A clinically compatible drug-screening platform based on organotypic cultures identifies vulnerabilities to prevent and treat brain metastasis

We report a medium-throughput drug-screening platform (METPlatform) based on organotypic cultures that allows to evaluate inhibitors against metastases growing in situ. By applying this approach to the unmet clinical need of brain metastasis, we identified several vulnerabilities. Among them, a blood-brain barrier permeable HSP90 inhibitor showed high potency against mouse and human brain metastases at clinically relevant stages of the disease, including a novel model of local relapse after neurosurgery. Furthermore, in situ proteomic analysis applied to metastases treated with the chaperone inhibitor uncovered a novel molecular program in brain metastasis, which includes biomarkers of poor prognosis and actionable mechanisms of resistance. Our work validates METPlatform as a potent resource for metastasis research integrating drug-screening and unbiased omic approaches that is compatible with human samples. Thus, this clinically relevant strategy is aimed to personalize the management of metastatic disease in the brain and elsewhere.

Macrocyclization as a Source of Desired Polypharmacology. Discovery of Triple PI3K/mTOR/PIM Inhibitors

The PI3K/AKT/mTOR and PIM kinase pathways contribute to the development of several hallmarks of cancer. Cotargeting of these pathways has exhibited promising synergistic therapeutic effects in liquid and solid tumor types. To identify molecules with combined activities, we cross-screened our collection of PI3K/(±mTOR) macrocycles (MCXs) and identified the MCX thieno[3,2-d]pyrimidine derivative 2 as a moderate dual PI3K/PIM-1 inhibitor. We report the medicinal chemistry exploration and biological characterization of a series of thieno[3,2-d]pyrimidine MCXs, which led to the discovery of IBL-302 (31), a potent, selective, and orally bioavailable triple PI3K/mTOR/PIM inhibitor. IBL-302, currently in late preclinical development (AUM302), has recently demonstrated efficacy in neuroblastoma and breast cancer xenografts. Additionally, during the course of our experiments, we observed that macrocyclization was essential to obtain the desired multitarget profile. As a matter of example, the open precursors 35-37 were inactive against PIM whereas MCX 28 displayed low nanomolar activity.

Abstract A275: Co-targeting PIM and PI3K/mTOR pathways with a single molecule: Novel orally available combined PIM/PI3K and PIM/PI3K/mTOR kinase inhibitors

The PI3K/AKT pathway is commonly activated in human cancer. Multiple small-molecule inhibitors have been developed to target PI3K/mTOR or AKT kinases, but the efficacy of these drugs is compromised by the stimulation of compensatory signaling pathways. The redundancy of oncogenic signaling pathways provides back-up mechanisms that allow cancer cells to escape to targeted therapies. One example of such compensatory pathways is that driven by PIM kinases, which produce parallel oncogenic signals to AKT and mTOR and share several downstream molecular targets. In fact, in mouse lymphoma models chemoresistance to doxorubicin caused by AKT is readily reversed by rapamycin, but PIM mediated resistance is refractory to mTORC1 inhibition. Moreover, PIM2 kinase can confer resistance of primary hematopoietic cells to rapamycin treatment. Furthermore, PIM 1 mediates resistance to AKT and PI3K/mTOR inhibition and suggests co-targeting to improve the efficacy of PI3K/AKT/mTOR inhibitors in anticancer therapy. The PI3K/AKT/mTOR and PIM pathways are activated and seem to be relevant for tumor progression in many lymphomas, leukemias and in some solid tumors. We have previously reported that the combination of PI3K inhibitor GDC-0941 with a PIM selective inhibitor, ETP-45299, was strongly synergistic in antiproliferation experiments in MV-4-11 AML cells. Therefore, combination of such activities in a single molecule might have the potential to achieve better clinical efficacy and prevent/suppress resistance in comparison with classical PI3K/AKT/mTOR inhibitors. During the course of our investigations in this field we have identified a new chemical series of compounds with dual (PIM/PI3K) and triple activity (PIM/PI3K/mTOR inhibitors). (WO2012/156756). In this work, we show the biochemical, cellular and in vivo characterization of dual PIM/PI3K ETP-539/(IBL-202) and triple PIM/PI3K/mTOR ETP-339/(IBL-301) inhibitors. These optimized lead compounds are low nanomolar pan PIM/PI3K and pan PIM/PI3K/mTOR inhibitors respectively. These dual and triple inhibitors show excellent kinase selectivity profile against a panel of 456 kinases. Both compounds have been profiled for their antiproliferative behavior. We have identified leukemia, lymphoma, colon, and NSCLC lines which exhibit a strong sensitivity to dual and triple inhibition with GI80 between 5-10 times more potent than PIM or PI3K selective reference inhibitors. Mechanistically, cells respond to dual and triple inhibitors with a clear cell cycle arrest and marked apoptosis in AML and NSCLC cell lines, and strong down regulation of biomarkers. Our dual and triple inhibitors are optimized with respect to their in vitro ADME properties and have excellent oral bioavailability. These inhibitors have been tested in vivo in xenograft (MV4:11 AML) and transgenic (KRAsV12NSCLC) cancer mouse models. Both compounds have demonstrated down regulation of biomarkers associated with their targeted profile and significant antitumor efficacy in both models after oral administration. These inhibitors have been well tolerated, with no signs of toxicity even 20 times above the efficacious dose.

