A homogeneous high-DAR antibody-drug conjugate platform combining THIOMAB antibodies and XTEN polypeptides

The antibody-drug conjugate (ADC) is a well-validated modality for the cell-specific delivery of small molecules with impact expanding rapidly beyond their originally-intended purpose of treating cancer. However, antibody-mediated delivery (AMD)...

Calicheamicin Antibody-Drug Conjugates with Improved Properties

Calicheamicin antibody-drug conjugates (ADCs) are effective therapeutics for leukemias with two recently approved in the United States: Mylotarg (gemtuzumab ozogamicin) targeting CD33 for acute myeloid leukemia and Besponsa (inotuzumab ozogamicin) targeting CD22 for acute lymphocytic leukemia. Both of these calicheamicin ADCs are heterogeneous, aggregation-prone, and have a shortened half-life due to the instability of the acid-sensitive hydrazone linker in circulation. We hypothesized that we could improve upon the heterogeneity, aggregation, and circulation stability of calicheamicin ADCs by directly attaching the thiol of a reduced calicheamicin to an engineered cysteine on the antibody via a disulfide bond to generate a linkerless and traceless conjugate. We report herein that the resulting homogeneous conjugates possess minimal aggregation and display high in vivo stability with 50% of the drug remaining conjugated to the antibody after 21 days. Furthermore, these calicheamicin ADCs are highly efficacious in mouse models of both solid tumor (HER2⁺ breast cancer) and hematologic malignancies (CD22⁺ non-Hodgkin lymphoma). Safety studies in rats with this novel calicheamicin ADC revealed an increased tolerability compared with that reported for Mylotarg. Overall, we demonstrate that applying novel linker chemistry with site-specific conjugation affords an improved, next-generation calicheamicin ADC.

Antibody-Mediated Delivery of Chimeric BRD4 Degraders. Part 2: Improvement of In Vitro Antiproliferation Activity and In Vivo Antitumor Efficacy

Heterobifunctional compounds that direct the ubiquitination of intracellular proteins in a targeted manner via co-opted ubiquitin ligases have enormous potential to transform the field of medicinal chemistry. These chimeric molecules, often termed proteolysis-targeting chimeras (PROTACs) in the chemical literature, enable the controlled degradation of specific proteins via their direction to the cellular proteasome. In this report, we describe the second phase of our research focused on exploring antibody-drug conjugates (ADCs), which incorporate BRD4-targeting chimeric degrader entities. We employ a new BRD4-binding fragment in the construction of the chimeric ADC payloads that is significantly more potent than the corresponding entity utilized in our initial studies. The resulting BRD4-degrader antibody conjugates exhibit potent and antigen-dependent BRD4 degradation and antiproliferation activities in cell-based experiments. Multiple ADCs bearing chimeric BRD4-degrader payloads also exhibit strong, antigen-dependent antitumor efficacy in mouse xenograft assessments that employ several different tumor models.

Antibody-Mediated Delivery of Chimeric BRD4 Degraders. Part 1: Exploration of Antibody Linker, Payload Loading, and Payload Molecular Properties

The biological and medicinal impacts of proteolysis-targeting chimeras (PROTACs) and related chimeric molecules that effect intracellular degradation of target proteins via ubiquitin ligase-mediated ubiquitination continue to grow. However, these chimeric entities are relatively large compounds that often possess molecular characteristics, which may compromise oral bioavailability, solubility, and/or in vivo pharmacokinetic properties. We therefore explored the conjugation of such molecules to monoclonal antibodies using technologies originally developed for cytotoxic payloads so as to provide alternate delivery options for these novel agents. In this report, we describe the first phase of our systematic development of antibody-drug conjugates (ADCs) derived from bromodomain-containing protein 4 (BRD4)-targeting chimeric degrader entities. We demonstrate the antigen-dependent delivery of the degrader payloads to PC3-S1 prostate cancer cells along with related impacts on MYC transcription and intracellular BRD4 levels. These experiments culminate with the identification of one degrader conjugate, which exhibits antigen-dependent antiproliferation effects in LNCaP prostate cancer cells.

Improved translation of stability for conjugated antibodies using an in vitro whole blood assay

For antibody-drug conjugates to be efficacious and safe, they must be stable in circulation to carry the payload to the site of the targeted cell. Several components of a drug-conjugated antibody are known to influence stability: 1) the site of drug attachment on the antibody, 2) the linker used to attach the payload to the antibody, and 3) the payload itself. In order to support the design and optimization of a high volume of drug conjugates and avoid unstable conjugates prior to testing in animal models, we wanted to proactively identify these potential liabilities. Therefore, we sought to establish an in vitro screening method that best correlated with in vivo stability. While traditionally plasma has been used to assess in vitro stability, our evaluation using a variety of THIOMAB^TM antibody-drug conjugates revealed several disconnects between the stability assessed in vitro and the in vivo outcomes when using plasma. When drug conjugates were incubated in vitro for 24 h in mouse whole blood rather than plasma and then analyzed by affinity capture LC-MS, we found an improved correlation to in vivo stability with whole blood (R² = 0.87, coefficient of determination) compared to unfrozen or frozen mouse plasma (R² = 0.34, 0.01, respectively). We further showed that this whole blood assay was also able to predict in vivo stability of other preclinical species such as rat and cynomolgus monkey, as well as in human. The screening method utilized short (24 h) incubation times, as well as a custom analysis software, allowing increased throughput and in-depth biotransformation characterization. While some instabilities that were more challenging to identify remain, the method greatly enhanced the process of screening, optimizing, and lead candidate selection, resulting in the substantial reduction of animal studies.

Preclinical optimization of Ly6E-targeted ADCs for increased durability and efficacy of anti-tumor response

Early success with brentuximab vedotin in treating classical Hodgkin lymphoma spurred an influx of at least 20 monomethyl auristatin E (MMAE) antibody-drug conjugates (ADCs) into clinical trials. While three MMAE-ADCs have been approved, most of these conjugates are no longer being investigated in clinical trials. Some auristatin conjugates show limited or no efficacy at tolerated doses, but even for drugs driving initial remissions, tumor regrowth and metastasis often rapidly occur. Here we describe the development of second-generation therapeutic ADCs targeting Lymphocyte antigen 6E (Ly6E) where the tubulin polymerization inhibitor MMAE (Compound 1) is replaced with DNA-damaging agents intended to drive increased durability of response. Comparison of a seco-cyclopropyl benzoindol-4-one (CBI)-dimer (compound 2) to MMAE showed increased potency, activity across more cell lines, and resistance to efflux by P-glycoprotein, a drug transporter commonly upregulated in tumors. Both anti-Ly6E-CBI and -MMAE conjugates drove single-dose efficacy in xenograft and patient-derived xenograft models, but seco-CBI-dimer conjugates showed reduced tumor outgrowth following multiple weeks of treatment, suggesting that they are less susceptible to developing resistance. In parallel, we explored approaches to optimize the targeting antibody. In contrast to immunization with recombinant Ly6E or Ly6E DNA, immunization with virus-like particles generated a high-affinity anti-Ly6E antibody. Conjugates to this antibody improve efficacy versus a previous clinical candidate both in vitro and in vivo with multiple cytotoxics. Conjugation of compound 2 to the second-generation antibody results in a substantially improved ADC with promising preclinical efficacy.

