Preclinical studies of BB-1701, a HER2-targeting eribulin-containing ADC with potent bystander effect and ICD activity.

BACKGROUND: Several HER2-targeting antibody-drug conjugates (ADC) have gained market approval for the treatment of HER2-expressing metastasis. Promising responses have been reported with the new generation of ADCs in patients who do not respond well to other HER2-targeting therapeutics. However, these ADCs still face challenges of resistance and/or severe adverse effects associated with their particular payload toxins. Eribulin, a therapeutic agent for the treatment of metastatic breast cancer and liposarcoma, is a new choice of ADC payload with a distinct mechanism of action and safety profile. METHODS: We've generated a novel HER2-tageting eribulin-containing ADC, BB-1701. The potency of BB-1701 was tested in vitro and in vivo against cancer cells where HER2-expressing levels vary in a large range. Bystander killing effect and toxin-induced immunogenic cell death (ICD) of BB-1701 were also tested. RESULTS: In comparison with HER2-targeting ADCs with DM1 and Dxd payload, eribulin-containing ADC demonstrated higher in vitro cytotoxicity in HER2-low cancer cell lines. BB-1701 also effectively suppressed tumors in models resistant to DM1 or Dxd containing ADCs. Mode of action studies showed that BB-1701 had a significant bystander effect on HER2-null cells adjacent to HER2-high cells. In addition, BB-1701 treatment induced ICD. Repeated doses of BB-1701 in nonhuman primates showed favorable pharmacokinetics and safety profiles at the intended clinical dosage, route of administration, and schedule. CONCLUSIONS: The preclinical data support the test of BB-1701 in patients with various HER2-expressing cancers, including those resistant to other HER2-targeting ADCs. A phase I clinical trial of BB-1701 (NCT04257110) in patients is currently underway.

Antibody-drug conjugate MORAb-202 exhibits long-lasting antitumor efficacy in TNBC PDx models.

The antibody-drug conjugate (ADC) MORAb-202, consisting of farletuzumab paired with a cathepsin B-cleavable linker and eribulin, targets folate receptor alpha (FRA), which is frequently overexpressed in various tumor types. MORAb-202 was highly cytotoxic to FRA-positive cells in vitro, with limited off-target killing of FRA-negative cells. Furthermore, MORAb-202 showed a clear in vitro bystander cytotoxic effect in coculture with FRA-positive/negative cells. In vivo antitumor efficacy studies of MORAb-202 were conducted with a single administration of MORAb-202 in triple-negative breast cancer (TNBC) patient-derived xenograft (PDx) models expressing low and high levels of FRA. MORAb-202 exhibited durable efficacy proportional to tumor FRA expression. Toxicology studies (Q3Wx2) in nonhuman primates suggested that the major observed toxicity of MORAb-202 is hematologic toxicity. Overall, these findings support the concept that MORAb-202 represents a promising investigational ADC for the treatment of TNBC patients.

Efficient Production of Homogeneous Lysine-Based Antibody Conjugates Using Microbial Transglutaminase.

Random conjugation of chemical linkers to endogenous lysines or cysteines within an antibody yields a heterogeneous mixture of conjugates with various drug-to-antibody ratios. One approach for generating homogeneous antibody conjugates utilizes enzymatic transfer of payloads onto a specific glycan or amino acid residue. Microbial transglutaminase (MTG) is an enzyme that catalyzes the formation of a stable isopeptide bond between a glutamine and a lysine. We have previously identified and reported several sites throughout the antibody structure where an engineered lysine is sufficient for transfer of a glutamine-based substrate onto the antibody. Whereas other enzymatic transfer strategies typically require significant antibody engineering to either modify the N-glycans or introduce a multi-amino acid enzyme recognition site, the lower contextual specificity of MTG for lysines allows just a single lysine point mutation in an antibody to be efficiently transamidated. Here we describe the molecular positioning of these single engineered lysine residues and the conjugation conditions for producing homogeneous antibody conjugates exemplified using azido- and auristatin F-based acyl donor substrates.

Specific loss of adipocyte CD248 improves metabolic health via reduced white adipose tissue hypoxia, fibrosis and inflammation.

