DNA damage induced by KP372-1 hyperactivates PARP1 and enhances lethality of pancreatic cancer cells with PARP inhibition

Nano-sensitizer with self-amplified drug release and hypoxia normalization properties potentiates efficient chemoradiotherapy of pancreatic cancer

The hypoxic nature of pancreatic cancer, one of the most lethal malignancies worldwide, significantly impedes the effectiveness of chemoradiotherapy. Although the development of oxygen carriers and hypoxic sensitizers has shown promise in overcoming tumor hypoxia. The heterogeneity of hypoxia-primarily caused by limited oxygen penetration-has posed challenges. In this study, we designed a hypoxia-responsive nano-sensitizer by co-loading tirapazamine (TPZ), KP372-1, and MK-2206 in a metronidazole-modified polymeric vesicle. This nano-sensitizer relies on efficient endogenous NAD(P)H quinone oxidoreductase 1-mediated redox cycling induced by KP372-1, continuously consuming periphery oxygen and achieving evenly distributed hypoxia. Consequently, the normalized tumor microenvironment facilitates the self-amplified release and activation of TPZ without requiring deep penetration. The activated TPZ and metronidazole further sensitize radiotherapy, significantly reducing the radiation dose needed for extensive cell damage. Additionally, the coloaded MK-2206 complements inhibition of therapeutic resistance caused by Akt activation, synergistically enhancing the hypoxic chemoradiotherapy. This successful hypoxia normalization strategy not only overcomes hypoxia resistance in pancreatic cancer but also provides a potential universal approach to sensitize hypoxic tumor chemoradiotherapy by reshaping the hypoxic distribution.

Molecular Basis of XRN2-Deficient Cancer Cell Sensitivity to Poly(ADP-ribose) Polymerase Inhibition

R-loops (RNA-DNA hybrids with displaced single-stranded DNA) have emerged as a potent source of DNA damage and genomic instability. The termination of defective RNA polymerase II (RNAPII) is one of the major sources of R-loop formation. 5'-3'-exoribonuclease 2 (XRN2) promotes genome-wide efficient RNAPII termination, and XRN2-deficient cells exhibit increased DNA damage emanating from elevated R-loops. Recently, we showed that DNA damage instigated by XRN2 depletion in human fibroblast cells resulted in enhanced poly(ADP-ribose) polymerase 1 (PARP1) activity. Additionally, we established a synthetic lethal relationship between XRN2 and PARP1. However, the underlying cellular stress response promoting this synthetic lethality remains elusive. Here, we delineate the molecular consequences leading to the synthetic lethality of XRN2-deficient cancer cells induced by PARP inhibition. We found that XRN2-deficient lung and breast cancer cells display sensitivity to two clinically relevant PARP inhibitors, Rucaparib and Olaparib. At a mechanistic level, PARP inhibition combined with XRN2 deficiency exacerbates R-loop and DNA double-strand break formation in cancer cells. Consistent with our previous findings using several different siRNAs, we also show that XRN2 deficiency in cancer cells hyperactivates PARP1. Furthermore, we observed enhanced replication stress in XRN2-deficient cancer cells treated with PARP inhibitors. Finally, the enhanced stress response instigated by compromised PARP1 catalytic function in XRN2-deficient cells activates caspase-3 to initiate cell death. Collectively, these findings provide mechanistic insights into the sensitivity of XRN2-deficient cancer cells to PARP inhibition and strengthen the underlying translational implications for targeted therapy.

NAD+ Metabolism Generates a Metabolic Vulnerability in Endocrine-Resistant Metastatic Breast Tumors in Females

Approximately 70% of human breast cancers express estrogen receptor-α (ERα), providing a potential target for endocrine therapy. However, 30% to 40% of patients with ER+ breast cancer still experience recurrence and metastasis, with a 5-year relative overall survival rate of 24%. In this study, we identified nicotinamide phosphoribosyltransferase (NAMPT), an important enzyme in nicotinamide adenine dinucleotide (NAD+) metabolism, to be increased in metastatic breast cancer (MBC) cells treated with fulvestrant (Fulv). We tested whether the blockade of NAD+ production via inhibition of NAMPT synergizes with standard-of-care therapies for ER+ MBC in vitro and in vivo. A synergistic effect was not observed when KPT-9274 was combined with palbociclib or tamoxifen or when Fulv was combined with other metabolic inhibitors. We show that NAMPT inhibitor KPT-9274 and Fulv works synergistically to reduce metastatic tumor burden. RNA-sequencing analysis showed that NAMPT inhibitor in combination with Fulv reversed the expression of gene sets associated with more aggressive tumor phenotype, and metabolomics analysis showed that NAMPT inhibition reduced the abundance of metabolites associated with several key tumor metabolic pathways. Targeting metabolic adaptations in endocrine-resistant MBC is a novel strategy, and alternative approaches aimed at improving the therapeutic response of metastatic ER+ tumors are needed. Our findings uncover the role of ERα-NAMPT crosstalk in MBC and the utility of NAMPT inhibition and antiestrogen combination therapy in reducing tumor burden and metastasis, potentially leading to new avenues of MBC treatment.

