Phycocyanobilin from Arthrospira platensis: A potential photodynamic anticancer agent

Abstract

Phycocyanobilin (PCB), a tetrapyrrole chromophore compound of Phycocyanin (PC) from Arthrospira platensis. Previous studies have shown that it has anti-inflammatory and immunomodulatory biological activities. In this work, we found that it can be used as a new anticancer photosensitizer, which is almost non-toxic readily available and less costly. A rapid production process of PCB was developed, with a yield of 19.2 ± 1.1 mg/g. By using semi-preparative liquid chromatography and silica gel column chromatography, PCB was refined to a purity of 99.97 ± 0.02%. Nuclear magnetic resonance spectroscopy and mass spectrometry were used to determine the PCB structure. The optimized wavelength of the light source that caused PCB to produce reactive oxygen species (ROS) was 660 nm. PCB had an estimated active oxygen quantum yield of 0.1595, 14.5 times that of PC (0.0110). Meanwhile, PCB produced ROS in MCF-7 cells under light conditions. After the protein of PC was partially removed, the quantum yield of active oxygen in PCB is greatly improved, which was helpful to enhance its anticancer activity. The photodynamic anticancer activity of PCB (IC50:8.26 ± 1.19 μM) was significantly enhanced compared with PC (IC50:255.29 ± 1.72 μM). PCB (without light) had no significant anticancer activity in vitro, but it showed strong anticancer activity in vivo, which was equivalent to the activity of the positive drug group: Zinc-Phthalocyanine (ZnPc) with light. This may be because PCB had the effect of eliminating inflammation and improving immunity. PCB significantly enhanced its anticancer activity under light conditions due to the production of reactive oxygen species. The experimental results showed that PCB had dual anticancer effects of chemotherapy and phototherapy in vivo, and had potential to become a new anticancer photosensitizer.