Effects of combined use of ribociclib with PARP1 inhibitor on cell kinetics in breast cancer

In the present study, antiproliferative and anticancer effects of Valamor (VLM), which contains the active component ribociclib, and DPQ, a poly(ADP-ribose) polymerase 1 inhibitor, alone and in combination were evaluated in the MCF-7 and MDA-MB-231 breast cancer cell lines in vitro. VLM was applied at concentrations of 40, 80 and 160 µg/ml, and DPQ was used at concentrations of 3, 6 and 9 µg/ml. The proliferation rate, cell index obtained from the real-time cell analysis system, mitosis activity, bromodeoxyuridine cell proliferation and caspase activity parameters were determined. In conclusion, the results obtained from cell kinetics parameters demonstrated the anticancer and antiproliferative effects of the combination of VLM and DPQ on breast cancer cells.

ANP32B promotes colorectal cancer cell progression and reduces cell sensitivity to PRAP1 inhibitor through up-regulating HPF1

ANP32B, a member of the acidic leucine-rich nuclear phosphoprotein 32 family member B, is aberrantly expressed in various cancers, including colorectal cancer. However, the function and mechanism of action of ANP32B in colorectal cancer remain unclear. The present study therefore analyzed the expression of ANP32B and its activity in colorectal cancer patient samples and colorectal cancer cell lines. ANP32B expression was found to be significantly upregulated in colorectal cancer patient samples and cell lines. Upregulation of ANP32B enhanced colorectal cancer cell proliferation and migration, whereas downregulation of ANP32B suppressed colorectal cancer cell proliferation. RNA sequencing analysis of differentially expressed genes in ANP32B silenced colorectal cancer cells showed that histone PARylation factor 1 (HPF1), which protects against DNA damage by interacting with the anti-tumor target PARP1, was significantly downregulated. Luciferase promoter assays testing the regulatory association between ANP32B and HPF1 showed that ANP32B interacted with the HPF1 promoter. Analysis of colorectal cancer samples from The Cancer Genome Atlas showed that ANP32B and HPF1 expression were positively correlated, and recovery assays showed that ANP32B promoted colorectal cancer progression by up-regulating HPF1. Overexpression of ANP32B also reduced the sensitivity of colorectal cancer cells to PARP1 inhibitor, consistent with the oncogenic role of ANP32B. ANP32B may alter the sensitivity of colorectal cancer cells to PARP1 inhibitor via a mechanism associated with the HPF1 gene. In summary, these findings showed that ANP32B acted as a tumor promoter, potentiating both colorectal cancer malignancy and drug resistance. Targeting the ANP32B/HPF1 axis may have benefit for patients with colorectal cancer.

Mutant-Huntingtin Molecular Pathways Elucidate New Targets for Drug Repurposing

The spectrum of neurodegenerative diseases known today is quite extensive. The complexities of their research and treatment lie not only in their diversity. Even many years of struggle and narrowly focused research on common pathologies such as Alzheimer's, Parkinson's, and other brain diseases have not brought cures for these illnesses. What can be said about orphan diseases? In particular, Huntington's disease (HD), despite affecting a smaller part of the human population, still attracts many researchers. This disorder is known to result from a mutation in the HTT gene, but having this information still does not simplify the task of drug development and studying the mechanisms of disease progression. Nonetheless, the data accumulated over the years and their analysis provide a good basis for further research. Here, we review studies devoted to understanding the mechanisms of HD. We analyze genes and molecular pathways involved in HD pathogenesis to describe the action of repurposed drugs and try to find new therapeutic targets.

Identification of [1,2,4]Triazolo[4,3-a]pyrazine PARP1 inhibitors with overcome acquired resistance activities

Poly(ADP-ribose) polymerase 1 (PARP1) inhibitors can selectively kill homologous recombination (HR) deficient cancer cells and elicit anticancer effect through a mechanism of synthetic lethality. In this study, we designed, synthesized and pharmacologically evaluated a series of [1,2,4]triazolo[4,3-a]pyrazine derivatives as a class of potent PARP1 inhibitors. Among them, compounds 17m, 19a, 19c, 19e, 19i and 19k not only displayed more potent inhibitory activities (IC50s < 4.1 nM) than 9 and 1 against PARP1, but also exhibited nanomolar range of antiproliferative effects against MDA-MB-436 (BRCA1-/-, IC50s < 1.9 nM) and Capan-1 (BRCA2-/-, IC50s < 21.6 nM) cells. Notably, 19k significantly inhibited proliferation of resistant Capan-1 cells (IC50s < 0.3 nM). Collectively, the newly discovered PARP1 inhibitors act as a useful pharmacological tool for investigating the mechanism of acquired resistance to PARP1 inhibitors, and may also represent promising therapeutic agents for the treatment of HR deficient cancers with the potential to overcome the acquired resistance.

