Final results of a phase 2, open-label study of indisulam, idarubicin, and cytarabine in patients with relapsed or refractory acute myeloid leukemia and high-risk myelodysplastic syndrome

Aberrant pre-mRNA processing in cancer

Dysregulation of the flow of information from genomic DNA to RNA to protein occurs within all cancer types. In this review, we described the current state of understanding of how RNA processing is dysregulated in cancer with a focus on mutations in the RNA splicing factor machinery that are highly prevalent in hematologic malignancies. We discuss the downstream effects of these mutations highlighting both individual genes as well as common pathways that they perturb. We highlight examples of how alterations in RNA processing have been harnessed for therapeutic intent as well as to promote the selective toxicity of cancer cells.

Recent advances in anticancer mechanisms of molecular glue degraders: focus on RBM39-dgrading synthetic sulfonamide such as indisulam, E7820, tasisulam, and chloroquinoxaline sulfonamide

Synthetic sulfonamide anticancer drugs, including E7820, indisulam, tasisulam, and chloroquinoxaline sulfonamide, exhibit diverse mechanisms of action and therapeutic potential, functioning as molecular glue degraders. E7820 targets RBM39, affecting RNA splicing and angiogenesis by suppressing integrin α2. Phase I studies have demonstrated some stability in advanced solid malignancies; however, further efficacy studies are required. Indisulam causes G1 cell cycle arrest and delays the G1/S transition by modulating splicing through RBM39 degradation via DCAF15. Despite its limited initial efficacy, it shows promise in combination therapies, particularly for hematopoietic malignancies and gliomas. Tasisulam inhibits VEGF signaling, suppresses angiogenesis, and induces apoptosis. Although early trials indicated broad activity, safety concerns have halted its development. Chloroquinoxaline sulfonamide, initially investigated for cell cycle arrest and topoisomerase II inhibition, was discontinued owing to its limited efficacy and toxicity, despite promising initial results. Recent studies revealed the structural interaction of E7820 with DCAF15 and RBM39, although phase II trials on myeloid malignancies have shown limited efficacy. Indisulam is effective against glioblastoma and neuroblastoma, with potential synergy in combination therapies and metabolic disruption. Recent research on tasisulam reveals its potential in cancer therapy by targeting RBM39 degradation through DCAF15-mediated pathways. Understanding these mechanisms could lead to new treatments that affect alternative splicing and improve cancer therapies Overall, although these drugs exhibit promising mechanisms of action, further research is required to optimize their clinical efficacy and safety.

Understanding mechanisms of resistance to FLT3 inhibitors in adult FLT3-mutated acute myeloid leukemia to guide treatment strategy

The presence of FLT3 mutations, including the most common FLT3-ITD (internal tandem duplications) and FLT3-TKD (tyrosine kinase domain), is associated with an unfavorable prognosis in patients affected by acute myeloid leukemia (AML). In this setting, in recent years, new FLT3 inhibitors have demonstrated efficacy in improving survival and treatment response. Nevertheless, the development of primary and secondary mechanisms of resistance poses a significant obstacle to their efficacy. Understanding these mechanisms is crucial for developing novel therapeutic approaches to overcome resistance and improve the outcomes of patients. In this context, the use of novel FLT3 inhibitors and the combination of different targeted therapies have been studied. This review provides an update on the molecular alterations involved in the resistance to FLT3 inhibitors, and describes how the molecular monitoring may be used to guide treatment strategy in FLT3-mutated AML.

Targeting RBM39 through indisulam induced mis-splicing of mRNA to exert anti-cancer effects in T-cell acute lymphoblastic leukemia

BACKGROUND

Despite the use of targeted therapeutic approaches, T-cell acute lymphoblastic leukemia (T-ALL) is still associated with a high incidence of complications and a poor prognosis. Indisulam (also known as E7070), a newly identified molecular glue compound, has demonstrated increased therapeutic efficacy in several types of cancer through the rapid degradation of RBM39. This study aimed to evaluate the therapeutic potential of indisulam in T-ALL, elucidate its underlying mechanisms and explore the role of the RBM39 gene.

METHODS

We verified the anticancer effects of indisulam in both in vivo and in vitro models. Additionally, the construction of RBM39-knockdown cell lines using shRNA confirmed that the malignant phenotype of T-ALL cells was dependent on RBM39. Through RNA sequencing, we identified indisulam-induced splicing anomalies, and proteomic analysis helped pinpoint protein changes caused by the drug. Comprehensive cross-analysis of these findings facilitated the identification of downstream effectors and subsequent validation of their functional roles.

RESULTS

Indisulam has significant antineoplastic effects on T-ALL. It attenuates cell proliferation, promotes apoptosis and interferes with cell cycle progression in vitro while facilitating tumor remission in T-ALL in vivo models. This investigation provides evidence that the downregulation of RBM39 results in the restricted proliferation of T-ALL cells both in vitro and in vivo, suggesting that RBM39 is a potential target for T-ALL treatment. Indisulam's efficacy is attributed to its ability to induce RBM39 degradation, causing widespread aberrant splicing and abnormal translation of the critical downstream effector protein, THOC1, ultimately leading to protein depletion. Moreover, the presence of DCAF15 is regarded as critical for the effectiveness of indisulam, and its absence negates the ability of indisulam to induce the desired functional alterations.

CONCLUSION

Our study revealed that indisulam, which targets RBM39 to induce tumor cell apoptosis, is an effective drug for treating T-ALL. Targeting RBM39 through indisulam leads to mis-splicing of pre-mRNAs, resulting in the loss of key effectors such as THOC1.

DCAF15 control of cohesin dynamics sustains acute myeloid leukemia

The CRL4-DCAF15 E3 ubiquitin ligase complex is targeted by the aryl-sulfonamide molecular glues, leading to neo-substrate recruitment, ubiquitination, and proteasomal degradation. However, the physiological function of DCAF15 remains unknown. Using a domain-focused genetic screening approach, we reveal DCAF15 as an acute myeloid leukemia (AML)-biased dependency. Loss of DCAF15 results in suppression of AML through compromised replication fork integrity and consequent accumulation of DNA damage. Accordingly, DCAF15 loss sensitizes AML to replication stress-inducing therapeutics. Mechanistically, we discover that DCAF15 directly interacts with the SMC1A protein of the cohesin complex and destabilizes the cohesin regulatory factors PDS5A and CDCA5. Loss of PDS5A and CDCA5 removal precludes cohesin acetylation on chromatin, resulting in uncontrolled chromatin loop extrusion, defective DNA replication, and apoptosis. Collectively, our findings uncover an endogenous, cell autonomous function of DCAF15 in sustaining AML proliferation through post-translational control of cohesin dynamics.

