Methoxyhispolon Methyl Ether, a Hispolon Analog, Thwarts the SRC/STAT3/BCL-2 Axis to Provoke Human Triple-Negative Breast Cancer Cell Apoptosis In Vitro.

Triple-negative breast cancer (TNBC) is the most aggressive subtype of breast cancer with few treatment options. A promising TNBC treatment approach is targeting the oncogenic signaling pathways pivotal to TNBC initiation and progression. Deregulated activation of signal transducer and activator of transcription 3 (STAT3) is fundamental to driving TNBC malignant transformation, highlighting STAT3 as a promising TNBC therapeutic target. Methoxyhispolon Methyl Ether (MHME) is an analog of Hispolon, an anti-cancer polyphenol found in the medicinal mushroom Phellinus linteus. Still, MHME's anti-cancer effects and mechanisms remain unknown. Herein, we present the first report about MHME's anti-TNBC effect and its action mechanism. We first revealed that MHME is proapoptotic and cytotoxic against human TNBC cell lines HS578T, MDA-MB-231, and MDA-MB-463 and displayed a more potent cytotoxicity than Hispolon's. Mechanistically, MHME suppressed both constitutive and interleukin 6 (IL-6)-induced activation of STAT3 represented by the extent of tyrosine 705-phosphorylated STAT3 (p-STAT3). Notably, MHME-evoked apoptosis and clonogenicity impairment were abrogated in TNBC cells overexpressing a dominant-active mutant of STAT3 (STAT3-C); supporting the blockade of STAT3 activation is an integral mechanism of MHME's cytotoxic action on TNBC cells. Moreover, MHME downregulated BCL-2 in a STAT3-dependent manner, and TNBC cells overexpressing BCL-2 were refractory to MHME-induced apoptosis, indicating that BCL-2 downregulation is responsible for MHME's proapoptotic effect on TNBC cells. Finally, MHME suppressed SRC activation, while v-src overexpression rescued p-STAT3 levels and downregulated apoptosis in MHME-treated TNBC cells. Collectively, we conclude that MHME provokes TNBC cell apoptosis through the blockade of the SRC/STAT3/BCL-2 pro-survival axis. Our findings suggest the potential of applying MHME as a TNBC chemotherapy agent.

Blockade of the SRC/STAT3/BCL-2 Signaling Axis Sustains the Cytotoxicity in Human Colorectal Cancer Cell Lines Induced by Dehydroxyhispolon Methyl Ether.

Colorectal cancer (CRC) is the third most prevalent human cancer globally. 5-Fluorouracil (5-FU)-based systemic chemotherapy is the primary strategy for advanced CRC treatment, yet is limited by poor response rate. Deregulated activation of signal transducer and activator of transcription 3 (STAT3) is fundamental to driving CRC malignant transformation and a poor prognostic marker for CRC, underscoring STAT3 as a promising CRC drug target. Dehydroxyhispolon methyl ether (DHME) is an analog of Hispolon, an anticancer polyphenol abundant in the medicinal mushroom Phellinus linteus. Previously, we have established DHME's cytotoxic effect on human CRC cell lines by eliciting apoptosis through the blockade of WNT/ß-catenin signaling, a preeminent CRC oncogenic pathway. Herein, we unraveled that compared with 5-FU, DHME is a more potent killer of CRC cells while being much less toxic to normal colon epithelial cells. DHME suppressed both constitutive and interleukin 6 (IL-6)-induced STAT3 activation represented by tyrosine 705 phosphorylation of STAT3 (p-STAT3 (Y705)); notably, DHME-induced CRC apoptosis and clonogenicity limitation were abrogated by ectopic expression of STAT3-C, a dominant-active STAT3 mutant. Additionally, we proved that BCL-2 downregulation caused by DHME-mediated STAT3 blockage is responsible for DHME-induced CRC cell apoptosis. Lastly, DHME inhibited SRC activation, and v-src overexpression restored p-STAT3 (Y705) levels along with lowering the levels of apoptosis in DHME-treated CRC cells. We conclude DHME provokes CRC cell apoptosis by blocking the SRC/STAT3/BCL-2 axis besides thwarting WNT/ß-catenin signaling. The notion that DHME targets two fundamental CRC signaling pathways underpins the potential of DHME as a CRC chemotherapy agent.

Dehydroxyhispolon Methyl Ether, A Hispolon Derivative, Inhibits WNT/ß-Catenin Signaling to Elicit Human Colorectal Carcinoma Cell Apoptosis.