Identification and evaluation of a novel PARP1 inhibitor for the treatment of triple-negative breast cancer

Triple-negative breast cancer (TNBC) is a particularly invasive subtype of breast cancer and usually has a poor prognosis due to the lack of effective therapeutic targets. Approximately 25% of TNBC patients carry a breast cancer susceptibility gene1/2 (BRCA1/2) mutation. Clinically, PARP1 inhibitors have been approved for the treatment of patients with BRCA1/2-mutated breast cancer through the mechanism of synthetic lethality. In this study, we identified compound 6 {systematic name: 2-[2-(4-Hydroxy-phenyl)-vinyl]-3H-quinazolin-4-one} as a novel PARP1 inhibitor from established virtual screening methods. Compound 6 exerted stronger PARP1 inhibitory activity and anti-cancer activity as compared to olaparib in BRCA1-mutated TNBC cells and TNBC patient-derived organoids. Unexpectedly, we found that compound 6 also significantly inhibited cell viability, proliferation, and induced cell apoptosis in BRCA wild-type TNBC cells. To further elucidate the underlying molecular mechanism, we found that tankyrase (TNKS), a vital promoter of homologous-recombination repair, was a potential target of compound 6 by cheminformatics analysis. Compound 6 not only decreased the expression of PAR, but also down-regulated the expression of TNKS, thus resulting in significant DNA single-strand and double-strand breaks in BRCA wild-type TNBC cells. In addition, we demonstrated that compound 6 enhanced the sensitivity of BRCA1-mutated and wild-type TNBC cells to chemotherapy including paclitaxel and cisplatin. Collectively, our study identified a novel PARP1 inhibitor, providing a therapeutic candidate for the treatment of TNBC.

Targeting DNA damage response as a potential therapeutic strategy for head and neck squamous cell carcinoma

Cells experience both endogenous and exogenous DNA damage daily. To maintain genome integrity and suppress tumorigenesis, individuals have evolutionarily acquired a series of repair functions, termed DNA damage response (DDR), to repair DNA damage and ensure the accurate transmission of genetic information. Defects in DNA damage repair pathways may lead to various diseases, including tumors. Accumulating evidence suggests that alterations in DDR-related genes, such as somatic or germline mutations, single nucleotide polymorphisms (SNPs), and promoter methylation, are closely related to the occurrence, development, and treatment of head and neck squamous cell carcinoma (HNSCC). Despite recent advances in surgery combined with radiotherapy, chemotherapy, or immunotherapy, there has been no substantial improvement in the survival rate of patients with HNSCC. Therefore, targeting DNA repair pathways may be a promising treatment for HNSCC. In this review, we summarized the sources of DNA damage and DNA damage repair pathways. Further, the role of DNA damage repair pathways in the development of HNSCC and the application of small molecule inhibitors targeting these pathways in the treatment of HNSCC were focused.

The impact of cycleanine in cancer research: a computational study

Cancer is imposing a global health burden because of the steady increase in new cases. Moreover, current anticancer therapeutics are associated with many drawbacks, mainly the emergence of resistance and the severe adverse effects. Therefore, there is a continuous need for developing new anticancer agents with novel mechanisms of action and lower side effects. Natural products have been a rich source of anticancer medication. Cycleanine, a natural product, was reported to exert an antiproliferative effect on ovarian cancer cells by causing apoptosis through activation of caspases 3/7 and cleavage of poly (ADP-ribose) polymerase to form poly (ADP-ribose) polymerase-1 (PARP1). It is well-established that PARP1 is associated with carcinogenesis, and different PARP1 inhibitors are approved as anticancer drugs. In this study, the cytotoxic activity of cycleanine was computationally investigated to determine whether it is a PARP1 inhibitor or a caspase activator. Molecular docking and molecular dynamics (MD) simulations were utilized for this purpose. The results showed that cycleanine has a good binding affinity to PARP1; moreover, MD simulation showed that it forms a stable complex with the enzyme. Consequently, the results showed that cycleanine is a potential inhibitor of the PARP1 enzyme.

