Inhibition of Stat3 increases doxorubicin sensitivity in a human metastatic breast cancer cell line

B7-H3 silencing increases paclitaxel sensitivity by abrogating Jak2/Stat3 phosphorylation

In many types of cancer, the expression of the immunoregulatory protein B7-H3 has been associated with poor prognosis. Previously, we observed a link between B7-H3 and tumor cell migration and invasion, and in present study, we have investigated the role of B7-H3 in chemoresistance in breast cancer. We observed that silencing of B7-H3, via stable short hairpin RNA or transient short interfering RNA transfection, increased the sensitivity of multiple human breast cancer cell lines to paclitaxel as a result of enhanced drug-induced apoptosis. Overexpression of B7-H3 made the cancer cells more resistant to the drug. Next, we investigated the mechanisms behind B7-H3-mediated paclitaxel resistance and found that the level of Stat3 Tyr705 phosphorylation was decreased in B7-H3 knockdown cells along with the expression of its direct downstream targets Mcl-1 and survivin. The phosphorylation of Janus kinase 2 (Jak2), an upstream molecule of Stat3, was also significantly decreased. In contrast, reexpression of B7-H3 in B7-H3 knockdown and low B7-H3 expressing cells increased the phosphorylation of Jak2 and Stat3. In vivo animal experiments showed that B7-H3 knockdown tumors displayed a slower growth rate than the control xenografts. Importantly, paclitaxel treatment showed a strong antitumor activity in the mice with B7-H3 knockdown tumors, but only a marginal effect in the control group. Taken together, our data show that in breast cancer cells, B7-H3 induces paclitaxel resistance, at least partially by interfering with Jak2/Stat3 pathway. These results provide novel insight into the function of B7-H3 and encourage the design and testing of approaches targeting this protein and its partners.

STAT3 modulates the DNA damage response pathway

The STAT3 transcription factor is well known to function as an anti-apoptotic factor, especially in numerous malignancies. Recently we showed that STAT3 is cytoprotective and that cells lacking STAT3 are more sensitive to oxidative stress. A key feature of oxidative stress involves activation of the DNA damage pathway. However, a role for STAT3 or its contribution in response to DNA damage has not been described. In the present study we show that cells lacking STAT3 are less efficient in repairing damaged DNA. Moreover, STAT3 deficient cells show reduced activity of the ATM-Chk2 and ATR-Chk1 pathways, both important pathways in sensing DNA damage. Finally we show that MDC1, a regulator of the ATM-Chk2 pathway and facilitator of the DNA damage response, is modulated by STAT3 at the transcriptional level. These findings demonstrate that STAT3 is necessary for efficient repair of damaged DNA, partly by modulating the ATM-Chk2 and ATR-Chk1 pathways.

Inhibition of the JAK-STAT3 pathway by andrographolide enhances chemosensitivity of cancer cells to doxorubicin

Andrographolide (Andro), a diterpenoid lactone isolated from a traditional herbal medicine Andrographis paniculata, is known to possess potent anti-inflammatory and anticancer properties. In this study, we sought to examine the effect of Andro on signal transducer and activator of transcription 3 (STAT3) pathway and evaluate whether suppression of STAT3 activity by Andro could sensitize cancer cells to a chemotherapeutic drug doxorubicin. First, we demonstrated that Andro is able to significantly suppress both constitutively activated and IL-6-induced STAT3 phosphorylation and subsequent nuclear translocation in cancer cells. Such inhibition is found to be achieved through suppression of Janus-activated kinase (JAK)1/2 and interaction between STAT3 and gp130. For understanding the biological significance of the inhibitory effect of Andro on STAT3, we next investigated the effect of Andro on doxorubicin-induced apoptosis in human cancer cells. In our study the constitutive activation level of STAT3 was found to be correlated to the resistance of cancer cells to doxorubicin-induced apoptosis. Both the short-term MTT assay and the long-term colony formation assay showed that Andro dramatically promoted doxorubicin-induced cell death in cancer cells, indicating that Andro enhances the sensitivity of cancer cells to doxorubicin mainly via STAT3 suppression. These observations thus reveal a novel anticancer function of Andro and suggest a potential therapeutic strategy of using Andro in combination with chemotherapeutic agents for treatment of cancer.

