Bryson W. Katona

Gain-of-function p53 mutants co-opt chromatin pathways to drive cancer growth

TP53 (which encodes p53 protein) is the most frequently mutated gene among all human cancers. Prevalent p53 missense mutations abrogate its tumour suppressive function and lead to a ‘gain-of-function’ (GOF) that promotes cancer. Here we show that p53 GOF mutants bind to and upregulate chromatin regulatory genes, including the methyltransferases MLL1 (also known as KMT2A), MLL2 (also known as KMT2D), and acetyltransferase MOZ (also known as KAT6A or MYST3), resulting in genome-wide increases of histone methylation and acetylation. Analysis of The Cancer Genome Atlas shows specific upregulation of MLL1, MLL2, and MOZ in p53 GOF patient-derived tumours, but not in wild-type p53 or p53 null tumours. Cancer cell proliferation is markedly lowered by genetic knockdown of MLL1 or by pharmacological inhibition of the MLL1 methyltransferase complex. Our study reveals a novel chromatin mechanism underlying the progression of tumours with GOF p53, and suggests new possibilities for designing combinatorial chromatin-based therapies for treating individual cancers driven by prevalent GOF p53 mutations.

Characterization of Enantiomeric Bile Acid-induced Apoptosis in Colon Cancer Cell Lines

Bile acids are steroid detergents that are toxic to mammalian cells at high concentrations; increased exposure to these steroids is pertinent in the pathogenesis of cholestatic disease and colon cancer. Understanding the mechanisms of bile acid toxicity and apoptosis, which could include nonspecific detergent effects and/or specific receptor activation, has potential therapeutic significance. In this report we investigate the ability of synthetic enantiomers of lithocholic acid (ent-LCA), chenodeoxycholic acid (ent-CDCA), and deoxycholic acid (ent-DCA) to induce toxicity and apoptosis in HT-29 and HCT-116 cells. Natural bile acids were found to induce more apoptotic nuclear morphology, cause increased cellular detachment, and lead to greater capase-3 and -9 cleavage compared with enantiomeric bile acids in both cell lines. In contrast, natural and enantiomeric bile acids showed similar effects on cellular proliferation. These data show that bile acid-induced apoptosis in HT-29 and HCT-116 cells is enantiospecific, hence correlated with the absolute configuration of the bile steroid rather than its detergent properties. The mechanism of LCA- and ent-LCA-induced apoptosis was also investigated in HT-29 and HCT-116 cells. These bile acids differentially activate initiator caspases-2 and -8 and induce cleavage of full-length Bid. LCA and ent-LCA mediated apoptosis was inhibited by both pan-caspase and selective caspase-8 inhibitors, whereas a selective caspase-2 inhibitor provided no protection. LCA also induced increased CD95 localization to the plasma membrane and generated increased reactive oxygen species compared with ent-LCA. This suggests that LCA/ent-LCA induce apoptosis enantioselectively through CD95 activation, likely because of increased reactive oxygen species generation, with resulting procaspase-8 cleavage.

Natural and enantiomeric etiocholanolone interact with distinct sites on the rat α1β2γ2l GABAA receptor

We have studied the ability of the androgen etiocholanolone and its enantiomer (ent-etiocholanolone) to modulate rat α1β2γ2L GABAA receptor function transiently expressed in human embryonic kidney cells. Studies on steroid enantiomer pairs can yield powerful new information on the pharmacology of steroid interactions with the GABAA receptor. Both steroids enhance currents elicited by GABA, but ent-etiocholanolone is much more powerful than etiocholanolone at producing potentiation. At a low GABA concentration (0.5 μM, <EC5), the presence of 10 μM ent-etiocholanolone potentiates whole-cell currents by almost 30-fold, whereas 10 μM etiocholanolone merely doubles the peak response. At higher GABA concentration (5 μM, ∼EC25), the potentiation curve for ent-etiocholanolone is positioned at lower concentrations than that for etiocholanolone. Single-channel kinetic analysis shows that exposure to etiocholanolone has a single effect on currents: the relative frequency of long openings is increased in the presence of steroid. But exposure to ent-etiocholanolone produces two kinetic effects: an increase in the relative frequency of long openings and a decrease in the frequency of long closed times. The presence of etiocholanolone does not inhibit potentiation by ent-etiocholanolone, suggesting that etiocholanolone is unable to interact with the sites through which ent-etiocholanolone modifies receptor function. The double mutation α1(N407A/Y410F) prevents potentiation by etiocholanolone but not by ent-etiocholanolone, and the α1(Q241A) and α1(I238N) point mutations fully abolish potentiation by etiocholanolone but not by ent-etiocholanolone. We conclude that etiocholanolone and its enantiomer interact with distinct sites on the α1β2γ2L GABAA receptor.

