Liver-targeted polymeric prodrugs delivered subcutaneously improve tafenoquine therapeutic window for malaria radical cure

Approximately 3.3 billion people live with the threat of Plasmodium vivax malaria. Infection can result in liver-localized hypnozoites, which when reactivated cause relapsing malaria. This work demonstrates that an enzyme-cleavable polymeric prodrug of tafenoquine addresses key requirements for a mass administration, eradication campaign: excellent subcutaneous bioavailability, complete parasite control after a single dose, improved therapeutic window compared to the parent oral drug, and low cost of goods sold (COGS) at less than $1.50 per dose. Liver targeting and subcutaneous dosing resulted in improved liver:plasma exposure profiles, with increased efficacy and reduced glucose 6-phosphate dehydrogenase-dependent hemotoxicity in validated preclinical models. A COGS and manufacturability analysis demonstrated global scalability, affordability, and the ability to redesign this fully synthetic polymeric prodrug specifically to increase global equity and access. Together, this polymer prodrug platform is a candidate for evaluation in human patients and shows potential for P. vivax eradication campaigns.

Abstract 2885: Discovery of a tripeptide-based camptothecin drug-linker for antibody-drug conjugates with potent antitumor activity and a broad therapeutic window

In efforts to bring forward antibody-drug conjugate (ADC) technologies that complement vedotin and enable new clinical-stage ADCs, we have investigated compounds that interact with topoisomerase 1, an enzyme involved in the unwinding of DNA. In connection with this, we developed a highly active and well-tolerated camptothecin drug-linker technology, in which the lead molecule consists of 7-aminomethyl-10,11-methylenedioxycamptothecin (AMDCPT) attached to a protease-cleavable valine-lysine-glycine (VKG) tripeptide linker unit. A hydrophilic and discrete polyethylene glycol unit was included to improve the properties of the drug-linker, enabling high ADC drug-loading, and reducing the propensity for aggregation. A VKG-AMDCPT ADC, with 8 drug-linkers/mAb (DAR8), displayed a pharmacokinetic profile coincident with parental unconjugated antibody, with a high degree of stability against retro-Michael reaction deconjugation. ADCs based on the VKG-AMDCPT were broadly active against cancer cells in vitro, and in mouse xenograft models, giving tumor regressions and complete responses with a single ≤3 mg/kg dose. These included both solid and hematologic tumor models, and models of bystander killing activity and multidrug resistance. A non-binding DAR8 ADC was well-tolerated in rats at 60 mg/kg, q7dx4. The VKG-AMDCPT drug-linker can be prepared from available materials in eight high-yielding steps, and this drug-linker is being employed in the anti-CD30 ADC, SGN-CD30C; an investigational new drug application is planned for 2020.

Citation Format: Ryan Lyski, Lauren Bou, Margo Zaval, Kim Emmerton, Nicole Okeley, Jessica Simmons, Francisco Zapata, David Ortiz, Erica McKinney, David Meyer, Maureen Ryan, Peter Senter, Scott Jeffrey. Discovery of a tripeptide-based camptothecin drug-linker for antibody-drug conjugates with potent antitumor activity and a broad therapeutic window [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 2885.

Abstract 2803: Novel auristatins with high activity on efflux-positive models and demonstrable bystander activity

Auristatins are a class of clinically validated antimitotic agents utilized as payloads in antibody-drug conjugates (ADCs). Auristatins display many of the desirable properties necessary for ADC cytotoxins, such as low nanomolar potency, cell permeability, and activity across multidrug-resistant (MDR+) cell lines. Herein, we report the development of novel auristatins, which have a unique combination of these favorable properties. The hydrophilic monomethyl auristatin F (MMAF) was chosen as the parent structure, and a medicinal chemistry campaign was undertaken to functionalize various sites of the auristatin with hydrophobic moieties in an effort to improve membrane permeability. The structure-activity relationships (SAR) of the new auristatins demonstrated clear trends correlating hydrophobicity, structure, and polarity with permeability and in vitro cytotoxicity. The highest-performing molecules showed a preference for hydrophobic functionalization at the N-terminal dolavaline. The payloads were linked to the C-terminal position of the auristatin with a lysosomally cleavable maleimido-dipeptide linker. Examination of the ADCs revealed low ng/mL activity in CD30+ and CD19+ cell lines in vitro. Anti-CD70 ADCs demonstrated high in vivo efficacy in a 786-O xenograft and complete remissions (CRs) in the efflux-positive renal cell carcinoma model. Anti-CD30 ADCs were dosed in a CD30+ and CD30- admixed Karpas/Karpas-35R xenograft model to demonstrate proof-of-concept in vivo bystander activity. In summary, these novel auristatins showed potential across multiple indications as ADC payloads.

