High-Throughput Testing of Novel-Novel Combination Therapies for Cancer: An Idea Whose Time Has Come

Combination therapies are essential to address the genetic complexity, plasticity, and heterogeneity of tumors and to overcome resistance mechanisms that confound single-agent approaches, and are a paradigm that became well established in the era of conventional cytotoxic chemotherapies. Today, we are well equipped to address many of the scientific, clinical, and collaboration challenges that have existed historically; however, the pace of testing rational combinations is modest. Our analysis shows that the volume of clinical trials testing multiple investigational pipeline agents ("novel-novel" combinations) is dismally low, as out of approximately 1,500 phase I to III investigational combination trials initiated in 2014-2015, only 80 were for novel-novel combinations, and only 9 of those involved more than one company. The Collaborative Novel-Novel Combination Therapies (CoNNCT) initiative aims to alleviate this bottleneck by developing a new, faster paradigm for early investigation of scientifically informed, novel-novel drug combinations. The initiative kicked off on March 7, 2016, when representatives from top academic centers, biopharma, nonprofits, the FDA, and other groups gathered to define an actionable path forward. Cancer Discov; 6(9); 956-62. ©2016 AACR.

Modulating the tumor immune microenvironment as an ovarian cancer treatment strategy

After more than 30 years of iterations of surgical debulking plus chemotherapy, the need for complementary ovarian cancer treatments has become clear. In the ovarian cancer microenvironment, myeloid immunosuppressive leukocytes, lymphocytes, fibroblasts and endothelial cells, as well as their secreted products, surface molecules and paracrine survival factors, all provide opportunities for novel interventions. The potential of targeting microenvironmental elements in ovarian cancer patients is underscored by recently successful anti-angiogenic therapies. The compartmentalized nature of ovarian cancer, its immunogenicity and its accessibility make it an ideal disease for targeting non-tumor host cells. This review discusses the 'state-of-the-art' of the field, with an emphasis on the potential of modulating the activity of abundant microenvironmental immune cells, which govern both angiogenesis and immunosuppression.

Avirulent Toxoplasma gondii generates therapeutic antitumor immunity by reversing immunosuppression in the ovarian cancer microenvironment

Reversing tumor-associated immunosuppression seems necessary to stimulate effective therapeutic immunity against lethal epithelial tumors. Here, we show this goal can be addressed using cps, an avirulent, nonreplicating uracil auxotroph strain of the parasite Toxoplasma gondii (T. gondii), which preferentially invades immunosuppressive CD11c(+) antigen-presenting cells in the ovarian carcinoma microenvironment. Tumor-associated CD11c(+) cells invaded by cps were converted to immunostimulatory phenotypes, which expressed increased levels of the T-cell receptor costimulatory molecules CD80 and CD86. In response to cps treatment of the immunosuppressive ovarian tumor environment, CD11c(+) cells regained the ability to efficiently cross-present antigen and prime CD8(+) T-cell responses. Correspondingly, cps treatment markedly increased tumor antigen-specific responses by CD8(+) T cells. Adoptive transfer experiments showed that these antitumor T-cell responses were effective in suppressing solid tumor development. Indeed, intraperitoneal cps treatment triggered rejection of established ID8-VegfA tumors, an aggressive xenograft model of ovarian carcinoma, also conferring a survival benefit in a related aggressive model (ID8-Defb29/Vegf-A). The therapeutic benefit of cps treatment relied on expression of IL-12, but it was unexpectedly independent of MyD88 signaling as well as immune experience with T. gondii. Taken together, our results establish that cps preferentially invades tumor-associated antigen-presenting cells and restores their ability to trigger potent antitumor CD8(+) T-cell responses. Immunochemotherapeutic applications of cps might be broadly useful to reawaken natural immunity in the highly immunosuppressive microenvironment of most solid tumors.

