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Few studies have investigated mechanisms of antiangiogenic drug resistance in mouse models that faithfully recapitulate clinically relevant spontaneous metastatic disease or evaluate the impact of therapy cessation on tumor and stromal cell growth. Generation of such models may be critical to study reported instances of antiangiogenic therapy-induced metastasis in animals that have often proved challenging to confirm in patients. Here we describe the derivation of several human and mouse tumor cell lines obtained from spontaneous metastatic lesions present after surgical removal of primary tumors and following long-term in vivo treatment with sunitinib or axitinib. Selected drug-resistant metastatic (kidney, breast, and melanoma) and non-malignant stromal cell variants (endothelial and fibroblast) were continuously exposed to drug in vitro and then evaluated following both short- and long-term treatment removal (48 hours and 6 months, respectively). Our results show that metastatic drug-resistant cells receiving sustained treatment were re-sensitized to therapy upon orthotopic re-implantation into treatment-naïve animals, suggesting a predominant host-mediated role in therapy failure. However, significant increases in tumor growth and metastatic potential were observed in all models when cells were re-implanted and therapy stopped, suggesting a tumor-dependent pro-metastatic mechanism activated by therapy withdrawal. Whole genome expression analysis for resistant cells on and off treatment revealed reversible and irreversible gene changes implicating a senescence-like phenotype capable of influencing metastatic potential. Senescent-like characteristics included increased cell size, decreased proliferation, cell cycle check-point protein alteration, and therapy-induced SA-β-galactosidase expression, depending on the cell line. Critically, antiangiogenic therapy could induce a senescence associated secretory phenotype (SASP) in both tumor and stroma cells which reversed or persisted following therapy cessation in certain instances. Importantly, we found that interleukin-6 (IL-6) - a major component of the SASP - was upregulated in resistant tumor and stroma cells, but only remained upregulated in stromal cells following therapy withdrawal. These results suggest that antiangiogenic treatment-induced senescence-like changes may contribute to treatment failure and contribute to pro-metastatic growth depending on cell origin (i.e., tumor or stroma) and whether treatment is sustained or stopped. Citation Format: Michalis Mastri, Amanda Tracz, Biao Liu, Christina R. Lee, John ML Ebos. A Senescence-like phenotype associates with rapid metastasis promotion following antiangiogenic drug resistance and therapy withdrawal. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3251.

Hepatitis C virus (HCV) infection is one of the commonest causes of liver cirrhosis and hepatocellular carcinoma. This review deals with treatment of chronic HCV infection with a combination of interferon and ribavirin. Recent trials have shown that approximately 40% of patients will clear HCV with combination treatment. This is an important advance in the treatment of this serious viral infection.