Activity of murine surrogate antibodies for durvalumab and tremelimumab lacking effector function and the ability to deplete regulatory T cells in mouse models of cancer

Preclinical studies of PD-L1 and CTLA-4 blockade have relied heavily on mouse syngeneic tumor models with intact immune systems, which facilitate dissection of immunosuppressive mechanisms in the tumor microenvironment. Commercially developed monoclonal antibodies (mAbs) targeting human PD-L1, PD-1, and CTLA-4 may not demonstrate cross-reactive binding to their mouse orthologs, and surrogate anti-mouse antibodies are often used in their place to inhibit these immune checkpoints. In each case, multiple choices exist for surrogate antibodies, which differ with respect to species of origin, affinity, and effector function. To develop relevant murine surrogate antibodies for the anti-human PD-L1 mAb durvalumab and the anti-human CTLA-4 mAb tremelimumab, rat/mouse chimeric or fully murine mAbs engineered for reduced effector function were developed and compared with durvalumab and tremelimumab. Characterization included determination of target affinity, in vivo effector function, pharmacokinetic profile, and anti-tumor efficacy in mouse syngeneic tumor models. Results showed that anti-PD-L1 and anti-CTLA-4 murine surrogates with pharmacologic properties similar to those of durvalumab and tremelimumab demonstrated anti-tumor activity in a subset of commonly used mouse syngeneic tumor models. This activity was not entirely dependent on antibody-dependent cellular cytotoxicity, antibody-dependent cellular phagocytosis effector function, or regulatory T-cell depletion, as antibodies engineered to lack these features showed activity in models historically sensitive to checkpoint inhibition, albeit at a significantly lower level than antibodies with intact effector function.

Abstract 917: Functional blocking of CD5 on T cells to enhance the efficacy of therapeutic PD-1 blockade in treatment of mouse 4T1 breast tumors

Blockade of programmed cell death protein 1 (PD-1) is approved for treatment of multiple human cancers and is the focus of multiple studies due to its key role in T cell function. However, only patients with ‘'hot'' tumors (i.e. those with increased numbers of tumor-infiltrating CD8+ T cells) respond well to the blockade. This suggests that new strategies to increase infiltration of CD8+ T cells into tumors will increase the number of tumor types and patients benefiting from anti-PD-1 therapy. CD5, a member of the scavenger receptor cysteine-rich (SRCR) superfamily, is expressed on T cells and a subset of B cells (B1a). It can attenuate TCR signaling and impair cytotoxic T lymphocyte (CTL) activation. CD5 knockout mice have increased anti-tumor immunity and reduced homograft tumor growth: reducing CD5 on CTLs may be therapeutically beneficial to enhance the anti-tumor response and increase tumor-infiltrating CD8+ T cells. We report that in vivo administration of anti-CD5 blocking MAb treatment increased primary T cell activation in response to 4T1 tumor cell homografts and ex vivo activation as measured by increased CD69, Fas, Fas ligand, IFNγ, PD-1, and apoptosis. Further, anti-CD5 treatment enhanced the capacity of primary T cells to kill 4T1 tumor cells ex vivo. Mice receiving anti-CD5 and anti-PD-1 in combination exhibited increased overall survival compared to mice treated with either agent alone. These data support the potential of blockade of CD5 function to enhance T cell-mediated anti-tumor immunity and PD-1 blockade treatment.

Citation Format: Faizah Alotaibi, Mateusz Rytelewski, Rene Figueredo, Ronak Zareardalan1, Saman Maleki Vareki, Xiufen Zheng, Meng Zhang, Peter Ferguson, Mikal El-Hajjar, Yousef Najajreh, Wei-ping Min, James Koropatnick. Functional blocking of CD5 on T cells to enhance the efficacy of therapeutic PD-1 blockade in treatment of mouse 4T1 breast tumors [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 917.

