Restoration of p53 activity by inhibition of the p53-MDM2 interaction has been considered an attractive approach for cancer treatment. However, the hydrophobic protein-protein interaction surface represents a significant challenge for the development of small-molecule inhibitors with desirable pharmacological profiles. RG7112 was the first small-molecule p53-MDM2 inhibitor in clinical development. Here, we report the discovery and characterization of a second generation clinical MDM2 inhibitor, RG7388, with superior potency and selectivity.

The p53 tumor suppressor is a potent transcription factor that plays a key role in the regulation of cellular responses to stress. It is controlled by its negative regulator MDM2, which binds directly to p53 and inhibits its transcriptional activity. MDM2 also targets p53 for degradation by the proteasome. Many tumors produce high levels of MDM2, thereby impairing p53 function. Restoration of p53 activity by inhibiting the p53-MDM2 interaction may represent a novel approach to cancer treatment. RG7112 (2g) is the first clinical small-molecule MDM2 inhibitor designed to occupy the p53-binding pocket of MDM2. In cancer cells expressing wild-type p53, RG7112 stabilizes p53 and activates the p53 pathway, leading to cell cycle arrest, apoptosis, and inhibition or regression of human tumor xenografts. KEYWORDS: MDM2, p53, RG7112, protein−protein interaction, cancer p53 is a potent tumor suppressor that activates the transcription of a subset of genes controlling cell-cycle progression and apoptosis.1−3 Dysregulation of the p53 pathway, including mutation or deletion of the p53 gene and changes in downstream signaling molecules, is the most frequent alteration in human cancers.4 MDM2 is a negative regulator of p53 that binds the transactivation domain of p53 and inhibits its ability to activate transcription.5−8 MDM2 is also an E3 ubiquitin ligase that targets p53 for proteosomal degradation.9 In a variety of solid tumors and hematologic malignancies, MDM2 overexpression is one of the mechanisms by which the wildtype p53 function is impaired.10 Given the central role of MDM2 in regulating p53 activity and stability, developing small-molecule inhibitors of MDM2 could offer a novel approach to treating cancers. 11,12The crystal structure of a p53-derived peptide bound to the p53 binding domain of MDM2 revealed the existence of a deep hydrophobic clef on the surface of the MDM2 molecule. 13Three amino acid residues from the p53 peptide (Phe19, Trp23, and Leu26) play critical roles in the binding between the two proteins by projecting hydrophobic side-chains deep into the cavity of the MDM2 molecule. These structural features of the p53-MDM2 complex suggested the likelihood of identifying small-molecule inhibitors that can successfully block the interaction between the two proteins. Compounds with the ability to inhibit the binding between p53 and MDM2 have been reported. 14−17 We previously reported the discovery of a series of 4,5-dihydroimidazolines called Nutlins. These compounds, exemplified by compound 1 (Figure 1), were discovered through screening and subsequent medicinal chemistry optimization. 18 Compound 1, also known as Nutlin-3a, has become a tool of choice to study p53 biology and therapeutic applications.19 Although these early lead compounds have shown good cellular activity and provided the mechanistic proof-of-concept for inhibiting p53-MDM2 interaction for cancer therapy, their pharmacological properties were suboptimal for clinical development. Here, we describe

The transition wave number from the EF 1 ⌺ g + ͑v =0,N =1͒ energy level of ortho-H 2 to the 54p1 1 ͑0͒ Rydberg state below the X + 2 ⌺ g + ͑v + =0,N + =1͒ ground state of ortho-H 2 + has been measured to be 25 209.997 56Ϯ ͑0.000 22͒ statistical Ϯ ͑0.000 07͒ systematic cm −1 . Combining this result with previous experimental and theoretical results for other energy level intervals, the ionization and dissociation energies of the hydrogen molecule have been determined to be 124 417.491 13͑37͒ and 36 118.069 62͑37͒ cm −1 , respectively, which represents a precision improvement over previous experimental and theoretical results by more than one order of magnitude. The new value of the ionization energy can be regarded as the most precise and accurate experimental result of this quantity, whereas the dissociation energy is a hybrid experimental-theoretical determination.