Citation Format: Philip N. Moquist, Tim D. Bovee, Andrew B. Waight, Sarah Owen, Jamie A. Mitchell, Margo Zaval, Marsha Quick, Sharsti Sandall, Kim K. Emmerton, Nicole Blesie, Robert P. Lyon, Peter Senter, Svetlana Doronina. Novel auristatins with high activity on efflux-positive models and demonstrable bystander activity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2803.

Abstract LB-066: Cysteine mutant location affects chemotype lability in site-specific antibody drug conjugates

Antibody Drug Conjugates (ADCs) combine the specificity of antibody therapies with the potency of highly toxic payloads and have become an established therapeutic tool for the treatment of multiple types of cancer. The design process for novel ADCs requires careful attention to the biological target and chemotype selection. Increasingly, the importance of linker attachment and location is also recognized as a critical variable for optimal therapeutic efficacy. For ADCs employing cysteine conjugation, the payload to be delivered has commonly been attached to the antibody backbone via reaction with the native cysteines of the inter-chain disulfides. These cysteines are found in the constant domain of the light chains, the CH1 domain and hinge region of the heavy chains. Alternatively, the chemotype can be conjugated to discrete locations on the antibody backbone by engineering cysteine mutations into the protein sequence, allowing for conjugation in a site-specific manner. For certain chemotypes, site-specific conjugation has demonstrated several distinct advantages over native disulfide conjugation, including homogenous ADC loading, malemide attachment stability and hydrophobic masking of the payload. These effects are particularly applicable to conjugates made at mutation site S239C, which is found on the interior face of the CH2 of the Fc region. Moreover, we have recently discovered that ADCs using the antimitotic tubulysin M show greatly improved chemotype stability when conjugated specifically to the S239C site. In plasma, the tubulysin M molecule is susceptible to the loss of an acetate side chain on the tubuvaline subunit, a change which greatly diminishes tubulin binding and cytotoxicity. Using ex vivo methods and mass spectroscopy we show that, compared to tubulysin M conjugates made to the native interchain disulfide bonds, conjugation to S239C protects the lability of this acetate group and demonstrates improved in vitro cytotoxicity following ADC plasma incubation. With the aim of identifying further protective conjugation locations, we generated and analyzed 20 additional cysteine mutation sites predicted to share similar biophysical properties to S239C. Top performing single mutations were further combined with S239C and evaluated for a combined effect on tubulysin M acetate stability. Surprisingly, several of the new cysteine mutation sites demonstrate a greater effect on tubulysin M stability when used in conjunction with S239C than when used alone. The results on acetate stability following plasma incubation are further reflected by enhanced cytotoxic potency in vitro using pre incubated tubulysin M ADCs. This data demonstrates that appropriate site-specific conjugation can protect against chemotype degradation, and in addition to the advantages of hydrophobic masking and malemide stability, these findings underline the importance of location of chemotype conjugation for optimal ADC design and engineering.