Inhibition of Oxidative Phosphorylation Reverses Bone Marrow Hypoxia Visualized in Imageable Syngeneic B-ALL Mouse Model

Abnormally low level of interstitial oxygen, or hypoxia, is a hallmark of tumor microenvironment and a known promoter of cancer chemoresistance. Inside a solid tumor mass, the hypoxia stems largely from inadequate supply of oxygenated blood through sparse or misshapen tumor vasculature whilst oxygen utilization rates are low in typical tumor's glycolytic metabolism. In acute leukemias, however, markers of intracellular hypoxia such as increased pimonidazole adduct staining and HIF-1α stabilization are observed in advanced leukemic bone marrows (BM) despite an increase in BM vasculogenesis. We utilized intravital fast scanning two-photon phosphorescence lifetime imaging microscopy (FaST-PLIM) in a BCR-ABL B-ALL mouse model to image the extracellular oxygen concentrations (pO₂) in leukemic BM, and we related the extracellular oxygen levels to intracellular hypoxia, vascular markers and local leukemia burden. We observed a transient increase in BM pO₂ in initial disease stages with intermediate leukemia BM burden, which correlated with an expansion of blood-carrying vascular network in the BM. Yet, we also observed increased formation of intracellular pimonidazole adducts in leukemic BM at the same time. This intermediate stage was followed by a significant decrease of extracellular pO₂ and further increase of intracellular hypoxia as leukemia cellularity overwhelmed BM in disease end-stage. Remarkably, treatment of leukemic mice with IACS-010759, a pharmacological inhibitor of mitochondrial Complex I, substantially increased pO₂ in the BM with advanced B-ALL, and it alleviated intracellular hypoxia reported by pimonidazole staining. High rates of oxygen consumption by B-ALL cells were confirmed by Seahorse assay including in ex vivo cells. Our results suggest that B-ALL expansion in BM is associated with intense oxidative phosphorylation (OxPhos) leading to the onset of metabolic BM hypoxia despite increased BM vascularization. Targeting mitochondrial respiration may be a novel approach to counteract BM hypoxia in B-ALL and, possibly, tumor hypoxia in other OxPhos-reliant malignancies.

CD5 blockade enhances ex vivo CD8+ T cell activation and tumour cell cytotoxicity

CD5 is expressed on T cells and a subset of B cells (B1a). It can attenuate TCR signalling and impair CTL activation and is a therapeutic targetable tumour antigen expressed on leukemic T and B cells. However, the potential therapeutic effect of functionally blocking CD5 to increase T cell anti-tumour activity against tumours (including solid tumours) has not been explored. CD5 knockout mice show increased anti-tumour immunity: reducing CD5 on CTLs may be therapeutically beneficial to enhance the anti-tumour response. Here, we show that ex vivo administration of a function-blocking anti-CD5 MAb to primary mouse CTLs of both tumour-naïve mice and mice bearing murine 4T1 breast tumour homografts enhanced their capacity to respond to activation by treatment with anti-CD3/anti-CD28 MAbs or 4T1 tumour cell lysates. Furthermore, it enhanced TCR signalling (ERK activation) and increased markers of T cell activation, including proliferation, CD69 levels, IFN-γ production, apoptosis and Fas receptor and Fas ligand levels. Finally, CD5 function-blocking MAb treatment enhanced the capacity of CD8⁺ T cells to kill 4T1-mouse tumour cells in an ex vivo assay. These data support the potential of blockade of CD5 function to enhance T cell-mediated anti-tumour immunity.

Merger of dynamic two-photon and phosphorescence lifetime microscopy reveals dependence of lymphocyte motility on oxygen in solid and hematological tumors

Background

Low availability of oxygen in tumors contributes to the hostility of the tumor microenvironment toward the immune system. However, the dynamic relationship between local oxygen levels and the immune surveillance of tumors by tumor infiltrating T-lymphocytes (TIL) remains unclear. This situation reflects a methodological difficulty in visualizing oxygen gradients in living tissue in a manner that is suitable for spatiotemporal quantification and contextual correlation with individual cell dynamics tracked by typical fluorescence reporter systems.

Methods

Here, we devise a regimen for intravital oxygen and cell dynamics co-imaging, termed ‘Fast’ Scanning Two-photon Phosphorescence Lifetime Imaging Microscopy (FaST-PLIM). Using FaST-PLIM, we image the cellular motility of T-lymphocytes in relation to the microscopic distribution of oxygen in mouse models of hematological and solid tumors, namely in bone marrow with or without B-cell acute lymphocytic leukemia (ALL), and in lungs with sarcoma tumors.

Results

Both in bone marrow leukemia and solid tumor models, TILs encountered regions of varying oxygen concentrations, including regions of hypoxia (defined as pO₂ below 5 mmHg), especially in advanced-stage ALL and within solid tumor cores. T cell motility was sustained and weakly correlated with local pO₂ above 5 mmHg but it was very slow in pO₂ below this level. In solid tumors, this relationship was reflected in slow migration of TIL in tumor cores compared to that in tumor margins. Remarkably, breathing 100% oxygen alleviated tumor core hypoxia and rapidly invigorated the motility of otherwise stalled tumor core TILs.

