PARPi Triggers the STING-Dependent Immune Response and Enhances the Therapeutic Efficacy of Immune Checkpoint Blockade Independent of BRCAness

Novel Bifunctional Conjugates Targeting PD-L1/PARP7 as Dual Immunotherapy for Potential Cancer Treatment

Bifunctional conjugates targeting PD-L1/PARP7 were designed, synthesized, and evaluated for the first time. Compounds B3 and C6 showed potent activity against PD-1/PD-L1 interaction (IC50 = 0.426 and 0.342 μM, respectively) and PARP7 (IC50 = 2.50 and 7.05 nM, respectively). They also displayed excellent binding affinity with hPD-L1, approximately 100-200-fold better than that of hPD-1. Both compounds restored T-cell function, leading to the increase of IFN-γ secretion. In the coculture assay, B3 and C6 enhanced the killing activity of MDA-MB-231 cells by Jurkat T cells in a concentration-dependent manner. Furthermore, B3 and C6 displayed significant in vivo antitumor efficacy in a melanoma B16-F10 tumor mouse model, more than 5.3-fold better than BMS-1 (a PD-L1 inhibitor) and RBN-2397 (a PARP7i clinical candidate) at the dose of 25 mg/kg, without observable side effects. These results provide valuable insight and understanding for developing bifunctional conjugates for potential anticancer therapy.

Androgen receptor, PARP signaling, and tumor microenvironment: the 'perfect triad' in prostate cancer?

Aberrations in the homologous recombination repair (HRR) pathway in prostate cancer (PCa) provide a unique opportunity to develop therapeutic strategies that take advantage of the reduced tumor ability to repair DNA damage. Poly-ADP-ribose polymerase (PARP) inhibitors (PARPi) have been shown to prolong the survival of PCa patients with HRR defects, particularly in those with Breast Cancer type 1 susceptibility protein/Breast Cancer type 2 susceptibility protein alterations. To expand the benefit of PARPi to patients without detectable HRR alterations, multiple preclinical and clinical studies are addressing potential synergies between PARPi and androgen receptor signaling inhibitors, and these strategies are also being evaluated in combination with other drugs such as immune checkpoint inhibitors. However, the effectiveness of these combining therapies could be hindered by multiple mechanisms of resistance, including also the role played by the immunosuppressive tumor microenvironment. In this review, we summarize the use of PARPi in PCa and the potential synergies with different molecular pathways. However, numerous unanswered questions remain, including the identification of the patient population that could benefit most from PARPi, determining whether to use PARPi as monotherapy or in combination, and finding the optimal timing of PARPi, expanding the use of genomic tests, and optimizing combination therapies.

Niraparib enhances antitumor immunity and contributes to the efficacy of PD-L1 blockade in cervical cancer

PURPOSE

With the development of immunotherapy research, the role of immune checkpoint blockade (ICB) in the treatment of cervical cancer has been emphasized, but many patients still can't receive long-term benefits from ICB. Poly ADP ribose polymerase inhibitor (PARPi) has been proved to exert significant antitumor effects in multiple solid tumors. Whether cervical cancer patients obtain better benefits from the treatment regimen of PARPi combined with ICB remains unclear.

METHODS

The alteration of PD-L1 expression induced by niraparib in cervical cancer cells and its underlying mechanism were assessed by western blot and immunofluorescence and quantitative real-time polymerase chain reaction (qRT-PCR).The regulation of PTEN by KDM5A was confirmed using Chromatin immunoprecipitation (ChIP) assay and RNA interference. Analyzing the relationship between PD-L1 and immune effector molecules through searching online databases. Therapeutic efficacy of niraparib, PD-L1 blockade or combination was assessed in syngeneic tumor model. The changes of immune cells and cytokines in vivo was detected by immunohistochemistry (IHC) and qRT-PCR.

RESULTS

We found that niraparib upregulated PD-L1 expression and potentiated the antitumor effects of PD-L1 blockade in a murine cervical cancer model. Niraparib inhibited the Pten expression by increasing the abundance of KDM5A, which expanded PD-L1 abundance through activating the PI3K-AKT-S6K1 pathway. PD-L1 was positively correlated with immune effector molecules including TNF-α, IFN-γ, granzyme A and granzyme B based on biological information analysis. Niraparib increased the infiltration of CD8+ T cells and the level of IFN-γ, granzyme B in vivo.

CONCLUSION

Our findings demonstrates the regulation of niraparib on local immune microenvironment of cervical cancer, and provides theoretical basis for supporting the combination of PARPi and PD-L1 blockade as a potential treatment for cervical cancer.

Beyond monotherapy: An era ushering in combinations of PARP inhibitors with immune checkpoint inhibitors for solid tumors

The introduction of PARP inhibitors (PARPis) and immune checkpoint inhibitors (ICIs) has marked a significant shift in the treatment landscape for solid tumors. Emerging preclinical evidence and initial clinical trials have indicated that the synergistic application of PARPis and ICIs may enhance treatment efficacy and potentially improve long-term patient outcomes. Nonetheless, how to identify specific tumor types and molecular subgroups most likely to benefit from this combination remains an area of ongoing research. This review thoroughly examines current studies on the co-administration of PARPis and ICIs across various solid tumors. It explores the underlying mechanisms of action, evaluates clinical efficacy, identifies potential responder populations, and delineates common adverse events alongside strategic management approaches. The aim is to offer a detailed understanding of this combination therapy, potentially guiding future therapeutic strategies for solid tumors.

New target therapies in prostate cancer: from radioligand therapy, to PARP-inhibitors and immunotherapy

Prostate cancer (PCa) remains a significant global health challenge, particularly in its advanced stages. Despite progress in early detection and treatment, PCa is the second most common cancer diagnosis among men. This review aims to provide an overview of current therapeutic approaches and innovations in PCa management, focusing on the latest advancements and ongoing challenges. We conducted a narrative review of clinical trials and research studies, focusing on PARP inhibitors (PARPis), phosphoinositide 3 kinase-protein kinase B inhibitors, immunotherapy, and radioligand therapies (RLTs). Data was sourced from major clinical trial databases and peer-reviewed journals. Androgen deprivation therapy and androgen-receptor pathway inhibitors remain foundational in managing castration-sensitive and early-stage castration-resistant PCa (CRPC). PARPi's, such as olaparib and rucaparib, have emerged as vital treatments for metastatic CRPC with homologous recombination repair gene mutations, highlighting the importance of personalized medicine. Immune checkpoint inhibitors (ICIs) have shown clinical benefit limited to specific subgroups of PCa, demonstrating significant improvement in efficacy in patients with microsatellite instability/mismatch repair or cyclin-dependent kinase 12 alteration, highlighting the importance of focusing ongoing research on identifying and characterizing these subgroups to maximize the clinical benefits of ICIs. RLTs have shown effectiveness in treating mCRPC. Different alpha emitters (like [225Ac]PSMA) and beta emitters compounds (like [177Lu]PSMA) impact treatment differently due to their energy transfer characteristics. Clinical trials like VISION and TheraP have demonstrated positive outcomes with RLT, particularly [177Lu]PSMA-617, leading to FDA approval. Ongoing trials and future perspectives explore the potential of [225Ac]PSMA, aiming to improve outcomes for patients with mCRPC. The landscape of PCa treatment is evolving, with significant advancements in both established and novel therapies. The combination of hormonal therapies, chemotherapy, PARPis, immunotherapy, and RLTs, guided by genetic and molecular insights, opens new possibilities for personalized treatment.

C5aR1 inhibition reprograms tumor associated macrophages and reverses PARP inhibitor resistance in breast cancer

Although Poly (ADP-ribose) polymerase (PARP) inhibitors (PARPi) have been approved in multiple diseases, including BRCA1/2 mutant breast cancer, responses are usually transient requiring the deployment of combination therapies for optimal efficacy. Here we thus explore mechanisms underlying sensitivity and resistance to PARPi using two intrinsically PARPi sensitive (T22) and resistant (T127) syngeneic murine breast cancer models in female mice. We demonstrate that tumor associated macrophages (TAM) potentially contribute to the differential sensitivity to PARPi. By single-cell RNA-sequencing, we identify a TAM_C3 cluster, expressing genes implicated in anti-inflammatory activity, that is enriched in PARPi resistant T127 tumors and markedly decreased by PARPi in T22 tumors. Rps19/C5aR1 signaling is selectively elevated in TAM_C3. C5aR1 inhibition or transferring C5aR1hi cells increases and decreases PARPi sensitivity, respectively. High C5aR1 levels in human breast cancers are associated with poor responses to immune checkpoint blockade. Thus, targeting C5aR1 may selectively deplete pro-tumoral macrophages and engender sensitivity to PARPi and potentially other therapies.

