss the results of the human clinical trials for GBM that have used Ads.

EXPERT OPINION

The transduction characteristics of Ads, and their safety profile, added to their capacity to achieve high levels of transgene expression have made them powerful vectors for the treatment of GBM. Recent gene therapy successes in the treatment of retinal diseases and systemic brain metabolic diseases encourage the development of gene therapy for malignant glioma. Exciting clinical trials are currently recruiting patients; although, it is the large randomized Phase III controlled clinical trials that will provide the final decision on the success of gene therapy for the treatment of GBM.

Adenoviral vector-mediated gene therapy for gliomas: coming of age

INTRODUCTION

Glioblastoma multiforme (GBM) is the most common primary brain tumor in adults and it carries a dismal prognosis. Adenoviral vector (Ad)-mediated gene transfer is being developed as a promising therapeutic strategy for GBM. Preclinical studies have demonstrated safety and efficacy of adenovirus administration into the brain and tumor mass in rodents and into the non-human primates' brain. Importantly, Ads have been safely administered within the tumor resection cavity in humans.

AREAS COVERED

This review gives background on GBM and Ads; we describe gene therapy strategies for GBM and discuss the value of combination approaches. Finally, we discuss the results of the human clinical trials for GBM that have used Ads.

EXPERT OPINION

The transduction characteristics of Ads, and their safety profile, added to their capacity to achieve high levels of transgene expression have made them powerful vectors for the treatment of GBM. Recent gene therapy successes in the treatment of retinal diseases and systemic brain metabolic diseases encourage the development of gene therapy for malignant glioma. Exciting clinical trials are currently recruiting patients; although, it is the large randomized Phase III controlled clinical trials that will provide the final decision on the success of gene therapy for the treatment of GBM.

Immune toxicities and long remission duration after ipilimumab therapy for metastatic melanoma: two illustrative cases

New antitumour immunotherapy strategies for stage iv metastatic melanoma include ipilimumab, a monoclonal antibody against ctla-4. Patterns of response with cancer immunotherapy differ from those with cytotoxic chemotherapy. We present two cases of long-duration immune-related responses with ipilimumab in a phase ii trial. A 66-year-old woman with multiple lung metastases from a scalp primary melanoma received 4 doses of ipilimumab with mixed clinical response. However, after the first maintenance dose, she developed severe ileitis and colitis that responded to steroid therapy. Four months later, she had surgery and radiotherapy for a single brain metastasis. Radiologically, stable disease continued for 36 months after the last ipilimumab dose, and partial response for 5 years after ipilimumab start. A 54-year-old man with cervical lymph node and pulmonary metastases from a scalp primary melanoma received three induction doses of ipilimumab. He developed alopecia universalis and widespread vitiligo, and he discontinued treatment because of hypophysitis. Maintenance ipilimumab was started after a 6-month drug-free interval, with no further adverse events over 15 cycles. At week 12, computed tomography imaging showed no lung metastases and partial response in a supraclavicular lymph node, which was positive on positron-emission tomography. Five years after starting ipilimumab, the supraclavicular lymph node was calcified, and the patient was off steroid therapy and asymptomatic. The foregoing patients demonstrate long responses with ipilimumab (in association with delayed severe colitis in one case, and a constellation of immune events, including alopecia universalis in another). Re-treatment with ipilimumab may be possible even after significant immune adverse events.

Targeted toxins for glioblastoma multiforme: pre-clinical studies and clinical implementation

Glioblastoma multiforme (GBM) is the most common primary brain tumor in adults. GBM is very aggressive due to its poor cellular differentiation and invasiveness, which makes complete surgical resection virtually impossible. Therefore, GBM's invasive nature as well as its intrinsic resistance to current treatment modalities makes it a unique therapeutic challenge. Extensive examination of human GBM specimens has uncovered that these tumors overexpress a variety of receptors that are virtually absent in the surrounding non-neoplastic brain. Human GBMs overexpress receptors for cytokines, growth factors, ephrins, urokinase-type plasminogen activator (uPA), and transferrin, which can be targeted with high specificity by linking their ligands with highly cytotoxic molecules, such as Diptheria toxin and Pseudomonas exotoxin A. We review the preclinical development and clinical translation of targeted toxins for GBM. In view of the clinical experience, we conclude that although these are very promising therapeutic modalities for GBM patients, efforts should be focused on improving the delivery systems utilized in order to achieve better distribution of the immuno-toxins in the tumor/resection cavity. Delivery of targeted toxins using viral vectors would also benefit enormously from improved strategies for local delivery.

