Background: Drug repositioning - the application of marketed drugs to new diseases - is a time and cost effective alternative to de novo drug development. Thalidomide is a hallmark example of drug repositioning success. Withdrawn from the market in 1961 after causing thousands of severe birth defects, its newly discovered anti-angiogenic and immunomodulatory properties cleared the way for Food and Drug Administration (FDA) approval in 2006 for multiple myeloma (MM). Although thalidomide has demonstrated remarkable success in the treatment of MM, responses are typically short-lived with the emergence of resistance. For complex diseases like cancer, multi-target therapeutics are well suited to address efficacy and drug resistance challenges. Here we have designed a novel therapeutic combination of drugs for MM that impacts all disease phenotypes.

Methods: Using a computer modeling system from Cellworks that mimics and simulates cancer disease physiology to predict clinical outcomes, we identified AT101 (Bcl2 antagonoist) and tesaglitazar (PPAR α/γ agonist) as a potentially effective drug combination for MM. This combination was shortlisted from over two hundred pharmacodynamic dose-response simulation studies using criteria of efficacy and synergy. Computer modeling predicted that this drug combination mechanistically targets apoptotic pathways and the combination of the agents provides greater than additive activity. These predictive findings were assessed in vitro using OPM2 and U266 human MM cell lines. AT101 and tesaglitazar growth inhibition was evaluated using the MTT assay and analysis of synergy was determined using the Bliss Independence model. Apoptotic induction was analyzed by immunoblotting for cleaved forms of caspases and PARP.

Results: 10 μM tesaglitazar and 2 μM AT101 display minimal and moderate growth inhibition respectively as single agents in OPM2 and U266 MM cell lines. Growth inhibition in these cell lines is dramatically enhanced when the drugs are used in combination, reducing cellular viability by 88% and 77% in OPM2 and U266 cells, respectively. Based upon the Bliss Independence model, the relationship between tesaglitazar and AT-101 is synergistic in both cell lines. Combination treatment in both cell lines results in increased apoptosis as indicated by enhanced cleavage of PARP and caspase 3 and 9.

Conclusions: Not only do these experiments identify AT101 and tesaglitazar as a potentially effective drug combination for the treatment of MM, these results also validate the use of rationally based, computer modeling to design effective therapeutics and predict clinical outcomes. Future studies will evaluate the mechanism of action for the synergistic interaction between tesaglitazar and AT101 in MM.

Citation Format: Nicole A. Doudican, Shireen Vali, Shweta Kapoor, Anay Talawdekar, Zeba Sultana, Taher Abbasi, Gautam Sethi, Seth J. Orlow, Amitabha Mazumder. In vitro validation of rationally designed therapeutic based on drug repositioning and combinations. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2104. doi:10.1158/1538-7445.AM2013-2104