Growth inhibition of different human colorectal cancer xenografts after a single intravenous injection of oncolytic vaccinia virus GLV-1h68

Background: Despite availability of efficient treatment regimens for early stage colorectal cancer, treatment regimens for late stage colorectal cancer are generally not effective and thus need improvement. Oncolytic virotherapy using replication-competent vaccinia virus (VACV) strains is a promising new strategy for therapy of a variety of human cancers. Methods: Oncolytic efficacy of replication-competent vaccinia virus GLV-1h68 was analyzed in both, cell cultures and subcutaneous xenograft tumor models. Results: In this study we demonstrated for the first time that the replication-competent recombinant VACV GLV-1h68 efficiently infected, replicated in, and subsequently lysed various human colorectal cancer lines (Colo 205, HCT-15, HCT-116, HT-29, and SW-620) derived from patients at all four stages of disease. Additionally, in tumor xenograft models in athymic nude mice, a single injection of intravenously administered GLV-1h68 significantly inhibited tumor growth of two different human colorectal cell line tumors (Duke’s type A-stage HCT-116 and Duke’s type C-stage SW-620), significantly improving survival compared to untreated mice. Expression of the viral marker gene ruc-gfp allowed for real-time analysis of the virus infection in cell cultures and in mice. GLV-1h68 treatment was well-tolerated in all animals and viral replication was confined to the tumor. GLV-1h68 treatment elicited a significant up-regulation of murine immune-related antigens like IFN-γ, IP-10, MCP-1, MCP-3, MCP-5, RANTES and TNF-γ and a greater infiltration of macrophages and NK cells in tumors as compared to untreated controls. Conclusion: The anti-tumor activity observed against colorectal cancer cells in these studies was a result of direct viral oncolysis by GLV-1h68 and inflammation-mediated innate immune responses. The therapeutic effects occurred in tumors regardless of the stage of disease from which the cells were derived. Thus, the recombinant vaccinia virus GLV-1h68 has the potential to treat colorectal cancers independently of the stage of progression

Nitric oxide short-circuits interleukin-12-mediated tumor regression

Interleukin-12 (IL-12) can promote tumor regression via activation of multiple lymphocytic and myelocytic eVectors. Whereas the cytotoxic mechanisms employed by T/NK/NKT cells in IL-12-mediated tumor kill are well deWned, the antitumor role of macrophage-produced cytotoxic metabolites has been more controversial. To this end, we investigated the speciWc role of nitric oxide (NO), a major macrophage eVector molecule, in post-IL-12 tumor regression. Analysis of tumors following a single intratumoral injection of slow-release IL-12 microspheres showed an IFN-dependent sevenfold increase in inducible nitric oxide synthase (iNOS) expression within 48 h. Flow cytometric analysis of tumor-resident leukocytes and in vivo depletion studies identiWed CD11b+ F4/80+ Gr1lo macrophages as the primary source of iNOS. Blocking of post-therapy iNOS activity with N-nitro-L-arginine methyl ester (L-NAME)dramatically enhanced tumor suppression revealing the inhibitory eVect of NO on IL-12-driven antitumor immunity. Superior tumor regression in mice receiving combination treatment was associated with enhanced survival and proliferation of activated tumor-resident CD8+ T-eVector/memory cells (Tem). These Wndings demonstrate that macrophageproduced NO negatively regulates the antitumor activity of IL-12 via its detrimental eVects on CD8+ T cells and identify L-NAME as a potent adjuvant in IL-12 therapy of cancer

Characterization of iNOS⁺ Neutrophil-like ring cell in tumor-bearing mice

Abstract Background Myeloid-derived Suppressor Cells (MDSC) have been identified as tumor-induced immature myeloid cells (IMC) with potent immune suppressive activity in cancer. Whereas strict phenotypic classification of MDSC has been challenging due to the highly heterogeneous nature of cell surface marker expression, use of functional markers such as Arginase and inducible nitric oxide synthase (iNOS) may represent a better categorization strategy. In this study we investigated whether iNOS could be utilized as a specific marker for the identification of a more informative homogenous MDSC subset. Methods Single-cell suspensions from tumors and other organs were prepared essentially by enzymatic digestion. Flow cytometric analysis was performed on a four-color flow cytometer. Morphology, intracellular structure and localization of iNOS+ ring cells in the tumor were determined by cytospin analysis, immunofluorescence microscopy and immunohistochemistry, respectively. For functional analysis, iNOS+ ring subset were sorted and tested in vitro cell culture experiments. Pharmacologic inhibition of iNOS was performed both in vivo and in vitro. Results The results showed that intracellular iNOS staining distinguished a granular iNOS+ SSChi CD11b+ Gr-1dim F4/80+ subset with ring-shaped nuclei (ring cells) among the CD11b+ Gr-1+ cell populations found in tumors. The intensity of the ring cell infiltrate correlated with tumor size and these cells constituted the second major tumor-infiltrating leukocyte subset found in established tumors. Although phenotypic analysis demonstrated that ring cells shared characteristics with tumor-associated macrophages (TAM), morphological analysis revealed a neutrophil-like appearance as detected by cytospin and immunofluorescence microscopy analysis. The presence of distinct iNOS filled granule-like structures located next to the cell membrane suggested that iNOS was stored in pre-formed vesicles and available for rapid release upon activation. Tumor biopsies showed large areas with infiltrating ring cells primarily surrounding necrotic areas. Importantly, these cells significantly impaired CD8+ T-cell proliferation and induced apoptotic death. The intratumoral accumulation and suppressive activity of ring cells could be blocked through pharmacologic inhibition of iNOS, demonstrating the critical role of this enzyme in mediating both the differentiation and the activity of these cells. Conclusions In this study, iNOS expression was linked to a homogeneous subset; ring cells with a particular phenotype and immune suppressive function, in a common and well-established murine tumor model; 4T-1. Since the absence of a Gr-1 homolog in humans has made the identification of MDSC much more challenging, use of iNOS as a functional marker of MDSC may also have clinical importance.</p