Potential Underprediction of Warfarin Drug Interaction From Conventional Interaction Studies and Risk Mitigation: A Case Study With Epacadostat, an IDO1 Inhibitor

1-MT inhibits the invasion of CBP-resistant ovarian cancer cells via down-regulating IDO expression and re-activating immune cells function

Background

The indoleamine 2, 3-dioxygenase (IDO) inhibitor 1-methyl-tryptophan (1-MT) is currently being used in clinical trials in patients with relapsed or refractory solid tumors by inhibiting tumor immune escape. A greater understanding of IDO activity is required to begin to understand the molecular mechanism by which drugs work. This study was conducted to investigate of the clinical significance of 1-methyl-tryptophan (1-MT) in treating carboplatin-resistant (CBP-resistant) ovarian cancer and its mechanism of action.

Methods

Using a medium dose, intermittent treatment method, a clinically relevant CBP-resistant human ovarian cancer cell line (SKOV3/CBP) was established. SKOV3/CBP cells were treated with normal serum (control) or 1-MT (0.25 ng/mL) for 4 h (SKOV3/CBP + 1-MT). Cell proliferation, invasion and IDO expression in SKOV3, SKOV3/CBP and SKOV3/CBP + 1-MT cells were determined by MTT assays, Matrigel invasion chambers assays and ELISAs, respectively. The half-maximal inhibitory concentration (IC₅₀) and resistance index (RI) were also calculated. The killing ability of the NK cells and CD8+ T cells co-cultured with SKOV3, SKOV3/CBP and SKOV3/CBP + 1-MT cells were determined by LDH activity assays and the INF-γcounting method.

Results

The SKOV3/CBP cell line displayed an increased IC₅₀ compared to the SKOV3 cell line (P < 0.05) under CBP treatment. Treatment with 1-MT significantly decreased the IC₅₀ and RI of SKOV3/CBP cells. Furthermore, 1-MT treatment not only reduced the invasion ability, but also suppressed IDO expression in the drug-resistant SKOV3/CBP + 1-MT cell line as compared to the SKOV3/CBP cell line. Furthermore, 1-MT enhanced the killing ability of NK cells and the amount of INF-γsecreted from CD8+ T cells which were co-cultured with the SKOV3/CBP cell line.

Conclusion

Our data suggested that 1-MT inhibits the invasion of CBP-resistant ovarian cancer cells via down-regulation of IDO expression which leads to re-activation of immune cell function. We provide a conceptual foundation for the clinical development of 1-MT as an anti-tumor immunomodulator for chemotherapy resistant ovarian cancer patients.

Inhibition Mechanism of Indoleamine 2, 3-Dioxygenase 1 (IDO1) by Amidoxime Derivatives and Its Revelation in Drug Design: Comparative Molecular Dynamics Simulations

For cancer treatment, in addition to the three standard therapies of surgery, chemotherapy, and radiotherapy, immunotherapy has become the fourth internationally-recognized alternative treatment. Indoleamine 2, 3-dioxygenase 1 (IDO1) catalyzes the conversion of tryptophan to kynurenine causing lysine depletion, which is an important target in the research and development of anticancer drugs. Epacadostat (INCB024360) is currently one of the most potent IDO1 inhibitors, nevertheless its inhibition mechanism still remains elusive. In this work, comparative molecular dynamics simulations were performed to reveal that the high inhibitory activity of INCB024360 mainly comes from two aspects: disturbing the ligand delivery tunnel and then preventing small molecules such as oxygen and water molecules from accessing the active site, as well as hindering the shuttle of substrate tryptophan with product kynurenine through the heme binding pocket. The scanning of key residues showed that L234 and R231 residues both were crucial to the catalytic activity of IDO1. With the association with INCB024360, L234 forms a stable hydrogen bond with G262, which significantly affects the spatial position of G262-A264 loop and then greatly disturbs the orderliness of ligand delivery tunnel. In addition, the cleavage of hydrogen bond between G380 and R231 increases the mobility of the GTGG conserved region, leading to the closure of the substrate tryptophan channel. This work provides new ideas for understanding action mechanism of amidoxime derivatives, improving its inhibitor activity and developing novel inhibitors of IDO1.