Enhancing immunotherapy outcomes by targeted remodeling of the tumor microenvironment via combined cGAS-STING pathway strategies

Immune checkpoint inhibitors (ICIs) represent a groundbreaking advance in the treatment of malignancies such as melanoma and non-small cell lung cancer, showcasing substantial therapeutic benefits. Nonetheless, the efficacy of ICIs is limited to a small subset of patients, primarily benefiting those with "hot" tumors characterized by significant immune infiltration. The challenge of converting "cold" tumors, which exhibit minimal immune activity, into "hot" tumors to enhance their responsiveness to ICIs is a critical and complex area of current research. Central to this endeavor is the activation of the cGAS-STING pathway, a pivotal nexus between innate and adaptive immunity. This pathway's activation promotes the production of type I interferon (IFN) and the recruitment of CD8+ T cells, thereby transforming the tumor microenvironment (TME) from "cold" to "hot". This review comprehensively explores the cGAS-STING pathway's role in reconditioning the TME, detailing the underlying mechanisms of innate and adaptive immunity and highlighting the contributions of various immune cells to tumor immunity. Furthermore, we delve into the latest clinical research on STING agonists and their potential in combination therapies, targeting this pathway. The discussion concludes with an examination of the challenges facing the advancement of promising STING agonists in clinical trials and the pressing issues within the cGAS-STING signaling pathway research.

Stimulating STING for cancer therapy: Taking the extracellular route

Ten years ago, the second messenger cGAMP was discovered as the activator of the anti-cancer STING pathway. The characterization of cGAMP's paracrine action and dominant extracellular hydrolase ENPP1 cemented cGAMP as an intercellular immunotransmitter that coordinates the innate and adaptive immune systems to fight cancer. In this Perspective, I look back at a decade of discovery of extracellular cGAMP biology and drug development aiming to supply or preserve extracellular cGAMP for cancer treatment. Reviewing our understanding of the cell type-specific regulatory mechanisms of STING agonists, including their transporters and degradation enzymes, I explain on a molecular and cellular level the successes and challenges of direct STING agonists for cancer therapy. Based on what we know now, I propose new ways to stimulate the STING pathway in a manner that is not only cancer specific, but also cell type specific to fully harness the anti-cancer effect of cGAMP while avoiding collateral damage.

Impact of Drp1-regulated changes in T cell activity on the combined antitumor effects of PARPi and PD-1 inhibitors

This study aimed to investigate the influence of dynamin-related protein 1 (Drp1)-regulated T cells on the antitumor effects of poly (ADP-ribose) polymerase inhibitors (PARPi) combined with programmed cell death protein 1 (PD-1) inhibitors to identify potential targets for enhancing immunotherapy efficacy. We found that T cells with high expression of Drp1 promoted the inhibitory and killing effects of the PARPi and PD-1 inhibitor combination on lung cancer cells in vivo and in vitro. This synergistic mechanism involves Drp1-regulated promotion of activation, migration, and intratumor infiltration of effector T cells; inhibition of negative immunomodulatory cells in the tumor microenvironment; and suppression of PARPi-induced upregulation of PD-L1 expression in tumor cells. These findings suggest that Drp1 could serve as a new target for comprehensively improving the tumor microenvironment, enhancing immunotherapy efficacy, and reversing immunotherapy resistance.

Syk-dependent homologous recombination activation promotes cancer resistance to DNA targeted therapy

Enhanced DNA repair is an important mechanism of inherent and acquired resistance to DNA targeted therapies, including poly ADP ribose polymerase (PARP) inhibition. Spleen associated tyrosine kinase (Syk) is a non-receptor tyrosine kinase acknowledged for its regulatory roles in immune cell function, cell adhesion, and vascular development. This study presents evidence indicating that Syk expression in high-grade serous ovarian cancer and triple-negative breast cancers promotes DNA double-strand break resection, homologous recombination (HR), and subsequent therapeutic resistance. Our investigations reveal that Syk is activated by ATM following DNA damage and is recruited to DNA double-strand breaks by NBS1. Once localized to the break site, Syk phosphorylates CtIP, a pivotal mediator of resection and HR, at Thr-847 to promote repair activity, particularly in Syk-expressing cancer cells. Inhibition of Syk or its genetic deletion impedes CtIP Thr-847 phosphorylation and overcomes the resistant phenotype. Collectively, our findings suggest a model wherein Syk fosters therapeutic resistance by promoting DNA resection and HR through a hitherto uncharacterized ATM-Syk-CtIP pathway. Moreover, Syk emerges as a promising tumor-specific target to sensitize Syk-expressing tumors to PARP inhibitors, radiation and other DNA-targeted therapies.

Distribution of PD-L1, TROP2 and HER2- "lowness" in early triple-negative breast cancer: an opportunity for treatment de-escalation

BACKGROUND

HER2, TROP2 and PD-L1 are novel targets in triple-negative breast cancer (TNBC). The combined expression status of these targets, and whether they can define prognostic subgroups, is currently undefined.

METHODS

Immunohistochemistry was used to determine HER2, TROP2 and PD-L1 levels in 459 TNBC cases, that received in the adjuvant/neoadjuvant setting active surveillance, CMF, anthracycline-, anthracycline plus taxane-, or carboplatin-containing regimes.

RESULTS

HER2-low patients with PD-L1 > 1 CPS (double-positive, herein "DP") had a mean PFS of 4768 days (95% CI: 4267-5268) versus 3522 days (95% CI: 3184-3861) for non-DP patients (P = 0.002). Regarding the received adjuvant treatment, DP patients (versus non-DP) receiving anthracyclines plus taxanes exhibited a mean PFS time of 4726 (95% CI: 4022-5430) versus 3302 (95% CI: 2818-3785) days (P = 0.039). Finally, 100% of DP patients that received a carboplatin-based regimen were long-term disease-free.

CONCLUSIONS

Early HER2-low, PD-L1-positive TNBC patients have a very good prognosis, particularly if treated with anthracycline/taxane- or carboplatin-containing regimes.

RECQL4 Inhibits Radiation-Induced Tumor Immune Awakening via Suppressing the cGAS-STING Pathway in Hepatocellular Carcinoma

Many patients with hepatocellular carcinoma (HCC) respond poorly to radiotherapy despite remarkable advances in treatment. A deeper insight into the mechanism of sensitivity of HCC to this therapy is urgently required. It is demonstrated that RECQL4 is upregulated in the malignant cells of patients with HCC. Elevated RECQL4 levels reduce the sensitivity of HCC to radiotherapy by repairing radiation-induced double-stranded DNA (dsDNA) fragments. Mechanistically, the inhibitory effect of RECQL4 on radiotherapy is due to the reduced recruitment of dendritic cells and CD8+ T cells in the tumor microenvironment (TME). RECQL4 disrupts the radiation-induced transformation of the TME into a tumoricidal niche by inhibiting the cGAS-STING pathway in dendritic cells. Knocking out STING in dendritic cells can block the impact of RECQL4 on HCC radiosensitivity. Notably, high RECQL4 expressions in HCC is significantly associated with poor prognosis in multiple independent cohorts. In conclusion, this study highlights how HCC-derived RECQL4 disrupts cGAS-STING pathway activation in dendritic cells through DNA repair, thus reducing the radiosensitivity of HCC. These findings provide new perspectives on the clinical treatment of HCC.

cGAS-STING, an important signaling pathway in diseases and their therapy

Since cyclic guanosine monophosphate-adenosine monophosphate synthase (cGAS)-stimulator of interferon genes (STING) signaling pathway was discovered in 2013, great progress has been made to elucidate the origin, function, and regulating mechanism of cGAS-STING signaling pathway in the past decade. Meanwhile, the triggering and transduction mechanisms have been continuously illuminated. cGAS-STING plays a key role in human diseases, particularly DNA-triggered inflammatory diseases, making it a potentially effective therapeutic target for inflammation-related diseases. Here, we aim to summarize the ancient origin of the cGAS-STING defense mechanism, as well as the triggers, transduction, and regulating mechanisms of the cGAS-STING. We will also focus on the important roles of cGAS-STING signal under pathological conditions, such as infections, cancers, autoimmune diseases, neurological diseases, and visceral inflammations, and review the progress in drug development targeting cGAS-STING signaling pathway. The main directions and potential obstacles in the regulating mechanism research and therapeutic drug development of the cGAS-STING signaling pathway for inflammatory diseases and cancers will be discussed. These research advancements expand our understanding of cGAS-STING, provide a theoretical basis for further exploration of the roles of cGAS-STING in diseases, and open up new strategies for targeting cGAS-STING as a promising therapeutic intervention in multiple diseases.

