Targeting effector pathways in RAC1P29S-driven malignant melanoma

Role of Hypoxia and Rac1 Inhibition in the Metastatic Cascade

The hypoxic condition has a pivotal role in solid tumors and was shown to correlate with the poor outcome of anticancer treatments. Hypoxia contributes to tumor progression and leads to therapy resistance. Two forms of a hypoxic environment might have relevance in tumor mass formation: chronic and cyclic hypoxia. The main regulators of hypoxia are hypoxia-inducible factors, which regulate the cell survival, proliferation, motility, metabolism, pH, extracellular matrix function, inflammatory cells recruitment and angiogenesis. The metastatic process consists of different steps in which hypoxia-inducible factors can play an important role. Rac1, belonging to small G-proteins, is involved in the metastasis process as one of the key molecules of migration, especially in a hypoxic environment. The effect of hypoxia on the tumor phenotype and the signaling pathways which may interfere with tumor progression are already quite well known. Although the role of Rac1, one of the small G-proteins, in hypoxia remains unclear, predominantly, in vitro studies performed so far confirm that Rac1 inhibition may represent a viable direction for tumor therapy.

Assessing the mechanism of fast-cycling cancer-associated mutations of Rac1 small Rho GTPase

Rho-GTPases proteins function as molecular switches alternating from an active to an inactive state upon Guanosine triphosphate (GTP) binding and hydrolysis to Guanosine diphosphate (GDP). Among them, Rac subfamily regulates cell dynamics, being overexpressed in distinct cancer types. Notably, these proteins are object of frequent cancer-associated mutations at Pro29 (P29S, P29L, and P29Q). To assess the impact of these mutations on Rac1 structure and function, we performed extensive all-atom molecular dynamics simulations on wild-type (wt) and oncogenic isoforms of this protein in GDP- and GTP-bound states. Our results unprecedentedly elucidate that P29Q/S-induced structural and dynamical perturbations of Rac1 core domain weaken the binding of the catalytic site Mg2+ ion, and reduce the GDP residence time within protein, enhancing the GDP/GTP exchange rate and Rac1 activity. This broadens our knowledge of the role of cancer-associated mutations on small GTPases mechanism supplying valuable information for future drug discovery efforts targeting specific Rac1 isoforms.

A comprehensive signature based on endoplasmic reticulum stress-related genes in predicting prognosis and immunotherapy response in melanoma

Melanoma is considered as one of the most invasion types of skin cancer with high mortality rates. Although combination of immune checkpoint therapy with local surgical excision provide a novel promising therapeutic strategies, the overall prognosis of melanoma patients remains unsatisfactory. Endoplasmic reticulum (ER) stress, a process of protein misfolding and undue accumulation, has been proven to play an indispensable regulatory role in tumor progression and tumor immunity. However, whether the signature based ER genes has predictive value for the prognosis and immunotherapy of melanoma has not been systematically manifested. In this study, the LASSO regression and multivariate Cox regression were applied to construct a novel signature for predicting melanoma prognosis both in the training and testing set. Intriguingly, we found that patients endowed with high- and low-risk scores displayed differences in clinicopathologic classification, immune cell infiltration level, tumor microenvironment, and immune checkpoint treatment response. Subsequently, based on molecular biology experiments, we validated that silencing the expression of RAC1, an ERG composed of the risk signature, could restrain the proliferation and migration, promote apoptosis, as well as increase the expression of PD-1/PD-L1 and CTLA4 in melanoma cells. Taken together, the risk signature was regarded as promising predictors for melanoma prognosis and might provide prospective strategies to ameliorate patients' response to immunotherapy.

Development and Utility of a PAK1-Selective Degrader

Overexpression of PAK1, a druggable kinase, is common in several malignancies, and inhibition of PAK1 by small molecules has been shown to impede the growth and survival of such cells. Potent inhibitors of PAKs 1-3 have been described, but clinical development has been hindered by recent findings that PAK2 function is required for normal cardiovascular function in adult mice. A unique allosteric PAK1-selective inhibitor, NVS-PAK1-1, provides a potential path forward, but has modest potency. Here, we report the development of BJG-05-039, a PAK1-selective degrader consisting of NVS-PAK1-1 conjugated to lenalidomide, a recruiter of the E3 ubiquitin ligase substrate adaptor Cereblon. BJG-05-039 induced selective degradation of PAK1 and displayed enhanced anti-proliferative effects relative to its parent compound in PAK1-dependent, but not PAK2-dependent, cell lines. Our findings suggest that selective PAK1 degradation may confer more potent pharmacological effects compared with catalytic inhibition and highlight the potential advantages of PAK1-targeted degradation.

