Poly ADP Ribose Polymerase Inhibitor Olaparib Targeting Microhomology End Joining in Retinoblastoma Protein Defective Cancer: Analysis of the Retinoblastoma Cell-Killing Effects by Olaparib after Inducing Double-Strand Breaks

Efficacy and safety of an oral combination therapy of niraparib and etoposide in platinum resistant/refractory ovarian cancer: a single arm, prospective, phase II study

OBJECTIVE

Non-platinum chemotherapy is used in platinum resistant/refractory ovarian cancer patients but offers limited efficacy, especially in those who develop platinum resistance after ≤2 lines of platinum based chemotherapy. This phase II study aimed to evaluate the efficacy and safety of oral niraparib plus etoposide in platinum resistant/refractory ovarian cancer.

METHODS

Platinum resistant/refractory ovarian cancer patients after ≤2 lines of platinum based chemotherapy, histologically confirmed as non-mucinous epithelial ovarian cancer, regardless of biomarker status, were eligible. Patients received niraparib with a starting dose of 200 mg/100 mg alternate once a day, and oral etoposide of 50 mg once a day, on days 1-20 of 30 days per cycle for a maximum of 6-8 cycles, followed by niraparib until disease progression or intolerable toxicity. The primary endpoint was investigator assessed progression free survival.

RESULTS

29 patients were enrolled from 22 May 2020 to 3 February 2023; 26 patients were included in the efficacy analysis set as per protocol. Median progression free survival was 4.2 months (95% confidence interval (CI) 3.9 to 4.4). Overall response rate was 26.9% (95% CI 8.7 to 45.2). Disease control rate was 57.7% (95% CI 37.3 to 78.0). Overall response rate in patients with a BRCA mutation and homologous recombination deficiency was 50% and 41.7%, respectively. Median progression free survival in patients with primary platinum resistance was 4.5 months (95% CI 3.6 to 5.3). 29 patients were included in the safety analysis set, and 8 (28%) patients experienced treatment related adverse events of grade ≥3. There was no treatment related discontinuation.

CONCLUSIONS

Niraparib combined with etoposide showed evidence of antitumor activity in platinum resistant/refractory ovarian cancer after ≤2 lines of platinum based chemotherapy, particularly in patients with a BRCA mutation, homologous recombination deficiency, or primary platinum resistance. This once-a-day oral combination was a convenient option.

TRIAL REGISTRATION NUMBER

NCT04217798.

Genomic instability and eye diseases

Background

Genetic information is stored in the bases of double-stranded DNA. However, the integrity of DNA molecules is constantly threatened by various mutagenic agents, including pollutants, ultraviolet light (UV), and medications. To counteract these environmental damages, cells have established multiple mechanisms, such as producing molecules to identify and eliminate damaged DNA, as well as reconstruct the original DNA structures. Failure or insufficiency of these mechanisms can cause genetic instability. However, the role of genome stability in eye diseases is still under-researched, despite extensive study in cancer biology.

Main text

As the eye is directly exposed to the external environment, the genetic materials of ocular cells are constantly under threat. Some of the proteins essential for DNA damage repair, such as pRb, p53, and RAD21, are also key during the ocular disease development. In this review, we discuss five ocular diseases that are associated with genomic instability. Retinoblastoma and pterygium are linked to abnormal cell cycles. Fuchs' corneal endothelial dystrophy and age-related macular degeneration are related to the accumulation of DNA damage caused by oxidative damage and UV. The mutation of the subunit of the cohesin complex during eye development is linked to sclerocornea.

Conclusions

Failure of DNA damage detection or repair leads to increased genomic instability. Deciphering the role of genomic instability in ocular diseases can lead to the development of new treatments and strategies, such as protecting vulnerable cells from risk factors or intensifying damage to unwanted cells.

Contribution of Microhomology to Genome Instability: Connection between DNA Repair and Replication Stress

Microhomology-mediated end joining (MMEJ) is a highly mutagenic pathway to repair double-strand breaks (DSBs). MMEJ was thought to be a backup pathway of homologous recombination (HR) and canonical nonhomologous end joining (C-NHEJ). However, it attracts more attention in cancer research due to its special function of microhomology in many different aspects of cancer. In particular, it is initiated with DNA end resection and upregulated in homologous recombination-deficient cancers. In this review, I summarize the following: (1) the recent findings and contributions of MMEJ to genome instability, including phenotypes relevant to MMEJ; (2) the interaction between MMEJ and other DNA repair pathways; (3) the proposed mechanistic model of MMEJ in DNA DSB repair and a new connection with microhomology-mediated break-induced replication (MMBIR); and (4) the potential clinical application by targeting MMEJ based on synthetic lethality for cancer therapy.

Mechanosensitive Ion Channel PIEZO1 Signaling in the Hall-Marks of Cancer: Structure and Functions

Simple Summary

Tumor cells obtain various unique characteristics, which known as hallmarks of cancers, including sustained proliferative signaling, apoptosis resistance, and metastasis. These characteristics are crucial for tumor cells survival and for supporting their rapid growth. Studies have revealed that tumorigenesis is also accompanied by alteration in mechanical properties. Tumor cells could sense various mechanical forces, such as compressive force, shear stress, and portal vein pressure, which in turn could affect tumor progression. Piezo1 is a mechanically sensitive ion channel protein that can be activated mechanically, and is closely related to various diseases. Recent studies showed that Piezo1 is overexpressed in numerous tumors and is associated with poor prognosis. Furthermore, previous studies revealed that Piezo1 mediates these cancer hallmarks, and thus links up mechanical forces with tumor progression. Therefore, the discovery of Piezo1 provides a new insight for elucidating the mechanism of tumor progression under a mechanical microenvironment.

Abstract

Tumor cells alter their characteristics and behaviors during tumorigenesis. These characteristics, known as hallmarks of cancer, are crucial for supporting their rapid growth, need for energy, and adaptation to tumor microenvironment. Tumorigenesis is also accompanied by alteration in mechanical properties. Cells in tumor tissue sense mechanical signals from the tumor microenvironment, which consequently drive the acquisition of hallmarks of cancer, including sustained proliferative signaling, evading growth suppressors, apoptosis resistance, sustained angiogenesis, metastasis, and immune evasion. Piezo-type mechanosensitive ion channel component 1 (Piezo1) is a mechanically sensitive ion channel protein that can be activated mechanically and is closely related to various diseases. Recent studies showed that Piezo1 mediates tumor development through multiple mechanisms, and its overexpression is associated with poor prognosis. Therefore, the discovery of Piezo1, which links-up physical factors with biological properties, provides a new insight for elucidating the mechanism of tumor progression under a mechanical microenvironment, and suggests its potential application as a tumor marker and therapeutic target. In this review, we summarize current knowledge regarding the role of Piezo1 in regulating cancer hallmarks and the underlying molecular mechanisms. Furthermore, we discuss the potential of Piezo1 as an antitumor therapeutic target and the limitations that need to be overcome.