BACKGROUND: A positive energy balance promotes white adipose tissue (WAT) expansion which is characterized by activation of a repertoire of events including hypoxia, inflammation and extracellular matrix remodelling. The transmembrane glycoprotein CD248 has been implicated in all these processes in different malignant and inflammatory diseases but its potential impact in WAT and metabolic disease has not been explored. METHODS: The role of CD248 in adipocyte function and glucose metabolism was evaluated by omics analyses in human WAT, gene knockdowns in human in vitro differentiated adipocytes and by adipocyte-specific and inducible Cd248 gene knockout studies in mice. FINDINGS: CD248 is upregulated in white but not brown adipose tissue of obese and insulin-resistant individuals. Gene ontology analyses showed that CD248 expression associated positively with pro-inflammatory/pro-fibrotic pathways. By combining data from several human cohorts with gene knockdown experiments in human adipocytes, our results indicate that CD248 acts as a microenvironmental sensor which mediates part of the adipose tissue response to hypoxia and is specifically perturbed in white adipocytes in the obese state. Adipocyte-specific and inducible Cd248 knockouts in mice, both before and after diet-induced obesity and insulin resistance/glucose intolerance, resulted in increased microvascular density as well as attenuated hypoxia, inflammation and fibrosis without affecting fat cell volume. This was accompanied by significant improvements in insulin sensitivity and glucose tolerance. INTERPRETATION: CD248 exerts detrimental effects on WAT phenotype and systemic glucose homeostasis which may be reversed by suppression of adipocyte CD248. Therefore, CD248 may constitute a target to treat obesity-associated co-morbidities.

MORAb-202, an Antibody-Drug Conjugate Utilizing Humanized Anti-human FRα Farletuzumab and the Microtubule-targeting Agent Eribulin, has Potent Antitumor Activity.

Microtubule-targeting agents (MTA) have been investigated for many years as payloads for antibody-drug conjugates (ADC). In many cases, these ADCs have shown limited benefits due to lack of efficacy or significant toxicity, which has spurred continued investigation into novel MTA payloads for next-generation ADCs. In this study, we have developed ADCs using the MTA eribulin, a derivative of the macrocyclic polyether natural product halichondrin B, as a payload. Eribulin ADCs demonstrated in vitro potency and specificity using various linkers and two different conjugation approaches. MORAb-202 is an investigational agent that consists of the humanized anti-human folate receptor alpha (FRA) antibody farletuzumab conjugated via reduced interchain disulfide bonds to maleimido-PEG2-valine-citrulline-p-aminobenzylcarbamyl-eribulin at a drug-to-antibody ratio of 4.0. MORAb-202 displayed preferable biophysical properties and broad potency across a number of FRA-positive tumor cell lines as well as demonstrated improved specificity in vitro compared with farletuzumab conjugated with a number of other MTA payloads, including MMAE, MMAF, and the reducible maytansine linker-payload sulfo-SPDB-DM4. A single-dose administration of MORAb-202 in FRA-positive human tumor cell line xenograft and patient-derived tumor xenograft models elicited a robust and durable antitumor response. These data support further investigation of MORAb-202 as a potential new treatment modality for FRA-positive cancers, using the novel MTA eribulin as a payload.

Tumor antigen CA125 suppresses antibody-dependent cellular cytotoxicity (ADCC) via direct antibody binding and suppressed Fc-γ receptor engagement.

Cancers employ a number of mechanisms to evade host immune responses. Here we report the effects of tumor-shed antigen CA125/MUC16 on suppressing IgG1-mediated antibody-dependent cellular cytotoxicity (ADCC). This evidence stems from prespecified subgroup analysis of a Phase 3 clinical trial testing farletuzumab, a monoclonal antibody to folate receptor alpha, plus standard-of-care carboplatin-taxane chemotherapy in patients with recurrent platinum-sensitive ovarian cancer. Patients with low serum CA125 levels treated with farletuzumab demonstrated improvements in progression free survival (HR 0.49, p = 0.0028) and overall survival (HR 0.44, p = 0.0108) as compared to placebo. Farletuzumab's pharmacologic activity is mediated in part through ADCC. Here we show that CA125 inhibits ADCC by directly binding to farletuzumab that in turn perturbs Fc-γ receptor engagement on effector cells.