Heme-containing enzymes and inhibitors for tryptophan metabolism

Iron-containing enzymes such as heme enzymes play crucial roles in biological systems. Three distinct heme-containing dioxygenase enzymes, tryptophan 2,3-dioxygenase (TDO), indoleamine 2,3-dioxygenase 1 (IDO1) and indoleamine 2,3-dioxygenase 2 (IDO2) catalyze the initial and rate-limiting step of l-tryptophan catabolism through the kynurenine pathway in mammals. Overexpression of these enzymes causes depletion of tryptophan and the accumulation of metabolic products, which contributes to tumor immune tolerance and immune dysregulation in a variety of disease pathologies. In the past few decades, IDO1 has garnered the most attention as a therapeutic target with great potential in cancer immunotherapy. Many potential inhibitors of IDO1 have been designed, synthesized and evaluated, among which indoximod (d-1-MT), INCB024360, GDC-0919 (formerly NLG-919), and an IDO1 peptide-based vaccine have advanced to the clinical trial stage. However, recently, the roles of TDO and IDO2 have been elucidated in immune suppression. In this review, the current drug discovery landscape for targeting TDO, IDO1 and IDO2 is highlighted, with particular attention to the recent use of drugs in clinical trials. Moreover, the crystal structures of these enzymes, in complex with inhibitors, and the mechanisms of Trp catabolism in the first step, are summarized to provide information for facilitating the discovery of new enzyme inhibitors.

Influence of Shenxiong Glucose Injection on the Activities of Six CYP Isozymes and Metabolism of Warfarin in Rats Assessed Using Probe Cocktail and Pharmacokinetic Approaches

Shenxiong glucose injection (SGI), a traditional Chinese medicine (TCM) preparation, has been widely used for the treatment of various cardiovascular and cerebrovascular diseases for many years. We assessed the potential influences of SGI on the activities of six CYP enzymes (CYP1A2, CYP2C11, CYP2C19, CYP2D4, CYP2E1, and CYP3A2) and on the pharmacokinetics of warfarin in rats. We compared plasma pharmacokinetics of six probe drugs (caffeine/CYP1A2, tolbutamide/CYP2C11, omeprazole/CYP2C19, metoprolol/CYP2D4, chlorzoxazone/CYP2E1, and midazolam/CYP3A2) and of warfarin between control and SGI-pretreated groups, to estimate the effect on the relative activities of the six isozymes and warfarin metabolism. There were no significant differences in the pharmacokinetic parameters of caffeine, omeprazole, metoprolol, chlorzoxazone, and midazolam between the SGI-pretreated and control groups. However, many pharmacokinetic parameters of tolbutamide in SGI-pretreated rats were affected significantly (p < 0.05), and indicated tolbutamide metabolism in the former group was markedly slower. Moreover, SGI reduced the clearance of warfarin. These results suggested SGI showed no effects on the enzyme activities of rat CYP1A2, CYP2C19, CYP2D4, CYP2E1, and CYP3A2, but inhibited the enzyme activity of CYP2C11, and improved the blood concentration of warfarin. This suggests that the dose of warfarin may need be adjusted when co-administrated with SGI.

Indoleamine 2,3-dioxygenase 1 (IDO1) inhibitors activate the aryl hydrocarbon receptor

Indoleamine 2,3-dioxygenase 1 (IDO1) plays a key role in the immune system by regulating tryptophan levels and T cell differentiation. Several tumor types overexpress IDO1 to avoid immune surveillance making IDO1 of interest as a target for therapeutic intervention. As a result, several IDO1 inhibitors are currently being tested in clinical trials for cancer treatment as well as several other diseases. Many of the IDO1 inhibitors in clinical trials naturally bear structural similarities to the IDO1 substrate tryptophan, as such, they fulfill many of the structural and functional criteria as potential AHR ligands. Using mouse and human cell-based luciferase gene reporter assays, qPCR confirmation experiments, and CYP1A1 enzyme activity assays, we report that some of the promising clinical IDO1 inhibitors also act as agonists for the aryl hydrocarbon receptor (AHR), best known for its roles in xenobiotic metabolism and as another key regulator of the immune response. The dual role as IDO antagonist and AHR agonist for many of these IDO target drugs should be considered for full interrogation of their biological mechanisms and clinical outcomes.