Targeting of palpable B16-F10 melanoma tumors with polyclonal antibodies on white blood cells

BACKGROUND

Antibodies and other recognition molecules direct cancer cell death by multiple types of immune cells. Therapy directed at only one target typically results in tumor regrowth because of tumor heterogeneity. Our goal is to direct therapy to multiple targets simultaneously. Our previous studies showed that multiple antibodies targeting mutated tumor proteins inhibited tumor growth when injected subcutaneously near the time of cancer cell implantation.

METHODS

A cocktail of rabbit antibodies against B16-F10 cell surface related mutated proteins were generated. Implanted B16-F10 cells were allowed to grow to palpable size before treatment. Antibodies were administered using different routes of exposure. Free antibody was compared to antibody armed on mouse splenic white blood cells (WBCs). Binding of the antibody cocktail was determined for mouse and human WBCs.

RESULTS

The antibody cocktail inhibited tumor growth and prolonged survival when administered as free antibody or armed on WBCs. The antibody cocktail armed on WBCs achieved similar tumor inhibition as free antibody but at a dose 1000-fold less. Armed WBCs achieved tumor inhibition by intravenous and subcutaneous administration. The antibody cocktail bound well to human WBCs and saturation dose was defined. Binding was stable under simulated in vivo condition in human plasma at 37 °C.

CONCLUSIONS

Antibodies targeting multiple tumor mutated proteins inhibited tumor growth and prolonged survival. Effective antibody dose was reduced 1000-fold by arming WBCs. Rabbit antibodies saturated human WBCs using <1 mg per billion cells. A phase I trial in cancer patients using this strategy has been approved by the FDA.

Development of Clinical-Grade Antibodies against Tumor-Specific Mutations to Target Neuroblastoma

OBJECTIVE

Tumor heterogeneity is a fundamental problem in treating cancer with monotargeting therapy, including chemical, antibody, and T cell therapies. Our goal is to target multiple mutated peptides found in a patient's cancer to increase antibody therapy effectiveness.

METHODS

Tumor samples were derived from patients with neuroblastoma. Whole-exome sequencing was performed of tumor and normal cells. Mutated proteins with missense mutations were selected from the patient tumor. These mutated proteins were further selected for the presence of missense mutations in the outer cell surface. Peptides representing a mutated section of the proteins were used for vaccinating rabbits and generating anti-peptide antibodies. The binding of individual polyclonal antibodies (pAbs) and the mixtures of pAbs were determined against the patient's tumor as cultured neuroblastoma cells and in a murine xenograft model. Antibodies were prepared according to FDA requirements of a phase I clinical protocol.

RESULTS

All of the generated rabbit pAbs bound with high affinity to the corresponding peptide used for vaccination. The pAbs also bound to low passage neuroblastoma cells. Mixed as cocktails, the pAbs had substantially increased binding to cells and bound well to the xenograft tissue. No binding was observed to the panel of normal human tissues. Preparation of pAbs by an academic lab to clinical-grade was approved by FDA for phase I clinical trial.

CONCLUSION

We describe a new strategy to make customized antibodies for individual cancer patients and present the data required to meet FDA specifications to begin a phase I clinical trial.

Preparation of clinical-grade WBCs using leukocyte reduction filters

OBJECTIVE

Our goal was to develop a simpler and less expensive method of obtaining human clinical-grade WBCs using an alternative method to continuous leukapheresis. Our purpose for the WBCs is to arm them with rabbit anticancer antibodies for a phase I clinical trial.

METHODS

Using leukocyte reduction filters (LRFs) discarded from the blood bank, we evaluated multiple variables to maximize recovery of WBCs with the lowest contamination of RBCs. Using an optimized protocol, full-scale runs according to FDA current Good Manufacturing Practice (cGMP) standards were completed with immediate filtration of blood obtained from donors participating in our study.

RESULTS

Forward flushing of the filter removed 85% to 95% of residual RBCs and platelets. When backward flushed with 800 mL, 95% of the WBCs recovered were contained in the first 400 mL. The number of recovered WBCs was in the range of 166-211 million/100 mL filtered blood. Subpopulations of WBCs recovered from the LRFs were in the same proportion as the donors' whole blood. Viability of recovered WBCs was 96-99%. Exogenous rabbit antibodies bound well to the recovered WBCs and were retained for at least 5 h without significant reduction. Three full scale runs of WBCs recovered from donor blood filtered through the LRF met all FDA specification of sterility, endotoxin levels, viability and stability.

CONCLUSION

Using LRFs, high quality clinical grade WBCs are readily obtained in quantities of 0.2 to 1.2 billion cells from 100 mL to 450 mL (1 unit) of whole blood.

A cocktail of polyclonal affinity enriched antibodies against melanoma mutations increases binding and inhibits tumor growth

BACKGROUND

Antibodies that target a single tumor antigen fail to cure stage IV cancer patients due to tumor heterogeneity and variable expression of antigen. Tumor cells with insufficient binding of antibody will not undergo antibody induced cytotoxicity. We describe targeting multiple tumor-specific antigens that resulted in homogeneous dense binding to mouse melanoma cells and significant tumor growth inhibition.

METHODS

Surface-related tumor-specific mutations on B16-F10 cells were identified. Peptides containing the single amino acid mutation were synthesized for 9 different neoantigens. Rabbits were vaccinated with each of these peptides and high affinity polyclonal antibodies to each peptide were obtained. The 9 antibodies were combined as a cocktail and mice with implanted B16-F10 cells were treated with and without PD1 inhibitor.

RESULTS

Even a single dose of the antibody cocktail inhibited tumor growth and prolonged survival. PD1 inhibitor alone had little effect on tumor growth. The antibody cocktail plus PD1 inhibition increased tumor response and 4 doses of the cocktail completely prevented tumor growth in 50% of the mice. Complete responses were durable. The complete responders were highly resistant to tumor re-challenge at 6 months. No adverse events were identified in the antibody treated mice.

CONCLUSIONS

Multiple tumor-specific cell surface-related neoantigens were abundant in B16-F10 cells. Antibodies to 9 of these neoantigens had variable binding but when combined had dense homogeneous binding. Even one dose of this cocktail of 9 antibodies improved survival and when multiple doses were combined with PD1 inhibition 50% of the mice were rendered permanently tumor free.

Multiple antibodies targeting tumor-specific mutations redirect immune cells to inhibit tumor growth and increase survival in experimental animal models

BACKGROUND

T cell therapy for cancer involves genetic introduction of a target-binding feature into autologous T cells, ex vivo expansion and single large bolus administration back to the patient. These reprogrammed T cells can be highly effective in killing cells, but tumor heterogeneity results in regrowth of cells that do not sufficiently express the single antigen being targeted. We describe a cell-based therapy that simultaneously targets multiple tumor-specific antigens.

METHODS

High-affinity polyclonal rabbit antibodies were generated against nine different surface-related tumor-specific mutations on B16F10 cells. Unsorted splenic effector cells from syngeneic mice were incubated with a cocktail of the nine anti-B16F10 antibodies. These 'armed' effector cells were used to treat mice previously inoculated with B16F10 melanoma cells.

RESULTS

The cocktail of nine antibodies resulted in dense homogeneous binding to histological sections of B16F10 cells. Five treatments with the armed effector cells and PD1 inhibition inhibited tumor growth and improved survival. Shortening the interval of the five treatments from every three days to every day increased survival. Arming effector cells with the four antibodies showing best binding to B16F10 cells even further increased survival.

CONCLUSIONS

This study demonstrates that ex vivo arming a mixed population of immune effector cells with antibodies targeting multiple tumor-specific mutated proteins in conjunction with PD1 inhibition delayed tumor growth and prolonged survival in mice inoculated with an aggressive melanoma. A remarkably low total antibody dose of less than 5 µg was sufficient to accomplish tumor inhibition. Scaling up to clinical level may be feasible.

Abstract 552: Anti-tumor effects of anti-neoantigen antibodies: Tumor growth retardation and increased survival in a syngeneic model of cancer

This study was designed to decrease tumor growth by treatment with multiple anti-neoantigen antibodies (Abs) combined with PD1 inhibition. Dramatic reduction in tumor growth was observed. Despite tremendous excitement of checkpoint inhibitors only a minority of patients have durable complete responses. Success of checkpoint inhibitors appears related to the immune response to neoantigens. We investigated the potential enhancement of checkpoint inhibitors by directing a cocktail of antibodies to multiple neoantigens simultaneous with PD1 inhibition. The choice of neoantigens was simply based on the potential rabbit humoral immunogenicity of a mutated epitope present at the tumor cell surface or secretary proteins, without assigning any weightage to the protein function. Rabbits were vaccinated with each of the 9 selected mutated epitopes of B16-F10 melanoma tumor proteins for generating antibodies. Rabbit polyclonal Abs were affinity purified for each antigen with EC50s mostly in picomolar range. All 9 polyclonal antibodies were mixed equally as a cocktail for treatment experiments. The tumor model was C57BL/J strain of mice implanted with 3x105 B16-F10 melanoma tumor cells in their dorsal flank region. The treatment with anti-neoantigen Abs cocktail were administered in two different schedules; 1) a single treatment by implanting tumor cells suspended in 0.2 mg Abs cocktail/mouse and 2) local injection (0.2 mg Abs cocktail/mouse) into the tumor implantation site on 3, 6, 9 and 13 days post-tumor implantation. Except for a completely untreated control group all mice received 4 intraperitoneal injections (0.2 mg/mouse) of anti-mouse PD1 Ab (clone RMP1-14) or its isotype control Ab (IgG2a, k). Normal rabbit polyclonal IgG was used as control against the 9 anti-neoantigen Abs cocktail. No treatment resulted in rapid growth of large tumors and these untreated mice either died or were euthanized by day 20. The treatment with anti-PD1 Ab or its isotype control Ab alone did not affect tumor growth and survival in comparison to untreated mice. Furthermore, PD1 inhibition combined with normal rabbit IgG had no effect on tumor growth or survival. However, the single treatment of tumor cells with the 9 Abs cocktail during implantation combined with PD1 inhibition significantly retarded tumor growth and increased survival. The results were even more dramatic with the group of mice that were implanted with tumor cells in PBS and received 4 treatments of the 9 Abs cocktail in combination to PD1 inhibition. All the animals in this group had substantial retardation of tumor growth and 50% of the mice have shown no tumor whatsoever out to post-implantation day sixty. This is the first study to show anti-tumor effects of multiple anti-neoantigen Abs. These results are important particularly in a poorly immunogenic tumor model which is non-responsive to PD1 checkpoint inhibitor therapy alone.

