Abstract 2699: Targeting an ubiquitin-activating enzyme in small-cell lung cancer (SCLC)
Authors: Majeed Safa , Aparnathi Mansi K. , Song Lifang , Schimmer Aaron D. , Tsao Ming S. , Liu Geoffrey , Lok Benjamin H. 
Published: August 2019

Abstract
Background: Despite valiant efforts to improve patient outcomes, small cell lung cancer (SCLC) (~15-17% of lung cancer) remains an aggressive lung cancer, with an overall five-year survival of 7%. Current first-line therapy (chemotherapy+/-radiation) has not changed in 30+ years. TAK-243, an inhibitor of the ubiquitin activating enzyme (UAE), E1 (encoded by UBA1), poses a novel approach for cancer therapy.
TAK-243 limits the formation of ubiquitin conjugates that ultimately mediate many cellular processes, including DNA repair signalling and protein degradation. Consequently, TAK-243 may disrupt cancer-specific dependencies of UAE to induce malignant cell death, and potentiate radiation-induced DNA damage. The discovery publication revealed that TAK-243 is especially potent in 2 SCLC cell-lines compared to healthy breast and fibroblastic tissues. With these limited data, the potential benefit of this novel agent as monotherapy and in combination with chemotherapy for SCLC has yet to be elucidated.
Methods: We assessed the anti-proliferative effect of TAK-243 monotherapy in a large panel (n = 10) of variant and classical SCLC cell-lines, including assorted MYC family member amplifications and different UBA1 mRNA expression levels. TAK-243 EC50 single agent doses were determined by treating cell-lines with incremental concentrations of TAK-243 (0-1μM). For combinatorial analysis, TAK-243 (0-1μM) was administered to cell-lines alongside cisplatin/etoposide (CE) at cell-line specific optimized doses yielding 30-35% kill by CE. Short-term efficacy was determined by a cell viability resazurin assay, 48 hours after treatment initiation. ΔEC50 was measured as the single agent EC50 subtracted by the EC50 of TAK-243+CE. Positive ΔEC50 values show potential synergy between TAK-243 and CE.
Results:
Single-agent therapy. SCLC cell-lines demonstrated a range of sensitives to TAK-243 monotherapy after 48 hours. The cell-lines tested are ranked from highest to lowest sensitivity: NCI-H82, NCI-H69, NCI-H1618, LX22 (ex-vivo cultured PDX), NCI-H1092, NCI-H446, SHP77 and NCI-H196; with EC50 values ranging from 18nM to 80nM. However, NCI-H526, NCI-H889, and SBC-5 were non-responsive to therapy at 1μM.
Combination therapy. TAK-243 upon combination treatment with CE revealed ΔEC50 values ranging from 5.23-14.54nM. NCI-H82, NCI-H69, SHP77 and NCI-H1092 demonstrated potential chemosensitivity to combination treatment.
Conclusions: These data begin to hint at synergy between TAK-243 and CE, where lower doses of TAK-243 may be required for certain SCLC cell-lines when used in combination. These preliminary results suggest that TAK-243 may have the potential to improve the current SCLC standard therapies in molecular defined subgroups. These results are being confirmed in additional cell-lines and through in vivo experiments using patient-derived xenograft models of SCLC.
*S.M and M.K.A contributed equally to this work
Citation Format: Safa Majeed, Mansi K. Aparnathi, Lifang Song, Aaron D. Schimmer, Ming S. Tsao, Geoffrey Liu, Benjamin H. Lok. Targeting an ubiquitin-activating enzyme in small-cell lung cancer (SCLC) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2699.