Reversal of multidrug resistance by guggulsterone in drug-resistant MCF-7 cell lines

Anti-cancer activity of guggulsterone by modulating apoptotic markers: a systematic review and meta-analysis

Background: Guggulsterone (pregna-4,17-diene-3,16-dione; C₂₁H₂₈O₂) is an effective phytosterol isolated from the gum resin of the tree Commiphora wightii (Family Burseraceae) and is responsible for many of the properties of guggul. This plant is widely used as traditional medicine in Ayurveda and Unani system of medicine. It exhibits several pharmacological activities, such as anti-inflammatory, analgesic, antibacterial, anti-septic and anticancer. In this article, the activities of Guggulsterone against cancerous cells were determined and summarized. Methods: Using 7 databases (PubMed, PMC, Google Scholar, Science Direct, Scopus, Cochrane and Ctri.gov), the literature search was conducted since conception until June 2021. Extensive literature search yielded 55,280 studies from all the databases. A total of 40 articles were included in the systematic review and of them, 23 articles were included in the meta-analysis.The cancerous cell lines used in the studies were for pancreatic cancer, hepatocellular carcinoma, head and neck squamous cell carcinoma, cholangiocarcinoma, oesophageal adenocarcinoma, prostrate cancer, colon cancer, breast cancer, gut derived adenocarcinoma, gastric cancer, colorectal cancer, bladder cancer, glioblastoma, histiocytic leukemia, acute myeloid leukemia and non-small cell lung cancer. The reliability of the selected studies was assessed using ToxRTool. Results: Based on this review, guggulsterone significantly affected pancreatic cancer (MiaPaCa-2, Panc-1, PC-Sw, CD18/HPAF, Capan1, PC-3), hepatocellular carcinoma (Hep3B, HepG2, PLC/PRF/5R), head and neck squamous cell carcinoma (SCC4, UM-22b, 1483), cholangiocarcinoma (HuCC-T1, RBE, Sk-ChA-1, Mz-ChA-1) and oesophageal adenocarcinoma (CP-18821, OE19), prostrate cancer (PC-3), colon cancer (HT-29), breast cancer (MCF7/DOX), gut derived adenocarcinoma (Bic-1), gastric cancer (SGC-7901), colorectal cancer (HCT116), bladder cancer (T24, TSGH8301), glioblastoma (A172, U87MG, T98G), histiocytic leukemia (U937), acute myeloid leukemia (HL60, U937) and non-small cell lung cancer (A549, H1975) by inducing apoptotic pathways, inhibiting cell proliferation, and regulating the expression of genes involved in apoptosis. Guggulsterone is known to have therapeutic and preventive effects on various categories of cancers. It can inhibit the progression of tumors and can even reduce their size by inducing apoptosis, exerting anti-angiogenic effects, and modulating various signaling cascades. In vitro studies reveal that Guggulsterone inhibits and suppresses the proliferation of an extensive range of cancer cells by decreasing intrinsic mitochondrial apoptosis, regulating NF-kB/STAT3/β-Catenin/PI3K/Akt/CHOP pathway, modulating the expression of associated genes/proteins, and inhibiting angiogenesis. Furthermore, Guggulsterone reduces the production of inflammatory markers, such as CDX2 and COX-2. The other mechanism of the Guggulsterone activity is the reversal of P-glycoprotein-mediated multidrug resistance. Twenty three studies were selected for meta-analysis following the PRISMA statements. Fixed effect model was used for reporting the odds ratio. The primary endpoint was percentage apoptosis. 11 of 23 studies reported the apoptotic effect at t = 24 h and pooled odds ratio was 3.984 (CI 3.263 to 4.865, p < 0.001). 12 studies used Guggulsterone for t > 24 h and the odds ratio was 11.171 (CI 9.148 to 13.643, 95% CI, p < 0.001). The sub-group analysis based on cancer type, Guggulsterone dose, and treatment effects. Significant alterations in the level of apoptotic markers were reported by Guggulsterone treatment. Conclusion: This study suggested that Guggulsterone has apoptotic effects against various cancer types. Further investigation of its pharmacological activity and mechanism of action should be conducted. In vivo experiments and clinical trials are required to confirm the anticancer activity.