Conclusions

This study demonstrates a versatile and highly contextual FaST-PLIM method for phosphorescence lifetime-based oxygen imaging in living animal tumor immunology models. The initial results of this method application to ALL and solid lung tumor models highlight the importance of oxygen supply for the maintenance of intratumoral T cell migration, define a 5 mmHg local oxygen concentration threshold for TIL motility, and demonstrate efficacy of supplementary oxygen breathing in TIL motility enhancement coincident with reduction of tumor hypoxia.

Electronic supplementary material

The online version of this article (10.1186/s40425-019-0543-y) contains supplementary material, which is available to authorized users.

Phosphorescence-optimized 2-photon lifetime and kinetic imaging reveals reanimation of tumor immune surveillance by hyper-oxygenation

Lymphocytes encounter varying oxygen levels as they traverse through healthy and diseased tissue. Hypoxia is a hallmark of the tumor microenvironment and can affect the anti-tumor immune response. However, despite the importance of T cell adaptation to differing oxygen concentrations in the tumor niche, there has been no method to study T cell spatiotemporal dynamics in the context of oxygen in vivo. To this end, we developed phosphorescence-optimized 2-photon lifetime and kinetic (2pOLAK) microscopy which enables co-imaging of phosphorescence lifetimes and cellular dynamics in highly fluorescent biological reporter systems. In conjunction with the PtP-C343 oxygen probe, 2pOLAK microscopy revealed the tissue oxygen landscapes and individual oxygen “experiences” of T cells as they moved through tissues in syngeneic models of metastatic lung cancer and acute leukemia. We found that T cells experienced hypoxia in leukemic bone marrow, and that the motility of these cells was significantly decreased relative to non-hypoxic T-cells in healthy bone marrow. Inhibition of oxidative phosphorylation slowed non-hypoxic T cell motility to a level comparable with that of hypoxic T cells. T cell motility was also decreased in hypoxic lung tumor cores, and it was significantly lower than in the tumor margin, where T cells experienced higher oxygen. Supplemental oxygenation increased the oxygen experienced by T cells in the tumor core and reanimated T cell motility. These studies describe a novel method for co-imaging tissue oxygen and cellular behavior, shed light on the role that oxygen availability plays in T cell dynamics in vivo, and suggest that counteracting hypoxia can improve tumor immune surveillance by restarting T cell motility.

Reciprocal positive selection for weakness - preventing olaparib resistance by inhibiting BRCA2

Human tumor heterogeneity promotes therapeutic failure by increasing the likelihood of resistant cell subpopulations. The PARP-1 inhibitor olaparib is approved for use in BRCA-mutated ovarian cancers but BRCA2-reversion mutations lead to functional homologous recombination repair (HRR) and olaparib resistance. To overcome that resistance and expand use of PARP1 inhibition to cancers with functional HRR, we developed an antisense strategy to render the majority of tumor cells in a population BRCA2-deficient. We predicted that this strategy would render HRR-proficient tumor cells sensitive to olaparib and prevent emergence of resistance in a tumor cell population heterogeneous for HRR proficiency. We report that BRCA2 downregulation sensitized multiple human tumor cell lines (but not non-cancer human kidney cells) to olaparib and, combined with olaparib, increased aneuploidy and chromosomal translocations in human tumor cells. In a mixed HRR-proficient and HRR-deficient cell population, olaparib monotherapy allowed outgrowth of HRR-proficient cells resistant to subsequent olaparib treatment. Combined BRCA2 inhibition and olaparib treatment prevented selection of HRR-proficient cells and inhibited proliferation of the entire population. Treatment with BRCA2 siRNA and olaparib decreased ovarian xenograft growth in mice more effectively than either treatment alone. In vivo use of BRCA2 antisense oligonucleotides may be a viable option to expand clinical use of olaparib and prevent resistance.

