The PI3K/AKT/mTOR (PAM) signaling pathway is a highly conserved signal transduction network in eukaryotic cells that promotes cell survival, cell growth, and cell cycle progression. Growth factor signalling to transcription factors in the PAM axis is highly regulated by multiple cross-interactions with several other signaling pathways, and dysregulation of signal transduction can predispose to cancer development. The PAM axis is the most frequently activated signaling pathway in human cancer and is often implicated in resistance to anticancer therapies. Dysfunction of components of this pathway such as hyperactivity of PI3K, loss of function of PTEN, and gain-of-function of AKT, are notorious drivers of treatment resistance and disease progression in cancer. In this review we highlight the major dysregulations in the PAM signaling pathway in cancer, and discuss the results of PI3K, AKT and mTOR inhibitors as monotherapy and in co-administation with other antineoplastic agents in clinical trials as a strategy for overcoming treatment resistance. Finally, the major mechanisms of resistance to PAM signaling targeted therapies, including PAM signaling in immunology and immunotherapies are also discussed. 

PI3K/AKT/mTOR signaling transduction pathway and targeted therapies in cancer

<h2>Summary</h2> Macrophages are phenotypically and functionally diverse in the tumor microenvironment (TME). However, how to remodel macrophages with a protumor phenotype and how to manipulate them for therapeutic purposes remain to be explored. Here, we show that in the TME, RARγ is downregulated in macrophages, and its expression correlates with poor prognosis in patients with colorectal cancer (CRC). In macrophages, RARγ interacts with tumor necrosis factor receptor-associated factor 6 (TRAF6), which prevents TRAF6 oligomerization and autoubiquitination, leading to inhibition of nuclear factor κB signaling. However, tumor-derived lactate fuels H3K18 lactylation to prohibit RARγ gene transcription in macrophages, consequently enhancing interleukin-6 (IL-6) levels in the TME and endowing macrophages with tumor-promoting functions via activation of signal transducer and activator of transcription 3 (STAT3) signaling in CRC cells. We identified that nordihydroguaiaretic acid (NDGA) exerts effective antitumor action by directly binding to RARγ to inhibit TRAF6-IL-6-STAT3 signaling. This study unravels lactate-driven macrophage function remodeling by inhibition of RARγ expression and highlights NDGA as a candidate compound for treating CRC. 

Histone lactylation inhibits RARγ expression in macrophages to promote colorectal tumorigenesis through activation of TRAF6-IL-6-STAT3 signaling.

Epigenetic regulation refers to the alteration of gene expression independent of changes in DNA sequence. It involves chemical modifications such as DNA methylation, histone methylation, and histone acetylation, which are regulated by a coordinated interplay of various regulators to ensure precise spatial and temporal regulation of gene expression. Epigenetic aberrations are commonly observed in cancer and are considered as hallmarks of cancer. In recent years, small molecules targeting specific epigenetic regulators have been developed and are demonstrating promising therapeutic potential in preclinical and clinical trials for cancer treatment. In this review, we summarize the essential regulatory mechanisms and dysfunctions of epigenetic regulators involved in DNA methylation, histone methylation, and histone acetylation during tumor development and progression. Moreover, we discuss the current advances and challenges in cancer epigenetic therapy that target these mechanisms in both hematologic malignancies and solid tumors. Finally, we discuss the potential of combining epigenetic drugs with other therapies, including chemotherapy, radiotherapy, targeted therapy, and immunotherapy, as a promising approach for cancer treatment. Overall, we aim to enhance the understanding of epigenetic regulation in cancer therapy and explore targeted therapeutic strategies based on these mechanisms, to ultimately advance cancer therapy and improve patient prognosis.