An Epigenetic Pathway Regulates Sensitivity of Breast Cancer Cells to HER2 Inhibition via FOXO/c-Myc Axis

Human epidermal growth factor receptor 2 (HER2) is upregulated in a subset of human breast cancers. However, the cancer cells often quickly develop an adaptive response to HER2 kinase inhibitors. We found that an epigenetic pathway involving MLL2 is crucial for growth of HER2(+) cells and MLL2 reduces sensitivity of the cancer cells to a HER2 inhibitor, lapatinib. Lapatinib-induced FOXO transcription factors, normally tumor-suppressing, paradoxically upregulate c-Myc epigenetically in concert with a cascade of MLL2-associating epigenetic regulators to dampen sensitivity of the cancer cells to lapatinib. An epigenetic inhibitor suppressing c-Myc synergizes with lapatinib to suppress cancer growth in vivo, partly by repressing the FOXO/c-Myc axis, unraveling an epigenetically regulated FOXO/c-Myc axis as a potential target to improve therapy.

EZH2 inhibition enhances the efficacy of an EGFR inhibitor in suppressing colon cancer cells

Metastatic colon cancer has a 5-year survival of less than 10% despite the use of aggressive chemotherapeutic regimens. As signaling from epidermal growth factor receptor (EGFR) is often enhanced and epigenetic regulation is often altered in colon cancer, it is desirable to enhance the efficacy of EGFR-directed therapy by co-targeting an epigenetic pathway. We showed that the histone methyltransferase EZH2, which catalyzes methylation of histone H3 lysine 27 (H3K27), was upregulated in colon cancers in The Cancer Genome Atlas (TCGA) database. Since co-inhibition of both EGFR and EZH2 has not been studied in colon cancer, we examined the effects of co-inhibition of EGFR and EZH2 on 2 colon cancer cell lines, HT-29 and HCT-15. Co-inhibition of EZH2 and EGFR with the small molecules UNC1999 and gefitinib, led to a significant decrease in cell number and increased apoptosis compared to inhibition of either pathway alone, and similar results were noted after EZH2 shRNA knockdown. Moreover, co-inhibition of EZH2 and EGFR also significantly induced autophagy, indicating that autophagy may play a role in the observed synergy. Together, these findings suggest that inhibition of both EZH2 and EGFR serves as an effective method to increase the efficacy of EGFR inhibitors in suppressing colon cancer cells.

Gastric Cancer Genomics: Advances and Future Directions

Advancement in the field of cancer genomics is revolutionizing the molecular characterization of a wide variety of different cancers. Recent application of large-scale, next-generation sequencing technology to gastric cancer, which remains a major source of morbidity and mortality throughout the world, has helped better define the complex genomic landscape of this cancer. These studies also have led to the development of novel genomically based molecular classification systems for gastric cancer, reinforced the importance of classic driver mutations in gastric cancer pathogenesis, and led to the discovery of new driver gene mutations that previously were not known to be associated with gastric cancer. This wealth of genomic data has significant potential to impact the future management of this disease, and the challenge remains to effectively translate this genomic data into better treatment paradigms for gastric cancer.

Barrett's esophagus surveillance: When, how often, does it work?

