Cancer biotherapy: targeting cancer cells with a plant-expressed virus-like particle

Abstract

Cancer continues to cause high mortality rates worldwide. Currently, treatments are limited by high cost, toxicity and poor specificity. Virus-like particles (VLPs), expressed in plants, are a promising platform for targeted cancer biotherapy due to their biocompatibility, uniform structure and capacity for surface modification. This study aimed to develop a plant-expressed Papaya mosaic virus (PapMV) virus-like particle as a vehicle for targeted cancer biotherapy and investigate its binding capability to a cancer cell line. PapMV VLPs were engineered and decorated with polygonatum cyrtonema lectin (PCL) via SpyTag/SpyCatcher technology to enable selective binding of VLP to tumor-associated glycans on cancer cells. The recombinant genes encoding chimeric PapMV coat protein (CP) and PCL fusion elements were co-expressed using a transient plant-based expression system in Nicotiana benthamiana DXT-FT plants to produce lectin-conjugated PapMV VLPs. Density gradient centrifugation, sodium dodecyl sulfate-polyacrylamide electrophoresis and western blotting verified protein expression and PCL-CP conjugation. Further structural analysis using transmission electron microscopy revealed uniform, assembled, rod-shaped VLPs. VLP tubules were purified via their 6-Histidine tag by using affinity beads and subsequently quantified and characterized. The results showed low expression levels of the chimeric PapMV VLPs and lectin-conjugated PapMV VLPs, ranging between ±0.042 to ±0.079 mg from 6.2 to 11.9 g harvested plant leaf biomass, respectively. These results indicated suboptimal expression of the recombinant genes. In vitro binding of the conjugated PCL-PapMV VLP to a HER2+ breast cancer cell line was assessed using a fluorophore-conjugated anti-His antibody, directed against the 6-His tag on the C-terminal of PapMV CP. However, no specific binding of the His-tagged PCL-PapMV VLPs to the target breast cancer cells was detected, indicating improper lectin orientation or steric hindrance affecting receptor accessibility. This highlights the importance of structural design in biological function. Although, chimeric PapMV VLPs were successfully expressed, assembled and conjugated to the co-expressed PCL lectin in plants via a SpyTag/SpyCatcher strategy, future studies should explore gene design strategies to optimise protein yield and enable VLP binding to target cancer cells.