Targeting ATR in patients with cancer

Pharmacological inhibition of the ataxia telangiectasia and Rad3-related protein serine/threonine kinase (ATR; also known as FRAP-related protein (FRP1)) has emerged as a promising strategy for cancer treatment that exploits synthetic lethal interactions with proteins involved in DNA damage repair, overcomes resistance to other therapies and enhances antitumour immunity. Multiple novel, potent ATR inhibitors are being tested in clinical trials using biomarker-directed approaches and involving patients across a broad range of solid cancer types; some of these inhibitors have now entered phase III trials. Further insight into the complex interactions of ATR with other DNA replication stress response pathway components and with the immune system is necessary in order to optimally harness the potential of ATR inhibitors in the clinic and achieve hypomorphic targeting of the various ATR functions. Furthermore, a deeper understanding of the diverse range of predictive biomarkers of response to ATR inhibitors and of the intraclass differences between these agents could help to refine trial design and patient selection strategies. Key challenges that remain in the clinical development of ATR inhibitors include the optimization of their therapeutic index and the development of rational combinations with these agents. In this Review, we detail the molecular mechanisms regulated by ATR and their clinical relevance, and discuss the challenges that must be addressed to extend the benefit of ATR inhibitors to a broad population of patients with cancer.

DNA damage response in brain tumors: A Society for Neuro-Oncology consensus review on mechanisms and translational efforts in neuro-oncology

DNA damage response (DDR) mechanisms are critical to maintenance of overall genomic stability, and their dysfunction can contribute to oncogenesis. Significant advances in our understanding of DDR pathways have raised the possibility of developing therapies that exploit these processes. In this expert-driven consensus review, we examine mechanisms of response to DNA damage, progress in development of DDR inhibitors in IDH-wild-type glioblastoma and IDH-mutant gliomas, and other important considerations such as biomarker development, preclinical models, combination therapies, mechanisms of resistance and clinical trial design considerations.

A Trisulfide Bond Containing Biodegradable Polymer Delivering Pt(IV) Prodrugs to Deplete Glutathione and Donate H2S to Boost Chemotherapy and Antitumor Immunity

The clinical application of cisplatin (CisPt) is limited by its dose-dependent toxicity. To overcome this, we developed reduction-responsive nanoparticles (NP(3S)s) for the targeted delivery of a platinum(IV) (Pt(IV)) prodrug to improve efficacy and reduce the toxicity. NP(3S)s could release Pt(II) and hydrogen sulfide (H2S) upon encountering intracellular glutathione, leading to potent anticancer effects. Notably, NP(3S)s induced DNA damage and activated the STING pathway, which is a known promoter for T cell activation. Comparative RNA profiling revealed that NP(3S)s outperformed CisPt in enhancing T cell immunity, antitumor immunity, and oxidative stress pathways. In vivo experiments showed that NP(3S)s accumulated in tumors, promoting CD8+ T cell infiltration and boosting antitumor immunity. Furthermore, NP(3S)s exhibited robust in vivo anticancer efficacy while minimizing the CisPt-induced liver toxicity. Overall, the results indicate NP(3S)s hold great promise for clinical translation due to their low toxicity profile and potent anticancer activity.

Targeting DHX9 Triggers Tumor-Intrinsic Interferon Response and Replication Stress in Small Cell Lung Cancer

Activating innate immunity in cancer cells through cytoplasmic nucleic acid sensing pathways, a phenomenon known as "viral mimicry," has emerged as an effective strategy to convert immunologically "cold" tumors into "hot." Through a curated CRISPR-based screen of RNA helicases, we identified DExD/H-box helicase 9 (DHX9) as a potent repressor of double-stranded RNA (dsRNA) in small cell lung cancers (SCLC). Depletion of DHX9 induced accumulation of cytoplasmic dsRNA and triggered tumor-intrinsic innate immunity. Intriguingly, ablating DHX9 also induced aberrant accumulation of R-loops, which resulted in an increase of DNA damage-derived cytoplasmic DNA and replication stress in SCLCs. In vivo, DHX9 deletion promoted a decrease in tumor growth while inducing a more immunogenic tumor microenvironment, invigorating responsiveness to immune-checkpoint blockade. These findings suggest that DHX9 is a crucial repressor of tumor-intrinsic innate immunity and replication stress, representing a promising target for SCLC and other "cold" tumors in which genomic instability contributes to pathology.

SIGNIFICANCE

One promising strategy to trigger an immune response within tumors and enhance immunotherapy efficacy is by inducing endogenous "virus-mimetic" nucleic acid accumulation. Here, we identify DHX9 as a viral-mimicry-inducing factor involved in the suppression of double-stranded RNAs and R-loops and propose DHX9 as a novel target to enhance antitumor immunity. See related commentary by Chiappinelli, p. 389. This article is featured in Selected Articles from This Issue, p. 384.

Targeting BRCA and PALB2 in Pancreatic Cancer

OPINION STATEMENT

An important subgroup of pancreatic ductal adenocarcinomas (PDACs) harbor pathogenic variants in BRCA1, BRCA2, or PALB2. These tumors are exquisitely sensitive to platinum-based chemotherapy and patients may experience deep and durable responses to this treatment. PARP inhibitors offer potential respite from the cumulative toxicities of chemotherapy as they significantly extend progression-free survival compared to a chemotherapy holiday. Given the lack of proven survival benefit, the decision to use a maintenance PARP inhibitor rather than continue chemotherapy should be individualized. Interestingly, in both published clinical trials of maintenance PARP inhibitors, there is a striking range of interpatient benefit: Even in the platinum-sensitive setting, roughly 25% of tumors appear to be PARP inhibitor refractory (progressive disease within 2 months of starting treatment), 50% sustain moderate benefit (up to 2 years), and 25% are hyper-responsive (more than 2 years of benefit). This finding highlights the need to refine our understanding of which patients will respond to maintenance PARP inhibitors, both by being able to identify biallelic loss and by deepening our knowledge of resistance mechanisms and who develops them. Recent data supports that reversion mutations are common in PARP inhibitor refractory patients, but we have little understanding of the mechanisms that drive delayed resistance and long-term responses. Identifying which patients are more prone to certain mechanisms of resistance and tackling them with specific treatment strategies are areas of active investigation. Additionally, given that PARP inhibitors have limited overall efficacy for most patients, upfront combination strategies are an important future strategy.

Microglial inflammation in genome instability: A neurodegenerative perspective

The maintenance of genome stability is crucial for cell homeostasis and tissue integrity. Numerous human neuropathologies display chronic inflammation in the central nervous system, set against a backdrop of genome instability, implying a close interplay between the DNA damage and immune responses in the context of neurological disease. Dissecting the molecular mechanisms of this crosstalk is essential for holistic understanding of neuroinflammatory pathways in genome instability disorders. Non-neuronal cell types, specifically microglia, are major drivers of neuroinflammation in the central nervous system with neuro-protective and -toxic capabilities. Here, we discuss how persistent DNA damage affects microglial homeostasis, zooming in on the cytosolic DNA sensing cGAS-STING pathway and the downstream inflammatory response, which can drive neurotoxic outcomes in the context of genome instability.