Cytotoxicity of synthetic derivatives against breast cancer and multi-drug resistant breast cancer cell lines: a literature-based perspective study

Cancer is the second most killer worldwide causing millions of people to lose their lives every year. In the case of women, breast cancer takes away the highest proportion of mortality rate than other cancers. Due to the mutation and resistance-building capacity of different breast cancer cell lines against conventional therapies, this death rate is on the verge of growth. New effective therapeutic compounds and treatment method is the best way to look out for in this critical time. For instance, new synthetic derivatives/ analogues synthesized from different compounds can be a ray of hope. Numerous synthetic compounds have been seen enhancing the apoptosis and autophagic pathway that directly exerts cytotoxicity towards different breast cancer cell lines. To cease the ever-growing resistance of multi-drug resistant cells against anti-breast cancer drugs (Doxorubicin, verapamil, tamoxifen) synthetic compounds may play a vital role by increasing effectivity, showing synergistic action. Many recent and previous studies have reported that synthetic derivatives hold potentials as an effective anti-breast cancer agent as they show great cytotoxicity towards cancer cells, thus can be used even vastly in the future in the field of breast cancer treatment. This review aims to identify the anti-breast cancer properties of several synthetic derivatives against different breast cancer and multi-drug-resistant breast cancer cell lines with their reported mechanism of action and effectivity.

Potential of guggulsterone, a farnesoid X receptor antagonist, in the prevention and treatment of cancer

Cancer is one of the most dreadful diseases in the world with a mortality of 9.6 million annually. Despite the advances in diagnosis and treatment during the last couple of decades, it still remains a serious concern due to the limitations associated with currently available cancer management strategies. Therefore, alternative strategies are highly required to overcome these glitches. The importance of medicinal plants as primary healthcare has been well-known from time immemorial against various human diseases, including cancer. Commiphora wightii that belongs to Burseraceae family is one such plant which has been used to cure various ailments in traditional systems of medicine. This plant has diverse pharmacological properties such as antioxidant, antibacterial, antimutagenic, and antitumor which mostly owes to the presence of its active compound guggulsterone (GS) that exists in the form of Z- and E-isomers. Mounting evidence suggests that this compound has promising anticancer activities and was shown to suppress several cancer signaling pathways such as NF-κB/ERK/MAPK/AKT/STAT and modulate the expression of numerous signaling molecules such as the farnesoid X receptor, cyclin D1, survivin, caspases, HIF-1α, MMP-9, EMT proteins, tumor suppressor proteins, angiogenic proteins, and apoptotic proteins. The current review is an attempt to summarize the biological activities and diverse anticancer activities (both in vitro and in vivo) of the compound GS and its derivatives, along with its associated mechanism against various cancers.

CyclinB1 deubiquitination by USP14 regulates cell cycle progression in breast cancer

Breast cancer is the most common malignant tumor among women in China, which seriously threatens women's physical and mental health. Tumorigenesis is closely related to the dysregulation of cell cycle. The cell cycle progression includes interphase and mitotic phase (M phase). Cyclin B1 is a key protein in regulating M phase, which is essential for the whole cell cycle progression. CyclinB1 can be degraded through ubiquitination mediated by the anaphase promoting complex/cyclosome (APC/C). However, the mechanism of how CyclinB1 is deubiquitinated in breast cancer still remains unclear. In this study, we discovered that CyclinB1 interacted with ubiquitin-specific peptidase 14 (USP14). Based on the deubiquitinating function of USP14, we detected the effect of USP14 on the ubiquitination of CyclinB1. Inhibiting the activity of USP14 or USP14 knockdown significantly increased the ubiquitination of CyclinB1. In accordance with this, knocking down USP14 arrested cell cycle at G2/M phase. Knocking down USP14 with siRNAs significantly inhibited the proliferation and migration of breast cancer cells. In conclusion, our study demonstrated that USP14 regulated the cell cycle of breast cancer cells by regulating the ubiquitination of CyclinB1, which will provide a solid theoretical basis for the development of anti-cancer drugs targeting USP14.

Paris saponin VII reverses chemoresistance in breast MCF-7/ADR cells

ETHNOPHARMACOLOGICAL RELEVANCE

The development of a multidrug-resistant (MDR) phenotype is a main obstacle to the successful treatment of breast cancer. Saponins of several herbs are considered as promising candidates for drug resistance treatment. We extracted Paris saponin VII (PS VII) from Trillium tschonoskii Maxim. and investigated whether it could sensitize chemoresistant breast cancer cells MCF-7/ADR to the cytotoxic effects of adriamycin.

