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Phosphorylated biomarkers are crucial for our understanding of drug mechanism of action and dose selection during clinical trials, particularly for drugs that target protein kinases, such as DNA-damage-response (DDR) inhibitors. However, tissue fixation conditions needed to preserve DDR-specific phospho-biomarkers have not been previously investigated. Using xenograft tissues and tightly controlled formalin fixation conditions, we assessed how preanalytical factors affect phosphorylated DDR biomarkers pRAD50(Ser635), ɣH2AX(Ser139), pKAP1(Ser824), and non-phosphorylated biomarkers cMYC and ATM. Cold ischemia times ranged from 15 min to 6 hr, and the fixation duration ranged from 24 hr to 4 weeks. Epitopes pRAD50 and pKAP1 appeared the most labile assessed with staining loss after just 15 min of cold ischemia time, while ATM was more robust showing consistent expression up to 1 hr of cold ischemia. Notably, ɣH2AX expression was lost with formalin fixation over 48 hr. The use of core needle biopsies where possible and novel fixation methods such as the 2-step temperature-controlled formalin approach may improve phosphorylated biomarker preservation; however, practical challenges may affect wider clinical application. The most essential tissue-processing step when downstream analysis includes DDR phosphorylated biomarkers is immediate tissue submersion in formalin, without delay, upon excision from the patient, followed by room temperature fixation for 24 hr.

AZD6738 (ceralasertib) is a potent and selective orally bioavailable inhibitor of ataxia telangiectasia and Rad3-related (ATR) kinase. ATR is activated in response to stalled DNA replication forks to promote G2–M cell-cycle checkpoints and fork restart. Here, we found AZD6738 modulated CHK1 phosphorylation and induced ATM-dependent signaling (pRAD50) and the DNA damage marker γH2AX. AZD6738 inhibited break-induced replication and homologous recombination repair. In vitro sensitivity to AZD6738 was elevated in, but not exclusive to, cells with defects in the ATM pathway or that harbor putative drivers of replication stress such as CCNE1 amplification. This translated to in vivo antitumor activity, with tumor control requiring continuous dosing and free plasma exposures, which correlated with induction of pCHK1, pRAD50, and γH2AX. AZD6738 showed combinatorial efficacy with agents associated with replication fork stalling and collapse such as carboplatin and irinotecan and the PARP inhibitor olaparib. These combinations required optimization of dose and schedules in vivo and showed superior antitumor activity at lower doses compared with that required for monotherapy. Tumor regressions required at least 2 days of daily dosing of AZD6738 concurrent with carboplatin, while twice daily dosing was required following irinotecan. In a BRCA2-mutant patient-derived triple-negative breast cancer (TNBC) xenograft model, complete tumor regression was achieved with 3 to5 days of daily AZD6738 per week concurrent with olaparib. Increasing olaparib dosage or AZD6738 dosing to twice daily allowed complete tumor regression even in a BRCA wild-type TNBC xenograft model. These preclinical data provide rationale for clinical evaluation of AZD6738 as a monotherapy or combinatorial agent. Significance: This detailed preclinical investigation, including pharmacokinetics/pharmacodynamics and dose–schedule optimizations, of AZD6738/ceralasertib alone and in combination with chemotherapy or PARP inhibitors can inform ongoing clinical efforts to treat cancer with ATR inhibitors.

Supplementary Figure from Identification of a Molecularly-Defined Subset of Breast and Ovarian Cancer Models that Respond to WEE1 or ATR Inhibition, Overcoming PARP Inhibitor Resistance

Supplementary Data from Identification of a Molecularly-Defined Subset of Breast and Ovarian Cancer Models that Respond to WEE1 or ATR Inhibition, Overcoming PARP Inhibitor Resistance

Purpose:PARP inhibitors (PARPi) induce synthetic lethality in homologous recombination repair (HRR)-deficient tumors and are used to treat breast, ovarian, pancreatic, and prostate cancers. Multiple PARPi resistance mechanisms exist, most resulting in restoration of HRR and protection of stalled replication forks. ATR inhibition was highlighted as a unique approach to reverse both aspects of resistance. Recently, however, a PARPi/WEE1 inhibitor (WEE1i) combination demonstrated enhanced antitumor activity associated with the induction of replication stress, suggesting another approach to tackling PARPi resistance.Experimental Design:We analyzed breast and ovarian patient-derived xenoimplant models resistant to PARPi to quantify WEE1i and ATR inhibitor (ATRi) responses as single agents and in combination with PARPi. Biomarker analysis was conducted at the genetic and protein level. Metabolite analysis by mass spectrometry and nucleoside rescue experiments ex vivo were also conducted in patient-derived models.Results:Although WEE1i response was linked to markers of replication stress, including STK11/RB1 and phospho-RPA, ATRi response associated with ATM mutation. When combined with olaparib, WEE1i could be differentiated from the ATRi/olaparib combination, providing distinct therapeutic strategies to overcome PARPi resistance by targeting the replication stress response. Mechanistically, WEE1i sensitivity was associated with shortage of the dNTP pool and a concomitant increase in replication stress.Conclusions:Targeting the replication stress response is a valid therapeutic option to overcome PARPi resistance including tumors without an underlying HRR deficiency. These preclinical insights are now being tested in several clinical trials where the PARPi is administered with either the WEE1i or the ATRi.

Supplementary Data from ATR Inhibitor AZD6738 (Ceralasertib) Exerts Antitumor Activity as a Monotherapy and in Combination with Chemotherapy and the PARP Inhibitor Olaparib