The Killer's Web: Interconnection between Inflammation, Epigenetics and Nutrition in Cancer

Inflammation is a key contributor to both the initiation and progression of tumors, and it can be triggered by genetic instability within tumors, as well as by lifestyle and dietary factors. The inflammatory response plays a critical role in the genetic and epigenetic reprogramming of tumor cells, as well as in the cells that comprise the tumor microenvironment. Cells in the microenvironment acquire a phenotype that promotes immune evasion, progression, and metastasis. We will review the mechanisms and pathways involved in the interaction between tumors, inflammation, and nutrition, the limitations of current therapies, and discuss potential future therapeutic approaches.

PARP inhibitors for prostate cancer

Poly(ADP-ribose) polymerase (PARP) inhibitors have transformed the treatment landscape for patients with metastatic castration-resistant prostate cancer (mCRPC) and alterations in DNA damage response genes. This has also led to widespread use of genomic testing in all patients with mCRPC. The current review will give an overview of (1) the current understanding of the interplay between DNA damage response and PARP enzymes; (2) the clinical landscape of PARP inhibitors, including the combination of PARP inhibitors with other agents such as androgen-receptor signaling agents; (3) biomarkers related to PARP inhibitor response and resistance; and (4) considerations for interpreting genomic testing results and treating patients with PARP inhibitors.

PARP1 roles in DNA repair and DNA replication: The basi(c)s of PARP inhibitor efficacy and resistance

Genome integrity is under constant insult from endogenous and exogenous sources. In order to cope, eukaryotic cells have evolved an elaborate network of DNA repair that can deal with diverse lesion types and exhibits considerable functional redundancy. PARP1 is a major sensor of DNA breaks with established and putative roles in a number of pathways within the DNA repair network, including repair of single- and double-strand breaks as well as protection of the DNA replication fork. Importantly, PARP1 is the major target of small-molecule PARP inhibitors (PARPi), which are employed in the treatment of homologous recombination (HR)-deficient tumors, as the latter are particularly susceptible to the accumulation of DNA damage due to an inability to efficiently repair highly toxic double-strand DNA breaks. The clinical success of PARPi has fostered extensive research into PARP biology, which has shed light on the involvement of PARP1 in various genomic transactions. A major goal within the field has been to understand the relationship between catalytic inhibition and PARP1 trapping. The specific consequences of inhibition and trapping on genomic stability as a basis for the cytotoxicity of PARP inhibitors remain a matter of debate. Finally, PARP inhibition is increasingly recognized for its capacity to elicit/modulate anti-tumor immunity. The clinical potential of PARP inhibition is, however, hindered by the development of resistance. Hence, extensive efforts are invested in identifying factors that promote resistance or sensitize cells to PARPi. The current review provides a summary of advances in our understanding of PARP1 biology, the mechanistic nature, and molecular consequences of PARP inhibition, as well as the mechanisms that give rise to PARPi resistance.

Phase I study of peposertib and avelumab with or without palliative radiotherapy in patients with advanced solid tumors

INTRODUCTION

We report results from a phase I, three-part, dose-escalation study of peposertib, a DNA-dependent protein kinase inhibitor, in combination with avelumab, an immune checkpoint inhibitor, with or without radiotherapy in patients with advanced solid tumors.

MATERIALS AND METHODS

Peposertib 100-400 mg twice daily (b.i.d.) or 100-250 mg once daily (q.d.) was administered in combination with avelumab 800 mg every 2 weeks in Part A or avelumab plus radiotherapy (3 Gy/fraction × 10 days) in Part B. Part FE assessed the effect of food on the pharmacokinetics of peposertib plus avelumab. The primary endpoint in Parts A and B was dose-limiting toxicity (DLT). Secondary endpoints were safety, best overall response per RECIST version 1.1, and pharmacokinetics. The recommended phase II dose (RP2D) and maximum tolerated dose (MTD) were determined in Parts A and B.

RESULTS

In Part A, peposertib doses administered were 100 mg (n = 4), 200 mg (n = 11), 250 mg (n = 4), 300 mg (n = 6), and 400 mg (n = 4) b.i.d. Of DLT-evaluable patients, one each had DLT at the 250-mg and 300-mg dose levels and three had DLT at the 400-mg b.i.d. dose level. In Part B, peposertib doses administered were 100 mg (n = 3), 150 mg (n = 3), 200 mg (n = 4), and 250 mg (n = 9) q.d.; no DLT was reported in evaluable patients. Peposertib 200 mg b.i.d. plus avelumab and peposertib 250 mg q.d. plus avelumab and radiotherapy were declared as the RP2D/MTD. No objective responses were observed in Part A or B; one patient had a partial response in Part FE. Peposertib exposure was generally dose proportional.

CONCLUSIONS

Peposertib doses up to 200 mg b.i.d. in combination with avelumab and up to 250 mg q.d. in combination with avelumab and radiotherapy were tolerable in patients with advanced solid tumors; however, antitumor activity was limited.

CLINICALTRIALS

GOV IDENTIFIER

NCT03724890.

Bibliometric analysis of research trends on the combination of immune checkpoint inhibitors and PARP inhibitors in solid tumors

Introduction

Immune checkpoint inhibitors (ICIs) has made significant achievements in the therapeutics of various tumor types, and recently growing evidence from preclinical studies and clinical trials has indicated that poly-ADP-ribose polymerase inhibitors (PARPi) are exhibiting encouraging synergism with ICIs. The aim of our current study is to explore the development pattern of literature related to the combined therapy of ICIs and PARPi in solid tumors from a bibliometric perspective.

Methods

Publications concerning the combination of ICIs and PARPi in solid tumors during 2008-2022 were extracted from the WOSCC database. VOSviewer and R-bibliometrix were applied to conduct bibliometrics.

Results

In total, 1113 articles were finally included. The USA was the most dominant country, and University of Texas MD Anderson Cancer Center was the most fruitful institute. Andreas Schneeweiss ranked first concerning the amount of publications in this research domain, and Timothy Yap had the most citations on this theme. The analysis of keyword co-occurrence indicated that research frontiers were shifted from the biological mechanisms of cell death to the combined strategy of ICIs and PARPi in clinical trials.

Conclusions

Our study comprehensively examined the publications on the combination of ICIs and PARPi in solid tumors from a bibliometric perspective. The research on this topic is in its rapid growth stage, and the USA is possessing an absolutely leading position in this field by its scientific accumulations and productivity. Moreover, the research frontiers have shifted from the mechanisms of ICIs and PARPi to their combined treatment in clinical application. In summary, our results demonstrated a comprehensive overview of the knowledge atlas and a valuable reference for the future investigations in this field.

Nanoparticle-Based Immunotherapy for Reversing T-Cell Exhaustion

T-cell exhaustion refers to a state of T-cell dysfunction commonly observed in chronic infections and cancer. Immune checkpoint molecules blockading using PD-1 and TIM-3 antibodies have shown promising results in reversing exhaustion, but this approach has several limitations. The treatment of T-cell exhaustion is still facing great challenges, making it imperative to explore new therapeutic strategies. With the development of nanotechnology, nanoparticles have successfully been applied as drug carriers and delivery systems in the treatment of cancer and infectious diseases. Furthermore, nanoparticle-based immunotherapy has emerged as a crucial approach to reverse exhaustion. Here, we have compiled the latest advances in T-cell exhaustion, with a particular focus on the characteristics of exhaustion that can be targeted. Additionally, the emerging nanoparticle-based delivery systems were also reviewed. Moreover, we have discussed, in detail, nanoparticle-based immunotherapies that aim to reverse exhaustion, including targeting immune checkpoint blockades, remodeling the tumor microenvironment, and targeting the metabolism of exhausted T cells, etc. These data could aid in comprehending the immunopathogenesis of exhaustion and accomplishing the objective of preventing and treating chronic diseases or cancer.

Molecular map of cGAS-STING pathway-related genes in bladder cancer: the perspective toward immune microenvironment and prognosis

BACKGROUND

The cGAS-STING pathway emerges as a pivotal innate immune pathway with the potential to profoundly influence all facets of tumor initiation and progression. The prognostic significance and immunological role of cGAS-STING pathway-related genes (CRGs) in individuals diagnosed with bladder cancer (BLCA) have not yet been fully elucidated.

METHODS

Performed unsupervised cluster analysis to identify distinct clusters. Utilizing LASSO and multivariate Cox regression analysis to construct a prognostic risk model. The IMvigor210, GSE13507 and GSE78220 cohorts were utilized to explore the potential value of risk score in immune therapy response and survival prediction.

