Nannocystin Reagents to Elucidate the Role of Elongation Factor 1a in Apoptosis

Project Summary Nannocystin reagents will be used to interrogate the role of the protein elongation factor 1A in apoptosis of cancer cells. Nannocystins are small molecule natural products isolated from myxobacteria that potently inhibit cancer cell proliferation and trigger apoptosis at an early time point. Nannocystin is a hybrid molecule consisting

of an upper tripeptide domain and a lower polyketide domain. Nannocystin binds the protein eukaryotic elongation factor 1α (EEF1A), however it is presently unclear how binding to this protein causes apoptosis. The related molecule didemnin B also binds EEF1A, inhibiting EEF1A-mediated elongation at micromolar

concentrations but triggering apoptosis at nanomolar concentrations. Elongation factors are vital for protein synthesis, but additional cellular roles have recently been found. In particular, EEF1A was found to inhibit p53's activity as a tumor suppressor, and cancer cells under stress increase EEF1A production. It is hypothesized that

nannocystin disrupts EEF1A-p53 binding, which releases p53 to activate the apoptosis pathway, leading to cell death. Nannocystin is thought to bind EEF1A at the same site as didemnin B. However, there are no cocrystal structures of EEF1A-nannocystin, and a recent structure-activity relationship study challenged this putative

binding model. Details of the binding site are critical for rational development of new anticancer therapeutics related to nannocystin. To investigate apoptosis in cancer cells, we propose studies in which nannocystin and molecular probe reagents will be prepared by total synthesis, an approach that requires efficient and convergent

chemical synthesis. We will also employ a tandem reaction between a simple alkene and alkyne to access the unique polyketide domain. This proposal has three specific aims: (1) to use Ru coupling and Co-promoted isomerization in the total synthesis of nannocystin, for which we have made significant progress toward both the

tripeptide and polyketide fragments; (2) to synthesize two bifunctional photoaffinity reagents to elucidate the site of binding between nannocystin and EEF1A, incorporating a novel tripeptide to introduce the photoaffinity probe, designed to covalently bond to the protein at the two extreme ends of the binding site; and (3) to determine if the

p53 pathway is involved in nannocystin-triggered apoptosis and identify the downstream effectors of p53 activation.