Structure-Activity Relationship of Hydroxycinnamic Acid Derivatives for Cooperating with Carnosic Acid and Calcitriol in Acute Myeloid Leukemia Cells

Abstract

Plant phenolic compounds have shown the ability to cooperate with one another at low doses in producing enhanced anticancer effects. This may overcome the limitations (e.g., poor bioavailability and high-dose toxicity) in developing these agents as cancer medicines. We have previously reported that the hydroxycinnamic acid derivative (HCAD) methyl-4-hydroxycinnamate and the phenolic diterpene carnosic acid (CA) can synergistically induce massive calcium-dependent apoptosis in acute myeloid leukemia (AML) at non-cytotoxic concentrations of each agent. Here, we explored the chemical nature of the synergy between HCADs and either CA, in inducing cytotoxicity, or the active metabolite of vitamin D (calcitriol), in enhancing the differentiation of AML cells. This was done by determining the structure–activity relationship of a series of hydroxycinnamic acids and their derivatives (methyl hydroxycinnamates and hydroxybenzylideneacetones) in combination with CA or calcitriol. The HCAD/CA synergy required the following critical structural elements of an HCAD molecule: (a) the para-hydroxyl on the phenolic ring, (b) the carbon C7–C8 double bond, and (c) the methyl-esterified carboxyl. Thus, the only HCADs capable of synergizing with CA were found to be methyl-4-hydroxycinnamate and methyl ferulate, which also most potently enhanced calcitriol-induced cell differentiation. Notably, the C7–C8 double bond was the major requirement for this HCAD/calcitriol cooperation. Our findings may contribute to the rational design of novel synergistically acting AML drugs based on prototype combinations of HCADs with other agents studied here.

Cytotoxicity of Thioalkaloid-Enriched Nuphar lutea Extract and Purified 6,6′-Dihydroxythiobinupharidine in Acute Myeloid Leukemia Cells: The Role of Oxidative Stress and Intracellular Calcium

“…The proapoptotic effects of different phytochemicals, such as the sesquiterpene lactone thapsigargin that is a specific inhibitor of sarco/endoplasmic reticulum Ca 2+ -ATPase [38], and plant polyphenols [39][40][41][42] on cancer cells have been associated with the alteration of the intracellular Ca 2+ homeostasis. We have recently reported that the combinations of curcumin or methyl 4-hydroxycinnamate with carnosic acid are capable of inducing apoptotic cell death of AML cells solely by triggering sustained Ca 2+ cyt accumulation, without inducing oxidative stress [14,15,43]. Here, we show that NUP-induced apoptosis is partially mediated by an increase in Ca 2+ cyt levels because this apoptotic effect was attenuated in cells preloaded with the intracellular Ca 2+ chelator BAPTA (Figure 11).…”

“…Immediately before experiment, cell samples were unfrozen, washed in RPMI supplemented with 20% BSA, 10 mM HEPES (pH = 7.4), 2 mM L-glutamine, 100 U/mL penicillin, 0.1 mg/mL streptomycin, 0.01 µg/mL insulin, 5 µg/mL holo-transferrin, and were then incubated at 1.5 × 10 5 cells/mL with test agents in the same medium, for 24 h at 37 • C in a 5% CO 2 environment. Cells were collected and analyzed by the annexin-V/propidium iodide binding assay (see Section 3.4 below) and cell viability assay [43]. Briefly, cell viability was determined on the basis of changes in cellular ATP levels using the CellTiter-Glo Luminescent Cell Viability Assay kit (Promega, Madison, WI) according to the manufacturer's instructions.…”