Citation Format: Andrew Waight, Chris Leiske, Travis Biechele, Patrick Burke, Rory Rohm, Peter Senter, Dennis Benjamin, Django Sussman. Cysteine mutant location affects chemotype lability in site-specific antibody drug conjugates [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr LB-066. doi:10.1158/1538-7445.AM2017-LB-066

Abstract 4334: A novel linker to enable alcohol-containing payloads for the preparation of antibody-drug conjugates

Antibody-drug conjugates (ADCs) have emerged as important therapeutics for treating cancer as evidenced by the recent FDA approval of brentuximab vedotin Adcetris™ and trastuzumab emtansineKadcyla™, and the large number of ADCs (>35) currently in clinical trials. ADCs are composed of two core units: the targeting antibody and the drug-linker. The drug-linker typically consists of a cytotoxic payload, a moiety for covalent attachment to the antibody, and a conditionally cleavable linker that is stable in circulation but releases the cytotoxic payload upon internalization into a target cell. The released payload will possess a residual chemical functional group that is used for attachment of the drug to the cleavable linker. Functional groups that have been exploited within the ADC field for this purpose include amines (primary and secondary), thiols, and carboxylic acids. Unfortunately, many potential ADC payloads do not possess any of these functional group ‘handles’ that allow for stable conjugation and release of the drug in an unmodified form. Use of these payloads often requires modification of the drug structure to introduce a handle for conjugation. To avoid this, we have developed new linker chemistry, the methylene-alkoxy-carbamate (MAC), which enables direct conjugation of drugs through alcohol functional groups. Such groups are present on a diverse array of synthetic drugs and cytotoxic natural products, thus, expanding the potential chemical space available for payload selection. As proof-of-concept, we have linked Auristatin E through the secondary alcohol of the norephedrine residue and characterized the stability and in vivo activity of the resulting ADCs. To further define the potential applicability of the MAC unit, we have examined its stability and release properties with a series of model systems including primary, secondary, and tertiary alcohols as well as a phenol. We have also explored the effect of substitution of the MAC nitrogen on these properties. This novel linker chemistry is currently being applied to new payloads that were inaccessible with previous technology.

Citation Format: Robert V. Kolakowski, Karl Haelsig, Scott Jeffrey, Peter Senter. A novel linker to enable alcohol-containing payloads for the preparation of antibody-drug conjugates. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4334.

Antibody-drug conjugates: an emerging modality for the treatment of cancer

Antibody-drug conjugates (ADCs) offer promise as a therapeutic modality that can potentially reduce the toxicities and poor therapeutic indices caused by the lack of specificity of conventional anticancer therapies. ADCs combine the potency of cytotoxic agents with the target selectivity of antibodies by chemically linking a cytotoxic payload to an antibody, potentially creating a synthetic molecule that will deliver targeted antitumor therapy that is both safe and efficacious. The ADC repertoire contains a range of payload molecules, antibodies, and linkers. Two ADC molecules, Kadcyla® and Adcetris®, have been approved by the FDA, and many more are currently in clinical development.

Abstract SY28-02: Tumor targeting with antimitotic monoclonal antibody drug conjugates

Monoclonal antibodies (mAbs) have played a major role in cancer medicine, with active drugs such as trastuzumab, cetuximab, bevacizumab and rituximab in a wide range of therapeutic applications. The mechanism of activity of these agents involves cell signaling, effector functions through interactions with Fcγ receptor positive cells, and complement fixation. The activity of mAbs can be enhanced through the generation of antibody drug conjugates (ADCs) that are capable of delivering cytotoxic agents with some degree of selectivity to tumor cells. Early work in this field involved the use of clinically approved anticancer drugs that generally were low in potency. Consequently, the resulting ADCs had suboptimal activities. Because of this, significant attention was directed towards the identification of appropriate drugs for targeted delivery, the most successful being antimitotic drugs such as monomethyl auristatin E (MMAE), and maytansinoids. These drugs inhibit tubulin polymerization and arrest cell growth in a cell-cycle dependent manner. Successful delivery of these agents requires drug, linker, and conjugation optimization, in addition to judicious selection of an antigen target on tumor cell surfaces. Brentuximab vedotin, a conjugate comprised of the anti-CD30 mAb cAC10 conjugated with MMAE through a highly stable peptide linker, is an example of how addressing these considerations can lead to ADCs with pronounced clinical efficacy. In August 2011, brentuximab vedotin received accelerated approval by the US Food and Drug Administration for use in relapsed or refractory Hodgkin lymphoma and relapsed or refractory systemic anaplastic large cell lymphoma, two diseases with significant unmet medical needs. An overview of how this targeted antimitotic drug was developed and how we are extending the technology will be provided.

