Daqing Sun

Adenosine is a determinant of metabolic control of organ function increasing oxygen supply through the A2 class of adenosine receptors and reducing oxygen demand through A1 adenosine receptors (A1AR). In the kidney, activation of A1AR in afferent glomerular arterioles has been suggested to contribute to tubuloglomerular feedback (TGF), the vasoconstriction elicited by elevations in [NaCl] in the macula densa region of the nephron. To further elucidate the role of A1AR in TGF, we have generated mice in which the entire A1AR coding sequence was deleted by homologous recombination. Homozygous A1AR mutants that do not express A1AR mRNA transcripts and do not respond to A1AR agonists are viable and without gross anatomical abnormalities. Plasma and urinary electrolytes were not different between genotypes. Likewise, arterial blood pressure, heart rates, and glomerular filtration rates were indistinguishable between A1AR(+/+), A1AR(+/-), and A1AR(-/-) mice. TGF responses to an increase in loop of Henle flow rate from 0 to 30 nl/min, whether determined as change of stop flow pressure or early proximal flow rate, were completely abolished in A1AR(-/-) mice (stop flow pressure response, -6.8 +/- 0.55 mmHg and -0.4 +/- 0.2 in A1AR(+/+) and A1AR(-/-) mice; early proximal flow rate response, -3.4 +/- 0.4 nl/min and +0.02 +/- 0.3 nl/min in A1AR(+/+) and A1AR(-/-) mice). Absence of TGF responses in A1AR-deficient mice suggests that adenosine is a required constituent of the juxtaglomerular signaling pathway. A1AR null mutant mice are a promising tool to study the functional role of A1AR in different target tissues.

We recently reported the discovery of AM-8553 (1), a potent and selective piperidinone inhibitor of the MDM2–p53 interaction. Continued research investigation of the N-alkyl substituent of this series, focused in particular on a previously underutilized interaction in a shallow cleft on the MDM2 surface, led to the discovery of a one-carbon tethered sulfone which gave rise to substantial improvements in biochemical and cellular potency. Further investigation produced AMG 232 (2), which is currently being evaluated in human clinical trials for the treatment of cancer. Compound 2 is an extremely potent MDM2 inhibitor (SPR KD = 0.045 nM, SJSA-1 EdU IC50 = 9.1 nM), with remarkable pharmacokinetic properties and in vivo antitumor activity in the SJSA-1 osteosarcoma xenograft model (ED50 = 9.1 mg/kg).

Megakaryocyte growth and development factor (MGDF) administered intraperitoneally (IP) to mice causes a dose-dependent thrombocytosis accompanied by a decrease in mean platelet volume. MGDF increases the number of megakaryocytes in the bone marrow and spleen. MGDF does not affect the circulating number of leukocytes. Carboplatin, a chemotherapeutic agent that causes thrombocytopenia in humans, administered to mice as a single IP injection at a nonlethal dose causes a significant, but reversible thrombocytopenia. The carboplatin-induced thrombocytopenia is accompanied by an increase in circulating endogenous MGDF that precedes the return of circulating platelets to a normal level. MGDF mRNA is constitutively present in the liver. After carboplatin treatment, hepatic MGDF mRNA does not increase in concordance with circulating MGDF. Circulating soluble MGDF receptor levels (c-mpl) do not change significantly during the course of carboplatin-induced thrombocytopenia. MGDF injected IP once daily beginning 1 day after injection of carboplatin reverses carboplatin-induced thrombocytopenia in a dose-dependent fashion. The normalization of circulating platelet numbers in carboplatin plus MGDF-treated mice is accompanied by a normalization of megakaryocyte numbers in the bone marrow. In conclusion, MGDF, by increasing the number of marrow megakaryocytes and circulating platelets is an effective therapy for carboplatin-induced thrombocytopenia in mice.

Structure-based rational design led to the discovery of novel inhibitors of the MDM2-p53 protein-protein interaction. The affinity of these compounds for MDM2 was improved through conformational control of both the piperidinone ring and the appended N-alkyl substituent. Optimization afforded 29 (AM-8553), a potent and selective MDM2 inhibitor with excellent pharmacokinetic properties and in vivo efficacy.

We recently reported the discovery of AMG 232 (1), a potent and selective piperidinone inhibitor of the MDM2-p53 protein-protein interaction. Compound 1 is currently being evaluated in human clinical trials for the treatment of cancer. This article provides an overview of its discovery from the de novo design of the piperidinone series to the structure-activity studies leading to the identification of 1. In addition, this article also describes the preclinical pharmacology and pharmacokinetics of 1, along with its drug metabolism and safety assessment.