STL1, a New AKT Inhibitor, Synergizes with Flavonoid Quercetin in Enhancing Cell Death in A Chronic Lymphocytic Leukemia Cell Line

Abstract

Using a pharmacophore model based on the experimental structure of AKT-1, we recently identified the compound STL1 (ZINC2429155) as an allosteric inhibitor of AKT-1. STL1, was able to reduce Ser473 phosphorylation, thus inhibiting the PI3K/AKT pathway. Moreover, we demonstrated that the flavonoid quercetin downregulated the phosphorylated and active form of AKT. However, in this case, quercetin inhibited the PI3K/AKT pathway by directly binding the kinases CK2 and PI3K. In the present work, we investigated the antiproliferative effects of the co-treatment quercetin plus STL1 in HG-3 cells, derived from a patient affected by chronic lymphocytic leukemia. Quercetin and STL1 in the mono-treatment maintained the capacity to inhibit AKT phosphorylation on Ser473, but did not significantly reduce cell viability. On the contrary, they activated a protective form of autophagy. When the HG-3 cells were co-treated with quercetin and STL1, their association synergistically (combination index < 1) inhibited cell growth and induced apoptosis. The combined treatment caused the switch from protective to non-protective autophagy. This work demonstrated that cytotoxicity could be enhanced in a drug-resistant cell line by combining the effects of different inhibitors acting in concert on PI3K and AKT kinases.

Senolytic Flavonoids Enhance Type-I and Type-II Cell Death in Human Radioresistant Colon Cancer Cells through AMPK/MAPK Pathway

“…We verified in HT500 cells that not only IR but also Q and F induce a protective form of autophagy (Figure 4). However, in the presence of the combined treatment, the level of autophagy is significantly higher (Figure 3) and an "autophagic switch" occurs, causing the transition from a protective form of autophagy to the not protective or lethal one, as described in different cellular models [28,57,58]. Both TIS and TIA may explain HT500 radioresistance through long-term regulation of intracellular redox status (ROS and GSH).…”

“…Caspase-3 specific activity was expressed as nmol of AFC produced per min per µg proteins at 37 • C in the presence of saturating concentrations of the substrate (50 µM). The determination of apoptotic nuclei was performed by counting in each sample, a minimum of 100-200 cells in duplicate in order to determine the percentage of apoptotic bodies, as previously described [28].…”

“…We previously demonstrated that Q could inhibit the PI 3 K/AKT pathway [28,46], whose hyper-activation is often associated with proliferation and/or resistance to apoptosis in cancer cells [47]. Therefore, we performed an immunoblot to detect the phosphorylated and active form of AKT (pAKT Ser472 ) in HT500 cells shortly after (20 min) the treatment with Q and F (40 µM).…”

“…In Burkitt's lymphoma cells, Q induces autophagic cell death by inhibiting PI 3 K/AKT/mTOR pathways and partially degrading mutant c-Myc [28], as well as inducing lethal autophagy in chronic lymphocytic leukemia cells through an AKT inhibitor called STL-1 [28,29]. In a recent study, Q increased the activity of AMPK kinase in human senescent fibroblasts, resulting in non-apoptotic cell death, a reduction in stress-induced senescent cells (senolytic action), and a suppression of pro-inflammatory responses associated with senescence (low levels of secreted IL-8 and IFN-β, senostatic effects) [30].…”

Drug Design by Pharmacophore and Virtual Screening Approach

“…The most promising compounds obtained by the screening have been further investigated by toxicity profile and ADMET analyses, together with molecular docking for better prediction of the potential binding [ 76 ]. Experimental studies confirmed the potential inhibitory role of at least one of the selected compounds [ 76 ] and, in addition, its synergic effect with quercetin to inhibition of cell growth and induce apoptosis [ 77 ].…”