Gene therapy and targeted toxins for glioma

The most common primary brain tumor in adults is glioblastoma. These tumors are highly invasive and aggressive with a mean survival time of 15-18 months from diagnosis to death. Current treatment modalities are unable to significantly prolong survival in patients diagnosed with glioblastoma. As such, glioma is an attractive target for developing novel therapeutic approaches utilizing gene therapy. This review will examine the available preclinical models for glioma including xenographs, syngeneic and genetic models. Several promising therapeutic targets are currently being pursued in pre-clinical investigations. These targets will be reviewed by mechanism of action, i.e., conditional cytotoxic, targeted toxins, oncolytic viruses, tumor suppressors/oncogenes, and immune stimulatory approaches. Preclinical gene therapy paradigms aim to determine which strategies will provide rapid tumor regression and long-term protection from recurrence. While a wide range of potential targets are being investigated preclinically, only the most efficacious are further transitioned into clinical trial paradigms. Clinical trials reported to date are summarized including results from conditionally cytotoxic, targeted toxins, oncolytic viruses and oncogene targeting approaches. Clinical trial results have not been as robust as preclinical models predicted; this could be due to the limitations of the GBM models employed. Once this is addressed, and we develop effective gene therapies in models that better replicate the clinical scenario, gene therapy will provide a powerful approach to treat and manage brain tumors.

Intensive induction chemotherapy without methotrexate in adult patients with localized osteosarcoma: results of the Institut Gustave-Roussy phase II trial

PURPOSE

To improve outcomes in localized osteosarcoma and to reduce the duration of preoperative chemotherapy, we conducted a phase ii trial assessing the efficacy of an intensive protracted regimen without methotrexate (api-ai regimen) in adolescent and adult patients with newly diagnosed disease.

PATIENTS AND METHODS

Induction chemotherapy consisted of 2 cycles (4 courses) of doxorubicin 60 mg/m(2) (days 1 and 15), cisplatin 100 mg/m(2) (day 1), and ifosfamide 5 g/m(2) (days 2 and 15). The primary endpoint was good histologic response [ghr (≤5% identifiable tumour cells)].

RESULTS

From March 1993 to March 2000, 32 patients [median age: 21 years (range: 15-49 years)] were administered 126 induction courses. The median time between chemotherapy courses was 15 days (range: 12-32 days). All but 3 patients underwent conservative surgery. Toxicity was mainly hematologic, with febrile neutropenia occurring in 35% of patients and grades 3-4 thrombocytopenia in 35%. The ghr rate was 47%. The median follow-up was 64 months (range: 30-115 months). The 5-year event-free and overall survivals were 65% [95% confidence interval (ci): 48%-79%] and 69% (95% ci: 50%-83%) respectively. Two secondary hematologic malignancies occurred: 1 acute myelocytic leukemia (M5) in a poor responder with concomitant relapse, and 1 myelodysplastic syndrome in a patient achieving ghr.

CONCLUSIONS

Despite hematologic toxicity, the results observed with the api-ai regimen compare favourably with those observed during previous induction chemotherapy containing methotrexate in adult patients and the pediatric population treated at our institution. These promising results have to be validated by an ongoing national multicentre trial coordinated by the French Sarcoma Group.