Systematic Variation of Pyrrolobenzodiazepine (PBD)-Dimer Payload Physicochemical Properties Impacts Efficacy and Tolerability of the Corresponding Antibody-Drug Conjugates

Cytotoxic pyrrolobenzodiazepine (PBD)-dimer molecules are frequently utilized as payloads for antibody-drug conjugates (ADCs), and many examples are currently in clinical development. In order to further explore this ADC payload class, the physicochemical properties of various PBD-dimer molecules were modified by the systematic introduction of acidic and basic moieties into their chemical structures. The impact of these changes on DNA binding, cell membrane permeability, and in vitro antiproliferation potency was, respectively, determined using a DNA alkylation assay, PAMPA assessments, and cell-based cytotoxicity measurements conducted with a variety of cancer lines. The modified PBD-dimer compounds were subsequently incorporated into CD22-targeting ADCs, and these entities were profiled in a variety of in vitro and in vivo experiments. The introduction of a strongly basic moiety into the PBD-dimer scaffold afforded a conjugate with dramatically worsened mouse tolerability properties relative to ADCs derived from related payloads, which lacked the basic group.

Development of a Cysteine-Conjugatable Disulfide FRET Probe: Influence of Charge on Linker Cleavage and Payload Trafficking for an Anti-HER2 Antibody Conjugate

Disulfide-linked bioconjugates allow the delivery of pharmacologically active or other cargo to specific tissues in a redox-sensitive fashion. However, an understanding of the kinetics, subcellular distribution, and mechanism of disulfide cleavage in such bioconjugates is generally lacking. Here, we report a modular disulfide-linked TAMRA-BODIPY based FRET probe that can be readily synthesized, modified, and conjugated to a cysteine-containing biomolecule to enable real-time monitoring of disulfide cleavage during receptor-mediated endocytosis in cells. We demonstrate the utility of this probe to study disulfide reduction during HER2 receptor-mediated uptake of a Cys-engineered anti-HER2 THIOMAB antibody. We found that introduction of positive, but not negative, charges in the probe improved retention of the BODIPY catabolite. This permitted the observation of significant disulfide cleavage in endosomes or lysosomes on par with proteolytic cleavage of a similarly charged valine-citrulline peptide-based probe. In general, the FRET probe we describe should enable real-time cellular monitoring of disulfide cleavage in other targeted delivery systems for mechanistic or diagnostic applications. Furthermore, modifications to the released BODIPY moiety permit evaluation of physicochemical properties that govern lysosomal egress or retention, which may have implications for the development of next-generation antibody-drug conjugates.

Biodistribution and efficacy of an anti-TENB2 antibody-drug conjugate in a patient-derived model of prostate cancer

TENB2, a transmembrane proteoglycan protein, is a promising target for antibody drug conjugate (ADC) therapy due to overexpression in human prostate tumors and rapid internalization. We previously characterized how predosing with parental anti-TENB2 monoclonal antibody (mAb) at 1 mg/kg in a patient-derived LuCap77 explant model with high (3+) TENB2 expression could (i) block target-mediated intestinal uptake of tracer (& 0.1 mg/kg) levels of radiolabeled anti-TENB2-monomethyl auristatin E ADC while preserving tumor uptake, and (ii) maintain efficacy relative to ADC alone. Here, we systematically revisit this strategy to evaluate the effects of predosing on tumor uptake and efficacy in LuCap96.1, a low TENB2-expressing (1+) patient-derived model that is more responsive to ADC therapy than LuCap77. Importantly, rather than using tracer (& 0.1 mg/kg) levels, radiolabeled ADC tumor uptake was assessed at 1 mg/kg – one of the doses evaluated in the tumor growth inhibition study – in an effort to bridge tissue distribution (PK) with efficacy (PD). Predosing with mAb up to 1 mg/kg had no effect on efficacy. These findings warrant further investigations to determine whether predosing prior to ADC therapy might improve therapeutic index by preventing ADC disposition and possible toxicological liabilities in antigen-expressing healthy tissues.

Evaluation and use of an anti-cynomolgus monkey CD79b surrogate antibody-drug conjugate to enable clinical development of polatuzumab vedotin

BACKGROUND AND PURPOSE

Polatuzumab vedotin is an antibody-drug conjugate (ADC) being developed for non-Hodgkin's lymphoma. It contains a humanized anti-CD79b IgG1 monoclonal antibody linked to monomethyl auristatin E (MMAE), an anti-mitotic agent. Polatuzumab vedotin binds to human CD79b only. Therefore, a surrogate ADC that binds to cynomolgus monkey CD79b was used to determine CD79b-mediated pharmacological effects in the monkey and to enable first-in-human clinical trials.

EXPERIMENTAL APPROACH

Polatuzumab vedotin, the surrogate ADC, and the corresponding antibodies were evaluated in different assays in vitro and in animals. In vitro assessments included binding to peripheral blood mononuclear cells from different species, binding to a human and monkey CD79b-expressing cell line, binding to human Fcγ receptors, and stability in plasma across species. In vivo, ADCs were assessed for anti-tumour activity in mice, pharmacokinetics/pharmacodynamics in monkeys, and toxicity in rats and monkeys.

KEY RESULTS

Polatuzumab vedotin and surrogate ADC bind with similar affinity to human and cynomolgus monkey B cells, respectively. Comparable in vitro plasma stability, in vivo anti-tumour activity, and mouse pharmacokinetics were also observed between the surrogate ADC and polatuzumab vedotin. In monkeys, only the surrogate ADC showed B-cell depletion and B-cell-mediated drug disposition, but both ADCs showed similar MMAE-driven myelotoxicity, as expected.

CONCLUSIONS AND IMPLICATIONS

The suitability of the surrogate ADC for evaluation of CD79b-dependent pharmacology was demonstrated, and anti-tumour activity, pharmacokinetics/pharmacodynamics, and toxicity data with both ADCs supported the entry of polatuzumab vedotin into clinical trials.

