Poly (ADP-ribose) polymerase inhibitor: an evolving paradigm in the treatment of prostate cancer

Pharmacological inhibition of poly (ADP-ribose) polymerase by olaparib, prevents acute lung injury associated cognitive deficits potentially through suppression of inflammatory response

Acute lung injury (ALI) has been reported to be associated with high mortality rate. Moreover, ALI survivors, frequently present chronic cognitive deterioration. We have previously shown that 'two hit' (hydrochloric acid + lipopolysaccharide) induced ALI resulted in cognitive dysfunction through the induction of systemic inflammation. The present study was designed to explore the potential anti-inflammatory effects of olaparib (Poly ADP-ribose polymerase-1 inhibitor), on ALI mediated cognitive impairment. Olaparib was administered at dose of 5 mg/kg body weight (i.p.) 30 min before each hit. Data show that olaparib pre-treatment markedly reduced the neutrophil infiltration, alveolar capillary damage, inflammatory cytokines level (TNF-α/IL-1β/IL-6) and oxidative stress in the lungs at 24 h after ALI induction. Also, olaparib pre-treatment ameliorated the ALI associated cognitive impairment as assessed by Morris water maze test on weekly basis for 2 consecutive weeks. Further, restoration of cognitive function was associated with normalization of serum levels of TNF-α/IL-1β and improved the blood brain barrier (BBB) function, as reflected by data on expression of occludin/claudin-5 and extravasation of Evans-blue/FITC dextran in hippocampus at 1 week post injury. Finally, increased mRNA expression of VCAM-1, TNF-α and IL-1β and NF-κB activation in hippocampus indicate induction of neuro-inflammation, which was downregulated upon olaparib administration. Further, olaparib treatment 1 week after ALI induction blunted the systemic inflammation which was associated with improved BBB and cognitive function. Altogether, our results showed that olaparib protects against ALI and associated cognitive deficits in mice, and thus may offer a new treatment avenue in the area.

PLCε knockdown enhances the radiosensitivity of castration‑resistant prostate cancer via the AR/PARP1/DNA‑PKcs axis

Radiotherapy (RT) has been used as a therapeutic option for treatment of prostate cancer (PCa) for a number of years; however, patients frequently develop RT resistance, particularly in castration-resistant PCa (CRPC), although the underlying mechanisms remain unknown. Understanding the underlying mechanism of RT resistance in CRPC may potentially highlight novel targets to improve therapeutic options for patients with PCa. In the present study, the expression levels of phospholipase Cε (PLCε), androgen receptor (AR) and DNA-dependent protein kinase catalytic subunit (PKcs) were examined in PCa tissue samples and PCa cells, and the effects of PLCε knockdown on AR and DNA damage repair (DDR)-related molecules were determined. The association between PLCε, AR and Poly (ADP-ribose) polymerase 1 (PARP1), as well as their respective roles in radiation resistance, were assessed using gene knockdown and pharmaceutical inhibitors or activators. A chromatin immunoprecipitation assay was used to determine the epigenetic regulatory effects of PLCε on PARP1. Animal experiments were performed to assess whether the mechanisms observed in vitro could be replicated in vivo. The expression levels of PLCε, AR and DNA-PKcs were significantly upregulated in PCa, particularly in CRPC. PLCε knockdown reduced the viability and increased apoptosis of cells subjected to radiation. Additionally, PLCε deficiency suppressed DDR progression by downregulating an AR and PARP1 positive feedback loop and the associated downstream molecules following radiation. PLCε depletion also increased the presence of histone H3 lysine 27 trimethylation in the PARP1 promoter region, suggesting increased methylation of the PARP1 gene and thus resulting in reduced expression of PARP1. In vivo, PLCε knockdown significantly potentiated the effects of radiation on tumor growth. Taken together, the results of the present study demonstrated that PLCε knockdown enhanced the radiosensitivity of CRPC by downregulating the AR/PARP1/DNA-PKcs axis.

Circulating tumor cells and γH2AX as biomarkers for responsiveness to radium-223 in advanced prostate cancer patients

Aim

Radium-223 improves overall survival in patients with metastatic castration-resistant prostate cancer to the bone. Radium-223 causes double-strand DNA breaks and produces γH2AX, a potential biomarker for response. We examined the feasibility of tracking γH2AX positivity and numeration in circulating tumor cells.

Patients & methods

Ten patients with biopsy-confirmed symptomatic M1b castration-resistant prostate cancer received radium-223 as standard of care and were assessed for γH2AX level changes following doses 1, 3 and 6.

Results

Trend tests confirmed that patients with ≥50% increase in circulating tumor cells positive for γH2AX postradium-223 therapy had a lower risk of death (p = 0.035).

Conclusion

Regular interval measurements of γH2AX are feasible. The potential correlation between γH2AX changes and overall survival warrants further investigation.

