Pretreatment of BMSCs with TZD solution decreases the proliferation rate of MCF­7 cells by reducing FGF4 protein expression.

The present study aimed to investigate the effects of bone marrow­derived mesenchymal stem cells (BMSCs) that had been pretreated with pioglitazone and/or rosiglitazone on the growth and proliferation rate of MCF­7 cells. The adhesive interaction between the BMSCs and the MCF­7 cancer cells revealed that the pretreatment of BMSCs with a combination of two types of thiazolidinedione drug reduced the growth and proliferation rate of the MCF­7 cells. The proliferation rate of the MCF­7 cells could also be reduced by the non­adhesive interaction of the cancer cells with BMSCs pretreated with pioglitazone and/or rosiglitazone. The growth and proliferation rate reduction effects on the MCF­7 cells may be attributed to the reduction in the protein level of fibroblast growth factor 4 (FGF4) in the conditioned medium of the pretreated BMSCs. The evidence that the low protein level of FGF4 in the conditioned medium of the pretreated BMSCs perturbed the proliferation rate of the MCF­7 cells by reducing the levels of Ki­67 and proliferating cell nuclear antigen transcripts in the cancer cells was also demonstrated in the present study using a FGF4­neutralizing antibody. All the above findings demonstrate that future studies on the correlation between FGF4 and pretreated BMSCs would be beneficial.

Modification of MCF-10A cells with pioglitazone and serum-rich growth medium increases soluble factors in the conditioned medium, likely reducing BT-474 cell growth.

In the present study, we aimed to preincubate MCF-10A cells with pioglitazone and/or serum-rich growth media and to determine adhesive and non-adhesive interactions of the preincubated MCF-10A cells with BT-474 cells. For this purpose, the MCF-10A cells were preincubated with pioglitazone and/or serum-rich growth media, at appropriate concentrations, for 1 week. The MCF-10A cells preincubated with pioglitazone and/or serum-rich growth media were then co-cultured adhesively and non-adhesively with BT-474 cells for another week. Co-culture of BT-474 cells with the preincubated MCF-10A cells, both adhesively and non-adhesively, reduced the growth of the cancer cells. The inhibitory effect of the preincubated MCF-10A cells against the growth of BT-474 cells was likely produced by increasing levels of soluble factors secreted by the preincubated MCF-10A cells into the conditioned medium, as immunoassayed by ELISA. However, only an elevated level of a soluble factor distinguished the conditioned medium collected from the MCF-10A cells preincubated with pioglitazone and serum-rich growth medium than that with pioglitazone alone. This finding was further confirmed by the induction of the soluble factor transcript expression in the preincubated MCF-10A cells, as determined using real-time PCR, for the above phenomenon. Furthermore, modification of the MCF-10A cells through preincubation did not change the morphology of the cells, indicating that the preincubated cells may potentially be injected into mammary fat pads to reduce cancer growth in patients or to be used for others cell-mediated therapy.

The mTOR inhibitor RAD001 sensitizes tumor cells to the cytotoxic effect of carboplatin in breast cancer in vitro.

AIM: The phosphatidylinositol 3-kinase (PI3K)/protein kinase B(AKT)/mammalian target of rapamycin (mTOR) signaling pathway is aberrantly activated in many types of cancer, including breast cancer. It is recognized that breast cancer cells develop resistance to a variety of standard therapies through the activation of this pathway. We hypothesized that targeting this signaling by the mTOR inhibitor RAD001 may potentiate the cytotoxicity of a conventional chemotherapeutic drug, carboplatin, and enhance the treatment efficacy for breast cancer. MATERIALS AND METHODS: Cell proliferation was measured with 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay; cell apoptosis with enzyme-linked immunosorbent assay (ELISA). Flow cytometry was used for the analysis of cell cycle distribution and mitochondrial membrane function. Gene expression at the protein level was determined by Western blot. RESULTS: MTOR inhibitor RAD001 enhanced the sensitivity of breast cancer cells to carboplatin. RAD001 in combination with carboplatin resulted in synergistic inhibition of cell proliferation and caspase-independent apoptosis in these cells. Moreover, in MCF-7 and BT-474 cells, synergistic effects of this combination on G2/M cell cycle arrest and regulation of different molecules responsible for cell cycle transition and apoptosis were observed. The p53 pathway was involved in the synergism of RAD001 and carboplatin on breast cancer cell proliferation and apoptosis, since the synergistic effect was demonstrated in all tested breast cancer cell lines with wild-type p53 and the use of p53 inhibitor partially antagonized the effect of RAD001 and carboplatin on p53 and p21 expression, as well as their inhibitory effect on cell proliferation. However, a synergistic effect of the combination of the two drugs on cell proliferation was observed in two p53-mutated cell lines with high AKT expression, suggesting that an alternative mechanism underlying the observed synergism exists. CONCLUSION: Our results suggest that the combination of RAD001 and carboplatin is a promising treatment approach for breast cancer. On the basis of these results, we have initiated a phase I/II clinical trial with the combination of carboplatin and RAD001 in patients with metastatic breast cancer.