KP372-1-Induced AKT Hyperactivation Blocks DNA Repair to Synergize With PARP Inhibitor Rucaparib via Inhibiting FOXO3a/GADD45α Pathway

Poly (ADP-ribose) polymerase (PARP) inhibitors (PARPi) have exhibited great promise in the treatment of tumors with homologous recombination (HR) deficiency, however, PARPi resistance, which ultimately recovers DNA repair and cell progress, has become an enormous clinical challenge. Recently, KP372-1 was identified as a novel potential anticancer agent that targeted the redox enzyme, NAD(P)H:quinone oxidoreductase 1 (NQO1), to induce extensive reactive oxygen species (ROS) generation that amplified DNA damage, leading to cancer cell death. To overcome PARPi resistance and expand its therapeutic utility, we investigated whether a combination therapy of a sublethal dose of KP372-1 with a nontoxic dose of PARPi rucaparib would synergize and enhance lethality in NQO1 over-expressing cancers. We reported that the combination treatment of KP372-1 and rucaparib induced a transient and dramatic AKT hyperactivation that inhibited DNA repair by regulating FOXO3a/GADD45α pathway, which enhanced PARPi lethality and overcame PARPi resistance. We further found that PARP inhibition blocked KP372-1-induced PARP1 hyperactivation to reverse NAD⁺/ATP loss that promoted Ca²⁺-dependent autophagy and apoptosis. Moreover, pretreatment of cells with BAPTA-AM, a cytosolic Ca²⁺ chelator, dramatically rescued KP372-1- or combination treatment-induced lethality and significantly suppressed PAR formation and γH2AX activation. Finally, we demonstrated that this combination therapy enhanced accumulation of both agents in mouse tumor tissues and synergistically suppressed tumor growth in orthotopic pancreatic and non-small-cell lung cancer xenograft models. Together, our study provides novel preclinical evidence for new combination therapy in NQO1⁺ solid tumors that may broaden the clinical utility of PARPi.

β-Hydroxyisovaleryl-Shikonin Exerts an Antitumor Effect on Pancreatic Cancer Through the PI3K/AKT Signaling Pathway

Pancreatic cancer (PC) is marked with a low survival rate and lack of recognized effective treatment strategy. We investigated the antitumor effect of β-hydroxyisovaleryl-shikonin (β-HIVS) on PC and the associated working mechanism. Cell toxicity was determined using Cell Counting Kit-8 (CCK-8) assay. Acridine Orange/Ethidium Bromide (AO/EB) double-fluorescent staining assay accompanied by flow cytometry was utilized to estimate cell apoptosis. Cell cycle, reactive oxygen species (ROS), and mitochondrial membrane potential were all evaluated using flow cytometry. Transwell and wound healing assays were performed to evaluate cell migration and invasion. Protein expression was analyzed by Western blots. A xenograft mouse model was employed to determine the antitumor effect of β-HIVS in vivo. PC cell viability gradually decreased with increasing β-HIVS while apoptosis was enhanced together with cell-cycle blockage in the G0–G1 phases. β-HIVS induced mitochondrial dysfunction, ROS production, and DNA damage and inhibited the invasive and migratory ability of PC cells. We further confirmed the suppression of EMT and PI3K/AKT pathways as underlying mechanisms. The mouse model treated with the increasing dose of β-HIVS displayed decreased tumor growth rate, along with increased apoptosis. Thus, β-HIVS exerts antitumor effects on PC through inducing apoptosis, ROS production, decreasing mitochondrial membrane potential, and suppressing signal pathways, such as PI3K/AKT. In summary, β-HIVS might be a promising strategy for PC treatment.

