Human translesion DNA polymerases ι and κ mediate tolerance to temozolomide in MGMT-deficient glioblastoma cells.

Glioblastoma (GBM) is a highly aggressive brain tumor associated with poor patient survival. The current standard treatment involves invasive surgery, radiotherapy, and chemotherapy employing temozolomide (TMZ). Resistance to TMZ is, however, a major challenge. Previous work from our group has identified candidate genes linked to TMZ resistance, including genes encoding translesion synthesis (TLS) DNA polymerases iota (PolÉ©) and kappa (Polκ). These specialized enzymes are known for bypassing lesions and tolerating DNA damage. Here, we investigated the roles of PolÉ© and Polκ in TMZ resistance, employing MGMT-deficient U251-MG glioblastoma cells, with knockout of either POLI or POLK genes encoding PolÉ© and Polκ, respectively, and assess their viability and genotoxic stress responses upon subsequent TMZ treatment. Cells lacking either of these polymerases exhibited a significant decrease in viability following TMZ treatment compared to parental counterparts. The restoration of the missing polymerase led to a recovery of cell viability. Furthermore, knockout cells displayed increased cell cycle arrest, mainly in late S-phase, and lower levels of genotoxic stress after TMZ treatment, as assessed by a reduction of γH2AX foci and flow cytometry data. This implies that TMZ treatment does not trigger a significant H2AX phosphorylation response in the absence of these proteins. Interestingly, combining TMZ with Mirin (double-strand break repair pathway inhibitor) further reduced the cell viability and increased DNA damage and γH2AX positive cells in TLS KO cells, but not in parental cells. These findings underscore the crucial roles of PolÉ© and Polκ in conferring TMZ resistance and the potential backup role of homologous recombination in the absence of these TLS polymerases. Targeting these TLS enzymes, along with double-strand break DNA repair inhibition, could, therefore, provide a promising strategy to enhance TMZ's effectiveness in treating GBM.

PARP14 is regulated by the PARP9/DTX3L complex and promotes interferon γ-induced ADP-ribosylation.

Protein ADP-ribosylation plays important but ill-defined roles in antiviral signalling cascades such as the interferon response. Several viruses of clinical interest, including coronaviruses, express hydrolases that reverse ADP-ribosylation catalysed by host enzymes, suggesting an important role for this modification in host-pathogen interactions. However, which ADP-ribosyltransferases mediate host ADP-ribosylation, what proteins and pathways they target and how these modifications affect viral infection and pathogenesis is currently unclear. Here we show that host ADP-ribosyltransferase activity induced by IFNγ signalling depends on PARP14 catalytic activity and that the PARP9/DTX3L complex is required to uphold PARP14 protein levels via post-translational mechanisms. Both the PARP9/DTX3L complex and PARP14 localise to IFNγ-induced cytoplasmic inclusions containing ADP-ribosylated proteins, and both PARP14 itself and DTX3L are likely targets of PARP14 ADP-ribosylation. We provide evidence that these modifications are hydrolysed by the SARS-CoV-2 Nsp3 macrodomain, shedding light on the intricate cross-regulation between IFN-induced ADP-ribosyltransferases and the potential roles of the coronavirus macrodomain in counteracting their activity.

DNA polymerase eta protects human cells against DNA damage induced by the tumor chemotherapeutic temozolomide.

Human DNA polymerases can bypass DNA lesions performing translesion synthesis (TLS), a mechanism of DNA damage tolerance. Tumor cells use this mechanism to survive lesions caused by specific chemotherapeutic agents, resulting in treatment relapse. Moreover, TLS polymerases are error-prone and, thus, can lead to mutagenesis, increasing the resistance potential of tumor cells. DNA polymerase eta (pol eta) - a key protein from this group - is responsible for protecting against sunlight-induced tumors. Xeroderma Pigmentosum Variant (XP-V) patients are deficient in pol eta activity, which leads to symptoms related to higher sensitivity and increased incidence of skin cancer. Temozolomide (TMZ) is a chemotherapeutic agent used in glioblastoma and melanoma treatment. TMZ damages cells' genomes, but little is known about the role of TLS in TMZ-induced DNA lesions. This work investigates the effects of TMZ treatment in human XP-V cells, which lack pol eta, and in its complemented counterpart (XP-V comp). Interestingly, TMZ reduces the viability of XP-V cells compared to TLS proficient control cells. Furthermore, XP-V cells treated with TMZ presented increased phosphorylation of H2AX, forming γH2AX, compared to control cells. However, cell cycle assays indicate that XP-V cells treated with TMZ replicate damaged DNA and pass-through S-phase, arresting in the G2/M-phase. DNA fiber assay also fails to show any specific effect of TMZ-induced DNA damage blocking DNA elongation in pol eta deficient cells. These results show that pol eta plays a role in protecting human cells from TMZ-induced DNA damage, but this can be different from its canonical TLS mechanism. The new role opens novel therapeutic possibilities of using pol eta as a target to improve the efficacy of TMZ-based therapies against cancer.

