Radiation enhances the invasion abilities of pulmonary adenocarcinoma cells via STAT3

Crosstalk between CXCL12/CXCR4/ACKR3 and the STAT3 Pathway

The reciprocal modulation between the CXCL12/CXCR4/ACKR3 axis and the STAT3 signaling pathway plays a crucial role in the progression of various diseases and neoplasms. Activation of the CXCL12/CXCR4/ACKR3 axis triggers the STAT3 pathway through multiple mechanisms, while the STAT3 pathway also regulates the expression of CXCL12. This review offers a thorough and systematic analysis of the reciprocal regulatory mechanisms between the CXCL12/CXCR4/ACKR3 signaling axis and the STAT3 signaling pathway in the context of diseases, particularly tumors. It explores the potential clinical applications in tumor treatment, highlighting possible therapeutic targets and novel strategies for targeted tumor therapy.

ABT-737, a BH3 Mimetic, Enhances the Therapeutic Effects of Ionizing Radiation in K-ras Mutant Non-Small Cell Lung Cancer Preclinical Model

PURPOSE

Tumor radioresistance and dose-limiting toxicity restrict the curative potential of radiotherapy, requiring novel approaches to overcome the limitations and augment the efficacy. Here, we investigated the effects of signal transducer and activator of transcription 3 (STAT3) activation and autophagy induction by irradiation on antiapoptotic proteins and the effectiveness of the BH3 mimetic ABT-737 as a radiosensitizer using K-ras mutant non-small cell lung cancer (NSCLC) cells and a Kras^G12D:p53^fl/fl mouse (KP mouse) model.

MATERIALS AND METHODS

A549 and H460 cells were irradiated, and the expression of Bcl-2 family proteins, JAK/STAT transcriptional pathway, and autophagic pathway were evaluated by immunoblotting. The radiosensitizing effects of ABT-737 were evaluated using A549 and H460 cell lines with clonogenic assays and also by a KP mouse model with microcomputed tomography and immunohistochemistry.

RESULTS

In A549 and H460 cells and mouse lung tissue, irradiation-induced overexpression of the antiapoptotic molecules Bcl-xL, Bcl-2, Bcl-w, and Mcl-1 through JAK/STAT transcriptional signaling induced dysfunction of the autophagic pathway. After treatment with ABT-737 and exposure to irradiation, the number of surviving clones in the cotreatment group was significantly lower than that in the group treated with radiation or ABT-737 alone. In the KP mouse lung cancer model, cotreatment with ABT-737 and radiation-induced significant tumor regression; however, body weight changes in the combination group were not significantly different, suggesting that combination treatment did not cause systemic toxicity.

CONCLUSION

These findings supported the radiosensitizing activity of ABT-737 in preclinical models, and suggested that clinical trials using this strategy may be beneficial in K-ras mutant NSCLC.

CXCR7 silencing inhibits the migration and invasion of human tumor endothelial cells derived from hepatocellular carcinoma by suppressing STAT3

C-X-C chemokine receptor type 7 (CXCR7) is reported to be overexpressed in tumor endothelial cells (TECs), which are the primary target cells of antivascular chemotherapy. However, the role of CXCR7 in TECs is not fully understood. In the present study, CXCR7 expression was inhibited in TECs derived from hepatocellular carcinoma (HCC) using short hairpin (sh)RNA plasmids to investigate the role of CXCR7 in the regulation of migration and invasion of TECs as well as its underlying mechanisms. The data showed that the downregulation of CXCR7 significantly inhibited the migration and invasion of TECs. Further study showed that silencing CXCR7 resulted in decreased phosphorylated signal transducer and activator of transcription 3 (STAT3) at Tyr705 and its downstream target genes in TECs, including matrix metalloproteinase‑2 (MMP2) and vascular endothelial growth factor (VEGF). However, restoring STAT3 phosphorylation abolished the CXCR7‑shRNA‑induced decrease in TECs migration and invasion, as well as the downregulation of MMP2 and VEGF in TECs. These findings indicate that CXCR7 may regulate the migration and invasion of TECs derived from HCC via the STAT3 signaling pathway and that CXCR7 could be a potential target for the antivascular therapy of HCC.