Alternative splicing in prostate cancer progression and therapeutic resistance

Prostate cancer (CaP) remains the second leading cause of cancer deaths in western men. CaP mortality results from diverse molecular mechanisms that mediate resistance to the standard of care treatments for metastatic disease. Recently, alternative splicing has been recognized as a hallmark of CaP aggressiveness. Alternative splicing events cause treatment resistance and aggressive CaP behavior and are determinants of the emergence of the two major types of late-stage treatment-resistant CaP, namely castration-resistant CaP (CRPC) and neuroendocrine CaP (NEPC). Here, we review recent multi-omics data that are uncovering the complicated landscape of alternative splicing events during CaP progression and the impact that different gene transcript isoforms can have on CaP cell biology and behavior. We discuss renewed insights in the molecular machinery by which alternative splicing occurs and contributes to the failure of systemic CaP therapies. The potential for alternative splicing events to serve as diagnostic markers and/or therapeutic targets is explored. We conclude by considering current challenges and promises associated with splicing-modulating therapies, and their potential for clinical translation into CaP patient care.

RBM39 is a potential prognostic biomarker with functional significance in hepatocellular carcinoma

Background

RNA-binding motif protein 39 (RBM39) is a well-known RNA-binding protein involved in tumorigenesis; however, its role in hepatocellular carcinoma (HCC) remains unclear. The aim of this study was to investigate the role of RBM39 in HCC.

Methods

The Cancer Genome Atlas (TCGA) and Gene Expression Omnibus (GEO) databases were used to analyze the differential expression of RBM39 in HCC and normal tissues. The prognostic and diagnostic value of RBM39 in HCC was accessed by Kaplan-Meier analysis, Cox regression, and receiver operating characteristic (ROC) curve analyses. Quantitative real-time polymerase chain reaction (qRT-PCR) and immunohistochemistry were used to validate the mRNA and protein expression of RBM39 in HCC. Moreover, gene set enrichment analysis (GSEA) was performed to identify key pathways related to RBM39. The correlation between RBM39 expression and immune cell infiltration was evaluated using a single-sample gene set enrichment analysis (ssGSEA). CCK8 and wound healing assays were performed to investigate the proliferation and migration abilities of HCC cells with RBM39 knockdown.

Results

RBM39 expression was upregulated in the HCC tissues. High RBM39 expression was significantly associated with advanced T stage, histological grade, and pathological stage and predicted poor overall survival (OS), disease-specific survival (DSS), and progress-free interval (PFI) in HCC patients. The upregulation of RBM39 expression was an independent prognostic factor for OS. Moreover, GSEA enrichment analysis indicated that RBM39 was functionally involved in pathways associated with the cell cycle, DNA replication, the p53 signaling pathway, and primary immunodeficiency. RBM39 expression was associated with infiltration of Th2 cells and dendritic cells (DC). RBM39 knockdown significantly inhibited the proliferation and migration of HCC cells.

Conclusions

These findings suggest that high RBM39 expression is associated with poor prognosis and promotes HCC cell proliferation and migration. Based on these results, RBM39 is a promising prognostic biomarker with functional significance for HCC.

Tumor Antigens beyond the Human Exome

With the advent of immunotherapeutics, a new era in the combat against cancer has begun. Particularly promising are neo-epitope-targeted therapies as the expression of neo-antigens is tumor-specific. In turn, this allows the selective targeting and killing of cancer cells whilst healthy cells remain largely unaffected. So far, many advances have been made in the development of treatment options which are tailored to the individual neo-epitope repertoire. The next big step is the achievement of efficacious "off-the-shelf" immunotherapies. For this, shared neo-epitopes propose an optimal target. Given the tremendous potential, a thorough understanding of the underlying mechanisms which lead to the formation of neo-antigens is of fundamental importance. Here, we review the various processes which result in the formation of neo-epitopes. Broadly, the origin of neo-epitopes can be categorized into three groups: canonical, noncanonical, and viral neo-epitopes. For the canonical neo-antigens that arise in direct consequence of somatic mutations, we summarize past and recent findings. Beyond that, our main focus is put on the discussion of noncanonical and viral neo-epitopes as we believe that targeting those provides an encouraging perspective to shape the future of cancer immunotherapeutics.

Indisulam synergizes with melphalan to inhibit Multiple Myeloma malignancy via targeting TOP2A

Multiple myeloma (MM) is the second most prevalent hematologic malignancy which remains uncurable. Numerous drugs have been discovered to inhibit MM cells. Indisulam, an aryl sulfonamide, has a potent anti-myeloma activity in vitro and in vivo. This study aims to explore the new mechanism of indisulam and investigate its potential use in combination with melphalan. We examined DNA damage in MM cells through various methods such as western blotting (WB), immunofluorescence, and comet assay. We also identified the role of topoisomerase IIα (TOP2A) using bioinformatic analyses. The impact of indisulam on the RNA and protein levels of TOP2A was investigated through qPCR and WB. Cell proliferation and apoptosis were assessed using CCK-8 assays, Annexin V/PI assays and WB. We predicted the synergistic effect of the combination treatment based on calculations performed on a website, and further explored the effect of indisulam in combination with melphalan on MM cell lines and xenografts. RNA sequencing data and basic experiments indicated that indisulam caused DNA damage and inhibited TOP2A expression by decreasing transcription and promoting degradation via the proteasome pathway. Functional experiments revealed that silencing TOP2A inhibited cell proliferation and induced apoptosis and DNA damage. Finally, Indisulam/melphalan combination treatment demonstrated a strong synergistic anti-tumor effect compared to single-agent treatments in vitro and in vivo. These findings suggest that combination therapies incorporating indisulam and melphalan have the potential to enhance treatment outcomes for MM.

Therapeutic strategies for aberrant splicing in cancer and genetic disorders

Accurate pre-mRNA splicing is essential for proper protein translation; however, aberrant splicing is commonly observed in the context of cancer and genetic disorders. Notably, in genetic diseases, these splicing abnormalities often play a pivotal role. Substantial challenges persist in accurately identifying and classifying disease-induced aberrant splicing, as well as in development of targeted therapeutic strategies. In this review, we examine prevalent forms of aberrant splicing and explore potential therapeutic approaches aimed at addressing these splicing-related diseases. This summary contributes to a deeper understanding of the complexities about aberrant splicing and provide a foundation for the development of effective therapeutic interventions in the field of genetic disorders and cancer.

Inflammation as a driver of hematological malignancies

Hematopoiesis is a tightly regulated process that produces all adult blood cells and immune cells from multipotent hematopoietic stem cells (HSCs). HSCs usually remain quiescent, and in the presence of external stimuli like infection or inflammation, they undergo division and differentiation as a compensatory mechanism. Normal hematopoiesis is impacted by systemic inflammation, which causes HSCs to transition from quiescence to emergency myelopoiesis. At the molecular level, inflammatory cytokine signaling molecules such as tumor necrosis factor (TNF), interferons, interleukins, and toll-like receptors can all cause HSCs to multiply directly. These cytokines actively encourage HSC activation, proliferation, and differentiation during inflammation, which results in the generation and activation of immune cells required to combat acute injury. The bone marrow niche provides numerous soluble and stromal cell signals, which are essential for maintaining normal homeostasis and output of the bone marrow cells. Inflammatory signals also impact this bone marrow microenvironment called the HSC niche to regulate the inflammatory-induced hematopoiesis. Continuous pro-inflammatory cytokine and chemokine activation can have detrimental effects on the hematopoietic system, which can lead to cancer development, HSC depletion, and bone marrow failure. Reactive oxygen species (ROS), which damage DNA and ultimately lead to the transformation of HSCs into cancerous cells, are produced due to chronic inflammation. The biological elements of the HSC niche produce pro-inflammatory cytokines that cause clonal growth and the development of leukemic stem cells (LSCs) in hematological malignancies. The processes underlying how inflammation affects hematological malignancies are still not fully understood. In this review, we emphasize the effects of inflammation on normal hematopoiesis, the part it plays in the development and progression of hematological malignancies, and potential therapeutic applications for targeting these pathways for therapy in hematological malignancies.

