Sofian Tijono

Identification of human-selective analogues of the vascular-disrupting agent 5,6-dimethylxanthenone-4-acetic acid (DMXAA)

Background:Species selectivity of DMXAA (5,6-dimethylxanthenone-4-acetic acid, Vadimezan) for murine cells over human cells could explain in part the recent disappointing phase III trials clinical results when preclinical studies were so promising. To identify analogues with greater human clinical potential, we compared the activity of xanthenone-4-acetic acid (XAA) analogues in murine or human cellular models.Methods:Analogues with a methyl group systematically substituted at different positions of the XAA backbone were evaluated for cytokine induction in cultured murine or human leukocytes; and for anti-vascular effects on endothelial cells on matrigel. In vivo antitumour activity and cytokine production by stromal or cancer cells was measured in human A375 and HCT116 xenografts.Results:Mono-methyl XAA analogues with substitutions at the seventh and eighth positions were the most active in stimulating human leukocytes to produce IL-6 and IL-8; and for inhibition of tube formation by ECV304 human endothelial-like cells, while 5- and 6-substituted analogues were the most active in murine cell systems.Conclusion:Xanthenone-4-acetic acid analogues exhibit extreme species selectivity. Analogues that are the most active in human systems are inactive in murine models, highlighting the need for the use of appropriate in vivo animal models in selecting clinical candidates for this class of compounds.

Discovery and characterisation of hydrazines as inhibitors of the immune suppressive enzyme, indoleamine 2,3-dioxygenase 1 (IDO1)

Screening of a fragment library identified 2-hydrazinobenzothiazole as a potent inhibitor of indoleamine 2,3-dioxygenase 1 (IDO1), an enzyme expressed by tumours that suppresses the immune system. Spectroscopic studies indicated that 2-hydrazinobenzothiazole interacted with the IDO1 haem and in silico docking predicted that the interaction was through hydrazine. Subsequent studies of hydrazine derivatives identified phenylhydrazine (IC50=0.25 ± 0.07 μM) to be 32-fold more potent than 2-hydrazinobenzothiazole (IC50=8.0 ± 2.3 μM) in inhibiting rhIDO1 and that it inhibited cellular IDO1 at concentrations that were noncytotoxic to cells. Here, phenylhydrazine is shown to inhibit IDO1 through binding to haem.

Dissection of stromal and cancer cell-derived signals in melanoma xenografts before and after treatment with DMXAA

Background:The non-malignant cells of the tumour stroma have a critical role in tumour biology. Studies dissecting the interplay between cancer cells and stromal cells are required to further our understanding of tumour progression and methods of intervention. For proof-of-principle of a multi-modal approach to dissect the differential effects of treatment on cancer cells and stromal cells, we analysed the effects of the stromal-targeting agent 5,6-dimethylxanthenone-4-acetic acid on melanoma xenografts.Methods:Flow cytometry and multi-colour immunofluorescence staining was used to analyse leukocyte numbers in xenografts. Murine-specific and human-specific multiplex cytokine panels were used to quantitate cytokines produced by stromal and melanoma cells, respectively. Human and mouse Affymetrix microarrays were used to separately identify melanoma cell-specific and stromal cell-specific gene expression.Results:5,6-Dimethylxanthenone-4-acetic acid activated pro-inflammatory signalling pathways and cytokine expression from both stromal and cancer cells, leading to neutrophil accumulation and haemorrhagic necrosis and a delay in tumour re-growth of 26 days in A375 melanoma xenografts.Conclusion:5,6-Dimethylxanthenone-4-acetic acid and related analogues may potentially have utility in the treatment of melanoma. The experimental platform used allowed distinction between cancer cells and stromal cells and can be applied to investigate other tumour models and anti-cancer agents.

