Tanshinone II-A: new perspectives for old remedies

Abstract

Tanshinone II-A (TSN) is the most abundant diterpene quinone isolated from Danshen (Salvia miltiorrhiza), which has been used in treating cardiovascular diseases for more than 2000 years in China. Interest in its versatile protective effects in cardiovascular, metabolic, neurodegenerative diseases, and cancers has been growing over the last decade. TSN is a multi-target drug, whose molecular targets include transcription factors, scavenger receptors, ion channels, kinases, pro- and anti-apoptotic proteins, growth factors, inflammatory mediators, microRNA, and others. More recently, enhanced or synergistic effects can be observed when TSN is used in combination therapy with cardioprotective and anti-cancer drugs. These combination therapy regimens may open new therapeutic avenues for the treatment of various kinds of human diseases.

Keywords::

• cancer
• combination therapy
• Danshen
• tanshinone II-A

1. Introduction

Traditional Chinese medicines (TCM), as a representative of alternative and complementary medicine, are commonly used in Asian countries for the treatment of cancer, cardiovascular, cerebrovascular, metabolic, and neurodegenerative diseases. Among the TCM, Danshen (Salvia miltiorrhiza) has drawn extensive attention as effective therapeutics against a number of diseases including atherosclerosis [1], hyperlipidemia [2], hypertension [3], stable angina pectoris [4], myocardial infarction [4], coronary artery disease [1], diabetes [4] and metabolic syndrome [5], as supported by published papers, approved patents and clinical trials in U.S. (Table 1). In China, Danshen formulations include Danshen Tablet, Danshen Capsule, and Dantonic Dripping Pill (DP, also referred to as Cardiotonic® Pill). According to the report from Tianjin-based Tasly Pharmaceutical Co., DP, as the most popular Chinese medicinal product in China for treating coronary heart disease, generates 205 million USD annually [6]. DP is a botanical drug which consists of extracts of Danshen (Radix Salviae miltiorrhizae) and San qi (Radix Panax notoginseng) with borneol. A systematic review of randomized controlled trials (RCT) of DP was published in 2010 [6], although all the RCT were conducted in China with Chinese patients and only published in Chinese medical journals. It is the first TCM approved for Phase II and Phase III clinical trials by the U.S. Food and Drug Administration (Table 1). In this editorial, we focus on the scientific literature and approved patents on the therapeutic use and molecular targets of tanshinone II-A (TSN), a major bioactive constituent isolated from Danshen. Combination therapy of TSN and other drugs are also discussed.

Table 1. Overview of clinical trials of Danshen and tanshinone II-A.

Clinicaltrials.gov identifier	Study title	Conditions
NCT01563770	Cardiovascular Effects of Salvia Miltiorrhiza Extract (Danshen)	Dyslipidemia Hypertension Vasodilation Oxidative stress Inflammation
NCT01637675	Efficacy and Safety Study of Tanshinone IIA Sodium Sulfonate to Treat Pulmonary Hypertension (STS)	Pulmonary hypertension Cardiovascular diseases Lung diseases
NCT01452477	Tanshinone in Polycystic Ovary Syndrome	Polycystic ovary syndrome
NCT01033630	Cardiovascular-Protective Effects of Herbal Medicine Danshen-Gegen*	Hypertension
NCT01502943	Studies of Traditional Chinese Medicine Clinical Efficacy Evaluation Index*	Coronary heart disease Stable angina pectoris
NCT00797953	Phase II Multi-Center Study of T89 to Treat Chronic Stable Angina*	Chronic stable angina pectoris
NCT01659580	Phase III Trial of Dantonic® (T89) Capsule to Prevent and Treat Stable Angina (CAESA)	Chronic table angina pectoris

Source: www.clinicaltrials.gov.

T89, also known as Dantonic Dripping Pill or Cardiotonic Pill.

*Trials that have been completed.

2. Literature and patent search

Data were identified through the search of PubMed for research articles and reviews, the websites of European Patent Office and US Patent Office for patents up to October 2012. In total, 607 publications were identified through the electronic database search on PubMed from 2002 to 2012. There is a trend of gradual increase in publications covering tanshinones (Figure 1). In recent years, many patents have been granted on the isolation, preparation, and pharmacological characterization of tanshinones; diverse TCM formula with Danshen as the major principle; structural modifications of TSN or other lead compounds from Danshen; and emerging new tanshinone derivatives (such as neo-tanshinlactone) for the treatment of cancer [7]. Based on published literature and granted patents, it can be concluded that TSN is an effective therapeutic agent against atherosclerosis [8], hypertension [3], obesity [9], metabolic syndrome [9], and other diseases.