Citation Format: Peter Senter. Tumor targeting with antimitotic monoclonal antibody drug conjugates. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr SY28-02. doi:10.1158/1538-7445.AM2013-SY28-02

Abstract 4631: Anti-CD70 antibody-drug conjugates containing pyrrolobenzodiazepine dimers demonstrate robust antitumor activity

Antibody-drug conjugates (ADCs) represent an important approach for the selective delivery of highly potent small molecules to malignant cells. Recently, we have adapted the highly cytotoxic class of minor groove DNA crosslinking agents, pyrrolobenzodiazepine dimers (PBDs), in order to conjugate them to monoclonal antibodies. These totally synthetic molecules alkylate guanine bases in a sequence-specific manner to cause cell death at pM concentrations. In this report, we describe for the first time a novel PBD that can be stably conjugated to the anti-CD70 monoclonal antibody (mAb) h1F6 via maleimide conjugation to engineered cysteine residues created by the single amino acid substitution S239C on each heavy chain. This results in a uniform loading of two drugs per antibody. The resulting ADC binds selectively to CD70 on renal cell carcinoma cell lines and releases the free drug upon internalization and cleavage of the dipeptide linker in the lysosome. The ADC retains the robust cytotoxicity of the free drug, displaying immunologically selective antitumor activity in xenograft models at well tolerated doses as low as 0.1 mg/kg. The PBDs represent a promising new class of cancer drugs for targeted delivery.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4631. doi:1538-7445.AM2012-4631

Abstract 2945: Antitumor activities of 2-fluorofucose, an orally active agent that inhibits cell-surface fucosylation

Fucose is a component of many carbohydrates that are found on the outer membranes of cancer cells. There is evidence that loss of this sugar from cell-surface glycoproteins can change cancer cell behavior, including growth and metastasis. We have previously demonstrated that 2-fluorofucose (SGD-2083) blocks the fucosylation of antibodies in vitro and in vivo due to the depletion of GDP-activated fucose inside cells. These findings provide the basis for evaluating the antitumor activities of SGD-2083, since alterations of the fucose content on cell surfaces could potentially impact tumor growth and adhesion. To explore this, SGD-2083 was given orally to mice with carcinoma and hematologic tumor xenografts. Significant antitumor activities were obtained in prostate, renal cell and colorectal carcinomas, but not in the two hematologic cancer models tested. The doses used to achieve efficacy were well-tolerated. FACS analysis was used to detect alterations in tumor cell surface fucosylation in animals that responded to treatment with SGD-2083. Signal reduction was observed on E-selectin ligand and several other cell surface fucose linkages, while little or no response to the treatment was observed in the fucosylation of cell surface P-selectin ligand. These results show that oral administration of SGD-2083 leads to the alteration of tumor cell surface fucosylation in a well-defined manner, and this may account for the observed activities of this novel antitumor agent.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2945. doi:1538-7445.AM2012-2945

Abstract C52: Enhancing the activities of endogenous antibodies

Many monoclonal antibodies (mAbs) exhibit activity through antibody dependent cellular cytotoxicity (ADCC), due to the binding interactions between the Fc portion of the mAb and Fc RIIIa on natural killer cells, macrophages and neutrophils. The strength of this interaction is affected by the glycosylation pattern at Asn-297 on mAb heavy chains. Defucosylated mAbs and mAbs with bisecting N-acetylglucosamine carbohydrates bind to Fc RIIIa with higher affinities, have more pronounced ADCC activities, and have demonstrated promising in vitro and in vivo activities. We have described a novel method for generating such mAbs involving the addition of simple fucose derivatives to the culture media of antibody-producing cell lines. This leads to the production of defucosylated mAbs with significantly (20–50 fold) increased ADCC activities, while minimally impacting production and cell viability. Generation of sugar engineered antibodies in this manner is distinguished from other technologies in that there is no need for genetic engineering and cell line modification. In addition, the technology has unique in vivo applications for endogenous production of defucosylated antibodies with high affinity binding to mouse Fc receptors. Here, we show for the first time that immunocompetent mice generate defucosylated antibodies when orally administered fucose derivatives such as fluorofucose. There were no apparent toxicities associated with treatment with fluorofucose at doses that led to greater than 90% defucosylation of circulating antibodies, Applications for these novel findings will be discussed.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr C52.