Engineering humanized antibody framework sequences for optimal site-specific conjugation of cytotoxins.

The prevailing techniques used to generate antibody-drug conjugates (ADCs) involve random conjugation of the linker-drug to multiple lysines or cysteines in the antibody. Engineering natural and non-natural amino acids into an antibody has been demonstrated to be an effective strategy to produce homogeneous ADC products with defined drug-to-antibody ratios. We recently reported an efficient residue-specific conjugation technology (RESPECT) where thiol-reactive payloads can be efficiently conjugated to a native unpaired cysteine in position 80 (C80) of rabbit light chains. Deimmunizing the rabbit variable domains through humanization is necessary to reduce the risk of anti-drug antibody responses in patients. However, we found that first-generation humanized RESPECT ADCs showed high levels of aggregation and low conjugation efficiency. We correlated these negative properties to the phenylalanine at position 83 present in most human variable kappa frameworks. When position 83 was substituted with selected amino acids, conjugation was restored and aggregation was reduced to levels similar to the chimeric ADC. This engineering strategy allows for development of second-generation humanized RESPECT ADCs with desirable biopharmaceutical properties.

Correlation of FCGRT genomic structure with serum immunoglobulin, albumin and farletuzumab pharmacokinetics in patients with first relapsed ovarian cancer.

Farletuzumab (FAR) is a humanized monoclonal antibody (mAb) that binds to folate receptor alpha. A Ph3 trial in ovarian cancer patients treated with carboplatin/taxane plus FAR or placebo did not meet the primary statistical endpoint. Subgroup analysis demonstrated that subjects with high FAR exposure levels (Cmin>57.6µg/mL) showed statistically significant improvements in PFS and OS. The neonatal Fc receptor (fcgrt) plays a central role in albumin/IgG stasis and mAb pharmacokinetics (PK). Here we evaluated fcgrt sequence and association of its promoter variable number tandem repeats (VNTR) and coding single nucleotide variants (SNV) with albumin/IgG levels and FAR PK in the Ph3 patients. A statistical correlation existed between high FAR Cmin and AUC in patients with the highest quartile of albumin and lowest quartile of IgG1. Analysis of fcgrt identified 5 different VNTRs in the promoter region and 9 SNVs within the coding region, 4 which are novel.

Generation of therapeutic immunoconjugates via Residue-Specific Conjugation Technology (RESPECT) utilizing a native cysteine in the light chain framework of Oryctolagus cuniculus.

The conjugation of toxins, dyes, peptides, or proteins to monoclonal antibodies is often performed via free thiol groups generated by either partial reduction methods or engineering free cysteine residues into the antibody sequence. Antibodies from the rabbit Oryctolagus cuniculus have an additional intrachain disulfide bond, whereby the light chain variable kappa domain is bridged to the constant kappa region between cysteine residues at positions 80 and 171, respectively. Chimerization of rabbit antibodies with human constant domains allows for the generation of a free thiol group at the light chain position 80 (C80) that can be used for site-specific conjugation. An efficient process for the purification and simultaneous removal of cysteinylation at the C80 site was developed. The unpaired C80 was shown to be efficiently conjugated using several different maleimido-based ligands. REsidue SPEcific Conjugation Technology (RESPECT) antibody-drug conjugates prepared using rabbit-human chimeric anti-human mesothelin rabbit antibodies and maleimido-PEG2-auristatin conjugated to C80 were shown to be highly potent and specific in vitro and effective in vivo in reduction of tumor growth in a highly aggressive mesothelin-expressing xenograft tumor model.

Novel antibody probes for the characterization of endosialin/TEM-1.

