Effect of a poly(ADP-ribose) polymerase-1 inhibitor against esophageal squamous cell carcinoma cell lines

Novel dual action PARP and microtubule polymerization inhibitor AMXI-5001 powerfully inhibits growth of esophageal carcinoma both alone and in combination with radiotherapy

Esophageal cancer is one of the leading causes of cancer deaths globally with an incidence that is concentrated in specific hot spots in Eastern Asia, the Middle East, Eastern Africa, and South America. 10-year overall survival for patients treated with standard of care chemoradiation followed by surgical resection is below 40% highlighting the need for novel therapeutics to treat this disease. We assessed the effect of AMXI-5001, a novel small molecule poly ADP-Ribose polymerase (PARP) inhibitor and microtubule polymerization inhibitor on tumor growth inhibition in both in-vitro and in-vivo murine models. We found that AMXI-5001 was the most potent growth inhibitor of 8 out of 9 different esophageal carcinoma cell lines compared to other clinically available PARP inhibitors, Olaparib, Niraparib, Rucaparib, and Talazoparib. We then confirmed the previously described mechanism of action of AMXI-5001 as a PARP-inhibitor and microtubule polymerization inhibitor using both a PARP trapping assay and immunofluorescence. To further assess AMXI-5001's potential as a therapeutic for esophageal carcinoma we evaluated the effect of AMXI-5001 in combination with standard chemotherapy agents, Cisplatin and 5 Fluorouracil. We showed that AMXI-5001 synergistically inhibits growth in KYSE-70, a squamous esophageal cell line in combination with these drugs. In addition, we found that AMXI-5001 was an effective radiosensitizer, and squamous esophageal carcinoma cell lines treated 24 hours prior to external beam radiation showed significantly more growth inhibition compared to controls. Finally, we assessed the effect of AMXI-5001 monotherapy and in combination with radiotherapy in a xenograft mouse model implanted with subcutaneous KYSE-70 cells. Compared to vehicle control, and those treated with either AMXI-5001 alone or radiation alone, mice treated with both AMXI-5001 and radiation had significant tumor response. In conclusion, AMXI-5001 is an orally bioavailable dual-action PARP and microtubule polymerization inhibitor that holds promise in the treatment of esophageal carcinoma.

Case Report: Olaparib Shows Satisfactory Clinical Outcomes Against Small Cell Esophageal Carcinoma With ATM Mutation

Small cell esophageal carcinoma (SCEC) is a rare, undifferential type of cancer, with a high degree of malignancy and early systemic metastasis. Radio-chemotherapy and surgery have been used as the primary treatment strategies for SCEC, but they both result in poor prognosis. There is need to develop an optimal standard treatment for the disease to improve prognosis and limit the related mortality. In this study, we described identification of driver mutations in ATM, a gene involved in homologous recombination deficiency (HRD) pathway, using next-generation sequencing on primary lesion and peripheral blood of a SCEC patient, who experienced recurrence after resection and radio-chemotherapy. In addition, we subjected the patient to olaparib, a PARP inhibitor, for the treatment of tumor with HRD and obtained a partial response. This is the first evidence implicating olaparib in successful treatment of SCEC with ATM mutation. The findings suggest that targeting mutations in HRD genes using olaparib or actionable genetic mutations using corresponding drugs, may be an effective therapeutic option for SCEC, although this requires further investigation.

Therapeutic Potential of PARP Inhibitors in the Treatment of Gastrointestinal Cancers

Gastrointestinal (GI) malignancies are a major global health burden, with high mortality rates. The identification of novel therapeutic strategies is crucial to improve treatment and survival of patients. The poly (ADP-ribose) polymerase (PARP) enzymes involved in the DNA damage response (DDR) play major roles in the development, progression and treatment response of cancer, with PARP inhibitors (PARPi) currently used in the clinic for breast, ovarian, fallopian, primary peritoneal, pancreatic and prostate cancers with deficiencies in homologous recombination (HR) DNA repair. This article examines the current evidence for the role of the DDR PARP enzymes (PARP1, 2, 3 and 4) in the development, progression and treatment response of GI cancers. Furthermore, we discuss the role of HR status as a predictive biomarker of PARPi efficacy in GI cancer patients and examine the pre-clinical and clinical evidence for PARPi and cytotoxic therapy combination strategies in GI cancer. We also include an analysis of the genomic and transcriptomic landscape of the DDR PARP genes and key HR genes (BRCA1, BRCA2, ATM, RAD51, MRE11, PALB2) in GI patient tumours (n = 1744) using publicly available datasets to identify patients that may benefit from PARPi therapeutic approaches.