Impact of STAT3 phosphorylation in glioblastoma stem cells radiosensitization and patient outcome

Glioblastoma (GBM) represents the most common and lethal primary malignant brain tumor. The standard treatment for glioblastoma patients involves surgical resection with concomitant radio and chemotherapy. Despite today’s clinical protocol, the prognosis for patients remains very poor with a median survival of 15 months. Tumor resistance and recurrence is strongly correlated with a subpopulation of highly radioresistant and invasive cells termed Glioblastoma Stem Cells (GSCs). The transcription factor STAT3 has been found to be constitutively activated in different tumors including GBM and enhanced tumor radioresistance. In this study, we assessed radiosensitization of GSC lines isolated from patients by inhibition of STAT3 activation using Stattic or WP1066. We showed that inhibitor treatment before cell irradiation decreased the surviving fraction of GSCs suggesting that STAT3 inhibition could potentiate radiation effects. Finally, we investigated STAT3 activation status on 61 GBM clinical samples and found a preferential phosphorylation of STAT3 on Serine727 (pS727). Moreover, we found that pS727 was associated with a significant lower overall patient survival and progression-free survival but not pY705. Taken together, our results suggest that pS727-STAT3 could be a potential prognostic marker and could constitute a therapeutic target to sensitize highly radioresistant GSCs.

Autophagy Promotes the Repair of Radiation-Induced DNA Damage in Bone Marrow Hematopoietic Cells via Enhanced STAT3 Signaling

Autophagy protects hematopoietic cells from radiation damage in part by promoting DNA damage repair. However, the molecular mechanisms by which autophagy regulates DNA damage repair remain largely elusive. Here, we report that this radioprotective effect of autophagy depends on STAT3 signaling in murine bone marrow mononuclear cells (BM-MNCs). Specifically, we found that STAT3 activation and nuclear translocation in BM-MNCs were increased by activation of autophagy with an mTOR inhibitor and decreased by knockout of the autophagy gene Atg7. The autophagic regulation of STAT3 activation is likely mediated by induction of KAP1 degradation, because we showed that KAP1 directly interacted with STAT3 in the cytoplasm and knockdown of KAP1 increased the phosphorylation and nuclear translocation of STAT3. Subsequently, activated STAT3 transcriptionally upregulated the expression of BRCA1, which increased the ability of BM-MNCs to repair radiation-induced DNA damage. This novel finding that activation of autophagy can promote DNA damage repair in BM-MNCs via the ATG-KAP1-STAT3-BRCA1 pathway suggests that autophagy plays an important role in maintaining genomic integrity of BM-MNCs and its activation may confer protection of BM-MNCs against radiation-induced genotoxic stress.

A sorafenib derivative and novel SHP-1 agonist, SC-59, acts synergistically with radiotherapy in hepatocellular carcinoma cells through inhibition of STAT3

Radiotherapy shows limited benefit as treatment for hepatocellular carcinoma (HCC). In this study, we aimed to overcome the radioresistance of HCC by using a novel sorafenib derivative, SC-59 that targets SHP-1-related signaling. HCC cell lines (SK-Hep1, Hep3B, and Huh7) were treated with sorafenib, SC-59, radiation, sorafenib plus radiation, or SC-59 plus radiation, and then apoptosis, colony formation, signal transduction and the phosphatase activity were analyzed. The synergistic effect of radiotherapy and SC-59 was analyzed using a combination index (CI) approach. In vivo efficacy was determined in a Huh7-bearing subcutaneous model. Mice were treated with radiation (5 Gy, one fraction per day) for 4 days, SC-59 (10mg/kg/day) for 24 days, or a combination. Tumor samples were further analyzed for p-STAT3 and SHP-1 activity. SC-59 displayed a better synergistic effect when used in combination with radiotherapy than sorafenib in HCC cell lines. SC-59 downregulated p-STAT3 and its downstream targets and increased SHP-1 phosphatase activity. Both ectopic STAT3 and inhibition of SHP-1 abolished SC-59-induced radiosensitization. Moreover, SC-59 significantly synergized radiotherapy in a Huh7 xenograft model by targeting SHP-1/STAT3 signaling. The novel sorafenib derivative, SC-59, acting as a SHP-1 agonist, displays a better synergistic effect when used in combination with radiotherapy than sorafenib for the treatment of HCC. Further clinical investigation is warranted.