Subtle structural alteration in indisulam switches the molecular mechanisms for the inhibitory effect on the migration of gastric cancer cells

Gastric cancer is a highly metastatic malignant tumor with high morbidity and mortality globally. Recent studies reported that sulfonamide derivatives such as indisulam exhibited inhibitory effects on the viability and migration of cancer cells. However, multiple clinical trials revealed that indisulam did not significantly prevent cancer progression due to metastasis and drug resistance. Therefore, it is necessary to discover new potent derivatives to explore alternative therapeutic strategies. Here, we synthesize multiple indisulam derivatives and examine their inhibitory effects on the viability and migration of gastric cancer cells. Among them, compounds SR-3-65 and WXM-1-170 exhibit better inhibitory effects on the migration of gastric cancer cells than indisulam. Mechanistically, we discover that they could attenuate the PI3K/AKT/GSK-3β/β-catenin signaling pathway and lead to the suppression of epithelial-to-mesenchymal transition (EMT)-related transcription factors. The influence of SR-3-65 on the migration of gastric cancer cells is blocked by the PI3K inhibitor LY294002 while SR-3-65 and WXM-1-170 reverse the effect of PI3K activator 740 Y-P on the migration of gastric cancer cells. Molecular docking and molecular dynamics simulation further confirm that PI3K is the target of SR-3-65. Our study unveils a novel mechanism by which SR-3-65 and WXM-1-170 inhibit the migration of gastric cancer cells. Together with the previous discovery, we reveal that subtle structural change in indisulam results in a striking switch on the molecular targets and their associated signaling pathways for the inhibition of the migration of gastric cancer cells. These findings might provide informative insights for the development of targeted therapy for gastric cancer.

Marine-Derived Anticancer Agents Targeting Apoptotic Pathways: Exploring the Depths for Novel Cancer Therapies

Extensive research has been conducted on the isolation and study of bioactive compounds derived from marine sources. Several natural products have demonstrated potential as inducers of apoptosis and are currently under investigation in clinical trials. These marine-derived compounds selectively interact with extrinsic and intrinsic apoptotic pathways using a variety of molecular mechanisms, resulting in cell shrinkage, chromatin condensation, cytoplasmic blebs, apoptotic bodies, and phagocytosis by adjacent parenchymal cells, neoplastic cells, or macrophages. Numerous marine-derived compounds are currently undergoing rigorous examination for their potential application in cancer therapy. This review examines a total of 21 marine-derived compounds, along with their synthetic derivatives, sourced from marine organisms such as sponges, corals, tunicates, mollusks, ascidians, algae, cyanobacteria, fungi, and actinobacteria. These compounds are currently undergoing preclinical and clinical trials to evaluate their potential as apoptosis inducers for the treatment of different types of cancer. This review further examined the compound's properties and mode of action, preclinical investigations, clinical trial studies on single or combination therapy, and the prospective development of marine-derived anticancer therapies.

RNA-binding protein RBM5 plays an essential role in acute myeloid leukemia by activating the oncogenic protein HOXA9

BACKGROUND

The oncogenic protein HOXA9 plays a critical role in leukemia transformation and maintenance, and its aberrant expression is a hallmark of most aggressive acute leukemia. Although inhibiting the upstream regulators of HOXA9 has been proven as a significant therapeutic intervention, the comprehensive regulation network controlling HOXA9 expression in leukemia has not been systematically investigated.

RESULTS

Here, we perform genome-wide CRISPR/Cas9 screening in the HOXA9-driven reporter acute leukemia cells. We identify a poorly characterized RNA-binding protein, RBM5, as the top candidate gene required to maintain leukemia cell fitness. RBM5 is highly overexpressed in acute myeloid leukemia (AML) patients compared to healthy individuals. RBM5 loss triggered by CRISPR knockout and shRNA knockdown significantly impairs leukemia maintenance in vitro and in vivo. Through domain CRISPR screening, we reveal that RBM5 functions through a noncanonical transcriptional regulation circuitry rather than RNA splicing, such an effect depending on DNA-binding domains. By integrative analysis and functional assays, we identify HOXA9 as the downstream target of RBM5. Ectopic expression of HOXA9 rescues impaired leukemia cell proliferation upon RBM5 loss. Importantly, acute protein degradation of RBM5 through auxin-inducible degron system immediately reduces HOXA9 transcription.

CONCLUSIONS

We identify RBM5 as a new upstream regulator of HOXA9 and reveal its essential role in controlling the survival of AML. These functional and molecular mechanisms further support RBM5 as a promising therapeutic target for myeloid leukemia treatment.

Molecular basis of RNA-binding and autoregulation by the cancer-associated splicing factor RBM39

Pharmacologic depletion of RNA-binding motif 39 (RBM39) using aryl sulfonamides represents a promising anti-cancer therapy but requires high levels of the adaptor protein DCAF15. Consequently, novel approaches to deplete RBM39 in an DCAF15-independent manner are required. Here, we uncover that RBM39 autoregulates via the inclusion of a poison exon into its own pre-mRNA and identify the cis-acting elements that govern this regulation. We also determine the NMR solution structures of RBM39's tandem RNA recognition motifs (RRM1 and RRM2) bound to their respective RNA targets, revealing how RRM1 recognises RNA stem loops whereas RRM2 binds specifically to single-stranded N(G/U)NUUUG. Our results support a model where RRM2 selects the 3'-splice site of a poison exon and the RRM3 and RS domain stabilise the U2 snRNP at the branchpoint. Our work provides molecular insights into RBM39-dependent 3'-splice site selection and constitutes a solid basis to design alternative anti-cancer therapies.

Current landscape of translational and clinical research in myelodysplastic syndromes/neoplasms (MDS): Proceedings from the 1st International Workshop on MDS (iwMDS) Of the International Consortium for MDS (icMDS)

Biological events that contribute to the pathogenesis of myelodysplastic syndromes/neoplasms (MDS) are becoming increasingly characterized and are being translated into rationally designed therapeutic strategies. Herein, we provide updates from the first International Workshop on MDS (iwMDS) of the International Consortium for MDS (icMDS) detailing recent advances in understanding the genetic landscape of MDS, including germline predisposition, epigenetic and immune dysregulation, the complexities of clonal hematopoiesis progression to MDS, as well as novel animal models of the disease. Connected to this progress is the development of novel therapies targeting specific molecular alterations, the innate immune system, and immune checkpoint inhibitors. While some of these agents have entered clinical trials (e.g., splicing modulators, IRAK1/4 inhibitors, anti-CD47 and anti-TIM3 antibodies, and cellular therapies), none have been approved for MDS. Additional preclinical and clinical work is needed to develop a truly individualized approach to the care of MDS patients.