RESULTS

A risk model was developed utilizing four CRGs in order to forecast the overall survival (OS) of BLCA patients. The risk score to be a standalone risk factor, which was further corroborated by the external validation set obtained from the GEO database (GSE13507). We established an integrated nomogram that combined risk scoring and clinical information, exhibiting commendable clinical practicality in predicting the overall survival period of BLCA patients. It is noteworthy that risk score could differentiate tumor microenvironments among different risk groups and individuals who were more responsive to immunotherapy in IMvigor210 and GSE13507 cohorts. In vitro experiments, we noted an up-regulation of IRF3 and IKBKB upon the activation of the cGAS-STING pathway. Conversely, the activation of the cGAS-STING pathway resulted in a down-regulation of POLR3G and CTNNB1.

CONCLUSIONS

CRG risk model shows promise as a potential stratification approach for bladder cancer patients.

Olaparib plus Durvalumab, with or without Bevacizumab, as Treatment in PARP Inhibitor-Naïve Platinum-Sensitive Relapsed Ovarian Cancer: A Phase II Multi-Cohort Study

PURPOSE

Early results from the phase II MEDIOLA study (NCT02734004) in germline BRCA1- and/or BRCA2-mutated (gBRCAm) platinum-sensitive relapsed ovarian cancer (PSROC) showed promising efficacy and safety with olaparib plus durvalumab. We report efficacy and safety of olaparib plus durvalumab in an expansion cohort of women with gBRCAm PSROC (gBRCAm expansion doublet cohort) and two cohorts with non-gBRCAm PSROC, one of which also received bevacizumab (non-gBRCAm doublet and triplet cohorts).

PATIENTS AND METHODS

In this open-label, multicenter study, PARP inhibitor-naïve patients received olaparib plus durvalumab treatment until disease progression; the non-gBRCAm triplet cohort also received bevacizumab. Primary endpoints were objective response rate (ORR; gBRCAm expansion doublet cohort), disease control rate (DCR) at 24 weeks (non-gBRCAm cohorts), and safety (all cohorts).

RESULTS

The full analysis and safety analysis sets comprised 51, 32, and 31 patients in the gBRCAm expansion doublet, non-gBRCAm doublet, and non-gBRCAm triplet cohorts, respectively. ORR was 92.2% [95% confidence interval (CI), 81.1-97.8] in the gBRCAm expansion doublet cohort (primary endpoint); DCR at 24 weeks was 28.1% (90% CI, 15.5-43.9) in the non-gBRCAm doublet cohort (primary endpoint) and 74.2% (90% CI, 58.2-86.5) in the non-gBRCAm triplet cohort (primary endpoint). Grade ≥ 3 adverse events were reported in 47.1%, 65.6%, and 61.3% of patients in the gBRCAm expansion doublet, non-gBRCAm doublet, and non-gBRCAm triplet cohorts, respectively, most commonly anemia.

CONCLUSIONS

Olaparib plus durvalumab continued to show notable clinical activity in women with gBRCAm PSROC. Olaparib plus durvalumab with bevacizumab demonstrated encouraging clinical activity in women with non-gBRCAm PSROC. No new safety signals were identified.

Novel dual inhibitors of PARP and HDAC induce intratumoral STING-mediated antitumor immunity in triple-negative breast cancer

PARP inhibitors and HDAC inhibitors have been approved for the clinical treatment of malignancies, but acquired resistance of or limited effects on solid tumors with a single agent remain as challenges. Bioinformatics analyses and a combination of experiments had demonstrated the synergistic effects of PARP and HDAC inhibitors in triple-negative breast cancer. A series of novel dual PARP and HDAC inhibitors were rationally designed and synthesized, and these molecules exhibited high enzyme inhibition activity with excellent antitumor effects in vitro and in vivo. Mechanistically, dual PARP and HDAC inhibitors induced BRCAness to restore synthetic lethality and promoted cytosolic DNA accumulation, which further activates the cGAS-STING pathway and produces proinflammatory chemokines through type I IFN-mediated JAK-STAT pathway. Moreover, these inhibitors promoted neoantigen generation, upregulated antigen presentation genes and PD-L1, and enhanced antitumor immunity when combined with immune checkpoint blockade therapy. These results indicated that novel dual PARP and HDAC inhibitors have antitumor immunomodulatory functions in triple-negative breast cancer. Novel dual PARP and HDAC inhibitors induce BRCAness to restore synthetic lethality, activating tumoral IFN signaling via the cGAS-STING pathway and inducing cytokine production, promoting neoantigen generation and presentation to enhance the immune response.

Emerging mechanisms and implications of cGAS-STING signaling in cancer immunotherapy strategies

The intricate interplay between the human immune system and cancer development underscores the central role of immunotherapy in cancer treatment. Within this landscape, the innate immune system, a critical sentinel protecting against tumor incursion, is a key player. The cyclic GMP-AMP synthase (cGAS) and stimulator of interferon genes (STING) pathway has been found to be a linchpin of innate immunity: activation of this signaling pathway orchestrates the production of type I interferon (IFN-α/β), thus fostering the maturation, differentiation, and mobilization of immune effectors in the tumor microenvironment. Furthermore, STING activation facilitates the release and presentation of tumor antigens, and therefore is an attractive target for cancer immunotherapy. Current strategies to activate the STING pathway, including use of pharmacological agonists, have made substantial advancements, particularly when combined with immune checkpoint inhibitors. These approaches have shown promise in preclinical and clinical settings, by enhancing patient survival rates. This review describes the evolving understanding of the cGAS-STING pathway's involvement in tumor biology and therapy. Moreover, this review explores classical and non-classical STING agonists, providing insights into their mechanisms of action and potential for optimizing immunotherapy strategies. Despite challenges and complexities, the cGAS-STING pathway, a promising avenue for enhancing cancer treatment efficacy, has the potential to revolutionize patient outcomes.

Olaparib in recurrent isocitrate dehydrogenase mutant high-grade glioma: A phase 2 multicenter study of the POLA Network

Background

Based on preclinical studies showing that IDH-mutant (IDHm) gliomas could be vulnerable to PARP inhibition we launched a multicenter phase 2 study to test the efficacy of olaparib monotherapy in this population.

Methods

Adults with recurrent IDHm high-grade gliomas (HGGs) after radiotherapy and at least one line of alkylating chemotherapy were enrolled. The primary endpoint was a 6-month progression-free survival rate (PFS-6) according to response assessment in neuro-oncology criteria. Pre-defined threshold for study success was a PFS-6 of at least 50%.

Results

Thirty-five patients with recurrent IDHm HGGs were enrolled, 77% at ≥ 2nd recurrence. Median time since diagnosis and radiotherapy were 7.5 years and 33 months, respectively. PFS-6 was 31.4% (95% CI [16.9; 49.3%]). Two patients (6%) had an objective response and 14 patients (40%) had a stable disease as their best response. Median PFS and median overall survival were 2.05 and 15.9 months, respectively. Oligodendrogliomas (1p/19q codeleted) had a higher PFS-6 (53.4% vs. 15.7%, P = .05) than astrocytomas while an initial diagnosis of grade 4 astrocytoma tended to be associated with a lower PFS-6 compared to grade 2/3 gliomas (0% vs 31.4%, P = .16). A grade 2 or 3 treatment-related adverse event was observed in 15 patients (43%) and 5 patients (14%), respectively. No patient definitively discontinued treatment due to side effects.

Conclusions

Although it did not meet its primary endpoint, the present study shows that in this heavily pretreated population, olaparib monotherapy was well tolerated and resulted in some activity, supporting further PARP inhibitors evaluation in IDHm HGGs, especially in oligodendrogliomas.

