Targeting PAK4 Inhibits Ras-Mediated Signaling and Multiple Oncogenic Pathways in High-Risk Rhabdomyosarcoma.

Rhabdomyosarcoma (RMS) is the most prevalent pediatric soft-tissue sarcoma. Multimodal treatment, including surgery and traditional chemotherapy with radiotherapy, has contributed to improvements in overall survival rates. However, patients with recurrent or metastatic disease have 5-year survival rates of less than 30%. One reason for the lack of therapeutic advancement is identification and targeting of critical signaling nodes. p21-activated kinases (PAK) are a family of serine/threonine kinases downstream of multiple critical tumorigenic receptor tyrosine kinase receptors and oncogenic regulators, including IGFR and RAS signaling, that significantly contribute to aggressive malignant phenotypes. Here, we report that RMS cell lines and tumors exhibit enhanced PAK4 expression levels and activity, which are further activated by growth factors involved in RMS development. Molecular perturbation of PAK4 in multiple RMS models in vitro and in vivo resulted in inhibition of RMS development and progression. Fusion-positive and -negative RMS models were sensitive to two PAK4 small-molecule inhibitors, PF-3758309 and KPT-9274, which elicited significant antitumor and antimetastatic potential in several primary and metastatic in vivo models, including a relapsed RMS patient-derived xenograft model. Transcriptomic analysis of PAK4-targeted tumors revealed inhibition of the RAS-GTPase, Hedgehog, and Notch pathways, along with evidence of activation of antitumor immune response signatures. This PAK4-targeting gene signature showed prognostic significance for patients with sarcoma. Overall, our results show for the first time that PAK4 is a novel and viable therapeutic target for the treatment of high-risk RMS. SIGNIFICANCE: These data demonstrate a novel oncogenic role for PAK4 in rhabdomyosarcoma and show that targeting PAK4 activity is a promising viable therapeutic option for advanced rhabdomyosarcoma.

Transglutaminase-2 promotes metastatic and stem-like phenotypes in osteosarcoma.

Osteosarcoma (OS) is a highly aggressive mesenchymal malignancy and the most common primary bone tumor in the pediatric population. OS frequently presents with or develops distal metastases. Patients with metastatic disease have extremely poor survival rates, thus necessitating improved molecular insights into OS metastatic biology. Utilizing our previously characterized genetically engineered mouse model (GEMM) of metastatic OS, we identified enhanced differential expression of Transglutaminase-2 (TGM2) in metastatic OS. However, the role of TGM2 in sarcoma development and metastatic progression remains largely undefined. To further investigate the role of TGM2 in OS metastasis, we performed both gain- and loss-of-function studies for TGM2 in human and mouse OS cell lines. Our data provide evidence that enhanced expression of TGM2 in metastatic OS contributes to migratory and invasive phenotypes. Besides the effects on metastatic phenotypes, we also observed that TGM2 contributes to OS stem-like properties. In addition, treatment with transglutaminase inhibitors had analogous effects on proliferation and migration to TGM2 knockdown. Finally, in vivo xenograft studies demonstrated that TGM2 functionally alters metastatic potential and survival outcome. Together, these data highlight TGM2 as a pro-metastatic factor in OS and a potential avenue for future therapeutic intervention to inhibit metastatic disease.

Enhanced inflammation and attenuated tumor suppressor pathways are associated with oncogene-induced lung tumors in aged mice.

Aging is often accompanied by a dramatic increase in cancer susceptibility. To gain insights into how aging affects tumor susceptibility, we generated a conditional mouse model in which oncogenic KrasG12D was activated specifically in lungs of young (3-5 months) and old (19-24 months) mice. Activation of KrasG12D in old mice resulted in shorter survival and development of higher-grade lung tumors. Six weeks after KrasG12D activation, old lung tissues contained higher numbers of adenomas than their young tissue counterparts. Lung tumors in old mice displayed higher proliferation rates, as well as attenuated DNA damage and p53 tumor suppressor responses. Gene expression comparison of lung tumors from young and old mice revealed upregulation of extracellular matrix-related genes in young tumors, indicative of a robust cancer-associated fibroblast response. In old tumors, numerous inflammation-related genes such as Ccl7, IL-1ß, Cxcr6, and IL-15ra were consistently upregulated. Increased numbers of immune cells were localized around the periphery of lung adenomas from old mice. Our experiments indicate that more aggressive lung tumor formation in older KrasG12D mice may be in part the result of subdued tumor suppressor and DNA damage responses, an enhanced inflammatory milieu, and a more accommodating tissue microenvironment.

