Biomedical subjects

Ira Pastan

Publications and source records attributed to Ira Pastan.

85 records · Page 5Linked to original sources

PubMed2002

Roles of inhibitory interneurons in the cerebellar cortex.

The roles of inhibitory interneurons in the cerebellar cortex were investigated. First, Golgi cells were specifically eliminated in transgenic mice in which Golgi cells expressed human interleukin-2 receptor alpha subunit (IL2Ralpha). Injection of exotoxin coupled to anti-IL2Ralpha antibody in the cerebellum of the transgenic mouse eliminated Golgi cells and abolished GABA and synaptic inhibition in the granular layer. After elimination of Golgi cells, acute severe ataxia and subsequent mild motor discoordination were observed. In the latter chronic phase, NMDA receptor-mediated synaptic response was reduced in granule cells. Our findings indicate that elimination of GABAergic inhibition in the granular layer caused overexcitation of granule cells resulting in severe ataxia, and then NMDA receptors in granule cells were downregulated, compensating for the reduction of GABAergic inhibition and improving motor control. In the second part, we report on the regulation mechanism of synaptic plasticity at inhibitory synapses on Purkinje cells (PCs). Inhibitory synaptic transmission on a PC is potentiated after repetitive PC depolarization. This synaptic plasticity (rebound potentiation, RP) was suppressed when a presynaptic neuron was activated during the PC depolarization. This synaptic regulation is unique in the sense that the homosynaptic activity suppresses the induction of synaptic plasticity. The mechanism of how presynaptic activity suppresses RP was examined. GABA released from the presynaptic terminal activated not only GABA(A) receptor but also GABA(B) receptor. The latter was coupled to Gi/o proteins, which downregulated adenylyl cyclase reducing cAMP and inactivated cAMP-dependent protein kinase (PKA). Downregulation of PKA suppressed RP induction.

Animals↗

PubMed2002

Improved cytotoxic activity toward cell lines and fresh leukemia cells of a mutant anti-CD22 immunotoxin obtained by antibody phage display.

Recombinant immunotoxins are fusion proteins composed of the Fv domains of antibodies fused to bacterial or plant toxins that are being developed for the targeted therapy of cancer. RFB4 (Fv)-Pseudomonas exotoxin 38 (PE38) is an immunotoxin that targets CD22 expressed on B cells and B-cell malignancies. A disulfide-stabilized form of RFB4 (Fv)-PE38 is being evaluated in a Phase I clinical trial. The aim of the present study was to improve the activity of RFB4 (Fv)-PE38 to more effectively treat patients with leukemias and lymphomas. To increase the affinity of RFB4 (Fv), we used the techniques of phage display and hot spot mutagenesis. We identified mutational hot spot sequences in heavy chain complementary determining region 3 (V(H) CDR3) and randomized these in a phage display library. Mutant phages were panned on CD22-positive Daudi cells. A variety of mutant Fvs were obtained, and the corresponding immunotoxins were prepared. Several mutant immunotoxins with increased binding affinity and cytotoxic activity were obtained. The most active immunotoxin contained amino acid residues Thr-His-Trp (THW) in place of Ser-Ser-Tyr (SSY) at positions 100, 100A, and 100B of the Fv and had an affinity improved from 85 nM to 6 nM. The THW mutant had a 5- to 10-fold increase in activity on various CD22-positive cell lines and was up to 50 times more cytotoxic to cells from patients with chronic lymphocytic leukemia and hairy-cell leukemia.

Amino Acid Sequence↗

PubMed2002

Novel anti-CD30 recombinant immunotoxins containing disulfide-stabilized Fv fragments.

PURPOSE: To develop a novel targeting reagent to CD30 expressed on Hodgkin'sdisease and anaplastic large cell lymphoma, we made a panel of recombinant immunotoxins specific for CD30 using Fvs of newly produced anti-CD30 monoclonal antibodies (MAbs) and a M(r) 38,000 truncated mutant of Pseudomonas exotoxin. EXPERIMENTAL DESIGN: A group of MAbs against CD30 was produced and characterized for their reactivity and epitopes. Recombinant immunotoxins were made using the Fv genes cloned from the hybridomas. Their cytotoxic activities were examined on various CD30-positive cell lines. RESULTS: Six MAbs were produced. All reacted with recombinant soluble CD30 and to a CD30-Fc fusion protein, and bound to native CD30 expressed on Hodgkin's lymphoma-derived cell lines. The epitopes of the six MAbs were classified into two groups by a mutual competition assay for the binding to CD30 on cells. Sequencing the cDNAs revealed that all of the variable chains are unique except one valiable light that is shared by two MAbs. We made four disulfide stabilized Fv-based recombinant immunotoxins, in which the valiable heavy, which is genetically fused with truncated mutant of Pseudomonas exotoxin, forms a disulfide bond with the valiable light. The purified immunotoxins bound to recombinant soluble CD30 immobilized on a biosensor chip with K(d)s of 4-400 nM. Fluorescence-activated cell sorter analysis confirmed their specific binding. In vitro cytotoxicity tests showed that the immunotoxins specifically kill a variety of CD30-positive lymphoma cell lines as well as CD30-transfected A431 cells. The IC(50) ranged from 0.3 to 100 ng/ml. CONCLUSIONS: Four anti-CD30 disulfide stabilized Fv immunotoxins were successfully produced. Two of these showed good cytotoxic activity to various CD30-positive cell lines. These newly produced immunotoxins should be additionally evaluated for the treatment of CD30-positive lymphomas.