Abstract 876: Imaging the interaction of leukemia and bone marrow microenvironment in murine model of ALL

Interactions of leukemia and the bone marrow (BM) microenvironment are known to play a key role in the survival and growth of leukemic cells, and we have shown that HIF-1α stabilization in BM stromal cells facilitates leukemia homing and progression (Chen et al. Blood 2012, 119:4971). Leukemic cells have been shown to hijack the homeostatic mechanisms of normal hematopoietic stem cells (HSCs) and take refuge within the BM niche. This mechanism is pivotal during chemotherapy and contributes to disease relapse. In this study, we aimed to characterize the time-dependent progression of BM hypoxia involving both acute lymphocytic leukemia (ALL) cells and components of the BM niche, using multiphoton intravital microscopy (MP-IVM) . We generated a transplantable, fluorescent leukemia model by retrovirally transducing C57Bl6-Ai14 murine BM cells that express red fluorescing tdTomato with the p190-Bcr/Abl oncogene (KG Harutyunyan et al, Blood 2014 124:2396). The resulting p190-Bcr/Abl tdTomato cells caused rapid development of ALL in non-irradiated C57Bl6 immunocompetent mice, manifested by infiltration of multiple organ and BM sites, followed by death within 14-18 days. We utilized Col2.3-GFPemd transgenic mice as recipients of leukemia to highlight the osteoblastic niche, and visualized vasculature by injection of TRITC-dextran. We showed the dynamic of homing and engraftment of ALL leukemic B cells (LBC) in OB-GFP recipient mice, with homing in the vicinity of blood vessels visualized by MP-IVM, followed by proliferation and leukemia expansion. This was accompanied by invasion of both vascular and osteoblastic components of BM microenvironment. Longitudinal assessment of hypoxia utilizing pimonidazole staining showed progressive development of BM hypoxia starting from Day 10 p.i., paralleling leukemia progression, despite the abundant vascularization of the BM. To assess the integrity of the BM vascular niche during leukemia progression the experimental mice were intravitally injected with low doses of an Alexa-Fluor-647-conjugated VE-cadherin antibody (MG. Poulos et al, Epub 2013 Sep 5) to visualize the number and morphology of the perfused vessels and to analyze the architecture of the hematopoietic compartment. We observed that at late stage of leukemia progression (day 12-14 p.i) BM vessels are disorganized as a result of expansion of leukemic B cells. Ongoing longitudinal imaging experiments will characterize the cellular origin of hypoxic niche cells and the dynamic of vasculature alteration in ALL. In summary, these findings demonstrate rapid development of intra-BM hypoxia that parallels leukemia progression and involves interactions between leukemia cells and BM niche cells, as well as disordered vasculature.

Citation Format: Karine G. Harutyunyan, Saradhi Mallampati, Anna Zal, Mateusz Rytelewski, Michael C. Gutkin, Jason M. Butler, Tomasz Zal, Marina Konopleva. Imaging the interaction of leukemia and bone marrow microenvironment in murine model of ALL [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 876. doi:10.1158/1538-7445.AM2017-876

Intravital Co-Imaging of Oxygen Tension and Immune Response in Leukemia using 2-Photon PLIM

Tumor infiltrating lymphocytes (TILs) must compete with cancer cells for metabolic resources that become depleted in result of cancerous metabolism and compromised blood supply. In bone marrow, highly proliferative acute leukemias utilize oxidative phosphorylation and deplete local oxygen supply resulting in bone marrow hypoxia which contributes to therapeutic resistance. We aim to decipher the role that metabolic reprogramming of leukemic blasts plays in modulating the bone marrow microenvironment, particularly the impact on local oxygen tension, and how this affects the anti-leukemia immune response. To characterize the spatiotemporal dynamics of leukemia infiltrating T cells during disease progression, and determine the impact of oxygen tension, OxPhos, and OxPhos inhibition on T cell function inside the leukemic bone marrow, we have utilized a novel oxygen probe, PtP-C343, and intravital 2-photon phosphorescence lifetime microscopy (2p-PLIM). Our initial results demonstrate sufficient spatial and temporal resolution of the combination 2p-PLIM to simultaneously reveal intravital oxygen gradients and track lymphocytes in single cell resolution. The combination 2p-PLIM and in vivo cell tracking will enable to study the dynamic regulation of the migratory behavior of cancer-infiltrating T lymphocytes by the intratumoral oxygen tension gradients.

