Enhanced targeting of triple-negative breast carcinoma and malignant melanoma by photochemical internalization of CSPG4-targeting immunotoxins.

Triple-negative breast cancer (TNBC) and malignant melanoma are highly aggressive cancers that widely express the cell surface chondroitin sulfate proteoglycan 4 (CSPG4/NG2). CSPG4 plays an important role in tumor cell growth and survival and promotes chemo- and radiotherapy resistance, suggesting that CSPG4 is an attractive target in cancer therapy. In the present work, we applied the drug delivery technology photochemical internalization (PCI) in combination with the novel CSPG4-targeting immunotoxin 225.28-saporin as an efficient and specific strategy to kill aggressive TNBC and amelanotic melanoma cells. Light-activation of the clinically relevant photosensitizer TPCS2a (fimaporfin) and 225.28-saporin was found to act in a synergistic manner, and was superior to both PCI of saporin and PCI-no-drug (TPCS2a + light only) in three TNBC cell lines (MDA-MB-231, MDA-MB-435 and SUM149) and two BRAFV600E mutated malignant melanoma cell lines (Melmet 1 and Melmet 5). The cytotoxic effect was highly dependent on the light dose and expression of CSPG4 since no enhanced cytotoxicity of PCI of 225.28-saporin compared to PCI of saporin was observed in the CSPG4-negative MCF-7 cells. The PCI of a smaller, and clinically relevant CSPG4-targeting toxin (scFvMEL-rGel) validated the CSPG4-targeting concept in vitro and induced a strong inhibition of tumor growth in the amelanotic melanoma xenograft A-375 model. In conclusion, the combination of the drug delivery technology PCI and CSPG4-targeting immunotoxins is an efficient, specific and light-controlled strategy for the elimination of aggressive cells of TNBC and malignant melanoma origin. This study lays the foundation for further preclinical evaluation of PCI in combination with CSPG4-targeting.

The TWEAK receptor Fn14 is a potential cell surface portal for targeted delivery of glioblastoma therapeutics.

UNLABELLED: Fibroblast growth factor-inducible 14 (Fn14; TNFRSF12A) is the cell surface receptor for the tumor necrosis factor (TNF) family member TNF-like weak inducer of apoptosis (TWEAK). The Fn14 gene is normally expressed at low levels in healthy tissues but expression is significantly increased after tissue injury and in many solid tumor types, including glioblastoma (GB; formerly referred to as 'GB multiforme'). GB is the most common and aggressive primary malignant brain tumor and the current standard-of-care therapeutic regimen has a relatively small impact on patient survival, primarily because glioma cells have an inherent propensity to invade into normal brain parenchyma, which invariably leads to tumor recurrence and patient death. Despite major, concerted efforts to find new treatments, a new GB therapeutic that improves survival has not been introduced since 2005. In this review article, we summarize studies indicating that (i) Fn14 gene expression is low in normal brain tissue but is upregulated in advanced brain cancers and, in particular, in GB tumors exhibiting the mesenchymal molecular subtype; (ii) Fn14 expression can be detected in glioma cells residing in both the tumor core and invasive rim regions, with the maximal levels found in the invading glioma cells located within normal brain tissue; and (iii) TWEAK: Fn14 engagement as well as Fn14 overexpression can stimulate glioma cell migration, invasion and resistance to chemotherapeutic agents in vitro. We also discuss two new therapeutic platforms that are currently in development that leverage Fn14 overexpression in GB tumors as a way to deliver cytotoxic agents to the glioma cells remaining after surgical resection while sparing normal healthy brain cells.

Design of an EGFR-targeting toxin for photochemical delivery: in vitro and in vivo selectivity and efficacy.

The number of epidermal growth factor receptor (EGFR)-targeting drugs in the development for cancer treatment is continuously increasing. Currently used EGFR-targeted monoclonal antibodies and tyrosine kinase inhibitors have specific limitations related to toxicity and development of resistance, and there is a need for alternative treatment strategies to maximize the clinical potential of EGFR as a molecular target. This study describes the design and production of a novel EGFR-targeted fusion protein, rGel/EGF, composed of the recombinant plant toxin gelonin and EGF. rGel/EGF was custom-made for administration by photochemical internalization (PCI), a clinically tested modality for cytosolic release of macromolecular therapeutics. rGel/EGF lacks efficient mechanisms for endosomal escape and is therefore minimally toxic as monotherapy. However, PCI induces selective and efficient cytosolic release of rGel/EGF in EGFR-expressing target cells by light-directed activation of photosensitizers accumulated selectively in tumor tissue. PCI of rGel/EGF was shown to be highly effective against EGFR-expressing cell lines, including head and neck squamous cell carcinoma (HNSCC) cell lines resistant to cetuximab (Erbitux). Apoptosis, necrosis and autophagy were identified as mechanisms of action following PCI of rGel/EGF in vitro. PCI of rGel/EGF was further shown as a highly tumor-specific and potent modality in vivo, with growth inhibitory effects demonstrated on A-431 squamous cell carcinoma (SCC) xenografts and reduction of tumor perfusion and necrosis induction in SCC-026 HNSCC tumors. Considering the small amount of rGel/EGF injected per animal (0.1 mg/kg), the presented in vivo results are highly promising and warrant optimization and production of rGel/EGF for further preclinical evaluation with PCI.

