Novel c-Myc-Targeting Compound N, N-Bis (5-Ethyl-2-Hydroxybenzyl) Methylamine for Mediated c-Myc Ubiquitin-Proteasomal Degradation in Lung Cancer Cells

The roles of protein ubiquitination in tumorigenesis and targeted drug discovery in lung cancer

The malignant lung cancer has a high morbidity rate and very poor 5-year survival rate. About 80% - 90% of protein degradation in human cells is occurred through the ubiquitination enzyme pathway. Ubiquitin ligase (E3) with high specificity plays a crucial role in the ubiquitination process of the target protein, which usually occurs at a lysine residue in a substrate protein. Different ubiquitination forms have different effects on the target proteins. Multiple short chains of ubiquitination residues modify substrate proteins, which are favorable signals for protein degradation. The dynamic balance adapted to physiological needs between ubiquitination and deubiquitination of intracellular proteins is beneficial to the health of the organism. Ubiquitination of proteins has an impact on many biological pathways, and imbalances in these pathways lead to diseases including lung cancer. Ubiquitination of tumor suppressor protein factors or deubiquitination of tumor carcinogen protein factors often lead to the progression of lung cancer. Ubiquitin proteasome system (UPS) is a treasure house for research and development of new cancer drugs for lung cancer, especially targeting proteasome and E3s. The ubiquitination and degradation of oncogene proteins with precise targeting may provide a bright prospect for drug development in lung cancer; Especially proteolytic targeted chimerism (PROTAC)-induced protein degradation technology will offer a new strategy in the discovery and development of new drugs for lung cancer.

N,N'-Diarylurea Derivatives (CTPPU) Inhibited NSCLC Cell Growth and Induced Cell Cycle Arrest through Akt/GSK-3β/c-Myc Signaling Pathway

Lung cancer is one of the most common malignancies worldwide. Non-small-cell lung cancer (NSCLC) accounts for more than 80% of lung cancers, shows chemotherapy resistance, metastasis, and relapse. The phosphatidylinositol-3 kinase (PI3K)/Akt pathway has been implicated in the carcinogenesis and disease progression of NSCLC, suggesting that it may be a promising therapeutic target for cancer therapy. Although phenylurea derivatives have been reported as potent multiple kinase inhibitors, novel unsymmetrical N,N'-diarylurea derivatives targeting the PI3K/Akt pathway in NSCLC cells remain unknown.

METHODS

N,N'-substituted phenylurea derivatives CTPPU and CT-(4-OH)-PU were investigated for their anticancer proliferative activity against three NSCLC cell lines (H460, A549, and H292) by 3-(4,5-dimethythiazol-2-yl)-2,5-diphenyl tetrazolium bromide, colony formation, Hoechst33342/PI staining assays, and apoptosis analysis. The protein expressions of Akt pathway-related proteins in response to CTPPU or CT-(4-OH)-PU were detected by Western blot analysis. The Kyoto Encyclopedia of Genes and Genomes mapper was used to identify the possible signaling pathways in NSCLC treated with CTPPU. The cell cycle was analyzed by flow cytometry. Molecular docking was used to investigate the possible binding interaction of CTPPU with Akt, the mammalian target of rapamycin complex 2 (mTORC2), and PI3Ks. Immunofluorescence and Western blot analysis were used to validate our prediction.

RESULTS

The cytotoxicity of CTPPU was two-fold higher than that of CT-(4-OH)-PU for all NSCLC cell lines. Similarly, the non-cytotoxic concentration of CTPPU (25 µM) dramatically inhibited the colony formation of NSCLC cells, whereas its relative analog CT-(4-OH)-PU had no effect. Protein analysis revealed that Akt and its downstream effectors, namely, phosphorylated glycogen synthase kinase (GSK)-3β (Ser9), β-catenin, and c-Myc, were reduced in response to CTPPU treatment, which suggested the targeting of Akt-dependent pathway, whereas CT-(4-OH)-PU had no effect on such cell growth regulatory signals. CTPPU induced G1/S cell cycle arrest in lung cancer cells. Immunofluorescence revealed that CTPPU decreased p-Akt and total Akt protein levels, which implied the effect of the compound on protein activity and stability. Next, we utilized in silico molecular docking analysis to reveal the potential molecular targets of CTPPU, and the results showed that the compound could specifically bind to the allosteric pocket of Akt and three sites of mTORC2 (catalytic site, A-site, and I-site), with a binding affinity greater than that of reference compounds. The compound cannot bind to PI3K, an upstream regulator of the Akt pathway. The effect of CTPPU on PI3K and Akt was confirmed. This finding indicated that the compound could decrease p-Akt but caused no effect on p-PI3K.

CONCLUSIONS

The results indicate that CTPPU significantly inhibits NSCLC cell proliferation by inducing G1/S cell cycle arrest via the Akt/GSK-3β/c-Myc signaling pathway. Molecular docking revealed that CTPPU could interact with Akt and mTORC2 molecules with a high binding affinity. These data indicate that CTPPU is a potential novel alternative therapeutic approach for NSCLC.