Background In high grade serous ovarian cancer (HGSOC), there is a spectrum of sensitivity to first line platinum‐based chemotherapy. This study molecularly characterizes HGSOC patients from two distinct groups of chemotherapy responders (good vs. poor). Methods Following primary debulking surgery and intravenous carboplatin/paclitaxel, women with stage III–IV HGSOC were grouped by response. Patients in the good response (GR) and poor response (PR) groups respectively had a progression‐free intervals (PFI) of ≥12 and ≤6 months. Analysis of surgical specimens interrogated genomic and immunologic features using whole exome sequencing. RNA‐sequencing detected gene expression outliers and inference of immune infiltrate, with validation by targeted NanoString arrays. PD‐L1 expression was scored by immunohistochemistry (IHC). Results A total of 39 patient samples were analyzed (GR = 20; PR = 19). Median PFI for GR and PR patient cohorts was 32 and 3 months, respectively. GR tumors were enriched for loss‐of‐function BRCA2 mutations and had a significantly higher nonsynonymous mutation rate compared to PR tumors (p = 0.001). Samples from the PR cohort were characterized by mutations in MGA and RAD51B and trended towards a greater rate of amplification of PIK3CA, MECOM, and ATR in comparison to GR tumors. Gene expression analysis by NanoString correlated increased PARP4 with PR and increased PD‐L1 and EMSY with GR. There was greater tumor immune cell infiltration and higher immune cell PD‐L1 protein expression in the GR group. Conclusions Our research demonstrates that tumors from HGSOC patients responding poorly to first line chemotherapy have a distinct molecular profile characterized by actionable drug targets including PARP4., In patients with suboptimally‐debulked, advanced high grade serous ovarian cancer (HGSOC), the spectrum of responses to first line platinum‐based chemotherapy (PtC) vary from durable to non‐existent, highlighting an unmet medical need for those with poor responses. Our study molecularly characterizes a cohort of HGSOC patients with distinct responses, either good or poor, to PtC. The good and poor responders have median progression‐free intervals of 32 and 3 months, respectively, and molecular analysis of tumors identifies differences in DNA damage response pathways and immunity, namely, tumors from poor responders to first line PtC have a distinct molecular profile characterized by actionable drug targets including PARP4.

Clinical tissue specimens are often unscreened, and preparation of tissue sections for analysis by mass spectrometry imaging (MSI) can cause aerosolization of particles potentially carrying an infectious load. We here present a decontamination approach based on ultraviolet-C (UV-C) light to inactivate clinically relevant pathogens such as herpesviridae, papovaviridae human immunodeficiency virus, or SARS-CoV-2, which may be present in human tissue samples while preserving the biodistributions of analytes within the tissue. High doses of UV-C required for high-level disinfection were found to cause oxidation and photodegradation of endogenous species. Lower UV-C doses maintaining inactivation of clinically relevant pathogens to a level of increased operator safety were found to be less destructive to the tissue metabolome and xenobiotics. These doses caused less alterations of the tissue metabolome and allowed elucidation of the biodistribution of the endogenous metabolites. Additionally, we were able to determine the spatially integrated abundances of the ATR inhibitor ceralasertib from decontaminated human biopsies using desorption electrospray ionization-MSI (DESI-MSI).

Background Schlafen 11 (SLFN11) has been linked with response to DNA-damaging agents (DDA) and PARP inhibitors. An in-depth understanding of several aspects of its role as a biomarker in cancer is missing, as is a comprehensive analysis of the clinical significance of SLFN11 as a predictive biomarker to DDA and/or DNA damage-response inhibitor (DDRi) therapies. Methods We used a multidisciplinary effort combining specific immunohistochemistry, pharmacology tests, anticancer combination therapies and mechanistic studies to assess SLFN11 as a potential biomarker for stratification of patients treated with several DDA and/or DDRi in the preclinical and clinical setting. Results SLFN11 protein associated with both preclinical and patient treatment response to DDA, but not to non-DDA or DDRi therapies, such as WEE1 inhibitor or olaparib in breast cancer. SLFN11-low/absent cancers were identified across different tumour types tested. Combinations of DDA with DDRi targeting the replication-stress response (ATR, CHK1 and WEE1) could re-sensitise SLFN11-absent/low cancer models to the DDA treatment and were effective in upper gastrointestinal and genitourinary malignancies. Conclusion SLFN11 informs on the standard of care chemotherapy based on DDA and the effect of selected combinations with ATR, WEE1 or CHK1 inhibitor in a wide range of cancer types and models.

Cáncer de mama y de ovario; Inhibición WEE1 Càncer de mama i d'ovari; Inhibició WEE1 Breast and ovarian cancer; WEE1 inhibition Purpose: PARP inhibitors (PARPi) induce synthetic lethality in homologous recombination repair (HRR)-deficient tumors and are used to treat breast, ovarian, pancreatic, and prostate cancers. Multiple PARPi resistance mechanisms exist, most resulting in restoration of HRR and protection of stalled replication forks. ATR inhibition was highlighted as a unique approach to reverse both aspects of resistance. Recently, however, a PARPi/WEE1 inhibitor (WEE1i) combination demonstrated enhanced antitumor activity associated with the induction of replication stress, suggesting another approach to tackling PARPi resistance. Experimental Design: We analyzed breast and ovarian patient-derived xenoimplant models resistant to PARPi to quantify WEE1i and ATR inhibitor (ATRi) responses as single agents and in combination with PARPi. Biomarker analysis was conducted at the genetic and protein level. Metabolite analysis by mass spectrometry and nucleoside rescue experiments ex vivo were also conducted in patient-derived models. Results: Although WEE1i response was linked to markers of replication stress, including STK11/RB1 and phospho-RPA, ATRi response associated with ATM mutation. When combined with olaparib, WEE1i could be differentiated from the ATRi/olaparib combination, providing distinct therapeutic strategies to overcome PARPi resistance by targeting the replication stress response. Mechanistically, WEE1i sensitivity was associated with shortage of the dNTP pool and a concomitant increase in replication stress. Conclusions: Targeting the replication stress response is a valid therapeutic option to overcome PARPi resistance including tumors without an underlying HRR deficiency. These preclinical insights are now being tested in several clinical trials where the PARPi is administered with either the WEE1i or the ATRi. This work was supported by the Spanish Instituto de Salud Carlos III (ISCIII), an initiative of the Spanish Ministry of Economy and Innovation partially supported by European Regional Development FEDER Funds (FIS PI17/01080 to V. Serra, PI12/02606 to J. Balmaña); European Research Area-NET, Transcan-2 (AC15/00063), Asociación Española contra el Cáncer (AECC; LABAE16020PORTT), the Agència de Gestió d'Ajuts Universitaris i de Recerca (AGAUR; 2017 SGR 540), La Marató TV3 (654/C/2019), and ERAPERMED2019–215 to V. Serra. We also acknowledge the GHD-Pink program, the FERO Foundation, and the Orozco Family for supporting this study (to V. Serra). V. Serra was supported by the Miguel Servet Program (ISCIII; CPII19/00033); M. Castroviejo-Bermejo and C. Cruz (AIOC15152806CRUZ) by AECC; A. Herencia-Ropero by Generalitat de Catalunya-PERIS (SLT017/20/000081); M. Palafox by Juan de la Cierva (FJCI-2015–25412); A. Lau by AECC and Generalitat de Catalunya-PERIS (INVES20095LLOP, SLT002/16/00477); A. Gris-Oliver by FI-AGAUR (2015 FI_B 01075). This work was supported by Breast Cancer Research Foundation (BCRF-19–08), Instituto de Salud Carlos III Project Reference number AC15/00062, and the EC under the framework of the ERA-NET TRANSCAN-2 initiative co-financed by FEDER, Instituto de Salud Carlos III (CB16/12/00449 and PI19/01181), and Asociación Española Contra el Cáncer (to J. Arribas). The xenograft program in the Caldas laboratory was supported by Cancer Research UK and also received funding from an EU H2020 Network of Excellence (EuroCAN). The RPPA facility is funded by NCI #CA16672.

