Biologically synthesized metal nanoparticles: recent advancement and future perspectives in cancer theranostics

Over the last two decades, nanotechnology has formed the most promising discipline within science likely to present solutions for the growing challenges in biomedical applications such as drug delivery, therapeutics and diagnostics [1–3]. Synthesis of metal nanoparticles, especially gold, silver and platinum (gold: AuNPs; copper, silver: AgNPs, platinum and quantum dots), with a particular shape, size and morphology is an important area of modern research. These nanoparticles are extensively used as an alternative strategy for cancer theranostics (therapeutics + diagnostics) due to their unusual physical, chemical, electronic and biological properties. Hence, economically cheap and eco-friendly methods for the synthesis of metal nanoparticles that could be useful for cancer theranostics are becoming an emerging field in biomedical research. In this context, biologically synthesized nanoparticles (b-NPs) using various biological sources (such as plants and microbes) overcome several disadvantages over chemically synthesized nanoparticles (c-NPs) [4–8]. Therefore, b-NPs are used for several biomedical applications especially in the area of cancer theranostics. Several groups including our own demonstrated the cancer cell imaging ability of b-NPs using fluorescence and computed tomography imaging techniques [9,10]. These b-NPs demonstrated powerful imaging abilities and could be used for cancer diagnostics applications. Green synthesized metal nanoparticles or b-NPs further play an important role for the delivery of drugs or therapeutic agents, and show various advantages over conventional chemical-based drug delivery systems. Several phytochemicals including proteins, lipids, carbohydrates create an external biomatrix around the metal nanoparticle surface that helps in facile and effective binding of drug molecules, thus avoiding the use of any external chemical capping agents. Dhar et al. demonstrated drug delivery efficacy of gold nanoparticles (synthesized from gellan-gum and sophorolipid-gellan gum) conjugated US FDA doxorubicin in human glioma cell lines (LN-229 and LN-18) and a human glioma stem cell line (HNGC-2) [11,12]. Recently, our group demonstrated the in vitro and in vivo delivery efficacy of doxorubicin using b-AuNPs and b-AgNPs in various cancer cell lines and in a mouse melanoma tumor model [8,13]. Moreover, Ganeshkumar et al. demonstrated the targeted delivery of 5-fluorouracil using folic acid conjugated b-AuNPs (derived from using the fruit peel extract of Punica granatum) in MCF-7 breast cancer cell lines with high targeting efficacy [14]. Taken together, these recent published reports demonstrated the drug delivery efficacy of b-NPs in cancer therapy. Another successful biomedical application is the use of b-NPs as anticancer agents due to the presence of medicinally active anticancer phytochemicals (polyphenols, flavonoids, taxol, isoflavons, etc.) in the bioresources, which attach over the nanogold surface during the biosynthesis process. However, the chemically synthesized nanoconjugates barely show any therapeutic activity. Biologically synthesized metal nanoparticles: recent advancement and future perspectives in cancer theranostics