Design optimization and characterization of Her2/neu-targeted immunotoxins: comparative in vitro and in vivo efficacy studies.

Targeted therapeutics are potential therapeutic agents because of their selectivity and efficacy against tumors resistant to conventional therapy. The goal of this study was to determine the comparative activity of monovalent, engineered anti-Her2/neu immunotoxins fused to recombinant gelonin (rGel) to the activity of bivalent IgG-containing immunoconjugates. Utilizing Herceptin and its derived humanized single-chain antibody (single-chain fragment variable, designated 4D5), we generated bivalent chemical Herceptin/rGel conjugate, and the corresponding monovalent recombinant immunotoxins in two orientations, 4D5/rGel and rGel/4D5. All the constructs showed similar affinity to Her2/neu-overexpressing cancer cells, but significantly different antitumor activities. The rGel/4D5 orientation construct and Herceptin/rGel conjugate were superior to 4D5/rGel construct in in vitro and in vivo efficacy. The enhanced activity was attributed to improved intracellular toxin uptake into target cells and efficient downregulation of Her2/neu-related signaling pathways. The Her2/neu-targeted immunotoxins effectively targeted cells with Her2/neu expression level >1.5 × 10(5) sites per cell. Cells resistant to Herceptin or chemotherapeutic agents were not cross-resistant to rGel-based immunotoxins. Against SK-OV-3 tumor xenografts, the rGel/4D5 construct with excellent tumor penetration showed impressive tumor inhibition. Although Herceptin/rGel conjugate demonstrated comparatively longer serum half-life, the in vivo efficacy of the conjugate was similar to the rGel/4D5 fusion. These comparative studies demonstrate that the monovalent, engineered rGel/4D5 construct displayed comparable in vitro and in vivo antitumor efficacy as bivalent Herceptin/rGel conjugate. Immunotoxin orientation can significantly impact the overall functionality and performance of these agents. The recombinant rGel/4D5 construct with excellent tumor penetration and rapid blood clearance may reduce the unwanted toxicity when administrating to patients, and warrants consideration for further clinical evaluation.

Treatment of acute lymphoblastic leukemia with an rGel/BLyS fusion toxin.

Acute lymphoblastic leukemia (ALL) is the most common malignancy affecting children and a major cause of mortality from hematopoietic malignancies in adults. A substantial number of patients become drug resistant during chemotherapy, necessitating the development of alternative modes of treatment. rGel (recombinant Gelonin)/BlyS (B-lymphocyte stimulator) is a toxin-cytokine fusion protein used for selective killing of malignant B-cells expressing receptors for B-cell-activating factor (BAFF/BLyS) by receptor-targeted delivery of the toxin, Gelonin. Here, we demonstrate that rGel/BLyS binds to ALL cells expressing BAFF receptor (BAFF-R) and upon internalization, it induces apoptosis of these cells and causes downregulation of survival genes even in the presence of stromal protection. Using an immunodeficient transplant model for human ALL, we show that rGel/BLyS prolongs survival of both Philadelphia chromosome-positive and negative ALL-bearing mice. Furthermore, we used AMD3100, a CXCR4 antagonist, to mobilize the leukemic cells protected in the bone marrow (BM) microenvironment and the combination with rGel/BLyS resulted in a significant reduction of the tumor load in the BM and complete eradication of ALL cells from the circulation. Thus, a combination treatment with the B-cell-specific fusion toxin rGel/BLyS and the mobilizing agent AMD3100 could be an effective alternative approach to chemotherapy for the treatment of primary and relapsed ALL.

A novel recombinant fusion toxin targeting HER-2/NEU-over-expressing cells and containing human tumor necrosis factor.

