PARP Inhibitor Olaparib Research Articles

A phase II single-arm trial of niraparib in platinum-sensitive metastatic castration-resistant prostate cancer with DNA repair defects (PLATPARP).

TPS291 Background: Platinum-based chemotherapy, either as monotherapy or in combination with taxanes, is increasingly used for patients with metastatic castration-resistant prostate cancer (mCRPC) harboring germline and/or somatic homologous recombination repair gene mutations (HRRm). However, clinical responses with platinum-based therapy are often of limited duration and limited by cumulative toxicities. The PARP inhibitor (PARPi) olaparib is approved for the treatment of mCRPC patients with pathogenic HRRm after progression on enzalutamide or abiraterone. Importantly, sensitivity to platinum-based chemotherapy may predict improved clinical outcomes with PARPi, and ‘maintenance’ PARPi strategies are routinely used in patients with advanced ovarian and pancreatic malignancies with HRRm with initial clinical response to platinum chemotherapy. We hypothesize that maintenance niraparib, a PARPi with demonstrated activity in mCRPC with HRRm, will prolong clinical responses to platinum-based chemotherapy with acceptable toxicity in mCRPC patients harboring germline and/or somatic HRRm. Methods: We are conducting an open-label, single-arm, phase II study to evaluate the clinical benefit of maintenance niraparib in biomarker-defined, platinum-sensitive mCRPC patients. Eligible subjects harbor a pathogenic germline and/or somatic mutation in BRCA1/2, ATM, FANCA, CDK12, RAD51B, RAD54L, PALB2, CHEK2, HDAC2, or BRIP1 and have received at least 3 cycles (or minimum 9 weeks) of platinum-based chemotherapy for the treatment of mCRPC per investigator discretion. Following ³4 weeks since completion of chemotherapy, subjects without evidence of clinical or radiographic disease progression receive investigational treatment with maintenance niraparib (starting dose 200 mg daily). The primary objective is an improvement in 6 month PFS rate (PFS6) (H0: PFS6 rate 25%; H1: PFS6 rate 50%; power 0.77 with one-sided α = 0.05). Serial plasma samples are obtained for correlative analyses of markers of response and/or resistance to maintenance niraparib. Eight of a planned total of 18 subjects have enrolled (N=3 germline BRCA2; N=2 somatic BRCA2; N=1 germline PALB2; N=1 germline ATM; N=1 germline CHEK2). This study incorporates a novel, combined genetic and clinical patient-selection approach for PARPi therapy to optimize clinical outcomes. Clinical trial information: NCT04288687 .

Synergistic effect of PARP inhibitor and BRD4 inhibitor in multiple models of ovarian cancer.

Ovarian cancer has the highest facility rate among gynaecological tumours. Current therapies including PARP inhibitors have a defect that ovarian tumour is easy to recurrent and become resistant to therapy. To solve this problem, we found that BRD4 inhibitor AZD5153 and PARP inhibitor olaparib had a widespread synergistic effect in multiple models with different gene backgrounds. AZD5153 sensitizes cells to olaparib and reverses the acquired resistance by down-regulating PTEN expression levels to destabilize hereditary materials. In this study, we used the following multiple ovarian cancer models PDX, PDO and 3D/2D cell lines to elucidate the co-effect of AZD5153 and olaparib in vivo and in vitro. The similar results of these models further proved that the mechanism identified was consistent with the biological process occurring in ovarian cancer patients after drug treatment. This consistency between the results of different models suggests the possibility of translating these laboratory research findings into clinical studies towards developing treatments.

In Vivo Efficacy Testing of Peptide Receptor Radionuclide Therapy Radiosensitization Using Olaparib.

Peptide receptor radionuclide therapy (PRRT), a form of internal targeted radiation treatment using [177Lu]Lu [DOTA0-Tyr3]octreotate, is used to treat patients with metastasized neuroendocrine tumors (NETs). Even though PRRT is now the second line of treatment for patients with metastasized NETs, the majority of patients will not be cured by the treatment. PRRT functions by inducing DNA damage upon radioactive decay and inhibition of DNA damage repair proteins could therefore be used as a strategy to potentiate PRRT. Previous work has shown promising results on the combination of PRRT with the PARP inhibitor olaparib in cell lines and mice and we have been taken the next step for further in vivo validation using two different xenografted mouse models. We observed that this combination therapy resulted in increased therapeutic efficacy only in one model and not the other. Overall, our findings indicate a tumor-type dependent anti-tumor response to the combination of PRRT and olaparib. These data emphasize the unmet need for the molecular stratification of tumors to predetermine the potential clinical value of combining PARP inhibition with PRRT.