Citation Format: Girja S. Shukla, Yu-Jing Sun, Stephanie C. Pero, David N. Krag. Anti-tumor effects of anti-neoantigen antibodies: Tumor growth retardation and increased survival in a syngeneic model of cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 552.

Identification of tumor-reactive B cells and systemic IgG in breast cancer based on clonal frequency in the sentinel lymph node

A better understanding of antitumor immune responses is the key to advancing the field of cancer immunotherapy. Endogenous immunity in cancer patients, such as circulating anticancer antibodies or tumor-reactive B cells, has been historically yet incompletely described. Here, we demonstrate that tumor-draining (sentinel) lymph node (SN) is a rich source for tumor-reactive B cells that give rise to systemic IgG anticancer antibodies circulating in the bloodstream of breast cancer patients. Using a synergistic combination of high-throughput B-cell sequencing and quantitative immunoproteomics, we describe the prospective identification of tumor-reactive SN B cells (based on clonal frequency) and also demonstrate an unequivocal link between affinity-matured expanded B-cell clones in the SN and antitumor IgG in the blood. This technology could facilitate the discovery of antitumor antibody therapeutics and conceivably identify novel tumor antigens. Lastly, these findings highlight the unique and specialized niche the SN can fill in the advancement of cancer immunotherapy.

Vaccine-draining lymph nodes of cancer patients for generating anti-cancer antibodies

Background

Our research is focused on using the vaccine draining lymph node to better understand the immune response to cancer vaccines and as a possible source of anti-cancer reagents. We evaluated vaccine draining lymph nodes archived from a clinical study in melanoma patients and determined the reaction of B cells to the vaccine peptides.

Methods

Mononuclear cells (MNCs) were recovered from cryopreserved lymph nodes that were directly receiving drainage from multi-peptide melanoma vaccine. The patients were enrolled on a vaccine study (NCT00089219, FDA, BB-IND No. 10825). B cell responses in the vaccine-draining lymph nodes were studied under both stimulated and un-stimulated conditions. Cryopreserved cells were stimulated with CD40L, stained with multiple human cell-surface markers (CD19, CD27, IgM) to identify different categories of B cell sub populations with flow cytometry. Hybridomas were generated from the lymph node cells after CD40L-stimulation. Cells were fused to murine plasmacytoma P3X63.Ag8.653 using Helix electrofusion chamber. ELISA was used to evaluate hybridoma derived antibody binding to vaccine peptides.

Results

Viable MNCs were satisfactorily recovered from lymph nodes cryopreserved from six vaccine study patients 8–14 years previously. B cell ELISPOT demonstrated responses for each patient to multiple vaccine peptides. CD40L stimulation of lymph node cells increased the proportion of CD19⁺ CD27⁺ cells from 12 to 65% of the sample and increased the proportion of class-switched cells. Screening of IgG secreting clones demonstrated binding to melanoma vaccine peptides.

Conclusions

B cells were successfully recovered and expanded from human cryopreserved vaccine-draining lymph nodes. Individual B cells were identified that secreted antibodies that bound to cancer vaccine peptides. The ability to reliably generate in vitro the same antibodies observed in the blood of vaccinated patients will facilitate research to understand mechanisms of human antibody activity and possibly lead to therapeutic antibodies.

Vaccine draining lymph nodes are a source of antigen-specific B cells

PURPOSE

Our research is focused on using vaccine draining lymph nodes as a source of immune cells to better understand the immune response and to attempt to generate new anti-cancer reagents. Following a vaccine, harvesting the lymph node can only be done once. We endeavored to determine the range of times that B cells secreting anti-KLH antibodies were present in the node of KLH-vaccinated mice.

RESULTS

Following vaccination the total number of mononuclear cells (MNCs) increased in the vaccine-draining lymph node (VDN). The percentage of MNCs that were B cells nearly doubled. B cells recovered from the node that secreted anti-KLH antibodies were evident by day 7. The number continued to increase and then slowly decreased over the observed time range to 28days after vaccination. The VDN, compared to the spleen, the bone marrow and the nonVDN, contained a higher percentage of B cells that secreted anti-KLH antibodies.

CONCLUSIONS

After a vaccine, there is a multi-week window of time when an increasing number of B cells are present in a VDN that secrete anti-KLH antibodies. These results support using the VDN as a source for B cells that secrete anti-vaccine antibodies.

Abstract 581: Bone marrow-derived B-cell hybridomas from neuroblastoma patients generate antibodies that bind to patients’ own tumors

Today antibody therapy is considered to be one of the most important and successful strategies to treat a variety of cancers. For example, the addition of antibodies such as Herceptin and Avastin to a chemotherapy regimen has shown improved survival in the treatment of breast cancer and colorectal cancer, respectively. Main problems with this kind of therapy are that many patients are not candidates because their tumors do not overexpress the drug target and that patient develop resistance to the targeted drug. A method to rapidly develop different sets of therapeutic antibodies would greatly contribute to the field of targeted anticancer therapy. This work evaluated the feasibility of using residual clinical material from pediatric neuroblastoma patients to generate antibodies to autologous tumor. Neuroblastoma is the most common extracranial solid tumor in children, accounting for 8-10% of all childhood cancers. Most patients with neuroblastoma are young and commonly present with metastatic disease. Bone marrow aspirate from neuroblatoma patients was the source material for the mononuclear cells and the tumor cells used in present study. Tumor cells were cultured and xenograft tumors were produced in mice. Hybridomas were generated by electrofusion of stimulated bone marrow mononuclear cells with plasmacytoma P3×63.Ag8.653 under hypo-osmolar condition using Eppendorf Multiporator/Helix chamber. Following hypoxanthine-aminopterin-thymidine (HAT) selection and monoclonal distribution, the culture supernatants were assayed for immunoglobulin secretion by ELISA. The supernatants from the positive clones were evaluated by immunofluorescence microscopy for binding to cultured neuroblastoma cells and neuroblastoma xenograft tissue sections derived from the same patient from which the hybridomas were generated. The results demonstrated that multiple hybridomas of bone marrow mononuclear cells secreted monoclonal antibodies that bound autologous neuroblastoma cells. Further evaluation of the tumor-binding antibodies on a panel of normal human tissues showed no binding to most of the tissues in the panel. Successful outcome of these experiments demonstrate the feasibility of generating human monoclonal antibodies from residual marrow specimens that bind autologous neuroblastoma cells. However, it remains to be determined whether these antibodies are bioactive and whether this approach will be generally applicable in more patients with neuroblastoma. It may be concluded that the strategy described here, which exploits the cancer patient's own immune repertoire, has a great potential for neuroblastoma target discovery and developing antibodies with possible therapeutic and/or diagnostic utility in cancer.

Citation Format: Girja S. Shukla, Giselle S. Sholler, Yujing Sun, Stephanie C. Pero, Chelsea L. Carman, Ping Zhao, David N. Krag. Bone marrow-derived B-cell hybridomas from neuroblastoma patients generate antibodies that bind to patients’ own tumors. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 581.

Species variation in pesticide-induced blood-brain barrier dysfunction

Neurological disorders following acute or chronic exposure to pesticides have been reported in a number of human cases. However, the mechanism(s) by which pesticides produce central nervous system dysfunction is not clear. The objective of the present study was to examine the functional status of blood-brain barrier (BBB) in rats and mice exposed to selected pesticides of different chemical groups. Adult male albino rats and mice were exposed (1/10 of LD50) daily to dichlorvos (organophosphate), lindane (organochlorine) and carbofuran (carbamate) through oral intubation for 3 days. The status of BBB was evaluated by determining brain sodium fluorescein dye uptake and brain uptake index (BUI) in relation to serum dye level. The brain dye uptake and BUI in pesticide-exposed rats did not differ significantly in comparison to that of controls. However, brain dye uptake and BUI were increased significantly in mice exposed to dichlorvos (85%, 40%), lindane (79%, 26%) and carbofuran (129%, 61%). The results of this study show that mouse BBB system is more sensitive to pesticide-induced breach as compared to that of rat. These variations may have a role in determining the outcome of pesticide neurotoxicity in different species.

Abstract 5019: Characterization of sentinel node-derived antibodies from breast cancer patients

Lymph nodes are one of the important sites in the body where immune responses to antigens are initiated. The tumor-draining lymph node or sentinel node is the first site where cancer cells and cancer-related antigens are most likely to spread. In response to antigen exposure and immune activation, the lymph node B cells undergo clonal expansion and somatic hypermutation, leading to the affinity-matured populations of effector B cells secreting antibodies that bind to the tumor. The cancer-draining node is therefore an ideal source of B cells that produce anticancer antibodies. In the present investigation, we have characterized the antibodies derived from immortalization of sentinel node B cells from 29 breast cancer patients. The antibodies were screened for their isotypes and for binding to breast cancers classified as luminal A, luminal B, HER2, and basal/normal subtypes, based on the expressions of estrogen, progesterone and HER2 receptors. The isotype analysis showed a higher percentages of antibodies belong to IgG (48%) and IgM (34%) isotypes along with a smaller share of IgA (18%). The cell-binding studies were conducted using ELISA, immunofluorescence microscopy, and flow cytometry techniques. Of the studied antibodies, about 28% showed binding to the tumor cells. The comparative studies of antibody-binding to breast tumor cells and non-cancer breast cells identified several antibodies showing differential binding profile. The binding analyses also demonstrated that all of the tumor-binding antibodies belonged to IgM isotype. It is evident from the results that the tumor-reactive antibodies are generated in the sentinel nodes of breast cancer patients; however, the absence of class-switched anti-tumor antibodies in the repertoire raises a possibility of tumor-induced node suppression leading to an inefficient humoral immune response towards tumor antigens. The results are important in assessing the tumor immune response/lymph node suppression, and the possible role of the autoantibodies in diagnosis and therapy of breast cancer.