Harnessing the effects of hypoxia-like inhibition on homology-directed DNA repair

Hypoxia is a hallmark feature of the tumor microenvironment which can promote mutagenesis and instability. This increase in mutational burden occurs as a result of the downregulation of DNA repair systems. Deficits in the DNA damage response can be exploited to induce cytotoxicity and treat advanced stage cancers. With the advent of precision medicine, agents such as Poly (ADP-ribose) polymerase (PARP) inhibitors have been used to achieve synthetic lethality in homology directed repair (HDR) deficient cancers. However, most cancers lack these predictive biomarkers. Treatment for the HDR proficient population represents an important unmet clinical need. There has been interest in the use of anti-angiogenic agents to promote tumor hypoxia and induce deficiency in a HDR proficient background. For example, the use of cediranib to inhibit PDGFR and downregulate enzymes of the HDR pathway can be used synergistically with a PARP inhibitor. This combination can improve therapeutic responses in HDR proficient cancers. Preclinical results and Phase II and III clinical trial data support the mechanistic rationale for the efficacy of these agents in combination. Future investigations should explore the effectiveness of cediranib and other anti-angiogenic agents with a PARP inhibitor to elicit an antitumor response and sensitize cancers to immunotherapy.

Pembrolizumab for metastatic castration-resistant prostate cancer: trials and tribulations

INTRODUCTION

Immunotherapies have revolutionized the management of various malignancies but have only recently been evaluated systematically in prostate cancer. Pembrolizumab, a programmed-death 1 (PD-1) blocking antibody, has been utilized in a small subset of prostate cancer patients with mismatch repair deficiency/microsatellite instability, but has now been assessed in broader populations of metastatic prostate cancer patients.

AREAS COVERED

The results of four pembrolizumab-based phase III clinical trials for metastatic castration-resistant prostate cancer (mCRPC) and metastatic hormone-sensitive prostate cancer (mHSPC) patients, including KEYNOTE-641, KEYNOTE-921, KEYNOTE-991, and KEYLYNK-010 are summarized. Programmed death-ligand 1 (PD-L1) expression, the efficacy of pembrolizumab in prostate cancer patients with certain molecular defects, and emerging pembrolizumab-based therapeutic combinations are also reviewed.

EXPERT OPINION

Pembrolizumab has not benefitted unselected metastatic prostate cancer patients when combined with chemotherapy, next-generation hormonal agents (NHA), or poly(ADP-ribose) polymerase inhibitors (PARPi). PD-L1 positivity does not predict the response to pembrolizumab in this disease. A small number of responding patients can likely be explained by rare genetic and molecular defects, and more innovative combination strategies are needed to improve outcomes in prostate cancer patients who are not sensitive to pembrolizumab. Emphasis should be placed on developing additional or alternative immuno-oncology approaches beyond classical immune checkpoint inhibition.

Exploiting the DNA Damage Response for Prostate Cancer Therapy

Prostate cancers that progress despite androgen deprivation develop into castration-resistant prostate cancer, a fatal disease with few treatment options. In this review, we discuss the current understanding of prostate cancer subtypes and alterations in the DNA damage response (DDR) that can predispose to the development of prostate cancer and affect its progression. We identify barriers to conventional treatments, such as radiotherapy, and discuss the development of new therapies, many of which target the DDR or take advantage of recurring genetic alterations in the DDR. We place this in the context of advances in understanding the genetic variation and immune landscape of CRPC that could help guide their use in future treatment strategies. Finally, we discuss several new and emerging agents that may advance the treatment of lethal disease, highlighting selected clinical trials.

Targeting the immune microenvironment for ovarian cancer therapy

Ovarian cancer (OC) is an aggressive malignancy characterized by a complex immunosuppressive tumor microenvironment (TME). Immune checkpoint inhibitors have emerged as a breakthrough in cancer therapy by reactivating the antitumor immune response suppressed by tumor cells. However, in the case of OC, these inhibitors have failed to demonstrate significant improvements in patient outcomes, and existing biomarkers have not yet identified promising subgroups. Consequently, there remains a pressing need to understand the interplay between OC tumor cells and their surrounding microenvironment to develop effective immunotherapeutic approaches. This review aims to provide an overview of the OC TME and explore its potential as a therapeutic strategy. Tumor-infiltrating lymphocytes (TILs) are major actors in OC TME. Evidence has been accumulating regarding the spontaneous TILS response against OC antigens. Activated T-helpers secrete a wide range of inflammatory cytokines with a supportive action on cytotoxic T-cells. Simultaneously, mature B-cells are recruited and play a significant antitumor role through opsonization of target antigens and T-cell recruitment. Macrophages also form an important subset of innate immunity (M1-macrophages) while participating in the immune-stimulation context. Finally, OC has shown to engage a significant natural-killer-cells immune response, exerting direct cytotoxicity without prior sensitization. Despite this initial cytotoxicity, OC cells develop various strategies to induce an immune-tolerant state. To this end, multiple immunosuppressive molecules are secreted to impair cytotoxic cells, recruit regulatory cells, alter antigen presentation, and effectively evade immune response. Consequently, OC TME is predominantly infiltrated by immunosuppressive cells such as FOXP3+ regulatory T-cells, M2-polarized macrophages and myeloid-derived suppressor cells. Despite this strong immunosuppressive state, PD-1/PD-L1 inhibitors have failed to improve outcomes. Beyond PD-1/PD-L1, OC expresses multiple other immune checkpoints that contribute to immune evasion, and each representing potential immune targets. Novel immunotherapies are attempting to overcome the immunosuppressive state and induce specific immune responses using antibodies adoptive cell therapy or vaccines. Overall, the OC TME presents both opportunities and obstacles. Immunotherapeutic approaches continue to show promise, and next-generation inhibitors offer exciting opportunities. However, tailoring therapies to individual immune characteristics will be critical for the success of these treatments.

Combined inhibition of Wee1 and Chk1 as a therapeutic strategy in multiple myeloma

Multiple myeloma (MM) is a hematological malignancy characterized by an abnormal clonal proliferation of malignant plasma cells. Despite the introduction of novel agents that have significantly improved clinical outcome, most patients relapse and develop drug resistance. MM is characterized by genomic instability and a high level of replicative stress. In response to replicative and DNA damage stress, MM cells activate various DNA damage signaling pathways. In this study, we reported that high CHK1 and WEE1 expression is associated with poor outcome in independent cohorts of MM patients treated with high dose melphalan chemotherapy or anti-CD38 immunotherapy. Combined targeting of Chk1 and Wee1 demonstrates synergistic toxicities on MM cells and was associated with higher DNA double-strand break induction, as evidenced by an increased percentage of γH2AX positive cells subsequently leading to apoptosis. The therapeutic interest of Chk1/Wee1 inhibitors' combination was validated on primary MM cells of patients. The toxicity was specific of MM cells since normal bone marrow cells were not significantly affected. Using deconvolution approach, MM patients with high CHK1 expression exhibited a significant lower percentage of NK cells whereas patients with high WEE1 expression displayed a significant higher percentage of regulatory T cells in the bone marrow. These data emphasize that MM cell adaptation to replicative stress through Wee1 and Chk1 upregulation may decrease the activation of the cell-intrinsic innate immune response. Our study suggests that association of Chk1 and Wee1 inhibitors may represent a promising therapeutic approach in high-risk MM patients characterized by high CHK1 and WEE1 expression.

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.

Revisiting the concept of neoadjuvant and induction therapy in head and neck cancer with the advent of immunotherapy

The treatment of locally advanced (LA) Head and Neck Squamous Cell Carcinoma (HNSCC) is based on surgery followed by (chemo)radiation or on curative (chemo)radiation, depending on site and stage. Despite optimal locoregional treatment, about 50% of patients recur, with a huge impact on prognosis and substantial morbidity. The advent of immunotherapy (IT) with immune checkpoint inhibitors (ICIs) changed the paradigm of systemic treatment for recurrent/metastatic (RM) disease, showing activity, efficacy, and safety in both platinum-resistant and platinum-naïve patients. Such data led clinicians to design clinical trials to investigate early administration of IT even in the neoadjuvant or window of opportunity setting. In this review, we examine the published and ongoing trials investigating IT in the neoadjuvant setting for LA HNSCC. We address the current challenges of this treatment modality: optimal patient selection for neoadjuvant IT; choosing the appropriate systemic approach to enhance response without compromising tolerability; determining the ideal study endpoint, with a focus on major pathological response as a potential surrogate for overall survival; evaluating treatment response through imaging, considering the discordance between radiological and pathological assessments; and the influence of neoadjuvant IT response on locoregional treatment de-escalation strategies.

