Differential antitumor activity of compounds targeting the ubiquitin-proteasome machinery in gastrointestinal stromal tumor (GIST) cells

In silico identification of 20S proteasome-β5 subunit inhibitors using structure-based virtual screening

Proteasome inhibitors have effective anti-tumor activity in cell culture and can induce apoptosis by interfering with the degradation of cell cycle proteins. 20S Proteasome is acknowledged to be a satisfactory target that has persistent properties against the human immune defense and is obligatory for the degradation of some vital proteins. This study aimed to identify potential inhibitors against 20S proteasome, specifically the β5 subunit, using structure-based virtual screening and molecular docking to reduce the number of ligands that should be eligible for experimental assays. A total of 4961 molecules with anticancer activity were screened from the ASINEX database. The filtered compounds that showed higher docking affinity were then used in more sophisticated molecular docking simulations with AutoDock Vina for validation. Finally, six drug molecules (BDE 28974746, BDE 25657353, BDE 29746159, BDD 27844484, BDE 29746109, and BDE 29746162) exhibited highly significant interactions compared to the positive controls were retained. Among these six molecules, three molecules (BDE 28974746, BDE 25657353, and BDD 27844484) showed high binding affinity and binding energy compared with Carfilzomib and Bortezomib. Molecular simulation and dynamics studies of the top three drug molecules in each case allowed us to draw further conclusions about their stability with the β5 subunit. Computed absorption, distribution, metabolism, excretion and toxicity studies on these derivatives showed encouraging results with very low toxicity, distribution, and absorption. These compounds may serve as potential hits for further biological evaluation in the development of new proteasome inhibitors.Communicated by Ramaswamy H. Sarma.

KIT genetic alterations in breast cancer

AIMS

Activating somatic mutations or gene amplification of KIT result in constitutive activation of its receptor tyrosine kinase, which is targetable in various solid tumours. Here, we sought to investigate the presence of KIT genetic alterations in breast cancer (BC) and characterise the histological and genomic features of these tumours.

METHODS

A retrospective analysis of 5,575 BCs previously subjected to targeted sequencing using the FDA-authorised Memorial Sloan Kettering-Integrated Mutation Profiling of Actionable Targets (MSK-IMPACT) assay was performed to identify BCs with KIT alterations. A histological assessment of KIT-altered BCs was conducted, and their repertoire of genetic alterations was compared with that of BCs lacking KIT genetic alterations, matched for age, histological type, oestrogen receptor/HER2 status and sample type.

RESULTS

We identified 18 BCs (0.32%), including 9 primary and 9 metastatic BCs, with oncogenic/likely oncogenic genetic alterations affecting KIT, including activating somatic mutations (n=4) or gene amplification (n=14). All KIT-altered BCs were of high histological grade, although no distinctive histological features were observed. When compared with BCs lacking KIT genetic alterations, no distinctive genetic features were identified. In two metastatic KIT-altered BCs in which the matched primary BC had also been analysed by MSK-IMPACT, the KIT mutations were found to be restricted to the metastatic samples, suggesting that they were late events in the evolution of these cancers.

CONCLUSIONS

KIT genetic alterations are vanishingly rare in BC. KIT-altered BCs are of high grade but lack distinctive histological features. Genetic alterations in KIT might be late events in the evolution and/or progression of BC.

Proteasome inhibitors as anticancer agents

INTRODUCTION

The therapeutic targeting of the ubiquitin-proteasome pathway (UPP) through inhibitors of the 20S proteasome core proteolytic activities has revolutionized the treatment of hematological malignancies and is paving the way for its extension to solid tumors.

AREAS COVERED

This review covers the progress made in the field of proteasome inhibitors, ranging from the first-generation bortezomib to the latest second-generation inhibitors such as carfilzomib and ixazomib as well as the proteasome inhibitors in clinical phase such as oprozomib and marizomib. The development of selective and potent proteasome inhibitors with improved pharmacological properties is described from the synthesis to their basic biological, and clinical validation.

EXPERT OPINION

Proteasome inhibitors have transformed the treatment landscape for hematological malignancies and hold great promise for cancer therapy. Combination therapies targeting multiple pathways, the development of novel inhibitors or 'hybrid-inhibitors,' and the optimization of treatment protocols are key areas for future exploration. The extension of proteasome inhibitors for the treatment of solid tumors, and their ability to pass the blood-brain barrier open new possibilities for treating central nervous system cancers. However, managing adverse effects, particularly those affecting the central nervous system, remains a critical consideration and a strategic 'working on' aspect for the near future.