Jnk signaling pathway-mediated regulation of Stat3 activation is linked to the development of doxorubicin resistance in cancer cell lines

We sought to identify altered transcription factors (Stat, AP1, and NF-kB) or signal proteins (Erk1/2, p38, Akt, Jnk, Jak, and c-Src) in cancer cell lines whose growth was arrested by doxorubicin (DOX) treatment. Jnk1 was the only signal protein to be activated. DOX increased Stat3 phosphorylation, nuclear localization, and transcriptional activity. Jnk1 activation appeared to be required for Stat3 activity. Stat3 activity via the Jnk pathway was conserved in other cell lines originating from other organs. Transcriptional activity of Stat3 was increased in cells surviving DOX treatment suggesting that Stat3 activation contributed to the resistance to cytotoxicity. To better understand the role of Stat3 in Jnk1 activation, we investigated its effect on the viability of DOX-treated cells. Co-treatment with DOX and Jnk inhibitor negatively correlated with the viability of cancer cells and reduced Stat3 activity. Taken together, these results indicate that Stat3 activation via the Jnk pathway promotes the resistance of cancer cells to DOX.

The Src inhibitor AZD0530 blocks invasion and may act as a radiosensitizer in lung cancer cells

BACKGROUND

With the emergence of Src inhibitors in clinical trials, improved knowledge of the molecular responses of cancer cells to these agents is warranted. This will facilitate the development of tests to identify patients who may benefit from these agents, allow drug activity to be monitored and rationalize the combination of these agents with other treatment modalities.

METHODS

This study evaluated the molecular and functional effects of Src inhibitor AZD0530 in human lung cancer cells, by Western blotting and reverse transcription-polymerase chain reaction, and by assays for cell viability, migration, and invasion.

RESULTS

Src was activated in four of five cell lines tested and the level corresponded with the invasive potential and the histologic subtype. Clinically relevant, submicromolar concentrations of AZD0530 blocked Src and focal adhesion kinase, resulting in significant inhibition of cell migration and Matrigel invasion. Reactivation of STAT3 and up-regulation of JAK indicated a potential mechanism of resistance. AZD0530 gave a potent and sustained blockage of AKT and enhanced the sensitivity to irradiation.

CONCLUSIONS

The results indicated that AZD0530, aside from being a potent inhibitor of tumor cell invasion which could translate to inhibition of disease progression in the clinic, may also lower resistance of lung cancer cells to pro-apoptotic signals.

STAT3 regulation of glioblastoma pathogenesis

Malignant gliomas are the most common primary brain tumors. Despite efforts to find effective treatments, these tumors remain incurable. The failure of malignant gliomas to respond to conventional cancer therapies may reflect the unique biology of these tumors, underscoring the need for new approaches in their investigation. Recently, progress has been made in characterization of the molecular pathogenesis of glioblastoma using a developmental neurobiological perspective, by exploring the role of signaling pathways that control the differentiation of neural stem cells along the glial lineage. The transcription factor STAT3, which has an established function in neural stem cell and astrocyte development, has been found to play dual tumor suppressive and oncogenic roles in glial malignancy depending on the mutational profile of the tumor. These findings establish a novel developmental paradigm in the study of glioblastoma pathogenesis and provide the rationale for patient-tailored therapy in the treatment of this devastating disease.

