Mouse Strains Influence Clearance and Efficacy of Antibody and Antibody-Drug Conjugate Via Fc-FcγR Interaction

To provide a better understanding of the pharmacokinetics-pharmacodynamics relationships of antibody-based drugs, we analyzed several chimeric and humanized monoclonal antibodies or antibody-drug conjugates (ADC) for PK and efficacy among four strains of mice. Notably, antibodies and ADCs displayed a dose-dependent drug disposition profile in the plasma of NSG mice. The increased clearance rate in NSG mice resulted in the reduction of antitumor activity of ADCs. Furthermore, we identified that the abnormal clearance was mediated by Fc-FcγR interaction by comparing antibodies that lack FcγR binding capacity. We also found a high percentage of FcγR-expressing macrophages in the bone marrow, spleen, and liver of NSG mice, which may be responsible for the abnormal distribution of antibodies. Overall, these findings suggest that preclinical evaluation of efficacy and pharmacokinetics of antibodies and ADCs need to consider mouse strain-induced variations.

Characterization of SGN-CD123A, A Potent CD123-Directed Antibody-Drug Conjugate for Acute Myeloid Leukemia

Treatment choices for acute myelogenous leukemia (AML) patients resistant to conventional chemotherapies are limited and novel therapeutic agents are needed. IL3 receptor alpha (IL3Rα, or CD123) is expressed on the majority of AML blasts, and there is evidence that its expression is increased on leukemic relative to normal hematopoietic stem cells, which makes it an attractive target for antibody-based therapy. Here, we report the generation and preclinical characterization of SGN-CD123A, an antibody-drug conjugate using the pyrrolobenzodiazepine dimer (PBD) linker and a humanized CD123 antibody with engineered cysteines for site-specific conjugation. Mechanistically, SGN-CD123A induces activation of DNA damage response pathways, cell-cycle changes, and apoptosis in AML cells. In vitro, SGN-CD123A-mediated potent cytotoxicity of 11/12 CD123⁺ AML cell lines and 20/23 primary samples from AML patients, including those with unfavorable cytogenetic profiles or FLT3 mutations. In vivo, SGN-CD123A treatment led to AML eradication in a disseminated disease model, remission in a subcutaneous xenograft model, and significant growth delay in a multidrug resistance xenograft model. Moreover, SGN-CD123A also resulted in durable complete remission of a patient-derived xenograft AML model. When combined with a FLT3 inhibitor quizartinib, SGN-CD123A enhanced the activity of quizartinib against two FLT3-mutated xenograft models. Overall, these data demonstrate that SGN-CD123A is a potent antileukemic agent, supporting an ongoing trial to evaluate its safety and efficacy in AML patients (NCT02848248). Mol Cancer Ther; 17(2); 554-64. ©2017 AACR.

Tumor-Associated Macrophages Can Contribute to Antitumor Activity through FcγR-Mediated Processing of Antibody-Drug Conjugates

The primary mechanism of antibody-drug conjugates (ADC) is targeted delivery of a cytotoxic payload to tumor cells via cancer-associated membrane receptors. However, the tumor microenvironment likely plays a role in ADC penetration, distribution, and processing and thus impacts the overall antitumor activity. Here, we report on the potential contribution of Fc-FcγR interactions between ADCs and tumor-associated macrophages (TAM) to the preclinical antitumor activities of ADCs. In the CD30⁺ L-428 Hodgkin lymphoma model, anti-CD30-vcMMAE and a non-binding control (hIgG-vcMMAE) demonstrated similar antitumor activity as well as similar payload release in the tumors. IHC analysis revealed L-428 tumors contained highly abundant TAMs, which were confirmed to bind ADCs by IHC and flow cytometry. The infiltration of TAMs was further found to correlate with the antitumor activity of the non-binding hIgG-vcMMAE in five additional xenograft models. hIgG1V1-vcMMAE, bearing a mutation in the Fc region which ablates Fc gamma receptor (FcγR) binding, lost antitumor activity in three TAM-high xenograft models, suggesting Fc-FcγR interactions modulate the TAM-ADC interaction. Our results suggest that TAMs can contribute to ADC processing through FcγR interaction in preclinical tumor models and may represent an important additional mechanism for drug release from ADCs. Correlative studies in clinical trials will further shed light on whether TAMs play a role in patients' response to ADC therapies. Mol Cancer Ther; 16(7); 1347-54. ©2017 AACR.

