Increased radiosensitivity by a combination of 9-cis-retinoic acid and interferon-y in breast cancer cells

Heparin-binding growth factor (HDGF) drives radioresistance in breast cancer by activating the STAT3 signaling pathway

Although reports implicate radioresistance as an important obstacle for the management of breast cancer, its molecular mechanism is elusive. Herein, we found that high HDGF levels are expressed significantly in breast cancer and exhibit a positive association with poor survival prognosis. Heparin-binding growth factor (HDGF) was upregulated in radioresistant breast cancer cells, however, its knockdown could reduce breast cancer radioresistant both in vitro and in vivo. Additionally, the binding of RXRα to HDGF promoter blocked HDGF transcriptional activity, consequently inhibiting breast cancer radioresistance. The enhanced radioresistant activity of HDGF is induced by TKT and STAT3, impacting the STAT3-Tyr705 and STAT3-Ser727 phosphorylation and STAT3 transcriptional activity. Notably, HDGF depletion renders radioresistant hypersensitive to the drug that targets STAT3 phosphorylation. This article demonstrates the novel function of HDGF as a promising molecular target for predicting radioresistance in breast cancer.

miR-191 promotes radiation resistance of prostate cancer through interaction with RXRA

Radiation therapy is a common treatment for prostate cancer, however recurrence remains a problem. MicroRNA expression is altered in prostate cancer and may promote therapy resistance. Through bioinformatic analyses of TCGA and CPC-GENE patient cohorts, we identified higher miR-191 expression in tumor versus normal tissue, and increased expression in higher Gleason scores. In vitro and in vivo experiments demonstrated that miR-191 overexpression promotes radiation survival, and contributes to a more aggressive phenotype. Retinoid X receptor alpha, RXRA, was discovered to be a novel target of miR-191, and knockdown recapitulated radioresistance. Furthermore, treatment of prostate cancer cells with the RXRA agonist 9-cis-retinoic acid restored radiosensitivity. Supporting this relationship, patients with high miR-191 and low RXRA abundance experienced quicker biochemical recurrence. Reduced RXRA translated to a higher risk of distant failure after radiotherapy. Notably, this miR-191/RXRA interaction was conserved in a novel primary cell line derived from radiorecurrent prostate cancer. Together, our findings demonstrate that miR-191 promotes prostate cancer survival after radiotherapy, and highlights retinoids as a potential option to improve radiotherapy response.

Retinoic acid induces apoptosis by a non-classical mechanism of ERK1/2 activation

Even though RA is involved in differentiation and apoptosis of normal and cancer cells, being sometimes used as adjuvant in chemotherapy, its mechanisms of action involve multiple overlapping pathways that still remain unclear. Recent studies point out that RA exerts rapid and non-genomic effects, which are independent of RAR/RXR-mediated gene transcription. In this work, we reported that RA treatment for 24 h decreases cell viability, induces apoptosis dependent on caspase-3 activation, and activates the transcription factor AP-1 in cultured Sertoli cells. Moreover, RA induced a rapid and non-classical stimulation of ERK1/2. ERK1/2 activation was mediated by MEK1/2, and the protein synthesis inhibitor cycloheximide did not alter the pattern of RA-induced ERK1/2 phosphorylation. Pharmacological inhibition of MEK1/2-ERK1/2 pathway with UO126 blocked caspase-3 activation, decreased AP-1 binding to DNA and inhibited apoptosis. Overall, our data suggest that a rapid and non-genomic effect of RA upon MEK1/2-ERK1/2 pathway leads to caspase-3 activation and caspase-3-dependent apoptosis in cultured Sertoli cells. The non-canonical RA signaling presented in this work evokes new perspectives of RA action, which may play an important role in mediating early biological effects of RA modulating cell death in normal and tumor cells.

Interferon-gamma mediated up-regulation of caspase-8 sensitizes medulloblastoma cells to radio- and chemotherapy

Loss of caspase-8 expression - which has been demonstrated in a subset of Medulloblastoma (MB) - might block important apoptotic signalling pathways and therefore contribute to treatment resistance. In this study, IFN-gamma mediated up-regulation of caspase-8 in human MB cells was found to result in chemosensitization to cisplatin, doxorubicin and etoposide, and sensitisation to radiation. These effects were more prominent in D425 and D341 MB cells (low basal caspase-8 expression) when compared to DAOY MB cells (high basal caspase-8 expression). IFN-gamma mediated chemosensitization and radiosensitization effects were reduced by treatment with the caspase-8 specific inhibitor z-IETD-fmk. Treatment of IFN-gamma resulted in activation of STAT1 in DAOY MB cells and to a lesser extent in D425, but not in D341, indicating that IFN-gamma acts in MB cells through STAT1-dependent and -independent signalling pathways. Taken together, our results demonstrate that IFN-gamma mediated restoration of caspase-8 in MB cells might enhance apoptotic pathways relevant to the response to chemo- and radiotherapy.

