PARP Inhibition, a New Therapeutic Avenue in Patients with Prostate Cancer

Challenges of diagnosing homologous recombination deficiencies in metastatic prostate cancer: a six-year experience from a single institution

PURPOSE

We evaluated the prevalence of homologous recombination deficiencies (HRD) to determine the efficacy of different techniques and clinical characteristics of patients.

METHODS

This retrospective study included patients with metastatic prostate cancer who underwent molecular testing at our hospital between 2016 and 2022. We used tumor tissue, ctDNA, and lymphocytes for somatic or germline testing. We analyzed the clinical characteristics and survival outcomes.

RESULTS

144 patients were tested (113 somatic, 21 germline, and 10 both). Technical issues prevented the analysis of 23 prostatic samples (18.7%). 12 (8.3%) patients had HRD. BRCA2 was the most frequent mutation (66.7%). Patients with HRD were younger (57.5 years). Patients with BRCA mutations had poorer survival (31.9 vs 56.3 months, p = 0.048).

CONCLUSION

In our institution, 8.3% of the patients had HRD. Tumor tissue analysis failed in 18.7% of tests. ctDNA analysis is an alternative detection method. BRCA mutations are correlated with poor prognosis.

A New Approach for Studying Poly(ADP-Ribose) Polymerase Inhibitors Using Permeabilized Adherent Cells

Poly(ADP-ribose) polymerase (PARP) inhibitors have been proposed as pharmacological agents in the treatment of various diseases. Recently, factors and mechanisms responsible for regulating PARP catalytic activity have been identified, some of which can significantly influence the effectiveness of inhibitors of this enzyme. In this regard, it is important to develop new models and methods that would reflect the cellular context in which PARP functions. We proposed to use digitonin-permeabilized adherent cells to study poly(ADP-ribosyl)ation reaction (PARylation) in order to maintain the nuclear localization of PARP and to control the concentrations of its substrate (NAD+) and tested compounds in the cell. A specific feature of the approach is that before permeabilization, cellular PARP is converted to the DNA-bound state under conditions preventing premature initiation of the PARylation reaction. Experiments were carried out in rat H9c2 cardiomyoblasts. The activity of PARP in permeabilized cells was analyzed by measuring the immunofluorescence of the reaction product poly(ADP-ribose). The method was verified in the studies of PARP inhibition by the classic inhibitor 3-aminobenzamide and a number of new 7-methylguanine derivatives. One of them, 7,8-dimethylguanine, was found to be a stronger inhibitor compared to 7-methylguanine, due to a formation of additional hydrophobic contact with the protein. The proposed approach opens up new prospects for studying the mechanisms of PARP activity regulation in cells and can be used in high-throughput screening of PARP inhibitors.

[Metastatic castration-resistant prostate cancer-what are rational sequential treatment options?]

BACKGROUND

In advanced prostate cancer, disease progression during ongoing androgen deprivation therapy (ADT) is referred to as castration-resistant prostate cancer (CRPC). Various therapeutic modalities are available for its treatment, including endocrine therapy, chemotherapy, poly (ADP-ribose) polymerase [PARP] inhibition, radionuclide therapy, and radioligand therapy.

OBJECTIVES

This review outlines practical aspects and considerations regarding treatment sequencing in mCRPC.

MATERIALS AND METHODS

The findings are based on existing prospective phase 3 studies that have demonstrated clinically relevant and statistically significant benefits in radiographically progression-free and/or overall survival.

RESULTS

Sequential therapy, aside from numerous patient-specific factors, depends on the treatment patients received in the hormone-sensitive prostate cancer (mHSPC) setting. Following pretreatment with ADT alone or ADT plus docetaxel in the mHSPC context, additional endocrine therapy is the standard approach. In the event of progression under combined endocrine therapy initiated in the mHSPC setting, docetaxel currently serves as the standard for the majority of patients. Patients who received triplet therapy as a pretreatment in the mHSPC scenario can be treated with radioligand therapy or second-line chemotherapy.

CONCLUSION

Various active and well-tolerated treatment options are available for patients with metastatic castration-resistant prostate cancer (mCRPC). The choice of therapy is primarily determined by previous treatments, but many other individual factors are also taken into consideration.

Niraparib restrains prostate cancer cell proliferation and metastasis and tumor growth in mice by regulating the lncRNA MEG3/miR-181-5p/GATA6 pathway

Background

Poly (ADP-ribose) polymerase (PARP) inhibitors (PARPi), have gained approval for treating patients with castration-resistant prostate cancer (CRPC). Maternally expressed gene 3 (MEG3), a long non-coding RNA (lncRNA), plays a role in inhibiting tumorigenesis through regulating DNA repair genes. This study aimed to investigate the association between the anti-prostate cancer (PCa) effect of niraparib, a representative PARPi, and MEG3 expression, as well as explore the downstream pathway involved.