The fucosylation inhibitor, 2-fluorofucose, inhibits vaso-occlusion, leukocyte-endothelium interactions and NF-ĸB activation in transgenic sickle mice

2-Fluorofucose (2FF) blocks the fucosylation and the tethering of sialyl-Lewis^x tetrasaccharide and structural variants on leukocytes and red blood cells to P- and E-selectins on activated endothelial cell surfaces. Because P- and E-selectin are required for vaso-occlusion in murine sickle cell disease (SCD), we investigated whether 2FF would inhibit vaso-occlusion in SCD mice. Microvascular stasis was measured in subcutaneous venules in NY1DD and HbSS-Townes SCD mice with dorsal skin-fold chambers after infusion of hemoglobin or exposure to hypoxia/reoxygenation. 2FF in drinking water or administered by gavage inhibited stasis in sickle mice in a dose-responsive manner. Significant inhibitory effects on stasis were seen 1 day post-treatment. 2FF treatment of SCD mice also significantly reduced leukocyte rolling and adhesion along the vessel walls of SCD mice and the static adhesion of neutrophils and sickle red blood cells isolated from 2FF-treated SCD mice to resting and activated endothelial cells. Total white blood cell counts increased in response to 2FF. NF-ĸB activation and VCAM-1 and E-selectin expression were inhibited in the livers of SCD mice consistent with an overall decrease in vascular inflammation and ischemia-reperfusion physiology. Pretreatment with 2FF completely eliminated heme-induced lethality in HbSS-Townes mice, consistent with the observed anti-inflammatory and anti-adhesive properties of 2FF in SCD mice. These data suggest that 2FF may be beneficial for preventing or treating vaso-occlusive crises in SCD patients.

SGN-LIV1A: a novel antibody-drug conjugate targeting LIV-1 for the treatment of metastatic breast cancer

In this article, we describe a novel antibody-drug conjugate (ADC; SGN-LIV1A), targeting the zinc transporter LIV-1 (SLC39A6) for the treatment of metastatic breast cancer. LIV-1 was previously known to be expressed by estrogen receptor-positive breast cancers. In this study, we show that LIV-1 expression is maintained after hormonal therapy in primary and metastatic sites and is also upregulated in triple-negative breast cancers. In addition to breast cancer, other indications showing LIV-1 expression include melanoma, prostate, ovarian, and uterine cancer. SGN-LIV1A consists of a humanized antibody conjugated through a proteolytically cleavable linker to monomethyl auristatin E, a potent microtubule-disrupting agent. When bound to surface-expressed LIV-1 on immortalized cell lines, this ADC is internalized and traffics to the lysozome. SGN-LIV1A displays specific in vitro cytotoxic activity against LIV-1-expressing cancer cells. In vitro results are recapitulated in vivo where antitumor activity is demonstrated in tumor models of breast and cervical cancer lineages. These results support the clinical evaluation of SGN-LIV1A as a novel therapeutic agent for patients with LIV-1-expressing cancer.

Abstract 3962: SGN-LIV1A: a development stage antibody drug-conjugate targeting LIV-1 for the treatment of metastatic breast cancer

LIV-1, also known as SLC39A6 or ZIP6, is a member of the zinc transporter family and was first identified as an estrogen-inducible gene in breast cancer derived cell lines. LIV-1, as a downstream target of STAT3, promotes the epithelial to mesenchymal transition that is important in the malignant progression to metastasis. Consistent with its role in cancer, we determined by immunohistochemical (IHC) analysis that LIV-1 is expressed in subtypes of metastatic breast cancers (ER+/HER2-, HER2+ and triple negative). In healthy human tissues, LIV-1 expression is limited to four hormonally-regulated organs. The broad expression of LIV-1 in metastatic breast cancer in combination with the limited expression in vital organs makes LIV-1 an excellent target for an antibody-drug conjugate (ADC). SGN-LIV1A is an ADC consisting of a humanized anti-LIV-1 mAb conjugated to the microtubule-disrupting agent, monomethyl auristatin E, via a protease-cleavable linker. In vitro, SGN-LIV1A shows target specific internalization and cytotoxic activity against a breast cancer cell line. In vivo studies also demonstrate antitumor activity of SGN-LIV1A in preclinical xenograft models with significant delay of tumor growth compared to control groups. These findings support further evaluation and development of SGN-LIVA as a therapeutic for the treatment of metastatic breast cancer.