OGG1 Inhibition Triggers Synthetic Lethality and Enhances The Effect of PARP Inhibitor Olaparib in BRCA1-Deficient TNBC Cells

Background

PARP1 plays a critical role in the base excision repair (BER) pathway, and PARP1 inhibition leads to specific cell death, through a synthetic lethal interaction, in the context of BRCA1/2 deficiency. To date, up to five different PARP inhibitors (PARPi), have been approved, nevertheless, the acquisition of resistance to PARPi is common and there is increasing interest in enhancing responses and expand their use to other tumour types.

Methods

We hypothesized that other BER members could be additional synthetic lethal partners with mutated BRCA genes. To test this, we decided to evaluate the glycosylase OGG1 as a potential candidate, by treating BRCA1 proficient and deficient breast cancer cells with PARPi olaparib and the OGG1 inhibitor TH5478.

Results

Knocking out BRCA1 in triple-negative breast cancer cell lines causes hypersensitivity to the OGG1 inhibitor TH5487. Besides, TH5487 enhances the sensitivity to the PARP inhibitor olaparib, especially in the context of BRCA1 deficiency, reflecting an additive interaction.

Discussion

These results provide the first evidence that OGG1 inhibition is a promising new synthetic lethality strategy in BRCA1-deficient cells, and could lead to a new framework for the treatment of hereditary breast and ovarian cancer.

Dual-target inhibitors based on PARP1: new trend in the development of anticancer research

PARP1 is a hot target, and its inhibitors have been approved for cancer therapy. However, some undesirable properties restrict the application of PARP1 inhibitors, including drug resistance, side effects and low efficiency. For multifactorial diseases, dual-target drugs have exhibited excellent synergistic effects, such as reduced drug resistance, low side effects and high therapeutic efficacy, by simultaneously regulating the main pathogenic and compensatory signal pathways of diseases. In recent years, several dual-target inhibitors based on PARP1 have been reported and have demonstrated unique advantages. In this review we summarize the research progress in dual-target inhibitors based on PARP1 and discuss the related drug design strategies and structure-activity relationships. This work is expected to provide references for the development of PARP1 inhibitors.

MAPK4 silencing together with a PARP1 inhibitor as a combination therapy in triple‑negative breast cancer cells

Triple‑negative breast cancer (TNBC) is the most common type of cancer among females worldwide and is associated with poor prognosis. Poly ADP‑ribose polymerase‑1 (PARP1) inhibitors are effective against TNBC with mutations in the breast cancer type 1 susceptibility protein (BRCA1) and/or BRCA2 genes; however, the development of resistance to PARP1 inhibitors limits their use. Thus, identifying strategies to overcome this resistance is urgently required. The aim of the present study was to investigate the potential function and mechanism of small interfering (si)RNA‑MAPK4 (siMAPK4) in enhancing the efficacy of a PARP1 inhibitor and reducing the resistance. In the present study, data on the mRNA expression level of MAPK4 in normal breast tissues and TNBC tissues were obtained from The Cancer Genome Atlas database. The mRNA and protein expression levels of MAPK4 in normal breast cells and TNBC cells were analyzed using reverse transcription‑quantitative PCR and western blotting, respectively. The phosphorylated (p) histone H2AX (γH2AX) protein expression was assessed via immunofluorescence. Cell Counting Kit‑8, wound healing and TUNEL assays were used to determine the proliferative, migratory and apoptotic abilities of HCC1937 cells. MAPK4 was highly expressed in TNBC patient tissues and cell lines. Moreover, overexpression of MAPK4 could promote HCC1937 cell proliferation. Treatment of HCC1937 cells with the combination of siMAPK4 and a PARP1 inhibitor olaparib decreased their proliferation and migration and increased their apoptosis. The protein expression levels of the DNA repair‑related proteins p‑DNA‑dependent protein kinase catalytic subunit (DNA‑PK) and RAD51 recombinase (RAD51) were inhibited in the siMAPK4 and siMAPK4 + olaparib groups. However, the marker of a double‑stranded break γH2AX showed increased protein expression in the siMAPK4 + olaparib group. As MAPK4 could phosphorylate AKT at threonine 308 (AKTT308), the current study restored p‑AKT^T308 using a constitutively active AKT plasmid (AKT‑CA). p‑DNA‑PK and RAD51 showed high expression and γH2AX exhibited lower protein expression in the AKT‑CA group. The present findings suggested that siMAPK4 can enhance the sensitivity of TNBC cells to PARP1 inhibitors.