Citation Format: Girja S. Shukla, Stephanie C. Pero, Yu-Jing Sun, Chelsea L. Carman, David N. Krag. Characterization of sentinel node-derived antibodies from breast cancer patients. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5019. doi:10.1158/1538-7445.AM2015-5019

Autologous antibodies that bind neuroblastoma cells

Antibody therapy of neuroblastoma is promising and our goal is to derive antibodies from patients with neuroblastoma for developing new therapeutic antibodies. The feasibility of using residual bone marrow obtained for clinical indications as a source of tumor cells and a source of antibodies was assessed. From marrow samples, neuroblastoma cells were recovered, grown in cell culture and also implanted into mice to create xenografts. Mononuclear cells from the marrow were used as a source to generate phage display antibody libraries and also hybridomas. Growth of neuroblastoma patient cells was possible both in vitro and as xenografts. Antibodies from the phage libraries and from the monoclonal hybridomas bound autologous neuroblastoma cells with some selectivity. It appears feasible to recover neuroblastoma cells from residual marrow specimens and to generate human antibodies that bind autologous neuroblastoma cells. Expansion of this approach is underway to collect more specimens, optimize methods to generate antibodies, and to evaluate the bioactivity of neuroblastoma-binding antibodies.

Abstract 3638: Vaccine-draining lymph nodes of cancer patients for generating anticancer antibodies

Human vaccine studies regularly demonstrate vaccine-induced antibodies in the blood. Characterization of these antibodies shows that they exhibit an extensive range of bioactive mechanisms. Unfortunately, there is not yet a reliable method by which to produce these important antibodies. Human antibodies may not require any molecular modification for therapeutic application and have a much faster pipeline to clinical studies than animal-derived antibodies. Lymph nodes are the primary destination of tumor or vaccine antigens. In the node, B cells undergo clonal expansion and somatic hypermutation, leading to the affinity-matured populations of effector B cells secreting antibodies that bind to the tumor or vaccine. The cancer vaccine-draining node is the ideal source of B cells that produce anticancer antibodies. Despite multiple human cancer vaccine studies, very little research has been done to recover the B cells responsible for vaccine-induced anticancer antibodies. In the present study, we used mononuclear cells from surgically removed vaccine-draining lymph nodes of melanoma patients vaccinated with 6 melanoma peptides derived from cancer-testis antigens and from melanocytic differentiation proteins for generating anti-vaccine peptide antibodies. The lymph node draining the vaccination site was localized by lymphatic mapping with a radiotracer. The development and maturity of B cells were assessed by determining phenotypic characters of lymph node cells using multicolor flow cytometry. The results showed that these vaccine-draining nodes contain high numbers of class-switched (CD19+CD27+IgD-IgM-) B cells and plasmablasts (CD19+CD38+IgM-). B-cell ELISpot assay was used to quantify the proportion of B cells in vaccine-draining lymph nodes that secrete anti-melanoma peptide antibodies. Positive ELISpot responses were observed in patients who also showed serum antibody-reactivity towards the vaccine peptides. The identification of lymph node cell samples exhibiting strong B-cell responses allows efficient generation and screening of hybridomas that secrete antibodies against cancer vaccine antigens. This study establishes a step-wise protocol for generating anti-cancer antibodies from vaccine-draining lymph nodes. We anticipate that the ability to reliably generate in vitro the same antibodies observed in the blood of vaccinated patients will further stimulate research to understand mechanisms of human antibody activity.

Citation Format: Girja S. Shukla, Stephanie C. Pero, Yu-jing Sun, Chelsea L. Carman, Walter C. Olson, Craig L. Slingluff, David N. Krag. Vaccine-draining lymph nodes of cancer patients for generating anticancer antibodies. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3638. doi:10.1158/1538-7445.AM2014-3638

Intravenous infusion of phage-displayed antibody library in human cancer patients: enrichment and cancer-specificity of tumor-homing phage-antibodies

Phage display is a powerful method for target discovery and selection of ligands for cancer treatment and diagnosis. Our goal was to select tumor-binding antibodies in cancer patients. Eligibility criteria included absence of preexisting anti-phage-antibodies and a Stage IV cancer status. All patients were intravenously administered 1 × 10(11) TUs/kg of an scFv library 1 to 4 h before surgical resection of their tumors. No significant adverse events related to the phage library infusion were observed. Phage were successfully recovered from all tumors. Individual clones from each patient were assessed for binding to the tumor from which clones were recovered. Multiple tumor-binding phage-antibodies were identified. Soluble scFv antibodies were produced from the phage clones showing higher tumor binding. The tumor-homing phage-antibodies and derived soluble scFvs were found to bind varying numbers (0-5) of 8 tested normal human tissues (breast, cervix, colon, kidney, liver, spleen, skin, and uterus). The clones that showed high tumor-specificity were found to bind corresponding tumors from other patients also. Clone enrichment was observed based on tumor binding and DNA sequence data. Clone sequences of multiple variable regions showed significant matches to certain cancer-related antibodies. One of the clones (07-2,355) that was found to share a 12-amino-acid-long motif with a reported IL-17A antibody was further studied for competitive binding for possible antigen target identification. We conclude that these outcomes support the safety and utility of phage display library panning in cancer patients for ligand selection and target discovery for cancer treatment and diagnosis.

Abstract 4736: Generation of tumor-specific antibodies from sentinel lymph nodes of breast cancer patients using hybridoma technology

The field of targeted therapy is providing an entirely new generation of highly active anticancer drugs. For example, addition of a targeted drug to a chemotherapy regimen has shown improved survival in the treatment of breast cancer (Herceptin) and colorectal cancer (Avastin). Main problems with this kind of therapy are that many patients are not candidates because their tumors do not overexpress the drug target and that patient develop resistance to the targeted drug. A method to rapidly develop different sets of therapeutic antibodies (Abs) would greatly contribute to the field of targeted anticancer therapy. Even more novel would be methods that can develop Abs derived from individual patients. The rationale behind this concept is solidly supported by a large number of SEREX studies demonstrating that the sera of cancer patients do contain autoantibodies against their own tumors. These autoantibodies may show greater cancer specificity as tolerance mechanisms usually inhibit Ab production against normal cells. We generated hybridomas from the sentinel nodes of 29 breast cancer patients. Surgically removed fresh breast tumors and sentinel nodes were used for this study. Sentinel lymph node cells were harvested by either scraping the cut surface or by removing a 2 mm slice of the nodes. Lymph nodes were mechanically disaggregated and sieved before Ficoll gradient centrifugation. The yield of lymphocytes varied from 0.5 to 50x106 cells. Following stimulation, mononuclear cells were fused with plasmacytoma P3X63.Ag8.653 under hypo-osmolar condition, using BTX Electro Cell Manipulator and microslide electrodes. Each immunoglobulin secreting clone was evaluated with ELISA for binding to a panel of breast cancer cell lines representing the 4 subclasses of breast cancer, and 2 non-cancer breast epithelial cell lines. Tumor cell lysate-binding was observed in 28% of the hybridoma clones. The lysate-binding clones were further evaluated with whole cell imaging, flow cytometry, and Western blotting. Approximately 10% of the tumor-binding clones were found to bind whole tumor cells with unique binding patterns. These clones were also found to bind to the patient's own tumor. Thus, we have identified several tumor-specific autoantibodies from breast cancer patients. Successful outcome of these experiments demonstrate the feasibility of rapidly generating human monoclonal Abs that have a great potential for tumor target discovery and their use in cancer therapy and diagnosis. The innovative aspect of this strategy is the exploitation of the cancer patient's own immune repertoire for generating therapeutic Abs. This is in contrast to most of the currently available therapeutic Abs for clinical use, which are derived from chimerization and humanization of rodent Abs. No currently available antibody is developed through the selective and regulatory processes of the human immune system.

