Selective inhibition of the BD2 bromodomain of BET proteins in prostate cancer.

Proteins of the bromodomain and extra-terminal (BET) domain family are epigenetic readers that bind acetylated histones through their bromodomains to regulate gene transcription. Dual-bromodomain BET inhibitors (DbBi) that bind with similar affinities to the first (BD1) and second (BD2) bromodomains of BRD2, BRD3, BRD4 and BRDt have displayed modest clinical activity in monotherapy cancer trials. A reduced number of thrombocytes in the blood (thrombocytopenia) as well as symptoms of gastrointestinal toxicity are dose-limiting adverse events for some types of DbBi1-5. Given that similar haematological and gastrointestinal defects were observed after genetic silencing of Brd4 in mice6, the platelet and gastrointestinal toxicities may represent on-target activities associated with BET inhibition. The two individual bromodomains in BET family proteins may have distinct functions7-9 and different cellular phenotypes after pharmacological inhibition of one or both bromodomains have been reported10,11, suggesting that selectively targeting one of the bromodomains may result in a different efficacy and tolerability profile compared with DbBi. Available compounds that are selective to individual domains lack sufficient potency and the pharmacokinetics properties that are required for in vivo efficacy and tolerability assessment10-13. Here we carried out a medicinal chemistry campaign that led to the discovery of ABBV-744, a highly potent and selective inhibitor of the BD2 domain of BET family proteins with drug-like properties. In contrast to the broad range of cell growth inhibition induced by DbBi, the antiproliferative activity of ABBV-744 was largely, but not exclusively, restricted to cell lines of acute myeloid leukaemia and prostate cancer that expressed the full-length androgen receptor (AR). ABBV-744 retained robust activity in prostate cancer xenografts, and showed fewer platelet and gastrointestinal toxicities than the DbBi ABBV-07514. Analyses of RNA expression and chromatin immunoprecipitation followed by sequencing revealed that ABBV-744 displaced BRD4 from AR-containing super-enhancers and inhibited AR-dependent transcription, with less impact on global transcription compared with ABBV-075. These results underscore the potential value of selectively targeting the BD2 domain of BET family proteins for cancer therapy.

Author Correction: Discovery of a selective catalytic p300/CBP inhibitor that targets lineage-specific tumours.

In the originally published version of this Letter, the authors Arthur F. Kluge, Michael A. Patane and Ce Wang were inadvertently omitted from the author list. Their affiliations are: I-to-D, Inc., PO Box 6177, Lincoln, Massachusetts 01773, USA (A.F.K.); Mitobridge, Inc. 1030 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA (M.A.P.); and China Novartis Institutes for BioMedical Research, No. 4218 Jinke Road, Zhangjiang Hi-Tech Park, Pudong District, Shanghai 201203, China (C.W.). These authors contributed to the interpretation of results and design of compounds. In addition, author 'Edward A. Kesicki' was misspelled as 'Ed Kesicki'. These errors have been corrected online.

Discovery of a selective catalytic p300/CBP inhibitor that targets lineage-specific tumours.

The dynamic and reversible acetylation of proteins, catalysed by histone acetyltransferases (HATs) and histone deacetylases (HDACs), is a major epigenetic regulatory mechanism of gene transcription and is associated with multiple diseases. Histone deacetylase inhibitors are currently approved to treat certain cancers, but progress on the development of drug-like histone actyltransferase inhibitors has lagged behind. The histone acetyltransferase paralogues p300 and CREB-binding protein (CBP) are key transcriptional co-activators that are essential for a multitude of cellular processes, and have also been implicated in human pathological conditions (including cancer). Current inhibitors of the p300 and CBP histone acetyltransferase domains, including natural products, bi-substrate analogues and the widely used small molecule C646, lack potency or selectivity. Here, we describe A-485, a potent, selective and drug-like catalytic inhibitor of p300 and CBP. We present a high resolution (1.95 Å) co-crystal structure of a small molecule bound to the catalytic active site of p300 and demonstrate that A-485 competes with acetyl coenzyme A (acetyl-CoA). A-485 selectively inhibited proliferation in lineage-specific tumour types, including several haematological malignancies and androgen receptor-positive prostate cancer. A-485 inhibited the androgen receptor transcriptional program in both androgen-sensitive and castration-resistant prostate cancer and inhibited tumour growth in a castration-resistant xenograft model. These results demonstrate the feasibility of using small molecule inhibitors to selectively target the catalytic activity of histone acetyltransferases, which may provide effective treatments for transcriptional activator-driven malignancies and diseases.