PJ34, a PARP1 inhibitor, attenuates acute allograft rejection after murine heart transplantation via regulating the CD4+ T lymphocyte response

Acute allografts rejection is the most important factor causing allograft disability for many patients undergoing organ transplantation. PJ34, which is a specific inhibitor of poly(ADP-ribose) polymerase 1, is involved in immune regulation, may be effective in preventing acute cardiac rejection. We performed the models of abdominal heterotopic heart transplantation. PJ34 was injected intraperitoneally daily (20 mg/kg/day) starting the day after surgery. The severity of rejection was determined by histology. The mRNA expression levels of cytokines and transcription factors in the grafts were measured by quantitative polymerase chain reaction (qPCR). The proportion and number of T-cell subpopulations in the spleens were analyzed by flow cytometry. In vitro, the effect of PJ34 on allogeneic responses was investigated. We found treatment with PJ34 prolonged allograft survival compared with normal saline treatment. Compared with the control group, PJ34 treatment reduced the proportion of CD4⁺ IFN-γ⁺ and CD4⁺ IL-17A⁺ cells and increased the percent of CD4⁺ IL-4⁺ and CD4⁺ Foxp3⁺ cells in the spleens. In vitro, PJ34 treatment significantly inhibited the mRNA levels of IFN-γ and IL-17A and promoted the mRNA levels of TGF-β and FOXP-3 in activated CD4⁺ T cells. Modulating the CD4⁺ T lymphocyte response with PJ34 could attenuate acute allografts rejection after murine heart transplantation. These findings indicate that PARP1 may be a promising therapeutic target to attenuate acute cardiac allograft rejection.

Anti-leukemic Activity of AIU2008 in FLT3-ITD-positive Acute Myeloid Leukemia

BACKGROUND/AIM

FMS-like tyrosine kinase 3 (FLT3) is a class III receptor tyrosine kinase involved in signal transduction underlying survival, proliferation, and differentiation of hematopoietic cells. An internal tandem duplication (ITD) in FLT3 in the juxtamembrane domain is a common mutation causing human acute myeloid leukemia (AML) and activates constitutive signaling.

MATERIALS AND METHODS

We evaluated the novel FLT3 inhibitor 5-(4-fluorophenyl)-N-(naphthalen-1-yl)oxazol-2-amine (AIU2008) for the treatment of AML.

RESULTS

AIU2008 was designed by modifying FLT3 inhibitor 7c, and showed improved anti-leukemic efficacy in FLT3-ITD-positive AML cells. Specifically, AIU2008 inhibited cell growth and apoptotic death. In addition, AIU2008 down-regulated DNA repair genes involved in homologous recombination and non-homologous end joining. It contributed to the synergistic inhibition of AML cell growth in combination treatment with PARP inhibitors.

CONCLUSION

AIU2008 is a promising FLT3 targeting agent, and may be used in combination with PARP inhibitors for the treatment of AML.

The cancer-testis gene, MEIOB, sensitizes triple-negative breast cancer to PARP1 inhibitors by inducing homologous recombination deficiency

Objective

The newly defined cancer-testis (CT) gene, MEIOB, was previously found to play key roles in DNA double-strand break (DSB) repair. In this study, we aimed to investigate the effects and mechanisms of MEIOB in the carcinogenesis of triple-negative breast cancers (TNBCs).

Methods

The Cancer Genome Atlas database was used to quantify the expression of MEIOB. Cox regression analysis was used to evaluate the association between MEIOB expression and the prognosis of human TNBC. The effects of MEIOB on cell proliferation and migration in TNBCs were also assessed in vitro. Patient-derived xenograft (PDX) models were used to assess the sensitivity of breast cancers with active MEIOB to PARP1 inhibitors.

Results

We confirmed MEIOB as a CT gene whose expression was restricted to the testes and breast tumors, especially TNBCs. Its activation was significantly associated with poor survival in breast cancer patients [overall, hazard ratio (HR) = 1.90 (1.16-2.06); TNBCs: HR = 7.05 (1.16-41.80)]. In addition, we found that MEIOB was oncogenic and significantly promoted the proliferation of TNBC cells. Further analysis showed that MEIOB participated in DSB repair in TNBCs. However, in contrast to its function in meiosis, it mediated homologous recombination deficiency (HRD) through the activation of polyADP-ribose polymerase (PARP)1 by interacting with YBX1. Furthermore, activated MEIOB was shown to confer sensitivity to PARP inhibitors, which was confirmed in PDX models.

