A phase 1 study to assess the safety, pharmacokinetics, and anti-tumor activity of the androgen receptor n-terminal domain inhibitor epi-506 in patients with metastatic castration-resistant prostate cancer.

BACKGROUND: EPI-506 is the first of a new class of drugs targeting the N-terminal domain (NTD) of the androgen receptor (AR), potentially overcoming known resistance mechanisms to androgen receptor pathway inhibitors (ARPIs) among men with metastatic castration resistant prostate cancer (mCRPC). METHODS: Patients with mCRPC who had progressed on prior ARPI were enrolled in this phase 1 open-label, adaptive 3 + 3 dose escalation study. The primary outcome was safety and tolerability of oral EPI-506. Secondary objectives included determination of the maximal tolerated dose (MTD), pharmacokinetic profile, and antitumor efficacy. RESULTS: 28 mCRPC patients were enrolled into 7 dose cohorts of EPI-506 ranging from 80-3600 mg given once daily and 1800 mg given twice daily. Six DLTs occurred in 4 patients; Grade 4 elevated amylase; Grade 3 abdominal pain; Grade 3 elevated ALT and Grade 3 elevated AST; Grade 2 nausea and Grade 1 vomiting which resulted in study drug intake of < 75% of the expected dose during the DLT assessment period. The most common drug-related adverse events included diarrhea, nausea and fatigue. Six patients had a PSA decline not meeting PSA response criteria. The study was terminated prior to reaching the MTD due to poor oral bioavailability. CONCLUSIONS: This phase 1 trial established the safety of EPI-506 and provides proof of concept for targeting the AR NTD. Next generation compounds with improved bioavailability and potency are in clinical development.

Cytopathic effects of the cytomegalovirus-encoded apoptosis inhibitory protein vMIA.

Replication of human cytomegalovirus (CMV) requires the expression of the viral mitochondria-localized inhibitor of apoptosis (vMIA). vMIA inhibits apoptosis by recruiting Bax to mitochondria, resulting in its neutralization. We show that vMIA decreases cell size, reduces actin polymerization, and induces cell rounding. As compared with vMIA-expressing CMV, vMIA-deficient CMV, which replicates in fibroblasts expressing the adenoviral apoptosis suppressor E1B19K, induces less cytopathic effects. These vMIA effects can be separated from its cell death-inhibitory function because vMIA modulates cellular morphology in Bax-deficient cells. Expression of vMIA coincided with a reduction in the cellular adenosine triphosphate (ATP) level. vMIA selectively inhibited one component of the ATP synthasome, namely, the mitochondrial phosphate carrier. Exposure of cells to inhibitors of oxidative phosphorylation produced similar effects, such as an ATP level reduced by 30%, smaller cell size, and deficient actin polymerization. Similarly, knockdown of the phosphate carrier reduced cell size. Our data suggest that the cytopathic effect of CMV can be explained by vMIA effects on mitochondrial bioenergetics.

Targeting acute myeloid leukemia dependency on VCP-mediated DNA repair through a selective second-generation small-molecule inhibitor.

The development and survival of cancer cells require adaptive mechanisms to stress. Such adaptations can confer intrinsic vulnerabilities, enabling the selective targeting of cancer cells. Through a pooled in vivo short hairpin RNA (shRNA) screen, we identified the adenosine triphosphatase associated with diverse cellular activities (AAA-ATPase) valosin-containing protein (VCP) as a top stress-related vulnerability in acute myeloid leukemia (AML). We established that AML was the most responsive disease to chemical inhibition of VCP across a panel of 16 cancer types. The sensitivity to VCP inhibition of human AML cell lines, primary patient samples, and syngeneic and xenograft mouse models of AML was validated using VCP-directed shRNAs, overexpression of a dominant-negative VCP mutant, and chemical inhibition. By combining mass spectrometry-based analysis of the VCP interactome and phospho-signaling studies, we determined that VCP is important for ataxia telangiectasia mutated (ATM) kinase activation and subsequent DNA repair through homologous recombination in AML. A second-generation VCP inhibitor, CB-5339, was then developed and characterized. Efficacy and safety of CB-5339 were validated in multiple AML models, including syngeneic and patient-derived xenograft murine models. We further demonstrated that combining DNA-damaging agents, such as anthracyclines, with CB-5339 treatment synergizes to impair leukemic growth in an MLL-AF9-driven AML murine model. These studies support the clinical testing of CB-5339 as a single agent or in combination with standard-of-care DNA-damaging chemotherapy for the treatment of AML.

