Ying-Jie Li

Betulinic Acid and its Derivatives as Potential Antitumor Agents

Betulinic acid (BA) is a lupane‐type pentacyclic triterpene, distributed ubiquitously throughout the plant kingdom. BA and its derivatives demonstrate multiple bioactivities, particularly an antitumor effect. This review critically describes the recent research on isolation, synthesis, and derivatization of BA and its natural analogs betulin and 23‐hydroxybetulinic acid. The subsequent part of the review focuses on the current knowledge of antitumor properties, combination treatments, and pharmacological mechanisms of these compounds. A 3D‐QSAR analysis of 62 BA derivatives against human ovarian cancer A2780 is also included to provide information concerning the structure–cytotoxicity relationships of these compounds.

Cabozantinib reverses multidrug resistance of human hepatoma HepG2/ adr cells by modulating the function of P-glycoprotein

Cabozantinib, a small‐molecule multitargeted tyrosine kinase inhibitor, has entered into a phase III clinical trial for the treatment of hepatocellular carcinoma (HCC). This study assessed the mechanistic effect of cabozantinib on the reversal of P‐glycoprotein (P‐gp)‐mediated multidrug resistance (MDR).

Autophagy and multidrug resistance in cancer

Multidrug resistance (MDR) occurs frequently after long-term chemotherapy, resulting in refractory cancer and tumor recurrence. Therefore, combatting MDR is an important issue. Autophagy, a self-degradative system, universally arises during the treatment of sensitive and MDR cancer. Autophagy can be a double-edged sword for MDR tumors: it participates in the development of MDR and protects cancer cells from chemotherapeutics but can also kill MDR cancer cells in which apoptosis pathways are inactive. Autophagy induced by anticancer drugs could also activate apoptosis signaling pathways in MDR cells, facilitating MDR reversal. Therefore, research on the regulation of autophagy to combat MDR is expanding and is becoming increasingly important. We summarize advanced studies of autophagy in MDR tumors, including the variable role of autophagy in MDR cancer cells.

Arenobufagin intercalates with DNA leading to G 2 cell cycle arrest via ATM/ATR pathway

Arenobufagin, a representative bufadienolide, is the major active component in the traditional Chinese medicine Chansu. It possesses significant antineoplastic activity in vitro. Although bufadienolide has been found to disrupt the cell cycle, the underlying mechanisms of this disruption are not defined. Here, we reported that arenobufagin blocked the transition from G2 to M phase of cell cycle through inhibiting the activation of CDK1-Cyclin B1 complex; The tumor suppressor p53 contributed to sustaining arrest at the G2 phase of the cell cycle in hepatocellular carcinoma (HCC) cells. Moreover, arenobufagin caused double-strand DNA breaks (DSBs) and triggered the DNA damage response (DDR), partly via the ATM/ATR-Chk1/Chk2-Cdc25C signaling pathway. Importantly, we used a synthetic biotinylated arenobufagin-conjugated chemical probe in live cells to show that arenobufagin accumulated mainly in the nucleus. The microscopic thermodynamic parameters measured using isothermal titration calorimetry (ITC) also demonstrated that arenobufagin directly bound to DNA in vitro. The hypochromicity in the UV-visible absorption spectrum, the significant changes in the circular dichroism (CD) spectrum of DNA, and the distinct quenching in the fluorescence intensity of the ethidium bromide (EB)-DNA system before and after arenobufagin treatment indicated that arenobufagin bound to DNA in vitro by intercalation. Molecular modeling suggested arenobufagin intercalated with DNA via hydrogen bonds between arenobufagin and GT base pairs. Collectively, these data provide novel insights into arenobufagin-induced cell cycle disruption that are valuable for the further discussion and investigation of the use of arenobufagin in clinical anticancer chemotherapy.

(+)- and (-)-Cajanusine, a Pair of New Enantiomeric Stilbene Dimers with a New Skeleton from the Leaves of Cajanus cajan

A pair of new enantiomeric stilbene dimers, (+)- and (-)-cajanusine [(+)-1 and (-)-1], with a unique coupling pattern were isolated from the leaves of Cajanus cajan . Their structures including absolute configurations were elucidated on the basis of comprehensive spectroscopic and single-crystal X-ray diffraction analyses, as well as CD calculations. The plausible biogenetic pathway of 1 was also proposed. Additionally, (±)-1, (+)-1, and (-)-1 exhibited inhibitory activities on the growth of human hepatocellular carcinoma cells.

