Therapeutic potential of SGN-CD19B, a PBD-based anti-CD19 drug conjugate, for treatment of B-cell malignancies

Patients with relapsed/refractory B-cell malignancies such as non-Hodgkin lymphoma (B-NHL) or acute lymphoblastic leukemia have a poor prognosis. Despite measurable clinical activity with new targeted therapies, many patients do not achieve a complete or durable response suggesting an opportunity to improve upon existing therapies. Here we describe SGN-CD19B, a pyrrolobenzodiazepine (PBD)-based anti-CD19 antibody drug conjugate (ADC) being investigated for treatment of B-cell malignancies, which has improved potency compared with other ADCs. CD19-expressing tumor cells rapidly internalize SGN-CD19B, and the released PBD drug induces DNA damage, resulting in G2/M cell cycle arrest and cell death. SGN-CD19B demonstrated activity against a broad panel of malignant B-cell lines and induced durable regressions in mice bearing xenografts derived from these B-cell malignancies. A single dose of SGN-CD19B induced durable regressions at 300 μg/kg (3 μg/kg drug equivalents); combination with rituximab decreased the curative dose to 100 μg/kg (1 μg/kg drug equivalents). These doses are significantly lower than the level of drug required with other ADC payloads. In cynomolgus monkeys, SGN-CD19B effectively depleted CD20+ B lymphocytes in peripheral blood and lymphoid tissues confirming that SGN-CD19B is pharmacodynamically active at well-tolerated doses. In summary, preclinical studies show SGN-CD19B is a highly active ADC, which releases a DNA cross-linking agent rather than a microtubule inhibitor. The distinct mechanism of action, broad potency, and potential to combine with rituximab suggest that SGN-CD19B may offer unique clinical opportunities in B-cell malignancies. A phase 1 clinical trial is in progress to investigate the therapeutic potential of SGN-CD19B in relapsed/refractory B-NHL. This trial was registered at www.clinicaltrials.gov as #NCT02702141.

The combination of vestibular impairment and congenital sensorineural hearing loss predisposes patients to ocular anomalies, including Usher syndrome

The co-occurrence of hearing impairment and visual dysfunction is devastating. Most deaf-blind etiologies are genetically determined, the commonest being Usher syndrome (USH). While studies of the congenitally deaf population reveal a variable degree of visual problems, there are no effective ophthalmic screening guidelines. We hypothesized that children with congenital sensorineural hearing loss (SNHL) and vestibular impairment were at an increased risk of having USH. A retrospective chart review of 33 cochlear implants recipients for severe to profound SNHL and measured vestibular dysfunction was performed to determine the ocular phenotype. All the cases had undergone ocular examination and electroretinogram (ERG). Patients with an abnormal ERG underwent genetic testing for USH. We found an underlying ocular abnormality in 81.81% (27/33) of cases; of which 75% had refractive errors, and 50% of those patients showed visual improvement with refractive correction. A total of 14 cases (42.42%; 14/33) had generalized rod-cone dysfunction on ERG suggestive of Usher syndrome type 1, confirmed by mutational analysis. This work shows that adding vestibular impairment as a criterion for requesting an eye exam and adding the ERG to detect USH increases the chances of detecting ocular anomalies, when compared with previous literature focusing only on congenital SNHL.

Development of Novel Quaternary Ammonium Linkers for Antibody-Drug Conjugates

A quaternary ammonium-based drug-linker has been developed to expand the scope of antibody-drug conjugate (ADC) payloads to include tertiary amines, a functional group commonly present in biologically active compounds. The linker strategy was exemplified with a β-glucuronidase-cleavable auristatin E construct. The drug-linker was found to efficiently release free auristatin E (AE) in the presence of β-glucuronidase and provide ADCs that were highly stable in plasma. Anti-CD30 conjugates comprised of the glucuronide-AE linker were potent and immunologically specific in vitro and in vivo, displaying pharmacologic properties comparable with a carbamate-linked glucuronide-monomethylauristatin E control. The quaternary ammonium linker was then applied to a tubulysin antimitotic drug that contained an N-terminal tertiary amine that was important for activity. A glucuronide-tubulysin quaternary ammonium linker was synthesized and evaluated as an ADC payload, in which the resulting conjugates were found to be potent and immunologically specific in vitro, and displayed a high level of activity in a Hodgkin lymphoma xenograft. Furthermore, the results were superior to those obtained with a related tubulysin derivative containing a secondary amine N-terminus for conjugation using previously known linker technology. The quaternary ammonium linker represents a significant advance in linker technology, enabling stable conjugation of payloads with tertiary amine residues. Mol Cancer Ther; 15(5); 938-45. ©2016 AACR.

What is the optimal timing for bilateral cochlear implantation in children?

Bilateral cochlear implants (CIs) have been provided to children who are deaf in both ears with intent to promote binaural hearing. If it is possible to establish binaural hearing with two CIs, these children would be able to make use of interaural level and timing differences to localize sound and to distinguish between sounds separated in space. These skills are central to the ability to attend to one particular sound amidst a number of sound sources. This may be particularly important for children because they are typically learning and interacting in groups. However, the development of binaural processing could be disrupted by effects of bilateral deafness, effects of unilateral CI use, or issues related to the child's age at onset of deafness and age at the time of the first and second cochlear implantation. This research aims to determine whether binaural auditory processing is affected by these variables in an effort to determine the optimal timing for bilateral cochlear implantation in children. It is now clear that the duration of bilateral deafness should be limited in children to restrict reorganization in the auditory thalamo-cortical pathways. It has also been shown that unilateral CI use can halt such reorganization to some extent and promote auditory development. At the same time, however, unilateral input might compromise the development of binaural processing if CIs are provided sequentially. Mismatches in responses from the auditory brainstem and cortex evoked by the first and second CI after a long period of unilateral CI use suggest asymmetry in the bilateral auditory pathways which is significantly more pronounced than in children receiving bilateral implants simultaneously. Moreover, behavioural responses to level and timing differences between implants suggest that these important binaural cues are not being processed normally by children who received a second CI after a long period of unilateral CI use and at older ages. In sum, there may be multiple sensitive periods in the developing auditory system, which must be considered when determining the optimal timing for bilateral cochlear implantation.