The ß-Carboline Harmine Induces Actin Dynamic Remodeling and Abrogates the Malignant Phenotype in Tumorigenic Cells.

Numerous studies have shown that alteration of actin remodeling plays a pivotal role in the regulation of morphologic and phenotypic changes leading to malignancy. In the present study, we searched for drugs that can regulate actin polymerization and reverse the malignant phenotype in cancer cells. We developed a cell-free high-throughput screening assay for the identification of compounds that induce the actin polymerization in vitro, by fluorescence anisotropy. Then, the potential of the hit compound to restore the actin cytoskeleton and reverse the malignant phenotype was checked in EWS-Fli1-transformed fibroblasts and in B16-F10 melanoma cells. A ß-carboline extracted from Peganum harmala (i.e., harmine) is identified as a stimulator of actin polymerization through a mechanism independent of actin binding and requiring intracellular factors involved in a process that regulates actin kinetics. Treatment of malignant cells with non-cytotoxic concentrations of harmine induces the recovery of a non-malignant cell morphology accompanied by reorganization of the actin cytoskeleton, rescued cell-cell adhesion, inhibition of cell motility and loss of anchorage-independent growth. In conclusion, harmine induces the reversion of the malignant phenotype by a process involving the modulation of actin dynamics and is a potential anti-tumor agent acting principally through a non-cytotoxic process.

CB-6644 Is a Selective Inhibitor of the RUVBL1/2 Complex with Anticancer Activity.

RUVBL1 and RUVBL2 are ATPases associated with diverse cellular activities (AAAs) that form a complex involved in a variety of cellular processes, including chromatin remodeling and regulation of gene expression. RUVBLs have a strong link to oncogenesis, where overexpression is correlated with tumor growth and poor prognosis in several cancer types. CB-6644, an allosteric small-molecule inhibitor of the ATPase activity of the RUVBL1/2 complex, interacts specifically with RUVBL1/2 in cancer cells, leading to cell death. Importantly, drug-acquired-resistant cell clones have amino acid mutations in either RUVBL1 or RUVBL2, suggesting that cell killing is an on-target consequence of RUVBL1/2 engagement. In xenograft models of acute myeloid leukemia and multiple myeloma, CB-6644 significantly reduced tumor growth without obvious toxicity. This work demonstrates the therapeutic potential of targeting RUVBLs in the treatment of cancer and establishes a chemical entity for probing the many facets of RUVBL biology.

Valosin-Containing Protein/p97 as a Novel Therapeutic Target in Acute Lymphoblastic Leukemia.

B acute lymphoblastic leukemia (B-ALL) cells are distinctively vulnerable to endoplasmic reticulum (ER) stress. Recently, inhibition of p97 was shown to induce ER stress and subsequently cell death in solid tumors and in multiple myeloma. We investigated the role of a novel, orally available, p97 inhibitor (CB-5083; Cleave Biosciences) in B-ALL. CB-5083 induced a significant reduction in viability in 10 human B-ALL cell lines, harboring the most common fusion-genes involved in pediatric and adult B-ALL, with IC50s ranging from 0.34 to 0.76 µM. Moreover, CB-5083 significantly reduced the colony formation of OP1 and NALM6 cells. Early and strong induction of apoptosis was demonstrated in BALL1 and OP1 cells, together with a robust cleavage of PARP. CB-5083 induced ER stress, as documented through: 1) prominent expression of chaperones (GRP78, GRP94, PDI, DNAJC3, and DNAJB9); 2) increased activation of IRE1-alpha, as demonstrated by the splicing of XBP1; and 3) activation of PERK, which resulted in a significant overexpression of CHOP, and its downstream genes. CB-5083 reduced the viability also in GRP78-/-, GRP94-/-, and XBP1-/- cells, suggesting that none of these proteins alone was strictly required for CB-5083 activity. Moreover, we showed that the absence of XBP1 (XBP1-/-) increased the sensitivity to CB-5083, leading to the hypothesis that XBP1 splicing counteracts the activity of CB-5083, probably mitigating ER stress. Finally, vincristine was synergistic with CB-5083 in both BALL1 and OP1 cells. In summary, the targeting of p97 with CB-5083 is a novel promising therapeutic approach that should be further evaluated in B-ALL.

