Concepts and advances in cancer therapeutic vulnerabilities in RAS membrane targeting.Semin Cancer Biol. 2019;54:121-130. [PMID: 29203271 DOI: 10.1016/j.semcancer.2017.11.021]

Recent Advances in Peptide Inhibitors Targeting Wild-Type Ras Protein Interactions in Cancer Therapy

Ras proteins are pivotal in the regulation of cell proliferation signals, and their dysregulation is intricately linked to the pathogenesis of various malignancies. Peptide inhibitors hold distinct advantages in targeting Ras proteins, attributable to their extensive binding domains, which result from the smooth surfaces of the proteins. The array of specific strategies includes the employment of full hydrocarbon chains, cyclic peptides, linear peptides, and N-terminal nucleation polypeptides. These methods effectively suppress the Ras signaling pathway through distinct mechanisms, highlighting their potential as anti-neoplastic agents. Moreover, cutting-edge methodologies, including the N-terminal aspartate nucleation strategy and the utilization of hydrocarbon-stapled peptides, are transforming the landscape of therapeutics aimed at Ras proteins. These innovations highlight the promise of peptide libraries and combinatorial chemistry in augmenting binding affinity, specificity, and cellular permeability, which are pivotal for the development of potent anti-cancer agents. The incorporation of dual therapeutic strategies, such as the synergy between peptide inhibitors and conventional chemotherapy or the use of radiotherapy enhancers, emerges as a compelling strategy to bolster the efficacy of cancer treatments targeting the Ras-MAPK pathway. Furthermore, recent studies have demonstrated that Ras-targeting stabilized peptides can amplify the radio-sensitivity of cancer cells, offering an innovative approach to enhance the efficacy of radiation therapy within cancer management.

An Alkyne-Containing Isoprenoid Analogue Based on a Farnesyl Diphosphate Scaffold Is a Biologically Functional Universal Probe for Proteomic Analysis

Prenylation consists of the modification of proteins with either farnesyl diphosphate (FPP) or geranylgeranyl diphosphate (GGPP) at a cysteine near the C-terminus of target proteins to generate thioether-linked lipidated proteins. In recent work, metabolic labeling with alkyne-containing isoprenoid analogues including C15AlkOPP has been used to identify prenylated proteins and track their levels in different diseases. Here, a systematic study of the impact of isoprenoid length on proteins labeled with these probes was performed. Chemical synthesis was used to generate two new analogues, C15hAlkOPP and C20AlkOPP, bringing the total number of compounds to eight used in this study. Enzyme kinetics performed in vitro combined with metabolic labeling in cellulo, resulted in the identification of 8 proteins for C10AlkOPP, 70 proteins for C15AlkOPP, 41 proteins for C15hAlkOPP, and 7 proteins for C20AlkOPP. While C10AlkOPP was the most selective for farnesylated proteins and C20AlkOPP was most selective for geranylgeranylated proteins, the number of proteins identified using those probes was relatively small. In contrast, C15AlkOPP labeled the most proteins including representatives from all classes of prenylated proteins. Functional analysis of these analogues demonstrated that C15AlkOPP was particularly well suited for biological studies since it was efficiently incorporated in cellulo, was able to confer correct plasma membrane localization of H-Ras protein and complement the effects of GGPP depletion in macrophages to yield correct cell polarization and filopodia. Collectively, these results indicate that C15AlkOPP is a biologically functional, universal probe for metabolic labeling experiments that has minimal effects on cellular physiology.

Deoxyribonucleic acid methylation driven aberrations in pancreatic cancer-related pathways

Pancreatic cancer (PanCa) presents a catastrophic disease with poor overall survival at advanced stages, with immediate requirement of new and effective treatment options. Besides genetic mutations, epigenetic dysregulation of signaling pathway-associated enriched genes are considered as novel therapeutic target. Mechanisms beneath the deoxyribonucleic acid methylation and its utility in developing of epi-drugs in PanCa are under trails. Combinations of epigenetic medicines with conventional cytotoxic treatments or targeted therapy are promising options to improving the dismal response and survival rate of PanCa patients. Recent studies have identified potentially valid pathways that support the prediction that future PanCa clinical trials will include vigorous testing of epigenomic therapies. Epigenetics thus promises to generate a significant amount of new knowledge of biological and medical importance. Our review could identify various components of epigenetic mechanisms known to be involved in the initiation and development of pancreatic ductal adenocarcinoma and related precancerous lesions, and novel pharmacological strategies that target these components could potentially lead to breakthroughs. We aim to highlight the possibilities that exist and the potential therapeutic interventions.

