Synthetic, Non-saccharide, Glycosaminoglycan Mimetics Selectively Target Colon Cancer Stem Cells

Abstract

Selective targeting of cancer stem-like cells (CSCs) is a paradigm-shifting approach. We hypothesized that CSCs can be targeted by interfering with functions of sulfated glycosaminoglycans, which play key roles in cancer cell growth, invasion and metastasis. We developed a tandem, dual screen strategy involving (1) assessing inhibition of monolayer versus spheroid growth and (2) assessing inhibition of primary versus secondary spheroid growth to identify G2.2, a unique sulfated nonsaccharide GAG mimetic (NSGM) from a focused library of 53 molecules, as a selective inhibitor of colon CSCs. The NSGM down-regulated several CSC markers through regulation of gene transcription, while closely related, inactive NSGMs G1.4 and G4.1 demonstrated no such changes. G2.2’s effects on CSCs were mediated, in part, through induction of apoptosis and inhibition of self-renewal factors. Overall, this work presents the proof-of-principle that CSCs can be selectively targeted through novel NSGMs, which are likely to advance fundamental understanding on CSCs while also aiding development of novel therapeutic agents.

Plasmin Regulation through Allosteric, Sulfated, Small Molecules

“…We reasoned that small, synthetic, homogenous, non-saccharide GAG mimetics (NSGMs) may offer an avenue for discovering novel plasmin inhibitors. In fact, Desai and co-workers have developed a sizeable number of NSGMs based on various scaffolds including sulfated flavonoids [30][31][32][33], sulfated benzofurans [34,35], sulfated tetrahydroisoquinolines [36], sulfated quinazolinones [37] and sulfated galloyl glucopyranosides [38,39] as modulators of a range of coagulation proteins. The NSGMs resemble sulfated GAGs in the form of presenting one or more sulfate groups to interact with GAG-binding domains on targeted proteins.…”

“…The monomeric scaffolds included chalcones (compounds 1-10), flavonoids (11)(12)(13)(14)(15)(16) [30][31][32], sucrose octasulfate (17) [40], quinazolinones (18 and 19) [37], and tetrahydro-isoquinolines (20)(21)(22)(23)(24)(25)(26)(27) [36], whereas the dimeric scaffolds comprised flavonoid-quinazolinone heterodimers (28)(29)(30)(31)(32)(33)(34) [37], bis-quinazolinones homodimers (35)(36)(37)(38)(39)(40)(41)(42)(43)(44)(45)(46)(47) [37], and bis-flavonoid homodimers (48-55). In addition to the inherent diversity of the scaffolds in this library, NSGMs also differed in the number (1 to 8) and orientation of the sulfate groups.…”

“…In addition to the inherent diversity of the scaffolds in this library, NSGMs also differed in the number (1 to 8) and orientation of the sulfate groups. NSGMs 11-30, and 35-41 were synthesized as reported earlier [30][31][32][33][34][35][36][37].…”

“…New NSGMs synthesized for the first time included 10 sulfated chalcones (1-10), six sulfated bis-quinazolinones homodimers (42)(43)(44)(45)(46)(47), four sulfated flavonoid-quinazolinone heterodimers (31)(32)(33)(34), and eight sulfated bis-flavonoid homodimers (48-55). The synthesis of the new NSGMs is described in detail in Supplementary Information (Schemes S1-S6).…”

“…Briefly, the synthesis of these NSGMs was achieved in 4 to 8 steps using traditional protection-deprotection chemistry following construction of the base scaffold with appropriate substitution pattern. The final step for the generation of each NSGM was chemical sulfation using trimethylamine-sulfur trioxide at elevated temperature, as described in our studies earlier [30][31][32][33][34][35][36][37][38][39][40][41][42]. For example, the synthesis of two promising plasmin inhibitors (Scheme 1) involved exploitation of the intramolecularly hydrogen bonded 5-OH group of quercetin 60 to selectively introduce a reactive handle (propargyl group in 63 or in situ alkyl bromide) that can be coupled with either an alkyl azide containing quinazolinone unit 32a or MOM-protected quercetin 61 to eventually give inhibitors 32 and 52, respectively.…”