Antitumor Activity of MEDI3726 (ADCT-401), a Pyrrolobenzodiazepine Antibody-Drug Conjugate Targeting PSMA, in Preclinical Models of Prostate Cancer.

Prostate-specific membrane antigen (PSMA) is a membrane-bound glutamate carboxypeptidase that is highly expressed in nearly all prostate cancers with the highest expression in metastatic castration-resistant prostate cancer (mCRPC). The prevalence of increased surface expression and constitutive internalization of PSMA make it an attractive target for an antibody-drug conjugate (ADC) approach to treating patients with mCRPC. MEDI3726 (previously known as ADCT-401) is an ADC consisting of an engineered version of the anti-PSMA antibody J591 site specifically conjugated to the pyrrolobenzodiazepine (PBD) dimer tesirine. MEDI3726 specifically binds the extracellular domain of PSMA and, once internalized, releases the PBD dimer to crosslink DNA and trigger cell death. In vitro, MEDI3726 demonstrated potent and specific cytotoxicity in a panel of PSMA-positive prostate cancer cell lines, consistent with internalization and DNA interstrand crosslinking. In vivo, MEDI3726 showed robust antitumor activity against the LNCaP and the castration-resistant CWR22Rv1 prostate cancer cell line xenografts. MEDI3726 also demonstrated durable antitumor activity in the PSMA-positive human prostate cancer patient-derived xenograft (PDX) LuCaP models. This activity correlated with increased phosphorylated Histone H2AX in tumor xenografts treated with MEDI3726. MEDI3726 is being evaluated in a phase I clinical trial as a treatment for patients with metastatic castrate-resistant prostate cancer (NCT02991911). Mol Cancer Ther; 17(10); 2176-86. ©2018 AACR.

CEA/CD3 bispecific antibody MEDI-565/AMG 211 activation of T cells and subsequent killing of human tumors is independent of mutations commonly found in colorectal adenocarcinomas.

Individual or combinations of somatic mutations found in genes from colorectal cancers can redirect the effects of chemotherapy and targeted agents on cancer cell survival and, consequently, on clinical outcome. Novel therapeutics with mechanisms of action that are independent of mutational status would therefore fulfill a current unmet clinical need. Here the CEA and CD3 bispecific single-chain antibody MEDI-565 (also known as MT111 and AMG 211) was evaluated for its ability to activate T cells both in vitro and in vivo and to kill human tumor cell lines harboring various somatic mutations commonly found in colorectal cancers. MEDI-565 specifically bound to normal and malignant tissues in a CEA-specific manner, and only killed CEA positive cells. The BiTE® antibody construct mediated T cell-directed killing of CEA positive tumor cells within 6 hours, at low effector-to-target ratios which were independent of high concentrations of soluble CEA. The potency of in vitro lysis was dependent on CEA antigen density but independent of the mutational status in cancer cell lines. Importantly, individual or combinations of mutated KRAS and BRAF oncogenes, activating PI3KCA mutations, loss of PTEN expression, and loss-of-function mutations in TP53 did not reduce the activity in vitro. MEDI-565 also prevented growth of human xenograft tumors which harbored various mutations. These findings suggest that MEDI-565 represents a potential treatment option for patients with CEA positive tumors of diverse origin, including those with individual or combinations of somatic mutations that may be less responsive to chemotherapy and other targeted agents.

EphB4 promotes or suppresses Ras/MEK/ERK pathway in a context-dependent manner: Implications for EphB4 as a cancer target.