Citation Format: Girja S. Shukla, Stephanie C. Pero, Yu-Jing Sun, Chelsea Carman, David N. Krag. Generation of tumor-specific antibodies from sentinel lymph nodes of breast cancer patients using hybridoma technology. [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 4736. doi:10.1158/1538-7445.AM2013-4736

Abstract 2511: Tumor cell-specific full-length human antibodies from Epstein-Barr virus-immortalized sentinel node B lymphocytes from breast cancer patients

It has been demonstrated that patients do develop autoantibodies to a solid tumor, but the level of the antibody response is too low to have significant antitumor effect. This means that there are B cell clones producing antitumor antibodies, but they are suppressed (or not activated sufficiently) by the complex immunoregulatory systems in cancer patients. When the B cell repertoire is transferred out of the human cancer patient, in vitro methods allow the selection of anti-tumor antibodies and can then allow unrestricted production of sufficient quantities for clinical use. There are a variety of options available for the in vitro generation of antibodies from human B cells that are basically based on the recombinant production following gene cloning, and on B cell immortalization, their propagation and antibody secretion in cell culture. Most popular forms of recombinant expression of antibodies are phage displayed scFv and Fab antibody libraries, which have disadvantage of loss of original heavy and light chain pairings, inability to display full antibody, and production in bacterial host cells. The antibodies produced by B cell immortalization do not suffer from these drawbacks and retain their original heavy and light chain pairings. We collected fresh sentinel nodes and breast tumor specimens from cancer patients and following B lymphocyte separation from sentinel nodes they were immortalized using Epstein-Barr virus (EBV). The antibodies secreted from the immortalized B cells were studied for binding to the tumor cells of established cell lines and to the tumor cell surface protein preparations from the same patient that the B cells were derived. Using cell-ELISA and dot blot techniques, we identified several antibodies that were found to bind intact tumor cells and to the cell surface protein preparations derived from patient's tumors. It is expected that cancer-specific antibodies identified by B cell immortalization method will be candidates for therapeutic and diagnostic applications and further studies to identify their target antigens and bioactivity will help in understanding the humoral immune response to these breast cancer antigens and their role in the cell proliferation and tumor growth. An innovative aspect of this study is the exploitation of the cancer patients’ own immune repertoire for generating therapeutic antibodies. This is in contrast to most of the currently available therapeutic antibodies for clinical use, which are derived from chimerization or humanization of rodent antibodies. Currently no commercially available mAb has been developed through the selective and regulatory processes of the human immune system. The ability to reliably and rapidly generate tumor-binding antibodies from patients’ own B cells will have broad applicability and provide a platform for developing innovative therapeutic and diagnostic reagents.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2511. doi:1538-7445.AM2012-2511

Structural basis of binding by cyclic nonphosphorylated peptide antagonists of Grb7 implicated in breast cancer progression

Growth-receptor-bound protein (Grb)7 is an adapter protein aberrantly overexpressed, along with the erbB-2 receptor in breast cancer and in other cancers. Normally recruited to focal adhesions with a role in cell migration, it is associated with erbB-2 in cancer cells and is found to exacerbate cancer progression via stimulation of cell migration and proliferation. The G7-18NATE peptide (sequence: WFEGYDNTFPC cyclized via a thioether bond) is a nonphosphorylated peptide that was developed for the specific inhibition of Grb7 by blocking its SH2 domain. Cell-permeable versions of G7-18NATE are effective in the reduction of migration and proliferation in Grb7-overexpressing cells. It thus represents a promising starting point for the development of a therapeutic against Grb7. Here, we report the crystal structure of the G7-18NATE peptide in complex with the Grb7-SH2 domain, revealing the structural basis for its interaction. We also report further rounds of phage display that have identified G7-18NATE analogues with micromolar affinity for Grb7-SH2. These peptides retained amino acids F2, G4, and F9, as well as the YDN motif that the structural biology study showed to be the main residues in contact with the Grb7-SH2 domain. Isothermal titration calorimetry measurements reveal similar and better binding affinity of these peptides compared with G7-18NATE. Together, this study facilitates the optimization of second-generation inhibitors of Grb7.

Abstract 1769: Phage display selection of cancer cell-binding and -internalizing ligands using random peptide libraries constructed at N-terminus of P99 cephalosporinase

The cancer researchers today are focused in developing new types of cancer treatments that use drugs or other substances to identify and kill cancer cells while doing very little or no damage to normal healthy cells. It is believed that an ability to home in on cancer cells makes chemotherapy both more effective and less likely to cause side effects. One of the strategies to achieve this goal depends on developing ligands that specifically bind/internalize to cancer cells and exert therapeutic effects of their own or guide a targeted delivery of a therapeutic agent (cytotoxic drug, gene, radionuclide, or enzyme) to the tumor cells. Phage display is one example of high throughput technologies that has been successfully utilized for the generation of massive ligand libraries and their selection against specific targets. We constructed novel phage-displayed random linear dodecapeptide (X12) and cysteine-constrained random decapeptide (CX10C) libraries at N-terminal end of the Enterobacter cloacae P99 cephalosporinase molecule (P99 β-lactamase: β-lactam hydrolase, E.C. # 3.5.2.6). The peptide-β-lactamase fusions were displayed at the amino terminus of the minor coat pIII protein of M13 filamentous phage. Several cancer cell-specific binding β-lactamase-peptide fusion ligands were isolated by selecting these libraries on live BT-474 human breast cancer cells. The identified ligands shared several significant motifs, which showed their selectivity and possible binding to some common cancer cell targets. β-Lactamase is a high turnover enzyme with several available chromogenic and fluorogenic substrates. The peptide fusion to this enzyme made the post-panning steps very fast and simple. The concentrations of β-lactamase-peptide fusions in phage samples, lysates and purified fusion proteins were normalized based on the β-lactamase activity. The clone screening was also based on assaying the residual cell-bound β-lactamase activity. Some of the cancer cell binding β-lactamase-peptide fusion proteins showed cell internalization by both immunofluorescence and β-lactamase activity-based procedures. The staining with FRET-based substrate CCF4 confirmed the functional integrity of the internalized β-lactamase, and demonstrated that at least a part of the internalized enzyme conjugate could escape the endosomal degradation pathway in intact form and reacted with the substrate present in the cytoplasm. The specificity of the selected ligands was assessed by studying their binding and internalization in 11 other cancer and non-cancer cell lines. The β-lactamase fusion to peptides not only accelerates the clone screening process but can also facilitate the tracking of ligand molecules in various biological studies. The cancer-specific affinity reagents selected from these libraries have a potential for their use in targeted therapies.

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 1769. doi:10.1158/1538-7445.AM2011-1769

Novel beta-lactamase-random peptide fusion libraries for phage display selection of cancer cell-targeting agents suitable for enzyme prodrug therapy

Novel phage-displayed random linear dodecapeptide (X(12)) and cysteine-constrained decapeptide (CX(10)C) libraries constructed in fusion to the amino-terminus of P99 beta-lactamase molecules were used for identifying beta-lactamase-linked cancer cell-specific ligands. The size and quality of both libraries were comparable to the standards of other reported phage display systems. Using the single-round panning method based on phage DNA recovery, we identified several beta-lactamase fusion peptides that specifically bind to live human breast cancer MDA-MB-361 cells. The beta-lactamase fusion to the peptides helped in conducting the enzyme activity-based clone normalization and cell-binding screening in a very time- and cost-efficient manner. The methods were suitable for 96-well readout as well as microscopic imaging. The success of the biopanning was indicated by the presence of approximately 40% cancer cell-specific clones among recovered phages. One of the binding clones appeared multiple times. The cancer cell-binding fusion peptides also shared several significant motifs. This opens a new way of preparing and selecting phage display libraries. The cancer cell-specific beta-lactamase-linked affinity reagents selected from these libraries can be used for any application that requires a reporter for tracking the ligand molecules. Furthermore, these affinity reagents have also a potential for their direct use in the targeted enzyme prodrug therapy of cancer.

Phage-displayed combinatorial peptide libraries in fusion to beta-lactamase as reporter for an accelerated clone screening: Potential uses of selected enzyme-linked affinity reagents in downstream applications

Phage-display selection of combinatorial libraries is a powerful technique for identifying binding ligands against desired targets. Evaluation of target binding capacity of multiple clones recovered from phage display selection to a specific target is laborious, time-consuming, and a rate-limiting step. We constructed phage-display combinatorial peptide libraries in fusion with a beta-lactamase enzyme, which acts as a reporter. Linear dodecapeptide and cysteine-constrained decapeptide libraries were created at the amino-terminus of the Enterobacter cloacae P99 cephalosporinase molecule (P99 beta-lactamase). The overall and positional diversity of amino acids in both libraries was similar to other phage-display systems. The libraries were selected against the extracellular domain of ErbB2 receptor (ErbB2(ECD)). The target-selected clones were already conjugated to an enzyme reporter, therefore, did not require subcloning or any other post-panning modifications. We used beta-lactamase enzyme activity-based assays for sample normalizations and clone binding evaluation. Clones were identified that bound to purified ErbB2(ECD) and ErbB2-overexpressing cell-lines. The peptide sequences of the selected binding clones shared significant motifs with several rationally designed peptide mimetics and phage-display derived peptides that have been reported to bind ErbB2(ECD). beta-Lactamase fusion to peptides saved time and resources otherwise required by the phage-ELISA of a typical phage display screening protocol. The beta-lactamase enzyme assay protocols is a one-step process that does not require secondary proteins, several steps of lengthy incubations, or washings and can be finished in a few minutes instead of hours. The clone screening protocol can be adopted for a high throughput platform. Target-specific beta-lactamase-linked affinity reagents selected by this procedure can be produced in bulk, purified, and used, without any modification, for a variety of downstream applications, including targeted prodrug therapy.

Abstract 720: Phage display selection of ligands against extracellular domain of ErbB2 receptor using novel β-lactamase-random peptide fusion libraries

There are now unprecedented opportunities for increased throughput to develop novel molecules that target cancer. Phage display is one example of a high throughput method of generating massive libraries of molecules that have different structural properties. We constructed novel phage-display random peptide libraries in fusion to β-lactamase (β-lactam hydrolase, E.C. # 3.5.2.6) enzyme as a reporter. The linear dodecapeptide (X12) and cysteine-constrained decapeptide (CX10C) libraries were created at the N-terminal end of the Enterobacter cloacae P99 cephalosporinase molecule (P99 β-lactamase), between the signal peptide and the enzyme protein. Peptide-β-lactamase fusions were displayed at the amino terminus of the minor coat pIII protein of filamentous (M13) phage. The overall representations of different amino acids in the random regions of both libraries were very good. The amino acid diversity at each position in the random regions of both the libraries was also good. The libraries were selected against the extracellular domain of ErbB2 receptor (ErbB2-ECD). The target-selected clones were already conjugated to an enzyme reporter, therefore, did not require subcloning or any other post-panning modifications. β-Lactamase is known for high turnover of its enzyme activity with several commercially available chromogenic and fluorogenic substrates. This helped us to develop a very sensitive and efficient assay for measuring concentrations and target-binding of β-lactamase-peptide fusion proteins in their both phage-displayed and soluble forms. The β-lactamase enzyme assay protocol is a one-step process and unlike a typical phage-ELISA it does not require secondary proteins, several steps of lengthy incubations, or washings and can be finished in a few minutes instead of hours. The clone screening protocol can be adopted for a high throughput platform. The identities of peptide-β-lactase fusion clones that bound to purified ErbB2-ECD and ErbB2-overexpressing MCF-7/ErbB2 and SK-BR-3 cell lines were determined by DNA sequencing of the random inserts. The peptide sequences of the selected binding clones were found to share significant motifs with several rationally designed peptide mimetics and phage-display derived peptides that have been reported to bind ErbB2-ECD. Target-specific β-lactamase-linked affinity reagents selected by this procedure can be produced in bulk and purified. The synthesis and successful use of cephalosporin prodrugs of mechanistically diverse anticancer agents, such as doxorubicin, taxol, platinum complexes, phenylenediamine mustard, and vinblastine have been reported in experimental studies. Using an appropriate β-lactam-substrate, the cancer cell-specific ligands selected from these libraries can be used directly for the targeted enzyme prodrug therapy and/or in vivo imaging of cancers.