Abstract 1284: Analysis of circulating CD70+ lymphocytes and CD70 transcript expression in a phase 1 clinical trial of the CD70-targeting antibody-drug conjugate SGN-75

Aberrant expression of CD70 has been reported in various cancers, e.g., non-Hodgkin lymphoma (NHL), renal cell carcinoma (RCC), and pancreatic carcinoma. An auristatin-based anti-CD70 drug conjugate, SGN-75 (h1F6-mcMMAF), has demonstrated antitumor activity in preclinical experiments modeling these malignancies and is currently being evaluated in a phase 1 clinical trial in relapsed/refractory NHL or metastatic RCC. Tumor expression aside, CD70 is expressed on a low and consistently detectable percentage of circulating normal T and B cells. Hence, we explored the utility of monitoring CD70+ lymphocytes in patients treated with SGN-75 as a potential pharmacodynamic marker for SGN-75. A flow cytometry assay utilizing an anti-CD70 monoclonal antibody whose binding to CD70+ cells is minimally affected in the presence of SGN-75 was developed. Applying this method, 8 of 8 patients (4 NHL and 4 RCC) with pre- and post-treatment blood samples demonstrated decreases in the percentage of CD70+ T and B cells post treatment with SGN-75. Conversely, there were no changes in the total lymphocytes or the activated CD25+ T lymphocytes, demonstrating target specificity of SGN-75. To complement the flow cytometry assay, a real-time quantitative PCR (qPCR) assay to measure CD70 mRNA in peripheral blood was developed. Amplification of CD70 mRNA was performed by a single-step reverse transcriptase PCR reaction with 97% amplification efficiency. A correlation between CD70 mRNA and protein expression was then established. CD70 mRNA expression in 13 tumor cell lines with CD70 receptor copy numbers ranging from 2,000 to 189,000 per cell showed significant correlation (ρ=0.8517, p=0.0002) between CD70 mRNA and cell surface protein expression. Similarly, correlation (ρ=0.8125, p=0.0004) was seen between CD70 mRNA expression levels and the percentage of CD70+ lymphocytes in healthy blood donor samples ranging from 1 to 10% CD70+ cells. Analysis of peripheral blood spiked with increasing numbers of the CD70+ 786-O or Caki-1 RCC cells showed corresponding increases in qPCR signals for CD70 mRNA. A reduction of CD70 mRNA was detected in 5 (2 NHL and 3 RCC) of 7 (2 NHL and 5 RCC) patients post SGN-75 treatment. Of the 5 patients showing reduction of CD70 mRNA 3 (2 NHL, 1 RCC) also had available blood samples for flow cytometric analysis; all 3 demonstrated a corresponding decline in the frequency of CD70+ circulating lymphocytes post SGN-75 treatment. Our data suggest that changes in the frequency of circulating CD70+ cells assayed by flow cytometry and CD70 mRNA level assay by qPCR can be potentially used as pharmacodynamic biomarkers for SGN-75 in clinical trials. Ongoing and future studies include correlating these biomarker changes with the pharamcokinetics of SGN-75 and clinical antitumor activity to assist in selecting the optimal dose and schedule for future development.

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 1284. doi:10.1158/1538-7445.AM2011-1284

Use it or lose it? Lessons learned from the developing brains of children who are deaf and use cochlear implants to hear

In the present paper, we review what is currently known about the effects of deafness on the developing human auditory system and ask: Without use, does the immature auditory system lose the ability to normally function and mature? Any change to the structure or function of the auditory pathways resulting from a lack of activity will have important implications for future use through an auditory prosthesis such as a cochlear implant. Data to date show that deafness in children arrests and disrupts normal auditory development. Multiple changes to the auditory pathways occur during the period of deafness with the extent and type of change being dependent upon the age and stage of auditory development at onset of deafness, the cause or type of deafness, and the length of time the immature auditory pathways are left without significant input. Structural changes to the auditory nerve, brainstem, and cortex have been described in animal models of deafness as well in humans who are deaf. Functional changes in deaf auditory pathways have been evaluated by using a cochlear implant to stimulate the auditory nerve with electrical pulses. Studies of electrically evoked activity in the immature deaf auditory system have demonstrated that auditory brainstem development is arrested and that thalamo-cortical areas are vulnerable to being taken over by other competitive inputs (cross-modal plasticity). Indeed, enhanced peripheral sight and detection of visual movement in congenitally deaf cats and adults have been linked to activity in specific areas of what would normally be auditory cortex. Cochlear implants can stimulate developmental plasticity in the auditory brainstem even after many years of deafness in childhood but changes in the auditory cortex are limited, at least in part, by the degree of reorganization which occurred during the period of deafness. Consequently, we must identify hearing loss rapidly (i.e., at birth for congenital deficits) and provide cochlear implants to appropriate candidates as soon as possible. Doing so has facilitated auditory development in the thalamo-cortex and allowed children who are deaf to perceive and use spoken language.

Preclinical characterization of SGN-70, a humanized antibody directed against CD70

PURPOSE

CD70 (CD27L) is a member of the tumor necrosis factor family aberrantly expressed on a number of hematologic malignancies and some carcinomas. CD70 expression on malignant cells coupled with its highly restricted expression on normal cells makes CD70 an attractive target for monoclonal antibody (mAb)-based therapies. We developed a humanized anti-CD70 antibody, SGN-70, and herein describe the antitumor activities of this mAb.

EXPERIMENTAL DESIGN

CD70 expression on primary tumors was evaluated by immunohistochemical staining of Hodgkin lymphoma, non-Hodgkin lymphoma, multiple myeloma, and renal cell carcinoma tissue microarrays. The CD70-binding and cytotoxic activities of SGN-70 were tested in vitro using a number of cell-based assays. The in vivo antitumor properties of SGN-70 were tested in severe combined immunodeficient mice bearing disseminated lymphoma and multiple myeloma xenografts. Mechanism-of-action studies were conducted using SGN-70v, a variant mAb with equivalent target-binding activity but impaired Fcgamma receptor binding compared with SGN-70.