Abstract 3718: Sensitization of human tumor cells to chemotherapy drugs by antisense downregulation of RAD51: Targeting DNA repair to induce synthetic lethality

The inherent genomic instability of cancer cells has been exploited as a tumor-selective drug target to treat tumors that are deficient in specific mechanisms of DNA repair. Inhibitors of poly(ADP-ribose) polymerase (PARP) are routinely used clinically against tumors deficient in BRCA1 or BRCA2, due to the poor capacity of these cells to undergo homologous recombination repair (HRR). This exploitation of a tumor cell deficiency to enhance selectivity to a particular drug is “synthetic lethality” (Nature 434: 913, 2005). To make use of this phenomenon in tumors that may not be inherently hypersensitive to a particular treatment, we have sought to induce synthetic lethality by down-regulating essential components of DNA repair, in particular BRCA2, to sensitize cells to chemotherapy drugs [Mol Oncol 8(8): 1429-1440, 2014]. Given that an important function of BRCA2 is to modulate the action of RAD51 in HRR, we determined whether antisense knockdown of RAD51 could enhance tumor cell sensitivity to the PARP inhibitor olaparib and the DNA-crosslinking agent cisplatin. Four different anti-RAD51 siRNA molecules (Dharmacon), targeting coding sequences, were tested against cell lines representative of different tumor types in an in vitro assay of proliferation (non-small cell lung cancer line A549b, colon carcinoma line HT-29, and prostate carcinoma lines DU145 and LNCaP). The siRNAs, as single agents, inhibited proliferation in a concentration-dependent fashion and to varying degrees, and sensitized tumor cells to olaparib. A sequence that targeted region 1169-1187 of the RAD51 cDNA (NM_002875.4) was utilized for further studies. At concentrations of anti-RAD51 siRNA 51a that inhibited proliferation of cell lines by less than 50%, 51a enhanced cytotoxicity of olaparib by over 90% and of cisplatin by 60-90%. In all cell lines except LNCaP (with mutant BRCA2) the combination of siRNAs against RAD51 and BRCA2 acted cooperatively to enhance cytotoxicity of olaparib and cisplatin. Notably, when used together, each siRNA down-regulated expression of its respective target mRNA, as demonstrated by quantitative RT-PCR, without interfering with the activity of the other. RAD51 can be exploited clinically as a target for inherent or induced synthetic lethality to DNA-damaging agents (e.g., cisplatin) or inhibitors of DNA repair (e.g., olaparib). Such treatment can include tumors with BRCA2-deficiency, either inherent or induced, to yield at least an additive anticancer effect. MR is a scholar of the CIHR Strategic Training Program in Cancer Research and Technology Transfer (CaRTT) and a recipient of the CIHR Banting and Best Canada Graduate Scholarship.

Citation Format: Peter J. Ferguson, Mateusz Rytelewski, Mark D. Vincent, James Koropatnick. Sensitization of human tumor cells to chemotherapy drugs by antisense downregulation of RAD51: Targeting DNA repair to induce synthetic lethality. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3718.

siRNA knockdown of mitochondrial thymidine kinase 2 (TK2) sensitizes human tumor cells to gemcitabine

Nucleoside metabolism enzymes are determinants of chemotherapeutic drug activity. The nucleoside salvage enzyme deoxycytidine kinase (dCK) activates gemcitabine (2', 2'-difluoro-2'-deoxycytidine) and is negatively regulated by deoxycytidine triphosphate (dCTP). Reduction of dCTP in tumor cells could, therefore, enhance gemcitabine activity. Mitochondrial thymidine kinase 2 (TK2) phosphorylates deoxycytidine to generate dCTP. We hypothesized that: (1) TK2 modulates human tumor cell sensitivity to gemcitabine, and (2) antisense knockdown of TK2 would decrease dCTP and increase dCK activity and gemcitabine activation. siRNA downregulation of TK2 sensitized MCF7 and HeLa cells (high and moderate TK2) but not A549 cells (low TK2) to gemcitabine. Combined treatment with TK2 siRNA and gemcitabine increased dCK. We also hypothesized that TK2 siRNA-induced drug sensitization results in mitochondrial damage that enhances gemcitabine effectiveness. TK2 siRNA and gemcitabine decreased mitochondrial redox status, DNA content, and activity. This is the first demonstration of a direct role for TK2 in gemcitabine resistance, or any independent role in cancer drug resistance, and further distinguishes TK2 function from that of other dTMP-producing enzymes [cytosolic TK1 and thymidylate synthase (TS)]. siRNA knockdown of TK1 and/or TS did not sensitize cancer cells to gemcitabine indicating that, among the 3 enzymes, only TK2 is a candidate therapeutic target for combination with gemcitabine.