World Antibody Drug Conjugate Summit Europe: February 21-23, 2011; Frankfurt, Germany

The World Antibody Drug Conjugate Summit Europe, organized by Biorbis/ Hanson Wade was held in Frankfurt, Germany on February 21-23, 2011. Antibody drug conjugates (ADCs), also called immunoconjugates, are becoming an increasingly important class of therapeutics as demonstrated by the attendance of nearly 100 delegates at this highly focused meeting. Updates on three ADCs that are in late-stage clinical development, trastuzumab emtansine (T-DM1), brentuximab vedotin (SGN-35) and inotuzumab ozogamicin (CMC-544), were presented by speakers from ImmunoGen, Genentech, Roche, Seattle Genetics and Pfizer. These ADCs have shown encouraging therapeutic effects against solid tumors (T-DM1) and hematological malignancies (SGN-35, CMC-544). The key feature of the new generation of ADCs is the effective combination of the cytotoxicity of natural or synthetic highly potent antineoplastic agents, tumor selective monoclonal antibodies and blood-stable optimized linkers. Early clinical data for ADCs were showcased by Progenics Pharmaceuticals (PSMA ADC), Celldex (CDX-011) and Biotest (BT-062). Takeda, MedImmune and sanofi-aventis outlined their strategies for process development and analytical characterization. In addition, presentations on duocarmycin based-ADCs, alpha emitting immunoconjugates and antibody-conjugated nanoparticles were given by representatives from Syntarga, Algeta and the University of Stuttgart, respectively.

Using creation science to demonstrate evolution: application of a creationist method for visualizing gaps in the fossil record to a phylogenetic study of coelurosaurian dinosaurs

It is important to demonstrate evolutionary principles in such a way that they cannot be countered by creation science. One such way is to use creation science itself to demonstrate evolutionary principles. Some creation scientists use classic multidimensional scaling (CMDS) to quantify and visualize morphological gaps or continuity between taxa, accepting gaps as evidence of independent creation and accepting continuity as evidence of genetic relatedness. Here, I apply CMDS to a phylogenetic analysis of coelurosaurian dinosaurs and show that it reveals morphological continuity between Archaeopteryx, other early birds, and a wide range of nonavian coelurosaurs. Creation scientists who use CMDS must therefore accept that these animals are genetically related. Other uses of CMDS for evolutionary biologists include the identification of taxa with much missing evolutionary history and the tracing of the progressive filling of morphological gaps in the fossil record through successive years of discovery.

Determining maximal tolerable dose of the monoclonal antibody BR96 labeled with 90Y or 177Lu in rats: establishment of a syngeneic tumor model to evaluate means to improve radioimmunotherapy

PURPOSE

To evaluate therapeutic strategies, it is essential to use biological models reflecting important aspects of the clinical situation. The aim of the present study was to compare the maximal tolerable dose of the monoclonal antibody BR96 labeled with 90Y or 177Lu in immunocompetent rats. Maximal tolerable dose was defined as the highest activity that allows 100% of the animals to survive without clinical signs, such as infections, bleeding, or diarrhea, and with <20% loss in body weight.

EXPERIMENTAL DESIGN

Increasing activity levels of BR96 labeled with 90Y or 177Lu were administered to groups of rats. Blood parameters, body weight, and general performance were monitored for 8 weeks.

RESULTS

Two days postinjection, all groups had decreased leukocyte counts down to 5% to 15% of initial values. Initiation of recovery (at 14-21 days) showed a dose-response relationship. All groups, except the group given the highest activity of 90Y, had complete resolution in their leukopenia. The decrease in platelets was delayed to days 7 to 14 postinjection with a dose-dependent response regarding both severity of the nadir (10-40% of initial value) and the start of recovery. Animals in the groups given the highest activities of both 90Y and 177Lu exhibited skin infections on day 21.