Single‑cell intratumoral stemness analysis reveals the involvement of cell cycle and DNA damage repair in two different types of esophageal cancer

Intratumoral heterogeneity, particularly the potential cancer stemness of single cancer cells, has not yet been fully elucidated in human esophageal cancer. Single‑cell transcriptome sequencing of two types of esophageal adenocarcinoma (EAC) and two types of esophageal squamous cell carcinoma (ESCC) tissues was performed, and the intratumoral cancer stemness of the types of esophageal cancer were characterized at the single‑cell level in the present study. By comparing the transcriptomic profiles of single cancer cells with high and low stemness in individual patients, it was revealed that the overexpression of cell cycle‑associated genes in EAC cells was highly correlated with stemness, whereas overexpression of genes involved in the signaling pathways of DNA replication and DNA damage repair was significantly correlated with stemness in ESCC. High expression of these stemness‑associated genes was correlated with poor prognosis of patients. Additionally, poly [ADP‑ribose] polymerase(PARP)4 was identified as a novel cancer stemness‑associated gene in ESCC and its association with survival was validated in a cohort of 121 patients with ESCC. These findings have profound potential implications for the use of cell cycle inhibitors in EAC and PARP inhibitors in ESCC, which may provide novel mechanistic insights into the plasticity of esophageal cancer.

First-in-Class Chemical Probes against Poly(ADP-ribose) Glycohydrolase (PARG) Inhibit DNA Repair with Differential Pharmacology to Olaparib

The enzyme poly(ADP-ribose) glycohydrolase (PARG) performs a critical role in the repair of DNA single strand breaks (SSBs). However, a detailed understanding of its mechanism of action has been hampered by a lack of credible, cell-active chemical probes. Herein, we demonstrate inhibition of PARG with a small molecule, leading to poly(ADP-ribose) (PAR) chain persistence in intact cells. Moreover, we describe two advanced, and chemically distinct, cell-active tool compounds with convincing on-target pharmacology and selectivity. Using one of these tool compounds, we demonstrate pharmacology consistent with PARG inhibition. Further, while the roles of PARG and poly(ADP-ribose) polymerase (PARP) are closely intertwined, we demonstrate that the pharmacology of a PARG inhibitor differs from that observed with the more thoroughly studied PARP inhibitor olaparib. We believe that these tools will facilitate a wider understanding of this important component of DNA repair and may enable the development of novel therapeutic agents exploiting the critical dependence of tumors on the DNA damage response (DDR).

Efficacy of poly (ADP-ribose) polymerase inhibitor olaparib against head and neck cancer cells: Predictions of drug sensitivity based on PAR-p53-NF-κB interactions

Poly (ADP-ribose) polymerase (PARP) is a key molecule in the DNA damage response (DDR), which is a major target of both chemotherapies and radiotherapies. PARP inhibitors therefore comprise a promising class of anticancer therapeutics. In this study, we evaluated the efficacy of the PARP inhibitor olaparib, and also sought to identify the mechanism and predictive marker associated with olaparib sensitivity in head and neck cancer (HNC) cells. A total of 15 HNC cell lines, including AMC HNC cells, were tested. AMC-HN3 and HN4 exhibited stronger responses to olaparib. Among cisplatin-resistant cell lines, only AMC HN9-cisR cells were significantly suppressed by olaparib. We found that basal poly (ADP-ribose) (PAR) levels, but not PARP-1 levels, correlated with olaparib sensitivity. AMC-HN3 and HN4 cells exhibited higher basal levels of NF-κB that decreased significantly after olaparib treatment. In contrast, apoptotic proteins were intrinsically expressed in AMC-HN9-cisR cells. As interference with p53 expression led to NF-κB reactivation, we concluded that elevated basal PAR and NF-κB levels are predictive of olaparib responsiveness in HNC cells; in addition, olaparib inhibits HNC cells via PAR-p53-NF-κB interactions.

