Stefan Hart

TACE cleavage of proamphiregulin regulates GPCR‐induced proliferation and motility of cancer cells

Communication between G protein‐coupled receptor (GPCR) and epidermal growth factor receptor (EGFR) signalling systems involves cell surface proteolysis of EGF‐like precursors. The underlying mechanisms of EGFR signal transactivation pathways, however, are largely unknown. We demonstrate that in squamous cell carcinoma cells, stimulation with the GPCR agonists LPA or carbachol specifically results in metalloprotease cleavage and release of amphiregulin (AR). Moreover, AR gene silencing by siRNA or inhibition of AR biological activity by neutralizing antibodies and heparin prevents GPCR‐induced EGFR tyrosine phosphorylation, downstream mitogenic signalling events, cell proliferation, migration and activation of the survival mediator Akt/PKB. Therefore, despite some functional redundancy among EGF family ligands, the present study reveals a distinct and essential role for AR in GPCR‐triggered cellular responses. Furthermore, we present evidence that blockade of the metalloprotease‐disintegrin tumour necrosis factor‐α‐converting enzyme (TACE) by the tissue inhibitor of metalloprotease‐3, a dominant‐negative TACE mutant or RNA interference suppresses GPCR‐stimulated AR release, EGFR activation and downstream events. Thus, TACE can function as an effector of GPCR‐mediated signalling and represents a key element of the cellular receptor cross‐talk network.

Fibroblast growth factor receptor 4 regulates proliferation, anti-apoptosis and alpha-fetoprotein secretion during hepatocellular carcinoma progression and represents a potential target for therapeutic intervention

BACKGROUND/AIMS FGFR4, a member of the fibroblast growth factor receptor family, has been recently associated with progression of melanoma, breast and head and neck carcinoma. Given its uniquely high expression in the liver, we investigated its contributory role to hepatocellular carcinoma (HCC). METHODS We performed a comprehensive sequencing of full-length FGFR4 transcript in 57 tumor/normal HCC tissue pairs, and quantified their mRNA expressions. Notable mutations and expression patterns were correlated with patient data. Clinically significant trends were examined in in vitro models. RESULTS We found eight genetic alterations including two highly frequent polymorphisms (V10I and G338R). Secretion of alpha-fetoprotein (AFP), a HCC biomarker, was increased among patients bearing homozygous Arg388 alleles. One-third of these patients exhibited increased FGFR4 mRNA expression in the matched tumor/normal tissue. Subsequent in vitro perturbation of FGFR4 signaling through both FGF19-stimulation and FGFR4 silencing confirmed a mechanistic link between FGFR4 activities and tumor aggressiveness. More importantly, inhibition of FGFR activity with PD173074 exquisitely blocked HuH7 (high FGFR4 expression) proliferation as compared to control cell lines. CONCLUSIONS FGFR4 contributes significantly to HCC progression by modulating AFP secretion, proliferation and anti-apoptosis. Its frequent overexpression in patients renders its inhibition a novel and much needed pharmacological approach against HCC.

GPCR-induced migration of breast carcinoma cells depends on both EGFR signal transactivation and EGFR-independent pathways

Abstract The epidermal growth factor receptor (EGFR) plays a key role in the regulation of important cellular processes under normal and pathophysiological conditions such as cancer. In human mammary carcinomas the EGFR is involved in regulating cell growth, survival, migration and metastasis and its activation correlates with the lack of response in hormone therapy. Here, we demonstrate in oestrogen receptor-positive and -negative human breast cancer cells and primary mammary epithelial cells a cross-communication between G protein-coupled receptors (GPCRs) and the EGFR. We present evidence that specific inhibition of ADAM15 or TACE blocks GPCR-induced and proHB-EGF-mediated EGFR tyrosine phosphorylation, downstream mitogenic signalling and cell migration. Notably, activation of the PI3K downstream mediator PKB/Akt by GPCR ligands involves the activity of sphingosine kinase (SPHK) and is independent of EGFR signal transactivation. We conclude that GPCR-induced chemotaxis of breast cancer cells is mediated by EGFR-dependent and -independent signalling pathways, with both parallel pathways having to act in concert to achieve a complete migratory response.