Evaluating the effectiveness of cancer drug sensitization in vitro and in vivo

Due to the high level of heterogeneity and mutations inherent in human cancers, single agent therapies, or combination regimens which target the same pathway, are likely to fail. Emphasis must be placed upon the inhibition of pathways that are responsible for intrinsic and/or adaptive resistance to therapy. An active field of investigation is the development and testing of DNA repair inhibitors that promote the action of, and prevent resistance to, commonly used chemotherapy and radiotherapy. We used a novel protocol to evaluate the effectiveness of BRCA2 inhibition as a means to sensitize tumor cells to the DNA damaging drug cisplatin. Tumor cell metabolism (acidification and respiration) was monitored in real-time for a period of 72 hr to delineate treatment effectiveness on a minute by minute basis. In combination, we performed an assessment of metastatic frequency using a chicken embryo chorioallantoic membrane (CAM) model of extravasation and invasion. This protocol addresses some of the weaknesses of commonly used in vitro and in vivo methods to evaluate novel cancer therapy regimens. It can be used in addition to common methods such as cell proliferation assays, cell death assays, and in vivo murine xenograft studies, to more closely discriminate amongst candidate targets and agents, and select only the most promising candidates for further development.

Abstract 1687: A BRCA2-targeting antisense oligodeoxynucleotide enhances cisplatin effectiveness by decreasing human tumor cell proliferation, metastatic frequency, and metabolic response

BRCA2 is involved in homologous recombination repair of double-stranded DNA breaks in human cells. Inactivating mutations in BRCA2 predispose to early onset cancer of the breast, ovary and other tissues. However, patients with tumors that harbor BRCA2 mutations respond better to cancer therapy. Therefore, reducing BRCA2 in cancer cells capable of homologous recombination repair may sensitize otherwise resistant tumors to DNA-damaging anti-cancer treatment. We developed a second generation antisense oligodeoxynucleotide (BR-1) that specifically targets BRCA2. BR-1 decreased BRCA2 mRNA and protein and inhibited BRCA2-mediated RAD51 repair focus formation. BR-1 potently sensitized A549 (lung), SKOV-3 (ovarian), and MDA-MB-231 (breast) cells to cisplatin as evidenced by decreased cell proliferation. However, non-cancerous HK-2 kidney cells were not sensitized to cisplatin by BR-1. In A549 cells BR-1 enhanced cisplatin or ionizing radiation-induced inhibition of in vitro colony formation. Cisplatin-resistant head and neck squamous cancer cells (HN-15a) were rendered as sensitive to cisplatin following BR-1 treatment as the parent population. In addition, BR-1 plus cisplatin treatment decreased A549 cell metastatic frequency in an in vivo chicken chorio-allantoic membrane (CAM) model by over 70% when compared with drug treatment alone. Treatment with BR-1 and cisplatin decreased cellular respiration (decreased oxygen consumption) compared to control oligonucleotide plus cisplatin treatment, suggesting that downregulation of BRCA2 in the context of platinating drug treatment alters cellular metabolism. This change in respiration occurred independently of changes in mitochondrial number. We are continuing to develop and test BR-1 with the aim of applying it in an adjuvant setting with cisplatin in human clinical trials in the future. Supported by grants from the Ontario Centres of Excellence (OCE)

Citation Format: Mateusz Rytelewski, Jessica Tong, Adrian Buensuceso, Hon Leong, Peter Ferguson, Saman Maleki Vareki, Christine Di Cresce, Larissa Romanow, Trevor Shepherd, Bonnie Deroo, Ann Chambers, Mark Vincent, James Koropatnick. A BRCA2-targeting antisense oligodeoxynucleotide enhances cisplatin effectiveness by decreasing human tumor cell proliferation, metastatic frequency, and metabolic response. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1687. doi:10.1158/1538-7445.AM2014-1687

Abstract 3765: Indoleamine 2,3-dioxygenase mediates immune-independent human tumor cell resistance to olaparib, γ radiation, and cisplatin

Indoleamine 2,3-dioxygenase-1 (IDO) is an immunosuppressive molecule expressed by most human tumors. IDO levels correlate with poor prognosis in cancer patients and IDO inhibitors are under investigation to enhance endogenous anticancer immunosurveillance. Little is known of immune-independent functions of IDO relevant to cancer therapy. We show, for the first time, that IDO mediates human tumor cell resistance to a PARP inhibitor (olaparib), γ radiation, cisplatin, and combined treatment with olaparib and radiation, in the absence of immune cells. Antisense-mediated reduction of IDO, alone and (in a synthetic lethal approach) in combination with antisense to the DNA repair protein BRCA2 sensitizes human lung cancer cells to olaparib and cisplatin. Antisense reduction of IDO decreased NAD+ in human tumor cells. NAD+ is essential for PARP activity and these data suggest that IDO mediates treatment resistance independent of immunity and at least partially due to a previously unrecognized role for IDO in DNA repair. Furthermore, IDO levels correlated with accumulation of tumor cells in G1 and depletion of cells in G2/M of the cell cycle, suggesting that IDO effects on cell cycle may also modulate sensitivity to radiation and chemotherapeutic agents. IDO is a potentially valuable therapeutic target in cancer treatment, independent of immune function and in combination with other therapies.