Abstract 3645: Glioma-derived factors induce the expansion of myeloid derived suppressor cells which mediate immune suppression and tumor progression

Glioblastoma multiforme (GBM) is the most common and aggressive primary brain cancer in adults. In spite of improved standard of care (surgery, chemotherapy and radiation) the median survival of GBM patients remains dismal. GBM's therapeutic challenges include its invasiveness, resistance to therapies, and immune suppression. We and others have shown that immune suppressive cells infiltrate the GBM microenvironment, i.e., regulatory T cells and myeloid derived suppressor cells (MDSC). Expansion of MDSCs can be triggered by factors produced by the tumor cells, which interfere with myelopoiesis and inhibit the maturation of myeloid precursor cells. We aimed to study whether intracranial GBMs release factors to the general circulation that induce expansion of MDSCs and their recruitment into the tumor mass. We first explored the ability of GBM cells to release soluble factors that induce MDSC expansion in vitro. When compared to control 3T3 mouse fibroblasts, conditioned media (CM) from GL26 and M7 brain tumor cells expressed high levels of ligands for the receptor for advanced glycation end products (RAGE), i.e., HMGB1, S100A8 and S100A9, which have been shown to play a critical role in the expansion of MDSCs in several cancer models. Tallying with these findings, CM from GL26 and M7 glioma cells induced an increase in the number of MDSC (Gr-1+/Cd11b+) and an inhibition of dendritic cell maturation in bone marrow cultures in vitro. We then implanted intracranial GL26 tumors in syngeneic C57/Bl6 mice and evaluated the infiltration of MDSCs into the brain tumor mass and their expansion in peripheral lymphoid organs during tumor progression, as well as the capacity of GBM cells to release immunossupressive factors in vivo. An increase in circulating RAGE ligands that correlated with tumor progression was observed in the serum of tumor-bearing mice. Expansion of MDSCs was detected in cervical lymph nodes, spleen and blood 2 weeks after tumor implantation. The presence of Gr-1+/Cd11b+ MDSCs was detected within the tumor by flow cytometry at 21 and 35 (moribund) days after implantation. These cells accounted for as much as 30% of total tumor infiltrating immune cells (CD45+). By Confocal microscopy, we found Gr-1+/CD11b+ MDSCs at the tumor border and within the brain tumor mass, as well as GBM cells expressing S1008 and S100A9 and exhibiting cytoplasmic HMGB1. Multiparameter immunophenotypic analysis of bone marrow showed an increase in hematopoietic stem cells and a reduction in common myeloid progenitors, indicating an inhibition of myeloid cells’ differentiation. Our results suggest that GBM-derived factors stimulate peripheral expansion of MDSCs and their recruitment into the tumor mass, eliciting immune-suppression and GBM progression. Thus, manipulation of MDSCs emerges as an attractive therapeutic target for brain cancer.

Supported by grants from NIH/NINDS

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 3645. doi:10.1158/1538-7445.AM2011-3645

Gene therapy and virotherapy: novel therapeutic approaches for brain tumors

Glioblastoma multiforme (GBM) is a deadly primary brain tumor in adults, with a median survival of ~12-18 months post-diagnosis. Despite recent advances in conventional therapeutic approaches, only modest improvements in median survival have been achieved; GBM usually recurs within 12 months post-resection, with poor prognosis. Thus, novel therapeutic strategies to target and kill GBM cells are desperately needed. Our group and others are pursuing virotherapy and gene therapy strategies for the treatment of GBM. In this review, we will discuss various virotherapy and gene therapy approaches for GBM currently under pre-clinical and clinical evaluation including direct or conditional cytotoxic, and/or immunostimulatory approaches. We also discuss cutting-edge technologies for drug/gene delivery and targeting brain tumors, including the use of stem cells as delivery platforms, the use of targeted immunotoxins, and the therapeutic potential of using GBM microvesicles to deliver therapeutic siRNAs or virotherapies. Finally, various animal models available to test novel GBM therapies are discussed.