MATERIALS AND METHODS

MCF-7/ADR cells were exposed to 0.5 μM PSVII plus different concentrations of adriamycin (0-100 μM). Then, MTT assay and adriamycin accumulation assay were used to assess cell proliferation and intracellular adriamycin retention. P glycoprotein levels and intracellular rhodamine 123 (Rh-123) accumulations were investigated to measure the expression and activity of P-glycoprotein. A xenograft model of nude mouse was utilized to observe the effect of PSVII in vivo.

RESULTS

Treatment with PSVII influenced cell viability of MCF-7/ADR cells, as well as sensitized MCF-7/ADR cells to the cytotoxic effects of adriamycin. Moreover, PSVII significantly downregulated MDR1 expression in MCF-7/ADR cells. Intravenous administration of PSVII significantly enhanced anticancer efficacy of adriamycin to MCF-7/ADR xenograft model in nude mice.

CONCLUSION

These findings suggested a possible application of PSVII in combination with chemotherapy and/or as neo-adjuvant therapy in the treatment of MDR breast cancer.

Googling the Guggul (Commiphora and Boswellia) for Prevention of Chronic Diseases

Extensive research during last 2 decades has revealed that most drugs discovered today, although costs billions of dollars for discovery, and yet they are highly ineffective in their clinical response. For instance, the European Medicines Agency has approved 68 anti-cancer drugs, and out of which 39 has reached the market level with no indication of increased survival nor betterment of quality of life. Even when drugs did improve survival rate compared to available treatment strategies, most of these were found to be clinically insignificant. This is a fundamental problem with modern drug discovery which is based on thinking that most chronic diseases are caused by alteration of a single gene and thus most therapies are single gene-targeted therapies. However, extensive research has revealed that most chronic diseases are caused by multiple gene products. Although most drugs designed by man are mono-targeted therapies, however, those designed by "mother nature" and have been used for thousands of years, are "multi-targeted" therapies. In this review, we examine two agents that have been around for thousands of years, namely "guggul" from Commiphora and Boswellia. Although we are all familiar with the search engine "google," this is another type of "guggul" that has been used for centuries and being explored for its various biological activities. The current review summarizes the traditional uses, chemistry, in vitro and in vivo biological activities, molecular targets, and clinical trials performed with these agents.

Guggulsterone sensitized drug-resistant human hepatocarcinoma cells to doxorubicin through a Cox-2/P-gp dependent pathway

Previous researches indicated that cyclooxygenase-2 (Cox-2) might be involved in P-glycoprotein (P-gp)-mediated multidrug resistance in hepatocellular carcinoma cells. Doxorubicin-resistant hepatocellular carcinoma PLC/PRF/5 cells (PLC/PRF/5R) and HepG2 (HepG2R) cells were developed in the present study. The modulatory effect of guggulsterone on Cox-2 and P-gp in PLC/PRF/5R and HepG2R cells was investigated. Cells proliferation, Cox-2 and P-gp expression, and prostaglandin E₂ release were examined using MTT, flow cytometry, western blot and ELISA assays. Small interfering RNA (siRNA) targeted against Cox-2 and multidrug resistance protein (Mdr-1) was used to regulate the expression of Cox-2 and P-gp. The results showed that co-administration of guggulsterone resulted in a significant increase in chemo-sensitivity of PLC/PRF/5R cells to doxorubicin, as compared with doxorubicin treatment alone. When doxorubicin (10µM) was combined with guggulsterone (50µM), the mean apoptotic population of PLC/PRF/5R cells was 20.16%. It was increased by 1.5 times, as compared with doxorubicin (10µM) treatment alone. Furthermore, guggulsterone had significantly inhibitory effect on the levels of Cox-2, P-gp and prostaglandin E₂. However, guggulsterone did not show significantly inhibitory effect on the expression of prostaglandin E receptors. In addition, Cox-2 siRNA simultaneously reduced the expression of Cox-2 and P-gp in PLC/PRF/5R cells. Mdr-1 siRNA had no influence on Cox-2, but inhibited P-gp expression. The present study suggested that guggulsterone might enhance the cytotoxic effect of doxorubicin to PLC/PRF/5R cells through a Cox-2/P-gp dependent pathway.