Poly (ADP) ribose polymerase inhibition: A potential treatment of malignant peripheral nerve sheath tumor

Poly (ADP) ribose polymerase (PARP) inhibitors, first evaluated nearly a decade ago, are primarily used in malignancies with known defects in DNA repair genes, such as alterations in breast cancer, early onset 1/2 (BRCA1/2). While no specific mutations in BRCA1/2 have been reported in malignant peripheral nerve sheath tumors (MPNSTs), MPNST cells could be effectively targeted with a PARP inhibitor to drive cells to synthetic lethality due to their complex karyotype and high level of inherent genomic instability. In this study, we assessed the expression levels of PARP1 and PARP2 in MPNST patient tumor samples and correlated these findings with overall survival. We also determined the level of PARP activity in MPNST cell lines. In addition, we evaluated the efficacy of the PARP inhibitor AZD2281 (Olaparib) in MPNST cell lines. We observed decreased MPNST cell proliferation and enhanced apoptosis in vitro at doses similar to, or less than, the doses used in cell lines with established defective DNA repair genes. Furthermore, AZD2281 significantly reduced local growth of MPNST xenografts, decreased the development of macroscopic lung metastases, and increased survival of mice with metastatic disease. Our results suggest that AZD2281 could be an effective therapeutic option in MPNST and should be further investigated for its potential clinical use in this malignancy.

Impact of Alternaria toxins on CYP1A1 expression in different human tumor cells and relevance for genotoxicity

The Alternaria toxins alternariol (AOH) and alternariol monomethyl ether (AME) have been reported previously to act as activators of the aryl hydrocarbon receptor (AhR) in murine hepatoma cells, thus enhancing the expression of cytochrome P450 (CYP) 1A monooxygenases. Concomitantly, both benzopyrones represent substrates of CYP1A, giving rise to catecholic metabolites. The impact of AOH and AME on CYP1A expression in human cells of different tissue origin colon (HT29), esophagus (KYSE510), liver (HepG2) and their effects on cell viability, generation of reactive oxygen species (ROS) and DNA integrity were investigated. ROS production was induced by both mycotoxins in all cell lines with AOH exhibiting the highest potency in esophageal cells concomitant with the most prominent CYP1A induction level. Of note, altertoxin-II (ATX-II), the more potent DNA-damaging mutagen formed by Alternaria alternata, induces CYP1A even at significant lower concentrations. AhR-siRNA knockdown in human esophageal cells supported the hypothesis of AhR-mediated CYP1A1 induction by AOH. However, DNA damage was minor at CYP1A1-inducing AOH concentrations. AhR-depletion did not affect the DNA-damaging properties of AOH indicating no substantial impact of AhR in this regard. However, in combination with xenobiotics prone to metabolic activation by CYP1A the induction of CYP1A by Alternaria toxins deserves further attention.

Systematic analysis of time-series gene expression data on tumor cell-selective apoptotic responses to HDAC inhibitors

SAHA (suberoylanilide hydroxamic acid or vorinostat) is the first nonselective histone deacetylase (HDAC) inhibitor approved by the US Food and Drug Administration (FDA). SAHA affects histone acetylation in chromatin and a variety of nonhistone substrates, thus influencing many cellular processes. In particularly, SAHA induces selective apoptosis of tumor cells, although the mechanism is not well understood. A series of microarray experiments was recently conducted to investigate tumor cell-selective proapoptotic transcriptional responses induced by SAHA. Based on that gene expression time series, we propose a novel framework for detailed analysis of the mechanism of tumor cell apoptosis selectively induced by SAHA. Our analyses indicated that SAHA selectively disrupted the DNA damage response, cell cycle, p53 expression, and mitochondrial integrity of tumor samples to induce selective tumor cell apoptosis. Our results suggest a possible regulation network. Our research extends the existing research.

PARP inhibitor activates the intrinsic pathway of apoptosis in primary lung cancer cells

This investigation was aimed to see whether PJ34(TM), a PARP inhibitor, could exert cytotoxicity in six nonsmall cell lung cancer cell lines developed from surgically resected tissues. Using various biochemical assays, we have seen that PJ34(TM) effects are consistent between untreated and treated samples but still somewhat variable between each cell line. Changes in protein expression and mitochondrial membrane potential between treated and untreated cells were indicating the possibility of apoptosis induction through an intrinsic pathway which causes cytotoxicity. Present results open the possibility of elucidating a decisive mechanism and effectiveness of chemotherapeutics specific to a patient.