Abstract 1909: B cells present tumor antigen and mediate anti-tumor immunity induced by a combined immune-stimulatory/conditional cytotoxic therapy for glioblastoma

Glioblastoma multiforme is a very invasive brain tumor of glial origin that bears a dismal prognosis. We have developed adenoviral vectors (Ads) expressing TK (Ad-TK; a conditional cytotoxic molecule) and Flt3L (Ad-Flt3L; an immune-stimulatory cytokine), which increase the survival of rodent models of glioblastoma. CD4+ and CD8+ T cells are necessary for Ad-TK+Ad-Flt3L-mediated tumor regression and immunological memory. Here we investigated whether B cells are also involved in GBM regression following Ad-TK+Ad-Flt3L treatment. While Ad-TK+Ad-Flt3L induced tumor regression and long term survival in 60% of the wild type (WT) mice, the treatment completely failed in B-cell deficient Igh6−/− mice. Similarly, in the treatment failed in WT mice depleted of total B cells (using anti-CD20 Abs), or marginal zone B cells (MZB, using anti-CD11a and anti-CD49d Abs). Although we did not find expansion of spleen CD19+ B cells, the number of MZB cells increased 7 days post-treatment. We did not find changes in the number of B cells within the tumor mass and we could not detect circulating Abs against tumor cells. Although B cells are well known by their role as producers of Ag specific immunoglobulins, they can also act as efficient antigen presenting cells (APCs). The clonal expression of BcR and the high specific avidity for Ag allow B cells to accumulate and concentrate low density extracellular Ag for presentation to T cells, lowering the threshold of Ag density required for triggering adaptive immune responses. Thus, we then studied whether B cells could be acting as tumor antigen presenting cells triggering the anti-tumoral immune response induced by Ad-TK+Ad-Flt3L. We found that treatment with Ad-TK+Ad-Flt3L led to an increase in the number of B cells in the cervical lymph nodes. B cells purified from the cervical lymph nodes of Ad-TK+Ad-Flt3L-treated mice, but not from control mice, significantly increased the proliferation of allogeneic T cells purified from spleen of naïve Balb/c mice. Tumor-specific T cell clonal expansion was studied in an ELISPOT using splenocytes from tumor-bearing WT or Igh6−/− mice treated with saline or Ad-TK+Ad-Flt3L, and stimulated with Trp2180–188, a MHCI-associated GL26 tumor antigen. Tumor-specific T cell precursors were detected only in Ad-TK+Ad-Flt3L-treated WT mice, but we did not observe any increase in the frequency of tumor antigen specific T cells in Igh6−/− mice. Our data indicate that B cells act as antigen presenting cells, facilitating the clonal expansion of tumor antigen specific T cells, which leads to brain tumor eradication and immunological memory.

Support: NIH/NINDS Grant 1R21-NS054143, 1UO1 NS052465 and 1RO1-NS057711 to M.G.C.; NIH/NINDS Grants 1 RO1 NS 054193, RO1 NS061107 and 1R21 NS047298 to P.R.L. M.C. is supported by NIH/NINDS 1F32 NS058156.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1909.

Retrospective practice review of treatment of metastatic non-small-cell lung cancer with second-line erlotinib

Background

Epidermal growth factor receptor tyrosine kinase inhibitors (egfr-tkis) and chemotherapy have both demonstrated efficacy in recurrent metastatic non-small-cell lung cancer (nsclc) following failure of first-line platinum-based chemotherapy. Although the 3 available therapeutic agents—docetaxel, erlotinib, and pemetrexed—have significantly changed the treatment landscape for recurrent nsclc, the optimal selection of second- and third-line therapy has not been established. This practice review examines the outcomes in clinical practice of using second-line erlotinib followed by third-line chemotherapy in the treatment of recurrent metastatic nsclc.

Methods

We conducted a retrospective review of nsclc patient charts at three Canadian institutions. Patients with recurrent nsclc who had received second-line erlotinib therapy followed by third-line chemotherapy were selected by census. A chart review assessed key outcomes that included time to progression (ttp), response, and change in performance status. Outcomes for specific patient subgroups were also examined.