Head and neck squamous cell carcinoma (HNSCC) is frequently locally advanced, but has a high risk of recurrence after initial treatment. Immune checkpoint blockade with PD-1/PD-L1 inhibitors has revolutionized treatment in the recurrent setting, but resistance to these therapies frequently occurs. Combination of checkpoint inhibitors with the ATR inhibitor ceralasertib could provide an exciting opportunity, with encouraging clinical activity reported in melanoma and non-small cell lung cancer (Kwon et al. 2022; Kim et al. 2022; Besse et al. OA15.05 IASLC 2022 WCLC). This phase 1b trial provided a unique opportunity to understand the immunomodulatory impact of DNA Damage Response (DDR) inhibitors in a clinical setting. NCT03022409 is an open-label, randomized window of opportunity trial where patients with HNSCC were treated with either the PARP inhibitor olaparib (300mg BID) or ceralasertib (160mg BID) for 9-21 days, prior to definitive surgery (or on-treatment biopsy). 21 patients were randomized; n=12 to ceralasertib and n=9 to olaparib, and ceralasertib data will be presented here. Translational endpoints on frozen and fixed tumor biopsies included spatial pharmacokinetics, pharmacodynamic biomarkers, multiplexed fluorescence of tumor infiltrating immune cells and gene expression panels. Blood assessments included cytokine detection, immune cell phenotyping and gene expression. Primary endpoint analysis utilized a bespoke prognostic immune-focused gene signature and secondary endpoint an IHC immunoscore, both aimed to measure if tumors would shift from a ‘cold’ to ‘hot/active’ immune state. We observed an ‘on-drug’ selective suppression of proliferating Ki67+ T-cells (but not total T-cells) in the tumor microenvironment and periphery, followed by a repopulation and median rebound of 63.8% and 187.5% above baseline levels for peripheral helper (CD4+Ki67+; n=8) and cytotoxic (CD8+Ki67+; n=7) T-cells respectively, when ceralasertib dose stopped. IL-12 plasma cytokine levels dropped on ceralasertib treatment and returned to baseline levels ‘off-drug’ in 8/10 patients. Type-I interferon (IFN1) gene expression associated signatures were also upregulated in PBMCs, suggestive of an immune priming effect. 0/2 and 2/4 patients on ceralasertib met their primary and secondary endpoints respectively, however, interpretation is limited due to small numbers of evaluable patients. 1 patient had a grade 3 serious adverse event of chest pain in the ceralasertib arm. There were no unexpected safety findings for either drug and adverse events were generally low grade. The translational data has generated new insights into the immunomodulatory effect of ceralasertib. Further evaluation of the combination of ceralasertib with immune checkpoint blockade is warranted to explore this novel immune mechanism of action. Citation Format: Gemma N. Jones, Sonia Iyer, Marta Milo, Pei-Jen Lou, Melonie A. Nance, Carlos A. Gomez-Roca, Nathan Standifer, Paola Marco-Casanova, Shaan Gill, Michael Surace, Richard Bystry, Maria Alexandrova, Sophie Willis, Jaime Rodriguez-Canales, Andreas Dannhorn, Bienvenu Loembé, Alan Lau, Natalia Lukashchuk, Elizabeth A. Harrington, Elhan Sanai, Emma Dean, Umamaheswar Duvvuri. Immunomodulatory effects of the ATR inhibitor ceralasertib in a window of opportunity biomarker trial in patients with head and neck squamous cell carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr CT198.

AZD0156 is a potent and selective, bioavailable inhibitor of ataxia-telangiectasia mutated (ATM) protein, a signaling kinase involved in the DNA damage response. We present preclinical data demonstrating abrogation of irradiation-induced ATM signaling by low doses of AZD0156, as measured by phosphorylation of ATM substrates. AZD0156 is a strong radiosensitizer in vitro, and using a lung xenograft model, we show that systemic delivery of AZD0156 enhances the tumor growth inhibitory effects of radiation treatment in vivo. Because ATM deficiency contributes to PARP inhibitor sensitivity, preclinically, we evaluated the effect of combining AZD0156 with the PARP inhibitor olaparib. Using ATM isogenic FaDu cells, we demonstrate that AZD0156 impedes the repair of olaparib-induced DNA damage, resulting in elevated DNA double-strand break signaling, cell-cycle arrest, and apoptosis. Preclinically, AZD0156 potentiated the effects of olaparib across a panel of lung, gastric, and breast cancer cell lines in vitro, and improved the efficacy of olaparib in two patient-derived triple-negative breast cancer xenograft models. AZD0156 is currently being evaluated in phase I studies (NCT02588105).

Purpose: This study reports the safety, tolerability, MTD, recommended phase II dose (RP2D), pharmacokinetic/pharmacodynamic profile, and preliminary antitumor activity of ceralasertib combined with carboplatin in patients with advanced solid tumors. It also examined exploratory predictive and pharmacodynamic biomarkers. Patients and Methods: Eligible patients (n = 36) received a fixed dose of carboplatin (AUC5) with escalating doses of ceralasertib (20 mg twice daily to 60 mg once daily) in 21-day cycles. Sequential and concurrent combination dosing schedules were assessed. Results: Two ceralasertib MTD dose schedules, 20 mg twice daily on days 4–13 and 40 mg once daily on days 1–2, were tolerated with carboplatin AUC5; the latter was declared the RP2D. The most common treatment-emergent adverse events (Common Terminology Criteria for Adverse Events grade ≥3) were anemia (39%), thrombocytopenia (36%), and neutropenia (25%). Dose-limiting toxicities of grade 4 thrombocytopenia (n = 2; including one grade 4 platelet count decreased) and a combination of grade 4 thrombocytopenia and grade 3 neutropenia occurred in 3 patients. Ceralasertib was quickly absorbed (tmax ∼1 hour), with a terminal plasma half-life of 8–11 hours. Upregulation of pRAD50, indicative of ataxia telangiectasia mutated (ATM) activation, was observed in tumor biopsies during ceralasertib treatment. Two patients with absent or low ATM or SLFN11 protein expression achieved confirmed RECIST v1.1 partial responses. Eighteen of 34 (53%) response-evaluable patients had RECIST v1.1 stable disease. Conclusions: The RP2D for ceralasertib plus carboplatin was established as ceralasertib 40 mg once daily on days 1–2 administered with carboplatin AUC5 every 3 weeks, with pharmacokinetic and pharmacodynamic studies confirming pharmacodynamic modulation and preliminary evidence of antitumor activity observed.