20 - Combination of the PARP inhibitor olaparib with the vascular disrupting agent NOV202 reduces tumor growth in BRCA1/2 mutated prostate cancer xenografts

20 - Combination of the PARP inhibitor olaparib with the vascular disrupting agent NOV202 reduces tumor growth in BRCA1/2 mutated prostate cancer xenografts

Genome destabilization-associated phenotypes arising as a consequence of therapeutic treatment are suppressed by Olaparib.

Malignancy is often associated with therapeutic resistance and metastasis, usually arising after therapeutic treatment. These include radio- and chemo-therapies, which cause cancer cell death by inducing DNA double strand breaks (DSBs). However, it is still unclear how resistance to these DSBs is induced and whether it can be suppressed. Here, we show that DSBs induced by camptothecin (CPT) and radiation jeopardize genome stability in surviving cancer cells, ultimately leading to the development of resistance. Further, we show that cytosolic DNA, accumulating as a consequence of genomic destabilization, leads to increased cGAS/STING-pathway activation and, ultimately, increased cell migration, a precursor of metastasis. Interestingly, these genomic destabilization-associated phenotypes were suppressed by the PARP inhibitor Olaparib. Recognition of DSBs by Rad51 and genomic destabilization were largely reduced by Olaparib, while the DNA damage response and cancer cell death were effectively increased. Thus, Olaparib decreases the risk of therapeutic resistance and cell migration of cells that survive radio- and CPT-treatments.

Synergy of ruthenium metallo-intercalator, [Ru(dppz)2(PIP)]2+, with PARP inhibitor Olaparib in non-small cell lung cancer cells

Poly(ADP-ribose) polymerase (PARP) are critical DNA repair enzymes that are activated as part of the DNA damage response (DDR). Although inhibitors of PARP (PARPi) have emerged as small molecule drugs and have shown promising therapeutic effects, PARPi used as single agents are clinically limited to patients with mutations in germline breast cancer susceptibility gene (BRCA). Thus, novel PARPi combination strategies may expand their usage and combat drug resistance. In recent years, ruthenium polypyridyl complexes (RPCs) have emerged as promising anti-cancer candidates due to their attractive DNA binding properties and distinct mechanisms of action. Previously, we reported the rational combination of the RPC DNA replication inhibitor [Ru(dppz)2(PIP)]2+ (dppz = dipyrido[3,2-a:2′,3′-c]phenazine, PIP = 2-(phenyl)-imidazo[4,5-f][1,10]phenanthroline), “Ru-PIP”, with the PARPi Olaparib in breast cancer cells. Here, we expand upon this work and examine the combination of Ru-PIP with Olaparib for synergy in lung cancer cells, including in 3D lung cancer spheroids, to further elucidate mechanisms of synergy and additionally assess toxicity in a zebrafish embryo model. Compared to single agents alone, Ru-PIP and Olaparib synergy was observed in both A549 and H1975 lung cancer cell lines with mild impact on normal lung fibroblast MRC5 cells. Employing the A549 cell line, synergy was confirmed by loss in clonogenic potential and reduced migration properties. Mechanistic studies indicated that synergy is accompanied by increased double-strand break (DSB) DNA damage and reactive oxygen species (ROS) levels which subsequently lead to cell death via apoptosis. Moreover, the identified combination was successfully able to inhibit the growth of A549 lung cancer spheroids and acute zebrafish embryos toxicity studies revealed that this combination showed reduced toxicity compared to single-agent Ru-PIP.

The natural product dehydrocurvularin induces apoptosis of gastric cancer cells by activating PARP-1 and caspase-3.