Results of a phase II open-label, nonrandomized trial of oral satraplatin in patients with metastatic breast cancer

Cisplatin and carboplatin have antitumor activity in breast cancer. Satraplatin, an orally bioavailable platinum analog, offers a potential alternative to intravenous chemotherapy. We conducted a multicenter phase II study of this agent as first- or second-line treatment of metastatic breast cancer. Satraplatin 80 mg/m(2) was taken PO Days 1-5 q 21 days in cycles 1 and 2, and if tolerated, increased to 100 mg/m(2) for subsequent cycles. Restaging studies to assess response were performed after every 2 cycles. Between November 2005 and March 2006, 40 patients were enrolled. Baseline characteristics: 48% prior adjuvant chemotherapy, 60% prior chemotherapy for MBC; median age, 62 years (ranges 43-83), 58% ER+/PR+, 23% ER+/PR-, 18% ER-/PR-/HER2-, and 5% HER2+. In 31 patients with measurable disease, there were two partial responses (PR; 6%; 95% CI 0, 15.2); and four patients (13%) had SD > or =6 months for a clinical benefit rate of 19%. Among the subanalysis of seven triple-negative patients with measurable disease, there were 2 SD and 2 PD. Median survival was 15 months and median progression-free survival was 2.7 months. The most common grade 3-4 toxicities were neutropenia (28%) and thrombocytopenia (25%). AEs leading to treatment discontinuation were nausea (n = 3), thrombocytopenia (n = 3), fever (n = 2), and vomiting (n = 2). This phase II study demonstrates oral satraplatin has limited activity as a single agent for MBC. Satraplatin, at a lower dose used in this study, could be combined with other chemotherapy agents in future trials in breast cancer.

Dehydrocostuslactone disrupts signal transducers and activators of transcription 3 through up-regulation of suppressor of cytokine signaling in breast cancer cells

This study investigates the anticancer effect of dehydrocostuslactone (DHE), a plant-derived sesquiterpene lactone, on human breast cancer cells. DHE inhibits cell proliferation by inducing cells to undergo cell cycle arrest and apoptosis. DHE suppresses the expression of cyclin D, cyclin A, cyclin-dependent kinase 2, and cdc25A and increases the amount of p53 and p21, resulting in G(0)/G(1)-S phase arrest in MCF-7 cells. In contrast, DHE caused S-G(2)/M arrest by increasing p21 expression and chk1 activation and inhibiting cyclin A, cyclin B, cdc25A, and cdc25C expression in MDA-MB-231 cells. DHE induces up-regulation of Bax and Bad, down-regulation of Bcl-2 and Bcl-XL, and nuclear relocation of the mitochondrial factors apoptosis-inducing factor and endonuclease G. We also found that DHE inhibits survival signaling through the Janus tyrosine kinase-signal transducer and activator of transcription-3 signaling by increasing the expression of suppressors of cytokine signaling (SOCS)-1 and SOCS-3. Reduction of SOCS-1 and SOCS-3 expression by small interfering RNA inhibits DHE-mediated signal transducer and activator of transcription-3 inhibition, p21 up-regulation, and cyclin-dependent kinase 2 blockade, supporting the hypothesis that DHE inhibits cell cycle progression and cell death through SOCS-1 and SOCS-3. Significantly, animal studies have revealed a 50% reduction in tumor volume after a 45-day treatment period. Taken together, this study provides new insights into the molecular mechanism of the DHE action that may contribute to the chemoprevention of breast cancer.

Phase II trial of tipifarnib plus neoadjuvant doxorubicin-cyclophosphamide in patients with clinical stage IIB-IIIC breast cancer

PURPOSE

Tipifarnib is a farnesyl transferase (FTase) inhibitor that has activity in metastatic breast cancer and enhances the efficacy of cytotoxic agents in preclinical models. We evaluated the biological effects of tipifarnib in primary breast cancers in vivo, whether adding tipifarnib to preoperative chemotherapy increased the pathologic complete response rate (pCR) at surgery, and determined whether biomarkers predictive of pCR could be identified.