Summary Background The Wee1 (WEE1hu) inhibitor adavosertib and gemcitabine have shown preclinical synergy and promising activity in early phase clinical trials. We aimed to determine the efficacy of this combination in patients with ovarian cancer. Methods In this double-blind, randomised, placebo-controlled, phase 2 trial, women with measurable recurrent platinum-resistant or platinum-refractory high-grade serous ovarian cancer were recruited from 11 academic centres in the USA and Canada. Women were eligible if they were aged 18 years or older, had an Eastern Cooperative Oncology Group performance status of 0–2, a life expectancy of more than 3 months, and normal organ and marrow function. Women with ovarian cancer of non-high-grade serous histology were eligible for enrolment in a non-randomised exploratory cohort. Eligible participants with high-grade serous ovarian cancer were randomly assigned (2:1), using block randomisation (block size of three and six) and no stratification, to receive intravenous gemcitabine (1000 mg/m2 on days 1, 8, and 15) with either oral adavosertib (175 mg) or identical placebo once daily on days 1, 2, 8, 9, 15, and 16, in 28-day cycles until disease progression or unacceptable toxicity. Patients and the team caring for each patient were masked to treatment assignment. The primary endpoint was progression-free survival. The safety and efficacy analysis population comprised all patients who received at least one dose of treatment. The trial is registered with ClinicalTrials.gov , NCT02151292 , and is closed to accrual. Findings Between Sept 22, 2014, and May 30, 2018, 124 women were enrolled, of whom 99 had high-grade serous ovarian cancer and were randomly assigned to adavosertib plus gemcitabine (65 [66%]) or placebo plus gemcitabine (34 [34%]). 25 women with non-high-grade serous ovarian cancer were enrolled in the exploratory cohort. After randomisation, five patients with high-grade serous ovarian cancer were found to be ineligible (four in the experimental group and one in the control group) and did not receive treatment. Median age for all treated patients (n=119) was 62 years (IQR 54–67). Progression-free survival was longer with adavosertib plus gemcitabine (median 4·6 months [95% CI 3·6–6·4] with adavosertib plus gemcitabine vs 3·0 months [1·8–3·8] with placebo plus gemcitabine; hazard ratio 0·55 [95% CI 0·35–0·90]; log-rank p=0·015). The most frequent grade 3 or worse adverse events were haematological (neutropenia in 38 [62%] of 61 participants in the adavosertib plus gemcitabine group vs ten [30%] of 33 in the placebo plus gemcitabine group; thrombocytopenia in 19 [31%] of 61 in the adavosertib plus gemcitabine group vs two [6%] of 33 in the placebo plus gemcitabine group). There were no treatment-related deaths; two patients (one in each group in the high-grade serous ovarian cancer cohort) died while on study medication (from sepsis in the experimental group and from disease progression in the control group). Interpretation The observed clinical efficacy of a Wee1 inhibitor combined with gemcitabine supports ongoing assessment of DNA damage response drugs in high-grade serous ovarian cancer, a TP53-mutated tumour type with high replication stress. This therapeutic approach might be applicable to other tumour types with high replication stress; larger confirmatory studies are required. Funding US National Cancer Institute Cancer Therapy Evaluation Program, Ontario Institute for Cancer Research, US Department of Defense, Princess Margaret Cancer Foundation, and AstraZeneca.

The poly (ADP-ribose) polymerase (PARP) inhibitor olaparib is FDA approved for the treatment of BRCA-mutated breast, ovarian and pancreatic cancers. Olaparib inhibits PARP1/2 enzymatic activity and traps PARP1 on DNA at single-strand breaks, leading to replication-induced DNA damage that requires BRCA1/2-dependent homologous recombination repair. Moreover, DNA damage response pathways mediated by the ataxia-telangiectasia mutated (ATM) and ataxia-telangiectasia mutated and Rad3-related (ATR) kinases are hypothesised to be important survival pathways in response to PARP-inhibitor treatment. Here, we show that olaparib combines synergistically with the ATR-inhibitor AZD6738 (ceralasertib), in vitro, leading to selective cell death in ATM-deficient cells. We observe that 24 h olaparib treatment causes cells to accumulate in G2-M of the cell cycle, however, co-administration with AZD6738 releases the olaparib-treated cells from G2 arrest. Selectively in ATM-knockout cells, we show that combined olaparib/AZD6738 treatment induces more chromosomal aberrations and achieves this at lower concentrations and earlier treatment time-points than either monotherapy. Furthermore, single-agent olaparib efficacy in vitro requires PARP inhibition throughout multiple rounds of replication. Here, we demonstrate in several ATM-deficient cell lines that the olaparib and AZD6738 combination induces cell death within 1–2 cell divisions, suggesting that combined treatment could circumvent the need for prolonged drug exposure. Finally, we demonstrate in vivo combination activity of olaparib and AZD6738 in xenograft and PDX mouse models with complete ATM loss. Collectively, these data provide a mechanistic understanding of combined PARP and ATR inhibition in ATM-deficient models, and support the clinical development of AZD6738 in combination with olaparib.

Background AZD0156 and AZD6738 are potent and selective inhibitors of ataxia-telangiectasia-kinase (ATM) and ataxia-telangiectasia-mutated and Rad3-related (ATR), respectively, important sensors/signallers of DNA damage. Methods We used multiplexed targeted-mass-spectrometry to select pRAD50(Ser635) as a pharmacodynamic biomarker for AZD0156-mediated ATM inhibition from a panel of 45 peptides, then developed and tested a clinically applicable immunohistochemistry assay for pRAD50(Ser635) detection in FFPE tissue. Results We found moderate pRAD50 baseline levels across cancer indications. pRAD50 was detectable in 100% gastric cancers (n = 23), 99% colorectal cancers (n = 102), 95% triple-negative-breast cancers (TNBC) (n = 40) and 87.5% glioblastoma-multiformes (n = 16). We demonstrated AZD0156 target inhibition in TNBC patient-derived xenograft models; where AZD0156 monotherapy or post olaparib treatment, resulted in a 34–72% reduction in pRAD50. Similar inhibition of pRAD50 (68%) was observed following ATM inhibitor treatment post irinotecan in a colorectal cancer xenograft model. ATR inhibition, using AZD6738, increased pRAD50 in the ATM-proficient models whilst in ATM-deficient models the opposite was observed, suggesting pRAD50 pharmacodynamics post ATR inhibition may be ATM-dependent and could be useful to determine ATM functionality in patients treated with ATR inhibitors. Conclusion Together these data support clinical utilisation of pRAD50 as a biomarker of AZD0156 and AZD6738 pharmacology to elucidate clinical pharmacokinetic/pharmacodynamic relationships, thereby informing recommended Phase 2 dose/schedule.