Citation Format: Django Sussman, Leia M. Smith, Martha E. Anderson, Steve Duniho, Joshua H. Hunter, Heather Kostner, Jamie B. Miyamoto, Albina Nesterova, Lori Westendorf, Heather A. Van Epps, Nancy Whiting, Dennis R. Benjamin. SGN-LIV1A: a development stage antibody drug-conjugate targeting LIV-1 for the treatment of metastatic breast cancer. [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 3962. doi:10.1158/1538-7445.AM2013-3962

Orally active fumagillin analogues: transformations of a reactive warhead in the gastric environment

Semisynthetic analogues of fumagillin, 1, inhibit methionine aminopeptidase-2 (MetAP2) and have entered the clinic for the treatment of cancer. An optimized fumagillin analogue, 3 (PPI-2458), was found to be orally active, despite containing a spiroepoxide function that formed a covalent linkage to the target protein. In aqueous acid, 3 underwent ring-opening addition of water and HCl, leading to four products, 4-7, which were characterized in detail. The chlorohydrin, but not the diol, products inhibited MetAP2 under weakly basic conditions, suggesting reversion to epoxide as a step in the mechanism. In agreement, chlorohydrin 6 was shown to revert rapidly to 3 in rat plasma. In an ex vivo assay, rats treated with purified acid degradants demonstrated inhibition of MetAP2 that correlated with the biochemical activity of the compounds. Taken together, the results indicate that degradation of the parent compound was compensated by the formation of active equivalents leading to a pharmacologically useful level of MetAP2 inhibition.

Abstract B204: Engineered cysteine antibodies: Improved antibody-drug conjugate vehicles

The use of monoclonal antibodies for the delivery of anticancer drugs to tumor cells is an emerging therapeutic modality and has been the subject of a great deal of investigation. In this study we have engineered antibody variants with an additional cysteine residue in the each heavy chain to provide a route towards homogenous two drugs per antibody loading while interfering with Fc gamma receptor binding. We have characterized the relationship between the site of drug conjugation and a number of key parameters including relative protein expression, conjugatability, drug-linker stability, effects on biophysical properties of the resulting antibody-drug conjugate (ADC), and in vitro cytotoxicity. We demonstrate that the site of conjugation affects many of these parameters and that Engineered Cysteine (EC) antibodies can be considered a viable next generation ADC approach.

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 B204.

Abstract 3620: LIV-1 antibody-drug conjugate: A novel therapeutic agent for breast and prostate cancer

LIV-1, also known as SLC39A6 or ZIP6, is a member of the zinc transporter family and was first identified as an estrogen-inducible gene in breast cancer. LIV-1, as a downstream target of STAT3, promotes the epithelial to mesenchymal transition that is important in the malignant progression to metastasis. Consistent with its role in cancer, we determined by immunohistochemical (IHC) analysis that LIV-1 is expressed by estrogen receptor-positive (ER+), hormone-treated tumors (both primary and metastatic sites) and ER-/PR-/Her2- (triple-negative) breast cancers. Hormone refractory metastatic prostate tumor samples express Liv-1, with expression confirmed in both bone and soft tissue metastatic sites by IHC. In healthy human tissues, LIV-1 expression is limited to hormonally-regulated organs (prostate, uterus, and breast). The broad expression of LIV-1 in prostate and breast cancer tumors in combination with the limited expression in vital organs makes LIV-1 an excellent target for an antibody-drug conjugate (ADC). We generated an ADC consisting of a humanized anti-LIV-1 mAb conjugated to the antitubulin agent monomethyl auristatin E (MMAE), via a plasma stable, enzyme-cleavable linker (vc). The humanized LIV-1 mAb bound with high affinity to both human and cynomolgous LIV-1. In vitro, anti-LIV-1-vcMMAE ADCs showed specific cytotoxic activity against a breast cancer cell line. In vivo studies also demonstrated antitumor activity of anti-LIV-1-vcMMAE ADCs in preclinical xenograft models with significant delay of tumor growth compared to control groups. These findings demonstrate that further evaluation and development of anti-LIV-1-vcMMAE is warranted as a promising and potential therapeutic agent for the treatment of prostate and ER+ and triple-negative breast cancers.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3620. doi:10.1158/1538-7445.AM2011-3620

Abstract 2831: Novel antibody-drug conjugates for selective tumor activation

Auristatin based antibody-drug conjugates (ADCs) have demonstrated profound activites, both preclinically and clinically. Upon internalization, the active auristatin is released through proteolytic degradation of the linker, where it induces cell kill through the inhibition of tubulin polymerization. Once released from the antibody, clearance of the auristatin proceeds via the hepatobiliary route. This finding prompted us to explore new auristatin-peptide drug linkers that had the capacity to release the active form of the drug in tumors, but an inactive form in the liver. To this end, we designed a novel in vivo screen in which multiple ADCs were cassette dosed in mice. LC-MS/MS was used to determine which sequences amongst approximately 800 new auristatin-peptide derivatives allowed for differential drug activation. Sequences were identified that allowed for more selective intratumoral release of the active drug.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2831. doi:10.1158/1538-7445.AM2011-2831