The natural product dehydrocurvularin (DSE2) is a fungal-derived macrolide with potent anticancer activity, but the mechanism is still unclear. We found that DSE2 effectively inhibited the growth of gastric cancer cells and induced the apoptosis by activating Poly(ADP-ribose) polymerase 1 (PARP-1) and caspase-3. Pharmacological inhibition and genetic knockdown with PARP-1 or caspase-3 suppressed DSE2-induced apoptosis. PARP-1 was previously reported to be cleaved into fragments during apoptosis. However, PARP-1 was barely cleaved in DSE2-induced apoptosis. DSE2 induced PARP-1 activation as indicated by rapid depletion of NAD+ and the concomitant formation of poly(ADP-ribosylated) proteins (PARs). Interestingly, the PARP-1 inhibitor (Olaparib) attenuated the cytotoxicity of DSE2. Moreover, the combination of Olaparib and Z-DEVD-FMK (caspase-3 inhibitor) further reduced the cytotoxicity. It has been shown that PARP-1 activation triggers cytoplasm-nucleus translocation of apoptosis-inducing factor (AIF). Caspase-3 inhibitors inhibited PARP-1 activation and suppressed PARP-1-induced AIF nuclear translocation. These results indicated that DSE2-induced caspase-3 activation may occur before PARP-1 activation. The ROS inhibitor, N-acetyl-cysteine, significantly inhibited the activation of caspase-3 and PARP-1, indicating that ROS overproduction contributed to DSE2-induced apoptosis. Using an in vivo approach, we further found that DSE2 significantly inhibited gastric tumor growth and promoted translocation of AIF to the nucleus. In conclusion, DSE2 induces gastric cell apoptosis by activating caspase-3 and PARP-1, and shows potent antitumor activity against human gastric carcinoma in vitro and in vivo.

PARP inhibitor olaparib induced differential protein expression in cervical cancer cells

PARP inhibitors are a potential class of chemotherapeutic drugs but PARP inhibitor response has not been explored systematically. We lack a specific understanding of the subset of the proteome preferentially modified in various cancers by PARP inhibitors. Implications of PARP inhibitor and PARP1 in cervical cancer treatment and resistance are not fully elucidated. We conducted a mass spectrometry-based proteomic analysis of cervical cancer Hela cells treated with olaparib. We aimed to identify the alteration in the protein signaling pathway induced by PARP inhibitors beyond the DNA damage response pathway. Our data demonstrate a significant reduction in PARP activity and enhanced cell death after olaparib treatment. We further observed articulated proteomic changes with a significant enrichment of proteins in diverse cellular processes. The differentially expressed proteins were predominantly associated with RNA metabolism, mRNA splicing, processing, and RNA binding. Our data also identified proteins that could probably contribute to survival mechanisms resulting in resistance to PARP inhibitors. Hence, we put forth the overview of proteomic changes induced by PARP inhibitor olaparib in cervical cancer cells. This study highlights the significant proteins modified during PARP inhibition and thus could be a probable target for combination therapies with PARP inhibitors in cervical cancer. Significance•This study provides the overview of proteomic changes induced by PARP inhibitor olaparib in cervical cancer Hela cells.•We demonstrated that Olaparib inhibited PARP1 activity in Hela cells in a dose-dependent manner while no change was observed in the expression of PARP1.•PARP inhibition potentially regulated the RNA metabolism, RNA binding proteins, metastasis-related genes, mitochondrial proteins, transcription factors and regulators, and ubiquitination proteins.•We also identified increased expression of tumor-promoting and drug resistance proteins that could contribute to the resistance mechanism to PARPi therapy.•This approach will be helpful to generate insights into precision oncology for personalized treatment and generate data repositories for future artificial intelligence-based research.

Ruthenium(II) Polypyridyl Complexes as FRET Donors: Structure- and Sequence-Selective DNA-Binding and Anticancer Properties.

Ruthenium(II) polypyridyl complexes (RPCs) that emit from metal-to-ligand charge transfer (MLCT) states have been developed as DNA probes and are being examined as potential anticancer agents. Here, we report that MLCT-emissive RPCs that bind DNA undergo Förster resonance energy transfer (FRET) with Cy5.5-labeled DNA, forming mega-Stokes shift FRET pairs. Based on this discovery, we developed a simple and rapid FRET binding assay to examine DNA-binding interactions of RPCs with diverse photophysical properties, including non-"light switch" complexes [Ru(dppz)2(5,5'dmb)]2+ and [Ru(PIP)2(5,5'dmb)]2+ (dppz = dipyridophenazine, 5,5'dmb = 5,5'-dimethyl-2,2'-bipyridine, PIP = 2-phenyl-imidazo[4,5-f][1,10]phenanthroline). Binding affinities toward duplex, G-quadruplex, three-way junction, and mismatch DNA were determined, and derived FRET donor-acceptor proximities provide information on potential binding sites. Molecules characterized by this method demonstrate encouraging anticancer properties, including synergy with the PARP inhibitor Olaparib, and mechanistic studies indicate that [Ru(PIP)2(5,5'dmb)]2+ acts to block DNA replication fork progression.

