Background 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.Patients and methodsWe 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.ResultsRAD51 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.ConclusionDetection 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.

DNA-dependent protein kinase (DNA-PK) is a critical player in the DNA damage response (DDR) and instrumental in the non-homologous end-joining pathway (NHEJ) used to detect and repair DNA double-strand breaks (DSBs). We demonstrate that the potent and highly selective DNA-PK inhibitor, AZD7648, is an efficient sensitizer of radiation- and doxorubicin-induced DNA damage, with combinations in xenograft and patient-derived xenograft (PDX) models inducing sustained regressions. Using ATM-deficient cells, we demonstrate that AZD7648, in combination with the PARP inhibitor olaparib, increases genomic instability, resulting in cell growth inhibition and apoptosis. AZD7648 enhanced olaparib efficacy across a range of doses and schedules in xenograft and PDX models, enabling sustained tumour regression and providing a clear rationale for its clinical investigation. Through its differentiated mechanism of action as an NHEJ inhibitor, AZD7648 complements the current armamentarium of DDR-targeted agents and has potential in combination with these agents to achieve deeper responses to current therapies.

Efforts to apply nanotechnology in cancer have focused almost exclusively on the delivery of cytotoxic drugs to improve therapeutic index. There has been little consideration of molecularly targeted agents, in particular kinase inhibitors, which can also present considerable therapeutic index limitations. We describe the development of Accurin polymeric nanoparticles that encapsulate the clinical candidate AZD2811, an Aurora B kinase inhibitor, using an ion pairing approach. Accurins increase biodistribution to tumor sites and provide extended release of encapsulated drug payloads. AZD2811 nanoparticles containing pharmaceutically acceptable organic acids as ion pairing agents displayed continuous drug release for more than 1 week in vitro and a corresponding extended pharmacodynamic reduction of tumor phosphorylated histone H3 levels in vivo for up to 96 hours after a single administration. A specific AZD2811 nanoparticle formulation profile showed accumulation and retention in tumors with minimal impact on bone marrow pathology, and resulted in lower toxicity and increased efficacy in multiple tumor models at half the dose intensity of AZD1152, a water-soluble prodrug of AZD2811. These studies demonstrate that AZD2811 can be formulated in nanoparticles using ion pairing agents to give improved efficacy and tolerability in preclinical models with less frequent dosing. Accurins specifically, and nanotechnology in general, can increase the therapeutic index of molecularly targeted agents, including kinase inhibitors targeting cell cycle and oncogenic signal transduction pathways, which have to date proved toxic in humans.

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, cellcycle 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).

Introduced in 1987, platinum-based chemotherapy remains standard of care for small cell lung cancer (SCLC), a most aggressive, recalcitrant tumor. Prominent barriers to progress are paucity of tumor tissue to identify drug targets and patient-relevant models to interrogate novel therapies. Following our development of circulating tumor cell patient-derived explants (CDX) as models that faithfully mirror patient disease, here we exploit CDX to examine new therapeutic options for SCLC. We investigated the efficacy of the PARP inhibitor olaparib alone or in combination with the WEE1 kinase inhibitor AZD1775 in 10 phenotypically distinct SCLC CDX and/or These CDX represent chemosensitive and chemorefractory disease including the first reported paired CDX generated longitudinally before treatment and upon disease progression. There was a heterogeneous depth and duration of response to olaparib/AZD1775 that diminished when tested at disease progression. However, efficacy of this combination consistently exceeded that of cisplatin/etoposide, with cures in one CDX model. Genomic and protein analyses revealed defects in homologous recombination repair genes and oncogenes that induce replication stress (such as MYC family members), predisposed CDX to combined olaparib/AZD1775 sensitivity, although universal predictors of response were not noted. These preclinical data provide a strong rationale to trial this combination in the clinic informed by prevalent, readily accessed circulating tumor cell-based biomarkers. New therapies will be evaluated in SCLC patients after first-line chemotherapy, and our data suggest that the combination of olaparib/AZD1775 should be used as early as possible and before disease relapse. .

ATM inhibitors, such as 7, have demonstrated the antitumor potential of ATM inhibition when combined with DNA double-strand break-inducing agents in mouse xenograft models. However, the properties of 7 result in a relatively high predicted clinically efficacious dose. In an attempt to minimize attrition during clinical development, we sought to identify ATM inhibitors with a low predicted clinical dose (<50 mg) and focused on strategies to increase both ATM potency and predicted human pharmacokinetic half-life (predominantly through the increase of volume of distribution). These efforts resulted in the discovery of 64 (AZD0156), an exceptionally potent and selective inhibitor of ATM based on an imidazo[4,5- c]quinolin-2-one core. 64 has good preclinical phamacokinetics, a low predicted clinical dose, and a high maximum absorbable dose. 64 has been shown to potentiate the efficacy of the approved drugs irinotecan and olaparib in disease relevant mouse models and is currently undergoing clinical evaluation with these agents.

We conclude that an MPO inhibitor is able to stop progression of emphysema and small airway remodeling and to partially protect against pulmonary hypertension, even when treatment starts relatively late in the course of long-term smoke exposure, suggesting that inhibition of MPO may be a novel and useful therapeutic treatment for COPD. Protection appears to relate to inhibition of oxidative damage and down-regulation of the smoke-induced inflammatory response.

Chronic hypercapnia is commonly found in patients with severe hypoxic lung disease and is associated with a greater elevation of pulmonary arterial pressure than that due to hypoxia alone. We hypothesized that hypercapnia worsens hypoxic pulmonary hypertension by augmenting pulmonary vascular remodeling and hypoxic pulmonary vasoconstriction (HPV). Rats were exposed to chronic hypoxia [inspiratory O(2) fraction (FI(O(2))) = 0.10], chronic hypercapnia (inspiratory CO(2) fraction = 0.10), hypoxia-hypercapnia (FI(O(2)) = 0.10, inspiratory CO(2) fraction = 0.10), or room air. After 1 and 3 wk of exposure, muscularization of resistance blood vessels and hypoxia-induced hematocrit elevation were significantly inhibited in hypoxia-hypercapnia compared with hypoxia alone (P < 0.001, ANOVA). Right ventricular hypertrophy was reduced in hypoxia-hypercapnia compared with hypoxia at 3 wk (P < 0.001, ANOVA). In isolated, ventilated, blood-perfused lungs, basal pulmonary arterial pressure after 1 wk of exposure to hypoxia (20.1 +/- 1.8 mmHg) was significantly (P < 0.01, ANOVA) elevated compared with control conditions (12.1 +/- 0.1 mmHg) but was not altered in hypoxia-hypercapnia (13.5 +/- 0.9 mmHg) or hypercapnia (11.8 +/- 1.3 mmHg). HPV (FI(O(2)) = 0.03) was attenuated in hypoxia, hypoxia-hypercapnia, and hypercapnia compared with control (P < 0.05, ANOVA). Addition of N(omega)-nitro-L-arginine methyl ester (10(-4) M), which augmented HPV in control, hypoxia, and hypercapnia, significantly reduced HPV in hypoxia-hypercapnia. Chronic hypoxia caused impaired endothelium-dependent relaxation in isolated pulmonary arteries, but coexistent hypercapnia partially protected against this effect. These findings suggest that coexistent hypercapnia inhibits hypoxia-induced pulmonary vascular remodeling and right ventricular hypertrophy, reduces HPV, and protects against hypoxia-induced impairment of endothelial function.