Y. Gloria Meng

Site-specific conjugation of a cytotoxic drug to an antibody improves the therapeutic index

Antibody-drug conjugates enhance the antitumor effects of antibodies and reduce adverse systemic effects of potent cytotoxic drugs. However, conventional drug conjugation strategies yield heterogenous conjugates with relatively narrow therapeutic index (maximum tolerated dose/curative dose). Using leads from our previously described phage display–based method to predict suitable conjugation sites, we engineered cysteine substitutions at positions on light and heavy chains that provide reactive thiol groups and do not perturb immunoglobulin folding and assembly, or alter antigen binding. When conjugated to monomethyl auristatin E, an antibody against the ovarian cancer antigen MUC16 is as efficacious as a conventional conjugate in mouse xenograft models. Moreover, it is tolerated at higher doses in rats and cynomolgus monkeys than the same conjugate prepared by conventional approaches. The favorable in vivo properties of the near-homogenous composition of this conjugate suggest that our strategy offers a general approach to retaining the antitumor efficacy of antibody-drug conjugates, while minimizing their systemic toxicity.

Albumin Binding as a General Strategy for Improving the Pharmacokinetics of Proteins

Plasma protein binding can be an effective means of improving the pharmacokinetic properties of otherwise short lived molecules. Using peptide phage display, we identified a series of peptides having the core sequence DICLPRWGCLW that specifically bind serum albumin from multiple species with high affinity. These peptides bind to albumin with 1:1 stoichiometry at a site distinct from known small molecule binding sites. Using surface plasmon resonance, the dissociation equilibrium constant of peptide SA21 (Ac-RLIEDICLPRWGCLWEDD-NH2) was determined to be 266 ± 8, 320 ± 22, and 467 ± 47 nm for rat, rabbit, and human albumin, respectively. SA21 has an unusually long half-life of 2.3 h when injected by intravenous bolus into rabbits. A related sequence, fused to the anti-tissue factor Fab of D3H44 (Presta, L., Sims, P., Meng, Y. G., Moran, P., Bullens, S., Bunting, S., Schoenfeld, J., Lowe, D., Lai, J., Rancatore, P., Iverson, M., Lim, A., Chisholm, V., Kelley, R. F., Riederer, M., and Kirchhofer, D. (2001) Thromb. Haemost. 85, 379–389), enabled the Fab to bind albumin with similar affinity to that of SA21 while retaining the ability of the Fab to bind tissue factor. This interaction with albumin resulted in reduced in vivoclearance of 25- and 58-fold in mice and rabbits, respectively, when compared with the wild-type D3H44 Fab. The half-life was extended 37-fold to 32.4 h in rabbits and 26-fold to 10.4 h in mice, achieving 25–43% of the albumin half-life in these animals. These half-lives exceed those of a Fab′2 and are comparable with those seen for polyethylene glycol-conjugated Fab molecules, immunoadhesins, and albumin fusions, suggesting a novel and generic method for improving the pharmacokinetic properties of rapidly cleared proteins.

Importance of Cellular Microenvironment and Circulatory Dynamics in B Cell Immunotherapy

B cell immunotherapy has emerged as a mainstay in the treatment of lymphomas and autoimmune diseases. Although the microenvironment has recently been demonstrated to play critical roles in B cell homeostasis, its contribution to immunotherapy is unknown. To analyze the in vivo factors that regulate mechanisms involved in B cell immunotherapy, we used a murine model for human CD20 (hCD20) expression in which treatment of hCD20+ mice with anti-hCD20 mAbs mimics B cell depletion observed in humans. We demonstrate in this study that factors derived from the microenvironment, including signals from the B cell-activating factor belonging to the TNF family/BLyS survival factor, integrin-regulated homeostasis, and circulatory dynamics of B cells define distinct in vivo mechanism(s) and sensitivities of cells in anti-hCD20 mAb-directed therapies. These findings provide new insights into the mechanisms of immunotherapy and define new opportunities in the treatment of cancers and autoimmune diseases.

