CHEMICAL INVESTIGATION AND ANTIPROLIFERATIVE STUDIES OF ISOLATED POLYISOPRENYLATED BENZOPHENONES FROM STEM-BARK OF Garcinia maingayi

In the current study, sequential solvents extraction from the stem bark of Garcinia maingayi, a native plant to Malaysia has led to the isolation of four polyisoprenylated benzophenones: 30-epi-cambogin (GB 1), 14-deoxy-30-epi-cambogin (GB 2), guttiferone F (GB 3), and 14-deoxy-guttiferone F (GB 4). The structures were elucidated using IR, optical rotation, and NMR spectral data. The compounds were evaluated for antiproliferative effect using MTT assay, apoptosis using Annexin V/7-AAD flow cytometry, cell cycle progression, and activation of caspases 3/7, 8 and 9 and BCL2 mRNA expression in MCF-7, HeLa, and HepG2 cancer cell lines. Compounds GB 1 to GB 4 exhibited a remarkable antiproliferative effect on HeLa, MCF-7, and HepG2 cells with IC50 values ranging from 5 to 45 µM. Compounds GB 1 to GB 4 induced significant cell cycle arrest in the G1 phase corroborated with the decrease in the number of MCF-7 and HepG2 cells in S and G2/M phases (P<0.05). Compounds GB 1 to GB 4 induced apoptosis at 48 h. Further, among these, compounds GB 1 and GB 2 induced significant levels of caspases 3 and 9 in HeLa cells, while GB 3 induced caspase 9 activities in both MCF-7 and HepG2 cells. No significant induction of caspase 8 was observed suggesting that the apoptotic effects are mainly mediated through the intrinsic pathway. Only compound GB 1 inhibited the BCL2 mRNA expression significantly in all treated cancer cells. In conclusion, these compounds possess anticancer properties and thus further investigation is crucial on the mechanistic study, structure-activity relationship, and identification of putative molecular targets.

Targeting MHC Regulation Using Polycyclic Polyprenylated Acylphloroglucinols Isolated from Garcinia bancana

Modulation of major histocompatibility complex (MHC) expression using drugs has been proposed to control immunity. Phytochemical investigations on Garcinia species have allowed the isolation of bioactive compounds such as polycyclic polyprenylated acylphloroglucinols (PPAPs). PPAPs such as guttiferone J (1), display anti-inflammatory and immunoregulatory activities while garcinol (4) is a histone acetyltransferases (HAT) p300 inhibitor. This study reports on the isolation, identification and biological characterization of two other PPAPs, i.e., xanthochymol (2) and guttiferone F (3) from Garcinia bancana, sharing structural analogy with guttiferone J (1) and garcinol (4). We show that PPAPs 1–4 efficiently downregulated the expression of several MHC molecules (HLA-class I, -class II, MICA/B and HLA-E) at the surface of human primary endothelial cells upon inflammation. Mechanistically, PPAPs 1–4 reduce MHC proteins by decreasing the expression and phosphorylation of the transcription factor STAT1 involved in MHC upregulation mediated by IFN-γ. Loss of STAT1 activity results from inhibition of HAT CBP/p300 activity reflected by a hypoacetylation state. The binding interactions to p300 were confirmed through molecular docking. Loss of STAT1 impairs the expression of CIITA and GATA2 but also TAP1 and Tapasin required for peptide loading and transport of MHC. Overall, we identified new PPAPs issued from Garcinia bancana with potential immunoregulatory properties.