Endosialin (Tumor Endothelial Marker-1 (TEM-1), CD248) is primarily expressed on pericytes of tumor-associated microvasculature, tumor-associated stromal cells and directly on tumors of mesenchymal origin, including sarcoma and melanoma. While the function of endosialin/TEM-1 is incompletely understood, studies have suggested a role in supporting tumor growth and invasion thus making it an attractive therapeutic target. In an effort to further understand its role in cancer, we previously developed a humanized anti-endosialin/TEM-1 monoclonal antibody (mAb), called ontuxizumab (MORAb-004) for testing in preclinical and clinical studies. We herein report on the generation of an extensive panel of recombinant endosialin/TEM-1 protein extracellular domain (ECD) fragments and novel mAbs against ECD motifs. The domain-specific epitopes were mapped against ECD sub-domains to identify those that can detect distinct structural motifs and can be potentially formatted as probes suitable for diagnostic and functional studies. A number of mAbS were shown to cross-react with the murine and human protein, potentially allowing their use in human animal models and corresponding clinical trials. In addition, pairing of several mAbs supported their use in immunoassays that can detect soluble endosialin/TEM-1 (sEND) in the serum of healthy subjects and cancer patients.

Derivatization of agelastatin A leading to bioactive analogs and a trifunctional probe.

(-)-Agelastatin A (AglA, 1), a member of the pyrrole-aminoimidazole marine alkaloid (PAI) family, possesses a unique tetracyclic structure and is one of the most potent anticancer PAIs isolated to date. In efforts to expand the SAR of these agents and delineate sites that tolerate modification while retaining activity, we synthesized several derivatives and tested their anticancer activity. The cytotoxic effects of these derivatives were measured against several cancer cell lines including cervical cancer (HeLa), epidermoid carcinoma (A431), ovarian (Igrov and Ovcar3), osteosarcoma (SJSA1), acute T cell leukemia (A3), epidermoid carcinoma (A431) in addition to primary human chronic lymphocytic leukemia (CLL) cells. New positions for modification of AglA and new substitutions were explored leading to novel derivatives, 14-chloro AglA (3) and 14-methyl AglA (12), that retained activity toward various cancer cell lines with decreased toxicity toward B- and T-cells. The SAR data informed the synthesis of a trifunctional probe bearing an alkyne and a diazirine potentially useful for cellular target identification.

Targeting endosialin/CD248 through antibody-mediated internalization results in impaired pericyte maturation and dysfunctional tumor microvasculature.

Over-expression of endosialin/CD248 (herein referred to as CD248) has been associated with increased tumor microvasculature in various tissue origins which makes it an attractive anti-angiogenic target. In an effort to target CD248, we have generated a human CD248 knock-in mouse line and MORAb-004, the humanized version of the mouse anti-human CD248 antibody Fb5. Here, we report that MORAb-004 treatment significantly impacted syngeneic tumor growth and tumor metastasis in the human CD248 knock-in mice. In comparison with untreated tumors, MORAb-004 treated tumors displayed overall shortened and distorted blood vessels. Immunofluorescent staining of tumor sections revealed drastically more small and dysfunctional vessels in the treated tumors. The CD248 levels on cell surfaces of neovasculature pericytes were significantly reduced due to its internalization. This reduction of CD248 was also accompanied by reduced α-SMA expression, depolarization of pericytes and endothelium, and ultimately dysfunctional microvessels. These results suggest that MORAb-004 reduced CD248 on pericytes, impaired tumor microvasculature maturation and ultimately suppressed tumor development.

Co-development of diagnostic vectors to support targeted therapies and theranostics: essential tools in personalized cancer therapy.