Barretts esophagus is a well-known risk factor for the development of esophageal adenocarcinoma. Current practice guidelines recommend endoscopic surveillance of patients with Barretts esophagus in an attempt to detect cancer at an early and potentially curable stage. This review addresses the rationale behind surveillance and criteria for inclusion of patients in surveillance programs as well as the appropriate technique and intervals that should be used. This work addresses other key topics in Barretts esophagus surveillance, including the efficacy of surveillance programs, physician compliance with surveillance guidelines, cost-effectiveness of surveillance programs, and areas for future research.

Efficacy of Peptide Receptor Radionuclide Therapy in a United States–Based Cohort of Metastatic Neuroendocrine Tumor Patients: Single-Institution Retrospective Analysis

Objectives The aim of this study was to analyze in a retrospective cohort study the outcomes of a United States–based group of metastatic neuroendocrine tumor (NET) patients who underwent peptide receptor radionuclide therapy (PRRT). Methods Twenty-eight patients from a single US NET Center were treated with PRRT. Toxicities were assessed using Common Terminology Criteria for Adverse Events version 4.03. Progression was determined by the Response Evaluation Criteria in Solid Tumors version 1.1. Univariate and multivariate Cox regression was performed to identify potential predictors of progression-free survival (PFS) and overall survival (OS). Results The median age at NET diagnosis was 56 years, 50% of the patients were male, 46% of NET primaries were located in the pancreas, 71% of tumors were nonfunctional, 25% were World Health Organization (WHO) grade III, and 20% had at least a 25% hepatic tumor burden. Anemia (36%) was the most common post-PRRT toxicity, followed by leukopenia (31%), nephrotoxicity (27%), and thrombocytopenia (24%). Median PFS was 18 months, and median OS was 38 months. Having a WHO grade III NET and receiving systemic chemotherapy prior to PRRT were found to be to independent predictors of shorter PFS and OS. Conclusions Peptide receptor radionuclide therapy is an effective therapy in a US population. Progression-free survival and OS were better in WHO grade I/II NETs and when PRRT was sequenced prior to systemic chemotherapy.

Harnessing the Hidden Antitumor Power of the MLL-AF4 Oncogene to Fight Leukemia

It is unclear whether the antiproliferative/proapoptotic activity of oncogenes can be pharmacologically reactivated in cancer cells. In this issue of Cancer Cell, Liu and colleagues report that a proteasome inhibitor reactivates an MLL-AF4 controlled antitumor program to kill leukemia cells in an oncogene dose- and cell type-dependent manner.

A counseling framework for moderate-penetrance colorectal cancer susceptibility genes

The inclusion of moderate-penetrance cancer susceptibility genes in multigene panel testing poses challenges regarding the optimal management of individuals found to have pathogenic variants in these genes. A recently published counseling framework has provided evidence-based guidance for moderate-penetrance breast and ovarian cancer genes.1 However, no such framework exists for moderate-penetrance colorectal cancer (CRC) susceptibility genes, including CHEK2, APC*I1307K, and monoallelic MUTYH, which are among the most common multigene panel testing findings.2 Currently the only recommendations to address this risk are from the National Comprehensive Cancer Network, which recommends that individuals who carry pathogenic CHEK2 or APC*I1307K variants irrespective of family history, or monoallelic MUTYH with a family history of CRC, undergo earlier and more frequent CRC screening, similar to individuals with a first-degree relative with CRC.3 Whether early and increased CRC screening is truly justified for such carriers in the absence of a family history of CRC is unknown. To better elucidate the appropriate timing of colonoscopy initiation, we calculated the cumulative lifetime risk (CLTR) of CRC as a multiple of the US Surveillance, Epidemiology, and End Results Program (SEER) estimates of ever developing CRC and the observed risk for selected genetic variants (CHEK2 1100delC, CHEK2 I157K, APC*I1307K, monoallelic MUTYH). Population age-specific incidence rates for CRCs were obtained from the 2010–2014 SEER cancer statistics for all races.4 Average relative-risk multipliers were derived from a systematic meta-analysis.5 We estimated 5-year and CLTR using previously described methods and applied the estimated odds ratio (OR) for each genetic variant to population agespecific incidence data.6