Discovery and Preclinical Characterization of GSK1278863 (Daprodustat), a Small Molecule Hypoxia Inducible Factor-Prolyl Hydroxylase Inhibitor for Anemia.

Decreased erythropoietin (EPO) production, shortened erythrocyte survival, and other factors reducing the response to EPO contribute to anemia in patients who have a variety of underlying pathologies such as chronic kidney disease. Treatment with recombinant human EPO (rHuEPO) at supraphysiologic concentrations has proven to be efficacious. However, it does not ameliorate the condition in all patients, and it presents its own risks, including cardiovascular complications. The transcription factors hypoxia-inducible factor (HIF) 1α and HIF2α control the physiologic response to hypoxia and invoke a program of increased erythropoiesis. Levels of HIFα are modulated by oxygen tension via the action of a family of HIF-prolyl hydroxylases (PHDs), which tag HIFα for proteasomal degradation. Inhibition of these PHDs simulates conditions of mild hypoxia, leading to a potentially more physiologic erythropoietic response and presenting a potential alternative to high doses of rHuEPO. Here we describe the discovery and characterization of GSK1278863 [2-(1,3-dicyclohexyl-6-hydroxy-2,4-dioxo-1,2,3,4-tetrahydropyrimidine-5-carboxamido) acetic acid], a pyrimidinetrione-glycinamide low nanomolar inhibitor of PHDs 1-3 that stabilizes HIFα in cell lines, resulting in the production of increased levels of EPO. In normal mice, a single dose of GSK1278863 induced significant increases in circulating plasma EPO but only minimal increases in plasma vascular endothelial growth factor (VEGF-A) concentrations. GSK1278863 significantly increased reticulocytes and red cell mass parameters in preclinical species after once-daily oral administration and has demonstrated an acceptable nonclinical toxicity profile, supporting continued clinical development. GSK1278863 is currently in phase 3 clinical trials for treatment of anemia in patients with chronic kidney disease.

Rational Design, Synthesis, and SAR of a Novel Thiazolopyrimidinone Series of Selective PI3K-beta Inhibitors.

A novel thiazolopyrimidinone series of PI3K-beta selective inhibitors has been identified. This chemotype has provided an excellent tool compound, 18, that showed potent growth inhibition in the PTEN-deficient breast cancer cell line MDA-MB-468 under anchorage-independent conditions, and it also demonstrated pharmacodynamic effects and efficacy in a PTEN-deficient prostate cancer PC-3 xenograft mouse model.

Chronic inhibition of hypoxia-inducible factor prolyl 4-hydroxylase improves ventricular performance, remodeling, and vascularity after myocardial infarction in the rat.

BACKGROUND: Hypoxia inducible factors (HIFs) are transcription factors that are regulated by HIF-prolyl 4-hydroxylases (PHDs) in response to changes in oxygen tension. Once activated, HIFs play an important role in angiogenesis, erythropoiesis, proliferation, cell survival, inflammation, and energy metabolism. We hypothesized that GSK360A, a novel orally active HIF-PHD inhibitor, could facilitate local and systemic HIF-1 alpha signaling and protect the failing heart after myocardial infarction (MI). METHODS AND RESULTS: GSK360A is a potent (nanomolar) inhibitor of HIF-PHDs (PHD1>PHD2 = PHD3) capable of activating the HIF-1 alpha pathway in a variety of cell types including neonatal rat ventricular myocytes and H9C2 cells. Male rats treated orally with GSK360A (30 mg x kg x d) had a sustained elevation in circulating levels of erythropoietin and hemoglobin and increased hemoxygenase-1 expression in the heart and skeletal muscle. In a rat model of established heart failure with systolic dysfunction induced by ligation of left anterior descending coronary artery, chronic treatment with GSK360A for 28 days prevented the progressive reduction in ejection fraction, ventricular dilation, and increased lung weight, which were observed in the vehicle-treated animals, for up to 3 months. In addition, the microvascular density in the periinfarct region was increased (>2-fold) in GSK360A-treated animals. Treatment was well tolerated (survival was 89% in the GSK360A group vs. 82% in the placebo group). CONCLUSIONS: Chronic post-myocardial infarction treatment with a selective HIF PHD inhibitor (GSK360A) exerts systemic and local effects by stabilizing HIF-1 alpha signaling and improves long-term ventricular function, remodeling, and vascularity in a model of established ventricular dysfunction. These results suggest that HIF-PHD inhibitors may be suitable for the treatment of post-MI remodeling and heart failure.

Emerging principles for the development of resistance to antihormonal therapy: implications for the clinical utility of fulvestrant.

We seek to evaluate the clinical consequences of resistance to antihormonal therapy by studying analogous animal xenograft models. Two approaches were taken: (1) MCF-7 tumors were serially transplanted into selective estrogen receptor modulator (SERM)-treated immunocompromised mice to mimic 5 years of SERM treatment. The studies in vivo were designed to replicate the development of acquired resistance to SERMs over years of clinical exposure. (2) MCF-7 cells were cultured long-term under SERM-treated or estrogen withdrawn conditions (to mimic aromatase inhibitors), and then injected into mice to generate endocrine-resistant xenografts. These tumor models have allowed us to define Phase I and Phase II antihormonal resistance according to their responses to E(2) and fulvestrant. Phase I SERM-resistant tumors were growth stimulated in response to estradiol (E(2)), but paradoxically, Phase II SERM and estrogen withdrawn-resistant tumors were growth inhibited by E(2). Fulvestrant did not support growth of Phases I and II SERM-resistant tumors, but did allow growth of Phase II estrogen withdrawn-resistant tumors. Importantly, fulvestrant plus E(2) in Phase II antihormone-resistant tumors reversed the E(2)-induced inhibition and instead resulted in growth stimulation. These data have important clinical implications. Based on these and prior laboratory findings, we propose a clinical strategy for optimal third-line therapy: patients who have responded to and then failed at least two antihormonal treatments may respond favorably to short-term low-dose estrogen due to E(2)-induced apoptosis, followed by treatment with fulvestrant plus an aromatase inhibitor to maintain low tumor burden and avoid a negative interaction between physiologic E(2) and fulvestrant.

