Cancer:
Chronic myelogenous leukemia, lung, breast, head and neck, prostate, acute myeloid leukemia, prostate
Action: Aryl hydrocarbon Receptor (AhR) regulator, inhibits angiogenesis
Indirubin is the active component of many plants from the Isatis (L.) genus, including Isatis tinctoria (L.).
Indirubin is the active ingredient of Danggui Longhui Wan, a mixture of plants that is used in traditional Chinese medicine to treat chronic diseases. Indirubin and its analogues are potent inhibitors of cyclin-dependent kinases (CDKs). The crystal structure of CDK2 in complex with indirubin derivatives shows that indirubin interacts with the kinase's ATP-binding site through van der Waals interactions and three hydrogen bonds. Indirubin-3'-monoxime inhibits the proliferation of a large range of cells, mainly through arresting the cells in the G2/M phase of the cell-cycle. These results have implications for therapeutic optimization of indigoids (Hoessel et al., 1999).
Formula; Huang Lian (Rhizoma Coptidis Recens), Huang Qin (Radix Scutellariae Baicalensis), Huang Bai (Cortex Phellodendri), Zhi Zi (Fructus Gardeniae Jasminoidis), Dang Gui (Radix Angelicae Sinensis), Lu Hui (Herba Aloes), Long Dan Cao (Radix Gentianae Longdancao), Da Huang (Radix et Rhizoma Rhei), Mu Xiang (Radix Aucklandiae Lappae), Qing Dai (Indigo Pulverata Levis), She Xiang (Secretio Moschus)
Leukemia
Indirubin, a 3, 2' bisindole isomer of indigo was originally identified as the active principle of a traditional Chinese preparation and has been proven to exhibit anti-leukemic effectiveness in chronic myelocytic leukemia. Indirubin was detected to represent a novel lead structure with potent inhibitory potential towards cyclin-dependent kinases (CDKs) resulting from high affinity binding into the enzymes ATP binding site. This seminal finding triggered research to improve the pharmacological activities of the parent molecule within comprehensive structure-activity studies. Molecular modifications made novel anti-cancer compounds accessible with strongly improved CDK inhibitory potential and with broad-spectrum anti-tumor activity.
This novel family of compounds holds strong promise for clinical anti-cancer activity and might be useful also in several important non-cancer indications, including Alzheimer's disease or diabetes (Eisenbrand et al., 2004).
Aryl Hydrocarbon Receptor (AhR) Regulator; Breast Cancer
The aryl hydrocarbon receptor (AhR), when activated by exogenous ligands such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), regulates expression of several phase I and phase II enzymes and is also involved in the regulation of cell proliferation. One putative endogenous ligand is indirubin, which was recently identified in human urine and bovine serum. We determined the effect of indirubin in MCF-7 breast cancer cells on induction of the activities of cytochromes P450 (CYP) 1A1 and 1B1. With 4 hours exposure, the effects of indirubin and TCDD at 10nM on CYP activity were comparable, but the effects of indirubin, unlike those of TCDD, were transitory. Indirubin-induced ethoxyresorufin-O-deethylase activity was maximal by 6–9 hours post-exposure and had disappeared by 24 hours, whereas TCDD-induced activities remained elevated for at least 72 hours.
Thus, if indirubin is an endogenous AhR ligand, then AhR-mediated signaling by indirubin is likely to be transient and tightly controlled by the ability of indirubin to induce CYP1A1 and CYP1B1, and hence its own metabolism (Spink et al., 2003).
Chronic Myelogenous Leukemia (CML)
Indirubin is the major active anti-tumor component of a traditional Chinese herbal medicine used for treatment of chronic myelogenous leukemia (CML). In a study investigating its mechanism of action, indirubin derivatives (IRDs) were found to potently inhibit Signal Transducer and Activator of Transcription 5 (Stat5) protein in CML cells.
Compound E804, which is the most potent in this series of IRDs, blocked Stat5 signaling in human K562 CML cells, imatinib-resistant human KCL-22 CML cells expressing the T315I mutant Bcr-Abl (KCL-22M), and CD34-positive primary CML cells from patients.
In sum, these findings identify IRDs as potent inhibitors of the SFK/Stat5 signaling pathway downstream of Bcr-Abl, leading to apoptosis of K562, KCL-22M and primary CML cells. IRDs represent a promising structural class for development of new therapeutics for wild type or T315I mutant Bcr-Abl-positive CML patients (Nam et al., 2012).
Lung Cancer
A novel indirubin derivative, 5'-nitro-indirubinoxime (5'-NIO), exhibits a strong anti-cancer activity against human cancer cells. Here, the 5'-NIO-mediated G1 cell-cycle arrest in lung cancer cells was associated with a decrease in protein levels of polo-like kinase 1 (Plk1) and peptidyl-prolyl cis/trans isomerase Pin1. These findings suggest that 5'-NIO have potential anti-cancer efficacy through the inhibition of Plk1 or/and Pin1 expression (Yoon et al., 2012).
The control lung tissue showed a normal architecture with clear alveolar spaces. Interestingly, the indirubin-3-monoxime treated groups showed reduced adenocarcinoma with appearance of alveolar spaces. Transmission Electron Microscopic (TEM) studies of lung sections of [B(α)P]-induced lung cancer mice showed the presence of phaemorphic cells with dense granules and increased mitochondria.
