Three-dimensional (3D) cultures have been proposed as higher fidelity models of in vivo tumors than 2D cultures. To determine whether this idea extends to drug pharmacodynamics, we examined whether 3D cultures of the human melanoma line A375 (grown as tumor spheroids) could replicate the timing and magnitude of the nuclear γH2AX response to the topoisomerase 1 inhibitor, topotecan observed in A375 tumor xenografts (Kinders et al, Clin Can Res 2010). The appearance of γH2AX-positive nuclear foci has been used as a biomarker for drug- and radiation-induced double-strand breaks in DNA; we reported previously that treatment of nu/nu mice harboring A375 xenografts with a single-dose of topotecan induced nuclear γH2AX foci in a dose- and time-dependent manner, which peaked 4 hours after drug administration. A375 spheroids were generated by seeding cells into ULA U-bottom plates; 4 hours of exposure to 0.1 μM topotecan elicited a γH2AX signal in these 3D cultures while cell viability and intracellular ATP levels remained unchanged, indicating a DNA damage repair response at the maximally tolerated topotecan concentration for human hematopoietic cells (Erickson-Miller et al, Can Chemo Pharmacol 2009). Extending drug exposure to 24 hours caused substantial loss of viable cells (calcein AM+) and 50% decline in ATP levels but no further increase in γH2AX. In contrast, the HT29 tumor line was refractory to topotecan in vivo, and exposing 3D cultures of HT-29 spheroids to 0.1 μM topotecan for 24 hours elicited a strong nuclear γH2AX biomarker response in only a small fraction of cells at the surface of the spheroids. Longer exposure durations or supra-pharmacological concentrations (1 μM) of topotecan were required to achieve a strong nuclear γH2AX response in HT-29 spheroids. These results support the hypothesis that the 3D pharmacodynamics (PD) of drug response is similar to PD drug response in vivo for the camptothecin class of topoisomerase 1 inhibitors. Funded by NCI Contract No. HHSN261200800001E.

Citation Format: David M. Evans, Rene Delosh, Julie Laudeman, Chad Ogle, Russell Reinhart, Michael Selby, Silvers Thomas, Robert Kinders, Tony Navas, Scott Lawrence, Anne Monks, Annamaria Rapisarda, Ralph E. Parchment, James H. Doroshow, Beverly Teicher. Similar 3D pharmacodynamic (3D-PD) responses of human tumor spheroids and xenografts to topoisomerase 1 inhibitor-induced DNA damage. [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 606.