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Abstract
Background Overexpression of vasoactive intestinal peptide (VIP) and its receptors (VPAC1/2) has been reported in various cancers, with higher expression levels associated with the growth and metastasis of tumors.1 2 Our previous data has shown that use of VIP receptor antagonist (ANT308) in subcutaneous and orthotopic murine PDAC models enhances anti-tumor response to anti-PD-1 immunotherapy.3 However, Genetically Engineered Mouse Models (GEMM) provide a more accurate model for the ontogeny and oncogenic transformation of PDAC. The tamoxifen-inducible KPC (KRAS LSL-G12D ;TP53 LoxP ;Pdx1-CreER) tumor mouse model reflects common genetic mutations in human PDAC and tumor ontology within the pancreas. We characterized VIP expression levels and the therapeutic efficacy of treatment with VIP receptor antagonist in a tamoxifen-induced TP53-deleted and KRAS-mutated GEMM PDAC model.
Methods KPC GEMM mice at 8–16 wks old were gavaged with tamoxifen at 250mg/kg for 5 days to induce oncogenic transformation. Tumor incidence and mouse survival was recorded. Tumor size was assessed by examining mice and ultrasound. To test pre-emotive treatment with VIP receptor antagonists and anti-PD1 antibodies, mice were treated one month after tamoxifen gavage with either ANT308, aPD-1, or the ANT308/aPD-1 combination. VIP, VPAC1, and VPAC2 expression in pancreas and established tumors was determined by immunofluorescent staining of tissue sections.
Results PDAC tumor development occurred between day 88 and day 145 following gavage, with a median time of 94 days. All mice died with large tumors by day 164 in the absence of any therapeutic intervention (figure 1). Mice in the control and single-agent treatment groups developed tumor and died before day 200 post tamoxifen. 10% of mice in the ANT308 + aPD-1 group remained tumor free until endpoint (figure 2). IF staining revealed increased VIP expression in pancreatic foci one month after tamoxifen treatment (figure 4), in accordance with the presence of pancreatic cancer lesions observed following Masson’s Trichome staining (figure 3).
Conclusions These data suggest that VIP plays a role in PDAC tumor ontology for KPC GEMM mice and will be further supported with anticipated VPAC1/2 staining. Combination treatment of ANT308 and aPD-1 enhances the anti-tumor response in these mice, but the extended latency period for autochthonous tumor development poses a difficulty for aligning treatment initiation with the inflammatory response. Results of an ongoing experiment that is testing the efficacy of pre-emotive treatment with ANT308/aPD1 in combination with a tumor-specific vaccine will be presented.
References
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Ravindranathan S, Passang T, Li JM, et al. Targeting vasoactive intestinal peptide-mediated signaling enhances response to immune checkpoint therapy in pancreatic ductal adenocarcinoma. Nat Commun. 2022;13:6418.
PDAC tumor incidence and survival in KPC GEMM model. Day 0 = first day of tamoxifen gavage (250mg/kg for 5 days), n= 13
Survival curve of KPC GEMM mice treated with ANT308 (20ug daily, 4wks), aPD-1 (200ug x4, 10 days) or combination of ANT308 and aPD-1
HE and Masson’s Trichrome staining of pancreas tissue from normal and PDAC KPC mice
Immunofluorescent imaging of KPC mouse (A) pancreas foci without tamoxifen, (B) pancreas foci one month after tamoxifen, and (C) tamoxifen-induced PDAC tumor tissue. Images show staining for VIP (red) and Hoechst (blue)
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