RESULTS

Immunohistochemical analysis identified CD70 expression on approximately 40% of multiple myeloma isolates and confirmed CD70 expression on a high percentage of Hodgkin lymphoma Reed-Sternberg cells, non-Hodgkin lymphoma, and renal cell carcinoma tumors. SGN-70 lysed CD70+ tumor cells via Fc-dependent functions, including antibody-dependent cellular cytotoxicity and phagocytosis and complement fixation. In vivo, SGN-70 treatment significantly decreased tumor burden and prolonged survival of tumor-bearing mice.

CONCLUSIONS

SGN-70 is a novel humanized IgG1 mAb undergoing clinical development for the treatment of CD70+ cancers. SGN-70 possesses Fc-dependent antibody effector functions and mediates antitumor activity in vivo.

Characterizing responses from auditory cortex in young people with several years of cochlear implant experience

OBJECTIVE

To determine if cortical responses evoked by a cochlear implant in children who are deaf differ from normal and to characterize these differences in children who achieve good versus fair speech perception outcomes post-implantation.

METHODS

Late latency-evoked potential responses were recorded at 28 scalp locations in 16 children who were deaf from infancy and experienced cochlear implant users. Speech perception measures indicated that 8 had good scores and 8 had fair scores. In each child, responses were evoked by 36ms electrical pulse trains delivered from a single-implant electrode at the apical and basal ends of the array and by 36ms tone bursts (0.5, 2, and 6kHz). Responses to the tone bursts were also recorded in 14 age-matched children with normal hearing.

RESULTS

We found (1) a dominant positive wave in all implant users and (2) a larger than normal negative amplitude peak in users with fair speech perception scores which had similar scalp topography to N1 but did not show the expected changes in amplitude with stimulus frequency.

CONCLUSIONS

Late latency-evoked potential responses in children using cochlear implants reflect abnormal and/or immature patterns of cortical activity.

SIGNIFICANCE

Limitations in auditory skills with a cochlear implant in children may be due to developmental processes in the cortex which are either slow to mature or which mature abnormally.

Auditory brainstem activity in children with 9–30 months of bilateral cochlear implant use

Bilateral cochlear implants aim to restore binaural processing along the auditory pathways in children with bilateral deafness. We assessed auditory brainstem activity evoked by single biphasic pulses delivered by an apical or basal electrode from the left, right and both cochlear implants in 13 children. Repeated measures were made over the first 9-30 months of bilateral implant use. In children with short or long periods of unilateral implant use prior to the second implantation, Wave eV of the auditory brainstem response was initially prolonged when evoked by the naïve versus experienced side. These differences tended to resolve in children first implanted <3 years of age but not in children implanted at older ages with long delays between implants. Latency differences were projected to persist for longer periods in children with long delays between implants compared with children with short delays. No differences in right versus left evoked eV latency were found in 2 children receiving bilateral implants simultaneously and their response latencies decreased over time. Binaural interaction responses showed effects of stimulating electrode position (responses were more detectable when evoked by an apical than basal pair of implant electrodes), and duration of delay between implants (measured by latency delays). The trends shown here suggest a negative impact of unilateral implant use on bilateral auditory brainstem plasticity.

Macrophages contribute to the antitumor activity of the anti-CD30 antibody SGN-30

Increased expression of CD30 is associated with a variety of hematologic malignancies, including Hodgkin disease (HD) and anaplastic large cell lymphoma (ALCL). The anti-CD30 monoclonal antibody SGN-30 induces direct antitumor activity by promoting growth arrest and DNA fragmentation of CD30(+) tumor cells. In this study, we investigated the contributions of Fc-mediated effector cell functions to SGN-30 activity. We determined that antibody-dependent cellular phagocytosis, mediated by macrophages, to contribute significantly to antitumor activity in vitro. To delineate the identity of the host effector cells involved in mediating antitumor activity in vivo, we studied the effects of effector cell ablation in a disseminated model of HD (L540cy). Depletion of macrophages markedly reduced efficacy of SGN-30, demonstrating that macrophages contribute significantly to SGN-30 efficacy in this model. These findings may have implications for patient stratification or combination treatment strategies in clinical trials conducted with SGN-30 in HD and ALCL.

Auditory brainstem activity and development evoked by apical versus basal cochlear implant electrode stimulation in children

OBJECTIVE

The role of apical versus basal cochlear implant electrode stimulation on central auditory development was examined. We hypothesized that, in children with early onset deafness, auditory development evoked by basal electrode stimulation would differ from that evoked more apically.

METHODS

Responses of the auditory nerve and brainstem, evoked by an apical and a basal implant electrode, were measured over the first year of cochlear implant use in 50 children with early onset severe to profound deafness who used hearing aids prior to implantation.

RESULTS

Responses at initial stimulation were of larger amplitude and shorter latency when evoked by the apical electrode. No significant effects of residual hearing or age were found on initial response amplitudes or latencies. With implant use, responses evoked by both electrodes showed decreases in wave and interwave latencies reflecting decreased neural conduction time through the brainstem. Apical versus basal differences persisted with implant experience with one exception; eIII-eV interlatency differences decreased with implant use.

CONCLUSIONS

Acute stimulation shows prolongation of basally versus apically evoked auditory nerve and brainstem responses in children with severe to profound deafness. Interwave latencies reflecting neural conduction along the caudal and rostral portions of the brainstem decreased over the first year of implant use. Differences in neural conduction times evoked by apical versus basal electrode stimulation persisted in the caudal but not rostral brainstem.

SIGNIFICANCE

Activity-dependent changes of the auditory brainstem occur in response to both apical and basal cochlear implant electrode stimulation.

