Fig. 4
CHL triggers cell cycle arrest and apoptosis in human colon cancer cells. a In CHL-treated HCT116 cells, fluorescence-activated cell sorting (FACS) identified cells arrested in S-phase, with the appearance of a sub-G1 peak at higher CHL concentrations, indicative of apoptosis. b S-phase arrest by CHL was concentration dependent. c FACS analysis combined with bromodeoxyuridine (BrdU) pulse-chase experiments corroborated the S-phase arrest, with BrdU incorporation localized to G0/G1 and G2/M lower quadrants. d The floating cell number increased with CHL concentration, and cells exhibited hallmarks of apoptosis such as membrane blebbing and nuclear condensation, coinciding with reduced mitochondrial membrane potential (∆ψm), arrow. e Detailed mechanistic studies excluded the pathway involving cytochrome c, Caspase-9, Caspase-3 and poly (ADP-ribose) polymerase (PARP) cleavage, and implicated Capase-8, Caspase-6, cleavage of nuclear lamins, and apoptosis inducing factor (AIF) released from mitochondria. At lower CHL concentrations, S-phase arrest involved the inhibition of ribonucleotide reductase, possibly by scavenging the tyrosyl radical in the enzyme active site, akin to the anticancer drug hydroxyurea. Synopsis of author’s prior mechanistic work [77, 78]