Induction of endoplasmic reticulum stress response by TZD18, a novel dual ligand for peroxisome proliferator-activated receptor alpha/gamma, in human breast cancer cells.

Previously we reported that the peroxisome proliferator-activated receptor alpha/gamma dual ligand TZD18 inhibited growth and induced apoptosis of leukemia and glioblastoma cells. Now we show that TZD18 also has the same effects against six human breast cancer cell lines. To obtain insights into the mechanism involved in TZD18-induced growth inhibition and apoptosis in breast cancer, the gene expression profiles of TZD18-treated and untreated MCF-7 and MDA-MB-231 cells were compared by microarray analysis. Results reveal that many genes implicated in endoplasmic reticulum stress signaling, such as CHOP (also known as DDIT3 or GADD153), GRP78 (HSPA5), and ATF4, are highly up-regulated, suggesting endoplasmic reticulum stress is induced. This is supported by our data that treatment of MCF-7 and MDA-MB-231 cells with TZD18 induces phosphorylation of PERK and the alpha subunit of eukaryotic initiation factor 2 (eIF2alpha), as well as an up-regulation of GRP78 and an activation of ATF6, all of which are specific markers for endoplasmic reticulum stress. Furthermore, this ligand increases the endoplasmic reticulum stress-related cell death-regulators such as CHOP, DR5, GADD34, Bax, and Bak in these cells. Importantly, knockdown of CHOP by small interference RNA antagonizes the TZD18-induced apoptosis, indicating a crucial role of CHOP in the apoptotic process triggered by TZD18. In addition, TZD18 also activates stress-sensitive mitogen-activated protein kinase (MAPK) pathways including p38, ERK, and JNK. The specific inhibitors of these MAPKs attenuated the TZD18-induced growth inhibition in these cells. These results clearly show that activation of these MAPKs is important for TZD18-induced growth inhibition. In summary, TZD18-treatment leads to the activation of endoplasmic reticulum stress response and, subsequently, growth arrest and apoptosis in breast cancer cells.

Compound 48, a novel dual PPAR alpha/gamma ligand, inhibits the growth of human CML cell lines and enhances the anticancer-effects of imatinib.

Compound 48 (C48) is a novel dual ligand for peroxisome proliferator-activated receptor alpha and gamma (PPAR alpha/gamma). Culture of imatinib-sensitive and -resistant CML cell lines with C48 resulted in a strong growth inhibition which associated with G0/G1 cell cycle arrest. However, it showed no obvious toxicity to normal CD34(+) hematopoietic stem cells. Decrease of pSTATs and pAKT were noticed suggesting that interference of AKT and STATs signaling may be the mechanisms for the effects of PPAR alpha/gamma ligands. Of more clinical importance, this ligand strongly enhanced the anticancer-effects of imatinib. Overall, our data suggest that the PPAR alpha/gamma ligands may have potentials in the treatment of CML in an adjuvant setting either before or after the development of imatinib resistance.

Anti-tumor effect of honokiol alone and in combination with other anti-cancer agents in breast cancer.