Conclusions

MEIOB played an oncogenic role in TNBC through its involvement in HRD. In addition, dysregulation of MEIOB sensitized TNBC cells to PARP inhibitors, so MEIOB may be a therapeutic target of PARP1 inhibitors in TNBC.

Discovery of Oxazol-2-amine Derivatives as Potent Novel FLT3 Inhibitors

Internal tandem duplication (ITD) of FMS-like tyrosine kinase 3 (FLT3) is the most common mutation in patients with acute myeloid leukemia (AML). FLT3-ITD⁺ induces constitutive activation of FLT3, causing an abnormally rapid proliferation of cancer cells. In this study, we identified novel FLT3 inhibitors and investigated 5-(4-fluorophenyl)-N-phenyloxazol-2-amine (compound 7; 7c) as candidates for the treatment of AML. The results showed that 7c inhibited the activities of FLT3 and mutated FLT3 in a cell-free kinase assay and Molm-13 and MV4-11 cells, as well as the proliferation of FLT3-ITD⁺ AML cells, increasing apoptosis. The anti-leukemic activity of 7c was confirmed by in vivo tumor growth inhibition in MV4-11 xenograft mice. Besides, 7c suppressed the expression of DNA damage repair genes. Combination treatment with 7c and olaparib (a poly (ADP-ribose) polymerase [PARP] inhibitor) synergistically inhibited cell proliferation in Molm-13 and MV4-11 cells. Our findings demonstrated that 7c is a therapeutic candidate targeting FLT3 for AML treatment and suggested that combination treatment with 7c and a PARP inhibitor may be an effective therapy regimen for FLT3-mutated AML.

Fluzoparib increases radiation sensitivity of non-small cell lung cancer (NSCLC) cells without BRCA1/2 mutation, a novel PARP1 inhibitor undergoing clinical trials

PROPOSE

Poly (ADP-ribose) polymerase 1 inhibitors were originally investigated as anti-cancer therapeutics with BRCA1/2 genes mutation. Here, we investigate the effectiveness of a novel PARP1 inhibitor fluzoparib, for enhancing the radiation sensitivity of NSCLC cells lacking BRCA1/2 mutation.

METHODS

We used MTS assays, western blotting, colony formation assays, immunofluorescence staining, and flow cytometry to evaluate the radiosensitization of NSCLC cells to fluzoparib and explore the underlying mechanisms in vitro. Through BRCA1 and RAD50 genes knockdown, we established dysfunctional homologous recombination (HR) DNA repair pathway models in NSCLC cells. We next investigated the radiosensitization effect of fluzoparib in vivo using human NSCLC xenograft models in mice. The expression of PARP1 and BRCA1 in human NSCLC tumor samples was measured by immunohistochemistry. Furthermore, we sequenced HR-related gene mutations and analyzed their frequencies in advanced NSCLC.

RESULTS

In vitro experiments in NSCLC cell lines along with in vivo experiments using an NSCLC xenograft mouse model demonstrated the radiosensitization effect of fluzoparib. The underlying mechanisms involved increased apoptosis, cell-cycle arrest, enhanced irradiation-induced DNA damage, and delayed DNA-damage repair. Immunohistochemical staining showed no correlation between the expression of PARP1 and BRCA1. Moreover, our sequencing results revealed high mutation frequencies for the BRCA1/2, CHEK2, ATR, and RAD50 genes.

CONCLUSION

The potential therapeutic value of fluzoparib for increasing the radiation sensitivity of NSCLC is well confirmed. Moreover, our findings of high mutation frequencies among HR genes suggest that PARP1 inhibition may be an effective treatment strategy for advanced non-small cell lung cancer patients.