Targeting tumor-stroma communication by blocking endothelin-1 receptors sensitizes high-grade serous ovarian cancer to PARP inhibition

PARP inhibitors (PARPi) have changed the treatment paradigm of high-grade serous ovarian cancer (HG-SOC). However, the impact of this class of inhibitors in HG-SOC patients with a high rate of TP53 mutations is limited, highlighting the need to develop combinatorial therapeutic strategies to improve responses to PARPi. Here, we unveil how the endothelin-1/ET-1 receptor (ET-1/ET-1R) axis, which is overexpressed in human HG-SOC and associated with poor prognosis, instructs HG-SOC/tumor microenvironment (TME) communication via key pro-malignant factors and restricts the DNA damage response induced by the PARPi olaparib. Mechanistically, the ET-1 axis promotes the p53/YAP/hypoxia inducible factor-1α (HIF-1α) transcription hub connecting HG-SOC cells, endothelial cells and activated fibroblasts, hence fueling persistent DNA damage signal escape. The ET-1R antagonist macitentan, which dismantles the ET-1R-mediated p53/YAP/HIF-1α network, interferes with HG-SOC/stroma interactions that blunt PARPi efficacy. Pharmacological ET-1R inhibition by macitentan in orthotopic HG-SOC patient-derived xenografts synergizes with olaparib to suppress metastatic progression, enhancing PARPi survival benefit. These findings reveal ET-1R as a mechanistic determinant in the regulation of HG-SOC/TME crosstalk and DNA damage response, indicating the use of macitentan in combinatorial treatments with PARPi as a promising and emerging therapy.

PARP inhibition promotes endothelial-like traits in melanoma cells and modulates pericyte coverage dynamics during vasculogenic mimicry.

Vasculogenic mimicry (VM) describes the ability of highly aggressive tumor cells to develop pseudovascular structures without the participation of endothelial cells. PARP1 is implicated in the activation of hypoxia-inducible factors, which are crucial in tumor neovascularization. We have explored the role of hypoxia and PARP inhibition in VM. In uveal melanoma xenografts, the PARP inhibitor olaparib improved in vivo pericyte coverage specifically of VM channels. This was concomitant with reduced metastasis in olaparib-treated VM+ tumors. PARP inhibition and hypoxia modulated melanoma tube formation in vitro, inducing a more sparse and regular tubular architecture. Whole-transcriptome profiling revealed that olaparib treatment under hypoxic conditions modulated the expression of genes implicated in vasculogenesis during tube formation, enhancing the endothelial-like phenotype of VM+ uveal melanoma cells. PARP inhibition, especially during hypoxia, upregulated PDGFβ, which is essential for pericyte recruitment. Our study indicates that PARP inhibitors may enhance the endothelial characteristics of VM+ cells, modulate pericyte coverage, and reduce metastatic spread in VM+ melanoma. © 2022 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

A radioiodinated rucaparib analogue as an Auger electron emitter for cancer therapy

IntroductionRadioligand therapy (RLT) is an expanding field that has shown great potential in the fight against cancer. Radionuclides that can be carried by selective ligands such as antibodies, peptides, and small molecules targeting cancerous cells have demonstrated a clear improvement in the move towards precision medicine. Poly (ADP-ribose) polymerase (PARP) is a family of enzymes involved in DNA damage repair signalling pathway, with PARP inhibitors olaparib, talazoparib, niraparib, veliparib, and rucaparib having FDA approval for cancer therapy in routine clinical use. Based on our previous work with the radiolabelled PARP inhibitor [18F]rucaparib, we replaced the fluorine-18 moiety, used for PET imaging, with iodine-123, a radionuclide used for SPECT imaging and Auger electron therapy, resulting in 8-[123I]iodo-5-(4-((methylamino)methyl)phenyl)-2,3,4,6-tetrahydro-1H-azepino[5,4,3-cd]indol-1-one, ([123I]GD1), as a potential radiopharmaceutical for RLT. Methods[123I]GD1 was synthesized via copper-mediated radioiodination from a selected boronic esters precursor. In vitro uptake, retention, blocking, and effects on clonogenic survival with [123I]GD1 treatment were tested in a panel of cancer cell lines. Enzymatic inhibition of PARP by GD1 was also tested in a cell-free system. The biodistribution of [123I]GD1 was investigated by SPECT/CT in mice following intravenous administration. ResultsCell-free enzymatic inhibition and in vitro blocking experiments confirmed a modest ability of GD1 to inhibit PARP-1, IC50 = 239 nM. In vitro uptake of [123I]GD1 in different cell lines was dose dependent, and radiolabelled compound was retained in cells for >2 h. Significantly reduced clonogenic survival was observed in vitro after exposure of cells for 1 h with as low as 50 kBq of [123I]GD1. The biodistribution of [123I]GD1 was further characterized in vivo showing both renal and hepatobiliary clearance pathways with a biphasic blood clearance. ConclusionWe present the development of a new theragnostic agent based on the rucaparib scaffold and its evaluation in in vitro and in vivo models. The data reported show that [123I]GD1 may have potential to be used as a theragnostic agent.