The p97 Inhibitor CB-5083 Is a Unique Disrupter of Protein Homeostasis in Models of Multiple Myeloma.

Inhibition of the AAA ATPase, p97, was recently shown to be a novel method for targeting the ubiquitin proteasome system, and CB-5083, a first-in-class inhibitor of p97, has demonstrated broad antitumor activity in a range of both hematologic and solid tumor models. Here, we show that CB-5083 has robust activity against multiple myeloma cell lines and a number of in vivo multiple myeloma models. Treatment with CB-5083 is associated with accumulation of ubiquitinated proteins, induction of the unfolded protein response, and apoptosis. CB-5083 decreases viability in multiple myeloma cell lines and patient-derived multiple myeloma cells, including those with background proteasome inhibitor (PI) resistance. CB-5083 has a unique mechanism of action that combines well with PIs, which is likely owing to the p97-dependent retro-translocation of the transcription factor, Nrf1, which transcribes proteasome subunit genes following exposure to a PI. In vivo studies using clinically relevant multiple myeloma models demonstrate that single-agent CB-5083 inhibits tumor growth and combines well with multiple myeloma standard-of-care agents. Our preclinical data demonstrate the efficacy of CB-5083 in several multiple myeloma disease models and provide the rationale for clinical evaluation as monotherapy and in combination in multiple myeloma. Mol Cancer Ther; 16(11); 2375-86. ©2017 AACR.

Discovery of a First-in-Class, Potent, Selective, and Orally Bioavailable Inhibitor of the p97 AAA ATPase (CB-5083).

The AAA-ATPase p97 plays vital roles in mechanisms of protein homeostasis, including ubiquitin-proteasome system (UPS) mediated protein degradation, endoplasmic reticulum-associated degradation (ERAD), and autophagy. Herein we describe our lead optimization efforts focused on in vitro potency, ADME, and pharmaceutical properties that led to the discovery of a potent, ATP-competitive, D2-selective, and orally bioavailable p97 inhibitor 71, CB-5083. Treatment of tumor cells with 71 leads to significant accumulation of markers associated with inhibition of UPS and ERAD functions, which induces irresolvable proteotoxic stress and cell death. In tumor bearing mice, oral administration of 71 causes rapid accumulation of markers of the unfolded protein response (UPR) and subsequently induces apoptosis leading to sustained antitumor activity in in vivo xenograft models of both solid and hematological tumors. 71 has been taken into phase 1 clinical trials in patients with multiple myeloma and solid tumors.

Targeting the AAA ATPase p97 as an Approach to Treat Cancer through Disruption of Protein Homeostasis.

p97 is a AAA-ATPase with multiple cellular functions, one of which is critical regulation of protein homeostasis pathways. We describe the characterization of CB-5083, a potent, selective, and orally bioavailable inhibitor of p97. Treatment of tumor cells with CB-5083 leads to accumulation of poly-ubiquitinated proteins, retention of endoplasmic reticulum-associated degradation (ERAD) substrates, and generation of irresolvable proteotoxic stress, leading to activation of the apoptotic arm of the unfolded protein response. In xenograft models, CB-5083 causes modulation of key p97-related pathways, induces apoptosis, and has antitumor activity in a broad range of both hematological and solid tumor models. Molecular determinants of CB-5083 activity include expression of genes in the ERAD pathway, providing a potential strategy for patient selection.

SAR156497, an exquisitely selective inhibitor of aurora kinases.

The Aurora family of serine/threonine kinases is essential for mitosis. Their crucial role in cell cycle regulation and aberrant expression in a broad range of malignancies have been demonstrated and have prompted intensive search for small molecule Aurora inhibitors. Indeed, over 10 of them have reached the clinic as potential anticancer therapies. We report herein the discovery and optimization of a novel series of tricyclic molecules that has led to SAR156497, an exquisitely selective Aurora A, B, and C inhibitor with in vitro and in vivo efficacy. We also provide insights into its mode of binding to its target proteins, which could explain its selectivity.