Novel technologies are being developed to improve patient therapy through the identification of targets and surrogate molecular signatures that can help direct appropriate treatment regimens for efficacy and drug safety. This is particularly the case in oncology whereby patient tumor and biofluids are routinely isolated and analyzed for genetic, immunohistochemical, and/or soluble markers to determine if a predictive biomarker signature (i.e., mutated gene product, differentially expressed protein, altered cell surface antigen, etc.) exists as a means for selecting optimal treatment. These biomarkers may be drug-specific targets and/or differentially expressed nucleic acids, proteins, or cell lineage profiles that can directly affect the patient's disease tissue or immune response to a therapeutic regimen. Improvements in diagnostics that can prescreen predictive response biomarker profiles will continue to optimize the ability to enhance patient therapy via molecularly defined disease-specific treatment. Conversely, patients lacking predictive response biomarkers will no longer needlessly be exposed to drugs that are unlikely to provide clinical benefit, thereby enabling patients to pursue other therapeutic options and lowering overall healthcare costs by avoiding futile treatment. While patient molecular profiling offers a powerful tool to direct treatment options, the difficulty in identifying disease-specific targets or predictive biomarker signatures that stratify a significant fraction within a disease indication remains challenging. A goal for drug developers is to identify and implement new strategies that can rapidly enable the development of beneficial disease-specific therapies for broad patient-specific targeting without the need of tedious predictive biomarker discovery and validation efforts, currently a bottleneck for development timelines. Successful strategies may gain an advantage by employing repurposed, less-expensive existing agents while potentially improving the therapeutic activity of novel, target-specific therapies that may otherwise have off-target toxicities or less efficacy in cells exhibiting certain pathways. Here, we discuss the use of co-developing diagnostic-targeting vectors to identify patients whose malignant tissue can specifically uptake a targeted anti-cancer drug vector prior to treatment. Using this system, a patient can be predetermined in real-time as to whether or not their tumor(s) can specifically uptake a drug-linked diagnostic vector, thus inferring the uptake of a similar vector linked to an anti-cancer agent. If tumor-specific uptake is observed, then the patient may be suitable for drug-linked vector therapy and have a higher likelihood of clinical benefit while patients with no tumor uptake should consider other therapeutic options. This approach offers complementary opportunities to rapidly develop broad tumor-specific agents for use in personalized medicine.

The antitumor activity of the human FOLR1-specific monoclonal antibody, farletuzumab, in an ovarian cancer mouse model is mediated by antibody-dependent cellular cytotoxicity.

Because of its high mortality rate, ovarian cancer is a leading cause of death among women and a highly unmet medical need. New therapeutic agents that are effective and well tolerated are needed and cancer antigen-specific monoclonal antibodies that have direct pharmacologic effects or can stimulate immunological responses represent a promising class of agents for the treatment of this disease. The human folate receptor α (FOLR1), which is overexpressed in ovarian cancer but largely absent in normal tissues, appears to play a role in the transformed phenotype in ovarian cancer, cisplatin sensitivity, and growth in depleted folate conditions and therefore has potential as a target for passive immunotherapy. The anti-FOLR1 monoclonal antibody MORAb-003 (farletuzumab) was previously shown to elicit antibody dependent cellular cytotoxicity (ADCC) and inhibit tumor growth of human tumor xenografts in nude mice. Because of its promising preclinical profile, farletuzumab has been evaluated in clinical trials as a potential therapeutic agent for ovarian cancer. In this report, we demonstrated that farletuzumab's antitumor effect against an experimental model of ovarian cancer is mediated by its ADCC activity.

Characterization of the human folate receptor alpha via novel antibody-based probes.

Folate receptor alpha (FRA) is a cell surface protein whose aberrant expression in malignant cells has resulted in its pursuit as a therapeutic target and marker for diagnosis of cancer. The development of immune-based reagents that can reproducibly detect FRA from patient tissue processed by varying methods has been difficult due to the complex post-translational structure of the protein whereby most reagents developed to date are highly structure-sensitive and have resulted in equivocal expression results across independent studies. The aim of the present study was to generate novel monoclonal antibodies (mAbs) using modified full length FRA protein as immunogen in order to develop a panel of mAbs to various, non-overlapping epitopes that may serve as diagnostic reagents able to robustly detect FRA-positive disease. Here we report the development of a panel of FRA-specific mAbs that are able to specifically detect FRA using an array of diagnostic platforms and methods. In addition, the methods used to develop these mAbs and their diverse binding properties provide additional information on the three dimensional structure of FRA in its native cell surface configuration.

Effect of chelator conjugation level and injection dose on tumor and organ uptake of 111In-labeled MORAb-009, an anti-mesothelin antibody.