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 720.

Cancer cell-specific internalizing ligands from phage displayed beta-lactamase-peptide fusion libraries

The present study was focused on identifying cancer cell-specific internalizing ligands using a new kind of phage display library in which the linear or cysteine-constrained random peptides were at amino-terminus fusion to catalytically active P99 beta-lactamase molecules. The size and quality of libraries were comparable to other reported phage display systems. Several cancer cell-specific binding and internalizing beta-lactamase-peptide fusion ligands were isolated by selecting these libraries on the live BT-474 human breast cancer cells. The identified ligands shared several significant motifs, which showed their selectivity and possible binding to some common cancer cell targets. The beta-lactamase fusion made the whole process of clone screening efficient and simple. The ligands selected from such libraries do not require peptide synthesis and modifications, and can be used directly for applications that require ligand tracking. In addition, the selected beta-lactamase-peptide ligands have a potential for their direct use in targeted enzyme prodrug therapy. The cancer-specific peptides can also be adopted for other kinds of targeted delivery protocols requiring cell-specific affinity reagents. This is first report on the selection of cell-internalized enzyme conjugates using phage display technology, which opens the possibility for new fusion libraries with other relevant enzymes.

Developing bifunctional beta-lactamase molecules with built-in target-recognizing module for prodrug therapy: identification of Enterobacter Cloacae P99 cephalosporinase loops suitable for randomization and phage-display selection

This study was focused on developing catalytically active beta-lactamase enzyme molecules that have target-recognizing sites built within their scaffold. Using phage-display approach, nine libraries were constructed by inserting the randomized linear or cysteine-constrained heptapeptides in the five different loops on the outer surface of P99 beta-lactamase molecule. The pIII signal peptide of Sec-pathway was employed for a periplasmic translocation of the beta-lactamase fusion protein, which we found more efficient than the DsbA signal peptide of SRP-pathway. The randomized heptapeptide loops replaced native amino acids between positions (34)Y-(37)K, (238)M-(246)A, (275)N-(280)A, (305)A-(311)S, or (329)I-(334)I of the P99 beta-lactamase molecules for generating the loop-1 to -5 libraries, respectively. The diversity of each loop library was judged by counting the primary and beta-lactamase-active clones. The linear peptide inserts in the loop-2 library showed the maximum number of the beta-lactamase-active clones, followed by the loop-5, loop-3, and loop-4. The insertion of the cysteine-constrained loops exhibited a dramatic loss of the enzyme-active beta-lactamase clones. The complexity of the loop-2 linear library, as determined by the frequency and diversity of amino acid distributions in the randomized region, appears consistent with the standards of other types of phage display library systems. The selection of the loop-2 linear library on streptavidin protein as a test target identified several beta-lactamase clones that specifically bound to streptavidin. In conclusion, this study identified the suitability of the loop-2 of P99 beta-lactamase for constructing a phage-display library of the beta-lactamase enzyme-active molecules that can be selected against a target. This is an enabling step in our long-term goal of developing bifunctional beta-lactamase molecules against cancer-specific targets for enzyme prodrug therapy of cancer.

Effect of manganese on the levels of DNA, RNA, DNase and RNase in cerebrum, cerebellum and rest of brain regions of rat

Levles of DNA, RNA, DNase, RNase and manganese in different regions of rat brain were studied after daily administration of manganese chloride (8 mg MnCl2-4H2O/kg intraperitoneally) for a period of 120 days. DNA and RNA contents decreased significantly in cerebrum, cerebellum and rest of the brain regions after manganese treatment. A decrease in the DNase and an increase in the RNase activity was observed in the cerebellum and rest of brain region of the manganese treated animals. The manganese content increased significantly in all the regions of the brain, the maximum concentration being in the rest of brain portion. The presence of excess manganese in brain presumably leads to alterations in the functional activity of lysosomal enzymes. The decrease in the levels of nucleic acids is perhaps a consequence of the degenerating and dead neurones.

Biopanning Phage-Display Libraries on Small Tissue Sections Captured by Laser Capture Microdissection

Phage-display technology has been widely used for developing tumor-targeting agents. Laser capture microdissection (LCM) has proven to be an accurate method to select specific cells from histological sections. Our goal was to develop a method to combine phage-display with LCM to obtain phage-displayed ligands that bind to selected cells in human solid tumors. Two panning strategies were evaluated and optimized. The first strategy was to pan on patient tissue mounted to LCM slides before LCM occurred. The poor panning output showed that phage did not tolerate the drying conditions during LCM. The second strategy was to pan on tumor cells from the patient tumor tissue that were isolated by LCM. The catapulted tumor cells were transferred to a filter unit which retained cells but allowed rinsing of unbound phage. Six commercially available filter units were evaluated and the one with the lowest nonspecific binding to phage was selected for the panning steps. The smallest number of cells (500) in which panning could be successfully accomplished was also determined. A micropipette system was developed to further decrease background by removing catapulted cells from the filter unit after panning was complete. This left behind nearly all background binding phage in the filter unit. This strategy led to the selection of individual phage antibody clones (5 out of 79 tested) specific for tumor cells of the patient's cancer tissue. Immunofluorescence staining on tumor tissues from the same patient showed that these clones have selective signals on tumor island cells, while the scFv library only showed low nonspecific signals on tumor tissues. We established a method of panning on a small number of LCM-captured solid tumor specimens. The quick identification of specific phage-displayed antibodies in the cancer tissue of human patients will greatly enhance the therapy and diagnosis of cancer.

Combination treatment with Grb7 peptide and Doxorubicin or Trastuzumab (Herceptin) results in cooperative cell growth inhibition in breast cancer cells

Grb7 has potential importance in the progression of cancer. We have previously identified a novel peptide that binds to the SH2 domain of Grb7 and inhibits its association with several different receptor tyrosine kinases. We have synthesised the Grb7 peptide, G7-18NATE, with two different cell penetrating peptides, Penetratin and Tat. In this study, we have shown that both Penetratin- and Tat-conjugated G7-18NATE peptides are able to inhibit the proliferation of SK-BR-3, ZR-75-30, MDA-MB-361 and MDA-MB-231 breast cancer cells. There was no significant effects on breast cancer MCF-7cells, non-malignant MCF 10A or 3T3 cells. In addition, there was no significant inhibition of proliferation by Penetratin or Tat alone or by their conjugates with arbitrary peptide sequence in any of the cell lines tested. We determined the EC₅₀ of G7-18NATE-P peptide for SK-BR-3 cell proliferation to be 7.663 × 10⁻⁶ M. Co-treatment of G7-18NATE-P peptide plus Doxorubicin in SK-BR-3 breast cancer cells resulted in an additional inhibition of proliferation, resulting in 56 and 84% decreases in the Doxorubicin EC₅₀ value in the presence of 5 × 10⁻⁶ and 1.0 × 10⁻⁵ M G7-18NATE-P peptide, respectively. Importantly, the co-treatment with Doxorubicin and the delivery peptide did not change the Doxorubicin EC₅₀. Since Grb7 associates with ErbB2, we assessed whether the peptide inhibitor would have a combined effect with a molecule that targets ErbB2, Herceptin. Co-treatment of Herceptin plus 1.0 × 10⁻⁵ M G7-18NATE-P peptide in SK-BR-3 cells resulted in a 46% decrease in the Herceptin EC₅₀ value and no decrease following the co-treatment with Herceptin and penetratin alone. This Grb7 peptide has potential to be developed as a therapeutic agent alone, in combination with traditional chemotherapy, or in combination with other targeting molecules.

Towards a ligand targeted enzyme prodrug therapy: Single round panning of a β-lactamase scaffold library on human cancer cells

A novel beta-lactamase scaffold library in which the target-binding moiety is built into the enzyme was generated using phage display technology. The binding element is composed of a fully randomized 8 amino acid loop inserted at position between Y34 and K37 on the outer surface of Enterobacter cloacae P99 cephalosporinase (beta-lactamase, E.C. 3.5.2.6) with all library members retaining catalytic activity. The frequency and diversity of amino acids distributions in peptide inserts from library clones were analyzed. The complexity of the randomized loop appears consistent with standards of other types of phage display library systems. The library was panned against SKBR3 human breast cancer cells in 1 round using rolling circle amplification of phage DNA to recover bound phage. Individual beta-lactamase clones, independent of phage, were rapidly assessed for their binding to SKBR3 cells using a simple high throughput screen based on cell-bound beta-lactamase activity. SKBR3 cell-binding beta-lactamase enzymes were also shown to bind specifically using an immunochemical method. Selected beta-lactamase clones were further studied for their protein expression, enzyme activity and binding to nontumor cell-lines. Overall, the approach outlined here offers the opportunity of rapidly selecting targeted beta-lactamase ligands that may have a potential for their use in enzyme prodrug therapy with cephalosporin-based prodrugs. It is expected that a similar approach will be useful in developing tumor-targeting molecules of several other enzyme candidates of cancer prodrug therapy.