Immune-mediated regression of established B16F10 melanoma by intratumoral injection of attenuated Toxoplasma gondii protects against rechallenge

Immune recognition of tumors can limit cancer development, but antitumor immune responses are often blocked by tumor-mediated immunosuppression. Because microbes or microbial constituents are powerful adjuvants to stimulate immune responses, we evaluated whether intratumoral administration of a highly immunogenic but attenuated parasite could induce rejection of an established poorly immunogenic tumor. We treated intradermal B16F10 murine melanoma by intratumoral injection of an attenuated strain of Toxoplasma gondii (cps) that cannot replicate in vivo and therefore is not infective. The cps treatment stimulated a strong CD8(+) T cell-mediated antitumor immune response in vivo that regressed established primary melanoma. The cps monotherapy rapidly modified the tumor microenvironment, halting tumor growth, and subsequently, as tumor-reactive T cells expanded, the tumors disappeared and rarely returned. The treatment required live cps that could invade cells and also required CD8(+) T cells and NK cells, but did not require CD4(+) T cells. Furthermore, we demonstrate that IL-12, IFN-γ, and the CXCR3-stimulating cytokines are required for full treatment efficacy. The treatment developed systemic antitumor immune activity as well as antitumor immune memory and therefore might have an impact against human metastatic disease. The approach is not specific for either B16F10 or melanoma. Direct intratumoral injection of cps has efficacy against an inducible genetic melanoma model and transplantable lung and ovarian tumors, demonstrating potential for broad clinical use. The combination of efficacy, systemic antitumor immune response, and complete attenuation with no observed host toxicity demonstrates the potential value of this novel cancer therapy.

Ovarian cancer progression is controlled by phenotypic changes in dendritic cells

We characterized the initiation and evolution of the immune response against a new inducible p53-dependent model of aggressive ovarian carcinoma that recapitulates the leukocyte infiltrates and cytokine milieu of advanced human tumors. Unlike other models that initiate tumors before the development of a mature immune system, we detect measurable anti-tumor immunity from very early stages, which is driven by infiltrating dendritic cells (DCs) and prevents steady tumor growth for prolonged periods. Coinciding with a phenotypic switch in expanding DC infiltrates, tumors aggressively progress to terminal disease in a comparatively short time. Notably, tumor cells remain immunogenic at advanced stages, but anti-tumor T cells become less responsive, whereas their enduring activity is abrogated by different microenvironmental immunosuppressive DCs. Correspondingly, depleting DCs early in the disease course accelerates tumor expansion, but DC depletion at advanced stages significantly delays aggressive malignant progression. Our results indicate that phenotypically divergent DCs drive both immunosurveillance and accelerated malignant growth. We provide experimental support for the cancer immunoediting hypothesis, but we also show that aggressive cancer progression after a comparatively long latency period is primarily driven by the mobilization of immunosuppressive microenvironmental leukocytes, rather than loss of tumor immunogenicity.

Reprogramming tumor-associated dendritic cells in vivo using miRNA mimetics triggers protective immunity against ovarian cancer

Modulating the activity of miRNAs provides opportunities for novel cancer interventions. However, low bioavailability and poor cellular uptake are major challenges for delivering miRNA mimetics specifically to tumor cells. Here, we took advantage of the spontaneous enhanced endocytic activity of ovarian cancer-associated dendritic cells (DC) to selectively supplement the immunostimulatory miRNA miR-155. In vivo processing of nanoparticles carrying oligonucleotide duplexes mimicking the bulged structure of endogenous pre-miRNA (but not siRNA-like oligonucleotides) dramatically augmented miR-155 activity without saturating the RNA-induced silencing complex. Endogenous processing of synthetic miR-155 favored Ago2 and, to a lesser extent, Ago4 loading, resulting in genome-wide transcriptional changes that included silencing of multiple immunosuppressive mediators. Correspondingly, tumor-infiltrating DCs were transformed from immunosuppressive to highly immunostimulatory cells capable of triggering potent antitumor responses that abrogated the progression of established ovarian cancers. Our results show both the feasibility and therapeutic potential of supplementing/replenishing miRNAs in vivo using nonviral approaches to boost protective immunity against lethal tumors. Thus, we provide a platform, an optimized design, and a mechanistic rationale for the clinical testing of nonviral miRNA mimetics.