Secondary-Type Mutations in Acute Myeloid Leukemia: Updates from ELN 2022

The characterization of the molecular landscape and the advent of targeted therapies have defined a new era in the prognostication and treatment of acute myeloid leukemia. Recent revisions in the European LeukemiaNet 2022 guidelines have refined the molecular, cytogenetic, and treatment-related boundaries between myelodysplastic neoplasms (MDS) and AML. This review details the molecular mechanisms and cellular pathways of myeloid maturation aberrancies contributing to dysplasia and leukemogenesis, focusing on recent molecular categories introduced in ELN 2022. We provide insights into novel and rational therapeutic combination strategies that exploit mechanisms of leukemogenesis, highlighting the underpinnings of splicing factors, the cohesin complex, and chromatin remodeling. Areas of interest for future research are summarized, and we emphasize approaches designed to advance existing treatment strategies.

Secondary Acute Myeloid Leukemia in Myelodysplastic Syndrome Patients Aged Over 60 Years

In myelodysplastic syndrome (MDS), neoplastic cells originate in hematopoietic stem cells of the bone marrow, causing dysplasia in multiple cell lines. This may ultimately lead to cytopenia and anemia. MDS generally occurs in patients aged over 60 years, and if left unchecked, it can lead to secondary acute myeloid leukemia (AML), which has a worse prognosis than de novo AML. Hence, it is important to find methods to treat and manage MDS and prevent secondary AML. This review tries to point out the best methods to find out the best possible treatment for MDS, which can lead to its remission or possibly cure and prevent it from progressing into AML. In order to do this, the pathogenesis of MDS is taken into account, and it is clear that the various molecular mutations that lead to the hematologic neoplasms directly affect the different chemotherapy agents that can be used. The different common mutations leading to MDS and secondary AML have been reviewed along with the drugs best inclined to target them. Some mutations lead to a worse prognosis than others, and ongoing mutations can lead to drug-resistant neoplasms. Thus, drugs targeting the mutations need to be used. The feasibility of an allogeneic stem cell transplant is also taken into account, as this can lead to a total cure of MDS. Methods of decreasing post-transplant recovery time and complications have been looked into, and more studies need to be done on the matter. Currently, it is clear that a more personalized approach to each individual case with its own set of drug combinations is the best approach to treating MDS and secondary leukemia and increasing the overall survival (OS).

Novel Investigational Agents and Pathways That May Influence the Future Management of Acute Myeloid Leukemia

Acute Myeloid leukemia (AML) is a clinically heterogeneous disease with a 5-year overall survival of 32% between 2012 to 2018. The above number severely dwindles with age and adverse risk of disease, presenting opportunities for new drug development and is an area of dire unmet need. Basic science and clinical investigators across the world have been working on many new and old molecule formulations and combination strategies to improve outcomes in this disease. In this review, we discuss select promising novel agents in various stages of clinical development for patients with AML.

Proteolysis-targeting chimeras in biotherapeutics: Current trends and future applications

The success of inhibitor-based therapeutics is largely constrained by the acquisition of therapeutic resistance, which is partially driven by the undruggable proteome. The emergence of proteolysis targeting chimera (PROTAC) technology, designed for degrading proteins involved in specific biological processes, might provide a novel framework for solving the above constraint. A heterobifunctional PROTAC molecule could structurally connect an E3 ubiquitin ligase ligand with a protein of interest (POI)-binding ligand by chemical linkers. Such technology would result in the degradation of the targeted protein via the ubiquitin-proteasome system (UPS), opening up a novel way of selectively inhibiting undruggable proteins. Herein, we will highlight the advantages of PROTAC technology and summarize the current understanding of the potential mechanisms involved in biotherapeutics, with a particular focus on its application and development where therapeutic benefits over classical small-molecule inhibitors have been achieved. Finally, we discuss how this technology can contribute to developing biotherapeutic drugs, such as antivirals against infectious diseases, for use in clinical practices.

Targeting splicing factors for cancer therapy

Alternative splicing (AS) of mRNAs is an essential regulatory mechanism in eukaryotic gene expression. AS misregulation, caused by either dysregulation or mutation of splicing factors, has been shown to be involved in cancer development and progression, making splicing factors suitable targets for cancer therapy. In recent years, various types of pharmacological modulators, such as small molecules and oligonucleotides, targeting distinct components of the splicing machinery, have been under development to treat multiple disorders. Although these approaches have promise, targeting the core spliceosome components disrupts the early stages of spliceosome assembly and can lead to nonspecific and toxic effects. New research directions have been focused on targeting specific splicing factors for a more precise effect. In this Perspective, we will highlight several approaches for targeting splicing factors and their functions and suggest ways to improve their specificity.

Alternative mRNA Splicing and Promising Therapies in Cancer

Cancer is among the leading causes of mortality worldwide. While considerable attention has been given to genetic and epigenetic sources of cancer-specific cellular activities, the role of alternative mRNA splicing has only recently received attention as a major contributor to cancer initiation and progression. The distribution of alternate mRNA splicing variants in cancer cells is different from their non-cancer counterparts, and cancer cells are more sensitive than non-cancer cells to drugs that target components of the splicing regulatory network. While many of the alternatively spliced mRNAs in cancer cells may represent "noise" from splicing dysregulation, certain recurring splicing variants have been shown to contribute to tumor progression. Some pathogenic splicing disruption events result from mutations in cis-acting splicing regulatory sequences in disease-associated genes, while others may result from shifts in balance among naturally occurring alternate splicing variants among mRNAs that participate in cell cycle progression and the regulation of apoptosis. This review provides examples of cancer-related alternate splicing events resulting from each step of mRNA processing and the promising therapies that may be used to address them.

Non-canonical functions of spliceosome components in cancer progression

Dysregulation of pre-mRNA splicing is a common hallmark of cancer cells and it is associated with altered expression, localization, and mutations of the components of the splicing machinery. In the last few years, it has been elucidated that spliceosome components can also influence cellular processes in a splicing-independent manner. Here, we analyze open source data to understand the effect of the knockdown of splicing factors in human cells on the expression and splicing of genes relevant to cell proliferation, migration, cell cycle regulation, DNA repair, and cell death. We supplement this information with a comprehensive literature review of non-canonical functions of splicing factors linked to cancer progression. We also specifically discuss the involvement of splicing factors in intercellular communication and known autoregulatory mechanisms in restoring their levels in cells. Finally, we discuss strategies to target components of the spliceosome machinery that are promising for anticancer therapy. Altogether, this review greatly expands understanding of the role of spliceosome proteins in cancer progression.

