De la découverte du poly(ADP-ribose) aux inhibiteurs PARP en thérapie du cancer

Polyadenosine diphosphate-ribose polymerase inhibitors: advances, implications, and challenges in tumor radiotherapy sensitization

Polyadenosine diphosphate-ribose polymerase (PARP) is a key modifying enzyme in cells, which participates in single-strand break repair and indirectly affects double-strand break repair. PARP inhibitors have shown great potential in oncotherapy by exploiting DNA damage repair pathways, and several small molecule PARP inhibitors have been approved by the U.S. Food and Drug Administration for treating various tumor types. PARP inhibitors not only have significant antitumor effects but also have some synergistic effects when combined with radiotherapy; therefore they have potential as radiation sensitizers. Here, we reviewed the advances and implications of PARP inhibitors in tumor radiotherapy sensitization. First, we summarized the multiple functions of PARP and the mechanisms by which its inhibitors exert antitumor effects. Next, we discuss the immunomodulatory effects of PARP and its inhibitors in tumors. Then, we described the theoretical basis of using PARP inhibitors in combination with radiotherapy and outlined their importance in oncological radiotherapy. Finally, we reviewed the current challenges in this field and elaborated on the future applications of PARP inhibitors as radiation sensitizers. A comprehensive understanding of the mechanism, optimal dosing, long-term safety, and identification of responsive biomarkers remain key challenges to integrating PARP inhibition into the radiotherapy management of cancer patients. Therefore, extensive research in these areas would facilitate the development of precision radiotherapy using PARP inhibitors to improve patient outcomes.

Mutation Patterns in Portuguese Families with Hereditary Breast and Ovarian Cancer Syndrome

Simple Summary

The pattern of Breast Cancer Genes 1 (BRCA1) and 2 (BRCA2) mutations in Hereditary Breast Ovarian Cancer (HBOC) families varies widely among different populations. About 30% of Portuguese HBOC can be associated with inherited cancer caused by BRCA1 or BRCA2 mutations. Three variants were identified (c.156_157insAlu in the BRCA2 gene and c.3331_3334del and c.2037delinsCC in the BRCA1 gene), accounting for about 50% of all Portuguese pathogenic mutations. Characterising the mutational spectrum in specific populations allows for a more efficient and cost-saving screening approach.

Abstract

Germline pathogenic variants in the Breast Cancer Genes 1 (BRCA1) and 2 (BRCA2) are responsible for Hereditary Breast and Ovarian Cancer (HBOC) syndrome. Genetic susceptibility to breast cancer accounts for 5–10% of all cases, phenotypically presenting with characteristics such as an autosomal dominant inheritance pattern, earlier age of onset, bilateral tumours, male breast cancer, and ovarian tumours, among others. BRCA2 pathogenic variant is usually associated with other cancers such as melanoma, prostate, and pancreatic cancers. Many rearrangements of different mutations were found in both genes, with some ethnic groups having higher frequencies of specific mutations due to founder effects. Despite the heterogeneity of germline BRCA1/BRCA2 mutations in Portuguese breast or/and ovarian cancer families, the first described founder mutation in the BRCA2 gene (c.156_157insAlu) and two other variants in the BRCA1 gene (c.3331_3334del and c.2037delinsCC) contribute to about 50% of all pathogenic mutations. Furthermore, the families with the BRCA1 c.3331_3334del or the c.2037delinsCC mutations share a common haplotype, suggesting that these may also be founder mutations in the Portuguese population. Identifying specific and recurrent/founder mutations plays an important role in increasing the efficiency of genetic testing since it allows the use of more specific, cheaper and faster strategies to screen HBOC families. Therefore, this review aims to describe the mutational rearrangements of founder mutations and evaluate their impact on the genetic testing criteria for HBOC families of Portuguese ancestry.