Triggering pyroptosis enhances the antitumor efficacy of PARP inhibitors in prostate cancer

PURPOSE

PARP inhibitors have revolutionized the treatment landscape for advanced prostate cancer (PCa) patients who harboring mutations in homologous recombination repair (HRR) genes. However, the molecular mechanisms underlying PARP inhibitors function beyond DNA damage repair pathways remain elusive, and identifying novel predictive targets that favorably respond to PARP inhibitors in PCa is an active area of research.

METHODS

The expression of GSDME in PCa cell lines and human PCa samples was determined by western blotting. Targeted bisulfite sequencing, gene enrichment analysis (GSEA), clone formation, construction of the stably transfected cell lines, lactate dehydrogenase (LDH) assay, western blotting as well as a mouse model of subcutaneous xenografts were used to investigate the role of GSDME in PCa. The combinational therapeutic effect of olaparib and decitabine was determined using both in vitro and in vivo experiments.

RESULTS

We have found low expression of GSDME in PCa. Interestingly, we demonstrated that GSDME activity is robustly induced in olaparib-treated cells undergoing pyroptosis, and that high methylation of the GSDME promoter dampens its activity in PCa cells. Intriguingly, genetically overexpressing GSDME does not inhibit tumor cell proliferation but instead confers sensitivity to olaparib. Furthermore, pharmacological treatment with the combination of olaparib and decitabine synergistically induces GSDME expression and cleavage through caspase-3 activation, thus promoting pyroptosis and enhancing anti-tumor response, ultimately resulting in tumor remission.

CONCLUSION

Our findings highlight a novel therapeutic strategy for enhancing the long-term response to olaparib beyond HRR-deficient tumors in PCa, underscoring the critical role of GSDME in regulating tumorigenesis.

At the Crossroads of the cGAS-cGAMP-STING Pathway and the DNA Damage Response: Implications for Cancer Progression and Treatment

The evolutionary conserved DNA-sensing cGAS-STING innate immunity pathway represents one of the most important cytosolic DNA-sensing systems that is activated in response to viral invasion and/or damage to the integrity of the nuclear envelope. The key outcome of this pathway is the production of interferon, which subsequently stimulates the transcription of hundreds of genes. In oncology, the situation is complex because this pathway may serve either anti- or pro-oncogenic roles, depending on context. The prevailing understanding is that when the innate immune response is activated by sensing cytosolic DNA, such as DNA released from ruptured micronuclei, it results in the production of interferon, which attracts cytotoxic cells to destroy tumors. However, in tumor cells that have adjusted to significant chromosomal instability, particularly in relapsed, treatment-resistant cancers, the cGAS-STING pathway often supports cancer progression, fostering the epithelial-to-mesenchymal transition (EMT). Here, we review this intricate pathway in terms of its association with cancer progression, giving special attention to pancreatic ductal adenocarcinoma and gliomas. As the development of new cGAS-STING-modulating small molecules and immunotherapies such as oncolytic viruses involves serious challenges, we highlight several recent fundamental discoveries, such as the proton-channeling function of STING. These discoveries may serve as guiding lights for potential pharmacological advancements.

Personalized medicine for metastatic prostate cancer: The paradigm of PARP inhibitors

Despite remarkable progress in the last decade, metastatic prostate cancer (mPCa) remains incurable. The approval of PARP inhibitors (PARPis) represents a milestone in this field, which definitively enters the era of precision medicine, as mPCa is often enriched for defects of homologous recombination repair genes. PARPis are now used as single agents for patients with metastatic castration-resistant PCa. Moreover, combinations of PARPis plus androgen-receptor targeted agents and immune checkpoint inhibitors, and earlier applications of PARPis in the metastatic hormone-sensitive PCa are under evaluation, representing the possible upcoming applications of these agents. Mechanisms of sensitization and resistance have been only partially elucidated. In our review, we summarize the current clinical evidence regarding PARPis in mPCa and the future directions of these targeted agents.

Combinatorial Treatment with PARP and MAPK Inhibitors Overcomes Phenotype Switch-Driven Drug Resistance in Advanced Melanoma

Metastatic melanoma is either intrinsically resistant or rapidly acquires resistance to targeted therapy treatments, such as MAPK inhibitors (MAPKi). A leading cause of resistance to targeted therapy is a dynamic transition of melanoma cells from a proliferative to a highly invasive state, a phenomenon called phenotype switching. Mechanisms regulating phenotype switching represent potential targets for improving treatment of patients with melanoma. Using a drug screen targeting chromatin regulators in patient-derived three-dimensional MAPKi-resistant melanoma cell cultures, we discovered that PARP inhibitors (PARPi) restore sensitivity to MAPKis, independent of DNA damage repair pathways. Integrated transcriptomic, proteomic, and epigenomic analyses demonstrated that PARPis induce lysosomal autophagic cell death, accompanied by enhanced mitochondrial lipid metabolism that ultimately increases antigen presentation and sensitivity to T-cell cytotoxicity. Moreover, transcriptomic and epigenetic rearrangements induced by PARP inhibition reversed epithelial-mesenchymal transition-like phenotype switching, which redirected melanoma cells toward a proliferative and MAPKi-sensitive state. The combination of PARP and MAPKis synergistically induced cancer cell death both in vitro and in vivo in patient-derived xenograft models. Therefore, this study provides a scientific rationale for treating patients with melanoma with PARPis in combination with MAPKis to abrogate acquired therapy resistance.

SIGNIFICANCE

PARP inhibitors can overcome resistance to MAPK inhibitors by activating autophagic cell death and reversing phenotype switching, suggesting that this synergistic combination could help improve the prognosis of patients with melanoma.

Heterogeneity and treatment landscape of ovarian carcinoma

Ovarian carcinoma is characterized by heterogeneity at the molecular, cellular and anatomical levels, both spatially and temporally. This heterogeneity affects response to surgery and/or systemic therapy, and also facilitates inherent and acquired drug resistance. As a consequence, this tumour type is often aggressive and frequently lethal. Ovarian carcinoma is not a single disease entity and comprises various subtypes, each with distinct complex molecular landscapes that change during progression and therapy. The interactions of cancer and stromal cells within the tumour microenvironment further affects disease evolution and response to therapy. In past decades, researchers have characterized the cellular, molecular, microenvironmental and immunological heterogeneity of ovarian carcinoma. Traditional treatment approaches have considered ovarian carcinoma as a single entity. This landscape is slowly changing with the increasing appreciation of heterogeneity and the recognition that delivering ineffective therapies can delay the development of effective personalized approaches as well as potentially change the molecular and cellular characteristics of the tumour, which might lead to additional resistance to subsequent therapy. In this Review we discuss the heterogeneity of ovarian carcinoma, outline the current treatment landscape for this malignancy and highlight potentially effective therapeutic strategies in development.

Crosstalk between immune checkpoint and DNA damage response inhibitors for radiosensitization of tumors

PURPOSE

This review article is intended to provide a perspective overview of potential strategies to overcome radiation resistance of tumors through the combined use of immune checkpoint and DNA repair inhibitors.

METHODS

A literature search was conducted in PubMed using the terms ("DNA repair* and DNA damage response* and intracellular immune response* and immune checkpoint inhibition* and radio*") until January 31, 2023. Articles were manually selected based on their relevance to the topics analyzed.

RESULTS

Modern radiotherapy offers a wide range of options for tumor treatment. Radiation-resistant subpopulations of the tumor pose a particular challenge for complete cure. This is due to the enhanced activation of molecular defense mechanisms that prevent cell death because of DNA damage. Novel approaches to enhance tumor cure are provided by immune checkpoint inhibitors, but their effectiveness, especially in tumors without increased mutational burden, also remains limited. Combining inhibitors of both immune checkpoints and DNA damage response with radiation may be an attractive option to augment existing therapies and is the subject of the data summarized here.

CONCLUSION

The combination of tested inhibitors of DNA damage and immune responses in preclinical models opens additional attractive options for the radiosensitization of tumors and represents a promising application for future therapeutic approaches.

Interferon epsilon and ovarian cancer

Most biologists know of the interferons IFNα, IFNβ, and IFNγ and their roles in immunity and infection, but they may not have heard of IFNε. A recent study in Nature suggests that IFNε can act as a tumor suppressor in serous ovarian cancers.

