Advance of Seriniquinone Analogues as Melanoma Agents

Abstract

Seriniquinone, a marine natural product, displayed potent cytotoxicity and selectivity against melanoma cancer cells. This selectivity, combined with a novel mode of action (MOA), prompted studies to translate a pharmacologically relevant lead. Herein, we report on structure-activity relationships (SARs), and provide a strategy to prepare analogues that retain activity and offer an improved water solubility and isomeric purity. From intermediates made on a gram-scale, derivatives were prepared and evaluated for their antiproliferation activity and melanoma selectivity. Overall these studies provide methods to install side chain motifs that demonstrate a common, and yet unique, biological profile.

Figure 1

Exemplary structures of FDA approved drugs for melanoma including Dabrafenib (BRAF inhibitor), Vemurafenib (BRAF inhibitor), Trametinib (Mitogen-activated protein kinase (MEK) inhibitor), Cobimetinib (MEK inhibitor), and Dacarbazine (DNA alkylator).^, Other agents (not shown) including Encorafenib (BRAF inhibitor) and Binimetinib (MEK inhibitor) have ended phase III, and NDA requests are filed.

Figure 2

Structures of seriniquinone (1) and core analogues 2–4.

Scheme 1. Synthesis of Core Analogues 2 and 3

Figure 3

Structures of the synthetic analogues 9a/9b, acid salt 10a/10b, and amides 11a/11b–14a/14b. These materials, prepared at milligram-scale for testing, were prepared as inseparable mixtures of regioisomers a and b.

Scheme 2. Gram-Scale Synthesis of Analogues 23–25

Figure 4

Hydrolytic release. Carbamate 24 hydrolyses to phenol 23 in aqueous media. Samples from DMSO stocks at 1.0 mg/mL (A, B) or 0.5 mg/mL (C, D) of 24 in PBS pH 7.2 undergo hydrolysis to purple salt 23 when diluted 20-fold and stored for 24 h at 23 °C.

Figure 5

Fluorescence emission spectra upon titration of ct-DNA into 20 μM doxorubicin, 60 μM 1, 60 μM 9a/9b, or 60 μM 24.

Figure 6

Relative DCD mRNA expression in HCT-116, Malme-3M, and SK-MEL-28 cells treated with 1, 23, and 24. Concentrations were given in HCT-116 by 1 μM (+) and 10 μM (++), and in Malme-3M or SK-MEL-28 by 30 nM (+) and 100 nM (++). Doxorubicin (D; 0.5 μM) and DMSO (0.5%) were used as positive and negative controls, respectively. Total RNA was extracted and subjected to quantitative PCR analysis by a one-step RT-PCR system to detect the mRNA expression of DCD and RPLPO (large ribosomal protein).

Figure 7

Confocal microscopic images of HCT-116 cells depicting the effects of 9a/9b and 24 on oxidative stress from CellROX Green (green) and nuclear counterstaining from NucBlue (blue).