Synthesis and biological evaluation of echinomycin analogues as potential colon cancer agent

Abstract

Colorectal cancer is the third most commonly diagnosed cancer and the second leading cause of cancer-related death, thus a novel chemotherapeutic agent for colon cancer therapy is needed. In this study, analogues of echinomycin, a cyclic peptide natural product with potent toxicity to several human cancer cell lines, were synthesized, and their biological activities against human colon cancer cells were investigated. Analogue 3 as well as 1 inhibit HIF-1α-mediated transcription. Notably, transcriptome analysis indicated that the cell cycle and its regulation were involved in the effects on cells treated with 3. Analogue 3 exhibited superior in vivo efficacy to echinomycin without significant toxicity in mouse xenograft model. The low dose of 3 needed to be efficacious in vivo is also noteworthy and our data suggest that 3 is an attractive and potentially novel agent for the treatment of colon cancer.

Figure 1

Chemical structures of echinomycin and its analogues.

Figure 2

Chemical structures of echinomycin analogues.

Figure 3

Synthesis of echinomycin analogues.

Figure 4

Apoptotic effect of echinomycin and 3 on SW620 cells evaluated by (a) Western blotting to measure cleaved caspase-3 and (b) TUNEL assay. *Indicates P < 0.005 by Student's t test. The error bars show the s.d. (n = 4).

Figure 5

Effect of echinomycin (1), 2 and 3 on HIF-1α-dependent transcription in SW620 cells. SW620 cells were transiently transfected with empty vector pCI-neo-3 × FLAG or HIF-1α expression vector pCI-neo-3 × FLAG-HIF-1α, together with pGL3-5 × HRE-Luc and pGL4.75 [hRluc/CMV]. One day after transfection, echinomycin (1), 2, or 3 was added to the cell culture media and incubated for an additional 16 h. The cells were lysed, and a dual luciferase assay was performed. Firefly luciferase activity was normalized to Renilla luciferase activity, and the data are presented as fold induction relative to the values obtained in cells DMSO-treated cells transfected with empty vector. The error bars represent standard deviations (n = 3). *P < 0.05 and **P < 0.01 compared to DMSO-treated cells transfected with HIF-1α (Student’s test).

Figure 6

Synthesis of echinomycin probes.

Figure 7

In vivo anticancer activity of echinomycin and 3 on the SW620 xenograft mice model. Male BALB/C nude mice were administered by intraperitoneal injection with the vehicle, echinomycin and 3, at dosages of 0.04 and 0.4 µg/mice (n = 10 each group), every day for 10 days (a, b). Average tumor volume (c) was measured. Data are expressed as the mean ± standard error (n = 8). *Indicates P < 0.05 by Student's t test. The error bars show the s.d. (n = 10).

Figure 8

Summary of SAR of echinomycin.