Colorectal cancer (CRC) is the fourth leading cause of cancer mortality worldwide. Aberrant activation of WNT/ß-catenin signaling present in the vast majority of CRC cases is indispensable for CRC initiation and progression, and thus is a promising target for CRC therapeutics. Hispolon is a fungal-derived polyphenol with a pronounced anticancer effect. Several hispolon derivatives, including dehydroxyhispolon methyl ether (DHME), have been chemically synthesized for developing lead molecules with stronger anticancer activity. Herein, a DHME-elicited anti-CRC effect with the underlying mechanism is reported for the first time. Specifically, DHME was found to be more cytotoxic than hispolon against a panel of human CRC cell lines, while exerting limited toxicity to normal human colon cell line CCD 841 CoN. Additionally, the cytotoxic effect of DHME appeared to rely on inducing apoptosis. This notion was evidenced by DHME-elicited upregulation of poly (ADP-ribose) polymerase (PARP) cleavage and a cell population positively stained by annexin V, alongside the downregulation of antiapoptotic B-cell lymphoma 2 (BCL-2), whereas the blockade of apoptosis by the pan-caspase inhibitor z-VAD-fmk attenuated DHME-induced cytotoxicity. Further mechanistic inquiry revealed the inhibitory action of DHME on ß-catenin-mediated, T-cell factor (TCF)-dependent transcription activity, suggesting that DHME thwarted the aberrantly active WNT/ß-catenin signaling in CRC cells. Notably, ectopic expression of a dominant-active ß-catenin mutant (∆N90-ß-catenin) abolished DHME-induced apoptosis while also restoring BCL-2 expression. Collectively, we identified DHME as a selective proapoptotic agent against CRC cells, exerting more potent cytotoxicity than hispolon, and provoking CRC cell apoptosis via suppression of the WNT/ß-catenin signaling axis.

Co-Delivery of Hispolon and Doxorubicin Liposomes Improves Efficacy Against Melanoma Cells.

Hispolon is a small molecular weight polyphenol that has antioxidant, anti-inflammatory, and anti-proliferative activities. Our recent study has demonstrated hispolon as a potent apoptosis inducer in melanoma cell lines. Doxorubicin is a broad spectrum first-line treatment for various kinds of cancers. In this study, co-delivery of doxorubicin and hispolon using a liposomal system in B16BL6 melanoma cell lines for synergistic cytotoxic effects was investigated. Liposomes were prepared using a lipid film hydration method and loaded with doxorubicin or hispolon. The formulations were characterized for particle size distribution, release profile, and encapsulation efficiency (EE). In addition, in vitro cytotoxicity, in vitro cell apoptosis, and cellular uptake were evaluated. Liposomes exhibited small particle size (mean diameter ~ 100 nm) and narrow size distribution (polydispersity index (< 0.2) and high drug EE% (> 90%). The release from liposomes showed slower release compared to free drug solution as an additional time required for the release of drug from the liposome lipid bilayer. Liposome loaded with doxorubicin or hispolon exhibited significantly higher cytotoxicity against B16BL6 melanoma cells as compared to doxorubicin solution or hispolon solution. Likewise, co-delivery of hispolon and doxorubicin liposomes showed two-fold and three-fold higher cytotoxicity, as compared to hispolon liposomes or doxorubicin liposomes, respectively. In addition, co-delivery of doxorubicin and hispolon in liposomes enhanced apoptosis more than the individual drugs in the liposome formulation. In conclusion, the co-delivery of hispolon and doxorubicin could be a promising therapeutic approach to improve clinical outcomes against melanoma.

X-ray crystal structures, density functional theory and docking on deacetylase enzyme for antiproliferative activity of hispolon derivatives on HCT116 colon cancer.

The antiproliferative action of hispolon derivatives is stronger than that of related curcumin against several tumor cell lines. Hispolon size, smaller than curcumin, fits better than curcumin into the active site of HDAC6, an enzyme involved in deacetylation of lysine residues. HDACs are considered potential targets for tumor drug discovery and hydroxamates are known inhibitors of HDACs. One of them, SAHA (Vorinostat) is used in clinical studies. Investigations into possible mechanisms for hispolon derivatives active against the HCT116 colon tumor cell line are done after examining the structural results obtained from hispolon X-ray crystal structures as well as performing associated computational docking and Density Functional Theory techniques on HDAC6. These studies show preference for the HDAC6 active site by chelating the Zn center, in contrast with other ineffective hispolon derivatives, that establish only a single bond to the metal center. Structure activity relationships make clear that hydrogenation of the hispolon bridge also leads to single bond (non chelate) hispolon-Zn binding, and consistently nullifies the antiproliferative action against HCT116 tumor.