Abstract 2590: Preclinical evaluation of ASG-5ME, a novel antibody-drug conjugate for pancreatic cancer

Antibody-drug conjugates (ADCs) have demonstrated promising activity and tolerability profiles in oncology clinical trials, including for Hodgkin lymphoma (brentuzumab vedotin) and breast cancer (trastuzumab-DM1), motivating the development of new ADCs targeting antigens in other prevalent cancers. An immunohistochemical survey of expression of the novel tumor antigen AGS-5 revealed strong staining in 90% of pancreatic cancer specimens tested. Importantly, this staining was largely uniform, with essentially all transformed cells demonstrating membranous staining. This observation along with the observation of equally abundant expression of AGS-5 in prostate and other cancers motivated the development of ASG-5ME, an ADC targeting AGS-5. The ADC is comprised of a fully human IgG2 monoclonal antibody conjugated to the potent tubulin-binding drug monomethylauristatin E, conjugated with an average of 3.7 drug molecules per antibody. Conjugation and analysis of this IgG2 ADC will be discussed. The resulting conjugate demonstrated antigen-dependent internalization and in vitro cytotoxicity at sub-saturating ADC concentrations, as well as potent in vivo antitumor activity in patient-derived xenograft models of pancreatic cancer. ASG-5ME has a long (12 day) T1/2 in mice. Taken together, these results support the clinical evaluation of ASG-5ME for treatment of pancreatic cancer

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2590.

Abstract 4395: SEA technology: A novel strategy for enhancing antibody effector function

The activity of monoclonal antibodies (mAbs) can be enhanced by a number of chemical and genetic strategies. We describe a novel strategy, Sugar Engineered Antibody (SEA) technology, for enhancing antibody-dependent cellular cytotoxicity (ADCC) through modification of the mAb carbohydrate. A series of small molecule fucose analogs were added to mAb-expressing Chinese hamster ovary (CHO) cells, with the resulting mAbs showing a significant reduction in their carbohydrate fucosylation. We demonstrate that these mAbs show markedly increased ADCC activity and improved CD16 binding. The fucose analogs inhibit GDP-mannose dehydratase (GMD), the first enzyme in de novo synthesis of GDP-fucose, and lead to global depletion of intracellular GDP-fucose. We also demonstrate that this strategy yields mAbs with significantly reduced fucosylation in large scale CHO cell culture and is broadly active across a variety of mAbs and expression systems. Since genetic modification of the mAb-producing cell line is not required, SEA technology can be readily applied from the mAb screening to manufacturing stage to generate effector function enhanced therapeutic antibodies.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4395.

Abstract 5334: Mechanism of cysteine-mcMMAF release from the stably linked antibody-drug conjugate SGN-75

The antibody-drug conjugate SGN-75 is composed of the humanized monoclonal antibody (mAb) h1F6 and the drug-linker mcMMAF conjugated through interchain disulfide cysteine residues. SGN-75 has been shown to be highly active against tumor cell lines both in vitro and in vivo. The mcMMAF drug-linker was designed to be protected from protease cleavage, and we have shown that cysteine-mcMMAF is the major released drug in vitro. We demonstrate that the cysteine residue in cysteine-mcMMAF comes from the mAb, implying antibody degradation as the mechanism for generation of cysteine-mcMMAF. Two isotope cysteine labeling approaches were utilized in which either total cysteine in tumor cells or the mAb cysteines of h1F6 were labeled with heavy isotope cysteine. Metabolic incorporation of heavy cysteine into CD70-expressing tumor cells or mAb-producing CHO cells using media depleted of cysteine and supplemented with heavy isotope cysteine gave complete labeling by heavy cysteine. Heavy cysteine-labeled cells were treated with unlabeled SGN-75, and unlabeled cells were treated with heavy-cysteine-labeled SGN-75. The results demonstrate that the mAb backbone of SGN-75 is the origin of the cysteine in cysteine-mcMMAF providing evidence that an active drug component can be released from a stably linked ADC through proteolytic degradation of the mAb inside of target cells.

Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5334.

Abstract 4394: Development of parallel conjugation and assay methodologies to screen for antibodies with optimal properties for use as antibody-drug conjugates

The activity of antibody-drug conjugates (ADCs) on cancer cells can be affected by a multitude of factors, such as binding affinity, rate of internalization, subcellular trafficking, and efficient drug release within the target cell population. Consequently, the properties of an ideal antibody for drug delivery are not necessarily the same as those for a therapeutic naked antibody. Furthermore, the use of indirect assays involving the use of secondary antibodies to screen for optimal ADCs can be misleading, since crosslinking on the cell surface can lead to altered downstream events, and the affinity of the secondary antibody constrains the dynamic range of the assay. When seeking candidate antibodies directed against a novel antigen for ADC therapy, it is therefore most desirable to screen a large panel in the form of ADCs and evaluate their cytotoxic activities, since these results provide a direct measurement of parameters that can affect cytotoxic activity. However, when dealing with microgram quantities of a large number of antibodies as is typical of an antibody discovery campaign, the yields from conventional conjugation methodologies are limiting. We developed a novel approach that addresses this issue and have successfully applied it to the discovery of optimal ADCs out of a large panel of candidate antibodies. The technology is currently being applied to the discovery of ADCs against antigens of interest for targeted drug delivery.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4394.

