Discovery of a Potent Chloroacetamide GPX4 Inhibitor with Bioavailability to Enable Target Engagement in Mice, a Potential Tool Compound for Inducing Ferroptosis In Vivo.

Compounds that inhibit glutathione peroxidase 4 (GPX4) hold promise as cancer therapeutics in their ability to induce a form of nonapoptotic cell death called ferroptosis. Our research identified 24, a structural analog of the potent GPX4 inhibitor RSL3, that has much better plasma stability (t1/2 > 5 h in mouse plasma). The bioavailability of 24 provided efficacious plasma drug concentrations with IP dosing, thus enabling in vivo studies to assess tolerability and efficacy. An efficacy study in mouse using a GPX4-sensitive tumor model found that doses of 24 up to 50 mg/kg were tolerated for 20 days but had no effect on tumor growth, although partial target engagement was observed in tumor homogenate.

[18F]BTK-1: A Novel Positron Emission Tomography Tracer for Imaging Bruton's Tyrosine Kinase.

PURPOSE: Bruton's tyrosine kinase (BTK) is a key component of B cell receptor (BCR) signaling, and as such a critical regulator of cell proliferation and survival. Aberrant BCR signaling is important in the pathogenesis of various B cell malignancies and autoimmune disorders. Here, we describe the development of a novel positron emission tomography (PET) tracer for imaging BTK expression and/or occupancy by small molecule therapeutics. METHODS: Radiochemistry was carried out by reacting the precursor with [18F]fluoride on a GE FX-FN TracerLab synthesis module to produce [18F]BTK-1 with a 6% decay-corrected radiochemical yield, 100 ± 6 GBq/µmol molar activity, and a radiochemical purity of 99%. Following intravenous administration of [18F]BTK-1 (3.63 ± 0.59 MBq, 0.084 ± 0.05 µg), 60-min dynamic images were acquired in two xenograft models: REC-1, an efficacious mantle cell lymphoma model, and U87MG, a non-efficacious glioblastoma model. Subsequent studies included vehicle, pretreatment (10 min prior to tracer injection), and displacement (30 min post-tracer injection) studies with different reversible BTK inhibitors to examine BTK binding. Human radiation dosimetry was estimated based on PET imaging in healthy rats. RESULTS: Uptake of [18F]BTK-1 was significantly higher in BTK expressing REC-1 tumors than non-BTK expressing U87MG tumors. Administration of BTK inhibitors prior to tracer administration blocked [18F]BTK-1 binding in the REC-1 tumor model consistent with [18F]BTK-1 binding to BTK. The predicted effective dose in humans was 0.0199 ± 0.0007 mSv/MBq. CONCLUSION: [18F]BTK-1 is a promising PET tracer for imaging of BTK, which could provide valuable information for patient selection, drug dose determination, and improving our understanding of BTK biology in humans.

ABT-165, a Dual Variable Domain Immunoglobulin (DVD-Ig) Targeting DLL4 and VEGF, Demonstrates Superior Efficacy and Favorable Safety Profiles in Preclinical Models.

Antiangiogenic therapy is a clinically validated modality in cancer treatment. To date, all approved antiangiogenic drugs primarily inhibit the VEGF pathway. Delta-like ligand 4 (DLL4) has been identified as a potential drug target in VEGF-independent angiogenesis and tumor-initiating cell (TIC) survival. A dual-specific biologic targeting both VEGF and DLL4 could be an attractive strategy to improve the effectiveness of anti-VEGF therapy. ABT-165 was uniquely engineered using a proprietary dual-variable domain immunoglobulin (DVD-Ig) technology based on its ability to bind and inhibit both DLL4 and VEGF. In vivo, ABT-165 induced significant tumor growth inhibition compared with either parental antibody treatment alone, due, in part, to the disruption of functional tumor vasculature. In combination with chemotherapy agents, ABT-165 also induced greater antitumor response and outperformed anti-VEGF treatment. ABT-165 displayed nonlinear pharmacokinetic profiles in cynomolgus monkeys, with an apparent terminal half-life > 5 days at a target saturation dose. In a GLP monkey toxicity study, ABT-165 was well-tolerated at doses up to 200 mg/kg with non-adverse treatment-related histopathology findings limited to the liver and thymus. In summary, ABT-165 represents a novel antiangiogenic strategy that potently inhibits both DLL4 and VEGF, demonstrating favorable in vivo efficacy, pharmacokinetic, and safety profiles in preclinical models. Given these preclinical attributes, ABT-165 has progressed to a phase I study. Mol Cancer Ther; 17(5); 1039-50. ©2018 AACR.