Over-expression of the proto-oncogene HER2/neu in breast cancer and certain other tumors appears to be a central mechanism that may be partly responsible for cellular progression of the neoplastic phenotype. Transfection of mammalian cells and over-expression of HER2/neu appears to result in reduced sensitivity to the cytotoxic effects of tumor necrosis factor (TNF) and reduced sensitivity to immune effector killing. The single-chain recombinant antibody sFv23 recognizes the cell-surface domain of HER2/neu. The cDNA for this antibody was fused to the cDNA encoding human TNF, and this sFv23/TNF fusion construct was cloned into a plasmid for expression in Escherichia coli. The fusion protein was expressed and purified by ion-exchange chromatography. SDS-PAGE demonstrated a single band at the expected m.w. (43 kDa). Western analysis confirmed the presence of both the antibody component and the TNF component in the final fusion product. The fusion construct was tested for TNF activity against L-929 cells and found to have biological activity similar to that of authentic TNF (SA 420 nM). The scFv23/TNF construct bound to SKBR-3 (HER2-positive) but not to A-375 human melanoma (HER2-negative) cells. Cytotoxicity studies against log-phase human breast carcinoma cells (SKBR-3-HP) over-expressing HER2/neu demonstrate that the sFv23/TNF fusion construct was 1, 000-fold more active than free TNF. Tumor cells expressing higher levels of HER2/neu (SKBR-3-LP) were relatively resistant to both the fusion construct and native TNF. These studies suggest that fusion constructs targeting the HER2/neu surface domain and containing TNF are more effective cytotoxic agents in vitro than native TNF and may be effective against tumor cells expressing intermediate, but not high, levels of HER2/neu.

Comparative cytotoxicity and pharmacokinetics of antimelanoma immunotoxins containing either natural or recombinant gelonin.

Immunotoxins are a class of targeted therapeutic agents under development by various research groups. The murine monoclonal antibody designated ZME-018 recognizes a high molecular weight glycoprotein present on most human melanoma cells and biopsy specimens and has been utilized for clinical imaging studies in patients with melanoma. The plant toxin gelonin is a ribosome-inactivating protein (RIP) with n-glycosidase activity similar to that of ricin A chain. In previous studies by our group, the gelonin toxin was sequenced, cloned and expressed in E. coli. The purified recombinant gelonin (RG) was found to have identical protein synthesis inhibitory activity to that of natural gelonin (NG). For comparative purposes, chemical conjugates of antibody ZME and either RG or NG were produced using the heterobifunctional crosslinking reagents SPDP and SMPT. The ZME-NG and ZME-RG immunotoxins were found to be 10(4)- to 10(5)-fold more cytotoxic to antigen-positive human melanoma cells than free toxin. NG toxin alone was cytotoxic to intact cells (IC(50) = 100 nM) while RG was nontoxic to cells at doses up to 1 microM. Both ZME-NG and ZME-RG immunoconjugates were nontoxic to antigen-negative (Me-180) cells. ZME-RG immunotoxins constructed with the more stable SMPT reagent were slightly more effective in culture than conjugates made with SPDP. Tissue distribution studies in tumor-bearing nude mice demonstrated that tumor uptake of the ZME-RG immunotoxin was similar to that of the intact ZME antibody with reduced distribution to normal organs compared to an immunoconjugate produced with NG. Pharmacokinetic studies showed that the terminal-phase plasma half-life of ZME-RG was similar to that of ZME itself (42 h vs 50 h) and almost threefold higher than that of ZME-NG (11.5 h). The area under the concentration curve (Cxt) for ZME-RG was 50% lower than that for ZME due to an increased apparent volume of distribution (Vd(a)) but was almost tenfold higher than the Cxt for ZME-NG. These studies suggest that immunoconjugates comprising RG demonstrate identical in vitro cytotoxic effects to immunoconjugates produced with NG and immunotoxins with RG display improved in vivo pharmacodynamics and tissue distribution compared to immunotoxins containing NG.

Phase I study of 90Y-labeled B72.3 intraperitoneal administration in patients with ovarian cancer: effect of dose and EDTA coadministration on pharmacokinetics and toxicity.