Improvements in observed and relative survival in follicular grade 1-2 lymphoma during 4 decades: the Stanford University experience.

Recent studies report an improvement in overall survival (OS) of patients with follicular lymphoma (FL). Previously untreated patients with grade 1 to 2 FL treated at Stanford University from 1960-2003 were identified. Four eras were considered: era 1, pre-anthracycline (1960-1975, n = 180); era 2, anthracycline (1976-1986, n = 426); era 3, aggressive chemotherapy/purine analogs (1987-1996, n = 471); and era 4, rituximab (1997-2003, n = 257). Clinical characteristics, patterns of care, and survival were assessed. Observed OS was compared with the expected OS calculated from Berkeley Mortality Database life tables derived from population matched by gender and age at the time of diagnosis. The median OS was 13.6 years. Age, gender, and stage did not differ across the eras. Although primary treatment varied, event-free survival after the first treatment did not differ between eras (P = .17). Median OS improved from 11 years in eras 1 and 2 to 18.4 years in era 3 and has not yet been reached for era 4 (P < .001), with no suggestion of a plateau in any era. These improvements in OS exceeded improvements in survival in the general population during the same period. Several factors, including better supportive care and effective therapies for relapsed disease, are likely responsible for this improvement.

Target 2035 - update on the quest for a probe for every protein.

Twenty years after the publication of the first draft of the human genome, our knowledge of the human proteome is still fragmented. The challenge of translating the wealth of new knowledge from genomics into new medicines is that proteins, and not genes, are the primary executers of biological function. Therefore, much of how biology works in health and disease must be understood through the lens of protein function. Accordingly, a subset of human proteins has been at the heart of research interests of scientists over the centuries, and we have accumulated varying degrees of knowledge about approximately 65% of the human proteome. Nevertheless, a large proportion of proteins in the human proteome (∼35%) remains uncharacterized, and less than 5% of the human proteome has been successfully targeted for drug discovery. This highlights the profound disconnect between our abilities to obtain genetic information and subsequent development of effective medicines. Target 2035 is an international federation of biomedical scientists from the public and private sectors, which aims to address this gap by developing and applying new technologies to create by year 2035 chemogenomic libraries, chemical probes, and/or biological probes for the entire human proteome.

The Bcl-2 family antagonist ABT-737 significantly inhibits multiple animal models of autoimmunity.

The Bcl-2 family of proteins plays a critical role in controlling immune responses by regulating the expansion and contraction of activated lymphocyte clones by apoptosis. ABT-737, which was originally developed for oncology, is a potent inhibitor of Bcl-2, Bcl-x(L), and Bcl-w protein function. There is evidence that Bcl-2-associated dysregulation of lymphocyte apoptosis may contribute to the pathogenesis of autoimmunity and lead to the development of autoimmune diseases. In this study, we report that ABT-737 treatment resulted in potent inhibition of lymphocyte proliferation as measured by in vitro mitogenic or ex vivo Ag-specific stimulation. More importantly, ABT-737 significantly reduced disease severity in tissue-specific and systemic animal models of autoimmunity. Bcl-2 family antagonism by ABT-737 was efficacious in treating animal models of arthritis and lupus. Our results suggest that treatment with a Bcl-2 family antagonist represents a novel and potentially attractive therapeutic approach for the clinical treatment of autoimmunity.

An inhibitor of Bcl-2 family proteins induces regression of solid tumours.