Abstract 4691: Polarization of macrophages with STING agonists

The functional plasticity of macrophages and their ability to support tumour growth or promote potent antitumor immunity make them an attractive target cancer therapy. Macrophages have been implicated in the complex antitumor activity of murine STING agonist, DMXAA, including disruption of tumor vasculature, induction of cytokine production, and promotion of durable antitumor immune responses. Many of these activities are lost in STING-/- mice, and DMXAA does not bind to human STING, providing a pertinent explanation for why the anti-tumour effects of DMXAA observed in mice were not recapitulated human clinical trials. Using PMA-differentiated THP-1 macrophages, we sought to identify human active analogues of DMXAA in vitro, comparing their capacity to induce cytokines indicative of a classically activated antitumour phenotype; the non-canonical STING agonist 2939-cGAMP was also included in our investigation. IP-10 (CXCL10) production, measured by ELISA, was used as an initial marker for activity, followed by multiplex cytokine analysis for broader characterisation compared to M(IFN-γ/LPS), M(IL-4/IL-13), and ‘resting’ M(media alone) macrophage phenotypes. Parallel experiments were also conducted with RAW264.7 murine macrophages to compare the DMXAA-induced cytokine profile directly with that of 2939-cGAMP. 2939-cGAMP induced 22-fold and 18-fold increases in IP-10 production in resting and M(IL-4/IL-13) THP-1 macrophages, respectively. By comparison, THP-1 macrophages were much less responsive to DMXAA and analogues tested to date. Furthermore, 2939-cGAMP induced a spectrum of cytokines similar to that observed in M(IFN-γ/LPS) macrophages, and markedly different to that of M(IL-4/IL-13) THP-1 macrophages. DMXAA, and analogues previously shown to have cytokine-inducing activity in human leukocytes did not produce cytokine spectra indicative of a classic M(IFN-γ/LPS) phenotype. Unlike human cells, however, cytokine spectra produced by RAW264.7 murine macrophages were comparable between DMXAA- and 2939-cGAMP-treated cells. These findings support previous data that suggest that STING agonists can promote macrophage polarisation towards an antitumour phenotype. While DMXAA is active in murine macrophages, only 2939-cGAMP can induce in human THP-1 cells, an M(IFN-γ/LPS)-like spectrum of cytokines often attributed to an antitumour macrophage phenotype. Citation Format: Kimiora L. Henare, Sofian M. Tijono, Lai-Ming Ching. Polarization of macrophages with STING agonists [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 4691. doi:10.1158/1538-7445.AM2017-4691

Abstract 4138:In vitroandin vivomodels for evaluation of inhibitors of tryptophan dioxygenases

Cancers co-opt indoleamine 2,3-dioxygenase 1 (IDO1) as a mechanism for evading the immune system, and IDO1 inhibitors have emerged as a promising new approach for the treatment cancer through their potential to restore antitumor immunity and to synergise with existing therapies. As part of our investigations into novel small molecule inhibitors of IDO1, we screened a number of human and murine tumor lines for expression of tryptophan dioxygenases. All the human and murine tumor lines that we tested were found not to express tryptophan dioxygenases unless induced with IFN-gamma. Our screen included testing 50 primary human melanoma lines developed from tumor samples obtained New Zealand Melanoma patients (NZMel lines) for expression of IDO1 and IDO2. After co-culture with IFN-gamma, 84% of the NZMel lines were IDO1+ and IDO2+; 4% were IDO1+ only; 2 % were IDO2+ only; whilst 10% did not express either IDO1 or IDO2. Tryprophan dioxygenase (TDO) was not detected in any of the NZMel lines before or after IFN-gamma exposure. To overcome the need for IFN-gamma induction for our cell based assays of IDO1 inhibitory activity of our novel compounds, we transfected the wild-type murine Lewis Lung carcinoma line (LLTC) to constitutively express murine IDO1 (LLTC-mIDO1) or human IDO1 (LLTC-hIDO1), and used these engineered lines to assay for potential species selectivity of our inhibitors. IDO1 expression in the lines was consistent and stable, but when LLTC-hIDO1 cells were implanted subcutaneously into syngeneic mice for in vivo testing of inhibitors, we found considerable heterogeneity in IDO1 expression between tumors. Approximately half of the tumors from the same batch of implants were completely negative for IDO1 expression by Western blot analysis. More intriguingly, when fragments of an IDO1+ or an IDO1- donor tumor were implanted into new recipients, the same degree of intertumoral heterogeneity in IDO1 expression was seen in the subsequent generation of tumors. In contrast, subcutaneous tumors developing from murine GL261 glioma cells similarly engineered to over-express hIDO1 (GL261-hIDO1) were homogeneous in their expression of hIDO1, and were used for subsequent in vivo studies of intratumoral IDO1expression on its effects on immune cell infiltrates and tumor growth. GL261-hIDO1 tumors had a significantly faster growth rate than the wild-type tumors, and 24 days after implantation, had reached a mean tumor volume of 3600 mm3 compared to a mean tumor volume of 500 mm3 of wild-type tumors. Analysis of the immune cell infiltrates, showed that 14-day GL261 wild-type tumors had a 3-fold higher percentage of CD3+ T cells than that in GL261-hIDO1 tumors. CD8+ cells made up 55% and 25% of the CD3+ cells in wild-type and GL261-hIDO1 tumors, respectively. Percentage of Foxp3+ (Treg) cells was higher in GL261-hIDO1 tumors compared to that in wild-type tumors. Citation Format: Lai-Ming Ching, Petr Tomek, Brian D. Palmer, Sofian Tijono, Kimiora Henare, Lukas M. Braun. In vitro and in vivo models for evaluation of inhibitors of tryptophan dioxygenases [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 4138. doi:10.1158/1538-7445.AM2017-4138