Cationic liposome codelivering PI3K pathway regulator improves the response of BRCA1-deficient breast cancer cells to PARP1 inhibition

Although some progresses have been made in breast cancer therapy, effective treatment for BRCA1-deficient breast cancer remains to be a great challenge. It has been demonstrated that the PI3K pathway is inappropriately activated in BRCA1-deficient breast cancers which can be downregulated by microRNA 451 (miR-451). In addition, although PARP1 inhibitors showed relatively positive results in both preclinical and clinical studies, additional efforts to decrease drug resistance as well as reduce systematic toxicity need to be addressed. To this end, by encapsulating the miR-451 mimic and PARP1 inhibitor in the same cationic liposome, we examined the potential of enhancing the response of PARP1 inhibition on BRCA1-deficient breast cancer by regulating the PI3K pathway. Our results revealed that in BRCA1-deficient human breast cancer cell line, PARP1 inhibition resulted in DNA damage with viability decrease, G2/M arrest as well as apoptosis. In contrast, single PI3K inhibition induced G1 arrest along with retarded cell proliferation. However, it was noted that combination of PARP inhibitor and PI3K regulator could exert synergetic function to evidently decrease cell proliferation compared with PARP inhibition alone, which was also confirmed by in vivo antitumor assay using xenograft tumor models. Collectively, our results offer an alternative but superior strategy for the therapy of BRCA1-deficient human breast cancers which may benefit the clinical applications.

Increased PARP1-DNA binding due to autoPARylation inhibition of PARP1 on DNA rather than PARP1-DNA trapping is correlated with PARP1 inhibitor's cytotoxicity

PARP1 inhibitors (PARPis) are used clinically during cancer therapy and are thought to exert their cytotoxicity through PARP1 polymerase inhibition and PARP1-DNA trapping. Here, we showed no significant correlation between PARP1-DNA trapping and cytotoxicity induced by PARPis. We complemented PARP1-knockout sublines with wild-type PARP1 and 11 mutants with different point mutations that affect the polymerase activity. When examining the PARPi talazoparib, the induced cytotoxicity was highly significantly correlated with cellular PARP1 polymerase activity, but not with its PARP1-DNA trapping or polymerase inhibition. Similarly, talazoparib's PARP1-DNA trapping revealed significant correlation with the polymerase activity rather than its inhibition. Differently, however, when evaluating purified wild-type and mutated PARP1, we identified an almost linear relationship between PARPis' inhibiting PARP1 dissociation from DNA and their cytotoxicity in 17 cancer cell lines. In contrast, no significant correlation existed between PARP1 polymerase inhibition in the histone-based systems and the cytotoxicity. After careful comparisons on different methods and detection targets, we conclude that the PARPi-mediated increase in PARP1-DNA binding by inhibiting autoPARylation of PARP1 on DNA rather than in PARP1-DNA trapping is correlated with PARPi's cytotoxicity. Accordingly, we established a new PARPi screening model that more closely predicts cytotoxicity.

Spectrum and Prevalence of Pathogenic Variants in Ovarian Cancer Susceptibility Genes in a Group of 333 Patients

Constitutional loss-of-function pathogenic variants in the tumor suppressor genes BRCA1 and BRCA2 are widely associated with an elevated risk of ovarian cancer (OC). As only ~15% of OC individuals carry the BRCA1/2 pathogenic variants, the identification of other potential OC-susceptibility genes is of great clinical importance. Here, we established the prevalence and spectrum of the germline pathogenic variants in the BRCA1/2 and 23 other cancer-related genes in a large Polish population of 333 unselected OC cases. Approximately 21% of cases (71/333) carried the BRCA1/2 pathogenic or likely pathogenic variants, with c.5266dup (p.Gln1756Profs*74) and c.3700_3704del (p.Val1234Glnfs*8) being the most prevalent. Additionally, ~6% of women (20/333) were carriers of the pathogenic or likely pathogenic variants in other cancer-related genes, with NBN and CHEK2 reported as the most frequently mutated, accounting for 1.8% (6/333) and 1.2% (4/333) of cases, respectively. We also found ten pathogenic or likely pathogenic variants in other genes: 1/333 in APC, 1/333 in ATM, 2/333 in BLM, 1/333 in BRIP1, 1/333 in MRE11A, 2/333 in PALB2, 1/333 in RAD50, and 1/333 in RAD51C, accounting for 50% of all detected variants in moderate- and low-penetrant genes. Our findings confirmed the presence of the additional OC-associated genes in the Polish population that may improve the personalized risk assessment of these individuals.

