O2176: Characterizing Sensitivity to Vincristine, Irinotecan, and Telomerase-targeted Therapy in Diffuse Anaplastic Wilms Tumor Patient-derived Xenografts

Background: Overall survival rates for children with Wilms tumor (WT) are above 90%, but those with advanced-stage diffuse anaplastic WT (DAWT) and those with favorable histology (FHWT) disease relapse suffer relatively poor outcomes. An ongoing clinical trial is studying the effect of addition of vincristine and irinotecan (VI) to an established chemotherapeutic regimen on survival outcomes in patients with newly-diagnosed DAWT and standard-risk relapsed FHWT patients. Our previous work established heterotopic WT patient-derived xenografts (WTPDX) that recapitulate the heterogeneous biology and chemotherapy responsiveness of both FHWT and DAWT. However, there is limited published data on responsiveness to VI in WT models. Additionally, our group previously described that telomerase activity is upregulated by various mechanisms in anaplastic WT. We sought to characterize the in vivo and in vitro sensitivity of anaplastic WTPDX and WT cell lines to vincristine and irinotecan with or without the telomerase-targeted drug 6-thio-2’-deoxyguanosine (6dG) to assess for synergistic response.

Methods: BALB/c scid mice bearing anaplastic histology heterotopic WTPDX (KT-51, KT-53, KT-60), were treated with 0.5 mg/kg vincristine (Q7DX3) IP and 0.625 mg/kg irinotecan (DX5)2 IP, or 0.5 mg/kg 6dG (DX5)3 IP, or in combination. Tumor volumes were measured weekly up to 12 weeks. WTPDX-derived tumor spheroids were established by tissue digestion using collagenase, plating in ultra-low-attachment plates followed by centrifugation. Drug sensitivities to vincristine, SN-38 (active metabolite of irinotecan), and 6dG monotherapy were measured in adherent anaplastic WT cell lines (WiT49 and PDM115) using PrestoBlue and in WTPDX-derived spheroids (PDM115, WiT49, KT-51, KT-53, KT-71) using CellTiterGlo3D. Colony formation assays were performed on adherent cell lines using crystal violet staining. DNA damage response to 6dG monotherapy was assessed in 2D culture with WiT49 and in tumor spheroids with KT-51 and KT-53.

Results: A median complete response was noted in vivo to vincristine + irinotecan (VI) in KT-53 and KT-60 but only a partial delay in tumor growth in KT-51. A partial delay to no response was found with 6dG monotherapy in KT-51, KT-53, and KT-60 with no additive tumor suppression when combined with VI. In vitro WT cell line and WTPDX-derived spheroids demonstrated variable sensitivity to vincristine (IC50 0.008-14.8 nM) and were more similar in their sensitivity to irinotecan (2.4-61.3 nM), with all being resistant to 6dG monotherapy (all 5+ uM). In 2D culture, 6dG + VI exhibited minimal synergistic effect in reducing colony formation in WiT49 cells. 6dG monotherapy induced variable DNA damage response in KT-51, KT-53, and WiT49.

Conclusion: Anaplastic WTPDX exhibit sensitivity in vivo and in vitro to vincristine and irinotecan but are resistant to telomerase-targeted 6dG monotherapy or in combination with VI. Future research will determine mechanisms of resistance to VI and identify targeted therapies that exhibit synergy with VI in WTPDX models.