PF-06409577 Activates AMPK Signaling and Inhibits Osteosarcoma Cell Growth

Autophagy Modulation as a Potential Therapeutic Strategy in Osteosarcoma: Current Insights and Future Perspectives

Autophagy, the process that enables the recycling and degradation of cellular components, is essential for homeostasis, which occurs in response to various types of stress. Autophagy plays an important role in the genesis and evolution of osteosarcoma (OS). The conventional treatment of OS has limitations and is not always effective at controlling the disease. Therefore, numerous researchers have analyzed how controlling autophagy could be used as a treatment or strategy to reverse resistance to therapy in OS. They highlight how the inhibition of autophagy improves the efficacy of chemotherapeutic treatments and how the promotion of autophagy could prove positive in OS therapy. The modulation of autophagy can also be directed against OS stem cells, improving treatment efficacy and preventing cancer recurrence. Despite promising findings, future studies are needed to elucidate the molecular mechanisms of autophagy and its relationship to OS, as well as the mechanisms underlying the functioning of autophagic modulators. Careful evaluation is required as autophagy modulation may have adverse effects on normal cells, and the optimization of autophagic modulators for use as drugs in OS is imperative.

HOXC13-driven TIMM13 overexpression promotes osteosarcoma cell growth

TIMM13 (translocase of inner mitochondrial membrane 13) located at the mitochondrial intermembrane space is vital for the integrity and function of mitochondria. We found that the mitochondrial protein TIMM13 is upregulated in human OS tissues and cells. In patient-derived primary OS cells and established cell lines, TIMM13 shRNA or knockout provoked mitochondrial dysfunction, causing mitochondrial depolarization, reactive oxygen species production, and oxidative injury, as well as lipid peroxidation, DNA damage, and ATP depletion. Moreover, TIMM13 depletion provoked OS cell apoptosis and inhibited cell proliferation and migration. Conversely, ectopic TIMM13 overexpression increased ATP contents, enhancing OS cell proliferation and migration. Moreover, we discovered that Akt-mTOR activation was inhibited with TIMM13 depletion in primary OS cells. Further studies revealed that HOXC13 (Homeobox C13)-dependent TIMM13 transcription was significantly increased in OS tissues and cells. Whereas TIMM13 transcription and expression were decreased following HOXC13 silencing in primary OS cells. In vivo, TIMM13 KO potently inhibited OS xenograft growth in the proximal tibia of nude mice. TIMM13 KO also induced Akt-mTOR inactivation, ATP depletion, oxidative injury, and apoptosis in the in situ OS tumors. Together, upregulation of the mitochondrial protein TIMM13 is important for OS cell growth, representing a novel and promising therapeutic target.

Triptonide Inhibits the Cervical Cancer Cell Growth via Downregulating the RTKs and Inactivating the Akt-mTOR Pathway

The high incidence and mortality of cervical cancer (CC) require an urgent need for exploring novel valuable therapeutics. Triptonide (TN) is a small molecule monomer extracted from the Chinese herb Tripterygium wilfordii Hook. Our results showed that TN, at only nanomolar concentrations, strongly inhibited growth, colony formation, proliferation, migration, and invasion of established and primary human cervical cancer cells. TN induced apoptosis and cell cycle arrest in cervical cancer cells. Moreover, cervical cancer cell in vitro migration and invasion were suppressed by TN. It was however noncytotoxic and proapoptotic to normal cervical epithelial cells and human skin fibroblast cells. Gene set enrichment analysis (GSEA) of RNA sequencing data of differentially expressed genes (DEGs) in TN-treated cervical cancer cells implied that DEGs were enriched in the receptor tyrosine kinase (RTK) signaling and PI3K-Akt-mTOR cascade. In cervical cancer cells, RTKs, including EGFR and PDGFRα, were significantly downregulated and Akt-mTOR activation was largely inhibited after TN treatment. In vivo, oral administration of TN significantly inhibited subcutaneous cervical cancer xenograft growth in nude mice. EGFR and PDGFRα downregulation as well as Akt-mTOR inactivation was detected in TN-treated HeLa xenograft tumor tissues. Thus, TN inhibits human cervical cancer cell growth in vitro and in vivo. Its anticervical cancer activity was associated with RTK downregulation and Akt-mTOR inactivation.