ADP Ribose Transferases↗

PubMed2002

Immunotoxins in cancer therapy.

Several antibodies have now been approved for the therapy of cancer. Two of these, rituximab (Rituxan) and alemtuzumab (CAMPATH; ILEX Oncology Inc), are capable of inducing cell death and tumor regressions when given alone. The third, trastuzumab (Herceptin), is not very effective by itself, but does potentiate the activity of paclitaxel (Taxol) and other chemotherapeutic agents. Unfortunately, most antibodies do not kill cancer cells unless they are armed with a cytotoxic agent, such as a radioisotope, a cytotoxic drug, or a protein toxin. Each of these have advantages and disadvantages.

Animals↗

PubMed2002

Antitumor activity of SS(dsFv)PE38 and SS1(dsFv)PE38, recombinant antimesothelin immunotoxins against human gynecologic cancers grown in organotypic culture in vitro.

PURPOSE: Mesothelin, a cell surface glycoprotein overexpressed in ovarian cancer, mesotheliomas, and some squamous cell carcinomas, is an attractive candidate for targeted therapy because it is not shed in significant amounts into the bloodstream and is not present in significant amounts on normal human tissues except for mesothelial cells. The objective of this study was to determine the antitumor activity of SS1(dsFv)PE38, a recombinant antimesothelin immunotoxin, against human gynecologic tumors grown in short-term culture in vitro. EXPERIMENTAL DESIGN: Tumor cells obtained from primary cultures of five ovarian and one cervical tumor were mixed with an equal proportion of NIH-3T3 fibroblasts and plated inside collagen gels in tissue culture plates. After 4-7 days of growth, these organotypic cultures were treated with media alone, SS1(dsFv)PE38, and a control immunotoxin RFB4(dsFv)PE38, which targets the CD22 antigen not present on gynecologic tumors, every other day x 3. The organotypic culture gels were then formalin fixed, paraffin embedded, and evaluated for immunotoxin sensitivity using light microscopic examination of H&E-stained slides and also evaluated for apoptosis using the terminal deoxynucleotidyl transferase-mediated nick end labeling assay. RESULTS: Tumors expressing mesothelin showed a significant dose-dependent sensitivity to SS1(dsFv)PE38 even at concentrations as low as 1 ng/ml, whereas no antitumor activity was seen at 100 ng/ml in tumors that did not express mesothelin. This activity was specifically attributable to mesothelin targeting because RFB4 (dsFv)-PE38 had no activity against mesothelin-expressing tumors. CONCLUSIONS: These results demonstrate that ovarian and cervical tumor cells obtained from patients can be grown in short-term culture using an organotypic culture model. Our results also show low concentrations of an immunotoxin targeting mesothelin is cytotoxic to mesothelin-expressing human tumors by inducing apoptosis.

3T3 Cells↗

PubMed2002

Targeted therapy against human lung cancer in nude mice by high-affinity recombinant antimesothelin single-chain Fv immunotoxin.

Several tumors, including mesothelioma and ovarian cancer, can overexpress mesothelin, a glycosylphosphatidylinositol-linked differentiation glycoprotein. The membrane-bound type of mesothelin is found in the blood of cancer patients at a very low level, which makes mesothelin a good candidate for targeted therapy of certain cancers. An antimesothelin disulfide-linked Fv (SS1 Fv) was fused to a truncated mutant of Pseudomonas exotoxin A to produce the recombinant immunotoxin SS1(dsFv)-PE38, which has a high binding affinity to mesothelin (Kd = 0.7 nM). Our studies in vitro showed that SS1(dsFv)-PE38 is significantly more cytotoxic to the high-mesothelin-producing NCI-H226 human non-small cell lung cancer cells than to human lung adenocarcinoma PC14PE6 cells, which do not express mesothelin. When administered at a nontoxic dose of 500 microg/kg on days 7, 9, and 11 to nude mice injected i.v. with the two human lung cancer cell lines, SS1(dsFv)-PE38 selectively inhibited experimental lung metastases produced by the mesothelin-producing NCI-H226 cells. Our data indicate that mesothelin-producing squamous cell carcinoma of the lung may be a good target for this immunotoxin.

