Estrogen Therapy Induces Receptor-Dependent DNA Damage Enhanced by PARP Inhibition in ER+ Breast Cancer

The emerging regulatory interface between DNA repair and steroid hormone receptors in cancer

Human cells potentiate highly diverse functions through tight transcriptional regulation and maintenance of genome integrity. While the DNA damage response (DDR) safeguards the genome, ligand-activated transcription factors, such as steroid hormone receptors (SHRs), provide complex transcriptional outputs. Interestingly, an increasing body of evidence reveals a direct biological and functional interplay between DDR factors and SHR cascades in cancer. SHRs can directly affect DDR gene expression, but DDR factors in turn act as transcriptional coregulators, enabling oncogenic SHR-mediated signaling, which has the potential for novel therapeutic interventions. With a focus on breast and prostate cancer, we describe in this review recent developments in, and insights into, the complex interplay between SHR signaling and the DDR, highlighting opportunities for future clinical interventions.

Advancements and challenges of R-loops in cancers: Biological insights and future directions

R-loops involve in various biological processes under human normal physiological conditions. Disruption of R-loops can lead to disease onset and affect the progression of illnesses, particularly in cancers. Herein, we summarized and discussed the regulative networks, phenotypes and future directions of R-loops in cancers. In this review, we highlighted the following insights: (1) R-loops significantly influence cancer development, progression and treatment efficiency by regulating key genes, such as PARPs, BRCA1/2, sex hormone receptors, DHX9, and TOP1. (2) Currently, the ATM, ATR, cGAS/STING, and noncanonical pathways are the main pathways that involve in the regulatory network of R-loops in cancer. (3) Cancer biology can be modulated by R-loops-regulated phenotypes, including RNA methylation, DNA and histone methylation, oxidative stress, immune and inflammation regulation, and senescence. (4) Regulation of R-loops induces kinds of drug resistance in various cancers, suggesting that targeting R-loops maybe a promising way to overcome treatment resistance. (5) The role of R-loops in tumorigenesis remains controversial, and senescence may be a crucial research direction to unravel the mechanism of R-loop-induced tumorigenesis. Looking forward, further studies are needed to elucidate the specific mechanisms of R-loops in cancer, laying the groundwork for preclinical and clinical research.

Combined strategies with PARP inhibitors for the treatment of BRCA wide type cancer

Genomic instability stands out as a pivotal hallmark of cancer, and PARP inhibitors (PARPi) emerging as a groundbreaking class of targeted therapy drugs meticulously crafted to inhibit the repair of DNA single-strand breaks(SSB) in tumor cells. Currently, PARPi have been approved for the treatment of ovarian cancer, pancreatic cancer, breast cancer, and prostate cancer characterized by homologous recombination(HR) repair deficiencies due to mutations in BRCA1/2 or other DNA repair associated genes and acquiring the designation of breakthrough therapy. Nonetheless, PARPi exhibit limited efficacy in the majority of HR-proficient BRCA1/2 wild-type cancers. At present, the synergistic approach of combining PARPi with agents that induce HR defects, or with chemotherapy and radiotherapy to induce substantial DNA damage, significantly enhances the efficacy of PARPi in BRCA wild-type or HR-proficient patients, supporting extension the use of PARPi in HR proficient patients. Therefore, we have summarized the effects and mechanisms of the combined use of drugs with PARPi, including the combination of PARPi with HR defect-inducing drugs such as ATRi, CHKi, HR indirectly inducing drugs like VEGFRi, CDKi, immune checkpoint inhibitors and drugs instigating DNA damage such as chemotherapy or radiotherapy. In addition, this review discusses several ongoing clinical trials aimed at analyzing the clinical application potential of these combined treatment strategies.

TRIM33 Is a Co-Regulator of Estrogen Receptor Alpha

Estrogen receptor alpha (ER)-positive breast cancer is responsible for over 60% of breast cancer cases in the U.S. Among patients diagnosed with early-stage ER+ disease, 1/3 will experience recurrence despite treatment with adjuvant endocrine therapy. ER is a nuclear hormone receptor responsible for estrogen-driven tumor growth. ER transcriptional activity is modulated by interactions with coregulators. Dysregulation of the levels of these coregulators is involved in the development of endocrine resistance. To identify ER interactors that modulate transcriptional activity in breast cancer, we utilized biotin ligase proximity profiling of ER interactomes. Mass spectrometry analysis revealed tripartite motif containing 33 (TRIM33) as an estrogen-dependent interactor of ER. shRNA knockdown showed that TRIM33 promoted ER transcriptional activity and estrogen-induced cell growth. Despite its known role as an E3 ubiquitin ligase, TRIM33 increased the stability of endogenous ER in breast cancer cells. TRIM33 offers a novel target for inhibiting estrogen-induced cancer cell growth, particularly in cases of endocrine resistance driven by ER (ESR1) gene amplification or overexpression.

Statistical Assessment of Drug Synergy from In Vivo Combination Studies Using Mouse Tumor Models

Drug combination therapy is a promising strategy for treating cancer; however, its efficacy and synergy require rigorous evaluation in preclinical studies before going to clinical trials. Existing methods have limited power to detect synergy in animal studies. Here, we introduce a novel approach to assess in vivo drug synergy with high sensitivity and low false discovery rate. It can accurately estimate combination index and synergy score under the Bliss independence model and the highest single agent (HSA) model without any assumption on tumor growth kinetics, study duration, data completeness and balance for tumor volume measurement. We show that our method can effectively validate in vitro drug synergy discovered from cell line assays in in vivo xenograft experiments, and can help to elucidate the mechanism of action for immune checkpoint inhibitors in syngeneic mouse models by combining an anti-PD-1 antibody and several tumor-infiltrating leukocytes depletion treatments. We provide a unified view of in vitro and in vivo synergy by presenting a parallelism between the fixed-dose in vitro and the 4-group in vivo combination studies, so they can be better designed, analyzed, and compared. We emphasize that combination index, when defined here via relative survival of tumor cells, is both dose and time dependent, and give guidelines on designing informative in vivo combination studies. We explain how to interpret and apply Bliss and HSA synergies. Finally, we provide an open-source software package named invivoSyn that enables automated analysis of in vivo synergy using our method and several other existing methods.

SIGNIFICANCE

This work presents a general solution to reliably determine in vivo drug synergy in single-dose 4-group animal combination studies.

Crosstalk between Wnt/β-catenin signaling pathway and DNA damage response in cancer: a new direction for overcoming therapy resistance

Wnt signaling plays an important role in regulating the biological behavior of cancers, and many drugs targeting this signaling have been developed. Recently, a series of research have revealed that Wnt signaling could regulate DNA damage response (DDR) which is crucial for maintaining the genomic integrity in cells and closely related to cancer genome instability. Many drugs have been developed to target DNA damage response in cancers. Notably, different components of the Wnt and DDR pathways are involved in crosstalk, forming a complex regulatory network and providing new opportunities for cancer therapy. Here, we provide a brief overview of Wnt signaling and DDR in the field of cancer research and review the interactions between these two pathways. Finally, we also discuss the possibility of therapeutic agents targeting Wnt and DDR as potential cancer treatment strategies.