Results

We identified 35 patients for this retrospective practice review. First-line platinum-doublet therapy demonstrated a mean ttp of 6.6 months and a 46% overall response rate (15 partial responses and 1 complete response). Second-line treatment with erlotinib produced the highest mean ttp of all lines of therapy (9.2 months) and an overall response rate of 40% (all being partial responses). In the third-line setting, in which most patients received docetaxel, the mean ttp was 4.3 months and the overall response rate was 18% (all being partial responses). Subgroup analysis showed that all patient subgroups demonstrated benefit from second-line erlotinib treatment; improved benefit was observed in patients who developed rash, in female patients, in never smokers, in Asian patients, in patients with positive egfr status, and in patients with adenocarcinoma histology.

Conclusions

For patients with advanced nsclc who progressed following first-line platinum-based chemotherapy, the data demonstrate that second-line egfr-tki treatment is efficacious and well-tolerated and that it does not appear to diminish the benefit of third-line chemotherapy.

HMGB1 mediates endogenous TLR2 activation and brain tumor regression

BACKGROUND

Glioblastoma multiforme (GBM) is the most aggressive primary brain tumor that carries a 5-y survival rate of 5%. Attempts at eliciting a clinically relevant anti-GBM immune response in brain tumor patients have met with limited success, which is due to brain immune privilege, tumor immune evasion, and a paucity of dendritic cells (DCs) within the central nervous system. Herein we uncovered a novel pathway for the activation of an effective anti-GBM immune response mediated by high-mobility-group box 1 (HMGB1), an alarmin protein released from dying tumor cells, which acts as an endogenous ligand for Toll-like receptor 2 (TLR2) signaling on bone marrow-derived GBM-infiltrating DCs.

METHODS AND FINDINGS

Using a combined immunotherapy/conditional cytotoxic approach that utilizes adenoviral vectors (Ad) expressing Fms-like tyrosine kinase 3 ligand (Flt3L) and thymidine kinase (TK) delivered into the tumor mass, we demonstrated that CD4(+) and CD8(+) T cells were required for tumor regression and immunological memory. Increased numbers of bone marrow-derived, tumor-infiltrating myeloid DCs (mDCs) were observed in response to the therapy. Infiltration of mDCs into the GBM, clonal expansion of antitumor T cells, and induction of an effective anti-GBM immune response were TLR2 dependent. We then proceeded to identify the endogenous ligand responsible for TLR2 signaling on tumor-infiltrating mDCs. We demonstrated that HMGB1 was released from dying tumor cells, in response to Ad-TK (+ gancyclovir [GCV]) treatment. Increased levels of HMGB1 were also detected in the serum of tumor-bearing Ad-Flt3L/Ad-TK (+GCV)-treated mice. Specific activation of TLR2 signaling was induced by supernatants from Ad-TK (+GCV)-treated GBM cells; this activation was blocked by glycyrrhizin (a specific HMGB1 inhibitor) or with antibodies to HMGB1. HMGB1 was also released from melanoma, small cell lung carcinoma, and glioma cells treated with radiation or temozolomide. Administration of either glycyrrhizin or anti-HMGB1 immunoglobulins to tumor-bearing Ad-Flt3L and Ad-TK treated mice, abolished therapeutic efficacy, highlighting the critical role played by HMGB1-mediated TLR2 signaling to elicit tumor regression. Therapeutic efficacy of Ad-Flt3L and Ad-TK (+GCV) treatment was demonstrated in a second glioma model and in an intracranial melanoma model with concomitant increases in the levels of circulating HMGB1.

CONCLUSIONS

Our data provide evidence for the molecular and cellular mechanisms that support the rationale for the clinical implementation of antibrain cancer immunotherapies in combination with tumor killing approaches in order to elicit effective antitumor immune responses, and thus, will impact clinical neuro-oncology practice.

