Abstract 328: DNA damage inhibitors with topotecan in a complex spheroid model in PDM and established cell lines
Authors: Beverly A. Teicher, Austin Doyle, John Wright, Charles Kunos, Thomas Silvers, Rene Delosh, Julie Laudeman, Russell Reinhart, Chad Ogle, Nathan Coussens, Joel Morris, James Doroshow
Journal: Cancer Research (2020)

Abstract Many solid tumor treatment regimens include combination chemotherapy. Over thirty-five human tumor cell lines, some recently developed and some well-established, were grown as complex spheroids, tumor cells mixed with HUVEC and MSC, to better model human solid tumors. The complex spheroids were established for 3 days, then the drug(s) and/or investigational agent(s) were added. After 7 days, the experiment was terminated with CellTiterGlo 3D. Cell viability was determined relative to a vehicle treated control and IC50s were calculated from concentration response curves. The response to topotecan was determined over a concentration range achievable in patients alone and in combination with nedisertib (M3814) or VX984, DNA PK inhibitors, M6620 or BAY-1895344, ATR inhibitors, MK-1775, a Wee-1 inhibitor, AZD-1390, an ATM inhibitor or olaparib or talazoparib, PARP inhibitors. The clinical Cmax of topotecan is 0.15 uM and the topotecan concentration range tested was 0.001 to 0.3 uM. Topotecan IC50's spanned more than 2 logs from 0.003 uM to &amp;gt;&amp;gt;0.3 uM. The ATRi inhibitors were tested over the concentration range from 0.01 to 10 uM. The M6620 IC50's covered 2 logs from 0.015 to &amp;gt;&amp;gt;1 uM and the BAY-189-5344 IC50 range was similar. Combinations of topotecan and M6620 produced greater than additive cytotoxicity in Rh28 and Rh30 rhabdomyosarcoma and 328373-195-R-J1 squamous cell carcinoma with &amp;gt;1 log increase in cell killing. BAY-1895344 in combination with topotecan was greater than additive in the COR L88 SCLC line and the 287954-098-R-J1 Ewing sarcoma line. The combination of topotecan and M6620 resulted in approximately additive cell killing in 929823-356-R-J2 squamous carcinoma, and NCI-H196 and NCI-H1618 SCLC with 4-6-fold increase in cell killing. Topotecan along with the ATM inhibitor AZD-1390, produced greater than additive cell killing in the 287954-098-R-J1 Ewing sarcoma line at the lower concentrations of topotecan (0.003 and 0.01 uM) tested. Primarily additive effects of the ATM inhibitor and topotecan were seen in most other cell lines tested. The combination of topotecan and the Wee-1 inhibitor MK1775 was tested in complex spheroids of the same cell lines. Only in the NCI-H196 SCLC line did topotecan and MK1775 produce greater than additive cell killing. There was a 1.5- to 4-fold increase in cell killing with topotecan and MK1775 in the RH28 and Rh30 rhabdomyosarcomas, 929823-356-R-J2 and 328373-195-R-J1 squamous cell carcinomas and the NCI-H1618 SCLC which was additive to sub-additive. The combination of topotecan with the DNA PK inhibitor M3814 produced little or no increase in cell killing (1.2- to 2-fold) compared with topotecan alone in complex spheroids. These findings may provide guidance regarding selection of agent combinations worthy of further investigation. This project was funded in part with federal funds from the NCI, NIH, under contract no. HHSN261200800001E. Citation Format: Beverly A. Teicher, Austin Doyle, John Wright, Charles Kunos, Thomas Silvers, Rene Delosh, Julie Laudeman, Russell Reinhart, Chad Ogle, Nathan Coussens, Joel Morris, James Doroshow. DNA damage inhibitors with topotecan in a complex spheroid model in PDM and established cell lines [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 328.