The defect chemistry of polycrystalline SrTiO3 has been studied by means of the equilibrium electrical conductivity as a function of temperature, oxygen activity, Sr/Ti ratio, and impurity additions. Reduction, excess TiO2 , and acceptor impurities all contribute to the oxygen vacancy content and their effects are therefore highly interdependent. The effect of added donor‐impurities,e.g., 500 ppm Nb, is highly dependent on the presence and amount of excess TiO2 .

Equilibrium electrical conductivity data for large-grained, polycrystalline, undoped BaTi03, as a function of temperature, 750" to lOOO"C, and oxygen partial pressure, 10-20

Nb-doped BaTi03 has been prepared with various Ba/(Ti +Nb) ratios such that single-phase products will be obtained if the charged donor center is assumed to be compensated in turn by Ba vacancies, Ti vacancies, equal concentrations of the two cation vacancies, oxygen interstitials, or electrons. For air-fired samples, examination by transmission electron microscopy showed that only the composition adjusted for compensation by titanium vacancies was single phase. The other compositions contained a Ti-rich second phase in order to achieve a matrix with the appropriate concentration of titanium vacancies. When sintered in a reducing atmosphere, compensation was by electrons, and a Ba-rich second phase was present in the composition adjusted to give compensation by titanium vacancies, The results indicate that for donor concentrations greater than ~0 . 5 mol% in BaTiO,, charge compensation is achieved by Ti vacancies under oxidizing conditions, and by electrons (as is well-known) under reducing conditions. The effect of compensating defects on grain growth is also discussed.

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The effect of added Al, as an acceptor impurity, on the equilibrium electrical conductivity of large-grained, polycrystalline BaTiO,, is consistent with a previously proposed defect model which involves only doubly ionized oxygen vacancies, electrons, holes, and acceptor impurities. The behavior is an extension of that of undoped BaTiO,, in which an accidental net acceptor excess already plays an important role. Comparison of the derived active acceptor content with the amount of added Al indicates that A1 is <50% effective in creating acceptor levels. The magnitude of a small Po,-independent conductivity component, necessary to fit the observed conductivity minima, increases with added A1 content. This is consistent with a contribution from extrinsic oxygen vacancy conduction.

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Resistance to androgen receptor (AR) blockade in castration-resistant prostate cancer (CRPC) is associated with sustained AR signaling, including through alternative splicing of AR (AR-SV). Inhibitors of transcriptional coactivators that regulate AR activity, including the paralog histone acetyltransferase proteins p300 and CBP, are attractive therapeutic targets for lethal prostate cancer. Herein, we validate targeting p300/CBP as a therapeutic strategy for lethal prostate cancer and describe CCS1477, a novel small-molecule inhibitor of the p300/CBP conserved bromodomain. We show that CCS1477 inhibits cell proliferation in prostate cancer cell lines and decreases AR- and C-MYC–regulated gene expression. In AR-SV–driven models, CCS1477 has antitumor activity, regulating AR and C-MYC signaling. Early clinical studies suggest that CCS1477 modulates KLK3 blood levels and regulates CRPC biopsy biomarker expression. Overall, CCS1477 shows promise for the treatment of patients with advanced prostate cancer. Significance: Treating CRPC remains challenging due to persistent AR signaling. Inhibiting transcriptional AR coactivators is an attractive therapeutic strategy. CCS1477, an inhibitor of p300/CBP, inhibits growth and AR activity in CRPC models, and can affect metastatic CRPC target expression in serial clinical biopsies. See related commentary by Rasool et al., p. 1011. This article is highlighted in the In This Issue feature, p. 995