Methods

The levels of MEG3, miR-181-5p, GATA binding protein 6 (GATA6) in clinical samples from PCa patients were accessed by RT-qPCR. PC3 cells were treated with niraparib, and the expression of MEG3, miR-181-5p, GATA6 expression was tested. PC3 cell proliferation, migration, and invasion were tested by CCK-8, wound healing, and Transwell assays, respectively. The bindings between miR-181-5p and MEG3/GATA6 were determined by dual-luciferase reporter gene assay. Furthermore, rescue experiments were conducted to investigate the underlying mechanism of MEG3/miR-181-5p/GATA6 axis in PCa progression. Additionally, mice were injected with PC3 cells transfected with sh-MEG3 and treated with niraparib, and the xenograft tumor growth was observed.

Results

MEG3 and GATA6 were upregulated and miR-181-5p was downregulated in PCa patients. Niraparib treatment substantially upregulated MEG3 and GATA6, and downregulated miR-181-5p expression in PCa cells. Niraparib effectively restrained PC3 cell proliferation, migration, and invasion. MiR-181-5p targeted to MEG3, and the inhibitory effects of MEG3 overexpression on PC3 cell proliferation and metastasis were abrogated by miR-181-5p overexpression. Moreover, GATA6 was identified as a target of miR-181-5p, and GATA6 silencing abolished the inhibitory effects of miR-181-5p inhibition on PC3 cell proliferation and metastasis. Besides, MEG3 silencing could abrogate niraparib-mediated tumor growth inhibition in mice.

Conclusions

Niraparib restrains prostate cancer cell proliferation and metastasis and tumor growth in mice by regulating the lncRNA MEG3/miR-181-5p/GATA6 pathway.

Micelle encapsulation zinc-doped copper oxide nanocomposites reverse Olaparib resistance in ovarian cancer by disrupting homologous recombination repair

Micelle Encapsulation Zinc-doped copper oxide nanocomposites (MEnZn-CuO NPs) is a novel doped metal nanomaterial prepared by our group based on Zinc doped copper oxide nanocomposites (Zn-CuO NPs) using non-micellar beam. Compared with Zn-CuO NPs, MEnZn-CuO NPs have uniform nanoproperties and high stability. In this study, we explored the anticancer effects of MEnZn-CuO NPs on human ovarian cancer cells. In addition to affecting cell proliferation, migration, apoptosis and autophagy, MEnZn-CuO NPs have a greater potential for clinical application by inducing HR repair defects in ovarian cancer cells in combination with poly (ADP-ribose) polymerase inhibitors for lethal effects.

Olaparib Conjugates with Selenopheno[3,2-c]quinolinone Inhibit PARP1 and Reverse ABCB1-Related Multidrug Resistance

The restoration of the efficacy of antitumor medicines is a cornerstone in the combat with multidrug resistant (MDR) cancers. The overexpression of the ABCB1 transporter is a major obstacle to conventional doxorubicin therapy. The synergy of ABCB1 suppression and PARP1 activity inhibition that hampers malignant cell DNA repair could be a powerful tool in anticancer therapy. Herein, we report the design and synthesis of three novel olaparib conjugates with selenophenoquinolinones, their ability to reverse doxorubicin resistance in uterus sarcoma cells as well as their mechanism of action. It was found that the most potent chemosensitizer among studied compounds preserves PARP1 inhibitory activity and attenuates cells' resistance to doxorubicin by inhibiting ABCB1 transporter activity. These results demonstrate that the conjugation of PARP inhibitors with selenophenoquinolinones is a prospective direction for the development of agents for the treatment of MDR cancers.

