Improving the Anti-Tumor Effect of Indoleamine 2,3-Dioxygenase Inhibitor CY1-4 by CY1-4 Nano-Skeleton Drug Delivery System

Abstract

Background: CY1-4, 9-nitropyridine [2',3':4,5] pyrimido [1,2-α] indole -5,11- dione, is an indoleamine 2,3-dioxygenase (IDO) inhibitor and a poorly water-soluble substance. It is very important to increase the solubility of CY1-4 to improve its bioavailability and therapeutic effect. In this study, the mesoporous silica nano-skeleton carrier material Sylysia was selected as the carrier to load CY1-4, and then the CY1-4 nano-skeleton drug delivery system (MSNM@CY1-4) was prepared by coating the hydrophilic polymer material Hydroxypropyl methylcellulose (HPMC) and the lipid material Distearoylphosphatidyl-ethanolamine-poly(ethylene glycol)₂₀₀₀ (DSPE-PEG₂₀₀₀) to improve the anti-tumor effect of CY1-4. Methods: The solubility and dissolution of MSNM@CY1-4 were investigated, and its bioavailability, anti-tumor efficacy, IDO inhibitory ability and immune mechanism were evaluated in vivo. Results: CY1-4 was loaded in MSNM@CY1-4 in an amorphous form, and MSNM@CY1-4 could significantly improve the solubility (up to about 200 times) and dissolution rate of CY1-4. In vivo studies showed that the oral bioavailability of CY1-4 in 20 mg/kg MSNM@CY1-4 was about 23.9-fold more than that in 50 mg/kg CY1-4 suspension. In B16F10 tumor-bearing mice, MSNM@CY1-4 significantly inhibited tumor growth, prolonged survival time, significantly inhibited IDO activity in blood and tumor tissues, and reduced Tregs in tumor tissues and tumor-draining lymph nodes to improve anti-tumor efficacy. Conclusions: The nano-skeleton drug delivery system (MSNM@CY1-4) constructed in this study is a potential drug delivery platform for improving the anti-tumor effect of oral poorly water-soluble CY1-4.

Keywords: MSNM@CY1-4; anti-tumor; anti-tumor immune; indoleamine 2,3-dioxygenase; nano-skeleton.

Figure 1

The chemical structural formula of CY1-4.

Figure 2

In vitro release of CY1-4 from MSNM@CY1-4 in (a) artificial gastric fluid (pH 1.2) and (b) artificial intestinal fluid (pH 6.8).

Figure 3

In vivo plasma concentration–time curve of CY1-4 after oral administration of MSNM@CY1-4.

Figure 4

In vivo anti-tumor study of MSNM@CY1-4 in B16F10 tumor-bearing C57BL/6 mice. (a) Schematic graph of the experimental design. (b) Tumor volume curves of tumor-bearing mice received different treatments. (c) Body weight changes of the tumor-bearing mice. (d) Survival curve of tumor-bearing mice received different treatments. Data are shown as mean ± SD, n = 6 (** p < 0.01 vs. control; $ p < 0.05, $$ p < 0.01 vs. 50 mg/kg CY1-4 suspension; # p < 0.05 vs. 10 mg/kg MSNM@CY1-4).

Figure 5

In vivo IDO inhibition study of MSNM@CY1-4 in B16F10 tumor-bearing C57BL/6 mice. (a) Schematic graph of the experimental design. (b) The Kyn/Trp ratio in (b₁) blood and (b₂) tumor following various treatments. (c) The photograph images (c₁) and weight (c₂) of tumors collected from mice on the 14th day after tumor inoculation. Data are shown as mean ± SD, n = 3 (* p < 0.05, ** p < 0.01 vs. control; $ p < 0.05, $$ p < 0.01 vs. CY1-4 suspension).

Figure 5

In vivo IDO inhibition study of MSNM@CY1-4 in B16F10 tumor-bearing C57BL/6 mice. (a) Schematic graph of the experimental design. (b) The Kyn/Trp ratio in (b₁) blood and (b₂) tumor following various treatments. (c) The photograph images (c₁) and weight (c₂) of tumors collected from mice on the 14th day after tumor inoculation. Data are shown as mean ± SD, n = 3 (* p < 0.05, ** p < 0.01 vs. control; $ p < 0.05, $$ p < 0.01 vs. CY1-4 suspension).

Figure 6

In vivo anti-tumor immunity response of MSNM@CY1-4 in B16F10 tumor-bearing C57BL/6 mice. (a) Schematic illustration of the experimental design. (b) Infiltration of (b₁) Tregs, (b₂) CD4⁺ T cells, and (b₃) CD8⁺ T cells in tumors through the flow cytometric examination. (c) Tumor-draining lymph node infiltration of (c₁) Tregs, (c₂) CD4⁺ T cells, and (c₃) CD8⁺ T cells through flow cytometric examination. Data are shown as mean ± SD, n = 3 (* p < 0.05, ** p < 0.01 vs. control).