Intracellular activation of SGN-35, a potent anti-CD30 antibody-drug conjugate

PURPOSE

SGN-35 is an antibody-drug conjugate (ADC) containing the potent antimitotic drug, monomethylauristatin E (MMAE), linked to the anti-CD30 monoclonal antibody, cAC10. As previously shown, SGN-35 treatment regresses and cures established Hodgkin lymphoma and anaplastic large cell lymphoma xenografts. Recently, the ADC has been shown to possess pronounced activity in clinical trials. Here, we investigate the molecular basis for the activities of SGN-35 by determining the extent of targeted intracellular drug release and retention, and bystander activities.

EXPERIMENTAL DESIGN

SGN-35 was prepared with (14)C-labeled MMAE. Intracellular ADC activation on CD30(+) and negative cell lines was determined using a combination of radiometric and liquid chromatograhpy/mass spectrometry-based assays. The bystander activity of SGN-35 was determined using mixed tumor cell cultures consisting of CD30(+) and CD30(-) lines.

RESULTS

SGN-35 treatment of CD30(+) cells leads to efficient intracellular release of chemically unmodified MMAE, with intracellular concentrations of MMAE in the range of 500 nmol/L. This was due to specific ADC binding, uptake, MMAE retention, and receptor recycling or resynthesis. MMAE accounts for the total detectable released drug from CD30(+) cells, and has a half-life of retention of 15 to 20 h. Cytotoxicity studies with mixtures of CD30(+) and CD30(-) cell lines indicated that diffusible released MMAE from CD30(+) cells was able to kill cocultivated CD30(-) cells.

CONCLUSIONS

MMAE is efficiently released from SGN-35 within CD30(+) cancer cells and, due to its membrane permeability, is able to exert cytotoxic activity on bystander cells. This provides mechanistic insight into the pronounced preclinical and clinical antitumor activities observed with SGN-35.

Carbamate analogues of fumagillin as potent, targeted inhibitors of methionine aminopeptidase-2

Inhibition of methionine aminopeptidase-2 (MetAP2) represents a novel approach to antiangiogenic therapy. We describe the synthesis and activity of fumagillin analogues that address the pharmacokinetic and safety liabilities of earlier candidates in this compound class. Two-step elaboration of fumagillol with amines yielded a diverse series of carbamates at C6 of the cyclohexane spiroepoxide. The most potent of these compounds exhibited subnanomolar inhibition of cell proliferation in HUVEC and BAEC assays. Although a range of functionalities were tolerated at this position, alpha-trisubstituted amines possessed markedly decreased inhibitory activity, and this could be rationalized by modeling based on the known fumagillin-MetAP2 crystal structure. The lead compound resulting from these studies, (3R,4S,5S,6R)-5-methoxy-4-((2R,3R)-2-methyl-3-(3-methylbut-2-enyl)oxiran-2-yl)-1-oxaspiro[2.5]octan-6-yl (R)-1-amino-3-methyl-1-oxobutan-2-ylcarbamate, (PPI-2458), demonstrated an improved pharmacokinetic profile relative to the earlier clinical candidate TNP-470, and has advanced into phase I clinical studies in non-Hodgkin's lymphoma and solid cancers.

Abstract B133: SEA technology: A novel strategy for enhancing antibody effector function

The activity of monoclonal antibodies (mAbs) can be enhanced by a number of chemical and genetic strategies. We describe a novel strategy for enhancing antibody-dependent cellular cytotoxicity (ADCC) through modification of the mAb carbohydrate during expression, designated Sugar Engineered Antibody (SEA) technology. A series of small molecule fucose analogs were added to mAb-expressing Chinese hamster ovary (CHO) cells, with the resulting mAbs showing a significant reduction in their carbohydrate fucosylation. We demonstrate that these mAbs show a substantial increase in ADCC activity and an improvement in CD16 binding. We find that the mechanism of action is inhibition of GDP-mannose dehydratase (GMD), the first enzyme in de novo synthesis of GDP-fucose, leading to a depletion of substrate for the fucosyltransferase responsible for mAb carbohydrate fucosylation. We also demonstrate that this strategy yields mAbs with significantly reduced fucosylation in large scale CHO cell culture as well as in additional expression systems such as hybridomas and transient transfectants. Since genetic modification of the mAb-producing cell line is not required, SEA technology can be readily applied from the mAb screening to manufacturing stage to generate effector function enhanced therapeutic antibodies.

