Small-Molecule Inhibitors of Acetyltransferase p300 Identified by High-Throughput Screening Are Potent Anticancer Agents

Abstract

Acetyltransferase p300 (KAT3B) plays key roles in signaling cascades that support cancer cell survival and sustained proliferation. Thus, p300 represents a potential anticancer therapeutic target. To discover novel anticancer agents that target p300, we conducted a high-throughput screening campaign. A library of 622,079 compounds was assayed for cytotoxicity to the triple-negative breast cancer (TNBC) cell line MDA-MB-231 but not to the human mammary epithelial cells. The resulting compounds were tested in a biochemical assay for inhibiting the enzymatic activity of p300. One compound (L002, NSC764414) displayed an IC50 of 1.98 μM against p300 in vitro, inhibited acetylation of histones and p53, and suppressed STAT3 activation in cell-based assays. L002 could be docked to the active site of the p300 catalytic domain. Biochemical tests of a series of related compounds revealed functional groups that may impact inhibitory potency of L002 against p300. Interestingly, these analogs showed inhibitory activities against CBP (the cellular paralog of p300), PCAF and GCN5, but not to other acetyltransferases (KAT5, KAT6B and KAT7), histone deacetylases (HDACs) and histone methyltransferases. Among the NCI-60 panel of cancer cell lines, leukemia and lymphoma cell lines were extremely sensitive to L002, whereas it is toxic to only a limited number of cell lines derived from solid tumors. Notably, breast cancer cell lines, especially those derived from TNBC, were highly susceptible to L002. In vivo, it potently suppressed tumor growth and histone acetylation of MDA-MB-468 xenografts. Thus, these new acetyltransferase inhibitors are potential anticancer therapeutics.

α-Tubulin Acetylation Elevated in Metastatic and Basal-like Breast Cancer Cells Promotes Microtentacle Formation, Adhesion, and Invasive Migration

“…Interestingly, overexpression of these enzymes are linked to progression of acute lymphoblastic leukemia (ALL) (45), enhanced lung cancer growth (46), and increased motility in melanoma cells (47). HAT inhibitors have also been shown to have potent anti-tumor activity against triple-negative breast cancer xenografts in vivo (48). These targeted therapies are mainly aimed at inhibiting histone acetyltransferase activity but should be further investigated to determine if HAT inhibition could also reduce tubulin acetylation at clinically tolerable levels.…”

Intrinsic cellular signaling mechanisms determine the sensitivity of cancer cells to virus-induced apoptosis

“…The viability of cells infected with viruses or treated with an inhibitor was determined using the CellTiter-Glo kit (Promega) as published56. The EC 50 of Ad-E1A12 against various cancer cell lines was determined by fitting viability data using nonlinear regression as implemented in the Prism 6 software.…”

“…Palpable tumors developed in two to three weeks. Tumor volume was determined as described56. When tumor volume reached approximately 100 mm 3 , mice were randomized into treatment groups (n = 5).…”

Inhibition of the HIF1α-p300 interaction by quinone- and indandione-mediated ejection of structural Zn(II)

“…ETPs have been shown to have targets other than p300, including histone methyl transferases (HKMTs) and thioredoxin reductase (TrxR), where reaction with thiols is also proposed [34,40,41]. A variety of quinone containing compounds have also been suggested to inhibit HIF-1α either directly [29,31] or indirectly by interacting with HIF-1α stabilizing protiens [30,57–60]. The prevalence of potentially reactive inhibitors against p300, and hypoxia system proteins thioredoxin (Trx) and TrxR, might indicate that proteins involved in this cascade are particularly sensitive to electrophilic molecules.…”

“…Interruption of the HIF-1α/p300(CBP) interaction has shown to negatively regulate oncogene expression and tumor growth [19–22]. Thus, the therapeutic significance of the HIF system has stimulated further high-throughput- and natural product-screening approaches for its inhibition [23–31]. The screens have employed both cell-based and isolated protein approaches; the cell-based approaches have yielded compounds that act indirectly on HIF, affecting the stability of HIF system proteins or by binding the hypoxia response elements (HREs) in DNA.…”