Abstract C056: MIV-818 stimulates an antitumor immune response in vitro and enhances the effects of pembrolizumab

Purpose: Investigation of immune-modulating activity of MIV-818. Background: MIV-818, a phosphoramidate prodrug of troxacitabine was designed to target the active metabolite troxacitabine-triphosphate to the liver while minimizing systemic exposure. MIV-818 is being developed for the treatment of cancer in the liver, and is currently being evaluated in a phase 1/2 study. Preclinical studies have demonstrated that some DNA damaging agents may further enhance antitumor immune responses in addition to direct cytotoxic effects. We therefore investigated whether MIV-818 induces similar immunomodulating effects as single agent or in combination with pembrolizumab. Methods: Immune-mediated tumor cell killing was determined by co-culturing labelled SKOV3 cancer cells with peripheral blood mononuclear cells (PBMC) and quantified over time using the IncuCyte ZOOM system. Effects on inflamed host tumor microenvironments (TMEs) were investigated by cytokine profiling co-cultures of activated PBMCs, primary fibroblasts or endothelial cells and HT29 colon adenocarcinoma cells. Effects on Staphylococcal enterotoxin B (SEB)-stimulated PBMC were determined by quantifying thymidine incorporation, and cytokine expression in supernatants. Results: Co-incubation of SKOV3 and PBM cells with MIV-818 induced a substantially higher level of apoptosis in the cancer cells (74±25%) compared to co-incubation in the absence of MIV-818 (37±23%). MIV-818 inhibited the proliferation of SKOV-3 cells in the absence PBMCs, but with no significant induction of apoptosis (IC50 7.5nM; ≤5% apoptosis). In a more complex model of the immune TME, MIV-818 treatment impacted inflammatory and angiogenesis-related responses in both the stromal and vascular co-culture systems, increasing IFNγ, IL-10, IL-17A, and TNFα in a manner comparable to that of pembrolizumab alone while also inhibiting IL-6. Combining MIV-818 with pembrolizumab further enhanced an immune-stimulatory effect by increasing IL-10, IL-17A and IFNy, while also modulating immune-related (GranB, IL-2, IL-6), and inflammation-related cytokines (VCAM-1, IP-10, TNFα). MIV-818 demonstrated dose-dependent inhibitory effect on proliferation of SEB-stimulated PBMCs. Despite this growth inhibitory effect, it led to a strong, dose-dependent, increase in IL-2 levels as a single agent which was further enhanced in combination with pembrolizumab. Conclusions: MIV-818 exerts favorable immunomodulating effects in vitro by increasing immune cytokine levels and the PBMC-mediated killing of cancer cells. These effects are further enhanced in combination with pembrolizumab and support future combination of MIV-818 with PD-(L)1 inhibitors in patients with HCC and other liver cancers. The effects of MIV-818 on tumor immune activation markers are being assessed the ongoing phase 1/2 clinical trial. Citation Format: Fredrik G Oberg, Karin Tunblad, Ana Slipicevic, Richard Bethell, Mark R Albertella. MIV-818 stimulates an antitumor immune response in vitro and enhances the effects of pembrolizumab [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr C056. doi:10.1158/1535-7163.TARG-19-C056