INTRODUCTION: Radiolabeling of a monoclonal antibody (mAb) with a metallic radionuclide requires the conjugation of a bifunctional chelator to the mAb. The conjugation, however, can alter the physical and immunological properties of the mAb, consequently affecting its tumor-targeting pharmacokinetics. In this study, we investigated the effect of the amount of 2-(p-isothiocyanatobenzyl)-cyclohexyl-diethylenetriamine-pentaacetic acid (CHX-A″) conjugated to MORAb-009, a mAb directed against mesothelin, and the effect of MORAb dose on the biodistribution of (111)In-labeled MORAb-009. METHODS: We used nude mice bearing the A431/K5 tumor as a mesothelin-positive tumor model and the A431 tumor as a mesothelin-negative control. To find the optimal level of CHX-A″ conjugation, CHX-A″-MORAb-009 conjugates with 2.4, 3.5 and 5.5 CHX-A″ molecules were investigated. To investigate the effect of injected MORAb-009 dose on neutralizing the shed mesothelin in the circulation, biodistribution studies were performed after the intravenous co-injection of (111)In-labeled MORAb-009 (2.4 CHX-A″/MORAb-009) with three different doses: 0.2, 2 and 30 µg of MORAb-009. RESULTS: The tumor uptake in A431/K5 tumor was four times higher than that in A431 tumor, indicating that the tumor uptake in A431/K5 was mesothelin mediated. The conjugate with 5.5 CHX-A″ showed a lower isoelectric point (pI) and lower immunoreactivity (IR) than the 2.4 CHX-A″ conjugate. These differences were reflected in the biodistribution of the (111)In label. The (111)In-labeled MORAb-009 conjugated with 2.4 CHX-A″ produced higher tumor uptake and lower liver and spleen uptakes than the 5.5 CHX-A″ conjugate. The biodistribution studies also revealed that the tumor uptake was significantly affected by the injected MORAb-009 dose and tumor size. The 30-µg dose produced higher tumor uptake than the 0.2- and 2-µg doses, whereas the 30-µg dose produced lower liver and spleen uptakes than the 0.2-µg dose. CONCLUSION: This study demonstrates that the number of chelate conjugation and the injected dose are two important parameters to achieve high tumor and low non-target organ uptake of (111)In-labeled MORAb-009. This study also suggests that the injected dose of mAb could be individualized based on the tumor size or the blood level of shed antigen in a patient to achieve the ideal tumor-to-organ radioactivity ratios.

Characterization of antibodies to CA 125 that bind preferentially to the cell-associated form of the antigen.

OBJECTIVE: Antibodies to CA 125 have been used to predict relapse of ovarian cancer, but have performed poorly as therapeutic agents. One rationale for this is antibody binding to circulating shed antigen. Our aim in this study was to develop antibodies to human CA 125 that have enhanced selectivity for the cell-associated form of the antigen. METHODS: Monoclonal antibodies were raised to a recombinant fragment of CA 125 that included sequence proximal to the putative membrane attachment site. Antibodies were characterized in terms of their binding site, affinity and selectivity for cell-associated CA 125. RESULTS: In assays using patient-derived CA 125, a subset of high-affinity (KD <5 nM) monoclonal antibodies demonstrated a 10- to greater than 200-fold increase in selectivity for cell-associated CA 125 when compared with controls. Based on mapping of the various monoclonal antibodies obtained, it was determined that shedding of CA 125 most likely occurs in the most C-terminal repeat domain. CONCLUSION: Results from competition analysis using patient-derived shed antigen predict that the antibodies described in this study may have significantly enhanced tumor-targeting properties when compared with existing antibodies to CA 125 in a tumor environment having high concentrations (>10,000 CA 125 units) of shed CA 125.

Synergistic effects of combined therapy using paclitaxel and [90Y-DOTA]776.1 on growth of OVCAR-3 ovarian carcinoma xenografts.