Altres ajuts: European Research Area-NET, Transcan-2 (AC15/00063), Asociación Española Contra el Cáncer (LABAE16020PORTT) i AIOC15152806CRUZ, Generalitat de Catalunya(PERIS, SLT002/16/00477 En el cas dels drets, per a usos comercials contactar amb: journals.permissions@oup.com BRCA1 and BRCA2 (BRCA1/2) -deficient tumors display impaired homologous recombination repair (HRR) and enhanced sensitivity to DNA damaging agents or to poly(ADP-ribose) polymerase (PARP) inhibitors (PARPi). Their efficacy in germline BRCA1/2 (gBRCA1/2)-mutated metastatic breast cancers has been recently confirmed in clinical trials. Numerous mechanisms of PARPi resistance have been described, whose clinical relevance in gBRCA-mutated breast cancer is unknown. This highlights the need to identify functional biomarkers to better predict PARPi sensitivity. We investigated the in vivo mechanisms of PARPi resistance in gBRCA1 patient-derived tumor xenografts (PDXs) exhibiting differential response to PARPi. Analysis included exome sequencing and immunostaining of DNA damage response proteins to functionally evaluate HRR. Findings were validated in a retrospective sample set from gBRCA1/2-cancer patients treated with PARPi. RAD51 nuclear foci, a surrogate marker of HRR functionality, were the only common feature in PDX and patient samples with primary or acquired PARPi resistance. Consistently, low RAD51 was associated with objective response to PARPi. Evaluation of the RAD51 biomarker in untreated tumors was feasible due to endogenous DNA damage. In PARPi-resistant gBRCA1 PDXs, genetic analysis found no in-frame secondary mutations, but BRCA1 hypomorphic proteins in 60% of the models, TP53BP1 -loss in 20% and RAD51 -amplification in one sample, none mutually exclusive. Conversely, one of three PARPi-resistant gBRCA2 tumors displayed BRCA2 restoration by exome sequencing. In PDXs, PARPi resistance could be reverted upon combination of a PARPi with an ataxia-telangiectasia mutated (ATM) inhibitor. Detection of RAD51 foci in gBRCA tumors correlates with PARPi resistance regardless of the underlying mechanism restoring HRR function. This is a promising biomarker to be used in the clinic to better select patients for PARPi therapy. Our study also supports the clinical development of PARPi combinations such as those with ATM inhibitors.

// Justin Greene 1, * , Anna Nguyen 1, * , Stacey M. Bagby 1 , Gemma N. Jones 4 , WM. Tai 1, 3 , Kevin S. Quackenbush 1 , Anna Schreiber 1 , Wells A. Messersmith 1 , Kalpana M. Devaraj 2 , Patrick Blatchford 1 , S. Gail Eckhardt 1 , Elaine B. Cadogan 4 , Gareth D. Hughes 4 , Aaron Smith 4 , Todd M. Pitts 1 and John J. Arcaroli 1 1 Division of Medical Oncology, University of Colorado Anschutz Medical Campus and University of Colorado Cancer Center, Aurora, CO, USA 2 Pathology Department, University of Colorado Anschutz Medical Campus, Aurora, CO, USA 3 Division of Medical Oncology, National Cancer Centre Singapore, Singapore 4 Innovative Medicines and Early Development, Oncology, AstraZeneca, Cambridge, UK * These authors contributed equally to this work Correspondence to: John J. Arcaroli, email: john.arcaroli@ucdenver.edu Keywords: ATM; DNA damage; IRN; PDTX; CRC Received: August 06, 2017 Accepted: November 09, 2017 Published: December 05, 2017 ABSTRACT Irinotecan, a standard of care therapy for CRC, elicits cytotoxic effects by generating double strand breaks resulting in DNA damage. The activation of the ATM pathway plays a fundamental role in regulating the cellular response and repair to DNA damage. The objective of this preclinical study was to determine whether ATM inhibition would enhance sensitivity to irinotecan treatment. Treatment effects of AZ31, irinotecan or AZ31 + irinotecan were investigated in CRC cell lines and CRC patient derived xenografts. Activation of ATM and downstream targets p-RAD50 and p-H2AX were evaluated by immunohistochemistry. Combinational effects were demonstrated in 4 out of 8 CRC explants. Interestingly, each of the combinational sensitive CRC PDX models were shown to be more resistant to irinotecan single agent therapy. Treatment with irinotecan significantly elevated the ATM pathway evident by an increase in the activation of H2AX and RAD50. Combinational therapy reduced the activation of H2AX and RAD50 when compared to irinotecan alone in the combination sensitive CRC098. AZ31 + irinotecan was effective at reducing tumor growth in tumors that exhibited resistance to irinotecan in our CRC PDX model. These findings support further investigation of this combinational therapy for the treatment of CRC patients.