Supported by grants to JK and WM from the Canadian Institutes of Health Research (CIHR).

Citation Format: Saman Maleki Vareki, Mateusz Rytelewski, Rene Figueredo, Di Chen, Peter J. Ferguson, Mark Vincent, Weiping Min, Xiufen Zheng, James Koropatnick. Indoleamine 2,3-dioxygenase mediates immune-independent human tumor cell resistance to olaparib, γ radiation, and cisplatin. [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 3765. doi:10.1158/1538-7445.AM2014-3765

BRCA2 inhibition enhances cisplatin-mediated alterations in tumor cell proliferation, metabolism, and metastasis

Tumor cells have unstable genomes relative to non-tumor cells. Decreased DNA integrity resulting from tumor cell instability is important in generating favorable therapeutic indices, and intact DNA repair mediates resistance to therapy. Targeting DNA repair to promote the action of anti-cancer agents is therefore an attractive therapeutic strategy. BRCA2 is involved in homologous recombination repair. BRCA2 defects increase cancer risk but, paradoxically, cancer patients with BRCA2 mutations have better survival rates. We queried TCGA data and found that BRCA2 alterations led to increased survival in patients with ovarian and endometrial cancer. We developed a BRCA2-targeting second-generation antisense oligonucleotide (ASO), which sensitized human lung, ovarian, and breast cancer cells to cisplatin by as much as 60%. BRCA2 ASO treatment overcame acquired cisplatin resistance in head and neck cancer cells, but induced minimal cisplatin sensitivity in non-tumor cells. BRCA2 ASO plus cisplatin reduced respiration as an early event preceding cell death, concurrent with increased glucose uptake without a difference in glycolysis. BRCA2 ASO and cisplatin decreased metastatic frequency in vivo by 77%. These results implicate BRCA2 as a regulator of metastatic frequency and cellular metabolic response following cisplatin treatment. BRCA2 ASO, in combination with cisplatin, is a potential therapeutic anti-cancer agent.

Suppression of immunodominant antitumor and antiviral CD8+ T cell responses by indoleamine 2,3-dioxygenase

Indoleamine 2,3-dioxygenase (IDO) is a tryptophan-degrading enzyme known to suppress antitumor CD8⁺ T cells (T_CD8). The role of IDO in regulation of antiviral T_CD8 responses is far less clear. In addition, whether IDO controls both immunodominant and subdominant T_CD8 is not fully understood. This is an important question because the dominance status of tumor- and virus-specific T_CD8 may determine their significance in protective immunity and in vaccine design. We evaluated the magnitude and breadth of cross-primed T_CD8 responses to simian virus 40 (SV40) large T antigen as well as primary and recall T_CD8 responses to influenza A virus (IAV) in the absence or presence of IDO. IDO^−/− mice and wild-type mice treated with 1-methyl-D-tryptophan, a pharmacological inhibitor of IDO, exhibited augmented responses to immunodominant epitopes encoded by T antigen and IAV. IDO-mediated suppression of these responses was independent of CD4⁺CD25⁺FoxP3⁺ regulatory T cells, which remained numerically and functionally intact in IDO^−/− mice. Treatment with L-kynurenine failed to inhibit T_CD8 responses, indicating that tryptophan metabolites are not responsible for the suppressive effect of IDO in our models. Immunodominant T antigen-specific T_CD8 from IDO^−/− mice showed increased Ki-67 expression, suggesting that they may have acquired a more vigorous proliferative capacity in vivo. In conclusion, IDO suppresses immunodominant T_CD8 responses to tumor and viral antigens. Our work also demonstrates that systemic primary and recall T_CD8 responses to IAV are controlled by IDO. Inhibition of IDO thus represents an attractive adjuvant strategy in boosting anticancer and antiviral T_CD8 targeting highly immunogenic antigens.