Selected Articles from This Issue

Highlights| December 02 2022 Selected Articles from This Issue Author & Article Information Online Issn: 1557-3125 Print Issn: 1541-7786 ©2022 American Association for Cancer Research2022American Association for Cancer Research Mol Cancer Res (2022) 20 (12): 1709. https://doi.org/10.1158/1541-7786.MCR-20-12-HI Related Content A commentary has been published: The C-terminus of Gain-of-Function Mutant p53 R273H Is Required for Association with PARP1 and Poly-ADP-Ribose A commentary has been published: A Recurrent ADPRHL1 Germline Mutation Activates PARP1 and Confers Prostate Cancer Risk in African American Families A commentary has been published: Regulation of Cyclin D1 Degradation by Ubiquitin-Specific Protease 27X Is Critical for Cancer Cell Proliferation and Tumor Growth View more A commentary has been published: Raptinal Induces Gasdermin E–Dependent Pyroptosis in Naïve and Therapy-Resistant Melanoma View less Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Cite Icon Cite Search Site Article Versions Icon Versions Version of Record December 2 2022 Citation Selected Articles from This Issue. Mol Cancer Res 1 December 2022; 20 (12): 1709. https://doi.org/10.1158/1541-7786.MCR-20-12-HI Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest Search Advanced Search African American men are particularly susceptible to prostate cancer incidence, but genetic factors mediating prostate cancer risk in African American men remain poorly defined. To search for genetic contributors to prostate cancer occurrence in African American men, Zhang and colleagues performed whole exome sequencing using blood samples from men from 20 families affected by hereditary prostate cancer. Sequencing revealed a rare non-synonymous ADPRHL1 variant, c.A233T, encoding a p.D78V amino acid conversion, that was present in men affected by prostate cancer in four of the families but not present in 170 unrelated healthy African American men. Functional studies demonstrated that the A233T variant increases prostate cancer cell growth and induces PARP activation. A233T variant-mediated PARP activation renders prostate cancer cells resistant to DNA damaging agents but susceptible to PARP inhibitor olaparib. The authors also found that ADPRHL1 abundance decreases during prostate cancer progression, suggesting A233T is a loss-of-function variant. Altogether, this... You do not currently have access to this content.

Abstract B030: Combined inhibition of BET proteins and PARP promotes impaired DNA damage repair response and cell cycle dysregulation in preclinical models of bladder cancer