Circ_0084043-miR-134-5p axis regulates PCDH9 to suppress melanoma

The low survival rates, poor responses, and drug resistance of patients with melanoma make it urgent to find new therapeutic targets. This study investigated whether the circ_0084043-miR-134-5p axis regulates the antitumor effect of protocadherin 9 (PCDH9) in melanoma. Ectopic expression or knock down (KD) of PCDH9 with a lentivirus vector, we explored its effects on the proliferation, invasion, and apoptosis of melanoma and verified its regulatory effect on ras-related C3 botulinum toxin substrate 1 (RAC1), proline-rich tyrosine kinase 2 (Pyk2), Cyclin D1, matrix metalloproteinase 2 (MMP2), and MMP9. We further observed the effect of KD circ_0084043 on the malignant behavior of melanoma and studied whether circ_0084043 sponged miR-134-5p and regulated PCDH9. We found that circ_0084043 was overexpressed in melanoma and associated with the malignant phenotype. PCDH9 was poorly expressed in human melanoma tissues, and overexpression of PCDH9 inhibited melanoma progression. Quantitative real-time PCR and Western blotting results showed that overexpression of PCDH9 could downregulate RAC1, MMP2, and MMP9 and upregulate Pyk2 and Cyclin D1. Circ_0084043 KD inhibited invasion and promoted apoptosis in melanoma cells. Circ_0084043 could sponge miR-134-5p and thus indirectly regulate PCDH9. Furthermore, we discovered that inhibiting circ_0084043 had an anti–PD-Ll effect. In vivo, PCDH9 overexpression inhibited melanoma tumor growth, but PCDH9 KD promoted it. In conclusion, PCDH9, which is regulated by the circ 0084043-miR-134-5p axis, can suppress malignant biological behavior in melanoma and influence the expression levels of Pyk2, RAC1, Cyclin D1, MMP2, and MMP9.

Rac1 as a Target to Treat Dysfunctions and Cancer of the Bladder

Bladder pathologies, very common in the aged population, have a considerable negative impact on quality of life. Novel targets are needed to design drugs and combinations to treat diseases such as overactive bladder and bladder cancers. A promising new target is the ubiquitous Rho GTPase Rac1, frequently dysregulated and overexpressed in bladder pathologies. We have analyzed the roles of Rac1 in different bladder pathologies, including bacterial infections, diabetes-induced bladder dysfunctions and bladder cancers. The contribution of the Rac1 protein to tumorigenesis, tumor progression, epithelial-mesenchymal transition of bladder cancer cells and their metastasis has been analyzed. Small molecules selectively targeting Rac1 have been discovered or designed, and two of them—NSC23766 and EHT 1864—have revealed activities against bladder cancer. Their mode of interaction with Rac1, at the GTP binding site or the guanine nucleotide exchange factors (GEF) interaction site, is discussed. Our analysis underlines the possibility of targeting Rac1 with small molecules with the objective to combat bladder dysfunctions and to reduce lower urinary tract symptoms. Finally, the interest of a Rac1 inhibitor to treat advanced chemoresistance prostate cancer, while reducing the risk of associated bladder dysfunction, is discussed. There is hope for a better management of bladder pathologies via Rac1-targeted approaches.

Overexpressed or hyperactivated Rac1 as a target to treat hepatocellular carcinoma

Despite novel targeted and immunotherapies, the prognosis remains bleak for patients with hepatocellular carcinoma (HCC), especially for advanced and/or metastatic forms. The rapid emergence of drug resistance is a major obstacle in the success of chemo-, targeted-, immuno-therapies of HCC. Novel targets are needed. The prominent roles of the small GTPase Rac1 in the development and progression of HCC are discussed here, together with its multiple protein partners, and the targeting of Rac1 with RNA-based regulators and small molecules. We discuss the oncogenic functions of Rac1 in HCC, including the contribution of Rac1 mutants and isoform Rac1b. Rac1 is a ubiquitous target, but the protein is frequently overexpressed and hyperactivated in HCC. It contributes to the aggressivity of the disease, with key roles in cancer cell proliferation, tumor metastasis and resistance to treatment. Small molecule targeting Rac1, indirectly or directly, have shown anticancer effects in HCC experimental models. Rac1-binding agents such as EHT 1864 and analogues offer novel opportunities to combat HCC. We discuss the different modalities to repress Rac1 overactivation in HCC with small molecules and the combination with reference drugs to promote cancer cell death and to repress cell invasion. We highlight the necessity to combine Rac1-targeted approach with appropriate biomarkers to select Rac1 activated tumors. Our analysis underlines the prominent oncogenic functions of Rac1 in HCC and discuss the modalities to target this small GTPase. Rac1 shall be considered as a valid target to limit the acquired and intrinsic resistance of HCC tumors and their metastatic potential.