ADP Ribose Transferases↗

PubMed2002

Characterization of overlapping XAGE-1 transcripts encoding a cancer testis antigen expressed in lung, breast, and other types of cancers.

Cancer testis (CT) antigens have an expression pattern that is predominantly restricted to testis in normal tissues, yet they are expressed in many different histological types of cancers. One previously described member of the CT antigen family, XAGE-1, was shown to be expressed in Ewing's sarcomas and rhabdomyosarcomas. Here we show that XAGE-1 is also expressed in breast cancer, prostate cancer, and different types of lung cancers, including lung squamous cell carcinoma, adenocarcinoma, small cell lung carcinoma, and non-small cell lung carcinoma. In addition, XAGE-1 mRNA was present in ovarian cancer, melanoma, glioblastoma, T-cell lymphoma, chronic myelogenous leukemia, and histiocytic lymphoma cell lines. We also characterized the XAGE-1 transcript by primer extension analysis and found that transcription of the XAGE-1 gene is initiated from two distinct start sites, resulting in two overlapping transcripts, XAGE-1a and XAGE-1b. XAGE-1a contains two in-frame ATG translational start codons; whereas XAGE-1b initiates downstream of the first ATG start codon. Our results suggest that XAGE-1b is the dominant transcript, and that translation begins with the second ATG start codon, producing a 9 kDa protein. Because XAGE-1 is expressed in such a diverse range of cancers, it has potential to be used as a target for many cancer immunotherapies.

Amino Acid Sequence↗

PubMed2002

PAGE4 is a cytoplasmic protein that is expressed in normal prostate and in prostate cancers.

PAGE4 is an X chromosome-linked cancer-testis antigen that was identified by expressed sequence tags database mining and a functional genomic approach. PAGE4 is preferentially expressed in normal male and female reproductive tissues and also in a variety of cancers including prostate. In the present study, we have used in situ hybridization to show that PAGE4 mRNA is expressed only in the epithelial cells of normal and prostate-cancer specimens. Analysis of the protein product encoded by the PAGE4 mRNA reveals that it encodes a Mr 16,000 protein and is detected in tissue extracts from both normal prostate and prostate cancer. Cell fractionation analysis of PAGE4 protein indicates that PAGE4 is localized in the cytoplasm of the cell. Furthermore, cDNA microarray analysis indicates that the expression of lipoprotein lipase, a gene frequently deleted in prostate cancer, is down-regulated in a cell line that expresses PAGE4.

3T3 Cells↗

PubMed2001

Cytotoxicity of Antiosteosarcoma Recombinant Immunotoxins Composed of TP-3 Fv Fragments and a Truncated Pseudomonas Exotoxin A.

SUMMARY: Regrowth of drug-resistant tumor cells is responsible for approximately half of an unselected osteosarcoma population still dying of the disease despite aggressive combination therapy. Two monoclonal antibodies, TP-1 (immunoglobulin 2a) and TP-3 (immunoglobulin 2b) are available, which specifically recognize an antigen on osteosarcoma cells. In this work, we have fused the variable (V) genes of TP-3 to a truncated fragment of Pseudomonas exotoxin A, referred to as PE38. Two immunotoxins were made that differed in the Fv portion: TP-3(scFv)-PE38, which contains a peptide linker, and TP-3(dsFv)-PE38, which contains a disulfide bond for stabilization of the association between the V domains. Recombinant TP-3 immunotoxins were expressed in Escherichia coli and purified from inclusion bodies. We describe the design and expression of these immunotoxins, and their properties with regard to antigen binding, stability, and cytotoxicity. Toxicity studies were done in mice. We found that the immunotoxins exhibited very similar in vitro properties, whereas in vivo TP-3(dsFv)-PE38 was much better tolerated than TP-3(scFv)-PE38.

Journal Article↗

PubMed1985

Structure and localization of genes encoding aberrant and normal epidermal growth factor receptor RNAs from A431 human carcinoma cells.