Preclinical pharmacokinetics and pharmacodynamics of DCLL9718A: An antibody-drug conjugate for the treatment of acute myeloid leukemia

Few treatment options are available for acute myeloid leukemia (AML) patients. DCLL9718A is an antibody-drug conjugate that targets C-type lectin-like molecule-1 (CLL-1). This receptor is prevalent on monocytes, neutrophils, and AML blast cells, and unlike CD33, is not expressed on hematopoietic stem cells, thus providing possible hematopoietic recovery. DCLL9718A comprises an anti-CLL-1 IgG1 antibody (MCLL0517A) linked to a pyrrolobenzodiazepine (PBD) dimer payload, via a cleavable disulfide-labile linker. Here, we characterize the in vitro and in vivo stability, the pharmacokinetics (PK) and pharmacodynamics (PD) of DCLL9718A and MCLL0517A in rodents and cynomolgus monkeys. Three key PK analytes were measured in these studies: total antibody, antibody-conjugated PBD dimer and unconjugated PBD dimer. In vitro, DCLL9718A, was stable with most (> 80%) of the PBD dimer payload remaining conjugated to the antibody over 96 hours. This was recapitulated in vivo with antibody-conjugated PBD dimer clearance estimates similar to DCLL9718A total antibody clearance. Both DCLL9718A and MCLL0517A showed linear PK in the non-binding rodent species, and non-linear PK in cynomolgus monkeys, a binding species. The PK data indicated minimal impact of conjugation on the disposition of DCLL9718A total antibody. Finally, in cynomolgus monkey, MCLL0517A showed target engagement at all doses tested (0.5 and 20 mg/kg) as measured by receptor occupancy, and DCLL9718A (at doses of 0.05, 0.1 and 0.2 mg/kg) showed strong PD activity as evidenced by notable reduction in monocytes and neutrophils.

Prediction of non-linear pharmacokinetics in humans of an antibody-drug conjugate (ADC) when evaluation of higher doses in animals is limited by tolerability: Case study with an anti-CD33 ADC

For antibody-drug conjugates (ADCs) that carry a cytotoxic drug, doses that can be administered in preclinical studies are typically limited by tolerability, leading to a narrow dose range that can be tested. For molecules with non-linear pharmacokinetics (PK), this limited dose range may be insufficient to fully characterize the PK of the ADC and limits translation to humans. Mathematical PK models are frequently used for molecule selection during preclinical drug development and for translational predictions to guide clinical study design. Here, we present a practical approach that uses limited PK and receptor occupancy (RO) data of the corresponding unconjugated antibody to predict ADC PK when conjugation does not alter the non-specific clearance or the antibody-target interaction. We used a 2-compartment model incorporating non-specific and specific (target mediated) clearances, where the latter is a function of RO, to describe the PK of anti-CD33 ADC with dose-limiting neutropenia in cynomolgus monkeys. We tested our model by comparing PK predictions based on the unconjugated antibody to observed ADC PK data that was not utilized for model development. Prospective prediction of human PK was performed by incorporating in vitro binding affinity differences between species for varying levels of CD33 target expression. Additionally, this approach was used to predict human PK of other previously tested anti-CD33 molecules with published clinical data. The findings showed that, for a cytotoxic ADC with non-linear PK and limited preclinical PK data, incorporating RO in the PK model and using data from the corresponding unconjugated antibody at higher doses allowed the identification of parameters to characterize monkey PK and enabled human PK predictions.

Automated On-tip Affinity Capture Coupled with Mass Spectrometry to Characterize Intact Antibody-Drug Conjugates from Blood

Antibody-drug conjugates (ADCs) present unique challenges for ligand-binding assays primarily due to the dynamic changes of the drug-to-antibody ratio (DAR) distribution in vivo and in vitro. Here, an automated on-tip affinity capture platform with subsequent mass spectrometry analysis was developed to accurately characterize the DAR distribution of ADCs from biological matrices. A variety of elution buffers were tested to offer optimal recovery, with trastuzumab serving as a surrogate to the ADCs. High assay repeatability (CV 3%) was achieved for trastuzumab antibody when captured below the maximal binding capacity of 7.5 μg. Efficient on-tip deglycosylation was also demonstrated in 1 h followed by affinity capture. Moreover, this tip-based platform affords higher throughput for DAR characterization when compared with a well-characterized bead-based method. Graphical Abstract ᅟ.

High-Throughput Cysteine Scanning To Identify Stable Antibody Conjugation Sites for Maleimide- and Disulfide-Based Linkers

THIOMAB antibody technology utilizes cysteine residues engineered onto an antibody to allow for site-specific conjugation. The technology has enabled the exploration of different attachment sites on the antibody in combination with small molecules, peptides, or proteins to yield antibody conjugates with unique properties. As reported previously ( Shen , B. Q. , et al. ( 2012 ) Nat. Biotechnol. 30 , 184 - 189 ; Pillow , T. H. , et al. ( 2017 ) Chem. Sci. 8 , 366 - 370 ), the specific location of the site of conjugation on an antibody can impact the stability of the linkage to the engineered cysteine for both thio-succinimide and disulfide bonds. High stability of the linkage is usually desired to maximize the delivery of the cargo to the intended target. In the current study, cysteines were individually substituted into every position of the anti-HER2 antibody (trastuzumab), and the stabilities of drug conjugations at those sites were evaluated. We screened a total of 648 THIOMAB antibody-drug conjugates, each generated from a trastuzamab prepared by sequentially mutating non-cysteine amino acids in the light and heavy chains to cysteine. Each THIOMAB antibody variant was conjugated to either maleimidocaproyl-valine-citrulline-p-aminobenzyloxycarbonyl-monomethyl auristatin E (MC-vc-PAB-MMAE) or pyridyl disulfide monomethyl auristatin E (PDS-MMAE) using a high-throughput, on-bead conjugation and purification method. Greater than 50% of the THIOMAB antibody variants were successfully conjugated to both MMAE derivatives with a drug to antibody ratio (DAR) of >0.5 and <50% aggregation. The relative in vitro plasma stabilities for approximately 750 conjugates were assessed using enzyme-linked immunosorbent assays, and stable sites were confirmed with affinity-capture LC/MS-based detection methods. Highly stable conjugation sites for the two types of MMAE derivatives were identified on both the heavy and light chains. Although the stabilities of maleimide conjugates were shown to be greater than those of the disulfide conjugates, many sites were identified that were stable for both. Furthermore, in vitro stabilities of selected stable sites translated across different cytotoxic payloads and different target antibodies as well as to in vivo stability.