EphB4 is a member of the Eph receptor tyrosine kinase family shown to act in neuronal guidance and mediate venal/arterial separation. In contrast to these more established roles, EphB4's function in cancer is much less clear. Here we illustrate both tumor promoting as well as suppressing roles of EphB4, by showing that its activation resulted in inhibition of the Ras/ERK pathway in endothelial cells but activation of the same pathway in MCF-7 breast cancer cells. This was true if EphB4 was stimulated with EphrinB2, its natural ligand, or an agonistic monoclonal antibody for EphB4. Correspondingly, EphB4 activation stimulated MCF7 growth while inhibiting HUVEC cell proliferation. The reason for these dramatic differences is due to functional coupling of EphB4 to different downstream effectors. Reduction of p120 RasGAP in HUVEC cells attenuated the inhibitory effect of EphB4 activation on the ERK pathway, whereas knockdown of PP2A in MCF7 cells attenuated EphB4 activation of the ERK pathway. This represents the first time a functional coupling between Eph receptor and PP2A has been demonstrated leading to activation of an oncogenic pathway. Our study illustrates the caveats and potential challenges of targeting EphB4 for cancer therapy due to the conflicting effects on cancer cell and endothelial cell compartments.

MEDI3617, a human anti-angiopoietin 2 monoclonal antibody, inhibits angiogenesis and tumor growth in human tumor xenograft models.

Angiopoietin 2 (Ang2) is an important regulator of angiogenesis, blood vessel maturation and integrity of the vascular endothelium. The correlation between the dynamic expression of Ang2 in tumors with regions of high angiogenic activity and a poor prognosis in many tumor types makes Ang2 an ideal drug target. We have generated MEDI3617, a human anti-Ang2 monoclonal antibody that neutralizes Ang2 by preventing its binding to the Tie2 receptor in vitro, and inhibits angiogenesis and tumor growth in vivo. Treatment of mice with MEDI3617 resulted in inhibition of angiogenesis in several mouse models including: FGF2-induced angiogenesis in a basement extract plug model, tumor and retinal angiogenesis. In xenograft tumor models, treatment with MEDI3617 resulted in a reduction in tumor angiogenesis and an increase in tumor hypoxia. The administration of MEDI3617 as a single agent to mice bearing human tumor xenografts resulted in tumor growth inhibition against a broad spectrum of tumor types. Combining MEDI3617 with chemotherapy or bevacizumab resulted in a delay in tumor growth and no body weight loss was observed in the combination groups. These results, combined with pharmacodynamic studies, demonstrate that treatment of tumor-bearing mice with MEDI3617 significantly inhibited tumor growth as a single agent by blocking tumor angiogenesis. Together, these data show that MEDI3617 is a robust antiangiogenic agent and support the clinical evaluation and biomarker development of MEDI3617 in cancer patients.

Discovery of a potent, selective, and orally bioavailable pyridinyl-pyrimidine phthalazine aurora kinase inhibitor.

The discovery of aurora kinases as essential regulators of cell division has led to intense interest in identifying small molecule aurora kinase inhibitors for the potential treatment of cancer. A high-throughput screening effort identified pyridinyl-pyrimidine 6a as a moderately potent dual inhibitor of aurora kinases -A and -B. Optimization of this hit resulted in an anthranilamide lead (6j) that possessed improved enzyme and cellular activity and exhibited a high level of kinase selectivity. However, this anthranilamide and subsequent analogues suffered from a lack of oral bioavailability. Converting the internally hydrogen-bonded six-membered pseudo-ring of the anthranilamide to a phthalazine (8a-b) led to a dramatic improvement in oral bioavailability (38-61%F) while maintaining the potency and selectivity characteristics of the anthranilamide series. In a COLO 205 tumor pharmacodynamic assay measuring phosphorylation of the aurora-B substrate histone H3 at serine 10 (p-histone H3), oral administration of 8b at 50 mg/kg demonstrated significant reduction in tumor p-histone H3 for at least 6 h.

Antitumor efficacy of IPI-504, a selective heat shock protein 90 inhibitor against human epidermal growth factor receptor 2-positive human xenograft models as a single agent and in combination with trastuzumab or lapatinib.