RNA splicing factors in normal hematopoiesis and hematologic malignancies: novel therapeutic targets and strategies

RNA splicing, a crucial transesterification-based process by which noncoding regions are removed from premature RNA to create mature mRNA, regulates various cellular functions, such as proliferation, survival, and differentiation. Clinical and functional studies over the past 10 y have confirmed that mutations in RNA splicing factors are among the most recurrent genetic abnormalities in hematologic neoplasms, including myeloid malignancies, chronic lymphocytic leukemia, mantle cell lymphoma, and clonal hematopoiesis. These findings indicate an important role for splicing factor mutations in the development of clonal hematopoietic disorders. Mutations in core or accessory components of the RNA spliceosome complex alter splicing sites in a manner of change of function. These changes can result in the dysregulation of cancer-associated gene expression and the generation of novel mRNA transcripts, some of which are not only critical to disease development but may be also serving as potential therapeutic targets. Furthermore, multiple studies have revealed that hematopoietic cells bearing mutations in splicing factors depend on the expression of the residual wild-type allele for survival, and these cells are more sensitive to reduced expression of wild-type splicing factors or chemical perturbations of the splicing machinery. These findings suggest a promising possibility for developing novel therapeutic opportunities in tumor cells based on mutations in splicing factors. Here, we combine current knowledge of the mechanistic and functional effects of frequently mutated splicing factors in normal hematopoiesis and the effects of their mutations in hematologic malignancies. Moreover, we discuss the development of potential therapeutic opportunities based on these mutations.

Experimental drugs in clinical trials for acute myeloid leukemia: innovations, trends, and opportunities

INTRODUCTION

Acute myeloid leukemia (AML) is a heterogeneous disease characterized by many cytogenetic and molecular alterations. Due to better knowledge of the molecular basis of AML, many targeted therapies have been introduced and registered, e.g. FMS-like tyrosine kinase 3 inhibitors, isocitrate dehydrogenase 1/2 mutation inhibitors, and Bcl-2 inhibitor. Despite that, the cure for AML remains an unmet clinical need in most patients.

AREAS COVERED

The review aims to present new, not yet registered drugs for AML. We searched the English literature for articles concerning AML, targeted drugs, menin inhibitors, DOT1L, BET, IDH inhibitors, FLT3, hedgehog inhibitors, Polo-like kinase inhibitors, RNA splicing, and immune therapies via PubMed. Publications from January 2000 to August 2022 were scrutinized. Additional relevant publications were obtained by reviewing the references from the chosen articles and Google search. Conference proceedings from the previous 5 years of The American Society of Hematology, the European Hematology Association, and the American Society of Clinical Oncology were searched manually. Additional relevant publications were obtained by reviewing the references.

EXPERT OPINION

For several years, the therapeutic approach in AML has become more individualized. Novel groups of drugs give hope for greater curability. High response rates have agents that restore the activity of the p53 protein. In addition, agents that work independently of a particular mutation seem promising for AML without any known mutation.

Indisulam Reduces Viability and Regulates Apoptotic Gene Expression in Pediatric High-Grade Glioma Cells

Pediatric high-grade glioma (pHGG) is one of the most aggressive brain tumors. Treatment includes surgery, radiotherapy, chemotherapy, or combination therapy in children older than 3−5 years of age. These devastating tumors are influenced by the hypoxic microenvironment that coordinatively increases the expression of carbonic anhydrases (CA9 and CA12) that are involved in pH regulation, metabolism, cell invasion, and resistance to therapy. The synthetic sulphonamide Indisulam is a potent inhibitor of CAs. The aim of this study was to evaluate the effects of Indisulam on CA9 and CA12 enzymes in pHGG cell lines. Our results indicated that, under hypoxia, the gene and protein expression of CA9 and CA12 are increased in pHGG cells. The functional effects of Indisulam on cell proliferation, clonogenic capacity, and apoptosis were measured in vitro. CA9 and CA12 gene and protein expression were analyzed by RT-PCR and western blot. The treatment with Indisulam significantly reduced cell proliferation (dose-time-dependent) and clonogenic capacity (p < 0.05) and potentiated the effect of apoptosis (p < 0.01). Indisulam promoted an imbalance in the anti-apoptotic BCL2 and pro-apoptotic BAX protein expression. Our results demonstrate that Indisulam contributes to apoptosis via imbalance of apoptotic proteins (BAX/BCL2) and suggests a potential to overcome chemotherapy resistance caused by the regulation these proteins.

Diversely substituted sulfamides for fragment-based drug discovery of carbonic anhydrase inhibitors: synthesis and inhibitory profile

A series of sulfamide fragments has been synthesised and investigated for human carbonic anhydrase inhibition. One of the fragments showing greater selectivity for cancer-related isoforms hCA IX and XII was co-crystalized with hCA II showing significant potential for fragment periphery evolution via fragment growth and linking. These opportunities will be identified in the future via the screening of this fragment structure for co-operative carbonic anhydrase binding with other structurally diverse fragments.[Figure: see text].

Recent advances in the pharmacological targeting of ubiquitin-regulating enzymes in cancer

As a post-translational modification that has pivotal roles in protein degradation, ubiquitination ensures that intracellular proteins act in a precise spatial and temporal manner to regulate diversified cellular processes. Perturbation of the ubiquitin system contributes directly to the onset and progression of a wide variety of diseases, including various subtypes of cancer. This highly regulated system has been for years an active research area for drug discovery that is exemplified by several approved drugs. In this review, we will provide an update of the main breakthrough scientific discoveries that have been leading the clinical development of ubiquitin-targeting therapies in the last decade, with a special focus on E1 and E3 modulators. We will further discuss the unique challenges of identifying new potential therapeutic targets within this ubiquitous and highly complex machinery, based on available crystallographic structures, and explore chemical approaches by which these challenges might be met.

Molecular Threat of Splicing Factor Mutations to Myeloid Malignancies and Potential Therapeutic Modulations

Splicing factors are frequently mutated in myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML). These mutations are presumed to contribute to oncogenic transformation, but the underlying mechanisms remain incompletely understood. While no specific treatment option is available for MDS/AML patients with spliceosome mutations, novel targeting strategies are actively explored, leading to clinical trials of small molecule inhibitors that target the spliceosome, DNA damage response pathway, and immune response pathway. Here, we review recent progress in mechanistic understanding of splicing factor mutations promoting disease progression and summarize potential therapeutic strategies, which, if successful, would provide clinical benefit to patients carrying splicing factor mutations.

Splicing dysregulation in human hematologic malignancies: beyond splicing mutations

Splicing is a fundamental process in pre-mRNA maturation. Whereas alternative splicing (AS) enriches the diversity of the proteome, its aberrant regulation can drive oncogenesis. So far, most attention has been given to spliceosome mutations (SMs) in the context of splicing dysregulation in hematologic diseases. However, in recent years, post-translational modifications (PTMs) and transcriptional alterations of splicing factors (SFs), just as epigenetic signatures, have all been shown to contribute to global splicing dysregulation as well. In addition, the contribution of aberrant splicing to the neoantigen repertoire of cancers has been recognized. With the pressing need for novel therapeutics to combat blood cancers, this article provides an overview of emerging mechanisms that contribute to aberrant splicing, as well as their clinical potential.