Potential therapeutic targets of Guggulsterone in cancer

Natural compounds capable of inducing apoptosis in cancer cells have always been of considerable interest as potential anti-cancer agents. Many such compounds are under screening and development with their potential evolution as a clinical drug benefiting many of the cancer patients. Guggulsterone (GS), a phytosterol isolated gum resin of the tree Commiphora mukul has been widely used in Indian traditional medicine as a remedy for various diseses. GS has been shown to possess cancer chemopreventive and therapeutic potential as established by in vitro and in vivo studies. GS has been shown to target constitutively activated survival pathways such as PI3-kinase/AKT, JAK/STAT, and NFκB signaling pathways that are involved in the regulation of growth and inflammatory responses via regulation of antiapoptotic and inflammatory genes. The current review focuses on the molecular targets of GS, cellular responses, and the animal model studies in various cancers. The mechanistic action of GS in different types of cancers also forms a part of this review. The perspective of translating this natural compound into a clinically approved drug with its pros and cons is also discussed.

Synergistic effects of A-B-C-type amphiphilic copolymer on reversal of drug resistance in MCF-7/ADR breast carcinoma

P-glycoprotein (P-gp) overexpression has become the most common cause of occurrence of multidrug resistance in clinical settings. We aimed to construct a micellar polymer carrier to sensitize drug-resistant tumors to doxorubicin (DOX). This A-B-C-type amphiphilic copolymer was prepared by the sequential linkage of β-cyclodextrin, hydrophobic poly(d,l-lactide), and hydrophilic poly(ethylene glycol). Upon incubation of the DOX-loaded micelles with DOX-resistant human breast carcinoma MCF-7/ADR cells, significantly enhanced cytotoxicity and apoptosis were achieved. A series of studies on the action mechanism showed that the polymer components such as β-cyclodextrin, hydrophobic poly(d,l-lactide) segment, and poly(ethylene glycol) coordinatively contributed to the improved intracellular ATP depletion and ATPase activity, increased intracellular uptake of P-gp substrates via competitive binding to P-gp, and decreased P-gp expression in MCF-7/ADR cells. More interestingly, a similar phenomenon was observed in the zebrafish xenograft model, resulting in ~64% inhibition of MCF-7/ADR tumor growth. These results implied that the polymeric micelles displayed great potentials as P-gp modulators to reverse DOX resistance in MCF-7/ADR breast carcinoma.

Alisol F 24 Acetate Enhances Chemosensitivity and Apoptosis of MCF-7/DOX Cells by Inhibiting P-Glycoprotein-Mediated Drug Efflux

Multidrug resistance (MDR) is a prime reason for numerous failed oncotherapy approaches. In the present study, we investigated whether Alisol F 24 acetate (ALI) could reverse the MDR of MCF-7/DOX cells, a multidrug-resistant human breast cancer cell line. We found that ALI was a potent P-glycoprotein (P-gp) inhibitor, in the Caco-2-monolayer cell model. ALI showed a significant and concentration-dependent cytotoxic effect on MCF-7/DOX cells in combination with doxorubicin by increasing intracellular accumulation and inducing nuclear migration of doxorubicin. However, ALI had no such effect on MCF-7 cells. In addition, ALI also promoted doxorubicin-induced early apoptosis of MCF-7/DOX cells in a time-dependent manner. These results suggest that ALI can enhance chemosensitivity of doxorubicin and reinforce its anti-cancer effect by increasing its uptake, especially inducing its nuclear accumulation in MCF-7/DOX cells. Therefore, ALI could be developed as a potential MDR-reversing agent in cancer chemotherapy in further study.

Guggulsterone and Its Role in Chronic Diseases

Guggulsterone is a plant sterol derived from gum resin of Commiphora wightii. The gum resin from guggul plants has been used for thousand years in Ayurveda to treat various disorders, including internal tumors, obesity, liver disorders, malignant sores and ulcers, urinary complaints, intestinal worms, leucoderma, sinuses, edema, and sudden paralytic seizures. Guggulsterone has been identified a bioactive components of this gum resin. This plant steroid has been reported to work as an antagonist of certain nuclear receptors, especially farnesoid X receptor, which regulates bile acids and cholesterol metabolism. Guggulsterone also mediates gene expression through the regulation of transcription factors, including nuclear factor-kappa B and signal transducer and activator of transcription 3, which plays important roles in the development of inflammation and tumorigenesis. Guggulsterone has been shown to downregulate the expression of proteins involved in anti-apoptotic, cell survival, cell proliferation, angiogenic, metastatic, and chemoresistant activities in tumor cells. This review aimed to clarify the cell signal pathways targeted by guggulsterone and the bioactivities of guggulsterone in animal models and humans.