microRNA-324-3p suppresses the aggressive ovarian cancer by targeting WNK2/RAS pathway

Ovarian cancer (OC) has the highest mortality rate among gynecological cancers, which progresses owing to dysregulated microRNAs (miRNAs) expression. Our study attempts to reveal the mechanism by which decreased miR-324-3p expression suppresses OC proliferation. Quantitative real-time PCR, western blotting, in situ hybridization, and immunohistochemistry were performed to estimate miR-324-3p and WNK2 expression levels in OC cells and tissues. Cell Counting Kit-8, colony formation, EdU, and transwell assays were performed to analyze the influence of miR-324-3p and WNK2 on the proliferation and invasion ability of OC cells. Subsequently, xenograft models were established to examine the effects of WNK2 on OC cell proliferation in vivo, and databases and luciferase reporter assays were used to test the relationship between miR-324-3p and WNK2 expression. Then, we showed that miR-324-3p expression is decreased in OC cells and tissues, indicating its inhibitory effect on OC cell proliferation. Quantitative real-time PCR and luciferase reporter assays demonstrated that miR-324-3p inhibited WNK2 expression by directly binding to its 3’ untranslated region. WNK2, an upregulated kinase, promotes the proliferation and invasion of OC cells by activating the RAS pathway. Moreover, WNK2 can partly reverse the inhibitory effects of miR-324-3p on OC cell proliferation. Hence, we demonstrate that miR-324-3p suppressed ovarian cancer progression by targeting the WNK2/RAS pathway. Our study provides theoretical evidence for the clinical application potential of miR-324-3p.

Dual-Targeted Therapy Circumvents Non-Genetic Drug Resistance to Targeted Therapy

The introduction of various targeted agents into the armamentarium of cancer treatment has revolutionized the standard care of patients with cancer. However, like conventional chemotherapy, drug resistance, either preexisting (primary or intrinsic resistance) or developed following treatment (secondary or acquired resistance), remains the Achilles heel of all targeted agents with no exception, via either genetic or non-genetic mechanisms. In the latter, emerging evidence supports the notion that intracellular signaling pathways for tumor cell survival act as a mutually interdependent network via extensive cross-talks and feedback loops. Thus, dysregulations of multiple signaling pathways usually join forces to drive oncogenesis, tumor progression, invasion, metastasis, and drug resistance, thereby providing a basis for so-called "bypass" mechanisms underlying non-genetic resistance in response to targeted agents. In this context, simultaneous interruption of two or more related targets or pathways (an approach called dual-targeted therapy, DTT), via either linear or parallel inhibition, is required to deal with such a form of drug resistance to targeted agents that specifically inhibit a single oncoprotein or oncogenic pathway. Together, while most types of tumor cells are often addicted to two or more targets or pathways or can switch their dependency between them, DTT targeting either intrinsically activated or drug-induced compensatory targets/pathways would efficiently overcome drug resistance caused by non-genetic events, with a great opportunity that those resistant cells might be particularly more vulnerable. In this review article, we discuss, with our experience, diverse mechanisms for non-genetic resistance to targeted agents and the rationales to circumvent them in the treatment of cancer, emphasizing hematologic malignancies.

Transcription factors specificity protein and nuclear receptor 4A1 in pancreatic cancer

Specificity protein (Sp) transcription factors (TFs) Sp1, Sp3 and Sp4, and the orphan nuclear receptor 4A1 (NR4A1) are highly expressed in pancreatic tumors and Sp1 is a negative prognostic factor for pancreatic cancer patient survival. Results of knockdown and overexpression of Sp1, Sp3 and Sp4 in pancreatic and other cancer lines show that these TFs are individually pro-oncogenic factors and loss of one Sp TF is not compensated by other members. NR4A1 is also a pro-oncogenic factor and both NR4A1 and Sp TFs exhibit similar functions in pancreatic cancer cells and regulate cell growth, survival, migration and invasion. There is also evidence that Sp TFs and NR4A1 regulate some of the same genes including survivin, epidermal growth factor receptor, PAX3-FOXO1, α5- and α6-integrins, β1-, β3- and β4-integrins; this is due to NR4A1 acting as a cofactor and mediating NR4A1/Sp1/4-regulated gene expression through GC-rich gene promoter sites. Several studies show that drugs targeting Sp downregulation or NR4A1 antagonists are highly effective inhibitors of Sp/NR4A1-regulated pathways and genes in pancreatic and other cancer cells, and the triterpenoid celastrol is a novel dual-acting agent that targets both Sp TFs and NR4A1.

