Synthesis and Biological Evaluation of Indolyl-Pyridinyl-Propenones Having Either Methuosis or Microtubule Disruption Activity

Abstract

Methuosis is a form of nonapoptotic cell death characterized by an accumulation of macropinosome-derived vacuoles with eventual loss of membrane integrity. Small molecules inducing methuosis could offer significant advantages compared to more traditional anticancer drug therapies that typically rely on apoptosis. Herein we further define the effects of chemical substitutions at the 2- and 5-indolyl positions on our lead compound 3-(5-methoxy-2-methyl-1H-indol-3-yl)-1-(4-pyridinyl)-2-propene-1-one (MOMIPP). We have identified a number of compounds that induce methuosis at similar potencies, including an interesting analogue having a hydroxypropyl substituent at the 2-position. In addition, we have discovered that certain substitutions on the 2-indolyl position redirect the mode of cytotoxicity from methuosis to microtubule disruption. This switch in activity is associated with an increase in potency as large as 2 orders of magnitude. These compounds appear to represent a new class of potent microtubule-active anticancer agents.

Synthesis and biological evaluation of isomeric methoxy substitutions on anti-cancer indolyl-pyridinyl-propenones: Effects on potency and mode of activity

“…Previous studies with U251 glioblastoma cells have established that the sulforhodamine B (SRB) colorimetric assay is useful for evaluating the loss of viable cells and for ranking the relative potency [11,15]. This assay is sensitive to both methuosis and microtubule disruption.…”

“…An initial search for compounds reported to induce cellular vacuolization led us to an indolyl-pyridinyl-propenone (IPP, also referred to as indole-derived chalcone) as a potential lead [13]. Associated structure-activity relationship (SAR) studies revealed that the optimized scaffold for induction of methuosis consists of a 2,5-disubstituted indole and a pyridine in the para -configuration, bridged by an α,β-unsaturated ketone [11,14,15]. Our previously reported IPP compounds, and their modes of biological activity, are summarized in Fig.…”

“…1) [11]. Similarly, certain 5-substituted analogues ( 2a–2c ), as well as the 2-des-methyl derivative 2d , also induced vacuole formation but were not cytotoxic [15]. While 5-methoxy ( 1a ) and 5-propoxyindole ( 1e ) analogues triggered cell death by methuosis, their structurally similar counterparts, namely 5-ethoxy ( 2a ) and 5-isopropoxyindole ( 2b ) caused cytoplasmic vacuolization without cell death.…”

“…Another novel insight into the biological effects of the IPP compounds was gathered from derivatives containing electron-withdrawing functionalities at the 2-indolyl position [15]. Derivatives containing trifluoromethyl ( 3a ) or alkyl carboxylate ( 3b–3d ) substitutions caused minimal to no vacuolization but remained highly cytotoxic.…”

“…In the present study we have synthesized and evaluated methoxy isomers of 1a to sequentially survey the 4-, 6- and 7-positions while initially holding the 2-position constant. Upon finding significant anti-mitotic activity for the 6-position isomer 9b , we immediately prepared its 2-trifluoromethyl version ( 15 ) by analogy to 3a where this type of functionality also led to microtubule disruption [15]. Finally, drawing from several reports describing N -methyl-indole-based trimethoxyphenyl chalcones as compounds affecting tubulin polymerization, we examined replacing the para -pyridine in our structural template with a trimethoxyphenyl group and, likewise, separately examined the effect of adding a methyl group to the indole nitrogen.…”