The Volume of Three-Dimensional Cultures of Cancer Cells InVitro Influences Transcriptional Profile Differences and Similarities with Monolayer Cultures and Xenografted Tumors.

Improving the congruity of preclinical models with cancer as it is manifested in humans is a potential way to mitigate the high attrition rate of new cancer therapies in the clinic. In this regard, three-dimensional (3D) tumor cultures in vitro have recently regained interest as they have been acclaimed to have higher similarity to tumors in vivo than to cells grown in monolayers (2D). To identify cancer functions that are active in 3D rather than in 2D cultures, we compared the transcriptional profiles (TPs) of two non-small cell lung carcinoma cell lines, NCI-H1650 and EBC-1 grown in both conditions to the TP of xenografted tumors. Because confluence, diameter or volume can hypothetically alter TPs, we made intra- and inter-culture comparisons using samples with defined dimensions. As projected by Ingenuity Pathway Analysis (IPA), a limited number of signal transduction pathways operational in vivo were better represented by 3D than by 2D cultures in vitro. Growth of 2D and 3D cultures as well as xenografts induced major changes in the TPs of these 3 modes of culturing. Alterations of transcriptional network activation that were predicted to evolve similarly during progression of 3D cultures and xenografts involved the following functions: hypoxia, proliferation, cell cycle progression, angiogenesis, cell adhesion, and interleukin activation. Direct comparison of TPs of 3D cultures and xenografts to monolayer cultures yielded up-regulation of networks involved in hypoxia, TGF and Wnt signaling as well as regulation of epithelial mesenchymal transition. Differences in TP of 2D and 3D cancer cell cultures are subject to progression of the cultures. The emulation of the predicted cell functions in vivo is therefore not only determined by the type of culture in vitro but also by the confluence or diameter of the 2D or 3D cultures, respectively. Consequently, the successful implementation of 3D models will require phenotypic characterization to verify the relevance of applying these models for drug development.

Flexible peritoneal windows for quantitative fluorescence and bioluminescence preclinical imaging.

At present, there is considerable interest in the use of in vivo fluorescence and bioluminescence imaging to track the onset and progression of pathologic processes in preclinical models of human disease. Optical quantitation of such phenomena, however, is often problematic, frequently complicated by the overlying tissue's scattering and absorption of light, as well as the presence of endogenous cutaneous and subcutaneous fluorophores. To partially circumvent this information loss, we report here the development of flexible, surgically implanted, transparent windows that enhance quantitative in vivo fluorescence and bioluminescence imaging of optical reporters. These windows are metal and glass free and thus compatible with computed tomography, magnetic resonance imaging, positron emission tomography, and single-photon emission computed tomography; they also permit visualization of much larger areas with fewer impediments to animal locomotion and grooming than those previously described. To evaluate their utility in preclinical imaging, we surgically implanted these windows in the abdominal walls of female athymic nude mice and subsequently inoculated each animal with 1 × 10(4) to 1 × 10(6) bioluminescent human ovarian cancer cells (SKOV3ip.1-luc). Longitudinal imaging studies of fenestrated animals revealed up to 48-fold gains in imaging sensitivity relative to nonfenestrated animals, with relatively few complications, allowing wide-field in vivo visualization of nascent metastatic ovarian cancer colonization.

FDG-PET as a pharmacodynamic biomarker for early assessment of treatment response to linifanib (ABT-869) in a non-small cell lung cancer xenograft model.

Linifanib (ABT-869) is a multitargeted receptor tyrosine kinase inhibitor. This work aims to evaluate F-fluorodeoxyglucose-positron emission tomography (FDG-PET) as a pharmacodynamic (PD) biomarker for linifanib treatment utilizing the Calu-6 model of human non-small cell lung (NSCLC) cancer in SCID-beige mice. Animals received either vehicle or 12.5 mg/kg linifanib orally twice a day for the duration of the study. Imaging was performed at -1, 1, 3, and 7 days after beginning treatment (n = 12-14 per group). Linifanib inhibited tumor growth and suppressed tumor metabolic activity. Changes in tumor FDG uptake were observed as early as 1 day after beginning linifanib treatment and were sustained for the duration of the study. This study confirms that linifanib is efficacious in this xenograft model of human NSCLC and confirms FDG-PET is a potential PD biomarker strategy for linifanib therapy.