Selection of Tumor-binding Ligands in Cancer Patients with Phage Display Libraries

Phage display has been used extensively in vitro and in animal models to generate ligands and to identify cancer-relevant targets. We report here the use of phage-display libraries in cancer patients to identify tumor-targeting ligands. Eight patients with stage IV cancer, including breast, melanoma, and pancreas, had phage-displayed random peptide or scFv library (1.6 x 10(8)-1 x 10(11) transducing units/kg) administered i.v.; tumors were excised after 30 minutes; and tumor-homing phage were recovered. In three patients, repeat panning was possible using phage recovered and amplified from that same patient's tumor. No serious side effects, including allergic reactions, were observed with up to three infusions. Patients developed antiphage antibodies that reached a submaximal level within the 10-day protocol window for serial phage administration. Tumor phage were recoverable from all the patients. Using a filter-based ELISA, several clones from a subset of the patients were identified that bound to a tumor from the same patient in which clones were recovered. The clone-binding to tumor was confirmed by immunostaining, bioassay, and real-time PCR-based methods. Binding studies with noncancer and cancer cell lines of the same histology showed specificity of the tumor-binding clones. Analysis of insert sequences of tumor-homing peptide clones showed several motifs, indicating nonrandom accumulation of clones in human tumors. This is the first reported series of cancer patients to receive phage library for serial panning of tumor targeting ligands. The lack of toxicity and the ability to recover clones with favorable characteristics are a first step for further research with this technology in cancer patients.

Selective delivery of therapeutic agents for the diagnosis and treatment of cancer

Research activity aimed towards achieving specific and targeted delivery of cancer therapeutics has expanded tremendously in the last decade, resulting in new ways of directing drugs to tumours, as well as new types of drugs. The available strategies exploit differences in the nature of normal and cancer cells and their microenvironment. The discovery and validation of cancer-associated markers, as well as corresponding ligands, is pivotal for developing selective delivery technology for cancer. Although most current clinical trials are either monoclonal antibody- or gene-based, methodological advances in combinatorial libraries of peptides, single chain variable fragments and small organic molecules are expected to change this scenario in the near future. Nanotechnology platforms today allow systematic and modular combinations of therapeutic agents and tumour-binding moieties that may generate novel, personalised agents for selective delivery in cancer. This paper discusses recent developments and future prospects of targeted delivery technologies in the management of cancer.

Phage display selection for cell-specific ligands: development of a screening procedure suitable for small tumor specimens

Phage display technology has been widely used for developing tumor-targeting agents. Most of the efforts were directed towards identifying phage-displayed ligands against cancer-relevant purified targets and cancer cell lines. Whole cell screening procedures typically use a relatively large sample size and are not ideally suited for complex tumor tissues. We describe here a screening protocol that is suitable for non-adherent tumor cells from biopsy specimens. It requires only approximately 20,000 cells/round for biopanning and approximately 10,000 cells/well for subsequent clone binding assessment by ELISA. We standardized the newly developed protocol using erbB2-overexpressing SKBR3 breast cancer cells and compared the results with conventional protocols employing about 10-times more plate-adhered fixed or live cells. The selection rate of SKBR3-binding clones from biopanning approximately 20,000 non-adherent SKBR3 cells by our filter cup protocol was comparable to that obtained from using approximately 200,000 plate-adhered cells. Assessment of clones selected from different phage libraries showed that clones from fixed or live cells, adherent or non-adherent cells, either biopanned in filter cup or plate share specific motifs and binding properties. Some of the clones from each biopanning protocol bound to purified erbB2 and shared motifs with erbB family of receptors and their known ligands. These results demonstrated that the protocol developed in this study was capable of selecting cell-specific ligands using relatively small numbers of cells. Screening cells from a fresh human breast cancer specimen using our protocol showed enrichment of tumor binding clones at successive rounds of selection and some of the selected clones were tumor-specific in comparison to normal breast cells. These protocols have direct application to screen for tumor-binding ligands with small tumor tissue specimens.

Selection of tumor-targeting agents on freshly excised human breast tumors using a phage display library

The selective delivery of therapeutic agents to tumor site without harming rest of the body is a major challenge in clinical oncology today. Phage display approach has been used for searching ligands for cell-surface macromolecules on cancer cells so that they can be employed as drug targeting agents. Although basic protocols for biopanning cells are available, they are not as such suitable for screening highly complex and diverse target as whole tumor. Present study is an attempt to select peptide ligands specific to whole tumors. The cells from freshly collected human breast tumors were biopanned with phage displayed disulfide-constrained random heptapeptide library, following subtraction on normal human breast cells. Comparative analysis of amino acid frequencies in tumor-selected peptides and in random peptides from unselected library showed that selection was not random. The binding assessment of tumor-selected clones, using highly sensitive chemiluminescence ELISA, demonstrated that 47-75% of selected clones, depending on a tumor, bound to tumor cells they were panned on. Furthermore, several clones bound exclusively or preferentially to tumor cells in comparison to normal breast cells. It was interesting to note that insert sequences of tumor-binding clones from different tumors shared significant motifs. It shows the possibility of identifying ligands that may bind to tumor-specific targets common in certain tumors. The results of this investigation on seven human breast tumors demonstrated that, using procedures developed in the present study, whole tumors can be panned successfully with phage displayed library and tumor-binding ligands can be identified rapidly in high throughput manner. This is an important enabling step in identifying lead molecules for developing novel, specific, and effective agents that can be used for the diagnosis and treatment of cancer.

A Sensitive and Rapid Chemiluminescence ELISA for Filamentous Bacteriophages

Filamentous bacteriophage (Ff) displayed random peptide and antibody libraries are widely used to identify specific, high affinity, binding ligands. A critical element in the identification of target-specific phages is to determine phage titers, not only at every round of selection, but also for normalizing phage titers of a set of individual clones for their comparative binding analysis. The conventional ELISA-based Ff titration methods require a minimum of 4-5 hr assay time and their lowest reported detection limit is approximately 50,000 particles/well. In this report, we present a sandwich ELISA that allows detection of approximately 1000 Ff particles/well in less than 2.5 hr. The values of correlation of coefficient (r2) for the curves at low phage concentrations (up to 106 TU/well) were about 0.999 in our ELISA. Experiments conducted at different temperatures suggest using 40 degrees C incubations when titering low phage concentration samples. Experiments were also conducted with conventional ELISA for comparison. Our ELISA method derives an advantage from using a chemiluminescence substrate that gives much larger signals and wide linear range of measurement, thus allowing discrimination between background and low Ff phage concentrations. In conclusion, the Ff titration method presented here is highly sensitive, rapid, and amenable to high throughput analysis.

Identification of a small peptide that inhibits the phosphorylation of ErbB2 and proliferation of ErbB2 overexpressing breast cancer cells

ErbB2 is overexpressed in approximately 30% of breast cancer patients with a correlation to poor prognosis. ErbB2 has been identified as a useful receptor for molecular targeting. A cyclic 20 amino acid phage display random peptide library was constructed using the fUSE5 gene III system. The library was panned against 2 different purified forms of the external domain of ErbB2. This resulted in the identification of several ErbB2-binding phage clones with variable binding to different ErbB2 preparations. One clone (EC-1) bound all preparations of ErbB2 including live cells and fresh frozen human breast cancer specimens. The synthetic peptide based on the deduced sequence of the EC-1 clone and its biotin-conjugated form retained binding affinity for purified ErbB2 and ErbB2 overexpressing cell lysates. EC-1 peptide was able to effectively inhibit the phosphorylation of ErbB2 on residues Y1248 and Y877 in a dose- and time-dependent manner. Furthermore, EC-1 peptide selectively inhibits the proliferation of ErbB2 overexpressing breast cancer cells. The linear portion of the cyclic EC-1 peptide was shown to be essential for binding ErbB2. In addition, 4 biased phage libraries were constructed allowing 4 different regions of the EC-1 peptide to have random sequence. Screening these EC-1 biased libraries did not result in higher affinity peptides but did demonstrate the importance of amino acids at position 1-4 on the N-terminal flanking arm and 11-15 within the cyclic ring. Interestingly, EC-1 contains homologous motifs with known ErbB receptor family ligands. We have identified a small peptide that binds to the extracellular domain of ErbB2, inhibits ErbB2 autophosphorylation and inhibits the proliferation of ErbB2 overexpressing cells. This supports the notion that small peptides can bind to targets important in cancer therapy even if a target does not have a natural ligand. Continuing research with this peptide includes increasing its affinity to ErbB2, evaluation of pharmacokinetics and evaluation of anti-proliferative effects with conjugate anti-cancer agents.

Cadmium-mediated oxidative stress in alveolar epithelial cells induces the expression of gamma-glutamylcysteine synthetase catalytic subunit and glutathione S-transferase alpha and pi isoforms: potential role of activator protein-1

Exposure of rat alveolar epithelial cells to 10 micromol/L CdCl2 causes time-dependent increases in steady-state mRNA levels of the gamma-glutamylcysteine synthetase catalytic (heavy) subunit (gamma-GCS) and of glutathione S-transferase isoforms (GST-alpha and GST-pi). The expression of gamma-GCS was significantly increased as early as 2 h after addition of cadmium. Maximal induction of gamma-GCS mRNA (approximately 4-fold), at 8 h, was subsequently followed by increases in gamma-GCS activity/protein and glutathione (GSH) levels. Maximal elevations in GST-pi (approximately 2-fold) and GST-alpha (approximately 10-fold) transcripts, at 8 and 24 h, respectively, were also accompanied by enhanced GST activity. Cadmium-induced oxidative stress, assessed by alterations in GSH homeostasis and an accelerated rate of intracellular oxidant production, could constitute early events in the signal transduction pathway mediating these responses. The dimeric transcription factor, activator protein-1 (AP-1), may also play a regulatory role in this process. This association is suggested by transcriptional activation of the immediate-early response genes, c-fos and c-jun, within 15 min after exposure to cadmium and by the enhancement of AP-1 DNA binding activity, involving a c-Jun protein complex, which is maximally induced (approximately 4-fold) by 2 h. These molecular changes likely function together to protect alveolar epithelial cells against cadmium toxicity.

