Robert D. Hubbard

Imidazo[2,1-b]thiazoles: multitargeted inhibitors of both the insulin-like growth factor receptor and members of the epidermal growth factor family of receptor tyrosine kinases.

The design and enzyme activities of a novel class of imidazo[2,1-b]thiazoles is presented.

Dual EGFR/ErbB-2 inhibitors from novel pyrrolidinyl-acetylenic thieno[3,2-d]pyrimidines

A novel class of substituted pyrrolidinyl-acetylenic thieno[3,2-d]pyrimidines has been identified that are potent and selective inhibitors of both EGFR/ErbB-2 receptor tyrosine kinases. The inhibitors are found to display a range of enzyme and cellular potency and also to display a varying level of covalent modification of the kinase targets. Selected molecules, including compound 15h, were found to be potent in enzymatic and cellular assays while also demonstrating exposure in the mouse from an oral dose.

Substituted 4-amino-1H-pyrazolo[3,4-d]pyrimidines as multi-targeted inhibitors of insulin-like growth factor-1 receptor (IGF1R) and members of ErbB-family receptor kinases

This Letter describes the lead discovery, optimization, and biological characterization of a series of substituted 4-amino-1H-pyrazolo[3,4-d]pyrimidines as potent inhibitors of IGF1R, EGFR, and ErbB2. The leading compound 11 showed an IGF1R IC(50) of 12 nM, an EGFR (L858R) IC(50) of 31 nM, and an ErbB2 IC(50) of 11 nM, potent activity in cellular functional and anti-proliferation assays, as well as activity in an in vivo pharmacodynamic assay.

Development of multitargeted inhibitors of both the insulin-like growth factor receptor (IGF-IR) and members of the epidermal growth factor family of receptor tyrosine kinases.

Emerging clinical and pre-clinical data indicate that both insulin-like growth factor receptor (IGF-IR) and members of the epidermal growth factor (EGF) family of receptor tyrosine kinases (RTKs) exhibit significant cross-talk in human cancers. Therefore, a small molecule that successfully inhibits the signaling of both classes of oncogenic kinases might provide an attractive agent for chemotherapeutic use. Herein, we disclose the structure activity relationships that led to the synthesis and biological characterization of 14, a novel small molecule inhibitor of both IGF-IR and members of the epidermal growth factor family of RTKs.

Insulin-like Growth Factor-1 Receptor and ErbB Kinase Inhibitor Combinations Block Proliferation and Induce Apoptosis through Cyclin D1 Reduction and Bax Activation

The insulin-like growth factor-1 receptor (IGF-1R) and ErbB family of receptors are receptor tyrosine kinases that play important roles in cancer. Lack of response and resistance to therapies targeting ErbB receptors occur and are often associated with activation of the IGF-1R pathway. Combinations of agents that inhibit IGF-1R and ErbB receptors have been shown to synergistically block cancer cell proliferation and xenograft tumor growth. To determine the mechanism by which targeting both IGF-1R and ErbB receptors causes synergistic effects on cell growth and survival, we investigated the effects of combinations of selective IGF-1R and ErbB kinase inhibitors on proliferative and apoptotic signaling. We identified A431 squamous cell carcinoma cells as most sensitive to combinations of ErbB and IGF-1R inhibitors. The inhibitor combinations resulted in not only blockade of A431 cell proliferation, but also induced apoptosis, which was not seen with either agent alone. Upon examining phosphorylation states and expression levels of proteins in the IGF-1R and ErbB signaling pathways, we found a correlation between the ability of combinations to inhibit proliferation and to decrease levels of phosphorylated Akt and cyclin D1. In addition, the massive cell death induced by combined IGF-1R/ErbB inhibition was associated with Mcl-1 reduction and Bax activation. Thus, targeting both IGF-1R and ErbB receptors simultaneously results in cell cycle arrest and apoptosis through combined effects on Akt, cyclin D1, and Bax activation.