The tumor-associated glycoprotein 72 (TAG-72) antigen is present on a high percentage of tumor types including ovarian carcinomas. Antibody B72.3 is a murine monoclonal recognizing the surface domain of the TAG-72 antigen and has been widely used in human clinical trials. After our initial encouraging studies (M. G. Rosenblum et al., J. Natl. Cancer Inst., 83: 1629-1636, 1991) of tissue disposition, metabolism, and pharmacokinetics in 9 patients with ovarian cancer, we designed an escalating dose, multi-arm Phase I study of 90Y-labeled B72.3 i.p. administration. In the first arm of the study, patients (3 pts/dose level) received an i.p. infusion of either 2 or 10 mg of B72.3 labeled with either 1, 10, 15, or 25 mCi of 90Y. Pharmacokinetic studies demonstrated that concentrations of 90Y-labeled B72.3 persist in peritoneal fluid with half-lives >24 h after i.p. administration. In addition, 90Y-labeled B72.3 was absorbed rapidly into the plasma with peak levels achieved within 48 h, and levels declined slowly thereafter. Cumulative urinary excretion of the 90Y label was 10-20% of the administered dose which suggests significant whole-body retention of the radiolabel. Biopsy specimens of bone and marrow obtained at 72 h after administration demonstrated significant content of the label in bone (0.015% of the dose/g) with relatively little in marrow (0.005% of the dose/g). The maximal tolerated dose was determined to be 10 mCi because of hematological toxicity and platelet suppression. This typically occurred on the 29th day after administration and was thought to be a consequence of the irradiation of the marrow from the bony deposition of the radiolabel. In an effort to suppress the bone uptake of 90Y, patients were treated with a continuous i.v. infusion of EDTA (25 mg/kg/12 h x 6) infused immediately before i.p. administration of the radiolabeled antibody. Patients (3 pts/dose level) were treated with doses of 10, 15, 20, 25, 30, 35, 40, or 45 mCi of 90Y-labeled B72.3 for a total of 38 patients. EDTA administration resulted in significant myeloprotection, which allowed escalation to the maximal tolerated dose of 40 mCi. Dose-limiting toxicity was thrombocytopenia and neutropenia. Studies of plasma and peritoneal fluid pharmacokinetics demonstrate no changes compared with patients without EDTA pretreatment. Cumulative urinary excretion of the radiolabel was not increased in patients pretreated with EDTA compared with the untreated group. However, analysis of biopsy specimens of bone and marrow demonstrated that bone and marrow content of the 90Y label was 15-fold lower (<0.001% injected dose/g) than a companion group without EDTA. Four responses were noted in patients who received 15-30 mCi of 90Y-labeled B72.3 with response durations of 1-12 months. These results demonstrate the myeloprotective ability of EDTA, which allows safe i.p. administration of higher doses of 90Y-labeled B72.3 and, therefore, clearly warrant an expanded Phase II trial in patients with minimal residual disease after standard chemotherapy or for the palliation of refractory ascites.

Recombinant immunotoxins directed against the c-erb-2/HER2/neu oncogene product: in vitro cytotoxicity, pharmacokinetics, and in vivo efficacy studies in xenograft models.

TAB-250 and BACH-250 are murine and human chimeric antibodies directed at the extracellular domain of the gp185c-erb-2 (HER2/neu) growth factor receptor overexpressed in a variety of tumor types, including ovarian and breast carcinoma. The ribosome-inhibiting plant toxin gelonin (rGel) was chemically coupled to both antibodies, and the resulting immunotoxins were purified and tested in vitro against human tumor cells expressing various levels of HER-2/neu and in vivo against human tumor xenograft models. The binding of both BACH-250 and BACH-250/rGel conjugate to target cells was essentially equivalent. Against SKOV-3 cells, the IC50 of BACH-250/rGel was 97 pM (17 ng/ml), whereas BACH-250 and rGel alone showed no cytotoxic effects. There was a clear correlation between expression levels of HER-2/neu and cytoimmunotoxin. Tissue distribution studies showed that the antibody and immunotoxin both concentrate 2-10-fold higher in tumors than in normal tissues, with optimal tumor uptake occurring 48-96 h after administration. Plasma clearance curves for BACH-250 and BACH-250/rGel showed terminal-phase half-lives of 26 and 72 h, respectively. In athymic mice bearing s.c. or i.p. SKOV-3 tumors, immunotoxin treatment slowed tumor growth by 99 and 94 % at days 35 and 49 after implantation, respectively, and lengthened the median survival by 40% (from 30 to 50 days) in mice bearing lethal i.p. tumors. We conclude that clinical development of BACH-250/rGel may be warranted in patients with HER2/neu-expressing malignancies.

Humanized M195 monoclonal antibody conjugated to recombinant gelonin: an anti-CD33 immunotoxin with antileukemic activity.