Abstract Background: Bladder cancer (BC) remains a common and deadly malignancy, with a projected 81,180 new diagnoses and 17,100 deaths in the United States in 2022. According to the MSK/TCGA Bladder Cancer dataset, mutations in DNA damage response (DDR) genes that are part of the homologous recombination (HR) pathway occurred in up to 55% of patients, representing a potential therapeutic target in BC. In previous work, we used UNC’s EpiG Diamond compound library to show that, as a class, inhibition of the methyl-lysine reader bromodomain and extra-terminal domain (BET) proteins potently abrogate BC cell line viability. Here, we evaluated mechanisms related to HR inhibition that could explain pan-BET inhibitor OTX-015’s potency in BC. Methods: 5637 and J82 BC cells were treated with 1 µM OTX-015 or 0.1% DMSO control for 48-hours, total RNA was extracted, and then bulk RNA-sequencing (RNA-seq) was performed on an Illumina NovaSeq 6000 (Novogene, Sacramento, CA). Expression data was analyzed using Geneious Prime v2022.2.1 (Biomatters, San Diego, CA). Cells were then treated with 1 μM OTX-015, 5 μM of the PARP inhibitor olaparib, or combination for gene and protein expression analysis. Gene expression changes in BRCA1, BRCA2, PALB2, and RAD51, as well as MYC as a positive control, were confirmed by RT-PCR in biological triplicates after 48-hour incubation, normalized to an SDHA housekeeper and compared to a 0.1% DMSO control. Western blotting evaluated OTX-015 and olaparib effects on BRCA1, BRCA2, c-MYC, PALB2, and RAD51 protein expression after 72-hour incubation, using a GAPDH loading control and compared to a 0.1% DMSO control. Last, cells were treated with the same treatment schema for 24-72 hours, fixed with methanol, stained with propidium iodide (25 μg/mL), and flow cytometry evaluated effects on cell cycle using a ThermoFisher Attune NxT and FlowJo v10.8.1 (BD Life Sciences, Ashland, OR). Results: Bulk RNA-seq analyses revealed significantly altered expression of HR pathway genes in 5637 and J82 cells treated with OTX-015±olaparib. In 5637 cells, OTX-015 alone significantly reduced BRCA1, BRCA2, PALB2 and RAD51 expression, (n=3; P<0.001 for all), but only PALB2 and RAD51 expression was significantly reduced after combination treatment (n=3; P<0.001 for both). In J82 cells, OTX-015 alone and combination treatment significantly reduced BRCA1, PALB2 and RAD51 expression, (n=3; P<0.001 for all). Similarly, both OTX-015 and combination treatment resulted in reduced BRCA1, c-MYC, PALB2 and RAD51 protein expression in both cell lines. In both cell lines, combination treatment resulted in a substantially increased G2/M fraction at 48 hours compared to 0.1% DMSO (5637 cells: 62.9% vs 12.6% G2/M; J82 cells: 28.2% vs 17.8% G2/M). Conclusions: These data indicate that OTX-015-mediated inhibition of RAD51 and PALB2 could be responsible for impaired HR. Cell cycle data revealed a G2/M stall, rather than an S phase stall, suggesting mechanisms independent from impaired HR could be responsible for cell cycle dysregulation. Citation Format: Ryan M. Kemper, Manfred Meng, Daniel J. Crona. Combined inhibition of BET proteins and PARP promotes impaired DNA damage repair response and cell cycle dysregulation in preclinical models of bladder cancer. [abstract]. In: Proceedings of the AACR Special Conference: Cancer Epigenomics; 2022 Oct 6-8; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2022;82(23 Suppl_2):Abstract nr B030.

High Efficacy of the PARP Inhibitor Olaparib Combined with High-Dose Chemotherapy and Autologous Stem-Cell Transplant for Refractory Lymphomas

More active HDC are needed for ASCT for refractory/poor-risk relapsed lymphomas. Enhancement of the activity of HDC through combination with DNA damage repair (DDR) inhibitors is a promising but unexplored avenue. The enzyme poly(ADP-ribose) polymerase (PARP) catalyzes PARylation at the DNA damage site, which initiates DDR. Olaparib, the first FDA-approved PARP inhibitor for use in selected solid tumors, has shown synergy with conventional-dose chemotherapy, albeit with increased myelotoxicity. We studied in vitro the interaction of olaparib, epigenetically potentiated with the histone deacetylase (HDAC) inhibitor vorinostat, with a combination of gemcitabine/busulfan/melphalan (GemBuMel), which we had developed previously. We observed a markedly increased cytotoxicity of vorinostat/GemBuMel when combined with olaparib in refractory B- and T-cell lymphoma lines (Valdez et al., Leuk Lymphoma 2017;58:2705-16). Our preclinical work led us to design and clinically study olaparib plus vorinostat/GemBuMel with ASCT in refractory lymphomas. PATIENTS AND METHODS: Patients ages 15-65 with refractory lymphomas and adequate end-organ function were eligible for this phase I trial (NCT03259503). Olaparib was given from day -11 to -3, at 7 dose levels (DL1-DL7), ranging from 25 to 300 mg PO twice daily. Vorinostat was given at 1,000 mg PO daily (days -10 to -3). Gemcitabine was administered at 2,475 mg/m2/day IV (days -8 and -3), infused as a loading dose of 75 mg/m2 followed by continuous infusion at 10 mg/m2/min over 4 hours. Busulfan dosing targeted 4,000 μM.min-1/day IV (days -8 to -5). Melphalan was infused at 60 mg/m2/day IV (days -3 and -2). Patients with CD20+ tumors received rituximab (375 mg/m2) IV on day -10. ASCT was on day 0. The trial goals were to identify the recommended phase 2 dose (RP2D) of olaparib, and estimate the overall (ORR), and complete response (CR) rates, event-free (EFS) and overall survival (OS) rates of the regimen. RESULTS: Between 10/19 and 06/22 we enrolled 30 patients: 18 Hodgkin, 6 DLBCL and 6 T-NHL, median age 34 (20-61), median prior lines of therapy 3 (range, 2-7), 8 prior CAR-T or other cellular immunotherapies. Eleven patients had PET+ tumors at HDC (3 of them in PD). An olaparib dose of 150 mg PO BID (DL4) was identified as the RP2D. There was 1 TRM (sepsis) at DL5. The toxicity profile was similar to that of vorinostat/GemBuMel without olaparib and included mucositis (17 grade 3, 11 grade 2), asymptomatic elevation of transaminases (10 grade 3, 7 grade 2), hyperbilirubinemia (7 grade 3, 2 grade 2, with no cases of VOD/SOS), colitis (2 grade 3, 3 grade 2), diarrhea (3 grade 3, 3 grade 2), and asymptomatic bradycardia during the HDC regimen (6 grade 1). Neutrophils and platelets engrafted promptly. The ORR and CR rates were both 100%. At median follow-up of 16 (range, 2-34) months, the EFS and OS rates are both 90%. There were only two relapses at 4 and 7 months, respectively, both in patients treated at DL1. Olaparib markedly inhibited PAR levels (measured by ELISA in PBMNC), which decreased significantly from baseline to day -5 (and became undetectable in those patients treated at the RP2D), with rapid PARylation recovery on day -2 (around 12 hours after the last dose of olaparib). CONCLUSION: In this first trial combining a PARP inhibitor and an HDAC inhibitor with HDC, olaparib/vorinostat/GemBuMel was safe and highly active in refractory relapsed lymphomas, including post-CAR-T relapses. Olaparib, in combination with HDAC inhibition, strongly potentiates HDC through inhibition of PARylation and DDR during treatment. The clinical data are encouraging and this approach warrants further evaluation.