PARP1 inhibitor olaparib (Lynparza) exerts synthetic lethal effect against ligase 4-deficient melanomas

Cancer including melanoma may be ''addicted" to double strand break (DSB) repair and targeting this process could sensitize them to the lethal effect of DNA damage. PARP1 exerts an important impact on DSB repair as it binds to both single- and double- strand breaks. PARP1 inhibitors might be highly effective drugs triggering synthetic lethality in patients whose tumors have germline or somatic defects in DNA repair genes. We hypothesized that PARP1-dependent synthetic lethality could be induced in melanoma cells displaying downregulation of DSB repair genes. We observed that PARP1 inhibitor olaparib sensitized melanomas with reduced expression of DNA ligase 4 (LIG4) to an alkylatimg agent dacarbazine (DTIC) treatment in vitro, while normal melanocytes remained intact. PARP1 inhibition caused accumulation of DSBs, which was associated with apoptosis in LIG4 deficient melanoma cells. Our hypothesis that olaparib is synthetic lethal with LIG4 deficiency in melanoma cells was supported by selective anti-tumor effects of olaparib used either alone or in combination with dacarbazine (DTIC) in LIG4 deficient, but not LIG4 proficient cells. In addition, olaparib combined with DTIC inhibited the growth of LIG4 deficient human melanoma xenografts. This work for the first time demonstrates the effectiveness of a combination of PARP1 inhibitor olaparib and alkylating agent DTIC for treating LIG4 deficient melanomas. In addition, analysis of the TCGA and transcriptome microarray databases revealed numerous individual melanoma samples potentially displaying specific defects in DSB repair pathways, which may predispose them to synthetic lethality triggered by PARP1 inhibitor combined with a cytotoxic drug.

Preclinical anti-cancer activity and multiple mechanisms of action of a cationic silver complex bearing N-heterocyclic carbene ligands

Organometallic complexes offer the prospect of targeting multiple pathways that are important in cancer biology. Here, the preclinical activity and mechanism(s) of action of a silver-bis(N-heterocyclic carbine) complex (Ag8) were evaluated. Ag8 induced DNA damage via several mechanisms including topoisomerase I/II and thioredoxin reductase inhibition and induction of reactive oxygen species. DNA damage induction was consistent with cytotoxicity observed against proliferating cells and Ag8 induced cell death by apoptosis. Ag8 also inhibited DNA repair enzyme PARP1, showed preferential activity against cisplatin resistant A2780 cells and potentiated the activity of temozolomide. Ag8 was substantially less active against non-proliferating non-cancer cells and selectively inhibited glycolysis in cancer cells. Ag8 also induced significant anti-tumour effects against cells implanted intraperitoneally in hollow fibres but lacked activity against hollow fibres implanted subcutaneously. Thus, Ag8 targets multiple pathways of importance in cancer biology, is less active against non-cancer cells and shows activity in vivo in a loco-regional setting.

Detection of BRCA1/2 mutations in circulating tumor DNA from patients with ovarian cancer

Approximately 25% of patients with ovarian cancer harbor a pathogenic BRCA1/2 mutation that has been associated with favorable responses for targeted therapy with poly (ADP-ribose) polymerase 1 (PARP1) inhibitors compared to wild-type individuals. The overall frequency of germline and somatic BRCA1/2 alterations is estimated at 13-15% and 3-10%, respectively. A high incidence of BRCA1/2 somatic variants significantly increases the number of patients eligible for treatment with PARP1 inhibitors. Here, we assessed circulating tumor DNA (ctDNA) from 121 patients with ovarian cancer for BRCA1/2 mutational analysis by next generation sequencing. A total number of patients carrying the pathogenic BRCA1/2 variants was 30/121 (24.8%), including 22 and 7 individuals with exclusively germline or somatic mutations, respectively and one patient with variants of both origin. Among this cohort, more than one known pathogenic BRCA1 and/or BRCA2 alterations were identified in 7/30 individuals. The most recurrent mutations were detected in the BRCA1 gene: c.5266dupC (p.Gln1756Profs^*74) with the frequency of ~18%, followed by c.3756_3759del (p.Ser1253Argfs^*10) and c.181T>G (p.Cys61Gly). In seven (5.8%) patients, coincidence of two or more BRCA1/2 pathogenic mutations have been identified. Our results clearly demonstrate that the detection of both germline and somatic BRCA1/2 mutations in ctDNA from ovarian cancer patients is feasible and may be a valuable complementary tool for identification of somatic alterations when the standard diagnostic procedures are insufficient. Finally, ctDNA can potentially allow to monitor the efficacy of PARP1 inhibitors and to detect a secondary reversion BRCA1/2 mutations.