Toxicity and Antigenotoxic Effect of Hispolon Derivatives: Role of Structure in Modulating Cellular Redox State and Thioredoxin Reductase.

Hispolon (HS), a bioactive polyphenol, and its derivatives such as hispolon monomethyl ether (HME), hispolon pyrazole (HP), and hispolon monomethyl ether pyrazole (HMEP) were evaluated for comparative toxicity and antigenotoxic effects. The stability of HS derivatives in biological matrices followed the order HS < HP ≈ HME < HMEP. The cytotoxicity analysis of HS derivatives indicated that HP and HMEP were less toxic than HS and HME, respectively, in both normal and tumor cell types. The mechanisms of toxicity of HS and HME involved inhibition of thioredoxin reductase (TrxR) and/or induction of reductive stress. From the enzyme kinetic and docking studies, it was established that HS and HME interacted with the NADPH-binding domain of TrxR through electrostatic and hydrophobic bonds, resulting in inhibition of the catalytic activity. Subsequently, treatment with HS, HP, and HMEP at a nontoxic concentration of 10 µM in Chinese Hamster Ovary (CHO) cells showed significant protection against radiation (4 Gy)-induced DNA damage as assessed by micronuclei and γ-H2AX assays. In conclusion, the above results suggested the importance of phenolic and diketo groups in controlling the stability and toxicity of HS derivatives. The pyrazole derivatives, HP and HMEP, may gain significance in the development of functional foods.

Diketo modification of curcumin affects its interaction with human serum albumin.

Curcumin isoxazole (CI) and Curcumin pyrazole (CP), the diketo modified derivatives of Curcumin (CU) are metabolically more stable and are being explored for pharmacological properties. One of the requirements in such activities is their interaction with circulatory proteins like human serum albumin (HSA). To understand this, the interactions of CI and CP with HSA have been investigated employing absorption and fluorescence spectroscopy and the results are compared with that of CU. The respective binding constants of CP, CI and CU with HSA were estimated to be 9.3×105, 8.4×105 and 2.5×105M-1, which decreased with increasing salt concentration in the medium. The extent of decrease in the binding constant was the highest in CP followed by CI and CU. This revealed that along with hydrophobic interaction other binding modes like electrostatic interactions operate between CP/CI/CU with HSA. Fluorescence quenching studies of HSA with these compounds suggested that both static and dynamic quenching mechanisms operate, where the contribution of static quenching is higher for CP and CI than that for CU. From fluorescence resonance energy transfer studies, the binding site of CU, CI and CP was found to be in domain IIA of HSA. CU was found to bind in closer proximity with Trp214 as compared to CI and CP and the same was responsible for efficient energy transfer and the same was also established by fluorescence anisotropy measurements. Furthermore docking simulation complemented the experimental observation, where both electrostatic as well as hydrophobic interactions were indicated between HSA and CP, CI and CU. This study is useful in designing more stable CU derivatives having suitable binding properties with proteins like HSA.

The in vitro antitumor activity of arene-ruthenium(II) curcuminoid complexes improves when decreasing curcumin polarity.

The antitumor activity of ruthenium(II) arene (p-cymene, benzene, hexamethylbenzene) derivatives containing modified curcumin ligands (HCurcI=(1E,4Z,6E)-5-hydroxy-1,7-bis(3,4-dimethoxyphenyl)hepta-1,4,6-trien-3-one and HCurcII=(1E,4Z,6E)-5-hydroxy-1,7-bis(4-methoxyphenyl)hepta-1,4,6-trien-3-one) is described. These have been characterized by IR, ESI-MS and NMR spectroscopy. The X-ray crystal structure of HCurcI has been determined and compared with its related Ru complex. Four complexes have been evaluated against five tumor cell lines, whose best activities [IC50 (µM)] are: breast MCF7, 9.7; ovarian A2780, 9.4; glioblastoma U-87, 9.4; lung carcinoma A549, 13.7 and colon-rectal HCT116, 15.5; they are associated with apoptotic features. These activities are improved when compared to the already known corresponding curcumin complex, (p-cymene)Ru(curcuminato)Cl, about twice for the breast and ovarian cancer, 4.7 times stronger in the lung cancer and about 6.6 times stronger in the glioblastoma cell lines. In fact, the less active (p-cymene)Ru(curcuminato)Cl complex only shows similar activity to two novel complexes in the colon cancer cell line. Comparing antitumor activity between these novel complexes and their related curcuminoids, improvement of antiproliferative activity is seen for a complex containing CurcII in A2780, A549 and U87 cell lines, whose IC50 are halved. Therefore, after replacing OH curcumin groups with OCH3, the obtained species HCurcI and its Ru complexes have increased antitumor activity compared to curcumin and its related complex. In contrast, HCurcII is less cytotoxic than curcumin but its related complex [(p-cymene)Ru(CurcII)Cl] is twice as active as HCurcII in 3 cell lines. Results from these novel arene-Ru curcuminoid species suggest that their increased cytotoxicity on tumor cells correlate with increase of curcuminoid lipophilicity.