Honokiol, an active component isolated and purified from Chinese traditional herb magnolia, was demonstrated to inhibit growth and induce apoptosis of different cancer cell lines such as human leukaemia, colon, and lung cancer cell lines; to attenuate the angiogenic activities of human endothelial cells in vitro; and to efficiently suppress the growth of angiosarcoma in nude mice. In this study, we have demonstrated that treatment of different human breast cancer cell lines with honokiol resulted in a time- and concentration-dependent growth inhibition in both estrogen receptor-positive and -negative breast cancer cell lines, as well as in drug-resistant breast cancer cell lines such as adriamycin-resistant and tamoxifen-resistant cell lines. The inhibition of growth was associated with a G1-phase cell cycle arrest and induction of caspase-dependent apoptosis. The effects of honokiol might be reversely related to the expression level of human epidermal growth receptor 2, (HER-2, also known as erbB2, c-erbB2) since knockdown of her-2 expression by siRNA significantly enhanced the sensitivity of the her-2 over-expressed BT-474 cells to the honokiol-induced apoptosis. Furthermore, inhibition of HER-2 signalling by specific human epidermal growth receptor 1/HER-2 (EGFR/HER-2) kinase inhibitor lapatinib synergistically enhanced the anti-cancer effects of honokiol in her-2 over-expressed breast cancer cells. Finally, we showed that honokiol was able to attenuate the PI3K/Akt/mTOR (Phosphoinositide 3-kinases/Akt/mammalian target of rapamycin) signalling by down-regulation of Akt phosphorylation and upregulation of PTEN (Phosphatase and Tensin homolog deleted on chromosome Ten) expression. Combination of honokiol with the mTOR inhibitor rapamycin presented synergistic effects on induction of apoptosis of breast cancer cells. In conclusion, honokiol, either alone or in combination with other therapeutics, could serve as a new, promising approach for breast cancer treatment.

Dual PPARalpha/gamma ligand TZD18 either alone or in combination with imatinib inhibits proliferation and induces apoptosis of human CML cell lines.

Despite progress in the treatment of early-stage chronic myeloid leukemia (CML), the accelerated and blastic phases of CML still remain a therapeutic challenge. Persistence of BCR-ABL-positive (bcr-abl(+)) cells or secondary resistance during imatinib therapy frequently occurs. In this study, we investigated the activity of a novel dual ligand specific for peroxisome proliferator-activated receptor alpha and gamma (PPARalpha/gamma) against CML blast crisis cell lines. Exposure of these cell lines (K562, KU812 and KCL22) to TZD18 resulted in a growth inhibition in a dose- and time-dependent manner. This effect may not be mediated through PPARgamma and PPARalpha activation, since antagonists of PPARgamma and/or PPARalpha could not reverse this inhibition. Western blotting analysis showed that expression of the cyclin dependent kinase inhibitor (CDKI) p27(kip1) was enhanced, whereas levels of cyclin E, cyclin D2 and cyclin dependent kinase 2 (CDK-2) were decreased when these cells were treated with TZD18. Most interestingly, TZD18 synergistically enhanced the antiproliferative and pro-apoptotic effect of imatinib. Overall, our findings strongly suggest that either TZD18, either alone or in combination with imatinib may be beneficial for the treatment of CML in myeloid blast crisis.

Peroxisome proliferator-activated receptor-gamma ligands inhibit proliferation and induce apoptosis in mantle cell lymphoma.

Peroxisome proliferator-activated receptor-gamma, a nuclear receptor and transcription factor, and its natural and synthetic ligands have become a focus of novel approaches to induction of apoptosis in solid tumors and hematologic malignancies, including malignant B-lineage cells. The effect on mantle cell lymphoma, a subtype with dismal prognosis, has not yet been analyzed. We investigated the effect of 15-deoxy-delta-12,14-prostaglandin J2 (15d-PGJ2), pioglitazone (PGZ) or rosiglitazone (RGZ) on human mantle cell lymphoma cell lines (GRANTA-519, Hbl-2 and JeKo-1). Mantle cell lymphoma cell lines exhibited a high expression of Peroxisome proliferator-activated receptor-gamma protein in Western blot analysis. MTT assays revealed anti-proliferative effects induced by both 15d-PGJ2, the natural activator of Peroxisome proliferator-activated receptor-gamma, and PGZ and RGZ, synthetic Peroxisome proliferator-activated receptor-gamma ligands, in a dose-dependent manner. At a dose of 50 micromol/l, 15d-PGJ2 induced growth inhibition in all cell lines. The anti-proliferative effect of PGZ and RGZ was slightly lower. Induction of apoptosis was indicated by annexin V staining. At a dose of 50 micromol/l, 15d-PGJ2 led to apoptosis in all cell lines (87-99%) after 48 h of incubation. Again, the apoptotic effect with thiazolidinediones was slightly lower at the same dose level. This is the first study evaluating Peroxisome proliferator-activated receptor-gamma expression and its therapeutic implications in human mantle cell lymphoma cells. Thiazolidinediones comprise anti-lymphoma activity in vitro and should be further explored for the treatment of mantle cell lymphoma.