Figure 1. Publications covering tanshinone from 2002–2012 and the chemical structures of tanshinone II-A and crypotanshinone.

3. Tanshinone II-A

Lipophilic tanshinones isolated from Danshen consist of 0.29% tanshinone II-A (TSN), 0.23% cryptotanshinone (CPT), 0.11% tanshinone I, and 0.054% 15, 16-dihydrotanshinone-I [5]. Of all of these tanshinones that have been identified, TSN and CPT have received the most attention, in that they are the most abundant and well-studied constituents of Danshen which exerts antioxidant and anti-inflammatory actions in many experimental animal models. The chemical structure of TSN and CPT are illustrated in Figure 1. Over the past decade, we [1,10-19] and others [20-24] have demonstrated that TSN has potential protective effects against atherosclerosis, cardiac hypertrophy, cardiac fibrosis, diabetes, neurodegenerative diseases, and various kinds of cancers. However, the poor water-solubility, poor intestinal absorption, and low oral bioavailability (about 2.9 – 3.4% in rats) [25] have hampered the clinical application of TSN. To overcome these problems, various approaches have been employed, such as the preparation of water-soluble derivative of TSN-sodium tanshinone II-A sulfonate (STS) [4], the preparation of TSN in discoidal and spherical HDL [26], and the development of new drug delivery systems for TSN such as solid dispersion pellets, nanoparticles, and microemulsions [26].

4. Molecular targets of tanshinone II-A

Studies in the past decade suggest that TSN hits the model of “one-drug-multi-target-multi-disease, which is shared by” TCM, such as berberine [27]. Based on published literature and granted patents, we summarized the molecular targets of TSN in Table 2. These targets, though some are not characterized in detail, will furnish the molecular basis for the clinical application of TSN to treat various kinds of diseases.

Table 2. Molecular targets of tanshinone II-A

Targets of tanshinone II-A	Specific target proteins
Transcription factors	NF-κB, PPAR-γ, Nrf-2, STAT-1, STAT-3, AP-1, Smad-3, Smad-7, HIF-1α, β-catenin
Scavenger receptors	CD36, SR-A, LOX-1
Cytokines and chemokines	IL-1β, IL-6, TNF-α, MCP-1, VCAM-1, ICAM-1, MIF, CXCR4, P-selectin
Ion channels and water channel	KCNE1, Kv2.1, ATP-sensitive K^+ channel, BK-Ca, AQP1, AQP5
microRNA	miR-1, miR-133
Enzymes	AMPK, p38, ERK, JNK, eNOS, MMP-2, MMP-7, MMP-9, CD40, iNOS, PLA2, PI3K/Akt, GPx
Pro-and anti-apoptotic proteins	Bcl-xl, Bcl-2, Bax, caspase-3
Growth factors and others	AT1R, ER, AR, VEGF, LC3-II, TGF-β, PCNA, ET-1, TF

AMPK: 5'-AMP-activated protein kinase; AP-1: Activator protein-1; AQP: Aquaporins; AR: Aldose reductase; AT₁R: Angiotensin II type 1 receptor; Bax: Bcl-2-associated X protein; Bcl-xl: B-cell lymphoma-extra large; Bcl-2: B-cell lymphoma 2; BK-Ca: Large conductance Ca²⁺-sensitive K⁺-channels; CXCR4: C-X-C chemokine receptor type 4; eNOS: Endothelial nitric oxide synthase; ER: Estrogen receptor; ERK: Extracellular signal-regulated kinases; ET-1: Endothelin-1; GPx: Glutathione peroxidase; HIF-1α: Hypoxia-inducible factor 1-alpha; ICAM-1: Intercellular adhesion molecule 1; iNOS: Inducible nitric oxide synthase; JNK: c-Jun N-terminal kinases; KCNE1: Potassium voltage-gated channel subfamily E member 1; Kv2.1: Potassium voltage-gated channel Shab-related subfamily member 1; LC3-II: Microtubule-associated protein 1A/1B-light chain 3-II; IL: Interleukin; LOX-1: Lectin-like oxidized LDL receptor-1; MCP-1: Monocyte chemotactic protein-1; MIF: Macrophage migration inhibitory factor; miR-1: Microrna-1; miR-133: Microrna-133; MMP: Matrix metalloproteinase; NF-κB : Nuclear factor kappa B; Nrf-2: Nuclear factor erythroid 2-related factor 2; PCNA: Proliferating cell nuclear antigen; PI3K: Phosphatidylinositol 3-kinases; PLA₂: Phospholipase A2; PPAR-γ: Peroxisome proliferator-activated receptor-gamma; SR-A: Scavenger receptor-A; STAT: Signal transducer and activator of transcription; TF: Tissue factor; TGF-β: Transforming growth factor-β; TNF-α: Tumor necrosis factor-alpha; VCAM-1: Vascular cell adhesion molecule 1; VEGF: Vascular endothelial growth factor.