An insight into the interaction between Indisulam and human serum albumin: Spectroscopic method, computer simulation and in vitro cytotoxicity assay

Indisulam (IDM) is a sulfanilamide anticancer agent and has been identified as a molecular glue recently. It shows potential for novel therapies development and brings more hope for curing human diseases. The affinity between molecular glues and plasma protein makes it significant to understand the characteristics of such substances. Therefore, the interaction between IDM and human serum albumin (HSA) was explored through solvent experiments, computer simulation experiments, enzyme kinetics experiments, and cell viability assay. The results revealed that IDM and HSA spontaneously formed stable binary complex with the binding constant of the order 10⁵ M^-1. IDM inserted in the site I of HSA, resulting the change in HSA secondary structure. And π electrons in IDM's benzene rings, as well as van der Waals forces and the H-bond, all helped to stabilize the HSA-IDM complex. The results of molecular dynamic simulation (MD) corresponded with the results from solvent experiment well. For instance, there were approximately 1-5 H-bonds between IDM and HSA. Lys199 and Arg218 were crucial energy contributors in the binding process. The esterase-like activity experiment confirmed that IDM inhibited the catalytic activity of HSA. In addition, cell experiment revealed that serum albumin can significantly reduce the cytotoxicity of IDM towards human embryonic kidney 293T (HEK293T) cells.

Perspectives of using microRNA-loaded nanocarriers for epigenetic reprogramming of drug resistant colorectal cancers

Epigenetic regulation by microRNAs (miRs) demonstrated a promising therapeutic potential of these molecules to regulate genetic activity in different cancers, including colorectal cancers (CRCs). The RNA-based therapy does not change genetic codes in tumor cells but can silence oncogenes and/or reactivate inhibited tumor suppressor genes. In many cancers, specific miRs were shown to promote or stop tumor progression. Among confirmed and powerful epigenetic regulators of colon carcinogenesis and development of resistance are onco-miRs, which include let-7, miR-21, miR-22, miR-23a, miR-27a, miR-34, miR-92, miR-96, miR-125b, miR-135b, miR-182, miR-200c, miR-203, miR-221, miR-421, miR-451, and others. Moreover, various tumor-suppressor miRs (miR-15b-5b, miR-18a, miR-20b, miR-22, miR-96, miR-139-5p, miR-145, miR-149, miR-197, miR-199b, miR-203, miR-214, miR-218, miR-320, miR-375-3p, miR-409-3p, miR-450b-5p, miR-494, miR-577, miR-874, and others) were found silenced in drug-resistant CRCs. Re-expression of tumor suppressor miR is complicated by the chemical nature of miRs that are not long-lasting compounds and require protection from the enzymatic degradation. Several recent studies explored application of miRs using nanocarrier complexes. This study critically describes the most successfully tested nanoparticle complexes used for intracellular delivery of nuclear acids and miRs, including micelles, liposomes, inorganic and polymeric NPs, dendrimers, and aptamers. Nanocarriers shield incorporated miRs and improve the agent stability in circulation. Attachment of antibodies and/or specific peptide or ligands facilitates cell-targeted miR delivery. Addressing in vivo challenges, a broad spectrum of non-toxic materials has been tested and indicated reliable advantages of lipid-based (lipoplexes) and polymer-based liposomes. Recent cutting-edge developments indicated that lipid-based complexes with multiple cargo, including several miRs, are the most effective approach to eradicate drug-resistant tumors. Focusing on CRC-specific miRs, this review provides a guidance and insights towards the most promising direction to achieve dramatic reduction in tumor growth and metastasis using miR-nanocarrier complexes.

Genetic and compound screens uncover factors modulating cancer cell response to indisulam

The authors identify that loss of SRPK1 sensitises cancer cells to indisulam treatment and loss of CAND1 confers resistance. Resistance is mediated through RBM39. Furthermore, pharmacological Bcl-xL inhibition prevents acquired resistance to indisulam.

Discovering biomarkers of drug response and finding powerful drug combinations can support the reuse of previously abandoned cancer drugs in the clinic. Indisulam is an abandoned drug that acts as a molecular glue, inducing degradation of splicing factor RBM39 through interaction with CRL4^DCAF15. Here, we performed genetic and compound screens to uncover factors mediating indisulam sensitivity and resistance. First, a dropout CRISPR screen identified SRPK1 loss as a synthetic lethal interaction with indisulam that can be exploited therapeutically by the SRPK1 inhibitor SPHINX31. Moreover, a CRISPR resistance screen identified components of the degradation complex that mediate resistance to indisulam: DCAF15, DDA1, and CAND1. Last, we show that cancer cells readily acquire spontaneous resistance to indisulam. Upon acquiring indisulam resistance, pancreatic cancer (Panc10.05) cells still degrade RBM39 and are vulnerable to BCL-xL inhibition. The better understanding of the factors that influence the response to indisulam can assist rational reuse of this drug in the clinic.

Interplay between A-to-I Editing and Splicing of RNA: A Potential Point of Application for Cancer Therapy

Adenosine-to-inosine RNA editing is a system of post-transcriptional modification widely distributed in metazoans which is catalyzed by ADAR enzymes and occurs mostly in double-stranded RNA (dsRNA) before splicing. This type of RNA editing changes the genetic code, as inosine generally pairs with cytosine in contrast to adenosine, and this expectably modulates RNA splicing. We review the interconnections between RNA editing and splicing in the context of human cancer. The editing of transcripts may have various effects on splicing, and resultant alternatively spliced isoforms may be either tumor-suppressive or oncogenic. Dysregulated RNA splicing in cancer often causes the release of excess amounts of dsRNA into cytosol, where specific dsRNA sensors provoke antiviral-like responses, including type I interferon signaling. These responses may arrest cell division, causing apoptosis and, externally, stimulate antitumor immunity. Thus, small-molecule spliceosome inhibitors have been shown to facilitate the antiviral-like signaling and are considered to be potential cancer therapies. In turn, a cytoplasmic isoform of ADAR can deaminate dsRNA in cytosol, thereby decreasing its levels and diminishing antitumor innate immunity. We propose that complete or partial inhibition of ADAR may enhance the proapoptotic and cytotoxic effects of splicing inhibitors and that it may be considered a promising addition to cancer therapies targeting RNA splicing.

Dysregulation and therapeutic targeting of RNA splicing in cancer

High-throughput sequencing and functional characterization of the cancer transcriptome have uncovered cancer-specific dysregulation of RNA splicing across a variety of cancers. Alterations in the cancer genome and dysregulation of RNA splicing factors lead to missplicing, splicing alteration-dependent gene expression and, in some cases, generation of novel splicing-derived proteins. Here, we review recent advances in our understanding of aberrant splicing in cancer pathogenesis and present strategies to harness cancer-specific aberrant splicing for therapeutic intent.