Ataxia telangiectasia mutated (ATM) kinase is a key factor in DNA double strand break response and is constitutively activated in glioblastoma, leading to marked radioresistance [Bartkova, Carruthers] and therefore an attractive radiosensitisation target in this disease. AZD1390, a potent ATM inhibitor optimized to cross the blood brain barrier, is being evaluated with radiotherapy in Phase 1 (NCT03423628). Positron emission tomography (PET) studies demonstrated AZD1390 brain exposure in healthy human subjects. This study characterises ATM inhibitor penetration and distribution in brain and GBM, as well as pharmacodynamic biomarker changes in human orthotopic GBM patient-derived explant (PDX) models. Radiation +/- AZD1390 treatment was evaluated for compound concentration in plasma and relative abundance in brain/ GBM regions by mass spectrometry imaging (MSI). Parallel samples were analysed by immunohistochemistry for biomarkers of DNA damage response and ATM signalling. We show AZD1390 penetrates brain tissue with preferential compound accumulation into tumour. Higher ratios of AZD1390 in GBM versus normal brain correlate with improved efficacy and greater levels of DNA damage. Moreover, AZD1390 in the GBM region was heterogeneously distributed with MSI characterized specific metabolic clusters having varied AZD1390 intensities. As expected, radiation treatment activated ATM signalling (indicated by increase in pRAD50 and γH2AX positive cells) which was effectively inhibited by AZD1390 co-treatment. Our work provides novel insights into ATM inhibitor pharmacokinetics in brain tumours and demonstrates the benefit of using MSI in conjunction with pharmacodynamic markers to provide a more complete picture of AZD1390 mechanism of action for future translational studies on clinical GBM samples. Citation Format: Lenka Oplustil O'Connor, Gregory Hamm, Maria Udriste, Stephanie Ling, Joanne Wilson, Steve Durant, Gareth Hughes, Sabina Cosulich, Wenlin Shao, Martin Pass, Gemma Jones, Andrew Pierce, Richard Goodwin, Mark O'Connor, Carl Barrett, Elizabeth Harrington. Characterization of ATM inhibitor (AZD1390) distribution and pharmacodynamic changes in brain and glioblastoma in preclinical models to inform on mechanism of action [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 6168.

Ceralasertib is a potent and selective ATP competitive inhibitor of ataxia telangiectasia and Rad3 related (ATR) in clinical development as monotherapy and in combination with olaparib (Lynparza) and durvalumab (Imfinzi) in patients with advanced solid tumors. Paired pre- and on-treatment tumour samples from seven patients during ceralasertib monotherapy in Phase 1 studies (NCT02223923, NCT02264678), all ATM expressing, showed increases in pRAD50 on treatment. This study aimed to robustly understand the relationship between ceralasertib pharmacokinetics, pRAD50 (pSer635) induction by immunohistochemistry and anti-tumor efficacy, in mouse xenografted models; to enable interpretation of paired clinical tumour samples. First, in vivo data were generated in a range of xenografted models (HBCx9 [TNBC, Xentech], HCC1806 [BC], OCI-Ly19 [DLBCL] and OE21 [HNSCC]) and NSCLC and HNSCC PDX models at Champions). Mouse ceralasertib doses (6.25 - 25mg/kg BID and 50mg/kg QD) reflected the observed free drug exposure achieved at clinical doses. In pharmacodynamic studies, animals were dosed continuously for 5 days, with PKPD endpoints being assessed on the 5th day. In anti-tumor studies, animals were randomized and treated for at least 28 days continuously. Increases in pRAD50 on treatment, versus control, were both dose and time dependent. There was a wide range of baseline pRAD50 expression (H-Scores ranging from 2 to 48) but the fold increase was consistent; a 3-fold increase being seen at the highest dose. Similarly, the anti-tumor activity was dose dependent with a range of sensitivities being observed across the models; the OCI-Ly19 model was most sensitive with %TGI ranging 43% to 104%. Mathematical modelling confirmed a consistent PKPD relationship for the fold increase of pRAD50. The effect was not saturated at the tested drug exposures and the slope relating drug in plasma to fold pRAD50 increases was estimated to be 0.75 uM-1. Modelling also demonstrated a relationship between pRAD50 and the observed anti-tumor activity, across all models. Of note, the fold induction required for efficacy increased with the baseline pRAD50 The hypothesis for this observation is that the baseline pRAD50 H-score is a functional measure of DDR signaling and so low pRAD50 may be indicative of impaired signaling and thus sensitivity to inhibition of DDR signaling. The results demonstrate the utility of generating PKPD-Efficacy relationships across a range of patient relevant xenografts and PDXs. Here, a marker of ATR inhibitor pharmacology, pRAD50, has been related to anti-tumor activity increasing our understanding of predictive markers of drug sensitivity. Clinical translation of these findings is being tested in a Phase I study, where patients provide paired tumour biopsies pre-treatment and following ceralasertib monotherapy dosing (NCT02264678). Citation Format: James William Thomas Yates, Zena Wilson, Gemma N. Jones, Kevin Harrington, Matthew Krebs, Magnus Dillon, Andrew J. Pierce, Emma Dean, Alan Lau. Quantification of the preclinical and clinical relationship between pRAD50 and efficacy after treatment with the ATR inhibitor ceralasertib (AZD6738) [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr LB-104.

Poor survival rates of patients with tumors arising from or disseminating into the brain are attributed to an inability to excise all tumor tissue (if operable), a lack of blood-brain barrier (BBB) penetration of chemotherapies/targeted agents, and an intrinsic tumor radio-/chemo-resistance. Ataxia-telangiectasia mutated (ATM) protein orchestrates the cellular DNA damage response (DDR) to cytotoxic DNA double-strand breaks induced by ionizing radiation (IR). ATM genetic ablation or pharmacological inhibition results in tumor cell hypersensitivity to IR. We report the primary pharmacology of the clinical-grade, exquisitely potent (cell IC50, 0.78 nM), highly selective [>10,000-fold over kinases within the same phosphatidylinositol 3-kinase–related kinase (PIKK) family], orally bioavailable ATM inhibitor AZD1390 specifically optimized for BBB penetration confirmed in cynomolgus monkey brain positron emission tomography (PET) imaging of microdosed 11C-labeled AZD1390 (Kp,uu, 0.33). AZD1390 blocks ATM-dependent DDR pathway activity and combines with radiation to induce G2 cell cycle phase accumulation, micronuclei, and apoptosis. AZD1390 radiosensitizes glioma and lung cancer cell lines, with p53 mutant glioma cells generally being more radiosensitized than wild type. In in vivo syngeneic and patient-derived glioma as well as orthotopic lung-brain metastatic models, AZD1390 dosed in combination with daily fractions of IR (whole-brain or stereotactic radiotherapy) significantly induced tumor regressions and increased animal survival compared to IR treatment alone. We established a pharmacokinetic-pharmacodynamic-efficacy relationship by correlating free brain concentrations, tumor phospho-ATM/phospho-Rad50 inhibition, apoptotic biomarker (cleaved caspase-3) induction, tumor regression, and survival. On the basis of the data presented here, AZD1390 is now in early clinical development for use as a radiosensitizer in central nervous system malignancies.