Developing Lipid Nanoparticle-Based siRNA Therapeutics for Hepatocellular Carcinoma Using an Integrated Approach

Successful siRNA therapeutics requires the optimal integration of multiple components, including an efficient delivery system, a disease indication that is appropriate for siRNA-based therapy, and a potent and nontoxic siRNA against a robust therapeutic target. Although all currently available delivery systems have limitations, it is important to recognize that a careful selection of the disease indication, therapeutic target, and siRNA molecule could partially compensate for deficiencies associated with the delivery system and makes it possible to advance a therapeutic siRNA regimen. In this study, we present the development of siRNA therapeutics for hepatocellular carcinoma using an integrated approach, including the development of an efficient lipid nanoparticle delivery system, the identification of a robust therapeutic target that does not trigger liver toxicity upon target knockdown, and the selection of potent and nonimmunogenic siRNA molecules against the target. The resulting siRNA-containing lipid nanoparticles produced significant antitumor efficacy in orthotopic hepatocellular carcinoma models, and, thus, represent a promising starting point for the development of siRNA therapeutics for hepatocellular carcinoma. Mol Cancer Ther; 12(11); 2308–18. ©2013 AACR.

Reversal of oncogene transformation and suppression of tumor growth by the novel IGF1R kinase inhibitor A-928605

BackgroundThe insulin-like growth factor (IGF) axis is an important signaling pathway in the growth and survival of many cell and tissue types. This pathway has also been implicated in many aspects of cancer progression from tumorigenesis to metastasis. The multiple roles of IGF signaling in cancer suggest that inhibition of the pathway might yield clinically effective therapeutics.MethodsWe describe A-928605, a novel pyrazolo [3,4-d]pyrimidine small molecule inhibitor of the receptor tyrosine kinases (IGF1R and IR) responsible for IGF signal transduction. This compound was first tested for its activity and selectivity via conventional in vitro kinome profiling and cellular IGF1R autophosphorylation. Additionally, cellular selectivity and efficacy of A-928605 were analyzed in an IGF1R oncogene-addicted cell line by proliferation, signaling and microarray studies. Finally, in vivo efficacy of A-928605 was assessed in the oncogene-addicted cell line and in a neuroblastoma model as a single agent as well as in combination with clinically approved therapeutics targeting EGFR in models of pancreatic and non-small cell lung cancers.ResultsA-928605 is a selective IGF1R inhibitor that is able to abrogate activation of the pathway both in vitro and in vivo. This novel compound dosed as a single agent is able to produce significant growth inhibition of neuroblastoma xenografts in vivo. A-928605 is also able to provide additive effects when used in combination with clinically approved agents directed against EGFR in non-small cell lung and human pancreatic tumor models.ConclusionThese results suggest that a selective IGF1R inhibitor such as A-928605 may provide a useful clinical therapeutic for IGF pathway affected tumors and warrants further investigation.

Advances towards the development of ATP-competitive small-molecule inhibitors of the insulin-like growth factor receptor (IGF-IR).

