Inhibition of PDK3 by artemisinin, a repurposed antimalarial drug in cancer therapy

Highlights

• The present study suggesting artemisinin as a potent inhibitor of PDK3.

• Artemisinin binds PDK3 with an admirable binding affinity and forms numerous interactions with the residues of active site.

• Molecular dynamics simulation studies show the formation of a stable complex of PDK3-artemisinin.

• Artemisinin may be implicated in targeting PDK3-related disorders.

Abstract

Cancer has emerged as a global concern because it affects a larger population and is a major cause of death worlwide. Despite advancements in medical technologies and cancer therapy, there is still a need for effective therapeutics. The development of new drug molecules is tedious, expensive, and laborious process that can take years to reach in clinical trials. In recent years, drug repurposing has gained popularity because it accelerates the process of drug discovery. We propose that antimalarial drug artemisinin (AMS) be repurposed in anticancer therapeutics. AMS can potentially alter major signaling pathways involved in cancer, including Wnt/β-catenin and PI3K signaling pathways. Pyruvate dehydrogenase kinase 3 (PDK3) is overexpressed in many cancer types, involved in these signaling and being considered as an attractive drug target for cancer therapy. The current study investigated the binding and PDK3 inhibitory potential AMS using combined computational and spectroscopic methods. We observed a significant binding affinity of AMS for PDK3. In addition, the kinase activity of PDK3 is significantly inhibited by AMS. We further complemented our findings with molecular docking and 100 ns MD simulation studies. We propose that AMS may be explored as a possible anticancer agent after getting the required clinical validation.

Introduction

Despite major progressions in technology that have significantly imporved the understanding of human disease, therapeutic outcomes are still limited against many life-threatening diseases [1], [2]. Most of the drugs fail at different stages of clinical trials; thus global pharmaceutical industry faces many challenges. Investors discourage industry due to the large amount spent on research and development [3]. Drug repositioning or repurposing has emerged to address all such challenges. This strategy uses approved and under investigation drugs for implications in other unrelated diseases [1]. It offers several advantages over the development and marketing of a new drug candidate, such as lower risks of failure as the drug has undergone various levels of trials.

Drug repositioning strategy saves time and money with the least investment [4]. The major benefit of repurposing drugs is to exploit many pathways and targets that the drug uses for its action [5]. Life-threatening diseases such as cancer are growing fast, claiming more than 10 million cases in the past year [6]. Chemotherapy, radiotherapy and surgical procedures are traditionally given to the patient. However, reoccurrence and chemo-resistance still remain as a hurdle [7]. Recently, drug repurposing has emerged as a new strategy in cancer therapeutics, saving time and exploring pathways for targeting in cancer therapeutics [8], [9]. Some of the examples of drug repurposing include valproic acid, metformin, artemisinin (AMS) and others. Metformin used typically in the treatment of Type 2 diabetes is repurposed as an anti-tumor drug, reducing G1 cyclin expression and inhibiting growth and progression of cancer cells [10]. Similarly, valproic acid used to control depression showed downregulating effects on c-Myc and is effective against Burkitt lymphoma [11].

Pyruvate dehydrogenase kinases (PDK) are a major switch in cancer cells and an important pyruvate dehydrogenase (PDH) complex component. PDH contains several enzymes performing catalytic and regulatory roles in converting pyruvate to acetyl-CoA. PDH activity is dependent on its phosphorylation status, regulated by PDKs [12]. PDK-mediated phosphorylation blocks its catalytic activity, modulating the metabolism from energy-efficient mitochondrial respiration to cytoplasmic glycolysis [13]. PDKs are present in four isoforms and possess different expression patterns [14], [15]. The isoform PDK3 is associated with a hypoxia-mediated metabolic switch [16]. PDK3 knockdown reduces hypoxic cell survival and lowers drug resistance conferred by PDK3 [17]. PDK3 is responsible for the onset, proliferation, migration and survival of many cancer types. PDK3 is predominantly present in gastric cancer [18], colon cancer [19], acute myeloid leukemia [20], lung cancer [21] and many more [22].

AMS and its chemically modified derivatives are considered an efficient drug in combating malaria and drug-resistant malaria. AMS possesses immunomodulation, antiviral, antibacterial, antitumor and anti-cancer properties [23], [24], [25], [26], [27]. It shows effectiveness against cancer types such as breast, lung, ovary, prostate cancer, etc. [28], [29], [30], [31], by targeting many signaling pathways such as PI3K/AKT/mTOR, NF-κB, Wnt/β-catenin and TGF-β/Smad signaling cascades [32], [33], [34], [35]. The possible mechanism of action includes suppression of cell proliferation, cell cycle arrest, favoring apoptosis and regulating enzymes to module tumor microenvironment [36], [37]. Hypoxia-induced PDK3 creates an acidic microenvironment and promotes the Warburg effect [22].

This study proposes that AMS could be repurposed in anti-cancer by targeting PDK3. Our study provides a possible mechanism for the action of the repurposed PDK3 targetted by AMS in cancer therapeutics. The importance of this study can be attributed to the established anticancer activity of AMS. The binding affinity of AMS with PDK3 was estimated by fluorescence measurements and Isothermal titration calorimetry (ITC). Kinase inhibition assay has further ascertained the PDK3 inhibitory potential of AMS. We further complemented our experimental findings with molecular docking and 100 ns all-atom MD simulation analysis.