The recently characterized immunotoxin HuM195-gelonin consists of a humanized anti-CD33 monoclonal antibody conjugated to the single-chain plant toxin gelonin. Binding of the immunotoxin to hematopoietic cells that express the CD33 differentiation antigen has been demonstrated and results in cytotoxicity due to ribosomal inactivation by gelonin. Blast cells from most patients with acute myelogenous leukemia express CD33, whereas normal stem cells necessary for maintenance of hematopoiesis do not. We asked whether an immunoconjugate using recombinant gelonin rather than plant gelonin is toxic to acute myelogenous leukemia (AML) cell lines and primary AML blasts obtained from patients and exposed to the immunotoxin in vitro. The CD33pos cell lines HL60, OCI/AML2, and OCI/ AML5 showed decreased proliferation when exposed to immunotoxin for 24-72 h. The CD33neg cell line OCI/AML3 was relatively resistant to HuM195, and all cell lines were resistant to equimolar concentrations of unconjugated antibody and gelonin. Primary blast cultures from seven patients with AML had CD33 detectable on 75.7-99.8% of cells by flow cytometry, and all showed dose-dependent decreases in clonogenic cell survival during 24-h incubation with the immunotoxin. Cells selected for low CD33 expression by cell sorting or by prolonged incubation with immunotoxin could reexpress CD33 at baseline levels and remained sensitive to immunotoxin. We conclude that humanized M195 conjugated to recombinant gelonin has antileukemic activity and should be considered for clinical testing in Phase I trials.

Effect of recombinant alpha-interferon on pharmacokinetics, biodistribution, toxicity, and efficacy of 131I-labeled monoclonal antibody CC49 in breast cancer: a phase II trial.

Preclinical studies have demonstrated that recombinant IFN-alpha (rIFN-alpha) can enhance the tumor associated glycoprotein 72 (TAG-72) on tumors. To determine whether rIFN-alpha could enhance TAG-72 expression in vivo in patients, 15 women with breast cancer were randomized to receive daily injections of rIFN-alpha (3 x 10(6) units/m2 for 14 days) beginning on day 1 (group 1 = 7 patients) or on day 6 (group 2 = 8 patients). On day 3, all patients received a 10-20-mCi tracer dose of 131I-CC49, a high-affinity murine monoclonal antibody reactive against TAG-72, followed by a therapy dose of 60-75 mCi/m2 of 131I-CC49 on day 6. Whole body and single-photon emission computed tomography scans along with whole blood pharmacokinetics were performed following tracer and treatment phases. Hematological toxicity was considerable; reversible grade 3-4 neutropenia and thrombocytopenia was observed in 12 of 15 patients. Twelve of 14 patients tested developed human antimouse antibodies 3-6 weeks after treatment. For group 1 patients, whole blood residence time increased significantly between that predicted from the tracer doses and therapy doses (42.6 +/- 4.7 versus 51.5 +/- 4.8 h, respectively; P < 0.01). The calculated radiation absorbed dose to red marrow from therapy compared to tracer activity was also significantly higher for this group (1.25 +/- 0.35 versus 1. 07 +/- 0.26 cGy/mCi; P < 0.05). Treatment with rIFN-alpha was found to enhance TAG-72 expression in tumors from patients receiving rIFN-alpha (group 1) by 46 +/- 19% (P < 0.05) compared to only 1.3 +/- 0.95% in patients not initially receiving IFN (group 2). The uptake of CC49 in tumors was also significantly increased in rIFN-alpha-treated patients. One partial and two minor tumor responses were seen. In summary, rIFN-alpha treatment altered the pharmacokinetics and tumor uptake of 131I-CC49 in patients at the expense of increased toxicity.

Phase Ia/Ib trial of anti-GD2 chimeric monoclonal antibody 14.18 (ch14.18) and recombinant human granulocyte-macrophage colony-stimulating factor (rhGM-CSF) in metastatic melanoma.

We performed a phase Ia/Ib trial of chimeric anti-GD2 monoclonal antibody 14.18 (ch14.18) in combination with recombinant human granulocyte-macrophage colony-stimulating factor (rhGM-CSF) to determine the maximum tolerated dose as well as immunologic and biologic responses to the regimen. Sixteen patients with metastatic malignant melanoma received escalating doses of ch14.18 (15-60 mg/m2) administered intravenously for 4 h on day 1. Twenty-four hours later, subcutaneous injections of rhGM-CSF were administered daily for a total of 14 days. Significant side effects were related to ch14.18 infusion and consisted of moderate to severe abdominal and/or extremity pain, blood pressure changes, headache, nausea, diarrhea, peripheral nerve dysesthesias, myalgias, and weakness. Dose-limiting toxicity was observed at 60 mg/m2 and consisted of severe hypertension, hypotension, and atrial fibrillation in one patient each, respectively. Significant increases in white blood cell count, granulocyte count, eosinophil count, and monocyte count occurred after rhGM-CSF treatment. Significant enhancement of in vitro and in vivo monocyte and neutrophil tumoricidal activity and antibody-dependent cellular cytotoxicity along with significant elevations in C-reactive protein and neopterin were observed. Despite these immunological and biological changes, no antitumor activity was seen. In short, the combination of ch14.18 and rhGM-CSF resulted in toxicity similar to that observed with ch14.18 alone without improvement in tumor response.