O Estado da Arte da Imunoterapia no Tratamento do Câncer de Mama Triplo-Negativo: Principais Drogas, Associações, Mecanismos de Ação e Perspectivas Futuras / The State-of-the-Art of Immunotherapy in the Triple-Negative Breast Cancer Treatment: Main Drugs, Combinations, Mechanisms of Action and Future Perspectives / El Estado del Arte de la Inmunoterapia en el Tratamiento del Cáncer de Mama Triple Negativo: Principales Fármacos, Asociaciones, Mecanismos de Acción y Perspectivas de Futuro

Introdução: O câncer de mama é o mais comumente diagnosticado em mulheres e uma das principais causas de morte por câncer em mulheres em todo o mundo. Apesar, ou talvez por causa, de sua natureza agressiva e da falta de tratamentos direcionados atuais, pesquisas clínicas e laboratoriais significativas estão fornecendo opções de tratamento diferenciadas. Historicamente, a quimioterapia tem sido a única opção viável de tratamento sistêmico para doenças precoces e avançadas. No entanto, ensaios clínicos publicados recentemente mostraram que a imunoterapia tem um papel importante no paradigma de tratamento dessa condição devastadora. Objetivo: Demonstrar o estado da arte da imunoterapia no tratamento do câncer de mama triplo-negativo. Método: Revisão integrativa de literatura, entre janeiro/2020 a março/2020, a partir das bases de dados PubMed, SciELO, InternationalClinical Trials Registry Platform e LILACS, por meio dos descritores "Imunoterapia", "Neoplasias da mama" e "Neoplasias de mama triplo negativas" e seus respectivos correspondentes em inglês. Resultados: Foram encontrados 465 artigos; destes, 457 foram excluídos após aplicação dos critérios metodológicos. Assim, restaram oito artigos que atendiam aos critérios de inclusão, demonstrando os principais agentes terapêuticos utilizados, mecanismos de ação e combinações terapêuticas. Encontraram-se 25 ensaios clínicos em andamento na plataforma de registro de ensaios clínicos InternationalClinical Trials Registry Platform. Conclusão: Embora a imunoterapia seja algo recente, seus resultados com agentes inibidores da PARP, PD-1 e PD-L1 demonstraram resultados satisfatórios. Novos ensaios com subgrupos estratificados de acordo com biomarcadores tumorais específicos são necessários, a fim de avaliar se algum subgrupo tem maior benefício ao tratamento.

Introduction: Breast cancer is the most commonly diagnosed cancer in women and is one of the leading causes of death from cancer in women worldwide. Despite, or perhaps because of its aggressive nature and current lack of targeted treatments, significant basic research and clinical trials are being conducted to provide new treatment options. Historically, chemotherapy has been the only viable systemic treatment option for early and advanced diseases. However, recently published clinical trials have shown that immunotherapy plays an important role in the treatment paradigm of this devastating clinical condition. Objective: To demonstrate the state-of-the-art results of immunotherapy in the treatment of triple-negative breast cancer. Method:An integrative literature review was carried out between January/2020 and March/2020, in PubMed, SciELO, International Clinical Trials Registry Platform and LILACS databases, using the keywords "Immunotherapy", "Breast Cancer", and "Triple Negative Breast Cancer" and its respective correspondents in Portuguese. Results: 465 articles were found; of those, 457 were excluded after applying the methodological criteria. Thus, 8 articles that met the inclusion criteria, showing the main therapeutic agents used, mechanisms of action and therapeutic combinations, remained. 25 clinical trials were found in progress on the International Clinical Trials Registry Platform. Conclusion: Although immunotherapy is somewhat recent, its results with PARP, PD-1 and PD-L1 inhibitors have shown satisfactory results. New trials with subgroups stratified according to specific tumor biomarkers are needed in order to assess if some subgroups have greater benefit to treatment.

Introducción: El cáncer de mama es el más comúnmente diagnosticado en las mujeres y es una de las principales causas de muerte por cáncer en mujeres de todo el mundo. A pesar de, o quizás debido a su naturaleza agresiva y la falta de tratamientos dirigidos actuales, investigaciones clínicas y de laboratorio significativas están proporcionando opciones de tratamiento diferenciadas. Históricamente, la quimioterapia ha sido la única opción viable para el tratamiento sistémico de enfermedades tempranas y avanzadas. Sin embargo, los ensayos clínicos publicados recientemente han demostrado que la inmunoterapia desempeña un papel importante en el paradigma del tratamiento de esta condición devastadora. Objetivo: Demostrar el estado del arte de la inmunoterapia en el cáncer de mama triple negativo. Método: Revisión integradora entre enero/2020 y marzo/2020, utilizando las bases de datos PubMed, SciELO, InternationalClinical Trials Registry Platform y LILACS, empleando las palabras clave "Inmunoterapia", "Cáncer de mama" y "Cáncer de mama triple negativo" y los respectivos términos en inglés. Resultados: Se encontraron 465 artículos; de estos, 457 fueron excluidos después de aplicar los criterios metodológicos. Así, quedaron 8 artículos que cumplían los criterios, que mostraban los principales agentes terapéuticos utilizados, mecanismos de acción y combinaciones terapéuticas. Se encontraron 25 ensayos clínicos en progreso en la plataforma InternationalClinical Trials Registry Platform. Conclusión: Aunque la inmunoterapia es algo reciente, sus resultados con inhibidores de PARP, PD-1 y PD-L1 han mostrado resultados satisfactorios. Se necesitan nuevos ensayos con subgrupos estratificados según biomarcadores tumorales específicos para evaluar si algún subgrupo tiene un mayor beneficio.