These results provide the rationale for further preclinical development of ETP-539/(IBL-202 and ETP-339/(IBL-301) and the basis for a potential clinical use in AML and NSCLC tumors.

Citation Information: Mol Cancer Ther 2013;12(11 Suppl):A275.

Citation Format: Carmen Blanco Aparicio, Oliver Renner, Elena Gomez-Casero, Antonio Cebriá, Nuria Ajenjo, Enara Aguirre, David Cebrián, Ma Carmen Rodriguez de Miguel, Belén Pequeño, MaIsabel Albarrán, Rosario Riesco, Ana Belén García, Rosa Alvarez, Michael O'Neill, Sonia Martinez, Joaquin Pastor. Co-targeting PIM and PI3K/mTOR pathways with a single molecule: Novel orally available combined PIM/PI3K and PIM/PI3K/mTOR kinase inhibitors. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr A275.

Abstract B228: Discovery of 6-Methyl-3-aryl-7,8-dihydro-6H-9-oxa-1,2,3a,4,6-pentaaza-cyclopenta[a]naphthalen-5-ylamine compounds as Pim kinase inhibitors with potent activity in tumoral cell lines and special binding mode

Proviral integration site for Moloney murine leukemia virus (PIM) kinases are potent oncogens. Pim-1, 2 and 3 are highly conserved kinases that have unique structural properties, and are characterized by a constitutive serine/threonine activity that does not depend on post-translational modifications for activation. Pim kinases activity supports in vitro and in vivo tumor cell growth and survival through modification of an increasing number of common as well as isoform-specific substrates including c-myc and Histone H3, which drive transcription, eukaryotic elongation factor 4E-BP-1 that regulates transcription and Bad that activates cell survival. Furthermore, cell cycle protein activation by Pim kinases is involved with proliferation, and through regulation of AMPK activity Pim kinases mediated control of energy metabolism. Pim kinases are overexpressed in a range of haematopoietic malignancies and solid cancers, and its overexpression is associated with drug resistance. Inhibition of PIM kinase activity may be an attractive therapeutic strategy with possible favourable toxicity profiles due to minimal phenotype of mice mutant for all Pim family members.

Knowledge of the three-dimensional structure of Pim1 is especially important for understanding the design of potent and selective Pim1 inhibitors as novel therapeutic agents. Using a rational strategy we have generated a novel chemical series, by introduction of a morpholine cycle in the C-7, C-8 position of the triazolopyridazine ring. Morpholine ring can be accommodated in the catalytic site due to a change in the conformation of the P-loop on the crystal structure to afford very potent and selective tricyclic compounds against PIM kinases. Depending on the amine C-6 substitution fragment we have observed different isoforms profiles. Here, we describe the exploration and biological characterization of C-6 tricyclic series, reporting its SAR/SPR (ADME).

We identified lead compounds with potency in the low nanomolar range vs. PIM1, 2 and 3 and high selectivity versus a panel of 24 protein kinases. The compounds display cellular activity by blocking PIM signaling, S112 P-Bad in H1299 Pim1 cells, in the low nanomolar range. The combination of the PI3K inhibitor GDC-0941 with Pim inhibitors was strongly synergistic in vitro in non solid and solid tumoral cell lines.

Finally, we assessed the effect of Pim kinase inhibition on Pim signaling in vivo in a mouse subcutaeneous tumor xenograft model employing a human mantle cell lymphoma cell line, Jeko-1. Results demonstrated that ETP-652 inhibited phosphorylation of S112 P-Bad in vivo.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr B228.

Pim 1 kinase inhibitor ETP-45299 suppresses cellular proliferation and synergizes with PI3K inhibition

The serine/threonine Pim 1 kinase is an oncogene whose expression is deregulated in several human cancers. Overexpression of Pim 1 facilitates cell cycle progression and suppresses apoptosis. Hence pharmacologic inhibitors of Pim 1 are of therapeutic interest for cancer. ETP-45299 is a potent and selective inhibitor of Pim 1 that inhibits the phosphorylation of Bad and 4EBP1 in cells and suppresses the proliferation of several non-solid and solid human tumor cell lines. The combination of the PI3K inhibitor GDC-0941 with ETP-45299 was strongly synergistic in MV-4-11 AML cells, indicating that the combination of selective Pim kinase inhibitors and PI3K inhibitor could have clinical benefit.