Immortalization of neuroendocrine pinealocytes from transgenic mice by targeted tumorigenesis using the tryptophan hydroxylase promoter.

Tryptophan hydroxylase (TPH) is the first enzyme in both serotonin and melatonin biosynthesis in neuroendocrine cells of the pineal gland. The lack of immortalized neuroendocrine pineal cell lines has been a major obstacle to the study of the tissue-specific and circadian regulation of TPH gene expression in the pineal gland. Previously, we demonstrated that a 6.1 kb 5' upstream region of the mouse TPH gene directs the restricted expression of a lacZ reporter gene to the pineal gland and the raphe nuclei of transgenic mice. Therefore, to develop TPH-expressing pineal cell lines we first established transgenic mice carrying a construct consisting of 6.1 kb of 5' flanking region fused to the SV40 T-antigen. These animals developed highly invasive pineal tumors and died at 12-15 weeks of age. The pineal tumors obtained from the transgenic mice were utilized to establish the immortalized pinealocyte-derived cell lines. These cells express two marker enzymes, TPH and serotonin N-acetyltransferase (NAT). In pineal gland TPH and NAT expressions have been known to be regulated during circadian cycle. The two established cell lines therefore promise to be a valuable in vitro model system for the study of the rhythmic nature of the pineal function at molecular level in mammal.

Cellular resistance to the antimelanoma immunotoxin ZME-gelonin and strategies to target resistant cells.

The development of cellular resistance to immunotoxins has been demonstrated in a variety of models and can involve a number of mechanisms. For the present study, an immunotoxin was utilized composed of an anti-melanoma antibody ZME-018 recognizing a 240-kDa surface glycoprotein (gp 240) and the plant toxin gelonin. Human melanoma cells (A375-M) were grown in the presence of increasing amounts of ZME-gelonin and a clonal variant (A-375-ZR) was developed that was 100-fold resistant to ZME-gelonin compared to parental cells. Scatchard analysis showed that the A375-M parental cells had 260 X 10(3) ZME-gelonin-binding sites/cell with relatively low affinity (5 nM). In contrast, resistant A375-ZR cells demonstrated a reduced number of low-affinity sites (160 x 10(3)/cel1), but showed a small number (47 x 10(3)) of higher-affinity sites (0.8 nM). Internalization rates and degradation rates of 125I-labeled ZME-gelonin were identical in both the parental and resistant cells. A375-ZR cells were found to be more resistant to vincristine and doxorubicin than were parental cells. Both cell lines were almost equally sensitive to native gelonin, 5-fluorouracil (5-FU), cisplatin. melphalan, carmustine, interferon gamma (IFNgamma) and IFNalpha. In addition. both cell lines were equally sensitive to another gelonin antibody conjugate that binds to cell-surface, GD2 (antibody 14G2A). However, resistant cells were twice as sensitive to the cytotoxic effects of etoposide than were parental cells. Finally, a variety of agents were tested in combination with ZME-gelonin against A375-ZR cells in an attempt to identify agents to augment immunotoxin cytotoxic effects against resistant cells. The agents 5-FU, cisplatin, IFNgamma, IFNalpha, and etoposide were the most effective in augmenting the cytotoxicity of ZME-gelonin against resistant cells. These studies suggest that development of resistance to one immunotoxin does not cause development of cross-resistance to other gelonin immunotoxins. Further, specific biological response modifiers and chemotherapeutic agents may be effective in augmenting the effectiveness of immunotoxins and specifically targeting or reducing the emergence of immunotoxin-resistant cells.

Antileukemic activity of recombinant humanized M195-gelonin immunotoxin in nude mice.

A leukemia-selective immunotoxin was constructed by linking recombinant gelonin (rGel), a single chain ribosome inhibitory protein, to recombinant humanized M195 antibody (HuM195), which recognizes the cell-surface protein designated CD33. CD33 is an antigen found on myeloid leukemia blasts as well as myeloid progenitor cells but it is not expressed in detectable amounts on the ultimate hematopoietic progenitor stem cell. Our previous studies indicated that a non-recombinant humanized immunotoxin displayed specific, potent toxicity towards CD33-positive cells but not to CD33-negative cells in vitro. In the current study, a recombinant humanized immunotoxin, HuM195-rGel, was evaluated in vivo in a nude mouse model of human myeloid leukemias. HuM195-rGel was found to target leukemia cells rapidly in vivo and was subsequently internalized into the cells. For trials in vivo, nude mice were injected (ip) with 10(7) log-phase HL60 human leukemia cells 10 days prior to the start of i.p. HuM195-rGel treatments. HuM195-rGel demonstrated significant tumor suppressive activity in this model. While all mice treated with either saline, rGel alone, or HuM195 plus unconjugated rGel (at 10 or 14 days after transplantation) had rapid tumor growth or early deaths, 50% of mice treated with HuM195-rGel failed to develop leukemic tumors for 5 months and the 50% had significantly retarded tumor growth after treatment with HuM195-rGel. Mice treated at later times (28 days after transplantation of leukemia cells) also showed delayed leukemia cell growth, but no cures. These data show that HuM195-rGel can target leukemia cells in vivo and can result in pronounced anti-leukemic effects.

