PARP1 PARylates and stabilizes STAT5 in FLT3-ITD acute myeloid leukemia and other STAT5-activated cancers

Transcriptional regulation mechanism of PARP1 and its application in disease treatment

Poly (ADP-ribose) polymerase 1 (PARP1) is a multifunctional nuclear enzyme that catalyzes poly-ADP ribosylation in eukaryotic cells. In addition to maintaining genomic integrity, this nuclear enzyme is also involved in transcriptional regulation. PARP1 can trigger and maintain changes in the chromatin structure and directly recruit transcription factors. PARP1 also prevents DNA methylation. However, most previous reviews on PARP1 have focused on its involvement in maintaining genome integrity, with less focus on its transcriptional regulatory function. This article comprehensively reviews the transcriptional regulatory function of PARP1 and its application in disease treatment, providing new ideas for targeting PARP1 for the treatment of diseases other than cancer.

PARP1 promotes EGFR-TKI drug-resistance via PI3K/AKT pathway in non-small-cell lung cancer

PURPOSE

Tyrosine kinase inhibitor (TKI) resistance is the main type of drug resistance in lung cancer patients with epidermal growth factor receptor (EGFR) mutations, but its underlying mechanism remains unclear. The purpose of this work was to investigate the mechanism by which PARP1 regulates EGFR-TKI resistance to identify potential targets for combating drug resistance.

METHODS

The GEO databases, TCGA databases, western blot and qPCR studies were used to investigate the expression of PARP1 in lung cancer cells and tissues and its correlation with the prognosis of lung cancer. The expression of PARP1 in lung cancer TKI resistant cell PC9-ER and TKI sensitive cell PC9 was analyzed by qPCR and western blot. After knocking down of PARP1, CCK-8 assays, colony formation, flow cytometry were used to investigate its impact on erlotinib sensitivity, cell survival, cell cycle, and apoptosis. RNA-seq was used to investigate the mechanism by which PARP1 participates in EGFR-TKI resistance, and the results were validated in vitro and in vivo studies.

RESULTS

PARP1 was highly expressed in both lung cancer tissues and cells. Subsequently, increased PARP1 expression was observed in PC9-ER compared with its parental cell line. Knockdown of PARP1 increased erlotinib sensitivity, promoted cell apoptosis, and suppressed cell growth. RNA-seq and previous studies have shown that the PI3K/AKT/mTOR/P70S6K pathway is involved in PARP1-mediated TKI resistance, and these results were confirmed by Western blot in vitro and in vivo.

CONCLUSION

PARP1 may serve as a potential therapeutic target for reversing EGFR-TKI resistance in NSCLC via the PI3K/AKT/mTOR/P70S6K pathway.

Targeting of STAT5 using the small molecule topotecan hydrochloride suppresses acute myeloid leukemia progression

Acute myeloid leukemia (AML) is a common type of acute leukemia in adults and relapse is one of the main reasons for treatment failure. FLT3‑ITD mutations are associated with poor prognosis, short disease‑free progression survival and high relapse rates in patients with AML. STAT5 is activated by FLT3‑ITD and drives the pathogenesis of AML. STAT5 activation is usually a hallmark of hematologic malignancies and occurs in ~70% of patients with AML. Moreover, STAT5 is a key molecule which regulates hematopoiesis, and its high expression is closely associated with drug resistance, thus direct targeting of STAT5 for AML is of great clinical value. The present study introduces a new small‑molecule inhibitor that targets STAT5, presenting a promising approach for AML therapy. A high throughput fluorescence polarization (FP) screening system for STAT5 was designed and established, and used to screen an existing compound library to obtain the highly active small molecule inhibitor, topotecan hydrochloride. Topotecan hydrochloride was demonstrated to be an effective inhibitor of STAT5 by molecular docking prediction and cellular thermal shift assay. Topotecan hydrochloride bound to STAT5, inhibiting its dimerization, phosphorylation and transcription of specific target genes. The compound exhibits cellular activity at the nanomolar level and significantly inhibits the proliferation of human AML cell lines and FLT3‑ITD+ AML cells. Furthermore, topotecan hydrochloride has the potential to exert an anti‑tumor effect in vivo. Overall, topotecan hydrochloride offers a new opportunity for the treatment of AML and other hematologic malignancies by directly targeting STAT5.

DNA damage accumulation and repair defects in FLT3-ITD acute myeloid leukemia: Implications for clonal evolution and disease progression

Acute myeloid leukemia is a group of hematological diseases that have a high mortality rate. During the development of this pathology, hematopoietic cells acquire chromosomal rearrangements and multiple genetic mutations, including FLT3-ITD. FLT3-ITD is a marker associated with a poor clinical prognosis and involves the activation of pathways such as PI3K/AKT, MAPK/ERK, and JAK/STAT that favor the survival and proliferation of leukemic cells. In addition, FLT3-ITD leads to overproduction of reactive oxygen species and defective DNA damage repair, both implicated in the appearance of new mutations and leukemic clones. Thus, the purpose of this review is to illustrate the molecular mechanisms through which FLT3-ITD generates genetic instability and how it facilitates clonal evolution with the generation of more resistant and aggressive cells. Likewise, this article discusses the feasibility of combined therapies with FLT3 inhibitors and inhibitors of DNA repair pathways.