Proteins in the Bcl-2 family are central regulators of programmed cell death, and members that inhibit apoptosis, such as Bcl-X(L) and Bcl-2, are overexpressed in many cancers and contribute to tumour initiation, progression and resistance to therapy. Bcl-X(L) expression correlates with chemo-resistance of tumour cell lines, and reductions in Bcl-2 increase sensitivity to anticancer drugs and enhance in vivo survival. The development of inhibitors of these proteins as potential anti-cancer therapeutics has been previously explored, but obtaining potent small-molecule inhibitors has proved difficult owing to the necessity of targeting a protein-protein interaction. Here, using nuclear magnetic resonance (NMR)-based screening, parallel synthesis and structure-based design, we have discovered ABT-737, a small-molecule inhibitor of the anti-apoptotic proteins Bcl-2, Bcl-X(L) and Bcl-w, with an affinity two to three orders of magnitude more potent than previously reported compounds. Mechanistic studies reveal that ABT-737 does not directly initiate the apoptotic process, but enhances the effects of death signals, displaying synergistic cytotoxicity with chemotherapeutics and radiation. ABT-737 exhibits single-agent-mechanism-based killing of cells from lymphoma and small-cell lung carcinoma lines, as well as primary patient-derived cells, and in animal models, ABT-737 improves survival, causes regression of established tumours, and produces cures in a high percentage of the mice.

Navitoclax, a targeted high-affinity inhibitor of BCL-2, in lymphoid malignancies: a phase 1 dose-escalation study of safety, pharmacokinetics, pharmacodynamics, and antitumour activity.

BACKGROUND: Proteins of the BCL-2 family regulate clonal selection and survival of lymphocytes, and are frequently overexpressed in lymphomas. Navitoclax is a targeted high-affinity small molecule that inhibits the anti-apoptotic activity of BCL-2 and BCL-XL. We aimed to assess the safety and antitumour activity of navitoclax in patients with lymphoid tumours, and establish the drug's pharmacokinetic and pharmacodynamic profiles. METHODS: In this phase 1 dose-escalation study, patients (aged ≥18 years) with relapsed or refractory lymphoid malignancies were enrolled and treated at seven sites in the USA between November, 2006, and November, 2009. A modified Fibonacci 3+3 design was used to assign patients to receive oral navitoclax once daily by one of two dosing schedules: intermittently for the first 14 days of a 21-day cycle (14/21) at doses of 10, 20, 40, 80, 110, 160, 225, 315, or 440 mg/day; or continuously for 21 days of a 21-day cycle (21/21) at doses of 200, 275, 325, or 425 mg/day. Study endpoints were safety, maximum tolerated dose, pharmacokinetic profile, pharmacodynamic effects on platelets and T cells, and antitumour activity. This trial is registered with ClinicalTrials.gov, number NCT00406809. FINDINGS: 55 patients were enrolled (median age 59 years, IQR 51-67), 38 to receive the 14/21 dosing schedule, and 17 to receive the 21/21 dosing schedule. Common toxic effects included grade 1 or 2 anaemia (41 patients), infection (39), diarrhoea (31), nausea (29), and fatigue (21); and grade 3 or 4 thrombocytopenia (29), lymphocytopenia (18), and neutropenia (18). On the intermittent 14/21 schedule, dose-limiting toxic effects were hospital admissions for bronchitis (one) and pleural effusion (one), grade 3 increase in aminotransferases (one), grade 4 thrombocytopenia (one), and grade 3 cardiac arrhythmia (one). To reduce platelet nadir associated with intermittent 14/21 dosing, we assessed a 150 mg/day lead-in dose followed by a continuous 21/21 dosing schedule. On the 21/21 dosing schedule, two patients did not complete the first cycle and were excluded from assessment of dose-limiting toxic effects; dose-limiting toxic effects were grade 4 thrombocytopenia (one), grade 3 increase in aminotransferases (one), and grade 3 gastrointestinal bleeding (one). Navitoclax showed a pharmacodynamic effect on circulating platelets and T cells. Clinical responses occurred across the range of doses and in several tumour types. Ten of 46 patients with assessable disease had a partial response, and these responders had median progression-free survival of 455 days (IQR 40-218). INTERPRETATION: Navitoclax has a novel mechanism of peripheral thrombocytopenia and T-cell lymphopenia, attributable to high-affinity inhibition of BCL-XL and BCL-2, respectively. On the basis of these findings, a 150 mg 7-day lead-in dose followed by a 325 mg dose administered on a continuous 21/21 dosing schedule was selected for phase 2 study. FUNDING: Abbott Laboratories, Genentech, and National Cancer Institute, National Institutes of Health.

