The benzylideneindolinone 6-chloro-3-(3′-trifluoromethylbenzylidene)-1,3-dihydroindol-2-one (4) was reported to exhibit potent and selective growth inhibitory effects on hepatocellular carcinoma (HCC). Corroborative evidence supported multi-receptor tyrosine kinase (RTK) inhibition as a possible mode of action. However, the poor physicochemical properties of 4 limited its furtherance as a lead compound. In this study, the modification of 4 was investigated with the aim of improving its potency and physicochemical profile. The 6-fluorobenzylideneindolinone 3-12 bearing a 3′-N-propylaminosulfonyl substituent was found to be a promising substitute. Compound 3-12 [6-fluoro-3-(3′-N-propylaminosulfonylbenzylidene)-1,3-dihydroindol-2-one] was found to be tenfold more soluble than 4 and to have sub-micromolar growth inhibitory activities on HCC cells. It is apoptogenic and inhibits the phosphorylation of several RTKs in HuH7, of which the inhibition of FGFR4 and HER3 are prominent. Compound 3-12 decreased the tumor load in a physiologically relevant orthotopic HCC xenograft murine model. Structure–activity relationships support pivotal roles for the fluoro and N′-propylaminosulfonyl moieties in enhancing cell-based activity and moderating the physicochemical profile (solubility, permeability) of 3-12.

Meisoindigo has been used as an indirubin substitute for the treatment of chronic myeloid leukemia (CML) for several years. In view of its poor solubility and erratic absorption, several investigations have focused on developing analogues with more desirable physicochemical profiles. Here, we investigated the structure–activity relationship (SAR) of meisoindigo with respect to its antiproliferative activity on leukemic K562 cells and found that appending a phenalkyl side chain onto the lactam NH resulted in analogues that retained good activity. Furthermore, analogues in which the phenyl ring was substituted with a basic heterocycle were significantly more soluble than meisoindigo while retaining acceptable antiproliferative profiles. The most promising analogue (E)-1-(2-(4-methylpiperazin-1-yl)ethyl)-[3,3′-biindolinylidene]-2,2′-dione (5-4) is more potent than meisoindigo across a panel of malignant cells, with at least 40 times greater solubility than meisoindigo, little or no tendency to aggregate in solution and capable of significantly extending the lifespans of animals with K562 induced xenografts. Mechanistically, it induced apoptotic cell death and disrupted the progression of K562 cells from the G₁ to G₂ phase. Taken together, our findings highlighted the feasibility of addressing the physicochemical deficits of the isoindigo scaffold by systematic modifications which was achieved without overt loss of growth inhibitory activity.

Curcumin arrests the proliferation of acute promyelocytic leukemia (APL) cells by stabilizing the misfolded nuclear receptor co-repressor (N-CoR) protein, thereby sensitizing APL cells to apoptosis induced by the unfolded protein response. This phenomenon was attributed to inhibition of the proteasomal and protease-induced breakdown of misfolded N-CoR by curcumin. Curcumin is, however, a modest inhibitor and affected the viability of APL cells at micromolar concentrations. Modifying curcumin at its conjugated β-diketone linker and terminal phenyl rings yielded potent congeners with sub-micromolar growth inhibitory activities which selectively kill APL cells over non-APL leukemic and nonmalignant cells. Analogues with pronounced APL-selective anti-proliferative activities, as observed in representative dibenzylidenecyclohexanones and dibenzylidenecyclopentanones, strongly promoted the accumulation of misfolded and nonfunctional N-CoR at significantly lower concentrations than their growth inhibitory IC₅₀ values. These compounds also inhibited the human 20S proteasome in an enzyme-based assay, thus providing convincing support for the prevailing hypothesis that impeding the degradation of N-CoR is a key mechanistic event contributing to APL cell death.

The ability of aurones to modulate the efflux activities of ABCG2 and ABCB1 was investigated by quantifying their effects on the accumulation of pheophorbide A (PhA) in ABCG2-overexpressing MDA-MB-231/R cells and calcein AM in ABCB1-overexpressing MDCKII/MDR1 cells. Key structural features for interactions at both ABCG2 and ABCB1 are a methoxylated ring A, an intact exocyclic double bond, and the location of the carbonyl bond on ring C. Modifications on rings B and C were less critical and served primarily to moderate activity and selectivity for one or both transporters. These SAR trends were quantified by Free–Wilson analyses and are reflected in a pharmacophore model for PhA accumulation. Several compounds were found to be equipotent with fumitremorgin C (FTC) in promoting PhA accumulation, and they also demonstrated strong affinities for ABCB1. These compounds were disubstituted on ring B with methoxy or a combination of methoxy and hydroxy groups. Taken together, our findings highlight the versatility of the aurone template as a lead scaffold for the design of dual-targeting ABCG2 and ABCB1 modulators.