Engineered anti-CD70 antibody with multiple effector functions exhibits in vitro and in vivo antitumor activities

Antigens expressed on malignant cells in the absence of significant expression on normal tissues are highly desirable targets for therapeutic antibodies. CD70 is a TNF superfamily member whose normal expression is highly restricted but is aberrantly expressed in hematologic malignancies including non-Hodgkin lymphoma (NHL), Hodgkin disease, and multiple myeloma. In addition, solid tumors such as renal cell carcinoma, nasopharyngeal carcinoma, thymic carcinoma, meduloblastoma, and glioblastoma express high levels of this antigen. To functionally target CD70-expressing cancers, a murine anti-CD70 monoclonal antibody was engineered to contain human IgG1 constant domains. The engineered antibody retained the binding specificity of the murine parent monoclonal antibody and was shown to induce Fc-mediated effector functions including antibody-dependent cellular cytotoxicity, complement-dependent cytotoxicity, and antibody-dependent cellular phagocytosis in vitro. Further, administration of this antibody significantly prolonged survival of severe combined immunodeficient (SCID) mice bearing CD70+ disseminated human NHL xenografts. Survival of these mice was dependent upon the activity of resident effector cells including neutrophils, macrophages, and natural killer (NK) cells. These data suggest that an anti-CD70 antibody, when engineered to contain human IgG1 constant domains, possesses effector cell–mediated antitumor activity and has potential utility for anticancer therapy.

Lymphocyte activation antigen CD70 expressed by renal cell carcinoma is a potential therapeutic target for anti-CD70 antibody-drug conjugates

Metastatic renal cell carcinoma (RCC) is an aggressive disease refractory to most existing therapeutic modalities. Identifying new markers for disease progression and drug targets for RCC will benefit this unmet medical need. We report a subset of clear cell and papillary cell RCC aberrantly expressing the lymphocyte activation marker CD70, a member of the tumor necrosis factor superfamily. Importantly, CD70 expression was found to be maintained at the metastatic sites of RCC. Anti-CD70 antibody-drug conjugates (ADC) consisting of auristatin phenylalanine phenylenediamine (AFP) or monomethyl auristatin phenylalanine (MMAF), two novel derivatives of the anti-tubulin agent auristatin, mediated potent antigen-dependent cytotoxicity in CD70-expressing RCC cells. Cytotoxic activity of these anti-CD70 ADCs was associated with their internalization and subcellular trafficking through the endosomal-lysosomal pathway, disruption of cellular microtubule network, and G2-M phase cell cycle arrest. The efficiency of drug delivery using anti-CD70 as vehicle was illustrated by the much enhanced cytotoxicity of antibody-conjugated MMAF compared with free MMAF. Hence, ADCs targeted to CD70 can selectively recognize RCC, internalize, and reach the appropriate subcellular compartment(s) for drug release and tumor cell killing. In vitro cytotoxicity of these ADCs was confirmed in xenograft models using RCC cell lines. Our findings provide evidence that CD70 is an attractive target for antibody-based therapeutics against metastatic RCC and suggest that anti-CD70 ADCs can provide a new treatment approach for advanced RCC patients who currently have no chemotherapeutic options.

Lysosomal trafficking and cysteine protease metabolism confer target-specific cytotoxicity by peptide-linked anti-CD30-auristatin conjugates

The chimeric anti-CD30 monoclonal antibody cAC10, linked to the antimitotic agents monomethyl auristatin E (MMAE) or F (MMAF), produces potent and highly CD30-selective anti-tumor activity in vitro and in vivo. These drugs are appended via a valine-citrulline (vc) dipeptide linkage designed for high stability in serum and conditional cleavage and putative release of fully active drugs by lysosomal cathepsins. To characterize the biochemical processes leading to effective drug delivery, we examined the intracellular trafficking, internalization, and metabolism of the parent antibody and two antibody-drug conjugates, cAC10vc-MMAE and cAC10vc-MMAF, following CD30 surface antigen interaction with target cells. Both cAC10 and its conjugates bound to target cells and internalized in a similar manner. Subcellular fractionation and immunofluorescence studies demonstrated that the antibody and antibody-drug conjugates entering target cells migrated to the lysosomes. Trafficking of both species was blocked by inhibitors of clathrin-mediated endocytosis, suggesting that drug conjugation does not alter the fate of antibody-antigen complexes. Incubation of cAC10vc-MMAE or cAC10vc-MMAF with purified cathepsin B or with enriched lysosomal fractions prepared by subcellular fractionation resulted in the release of active, free drug. Cysteine protease inhibitors, but not aspartic or serine protease inhibitors, blocked antibody-drug conjugate metabolism and the ensuing cytotoxicity of target cells and yielded enhanced intracellular levels of the intact conjugates. These findings suggest that in addition to trafficking to the lysosomes, cathepsin B and perhaps other lysosomal cysteine proteases are requisite for drug release and provide a mechanistic basis for developing antibody-drug conjugates cleavable by intracellular proteases for the targeted delivery of anti-cancer therapeutics.

Preclinical antilymphoma activity of a humanized anti-CD40 monoclonal antibody, SGN-40

SGN-40 is a humanized IgG1 antihuman CD40 that is currently in a phase I clinical trial for the treatment of multiple myeloma. As surface CD40 expression on B-lineage cells is maintained from pro-B cells to plasma cells, SGN-40 may be applicable to treatment of other B-cell neoplasias, including non-Hodgkin's lymphoma. In this study, we examined potential in vitro and in vivo anti-B-lineage lymphoma activity of SGN-40. Recombinant SGN-40 was expressed and purified from Chinese hamster ovary cells and characterized based on binding affinity, specificity, and normal B-cell stimulation. The ability of SGN-40 to target neoplastic B cells was examined in vitro by proliferation inhibition, cytotoxicity, and antibody-dependent cell cytotoxicity assays and in vivo by human lymphoma xenograft models. Recombinant SGN-40 showed high affinity, Kd of approximately 1 nmol/L, and specific binding to CD40. Whereas SGN-40 was a weak agonist in stimulating normal B-cell proliferation in the absence of IL-4 and CD40L, it delivered potent proliferation inhibitory and apoptotic signals to, and mediated antibody-dependent cytotoxicity against, a panel of high-grade B-lymphoma lines. These in vitro antilymphoma effects were extended to disseminated and s.c. xenograft CD40 tumor models. In these xenograft models, the antitumor activity of SGN-40 was comparable with that of rituximab. The preclinical in vitro and in vivo antilymphoma activity of SGN-40 observed in this study provides a rationale for the clinical testing of SGN-40 in the treatment of CD40+ B-lineage lymphomas.

