Andrographolide is a crystalline diterpenoid lactone. It consists of an α-alkylidene- g-butyrolactone moiety and three hydroxyls at C-3, C-14 and C-19, which are responsible for its biological activities. It is the major bioactive ingredient of the medicinal plant Andrographis paniculata and it has been used in Asia for a variety of non-malignant conditions. We previously reported that Andrographolide results in mitochondrial-mediated apoptosis in lymphoma cell lines and fresh malignant cells from patients with lymphoma (Yang et al. Clin Cancer Res 2010:16:4755). Based on the mechanism of action in lymphoma and a prior report in APL (Manikam et al. J Pharm Pharmacol 2009:61:9), we hypothesized that andrographolide may have biological activity in acute promyelocytic leukemia (APL) an that this may be related to reactive oxygen species (ROS). We therefore investigated the effects of andrographolide on cell viability, apoptosis induction, mitochondrial membrane poential and signaling pathways in 3 APL cell lines, the ATRA sensitive line NB4 and the ATRA-resistant lines NB4–007/6 and NB4–306 and 3 samples from patients with APL.
NB4 (ATRA sensitive cell line), NB4–007/6 and NB4–306 (ATRA resistant cell lines) were cultured in RPMI-1640 under standard conditions. Cell viability was measured using the trypan blue or propidium iodide exclusion method. Fresh leukemic cells were obtained from 3 patients after informed consent according to an NU IRB approved protocol. One had ATRA-resistant APL and 2 had de-novo untreated APL. We measured apoptosis by Annexin V-FITC by FACS. We measured mitochondrial membrane potential and cell differentiation by standard techniques.
Incubation with increasing concentrations of andrographolide demonstrates loss of cell viability as measured by MTT assay. The IC50 at 48 hours was 6uM for NB4–306, 6.5uM for NB4–007/6 and 9uM for NB4. Apoptosis by Annexin V/FACS demonstrated that at 48 hours there was increasing apoptosis in all 3 cell lines and that the ATRA-resistant cell lines NB4–007/6 and NB4–306 were significantly more sensitive to andrographolide than the ATRA sensitive cell line NB4 (p< 0.025). This was accompanied by PARP and caspase 3-cleavage. There was evidence of decrease in mitochondrial membrane potential, but no effect on differentiation as measured by CD11b expression by flow. We next interrogated signaling pathways and found that in the ATRA resistant line NB4–007/6 there was an increase in phosphorylation of the Forkhead box O transcription factors p-FOXO1 at Thr24 and up-regulation of FasL (which peaked at 6 hours) and p27Kip1. We also demonstrated that andrographolide caused N-acetyl L- cysteine (NAC) reversible down regulation of c-MYC (in the ATRA resistant lines) and p-AKT (T308) (in the ATRA sensitive line) expression. In fresh patient specimens (n=3) there was dose dependent increase in apoptosis at 48 hours (>70% at 10uM, 85% at 20uM). From prior reports and our own data we suspected that the effects of andrographolide were dependent on reactive oxygen species (ROS), and indeed apoptosis was completely inhibited by NAC.
Taken together, these data suggest that andrographolide, a novel natural diterpenoid lactone with significant biological activity in cancer, may have activity in patients with ATRA-resistant APL by a mechanism of action that is distinct from ATRA. We believe that these data provide a compelling rationale to add this natural diterpenoid lactone to the clinical trial agenda in APL.
No relevant conflicts of interest to declare.
Asterisk with author names denotes non-ASH members.