EXTH-63. COMBINED INHIBITION OF TOP1 AND PARP: A NOVEL THERAPEUTIC STRATEGY FOR GBM WITH PTEN DEFICIENCY

Abstract BACKGROUND Glioblastoma (GBM) is the most aggressive and lethal type of brain tumor. Activation of PI3K/mTOR pathway along with the loss of its primary negative regulator, phosphatase and tensin homolog (PTEN), occurs in nearly 50% of GBM patients. As PTEN is known to promote DNA damage repair deficiency, here we investigated whether PTEN deficiency presents a vulnerability to a simultaneous induction of DNA damage and suppression of repair mechanisms by combining topoisomerase I (TOP1) and PARP inhibitors. METHODS We used patient-derived GBM cells and stem-like cells to determine response to LMP400 (Indotecan), a novel non-camptothecin TOP1 inhibitor, and the PARP inhibitors Olaparib or Niraparib. Treatment efficacy was also determined using cell viability, cell cycle, DNA damage, repair, and apoptosis assays in a pair of isogenic PTEN-null and PTEN-WT glioma cell lines derived from a genetically engineered mouse GBM model. RNAseq analysis was performed to identify treatment-induced dysregulated pathways. RESULTS PTEN-deficient cells are highly sensitive to LMP400 and PTEN rescue lessens sensitivity to the treatment. Combining LMP400 with PARP inhibitors, Olaparib or Niraparib, leads to synergistic cytotoxicity. LMP400/Niraparib combination induces G2/M cell cycle arrest, DNA damage, suppression of homologous recombination (HR)-related proteins and activation of caspase 3/7 activity significantly more in PTEN-null cells compared to isogenic PTEN-WT cells. Gene set enrichment analysis revealed suppression of cell cycle and DNA damage repair as well as activation of cell death pathways. Finally, CRISPR-Cas9 KO screening suggests that LMP400 is not likely to be a substrate for ABC transporters, suggesting the brain penetration and supporting the use in brain tumor patients. CONCLUSION Combined inhibition of TOP1 and PARP induces synergistic antiglioma effects selectively in PTEN-null glioblastoma cells, providing a strong scientific premise for a clinical trial of combined treatment with LMP400 and Niraparib in a subset of GBM with PTEN deficiency.

Post-Neoadjuvant Treatment Strategies for Patients with Early Breast Cancer.