The p38 kinases MKK4 and MKK6 suppress metastatic colonization in human ovarian carcinoma.

Despite considerable efforts to improve early detection of ovarian cancer, the majority of women at time of diagnosis will have metastatic disease. Understanding and targeting the molecular underpinnings of metastasis continues to be the principal challenge in the clinical management of ovarian cancer. Whereas the multistep process of metastasis development has been well established in both clinical and experimental models, the molecular factors and signaling pathways involved in successful colonization of a secondary site by disseminated cancer cells are not well defined. We have previously identified mitogen-activated protein kinase (MAPK) kinase 4/c-Jun NH2-terminal kinase (JNK)-activating kinase (MKK4/JNKK1/SEK1, hereafter referred to as MKK4) as a metastasis suppressor protein in ovarian carcinoma. In this study, we elucidate key mechanisms of MKK4-mediated metastasis suppression. Through the use of a kinase-inactive mutant, we show that MKK4 kinase activity is essential for metastasis suppression and prolongation of animal survival. Because MKK4 can activate either of two MAPKs, p38 or JNK, we expressed MKK6 or MKK7, specific activators of these MAPKs, respectively, to delineate which MAPK signaling module was involved in MKK4-mediated metastasis suppression. We observed that MKK6 expression suppressed metastatic colonization whereas MKK7 had no effect. Our finding that MKK4 and MKK6 both suppress metastasis points to the p38 pathway as an important regulatory pathway for metastatic colonization in ovarian cancer.

Suppression of metastatic colonization by the context-dependent activation of the c-Jun NH2-terminal kinase kinases JNKK1/MKK4 and MKK7.

Advances in clinical, translational, and basic studies of metastasis have identified molecular changes associated with specific facets of the metastatic process. Studies of metastasis suppressor gene function are providing a critical mechanistic link between signaling cascades and biological outcomes. We have previously identified c-Jun NH2-terminal kinase (JNK) kinase 1/mitogen-activated protein kinase (MAPK) kinase 4 (JNKK1/MKK4) as a prostate cancer metastasis suppressor gene. The JNKK1/MKK4 protein is a dual-specificity kinase that has been shown to phosphorylate and activate the JNK and p38 MAPKs in response to a variety of extracellular stimuli. In this current study, we show that the kinase activity of JNKK1/MKK4 is required for suppression of overt metastases and is sufficient to prolong animal survival in the AT6.1 model of spontaneous metastasis. Ectopic expression of the JNK-specific kinase MKK7 suppresses the formation of overt metastases, whereas the p38-specific kinase MKK6 has no effect. In vivo studies show that both JNKK1/MKK4 and MKK7 suppress the formation of overt metastases by inhibiting the ability of disseminated cells to colonize the lung (secondary site). Finally, we show that JNKK1/MKK4 and MKK7 from disseminated tumor cells are active in the lung but not in the primary tumor, providing a biochemical explanation for why their expression specifically suppressed metastasis while exerting no effect on the primary tumor. Taken together, these studies contribute to a mechanistic understanding of the context-dependent function of metastasis regulatory proteins.

Metastasis suppressor genes: from gene identification to protein function and regulation.

In the past decade, findings from various disciplines of research have stimulated a reevaluation of fundamental concepts of the biology of metastasis. The convergence of two avenues of research has largely been responsible for this shift. First, clinical and experimental studies of specific steps of the metastatic cascade have shown that cancer cells often disseminate early in the natural history of disease and can persist at secondary sites for extended periods of time. These findings suggest that disseminated cells remain subject to growth regulation at distant sites as "dormant" single cells or microscopic metastases consisting of small numbers of cells. Second, complementary functional, biochemical, and signal transduction studies have identified a specific class of proteins that suppress the formation of overt metastases. These proteins are encoded by metastasis suppressor genes, which are operationally defined as genes that suppress in vivo metastasis without inhibiting primary tumor growth when expressed ectopically in metastatic cell lines. While metastasis suppressor proteins may affect many steps in metastatic development, recent evidence specifically implicates several of these proteins in the regulation of growth of disseminated cells at secondary sites. This review describes the evolving understanding of rate-limiting steps of metastatic growth, and the role of metastasis suppressor proteins in the regulation of these processes. We will give an overview of the studies of metastasis suppressor protein function, which have shifted our attention toward mechanisms of growth control at the secondary site (i.e., "metastatic colonization"). Emphasis is placed upon the complimentary research in the fields of metastasis and signal transduction that has identified signaling pathways controlling metastatic colonization. We also discuss the regulation of metastasis suppressor proteins and the potential biological and biochemical mechanisms responsible for their organ-type specificity. Finally, the implication of these emerging concepts on the development of therapeutic strategies will be presented.