Proteomic Characterization of Prostate Cancer to Distinguish Nonmetastasizing and Metastasizing Primary Tumors and Lymph Node Metastases

Patients with metastatic prostate cancer (PCa) have a poorer prognosis than patients with organ-confined tumors. We strove to uncover the proteome signature of primary PCa and associated lymph node metastases (LNMs) in order to identify proteins that may indicate or potentially promote metastases formation. We performed a proteomic comparative profiling of PCa tissue from radical prostatectomy (RPE) of patients without nodal metastases or relapse at the time of surgical resection (n=5) to PCa tissue from RPE of patients who suffered from nodal relapse (n=5). For the latter group, we also included patient-matched tissue of the nodal metastases. All samples were formalin fixed and paraffin embedded. We identified and quantified more than 1200 proteins by liquid chromatography tandem mass spectrometry with subsequent label-free quantification. An increase of ribosomal or proteasomal proteins in LNM (compared to corresponding PCa) became apparent, while extracellular matrix components rather decreased. Immunohistochemistry (IHC) corroborated accumulation of poly-(ADP-ribose)-polymerase 1 and N-myc-downstream-regulated-gene 3, alpha/beta hydrolase domain-containing protein 11, and protein phosphatase slingshot homolog 3 in LNM. These findings strengthen the present interest in examining PARP inhibitors for the treatment of aggressive PCa. IHC also corroborated increased abundance of retinol dehydrogenase 11 in metastasized primary PCa compared to organ-confined PCa. Generally, metastasizing primary tumors were characterized by an enrichment of proteins involved in cellular lipid metabolic processes with concomitant decrease of cell adhesion proteins. This study highlights the usefulness of a combined proteomic-IHC approach to explore novel aspects in tumor biology. Our initial results open novel opportunities for follow-up studies.

PARP inhibitors as potential therapeutic agents for various cancers: focus on niraparib and its first global approval for maintenance therapy of gynecologic cancers

Poly (ADP-ribose) polymerases (PARPs) are an important family of nucleoproteins highly implicated in DNA damage repair. Among the PARP families, the most studied are PARP1, PARP2 and PARP 3. PARP1 is found to be the most abundant nuclear enzyme under the PARP series. These enzymes are primarily involved in base excision repair as one of the major single strand break (SSB) repair mechanisms. Being double stranded, DNA engages itself in reparation of a sub-lethal SSB with the aid of PARP. Moreover, by having a sister chromatid, DNA can also repair double strand breaks with either error-free homologous recombination or error-prone non-homologous end-joining. For effective homologous recombination repair, DNA requires functional heterozygous breast cancer genes (BRCA) which encode BRCA1/2. Currently, the development of PARP inhibitors has been one of the promising breakthroughs for cancer chemotherapy. In March 2017, the United States Food and Drug Administration (FDA) approved niraparib for maintenance therapy of recurrent gynecologic cancers (epithelial ovarian, primary peritoneal and fallopian tube carcinomas) which are sensitive to previous platinum based chemotherapy irrespective of BRCA mutation and homologous recombination deficiency status. It is the third drug in this class to receive FDA approval, following olaparib and rucaparib and is the first global approval for maintenance therapy of the aforementioned cancers. Niraparib preferentially blocks both PARP1 and PARP2 enzymes. The daily tolerated dose of niraparib is 300 mg, above which dose limiting grade 3 and 4 toxicities were observed. In combination with humanized antibody, pembrolizumab, it is also under investigation for those patients who have triple negative breast cancer. By and large, there are several clinical trials that are underway investigating clinical efficacy and safety, as well as other pharmacokinetic and pharmacodynamic profiles of this drug for various malignancies.

"Back to a false normality": new intriguing mechanisms of resistance to PARP inhibitors

Several evidences have shown that BRCA mutations increased tumor-cells sensitivity to PARP inhibitors by synthetic lethality leading to an accelerated development of several compounds targeting the PARP enzymes system as anticancer agents for clinical setting. Most of such compounds have been investigated in ovarian and breast cancer, showing promising efficacy in BRCA-mutated patients. Recently clinical studies of PARP-inhibitors have been extended across different tumor types harboring BRCA-mutations, including also “BRCA-like” sporadic tumors with homologous recombination deficiency (HRD). This review summarizes the biological background underlying PARP-inhibition, reporting the results of the most relevant clinical trials carried out in patients treated with PARP inhibitors alone or in combination with chemotherapy. Molecular mechanisms responsible for the occurrence of both primary and acquired resistance have been elucidated, in order to support the development of new treatment strategies.