Growth inhibition and apoptosis in human Philadelphia chromosome-positive lymphoblastic leukemia cell lines by treatment with the dual PPARalpha/gamma ligand TZD18.

Treatment of adult Philadelphia chromosome-positive lymphocytic leukemia is rarely successful. We report here the effects of TZD18, a novel dual ligand specific for peroxisome proliferator-activated receptor alpha and gamma (PPARalpha/gamma) on Ph(+) lymphocytic leukemia cell lines BV173, SD1, and SupB-15. Exposure of these cells to TZD18 resulted in growth inhibition in a dose- and time-dependent manner that was associated with G(1) cell cycle arrest. This effect was much stronger than that mediated by the PPARgamma ligand pioglitazone (PGZ), which also belongs to the thiazolidinediones (TZD) class of ligands. However, it may not be mediated through PPARgamma or PPARalpha activation because antagonists of PPARgamma and PPARalpha cannot reverse it. Study of the key regulators of cell cycle progression by Western blot analysis showed that the expression of the cyclin-dependent kinase inhibitor (CDKI) p27(kip1), but not that of p21(cip1), was enhanced, whereas that of c-Myc, cyclin E, cyclin D2, and cyclin-dependent kinases 2 and 4 (CDK-2 and CDK-4) was decreased when these cells were treated with TZD18 (10 or 20 microM). Therefore, the up-regulation of p27(kip1) and the down-regulation of CDK-2 and CDK-4 may, at least in part, account for the G(1) cell cycle arrest. Furthermore, a remarkable induction of apoptosis was observed in the cells treated with this dual ligand. No obvious alteration of bcl-2 protein level occurred, but bax was up-regulated in these TZD18-treated cells. Activation of caspase 8 and caspase 9 by TZD18 was also observed. Importantly, NF-kappaB DNA-binding activity was markedly decreased by the TZD18 treatment. In addition, TZD18 enhanced the growth inhibitory effect of imatinib, a specific tyrosine kinase inhibitor therapeutically used in the treatment of Ph(+) leukemia. Overall, our findings strongly suggest that TZD18 may offer a new therapeutic approach to aid in the treatment of Ph(+) lymphocytic leukemia.

Peroxisome proliferator-activated receptor-gamma ligands for the treatment of breast cancer.

Pioglitazone and rosiglitazone are thiazolidinediones used for the treatment of Type 2 diabetes mellitus. They modulate glucose and fat metabolism, mainly by binding to the nuclear hormone receptor peroxisome proliferator-activated receptor (PPAR)-gamma. PPAR-gamma signalling is involved in a number of other disease conditions including cancer. In breast cancer cells, PPAR-gamma ligands inhibit proliferation and induce apoptosis both in vitro and in vivo. PPAR-gamma ligands also inhibit tumour angiogenesis and invasion. The only published clinical trial using a PPAR-gamma ligand in patients with metastatic breast cancer failed to show any clinical benefits. The mechanism of action of the thiazolidinediones in breast cancer cells is not fully understood but involves interactions with other nuclear hormone receptors, transcriptional co-activators and repressors as well as PPAR-gamma-independent effects. A better understanding of these mechanisms will be needed before PPAR-gamma ligands may be useful in the treatment of breast cancer patients.

Ligands of peroxisome proliferator-activated receptor gamma induce apoptosis in multiple myeloma.

The activation of proliferator-activated receptor gamma (PPAR-gamma) by its natural and synthetic ligands induces apoptosis in several tumor cell lines, including malignant B-lineage cells. We investigated whether treatment with pioglitazone (PGZ), rosiglitazone (RGZ) or 15-deoxy-Delta12,14-prostaglandin J2 (15d-PGJ2) inhibited tumor cell growth in five human multiple myeloma cell lines (LP-1, U-266, RPMI-8226-S, OPM-2 and IM-9) and human bone marrow myeloma cells expressing PPAR-gamma protein. MTT assays revealed growth arrest induced by the natural activator of PPAR-gamma 15d-PGJ2 and a lower antiproliferative effect with thiazolidinediones (PGZ and RGZ) in a dose-dependent manner. Induction of apoptosis was indicated by Annexin-V staining. At a dose of 50 microM, 15d-PGJ2 led to a high rate of apoptosis in all cell lines (60-92%). Furthermore, induction of apoptosis in sorted bone marrow plasma cells from myeloma patients was detected. Thiazolidinediones comprise anti-myeloma activity in vitro and should be explored further for the treatment of multiple myeloma.