Toll like receptor 3 expression and efficacy of adjuvant treatment with polyadenylic-polyuridylic acid in patients with axillary node positive breast cancer: Results from two randomized trials

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Background: Toll like receptor 3 (TLR3) are transmembrane receptors involved in the cellular response to danger signal and specifically activated by double stranded RNA. Based on these data, we hypothesized that the TLR3 expression by tumor cells is associated with the efficacy of a treatment with double stranded RNA in cancer patients. Patients and Methods: TLR3 expression was assessed by immunohistochemistry in 336 patients with axillary node positive breast cancer. These patients were selected to have been included in two randomized trials that compared a post-operative administration of polyadenylic-polyuridylic acid (polyAU) to either no treatment (n = 174, trial I) or an adjuvant chemotherapy by CMF regimen (n = 162, trial II). In the trial II, locoregional and pelvic radiotherapy were given in the polyAU arm. Results: TLR3 was found to be overexpressed in 45 tumors (13%). Median follow-up were 23 and 17 years for living patients included in the trials I and II respectively. When the analysis focused on the first trial, the 20 year overall survival rates were 87% (95% CI: 53–97%) and 32% (95% CI: 12–63%) for patients with TLR3-overexpressing tumour treated (n = 8) or not (n = 11) with polyAU (p = 0.03). In the same trial, the 20 year overall survival rates were 43% (95% CI: 33–54%) and 35% (95% CI: 25–46%) for patients with TLR3-negative tumor treated (n = 81) or not (n = 74) with polyAU (p = 0.32). When the analysis focused on the Trial II, the 15 year overall survival were 62% (95% CI: 45%-91%) and 21% (95% CI: 8%-47%) for patients with TLR3-overexpressing tumors treated (n = 12) or not (n = 14) with polyAU (p = 0.005). In the same trial, 15 year overall survival rates were 31% (95% CI: 21%-42%) and 39% (95% CI: 28%-51%) for patients with TLR3-negative tumors treated (n = 66) or not (n = 70) with polyAU (p = 0.39). Conclusion: This study suggests that the post-operative administration of polyadenylic-polyuridylic acid improves outcome of patient with TLR3-overexpressing, node-positive breast cancer.

[Table: see text]

Expression of chemokine receptors predicts the site of metastatic relapse in patients with axillary node positive primary breast cancer

BACKGROUND

Recent studies have suggested that chemokine receptors are involved in development of organ-specific pattern of metastases. In the present study, we evaluated the association between the chemokine receptors expressed in primary tumor cells and the site of metastatic relapse in patients with breast cancer.

METHODS

Primary tumors were obtained from 142 patients with axillary node-positive breast cancer and stained for CX3CR1, CXCR4, CCR6, and CCR7 expression. All statistical analyses were adjusted for systemic post-operative treatment.

RESULTS

After a median follow-up of 13 years, none of the chemokine receptors was associated with overall survival or disease free survival. However, expression of chemokine receptors was found to be associated with increased risk of relapse in certain organs. By estimating the Mantel-Haenszel odds ratios (OR), CXCR4 was associated with increased risk of metastasis to the liver (OR = 3.71, P = 0.005), CX3CR1 was associated with metastasis to the brain (OR = 13.18, P = 0.01). Patients with CCR6 positivity were more likely to develop a first metastasis in the pleura (OR = 2.82, P = 0.06). In addition, CCR7 expression was associated with the occurrence of skin metastases (11% versus 0%, P = 0.017).

INTERPRETATION

Expression of chemokine receptors in the primary tumor predicts the site of metastatic relapse in patients with axillary node positive breast cancer. This study, in concordance with the data obtained in animal models, suggests that the chemokine receptors family could be the biological support of the 'seed and soil' theory.

[Expression of chemokine receptors by cancer cells]

Chemokine receptors are involved in the trafficking of leucocytes. It has been shown recently that chemokine receptors (CXCR4, CCR7...) are expressed by breast cancer cells and could be involved in the metastasis phenomenon. Since this discovery, new data have been generated in this topic. These data confirm that chemokine receptors are involved in the occurrence of metastases, suggest that their expression is regulated by genes involved in the carcinogenesis and/or angiogenesis (VHL...) and that inhibitors could be of interest in the treatment of breast cancer. In this paper, we will review all these data and will discuss the perspectives that opens this new concept.