The lung sections of mice treated with indirubin-3-monoxime showed the presence of shrunken, fragmented, and condensed nuclei implying apoptosis. The effects were dose-dependent and prominent in 10 mg/kg/5 d/week groups, suggesting the therapeutic role of indirubin analogue against this deadly human malignancy. These results indicate that indirubin-3-monoxime brings anti-tumor effect against [B(α)P]-induced lung cancer by its apoptotic action in A/J mice (Ravichandran et al., 2010).
Head and Neck Cancer
The effects of 5'-nitro-indirubinoxime (5'-NIO), an indirubin derivative, on metastasis of head and neck cancer cells were investigated and the underlying molecular mechanisms involved in this process explored.
After treatment of head and neck cancer cells with 5'-NIO, cell metastatic behaviors such as colony formation, invasion, and migration were inhibited in a concentration-dependent manner. 5'-NIO inhibited the beta1 Integrin/FAK/Akt pathway which can then facilitate invasion and/or migration of cancer cells through the extracellular matrix (ECM). Moreover, treatment of head and neck cancer cell with Integrin β1 siRNA or FAK inhibitor effectively inhibited the invasion and migration, suggesting their regulatory role in invasiveness and migration of head and neck cancer cells. It was concluded that 5'-NIO inhibits the metastatic ability of head and neck cancer cells by blocking the Integrin β1/FAK/Akt pathway (Kim et al., 2011).
Prostate Cancer; Inhibits Angiogenesis
Indirubin, the active component of a traditional Chinese herbal medicine, Banlangen, has been shown to exhibit anti-tumor and anti-inflammation effects; however, its role in tumor angiogenesis, the key step involved in tumor growth and metastasis, and the involved molecular mechanism is unknown.
To address this shortfall in the existing research, it was identified that indirubin inhibited prostate tumor growth through inhibiting tumor angiogenesis. It was found that indirubin inhibited angiogenesis in vivo. The inhibition activity of indirubin in endothelial cell migration, tube formation and cell survival in vitro has also been shown. Furthermore, indirubin suppressed vascular endothelial growth factor receptor 2-mediated Janus kinase (JAK)/STAT3 signaling pathway. This study provided the first evidence for anti-tumor angiogenesis activity of indirubin and the related molecular mechanism.
These investigations suggest that indirubin is a potential drug candidate for angiogenesis-related diseases (Zhang et al., 2011).
Acute Myeloid Leukemia
Indirubin derivatives were identified as potent FLT3 tyrosine kinase inhibitors with anti-proliferative activity at acute myeloid leukemic cell lines, RS4;11 and MV4;11 which express FLT3-WT and FLT3-ITD mutation, respectively. Among several 5 and 5'-substituted indirubin derivatives, 5-fluoro analog, 13 exhibited potent inhibitory activity at FLT3 (IC(50)=15 nM) with more than 100-fold selectivity versus 6 other kinases and potent anti-proliferative effect for MV4;11 cells (IC(50)=72 nM) with 30-fold selectivity versus RS4;11 cells.
Cell cycle analysis indicated that compound 13 induced cell-cycle arrest at G(0)/G(1) phase in MV4;11 cells (Choi et al., 2010).
References
Choi SJ, Moon MJ, Lee SD, et al. (2010). Indirubin derivatives as potent FLT3 inhibitors with anti-proliferative activity of acute myeloid leukemic cells. Bioorg Med Chem Lett, 20(6):2033-7.
Eisenbrand G, Hippe F, Jakobs S, Muehlbeyer S. (2004). Molecular mechanisms of indirubin and its derivatives: novel anti-cancer molecules with their origin in traditional Chinese phytomedicine. J Cancer Res Clin Oncol, 130(11):627-35
Hoessel R, Leclerc S, Endicott JA, et al. (1999). Indirubin, the active constituent of a Chinese antileukaemia medicine, inhibits cyclin-dependent kinases. Nat Cell Biol, 1(1):60-7.
Kim SA, Kwon SM, Kim JA, et al. (2011). 5'-Nitro-indirubinoxime, an indirubin derivative, suppresses metastatic ability of human head and neck cancer cells through the inhibition of Integrin β 1/FAK/Akt signaling. Cancer Lett, 306(2):197-204.
Nam S, Scuto A, Yang F, et al. (2012). Indirubin derivatives induce apoptosis of chronic myelogenous leukemia cells involving inhibition of Stat5 signaling. Mol Oncol, 6(3):276-83.
Ravichandran K, Pal A, Ravichandran R. (2010). Effect of indirubin-3-monoxime against lung cancer as evaluated by histological and transmission electron microscopic studies. Microsc Res Tech, 73(11):1053-8.
Spink BC, Hussain MM, Katz BH, Eisele L, Spink DC. (2003). Transient induction of cytochromes P450 1A1 and 1B1 in MCF-7 human breast cancer cells by indirubin. Biochem Pharmacol, 66(12):2313-21.
Yoon HE, Kim SA, Choi HS, et al. (2012). Inhibition of Plk1 and Pin1 by 5'-nitro-indirubinoxime suppresses human lung cancer cells. Cancer Lett, 316(1):97-104.
Zhang X, Song Y, Wu Y, et al. (2011). Indirubin inhibits tumor growth by anti-tumor angiogenesis via blocking VEGFR2-mediated JAK/STAT3 signaling in endothelial cell. Int J Cancer, 129(10):2502-11. doi: 10.1002/ijc.25909.