Peroxisome proliferator-activated receptor gamma and retinoid X receptor ligands are potent inducers of differentiation and apoptosis in leukemias.

The peroxisome proliferator-activated receptor gamma (PPAR gamma) is a member of the nuclear receptor family that forms heterodimers with retinoid X receptor. These heterodimers bind to DNA and activate the transcription of target genes. Here, we report that the PPAR gamma receptor protein is expressed in primary myeloid and lymphoid leukemias and in lymphoma and myeloma cell lines. In this study, we compared the activity of several PPAR gamma ligands including BRL49653 (rosiglitazone), 15-deoxy-Delta 12,14-prostaglandin J(2), and the novel triterpenoid 2-cyano-3,12-dioxooleana-1,9-dien-28-oic acid on leukemia cells. Exposure to these PPAR gamma ligands induced apoptosis in myeloid (U937 and HL-60) and lymphoid (Su-DHL, Sup-M2, Ramos, Raji, Hodgkin's cell lines, and primary chronic lymphocytic leukemia) cells. A similar exposure to these PPAR gamma ligands induced the differentiation of myeloid leukemic cells. A combination of PPAR gamma ligands with a retinoid X receptor agonist (i.e., LG100268) or a retinoic acid receptor agonist (i.e., all trans-retinoic acid) enhanced differentiating and growth-inhibitory effects. 2-Cyano-3,12-dioxooleana-1,9-dien-28-oic acid induced differentiation and apoptosis with much greater potency than the other PPAR gamma ligands in established cell lines and primary chronic lymphocytic leukemia samples. Exposure to 2-cyano-3,12-dioxooleana-1,9-dien-28-oic acid induced mitochondrial depolarization and caspase activation, which was associated with apoptosis induction. In Bcl-2-overexpressing chronic lymphocytic leukemia cells, the small-molecule Bcl-2 inhibitor HA14-1 sensitized these cells to 2-cyano-3,12-dioxooleana-1,9-dien-28-oic acid-induced apoptosis. These results suggest that PPAR gamma ligation alone and in combination with retinoids holds promise as novel therapy for leukemias by activating the transcriptional activity of target genes that control apoptosis and differentiation in leukemias.

A novel PPAR alpha/gamma dual agonist inhibits cell growth and induces apoptosis in human glioblastoma T98G cells.

AIM: To examine the effect of a novel peroxisome proliferator-activated receptor (PPAR) alpha/gamma dual agonist TZD18 on cell proliferation and apoptosis in human glioblastoma T98G cells and its possible mechanism. METHODS: RT-PCR, MTT, TUNEL, Flow cytometry, and Western blot analysis were employed. RESULTS: TZD18 inhibited the growth of T98G cells in a concentration-dependent manner, which was associated with a G1 to S cell cycle arrest. Besides, significant apoptosis was induced after treatment with a non-toxic dose of TZD18. During the process, the expression of Bcl-2 protein was down-regulated, while that of Bax and p27kip proteins was up-regulated, and the activity of caspase-3 was elevated. However, this effect appeared to be PPARalpha and PPARgamma independent since their antagonists could not reverse this effect. CONCLUSIONS: TZD18, a novel PPARalpha/gamma dual agonist, inhibited cell growth and induce apoptosis in human glioblastoma T98G cells in vitro, indicating a therapeutic potential for TZD18 in the treatment of glioblastoma.

Somatic mutations in peroxisome proliferator-activated receptor-gamma are rare events in human cancer cells.