Epigenetic regulation in cancer therapy: From mechanisms to clinical advances

Dysregulation of cholesterol homeostasis is implicated in the development and progression of hepatocellular carcinoma (HCC) that is characterized by intrahepatic and early extrahepatic metastasis. A better understanding of the underlying mechanisms regulating cholesterol metabolism in HCC could help identify strategies to circumvent the aggressive phenotype. Here, we found that high expression of intracellular SPARC was significantly associated with elevated cholesterol levels and an enhanced invasive phenotype in HCC. SPARC potentiated cholesterol accumulation in HCC cells during tumor progression by stabilizing the ApoE protein. Mechanistically, SPARC competitively bound to ApoE, impairing its interaction with the E3 ligase tripartite motif containing 21 (TRIM21) and preventing its ubiquitylation and subsequent degradation. ApoE accumulation led to cholesterol enrichment in HCC cells, stimulating PI3K-AKT signaling and inducing epithelial-mesenchymal transition (EMT). Importantly, sorafenib-resistant HCC cells were characterized by increased expression of intracellular SPARC, elevated cholesterol levels, and enhanced invasive capacity. Inhibiting SPARC expression or reducing cholesterol levels enhanced the sensitivity of HCC cells to sorafenib treatment. Together, these findings unveil interplay between SPARC and cholesterol homeostasis. Targeting SPARC-triggered cholesterol-dependent oncogenic signaling is a potential therapeutic strategy for advanced HCC.

SPARC stabilizes ApoE to induce cholesterol-dependent invasion and sorafenib resistance in hepatocellular carcinoma.

Abstract Background Serotonin (5‐hydroxytryptamine) is a multifunctional bioamine serving as a neurotransmitter, peripheral hormone and mitogen in the vertebrate system. It has pleiotropic activities in central nervous system and gastrointestinal function via an orchestrated action of serotonergic elements, particularly serotonin receptor‐mediated signalling cascades. The mitogenic properties of serotonin have garnered recognition for years and have been exploited for repurposing serotonergic‐targeted drugs in cancer therapy. However, emerging conflicting findings necessitate a more comprehensive elucidation of serotonin's role in cancer pathogenesis. Main body and conclusion Here, we provide an overview of the biosynthesis, metabolism and action modes of serotonin. We summarise our current knowledge regarding the effects of the peripheral serotonergic system on tumourigenesis, with a specific emphasis on its immunomodulatory activities in human cancers. We also discuss the dual roles of serotonin in tumour pathogenesis and elucidate the potential of serotonergic drugs, some of which display favourable safety profiles and impressive efficacy in clinical trials, as a promising avenue in cancer treatment. Key points Primary synthesis and metabolic routes of peripheral 5‐hydroxytryptamine in the gastrointestinal tract. Advanced research has established a strong association between the serotonergic components and carcinogenic mechanisms. The interplay between serotonergic signalling and the immune system within the tumour microenvironment orchestrates antitumour immune responses. Serotonergic‐targeted drugs offer valuable clinical options for cancer therapy. 

Serotonin signalling in cancer: Emerging mechanisms and therapeutic opportunities

Metastatic colorectal cancer (mCRC) is characterized by poorer prognosis of patients and limited therapeutic approach, partly due to the lack of effective target. Using mouse models and tumor organoids, this study reported a tripartite motif 21 (TRIM21) protein, exerting potential inhibitory effects on the invasion and metastasis of CRC. Mechanistically, TRIM21 directly interacted with and ubiquitinated MST2 at lysine 473 (K473) via K63-linkage. This ubiquitination enabled the formation of MST2 homodimer and enhanced its kinase activity, ultimately resulting in the functional inactivation of yes-associated protein (YAP) and inhibition of an epithelial-mesenchymal transition (EMT) feature. We identified that vilazodone, an antidepressant, directly bound to TRIM21 to exert effective anti-metastatic action both in vitro and in vivo. Collectively, these findings revealed a previously unrecognized interplay between TRIM21 and the Hippo-YAP signaling. These results suggested that vilazodone could be repositioned as an anti-tumor drug to inhibit CRC metastasis by targeting TRIM21. 

TRIM21 is a druggable target for the treatment of metastatic colorectal cancer through ubiquitination and activation of MST2.

The PIK3CA-E545K-SIRT4 signaling axis reduces radiosensitivity by promoting glutamine metabolism in cervical cancer.

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TRIM21 is a druggable target for the treatment of metastatic colorectal cancer through ubiquitination and activation of MST2.

SPARC stabilizes ApoE to induce cholesterol-dependent invasion and sorafenib resistance in hepatocellular carcinoma.

The PIK3CA-E545K-SIRT4 signaling axis reduces radiosensitivity by promoting glutamine metabolism in cervical cancer.