Bv8 regulates myeloid-cell-dependent tumour angiogenesis

Bone-marrow-derived cells facilitate tumour angiogenesis, but the molecular mechanisms of this facilitation are incompletely understood. We have previously shown that the related EG-VEGF and Bv8 proteins, also known as prokineticin 1 (Prok1) and prokineticin 2 (Prok2), promote both tissue-specific angiogenesis and haematopoietic cell mobilization. Unlike EG-VEGF, Bv8 is expressed in the bone marrow. Here we show that implantation of tumour cells in mice resulted in upregulation of Bv8 in CD11b+Gr1+ myeloid cells. We identified granulocyte colony-stimulating factor as a major positive regulator of Bv8 expression. Anti-Bv8 antibodies reduced CD11b+Gr1+ cell mobilization elicited by granulocyte colony-stimulating factor. Adenoviral delivery of Bv8 into tumours was shown to promote angiogenesis. Anti-Bv8 antibodies inhibited growth of several tumours in mice and suppressed angiogenesis. Anti-Bv8 treatment also reduced CD11b+Gr1+ cells, both in peripheral blood and in tumours. The effects of anti-Bv8 antibodies were additive to those of anti-Vegf antibodies or cytotoxic chemotherapy. Thus, Bv8 modulates mobilization of CD11b+Gr1+ cells from the bone marrow during tumour development and also promotes angiogenesis locally.

Cross-species Vascular Endothelial Growth Factor (VEGF)-blocking Antibodies Completely Inhibit the Growth of Human Tumor Xenografts and Measure the Contribution of Stromal VEGF

To fully assess the role of VEGF-A in tumor angiogenesis, antibodies that can block all sources of vascular endothelial growth factor (VEGF) are desired. Selectively targeting tumor-derived VEGF overlooks the contribution of host stromal VEGF. Other strategies, such as targeting VEGF receptors directly or using receptor decoys, result in inhibiting not only VEGF-A but also VEGF homologues (e.g. placental growth factor, VEGF-B, and VEGF-C), which may play a role in angiogenesis. Here we report the identification of novel anti-VEGF antibodies, B20 and G6, from synthetic antibody phage libraries, which block both human and murine VEGF action in vitro. Their affinity-improved variants completely inhibit three human tumor xenografts in mice of skeletal muscle, colorectal, and pancreatic origins (A673, HM-7, and HPAC). Avastin, which only inhibits the tumor-derived human VEGF, is ∼90% effective at inhibiting HM-7 and A673 growth but is <50% effective at inhibiting HPAC growth. Indeed, HPAC tumors contain more host stroma invasion and stroma-derived VEGF than other tumors. Thus, the functional contribution of stromal VEGF varies greatly among tumors, and systemic blockade of both tumor and stroma-derived VEGF is sufficient for inhibiting the growth of tumor xenografts.

Comparisons of the intraocular tissue distribution, pharmacokinetics, and safety of 125I-labeled full-length and fab antibodies in rhesus monkeys following intravitreal administration

Access of recombinant proteins to the retina following intravitreal administration is poorly understood. A study was conducted in male Rhesus monkeys (15 to 28 mo of age; 2.8-3.3 kg) in order to compare the intraocular tissue distribution, pharmacokinetics, and safety of 125Iodine (I)-labeled full-length humanized rhuMAb HER2 antibody (148 kD) and of 125I-labeled humanized rhuMAb vascular endothelial growth factor Fab antibody (48.3 kD) following bilateral bolus intravitreal injection on day 0 (5 animals/group). The dose administered to each eye was 25 μg (9-10 μCi) in 50 μl. Animals were euthanatized on day 0 (1 hr postdose) and on days 1, 4, 7, and 14. Safety assessment included direct ophthalmoscopy, intraocular pressure measurements, clinical observations, body weight, and hematology and clinical chemistry panels. Blood and vitreous samples were collected daily (blood only) and at necropsy for pharmacokinetics and analysis for antibodies to the test materials; the ocular tissue distribution of the test material was evaluated by microautoradiography. All animals completed the study. Microautoradiography demonstrated that the full-length antibody did not penetrate the inner limiting membrane of the retina at any of the time points examined. In contrast, the Fab antibody fragment diffused through the neural retina to the retinal pigment epithelial layer at the 1-hr time point and persisted in this location for up to 7 days. Systemic exposure to test material was low but variable: the highest plasma concentration of the full-length antibody was 20.3 ng/ml, whereas plasma concentrations for the Fab antibody remained below the limit of quantitation (i.e., <7.8 ng/ml). An immune response to the test material was not evident in either treatment group. The half-life in vitreous was 5.6 days for the full-length antibody and 3.2 days for the Fab antibody. The shorter intravitreal half-life of the Fab antibody is related to its smaller size and its significant diffusion through the retinal layers. The differences in pharmacokinetics and tissue distribution that are noted between the full-length and Fab antibodies in this study identify potential therapeutic approaches that may be exploited in specific disease conditions.