Somatic Mutations in Core Spliceosome Components Promote Tumorigenesis and Generate an Exploitable Vulnerability in Human Cancer

Simple Summary

High throughput exome sequencing approaches have disclosed recurrent cancer-associated mutations in spliceosomal components, which drive aberrant pre-mRNA processing events and support the tumor phenotype. At the same time, mutations in spliceosome genes and aberrant splicing regulation establish a selective vulnerability of cancer cells to splicing-targeting approaches, which could be exploited therapeutically. It is conceivable that a better understanding of the mechanisms and roles of abnormal splicing in tumor metabolism will facilitate the development of a novel generation of tumor-targeting drugs. In this review, we describe recent advances in the elucidation of the biological impact and biochemical effects of somatic mutations in core spliceosome components on splicing choices and their associated targetable vulnerabilities.

Abstract

Alternative pre-mRNA processing enables the production of distinct mRNA and protein isoforms from a single gene, thus greatly expanding the coding potential of eukaryotic genomes and fine-tuning gene expression programs. Splicing is carried out by the spliceosome, a complex molecular machinery which assembles step-wise on mRNA precursors in the nucleus of eukaryotic cells. In the last decade, exome sequencing technologies have allowed the identification of point mutations in genes encoding splicing factors as a recurrent hallmark of human cancers, with higher incidence in hematological malignancies. These mutations lead to production of splicing factors that reduce the fidelity of the splicing process and yield splicing variants that are often advantageous for cancer cells. However, at the same time, these mutations increase the sensitivity of transformed cells to splicing inhibitors, thus offering a therapeutic opportunity for novel targeted strategies. Herein, we review the recent literature documenting cancer-associated mutations in components of the early spliceosome complex and discuss novel therapeutic strategies based on small-molecule spliceosome inhibitors that exhibit strong anti-tumor effects, particularly against cancer cells harboring mutations in spliceosomal components.

Reprogramming RNA processing: an emerging therapeutic landscape

The production of a mature mRNA requires coordination of multiple processing steps, which ultimately control its content, localization, and stability. These steps include some of the largest macromolecular machines in the cell, which were, until recently, considered undruggable due to their biological complexity. Building from an expanded understanding of the underlying mechanisms that drive these processes, a new wave of therapeutics is seeking to target RNA processing. With a focus on impacting gene regulation at the RNA level, such modalities offer potential for sequence-specific resolution in drug design. Here, we review our current understanding of RNA-processing events and their role in gene regulation, with a focus on the therapeutic opportunities that have emerged within this landscape.

Translating recent advances in the pathogenesis of acute myeloid leukemia to the clinic

Despite FDA approval of nine new drugs for patients with acute myeloid leukemia (AML) in the United States over the last 4 years, AML remains a major area of unmet medical need among hematologic malignancies. In this review, we discuss the development of promising new molecular targeted approaches for AML, including menin inhibition, novel IDH1/2 inhibitors, and preclinical means to target TET2, ASXL1, and RNA splicing factor mutations. In addition, we review progress in immune targeting of AML through anti-CD47, anti-SIRPα, and anti-TIM-3 antibodies; bispecific and trispecific antibodies; and new cellular therapies in development for AML.

Identification of Novel and Potent Indole-Based Benzenesulfonamides as Selective Human Carbonic Anhydrase II Inhibitors: Design, Synthesis, In Vitro, and In Silico Studies

In recent decades, human carbonic anhydrase inhibitors (hCAIs) have emerged as an important therapeutic class with various applications including antiglaucoma, anticonvulsants, and anticancer agents. Herein, a novel series of indole-based benzenesulfonamides were designed, synthesized, and biologically evaluated as potential hCAIs. A regioisomerism of the sulfonamide moiety was carried out to afford a total of fifteen indole-based benzenesulfonamides possessing different amide linkers that enable the ligands to be flexible and develop potential H-bond interaction(s) with the target protein. The activity of the synthesized compounds was evaluated against four hCA isoforms (I, II, IX and, XII). Compounds 2b, 2c, 2d, 2f, 2h and 2o exhibited potent and selective profiles over the hCA II isoform with K_i values of 7.3, 9.0, 7.1, 16.0, 8.6 and 7.5 nM, respectively. Among all, compound 2a demonstrated the most potent inhibition against the hCA II isoform with an inhibitory constant (K_i) of 5.9 nM, with 13-, 34-, and 9-fold selectivity for hCA II over I, IX and XII isoforms, respectively. Structure–activity relationship data attained for various substitutions were rationalized. Furthermore, a molecular docking study gave insights into both inhibitory activity and selectivity of the target compounds. Accordingly, this report presents a successful scaffold hoping approach that reveals compound 2a as a highly potent and selective indole-based hCA II inhibitor worthy of further investigation.

Activable Targeted Protein Degradation Platform Based on Light-triggered Singlet Oxygen

Targeted protein degradation technologies (e.g., PROTACs) that can selectively degrade intracellular protein are an emerging class of promising therapeutic modalities. Herein, we describe the conjugation of photosensitizers and protein ligands (PS-Degrons), as an activable targeted protein degradation platform. PS-Degrons are capable of degrading protein of interest via light-triggered ¹O₂, which is orthogonal and complementary to existing technologies. This generalizable platform allows controllable knockdown of the target protein with high spatiotemporal precision. Our lead compound PSDalpha induces a complete degradation of human estrogen receptor α (ERα) under visible light. The high degrading ERα efficacy of PSDalpha enables an excellent anti-proliferation performance on MCF-7 cells. Our results establish a modular strategy for the controllable degradation of target proteins, which can hopefully overcome the systemic toxicity in clinical treatment of PROTACs. We anticipate that PS-Degrons would open a new chapter for biochemical research and for the therapeutics.

Clinical factors predictive of recurrent febrile neutropenia in adult patients with acute leukemia

Febrile neutropenia (FN) is considered an oncologic emergency in acute leukemia. There were 250 FN events in 124 hospitalized patients with hematologic malignancy. These data imply that two FN events may occur per patient, yet data on the prevalence, risk factors, and outcomes of recurrent FN in adult patients with leukemia are limited. A retrospective cohort study was conducted that enrolled adult patients diagnosed with acute leukemia who developed FN. The eligible patients were categorized as with or without recurrent FN. A stepwise, multivariate logistic regression analysis was performed to identify predictors of recurrent FN. A total of 203 patients met the study criteria; of these, 46 (22.66%) had recurrent FN, and this group had a median of three recurrent FN emergencies. After adjusted, three independent factors remained in the final model including ALL, FN at admission, and treatment with idarubicin (3 days) and cytarabine (7 days). The three factors were positively associated with recurrent FN with adjusted odds ratios of 6.253, 4.068, and 10.757, respectively. No significant differences were found between the two groups in terms of other sources of infection, other pathogens, ICU stay, hospital stay, and mortality. ALL and FN at admission and treatment with idarubicin (3 days) and cytarabine (7 days) were associated with recurrent FN in acute leukemia patients with FN. Clinical outcomes for patients with or without recurrent FN were mostly comparable; however, due to its small sample size, further studies are required to confirm the results of this study.

