Loss-of-function mutations in the CBP/CREBBP gene, which encodes a histone acetyltransferase (HAT), are present in a variety of human tumors, including lung, bladder, gastric, and hematopoietic cancers. Consequently, development of a molecular targeting method capable of specifi cally killing CBP-defi cient cancer cells would greatly improve cancer therapy. Functional screening of synthetic-lethal genes in CBP -defi cient cancers identifi ed the CBP paralog p300/EP300 . Ablation of p300 in CBP -knockout and CBP -defi cient cancer cells induced G 1 -S cell-cycle arrest, followed by apoptosis. Genome-wide gene expression analysis revealed that MYC is a major factor responsible for the synthetic lethality. Indeed, p300 ablation in CBP -defi cient cells caused downregulation of MYC expression via reduction of histone acetylation in its promoter, and this lethality was rescued by exogenous MYC expression. The p300-HAT inhibitor C646 specifi cally suppressed the growth of CBP -defi cient lung and hematopoietic cancer cells in vitro and in vivo ; thus p300 is a promising therapeutic target for treatment of CBP -defi cient cancers. SIGNIFICANCE:Targeting synthetic-lethal partners of genes mutated in cancer holds great promise for treating patients without activating driver gene alterations. Here, we propose a "synthetic lethalbased therapeutic strategy" for CBP -defi cient cancers by inhibition of the p300 HAT activity. Patients with CBP -defi cient cancers could benefi t from therapy using p300-HAT inhibitors. Cancer Discov; 6(4); 430-45.

To evaluate the sensitization potential of chemicals in cosmetics, using non-animal methods, a number of in vitro safety tests have been designed. Current assays are based on the expression of cell surface markers, such as CD86 and CD54, which are associated with the activation of dendritic cells, in skin sensitization tests. However, these markers are influenced by culture conditions through activating danger signals. In this study, we investigated the relationship between extracellular pH and the expression of the skin sensitization test human cell line activation test (h-CLAT) markers CD86 and CD54. We measured expression levels after THP-1 cells were exposed to representative contact allergens, i.e., 2,4-dinitrochlorobenzene and imidazolidinyl urea, under acidic conditions. These conditions were set by exposure to hydrochloric acid, lactic acid, and citric acid. An acidic extracellular pH (6-7) suppressed the augmentation of CD86 and CD54 levels by the sensitizer. Additionally, when the CD86/CD54 expression levels were suppressed, a reduction in the intracellular pH was confirmed. Furthermore, we observed that Na/H exchanger 1 (NHE-1), a protein that contributes to the regulation of extracellular/intracellular pH, is involved in CD86 and CD54 expression. These findings suggest that the extracellular/intracellular pH has substantial effects on in vitro skin sensitization markers and should be considered in evaluations of the safety of mixtures and commercial products in the future.

The human cell line activation test (h-CLAT) is a skin sensitization test that measures the expression of cell surface proteins CD86 and CD54 to evaluate the skin sensitization potential of test chemicals. However, some skin irritants have been reported to induce dramatically high CD54 expression leading to false-positive h-CLAT results. Furthermore, CD54 expression is strongly induced by cytokines, such as interleukin (IL)-1β and tumor necrosis factor (TNF)-α, or danger signals that activate its signaling pathways. In this study, we focused on the relationship between CD54 expression and the Nucleotide binding domain, leucine-rich-containing family, pyrin domain containing 3 (NLRP3) inflammasome, a protein complex that plays a pivotal role in intra-cellular inflammation. We observed the activation of caspase-1 and production of IL-1β after exposure of THP-1 cells to 2,4-dinitrochlorobenzene (DNCB, sensitizer), octanoic acid (OA, non-sensitizer), and salicylic acid (SA, non-sensitizer), implying NLRP3 activation. These observations confirmed the activation of the inflammasome by CD54-only positive chemicals. CD54 expression, induced by OA and SA, was suppressed by potassium chloride, a typical inhibitor of NLRP3 inflammasome activation. These results suggested that the NLRP3 inflammasome may be activated in THP-1 cells resulting in the expression of CD54, and subsequently leading to false-positive results.

<p>Supplementary Figure S1. Identification of the p300 gene as a synthetic lethal hit. Supplementary Figure S2. Identification of MYC as a key factor in determining cancer cell survival under p300 depletion in CBP-KO cells or CBP depletion in p300-KO cells. Supplementary Figure S3. MYC transcriptional initiation is inactivated by suppression of histone H3K18/K27 acetylation upon p300 depletion in CBP-deficient cancer cells. Supplementary Figure S4. p300 depletion is lethal in cancer cells harboring loss-offunction mutations in CBP. Supplementary Figure S5. Response of CBP-deficient lung cancer cells to the p300 HAT inhibitor C646. Supplementary Figure S6. Depletion or inhibition of p300 suppresses growth of hematopoietic cancers with loss-of-function mutation of CBP. Supplementary Figure S7. Effect to BRD4 localization in the MYC locus in p300 depletion in CBP-deficient cancer cells. Supplementary Figure S8. CBP/CREBBP and p300/EP300 aberrations and known druggable aberrations of FGFR1 or ERBB2 amplification in lung squamous cell carcinomas and stomach adenocarcinomas. Supplementary Table S1. Raw data of survival fraction in siRNA screen. Supplementary Table S2. The top13 statistically significant pathways obtained from WikiPathways analysis. Supplementary Table S3. Genes commonly involved in the 13 functional pathways. Supplementary Table S4. CBP and p300 mutations in a variety of cancers. Supplementary Table S5. Gene status of tumor cell lines. Supplementary Table S6. siRNAs used in this study. Supplementary Table S7. Antibody for immunoblotting used in this study. Supplementary Table S8. TaqMan® Gene Expression Assays used in this study. Supplementary Table S9. Primer used in this study.</p>

<p>Supplementary Figure S1. Identification of the p300 gene as a synthetic lethal hit. Supplementary Figure S2. Identification of MYC as a key factor in determining cancer cell survival under p300 depletion in CBP-KO cells or CBP depletion in p300-KO cells. Supplementary Figure S3. MYC transcriptional initiation is inactivated by suppression of histone H3K18/K27 acetylation upon p300 depletion in CBP-deficient cancer cells. Supplementary Figure S4. p300 depletion is lethal in cancer cells harboring loss-offunction mutations in CBP. Supplementary Figure S5. Response of CBP-deficient lung cancer cells to the p300 HAT inhibitor C646. Supplementary Figure S6. Depletion or inhibition of p300 suppresses growth of hematopoietic cancers with loss-of-function mutation of CBP. Supplementary Figure S7. Effect to BRD4 localization in the MYC locus in p300 depletion in CBP-deficient cancer cells. Supplementary Figure S8. CBP/CREBBP and p300/EP300 aberrations and known druggable aberrations of FGFR1 or ERBB2 amplification in lung squamous cell carcinomas and stomach adenocarcinomas. Supplementary Table S1. Raw data of survival fraction in siRNA screen. Supplementary Table S2. The top13 statistically significant pathways obtained from WikiPathways analysis. Supplementary Table S3. Genes commonly involved in the 13 functional pathways. Supplementary Table S4. CBP and p300 mutations in a variety of cancers. Supplementary Table S5. Gene status of tumor cell lines. Supplementary Table S6. siRNAs used in this study. Supplementary Table S7. Antibody for immunoblotting used in this study. Supplementary Table S8. TaqMan® Gene Expression Assays used in this study. Supplementary Table S9. Primer used in this study.</p>