Phase I Study of a Novel Oral Janus Kinase 2 Inhibitor, SB1518, in Patients With Relapsed Lymphoma: Evidence of Clinical and Biologic Activity in Multiple Lymphoma Subtypes

PURPOSE The Janus kinase 2/signal transducers and activators of transcription (JAK2/STAT) pathway plays an important role in the pathogenesis of hematologic malignancies. We conducted a phase I dose-finding and pharmacokinetic/pharmacodynamic study of SB1518, a potent JAK2 inhibitor, in patients with relapsed lymphoma. PATIENTS AND METHODS Patients with relapsed or refractory Hodgkin or non-Hodgkin lymphoma of any type except Burkitts or CNS lymphoma were enrolled. Patient cohorts received escalating doses of SB1518 orally once daily for 28-day cycles. Response was evaluated after 8 weeks. RESULTS Thirty-four patients received doses of 100 to 600 mg/d. The maximum tolerated dose was not reached. Treatment was well tolerated, with mostly grade 1 and 2 toxicities. Gastrointestinal toxicities were the most common treatment-related events. Cytopenias were infrequent and modest. Pharmacologically active concentrations were achieved at all doses. Dose-related linear increases in area under the concentration-time curve were seen on day 1, with no significant accumulation on day 15. Mean terminal half-life was 1 to 4 days, and mean time to peak concentration ranged from 5 to 9 hours. SB1518 inhibited JAK2 signaling at 4 hours postdose at all levels. Increases in fms-like tyrosine kinase-3 (FLT-3) ligand, reflecting FLT-3 inhibition, were seen in most patients. There were three partial responses (≥300 mg/d) and 15 patients with stable disease (SD), with most responses lasting longer than 2 months. Seven of 13 SDs had tumor reductions of 4% to 46%. CONCLUSION SB1518 has encouraging activity in relapsed lymphoma, providing the first proof-of-principle of the potential therapeutic value of targeting the JAK/STAT pathway in lymphoma in the clinical setting.

Beyond Herceptin and Gleevec

Identification of the key role of protein kinases as potential oncoproteins has led to the emergence of a new era of target-directed therapies. Among a variety of novel therapeutic strategies two have shown the most promise and led to a variety of therapeutic agents in clinical development. One approach utilises humanised monoclonal antibodies generated against the extracellular domain of transmembrane protein kinases. The second approach is the generation of small molecule ATP analogues targeting the kinase domain itself. The approval of agents such as Herceptin for the treatment of advanced breast cancer and Gleevec for chronic myelogenous leukemia and gastrointestinal stromal tumours are the first examples of gene-based cancer drugs and represent the first example of a novel strategy in anti-cancer therapy.

Discovery of the Macrocycle 11-(2-Pyrrolidin-1-yl-ethoxy)-14, 19-dioxa-5,7,26-triaza-tetracyclo[19.3.1.1(2,6).1(8,12)]heptacosa-1(25),2(26),3,5,8,10,12(27),16,21,23-decaene (SB1518), a Potent Janus Kinase 2/Fms-Like Tyrosine Kinase-3 (JAK2/FLT3) Inhibitor for the Treatment of Myelofibrosis and Lymphoma

Discovery of the activating mutation V617F in Janus Kinase 2 (JAK2(V617F)), a tyrosine kinase critically involved in receptor signaling, recently ignited interest in JAK2 inhibitor therapy as a treatment for myelofibrosis (MF). Herein, we describe the design and synthesis of a series of small molecule 4-aryl-2-aminopyrimidine macrocycles and their biological evaluation against the JAK family of kinase enzymes and FLT3. The most promising leads were assessed for their in vitro ADME properties culminating in the discovery of 21c, a potent JAK2 (IC(50) = 23 and 19 nM for JAK2(WT) and JAK2(V617F), respectively) and FLT3 (IC(50) = 22 nM) inhibitor with selectivity against JAK1 and JAK3 (IC(50) = 1280 and 520 nM, respectively). Further profiling of 21c in preclinical species and mouse xenograft and allograft models is described. Compound 21c (SB1518) was selected as a development candidate and progressed into clinical trials where it is currently in phase 2 for MF and lymphoma.

Mammary gland remodeling depends on gp130 signaling through Stat3 and MAPK

The interleukin-6 (IL6) family of cytokines signals through the common receptor subunit gp130, and subsequently activates Stat3, MAPK, and PI3K. Stat3 controls cell death and tissue remodeling in the mouse mammary gland during involution, which is partially induced by IL6 and LIF. However, it is not clear whether Stat3 activation is mediated solely through the gp130 pathway or also through other receptors. This question was explored in mice carrying two distinct mutations in the gp130 gene; one that resulted in the complete ablation of gp130 and one that led to the loss of Stat3 binding sites (gp130Δ/Δ). Deletion of gp130 specifically from mammary epithelium resulted in a complete loss of Stat3 activity and resistance to tissue remodeling comparable to that seen in the absence of Stat3. A less profound delay of mammary tissue remodeling was observed in gp130Δ/Δ mice. Stat3 tyrosine and serine phosphorylation was still detected in these mice suggesting that Stat3 activation could be the result of gp130 interfacing with other receptors. Experiments in primary mammary epithelial cells and transfected COS-7 cells revealed a p44/42 MAPK and EGFR-dependent Stat3 activation. Moreover, the gp130-dependent EGFR activation was independent of EGF ligands, suggesting a cytoplasmic interaction and cross-talk between these two receptors. These experiments establish that two distinct Stat3 signaling pathways emanating from gp130 are utilized in mammary tissue.