Citation Information: Mol Cancer Ther 2009;8(12 Suppl):B133.

The pharmacologic basis for antibody-auristatin conjugate activity

Antibody-drug conjugates (ADCs) made with auristatin antimitotic agents have shown significant preclinical and clinical oncology activity. SGN-75 is composed of the anti-CD70 antibody h1F6 conjugated to monomethylauristatin F through a noncleavable maleimidocaproyl linkage. To understand the pharmacologic basis of the activity of this ADC, its pharmacokinetics and biodistribution were evaluated in a mouse xenograft model with use of a dual-radiolabeled ADC. The concentrations of antibody, total auristatin (conjugated plus unconjugated), and unconjugated auristatin were measured simultaneously in serum, tumor, and 16 normal tissues. Serum pharmacokinetic parameters for antibody and total auristatin were similar with very little unconjugated auristatin observed, demonstrating a high degree of stability. The kinetic values in normal tissues generally tracked with serum: the first time point (1 h) had the highest antibody and total auristatin concentrations with low unconjugated auristatin concentrations, with the exception of organs expected to be involved in hepatobiliary clearance of the ADC, where total and unconjugated auristatin concentrations peaked at 4 h and then rapidly decreased. In tumors, antibody concentrations were maximal at 1 day, with total auristatin increasing until 2 days. Intratumoral unconjugated auristatin was a substantial fraction of the total auristatin and reached concentrations much higher than in normal tissues. The exposure of the tumor to total and unconjugated auristatin was tens to hundreds times higher than normal tissue exposure. The data establish the pharmacologic basis of activity of the ADC through specific tumor targeting, intratumoral auristatin retention, and ADC stability in the systemic circulation.

Prognostic variables in newly diagnosed children and adolescents with acute myeloid leukemia: Children's Cancer Group Study 213

The objective of this study was to identify biologic parameters that were associated with either exceptionally good or poor outcome in childhood acute myeloid leukemia (AML). Among the children with AML who entered Children's Cancer Group trial 213, 498 patients without Down syndrome or acute promyelocytic leukemia (APL) comprise the basis for this report. Univariate comparisons of the proportion of patients attaining complete remission after induction (CR) indicate that, at diagnosis, male gender, low platelet count (< or =20 000/microl), hepatomegaly, myelodysplastic syndrome (MDS), French-American- British (FAB) category M5, high (>15%) bone marrow (BM) blasts on day 14 of the first course of induction, and +8 are associated with lower CR rates, while abnormal 16 is associated with a higher CR rate. Multivariate analysis suggests high platelet count at diagnosis (>20 000/microl), absence of hepatomegaly, < or =15% day 14 BM blast percentage, and abnormal 16 are independent prognostic factors associated with better CR. Univariate analysis demonstrated a significant favorable relationship between platelet count at diagnosis (>20 000/microl), absence of hepatomegaly, low percentage of BM blasts (< or =15%), and abnormal 16 with overall survival. Absence of hepatomegaly, < or =15% day 14 BM blast percentage, and abnormal 16 were determined to be independent prognostic factors associated with better survival.

Detection and selective dissociation of intact ribosomes in a mass spectrometer

Intact Escherichia coli ribosomes have been projected into the gas phase of a mass spectrometer by means of nanoflow electrospray techniques. Species with mass/charge ratios in excess of 20,000 were detected at the level of individual ions by using time-of-flight analysis. Once in the gas phase the stability of intact ribosomes was investigated and found to increase as a result of cross-linking ribosomal proteins to the rRNA. By lowering the Mg(2+) concentration in solutions containing ribosomes the particles were found to dissociate into 30S and 50S subunits. The resolution of the charge states in the spectrum of the 30S subunit enabled its mass to be determined as 852,187 +/- 3,918 Da, a value within 0.6% of that calculated from the individual proteins and the 16S RNA. Further dissociation into smaller macromolecular complexes and then individual proteins could be induced by subjecting the particles to increasingly energetic gas phase collisions. The ease with which proteins dissociated from the intact species was found to be related to their known interactions in the ribosome particle. The results show that emerging mass spectrometric techniques can be used to characterize a fully functional biological assembly as well as its isolated components.