Cadmium-induced elevations in the gene expression of the regulatory subunit of gamma-glutamylcysteine synthetase in rat lung and alveolar epithelial cells

The controlled step in de novo glutathione (GSH) synthesis is catalyzed by gamma-glutamylcysteine synthetase (gamma-GCS), a dimeric enzyme consisting of a heavy catalytic subunit (gamma-GCS-HS) and a light regulatory subunit (gamma-GCS-LS). We have previously reported that exposure to cadmium (Cd) induces pulmonary gamma-GCS-HS mRNA and protein, and that these alterations are accompanied by increases in GSH synthesis and its steady-state level. The current study was designed to test the hypothesis that Cd exposure also up-regulates the expression of the regulatory gamma-GCS subunit. By using northern blotting, we have demonstrated that a single Cd aerosol exposure of adult male Lewis rats results in time- and dose-dependent increases in pulmonary levels of gamma-GCS-LS mRNA. Transcripts of gamma-GCS-LS in rat lung are maximally elevated (8-fold) 2 h following Cd inhalation exposure and remain significantly higher than air controls at 24 h. This response is highly correlated with Cd dose, ranging from 0.9 to 5 mg Cd per m(3), and with lung Cd burden. We also observed Cd-induced up-regulation of gamma-GCS-LS mRNA expression in alveolar epithelial cells exposed to Cd in vitro, either acutely or after repeated passaging in Cd-containing medium. The magnitude of the gamma-GCS regulatory subunit induction observed in Cd-treated cells was approximately five times greater than the induction of the catalytic subunit. These modifications in the expression of gamma-GCS subunits may offer protection from Cd toxicity.

Suppressed oxidant-induced apoptosis in cadmium adapted alveolar epithelial cells and its potential involvement in cadmium carcinogenesis

Apoptosis involves a series of genetically programmed events associated with endonucleolytic cleavage of DNA. This process is triggered by a variety of agents, including oxidants such as hydrogen peroxide (H(2)O(2)) and it plays a key role in eliminating pre-neoplastic cells from the lung. Failure to do so could favor tumor promotion. The current study demonstrated that alveolar epithelial cells, adapted to cadmium (CdCl(2)) by repeated in vitro exposure, exhibit lower levels of H(2)O(2)-induced apoptosis than similarly challenged non-adapted cells. An immunologic assay, measuring cytoplasmic histone-associated DNA fragments, indicated maximal apoptosis 24 h after exposure to 400 microM H(2)O(2). Non-adapted cells showed a 13-fold increase in oxidant-induced apoptosis while Cd-adapted cells had only a 4-fold elevation. A terminal deoxyribonucleotidyl transferase mediated dUTP nick end labeling (TUNEL) method was used to assess the percentage of cells with DNA breaks consistent with apoptosis. Cd-adapted and non-adapted cells that were not exposed to H(2)O(2) did not differ in TUNEL positivity. However, after H(2)O(2) treatment, the percentage of TUNEL positive cells was 4-fold higher in non-adapted cultures than in adapted ones. Suppression of oxidant-induced apoptosis is due, in part, to up-regulation in the gene expression of several resistance factors including metallothioneins (MT-1 and MT-2), glutathione S-transferases (GST-alpha and GST-pi), and gamma-glutamylcysteine synthetase catalytic subunit (gamma-GCS). These steady-state mRNA changes, determined by Northern blotting, were accompanied by increased levels of MT and gamma-GCS protein, GST activity, and glutathione (GSH). Suppressed oxidant-induced apoptosis, resulting at least in part from these response modifications, could leave pre-neoplastic or neoplastic cells alive, favor clonal expansion, and ultimately lead to cancer development.

Cerebral antioxidant status and free radical generation following glutathione depletion and subsequent recovery

This study was aimed to evaluate the oxidative damage, production of reactive oxygen species and the status of antioxidative defenses following cerebral GSH depletion induced by two classical depletors, diethylmaleate (DEM, 3 mmol/kg, i.p.) and phorone (PHO, 4 mmol/kg, i.p.). The treatment decreased (40-43%) brain glutathione levels at 2 h, followed by a partial recovery at 24 h. Cerebral glutathione depletion by these agents increased the levels of superoxide anion and hydroxyl radical at both the time intervals; however, hydrogen peroxide was high at 24 h only. It also produced a dramatic increase in the protein carbonyls at 2 h but not at 24h, without any significant effect on lipid peroxidation and conjugated diene levels. These rats showed a significantly lowered superoxide dismutase activity both at 2 h and 24 h of exposure, as compared to controls. Glutathione depletion enhanced catalase activity markedly at 2 h, followed by some recovery at 24 h. While Se-independent glutathione peroxidase (GPx) and glutathione S-transferase activities were increased at both 2 and 24 h time intervals, Se-dependent GPx and glucose-6-phosphate dehydrogenase were induced at 2 h only. Glutathione depletion decreased ceruloplasmin and vitamin E levels significantly at 2 h. However, ascorbic acid remained unaffected. It may be concluded that an acute cerebral glutathione depletion generates higher levels of reactive oxygen species, which may be responsible for oxidative modification of proteins. Some of these changes appear to recover soon after an activation of a variety of cellular antioxidant defense mechanisms and glutathione restoration. It appears that central nervous system is highly vulnerable to oxidative damage following a moderate glutathione depletion that may result from certain diseases or xenobiotic exposures.

Enhanced expression of pulmonary gamma-glutamylcysteine synthetase heavy subunit in rats exposed to cadmium aerosols

This investigation sought to determine the effect of cadmium (Cd) aerosol exposure on the pulmonary expression of the heavy subunit (HS) of gamma-glutamylcysteine synthetase (gamma-GCS), the rate-limiting enzyme in de novo synthesis of glutathione (GSH). Using Northern hybridization analysis, we demonstrated that CdO inhalation caused time- and dose-dependent increases in the steady-state levels of gamma-GCS-HS mRNA that were highly correlated with lung Cd burden. Observed increases in gamma-GCS-HS gene expression were maximal 2 h following a single aerosol exposure to Cd and appeared to be triggered by an oxidant stress, characterized by a decline in the reduced to oxidized glutathione ratio. Immunoblotting of proteins in lung extracts from treated and untreated animals produced a single protein band corresponding to a molecular weight of 73 kDa. Elevated levels of gamma-GCS-HS mRNA and gamma-GCS-HS protein in lungs of Cd-exposed animals were also accompanied by higher gamma-GCS enzymatic activity and elevations in glutathione (GSH). Immunohistochemical and in situ hybridization studies were used to identify compartments in the lung where Cd-induced expression of gamma-GCS-HS was localized. The most prominent staining for gamma-GCS-HS protein and gamma-GCS-HS mRNA was observed in the alveolar epithelium of Cd-exposed animals. Quantitative image analysis confirmed a good agreement between relative levels of protein and mRNA transcripts for gamma-GCS-HS. These observations suggest that resistance to Cd toxicity in the lung may reflect the ability of specific lung cells to upregulate gamma-GCS expression and increase de novo GSH synthesis as an adaptive response.

Potential role of cerebral glutathione in the maintenance of blood-brain barrier integrity in rat

Using the model of glutathione (GSH) depletion, possible role of GSH in the maintenance of blood-brain barrier (BBB) integrity was evaluated in rats. Administration (i.p.) of GSH depletors, diethyl maleate (DEM, 1-4 mmol/kg), phorone (2-3 mmol/kg) and 2-cyclohexene-1-one (CHX, 1 mmol/kg), to male adults was found to deplete brain and liver GSH and increase the BBB permeability to micromolecular tracers (sodium fluorescein and [14C]sucrose) in a dose-dependent manner at 2h. However, BBB permeability to macromolecular tracers such as horseradish peroxidase and Evan's blue remained unaltered. It was also shown that observed BBB permeability dysfunction was associated with brain GSH depletion. A lower magnitude of BBB increase in rat neonates, as compared to adults, indicated a possible bigger role of GSH in the BBB function of mature brain. The treatment with N-acetylcysteine, methionine and GSH provided a partial to full protection against DEM-induced brain (microvessel) GSH depletion and BBB dysfunction; however, the treatment with alpha-tocopherol, ascorbic acid and turmeric were not effective. Our studies showed that cerebral GSH plays an important role in maintaining the functional BBB integrity.

Developmental pattern of reactive oxygen species generation and antioxidative defense machinery in rat cerebral microvessels

The developmental profile of certain enzymatic antioxidants as well as the generation of reactive oxygen species was studied in the rat cerebral microvessels during first three weeks of life and the levels were compared to those present in adults. The data showed a higher generation of superoxide anion (+67%) and H2O2 (+200%) at postnatal day (PND) 21. Superoxide anion production was significantly lower (-24%) at PND 14 and almost comparable to adult values at PND 7. The activity of superoxide dismutase increased with development and attained an adult level at PND 21. Catalase was higher in neonates with a maximum activity at PND 7 and 14 (+68, 69%). The measurement of microvessel glutathione and glutathione-related antioxidant enzymes showed that glutathione level was higher at PND 7, which declined to an adult level at PND 14. Se-dependent GPx showed a marked increase between PND 14 and 21, however, it declined in adults. The activity of Se-independent glutathione peroxidase was very low in cerebral microvessels. Glutathione reductase activity in 7-day-old, that was comparable to adult level, declined at PND 14 and 21. The level of glutathione S-transferase was higher (+43%) at PND 21. The activity of microvessel marker enzyme gamma-glutatmyl transpeptidase increased with age, whereas, alkaline phosphatase showed a slight increase up to PND 14 and thereafter it declined. Lipid peroxidation was found to be significantly lower (-18%) at PND 21 as compared to adults. It may be concluded that developing cerebral microvessels contain high levels of several antioxidant enzymes that are more or equal to those present in adult brain microvessels.