Design, synthesis, and in vitro evaluation of dipeptide-based antibody minor groove binder conjugates

Antibody-drug conjugates (ADCs) were prepared consisting of DNA minor groove binder drugs (MGBs) attached to monoclonal antibodies (mAbs) through peptide linkers designed to release drugs inside the lysosomes of target cells. The site of linker attachment on the MGB was at the 5-position on the B-ring, since model studies showed that attachment of an electron-withdrawing group (i.e., acyl, carbamoyl) at this position increased the stability of the molecule. Because of the hydrophobic nature of the MGBs, several measures were required to overcome their tendencies to induce mAb aggregation upon conjugation. This is exemplified in the series of ADCs containing the amino-CBI drug 1. Initial adducts were prepared using the peptide sequence valine-citrulline, attached to a self-immolative para-aminobenzyl carbamate spacer. The resulting ADCs were completely aggregated. Removal of the self-immolative spacer, introduction of a more hydrophilic valine-lysine sequence, and incorporation of a tetraethyleneglycol unit between the mAb and the peptide resulted in conjugates that were nonaggregated, even with as many as eight drugs per mAb. These results were extended to include the hydroxy aza-CBI drug 2, which was linked to the valine-lysine sequence through a para-aminobenzyl ether self-immolative spacer. The resulting mAb conjugates were monomeric and released the hydroxy aza-CBI drug upon treatment with human cathepsin B. In vitro cytotoxicity assays established that the mAb-MGB drug conjugates were highly cytotoxic and effected immunologically specific cell kill at subsaturating doses. The results provide a general strategy for MGB prodrug design and illustrate the importance of linker hydrophilicity in making nonaggregated, active mAb-MGB conjugates.

Efficient elimination of B-lineage lymphomas by anti-CD20-auristatin conjugates

The anti-CD20 antibody rituximab is useful in the treatment of certain B-cell malignancies, most notably non-Hodgkin's lymphoma. Its efficacy has been increased when used in combination with chemotherapy, yet anti-CD20 monoclonal antibodies (mAbs) directly conjugated with drugs such as doxorubicin (Dox) have failed to deliver drug or to demonstrate antitumor activity. We have produced anti-CD20 antibody-drug conjugates that possess potent antitumor activity by using the anti-mitotic agent, monomethyl auristatin E (MMAE), linked via the lysosomally cleavable dipeptide, valine-citrulline (vc). Two anti-CD20 conjugates, rituximab-vcMMAE and 1F5-vcMMAE, were selectively cytotoxic against CD20(+) B-lymphoma cell lines, with IC(50) values ranging from 50 ng/mL to 1 microg/mL. Unlike rituximab, which showed diffuse surface localization, rituximab-vcMMAE capped and was internalized within 4 hours after binding to CD20(+) B cells. Internalization of rituximab-vcMMAE was followed by rapid G(2)-M phase arrest and onset of apoptosis. Anti-CD20 antibody-drug conjugates prepared with Dox were internalized and localized as with rituximab-vcMMAE, yet these were not effective for drug delivery (IC(50) > 50 microg/mL). Consistent with in vitro activity, rituximab-vcMMAE showed antitumor efficacy in xenograft models of CD20-positive lymphoma at doses where rituximab or rituximab-Dox conjugates were ineffective. These data indicate that anti-CD20-based antibody-drug conjugates are effective antitumor agents when prepared with a stable, enzyme-cleavable peptide linkage to highly potent cytotoxic agents such as MMAE.

Comparisons of the in vitro susceptibility testing results for garenoxacin using six different national methods: report from the garenoxacin international bridging study

BACKGROUND

Laboratories worldwide carry out MIC/disc diffusion (DD) tests using various national methods, often published by local organizations. Potentially different results may complicate drug development or registration between the US methods and those used in the European Union (EU). This study uses a new des-F(6)quinolone, garenoxacin, to compare in vitro results among the most utilized antimicrobial susceptibility testing methods.

METHODS

Investigators in France, Germany, Spain, Sweden and the UK tested two bacterial collections designated, challenge (CC; n = 330) containing quinolone-resistant strains and national (NC; n = 540) that were recent clinical isolates (2000-2001). Results were compared with values derived from the National Committee for Clinical Laboratory Standards (NCCLS) methods, carried out by the US coordinating site. Discords (greater than four-fold) between MIC method results were repeated. Results were analysed for variation from the NCCLS results (+/-1-2 dilutions or greater than 3-6 mm) and by regression statistics. Ciprofloxacin was used as the control quinolone agent.

RESULTS

CC and NC testing compliance averaged 98.4% and 86.4% among participating centres, respectively, and correlation (r) of the national method to the NCCLS MIC was: France (0.98), Germany (0.95), Spain (0.98), Sweden (0.96) and UK (0.95). CC produced MIC results that were identical to the NCCLS (Spain) to 0.6 x log(2) greater (Germany), but the percentage of strains +/-2 dilutions versus NCCLS MIC results was 98% (Germany)-100% (Sweden, UK). Similar patterns were observed for the NC (r = 0.93-0.98), and all nations had >99% of results within +/-2 dilutions (+/-6 mm for disc tests) of NCCLS values. MIC results from four national methods were slightly elevated compared to the NCCLS result (average 0.2 x log(2)). Control ciprofloxacin MIC and DD test results showed similar patterns.

CONCLUSIONS

Inter-method garenoxacin susceptibility test results indicate that MIC and zone diameter endpoints derived from five EU methods compare favourably to the NCCLS method results, and generally were identical or a fraction of a log(2) dilution step higher. In contrast, zone diameters for garenoxacin and ciprofloxacin were routinely larger for the EU methods. This unique inter-method 'bridging' experiment allows regulatory agencies to better correlate in vitro testing results derived from procedures that use different national methodologies.

cAC10-vcMMAE, an anti-CD30-monomethyl auristatin E conjugate with potent and selective antitumor activity

