The Natural Compound Oblongifolin C Exhibits Anticancer Activity by Inhibiting HSPA8 and Cathepsin B In Vitro

Abstract

PPAPs (Polycyclic polyprenylated acylphloroglucinols) are a class of compounds with diverse bioactivities, including anticancer effects. Oblongifolin C (OC) is a PPAP isolated from the plant of Garcinia yunnanensis Hu. We previously discovered that OC induces apoptosis, inhibits autophagic flux, and attenuates metastasis in cancer cells. However, the protein targets and the detailed mechanism of action of OC remain unclear. To identify protein targets of OC, a non-labeled protein fishing assay was performed, and it was found that OC may interact with several proteins, including the heat shock 70 kDa protein 8 (HSPA8). Expanding on our previous studies on protein cathepsin B, this current study applied Surface Plasmon Resonance (SPR) and Isothermal Titration Calorimetry (ITC) to confirm the potential binding affinity between OC and two protein targets. This study highlights the inhibitory effect of OC on HSPA8 in cancer cells under heat shock stress, by specifically inhibiting the translocation of HSPA8. OC also enhanced the interaction between HSPA8, HSP90, and p53, upregulated the expression of p53 and significantly promoted apoptosis in cisplatin-treated cells. Additionally, a flow cytometry assay detected that OC sped up the apoptosis rate in HSPA8 knockdown A549 cells, while overexpression of HSPA8 delayed the OC-induced apoptosis rate. In summary, our results reveal that OC potentially interacts with HSPA8 and cathepsin B and inhibits HSPA8 nuclear translocation and cathepsin B activities, altogether suggesting the potential of OC to be developed as an anticancer drug.

Anticancer Properties and Mechanism of Action of Oblongifolin C, Guttiferone K and Related Polyprenylated Acylphloroglucinols

“…The most innovative part of the mechanism of action of Ob-C and Gt-K is linked to the heat shock protein HSPA8. Ob-C binds tightly to this chaperone protein [ 86 ] and our modeling analysis suggests that Gt-K could be an even better HSPA8 binder than Ob-C. On the one hand, this information brings new ideas for the potential use of the natural products in different pathologies, taking advantage of the multiple functions of HSPA8 in cancer and in autoimmune diseases, as mentioned above [ 90 ]. HSPA8 is also a host factor involved in infectious bronchitis virus (IBV, a coronavirus) infection [ 102 ].…”

“…These two protein targets were identified in the frame of a protein-fishing study with Ob-C and fully characterized as Ob-C interacting proteins. Ob-C potently interacts with the purified HSPA8 protein in vitro (Kd = 6.2 μM and 11.8 μM, measured by ITC and SPR, respectively) and can also bind purified cathepsin B (Kd = 25.6 μM and 39.3 μM by ITC (isothermal titration calorimetry) and SPR (surface plasmon resonance), respectively) [ 86 ]. Under heat shock stress, Ob-C inhibited the nuclear translocation of HSPA8 and significantly increased the expression level of the tumor suppressor p53 in A549 cancer cells.…”

“…Under heat shock stress, Ob-C inhibited the nuclear translocation of HSPA8 and significantly increased the expression level of the tumor suppressor p53 in A549 cancer cells. Moreover, the compound promoted the interaction between p53 and HSPA8, and significantly enhanced apoptosis in cisplatin-treated cells [ 86 ]. This key study strongly supports the idea that HSPA8 is a primary target of Ob-C.…”

“…6 Molecular model for the binding of Gt-K to HSPA8. The structure derives from the crystal structure of the ATPase fragment of a 70K heat-shock cognate protein solved by X-ray diffraction (PDB code: 3HSC) [ 86 ]. A binding site centered on residue Arg272 was identified using the software Discovery Studio Visualizer, to map the position of the cavities susceptible to accommodate the ligand.…”

Targeting novel coronavirus SARS-CoV-2 spike protein with phytoconstituents of Momordica charantia

“…To date, only a few natural compounds have been identified as therapeutic with specificity for cellular and molecular targets. For instance, Taxol binds to β-tubulin, which distorts the cytoskeleton framework and causes cell-cycle arrest and, subsequently, cell death, has been used for several decades to treat various tumors [ 34 ]. Furthermore, natural compounds exhibit a myriad of biological activities, including antiviral activity.…”