Determination of Viability of Human Cartilage Allografts by a Rapid and Quantitative Method Not Requiring Cartilage Digestion

Fresh osteochondral allograft transplantation is increasingly used for the treatment of cartilage pathologies of the knee. It is believed that transplantation success depends on the presence of viable chondrocytes in the graft, but methods to evaluate graft viability require the isolation of chondrocytes by enzymatic digestion of the cartilage and/or the use of radioactive precursors. We have adapted the well-known cell viability assay based on the reduction of tetrazolium derivatives to evaluate cartilage viability. We took advantage from the histological properties of cartilage tissue and the fact that some tetrazolium derivatives (e.g., WST-1, XTT) give soluble reduction products that can permeate the hyaline cartilage matrix. We have validated this assay in human cartilage explants from arthrotomy interventions and deceased donors, measuring the reduced product in the explant supernatant. Using this method we have compared the performance of several culture media in cartilage viability. From those tested, DMEM supplemented with fetal bovine serum results in higher viability of the cartilage and the explants remain viable at least 15 days in culture at 37°C. Cartilage cells continued expressing chondrocyte-specific genes, suggesting the maintenance of chondrogenic phenotype. The described method offers a quantitative and convenient method to measure the viability of human cartilage grafts.

p38alpha MAP kinase as a sensor of reactive oxygen species in tumorigenesis

p38alpha is a stress-activated protein kinase that negatively regulates malignant transformation induced by oncogenic H-Ras, although the mechanisms involved are not fully understood. Here, we show that p38alpha is not a general inhibitor of oncogenic signaling, but that it specifically modulates transformation induced by oncogenes that produce reactive oxygen species (ROS). This inhibitory effect is due to the ROS-induced activation of p38alpha early in the process of transformation, which induces apoptosis and prevents the accumulation of ROS and their carcinogenic effects. Accordingly, highly tumorigenic cancer cell lines have developed a mechanism to uncouple p38alpha activation from ROS production. Our results indicate that oxidative stress sensing plays a key role in the inhibition of tumor initiation by p38alpha.

Myc antagonizes Ras-mediated growth arrest in leukemia cells through the inhibition of the Ras-ERK-p21Cip1 pathway

Even though RAS usually acts as a dominant transforming oncogene, in primary fibroblasts and some established cell lines Ras inhibits proliferation. This can explain the virtual absence of RAS mutations in some types of tumors, such as chronic myeloid leukemia (CML). We report that in the CML cell line K562 Ras induces p21Cip1 expression through the Raf-MEK-ERK pathway. Because K562 cells are deficient for p15INK4b, p16INK4a, p14ARF, and p53, this would be the main mechanism whereby Ras up-regulates p21 expression in these cells. Accordingly, we also found that Ras suppresses K562 growth by signaling through the Raf-ERK pathway. Because c-Myc and Ras cooperate in cell transformation and c-Myc is up-regulated in CML, we investigated the effect of c-Myc on Ras activity in K562 cells. c-Myc antagonized the induction of p21Cip1 mediated by oncogenic H-, K-, and N-Ras and by constitutively activated Raf and ERK2. Activation of the p21Cip1 promoter by Ras was dependent on Sp1/3 binding sites in K562. However, mutational analysis of the p21 promoter and the use of a Gal4-Sp1 chimeric protein strongly suggest that c-Myc affects Sp1 transcriptional activity but not the binding of Sp1 to the p21 promoter. c-Myc-mediated impairment of Ras activity on p21 expression required a transactivation domain, a DNA binding region, and a Max binding region. Moreover, the effect was independent of Miz1 binding to c-Myc. Consistent with its effect on p21Cip1 expression, c-Myc rescued cell growth inhibition induced by Ras. The data suggest that in particular tumor types, such as those associated with CML, c-Myc contributes to tumorigenesis by inhibiting Ras antiproliferative activity.

Subcellular Localization Determines the Protective Effects of Activated ERK2 against Distinct Apoptogenic Stimuli in Myeloid Leukemia Cells