Enhanced TAG-72 expression and tumor uptake of radiolabeled monoclonal antibody CC49 in metastatic breast cancer patients following alpha-interferon treatment.

The IFNs, alpha and gamma, have been shown to enhance the tumor-associated glycoprotein (TAG-72) on adenocarcinoma cells in vitro and in mice with human breast cancer xenografts, resulting in improved targeting of monoclonal antibody CC49. To determine the effect of IFN-alpha on biodistribution and tumor uptake of 131I-labeled CC49, patients with metastatic breast cancer were randomized to either receive or not receive IFN-alpha (3 million units daily for 14 days) by s.c. injection. Three days after beginning IFN-alpha, all patients received 10-20 mCi of 131I-CC49 (specific activity, 16.7 mCi/mg) i.v. Total-body Anger camera scans, along with total-body blood and plasma pharmacokinetics, were performed. Tumor biopsies were taken in all patients before and 48 h after IFN-alpha treatment. There were no significant differences in number of metastases imaged or whole-body, blood and plasma pharmacokinetics between IFN-alpha-treated and untreated patients. Quantitative immunohistochemistry on biopsy specimens from IFN-alpha-treated patients demonstrated a significant increase in mean +/- SEM TAG-72 expression (45.7 +/- 19.4%) compared to patients that were not given IFN-alpha (1.3 +/- 0.95%; P < 0.05). Although slight increases in the percent injected dose of 131I-CC49 in tumor occurred after IFN-alpha-treatment, the changes were not significant at the P < 0.05 level. These data suggest that IFN-alpha may be useful in enhancing TAG-72 antigen expression in vivo in humans, despite modest improvement in tumor uptake of CC49, possibly because of limited tumor access or other unknown factors.

Potentiation of antiproliferative effects of monoclonal antibody Lym-1 and immunoconjugate Lym-1-gelonin on human Burkitt's lymphoma cells with gamma-interferon and tumor necrosis factor.

A type I ribosome inactivating protein, gelonin, was linked to Lym-1, a murine monoclonal antibody reactive with a polymorphic determinant of class II HLA-DR histocompatibility leukocyte antigen (HLA) on human lymphoma cells, via a disulfide linkage using the heterobifunctional cross-linking agent, N-succinimidyl-3-(2-pyridyldithio) propionate. This immunotoxin was purified from unreacted gelonin and unconjugated Lym-1 by fast protein liquid chromatography using sephacryl S-300 gel filtration and blue sepharose affinity gradient separation. Binding of Lym-1-gelonin immunoconjugate to human Raji Burkitt's lymphoma cells was demonstrated by indirect immunofluorescence using flow cytometry. Lym-1-gelonin was very active in 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium salt and sulforhodamine B in vitro cytotoxicity assays against the Raji lymphoma cell line and confirmed the fact that monoclonal antibody Lym-1 internalizes into human lymphoma cells. A weaker cytostatic antiproliferative effect was also noted for unconjugated Lym-1. gamma-interferon augmented the antiproliferative effects of Lym-1-gelonin conjugate and unconjugated Lym-1, by having a direct cytotoxic effect on the Raji cells. Tumor necrosis factor-alpha also enhanced the antiproliferative effect of unconjugated Lym-1, but did not significantly augment the cytotoxic activity of the Lym-1-gelonin conjugate. These results suggest that anti-HLA class II monoclonal antibodies may be useful in constructing immunotoxins for the treatment of human lymphomas and leukemias expressing HLA class II antigens, and that unconjugated anti-HLA class II monoclonal antibodies may be therapeutically useful in conjunction with recombinant cytokines, especially gamma-interferon.

An antimelanoma immunotoxin containing recombinant human tumor necrosis factor: tissue disposition, pharmacokinetic, and therapeutic studies in xenograft models.

