BACKGROUND: Patients with diffuse anaplastic Wilms tumor (DAWT) experience relatively poor oncologic outcomes. Previous work has described mechanisms of telomerase upregulation in DAWT, posing a potential therapeutic target. METHODS: We assessed in vitro sensitivity to vincristine, irinotecan, and telomerase-targeting drug 6-thio-2'-deoxyguanosine (6 dG) in DAWT cell lines WiT49 and PDM115 and in spheroids derived from cell lines and four DAWT patient-derived xenografts (PDX). We also tested in vivo response to vincristine/irinotecan (VI), 6 dG, or combination in WTPDX. RESULTS: Sensitivity to vincristine varied with EC(50) between 0.13 and 44.92 nM in spheroids, with EC(50) for SN-38 (irinotecan active metabolite) from 3.06 to 70.96 nM. All were resistant to 6 dG monotherapy with EC(50) from 3.06 to 50+ μM. In KT-51, 10 μM 6 dG significantly slowed spheroid growth. 6 dG treatment increased DNA damage response markers pChk1 S345, p53 and γH2AX levels in KT-51, KT-53 and KT-60 spheroids. In WiT49 2D culture, treatment of sub-toxic doses of 6 dG did not induce apoptosis or cell cycle arrest and exhibited minimal synergistic capacity with VI; TERT overexpression did not increase 6 dG sensitivity. In vivo treatment of KT-51, KT-53, and KT-60 with VI exhibited variable responses from progressive disease to complete clinical responses, but 6 dG monotherapy resulted in no tumor responses and 6 dG addition to VI conferred no increased tumor suppression. CONCLUSIONS: DAWT models are variably sensitive to VI but are resistant to 6 dG monotherapy or combination with VI. Future research will address limitations of preclinical WT model systems and assess additional targeted therapies for high-risk WT subtypes.