6,6′-((Methylazanedyl)bis(methylene))bis(2,4-dimethylphenol) Induces Autophagic Associated Cell Death through mTOR-Mediated Autophagy in Lung Cancer

Autophagy is the multistep mechanism for the elimination of damaged organelles and misfolded proteins. This mechanism is preceded and may induce other program cell deaths such as apoptosis. This study unraveled the potential pharmacological effect of 24MD in inducing the autophagy of lung cancer cells. Results showed that 24MD was concomitant with autophagy induction, indicating by autophagosome staining and the induction of ATG5, ATG7 and ubiquitinated protein, p62 expression after 12-h treatment. LC3-I was strongly conversed to LC3-II, and p62 was downregulated after 24-h treatment. The apoptosis-inducing activity was found after 48-h treatment as indicated by annexin V-FITC/propidium iodide staining and the activation of caspase-3. From a mechanistic perspective, 24-h treatment of 24MD at 60 μM substantially downregulated p-mTOR. Meanwhile, p-PI3K and p-Akt were also suppressed by 24MD at concentrations of 80 and 100 μM, respectively. We further confirmed m-TOR-mediated autophagic activity by comparing the effect of 24MD with rapamycin, a potent standard mTOR1 inhibitor through Western blot and immunofluorescence assays. Although 24MD could not suppress p-mTOR as much as rapamycin, the combination of rapamycin and 24MD could increase the mTOR suppressive activity and LC3 activation. Changing the substituent groups (R groups) from dimethylphenol to ethylphenol in EMD or changing methylazanedyl to cyclohexylazanedyl in 24CD could only induce apoptosis activity but not autophagic inducing activity. We identified 24MD as a novel compound targeting autophagic cell death by affecting mTOR-mediated autophagy.

Aspiletrein A Induces Apoptosis Cell Death via Increasing Reactive Oxygen Species Generation and AMPK Activation in Non-Small-Cell Lung Cancer Cells

Lung cancer remains a leading cause of death in cancer patients, and deregulation of apoptosis is a serious concern in clinical practice, even though therapeutic intervention has been greatly improved. Plants are a versatile source of biologically active compounds for anticancer drug discovery, and aspiletrein A (AA) is a steroidal saponin isolated from Aspidistra letreae that has a potent cytotoxic effect on various cancer cell lines. In this study, we investigated and determined the underlying molecular mechanism by which AA induces apoptosis. AA strongly induced apoptosis in NSCLC cells by mediating ROS generation and thereby activating AMP-activated protein kinase (AMPK) signaling. Consequently, downstream signaling and levels of phosphorylated mTOR and Bcl-2 were significantly decreased. Pretreatment with either an antioxidant, N-acetylcysteine, or an AMPK inhibitor, compound C, could reverse the apoptosis-inducing effect and counteract the effect of AA on the AMPK signaling pathway. Decreased levels of Bcl-2 were due to AA-mediating Bcl-2 degradation via a ROS/AMPK/mTOR axis-dependent proteasomal mechanism. Consistently, the apoptotic-inducing effect of AA was also observed in patient-derived malignant lung cancer cells, and it suppressed an in vitro 3D-tumorigenesis. This study identified the underlying mechanism of AA on lung cancer apoptosis, thereby facilitating potential research and development of this compound for further clinical implications.

The Ubiquitin System: An Emerging Therapeutic Target for Lung Cancer

The ubiquitin system, present in all eukaryotes, contributes to regulating multiple types of cellular protein processes such as cell signaling, cell cycle, and receptor trafficking, and it affects the immune response. In most types of cancer, unusual events in ubiquitin-mediated signaling pathway modulation can lead to a variety of clinical outcomes, including tumor formation and metastasis. Similarly, ubiquitination acts as a core component, which contributes to the alteration of cell signaling activity, dictating biosignal turnover and protein fates. As lung cancer acquires the most commonly mutated proteins, changes in the ubiquitination of the proteins contribute to the development of lung cancer. Various inhibitors targeting the ubiquitin system have been developed for clinical applications in lung cancer treatment. In this review, we summarize the current research advances in therapeutics for lung cancer by targeting the ubiquitin system.

The role of ubiquitination and deubiquitination in cancer metabolism

Metabolic reprogramming, including enhanced biosynthesis of macromolecules, altered energy metabolism, and maintenance of redox homeostasis, is considered a hallmark of cancer, sustaining cancer cell growth. Multiple signaling pathways, transcription factors and metabolic enzymes participate in the modulation of cancer metabolism and thus, metabolic reprogramming is a highly complex process. Recent studies have observed that ubiquitination and deubiquitination are involved in the regulation of metabolic reprogramming in cancer cells. As one of the most important type of post-translational modifications, ubiquitination is a multistep enzymatic process, involved in diverse cellular biological activities. Dysregulation of ubiquitination and deubiquitination contributes to various disease, including cancer. Here, we discuss the role of ubiquitination and deubiquitination in the regulation of cancer metabolism, which is aimed at highlighting the importance of this post-translational modification in metabolic reprogramming and supporting the development of new therapeutic approaches for cancer treatment.

DPEP1 promotes the proliferation of colon cancer cells via the DPEP1/MYC feedback loop regulation

DPEP1 is highly expressed in the colorectal carcinoma tissues and colon cancer cells. However, the function and underlying mechanism of DPEP1 in the colon cancer cells are still poorly understood. Here, we found that transcription factor MYC could occupy on the DPEP1 promoter and activate its activities, and DPEP1 was up-regulated by MYC proteins in mRNA and protein levels in a dose-dependent manner in colon cancer cells. The expression levels of DPEP1 were positively correlated with that of MYC in colorectal tumor tissues. Moreover, Laser confocal images and Co-immunoprecipitation (Co-IP) revealed that DPEP1 and MYC proteins could bind to each other in the colon cancer cells. In turn, DPEP1 could enhance the stability of MYC proteins by extending the half-life of MYC proteins in colon cancer cells. Thus, DPEP1 and MYC proteins might form a positive feedback loop to maintain their high expression levels in colon cancer cells. In function, the MTT, EdU, Clone Formation assays and xenograft tumors assays demonstrated that DPEP1 could boost the proliferation of colon cancer cells through the DPEP1/MYC positive feedback loop in vitro and in vivo. Theoretically, DPEP1 may serve as a colon cancer biomarker and a novel target of colorectal carcinogenesis therapy.