The prosurvival BCL-2 family protein BCL-X(L) is often overexpressed in solid tumors and renders malignant tumor cells resistant to anticancer therapeutics. Enhancing apoptotic responses by inhibiting BCL-X(L) will most likely have widespread utility in cancer treatment and, instead of inhibiting multiple prosurvival BCL-2 family members, a BCL-X(L)-selective inhibitor would be expected to minimize the toxicity to normal tissues. We describe the use of a high-throughput screen to discover a new series of small molecules targeting BCL-X(L) and their structure-guided development by medicinal chemistry. The optimized compound, WEHI-539 (7), has high affinity (subnanomolar) and selectivity for BCL-X(L) and potently kills cells by selectively antagonizing its prosurvival activity. WEHI-539 will be an invaluable tool for distinguishing the roles of BCL-X(L) from those of its prosurvival relatives, both in normal cells and notably in malignant tumor cells, many of which may prove to rely upon BCL-X(L) for their sustained growth.

A trifluoromethyl ketone analogue of arachidonic acid in which the COOH group is replaced with COCF3 (AACOCF3) was prepared and found to be a tight- and slow-binding inhibitor of the 85-kDa cytosolic human phospholipase A2 (cPLA2). Enzyme inhibition was observed when AACOCF3 was tested in assays using either phospholipid vesicles or phospholipid/Triton X-100 mixed micelles. The fact that the inhibition developed over several minutes in both assays establishes that AACOCF3 inhibits by direct binding to the enzyme rather than by decreasing the fraction of enzyme bound to the substrate interface. From the measured values of the inhibitor association and dissociation rate constants, an upper limit of the equilibrium dissociation constant for the Ca(2+).AACOCF3.PLA2 complex of 5 x 10(-5) mole fraction was obtained. Thus, detectable inhibition of cPLA2 by AACOCF3 occurs when this compound is present in the assay at a level of one inhibitor per several thousand substrates. Arachidonic acid analogues in which the COOH group is replaced by COCH3, CH(OH)CF3, CHO, or CONH2 did not detectably inhibit the cPLA2. The arachidonyl ketones AACOCF2CF3 and AACOCF2Cl were found by 19F NMR to be less hydrated than AACOCF3 in phospholipid/Triton X-100 mixed micelles, and compared to AACOCF3 these compounds are also weaker inhibitors of cPLA2. In keeping with the fact that cPLA2 displays substrate specificity for arachidonyl-containing phospholipids, the arachidic acid analogue C19H39COCF3 is a considerably less potent inhibitor compared to AACOCF3.(ABSTRACT TRUNCATED AT 250 WORDS)

The affinities of a large number of deoxy and fluorodeoxy sugars for the glucose binding site in glycogen phosphorylase have been measured, and polarities and relative strengths of the hydrogen bonds at each position have been predicted on the basis of these data. Comparison with the recently refined X-ray crystal structure of the phosphorylase-glucose complex shows a generally good correlation between predicted and observed bond strengths, vindicating this approach to the evaluation of hydrogen bonding. Estimates of the net contributions of hydrogen bonds of different types (neutral-neutral and neutral-charged) are essentially identical with those obtained by a complementary approach on the tyrosyl tRNA synthetase-substrate complex [Fersht, A. R., Shi, J. P., Knill-Jones, J., Lowe, D. M., Wilkinson, A. J., Blow, D. M., Brick, P., Cortes, P., Waye, M. M. Y., & Winter, G. (1985) Nature (London) 314, 235-238]. The carbohydrate binding site structure determined is compared with that recently determined for the arabinose binding protein.

Acetylation of histones by lysine acetyltransferases (KATs) is essential for chromatin organization and function. Among the genes coding for the MYST family of KATs (KAT5-KAT8) are the oncogenes KAT6A (also known as MOZ) and KAT6B (also known as MORF and QKF). KAT6A has essential roles in normal haematopoietic stem cells and is the target of recurrent chromosomal translocations, causing acute myeloid leukaemia. Similarly, chromosomal translocations in KAT6B have been identified in diverse cancers. KAT6A suppresses cellular senescence through the regulation of suppressors of the CDKN2A locus, a function that requires its KAT activity. Loss of one allele of KAT6A extends the median survival of mice with MYC-induced lymphoma from 105 to 413 days. These findings suggest that inhibition of KAT6A and KAT6B may provide a therapeutic benefit in cancer. Here we present highly potent, selective inhibitors of KAT6A and KAT6B, denoted WM-8014 and WM-1119. Biochemical and structural studies demonstrate that these compounds are reversible competitors of acetyl coenzyme A and inhibit MYST-catalysed histone acetylation. WM-8014 and WM-1119 induce cell cycle exit and cellular senescence without causing DNA damage. Senescence is INK4A/ARF-dependent and is accompanied by changes in gene expression that are typical of loss of KAT6A function. WM-8014 potentiates oncogene-induced senescence in vitro and in a zebrafish model of hepatocellular carcinoma. WM-1119, which has increased bioavailability, arrests the progression of lymphoma in mice. We anticipate that this class of inhibitors will help to accelerate the development of therapeutics that target gene transcription regulated by histone acetylation.