EXPERIMENTAL DESIGN

Forty-four patients with stage IIB-IIIC breast cancer received up to four cycles of neoadjuvant doxorubicin-cyclophosphamide (AC) every 2 weeks plus tipifarnib and filgrastim followed by surgery. Enzymatic assays measuring FTase activity and Western blotting for phospho (p)-signal transducer and activator of transcription 3 (STAT3), phospho-extracellular signal-regulated kinase, p-AKT, and p27 were done in 11 patients who agreed to optional tissue biopsies before therapy and 2 hours after the final dose of tipifarnib during the first cycle, and predictive biomarkers were evaluated by immunohistochemistry in 33 patients. The trial was powered to detect an improvement in breast pCR rate of 10% or less expected for AC alone to 25% for AC-tipifarnib (alpha = 0.05, beta = 0.10).

RESULTS

Eleven patients had a breast pCR (25%; 95% confidence interval, 13-40%). FTase enzyme activity decreased in all patients (median, 91%; range, 24-100%) and p-STAT3 expression decreased in 7 of 9 (77%) patients. Low tumor Ki-67 expression (below the median of 60%) at baseline was significantly associated with resistance to therapy (P = 0.01).

CONCLUSION

Tipifarnib inhibits FTase activity in human breast tumors in vivo, is associated with down-regulation of p-STAT3, and enhances the breast pCR rate, thus meriting further evaluation.

Efficient killing of SW480 colon carcinoma cells by a signal transducer and activator of transcription (STAT) 3 hairpin decoy oligodeoxynucleotide--interference with interferon-gamma-STAT1-mediated killing

The signal transducers and activators of transcription (STATs) convey signals from the membrane to the nucleus in response to cytokines or growth factors. STAT3 is activated in response to cytokines involved mostly in cell proliferation; STAT1 is activated by cytokines, including interferon-gamma, involved in defence against pathogens and the inhibition of cell proliferation. STAT3, which is frequently activated in tumour cells, is a valuable target with respect to achieving inhibition of tumour cell proliferation. Indeed, its inhibition results in cell death. We previously observed that inhibition of the transcription factor nuclear factor-kappaB, a key regulator of cell proliferation, with decoy oligodeoxynucleotides results in cell death. We used a similar approach for STAT3. A hairpin STAT3 oligodeoxynucleotide was added to a colon carcinoma cell line in which it induced cell death as efficiently as the STAT3 inhibitor stattic. The hairpin STAT3 oligodeoxynucleotide co-localized with STAT3 within the cytoplasm, prevented STAT3 localization to the nucleus, blocked a cyclin D1 reporter promoter and associated with STAT3 in pull-down assays. However, the same cells were efficiently killed by interferon-gamma. This effect was counteracted by the STAT3 oligodeoxynucleotide, which was found to efficiently inhibit STAT1. Thus, although it can inhibit STAT3, the hairpin STAT3 oligodeoxynucleotide appears also to inhibit STAT1-mediated interferon-gamma cell killing, highlighting the need to optimize STAT3-targeting oligodeoxynucleotides.

Tpl-2/Cot and COX-2 in breast cancer

BACKGROUND

Breast cancer is the most common cancer in women worldwide and although mortality (129,000/year) stagnates, incidence (370,000/year) is increasing. In addition to histological type, grade, stage, hormonal and c-erbB2 status there is therefore a strong need for new and reliable prognostic and predictive factors.

METHODS AND RESULTS

This minireview focuses on two potential prognostic and predictive candidates Tpl2/Cot and COX-2 and summarise information about them.

CONCLUSION

Tumor progression locus 2 (Tpl2/Cot) is a serine/threonine protein kinase belonging to the family of MAP3 kinases. Activated Tpl2/Cot leads to induction of ERK1/2, JNK, NF-kappaB and p38MAPK pathways. The first study on Tpl2/Cot mRNA in breast cancer showed its increase in 40 % of cases of breast cancer but no available data exist on protein expression. Cyclo-oxygenase 2 (COX-2) is inducible by growth and inflammatory factors and contributes to the development of various tumours. Expression of COX-2 in breast cancer varied from 5-100 % in reviewed papers with significantly higher values in poorly differentiated tumours. Tpl2/Cot and COX-2 have their importance in different intracellular pathways and some of these are involved in cancer development. Briefly, the results from recent studies suggest that Tpl2/Cot and COX-2 could be prognostic factors in breast cancer.