BACKGROUND: Peroxisome proliferator-activated receptor-gamma (PPAR-gamma) is a nuclear hormone receptor activated after binding a lipophilic ligand, such as naturally occurring 15dPGJ2. There is striking evidence that PPAR-gamma activation leads not only to an increase in insulin sensitivity, but also to tumor cell apoptosis and cell cycle arrest. A growing number of diabetes mellitus II patients currently benefit from treatment with synthetic PPAR-gamma agonists, the thiazolidinediones (TZDs), which sensitize peripheral cells towards insulin. Furthermore, some TZDs are undergoing clinical investigations for the treatment of malignant diseases. Therefore, detailed information on the frequency of genetic alterations of PPAR-gamma in malignant tumor cells is necessary. MATERIAL/METHODS: PPAR-gamma DNA of 33 histologically different tumor cells was isolated, purified, and all coding regions were separately amplified by PCR. The coding exons were then analyzed by single-stranded conformational polymorphism (SSCP) and bidirectional DNA sequencing. RESULTS: In five breast cancer brain metastasis samples from patients and 28 cancer cell lines derived from lymphoma, glioblastoma, and breast carcinoma we found only one coding region shift in exon 5b of the glioblastoma U373 DNA. This silent mutation does not lead to a change in amino acid alignment. No further polymorphisms, including those which have already been described, could be detected in any other sample. CONCLUSIONS: We conclude that somatic mutations in the PPAR gene are exceedingly rare events in malignant tumor cells. This makes PPAR-gamma more unlikely to act as a tumor suppressor gene, making it a stable and suitable target for TZD biological cancer therapy.

Peroxisome proliferator-activated receptor gamma ligands induce growth inhibition and apoptosis of human B lymphocytic leukemia.

This study examined the expression and structural intactness of peroxisome proliferator-activated receptor gamma (PPARgamma) in human acute lymphocytic leukemia (ALL) cells and determined the effect of PPARgamma ligands on growth and apoptosis of these cells. We noted that all lymphocytic leukemia cell lines expressed PPARgamma and no PPARgamma mutations were found in these cell lines as indicated by SSCP analysis. Effect of the PPARgamma ligands on the proliferation, differentiation and apoptosis of B type ALL cells was further examined. Treatment of these cells with the PPARgamma ligands Pioglitazone (PGZ) and 15-deoxy-delta (12,14)-prostaglandin J2 (15d-PGJ2) resulted in growth inhibition in a dose-dependent manner which was associated with a G1 to S cell cycle arrest. However, this effect appeared to be PPARgamma-independent since several PPARgamma antagonists could not reverse this effect. No differentiation was induced by this treatment. Four out of five cell lines underwent apoptosis after culture with the PPARgamma ligands. This effect was partially caspase-dependent because a pan-caspase inhibitor partially reversed this effect. In conclusion, our results suggest that PPARgamma ligands may offer a new therapeutic approach to aid in the treatment of ALL.

Ligands for PPARgamma and RAR cause induction of growth inhibition and apoptosis in human glioblastomas.

High-grade gliomas are characterized by a rapid proliferation rate, invasiveness and angiogenesis. Our previous data indicated that the combination of ligands for peroxisome proliferator-activated receptor gamma (PPARgamma) and retinoic acid receptor (RAR) induces apoptosis of breast cancer cells in vitro and in a murine model. In this study, we have shown that 11 glioblastoma cell lines and nine fresh glioblastoma tissue samples from patients expressed high-levels of PPARgamma. In contrast, glia from nine healthy human brains expressed very low levels of PPARgamma. No mutations or polymorphisms of the PPARgamma gene were observed in these cell lines. The effect of the PPARgamma ligand Pioglitazone (PGZ) either in the absence or in the presence of a RAR ligand [all-trans retinoic acid (ATRA)] on the proliferation and apoptosis of glioblastoma cells was examined using two glioblastoma cell lines (N39 and DBTRG05MG). PGZ and/or ATRA inhibited significantly the proliferation of both cell lines. Flow cytometry analysis showed that G1 cell cycle arrest was induced by these ligands. In addition, apoptosis occurred in both cell lines treated with either PGZ or ATRA, which was associated with a downregulation of bcl-2 and an upregulation of bax proteins. An enhanced effect was observed when PGZ and ATRA were combined. Furthermore, treatment of fresh glioblastoma tissue from patients with PGZ, either alone or in combination with ATRA, induced a significant level of tumor cell apoptosis together with a downregulation of bcl-2 protein level as compared with untreated control brain tissue. Taken together, our data demonstrated that PGZ, either alone or in combination with ATRA, induced apoptosis and inhibited proliferation of glioblastoma cells, and more interestingly, induced apoptosis of fresh glioblastoma cells from patients. Therefore, we conclude that these ligands may possess adjuvant therapeutic potential for patients with glioblastoma.