Potent Vinblastine C20′ Ureas Displaying Additionally Improved Activity Against a Vinblastine-Resistant Cancer Cell Line

Abstract

A series of disubstituted C20′–urea derivatives of vinblastine were prepared from 20′-aminovinblastine that was made accessible through a unique Fe(III)/NaBH4- mediated alkene functionalization reaction of anhydrovinblastine. Three analogs were examined across a panel of 15 human tumor cell lines, displaying remarkably potent cell growth inhibition activity (avg. IC50 = 200–300 pM), being 10–200-fold more potent than vinblastine (avg. IC50 = 6.1 nM). Significantly, the analogs also display further improved activity against the vinblastine-resistant HCT116/VM46 cell line that bears the clinically relevant overexpression of Pgp, exhibiting IC50 values on par with that of vinblastine against the sensitive HCT116 cell line, 100–200-fold greater than the activity of vinblastine against the resistant HCT116/VM46 cell line, and display a reduced 10–20-fold activity differential between the matched sensitive and resistant cell lines (vs 100-fold for vinblastine).

Ultrapotent vinblastines in which added molecular complexity further disrupts the target tubulin dimer–dimer interface

“…Methods that measure competitive binding at the vinblastine tubulin binding site are more predictive, and these typically involve measurement of the competitive displacement of radiolabeled vinblastine or fluorescently labeled vinblastine probes. We have previously used the competitive displacement of 3 H-vinblastine to assess the tubulin binding of selected members of the vinblastine C20′ ureas (20,21). This assay involves filtering coincubation solutions through DE-81 filter disks, which sequester tubulin and its bound ligands from solution (28,29).…”

“…One general observation made in these studies is that, although modifications to the key structural features of vinblastine typically result in reductions in biological activity, addition of structural features can substantially improve them (20,21,35,36). This includes not only our demonstration of the impact of the addition of an indole C10′ fluorine substituent (35) and the incorporation of the C20′ ethyl group into a benign more complex cis-fused C15′-C20′ six-membered ring (36), but also the discovery of the improved activity of C20′ urea replacements for the tertiary alcohol (20,21). Herein, we reported the discovery of compounds in this latter series that are now a stunning 100-fold more potent than vinblastine.…”

“…In subsequent studies, we identified the key structural features of such ureas that contribute to their activity, including the importance of the H-bond donor site on the C20′ nitrogen substituent (20). We additionally defined a trend in activity where substitution of the urea terminal nitrogen improves the differential in activity of the derivatives against matched sensitive and resistant tumor cell lines (NR 2 > NHR > NH 2 ), discovered a series of potent disubstituted C20′ ureas (e.g., 8 and 9) that displayed further improved activity against resistant tumor cell lines, and established that sterically demanding C20′ ureas were surprisingly well tolerated (20,21).…”

Total synthesis of (−)-kopsinine and ent-(+)-kopsinine

“…In efforts that have targeted key members of the Aspidosperma alkaloids, including minovine, 1 (−)-aspidospermine and (+)-spegazzinine, 2 (+)- N -methylaspidospermidine, (−)-vindorosine and (−)-vindoline, 3 as well as their extension to the total synthesis of vinblastine 4 and related natural products including vincristine 5 and key analogues, 6 we introduced a powerful intramolecular tandem [4 + 2]/[3 + 2] cycloaddition cascade of 1,3,4-oxadiazoles that provides the stereochemically-rich pentacyclic core of the natural products in a single step. 7,8 We have subsequently disclosed the use of the common Aspidosperma -like pentacyclic intermediate 1 , assembled using this key cycloaddition cascade and bearing a functionalized C5 ethyl substituent (primary alcohol), in the divergent 9 total synthesis of a series of additional alkaloids.…”

Synthesis of a Potent Vinblastine: Rationally Designed Added Benign Complexity

“…9 Among the most significant of the observations made to date in these studies is that while removal of individual substituents or key structural components of the natural products typically results in reductions in biological activity, 8–14 addition of structural features can substantially improve biological properties. 15,16 As a result of our demonstration of the importance of the addition of a key indole C10′ substituent (10′-fluorovinblasine) 15 and with the discovery of the remarkable impact of select C20′ alcohol replacements (C20′ ureas), 16 it appeared that the spatial placement of the indole at one end of velbanamine and the C20′ ethyl group at the other are two especially important features of the structure. The X-ray structure of tubulin-bound vinblastine 5 (Figure 2) indicates both fit into well-defined protein pockets on the tubulin α and β subunits, respectively, deeply embedded in the tubulin binding site with each occupying corners of a T-shaped bound conformation of vinblastine.…”