CONCLUSIONS

The results showed good reproducibility and dose-dependent toxicity for both radionuclides, indicating that the maximal tolerable dose for 177Lu-BR96 (1,000 MBq/kg) is 1.7 times that for 90Y-BR96 (600 MBq/kg) in rats. This model makes it feasible to evaluate strategies to escalate therapeutic doses to tumors without increasing normal tissue toxicity.

EphB2 as a Therapeutic Antibody Drug Target for the Treatment of Colorectal Cancer

Analysis of human colorectal cancer specimens revealed overexpression of the EphB2 receptor tyrosine kinase. Monoclonal antibodies (MAbs) to extracellular sequence of EphB2 were raised and tested for activity against colorectal cancer cells. One of the MAbs, 2H9, effectively blocked the interaction of ephB2 with ephrin ligands and inhibited the resulting autophosphorylation of the receptor. However, this antibody did not affect the proliferation of cancer cells expressing ephB2. Immunocytochemical analysis revealed rapid internalization of the MAb 2H9 on binding ephB2, suggesting that target-dependent cell killing could be achieved with an antibody-drug conjugate. When MAb 2H9 was conjugated to monomethylauristatin E through a cathepsin B-cleavable linker, it specifically killed ephB2-expressing cancer cells in vitro and in vivo. Our results suggest that ephB2 is an attractive target for immunoconjugate cancer therapy.

Efficient targeting of conserved cryptic epitopes of infectious agents by single domain antibodies. African trypanosomes as paradigm

Antigen variation is a successful defense system adopted by several infectious agents to evade the host immune response. The principle of this defense strategy in the African trypanosome paradigm involves a dense packing of variant surface glycoproteins (VSG) exposing only highly variable and immuno-dominant epitopes to the immune system, whereas conserved epitopes become inaccessible for large molecules. Reducing the size of binders that target the conserved, less-immunogenic, cryptic VSG epitopes forms an obvious solution to combat these parasites. This goal was achieved by introducing dromedary Heavy-chain antibodies. We found that only these unique antibodies recognize epitopes common to multiple VSG classes. After phage display of their antigen-binding repertoire, we isolated a single domain antibody fragment with high specificity for the conserved Asn-linked carbohydrate of VSG. In sharp contrast to labeled concanavalin-A that stains only the flagellar pocket where carbohydrates are accessible because of less dense VSG packing, the single domain binder stains the entire surface of viable parasites, irrespective of the VSG type expressed. This corroborates the idea that small antibody fragments, but not larger lectins or conventional antibody fragments, are able to penetrate the dense VSG coat to target their epitope. The diagnostic potential of this fluorescently labeled binder was proven by the direct, selective, and sensitive detection of parasites in blood smears. The employment of this binder as a molecular recognition unit in immuno-toxins designed for trypanosomosis therapy becomes feasible as well. This was illustrated by the specific trypanolysis induced by an antibody::beta-lactamase fusion activating a prodrug.

E-selectin up-regulation allows for targeted drug delivery in prostate cancer

We have used the Eos Hu03 GeneChip array, which represents over 92% of the transcribed human genome, to measure gene expression in a panel of normal and diseased human tissues. This analysis revealed that E-selectin mRNA is selectively overexpressed in prostate cancer epithelium, a finding that correlated strongly with E-selectin protein expression as assessed by immunohistochemistry. Antibodies against E-selectin that blocked function failed to impede cancer cell growth, suggesting that overexpression of E-selectin was not essential for cell growth. However, a novel auristatin E-based antibody drug conjugate (ADC), E-selectin antibody valine-citrulline monomethyl-auristatin E, was a potent and selective agent against E-selectin-expressing cancer cell lines in vitro, with the degree of cytotoxicity varying with surface antigen density. Interestingly, sensitivity to the ADC differed among cell lines from different tissues expressing similar amounts of E-selectin and was found to correlate with sensitivity to free auristatin E. Furthermore, E-selectin-expressing tumors grown as xenografts in severe combined immunodeficient mice were responsive to treatment with E-selectin antibody valine-citrulline monomethyl-auristatin E in vivo, with more than 85% inhibition of tumor growth observed in treated mice. These findings demonstrate that an E-selectin-targeting ADC has potential as a prostate cancer therapy and validates a genomics-based paradigm for the identification of cancer-specific antigens suitable for targeted therapy.