Post-translational modification of KRAS: potential targets for cancer therapy

Aberrant activation of the RAS superfamily is one of the critical factors in carcinogenesis. Among them, KRAS is the most frequently mutated one which has inspired extensive studies for developing approaches to intervention. Although the cognition toward KRAS remains far from complete, mounting evidence suggests that a variety of post-translational modifications regulate its activation and localization. In this review, we summarize the regulatory mode of post-translational modifications on KRAS including prenylation, post-prenylation, palmitoylation, ubiquitination, phosphorylation, SUMOylation, acetylation, nitrosylation, etc. We also highlight the recent studies targeting these modifications having exhibited potent anti-tumor activities.

Molecular Therapeutics of Pancreatic Ductal Adenocarcinoma: Targeted Pathways and the Role of Cancer Stem Cells

Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal cancers in humans due to late detection and highly metastatic characteristics. PDAC cells vary in their tumorigenic capabilities with the presence of a subset of PDAC cells known as pancreatic cancer stem cells (CSCs), which are more resistant to currently used therapeutics. Here, we describe the role of CSCs and tumour stroma in developing therapeutic strategies for PDAC and suggest that developmental plasticity could be considered a hallmark of cancers. We provide an overview of the molecular targets in PDAC treatments, including targeted therapies of cellular processes such as proliferation, evasion of growth suppressors, activating metastasis, and metabolic effects. Since PDAC is an inflammation-driven cancer, we also revisit therapeutic strategies targeting inflammation and immunotherapy. Lastly, we suggest that targeting epigenetic mechanisms opens therapeutic routes for heterogeneous cancer cell populations, including CSCs.

LGALS1 acts as a pro-survival molecule in AML

The galectin LGALS1 is a glycan binding protein that regulates intracellular (e.g. signal transduction) and extracellular processes (e.g. immunity, leukocyte mobilization) that support cell survival. The protein is best known for its role in RAS signaling. LGALS1 is important in acute lymphoblastic leukemia but its role in acute myeloid leukemia is not well defined. We previously found suppression of LGALS1 in AML cell lines OCI-AML3 and THP-1 sensitized both cell lines to BCL2 inhibitor ABT-737. In this study, we used an in vivo murine OCI-AML3 xenograft model to test whether reduction expression of LGALS1 affects survival. Mice bearing the OCI-AML3 cells with LGALS1 shRNA survived significantly longer than mice with control OCI-AML3 cells. Gene expression profiling using RNASeq was performed using the control and LGALS1 shRNA of p53 WT OCI-AML3 and p53 mutant THP-1 cells. The data reveal distinct differences between the two cell lines in number of genes affected, in pathways associated with these genes, in expression of oncogenes, and in the transcription factors involved. The p53 pathway is prominent in OCI-AML3 cells. An examination of LGALS1 mRNA in an AML patient population reveals elevated LGALS1 mRNA is associated with shorter disease free survival and increased blasts in the BM. This data with the xenograft model data presented suggest LGALS1 may be important in the AML microenvironment. In summary, the data presented here suggest that a strategy targeting LGALS1 may benefit AML patients.

Galectin-8 binds to the Farnesylated C-terminus of K-Ras4B and Modifies Ras/ERK Signaling and Migration in Pancreatic and Lung Carcinoma Cells

K-Ras is the most prominent driver of oncogenesis and no effective K-Ras inhibitors have been established despite decades of intensive research. Identifying new K-Ras-binding proteins and their interaction domains offers the opportunity for defining new approaches in tackling oncogenic K-Ras. We have identified Galectin-8 as a novel, direct binding protein for K-Ras4B by mass spectrometry analyses and protein interaction studies. Galectin-8 is a tandem-repeat Galectin and it is widely expressed in lung and pancreatic carcinoma cells. siRNA-mediated depletion of Galectin-8 resulted in increased K-Ras4B content and ERK1/2 activity in lung and pancreatic carcinoma cells. Moreover, cell migration and cell proliferation were inhibited by the depletion of Galectin-8. The K-Ras4B–Galectin-8 interaction is indispensably associated with the farnesylation of K-Ras4B. The lysine-rich polybasic domain (PBD), a region that is unique for K-Ras4B as compared to H- and N-Ras, stabilizes the interaction and accounts for the specificity. Binding assays with the deletion mutants of Galectin-8, comprising either of the two carbohydrate recognition domains (CRD), revealed that K-Ras4B only interacts with the N-CRD, but not with the C-CRD. Structural modeling uncovers a potential binding pocket for the hydrophobic farnesyl chain of K-Ras4B and a cluster of negatively charged amino acids for interaction with the positively charged lysine residues in the N-CRD. Our results demonstrate that Galectin-8 is a new binding partner for K-Ras4B and it interacts via the N-CRD with the farnesylated PBD of K-Ras, thereby modulating the K-Ras effector pathways as well as cell proliferation and migration.