Acerinol, a cyclolanstane triterpenoid from Cimicifuga acerina, reverses ABCB1-mediated multidrug resistance in HepG2/ADM and MCF-7/ADR cells.

Persistent cancer chemotherapy can lead to multidrug resistance which is one of the most common reasons for failure of chemotherapy. The ABCB1 transporter is a member of the ATP-binding cassette superfamily and it is frequently over-expressed in multidrug resistant cancer cells. Active ingredients derived from traditional Chinese medicinal herbs have been reported to reverse multidrug resistance mediated by ATP-binding cassette transporters. In this study, acerinol, isolated from Cimicifuga acerina, was tested for its potential to modulate the ABCB1 transporter. Our results demonstrated that acerinol could increase the chemosensitivity of ABCB1-overexpressing HepG2/ADM and MCF-7/ADR cells to chemotherapeutic drugs, doxorubicin, vincristine and paclitaxel. Furthermore, it could also increase the retention of ABCB1 substrates doxorubicin and rhodamine 123 in HepG2/ADM and MCF-7/ADR cells. A mechanistic study showed that acerinol significantly stimulated the activity of ABCB1 ATPase without affecting the expression of ABCB1 on neither mRNA nor protein level. Acerinol was also found to reverse the resistance of MCF-7/ADR cells to vincristine, dependent partly on ABCB1. In addition, acerinol׳s action was reversible, suggesting that acerinol may act as a competitive inhibitor of ABCB1 by competing with other drug substrates like doxorubicin. Indeed, docking analysis indicated that acerinol would most likely bind to the sites on ABCB1 that partly overlapped with that of verapamil. In conclusion, the present study is the first to show that acerinol from C. acerina significantly enhances the cytotoxicity of chemotherapeutic drugs by modulating the function of ABCB1. It is hopeful to develop acerinol as a new multidrug resistance reversal agent.

Ganoderma lucidum derived ganoderenic acid B reverses ABCB1-mediated multidrug resistance in HepG2/ADM cells

Chemotherapy is one of the most common therapeutic option for metastatic tumors and hematological malignancies. ABCB1-mediated multidrug resistance is the major obstacle for chemotherapy. Natural products with diversified structures are ideal source of ABCB1 modulators. Ganoderenic acid B, a lanostane-type triterpene isolated from Ganoderma lucidum, exhibited potent reversal effect on ABCB1-mediated multidrug resistance of HepG2/ADM cells to doxorubicin, vincristine and paclitaxel. Similarly, ganoderenic acid B could also significantly reverse the resistance of ABCB1-overexpressing MCF-7/ADR cells to doxorubicin. Furthermore, ganoderenic acid B notably enhanced intracellular accumulation of rhodamine-123 in HepG2/ADM cells through inhibition of its efflux. ABCB1 siRNA interference assay indicated that the reversal activity of ganoderenic acid B was dependent on ABCB1. Further mechanistic investigations found that ganoderenic acid B did not alter the expression level of ABCB1 and the activity of ABCB1 ATPase. Molecular docking model displayed that the positions of ganoderenic acid B binding to ABCB1 were different from the region of verapamil interacted with ABCB1. Collectively, ganoderenic acid B can enhance the cytotoxicity of chemotherapeutics towards ABCB1-mediated MDR cancer cells via inhibition of the transport function of ABCB1. These findings provide evidence that ganoderenic acid B has the potential to be developed into an ABCB1-mediated multidrug resistance reversal agent.

B4G2 induces mitochondrial apoptosis by the ROS-mediated opening of Ca(2+)-dependent permeability transition pores.