CD277 is a negative co-stimulatory molecule universally expressed by ovarian cancer microenvironmental cells

CD277, a member of the butyrophilin subfamily 3 (BTN3), shares significant sequence similarities and predicted common structural features with inhibitory B7-H4 and other members of the B7 superfamily. Here we report that CD277 is consistently expressed in stromal, as well as tumor cells in the microenvironment of human advanced ovarian carcinoma specimens, both of primary and metastatic origin. MHC-II+ myeloid antigenpresenting leukocytes (dendritic cells and macrophages) express significantly higher levels of surface CD277, compared to other tumor-infiltrating leukocyte subsets, and this expression is significantly up-regulated by multiple common tumor microenvironmental signals, including VEGF and CCL3. Most importantly, engagement of CD277 on the surface of TCR-stimulated T cells inhibits their otherwise robust expansion and production of Th1 cytokines by preventing the up-regulation of cFLIP. Our results point to a role for CD277 up-regulated by microenvironmental signals in the acquisition of a regulatory phenotype by tumor-associated myeloid cells. Consequently, CD277, and likely other butyrophilins and butyrophilin-like molecules, emerge as regular players in the orchestration of immunosuppressive networks in ovarian cancer, and therefore new targets for interventions to overcome immune evasion and boost anti-tumor immunity in cancer patients.

CD4+ T cells elicit host immune responses to MHC class II-negative ovarian cancer through CCL5 secretion and CD40-mediated licensing of dendritic cells

T cell adoptive transfer strategies that have produced clinical remissions against specific tumors have so far produced disappointing results against ovarian cancer. Recent evidence suggests that adoptively transferred CD4(+) T cells can trigger endogenous immune responses in particular patients with ovarian cancer through unknown mechanisms. However, conflicting reports suggest that ovarian cancer-infiltrating CD4(+) T cells are associated with negative outcomes. In this study, we elucidate the phenotypic attributes that enable polyclonal CD4(+) T cells briefly primed against tumor Ags to induce therapeutically relevant endogenous antitumor immune responses. Our results unveil a therapeutic mechanism whereby tumor-primed CD4(+) T cells transferred into ovarian cancer-bearing mice secrete high levels of CCL5, which recruits endogenous CCR5(+) dendritic cells to tumor locations and activate them through CD40-CD40L interactions. These newly matured dendritic cells are then able to prime tumor-specific endogenous CD8(+) T cells, which mediate long-term protection. Correspondingly, administration of tumor-primed CD4(+) T cells significantly delayed progression of MHC class II(-) ovarian cancers, similarly to CD8(+) T cells only, and directly activated wild-type but not CD40-deficient dendritic cells recruited to the tumor microenvironment. Our results unveil a CCL5- and CD40L-dependent mechanism of transferring immunity from exogenously activated CD4(+) T cells to tumor-exposed host cells, resulting in sustained antitumor effects. Our data provide a mechanistic rationale for incorporating tumor-reactive CD4(+) T cells in adoptive cell transfer immunotherapies against ovarian cancer and underscore the importance of optimizing immunotherapeutic strategies for the specific microenvironment of individual tumors.

