Date Published: January 29, 2019
Publisher: Public Library of Science
Author(s): Hristo P. Varbanov, Fabien Kuttler, Damiano Banfi, Gerardo Turcatti, Paul J. Dyson, Irina V. Lebedeva.
Drug combinations are extensively used to treat cancer and are often selected according to complementary mechanisms. Here, we describe a cell-based high-throughput screening assay for identification of synergistic combinations between broadly applied platinum-based chemotherapeutics and drugs from a library composed of 1280 chemically and pharmacologically diverse (mostly FDA approved) compounds. The assay was performed on chemoresistant cell lines derived from lung (A549) and pancreatic (PANC-1) carcinoma, where platinum-based combination regimens are currently applied though with limited success. The synergistic combinations identified during the screening were validated by synergy quantification using the combination index method and via high content fluorescent microscopy analysis. New promising synergistic combinations discovered using this approach include compounds currently not used as anticancer drugs, such as cisplatin or carboplatin with hycanthone and cisplatin with spironolactone in pancreatic carcinoma, and carboplatin and deferoxamine in non-small cell lung cancer. Strong synergy between cisplatin or carboplatin and topotecan in PANC-1 cells, compared to A549 cells, suggests that this combination, currently used in lung cancer treatment regimens, could be applied to pancreatic carcinoma as well. Several drugs used to treat diseases other than cancer, including pyrvinium pamoate, auranofin, terfenadine and haloprogin, showed strong cytotoxicity on their own and synergistic interactions with platinum drugs. This study demonstrates that non-obvious drug combinations that would not be selected based on complementary mechanisms can be identified via high-throughput screening.
Cancer, one of the leading causes of death, is a term used to describe a large group of related diseases featuring over 100 subtypes, which differ significantly in terms of incidence, mortality and prevalence [1–4]. Advances in treatment strategies together with earlier diagnosis have systematically increased the survival of cancer patients [5,6]. Amongst these advances, the introduction of cisplatin has arguably led to one of the key improvements. For example, the cure rate of patients diagnosed with testicular cancer increased from 10 to over 95% after the introduction of cisplatin (FDA approval in 1978) [7–9]. At present, cisplatin and its analogues carboplatin and oxaliplatin (Fig 1) are extensively used in cancer chemotherapy, usually in combinations with other drugs [8,10–12]. Indeed, 36 of 75 anticancer treatment regimens listed in Martindale drug reference book are platinum-based , while Pt drugs are prescribed to nearly halve of the patients undergoing chemotherapy in Australia . Furthermore, preclinical and clinical efficacy of new anticancer drug candidates is commonly trialed in combination with platinum chemotherapeutics [11,14].
Combinations of Pt drugs (see Fig 1) and other known drugs, which act synergistically against PANC-1 and A549 cells were identified in this study following a step-wise protocol (summarized in Fig 2). The method can easily be applied to other cancer cell types that grow in culture.
Currently, there is still no adequate treatment of lung and pancreatic carcinomas, and consequently they remain amongst the most deadly cancers. Combinations, featuring Pt drugs are among the most efficient treatments available, however, survival rates are still very low (5-year survival rates of under 10%), highlighting the necessity for development of new therapeutic options for these malignancies. In an attempt to improve platinum-based chemotherapy of problematic cancers, we have established a cell-based screening assay that identifies compounds, which either potentiate the activity or synergize with Pt drugs. These compounds are identified from a library with FDA approved drugs using a systematic screening approach. As drug combinations and synergy determination can be problematic, screening was followed by hit confirmation and validation procedures, including synergy quantification and HCA.