RNA-binding proteins as drivers of AML and novel therapeutic targets

Acute myeloid leukemia (AML) is a group of genetically complex and heterogeneous invasive hematological malignancies with a low 5-year overall survival rate of 30%, which highlights the urgent need for improved treatment measures. RNA-binding proteins (RBPs) regulate the abundance of isoforms of related proteins by regulating RNA splicing, translation, stability, and localization, thereby affecting cell differentiation and self-renewal. It is increasingly believed that RBPs are essential for normal hematopoiesis, and RBPs play a key role in hematological tumors, especially AML, by acting as oncogenes or tumor suppressors. In addition, targeting an RBP that is significantly related to AML can trigger the apoptosis of leukemic stem cells or promote the proliferation of stem and progenitor cells by modulating the expression of important pathway regulatory factors such as HOXA9, MYC, and CDKN1A. Accordingly, RBPs involved in normal myeloid differentiation and the occurrence of AML may represent promising therapeutic targets.

Synthesis and Anticancer Activity of Pentafluorobenzenesulfonamide Derivatives as Caspase-Dependent Apoptosis-Inducing Agents

Arylsulfonamides are ubiquitous in a number of anticancer agents, and fluorine substitution on aromatic rings often improves drug profile. Herein, a series of novel pentafluorobenzenesulfonamide derivatives with different molecular scaffolds were readily synthesized and assessed for their antitumor activities against multiple cancer cell lines, including A549, HepG2, HuCCA-1, and MOLT-3. Dihydroimidazoline-containing analogue and its Diels-Alder cycloadducts exhibited enhanced cytotoxicity at micromolar range while the incorporation of other heterocyclic cores via nucleophilic substitution reaction resulted in diminished potency. Selected analogues were shown to induce the accumulation of cleaved forms of Casp-9, Casp-7 and PARP in cancer cells, indicating intrinsic apoptosis via a caspase-dependent process.

Advancing targeted protein degradation for cancer therapy

The human proteome contains approximately 20,000 proteins, and it is estimated that more than 600 of them are functionally important for various types of cancers, including nearly 400 non-enzyme proteins that are challenging to target by traditional occupancy-driven pharmacology. Recent advances in the development of small-molecule degraders, including molecular glues and heterobifunctional degraders such as proteolysis-targeting chimeras (PROTACs), have made it possible to target many proteins that were previously considered undruggable. In particular, PROTACs form a ternary complex with a hijacked E3 ubiquitin ligase and a target protein, leading to polyubiquitination and degradation of the target protein. The broad applicability of this approach is facilitated by the flexibility of individual E3 ligases to recognize different substrates. The vast majority of the approximately 600 human E3 ligases have not been explored, thus presenting enormous opportunities to develop degraders that target oncoproteins with tissue, tumour and subcellular selectivity. In this Review, we first discuss the molecular basis of targeted protein degradation. We then offer a comprehensive account of the most promising degraders in development as cancer therapies to date. Lastly, we provide an overview of opportunities and challenges in this exciting field.

RNA-binding protein 39: a promising therapeutic target for cancer

RNA-binding motif protein 39 (RBM39), as a key factor in tumor-targeted mRNA and protein expression, not only plays a vital role in tumorigenesis, but also has broad development prospects in clinical treatment and drug research. Moreover, since RBM39 was identified as a target of sulfonamides, it has played a key role in the emerging field of molecule drug development. Hence, it is of great significance to study the interaction between RBM39 and tumors and the clinical application of drug-targeted therapy. In this paper, we describe the possible multi-level regulation of RBM39, including gene transcription, protein translation, and alternative splicing. Importantly, the molecular function of RBM39 as an important splicing factor in most common tumors is systematically outlined. Furthermore, we briefly introduce RBM39’s tumor-targeted drug research and its clinical application, hoping to give reference significance for the molecular mechanism of RBM39 in tumors, and provide reliable ideas for in-depth research for future therapeutic strategies.

Therapeutic approaches targeting splicing factor mutations in myelodysplastic syndromes and acute myeloid leukemia

PURPOSE OF REVIEW

Mutations in components of the spliceosome are the most common acquired lesions in myelodysplastic syndromes (MDS) and are frequently identified in other myeloid malignancies with a high rate of progression to acute myeloid leukemia (AML) including chronic myelomonocytic leukemia and primary myelofibrosis. The only curative option for these disorders remains allogeneic stem-cell transplantation, which is associated with high morbidity and mortality in these patients. The purpose of this review is to highlight the recent therapeutic developments and strategies being pursued for clinical benefit in splicing factor mutant myeloid malignancies.

RECENT FINDINGS

Cells harboring splicing factor mutations have increased aberrant splicing leading to R-loop formation and cell cycle stalling that create dependencies on Checkpoint kinase 1 (CHK1) activation and canonical splicing maintained by protein arginine methyltransferase activity. Both targeting of the spliceosome and targeting of the downstream consequences of splicing factor mutation expression show promise as selective strategies for the treatment of splicing factor-mutant myeloid malignancies.

SUMMARY

An improved understanding of the therapeutic vulnerabilities in splicing factor-mutant MDS and AML has led to the development of clinical trials of small molecule inhibitors that target the spliceosome, ataxia telangectasia and Rad3 related (ATR)-CHK1 pathway, and methylation of splicing components.

Targeting KRAS4A splicing through the RBM39/DCAF15 pathway inhibits cancer stem cells

The commonly mutated human KRAS oncogene encodes two distinct KRAS4A and KRAS4B proteins generated by differential splicing. We demonstrate here that coordinated regulation of both isoforms through control of splicing is essential for development of Kras mutant tumors. The minor KRAS4A isoform is enriched in cancer stem-like cells, where it responds to hypoxia, while the major KRAS4B is induced by ER stress. KRAS4A splicing is controlled by the DCAF15/RBM39 pathway, and deletion of KRAS4A or pharmacological inhibition of RBM39 using Indisulam leads to inhibition of cancer stem cells. Our data identify existing clinical drugs that target KRAS4A splicing, and suggest that levels of the minor KRAS4A isoform in human tumors can be a biomarker of sensitivity to some existing cancer therapeutics.

Splicing factor mutations in hematologic malignancies

Mutations in genes encoding RNA splicing factors were discovered nearly ten years ago and are now understood to be amongst the most recurrent genetic abnormalities in patients with all forms of myeloid neoplasms and several types of lymphoproliferative disorders as well as subjects with clonal hematopoiesis. These discoveries implicate aberrant RNA splicing, the process by which precursor RNA is converted into mature messenger RNA, in the development of clonal hematopoietic conditions. Both the protein as well as the RNA components of the splicing machinery are affected by mutations at highly specific residues and a number of these mutations alter splicing in a manner distinct from loss of function. Importantly, cells bearing these mutations have now been shown to generate mRNA species with novel aberrant sequences, some of which may be critical to disease pathogenesis and/or novel targets for therapy. These findings have opened new avenues of research to understand biological pathways disrupted by altered splicing. In parallel, multiple studies have revealed that cells bearing change-of-function mutation in splicing factors are preferentially sensitized to any further genetic or chemical perturbations of the splicing machinery. These discoveries are now being pursued in several early phase clinical trials using molecules with diverse mechanisms of action. Here we review the molecular effects of splicing factor mutations on splicing, mechanisms by which these mutations drive clonal transformation of hematopoietic cells, and the development of new therapeutics targeting these genetic subsets of hematopoietic malignancies.