Solvent effects on the conformation of the transmembrane peptide gramicidin A: insights from electrospray ionization mass spectrometry

The binding of sodium ions to the transmembrane channel peptide gramicidin A has permitted the use of electrospray ionization mass spectrometry to study its conformation in different solvent environments. The mass spectra of the peptide in the various solvents suggest that different conformations of gramicidin A differ in their ability to bind metal ions. The data are consistent with monomeric behavior of gramicidin A in trifluoroethanol and dimethyl sulfoxide solutions, but reveal the presence of noncovalent intermolecular interactions in ethanol solution through the observation of heterodimers formed between the naturally occurring variants of the peptide. The addition of 50% v/v of water to the ethanolic solution causes changes in the circular dichroism spectrum of the peptide, suggestive of a shift in the equilibrium mixture of conformers present toward monomeric species, a result supported by its mass spectrum. The structure of gramicidin A in trifluoroethanol has also been investigated by hydrogen exchange measurements monitored by mass spectrometry. The observation of significant protection against exchange suggests that the monomeric peptide is highly structured in trifluoroethanol. The results indicate that mass spectrometry has the potential to probe the conformational behavior of neutral hydrophobic peptides in environments that mimic their functional states.

Cholecystectomy is becoming an increasingly common operation in children

PURPOSE

To determine the cause of a marked rise in cholecystectomy at a regional children's hospital.

METHODS

Retrospective review of 185 patients undergoing cholecystectomy since 1984. The years 1984 to 1990 (group I) and 1991 to 1996 (group II) were compared.

RESULTS

Cholecystectomy for gallbladder disease increased from 4.4/year (group I) to 16.3/ year (group II). Abdominal ultrasound examinations increased during this time. The ratio of children diagnosed with gallstones and then undergoing cholecystectomy also increased (P = 0.005). In group 11, 43% of children had no apparent etiology for gallstones, and more children developed complications of gallstones and evidence of choledocholithiasis.

CONCLUSIONS

(1) The increased incidence of cholecystectomy is probably multifactorial. (2) Gallstone identification has increased owing to increased patient visits and more liberal use of ultrasonography in patients with abdominal pain. (3) More patients with cholelithiasis now undergo cholecystectomy perhaps because of a change in physician perception of the disease and an apparent increase in complications from gallstones.

Acute renal failure associated with suspected Amanita smithiana mushroom ingestions: a case series

Mushroom poisoning leading to acute renal failure is extremely rare in North America. Cortinarius species and Amanita smithiana both can cause acute renal failure and inhabit the Pacific northwest. This article describes 4 patients who presented in acute renal failure and who ingested mushrooms described as resembling A. smithiana. Two patients (a 74-year-old Korean couple) described eating mushrooms with an approximately 6 x 0.5-inch stipe with a white cap, 1.25-1.5 inches in diameter. The other 2 patients (a 55-year-old male and a 30-year-old female) also described a white-capped mushroom. All believed they were eating the matsutake (Tricholoma magnivalere) mushroom, which can be mistaken for A. smithiana. Onset of gastrointestinal symptoms ranged from 20 minutes to 12 hours, and presentation in acute renal failure ranged from 4 to 6 days postingestion (initial BUN and creatinine were 72-91 mg/dL and 12-13.9 mg/dL, respectively). One patient had underlying mild renal insufficiency and one had hypertension that was under control, while the others had no risk factors for renal disease. None had any other explanation for the episode of acute renal failure. All underwent acute hemodialysis for at least several weeks, eventually returning to baseline renal function.

Mass spectrometry of ribosomes and ribosomal subunits

Nanoflow electrospray ionization has been used to introduce intact Escherichia coli ribosomes into the ion source of a mass spectrometer. Mass spectra of remarkable quality result from a partial, but selective, dissociation of the particles within the mass spectrometer. Peaks in the spectra have been assigned to individual ribosomal proteins and to noncovalent complexes of up to five component proteins. The pattern of dissociation correlates strongly with predicted features of ribosomal protein-protein and protein-RNA interactions. The spectra allow the dynamics and state of folding of specific proteins to be investigated in the context of the intact ribosome. This study demonstrates a potentially general strategy to probe interactions within complex biological assemblies.

EWS/FLI-1 fusion transcripts in three peripheral primitive neuroectodermal tumors of the kidney

Although primitive neuroectodermal tumor (PNET) is a well-recognized entity, its renal localization as a primary site has not been appreciated. Only nine cases of renal PNET exist in the literature. The paucity of renal PNET could be explained by the lack of objective diagnostic techniques that would facilitate its distinction from other primitive round cell tumors of the kidney, such as the more widely recognized monophasic Wilms' tumor and clear-cell sarcoma of the kidney (CCSK), as well as renal carcinoid, or neuroblastoma invading the kidney from the adjacent adrenal gland. The recently identified specific fusion transcripts detectable by reverse transcription polymerase chain reaction (RT-PCR) have provided us with a valuable tool for the detection of renal PNET. This article reports three renal PNET that expressed EWS/FLI-1 fusion transcripts by RT-PCR, in addition to positive staining for MIC2 protein and neuron-specific enolase (NSE). One also exhibited dense core granules in cell processes by electron microscopy. Employment of such methodology will lead to a more accurate classification of renal tumors.