Long-Term Outcomes of Patients With Early Stage Nonbulky Hodgkin Lymphoma Treated With Combined Modality Therapy in the Stanford V Trials (the G4 and G5 Studies).

PURPOSE: Combined modality therapy (CMT) is standard therapy for early-stage Hodgkin lymphoma (ESHL). We previously reported excellent outcomes with the abbreviated Stanford V regimen. Herein we report updated results with median follow-up >10 years on survival, therapy-related late effects, and impact of disease risk factors on patient outcomes. METHODS AND MATERIALS: The G4 and G5 studies enrolled patients with stage I-IIA nonbulky ESHL. Patients received 8 weeks of Stanford V chemotherapy followed by 30 Gy modified involved-field radiation therapy (mIFRT) (G4) or Stanford V-C + 20 Gy mIFRT (G5). Patients were categorized as favorable or unfavorable risk per German Hodgkin Study Group (GHSG) criteria and outcomes between groups compared. RESULTS: A total of 129 patients were enrolled (68 favorable and 61 unfavorable risk). In the G4 study (n = 87), at median follow-up of 19.7 years, 5-, 10-, and 15-year progression-free survival (PFS) and overall survival (OS) were 95.4%/97.7%, 91.8%/96.5%, and 91.8%/95.3%, respectively. In the G5 study (n = 42), at median follow-up of 13.5 years, the 5-, 10-, and 15-year PFS and OS were 92.9%/100%, 92.9%/100%, and 88.4%/91.9%, respectively. PFS (P = .86) and OS (P = .86) were not significantly different between studies. There were also no significant differences between studies in patients with favorable or unfavorable risk for PFS (F: P = .53; U: P = .96), OS (F: P = .99; U: P = .78), secondary malignancies (F: P = .74; U: P = 1.0), and cardiovascular complications (F: no cases; U: P = 1.0). CONCLUSIONS: The G4 and G5 studies achieve high rates of durable remission; 20 versus 30 Gy mIFRT and cyclophosphamide substituted for mechlorethamine did not compromise nodal control, PFS, or OS in both favorable and unfavorable risk disease. These results support the efficacy of CMT in early-stage disease and lower-dose radiation therapy in patients with favorable and nonbulky unfavorable ESHL.

Discovery of a Potent and Selective Covalent p300/CBP Inhibitor.

Aberrant gene activation driven by the histone acetyltransferases p300 and CREB binding protein (CBP) has been linked to several diseases, including cancers. Because of this, many efforts have been aimed toward the targeting of the closely related paralogues, p300 and CBP, but these endeavors have been exclusively directed toward noncovalent inhibitors. X-ray crystallography of A-485 revealed that both p300 and CBP possess a cysteine (C1450) near the active site, thus rendering covalent inhibition an attractive chemical approach. Herein we report the development of compound 2, an acrylamide-based inhibitor of p300/CBP that forms a covalent adduct with C1450. We demonstrated using mass spectrometry that compound 2 selectively targets C1450, and we also validated covalent binding using kinetics experiments and cellular washout studies. The discovery of covalent inhibitor 2 gives us a unique tool for the study of p300/CBP biology.

Expanding the Repertoire for "Large Small Molecules": Prodrug ABBV-167 Efficiently Converts to Venetoclax with Reduced Food Effect in Healthy Volunteers.

Since gaining approval for the treatment of chronic lymphocytic leukemia (CLL), the BCL-2 inhibitor venetoclax has transformed the treatment of this and other blood-related cancers. Reflecting the large and hydrophobic BH3-binding groove within BCL-2, venetoclax has significantly higher molecular weight and lipophilicity than most orally administered drugs, along with negligible water solubility. Although a technology-enabled formulation successfully achieves oral absorption in humans, venetoclax tablets have limited drug loading and therefore can present a substantial pill burden for patients in high-dose indications. We therefore generated a phosphate prodrug (3, ABBV-167) that confers significantly increased water solubility to venetoclax and, upon oral administration to healthy volunteers either as a solution or high drug-load immediate release tablet, extensively converts to the parent drug. Additionally, ABBV-167 demonstrated a lower food effect with respect to venetoclax tablets. These data indicate that beyond-rule-of-5 molecules can be successfully delivered to humans via a solubility-enhancing prodrug moiety to afford robust exposures of the parent drug following oral dosing.

