Abstract 2691: A triple combination of fostrox (MIV-818) with immune checkpoint and kinase inhibition shows increased anti-tumor efficacy in vivo
Authors: Oberg Fredrik G. , Bhoi Sujata , Jensen Malene , Tunblad Karin , Wallberg Hans 
Published: April 2023

Abstract
Background: Fostroxacitabine bralpamide (fostrox) is an orally administered liver-targeted troxacitabine-based nucleotide prodrug currently undergoing phase 1/2a clinical trial in advanced hepatocellular carcinoma (HCC), in combination with pembrolizumab or lenvatinib (NCT03781934). In phase 1 monotherapy fostrox has demonstrated proof-of-concept in advanced HCC, intrahepatic cholangiocarcinoma and liver metastasis from gastrointestinal solid tumors. Liver-selective fostrox-induced DNA-damage and tumor cell killing has the potential to enhance the anti-tumor activity in combination with checkpoint blockade, and inhibition of angiogenesis leads to increased levels of the active metabolite of fostrox. We therefore investigated a triple combination of fostrox with anti-PD1 and lenvatinib in nonclinical tumor models in vivo.
Methods: Combinations of fostrox with anti-PD1 and lenvatinib treatment were evaluated in the subcutaneous syngeneic mouse CT26 model1. Groups of 8 mice were randomized using the Matched Distribution method based on tumor size day 1. Treatment was with fostrox (BID days 1-5, p.o.), anti-PD1 (BIW for 3 weeks, i.p.), and lenvatinib (QD for 21 days, p.o.). Tumours were measured three times weekly during the dosing phase, and statistical differences between the treatment groups was analyzed by two-way ANOVA. Pharmacodynamic response to fostrox, induction of DNA-damage (phospo-ser139-H2AX), was assessed by immunohistochemistry (IHC). Tumor infiltrating lymphocytes (TILs) were assessed by IHC evaluating the expression level of CD8, CD4, LAG-3, and PD-L1.
Results: Treatment with the triple combination of fostrox (30mg/kg) plus anti-PD1 (3mg/kg) and lenvatinib (5mg/kg) showed a significantly (p&lt;0.0001) improved anti-tumor efficacy compared with any double combination, fostrox plus anti-PD1, fostrox plus lenvatinib, or anti-PD1 plus lenvatinib, in the CT26 tumor model. A low basal level of DNA damage was observed, which was increased by fostrox treatment. Analysis of CD8, CD4, LAG-3 and PD-L1 expression levels indicated increased TILs.
Conclusions: The triple combination of fostrox with anti-PD1 and lenvatinib showed enhanced efficacy in a nonclinical tumor model, and changes in TILs were consistent with increased immune-mediated anti-tumor activity. The results indicate a potential for increased anti-tumor efficacy using a triple combination of fostrox plus checkpoint inhibition and anti-angiogenic therapy.
1The study was approved by the Institutional Animal Care and Use Committee (IACUC) of CrownBio UK, and conducted in accordance with the regulations of the Association for Assessment and Accreditation of Laboratory Animal Care (AAALAC)
Citation Format: Fredrik G. Oberg, Sujata Bhoi, Malene Jensen, Karin Tunblad, Hans Wallberg. A triple combination of fostrox (MIV-818) with immune checkpoint and kinase inhibition shows increased anti-tumor efficacy in vivo [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2691.