The chimeric monoclonal antibody cAC10, directed against CD30, induces growth arrest of CD30+ cell lines in vitro and has pronounced antitumor activity in severe combined immunodeficiency (SCID) mouse xenograft models of Hodgkin disease. We have significantly enhanced these activities by conjugating to cAC10 the cytotoxic agent monomethyl auristatin E (MMAE) to create the antibody-drug conjugate cAC10-vcMMAE. MMAE, a derivative of the cytotoxic tubulin modifier auristatin E, was covalently coupled to cAC10 through a valine-citrulline peptide linker. The drug was stably attached to the antibody, showing only a 2% release of MMAE following 10-day incubation in human plasma, but it was readily cleaved by lysosomal proteases after receptor-mediated internalization. Release of MMAE into the cytosol induced G2/M-phase growth arrest and cell death through the induction of apoptosis. In vitro, cAC10-vcMMAE was highly potent and selective against CD30+ tumor lines (IC50 less than 10 ng/mL) but was more than 300-fold less active on antigen-negative cells. In SCID mouse xenograft models of anaplastic large cell lymphoma or Hodgkin disease, cAC10-vcMMAE was efficacious at doses as low as 1 mg/kg. Mice treated at 30 mg/kg cAC10-vcMMAE showed no signs of toxicity. These data indicate that cAC10-vcMMAE may be a highly effective and selective therapy for the treatment of CD30+ neoplasias.

Comparative antimicrobial spectrum and activity of BMS284756 (T-3811; a desfluoroquinolone) tested against an international collection of staphylococci and enterococci, including in vitro test development and intermethod comparisons

The study was initiated to determine the in vitro activity and MIC/disk test comparisons of BMS284756, a new des-fluoro(6)-quinolone, against isolates of staphylococci and enterococci from the SENTRY Antimicrobial Surveillance Program, 2000. Isolates were tested by reference broth microdilution and standardized disk diffusion methods. Against 3,789 strains of gram-positive cocci from the SENTRY Program (2000), the BMS284756 MIC90 and percentage susceptible at < or = 2 and < or = 4 microg/ml were: Staphylococcus aureus (4 microg/ml; 89.3 and 97.1%), coagulase-negative staphylococci (CoNS; 4 microg/ml; 86.1 and 96.0%) and enterococci (> 4 microg/ml; 62.0 and 76.2%). Also tested were selected staphylococci (300 strains) and enterococci (102 strains) by two standardized methods. The activity of BMS284756 was highly correlated with oxacillin resistance among staphylococci. Oxacillin-susceptible staphylococci were all inhibited by BMS284756 at < or = 0.5 microg/ml, whereas oxacillin-resistant strains required inhibitory concentrations of > or = 1 microg/ml. Excellent correlation was observed between the MIC and 5-microg disk zone diameter for staphylococci and enterococci (r=0.91 to 0.93). Among vancomycin-susceptible enterococci, 67% of Enterococcus faecalis, 25% of E. faecium, and 76% of other Enterococcus spp. isolates were inhibited by BMS284756 at < or = 2 microg/ml. All vancomycin-resistant enterococci (VRE; 11 E. faecalis and 15 E. faecium) were inhibited by > or = 2 microg/ml of BMS284756. Among the non-VRE, non-faecium enterococcal isolates (n=64), 62% were inhibited by < or = 0.5 microg/ml. BMS284756 showed excellent activity against oxacillin-susceptible staphylococci and moderate activity against enterococci other than VRE and E. faecium. Acceptable correlations were observed between MIC and disk test results for both tested genus groups.

Antimicrobial susceptibility testing of clinical isolates of Bordetella pertussis from northern California: report from the SENTRY Antimicrobial Surveillance Program

Reports of an increased clinical incidence of pertussis and the development of resistance by Bordetella pertussis to erythromycin prompted the collection and testing of recent clinical isolates from patients in northern California against a range of antimicrobial agents by the Etest (AB BIODISK, Solna, Sweden) method. All isolates were fully susceptible to all eight agents tested (MIC, <or=0.38 microg/ml), including newer fluoroquinolones, such as gatifloxacin (MIC of which 90% of the isolates tested are inhibited, 0.006 microg/ml), which may be used in cases of adolescent or adult pertussis. Continued surveillance of B. pertussis isolates appears to be a prudent practice.

Neisseria meningitidis with decreased susceptibility to penicillin: report from the SENTRY antimicrobial surveillance program, North America, 1998-99

The purpose of this study was to estimate the prevalence of Neisseria meningitidis with decreased susceptibility to penicillin (MIC, >0.06 microg/mL) in North America (NA). Antimicrobial susceptibility testing by Etest (AB BIODISK, Solna, Sweden) was performed on 53 invasive clinical isolates obtained from 11 SENTRY Antimicrobial Surveillance Program participants in NA (9 states, 2 provinces) during 1998-99. All strains were markedly susceptible to ciprofloxacin (MIC(90), 0.008 microg/mL) and cefotaxime (MIC(90), < or = 0.002 microg/mL). Only 54.7% were susceptible to trimethoprim-sulfamethoxazole (TMP/SMX) at < or = 0.5/9.5 microg/mL. One strain was resistant to rifampin (MIC, > 32 microg/mL) and 16 isolates (30.2%) were relatively resistant to penicillin with MICs ranging from 0.094 to 0.25 microg/mL. No beta-lactamase production was detected. The serogroup distribution was 40% Y, 28% B, 24% C, 2% W-135, and 6% of strains were nongroupable. The prevalence of N. meningitidis with decreased susceptibility to penicillin in NA appears higher than previous reports.

Effect of residual hearing prior to cochlear implantation on speech perception in children

We examined the impact of residual hearing prior to cochlear implantation on pre- and postimplantation speech perception outcomes in children. Stimulation of the auditory system prior to implantation because of the presence of residual hearing is important for development of the central auditory pathways, whereas, in the absence of such stimulation, the pathways show less development. We hypothesized that children who had some degree of residual hearing preimplantation achieve better speech perception skills than their peers with poorer hearing. From the 133 children followed in our program, we identified 37 children who had an audiometric pure-tone average of better than 95 dB HL in the better ear at any time preimplantation. Psychophysical speech perception measures, the Word Identification Picture Inventory and the Phonetically Balanced Kindergarten list, in these children were compared with those of 96 implanted children who had poorer hearing prior to implantation. Children with more residual hearing showed higher speech perception scores both before implantation and over their first year of implant use than children with poorer hearing, suggesting that there is an advantage in having a greater degree of residual hearing preimplantation. We suggest that this advantage is promoted, in part, by the greater potential for auditory stimulation provided by high-gain hearing aids in children with greater degrees of residual hearing. This advantage appears to be maintained at least over 1 year postimplantation, yet the rates of development of postimplantation speech perception are not different between the groups. We suggest that this may be due to the unique aspects of electrical stimulation from a cochlear implant. Our findings suggest that it is important to minimize the delay of speech perception skills in the preimplantation phase, particularly in children with poor residual hearing. This can be accomplished by implanting children with congenital severe to profound hearing loss at young ages and children with acquired hearing loss soon after the onset. Also, auditory stimulation prior to implantation should be maximized through the consistent use of hearing aids and therapy that emphasizes development of auditory skills.