Proteasomal pathway inhibition as a potential therapy for NF2-associated meningioma and schwannoma

BACKGROUND

Neurofibromatosis 2 (NF2) is an inherited disorder caused by bi-allelic inactivation of the NF2 tumor suppressor gene. NF2-associated tumors, including schwannoma and meningioma, are resistant to chemotherapy, often recurring despite surgery and/or radiation, and have generally shown cytostatic response to signal transduction pathway inhibitors, highlighting the need for improved cytotoxic therapies.

METHODS

Leveraging data from our previous high-throughput drug screening in NF2 preclinical models, we identified a class of compounds targeting the ubiquitin-proteasome pathway (UPP), and undertook studies using candidate UPP inhibitors, ixazomib/MLN9708, pevonedistat/MLN4924, and TAK-243/MLN7243. Employing human primary and immortalized meningioma (MN) cell lines, CRISPR-modified Schwann cells (SCs), and mouse Nf2-/- SCs, we performed dose response testing, flow cytometry-based Annexin V and cell cycle analyses, and RNA-sequencing to identify potential underlying mechanisms of apoptosis. In vivo efficacy was also assessed in orthotopic NF2-deficient meningioma and schwannoma tumor models.

RESULTS

Testing of three UPP inhibitors demonstrated potent reduction in cell viability and induction of apoptosis for ixazomib or TAK-243, but not pevonedistat. In vitro analyses revealed that ixazomib or TAK-243 downregulates expression of c-KIT and PDGFRα, as well as the E3 ubiquitin ligase SKP2 while upregulating genes associated with endoplasmic reticulum stress-mediated activation of the unfolded protein response (UPR). In vivo treatment of mouse models revealed delayed tumor growth, suggesting a therapeutic potential.

CONCLUSIONS

This study demonstrates the efficacy of proteasomal pathway inhibitors in meningioma and schwannoma preclinical models and lays the groundwork for use of these drugs as a promising novel treatment strategy for NF2 patients.

TRIM9 Interacts with ZEB1 to Suppress Esophageal Cancer by Promoting ZEB1 Protein Degradation via the UPP Pathway

Background

Esophageal cancer remains one of the most lethal malignant diseases globally. Previous studies indicated that TRIM9 (Tripartite Motif Containing 9) is a potential marker in breast cancer patients. Therefore, in the current research, we intended to clarify the regulatory network of TRIM9 and its relative role in esophageal cancer patients. We aimed to elucidate the regulatory role of TRIM9 in esophageal cancer.

Methods

Clinical tumor tissue samples combined with cancer cell line models were utilized to explore the TRIM9 expression pattern. Functional experiments including transwell assay, cell viability assay, and ubiquitination blocking experiments were performed to evaluate the role of the TRIM9/ZEB1 (zinc finger E-box binding homeobox 1) axis and UPP pathway in esophageal cancer progression and exacerbation.

Results

Both esophageal cancer samples and cell line models showed significantly suppressed levels of TRIM9. Functional experiments confirmed that TRIM9 overexpression inhibited the cell viability, invasiveness, and stem-like phenotype of cancer cells. Subsequent investigations suggested that TRIM9-ZEB1 interaction accelerated ZEB1 protein degradation through the modulation of the UPP pathway, which confirmed the protective role of TRIM9 in esophageal cancer progression and metastasis.

Conclusion

This study concluded that TRIM9 was a tumor suppressor that interacted with ZEB1 and accelerated ZEB1 protein degradation via the ubiquitin-proteasome pathway (UPP). Our research emphasized TRIM9-ZEB1 interaction as a valuable target for esophageal cancer treatment in future development. More detailed studies are needed to further consolidate our findings.

Targeting the translational machinery in gastrointestinal stromal tumors (GIST): a new therapeutic vulnerability