An Anti-GDNF Family Receptor Alpha 1 (GFRA1) Antibody-Drug Conjugate for the Treatment of Hormone Receptor-Positive Breast Cancer

Luminal A (hormone receptor-positive) breast cancer constitutes 70% of total breast cancer patients. In an attempt to develop a targeted therapeutic for this cancer indication, we have identified and characterized Glial cell line-Derived Neurotrophic Factor (GDNF) Family Receptor Alpha 1 (GFRA1) antibody-drug conjugates (ADC) using a cleavable valine-citrulline-MMAE (vcMMAE) linker-payload. RNAseq and IHC analysis confirmed the abundant expression of GFRA1 in luminal A breast cancer tissues, whereas minimal or no expression was observed in most normal tissues. Anti-GFRA-vcMMAE ADC internalized to the lysosomes and exhibited target-dependent killing of GFRA1-expressing cells both in vitro and in vivo The ADCs using humanized anti-GFRA1 antibodies displayed robust therapeutic activity in clinically relevant cell line-derived (MCF7 and KPL-1) tumor xenograft models. The lead anti-GFRA1 ADC cross-reacts with rodent and cynomolgus monkey GFRA1 antigen and showed optimal pharmacokinetic properties in both species. These properties subsequently enabled a target-dependent toxicity study in rats. Anti-GFRA1 ADC is well tolerated in rats, as seen with other vcMMAE linker-payload based ADCs. Overall, these data suggest that anti-GFRA1-vcMMAE ADC may provide a targeted therapeutic opportunity for luminal A breast cancer patients. Mol Cancer Ther; 17(3); 638-49. ©2017 AACR.

Discovery of Peptidomimetic Antibody-Drug Conjugate Linkers with Enhanced Protease Specificity

Antibody-drug conjugates (ADCs) have become an important therapeutic modality for oncology, with three approved by the FDA and over 60 others in clinical trials. Despite the progress, improvements in ADC therapeutic index are desired. Peptide-based ADC linkers that are cleaved by lysosomal proteases have shown sufficient stability in serum and effective payload-release in targeted cells. If the linker can be preferentially hydrolyzed by tumor-specific proteases, safety margin may improve. However, the use of peptide-based linkers limits our ability to modulate protease specificity. Here we report the structure-guided discovery of novel, nonpeptidic ADC linkers. We show that a cyclobutane-1,1-dicarboxamide-containing linker is hydrolyzed predominantly by cathepsin B while the valine-citrulline dipeptide linker is not. ADCs bearing the nonpeptidic linker are as efficacious and stable in vivo as those with the dipeptide linker. Our results strongly support the application of the peptidomimetic linker and present new opportunities for improving the selectivity of ADCs.

Pyrrolobenzodiazepine Dimer Antibody-Drug Conjugates: Synthesis and Evaluation of Noncleavable Drug-Linkers

Three rationally designed pyrrolobenzodiazepine (PBD) drug-linkers have been synthesized via intermediate 19 for use in antibody-drug conjugates (ADCs). They lack a cleavable trigger in the linker and consist of a maleimide for cysteine antibody conjugation, a hydrophilic spacer, and either an alkyne (6), triazole (7), or piperazine (8) link to the PBD. In vitro IC₅₀ values were 11-48 ng/mL in HER2 3+ SK-BR-3 and KPL-4 (7 inactive) for the anti-HER2 ADCs (HER2 0 MCF7, all inactive) and 0.10-1.73 μg/mL (7 inactive) in CD22 3+ BJAB and WSU-DLCL2 for anti-CD22 ADCs (CD22 0 Jurkat, all inactive at low doses). In vivo antitumor efficacy for the anti-HER2 ADCs in Founder 5 was observed with tumor stasis at 0.5-1 mg/kg, 1 mg/kg, and 3-6 mg/kg for 6, 8, and 7, respectively. Tumor stasis at 2 mg/kg was observed for anti-CD22 6 in WSU-DLCL2. In summary, noncleavable PBD-ADCs exhibit potent activity, particularly in HER2 models.

Stabilizing a Tubulysin Antibody-Drug Conjugate To Enable Activity Against Multidrug-Resistant Tumors

The tubulysins are promising anticancer cytotoxic agents due to the clinical validation of their mechanism of action (microtubule inhibition) and their particular activity against multidrug-resistant tumor cells. Yet their high potency and subsequent systemic toxicity make them prime candidates for targeted therapy, particularly in the form of antibody-drug conjugates (ADCs). Here we report a strategy to prepare stable and bioreversible conjugates of tubulysins to antibodies without loss of activity. A peptide trigger along with a quaternary ammonium salt linker connection to the tertiary amine of tubulysin provided ADCs that were potent in vitro. However, we observed metabolism of a critical acetate ester of the drug in vivo, resulting in diminished conjugate activity. We were able to circumvent this metabolic liability with the judicious choice of a propyl ether replacement. This modified tubulysin ADC was stable and effective against multidrug-resistant lymphoma cell lines and tumors.

Attachment Site Cysteine Thiol pKa Is a Key Driver for Site-Dependent Stability of THIOMAB Antibody-Drug Conjugates

The incorporation of cysteines into antibodies by mutagenesis allows for the direct conjugation of small molecules to specific sites on the antibody via disulfide bonds. The stability of the disulfide bond linkage between the small molecule and the antibody is highly dependent on the location of the engineered cysteine in either the heavy chain (HC) or the light chain (LC) of the antibody. Here, we explore the basis for this site-dependent stability. We evaluated the in vivo efficacy and pharmacokinetics of five different cysteine mutants of trastuzumab conjugated to a pyrrolobenzodiazepine (PBD) via disulfide bonds. A significant correlation was observed between disulfide stability and efficacy for the conjugates. We hypothesized that the observed site-dependent stability of the disulfide-linked conjugates could be due to differences in the attachment site cysteine thiol pK_a. We measured the cysteine thiol pK_a using isothermal titration calorimetry (ITC) and found that the variants with the highest thiol pK_a (LC K149C and HC A140C) were found to yield the conjugates with the greatest in vivo stability. Guided by homology modeling, we identified several mutations adjacent to LC K149C that reduced the cysteine thiol pK_a and, thus, decreased the in vivo stability of the disulfide-linked PBD conjugated to LC K149C. We also present results suggesting that the high thiol pK_a of LC K149C is responsible for the sustained circulation stability of LC K149C TDCs utilizing a maleimide-based linker. Taken together, our results provide evidence that the site-dependent stability of cys-engineered antibody-drug conjugates may be explained by interactions between the engineered cysteine and the local protein environment that serves to modulate the side-chain thiol pK_a. The influence of cysteine thiol pK_a on stability and efficacy offers a new parameter for the optimization of ADCs that utilize cysteine engineering.