SIX4 Controls Anti-PD-1 Efficacy by Regulating STING Expression

The cGAS/STING cytosolic DNA-sensing pathway plays a significant role in antitumor immunity. Expression of STING is tightly regulated and commonly reduced or defective in many types of cancer. We have identified SIX4 as a significant regulator of STING expression in colon cancer cells. We showed that knockout of SIX4 decreased STING expression at the mRNA and protein levels while ectopic expression of SIX4 increased STING expression. Depletion of SIX4 led to attenuated STING activation and downstream signaling. Reexpression of SIX4 or ectopic expression of STING in SIX4 knockout cells reversed the effect. Ectopic expression of SIX4 enhanced DMXAA and cGAMP-induced STING activation and downstream signaling. Importantly, decrease of SIX4 expression substantially decreased tumor infiltration of CD8+ T cells and reduced the efficacy of PD-1 antibodies to diminish tumor growth in immune competent mice in vivo. Finally, analysis of The Cancer Genome Atlas colon cancer dataset indicated that tumors with high SIX4 expression were significantly enriched in the Inflammatory Response pathway. SIX4 expression also correlated with expression of multiple IFN-stimulated genes, inflammatory cytokines, and CD8A. Taken together, our results implicate that SIX4 is a principal regulator of STING expression in colon cancer cells, providing an additional mechanism and genetic marker to predict effective immune checkpoint blockade therapy responses.

SIGNIFICANCE

Our studies demonstrate that SIX4 is an important regulator of STING expression, providing a genetic marker or a therapeutic target to predict or enhance immune checkpoint blockade therapy responses in colon cancer.

Mutant RB1 enhances therapeutic efficacy of PARPis in lung adenocarcinoma by triggering the cGAS/STING pathway

Poly (ADP-ribose) polymerase inhibitors (PARPis) are approved for cancer therapy according to their synthetic lethal interactions, and clinical trials have been applied in non-small cell lung cancer. However, the therapeutic efficacy of PARPis in lung adenocarcinoma (LUAD) is still unknown. We explored the effect of a mutated retinoblastoma gene (RB1) on PARPi sensitivity in LUAD. Bioinformatic screening was performed to identify PARPi-sensitive biomarkers. Here, we showed that viability of LUAD cell lines with mutated RB1 was significantly decreased by PARPis (niraparib, rucaparib, and olaparib). RB1 deficiency induced genomic instability, prompted cytosolic double-stranded DNA (dsDNA) formation, activated the cGAS/STING pathway, and upregulated downstream chemokines CCL5 and CXCL10, triggering immune cell infiltration. Xenograft experiments indicated that PARPi treatment reduced tumorigenesis in RB1-KO mice. Additionally, single-cell RNA sequencing analysis showed that malignant cells with downregulated expression of RB1 had more communications with other cell types, exhibiting activation of specific signaling such as GAS, IFN response, and antigen-presenting and cytokine activities. Our findings suggest that RB1 mutation mediates the sensitivity to PARPis through a synthetic lethal effect by triggering the cGAS/STING pathway and upregulation of immune infiltration in LUAD, which may be a potential therapeutic strategy.

MiR-181a targets STING to drive PARP inhibitor resistance in BRCA- mutated triple-negative breast cancer and ovarian cancer

BACKGROUND

Poly (ADP-ribose) polymerase inhibitors (PARPi) are approved for the treatment of BRCA-mutated breast cancer (BC), including triple-negative BC (TNBC) and ovarian cancer (OvCa). A key challenge is to identify the factors associated with PARPi resistance; although, previous studies suggest that platinum-based agents and PARPi share similar resistance mechanisms.

METHODS

Olaparib-resistant (OlaR) cell lines were analyzed using HTG EdgeSeq miRNA Whole Transcriptomic Analysis (WTA). Functional assays were performed in three BRCA-mutated TNBC cell lines. In-silico analysis were performed using multiple databases including The Cancer Genome Atlas, the Genotype-Tissue Expression, The Cancer Cell Line Encyclopedia, Genomics of Drug Sensitivity in Cancer, and Gene Omnibus Expression.

RESULTS

High miR-181a levels were identified in OlaR TNBC cell lines (p = 0.001) as well as in tumor tissues from TNBC patients (p = 0.001). We hypothesized that miR-181a downregulates the stimulator of interferon genes (STING) and the downstream proinflammatory cytokines to mediate PARPi resistance. BRCA1 mutated TNBC cell lines with miR-181a-overexpression were more resistant to olaparib and showed downregulation in STING and the downstream genes controlled by STING. Extracellular vesicles derived from PARPi-resistant TNBC cell lines horizontally transferred miR-181a to parental cells which conferred PARPi-resistance and targeted STING. In clinical settings, STING levels were positively correlated with interferon gamma (IFNG) response scores (p = 0.01). In addition, low IFNG response scores were associated with worse response to neoadjuvant treatment including PARPi for high-risk HER2 negative BC patients (p = 0.001). OlaR TNBC cell lines showed resistance to platinum-based drugs. OvCa cell lines resistant to platinum showed resistance to olaparib. Knockout of miR-181a significantly improved olaparib sensitivity in OvCa cell lines (p = 0.001).

CONCLUSION

miR-181a is a key factor controlling the STING pathway and driving PARPi and platinum-based drug resistance in TNBC and OvCa. The miR-181a-STING axis can be used as a potential marker for predicting PARPi responses in TNBC and OvCa tumors.

Pembrolizumab in mCRPC - Combination therapies as breakthrough to success?

PURPOSE OF REVIEW

Immune checkpoint inhibitors (ICIs) have shown promising antitumor activity in various malignant diseases. This narrative review provides an update on ongoing clinical studies investigating the only FDA-approved ICI programmed death receptor 1 (PD-1) inhibitor pembrolizumab in mono- and combination therapy in patients with metastatic castration-resistant prostate cancer (mCRPC).

RECENT FINDINGS

Although most clinical trials investigating pembrolizumab as mono- or combinational therapy did not meet their primary endpoints, there exist subgroups of patients that demonstrate impressive responses rates justifying further investigation of ICI in prostate cancer. Beside combination of pembrolizumab with approved mCRPC agents, innovative approaches, like combining pembrolizumab with radioligands, deoxyribonucleic acid vaccines or innovative immunotherapeutic agents (i.e., ONC-392, AMG160, BXCL701) are ongoing exerting promising preliminary findings.

SUMMARY

ICI monotherapy seems to be effective in a small biomarker-preselected population, however, there is evidence that especially novel ICI combination approaches can improve patient survival, which could ultimately refocus and revolutionize the treatment of mCRPC.

Niraparib and dostarlimab for the treatment of recurrent platinum-resistant ovarian cancer: results of a Phase II study (MOONSTONE/GOG-3032)

OBJECTIVE

This study assessed the efficacy, safety, and health-related quality of life (HRQoL) of the treatment regimen of dostarlimab, a programmed death-1 inhibitor, combined with niraparib, a poly (ADP-ribose) polymerase inhibitor, in patients with BRCA wild type (BRCAwt) recurrent platinum-resistant ovarian cancer (PROC) who had previously received bevacizumab treatment.

METHODS

This Phase II, open-label, single-arm, multicenter study, conducted in the USA, enrolled patients with recurrent PROC to receive niraparib and dostarlimab until disease progression or unacceptable toxicity (up to 3 years). A preplanned interim futility analysis was performed after the first 41 patients had undergone ≥1 radiographic evaluation (approximately 9 weeks from the first treatment).

RESULTS

The prespecified interim futility criterion was met and the study was therefore terminated. For the 41 patients assessed, the objective response rate (ORR) was 7.3% (95% confidence interval: 1.5-19.9); no patients achieved a complete response, 3 patients (7.3%) achieved a partial response (duration of response; 3.0, 3.8, and 9.2 months, respectively), and 9 patients (22.0%) had stable disease. In total, 39 patients (95.1%) experienced a treatment-related adverse event, but no new safety issues were observed. HRQoL, assessed using FOSI, or Functional Assessment of Cancer Therapy - Ovarian Symptom Index scores, worsened over time compared with baseline scores.

CONCLUSIONS

The study was terminated due to the observed ORR at the interim futility analysis. This highlights a need for effective therapies in treating patients with recurrent BRCAwt PROC.