Human PARP1 substrates and regulators of its catalytic activity: An updated overview

Poly (ADP-ribose) polymerase 1 (PARP1) is a key DNA damage sensor that is recruited to damaged sites after DNA strand breaks to initiate DNA repair. This is achieved by catalyzing attachment of ADP-ribose moieties, which are donated from NAD⁺, on the amino acid residues of itself or other acceptor proteins. PARP inhibitors (PARPi) that inhibit PARP catalytic activity and induce PARP trapping are commonly used for treating BRCA1/2-deficient breast and ovarian cancers through synergistic lethality. Unfortunately, resistance to PARPi frequently occurs. In this review, we present the novel substrates and regulators of the PARP1-catalyzed poly (ADP-ribosyl)ation (PARylatison) that have been identified in the last 3 years. The overall aim is the presentation of protein interactions of potential therapeutic intervention for overcoming the resistance to PARPi.

The role of E3 ubiquitin ligase WWP2 and the regulation of PARP1 by ubiquitinated degradation in acute lymphoblastic leukemia

Acute lymphoblastic leukemia (ALL) has been a huge threat for people's health and finding effective target therapy is urgent and important. WWP2, as one of E3 ubiquitin ligase, is involved in many biological processes by specifically binding to substrates. PARP1 plays a role in cell apoptosis and is considered as a therapeutic target of certain cancers. In this study, we firstly found that WWP2 expressed higher in newly diagnosed ALL patients comparing with complete remission (CR) ALL patients and normal control people, and WWP2 in relapse ALL patients expressed higher than normal control people. WWP2 expression was related with the FAB subtype of ALL and the proportion of blast cells in bone marrow blood tested by flow cytometry. We demonstrated knockout WWP2 inhibited the ALL growth and enhanced apoptosis induced by Dox in vitro and vivo for the first time. WWP2 negatively regulated and interacted with PARP1 and WWP2 mechanically degraded PARP1 through polyubiquitin-proteasome pathway in ALL. These findings suggested WWP2 played a role in ALL development as well as growth and apoptosis, and also displayed a regulatory pathway of PARP1, which provided a new potential therapeutic target for the treatment of ALL.

Pharmacologic Induction of BRCAness in BRCA-Proficient Cancers: Expanding PARP Inhibitor Use

The poly(ADP-ribose) polymerase (PARP) family of proteins has been implicated in numerous cellular processes, including DNA repair, translation, transcription, telomere maintenance, and chromatin remodeling. Best characterized is PARP1, which plays a central role in the repair of single strand DNA damage, thus prompting the development of small molecule PARP inhibitors (PARPi) with the intent of potentiating the genotoxic effects of DNA damaging agents such as chemo- and radiotherapy. However, preclinical studies rapidly uncovered tumor-specific cytotoxicity of PARPi in a subset of cancers carrying mutations in the BReast CAncer 1 and 2 genes (BRCA1/2), which are defective in the homologous recombination (HR) DNA repair pathway, and several PARPi are now FDA-approved for single agent treatment in BRCA-mutated tumors. This phenomenon, termed synthetic lethality, has now been demonstrated in tumors harboring a number of repair gene mutations that produce a BRCA-like impairment of HR (also known as a 'BRCAness' phenotype). However, BRCA mutations or BRCAness is present in only a small subset of cancers, limiting PARPi therapeutic utility. Fortunately, it is now increasingly recognized that many small molecule agents, targeting a variety of molecular pathways, can induce therapeutic BRCAness as a downstream effect of activity. This review will discuss the potential for targeting a broad range of molecular pathways to therapeutically induce BRCAness and PARPi synthetic lethality.

PARP Inhibitors and Myeloid Neoplasms: A Double-Edged Sword

Simple Summary

Poly(ADP-ribose) polymerase (PARP) inhibitors, which are medications approved to treat various solid tumors, including breast, prostate, ovarian, and prostate cancers, are being examined in hematological malignancies. This review summarizes the potential role of PARP inhibitors in the treatment of myeloid diseases, particularly acute myeloid leukemia (AML). We review ongoing clinical studies investigating the safety and efficacy of PARP inhibitors in the treatment of AML, focusing on specific molecular and genetic AML subgroups that could be particularly sensitive to PARP inhibitor treatment. We also discuss reports describing an increased risk of treatment-related myeloid neoplasms in patients receiving PARP inhibitors for solid tumors.

Abstract

Despite recent discoveries and therapeutic advances in aggressive myeloid neoplasms, there remains a pressing need for improved therapies. For instance, in acute myeloid leukemia (AML), while most patients achieve a complete remission with conventional chemotherapy or the combination of a hypomethylating agent and venetoclax, de novo or acquired drug resistance often presents an insurmountable challenge, especially in older patients. Poly(ADP-ribose) polymerase (PARP) enzymes, PARP1 and PARP2, are involved in detecting DNA damage and repairing it through multiple pathways, including base excision repair, single-strand break repair, and double-strand break repair. In the context of AML, PARP inhibitors (PARPi) could potentially exploit the frequently dysfunctional DNA repair pathways that, similar to deficiencies in homologous recombination in BRCA-mutant disease, set the stage for cell killing. PARPi appear to be especially effective in AML with certain gene rearrangements and molecular characteristics (RUNX1-RUNX1T1 and PML-RARA fusions, FLT3- and IDH1-mutated). In addition, PARPi can enhance the efficacy of other agents, particularly alkylating agents, TOP1 poisons, and hypomethylating agents, that induce lesions ordinarily repaired via PARP1-dependent mechanisms. Conversely, emerging reports suggest that long-term treatment with PARPi for solid tumors is associated with an increased incidence of myelodysplastic syndrome (MDS) and AML. Here, we (i) review the pre-clinical and clinical data on the role of PARPi, specifically olaparib, talazoparib, and veliparib, in aggressive myeloid neoplasms and (ii) discuss the reported risk of MDS/AML with PARPi, especially as the indications for PARPi use expand to include patients with potentially curable cancer.