IPI-504 is a novel, highly soluble small-molecule inhibitor of heat shock protein 90 (Hsp90), a protein chaperone essential for regulating homeostasis of oncoproteins and cell signaling proteins. Human epidermal growth factor receptor 2 (HER2; ErbB2) oncoprotein, expressed in a subset of metastatic breast cancers, is a Hsp90 client protein. In this study, we investigated the antitumor activity and the mechanism of action of IPI-504 in HER2(+), trastuzumab-sensitive and trastuzumab-refractory cell lines in vitro and in vivo. IPI-504 exhibited potent antiproliferative activities (range of IC(50), 10-40 nmol/L) against several tumor cell lines examined, whereby mechanism of action was mediated through HER2 and Akt degradation. Both intravenous and oral administration of IPI-504 assessed in multiple schedules showed potent tumor growth inhibition in vivo with corresponding degradation of HER2. The tolerability and efficacy of IPI-504 combined with either trastuzumab or lapatinib were also investigated in HER2(+) tumor xenograft models. Combination of IPI-504 with trastuzumab significantly enhanced tumor growth delay and induced greater responses when compared with either agent alone. Although, as expected, trastuzumab alone did not exhibit any significant antitumor activity in the trastuzumab-resistant JIMT-1 model, IPI-504 administered in combination with trastuzumab yielded greater antitumor efficacy than either agent alone. Finally, combination of IPI-504 and lapatinib was well tolerated up to 50 mg/kg IPI-504 and 100 mg/kg lapatinib and resulted in significant delay in tumor growth, including partial and complete tumor responses. These lines of evidence support the development of IPI-504 in HER2-positive breast cancers as a single agent and in combination with either trastuzumab or lapatinib

Selective targeting and potent control of tumor growth using an EphA2/CD3-Bispecific single-chain antibody construct.

The EphA2 receptor tyrosine kinase is frequently overexpressed and functionally altered in malignant cells and thus provides opportunities for selective targeting of tumor cells. We describe here the development of a novel, bispecific single-chain antibody (bscAb) referred to as bscEphA2xCD3. This molecule simultaneously targets EphA2 on tumor cells and the T-cell receptor/CD3 complex on T cells and possesses structural and functional characteristics of the recently developed BiTE technology. An EphA2-specific single-chain antibody was selected for recognition of an epitope that is preferentially exposed on malignant cells based on the concept of epitope exclusion; this was fused to a CD3-specific single-chain antibody to generate bscEphA2xCD3. The resultant bscAb redirected unstimulated human T cells to lyse EphA2-expressing tumor cells both in vitro and in vivo. In separate experiments, efficient tumor cell lysis was achieved in vitro at drug concentrations

Direct targeting of alphavbeta3 integrin on tumor cells with a monoclonal antibody, Abegrin.

The humanized monoclonal antibody Abegrin, currently in phase II trials for treatment of solid tumors, specifically recognizes the integrin alphavbeta3. Due to its high expression on mature osteoclasts, angiogenic endothelial cells, and tumor cells, integrin alphavbeta3 functions in several pathologic processes important to tumor growth and metastasis. Targeting of this integrin with Abegrin results in antitumor, antiangiogenic, and antiosteolytic activities. Here, we exploit the species specificity of Abegrin to evaluate the effects of direct targeting of tumor cells (independent of targeting of endothelia or osteoclasts). Flow cytometry analysis of human tumor cell lines shows high levels of alphavbeta3 on many solid tumors, including cancers of the prostate, skin, ovary, kidney, lung, and breast. We also show that tumor growth of alphavbeta3-expressing tumor cells is inhibited by Abegrin in a dose-dependent manner. We present a novel finding that high-dose administration can actively impair the antitumor activity of Abegrin. We also provide evidence that antibody-dependent cellular cytotoxicity contributes to in vitro and in vivo antitumor activity. Finally, it was observed that peak biological activity of Abegrin arises at serum levels that are consistent with those achieved in clinical trials. These results support a concept that Abegrin can be used to achieve selective targeting of the many tumor cells that express alphavbeta3 integrin. In combination with the well-established concept that alphavbeta3 plays a key role in cancer-associated angiogenesis and osteolytic activities, this triad of activity could provide new opportunities for therapeutic targeting of cancer.

Discovery and evaluation of dual CDK1 and CDK2 inhibitors.