Recent advances in cancer therapy using PARP inhibitors

When DNA repair is inadequate it increases the chances of the genome becoming unstable and it undergoes a malignant mutation. The deficiency of DNA repair PARP proteins may be leveraged for cancer therapy by increasing genomic instability and causing massive DNA damage in cancer cells. DNA repair components are under increased demand in cancer cells because of the continuous replication of DNA. The oncogenic loss of BRCA and an inefficient DNA repair led to cancer cells being dependent on particular DNA repair pathways, like the Poly (ADP-ribose) polymerase pathway. Breast cancer gene 1 and 2 plays a crucial role in DNA repair and genome integrity explaining how BRCA1 and BRCA2 mutations raise the menace of cancer. PARP inhibitors inhibit the base exclusion repair pathway, resulting in the buildup of unrepaired single strand breaks, which cause inflated replication forks in the S phase and subsequently the development of damaging double stranded breaks. Cells having BRCA mutations are unable to repair DNA breaks, leading to apoptosis and eventually death of cancer cells. Numerous indicators, such as a lack of homologous recombination and a high degree of replication pressure, indicate that this therapy will be very effective. Combining PARP inhibitors with chemotherapy, an immune checkpoint inhibitor, and a targeted drug is an effective strategy for combating PARP inhibitors resistance. Several PARP-based combination approaches are in preclinical and clinical development. Various clinical trials are successfully completed and some are undergoing to evaluate the efficacy of these molecules. This review will describe the current views and clinical updates on PARP inhibitors.

Comprehensive analysis of TP53 and SPOP mutations and their impact on survival in metastatic prostate cancer

Background

Although TP53 and SPOP are frequently mutated in metastatic prostate cancer (PCa), their prognostic value is ambiguous, and large sample studies are lacking, especially when they co-occur with other genetic alterations.

Methods

Genomic data and patients’ clinical characteristics in PCa were downloaded from the cBioPortal database. We extensively analyzed other gene alterations in different mutation status of TP53 and SPOP. We further subdivided TP53 and SPOP mutation into subgroups based on different mutation status, and then evaluated the prognostic value. Two classification systems for TP53 survival analysis were used.

Results

A total of 2,172 patients with PCa were analyzed in our study, of which 1,799 were metastatic PCa patients. The mutual exclusivity analysis showed that TP53 and SPOP mutation has a strong mutual exclusion (p<0.001). In multivariable analysis, truncating TP53 mutations (HR=1.773, 95%CI:1.403-2.239, p<0.001) and other TP53 mutations(HR=1.555, 95%CI:1.267-1.908, p<0.001) were independent negative prognostic markers in metastatic PCa, whereas SPOP mutations(HR=0.592, 95%CI:0.427-0.819, p<0.001) were an independent prognostic factor for better prognosis. Mutations in TP53 were significantly associated with wild-type status for SPOP and CDK12, structural variants/fusions for TMPRSS2 and ERG, AR amplification and PTEN deletion (p<0.001). And truncating TP53 mutations have higher AR amplification rates than other TP53 mutations (p=0.022). Consistently, truncating TP53 mutations had a worse prognosis than other TP53 mutations (p<0.05). Then Kaplan-Meier survival curve showed that Co-occurring TP53 mutations in AR amplification or PTEN deletion tumors significantly reduced survival (p<0.05). Furthermore, those with SPOP-mutant tumors with co-occurring TP53 truncating mutations had shorter overall survival than those with SPOP-mutant tumors with wild-type or other TP53 mutations.

Conclusions

This study found that TP53 and SPOP mutations were mutually exclusive and both were independent prognostic markers for metastatic PCa. Genomic alteration and survival analysis revealed that TP53 and SPOP mutations represented distinct molecular subtypes. Our data suggest that molecular stratification on the basis of TP53 and SPOP mutation status should be implemented for metastatic PCa to optimize and modify clinical decision-making.

Osteoclasts directly influence castration-resistant prostate cancer cells

Metastasis to bone is the leading cause of death from prostate cancer. Interaction between tumor cells and bone cells can promote progression and influence tumor phenotype. It is known that prostate cancer cells support osteoclast differentiation, and degradation of bone matrix by osteoclasts releases growth factors stimulating tumor cell proliferation and invasion. In the present study osteolytic (PC-3) and osteoblastic (LNCaP-19) castration-resistant prostate cancer (CRPC) cells were co-cultured with mature osteoclasts or their precursor cells (RAW 264.7) to characterize direct effects of mature osteoclasts on CRPC cells. Osteoclasts increased proliferation and decrease apoptosis of CRPC cells as assessed with flow cytometry. RNA sequencing revealed that osteolytic CRPC cells were more responsive to osteoclast stimulation regarding gene expression, but the overall induced expression patterns were similar between the prostate cancer cell lines. Genes related to DNA repair were upregulated by osteoclasts, while genes related to endoplasmic reticulum stress-induced apoptosis and cholesterol synthesis were downregulated. The results of this study shows that osteoclasts directly influence CRPC cells, increasing proliferation, decreasing apoptosis, and affecting gene expression pathways that can affect sensitivity to DNA damage and endoplasmic reticulum function. This suggests targeting of osteoclasts to be a possible way to affect efficacy of other drugs by combination regimens in treating prostate cancer metastases.