Although KIT-mutant GISTs can be effectively treated with tyrosine kinase inhibitors (TKIs), many patients develop resistance to imatinib mesylate (IM) as well as the FDA-approved later-line agents sunitinib, regorafenib and ripretinib. Resistance mechanisms mainly involve secondary mutations in the KIT receptor tyrosine kinase gene indicating continued dependency on the KIT signaling pathway. The fact that the type of secondary mutation confers either sensitivity or resistance towards TKIs and the notion that secondary mutations exhibit intra- and intertumoral heterogeneity complicates the optimal choice of treatment in the imatinib-resistant setting. Therefore, new strategies that target KIT independently of its underlying mutations are urgently needed. Homoharringtonine (HHT) is a first-in-class inhibitor of protein biosynthesis and is FDA-approved for the treatment of chronic myeloid leukemia (CML) that is resistant to at least two TKIs. HHT has also shown activity in KIT-mutant mastocytosis models, which are intrinsically resistant to imatinib and most other TKIs. We hypothesized that HHT could be effective in GIST through downregulation of KIT expression and subsequent decrease of KIT activation and downstream signaling. Testing several GIST cell line models, HHT led to a significant reduction in nascent protein synthesis and was highly effective in the nanomolar range in IM-sensitive and IM-resistant GIST cell lines. HHT treatment resulted in a rapid and complete abolishment of KIT expression and activation, while KIT mRNA levels were minimally affected. The response to HHT involved induction of apoptosis as well as cell cycle arrest. The antitumor activity of HHT was confirmed in a GIST xenograft model. Taken together, inhibition of protein biosynthesis is a promising strategy to overcome TKI resistance in GIST.

The Ubiquitin-Proteasome Pathway and Resistance Mechanisms Developed Against the Proteasomal Inhibitors in Cancer Cells

BACKGROUND

The ubiquitin-proteasome pathway is crucial for all cellular processes and is, therefore, a critical target for the investigation and development of novel strategies for cancer treatment. In addition, approximately 30% of newly synthesized proteins never attain their final conformations due to translational errors or defects in post-translational modifications; therefore, they are also rapidly eliminated by the ubiquitin-proteasome pathway.

OBJECTIVE

Here, an effort was made to outline the recent findings deciphering the new molecular mechanisms involved in the regulation of ubiquitin-proteasome pathway as well as the resistance mechanisms developed against proteasome inhibitors in cell culture experiments and in the clinical trials.

RESULTS

Since cancer cells have higher proliferation rates and are more prone to translational errors, they require the ubiquitin-proteasome pathway for selective advantage and sustained proliferation. Therefore, drugs targeting the ubiquitin-proteasome pathway are promising agents for the treatment of both hematological and solid cancers.

CONCLUSION

A number of proteasome inhibitors are approved and used for the treatment of advanced and relapsed multiple myeloma. Unfortunately, drug resistance mechanisms may develop very fast within days of the start of the proteasome inhibitor-treatment either due to the inherent or acquired resistance mechanisms under selective drug pressure. However, a comprehensive understanding of the mechanisms leading to the proteasome inhibitor-resistance will eventually help the design and development of novel strategies involving new drugs and/or drug combinations for the treatment of a number of cancers.

Proteasome Inhibition Suppresses KIT-Independent Gastrointestinal Stromal Tumors Via Targeting Hippo/YAP/Cyclin D1 Signaling

Purpose: Gastrointestinal stromal tumors (GISTs) are the most common malignant tumor of mesenchymal origin of the digestive tract. A yet more challenging resistance mechanism involves transition from oncogenic KIT to a new imatinib-insensitive oncogenic driver, heralded by loss of KIT expression. Our recent studies have shown that inhibition of cyclin D1 and Hippo signaling, which are overexpressed in KIT-independent GIST, is accompanied by anti-proliferative and apoptosis-promoting effects. PRKCQ, JUN, and the Hippo/YAP pathway coordinately regulate GIST cyclin D1 expression. Thus, targeting of these pathways could be effective therapeutically for these now untreatable tumors.

Methods: Targeting cyclin D1 expression of small molecular drugs was screened by a cell monolayer growth and western blotting. The biologic mechanisms of bortezomib to KIT-independent GISTs were assessed by immunoblotting, qRT-PCR, cell viability, colony growth, cell cycle analysis, apoptosis, migration and invasiveness.

Results: In the initial small molecular inhibitor screening in KIT-independent GIST62, we found that bortezomib-mediated inhibition of the ubiquitin-proteasome machinery showed anti-proliferative effects of KIT-independent GIST cells via downregulation of cyclin D1 and induction of p53 and p21. Treatment with proteasome inhibitor, bortezomib, led to downregulation of cyclin D1 and YAP/TAZ and an increase in the cleaved PARP expression in three KIT-independent GIST cell lines (GIST48B, GIST54, and GIST226). Additionally, it induced p53 and p21 expression in GIST48B and GIST54, increased apoptosis, and led to cell cycle G1/G2-phase arrest, decreased cell viability, colony formation, as well as migration and invasiveness in all GIST cell lines.

Conclusion: Although our findings are early proof-of-principle, there are signs of a potential effective treatment for KIT-independent GISTs, the data highlight that targeting of cyclin D1 and Hippo/YAP by bortezomib warrants evaluation as a novel therapeutic strategy in KIT-independent GISTs.