Decoupling stability and release in disulfide bonds with antibody-small molecule conjugates

Disulfide bonds provide a bioactivatable connection with applications in imaging and therapy. The circulation stability and intracellular release of disulfides are problematically coupled in that increasing stability causes a corresponding decrease in cleavage and payload release. However, an antibody offers the potential for a reversible stabilization. We examined this by attaching a small molecule directly to engineered cysteines in an antibody. At certain sites this unhindered disulfide was stable in circulation yet cellular internalization and antibody catabolism generated a disulfide catabolite that was rapidly reduced. We demonstrated that this stable connection and facile release is applicable to a variety of payloads. The ability to reversibly stabilize a labile functional group with an antibody may offer a way to improve targeted probes and therapeutics.

Linker Immolation Determines Cell Killing Activity of Disulfide-Linked Pyrrolobenzodiazepine Antibody-Drug Conjugates

Disulfide bonds could be valuable linkers for a variety of therapeutic applications requiring tunable cleavage between two parts of a molecule (e.g., antibody-drug conjugates). The in vitro linker immolation of β-mercaptoethyl-carbamate disulfides and DNA alkylation properties of associated payloads were investigated to understand the determinant of cell killing potency of anti-CD22 linked pyrrolobenzodiazepine (PBD-dimer) conjugates. Efficient immolation and release of a PBD-dimer with strong DNA alkylation properties were observed following disulfide cleavage of methyl- and cyclobutyl-substituted disulfide linkers. However, the analogous cyclopropyl-containing linker did not immolate, and the associated thiol-containing product was a poor DNA alkylator. As predicted from these in vitro assessments, the related anti-CD22 ADCs showed different target-dependent cell killing activities in WSU-DLCL2 and BJAB cell lines. These results demonstrate how the in vitro immolation models can be used to help design efficacious ADCs.

Mechanism-Based Pharmacokinetic/Pharmacodynamic Model for THIOMAB™ Drug Conjugates

PURPOSE

THIOMAB™ drug conjugates (TDCs) with engineered cysteine residues allow site-specific drug conjugation and defined Drug-to-Antibody Ratios (DAR). In order to help elucidate the impact of drug-loading, conjugation site, and subsequent deconjugation on pharmacokinetics and efficacy, we have developed an integrated mathematical model to mechanistically characterize pharmacokinetic behavior and preclinical efficacy of MMAE conjugated TDCs with different DARs. General applicability of the model structure was evaluated with two different TDCs.

METHOD

Pharmacokinetics studies were conducted for unconjugated antibody and purified TDCs with DAR-1, 2 and 4 for trastuzumab TDC and Anti-STEAP1 TDC in mice. Total antibody concentrations and individual DAR fractions were measured. Efficacy studies were performed in tumor-bearing mice.

RESULTS

An integrated model consisting of distinct DAR species (DAR0-4), each described by a two-compartment model was able to capture the experimental data well. Time series measurements of each Individual DAR species allowed for the incorporation of site-specific drug loss through deconjugation and the results suggest a higher deconjugation rate from heavy chain site HC-A114C than the light chain site LC-V205C. Total antibody concentrations showed multi-exponential decline, with a higher clearance associated with higher DAR species. The experimentally observed effects of TDC on tumor growth kinetics were successfully described by linking pharmacokinetic profiles to DAR-dependent killing of tumor cells.

CONCLUSION

Results from the integrated model evaluated with two different TDCs highlight the impact of DAR and site of conjugation on pharmacokinetics and efficacy. The model can be used to guide future drug optimization and in-vivo studies.

Abstract 4494: A clinical candidate anti-mesothelin-MMAE antibody-drug conjugate (ADC) for therapy of mesothelin-expressing cancers

Mesothelin (MSLN) is a cell surface glycoprotein widely expressed in a variety of cancers, with prevalence levels by IHC of 85% in ovarian, 75% in pancreatic and 45% in mesothelioma, and normal expression limited to the mesothelia, suggesting it could be an ideal target for antibody-drug conjugate therapy of these cancers. We have generated a high affinity (subnanomolar), humanized antibody to MSLN and conjugated it to auristatin anti-mitotic drugs (monomethylauristatin E and F, Seattle Genetics) via an uncleavable linker (anti-MSLN-mc-MMAF) or a cathepsin-cleavable valine-citrulline linker (anti-MSLN-mc-vc-PAB-MMAE/F) for comparison. The in vivo efficacy obtained in an ovarian transplant model was superior with the anti-MSLN-MMAE ADC. Anti-MSLN-MMAE was specifically internalized by MSLN-expressing cells in vitro, resulting in cell death compared to control ADCs. Pancreatic, ovarian and mesothelioma tumor cell lines endogenously expressing physiological levels of MSLN were identified and established as xenografts in mice. A single dose of anti-MSLN ADC was sufficient to inhibit or shrink tumor growth in models of each of the three indications in vivo, as well as inducing complete regressions in primary human pancreatic models, even those expressing low levels of MSLN typical of most human pancreatic tumors. Additionally, anti-MSLN-MMAE (at suboptimal doses) appeared to synergize with gemcitabine at clinically relevant doses in an HPAC xenograft model. Furthermore, anti-MSLN-MMAE was well tolerated in non-clinical toxicity studies (see accompanying abstract by Gupta et al.). Our data suggest that anti-MSLN-vc-MMAE is a promising clinical candidate for the treatment of several types of mesothelin-positive cancers.

Citation Format: Suzie J. Scales, Nidhi Gupta, Glenn Pacheco, Ron Firestein, Dorothy M. French, Josefa Chuh, Yin Zhang, Leanne Berry, Jenny Bostrom, Elizabeth Luis, Aimee Fourie O'Donohue, Katherine R. Kozak, Sarajane Ross, Mark S. Dennis, Jay Tibbitts, Susan D. Spencer. A clinical candidate anti-mesothelin-MMAE antibody-drug conjugate (ADC) for therapy of mesothelin-expressing cancers. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4494. doi:10.1158/1538-7445.AM2014-4494

Abstract 4502: Nonclinical characterization and tolerability of a surrogate anti-mesothelin-MMAE antibody-drug conjugate

Mesothelin (MSLN) is a cell surface glycoprotein widely expressed in several cancers with normal expression limited to the serosal mesothelia, features of an ideal target for antibody-based therapy. SS1P, a (dsFv)-PE38 immunotoxin to MSLN that kills cells by inhibition of protein synthesis, exhibits minor clinical responses as monotherapy, but was dose-limited by pleuritis, likely an antigen-dependent toxicity (Hassan et al., (2007) Clin Cancer Res 13 p3144). As mesothelial cells divide infrequently, we evaluated whether an anti-mitotic antibody-drug conjugate (ADC) directed to MSLN would be better tolerated. Our humanized lead anti-MSLN-MMAE (mc-vc-PAB-monomethylauristatin E) conjugate shows excellent preclinical activity (see accompanying abstract by Scales et al), but is specific to human MSLN, so a surrogate ADC that cross-reacts with cynomolgus monkey and rat MSLN was generated for non-clinical toxicity studies.