The search for molecular targets that are specific to cancer has led to a greater understanding of how certain classes of receptor tyrosine kinases (RTK) transform external stimuli, via growth factors, into internal proliferative responses. A small subset of receptor tyrosine kinases has been successfully exploited for clinical utility, such as Bcr/Abl, c-Kit, platelet-derived growth factor receptor (PDGFR), members of the epidermal growth factor receptor family (EGFR and ErbB-2), and vascular endothelial growth factor receptor (VEGFR). The ability to interrogate these targets with antibodies, small molecules, or both, has led to new agents in the fight against cancer. However, the agents derived from the above targets are far from ideal, in that these agents have yet to achieve the broad clinical utility that was initially envisioned. The efficacy of these agents has been hampered by the requirement of an activating mutation for clinically relevant activity, which has been proposed for anti-EGFR therapies, the development of chemoresistance by the generation of specific deleterious mutations, as in the case of Bcr/Abl, or by switching to alternative proliferative or survival pathways mediated by other receptor tyrosine kinases, as occurs with antibodies targeting ErbB-2. The search for alternative RTKs that play critical roles in either regulating proliferation or allowing cancer cells to escape programmed cell death has yielded the insulin-like growth factor receptor (IGF-IR) as a potential target. As will be discussed below, the ability of IGFIR to simultaneously regulate both proliferative and anti-apoptotic aspects of cell signaling indicate that selective inhibition of the receptor might yield clinically useful therapeutics. The IGF system is composed of multiple ligands and receptors. The IGF-IR is a disulfide-bound dimer of two extracellular a subunits that contribute to ligand binding, and two b subunits that span the plasma membrane and contain the cytoplasmic tyrosine kinase domains (Figure 1). IGF-IR can be activated by IGF-I, IGF-II, and insulin, although the affinity of IGF-IR for insulin is much lower than for the other two ligands. Two splice variants of the insulin receptor, IRA and IRB, differ by an insertion of 12 amino acids at the C terminus of the alpha subunits of IRB (Figure 1). IRB only binds to insulin with high affinity, whereas IRA can bind to both insulin and IGF-II. [6] Another receptor for IGF-II exists, but it does not have a cytoplasmic tyrosine kinase domain. Instead, IGF-IIR, which is also known as the mannose-6-phosphate receptor, regulates the amount of IGF-II available to bind to IGF-IR by mediating IGF-II endocytosis and degradation. The concentrations of IGF-I and IGF-II available for receptor activation are also controlled by IGF binding proteins (IGFBPs). Additional complexity is introduced in the IGF system by the presence of hybrid receptors composed of heterodimers of IGF-IR and IR (Figure 1). The binding of IGF-I, insulin, and IGFII to hybrid receptors is determined by which IR isoform is present in the heterodimer. Hybrid receptors that are composed of IGF-IR and IRA are activated by all three ligands, whereas hybrids containing IRB only bind to IGF-I with high affinity and IGF-II with lower affinity. Therefore, the responses of different cell types to IGF-I, IGF-II, and insulin are determined by the relative numbers and composition of which homodimeric and hybrid receptors are present. The IGF-axis plays a role in several cellular processes that are activated in transformed cells, including cell proliferation and survival, angiogenesis, metastasis, and invasion. The IGF-IR is required for transformation of fibroblasts by several different oncogenes, including H-Ras, the SV40 large T antigen, and activated c-Src. IGF-IR also mediates anchorage-independent growth and survival of cancer cells in response to cellular stress. Figure 1. Receptors and ligands of the IGF system. Activation of IGF-IR or hybrid receptors by IGF-I or IGF-II or activation of IRA by IGF-II or insulin leads to proliferation and survival of cells. Activation of IRB by insulin results in regulation of glucose uptake and cellular metabolism.

Fragment-Based, Structure-Enabled Discovery of Novel Pyridones and Pyridone Macrocycles as Potent Bromodomain and Extra-Terminal Domain (BET) Family Bromodomain Inhibitors

Members of the BET family of bromodomain containing proteins have been identified as potential targets for blocking proliferation in a variety of cancer cell lines. A two-dimensional NMR fragment screen for binders to the bromodomains of BRD4 identified a phenylpyridazinone fragment with a weak binding affinity (1, Ki = 160 μM). SAR investigation of fragment 1, aided by X-ray structure-based design, enabled the synthesis of potent pyridone and macrocyclic pyridone inhibitors exhibiting single digit nanomolar potency in both biochemical and cell based assays. Advanced analogs in these series exhibited high oral exposures in rodent PK studies and demonstrated significant tumor growth inhibition efficacy in mouse flank xenograft models.

Synthesis and stereochemical effects of pyrrolidinyl-acetylenic thieno[3,2-d]pyrimidines as EGFR and ErbB-2 inhibitors.

A novel class of pyrrolidinyl-acetyleneic thieno[3,2-d]pyrimidines has been identified which potently inhibit the EGFR and ErbB-2 receptor tyrosine kinases. Synthetic modifications of the pyrrolidine carbamate moiety result in a range of effects on enzyme and cellular potency. In addition, the impact of the absolute stereochemical configuration on cellular potency and oral mouse pharmacokinetics is described.