Inhibition of p90 ribosomal S6 kinase potentiates cisplatin activity in A549 human lung adenocarcinoma cells

p90RSK pathway inhibition synergizes with cisplatin in TMEM16A overexpressing head and neck cancer

Head and neck squamous cell carcinoma (HNSCC) constitutes one of the most common types of human cancers and often metastasizes to lymph nodes. Platinum-based chemotherapeutic drugs are commonly used for treatment of a wide range of cancers, including HNSCC. Its mode of action relies on its ability to impede DNA repair mechanisms, inducing apoptosis in cancer cells. However, due to acquired resistance and toxic side-effects, researchers have been focusing on developing novel combinational therapeutic strategies to overcome cisplatin resistance. In the current study, we identified p90RSK, an ERK1/2 downstream target, as a key mediator and a targetable signaling node against cisplatin resistance. Our results strongly support the role of p90RSK in cisplatin resistance and identify the combination of p90RSK inhibitor, BI-D1870, with cisplatin as a novel therapeutic strategy to overcome cisplatin resistance. In addition, we have identified TMEM16A expression as a potential upstream regulator of p90RSK through the ERK pathway and a biomarker of response to p90RSK targeted therapy in the context of cisplatin resistance.

Embelin inhibits viability of cutaneous T cell lymphoma cell lines HuT78 and H9 by targeting inhibitors of apoptosis

Cutaneous T cell lymphoma (CTCL) is a varied group of neoplasms that affects the skin. Acquired resistance against chemotherapeutic drugs and associated toxic side effects are limitations that warrant search for novel drugs against CTCL. Embelin (EMB) is a naturally occurring benzoquinone derivative that has gained attention owing to its anticancer pharmacological actions and nontoxic nature. We assessed the anticancer activity of EMB against CTCL cell lines, HuT78, and H9. EMB inhibited viability of CTCL cells in a dose-dependent manner. EMB activated extrinsic and intrinsic pathways of apoptosis as shown by the activation of initiator and executioner caspases. EMB-induced apoptosis also involved suppression of inhibitors of apoptosis, XIAP, cIAP1, and cIAP2. PARP cleavage and upregulation of pH2AX indicated DNA damage induced by EMB. In conclusion, we characterized a novel apoptosis-inducing activity of EMB against CTCL cells, implicating EMB as a potential therapeutic agent against CTCL.

P90 ribosomal S6 kinases: A bona fide target for novel targeted anticancer therapies?

The 90 kDa ribosomal S6 kinase (RSK) family of proteins is a group of highly conserved Ser/Thr kinases. They are downstream effectors of the Ras/ERK/MAPK signaling cascade. ERK1/2 activation directly results in the phosphorylation of RSKs, which further, through interaction with a variety of different downstream substrates, activate various signaling events. In this context, they have been shown to mediate diverse cellular processes like cell survival, growth, proliferation, EMT, invasion, and metastasis. Interestingly, increased expression of RSKs has also been demonstrated in various cancers, such as breast, prostate, and lung cancer. This review aims to present the most recent advances in the field of RSK signaling that have occurred, such as biological insights, function, and mechanisms associated with carcinogenesis. We additionally present and discuss the recent advances but also the limitations in the development of pharmacological inhibitors of RSKs, in the context of the use of these kinases as putative, more efficient targets for novel anticancer therapeutic approaches.

BI-D1870 Induces Mitotic Dysfunction and Apoptosis in Neuroblastoma by Regulating the PI3K-Akt-mTORC1 Signal Axis

Introduction: Neuroblastoma (NB) is one of the most common extracranial solid malignant tumors in children. The 5-year survival rate of high-risk or refractory NB is less than 50%. Therefore, developing new effective therapeutics for NB remains an urgent challenge. Materials and Methods: Based on the NB dataset TARGET-NBL in the TCGA database, the prognosis-related genes were analyzed using univariate cox regression (p < 0.01). The protein network interaction of prognostic genes was analyzed using STRING to obtain 150 hub genes with HR > 1 and 150 hub genes with HR < 1. The Connectivity Map database was used to predict a therapeutic drug: BI-D1870, a ribosomal S6 kinase inhibitor. The inhibitory effect of BI-D1870 on NB was investigated through in vivo and in vitro experiments, and its inhibitory mechanism was explored. Results: Both the in vivo and in vitro experiments showed that BI-D1870 could inhibit tumor proliferation and induce tumor apoptosis. Furthermore, we proved that BI-D1870 caused G2/M phase arrest and mitosis damage in cells. RNA-seq of cells showed that BI-D1870 may inhibit the growth of NB by inhibiting the PI3K-Akt-mTOR axis. Western blot and immunofluorescence testing showed that BI-D1870 inhibited the PI3K-Akt-mTORC1 signal pathway to regulate the phosphorylation of RPS6 and 4E BP1 proteins, inhibit protein translation, and inhibit microtubule formation, thus preventing mitotic proliferation and inducing apoptosis. Conclusions: This study provides strong support that BI-D1870 may be a potential adjuvant therapy for NB.