OBJECTIVE: 776.1 is a monoclonal antibody prepared against the human ovarian cancer antigen CA 125 that demonstrates preferential binding to the cell-associated form of the antigen and has shown promising results as an yttrium-90-labeled antibody in pre-clinical studies examining the effects on tumor growth in a murine xenograft model of human ovarian cancer. The purpose of the present study was to examine the effects of combined therapy with [90Y-DOTA]776.1 and paclitaxel compared with monotherapy with either agent on the growth of OVCAR-3 xenografts in nude mice. METHODS: Mice bearing OVCAR-3 xenografts were treated with paclitaxel alone, 50 microCi or 150 microCi [90Y-DOTA]776.1 alone, or a combination of both treatments. Control groups were included which consisted of a nonspecific antibody, MOPC-21, labeled to a similar degree, administered as monotherapy or in combination with paclitaxel. The effects of administration of radioimmunotherapy prior to or following chemotherapy were also examined. RESULTS: Treatment with paclitaxel and [90Y-DOTA]776.1 had a synergistic anti-tumor effect on the growth of OVCAR-3 xenografts. Synergy was only observed when a tumor-specific antibody was used in radioimmunotherapy. While no difference in tumor growth was observed with order of dosing, reduced toxicity was seen when paclitaxel was administered prior to radioimmunotherapy. CONCLUSION: The combination of radioimmunotherapy using an anti-CA 125 monoclonal antibody and chemotherapy with paclitaxel was shown to be effective in an in vivo model of ovarian cancer and may hold promise as a treatment regimen for patients with ovarian cancer.

Radiotherapy of human xenograft NSCLC tumors in nude mice with a 90Y-labeled anti-tissue factor antibody.

Tissue factor (TF) is a type I transmembrane protein and the initiator of the extrinsic blood coagulation pathway. TF plays a critical role in tumor development and its overexpression is observed in many tumors. To understand the prevalence and relative level of TF expression in non-small-cell lung cancer (NSCLC), we analyzed 50 NSCLC tumors by immunohistochemical staining and found that 88% of human NSCLC tumors overexpressed TF. We then generated a high affinity anti-TF antibody, TF278, which specifically binds TF on the surface of cells and is internalized upon binding. An 111In-labeled TF278 demonstrated favorable tumor accumulation in an SW-900 xenograft tumor model with a maximum mean percent of injected dose per gram of tissue (%ID/g) of 73.1% at 96 hours postinjection. In addition, we labeled the antibody with 90Y and tested its ability to inhibit the growth of tumors in an SW-900 xenograft tumor model in immunocompromised mice. The 90Y-TF278 slowed the growth of SW-900 tumors at a 50 microCi dose and completely regressed SW-900 tumors at a 150 microCi dose with little toxicity.

Pharmacokinetics, biodistribution, and radioimmunotherapy with monoclonal antibody 776.1 in a murine model of human ovarian cancer.

776.1 is a murine IgG1 monoclonal antibody to the human ovarian cancer antigen CA 125 that has the unique property of having a clear preference for binding to the cell-associated form of the antigen. We have examined the tumor localization properties and efficacy of 776.1 in a subcutaneous OVCAR-3 xenograft mouse model of human ovarian cancer. Biodistribution experiments using (125)I-labeled 776.1 demonstrated a peak uptake in tumors at 72 hours postinjection, with an average of 17.7% of injected dose per gram localized to the tumor. Little uptake in other organs was observed. Further experiments using CA 125-transfected syngeneic tumors, as well as an immunoprecipitation assay using human chimeric 776.1, both clearly demonstrated that 776.1 localizes to the tumor in a CA 125-dependent manner. DOTA-776.1 (1,4,7,10-tetraazacyclododecane-N,N',N",N'" tetraacetic acid-conjugated 776.1) was labeled with (90)Y and used in efficacy studies. [(90)Y-DOTA]776.1 at a single dose of 150 microCi was able to mediate efficient reduction of tumor growth, with regression observed in a subset of animals for a period ranging from 3 to 48 days, equivalent to 3 weekly administrations of cisplatin at 6 mg/kg. No significant regression was observed in groups receiving [(90)Y-DOTA]MOPC-21 control antibody at any dose. These results suggest that 776.1 may be a promising radioimmunotherapeutic agent for the treatment of human ovarian cancer.