5. Combination therapy

Combination therapy of bioactive herbal ingredients with Western medicine represents a new emerging field in the management of human diseases. Combined use of TSN with other drugs with different mechanisms of action can potentiate the pharmacological effects; reduce side-effects through decreasing the doses of both agents and improve pharmacodynamic and pharmacokinetic properties of drugs. Following combination strategies may be applied in clinical studies in future.

5.1 Tanshinone II-A/statins

We have previously filed a patent application describing the preventive effect of TSN against atherosclerosis in high-fat-diet-fed rabbits [8]. Considering that TSN does not affect lipid metabolism [10-12,14], but has hepatoprotective properties [28,29], Xu et al. described the preparation of a pharmaceutical composition containing TSN and HMG-CoA reductase [30]. However, the pharmacological effects of this combination strategy remain unknown. More recently, we observed that, in athero-prone ApoE knockout mice fed a high-cholesterol-diet, TSN and atorvastatin in combination can reduce and stabilize atherosclerotic plaques in synergism, for the atheroprotective mechanisms of TSN (lipid-independent) and atorvastatin (lipid-lowering) are different [31]. The safety profile and favorable results demonstrated in this combination therapy support its use not only in patients with atherosclerosis who don't tolerate statins, but also in those who don't achieve therapeutic goals with single therapy with statins. In addition, TSN/atorvastatin combination therapy has the potential to overcome the unwanted side-effects of statins (such as life-threatening rhabdomyolysis and liver damage).

5.2 Tanshinone II-A/Angiotensin II-type I receptor blockers

Oral administration of TSN decreased systolic blood pressure of spontaneously hypertensive rats (SHRs) [32]. In contrast, we fail to observe the blood pressure-lowering effect of TSN in stroke-prone 2-kidney-2-clip renohypertensive rats [15,16]. Consistent with our reports, Li et al. [33] observed that TSN prevents left ventricular hypertrophy in the myocardium of hypertensive rats with abdominal aorta constriction, independent of blood pressure. Therefore, it is conceivable that TSN and angiotensin II-type I receptor blockers (ARBs) may have a synergistic protective effects on patients with hypertension.

5.3 Other combination strategies

P-glycoprotein (P-gp) functions as a drug export pump that decreases intracellular concentrations of chemotherapeutic agents. TSN is a potential P-gp inhibitor during chemotherapy as it potentiates the efficacy of 5-FU in a colon cancer nude SCID mouse model [34]. Furthermore, TSN can be used in combination with other bioactive constituents from TCM. Wang et al. [35] recently disclosed a patent describing a medicinal composition of tanshinone II-A sulfate and ferulic acid to treat cardiovascular and cerebrovascular diseases.

6. Expert opinion

Although substantial progress has been made in elucidating the cellular and molecular targets of TSN, it remains unknown which are direct targets as well as the mechanisms of its multi-targeted actions. Preclinical studies have clearly demonstrated the efficacy of TSN in experimental animal models. Such information will be essential in translating the beneficial effects into clinical practice. At present, several clinical trials with TSN are already ongoing or completed in U.S. and we are waiting to see whether TSN (either used alone or in combination with other drugs) can be a therapeutic agent. Combining all available data, we expect that TSN could be considered as an effective therapeutic agent against various kinds of diseases, also it may serve as the lead compound or novel drug candidate in the battle against various kinds of human diseases.

Declaration of interest

The authors state no other conflicts of interest and have received no payment in preparation of this manuscript.

Acknowledgments

The authors gratefully acknowledge the contribution of investigators dedicated to the isolation, preparation, and pharmacological characterization of tanshinones and their derivatives, and we apologize to those investigators whose work we could not cite due to reference limit. This work was supported by research grants from the National Natural Science Foundation of China (No. 81072641, No. 81273499), the National Science and Technology Major Project of China “Key New Drug Creation and Manufacturing Program” (No. 2011ZX09401-307) Team Item of Natural Science Foundation of Guangdong Province (No. S2011030003190), Major Project of Guangdong Province (No. 2008A030201013, No. 2012A080201007), Major Project of Department of Education of Guangdong Province (No.CXZD1006), and ‘‘New Investigator Award” from Ministry of Education of China.