Assessment of Predictive Biomarkers in Breast Cancer: Challenges and Updates

The management of patients with breast cancer (BC) relies on the assessment of a defined set of well-established prognostic and predictive markers. Despite overlap, prognostic markers are used to assess the risk of recurrence and the likely benefit of systemic therapy, whereas predictive markers are used to determine the type of systemic therapy to be offered to an individual patient. In this review, we provide an update and present some challenges in the assessment of the main BC-specific molecular predictive markers, namely hormone receptors (oestrogen receptor [ER] and progesterone receptor [PR]), human epidermal growth factor receptor 2 (HER2), and KI67. As the main platform for assessing these markers in BC is immunohistochemistry (IHC), we address the cut-off values used to define positivity, the ER-low subgroup, the existence and significance of the ER-/PR+ phenotype, the use of PR in routine practice, and the role of hormone receptors in ductal carcinoma in situ. We discuss the newly introduced HER2-low class of BC and the clinical/biological difference between different HER2 groups (e.g., HER2 IHC score 3+ BCs vs. those with a HER2 IHC score 2+ with HER2 gene amplification). The review concludes with an update on the applications of KI67 assessment in BC and observations on the role of immune checkpoint identification in BC.

Sensitizing thermochemotherapy with a PARP1-inhibitor

Cis-diamminedichloroplatinum(II) (cisplatin, cDDP) is an effective chemotherapeutic agent that induces DNA double strand breaks (DSBs), primarily in replicating cells. Generally, such DSBs can be repaired by the classical or backup non-homologous end joining (c-NHEJ/b-NHEJ) or homologous recombination (HR). Therefore, inhibiting these pathways in cancer cells should enhance the efficiency of cDDP treatments. Indeed, inhibition of HR by hyperthermia (HT) sensitizes cancer cells to cDDP and in the Netherlands this combination is a standard treatment option for recurrent cervical cancer after previous radiotherapy. Additionally, cDDP has been demonstrated to disrupt c-NHEJ, which likely further increases the treatment efficacy. However, if one of these pathways is blocked, DSB repair functions can be sustained by the Poly-(ADP-ribose)-polymerase1 (PARP1)-dependent b-NHEJ. Therefore, disabling b-NHEJ should, in principle, further inhibit the repair of cDDP-induced DNA lesions and enhance the toxicity of thermochemotherapy. To explore this hypothesis, we treated a panel of cancer cell lines with HT, cDDP and a PARP1-i and measured various end-point relevant in cancer treatment. Our results demonstrate that PARP1-i does not considerably increase the efficacy of HT combined with standard, commonly used cDDP concentrations. However, in the presence of a PARP1-i, ten-fold lower concentration of cDDP can be used to induce similar cytotoxic effects. PARP1 inhibition may thus permit a substantial lowering of cDDP concentrations without diminishing treatment efficacy, potentially reducing systemic side effects.

Traitement des rechutes tardives du cancer de l’ovaire

TREATMENT FOR PLATINUM SENSITIVE RELAPSES OF OVARIAN CANCER

Despite large improvements in treatment efficacy, the cure rate of ovarian cancer has not radically changed. Relapses both remain frequent and are still synonymous with chronic disease. Most of them are platinum-sensitive, and can be successfully treated with successive lines of chemotherapy. Surgery may have a role to play but its real impact, population selection criteria, and adequate timing still have to be established. Regarding medical treatments, the availability of new targeted therapeutics, such as bevacizumab and olaparib, complicates decision making. Moreover, allergic drug reactions to platins worsen treatment management. In practice, treatment decision making integrates patient profiles and wishes, types and numbers of previous medical treatments along with BRCA status.

Expanding functions of ADP-ribosylation in the maintenance of genome integrity

Cell response to genotoxic stress requires a complex network of sensors and effectors from numerous signaling and repair pathways, among them the nuclear poly(ADP-ribose) polymerase 1 (PARP1) plays a central role. PARP1 is catalytically activated in the setting of DNA breaks. It uses NAD⁺ as a donor and catalyses the synthesis and subsequent covalent attachment of branched ADP-ribose polymers onto itself and various acceptor proteins to promote repair. Its inhibition is now considered as an efficient therapeutic strategy to potentiate the cytotoxic effect of chemotherapy and radiation or to exploit synthetic lethality in tumours with defective homologous recombination mediated repair. Still, efforts made on understanding the role of PARylation in DNA repair continues to yield novel discoveries. Over the last years, our knowledge in this field has been particularly advanced by the discovery of novel biochemical and functional properties featuring PARP1, by the characterization of the other PARP family members and by the identification of a panel of enzymes capable of erasing poly(ADP-ribose). The aim of this review is to provide an overview of these newest findings and their relevance in genome surveillance.