Abstract A142: Drug combination screen to identify novel synergy with Minnelide

Triptolide, which was initially extracted from a Chinese medicinal herb, demonstrates potent antitumor, anti-inflammatory, and immunosuppressive properties, yet it is clinically limited due to its poor solubility, bioavailability, and toxicity. Minnelide, a water-soluble analog of triptolide, has potent antiproliferative activity. It is currently in Phase I/II clinical trials for Acute Myeloid Leukemia (AML) and 7 solid tumor indications, including advanced gastrointestinal tumors, pancreatic cancer, and colorectal cancer. To overcome the potential drug resistance and to improve the drug potency as well as to minimize the drug toxicity, we conducted a high throughput screening (HTS) for drug synergy, combining Minnelide with compounds from the LOPAC and/or Prestwick libraries in 3 different cancer cell lines: BxPC3 (pancreatic), HT29 (colon) and SNU5 (gastric). LOPAC and Prestwick libraries consist of drugs approved by FDA and/or drugs that have reached clinical trial stages, representing 2,274 unique compounds in total. After quality control evaluation and data normalization, hits were selected if greater than 20% inhibition was achieved when combined compared with Minnelide alone. A total of 43, 54, and 47 hits were identified for each cell line, representing an average hit rate of 2.1%. We further prioritized the hits by selecting those that were common in two or more cell lines, which resulted in 9 compounds from Prestwick library and 20 compounds from LOPAC library (Harmane is in common between the two libraries). Only 17 compounds were available for purchase for hits confirmation, which was conducted in a similar manner as in primary HTS, except that drugs were tested in a dose-dependent manner instead of a single concentration done in HTS, a duplicated biological run was performed, and a total of 9 cell lines were screened, with 3 cell lines for each tumor type (pancreatic, colon and gastric). IC50 and Combination Index (CI) values for each drug combination were calculated for each cell line. A fold change of 2 or more for the IC50 values and CI value 50% of the cell lines tested, with Harmane and Harmine demonstrating synergy in all 9 cell lines tested. In addition, CGS-15943, Amiloride, Naphthalimide, and Idazoxan indicated good synergy with Minnelide in at least 6 out of 9 cell lines. Interestingly, Phenamil, an irreversible inhibitor of amiloride-sensitive Na+ channels, showed synergy in all cell lines tested for pancreatic and colon cancers, but not in gastric cancer cell lines. Overall, our study shed light on potential drug combinations with Minnlide for clinical use. Citation Format: Nanyun Tang, Chris Sereduk, Ashok Saluja, Mohana Velagapudi, Haiyong Han, Daniel D Von Hoff, Hongwei Holly Yin. Drug combination screen to identify novel synergy with Minnelide [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr A142. doi:10.1158/1535-7163.TARG-19-A142