N-aryl-benzimidazolones as novel small molecule HSP90 inhibitors.

We describe the development of a novel series of N-aryl-benzimidazolone HSP90 inhibitors (9) targeting the N-terminal ATP-ase site. SAR development was influenced by structure-based design based around X-ray structures of ligand bound HSP90 complexes. Lead compounds exhibited high binding affinities, ATP-ase inhibition and cellular client protein degradation.

Discovery of a potent and selective Bcl-2 inhibitor using SAR by NMR.

The Bcl-2 family of proteins plays a major role in the regulation of apoptosis, or programmed cell death. Overexpression of the anti-apoptotic members of this family (Bcl-2, Bcl-x(L), and Mcl-1) can render cancer cells resistant to chemotherapeutic agents and therefore these proteins are important targets for the development of new anti-cancer agents. Here we describe the discovery of a potent, highly selective, Bcl-2 inhibitor using SAR by NMR and structure-based drug design which could serve as a starting point for the development of a Bcl-2 selective anti-cancer agent. Such an agent would potentially overcome the Bcl-x(L) mediated thrombocytopenia observed with ABT-263.

Tumour-selective antivascular effects of the novel anti-mitotic compound A-318315: An in vivo rat regional haemodynamic study.

1. It has been shown that tubulin-binding agents can destabilize cellular microtubules and suppress tumour growth; but it has also become apparent that some compounds can exert anti-vascular effects within the neovasculature of a solid tumour. To date, the difficulty with these targets has been the ability to selectivity induce vascular damage to the tumour while leaving normal vasculature unaffected. The data presented here characterizes the in vivo, tumour selective, anti-vascular effects of the novel tubulin-binding agent A-318315. 2. To that purpose, we have used an anaesthetized in vivo rat model designed to quantify acute changes in regional vascular resistance (VR) in both tumour and non-tumour vascular beds, simultaneously. Tissue-isolated tumours (approximately 1.25 gm) with blood flow supplied by a single epigastric artery were grown in the hindlimb of adult male rats. Blood flow to the tumour, mesenteric, renal and normal (non-tumour epigastric) arteries was measured pre-dose and post-dose under anaesthesia. 3. A-318315 was tested at 3, 10 and 30 mg/kg, i.v. These doses produced modest, transient increases in mean arterial pressure with little to no effect on heart rate. At peak effect, tumour VR increased to 175 +/- 47, 337 +/- 77 and 751 +/- 151% above the baseline, for the 3, 10 and 30 mg/kg doses, respectively, whereas VR was only modestly and transiently increased in normal epigastric (88 +/- 19%), mesenteric (33 +/- 3.3%) and renal arteries (17 +/- 8.6%). 4. These data demonstrate that A-318315 produces marked reductions in tumour blood flow in the rat at doses that exert minor effects on normal vascular function.

Long-term outcomes of patients with unfavorable stage I-II classic Hodgkin lymphoma treated with Stanford V chemotherapy and limited field irradiation.

Management of stage I-II unfavorable risk Hodgkin lymphoma (HL) strives to reduce toxicity while maintaining tumor control. Compared to ABVD or BEACOPP, Stanford V chemotherapy contains less doxorubicin and bleomycin. We report long-term outcomes of patients with stage I-II classic HL with European risk factors treated with Stanford V combined modality therapy (CMT). From our institutional cancer registry, we identified 168 patients with ≥1 European risk factor treated with 8-12 weeks of Stanford V CMT and consolidative radiotherapy between 1990 and 2016. Outcomes were analyzed after classification by EORTC and GHSG unfavorable criteria. With median follow-up of 8.4 years, 10-year overall survival and progression-free survival for the entire cohort were 95% and 88%, respectively. Thirteen of 18 relapses were salvaged successfully. There were no cases of MDS or AML after primary therapy. Long-term outcomes of stage I-II unfavorable risk HL treated with Stanford V CMT are comparable to ABVD or BEACOPP regimens.