Inhibition of prostate cancer metastatic colonization by approximately 4.2 Mb of human chromosome 12.

Our previous studies demonstrate that introduction of a approximately 70 cM region (now estimated at 63.75 Mb by the Human Genome Project) of human chromosome 12 into the highly metastatic Dunning rat prostate cancer cell line AT6.1 results in >30-fold (>/=90%) reduction in the number of overt metastases in spontaneous metastasis assays. We report the further localization and biological characterization of the metastasis-suppressor activity encoded by a reduced region of chromosome 12. To localize this metastasis-suppressor activity, a panel of AT6.1 microcell hybrids that retain varying portions of human chromosome 12 was constructed and subjected to sequence-tagged site (STS)-based PCR analysis and assessment of in vivo metastatic ability. Data from these complementary approaches localized the metastasis-suppressor activity to a approximately 4.2 Mb portion of human chromosome 12q24.3 comprised of 3 separate regions. Reverse transcriptase-polymerase chain reaction (RT-PCR) and immunoblotting were used for differential expression analyses to identify which characterized genes, predicted gene sequences and expressed sequence tags (ESTs) within this region could be responsible for the observed metastasis suppression. Comprehensive in vivo studies showed that suppressed AT6.1-12 hybrids that retain the metastasis-suppressor region on 12q24.3 are capable of arriving at the secondary site, but are not able to persist there. Thus, unlike other metastasis-suppressor genes characterized to date, the metastasis-suppressor gene encoded by this region appears to utilize a different biologic mechanism to suppress the growth of overt metastases at the secondary site.

MKK4 and metastasis suppression: a marriage of signal transduction and metastasis research.

MAP kinase kinase 4 (MKK4) is a member of the stress-activated protein kinase (SAPK) signaling cascade and is involved in the regulation of many cellular processes. We have recently demonstrated a functional role for MKK4 in the suppression of metastases. In this review, we discuss the established cellular and biochemical functions of MKK4, as well as a new function for MKK4 as a metastasis suppressor gene. Because of the importance of signaling studies to this translational work, a detailed example of the strategy and tools that can be employed to define the biochemical mechanism of MKK4-mediated metastasis suppression is presented. Finally, the potential therapeutic utility of these findings is discussed.

Mitogen-activated protein kinase kinase 4 (MKK4) acts as a metastasis suppressor gene in human ovarian carcinoma.

Despite improvements in chemotherapy and the recognition that aggressive surgical cytoreduction is beneficial, the majority of patients diagnosed with ovarian cancer will die as a result of metastatic disease. The molecular changes associated with acquisition of metastatic ability in ovarian cancer are poorly understood. We hypothesize that metastasis suppressor gene inactivation or down-regulation plays a role in ovarian cancer progression. Mitogen-activated protein kinase kinase 4 (MKK4), a member of the stress-activated protein kinase signaling cascade, has been identified recently as a metastasis-suppressor gene. An immunohistochemical approach was taken to test the possibility that MKK4 dysregulation occurs during the development of clinical ovarian cancer metastases. MKK4 expression was evaluated in normal and metastatic ovarian tissues. Normal ovarian epithelial cells showed high intensity staining for MKK4, whereas metastatic tissues showed a statistically significant decrease in expression. These results support a role for MKK4 dysregulation in the development of clinical disease. A functional approach was taken to test the ability of MKK4 to suppress metastatic colonization, the process whereby disseminated cancer cells lodge and grow at a secondary site in vivo. The SKOV3ip.1 human ovarian cancer cell line was chosen for these studies because it lacks endogenous MKK4 expression but retains both upstream and downstream components of the signaling cascade of MKK4. Ectopic expression of MKK4 in these cells, when injected into female SCID mice, suppressed the number of overt metastatic implants by nearly 90%. Furthermore, MKK4 expression increased the life span of the animals by 70%. Taken together, these data support a role for MKK4 in the suppression of metastatic colonization in ovarian cancer.