Uncovering of a novel non-taxane anticancer secondary metabolite from Taxol-producing endophytic fungus: Optimization of culture parameters and whole-genome sequence analysis for improved taxane production biosynthesis.

Abstract

Cancer-related mortalities and morbidities have proven to be a great health burden for human society with immense economic implications. With uncontrolled proliferation of cells as the fundamental principle underlying its clinical onset, progression and metastasis, the remedial approaches for the prevention of its onset and interventions in later stages have largely centered on surgical removal of solid tumors, radiotherapy as well as pharmaceutical interventions with small molecular organic compounds of either Natural or Synthetic Origins. Several classes of natural compounds, also known as Secondary Metabolites (SMs) have provided many of the all-time successful, clinically used anticancer drugs such as Taxol, vinca alkaloids, camptothecin, podophyllotoxin, among others (Cragg and Newmann, 2013). The vast majority of these anticancer SMs had been obtained from the large-scale screening of extracts of traditionally reported medicinal plants and several microbial organisms including endophytic microorganisms through the Bioassay-Guided Fractionation (BGF). BGF typically employs the assay of in vitro proliferation inhibition of human cancer cells. Taxol, also known as Paclitaxel is one such anticancer drug which incidentally was the first billion-dollar drug in the history of the worldwide pharma trade. This thesis work had been originally envisaged to enhance the yields of Taxol from an endophytic fungus, Fusarium solani IISc-1 which had earlier been isolated in the laboratory from the stem cuttings of the Taxol-producing yew tree, Taxus celebica (Chakaravarthi et al., 2008, 2013; Chakravarthi, Ph.D. thesis, 2011). Several endophytic fungi have been known to produce this valuable drug with yet to be realized commercial potential (Kusari et al. 2014). After initial experiments with the fungus covering some of these objectives using heavy metal stress and pH optimization studies, sudden attenuation of Taxol-production by the fungus coupled to the loss of revival of stored original fungal stocks led to the midway course-correction in adding a new objective on “search of novel non-taxane anticancer secondary metabolites” from this fungus by BGF. SM production loss is particularly well-known for the fungi as they have been proved to harbor several diverse cryptic SM biosynthetic pathways that remain silenced during most laboratory culture conditions. This search indeed paved the way for the isolation, identification and characterization of a novel, non-taxane anticancer SM, FsF3, identified as 2’-(E/Z) octadecyl-2-enyl-cyclohexanone