Background/Aims: Hepatocellular carcinoma (HCC) is the most common type of liver cancer. At present, only sorafenib is approved to treat HCC. In this study, we found that a 23-hydroxybetulinic acid derivative, B4G2, exhibited potent antiproliferative activity in HCC cell lines. Methods: We used four HCC cell lines (HepG2, HepG2/ADM, Hep3B and Bel-7402) to evaluate the anti-tumour activity and explore underlying mechanisms by which B4G2 induces apoptosis. Results: Among these cell lines, HepG2 showed the highest sensitivity to B4G2. HepG2 cells treated with B4G2 showed a depolarized mitochondrial membrane potential, released cytochrome c, activated caspase-9 and caspase-3 and cleaved poly ADP-ribose polymerase (PARP). However, Z-VAD-FMK, a pan-caspase inhibitor, did not attenuate B4G2-induced apoptosis, implying that the induction of mitochondrial apoptosis by B4G2 may be independent of caspases. Moreover, pre-treatment with MgCl2, a blocker of Ca2+-dependent permeability transition (PT) pores, attenuated the depolarization of the mitochondrial potential and decreased the population of apoptotic cells, indicating that B4G2-induced apoptosis was partly dependent on the opening of the Ca2+-dependent PT pores. B4G2 also increased the levels of intracellular calcium and reactive oxygen species (ROS). Furthermore, an ROS scavenger, N-acetyl-cysteine (NAC), markedly decreased the accumulation of intracellular calcium and apoptosis. Conclusion: This is the first demonstration that B4G2 inhibits the growth of HCC cells and induces mitochondrial apoptosis in hepatocellular carcinoma cells by the ROS-mediated opening of Ca2+-dependent permeability transition pores.

A piperazidine derivative of 23-hydroxy betulinic acid induces a mitochondria-derived ROS burst to trigger apoptotic cell death in hepatocellular carcinoma cells

BackgroundElevated production of reactive oxygen species (ROS) and an altered redox state have frequently been observed in hepatocellular carcinoma (HCC); therefore, selective killing of HCC cells by chemotherapeutic agents that stimulate ROS generation or impair antioxidant systems may be a feasible approach in HCC chemotherapy. Recently, betulinic acid and its derivatives have attracted attention because they showed anti-cancer effects via a ROS- and mitochondria-related mechanism. However, the source of ROS overproduction and the role of mitochondria were poorly identified, and the weak in vivo antitumour activity of these compounds limits their development as drugs.MethodsCytotoxicity was detected using MTT assays. In vivo anti-HCC effects were assessed using nude mice bearing HepG2 tumour xenografts. Cell cycle analysis, apoptosis rate and mitochondrial membrane potential were measured by flow cytometry. ROS production was detected using a microplate reader or a fluorescence microscope. Changes in gene and protein levels were measured by RT-PCR and western blotting, respectively. Other assays were performed using related detection kits.ResultsB5G9, a piperazidine derivative of 23-hydroxy betulinic acid (23-HBA), showed excellent in vivo anti-HCC effects, with a tumour growth inhibitory rate of greater than 80%, and no significant side effects. B5G9 stimulated the production of ROS, which were derived from the mitochondria, but it had no effect on various other antioxidant systems. Moreover, B5G9 induced mitochondrial dysfunction, which was characterized by morphological changes, membrane potential collapse, membrane permeabilization, and decreases in the O2 consumption rate and ATP production. Furthermore, mtDNA-depleted ρ0 HepG2 cells were less sensitive to B5G9 treatment than wt HepG2 cells, indicating the importance of mitochondria in B5G9-induced cell death.ConclusionWe discovered a piperazidine derivative of 23-HBA, B5G9, with excellent anti-HCC effects both in vivo and in vitro and no obvious toxic effects. The underlying mechanism was associated with mitochondria-derived ROS overproduction, and mitochondria played essential roles in B5G9-induced cell death. This study identified a potential agent for anti-HCC therapy and elucidated the mitochondria-related mechanism of BA and its derivatives.

B5H7, a Morpholine Derivative of 23-Hydroxybetulinic Acid, Reverses Doxorubicin Resistance in HepG2/ADM

Multidrug resistance (MDR) is the major cause of the failure of cancer chemotherapy. Development of MDR reversers is an important strategy to improve the efficacy of cancer chemotherapy. Here, we have found a morpholine derivative of 23-hydroxybetulinic acid, B5H7, with a reversal effect on MDR cancer cells. Our studies showed that B5H7 enhanced cytotoxicity of doxorubicin, but no cisplatin in MDR cancer cells HepG2/ADM. And we found that B5H7 not only increased the intracellular accumulation of P-glycoprotein substrates doxorubicin and rhodamine123, but also reduced the efflux of rhodamine123 in HepG2/ADM cells. Further studies showed B5H7 did not alter the protein level of P-glycoprotein and it also had no effect on P-glycoprotein ATPase activity. Taken together, we have found that B5H7 could reverse doxorubicin resistance in HepG2/ADM cells by inhibiting the transport function of P-glycoprotein. These findings contribute to developing B5H7 as an adjuvant to anticancer chemotherapy with doxorubicin.