Potentiation of temozolomide cytotoxicity by poly(ADP)ribose polymerase inhibitor ABT-888 requires a conversion of single-stranded DNA damages to double-stranded DNA breaks.

Poly(ADP-ribose) polymerase (PARP) senses DNA breaks and facilitates DNA repair via the polyADP-ribosylation of various DNA binding and repair proteins. We explored the mechanism of potentiation of temozolomide cytotoxicity by the PARP inhibitor ABT-888. We showed that cells treated with temozolomide need to be exposed to ABT-888 for at least 17 to 24 hours to achieve maximal cytotoxicity. The extent of cytotoxicity correlates with the level of double-stranded DNA breaks as indicated by gammaH2AX levels. In synchronized cells, damaging DNA with temozolomide in the presence of ABT-888 during the S phase generated high levels of double-stranded breaks, presumably because the single-stranded DNA breaks resulting from the cleavage of the methylated nucleotides were converted into double-stranded breaks through DNA replication. As a result, treatment of temozolomide and ABT-888 during the S phase leads to higher levels of cytotoxicity. ABT-888 inhibits poly(ADP-ribose) formation in vivo and enhances tumor growth inhibition by temozolomide in multiple models. ABT-888 is well tolerated in animal models. ABT-888 is currently in clinical trials in combination with temozolomide.

ABT-751, a novel tubulin-binding agent, decreases tumor perfusion and disrupts tumor vasculature.

ABT-751 is an orally bioavailable tubulin-binding agent that is currently under clinical development for cancer treatment. In preclinical studies, ABT-751 showed antitumor activity against a broad spectrum of tumor lines including those resistant to conventional chemotherapies. In this study, we investigated the antivascular properties of ABT-751 in a rat subcutaneous tumor model using dynamic contrast-enhanced magnetic resonance imaging. A single dose of ABT-751 (30 mg/kg, intravenously) induced a rapid, transient reduction in tumor perfusion. After 1 h, tumor perfusion decreased by 57% before recovering to near pretreatment levels within 6 h. In contrast, ABT-751 produced little change in muscle perfusion at either time point. To further elucidate mechanisms of drug action at the cellular level, we examined the effects of ABT-751 on endothelial cells using an in-vitro assay. ABT-751, at concentrations corresponding to plasma levels achieved in vivo, caused endothelial cell retraction and significant loss of microtubules within 1 h. The severity of these morphological changes was dose-dependent but reversible within 6 h after the discontinuation of the drug. Taken together, these results show that ABT-751 is a tubulin-binding agent with antivascular properties. Microtubule disruption and morphological changes in vascular endothelial cells may be responsible, at least in part, for the dysfunction of tumor blood vessels after ABT-751 treatment.

Dynamic CD8 T-cell responses to tumor-associated Epstein-Barr virus antigens in patients with Epstein-Barr virus-negative Hodgkin's disease.

In almost half of patients diagnosed with Hodgkin's disease (HD), the malignant Reed-Sternberg (RS) cells express Epstein-Barr virus (EBV) antigens. Multiple translational efforts are actively investigating antitumor immune strategies by stimulating cytotoxic T lymphocytes (CTL) against tumor-associated EBV antigens. It has previously been believed that this therapeutic strategy and presence of EBV-specific CTLs are limited to EBV-positive HD. In an effort to explore the EBV-specific immune response, here we characterize EBV-specific CTL responses to lytic and latent EBV antigens in 12 consecutive EBV carriers with EBV-negative HD. Compared to healthy donors, we detected weak, baseline EBV-specific responses to both lytic and latent antigens by IFN-gamma ELISPOT in patients with EBV-negative HD at diagnosis. Chemoradiotherapy was associated temporally with a decrease EBV-specific responses. At final follow-up (24 months), recovery of EBV-specific CTL responses was observed with robustness of lytic-specific response equivalent to healthy controls. We confirm evidence of EBV-specific CTLs in patients with EBV-negative HD and provide the first report of dynamic variance in this population during treatment. Our observation challenges prior belief that patients with HD remain immunodeficient following therapy and argues that the clinical significance of the EBV-specific immune response in EBV-negative HD should be further investigated.