While both the lead and the surrogate antibodies recognize human MSLN, they bound to different epitopes and the surrogate binding was sensitive to glycosylation, only recognizing a subset of cell lines expressing human MSLN with high affinity. The affinity of the surrogate antibody for cynomolgus monkey MSLN is 5 to 22-fold lower than that of the lead antibody for human MSLN, depending on its glycosylation pattern in the human parental cell line to which it was compared. Nonetheless, the surrogate antibody detects endogenous MSLN in monkey pleura and the surrogate ADC exhibits robust cytotoxic activity against monkey MSLN-expressing cells in vitro. Importantly, the surrogate ADC demonstrated comparable in vivo efficacy to the lead ADC against BJAB xenografts expressing monkey or human MSLN respectively, thus validating its use in safety studies. We thus conducted a repeat-dose monkey toxicity study with a clinically relevant (q3w x5) dosing schedule, which yielded similar results for both surrogate and lead ADCs (the primary finding being reversible myelotoxicity, an antigen-independent toxicity similar to those of other IgG1-MMAE ADCs (Li et al., (2013), Mol Can Thera 12 p1255)). Unlike SS1P, there was no evidence of target-dependent pleuritis, nor any other serositis. Our data suggest that anti-MSLN-MMAE ADCs may be safer than SS1P and helped define the Phase I starting dose.

Citation Format: Nidhi Gupta, Willy A. Solis, Reina N. Fuji, Amy Oldendorp, Glenn Pacheco, Elizabeth Luis, Josefa Chuh, Dorothy M. French, Elizabeth Drake, Mark S. Dennis, Katherine R. Kozak, Sarajane Ross, Jay Tibbitts, Susan D. Spencer, Suzie J. Scales. Nonclinical characterization and tolerability of a surrogate anti-mesothelin-MMAE antibody-drug conjugate. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4502. doi:10.1158/1538-7445.AM2014-4502

An antimesothelin-monomethyl auristatin e conjugate with potent antitumor activity in ovarian, pancreatic, and mesothelioma models

Mesothelin (MSLN) is an attractive target for antibody-drug conjugate therapy because it is highly expressed in various epithelial cancers, with normal expression limited to nondividing mesothelia. We generated novel antimesothelin antibodies and conjugated an internalizing one (7D9) to the microtubule-disrupting drugs monomethyl auristatin E (MMAE) and MMAF, finding the most effective to be MMAE with a lysosomal protease-cleavable valine-citrulline linker. The humanized (h7D9.v3) version, αMSLN-MMAE, specifically targeted mesothelin-expressing cells and inhibited their proliferation with an IC50 of 0.3 nmol/L. Because the antitumor activity of an antimesothelin immunotoxin (SS1P) in transfected mesothelin models did not translate to the clinic, we carefully selected in vivo efficacy models endogenously expressing clinically relevant levels of mesothelin, after scoring mesothelin levels in ovarian, pancreatic, and mesothelioma tumors by immunohistochemistry. We found that endogenous mesothelin in cancer cells is upregulated in vivo and identified two suitable xenograft models for each of these three indications. A single dose of αMSLN-MMAE profoundly inhibited or regressed tumor growth in a dose-dependent manner in all six models, including two patient-derived tumor xenografts. The robust and durable efficacy of αMSLN-MMAE in preclinical models of ovarian, mesothelioma, and pancreatic cancers justifies the ongoing phase I clinical trial.

Site-specific trastuzumab maytansinoid antibody-drug conjugates with improved therapeutic activity through linker and antibody engineering

Antibody-drug conjugates (ADCs) have a significant impact toward the treatment of cancer, as evidenced by the clinical activity of the recently approved ADCs, brentuximab vedotin for Hodgkin lymphoma and ado-trastuzumab emtansine (trastuzumab-MCC-DM1) for metastatic HER2+ breast cancer. DM1 is an analog of the natural product maytansine, a microtubule inhibitor that by itself has limited clinical activity and high systemic toxicity. However, by conjugation of DM1 to trastuzumab, the safety was improved and clinical activity was demonstrated. Here, we report that through chemical modification of the linker-drug and antibody engineering, the therapeutic activity of trastuzumab maytansinoid ADCs can be further improved. These improvements include eliminating DM1 release in the plasma and increasing the drug load by engineering four cysteine residues into the antibody. The chemical synthesis of highly stable linker-drugs and the modification of cysteine residues of engineered site-specific antibodies resulted in a homogeneous ADC with increased therapeutic activity compared to the clinically approved ADC, trastuzumab-MCC-DM1.

An integrated approach to identify normal tissue expression of targets for antibody-drug conjugates: case study of TENB2

BACKGROUND AND PURPOSE

The success of antibody-drug conjugates (ADCs) depends on the therapeutic window rendered by the differential expression between normal and pathological tissues. The ability to identify and visualize target expression in normal tissues could reveal causes for target-mediated clearance observed in pharmacokinetic characterization. TENB2 is a prostate cancer target associated with the progression of poorly differentiated and androgen-independent tumour types, and ADCs specific for TENB2 are candidate therapeutics. The objective of this study was to locate antigen expression of TENB2 in normal tissues, thereby elucidating the underlying causes of target-mediated clearance.

EXPERIMENTAL APPROACH

A series of pharmacokinetics, tissue distribution and mass balance studies were conducted in mice using a radiolabelled anti-TENB2 ADC. These data were complemented by non-invasive single photon emission computed tomography - X-ray computed tomography imaging and immunohistochemistry.

KEY RESULTS

The intestines were identified as a saturable and specific antigen sink that contributes, at least in part, to the rapid target-mediated clearance of the anti-TENB2 antibody and its drug conjugate in rodents. As a proof of concept, we also demonstrated the selective disposition of the ADC in a tumoural environment in vivo using the LuCaP 77 transplant mouse model. High tumour uptake was observed despite the presence of the antigen sink, and antigen specificity was confirmed by antigen blockade.