Review: Precision medicine and driver mutations: Computational methods, functional assays and conformational principles for interpreting cancer drivers

At the root of the so-called precision medicine or precision oncology, which is our focus here, is the hypothesis that cancer treatment would be considerably better if therapies were guided by a tumor’s genomic alterations. This hypothesis has sparked major initiatives focusing on whole-genome and/or exome sequencing, creation of large databases, and developing tools for their statistical analyses—all aspiring to identify actionable alterations, and thus molecular targets, in a patient. At the center of the massive amount of collected sequence data is their interpretations that largely rest on statistical analysis and phenotypic observations. Statistics is vital, because it guides identification of cancer-driving alterations. However, statistics of mutations do not identify a change in protein conformation; therefore, it may not define sufficiently accurate actionable mutations, neglecting those that are rare. Among the many thematic overviews of precision oncology, this review innovates by further comprehensively including precision pharmacology, and within this framework, articulating its protein structural landscape and consequences to cellular signaling pathways. It provides the underlying physicochemical basis, thereby also opening the door to a broader community.

Decoding the sweet regulation of apoptosis: the role of glycosylation and galectins in apoptotic signaling pathways

Glycosylation and glycan-binding proteins such as galectins play an important role in the control of cell death signaling. Strikingly, very little attention has been given so far to the understanding of the molecular details behind this key regulatory network. Glycans attached to the death receptors such as CD95 and TRAIL-Rs, either alone or in a complex with galectins, might promote or inhibit apoptotic signals. However, we have just started to decode the functions of galectins in the modulation of extrinsic and intrinsic apoptosis. In this work, we have discussed the current understanding of the glycosylation-galectin regulatory network in CD95- as well as TRAIL-R-induced apoptosis and therapeutic strategies based on targeting galectins in cancer.

Galectins as regulators of cell survival in the leukemia niche

The microenvironment within the bone marrow (BM) contains support cells that promote leukemia cell survival and suppress host anti-tumor defenses. Galectins are a family of beta-galactoside binding proteins that are critical components in the tumor microenvironment. Galectin 1 (LGALS1) and Galectin 3 (LGALS3) as regulators of RAS signaling intracellularly and as inhibitors of immune cells extracellularly are perhaps the best studied members for their role in leukemia biology. Interest in Galectin 9 (LGALS9) is growing as this galectin has been identified as an immune checkpoint molecule. LGALS9 also supports leukemia stem cells (LSCs) though a mechanism of action is not clear. LGALS1 and LGALS3 each participate in a diverse number of survival pathways that promote drug resistance by supporting pro-tumor molecules such BCL2, MCL-1, and MYC and blocking tumor suppressors like p53. Acute myeloid leukemia (AML) BM mesenchymal stromal cells (MSC) have protein signatures that differ from healthy donor MSC. Elevated LGALS3 protein in AML MSC is associated with refractory disease/relapse demonstrating that MSC derived galectin impacts patient survival. LGALS3 is a critical determining factor whether MSC differentiate into adipocytes or osteoblasts so the galectin influences the cellular composition of the leukemia niche. Both LGALS3 and LGALS1 when secreted can suppress immune function. Both galectins can induce apoptosis of T cells. LGALS3 also modulates T cell receptor endocytosis and impairs interferon mediated chemokine production by binding glycosylated interferon. LGALS3 as a TIM3 binding partner acts to suppress T cell function. Galectins also impact leukemia cell mobilization and may participate in homing mechanisms. LGALS3 participates in transport mechanism of integrins, receptors, and other molecules that control cell adhesion and cell:cell interactions. The diversity of these various functions demonstrate the importance of these galectins in the leukemia niche. This review will cover the role of LGALS1, LGALS3, and LGALS9 in the various processes that are critical for maintaining leukemia cells in the tumor microenvironment.