G-CSF-initiated myeloid cell mobilization and angiogenesis mediate tumor refractoriness to anti-VEGF therapy in mouse models

Recent studies suggest that tumor-associated CD11b+Gr1+ myeloid cells contribute to refractoriness to antiangiogenic therapy with an anti-VEGF-A antibody. However, the mechanisms of peripheral mobilization and tumor-homing of CD11b+Gr1+ cells are unclear. Here, we show that, compared with other cytokines [granulocyte-macrophage colony stimulating factor (GM-CSF), stromal derived factor 1α, and placenta growth factor], G-CSF and the G-CSF-induced Bv8 protein have preferential expression in refractory tumors. Treatment of refractory tumors with the combination of anti-VEGF and anti-G-CSF (or anti-Bv8) reduced tumor growth compared with anti-VEGF-A monotherapy. Anti-G-CSF treatment dramatically suppressed circulating or tumor-associated CD11b+Gr1+ cells, reduced Bv8 levels, and affected the tumor vasculature. Conversely, G-CSF delivery to animals bearing anti-VEGF sensitive tumors resulted in reduced responsiveness to anti-VEGF-A treatment through induction of Bv8-dependent angiogenesis. We conclude that, at least in the models examined, G-CSF expression by tumor or stromal cells is a determinant of refractoriness to anti-VEGF-A treatment.

Association between HER-2/neu and Vascular Endothelial Growth Factor Expression Predicts Clinical Outcome in Primary Breast Cancer Patients

Purpose: Activation or overexpression of HER-2/neu is associated with up-regulation of vascular endothelial growth factor (VEGF) in human breast cancer cells in vitro. Preclinical experiments indicate that increased expression of VEGF may in part mediate the biologically aggressive phenotype of HER-2/neu-overexpressing human breast cancer. It was the purpose of this study to: (a) evaluate the association between HER-2/neu and VEGF expression in a large clinical cohort of primary breast cancer patients; (b) compare the prognostic significance of VEGF isoforms; and (c) analyze the combined effects of HER-2/neu and VEGF on clinical outcome. Experimental Design: HER-2/neu and VEGF were measured by ELISA in primary breast tumor tissue lysates from 611 unselected patients with a median clinical follow-up of 50 months. At least six VEGF isoforms consisting of 121, 145, 165, 183, 189, or 206 amino acids are generated as a result of alternative splicing. The VEGF121–206 ELISA uses antibodies that bind to VEGF121 and, therefore, detects all of the VEGF isoforms with 121 and more amino acids. The VEGF165–206 ELISA uses antibodies that bind to VEGF165 and, therefore, detects all of the VEGF isoforms with 165 and more amino acids. VEGF121–206 and VEGF165–206 were analyzed both as continuous and categorical variables, using detectable expression as a cutoff for positivity. Cell lines with defined HER-2/neu expression levels were used to establish a cutoff point for HER-2/neu overexpression in breast tumor samples. Results: Our findings indicate a significant positive association between HER-2/neu and VEGF expression. VEGF121–206 and VEGF165–206 expression was detectable in 88 (77.2%) and 100 (87.7%), respectively, of the 114 patients with HER-2/neu-overexpressing tumors, in contrast to 271 (54.5%) and 353 (71.0%), respectively, of the 497 patients with nonoverexpressing tumors (χ2 test: P < 0.001 for both VEGF121–206 and VEGF165–206). VEGF121–206 and VEGF165–206 demonstrate a comparable prognostic significance for survival in unselected primary breast cancer patients (univariate analysis: VEGF121–206, P = 0.0068; VEGF165–206, P = 0.0046; multivariate analysis: VEGF121–206, P = 0.1475; VEGF165–206, P = 0.1483). When the analyses were performed separately for node-negative and node-positive patients, VEGF121–206 and VEGF165–206 were of prognostic significance for survival only in node-positive patients (univariate analysis: VEGF121–206, P = 0.0003; VEGF165–206, P = 0.0038; multivariate analysis: VEGF121–206, P = 0.0103; VEGF165–206, P = 0.0150). A biological concentration-effect relationship between VEGF expression and survival (VEGF121–206, P = 0.0280; VEGF165–206, P = 0.0097) suggests that VEGF levels, as determined by ELISA, could be of importance as a predictive marker for therapeutic strategies that target VEGF. Combining HER-2/neu and VEGF121–206/VEGF165–206 results in additional prognostic information for survival (VEGF121–206, P = 0.0133; VEGF165–206, P = 0.0092). Conclusion: The positive association between HER-2/neu and VEGF expression implicates VEGF in the aggressive phenotype exhibited by HER-2/neu overexpression, and supports the use of combination therapies directed against both HER-2/neu and VEGF for treatment of breast cancers that overexpress HER-2/neu.

