Functionalised gold nanoparticles using abietane diterpenoids from Plectranthus grandidentatus Gürke for cancer therapy

Nanoparticles (NPs) are very small particles with distinct properties stemming from their nanometric size and large surface area, setting them apart from bulk materials. NPs provide many benefits, such as high drug loading capacity, specific targeting, prolonged circulation, and minimized side effects. Over the past few years, metal-based NPs, such as gold NPs (AuNPs), have gained special attention due their surface plasmon resonance properties and use in drug and gene delivery, particularly in cancer treatment and theragnostics. Abietane diterpenoids, such as 7α-acetoxy-6β-hydroxyroyleanone (Roy) isolated from Plectranthus spp., are known to be cytotoxic agents, ideal for chemotherapeutic applications. Yet, their poor water solubility and low bioavailability limit their therapeutic efficacy. Harnessing the effectiveness of AuNPs, several nanosystems were made using Roy, the natural diterpene, and an ester derivative. After characterization of size, PDI, zeta potential and encapsulation efficiency, antitumour analysis using in vitro cancer cell models of breast cancer (MDA-MB-231, 4T1 and MCF7) were used to probe cytotoxic effect. Roy-functionalised AuNPs showed increased antitumour activity when compared with Roy alone, showcasing the improved antitumoral effect of the nanoformulation. In addition, the Roy-functionalised AuNPs showed selectivity for cancer cells over healthy human fibroblast (HDF) cells, a promising incentive for further development of natural diterpenoid nanosystems in cancer therapy.