Oxaspirol B with p97 Inhibitory Activity and Other Oxaspirols from Lecythophora sp. FL1375 and FL1031, Endolichenic Fungi Inhabiting Parmotrema tinctorum and Cladonia evansii

Abstract

A new metabolite, oxaspirol D (4), together with oxaspirols B (2) and C (3) were isolated from Lecythophora sp. FL1375, an endolichenic fungus isolated from Parmotrema tinctorum, whereas Lecythophora sp. FL1031 inhabiting the lichen Cladonia evansii afforded oxaspirols A (1), B (2), and C (3). Of these, oxaspirol B (2) showed moderate p97 ATPase inhibitory activity. A detailed characterization of all oxaspirols was undertaken because structures proposed for known oxaspirols have involved incomplete assignments of NMR spectroscopic data leading only to their planar structures. Thus, the naturally occurring isomeric mixture (2a and 2b) of oxaspirol B was separated as their diacetates (5a and 5b) and the structures and absolute configurations of 1, 2a, 2b, 3, and 4 were determined by the application of spectroscopic techniques including two-dimensional NMR and the modified Mosher's ester method. Oxaspirol B (2) and its diacetates 5a and 5b were evaluated for their ATPase inhibitory activities of p97, p97 mutants, and other ATP-utilizing enzymes, and only 2 was found to be active, indicating the requirement of some structural features in oxaspirols for their activity. Additional biochemical and cellular assays suggested that 2 was a reversible, non-ATP competitive, and specific inhibitor of p97.

Targeting p97 to Disrupt Protein Homeostasis in Cancer

“…Eeyrestatins (EerI and II) were the earliest identified p97 inhibitors that inhibited ERAD, albeit with low potency ( 83 , 84 ). Several chemically distinct classes of p97 inhibitors have been identified since then ( 85 – 88 ). The compounds, described below, have led to the identification of a molecule (CB-5083) with drug-like properties, which is currently being tested in the clinic ( 21 ).…”

VCP inhibitors induce endoplasmic reticulum stress, cause cell cycle arrest, trigger caspase‐mediated cell death and synergistically kill ovarian cancer cells in combination with Salubrinal

“…Several groups have recently developed specific inhibitors against VCP (Alverez et al, 2015(Alverez et al, , 2016Bursavich et al, 2010;Chou et al, 2010Chou et al, , 2011Chou et al, , 2013Chou et al, , 2014Fang et al, 2015;Gui et al, 2016;Magnaghi et al, 2013;Polucci et al, 2013;Wijeratne et al, 2016), these efforts were reviewed and summarized elsewhere (Chapman et al, 2015). Among these specific inhibitors, DBeQ was initially developed as a reversible inhibitor of VCP/p97 that compromises protein homeostasis through impairment of both ubiquitin proteasome system (UPS) and autophagic protein clearance.…”

A covalent p97/VCP ATPase inhibitor can overcome resistance to CB-5083 and NMS-873 in colorectal cancer cells

“…However, Withaferin A 27-Acetate exhibited anti-proliferative effects in cancer cell lines at 10-fold lower concentration, suggesting additional modes of action. Clotrimazole [37], Oxaspirol B [38], and 5'-I-Fuligocandin B [39] exhibited p97 inhibition activity with IC 50 values of 12 μM, 31.2 ± 3.0 μM and 7.0 μM, respectively. However, their mechanisms of action are unclear.…”