RSK inhibitors as potential anticancer agents: Discovery, optimization, and challenges

Ribosomal S6 kinase (RSK) family is a group of serine/threonine kinases, including four isoforms (RSK1/2/3/4). As a downstream effector of the Ras-mitogen-activated protein kinase (Ras-MAPK) pathway, RSK participates in many physiological activities such as cell growth, proliferation, and migration, and is intimately involved in tumor occurrence and development. As a result, it is recognized as a potential target for anti-cancer and anti-resistance therapies. There have been several RSK inhibitors discovered or designed in recent decades, but only two have entered clinical trials. Low specificity, low selectivity, and poor pharmacokinetic properties in vivo limit their clinical translation. Published studies performed structure optimization by increasing interaction with RSK, avoiding hydrolysis of pharmacophores, eliminating chirality, adapting to binding site shape, and becoming prodrugs. Besides enhancing efficacy, the focus of further design will move towards selectivity since there are functional differences among RSK isoforms. This review summarized the types of cancers associated with RSK, along with the structural characteristics and optimization process of the reported RSK inhibitors. Furthermore, we addressed the importance of RSK inhibitors' selectivity and discussed future drug development directions. This review is expected to shed light on the emergence of RSK inhibitors with high potency, specificity, and selectivity.

ERK inhibitor: A candidate enhancing therapeutic effects of conventional chemo-radiotherapy in esophageal squamous cell carcinoma

For patients with esophageal squamous cell carcinoma (ESCC), standard therapeutic methods (cisplatin and radiotherapy) have been found to be ineffective and severely toxic. Targeted therapy emerges as a promising solution for this dilemma. It has been reported that targeted therapies are applied alone or in combination with standard conventional therapies for the treatment of a variety of cancers. To the best of our knowledge, in patients with ESCC, the combinational methods containing standard therapy and ERK-targeted therapy have yet to be explored. To analyze the prognostic role of p-ERK in ESCC patients, the Kaplan-Meier analysis and Cox regression model were used. To assess the effects of ERK-targeted therapy (GDC0994) on ESCC cells, in vitro studies including CCK-8 assay, colony formation assay, and scratch wound healing assay were conducted. In addition, the changes in cell cycle distribution and apoptosis were analyzed by flow cytometry. Besides, to assess the efficacy of different therapies in vivo, the xenograft tumor models were established by subcutaneously inoculating tumor cells into the flank/leg of mice. In patients with ESCC, a strong correlation between the high expression level of p-ERK and the poor prognosis (p < 0.01, Log-Rank test) has been identified. By analyzing the results from CCK-8 and scratch wound healing assays, we demonstrated that the ERK inhibitor repressed the viability and migration of ESCC cells. In addition, following the treatment of GDC0994, the volumes of xenograft tumors significantly decreased (p < 0.001, one-way ANOVA). Furthermore, blocking the mitogen-activated protein kinase (MAPK/ERK) pathway enhanced the therapeutic efficacy of both cisplatin and radiotherapy (p < 0.05). These findings imply the role of p-ERK in the prognosis of ESCC patients and the therapeutic value of ERK inhibitors in ESCC.

Immune infiltration landscape on prognosis and therapeutic response and relevant epigenetic and transcriptomic mechanisms in lung adenocarcinoma

Objective

Lung adenocarcinoma (LUAD) is the most prevalent lung cancer subtype, but its immune infiltration features are not comprehensively understood. To address the issue, the present study was initiated to describe the immune infiltrations across LUAD from cellular compositional, functional, and mechanism perspectives.

Methods

We adopted five LUAD datasets (GSE32863, GSE43458, GSE75037, TCGA-LUAD, and GSE72094). Differentially expressed genes between LUAD and controls were selected for co-expression network analysis. Risky immune cell types were determined for classifying LUAD patients as diverse subtypes, followed by a comparison of antitumor immunity and therapeutic response between subtypes. Then, LUAD- and subtype-related key module genes affected by DNA methylation were determined for quantifying a scoring scheme. EXO1 was chosen for functional analysis via in vitro assays.

Results

Two immune cell infiltration-based subtypes (C1 and C2) were established across LUAD, with poorer prognostic outcomes and lower infiltration of immune cell types in C1. Additionally, C1 presented higher responses to immune checkpoint blockade and targeted agents (JNK inhibitor VIII, BI-D1870, RO-3306, etc.). The scoring system (comprising GAPDH, EXO1, FYN, CFTR, and KLF4) possessed higher accuracy in estimating patients’ prognostic outcomes. EXO1 upregulation contributed to the growth, migration, and invasion of LUAD cells. In addition, EXO1 facilitated PD-L1 and sPD-L1 expression in LUAD cells.

Conclusion

Altogether, our findings offer a comprehensive understanding of the immune infiltration landscape on prognosis and therapeutic response of LUAD as well as unveil potential epigenetic and transcriptomic mechanisms, which might assist personalized treatment.

TIFA promotes CRC cell proliferation via RSK- and PRAS40- dependent manner

Previous studies have reported that TIFA plays different roles in various tumor types. However, the function of TIFA in colorectal cancer (CRC) remains unclear. Here, we showed that the expression of TIFA was markedly increased in CRC versus normal tissue, and positively correlated with CRC TNM stages. In agreement, we found that the CRC cell lines show increased TIFA expression levels versus normal control. The knockdown of TIFA inhibited cell proliferation but had no effect on cell apoptosis in vitro or in vivo. Moreover, the ectopic expression of TIFA enhanced cell proliferation ability in vitro and in vivo. In contrast, the expression of mutant TIFA (T9A, oligomerization site mutation; D6, TRAF6 binding site deletion) abolished TIFA‐mediated cell proliferation enhancement. Exploration of the underlying mechanism revealed that the protein synthesis‐associated kinase RSK and PRAS40 activation were responsible for TIFA‐mediated CRC progression. In summary, these findings suggest that TIFA plays a role in mediating CRC progression. This could provide a promising target for CRC therapy.