Adenosine monophosphate activated protein kinase contributes to skeletal muscle health through the control of mitochondrial function

Skeletal muscle is one of the largest organs in the body and the largest protein repository. Mitochondria are the main energy-producing organelles in cells and play an important role in skeletal muscle health and function. They participate in several biological processes related to skeletal muscle metabolism, growth, and regeneration. Adenosine monophosphate-activated protein kinase (AMPK) is a metabolic sensor and regulator of systemic energy balance. AMPK is involved in the control of energy metabolism by regulating many downstream targets. In this review, we propose that AMPK directly controls several facets of mitochondrial function, which in turn controls skeletal muscle metabolism and health. This review is divided into four parts. First, we summarize the properties of AMPK signal transduction and its upstream activators. Second, we discuss the role of mitochondria in myogenesis, muscle atrophy, regeneration post-injury of skeletal muscle cells. Third, we elaborate the effects of AMPK on mitochondrial biogenesis, fusion, fission and mitochondrial autophagy, and discuss how AMPK regulates the metabolism of skeletal muscle by regulating mitochondrial function. Finally, we discuss the effects of AMPK activators on muscle disease status. This review thus represents a foundation for understanding this biological process of mitochondrial dynamics regulated by AMPK in the metabolism of skeletal muscle. A better understanding of the role of AMPK on mitochondrial dynamic is essential to improve mitochondrial function, and hence promote skeletal muscle health and function.

PF-06409577 inhibits renal cyst progression by concurrently inhibiting the mTOR pathway and CFTR channel activity

Renal cyst development and expansion in autosomal dominant polycystic kidney disease (ADPKD) involves over-proliferation of cyst-lining epithelial cells and excessive cystic fluid secretion. While metformin effectively inhibits renal cyst growth in mouse models of ADPKD it exhibits low potency, and thus an adenosine monophosphate-activated protein kinase (AMPK) activator with higher potency is required. Herein, we adopted a drug repurposing strategy to explore the potential of PF-06409577, an AMPK activator for diabetic nephropathy, in cellular, ex vivo and in vivo models of ADPKD. Our results demonstrated that PF-06409577 effectively down-regulated mammalian target of rapamycin pathway-mediated proliferation of cyst-lining epithelial cells and reduced cystic fibrosis transmembrane conductance regulator-regulated cystic fluid secretion. Overall, our data suggest that PF-06409577 holds therapeutic potential for ADPKD treatment.

The anti-osteosarcoma cell activity by the sphingosine kinase 1 inhibitor SKI-V

Sphingosine kinase 1 (SphK1) expression and activity are elevated in human osteosarcoma (OS) and is a promising target of therapy. SKI-V is a non-competitive and highly-efficient non-lipid SphK1 inhibitor. The potential anti-OS cell activity by the SphK1 inhibitor was studied here. In primary OS cells and immortalized cell lines, SKI-V robustly suppressed cell survival, growth and proliferation as well as cell mobility, and inducing profound OS cell death and apoptosis. The SphK1 inhibitor was however non-cytotoxic nor pro-apoptotic in human osteoblasts. SKI-V robustly inhibited SphK1 activation and induced accumulation of ceramides, without affecting SphK1 expression in primary OS cells. The SphK1 activator K6PC-5 or sphingosine-1-phosphate partially inhibited SKI-V-induced OS cell death. We showed that SKI-V concurrently blocked Akt-mTOR activation in primary OS cells. A constitutively-active Akt1 (ca-Akt1, S473D) construct restored Akt-mTOR activation and mitigated SKI-V-mediated cytotoxicity in primary OS cells. In vivo, daily injection of SKI-V potently suppressed OS xenograft tumor growth in nude mice. In SKI-V-administrated OS xenograft tissues, SphK1 inhibition, ceramide increase and Akt-mTOR inhibition were detected. Together, SKI-V exerts significant anti-OS activity by inhibiting SphK1 and Akt-mTOR cascades in OS cells.