CONCLUSIONS AND IMPLICATIONS

Our findings provide the anatomical location and biological interpretation of target-mediated clearance of anti-TENB2 antibodies and corresponding drug conjugates. Further investigations may be beneficial in addressing the relative contributions to ADC disposition from antigen expression in both normal and pathological tissues.

DCDT2980S, an anti-CD22-monomethyl auristatin E antibody-drug conjugate, is a potential treatment for non-Hodgkin lymphoma

Antibody-drug conjugates (ADC), potent cytotoxic drugs linked to antibodies via chemical linkers, allow specific targeting of drugs to neoplastic cells. We have used this technology to develop the ADC DCDT2980S that targets CD22, an antigen with expression limited to B cells and the vast majority of non-Hodgkin lymphomas (NHL). DCDT2980S consists of a humanized anti-CD22 monoclonal IgG1 antibody with a potent microtubule-disrupting agent, monomethyl auristatin E (MMAE), linked to the reduced cysteines of the antibody via a protease cleavable linker, maleimidocaproyl-valine-citrulline-p-aminobenzoyloxycarbonyl (MC-vc-PAB). We describe the efficacy, safety, and pharmacokinetics of DCDT2980S in animal models to assess its potential as a therapeutic for the treatment of B-cell malignancies. We did not find a strong correlation between in vitro or in vivo efficacy and CD22 surface expression, nor a correlation of sensitivity to free drug and in vitro potency. We show that DCDT2980S was capable of inducing complete tumor regression in xenograft mouse models of NHL and can be more effective than rituximab plus combination chemotherapy at drug exposures that were well tolerated in cynomolgus monkeys. These results suggest that DCDT2980S has an efficacy, safety, and pharmacokinetics profile that support potential treatment of NHL.

Total antibody quantification for MMAE-conjugated antibody-drug conjugates: impact of assay format and reagents

Antibody-drug conjugates (ADCs) are target-specific anticancer agents consisting of cytotoxic drugs covalently linked to a monoclonal antibody. The number of ADCs in the clinic is growing, and therefore thorough characterization of the quantitative assays used to measure ADC concentrations in support of pharmacokinetic, efficacy, and safety studies is of increasing importance. Cytotoxic drugs such as the tubulin polymerization inhibiting auristatin, monomethyl auristatin E, have been conjugated to antibodies via cleavable linkers (MC-vc-PAB) through internal cysteines. This results in a heterogeneous mixture of antibody species with drug-to-antibody ratios (DAR) ranging from 0 to 8. In order to characterize the assays used to quantitate total MC-vc-PAB-MMAE ADCs (conjugated and unconjugated antibody), we used purified fractions with defined DARs from 6 therapeutic antibodies to evaluate different assay formats and reagents. Our investigations revealed that for quantitation of total antibody, including all unconjugated and conjugated antibody species, sandwich ELISA formats did not always allow for recovery of all purified DAR fractions (DAR 0-8) to within ±20% of the expected values at the reagent concentrations tested. In evaluating alternative approaches, we found that the recovery of DAR fractions with semihomogeneous assay (SHA) formats, in which sample, capture, and detection reagents are preincubated in solution, were less affected by the antibody's MMAE drug load as compared to traditional stepwise sandwich ELISAs. Thus, choosing the optimal assay format and reagents for total antibody assays is valuable for developing accurate quantitative assays.

Micro-volume wall-less immunoassays using patterned planar plates

Miniaturization of immunoassays has numerous potential advantages over traditional ELISAs. Here we present a novel approach using patterned planar plates (PPPs). These 'wall-less' plates consist of a 16 × 24 array of 2 mm diameter hydrophilic regions surrounded by a hydrophobic polytetrafluoroethylene (PTFE) coating. Assays are performed by adding 2 μL droplets to the hydrophilic areas. These droplets are overlaid with an immiscible mixture of perfluorocarbon liquid (PFCL) that essentially eliminates evaporation. During wash steps, a thin film of PFCL covers the hydrophobic coating and prevents its wetting by wash buffer; as a result, the hydrophilic wells remain intact and inter-well cross-contamination is prevented. We compared the performance of three immunoassays using PPPs versus traditional 384-well ELISA plates. These included assays for soluble FcRH5 in human serum, SDF-1 in mouse serum, and human IgG in mouse plasma. The results show that the PPP assays were closely comparable to the ELISAs in terms of sensitivity, linearity of dilution, and sample quantitation. Moreover, the PPP assays were rapid to perform, easily adapted from ELISA protocols, and used 10- to 50-fold less sample and reagent volume as compared to 384- or 96-well plate ELISAs. As an additional advantage, PPPs conform to established microplate dimensional standards making them compatible with pre-existing equipment and workflows. PPPs therefore represent an attractive and broadly applicable approach to flexible miniaturization of plate-based immunochemical assays.

Differential effects of predosing on tumor and tissue uptake of an 111In-labeled anti-TENB2 antibody-drug conjugate

TENB2, also known as tomoregulin or transmembrane protein with epidermal growth factor-like and 2 follistatin-like domains, is a transmembrane proteoglycan overexpressed in human prostate tumors. This protein is a promising target for antimitotic monomethyl auristatin E (MMAE)-based antibody-drug conjugate (ADC) therapy. Nonlinear pharmacokinetics in normal mice suggested that antigen expression in normal tissues may contribute to targeted mediated disposition. We evaluated a predosing strategy with unconjugated antibody to block ADC uptake in target-expressing tissues in a mouse model while striving to preserve tumor uptake and efficacy.

METHODS

Unconjugated, unlabeled antibody was preadministered to mice bearing the TENB2-expressing human prostate explant model, LuCaP 77, followed by a single administration of (111)In-labeled anti-TENB2-MMAE for biodistribution and SPECT/CT studies. A tumor-growth-inhibition study was conducted to determine the pharmacodynamic consequences of predosing.

RESULTS

Preadministration of anti-TENB2 at 1 mg/kg significantly increased blood exposure of the radiolabeled ADC and reduced intestinal, hepatic, and splenic uptake while not affecting tumor accretion. Similar tumor-to-heart ratios were measured by SPECT/CT at 24 h with and without the predose. Consistent with this, the preadministration of 0.75 mg/kg did not interfere with efficacy in a tumor-growth study dosed at 0.75 mg or 2.5 mg of ADC per kilogram.

CONCLUSION

Overall, the potential to mask peripheral, nontumor antigen uptake while preserving tumor uptake and efficacy could ameliorate toxicity and may significantly affect future dosing strategies for ADCs.