Factors contributing to limited open-set speech perception in children who use a cochlear implant

Cochlear implants have enabled many children with severe to profound sensorineural hearing loss to develop speech perception skills. However, some children experience few gains while others develop high levels of speech perception. We identified potential factors contributing to poor performance with an implant by studying implanted children who do not develop functional speech perception. Five children were identified as developing no open-set word recognition skills after at least 2 years of implant use. This study group was compared to a randomly selected control group (n=10) and an age-matched control group (n=5). Pre-implant factors were examined using a Graded Profile Analysis and post-implant factors were assessed in a retrospective chart review. A greater number of pre-implant concerns were raised in the study group than in randomized controls (P<0.01). Chronological age and duration of deafness were pre-implant concerns in all study group subjects. A greater number of post-implant concerns were found in the study group than in randomly selected controls (P<0.005). We conclude that while appropriate selection of candidates for cochlear implantation is important in predicting speech perception outcomes, post-implant follow-up is also essential and must include regular monitoring of equipment, monitoring of stimulation levels with use of objective measures of stimulation levels if necessary, and consistent habilitation.

Two-year assessment of the pathogen frequency and antimicrobial resistance patterns among organisms isolated from skin and soft tissue infections in Latin American hospitals: results from the SENTRY antimicrobial surveillance program, 1997-98. SENTRY Study Group

OBJECTIVES

This study was conducted to evaluate the frequency of occurrence and antimicrobial susceptibility of bacterial isolates collected from patients with skin and soft tissue infections (SSTI) in Latin American hospitals, as part of the SENTRY Antimicrobial Surveillance Program. The dissemination of multidrug-resistant methicillin-resistant Staphylococcus aureus (MDR-MRSA) among the Latin American countries also was studied.

MATERIAL AND METHODS

A total of 885 bacterial isolates were analyzed. At the monitoring laboratory, antimicrobial susceptibility testing utilizing the reference broth microdilution method and confirmation of species identification were performed. Enterobacteriaceae possibly producing extended-spectrum beta-lactamases (ESBL) and MDR-MRSA isolates were genotyped by ribotyping using the RiboPrinter and by pulsed-field gel electrophoresis.

RESULTS

Staphylococcus aureus (31%) was the most common etiologic agent causing SSTI, followed by Escherichia coli (13.4%) and Pseudomonas aeruginosa (11%). Thirty-one percent of S. aureus isolates were resistant to oxacillin (methicillin). The presence of ESBL phenotypes was markedly higher among the Klebsiella pneumoniae (35.5%) than E. coli isolates (10. 2%). Meropenem was the compound with the highest susceptibility rate among the Enterobacteriaceae (100%) and P. aeruginosa (95%) isolates. A great genetic similarity was observed among the MDR-MRSA in Latin America.

CONCLUSION

High resistance rates to antimicrobial drugs among the most frequent bacterial pathogens were observed in 10 medical centers in Latin America. This study also demonstrated a clonal dissemination of a MDR-MRSA strain in several nations.

Activity and spectrum of 22 antimicrobial agents tested against urinary tract infection pathogens in hospitalized patients in Latin America: report from the second year of the SENTRY antimicrobial surveillance program (1998)

The potency and spectrum of various antimicrobial agents tested against 434 bacterial isolates causing urinary tract infection (UTI) in hospitalized patients in Latin America were evaluated. The genotypes of the extended-spectrum beta-lactamase-producing and selected multi-resistant isolates were also evaluated by molecular typing techniques. Escherichia coli (60.4%) was the most common aetiological agent causing UTI, followed by Klebsiella spp. (11.2%) and Pseudomonas aeruginosa (8.3%). In contrast, Enterococcus spp. isolates caused only 2.3% of UTIs. Fewer than 50% of E. coli isolates were susceptible to broad-spectrum penicillins. The resistance rates to ciprofloxacin and the new quinolones were also high among these isolates. The molecular characterization of ciprofloxacin-resistant E. coli showed that most of them have a double mutation in the gyrA gene associated with a single mutation in the parC gene. The Klebsiella pneumoniae isolates studied demonstrated high resistance rates to beta-lactam drugs, including broad-spectrum cephalosporins. The carbapenems were the compounds with the highest susceptibility rate among these isolates (100.0% susceptible) followed by cefepime (91.7% susceptible). Meropenem, imipenem and cefepime were also the most active drugs against Enterobacter spp. Among P. aeruginosa isolates, meropenem (MIC(50), 2 mg/L) was the most active compound, followed by imipenem (MIC(50), 4 mg/L), cefepime (MIC(50), 8 mg/L) and ceftazidime (MIC(50), 16 mg/L). The results presented in this report confirm that bacterial resistance continues to be a great problem in Latin American medical institutions.

Occurrence of single-point gyrA mutations among ciprofloxacin-susceptible Escherichia coli isolates causing urinary tract infections in Latin America

To detect if isolates susceptible to quinolones already carry mutations in the gyrA and parC genes, we selected 12 ciprofloxacin-susceptible Escherichia coli strains collected from patients with urinary tract infections in Latin America in 1998, as part of ongoing SENTRY Antimicrobial Surveillance Program. The isolates studied exhibited minimal inhibitory concentrations (MICs) for ciprofloxacin between < or = 0.015 microg/mL and 0.5 microg/mL. The molecular characterization of quinolone resistance was determinated by amplification of the gyrA and parC by PCR followed by sequencing of the respective amplicons. We observed that E. coli isolates exhibiting MIC, < or = 0.06 microg/mL for ciprofloxacin did not show mutations in either topoisomerase. On the other hand, all isolates with MIC between 0.12 microg/mL and 0.5 microg/mL demonstrated single mutation in the gyrA gene. The most frequent mutation occurred at position 83, where the amino acid serine was replaced by leucine. No mutations in the parC gene were observed. To preserve the potency and prevent the development of resistance, we suggest that quinolone usage should be rational, especially in the treatment of urinary tract infections, and in the prophylaxis of immunosupressed patient populations.