Synergistic induction of the MUC4 mucin gene by interferon-gamma and retinoic acid in human pancreatic tumour cells involves a reprogramming of signalling pathways

The transmembrane mucin, MUC4, is aberrantly expressed with a high incidence in human pancreatic adenocarcinomas and plays an important role in the pathogenesis of the disease. Our recent studies have shown that interferon-gamma (IFNgamma) and retinoic acid (RA) are important regulators of MUC4 in pancreatic tumour cells. Induction of MUC4 by IFNgamma occurs via a novel pathway involving upregulation of the signal transducer and activator of transcription 1 (STAT-1), whereas its stimulation by RA requires mediation by the transforming growth factor beta-2 (TGFbeta-2). In this study, we have investigated the molecular mechanisms underlying the interaction of IFNgamma and RA in MUC4 regulation in pancreatic tumour cells. We demonstrate that these reagents exert a synergistic induction of MUC4. Interestingly, while the upregulation of STAT-1 by IFNgamma is partially inhibited by RA, IFNgamma is shown to repress RA-driven TGFbeta-2 induction, pointing to the involvement of alternative mechanism(s) in IFNgamma-RA synergism. Moreover, a dose-dependent and cooperative induction of MUC4 promoter activity suggests a regulation at the transcriptional level, most likely by STAT-1 and RAR/RXR (RA receptor/retinoic X receptor) or other IFNgamma/RA-induced secondary intermediate effectors. Our findings provide potential mechanisms that may account for the aberrant expression of MUC4 in pancreatic tumour cells and expose a novel molecular mechanism of gene induction, whereby a reprogramming of signalling pathway through alternative route(s) operates during a synergistic interaction of biological modifiers.

Retinol measurements and retinoid receptor gene expression in patients with multiple sclerosis

Treatment with interferon (IFN)-beta1a has been associated with decreased disease activity in patients with multiple sclerosis (MS). In several biological systems, type 1 IFNs and retinoids have been demonstrated to have synergistic effects. In these studies, we measured blood and cerebrospinal fluid (CSF) retinol levels and naïve and memory T-helper cell subset percentages in samples from a group of patients with MS. We also examined retinol receptor expression in peripheral blood cells from MS patients with or without a history of prior treatment with IFN-beta1a. The mean plasma retinol level for untreated relapsing-remitting (RR) MS patients was lower than for patients with noninflammatory neurological disease. Among IFN-beta1a-treated RR patients, mean levels were slightly higher than for RR patients not on treatment Lower plasma retinol levels among the MS patents studied were associated with higher CSF retinol index measurements--a measure that was calculated to correct for nonspecific leakage of retinol from blood into CSF. Far the MS samples examined, there was a borderline statstically significant direct correlation between CSF retinol index measurements and CSF memory T-helper cell percentages. Examination of peripheral blood from untreated RR patents for retinoid receptor mRNA expression revealed the expression of the retinoic add receptor (RAR)-alpha, RAR-gamma, and retinoic X receptor (RXR)-alpha receptor subtypes. For RR patients on IFN-beta1a therapy, expression of the some RAR subtypes was noted as well as expression of RXR-beta and RXR-gamma. These studies suggest an association between plasma retinol levels and clincal disease activity in patents with MS and that treatment with IFN-beta1a may be associated with activation of specific retnoid receptor subtypes.

Enhancement of fractionated-dose irradiation by retinoic acid plus interferon

PURPOSE

To evaluate the relative cytotoxicity of fractionated-dose radiation in the presence and absence of 13-cis-retinoic acid (RA) plus alpha-2a-interferon (IFN), as a function of overall treatment time.

METHODS AND MATERIALS

Studies were performed with the human squamous cell carcinoma line FaDu, in vitro. Attached exponential phase cells were treated with RA + IFN for 8-10 h and then exposed to single graded doses of radiation, or 1 to 6 doses of radiation at 2 Gy per dose, or to 5 doses of radiation at 2 Gy/dose with a time interval of 4-24 h between treatments. Following irradiation, the cells were incubated with drugs present throughout colony formation, and the fraction of survivors in the presence and absence of the combined drugs was calculated.

RESULTS

For single graded-dose irradiation, the surviving fraction ratio at 2 Gy in the absence vs. presence of drugs was 1.27 +/- 0.19 in 3 repeat experiments. Following administration of 6 doses of radiation at 2 Gy/fraction with a 5-h time interval between treatments and, after correcting for cell proliferation between treatments, the surviving fractions differed by a factor of 3.25, again indicating an average difference in survival of 1.26 after each of the 6 2-Gy/fractions. Treatment with 5 2-Gy doses of irradiation with 24 vs. 4 h elapsing between doses, resulted in a 3-fold greater decrease in survival in the presence of drugs vs. no drug. The relatively greater cell kill due to 24 vs. 4 h between treatments was due to drug inhibition of cell proliferation between the more prolonged treatments.

CONCLUSIONS

The results of this study indicate that retinoic acid plus interferon both sensitizes and inhibits cell proliferation during treatment. These results suggest that this combination of radiation and drugs, when used concurrently, may be effective for inhibiting tumor cell proliferation or accelerated repopulation during clinical fractionated radiotherapy.

Interferon-gamma (IFN-gamma) as a potential radio- and chemo-protectant

Interferons (IFN) have had increasing clinical usage in the treatment of a variety of disorders, at times being used in combination with chemo- or radiotherapy. However, interferons may have inhibitory effects on hematopoietic stem cell proliferation and the effects of this cytokine's use on long-term hematologic function have not been studied. We performed the competitive repopulation assay in the murine system, using cells exposed to irradiation or single-dose chemotherapy with or without concomitant IFN-gamma use. IFN-gamma alone had no deleterious effects on hematopoietic stem cell productivity. We measured the repopulating ability of exhaustible multilineage precursors that were present at early stages of marrow repopulation after competitive repopulation (30 days). These progenitors were minimally impacted by cyclophosphamide (CTX) with or without IFN-gamma. Irradiation (XRT) and CTX alone produced significant repopulating defects in the most primitive hematopoietic stem cell, PHSC. Addition of IFN to either treatment regimen resulted in protection of PHSC, with improved repopulating ability, although the levels of donor marrow reached control levels only when CTX and IFN were used together. The results of multiple use of IFN with chemotherapy must be studied further, but IFN may offer hematologic radio- and chemoprotection, in addition to its antitumor properties in clinical protocols for treatment of cancers.