Effects of anti-VEGF on pharmacokinetics, biodistribution, and tumor penetration of trastuzumab in a preclinical breast cancer model

Both human epidermal growth factor receptor 2 (HER-2/neu) and VEGF overexpression correlate with aggressive phenotypes and decreased survival among breast cancer patients. Concordantly, the combination of trastuzumab (anti-HER2) with bevacizumab (anti-VEGF) has shown promising results in preclinical xenograft studies and in clinical trials. However, despite the known antiangiogenic mechanism of anti-VEGF antibodies, relatively little is known about their effects on the pharmacokinetics and tissue distribution of other antibodies. This study aimed to measure the disposition properties, with a particular emphasis on tumor uptake, of trastuzumab in the presence or absence of anti-VEGF. Radiolabeled trastuzumab was administered alone or in combination with an anti-VEGF antibody to mice bearing HER2-expressing KPL-4 breast cancer xenografts. Biodistribution, autoradiography, and single-photon emission computed tomography-X-ray computed tomography imaging all showed that anti-VEGF administration reduced accumulation of trastuzumab in tumors despite comparable blood exposures and similar distributions in most other tissues. A similar trend was also observed for an isotype-matched IgG with no affinity for HER2, showing reduced vascular permeability to macromolecules. Reduced tumor blood flow (P < 0.05) was observed following anti-VEGF treatment, with no significant differences in the other physiologic parameters measured despite immunohistochemical evidence of reduced vascular density. In conclusion, anti-VEGF preadministration decreased tumor uptake of trastuzumab, and this phenomenon was mechanistically attributed to reduced vascular permeability and blood perfusion. These findings may ultimately help inform dosing strategies to achieve improved clinical outcomes.

Impact of drug conjugation on pharmacokinetics and tissue distribution of anti-STEAP1 antibody-drug conjugates in rats

Antibody-drug conjugates (ADCs) are designed to combine the exquisite specificity of antibodies to target tumor antigens with the cytotoxic potency of chemotherapeutic drugs. In addition to the general chemical stability of the linker, a thorough understanding of the relationship between ADC composition and biological disposition is necessary to ensure that the therapeutic window is not compromised by altered pharmacokinetics (PK), tissue distribution, and/or potential organ toxicity. The six-transmembrane epithelial antigen of prostate 1 (STEAP1) is being pursued as a tumor antigen target. To assess the role of ADC composition in PK, we evaluated plasma and tissue PK profiles in rats, following a single dose, of a humanized anti-STEAP1 IgG1 antibody, a thio-anti-STEAP1 (ThioMab) variant, and two corresponding thioether-linked monomethylauristatin E (MMAE) drug conjugates modified through interchain disulfide cysteine residues (ADC) and engineered cysteines (TDC), respectively. Plasma PK of total antibody measured by enzyme-linked immunosorbent assay (ELISA) revealed ∼45% faster clearance for the ADC relative to the parent antibody, but no apparent difference in clearance between the TDC and unconjugated parent ThioMab. Total antibody clearances of the two unconjugated antibodies were similar, suggesting minimal effects on PK from cysteine mutation. An ELISA specific for MMAE-conjugated antibody indicated that the ADC cleared more rapidly than the TDC, but total antibody ELISA showed comparable clearance for the two drug conjugates. Furthermore, consistent with relative drug load, the ADC had a greater magnitude of drug deconjugation than the TDC in terms of free plasma MMAE levels. Antibody conjugation had a noticeable, albeit minor, impact on tissue distribution with a general trend toward increased hepatic uptake and reduced levels in other highly vascularized organs. Liver uptakes of ADC and TDC at 5 days postinjection were 2-fold and 1.3-fold higher, respectively, relative to the unmodified antibodies. Taken together, these results indicate that the degree of overall structural modification in anti-STEAP1-MMAE conjugates has a corresponding level of impact on both PK and tissue distribution.

Characterization of the rat urokinase plasminogen activator receptor promoter in PC12 cells

Rat PC12 pheochromocytoma cells treated with nerve growth factor (NGF) extend "neurites" and initiate a neuronal differentiation pathway. Although neurotrophins, growth factors [e.g., epidermal growth factor (EGF)], and other ligands induce many common primary response genes (PRGs) in PC12 cells, a unique PRG subset is induced preferentially by NGF. Expression of one NGF preferentially induced gene, urokinase plasminogen activator receptor (UPAR), is required for NGF-induced neurite extension and neuronal differentiation. A 2.1-kb fragment of the rat UPAR 5' regulatory region confers differential expression by NGF versus EGF, following transfection of a luciferase reporter construct into PC12 cells. Deletion studies identified a region between -100 and -50 nucleotides from the transcription start site as the region conferring preferential NGF induction. Sequence comparisons among rat, human, and murine UPAR promoters identified two common potential regulatory regions. Site-directed mutation identified an activator protein-1 (AP-1) region between -66 and -72 bp, required for luciferase reporter activation by NGF. Electrophoretic mobility shift and antibody supershift assays demonstrated that specific Fos and Jun family members preferentially bind to this site following NGF treatment. We conclude that preferential activation of transcription factor binding at this AP-1 site mediates preferential NGF activation of the UPAR gene.

Characterization of serum biomarkers for detection of early stage ovarian cancer

We have previously reported the identification of three ovarian cancer biomarker panels comprised of SELDI-TOF-MS peaks representing 14 differentially expressed serum proteins for the diagnosis of ovarian cancer. Using micro-LC-MS/MS, we identified five m/z peaks as transthyretin (TTR 13.9 kDa, TTR fragment 12.9 kDa), beta-hemoglobin (Hb, 15.9 kDa), apolipoprotein AI (ApoAI, 28 kDa) and transferrin (TF, 79 kDa). Western and/or ELISA methods confirmed the differential expression of TTR, Hb, and TF, and multivariate analyses resulted in improving the detection of early stage ovarian tumors (low malignant potential and malignant; receiver operating characteristic, ROC 0.933) as compared to cancer antigen CA125 alone (ROC 0.833). Interestingly, when CA125 was included with our markers in the multivariate analysis, the ROC increased to 0.959. Furthermore, multivariate analysis with only the mucinous subtype of early stage ovarian tumors, showed our markers to greatly improve the detection of disease (ROC 0.959) as compared to CA125 alone (ROC 0.613). Interestingly, the combination of CA125 with our markers did not seem to further improve the detection of mucinous tumors (ROC 0.955). We conclude that TTR, Hb, ApoAI and TF, when combined with CA125 should significantly improve the detection of early stage ovarian cancer.