Vitamin B5 supports MYC oncogenic metabolism and tumor progression in breast cancer.

Tumors are intrinsically heterogeneous and it is well established that this directs their evolution, hinders their classification and frustrates therapy1-3. Consequently, spatially resolved omics-level analyses are gaining traction4-9. Despite considerable therapeutic interest, tumor metabolism has been lagging behind this development and there is a paucity of data regarding its spatial organization. To address this shortcoming, we set out to study the local metabolic effects of the oncogene c-MYC, a pleiotropic transcription factor that accumulates with tumor progression and influences metabolism10,11. Through correlative mass spectrometry imaging, we show that pantothenic acid (vitamin B5) associates with MYC-high areas within both human and murine mammary tumors, where its conversion to coenzyme A fuels Krebs cycle activity. Mechanistically, we show that this is accomplished by MYC-mediated upregulation of its multivitamin transporter SLC5A6. Notably, we show that SLC5A6 over-expression alone can induce increased cell growth and a shift toward biosynthesis, whereas conversely, dietary restriction of pantothenic acid leads to a reversal of many MYC-mediated metabolic changes and results in hampered tumor growth. Our work thus establishes the availability of vitamins and cofactors as a potential bottleneck in tumor progression, which can be exploited therapeutically. Overall, we show that a spatial understanding of local metabolism facilitates the identification of clinically relevant, tractable metabolic targets.

Metabolomic approaches for enzyme function and pathway discovery in bacteria.

Most of the chemical diversity present in the natural world derives from the incredible ability of enzymes to act on and control metabolism. Yet, thousands of enzymes have no defined function. The capacity to probe, investigate and assign previously unknown enzyme function with speed and confidence is therefore highly sought-after. Metabolomics is becoming a dominant player in the field of functional genomics and, when coupled with genetic tools and protein biochemistry techniques, has enabled unbiased, de novo annotation of orphan enzymes both in vitro and ex vivo. In this chapter, we describe two distinct experimental and analytical metabolomic methodologies used to reveal enzyme function. Activity-based metabolomic profiling (ABMP) is an in vitro technique that enables tracking of enzyme-induced changes in a complex metabolite extract. Global metabolomic profiling permits the comparison of extracted cellular metabolome of groups of samples (e.g., wild-type versus mutant bacteria). The methods we describe present the advantage of generating cell extracts containing a broad range of metabolites in their native states, which can then be used to identify substrates for orphan enzymes. This chapter aims to provide a guide for the use of these metabolomic techniques by scientists interested in identifying bona fide physiological substrates of orphan enzymes and the metabolic pathways they belong to.

In vitro elucidation of the crucial but complex oxidative tailoring steps in rufomycin biosynthesis enables one pot conversion of rufomycin B to rufomycin C.

The antimycobacterial peptides, rufomycins, have their antibiotic activity conferred by oxidative tailoring of the cyclic peptide. Here we elucidate the roles of cytochrome P450s RufS and RufM in regioselective epoxidation and alkyl oxidation respectively and demonstrate how RufM and RufS create a complex product profile dependent on redox partner availability. Finally, we report the in vitro one pot conversion of rufomycin B to rufomycin C.

New chemistry from natural product biosynthesis.

Catalysts are a vital part of synthetic chemistry. However, there are still many important reactions for which catalysts have not been developed. The use of enzymes as biocatalysts for synthetic chemistry is growing in importance due to the drive towards sustainable methods for producing both bulk chemicals and high value compounds such as pharmaceuticals, and due to the ability of enzymes to catalyse chemical reactions with excellent stereoselectivity and regioselectivity. Such challenging transformations are a common feature of natural product biosynthetic pathways. In this mini-review, we discuss the potential to use biosynthetic pathways as a starting point for biocatalyst discovery. We introduce the reader to natural product assembly and tailoring, then focus on four classes of enzyme that catalyse C─H bond activation reactions to functionalize biosynthetic precursors. Finally, we briefly discuss the challenges involved in novel enzyme discovery.