ERKs, mitogen-activated protein kinases, are well characterized as key mediators in the conveyance of signals that promote cell survival in cells of hemopoietic origin, a key factor in the upbringing of leukemogenesis. It is also well known that ERKs phosphorylate a wide array of substrates distributed throughout distinct cellular locations such as the nucleus, cytoplasm, and cell periphery, but the relative contribution of these compartmentalized signal components to the overall survival signal generated by activation of ERKs has yet to be established. To this end, we have utilized constitutively activated forms of ERK2, whose expression is restricted to the nucleus or to the cytoplasm, to investigate the consequences of compartmentalized activation of ERK in the survival of chronic myelogenous leukemia cells subjected to distinct apoptogenic stimuli. We show that cytoplasmic ERK2 activity protected against apoptosis caused by prolonged serum starvation, whereas ERK2 activation restricted to the nucleus antagonized apoptosis induced by the Bcr-Abl inhibitor STI571. On the other hand, neither cytoplasmic nor nuclear ERK2 activities were effective in counteracting apoptosis induced by UV light. These results demonstrate that the protective effects of ERK2 against defined apoptogenic stimuli are strictly dependent on the cellular localization where ERK activation takes place. Furthermore, we present evidence suggesting that the complex I kappa B-NF kappa B participates on ERK2-mediated survival mechanisms, in a fashion dependent on the cellular location where ERK2 is active and on the causative apoptogenic stimulus.

The Rho family GTPase Cdc42 regulates the activation of Ras/MAP kinase by the exchange factor Ras-GRF

The Ras guanine-nucleotide exchange factor Ras-GRF/Cdc25(Mn) harbors a complex array of structural motifs that include a Dbl-homology (DH) domain, usually found in proteins that interact functionally with the Rho family GTPases, and the role of which is not yet fully understood. Here, we present evidence that Ras-GRF requires its DH domain to translocate to the membrane, to stimulate exchange on Ras, and to activate mitogen-activated protein kinase (MAPK). In an unprecedented fashion, we have found that these processes are regulated by the Rho family GTPase Cdc42. We show that GDP- but not GTP-bound Cdc42 prevents Ras-GRF recruitment to the membrane and activation of Ras/MAPK, although no direct association of Ras-GRF with Cdc42 was detected. We also demonstrate that catalyzing GDP/GTP exchange on Cdc42 facilitates Ras-GRF-induced MAPK activation. Moreover, we show that the potentiating effect of ionomycin on Ras-GRF-mediated MAPK stimulation is also regulated by Cdc42. These results provide the first evidence for the involvement of a Rho family G protein in the control of the activity of a Ras exchange factor.

Myeloid leukemia cell growth and differentiation are independent of mitogen-activated protein kinase ERK1/2 activation

The mitogen-activated protein kinase ERK1/2 pathway is essential in the control of cell proliferation and differentiation in most cellular systems. As such, it has been considered a potential target for antineoplastic therapy. For this purpose, we have examined the role of ERK activation in myeloid leukemia cell growth and differentiation. Using a representative set of myeloid leukemia cell lines, we show that cell proliferation was not accompanied by increases on ERK1/2 activation, and mitogenic stimulation did not enhance ERK activity. Moreover, abolition of ERK function by the inhibitor PD98059 or by a dominant inhibitory mutant ERK2 had no significant effects on proliferation. With the aid of various differentiation inducers, we found that within the same cell line, differentiation to a given lineage could occur with and without ERK1/2 activation, depending on the stimulus. Also, a differentiator could have the same effect in the presence or absence of ERK stimulation, depending on the cell line. ERK inhibition did not affect the differentiation elicited by stimuli whose effects were accompanied by ERK activation. Finally, constitutive ERK activity was also ineffective on proliferation and differentiation. Thus, our results indicate that ERK1/2 activation is not an essential requirement for leukemic cell growth and differentiation.

Regulation of c-Myc and Max in megakaryocytic and monocytic-macrophagic differentiation of K562 cells induced by protein kinase C modifiers: c-Myc is down-regulated but does not inhibit differentiation

We have studied the regulation and role of c-Myc and Max in the differentiation pathways induced in K562 cells by 12-O-tetradecanoyl phorbol-13 acetate (TPA) and staurosporine, an activator and inhibitor, respectively, of protein kinase C (PKC). We found that staurosporine induced megakaryocytic differentiation, as revealed by the cellular ultrastructure, platelet formation, and DNA endoreduplication. In contrast, TPA induced a differentiated phenotype that more closely resembled that of the monocyte-macrophage lineage. c-myc expression was down-regulated in K562 differentiated by both TPA and staurosporine, whereas max expression did not change in either case. Although PKC enzymatic activity was low in cells terminally differentiated with TPA and staurosporine, inhibition of PKC activity by itself did not induce c-myc down-regulation. We conclude that the c-myc gene is switched off as a consequence of the differentiation process triggered by these drugs in a manner independent from PKC. Ectopic overexpression of c-Myc in K562 cells did not affect the monocytic-macrophagic and megakaryocytic differentiation, indicating that c-Myc suppression is not required for these processes in K562. Similarly, both differentiation pathways were not affected by Max overexpression or by concomitant overexpression of c-Myc and Max. This result is in contrast with the inhibition of erythroid differentiation of K562 exerted by c-Myc, suggesting divergent roles for c-Myc/Max, depending on the differentiation pathway.