The Correlation Between PARP1 and BRCA1 in AR Positive Triple-negative Breast Cancer

Triple-negative breast cancer (TNBC) lacks estrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor 2 (HER-2) expression and thus cannot benefit from conventional hormonal or anti-HER2 targeted therapies. Anti-androgen therapy has shown a certain effect on androgen receptor (AR) positive TNBC. The emerging researches have proved that poly (ADP-ribose) polymerase (PARP) inhibitor is effective in BRCA1-deficient breast cancers. We demonstrated that combination of AR antagonist (bicalutamide) and PARP inhibitor (ABT-888) could inhibit cell viability and induce cell apoptosis significantly whatever in vitro or in vivo setting in AR-positive TNBC. Previous studies have proved that both BRCA1 and PARP1 have close connections with AR in prostate cancer. We explored the correlation among AR, PARP1 and BRCA1 in TNBC for the first time. After BRCA1 overexpression, the expression of AR and PARP1 were decreased in mRNA and protein levels. Additionally, AR positively regulated PARP1 while PARP1 also up-regulated AR expression in vitro. We also confirmed BRCA1 expression was negatively correlated with AR and PARP1 in TNBC patients using a tissue microarray with TNBC patient samples. These results suggest that the combination of bicalutamide and PARP inhibitor may be a potential strategy for TNBC patients and merits further evaluation.

Association between single-nucleotide polymorphisms in DNA double-strand break repair genes and prostate cancer aggressiveness in the Spanish population

BACKGROUND

Novel predictors of prognosis and treatment response for prostate cancer (PCa) are required to better individualize treatment. Single-nucleotide polymorphisms (SNPs) in four genes directly (XRCC5 (X-ray repair complementing defective repair in Chinese hamster cells 5) and XRCC6 (X-ray repair complementing defective repair in Chinese hamster cells 6)) or indirectly (PARP1 and major vault protein (MVP)) involved in non-homologous end joining were examined in 494 Spanish PCa patients.

METHODS

A total of 22 SNPs were genotyped in a Biotrove OpenArray NT Cycler. Clinical tumor stage, diagnostic PSA serum levels and Gleason score at diagnosis were obtained for all participants. Genotypic and allelic frequencies were determined using the web-based environment SNPator.

RESULTS

(XRCC6) rs2267437 appeared as a risk factor for developing more aggressive PCa tumors. Those patients carrying the GG genotype were at higher risk of developing bigger tumors (odds ratio (OR)=2.04, 95% confidence interval (CI) 1.26-3.29, P=0.004), present higher diagnostic PSA levels (OR=2.12, 95% CI 1.19-3.78, P=0.011), higher Gleason score (OR=1.65, 95% CI 1.01-2.68, P=0.044) and D'Amico higher risk tumors (OR=2.38, 95% CI 1.24-4.58, P=0.009) than those patients carrying the CC/CG genotypes. Those patients carrying the (MVP) rs3815824 TT genotype were at higher risk of presenting higher diagnostic PSA levels (OR=4.74, 95% CI 1.40-16.07, P=0.013) than those patients carrying the CC genotype. When both SNPs were analyzed in combination, those patients carrying the risk genotypes were at higher risk of developing D'Amico higher risk tumors (OR=3.33, 95% CI 1.56-7.17, P=0.002).

CONCLUSIONS

We believe that for the first time, genetic variants at XRCC6 and MVP genes are associated with risk of more aggressive disease, and would be taken into account when assessing the malignancy of PCa.

PARP inhibitor, olaparib ameliorates acute lung and kidney injury upon intratracheal administration of LPS in mice

We have previously shown that PARP-1 inhibition provides protection against lung inflammation in the context of asthma and acute lung injury. Olaparib is a potent new generation PARP inhibitor that has been approved for human testing. The present work was designed to evaluate its beneficial potential against LPS-induced acute lung injury and acute kidney injury upon intratracheal administration of the endotoxin in mice. Administration of olaparib at different doses, 30 min after LPS treatment showed that single intraperitoneal injection of the drug at 5 mg/kg b.wt. reduced the total number of inflammatory cells particularly neutrophils in the lungs. This was associated with reduced pulmonary edema as the total protein content in the bronchoalveolar fluid was found to be decreased substantially. Olaparib provided strong protection against LPS-mediated secondary kidney injury as reflected by restoration of serum levels of urea, creatinine, and uric acid toward normal. The drug restored the LPS-mediated redox imbalance toward normal in lung and kidney tissues as assessed by measuring malondialdehyde and GSH levels. Finally, RT-PCR data revealed that olaparib downregulates the LPS-induced expression of NF-κB-dependent genes namely TNF-α, IL-1β, and VCAM-1 in the lungs without altering the expression of total p65NF-κB. Overall, the data suggest that olaparib has a strong potential to protect against LPS-induced lung injury and associated dysfunctioning of kidney in mice. Given the fact that olaparib is approved by FDA for human testing, our findings can pave the way for testing of the drug on humans inflicted with acute lung injury.