Pre-surgical treatments in patients with early breast cancer allows a direct estimation of treatment efficacy, by comparing the tumor and the treatment. Patients who achieve a pathological complete response at surgery have a better prognosis, with lower risk of disease recurrence and death. Hence, clinical research efforts have been focusing on high-risk patients with residual disease at surgery, who may be "salvaged" through additional treatments administered in the post-neoadjuvant setting. In the present review, we aim to illustrate the development and advantages of the post-neoadjuvant setting, and to discuss the available strategies for patients with early breast cancer, either approved or under investigation. This review was written after literature search on main scientific databases (e.g., PubMed) and conference proceedings from major oncology conferences up to 1 August 2022. T-DM1 and capecitabine are currently approved as post-neoadjuvant treatments for patients with HER2-positive and triple-negative breast cancer, respectively, with residual disease at surgery. More recently, other treatment strategies have been approved for patients with high-risk early breast cancer, including the immune checkpoint inhibitor pembrolizumab, the PARP inhibitor olaparib and the CDK 4/6 inhibitor abemaciclib. Novel agents and treatment combinations are currently under investigation as promising post-neoadjuvant treatment strategies.

Cost-effectiveness of poly-(ADP-ribose) polymerase (PARP)-inhibitors for the maintenance treatment after responding to first- and second-line chemotherapy in advanced ovarian cancer.

The introduction of inhibitors of poly-(ADP-ribose) polymerase (PARP) for the treatment of women with epithelial ovarian cancers (EOC) has radically changed the treatment in maintenance setting after responding to first- and second-line chemotherapy. The aim of this paper was to assess the pharmacological costs of PARP inhibitors (olaparib, niraparib, rucaparib and veliparib) in maintenance treatment after responding to first-line chemotherapy in EOC. Incremental cost-effectiveness ratio (ICER) was calculated as the ratio between the difference of the costs in the intervention and in the control groups (pharmacy costs) and the difference between the effect in the intervention and in the control groups (progression-free survival (PFS)). We have considered the pivotal phase III randomized controlled trials (RCTs). Three different populations were considered: the overall population, patients with germline BRCA mutation (gBRCA) and homologous recombination deficiency (HRD) patients non-gBRCA mutation. Three thousand four hundred and twenty patients and 1209 patients were considered in maintenance treatment after responding to first- and second-line chemotherapy in EOC, respectively. At the actual price, the treatment with PARP inhibitors is not cost-effective in maintenance treatment after responding to first-line and second-line chemotherapy in EOC. A reduction in pharmacological costs is mandatory.

GZ17-6.02 kills prostate cancer cells in vitro and in vivo.

GZ17-6.02 is undergoing clinical evaluation in solid tumors and lymphoma. We defined the biology of GZ17-6.02 in prostate cancer cells and determined whether it interacted with the PARP1 inhibitor olaparib to enhance tumor cell killing. GZ17-6.02 interacted in a greater than additive fashion with olaparib to kill prostate cancer cells, regardless of androgen receptor expression or loss of PTEN function. Mechanistically, GZ17-6.02 initially caused peri-nuclear activation of ataxia-telangiectasia mutated (ATM) that was followed after several hours by activation of nuclear ATM, and which at this time point was associated with increased levels of DNA damage. Directly downstream of ATM, GZ17-6.02 and olaparib cooperated to activate the AMP-dependent protein kinase (AMPK) which then activated the kinase ULK1, resulting in autophagosome formation that was followed by autophagic flux. Knock down of ATM, AMPKα or the autophagy-regulatory proteins Beclin1 or ATG5 significantly reduced tumor cell killing. GZ17-6.02 and olaparib cooperated to activate protein kinase R which phosphorylated and inactivated eIF2α, i.e., enhanced endoplasmic reticulum (ER) stress signaling. Knock down of eIF2α also significantly reduced autophagosome formation and tumor cell killing. We conclude that GZ17-6.02 and olaparib interact to kill prostate cancer cells in vitro by increasing autophagy and by enhancing ER stress signaling. In vivo, GZ17-6.02 as a single agent profoundly reduced tumor growth and significantly prolonged animal survival. GZ17-6.02 interacted with olaparib to further suppress the growth of LNCaP tumors without ultimately enhancing animal survival. Our data support the consideration of GZ17-6.02 as a possible therapeutic agent in patients with AR+ prostate cancer.

193P Experience with olaparib in the treatment of BRCA-associated tumors in real clinical practice: Experience of re-challenge mode of olaparib usage

The PARP inhibitor olaparib has shown promising results in the treatment of patients with BRCA-associated tumors. By revealing more and more tumors, the development of which is caused by disorders in the BRCA gene, PARP inhibitors are also expanding their indications. Olaparib shows statistical improvement in ovarian cancer, breast cancer, prostate cancer and pancreatic cancer over standard options while showing a moderate toxic profile. All this makes olaparib a significant option in the planning of patient treatment tactics.