Emerging role for the Serum Response Factor (SRF) as a potential therapeutic target in cancer

INTRODUCTION

The Serum Response Factor (SRF) is a transcription factor involved in three hallmarks of cancer: the promotion of cell proliferation, cell death resistance and invasion and metastasis induction. Many studies have demonstrated a leading role in the development and progression of multiple cancer types, thus highlighting the potential of SRF as a prognostic biomarker and therapeutic target, especially for cancers with poor prognosis.

AREAS COVERED

This review examines the role of SRF in several cancers in promoting cellular processes associated with cancer development and progression. SRF co-factors and signalling pathways are discussed as possible targets to inhibit SRF in a tissue and cancer-specific way. Small-molecule inhibitors of SRF, such as the CCGs series of compounds and lestaurtinib, which could be used as cancer therapeutics, are also discussed.

EXPERT OPINION

Targeting of SRF and its co-factors represents a promising therapeutic approach. Further understanding of the molecular mechanisms behind the action of SRF could provide a pipeline of novel molecular targets and therapeutic combinations for cancer. Basket clinical trials and the use of SRF immunohistochemistry as companion diagnostics will help testing of these new targets in patients.

RAC1 Activation as a Potential Therapeutic Option in Metastatic Cutaneous Melanoma

Metastasis is a complex process by which cancer cells escape from the primary tumor to colonize distant organs. RAC1 is a member of the RHO family of small guanosine triphosphatases that plays an important role in cancer migration, invasion, angiogenesis and metastasis. RAC1 activation has been related to most cancers, such as cutaneous melanoma, breast, lung, and pancreatic cancer. RAC1P29S driver mutation appears in a significant number of cutaneous melanoma cases. Likewise, RAC1 is overexpressed or hyperactivated via signaling through oncogenic cell surface receptors. Thus, targeting RAC1 represents a promising strategy for cutaneous melanoma therapy, as well as for inhibition of other signaling activation that promotes resistance to targeted therapies. In this review, we focus on the role of RAC1 in metastatic cutaneous melanoma emphasizing the anti-metastatic potential of RAC1- targeting drugs.

p21-Activated Kinases in Thyroid Cancer

The family of p21-activated kinases (PAKs) are oncogenic proteins that regulate critical cellular functions. PAKs play central signaling roles in the integrin/CDC42/Rho, ERK/MAPK, PI3K/AKT, NF-κB, and Wnt/β-catenin pathways, functioning both as kinases and scaffolds to regulate cell motility, mitosis and proliferation, cytoskeletal rearrangement, and other cellular activities. PAKs have been implicated in both the development and progression of a wide range of cancers, including breast cancer, pancreatic melanoma, thyroid cancer, and others. Here we will discuss the current knowledge on the structure and biological functions of both group I and group II PAKs, as well as the roles that PAKs play in oncogenesis and progression, with a focus on thyroid cancer and emerging data regarding BRAF/PAK signaling.

RAC1 as a Therapeutic Target in Malignant Melanoma

Small GTPases of the RAS and RHO families are related signaling proteins that, when activated by growth factors or by mutation, drive oncogenic processes. While activating mutations in KRAS, NRAS, and HRAS genes have long been recognized and occur in many types of cancer, similar mutations in RHO family genes, such as RAC1 and RHOA, have only recently been detected as the result of extensive cancer genome-sequencing efforts and are linked to a restricted set of malignancies. In this review, we focus on the role of RAC1 signaling in malignant melanoma, emphasizing recent advances that describe how this oncoprotein alters melanocyte proliferation and motility and how these findings might lead to new therapeutics in RAC1-mutant tumors.