Reversal of doxorubicin resistance by guggulsterone of Commiphora mukul in vivo

Our previous study has shown co-administration of guggulsterone resulted in significant increase in chemosensitivity of multidrug-resistant human breast cancer MCF-7/DOX cells to doxorubicin (DOX) in vitro. The present study was designed to investigate whether guggulsterone had the similar modulatory activities in vivo. MCF-7/DOX and MCF-7 xenograft mice models were established. At the end of the experiment (day 28), doxorubicin treatment alone did not significantly inhibit tumor growth in MCF-7/DOX xenograft, indicating that it retained doxorubicin resistance. Whereas, doxorubicin treatment alone significantly inhibited tumor growth in MCF-7 xenograft, suggesting that it maintained doxorubicin sensitivity. When doxorubicin and guggulsterone were co-administrated, their antitumor activities were augmented in MCF-7/DOX xenograft. However, combination therapy did not enhance the antitumor effects of doxorubicin in MCF-7 xenograft. The expression of proliferative cell nuclear antigens PCNA and Ki67 after doxorubicin treatment alone was not significantly different from that of vehicle group in MCF-7/DOX xenograft. On the contrary, doxorubicin treatment alone significantly reduced PCNA and Ki67 expression in MCF-7 xenograft. Combination therapy also significantly reduced PCNA and Ki67 expression in MCF-7/DOX xenograft, compared to doxorubicin treatment alone. However, combination therapy did not enhance the inhibitory effects of doxorubicin on PCNA and Ki67 expression in MCF-7 xenograft. Examining the apoptotic index by TUNEL assay showed similar results. Further studies demonstrated the inhibitory effects of guggulsterone on Bcl-2 and P-glycoprotein expression were the possible reason to increase chemosensitivity of MCF-7/DOX cells to doxorubicin in vivo. Examining body weight, hematological parameters, hepatic, cardiac and gastrointestinal tracts histopathology revealed that no significant signs of toxicity were related to guggulsterone. Guggulsterone might reverse doxorubicin resistance in vivo, with no severe side effects.

Guggulsterone of Commiphora mukul resin reverses drug resistance in imatinib-resistant leukemic cells by inhibiting cyclooxygenase-2 and P-glycoprotein

The purpose of this study was to investigate the effects of guggulsterone on cyclooxygenase-2 and P-glycoprotein mediated drug resistance in imatinib-resistant K562 cells (K562/IMA). MTT cytotoxicity assay, flow cytometry, western blot analysis, and ELISA were performed to investigate the anti-proliferative effect, the reversal action of drug resistance, and the inhibitory effect on cyclooxygenase-2, P-glycoprotein, BCR/ABL kinase, and PGE2 release in K562/IMA cells by guggulsterone. The results showed that co-administration of guggulsterone resulted in a significant increase in chemo-sensitivity of K562/IMA cells to imatinib, compared with imatinib treatment alone. Rhodamine123 accumulation in K562/IMA cells was significantly enhanced after incubation with guggulsterone (60, 120 μM), compared with untreated K562/IMA cells (p<0.05). When imatinib (1 μM) was combined with guggulsterone (60, 120 μM), the mean apoptotic population of K562/IMA cells was 15.47% and 24.91%. It was increased by 3.82 and 6.79 times, compared with imatinib (1 μM) treatment alone. Furthermore, guggulsterone had significantly inhibitory effects on the levels of cyclooxygenase-2, P-glycoprotein and prostaglandin E2. However, guggulsterone had little inhibitory effect on the activity of BCR/ABL kinase. The present study indicates guggulsterone induces apoptosis by inhibiting cyclooxygenase-2 and down-regulating P-glycoprotein expression in K562/IMA cells.

Induction of the connexin 32 gene by epigallocatechin-3-gallate potentiates vinblastine-induced cytotoxicity in human renal carcinoma cells

BACKGROUND/AIM

Enforced expression of the connexin (Cx) 32 gene, a member of the gap junction gene family and a tumor suppressor gene in human renal cell carcinoma (RCC), enhanced vinblastine (VBL)-induced cytotoxicity in RCC cells due to suppression of multidrug resistance 1 (MDR1) expression. Furthermore, in RCC the Cx32 gene is silenced by hypermethylation of CpG islands in a promoter region of the Cx gene. In this study, we investigated if the green tea polyphenol epigallocatechin-3-gallate (EGCG) could enhance susceptibility of RCC cells (Caki-1, a human metastatic RCC cell) to VBL.