Targeted delivery in primary and metastatic brain tumors: summary report of the seventh annual meeting of the Blood-Brain Barrier Disruption Consortium

The November 2000 NIH report of the Brain Tumor Progress Review Group identified delivering and targeting therapeutic agents as a priority in the treatment of malignant brain tumors. For this reason, the seventh annual Blood-Brain Barrier Disruption Consortium meeting, partially funded by an NIH R13 Grant, focused on recent advances in targeted delivery to the central nervous system, clinical trials for primary and metastatic brain tumors using enhanced chemotherapy delivery, and strategies to lessen the toxicities associated with dose intensive treatments, using thiols.

The influence of periodate oxidation on monoclonal antibody avidity and immunoreactivity

Eight monoclonal antibodies of different classes and isotypes and rabbit IgG were oxidized under a variety of conditions with 5-50 mM periodate. The number of aldehyde groups generated per immunoglobulin were measured by reduction with tritiated sodium borohydride or coupling of fluoresceinthiosemicarbazide. There were up to 25.5 aldehyde groups detected on the periodate-oxidized antibody 96.5, measured by borohydride reduction whereas the same conditions led to only 9.6 aldehydes per IgG on the antibody L6 of the same IgG2A isotype. Fluoresceinthiosemicarbazide bound to oxidized antibodies but not to the same extent as tritium. On mildly oxidized IgMs it was possible to generate more than 200 aldehyde groups per antibody molecule. Depending on the conditions and the antibody used periodate oxidation could lead to antibody crosslinking. The avidities of the modified antibodies were determined by Scatchard analyses and inhibition assays. A new mathematical method to evaluate the immunoreactivities of modified antibodies relative to the unlabeled native antibody from inhibition binding data was established. Periodate concentrations higher than 50 mM decreased the avidities and immunoreactivities of all IgGs tested. This effect is more pronounced if the oxidation is performed at pH 5.6 and 25 degrees C instead of pH 4.6 and 0 degree C. The BR96 antibody is inactivated even under mild oxidation conditions.

Specific activation of the prodrug mitomycin phosphate by a bispecific anti-CD30/anti-alkaline phosphatase monoclonal antibody

The bispecific monoclonal antibody (Bi-MAb) HRS-3/AP-1 was developed by somatic hybridization of the 2 mouse hybridoma cell lines HRS-3 and AP-1, which produce monoclonal antibodies with reactivity against the Hodgkin's- and Reed-Sternberg cell-associated CD30 antigen and alkaline phosphatase, respectively. After an active incubation with alkaline phosphatase, respectively. After an active incubation with alkaline phosphatase, purified whole immunoglobulin molecules and F(ab')2 fragments of the Bi-MAb were equally effective in converting a relatively noncytotoxic prodrug, mitomycin phosphate (MOP), into mitomycin alcohol, which was 100 times more toxic to the Hodgkin's- and Reed-Sternberg cell line L540 (CD30+) than MOP. The cytotoxic activity of MOP was unaffected when the cells were pretreated with either the Bi-MAb or the enzyme alone. The Bi-MAb HRS-3/AP-1 did not bind to HPB-ALL cells (CD30-) and was not able to activate MOP on these cells. In cocultivation experiments with HPB-ALL and L540 cells, the activation of MOP by the Bi-MAb HRS-3/AP-1 and alkaline phosphatase led to considerable cytotoxicity against the antigen-negative bystander cells. Thus, this immunotherapeutic approach might be effective in tumors in which not all the tumor cells express the respective tumor antigen.