Humoral hypercalcemia due to an occult renal adenoma

Humoral hypercalcemia refers to the elevated blood calcium levels caused by neoplasms which release a bone resorptive substance into the circulation. Previously reported infants with malignant and benign solid tumors causing humoral hypercalcemia have presented with large abdominal masses. The case we describe, a hypercalcemic infant due to an occult parathyroid hormone-related protein-containing metanephric adenoma of the kidney, shows that radionuclide bone scanning can be a useful test to identify humoral hypercalcemia. Humoral hypercalcemia stemming from a soft tissue neoplasm should be ruled out, even in the absence of clinical signs of a tumor, if bone scans show generalized uptake in the absence of hypervitaminosis D or radiological signs of bone lesions, and serum parathyroid hormone is low.

Cellular composition of the angiofibromas in tuberous sclerosis

The angiofibroma of tuberous sclerosis is associated with a proliferation of dermal spindle cells that have been considered to be fibroblasts on the basis of a variety of techniques, although some cells have a glial appearance. This study of six angiofibromas demonstrated an increase in S100-positive, peanut agglutinin-negative spindle cells in the dermis in addition to increased numbers of epidermal melanocytes. The second major spindle cell population in the dermis proved to be dermal dendrocytes based on their expression of factor XIIIa. The number of these cells decreases in older patients, in whom the lesions were generally less cellular and more fibrotic. The angiofibroma of tuberous sclerosis is a hamartoma involving increased numbers of dermal dendrocytes, neurosustentacular cells, blood vessels, and melanocytes, in addition to collagen.

Morphologic, immunologic, and cytogenetic classification of acute myeloid leukemia and myelodysplastic syndrome in childhood: a report from the Childrens Cancer Group

The purposes of this report are to reaffirm concordance difficulties with the acute myeloid leukemia (AML) French-American-British (FAB) classification, to present the frequency of previously delineated AML syndromes in pediatric patients and to describe additional characteristic AML profiles utilizing composite morphologic, cytogenetic and immunophenotypic data. Profiles of 124 children with acute myeloid leukemia (AML) and 13 children with myelodysplastic syndrome entered on the Childrens Cancer Group (CCG) pilot study CCG-2861 were examined. Concordance between institutions and reviewers for FAB designation was 65%. Discordance was found principally between M1 and M2, M2 and M4, and M4 and M5. In 49% of marrow specimens, leukemic blasts expressed at least one T lineage-related antigen; 24% expressed the B lineage-related antigen CD19. CDw14 correlated with FAB M4 or M5 morphology and was the only surface antigen associated with a specific FAB subtype. Normal karyotypes were found for 15% of the 75 children with satisfactory karyotype preparations. Recurring aberrations, found in 76% of children, included t(15;17)(q22;q11), t(8;21)(q22;q22), inv(16)(p13q22), rearrangements of band 11q23, t(6;9) (p23;q34), trisomy 8 and monosomy 7. Results from this pilot study and from the current CCG randomized trial correlating morphology, immunophenotyping and cytogenetics, will help to classify AML into unique subgroups with differing clinical consequences or therapy requirements.

Solution structure of the GTPase activating domain of alpha s

We have used heteronuclear three-dimensional NMR spectroscopy to determine the solution structure of a 141 residue protein containing the GTPase activating domain from the alpha chain of the heterotrimeric G protein Gs. The domain contains six alpha-helices and is stable and structured in solution despite having been excised from the intact Gs protein. The N-terminal ten and C-terminal 11 residues of the protein are unstructured in solution while the core is well determined by the 2483 distance and torsion restraints derived from the NMR spectra. The final ensemble of 14 structures, generated with a hybrid distance geometry/simulated annealing protocol, have an average to-the-mean backbone root-mean-square deviation of 0.39 A for the core residues 89 to 201. The majority of the structure is remarkably similar to that observed for the cognate domains in crystal structures of the homologous proteins alpha t and alpha i1. However, the orientations of the second helix and the subsequent interhelical loops differ markedly among the three proteins. This structural divergence, along with functional studies of chimeric proteins, suggests that this region of the domain interacts with either the downstream effector adenylyl cyclase or with some other intermediary protein.