Design, synthesis and in vitro cell-based evaluation of the anti-cancer activities of hispolon analogs.

Phytochemicals play an important role in cancer therapy. Hispolon and 26 of its analogs (9 known and 17 new) were synthesized and evaluated for their antiproliferative activities in a panel of six independent human cancer cell lines using the in vitro cell-based MTT assay. Among the hispolon analogs tested, compound VA-2, the most potent overall, produced its most significant effect in the colon cancer cell lines HCT-116 (IC50 1.4 ± 1.3 µM) and S1 (IC50 1.8 ± 0.9 µM) compared to its activity in the normal HEK293/pcDNA3.1 cell line (IC50 15.8±3.7 µM; p<0.01 for each comparison). Based on our results, VA-2 was about 9- to 11-times more potent in colon cancer cells and 2- to 3-times more potent in prostate cancer cells compared to HEK293/pcDNA3.1 cells. Morphological analysis of VA-2 showed significant reduction of cell number, while the cells' sizes were also markedly increased and were obvious at 68 h of treatment with 1 µM in HCT-116 (colon) and PC-3 (prostate) cancer cells. A known analog, compound VA-4, prepared by simple modifications on the aromatic functional groups of hispolon, inhibited prostate and colon cancer cell lines with IC50 values <10 µM. In addition, hispolon isoxazole and pyrazole analogs, VA-7 and VA-15 (known), respectively, have shown significant activity with the mean ICv values in the range 3.3-10.7 µM in all the cancer cell lines tested. Activity varied among the analogs in which aromatic functional groups and ß-diketone functional groups are modified. But the activity of analogs VA-16 to VA-27 was completely lost when the side chain double-bond was hydrogenated indicating the crucial role of this functionality for anticancer activity. Furthermore, many of the compounds synthesized were not substrates for the ABCB1-transporter, the most common cause of multidrug resistance in anti-cancer drugs, suggesting they may be more effective anticancer agents.

Bisdemethylcurcumin and structurally related hispolon analogues of curcumin exhibit enhanced prooxidant, anti-proliferative and anti-inflammatory activities in vitro.

Curcumin, a component of turmeric (Curcuma longa), exhibits anti-inflammatory and anti-proliferative activities through the generation of reactive oxygen species (ROS). Curcumin (diferuloylmethane) contains two hydroxyl, two methoxy and two phenyl groups but how these groups contribute to its activity is poorly understood. We synthesized analogues that varied in inclusion of these groups and compared their activity. We found that bisdemethylcurcumin (BDC) was more potent than curcumin as an anti-inflammatory agent as indicated by suppression of TNF-induced NF-kappaB activation, more potent as an anti-proliferative agent, and more potent in inducing ROS. Hispolon, which lacks one aromatic unit in relation to curcumin, also exhibited enhanced anti-inflammatory and anti-proliferative activities. When synthetic curcumin (Cur-S) was compared with bisdemethylcurcumin (BDC), hispolon, hispolon methyl ether (HME), dehydroxy hispolon (DH), hydroxy hispolon (HH), methoxy hispolon methyl ether (MHME), and methoxy hispolon (MH), we found that following order of anti-inflammatory activity: BDC=Hispolon>HME>HH>Cur-S>MHME>MH>DH; for anti-proliferative: Hispolon>BDC>MHME>Cur-S>MH>HME=HH>DH; and for prooxidant: BDC>Cur-S=MHME>HH>MH+HME>DH (254-1414 mean fluorescence intensity). Thus, dehydroxy hispolon was least potent for all three activities. Overall the results indicate that the substitution of a hydroxyl group for a methoxy group at the meta positions of the phenyl rings in curcumin significantly enhanced the anti-inflammatory activity, and the removal of phenyl ring at the 7(th) position of the heptadiene back bone and addition of hydroxyl group significantly increased the anti-proliferative activity of curcumin.