Granulocyte-colony stimulating factor promotes lung metastasis through mobilization of Ly6G+Ly6C+ granulocytes

Priming of the organ-specific premetastatic sites is thought to be an important yet incompletely understood step during metastasis. In this study, we show that the metastatic tumors we examined overexpress granulocyte-colony stimulating factor (G-CSF), which expands and mobilizes Ly6G+Ly6C+ granulocytes and facilitates their subsequent homing at distant organs even before the arrival of tumor cells. Moreover, G-CSF–mobilized Ly6G+Ly6C+ cells produce the Bv8 protein, which has been implicated in angiogenesis and mobilization of myeloid cells. Anti–G-CSF or anti-Bv8 antibodies significantly reduced lung metastasis. Transplantation of Bv8 null fetal liver cells into lethally irradiated hosts also reduced metastasis. We identified an unexpected role for Bv8: the ability to stimulate tumor cell migration through activation of one of the Bv8 receptors, prokineticin receptor (PKR)-1. Finally, we show that administration of recombinant G-CSF is sufficient to increase the numbers of Ly6G+Ly6C+ cells in organ-specific metastatic sites and results in enhanced metastatic ability of several tumors.

An interleukin-17–mediated paracrine network promotes tumor resistance to anti-angiogenic therapy

Although angiogenesis inhibitors have provided substantial clinical benefit as cancer therapeutics, their use is limited by resistance to their therapeutic effects. While ample evidence indicates that such resistance can be influenced by the tumor microenvironment, the underlying mechanisms remain incompletely understood. Here, we have uncovered a paracrine signaling network between the adaptive and innate immune systems that is associated with resistance in multiple tumor models: lymphoma, lung and colon. Tumor-infiltrating T helper type 17 (TH17) cells and interleukin-17 (IL-17) induced the expression of granulocyte colony-stimulating factor (G-CSF) through nuclear factor κB (NF-κB) and extracellular-related kinase (ERK) signaling, leading to immature myeloid-cell mobilization and recruitment into the tumor microenvironment. The occurrence of TH17 cells and Bv8-positive granulocytes was also observed in clinical tumor specimens. Tumors resistant to treatment with antibodies to VEGF were rendered sensitive in IL-17 receptor (IL-17R)-knockout hosts deficient in TH17 effector function. Furthermore, pharmacological blockade of TH17 cell function sensitized resistant tumors to therapy with antibodies to VEGF. These findings indicate that IL-17 promotes tumor resistance to VEGF inhibition, suggesting that immunomodulatory strategies could improve the efficacy of anti-angiogenic therapy.