METHODS

The effects of EGCG on Caki-1 cells were estimated by WST-1 (cell viability), real-time RT-PCR (mRNA level) and immunoblotting (protein level). We estimated the methylation status in the promoter region of the Cx32 gene in RCC cells by methylation-specific PCR. Each protein function was inhibited by small interfering RNA (siRNA) and specific inhibitors.

RESULTS

The EGCG treatment elicited significant upregulation of Cx32 in Caki-1 cells, and the induction of the Cx led to the suppression of MDR1 mRNA expression through inactivation of Src and subsequent activation of c-Jun NH2-terminal kinase (JNK). Chemical sensitivity to VBL in Caki-1 cells was increased by EGCG pretreatment, and this effect was abrogated by siRNA-mediated knockdown of Cx32.

CONCLUSION

This study suggests that the restoration of Cx32 by EGCG pretreatment improves chemical tolerance on VBL in Caki-1 cells via the inactivation of Src and the activation of JNK.

Guggulsterone regulates the function and expression of P-glycoprotein in rat brain microvessel endothelial cells

Our previous studies found that guggulsterone could inhibit P-glycoprotein-mediated multidrug resistance in P-glycoprotein over-expressed human cancer cell lines. However, the effects of guggulsterone on the ;P-glycoprotein function and expression in rat brain microvessel endothelial cells (rBMECs) are poorly understood. In the present study, we investigated whether guggulsterone has a modulative effect on the function and expression of P-glycoprotein in rBMECs. rhodamine 123 acts as a good substrate for P-glycoprotein, and agents that block P-glycoprotein have been found to increase the retention of rhodamine in cells. The results showed that the accumulation of rhodamine 123 in rBMECs was potentiated in a time-dependent manner after incubation with 30, 100 μM guggulsterone (P<0.05). Efflux of intracellular rhodamine 123 was decreased in a time-dependent manner from after 30, 100 μM guggulsterone treatment. The inhibitory effect of guggulsterone on P-glycoprotein function was reversible and remained at 120 min after removal of 30, 100 μM guggulsterone from the medium. Further results showed that guggulsterone (30, 100 μM) down-regulated the expression of P-glycoprotein, and had no influence on the expression of breast cancer resistance protein in rBMECs. In addition, the present study revealed that guggulsterone promoted the activity of P-glycoprotein ATPase in a dose-dependent manner. These results indicated that guggulsterone suppressed the function and expression of P-glycoprotein in rBMECs primary cultures.

Reversion of P-glycoprotein-mediated multidrug resistance by guggulsterone in multidrug-resistant human cancer cell lines

Multidrug resistance (MDR) presents a serious problem in cancer chemotherapy. Our previous studies have shown that guggulsterone could reverse MDR through inhibiting the function and expression of P-glycoprotein (P-gp). The present study is to further investigate the reversal effects of guggulsterone on MDR in drug-resistant cancer cell lines. The effects of guggulsterone on MDR1mRNA gene expression, intracellular pH, P-gp ATPase activity and glucosylceramide synthase (GCS) expression were assessed by RT-PCR, Laser Scanning Confocal Microscope using the pH-sensitive fluorescent probe BCECF-AM, Pgp-Glo assay system, and flow cytometric technology, respectively. The results showed that guggulsterone ranging from 2.5 to 80 μM significantly promoted the activity of P-gp ATPase in a dose-dependent manner. The intracellular pH of K562/DOX cells was found to be higher than K562 cells. After treatment with guggulsterone (1, 3, 10, 30, 100 μM), intracellular pH of K562/DOX cells decreased in a dose- and time-dependent manner. However, the present study revealed that guggulsterone ranging from 3 to 100 μM had little influence on MDR1 gene expression in K562/DOX cells. Further, the isogenic doxorubicin-resistant MCF-7/DOX cells exhibited a 4.9-fold increase in GCS level as compared with parental MCF-7 human breast cancer cells. After treatment with guggulsterone (0.1, 1, 10 μM) for 48 h, MCF-7/DOX cells were found to have no change of GCS protein expression amount. Guggulsterone might be a potent MDR reversal agent, and its mechanism on MDR needs more research.