In eukaryotic cells, cyclin-dependent kinase (CDK) complexes regulate the temporal progression of cells through the cell cycle. Deregulation in the cell cycle is an essential component in the evolution of cancer. Here, we validate CDK1 and CDK2 as potential therapeutic targets using novel selective small-molecule inhibitors of cyclin B1/CDK1 and cyclin E2/CDK2 enzyme complexes (CDKi). Flow cytometry-based methods were developed to assess intracellular retinoblastoma (Rb) phosphorylation to show inhibition of the CDK pathway. Tumor cells treated with CDK inhibitors showed an overall decrease in cell proliferation, accumulation of cells in G1 and G2, and apoptosis in a cell line-specific manner. Although CDK inhibitors activate p53, the inhibitors were equipotent in arresting the cell cycle in isogenic breast and colon tumor cells lacking p53, suggesting the response is independent of p53. In vivo, the CDK inhibitors prevented the growth of colon and prostate tumors, blocked proliferation of tumor cells, and inhibited Rb phosphorylation. The discovery and evaluation of novel potent and selective CDK1 and CDK2 inhibitors will help delineate the role that CDK complexes play in regulating tumorigenesis.

Suppression of angiogenesis and tumor growth by selective inhibition of angiopoietin-2.

Angiopoietin-2 (Ang2) exhibits broad expression in the remodeling vasculature of human tumors but very limited expression in normal tissues, making it an attractive candidate target for antiangiogenic cancer therapy. To investigate the functional consequences of blocking Ang2 activity, we generated antibodies and peptide-Fc fusion proteins that potently and selectively neutralize the interaction between Ang2 and its receptor, Tie2. Systemic treatment of tumor-bearing mice with these Ang2-blocking agents resulted in tumor stasis, followed by elimination of all measurable tumor in a subset of animals. These effects were accompanied by reduced endothelial cell proliferation, consistent with an antiangiogenic therapeutic mechanism. Anti-Ang2 therapy also prevented VEGF-stimulated neovascularization in a rat corneal model of angiogenesis. These results imply that specific Ang2 inhibition may represent an effective antiangiogenic strategy for treating patients with solid tumors.

Deregulation of cyclin E2 expression and associated kinase activity in primary breast tumors.

The increased expression of G(1) cyclins has been associated with the many types of human tumors. In primary solid tumors however, the expression and activity of cyclin E2, the newest member of the G(1) cyclin family, is largely unknown. In this study we have analysed the expression of the E-type cyclins in primary solid tumors from breast, lung, uterus, ovary, colon, and rectal tissues. Relative gene expression was analysed by quantitative real-time reverse transcription polymerase chain reaction (Taqman). The levels of cyclin E1 and cyclin E2 were significantly elevated (23 vs 38%, respectively) in primary breast tumor samples relative to normal breast tissue controls. We also observed an inverse correlation between the expression of cyclin E1/E2 and estrogen receptor in breast tumors. Our results demonstrate that the expression and associated catalytic activity for both cyclin E1 and cyclin E2 is elevated in primary breast tumors when compared to normal breast tissue. The increased level of cyclin E2 in breast tumors suggests that, similar to cyclin E1, it may contribute to the pathogenesis of breast cancer.

Cyclin E2, the cycle continues.

The eukaryotic cell cycle is regulated by a family of serine/threonine protein kinases known as cyclin-dependent kinases (CDKs). The activation of a CDK is dependent on its association with a cyclin regulatory subunit. The formation of distinct cyclin-CDK complexes controls the progression through the first gap phase (G(1)) and initiation of DNA synthesis (S phase). These complexes are in turn regulated by protein phosphorylation and cyclin-dependent kinase inhibitors (CKIs). Cyclin E2 has emerged as the second member of the E-type cyclin family. Cyclin E2-associated kinase activity is regulated in a cell cycle dependent manner with peak activity at the G(1) to S transition. Ectopic expression of cyclin E2 in human cells accelerates G(1), suggesting that cyclin E2 is rate limiting for G(1) progression. Although the pattern and level of cyclin E2 expression in some primary tumor and normal tissue RNAs are distinct from cyclin E1, both E-type cyclins appear to have inherent functional redundancies. This functional redundancy has facilitated the rapid characterization of cyclin E2 and uncovered unique features associated with each E-type cyclin.