No abstract

The B̃-X̃ laser-induced-fluorescence spectrum of jet-cooled isopropoxy radical (i-C3H7O[middle dot]) has been recorded. Using an isolated state model the observed rotational and fine structure of the origin band has been well simulated to determine rotational constants for both the X̃ and B̃ states and the electron spin-rotation constants of the X̃ state. The line intensities are well simulated with a parallel transition type, requiring the same symmetry for the levels involved of each the X̃ and B̃ state, which confirms the previous suggestion that going from ethoxy (C2H5O[middle dot]) to isopropoxy, the energy ordering of the electron configurations with in- and out-of-plane half-filled p-orbitals of the oxygen atom is reversed and the ground vibronic symmetry changes from a" to a'. However, the observed spin-rotation coupling constants are not consistent with their predication from either semi-empirical theory or quantum chemical calculations. Additionally, the lack of observed transitions involving the out-of-plane transition moment component is not consistent with high level electronic structure calculations suggesting mixing of vibronic levels by strong spin-orbit coupling. A new twofold model has been developed that explicitly includes Coriolis and spin-orbit coupling between different vibronic levels. This model renders the discrepancy between theoretical and experimental spin-rotation constants moot. Moreover, it determines independently the contributions to the observed splitting between the lowest two levels, resulting from non-relativistic kinetic and Coulombic effects, and that due to the relativistic spin-orbit interaction. The experimental values show that these effects are comparable, but that the vibronic one is slightly more important. This result is at variance with state-of-the-art electronic structure calculations which otherwise do a remarkably good job of describing the ground state of isopropoxy.

The laser-induced fluorescence and laser-excited dispersed fluorescence spectra of the cyclohexoxy radical has been observed under two sets of free-jet-cooling conditions, characterized by rotational temperatures of approximately 1 and 100 K. Although five conformers of cyclohexoxy are possible, it appears that all presently observed spectral bands can be accounted for by a single one. All cold spectral bands are assigned to the B-X electronic transition of the cyclohexoxy radical. Transitions to both a' and a" B state vibrational levels are observed and allowed due to a substantial pseudo-Jahn-Teller effect in the X state. Hot bands are also observed, which we attributed to transitions to the B state from the low-lying A electronic state. Analysis of the spectra yields vibrational frequencies for the X, A, and B states as well as the energy separations of their vibrationless levels.

The magnetic transitions and magnetic and magnetostrictive properties of Tb x Dy 1−x ͑Fe 0.8 Co 0.2 ͒ 2 ͑0.20ഛ x ഛ 0.40͒ compounds have been investigated. The spin-reorientation temperature T SR decreases from above to below room temperature, when x is increased from 0.25 to 0.40. The easy magnetization direction at room temperature of the Laves phase lies along the ͗100͘ axis in compounds with 0.20ഛ x ഛ 0.27, while it lies along the ͗111͘ axis as 0.30ഛ x ഛ 0.40. The magnetocrystalline anisotropy constant K 1 at room temperature reaches a minimum value at x = 0.30, indicating it is near the composition for anisotropy compensation. The large polycrystalline saturation magnetostriction s Ϸ 980 ppm is observed for x = 0.30, which can be ascribed to the large magnetostriction coefficients 111 and 100 . 100 has a value larger than 600 ppm for the compounds with 0.30ഛ x ഛ 0.35, which can be attributed to the change of the filling of the 3d band due to Co substitution for Fe. Tb 0.30 Dy 0.70 ͑Fe 0.8 Co 0.2 ͒ 2 with a high magnetostriction and a low anisotropy is found to be a good candidate material for magnetostriction applications. A detailed spin configuration diagram for Tb x Dy 1−x ͑Fe 0.8 Co 0.2 ͒ 2 Laves phase around the composition for the anisotropy compensation is given, which should be a guide to develop novel magnetostrictive materials for applications in this series.

The transition wave numbers from selected rovibrational levels of the EF 1 ⌺ g + ͑v =0͒ state to selected np Rydberg states of ortho-and para-D 2 located below the adiabatic ionization threshold have been measured at a precision better than 10 −3 cm −1 . Adding these wave numbers to the previously determined transition wave numbers from the X 1 ⌺ g + ͑v =0, N =0,1͒ states to thestates of D 2 and to the binding energies of the Rydberg states calculated by multichannel quantum defect theory, the ionization energies of ortho-and para-D 2 are determined to be 124 745.394 07͑58͒ cm −1 and 124 715.003 77͑75͒ cm −1 , respectively. After re-evaluation of the dissociation energy of D 2 + and using the known ionization energy of D, the dissociation energy of D 2 is determined to be 36 748.362 86͑68͒ cm −1 . This result is more precise than previous experimental results by more than one order of magnitude and is in excellent agreement with the most recent theoretical value 36 748.3633͑9͒ cm −1 ͓K. Piszczatowski, G. Łach, M. Przybytek et al., J. Chem. Theory Comput. 5, 3039 ͑2009͔͒. The ortho-para separation of D 2 , i.e., the energy difference between the N = 0 and N = 1 rotational levels of the X 1 ⌺ g + ͑v =0͒ ground state, has been determined to be 59.781 30͑95͒ cm −1 .