Glutathione depletion and oxidative damage in mitochondria following exposure to cadmium in rat liver and kidney

The dose-dependent effects of cadmium (Cd) on mitochondria and post-mitochondrial supernatant (PMS) of liver and kidney were investigated in adult male albino rats. Two groups of rats were injected intraperitoneally with 0.1 mg Cd/kg body weight and 1 mg/kg body weight, respectively, for a period of 3 months (5 days/week). This resulted in a significant decrease in total glutathione (GSH) levels, irrespective of the doses, in mitochondrial as well as in PMS fractions of liver and kidney. In contrast, end products of lipid and protein were significantly increased in a dose-dependent manner in subcellular fractions of liver and kidney. These results suggest that the depletion of tissue glutathione levels is not a primary reason of the observed oxidative damage in liver and kidney caused by Cd.

Functional impairment of blood-brain barrier following pesticide exposure during early development in rats

1. The effect of certain pesticides on the functional integrity of the developing blood-brain barrier (BBB) was studied following single and repeated exposure, and after subsequent withdrawal in rats. 2. Ten-day-old rat pups exposed orally to quinalphos (QP, organophosphate), cypermethrin (CM, pyrethroid) and lindane (LD, organochlorine) at a dose of 1/50th of LD50, showed a significant increase in the brain uptake index (BUI) for a micromolecular tracer, sodium fluorescein (SF), by 97, 37 and 72%, respectively, after 2 h. Residual increases in the BUI were found even after 3 days of the single treatment of QP (28%) and LD (23%). 3. Repeated exposure for 8 days (postnatal days (PND) 10-17) with QP, CM and LD increased the BBB permeability by 130, 80 and 50%, respectively. Recovery from these changes was complete in QP and LD-treated animals after 13 days (PND 18-30) of withdrawal. However, CM showed persistent effects that were normalized only after 43 days (PND 18-60) of withdrawal. 4. A single dose reduced to 1/100th of LD50 also increased BUI in 10-day-old rat pups following QP (20%) and CM (28%) exposure at 2 h. 5. An age-dependent effect of these pesticides was evident from the study showing higher magnitude of BUI changes in 10-day-old rats as compared to that in 15-day-old rats. Furthermore, adult rats did not show any effect on BBB permeability even at a higher dose (1/25th of LD50) of these pesticides given alone or in combination with piperonyl butoxide (600 mg/kg, i.p.) for 3 consecutive days. 6. This study showed that developing BBB is highly vulnerable to single or repeated exposure of certain pesticides. The observed persistent effects during brain development even after withdrawal of the treatment may produce some neurological dysfunction at later life as well.

Characterization of cadmium-induced apoptosis in rat lung epithelial cells: evidence for the participation of oxidant stress

The mode of cadmium-induced cell death was investigated in a rat lung epithelial cell line. Cells, grown to near confluence, were exposed to 0-30 microM CdCl2 for 0-72 h. Phase contrast microscopy and fluorescent nuclear staining showed that Cd caused morphological alterations in lung epithelial cells that are characteristic of apoptosis. These changes included cell shrinkage, detachment of the cell from its neighbors, cytoplasmic and chromatin condensation, and fragmentation of the nucleus into multiple chromatin bodies surrounded by remnants of the nuclear envelope. Apoptotic DNA degradation was validated and quantitated using a sensitive enzyme-linked immunosorbent assay (ELISA) which measures the amount of histone-bound DNA fragments in the cytosol. Using this technique, a maximum level of apoptosis (5-fold higher than control) was observed in cultures exposed for 48 h to 20 microM CdCl2. The terminal deoxyribonucleotidyl transferase mediated dUTP nick end labeling method (TUNEL) was subsequently used to determine the percentage of cells that contained Cd-induced DNA strand breaks. After 48 h, approximately 54% of the cells exposed to 20 microM Cd were TUNEL positive compared to less than 2% for control cells. Although the mechanisms by which Cd initiates apoptosis in these cells are presently not known, reactive oxygen species are likely to play a role. This possibility is supported by the finding that the first morphological features indicative of apoptosis were preceded by the up-regulation of oxidant stress genes (glutathione S-transferase-alpha, gamma-glutamylcysteine synthetase, and metallothionein-1), activation of redox sensitive transcription factors (AP-1 and NF-kappaB), and changes in various forms of glutathione (reduced, oxidized, and protein-bound).

Effect of pyrethroid-based liquid mosquito repellent inhalation on the blood-brain barrier function and oxidative damage in selected organs of developing rats

Pesticides have been implicated in various neurological disorders in humans and experimental animals. Our earlier studies have demonstrated a high vulnerability of developing blood-brain barrier (BBB) towards very low level exposure of quinalphos, cypermethrin and lindane. Earlier it has been observed that a cypermethrin-induced increase in the BBB permeability of neonatal rats was found to be persistent, requiring a longer period of withdrawal for complete recovery. These observations lead us to investigate the effect of a commonly available liquid mosquito repellent (MR) containing a pyrethroid compound, allethrin (3.6% w/v), on the functional integrity of the developing BBB and on certain parameters of oxidative damage in brain, liver and kidney. Two-day-old rat pups were allowed to inhale the MR (18 h per day) for 8 days (postnatal days (PND) 2-9). Rats exposed to MR were further withdrawn from the exposure for 8 days (PND 10-17) to study whether the changes induced following inhalation are reversible. Results of the study have shown a significant increase in the BBB permeability (45%) of the MR-exposed rat pups to a micromolecular tracer, sodium fluorescein (mol. wt. 376), used for the quantitative assessment of the BBB permeability, suggesting a delayed maturity of the BBB system. Brain glutathione (GSH) levels were also decreased (17%) in the exposed individuals. The oxidatively damaged end-products of lipids, measured as lipid hydroperoxides and conjugated dienes, were found to be increased in brain (42%, 16%), liver (34%, 20%) and kidney (68%, 29%), respectively. The oxidative product of protein, measured as protein carbonyls, was also increased significantly in liver (43%) and kidney (16%) of the MR-exposed rat pups as compared to age-matched controls. The biochemical changes that occurred in the BBB permeability and the oxidatively damaged end-products following MR inhalation in neonatal rats were, however, found to be completely recovered except for an increase in brain GSH (28%) level. The results suggest the possibility of health risk due to exposure to pesticide-based mosquito repellents, especially when exposure takes place in individuals at an early age.

Profile of reactive oxygen species generation and antioxidative mechanisms in the maturing rat kidney

The antioxidative potential and reactive oxygen species generation were assessed in rat kidney during early critical periods of development and maturation. Superoxide anion generation was found to be low in kidney during early postnatal days of development, whereas hydrogen peroxide levels remained unaltered during development. The levels of thiobarbituric acid reactive substances and protein carbonyls in developing kidney were higher during early postnatal days, up to 26 days after birth, compared to the adult levels. Kidney sulphydryl contents were significantly less during early periods (9 days postnatally) of development compared to adults but attain adult value by postnatal day 26. The levels of ascorbic acid and ceruloplasmin were also higher in developing kidney than in adults. Among enzymic antioxidants, the levels of glutathione peroxidase (GPx) enzyme in developing kidney were high during the early developmental period of the study as compared to adults; however, superoxide dismutase (SOD), catalase (CAT) and glutathione reductase (GR) were found to be significantly low at early postnatal days up to 16 days of age, which subsequently attained maturational level by the age of 26 days. The levels of antioxidant enzymes and sulphydryl contents in the developing kidney during early periods after birth are low but they increase subsequently with increasing age. Therefore, the present finding suggests that immature kidneys are in a highly dynamic stage of development during the early period and are equipped with antioxidative defence mechanisms that may have a predominant role in protecting against oxidative challenge.

Effects of neonatal quinalphos exposure and subsequent withdrawal on free radical generation and antioxidative defenses in developing rat brain

Ten-day-old rat pups were given quinalphos (QP, 0.5 mg kg(-1)) orally up to postnatal days (PND) 21 or 45. A group of rats exposed to QP was withdrawn from the treatment at PND 21 and was killed at PND 45 for the withdrawal study. Acetylcholinesterase decreased in the brain and blood after QP exposure but recovered after withdrawal. Superoxide radical generation in brain was increased by 43%, 59% and 39% following exposure up to PND 21 and 45 and in the withdrawal group, respectively. Quinalphos did not alter hydrogen peroxide formation but increased hydroxyl radical (19%) production at PND 45. Quinalphos elevated the activities of superoxide dismutase by 30%, (although the increase from 0.24 to 0.31 was physiologically not significant) and catalase by 50% at PND 21, which up on withdrawal of the exposure at PND 22 recovered partially or completely at PND 45. However, the continuous exposure up to PND 45 decreased superoxide dismutase (63%) and catalase (31%) activities. Selenium-independent glutathione peroxidase (GPx) was increased at PND 21 (31%) and PND 45 (152%) after QP exposure and there was complete recovery after withdrawal. Selenium-dependent GPx, which was elevated slightly at PND 21, was also normalized after withdrawal. Prolonged exposure to QP did not alter the ascorbic acid content and produced a marked decrease in cerruloplasmin (46%) levels. Brain glutathione levels increased marginally in QP-exposed rats and became normal in the withdrawal group. Quinalphos exposure up to PND 45 enhanced brain lipid peroxidation (28%) and decreased vitamin E levels (15%). It appears that neonatal QP exposure produces cerebral oxidative stress, which may result in deleterious effects on central nervous system function immediately and in later life.