Bladder cancer selective chemotherapy with potent NQO1 substrate co-loaded prodrug nanoparticles

Currently, clinical intravesical instillation chemotherapy has been greatly compromised by the toxicological and physiological factors. New formulations that can specifically and efficiently kill bladder cancer cells are in urgent need to overcome the low residence efficiency and dose limiting toxicity of current ones. The combination of mucoadhesive nanocarriers and cancer cell selective prodrugs can to great extent address these limitations. However, the insignificant endogenous stimulus difference between cancer cells and normal cells in most cases and the high local drug concentration make it essential to develop new drugs with broader selectivity-window. Herein, based on the statistically different NQO1 expression between cancerous and normal bladder tissues, the reactive oxygen species (ROS) activatable epirubicin prodrug and highly potent NQO1 substrate, KP372-1, was co-delivered using a GSH-responsive mucoadhesive nanocarrier. After endocytosis, epirubicin could be promptly activated by the NQO1-dependent ROS production caused by KP372-1, thus specifically inhibiting the proliferation of bladder cancer cells. Since KP372-1 is much more potent than some commonly used NQO1 substrates, for example, β-lapachone, the cascade drug activation could occur under much lower drug concentration, thus greatly lowering the toxicity in normal cells and broadening the selectivity-window during intravesical bladder cancer chemotherapy.

Oxidative Stress Markers Are Associated with a Poor Prognosis in Patients with Pancreatic Cancer

Pancreatic cancer is a malignancy of rising prevalence, especially in developed countries where dietary patterns and sedentariness favor its onset. This malady ranks seventh in cancer-related deaths in the world, although it is expected to rank second in the coming years, behind lung cancer. The low survival rate is due to the asymptomatic course of the early stages, which in many cases leads to metastases when becoming evident in advanced stages. In this context, molecular pathology is on the way towards finding new approaches with biomarkers that allow a better prognosis and monitoring of patients. So the present study aims to evaluate a series of molecular biomarkers, PARP1, NOX1, NOX2, eNOS and iNOS, as promising candidates for prognosis and survival by using immunohistochemistry. The analysis performed in 41 patients with pancreatic cancer showed a correlation between a high expression of all these components with a low survival rate, with high statistical power for all. In addition, a 60-month longitudinal surveillance program was managed, accompanied by several clinical parameters. The derivative Kaplan–Meier curves indicated a low cumulative survival rate as well. Ultimately, our research emphasized the value of these molecules as survival-associated biomarkers in pancreatic cancer, offering new gates for clinical management.

VDAC1 oligomerization may enhance DDP-induced hepatocyte apoptosis by exacerbating oxidative stress and mitochondrial DNA damage

Cisplatin (DDP)‐based chemotherapy is a preferred treatment for a broad spectrum of cancers, but the precise mechanisms of its hepatotoxicity are not yet clear. Recently, the role of voltage‐dependent anion channel protein 1 (VDAC1) in mitochondrial activity and cell apoptosis has attracted much attention. Our aim was to investigate the effects of mitochondrial outer membrane protein VDAC1 oligomerization in DDP‐induced hepatocyte apoptosis. L‐02 hepatocytes were divided into 4 groups: (a) control group, (b) 4,4'diisothiocyanate‐2,2'‐disulfonic acid (DIDS; 40 μm) group, (c) DDP (5 μm) group, and (d) DDP and DIDS combination group. Cell apoptosis was tested by Annexin V/FITC assay, protein expression of caspase‐3, γH2AX and NDUFB6 were observed by western blot assay, reactive oxygen species (ROS), and mitochondrial superoxide anion radical (O₂^•−) were detected by DCFH‐DA and MitoSOX probe, and DNA damage was assessed by comet assay. Moreover, the activity of mitochondrial respiratory chain complex I was determined by the colorimetry method. Compared with the control group, apoptosis rate and activated cleaved‐caspase‐3 protein, ROS and O₂^•− generation, DNA damage marker comet tail length, and γH2AX protein level increased in the DDP treatment group (P < 0.05). Activity of mitochondrial COXI decreased after DDP treatment (P < 0.05). DIDS, as a VDAC1 oligomerization inhibitor, antagonized DDP‐induced apoptosis by diminishing oxidative stress and DNA damage and protecting mitochondrial complex protein. These results show that VDAC1 oligomerization may play an important role in DDP‐induced hepatocyte apoptosis by increasing ROS and mtDNA leakage from VDAC1 pores, exacerbating oxidative stress and mtDNA damage.