A431 cells have an amplification of the epidermal growth factor (EGF) receptor gene, the cellular homolog of the v-erb B oncogene, and overproduce an aberrant 2.9-kilobase RNA that encodes a portion of the EGF receptor. A cDNA (pE15) for the aberrant RNA was cloned, sequenced, and used to analyze genomic DNA blots from A431 and normal cells. These data indicate that the aberrant RNA is created by a gene rearrangement within chromosome 7, resulting in a fusion of the 5' portion of the EGF receptor gene to an unidentified region of genomic DNA. The unidentified sequences are amplified to about the same degree (20- to 30-fold) as the EGF receptor sequences. In situ hybridization to chromosomes from normal cells and A431 cells show that both the EGF receptor gene and the unidentified DNA are localized to the p14-p12 region of chromosome 7. By using cDNA fragments to probe DNA blots from mouse-A431 somatic cell hybrids, the rearranged receptor gene was shown to be associated with translocation chromosome M4.

Amino Acid Sequence↗

PubMedDate not supplied

Mutants of immunotoxin anti-Tac(dsFv)-PE38 with variable number of lysine residues as candidates for site-specific chemical modification. 1. Properties of mutant molecules.

Chemical modification of proteins with substances such as poly(ethylene glycol) can add useful properties to proteins. Currently PEGylation is done in a random manner utilizing amino residues dispersed throughout a protein. For proteins such as immunotoxins, which have several different functional domains, random modification leads to inactivation. To determine if we could produce an immunotoxin with a diminished number of lysine residues so that chemical modification could be restricted to certain regions of the protein, we chose the recombinant immunotoxin anti-Tac(dsFv)-PE38 that has 13 lysine residues in the Fv portion and 3 in the toxin. We prepared a series of mutants with 0-12 lysines in the Fv and 0 or 3 in the toxin. Almost all of these molecules retain full biological activity. Our data indicate that replacement of lysine residues can be achieve without loss of biological potency. These molecules are a useful starting point to carry out site-specific PEGylation experiments.

Amino Acid Sequence↗

PubMedDate not supplied

Selective elimination of human regulatory T lymphocytes in vitro with the recombinant immunotoxin LMB-2.

CD4(+)CD25(+) T-regulatory cells (T(reg)) can inhibit the proliferation and cytokine secretion of CD4(+)CD25(-) helper T cells in mice and humans. In murine tumor models, the presence of these T(reg) cells can inhibit the antitumor effectiveness of T-cell transfer and active immunization approaches. We have thus initiated efforts to eliminate T(reg) cells selectively from human peripheral blood mononuclear cells (PBMCs) to potentially bolster antitumor responses. LMB-2 is a recombinant immunotoxin that is a fusion of a single-chain Fv fragment of the anti-Tac anti-CD25 monoclonal antibody to a truncated form of the bacterial Pseudomonas exotoxin A. In vitro incubation of human PBMCs with LMB-2 reduced the levels of CD4(+)CD25(+) and Foxp3-expressing cells without impairing the function of the remaining lymphocytes. The short in vivo half-life of LMB-2 makes it an attractive candidate for reducing human T(reg) cells in vivo before the administration of cancer vaccine or cell transfer immunotherapy approaches.

Animals↗

PubMedDate not supplied

Modulation by the ATP/GTP ratio of the phosphorylation level of P-glycoprotein and of various plasma membrane proteins of KB-V1 multidrug resistant cells.

The level of protein phosphorylation is known to affect the properties of various membrane proteins. We have previously shown that GTP is capable of greatly enhancing the phosphorylation by [gamma-32P]ATP of P-glycoprotein (Pgp) from KB-V1 cells (3). Investigating the possibility of a general modulation of [gamma-32P]ATP plasma membrane protein phosphorylation, we found that phosphorylation of other membrane proteins are also modulated by various combinations of [ATP + GTP]. The ATP/GTP ratio giving the highest phosphorylation level depended on the protein studied. Modulation of the [gamma-32P]ATP-mediated phosphorylation of numerous membrane proteins requires hydrolysis of both ATP and GTP. ADP and GDP also increased [gamma-32P]ATP-driven phosphorylation but to a lesser extent than GTP. This plasma membrane endogenous phosphorylation activity was neither inhibited by specific inhibitors of protein kinase C, nor by inhibitors of cAMP- or cGMP-dependent protein kinases or of casein kinase II, respectively. Mastoparan, a G-protein regulator, increased the phosphorylation of some proteins that were already enhanced by the presence of [ATP + GTP] mixtures, especially proteins migrating in gels at the same position as P-glycoprotein.

ATP Binding Cassette Transporter, Subfamily B, Mem↗