PARP1/2 inhibitors (PARPi) are the first approved targeted DNA damage response (DDR) inhibitors and have been shown to have clinical benefit, particularly in tumors harboring mutations in BRCA1/BRCA2 and other genes of homologous recombination repair (HRR). However, resistance to PARPi monotherapy will impact on both the breadth and depth of response. We showed that HRR-mutant TNBC and ovarian cancer patient-derived tumor xenograft (PDX) models frequently exhibit innate or acquired PARP inhibitor resistance and that this resistance is linked to a proficient or reactivated HRR, indicated by the ability to form RAD51 foci. A key component of PARPi mechanism of action results from trapping PARP onto DNA, which has the potential to generate replication stress. Moreover, recent data demonstrate that PARP1, along with components of the HRR, are associated with the re-start and protection of stalled replication forks. Here, we assessed whether combinations of the PARPi olaparib together with inhibitors of the replication stress response (RSR) could reverse PARPi resistance in our PDX cohort and we analyzed the effects on RSR by immunofluorescence and immunoblotting. Our data demonstrate that 7/27 models exhibit WEE1i (AZD1775) single agent activity measured as tumor regressions (≤ -30% change in tumor volume), all of which were PARPi resistant. Of the PARPi and WEE1i resistant models, 5 responded to combination treatment and demonstrated a significant increase in the RSR markers pRPA32 and pan-γH2AX compared to either single agent treatment alone. For monotherapy ATRi treatment, there were three models showing tumor regression with AZD6738, all harbored ATM mutations, two also responding to WEE1i monotherapy and one responded to olaparib monotherapy. There were an additional two models that responded to the combination of PARPi plus ATRi, and one of these also responded to the WEE1i/PARPi combination. Together, our analysis demonstrates that by targeting the replication stress response we could cause tumor regression in 13/20 PARPi resistant PDX models and in 6 of these cases the response required PARP inhibition, with DDR signalling indicating that the PARPi was impacting on the RSR. Further insights will be presented into which genetic backgrounds and acquired PARPi resistant mechanisms are reversed by targeting either WEE1 or ATR, thus highlighting the potential for how PARPi resistance can be reversed by targeting alternative DDR dependencies. Citation Format: Mark J. O'Connor, Cristina Cruz, Marta Castroviejo-Bermejo, Urszula M. Polanska, Gemma N. Jones, Anderson Wang, Zhongwu Lai, Josep Forment, Krishna Bulusu, Alba Llop-Guevara, Brian Dougherty, Cristina Saura, Rachel Brough, Chris J. Lord, Alejandra Bruna, Carlos Caldas, Stephen Fawell, J Carl Barrett, Susan E. Critchlow, Judith Balmaña, Elaine Cadogan, Violeta Serra. Reversing PARP inhibitor resistance by targeting the replication stress response [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 932.

Osteogenesis imperfecta (OI) is a genetic bone pathology with prenatal onset, characterized by brittle bones in response to abnormal collagen composition. There is presently no cure for OI. We previously showed that human first trimester fetal blood mesenchymal stem cells (MSCs) transplanted into a murine OI model (oim mice) improved the phenotype. However, the clinical use of fetal MSC is constrained by their limited number and low availability. In contrast, human fetal early chorionic stem cells (e-CSC) can be used without ethical restrictions and isolated in high numbers from the placenta during ongoing pregnancy. Here, we show that intraperitoneal injection of e-CSC in oim neonates reduced fractures, increased bone ductility and bone volume (BV), increased the numbers of hypertrophic chondrocytes, and upregulated endogenous genes involved in endochondral and intramembranous ossification. Exogenous cells preferentially homed to long bone epiphyses, expressed osteoblast genes, and produced collagen COL1A2. Together, our data suggest that exogenous cells decrease bone brittleness and BV by directly differentiating to osteoblasts and indirectly stimulating host chondrogenesis and osteogenesis. In conclusion, the placenta is a practical source of stem cells for the treatment of OI.

Induced pluripotent stem cells (iPSCs) with potential for therapeutic applications can be derived from somatic cells via ectopic expression of a set of limited and defined transcription factors. However, due to risks of random integration of the reprogramming transgenes into the host genome, the low efficiency of the process, and the potential risk of virally induced tumorigenicity, alternative methods have been developed to generate pluripotent cells using nonintegrating systems, albeit with limited success. Here, we show that c-KIT+ human first-trimester amniotic fluid stem cells (AFSCs) can be fully reprogrammed to pluripotency without ectopic factors, by culture on Matrigel in human embryonic stem cell (hESC) medium supplemented with the histone deacetylase inhibitor (HDACi) valproic acid (VPA). The cells share 82% transcriptome identity with hESCs and are capable of forming embryoid bodies (EBs) in vitro and teratomas in vivo. After long-term expansion, they maintain genetic stability, protein level expression of key pluripotency factors, high cell-division kinetics, telomerase activity, repression of X-inactivation, and capacity to differentiate into lineages of the three germ layers, such as definitive endoderm, hepatocytes, bone, fat, cartilage, neurons, and oligodendrocytes. We conclude that AFSC can be utilized for cell banking of patient-specific pluripotent cells for potential applications in allogeneic cellular replacement therapies, pharmaceutical screening, and disease modeling. ispartof: Molecular Therapy vol:20 issue:10 pages:1953-1967 ispartof: location:United States status: published

Stem cells have considerable potential to repair damaged organs and tissues. We previously showed that prenatal transplantation of human first trimester fetal blood mesenchymal stem cells (hfMSCs) in a mouse model of osteogenesis imperfecta (oim mice) led to a phenotypic improvement, with a marked decrease in fracture rate. Donor cells differentiated into mature osteoblasts, producing bone proteins and minerals, including collagen type Iα2, which is absent in nontransplanted mice. This led to modifications of the bone matrix and subsequent decrease of bone brittleness, indicating that grafted cells directly contribute to improvement of bone mechanical properties. Nevertheless, the therapeutic effect was incomplete, attributing to the limited level of engraftment in bone. In this study, we show that although migration of hfMSCs to bone and bone marrow is CXCR4-SDF1 (SDF1 is stromal-derived factor) dependent, only a small number of cells present CXCR4 on the cell surface despite high levels of internal CXCR4. Priming with SDF1, however, upregulates CXCR4 to increase the CXCR4+ cell fraction, improving chemotaxis in vitro and enhancing engraftment in vivo at least threefold in both oim and wild-type bone and bone marrow. Higher engraftment in oim bones was associated with decreased bone brittleness. This strategy represents a step to improve the therapeutic benefits of fetal cell therapy toward being curative.

2538Background: Knowledge of the success rates in obtaining baseline and on treatment tumour biopsies with sufficient evaluable tumour tissue is valuable in guiding strategies for evaluation of PD ...