Estrogen receptors as therapeutic targets in breast cancer.

The estrogen receptor alpha (ERalpha) has proven to be the single most important target in breast cancer over the last 30 years. The use of the selective ER modulator (SERM) tamoxifen for the treatment and prevention of breast cancer has changed therapeutics. The SERM raloxifene, approved for the treatment of osteoporosis, lacks tamoxifen's increased risk for endometrial cancer and is being evaluated for the prevention of breast cancer. Other SERMs approved or under development for use against breast cancer or osteoporosis include toremifene, GW5638, GW7604 (the active metabolite of GW5638), idoxifene, lasofoxifene, arzoxifene, bazedoxifene, EM-800 and acolbifene (the active metabolite of EM-800). Aromatase inhibitors (AIs) have recently proven to be more efficacious than tamoxifen as first-line therapy, efficacious for second-line therapy (e.g. against tamoxifen-resistant disease), and useful for extended adjuvant therapy after tamoxifen. The AIs include the non-steroidal agents letrozole and anastrole, and the steroidal agent exemestane. The pure antiestrogen fulvestrant has proven to be just as effective as AIs. Other pure antiestrogens, ZK-703, ZK-253, RU 58668 and TAS-108 show great promise. The development of resistance to endocrine therapy remains a clinically important problem, and laboratory models based on human breast cancer cells grown as tumors in immune-compromised mice have led to important insights into this problem. Progesterone receptor-negative status of ER-positive breast cancers may reflect altered growth factor receptor signaling, and helps to explain why this subclass of tumors exhibits lower response rates to tamoxifen compared to cancers typed progesterone receptor-positive. Crosstalk among plasma membrane-localized ER, growth factor receptor signaling, and nuclear-localized ER provide further insights into antihormonal-resistant breast cancer.

Methylguanine methyltransferase activity deficiency in immature rat mammary epithelial cells parallels increased carcinogenic susceptibility.

The prepubertal breast is more susceptible than the mature breast to the carcinogenic effects of ionizing radiation, and potentially to cigarette smoke and alkylating chemotherapeutics. Mammary epithelial cells (MECs) from sexually immature (3-week (wk)-old) Fischer 344 rats were more sensitive than mature (8-wk-old) rats to the carcinogenic, lethal, and mutagenic effects of N-nitroso-N-methylurea (NMU). The work reported here was undertaken to better define this age-specific susceptibility of the mammary gland to NMU. Using the alkaline comet assay, it was found that MECs from immature but not mature rats displayed an increase in single-strand DNA breaks or alkali-labile lesions 2 h following NMU treatment. Hoechst staining indicated apoptosis was not responsible for the increase. Inhibition of methylguanine methyltransferase (MGMT) did not affect immature MECs but caused mature MECs to recapitulate the immature response to NMU. Direct measurement of MGMT activity revealed that immature MECs are significantly deficient in MGMT activity relative to mature MECs. MECs had the lowest MGMT activity of all organs tested. Immature kidneys, which preferentially developed nephroblastomas after NMU treatment, also displayed significantly lower MGMT activity than mature kidneys. These results suggest that age-related differences in MGMT activity may play a significant role in age-differential susceptibility to rat mammary gland and kidney carcinogenesis, and argue the importance of extending these studies to humans. They also provide a mechanistic basis for studying, as potentially initiating events in breast cancer, exposures of prepubertal girls to alkylating agents, to which humans are exposed in cigarette smoke, the diet, and as chemotherapy.

Mammary glands of sexually immature rats are more susceptible than those of mature rats to the carcinogenic, lethal, and mutagenic effects of N-nitroso-N-methylurea.

Knowing that the prepubertal period is a time of enhanced susceptibility for radiation-induced human breast cancer, we used the Fischer 344 rat model to explore the age-differential susceptibility of the mammary gland to the carcinogenic, lethal, and mutagenic effects of two structurally diverse chemical carcinogens, N-nitroso-N-methylurea (NMU), and 7,12-dimethylbenz(a)anthracene (DMBA). Mammary carcinoma incidences and multiplicities were significantly greater in immature than mature NMU-treated rats while mammary carcinoma incidences and multiplicities were significantly lower in immature than mature DMBA-treated rats. The survival of mammary clonogens of mature NMU-treated rats in limiting dilution transplantation assays was greater than that of the survival of mammary clonogens of immature NMU-treated rats. No differences were found in the survival of mammary cells from immature and mature rats exposed to DMBA. Although there were no mutation spectra differences, mammary epithelial cells of immature NMU-treated rats had greater mutation frequencies than those of mature NMU-treated rats. Together these results support the hypothesis that the mammary gland of immature rats is more susceptible to the carcinogenic, lethal, and mutagenic effects of alkylating agents represented by NMU in a carcinogen-class-specific manner. Further, the results suggest the importance of mechanistic and epidemiological studies of the susceptibility of the prepubertal breast to specific carcinogens such as alkylating agents.