In situ stimulation of CD40 and Toll-like receptor 3 transforms ovarian cancer-infiltrating dendritic cells from immunosuppressive to immunostimulatory cells

Boosting therapeutically relevant immunity against lethal epithelial tumors may require targeting tumor-induced immunosuppression on an individualized basis. Here, we show that, in the ovarian carcinoma microenvironment, CD11c(+)MHC-II(+) dendritic cells spontaneously engulf tumor materials but, rather than enhancing antitumor immunity, suppress T-cell function. In situ costimulation of CD40 and Toll-like receptor (TLR) 3 on tumor-infiltrating dendritic cells decreased their L-arginase activity, enhanced their production of type I IFN and interleukin-12 (p70), augmented their capacity to process antigens, and up-regulated costimulatory molecules in vivo in mice and in vitro in human dissociated tumors. Synergistic CD40/TLR activation also induced the migration of activated dendritic cells to lymphatic locations and promoted their capacity to present antigens. Correspondingly, without exogenous antigen, combined CD40/TLR agonists boosted measurable T-cell-mediated antitumor immunity and induced the rejection of otherwise lethal i.p. ovarian carcinomas. Our results highlight the potential of transforming tumor-infiltrating dendritic cells (the most abundant leukocyte subset in the solid ovarian carcinoma microenvironment) from an immunosuppressive to an immunostimulatory cell type. Combined administration of synergistic CD40 and TLR3 agonists could enhance their individual therapeutic effects against ovarian and other lethal epithelial cancers.

Polyethylenimine-based siRNA nanocomplexes reprogram tumor-associated dendritic cells via TLR5 to elicit therapeutic antitumor immunity

The success of clinically relevant immunotherapies requires reversing tumor-induced immunosuppression. Here we demonstrated that linear polyethylenimine-based (PEI-based) nanoparticles encapsulating siRNA were preferentially and avidly engulfed by regulatory DCs expressing CD11c and programmed cell death 1-ligand 1 (PD-L1) at ovarian cancer locations in mice. PEI-siRNA uptake transformed these DCs from immunosuppressive cells to efficient antigen-presenting cells that activated tumor-reactive lymphocytes and exerted direct tumoricidal activity, both in vivo and in situ. PEI triggered robust and selective TLR5 activation in vitro and elicited the production of hallmark TLR5-inducible cytokines in WT mice, but not in Tlr5-/- littermates. Thus, PEI is a TLR5 agonist that, to our knowledge, was not previously recognized. In addition, PEI-complexed nontargeting siRNA oligonucleotides stimulated TLR3 and TLR7. The nonspecific activation of multiple TLRs (specifically, TLR5 and TLR7) reversed the tolerogenic phenotype of human and mouse ovarian tumor-associated DCs. In ovarian carcinoma-bearing mice, this induced T cell-mediated tumor regression and prolonged survival in a manner dependent upon myeloid differentiation primary response gene 88 (MyD88; i.e., independent of TLR3). Furthermore, gene-specific siRNA-PEI nanocomplexes that silenced immunosuppressive molecules on mouse tumor-associated DCs elicited discernibly superior antitumor immunity and enhanced therapeutic effects compared with nontargeting siRNA-PEI nanocomplexes. Our results demonstrate that the intrinsic TLR5 and TLR7 stimulation of siRNA-PEI nanoparticles synergizes with the gene-specific silencing activity of siRNA to transform tumor-infiltrating regulatory DCs into DCs capable of promoting therapeutic antitumor immunity.

Depletion of dendritic cells delays ovarian cancer progression by boosting antitumor immunity

Dendritic cells (DC) and cytokines that expand myeloid progenitors are widely used to treat cancer. Here, we show that CD11c(+)DEC205(+) DCs coexpressing alpha-smooth muscle actin and VE-cadherin home to perivascular areas in the ovarian cancer microenvironment and are required for the maintenance of tumor vasculature. Consequently, depletion of DCs in mice bearing established ovarian cancer by targeting different specific markers significantly delays tumor growth and enhances the effect of standard chemotherapies. Tumor growth restriction was associated with vascular apoptosis after DC ablation followed by necrosis, which triggered an antitumor immunogenic boost. Our findings provide a mechanistic rationale for selectively eliminating tumor-associated leukocytes to promote antitumor immunity while impeding tumor vascularization and to develop more effective DC vaccines based on a better understanding of the tumor microenvironment.