Acute high dose arteether toxicity in rats

Acute high dose administration of the artemisinin antimalarial, beta-arteether (AE), was evaluated in rats using an auditory discrimination task (ADT) and histology. After rats were trained on the ADT, AE (25, 75, 125 mg/kg, i.m.) or vehicle (sesame oil) was administered and behavioral performance was evaluated for 11 consecutive days. Histological evaluation of the brains was performed using thionine and cupric-silver staining. Damaged cells were counted in specific brainstem nuclei of all rats and a qualitative analysis of the rostral-caudal extent of selected brains was performed. Behavioral performance was not significantly affected by any treatment although some evidence of disruption was observed, particularly after the largest dose. At 125 mg/kg, AE produced statistically significant neuropathology, including chromatolysis, in the nucleus trapezoideus and nucleus superior olive. AE at 75 mg/kg, produced significant neuropathology in the nucleus trapezoideus. Neither AE at 25 mg/kg, nor vehicle produced damage. Qualitative analysis revealed a pattern of neuropathology focused in the brainstem. The results show that, in rats, a single dose of AE can produce a pattern of brainstem neuropathology and that specific brainstem nuclei, including auditory nuclei, are particularly vulnerable. These results are consistent with, and extend, previous studies demonstrating brainstem neurotoxicity from repeated AE administration. Moreover, early detection of AE-induced neuropathology is problematic and may require selective examination of brainstem functions.

The role of a graded profile analysis in determining candidacy and outcome for cochlear implantation in children

Assessment of candidacy for cochlear implantation in children continues to present a challenge to cochlear implant programs. The efficacy of implantation depends on a number of factors and as a result a multidisciplinary approach has been adopted. At the Cochlear Implant Program at The Hospital for Sick Children, Toronto, we use a graded profile analysis (GPA) which has been adapted from the Children's Implant Profile (CHIP) developed by Hellman (S.A. Hellman, P.M. Chute, R.E. Kretschmer, M.E., Nevins, S.C. Parisier, L.C. Thurston, The development of a Children's Implant Profile, Am. Ann. Deaf. 136 (1991) 77-81). This structured assessment allows each potential candidate to be 'scored' in each category of assessment giving a potential range of -14 to +14. In this retrospective study of 109 candidates we examine the relationship between GPA scores and decision to implant. For those patients who were implanted, the relationship between GPA score and speech perception outcomes was also evaluated. Three distinct groups of children emerged from the analysis. The first group had scores less than 5 and were not considered to be suitable for implantation. Within the second group who scored between 5 and 8, there was no clear relationship between decision to implant and score. The last group, who scored 9-14, was considered to be generally suitable for implantation provided that there were no medical contraindications and the parents consented to implantation. There was a significant association between rate of improvement of speech perception and GPA score. Those patients with scores of 9 to +14 improved at a faster rate than group 5-8 (P < 0.05). The implications of these findings are discussed.

Synthesis and immunosuppressive activity of ruthenium complexes

The syntheses and immunosuppressive activity of ruthenium complexes are described. One of the complexes (1a) was shown to be a potent inhibitor of human T-lymphocyte proliferation with an IC50 of 5 nM. The activity of these complexes compares favorably to the well known immunosuppressants Cyclosporin A and Rapamycin.

College health in the national blueprint for a healthy campus 2000

Beginning in 1985, an ACHA task force studied national health objectives to determine how well colleges and universities were achieving nationally defined health goals. The task force found that the college-aged population was not specifically recognized as a concern among health planners and that little consistent data on the health status of students existed. The task force worked closely with federal agencies in identifying relevant issues and focusing on the higher education community's commitment to disease promotion and positive health behaviors.

An organizational model for developing multidisciplinary clinical research in the academic medical center

OBJECTIVE

To assess the impact of a new organizational model designed to stimulate multidisciplinary clinical research.

METHODS

We conducted a prospective, 3 1/2-year followup of a research training program for residents, fellows, faculty, nurses, and allied health professionals in rheumatology and orthopedic surgery. Program components included a multidisciplinary clinical research conference, a clinical research methods curriculum, consultations, a patient registry, and regular meetings of a Research Methodology Core group. Measures included participation in each program component and the number of new investigators who developed funded clinical research projects.

RESULTS

The multidisciplinary clinical research conference was attended by 369 new health professionals; 218 professionals participated in at least one of the courses; and 280 consultations were provided to 108 professionals. Thirteen new investigators developed 17 new grant proposals, of which 14 were externally funded. Investigators who successfully procured funding for new projects demonstrated significantly more participation in program components compared with those who did not (P < 0.001 overall).

CONCLUSION

Participation in the program was significantly correlated with the development of new prospective patient-based studies. We conclude that our model has the potential to foster such research in other settings.

Acidic fibroblast growth factor stimulates adrenal chromaffin cells to proliferate and to extend neurites, but is not a long-term survival factor

Acidic fibroblast growth factor (aFGF) is a heparin-binding polypeptide that is a mitogen for endothelial cells and glial cells, as well as a differentiation factor for PC12 cells and certain neurons. We show here that aFGF is as potent as nerve growth factor (NGF) in stimulating both neuritic outgrowth and proliferation in adrenal chromaffin cells from young rats, but it fails to support long-term survival. Heparin strongly potentiates aFGF-dependent neuritic outgrowth but not aFGF-dependent proliferation. As is the case with NGF, phorbol myristate acetate depresses aFGF-induced cell division and increases the outgrowth of neurites. On the other hand, dexamethasone antagonizes neuritic outgrowth elicited by both NGF and aFGF but inhibits only proliferation induced by NGF. The effects of basic FGF (bFGF) are similar but not identical to those of aFGF. Thus the regulatory pathways controlled by aFGF, bFGF, and NGF are partially distinct.