5561Background: Patients with advanced high grade serous ovarian cancer (SOC) who undergo a suboptimal debulking primary surgery typically have adverse clinical outcomes. However, a spectrum of sen...

ATM plays a central role in the detection, signalling, and repair of DNA double-strand breaks (DSB), the most cytotoxic lesion induced by ionizing radiation (IR) and certain chemotherapies. ATM is also activated by reactive oxygen species (ROS) induced by cellular exposures to IR. Genetic ablation and pharmacologic inhibition of ATM is associated with extreme hypersensitivity of glioblastoma multiforme (GBM) tumor cells to IR, especially those with checkpoint defects such as p53 abrogations. GBM is the most common and lethal form of brain tumor. Median survival of patients is 12-15 months, despite surgery, fractionated radiotherapy, and temozolomide standard of care. Poor survival is attributed to an inability to excise all tumor tissue (if operable), dissemination of disease into regions with an intact blood-brain barrier (BBB), and an intrinsic radio- and chemo-resistance. With ATM activity robustly upregulated in GBM stem cells, ATM represents an attractive radiosensitization target. Here, we describe the activity of AZD1390, a potent, selective, and orally bioavailable ATM inhibitor optimized for BBB penetration in preclinical model species. AZD1390 demonstrates exquisitely potent cellular inhibition of ATM activity (IC50 0.78 nM) with >1000-fold activity over closely related (PIKKs) and distant kinases. We confirm target and pathway engagement by Western blot and imaging pan-nuclear and discreet pATM foci staining (IC50 0.6-3nM). Radiosensitization of a panel of GBM cell lines and NCI-H2228 lung cells was confirmed in antiproliferation and clonogenic assays (IC50 3 nM). DEF37 of 2.7 was seen in p53 mutant GBM cells dosed at 3nM and p53 mutant GBM cell lines were more radiosensitized than wild type cells. Radiosensitization was confirmed in vivo in mouse orthotopic NCI-H2228 lung tumor models implanted directly into brain or via carotid artery injection showing dose-dependent tumor growth inhibition and remarkable increases in survival of mice when dosing AZD1390 PO an hour before four daily fractions of 2.5 Gy IR to the whole head. 20 mg/kg QD or BID gave the best survival benefit that correlated with bioluminescent tumor growth inhibition. Doses lower than 2 mg/kg were not efficacious, suggesting free brain PK cover over ATM IC50 of 3 hours or more are required for efficacy. Efficacy was also achieved in a dose-dependent manner in orthotopic GL261 murine GBM syngeneic models dosed in combination with either whole head radiotherapy or stereotactic beam radiotherapy. A PK PD efficacy relationship was establish by correlating AZD1390 free brain PK levels, phospho-ATM/Rad50 detection in tumor by IHC, and tumor growth inhibition and survival. Significant brain exposure was observed in a nonhuman primate PET study utilizing 11C-labelled AZD1390, further supporting the ability of the compound to efficiently cross the BBB. With confirmation that AZD1390 is not a substrate for human efflux transporters and having favorable pharmacokinetic and pharmacodynamic properties, AZD1390 is now in early clinical development for use as a radiosensitizer in central nervous system malignancies. Citation Format: Steve T. Durant, Kurt G. Pike, Nicola Colclough, Lucy Riches, Antonio Garcia-Trinidad, Thomas Hunt, Stephanie Ling, Jonathan Stott, Ian Barrett, Li Zheng, Yingchun Wang, Kan Chen, Tianwei Zhang, Venkatesh Pilla Reddy, Andrew Sykes, Peter Johnstrom, Gemma Jones, Andrew Pierce, Jeremy Karlin, Jenna Kahn, Jasmine Allen, Kristoffer Valerie, Ruth Illingworth, Martin Pass. AZD1390, a potent and selective orally bioavailable blood-brain barrier-penetrant ATM inhibitor, radiosensitizes and improves survival of orthotopic glioma and metastatic brain tumor models [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr A104.

Human mid-trimester amniotic fluid stem cells (AFSC) have promising applications in regenerative medicine, being broadly multipotent with an intermediate phenotype between embryonic (ES) and mesenchymal stem cells (MSC). Despite this propluripotent phenotype, AFSC are usually cultured in adherence in a serum-based expansion medium, and how expansion in conditions sustaining pluripotency might affect their phenotype remains unknown. We recently showed that early AFSC from first trimester amniotic fluid, which endogenously express Sox2 and Klf4, can be reprogrammed to pluripotency without viral vectors using the histone deacetylase inhibitor valproic acid (VPA). Here, we show that mid-trimester AFSC cultured under MSC conditions contained a subset of cells endogenously expressing telomerase, CD24, OCT4, C-MYC, and SSEA4, but low/null levels of SOX2, NANOG, KLF4, SSEA3, TRA-1-60, and TRA-1-81, with cells unable to form embryoid bodies (EBs) or teratomas. In contrast, AFSC cultured under human ESC conditions were smaller in size, grew faster, formed colonies, upregulated OCT4 and C-MYC, and expressed KLF4 and SOX2, but not NANOG, SSEA3, TRA-1-60, and TRA-1-81. Supplementation with VPA for 5 days further upregulated OCT4, KLF4, and SOX2, and induced expression of NANOG, SSEA3, TRA-1-60, and TRA-1-81, with cells now able to form EBs and teratomas. We conclude that human mid-trimester AFSC, which may be isolated autologously during pregnancy without ethics restriction, can acquire pluripotent characteristics without the use of ectopic factors. Our data suggest that this medium-dependant approach to pluripotent mid-trimester AFSC reflects true reprogramming and not the selection of prepluripotent cells.

Foetal stem cells (FSCs) can be isolated during gestation from many different tissues such as blood, liver and bone marrow as well as from a variety of extraembryonic tissues such as amniotic fluid and placenta. Strong evidence suggests that these cells differ on many biological aspects such as growth kinetics, morphology, immunophenotype, differentiation potential and engraftment capacityin vivo. Despite these differences, FSCs appear to be more primitive and have greater multi-potentiality than their adult counterparts. For example, foetal blood haemopoietic stem cells proliferate more rapidly than those found in cord blood or adult bone marrow. These features have led to FSCs being investigated for pre- and post-natal cell therapy and regenerative medicine applications. The cells have been used in pre-clinical studies to treat a wide range of diseases such as skeletal dysplasia, diaphragmatic hernia and respiratory failure, white matter damage, renal pathologies as well as cancers. Their intermediate state between adult and embryonic stem cells also makes them an ideal candidate for reprogramming to the pluripotent status.