Inhibition of BRCA2 and Thymidylate Synthase Creates Multidrug Sensitive Tumor Cells via the Induction of Combined "Complementary Lethality"

A high mutation rate leading to tumor cell heterogeneity is a driver of malignancy in human cancers. Paradoxically, however, genomic instability can also render tumors vulnerable to therapeutic attack. Thus, targeting DNA repair may induce an intolerable level of DNA damage in tumor cells. BRCA2 mediates homologous recombination repair, and BRCA2 polymorphisms increase cancer risk. However, tumors with BRCA2 mutations respond better to chemotherapy and are associated with improved patient prognosis. Thymidylate synthase (TS) is also involved in DNA maintenance and generates cellular thymidylate. We determined that antisense downregulation of BRCA2 synergistically potentiated drugs with mechanisms of action related to BRCA2 function (cisplatin, melphalan), a phenomenon we named “complementary lethality.” TS knockdown induced complementary lethality to TS-targeting drugs (5-FUdR and pemetrexed) but not DNA cross-linking agents. Combined targeting of BRCA2 and TS induced complementary lethality to both DNA-damaging and TS-targeting agents, thus creating multidrug sensitive tumors. In addition, we demonstrated for the first time that simultaneous downregulation of both targets induced combined complementary lethality to multiple mechanistically different drugs in the same cell population. In this study, we propose and define the concept of “complementary lethality” and show that actively targeting BRCA2 and TS is of potential therapeutic benefit in multidrug treatment of human tumors. This work has contributed to the development of a BRCA2-targeting antisense oligdeoxynucleotide (ASO) “BR-1” which we will test in vivo in combination with our TS-targeting ASO “SARI 83” and attempt early clinical trials in the future.

Differential regulation of simultaneous antitumor and alloreactive CD8(+) T-cell responses in the same host by rapamycin

Rapamycin is an immunosuppressive agent routinely used in organ transplantation but also paradoxically exerts antiviral and antitumor activities. Pathogen-specific memory CD8(+) T-cell (T(CD8) ) responses were recently found to be augmented by rapamycin. However, whether rapamycin influences the magnitude and quality of anticancer T(CD8) responses is unknown. Importantly, how rapamycin may regulate simultaneous virus/tumor-specific and alloreactive T(CD8) in the same host remains unexplored. To answer these questions, we primed wild-type mice with allogeneic cells concomitantly expressing simian virus 40 large tumor antigen (T Ag), a viral oncoprotein with well-defined epitopes. Rapamycin selectively enhanced the cross-priming of T(CD8) specific for T Ag's most immunodominant epitope called site IV but not T(CD8) alloreactivity. Rapamycin-treated mice also had a high percentage of splenic CD127(high) KLRG1(low) T(CD8) and an increased frequency of site IV-specific T cells long after the peak of their primary response. When site IV was presented as a cytosolic minigene encoded by a recombinant vaccinia virus, rapamycin failed to boost the site IV-specific response. Therefore, the nature and presentation mode of antigen determine the susceptibility to the adjuvant effect of rapamycin. Our findings reveal the unexpected benefit of rapamycin treatment in recipients of allografts co-expressing tumor/viral Ags.

Abstract C225: Differential regulation of simultaneous antitumor and alloreactive CD8+ T cell responses in the same host by rapamycin

Rapamycin is an immunosuppressive agent routinely used in organ transplantation, but also paradoxically, exerts antiviral and anti-tumor activities. Pathogen-specific memory CD8+ T cell (TCD8) responses were recently found to be augmented by rapamycin. However, whether rapamycin influences the magnitude and quality of anticancer TCD8 responses is unknown. Importantly, how rapamycin may regulate simultaneous virus/tumor-specific and alloreactive TCD8 in the same host remains unexplored. To answer these questions, we primed wild-type mice with allogeneic cells concomitantly expressing simian virus 40 large tumor antigen (T Ag), a viral oncoprotein with well-defined epitopes. Rapamycin selectively improved the cross-priming of TCD8 specific for T Ag's most immunodominant epitope called site IV. Rapamycin-treated mice also had a high percentage of splenic CD127highKLRG1low TCD8 as well as an increased frequency of site IV-specific T cells long after the peak of their primary response. When site IV was presented as a cytosolic minigene encoded by a recombinant vaccinia virus, rapamycin failed to enhance the site IV-specific response. Therefore, the nature and presentation mode of antigen determine the susceptibility to the adjuvant effect of rapamycin. Our findings reveal the unexpected benefit of rapamycin treatment in recipients of allografts co-expressing tumor/viral Ags.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr C225.