Dissecting the Epidermal Growth Factor Receptor Signal Transactivation Pathway

Interreceptor cross-talk has emerged as a general concept in cellular signaling cascades. Therein epidermal growth factor receptor (EGFR) signal transactivation represents the so far best investigated cross-talk mechanism comprising heterogeneous receptor families. In this signaling process G protein-coupled receptor (GPCR) stimulation induces phosphorylation of the EGFR, combining the broad diversity of GPCRs with the potent signaling capacities of this receptor tyrosine kinase. Early reports attributed this transactivation mechanism to solely intracellular pathways as no EGF-like ligands could be detected in conditioned media of GPCR agonist-stimulated cells. However, Prenzel and colleagues demonstrated the involvement of metalloproteinase-mediated release of EGF-like ligands as the predominant mechanism of EGFR signal transactivation, providing a point of convergence for different intracellular effector proteins. Since this discovery, numerous investigations revealed the broad relevance of metalloproteinase-mediated ligand-dependent EGFR signal transactivation for coupling GPCRs to various cellular signaling responses. Here we describe methods to investigate GPCR-stimulated EGFR signal transactivation allowing the identification of both the EGF-like ligands and the metalloproteinases involved.

Discovery of the Macrocycle (9E)-15-(2-(Pyrrolidin-1-yl)ethoxy)-7,12,25-trioxa-19,21,24-triaza-tetracyclo[18.3.1.1(2,5).1(14,18)]hexacosa-1(24),2,4,9,14(26),15,17,20,22-nonaene (SB1578), a Potent Inhibitor of Janus Kinase 2/Fms-LikeTyrosine Kinase-3 (JAK2/FLT3) for the Treatment of Rheumatoid Arthritis

Herein, we describe the synthesis and SAR of a series of small molecule macrocycles that selectively inhibit JAK2 kinase within the JAK family and FLT3 kinase. Following a multiparameter optimization of a key aryl ring of the previously described SB1518 (pacritinib), the highly soluble 14l was selected as the optimal compound. Oral efficacy in the murine collagen-induced arthritis (CIA) model for rheumatoid arthritis (RA) supported 14l as a potential treatment for autoimmune diseases and inflammatory disorders such as psoriasis and RA. Compound 14l (SB1578) was progressed into development and is currently undergoing phase 1 clinical trials in healthy volunteers.

Structure and ligand-based design of mTOR and PI3-kinase inhibitors leading to the clinical candidates VS-5584 (SB2343) and SB2602.

Phosphoinositide 3-kinases (PI3Ks) and the mammalian target of rapamycin (mTOR) act as critical effectors in a commonly deregulated cell signaling pathway in human cancers. The abnormal activation of the PI3K/mTOR pathway has been shown to play a role in initiation, progression, and metastasis of human tumors. Being one of the most frequently activated pathways in cancer, much effort has been directed toward inhibition of the PI3K/mTOR pathway as a novel oncology therapy. Previous work by a number of groups has revealed several selective PI3K and dual mTOR/PI3K inhibitors. However, there are few reports of therapeutic agents with a pan-PI3K/mTOR inhibitory profile within a narrow concentration range. We therefore initiated a drug discovery project with the aim of discovering dual mTOR/PI3K inhibitors which would equipotently inhibit the 4 isoforms of PI3K, α, β, γ, and δ, and mTOR a compelling profile for powerful blockage of the PI3K/mTOR pathway. A pharmacophore model was generated and used for designing a series of novel compounds, based on a purine scaffold, which potently inhibited mTOR and PI3Ks. These compounds contained a phenol headgroup essential for binding to the target proteins. Early efforts concentrated on finding replacements for the phenol as it was rapidly conjugated resulting in a short half-life in vivo. Compounds with a variety of headgroups were docked into the PI3Kα and mTOR ATP-binding sites, and aminopyrimidine and aminopyrazine were found to make excellent phenol replacements. Further structure guided optimization of side chains in the 8- and 9-positions of the purine resulted in potent inhibitors with good PKDM properties. As the PI3 kinases play a role in insulin signaling, it is believed that targeting mTOR selectively may give the benefit of blocking the AKT-pathway while avoiding the potential side effects associated with PI3K inhibition. As a result we designed a further series of selective mTOR kinase inhibitors. The project was successfully concluded by progressing both a dual mTOR/PI3K inhibitor, SB2343, and a selective mTOR inhibitor, SB2602, into preclinical development. SB2343 has since entered phase 1 clinical development as VS-5584.