Cross-species identification of a plasma microRNA signature for detection, therapeutic monitoring, and prognosis in osteosarcoma.

Osteosarcoma (OS) is the primary bone tumor in children and young adults. Currently, there are no reliable, noninvasive biologic markers to detect the presence or progression of disease, assess therapy response, or provide upfront prognostic insights. MicroRNAs (miRNAs) are evolutionarily conserved, stable, small noncoding RNA molecules that are key posttranscriptional regulators and are ideal candidates for circulating biomarker development due to their stability in plasma, ease of isolation, and the unique expressions associated with specific disease states. Using a qPCR-based platform that analyzes more than 750 miRNAs, we analyzed control and diseased-associated plasma from a genetically engineered mouse model of OS to identify a profile of four plasma miRNAs. Subsequent analysis of 40 human patient samples corroborated these results. We also identified disease-specific endogenous reference plasma miRNAs for mouse and human studies. Specifically, we observed plasma miR-205-5p was decreased 2.68-fold in mice with OS compared to control mice, whereas, miR-214, and miR-335-5p were increased 2.37- and 2.69-fold, respectively. In human samples, the same profile was seen with miR-205-5p decreased 1.75-fold in patients with OS, whereas miR-574-3p, miR-214, and miR-335-5p were increased 3.16-, 8.31- and 2.52-fold, respectively, compared to healthy controls. Furthermore, low plasma levels of miR-214 in metastatic patients at time of diagnosis conveyed a significantly better overall survival. This is the first study to identify plasma miRNAs that could be used to prospectively identify disease, potentially monitor therapeutic efficacy and have prognostic implications for OS patients.

Mouse tissues that undergo neoplastic progression after K-Ras activation are distinguished by nuclear translocation of phospho-Erk1/2 and robust tumor suppressor responses.

Mutation of K-Ras is a frequent oncogenic event in human cancers, particularly cancers of lungs, pancreas, and colon. It remains unclear why some tissues are more susceptible to Ras-induced transformation than others. Here, we globally activated a mutant oncogenic K-Ras allele (K-Ras(G12D)) in mice and examined the tissue-specific effects of this activation on cancer pathobiology, Ras signaling, tumor suppressor, DNA damage, and inflammatory responses. Within 5 to 6 weeks of oncogenic Ras activation, mice develop oral and gastric papillomas, lung adenomas, and hematopoietic hyperproliferation and turn moribund. The oral, gastric, and lung premalignant lesions display activated extracellular signal-regulated kinases (Erk)1/2 and NF-κB signaling as well as activated tumor suppressor and DNA damage responses. Other organs such as pancreas, liver, and small intestine do not exhibit neoplastic progression within 6 weeks following K-Ras(G12D) activation and do not show a potent tumor suppressor response. Even though robust Erk1/2 signaling is activated in all the tissues examined, the pErk1/2 distribution remains largely cytoplasmic in K-Ras(G12D)-refractory tissues (pancreas, liver, and intestines) as opposed to a predominantly nuclear localization in K-Ras(G12D)-induced neoplasms of lung, oral, and gastric mucosa. The downstream targets of Ras signaling, pElk-1 and c-Myc, are elevated in K-Ras(G12D)-induced neoplastic lesions but not in K-Ras(G12D)-refractory tissues. We propose that oncogenic K-Ras-refractory tissues delay oncogenic progression by spatially limiting the efficacy of Ras/Raf/Erk1/2 signaling, whereas K-Ras-responsive tissues exhibit activated Ras/Raf/Erk1/2 signaling, rapidly form premalignant tumors, and activate potent antitumor responses that effectively prevent further malignant progression.