The ability of monoclonal antibody conjugates to re-direct plant or bacterial toxins, chemotherapeutic agents and radionuclides to selected target cells has been well-documented. Recombinant human tumor necrosis factor (TNF) is a macrophage-derived, non-glycosylated (17 kDa) peptide with a broad range of biological and immunological effects including antiviral activity, cytotoxic and cytostatic effects. A conjugate of the antimelanoma antibody ZME-018 and TNF in previous studies has shown melanoma-selective cytotoxic effects in vitro. Pharmacokinetic studies of the ZME-TNF immunotoxin showed that the agent cleared from plasma biphasically with alpha- and beta-phase half-lives similar to that of ZME itself (72 min and 36 h compared to 84 min and 41 h respectively). In contrast, TNF itself was cleared rapidly from plasma with a terminal-phase half-life of only 2.7 h. The clearance rate of ZME-TNF from plasma (Clp) was almost tenfold more rapid than for ZME (1.1 versus 0.16 ml/kg x min) but was threefold slower than the clearance for TNF itself (3.4 ml/kg x min). Tissue distribution studies in nude mice bearing human melanoma xenografts showed similar tumor localization of the immunotoxin compared to the free antibody and slightly higher concentrations in liver and kidney compared to ZME itself. Treatment of nude mice bearing well-developed A375 tumors with the immunotoxin resulted in a statistically significant (P < 0.002) suppression in tumor growth rate (fivefold increase) compared to saline-treated controls, which increased 20-fold over the same period. These studies demonstrate the feasibility of this approach and suggest that TNF may represent a non-antigenic alternative to immunotoxins containing plant and bacterial toxins.

Pharmacokinetics, tissue distribution, and in vivo antitumor effects of the antimelanoma immunotoxin ZME-gelonin.

Antibody ZME-018 is directed against the gp240 glycoprotein on the surface of more than 80% of human melanoma cell lines and fresh biopsy specimens. Previous studies in our laboratory described the in vitro cytotoxicity and specificity of an immunoconjugate composed of mAb ZME-018 and the plant toxin gelonin. The present study described the in vivo pharmacokinetics and therapeutic effects of ZME-gelonin in human xenograft/nude mouse models. Pharmacokinetic studies of 125I-labeled ZME-018 and ZME-gelonin demonstrated a shorter terminal-phase plasma half-life of the immunoconjugate than native ZME (20.6 h compared to 41.3 h). The initial volume of distribution of the ZME-gelonin was also higher compared to that of ZME alone (2.85 ml compared to 1.94 ml) suggesting an enhanced distribution of the conjugate outside the vasculature. The corresponding area under the concentration/time curve for the ZME-gelonin conjugate was 40% lower than that of ZME alone (80.8 compared to 139.6 microCi.ml-1 x min). In nude mice bearing well-developed human tumor A375 melanoma xenografts, administration of 125I-labeled ZME and ZME-gelonin resulted in tumor-to-blood ratios of 1.9 +/- 0.5 and 1.5 +/- 0.6 respectively by 72 h. Compared with ZME, ZME-gelonin conjugate caused an increase in the content of radiolabel in kidney, spleen and liver. Treatment of nude mice bearing well-developed (150 mm3) s.c. A375-M xenografts with divided doses of ZME-gelonin, ZME, gelonin, or saline resulted in suppression of tumor growth in the immunotoxin group but virtually no retardation of tumor growth in the control groups. Using a murine model for a rapidly growing lethal metastatic human melanoma, treatment with ZME-gelonin resulted in a mean survival of 44 days, 213% increase in mean survival time compared with the saline treatment (14.2 +/- 2 day survival). Given these encouraging results, we are proceeding with further preclinical development of this immunotoxin.

Characterization of murine and humanized anti-CD33, gelonin immunotoxins reactive against myeloid leukemias.

M195 antibodies recognize CD33, an antigen present on acute myeloid leukemia blasts as well as some myeloid progenitor cells, but not on the ultimate hematopoietic progenitor stem cell. Immunotoxins (IT) reactive with human myeloid leukemias were constructed by conjugating gelonin, a single-chain ribosome-inactivating protein, to murine and genetically engineered, humanized M195 antibodies via an N-succinimidyl-3-(2-pyridyl-dithio)-propionate linkage. No losses of gelonin cytotoxic activity or M195 binding activity were observed after conjugation of up to two toxin molecules per antibody. Toxin conjugates displayed specific, potent toxicity for CD33+ cells. The murine and humanized IT were not toxic to CD33- cells and were 600 and 4500 times more potent, respectively, than free gelonin in inhibiting CD33+ HL60 cells. Treatment of HL60 cells with 1 micrograms/ml HuM195-gelonin resulted in more than 1000 times lower colony formation; normal bone marrow mononuclear cell colony-forming units treated with HuM195-IT were reduced by a factor of 10. HL60 leukemia cells could be effectively purged from an excess of normal bone marrow cells. Exposure of target cells to IT for as little as 30 min was as effective as continuous exposure of IT for up to 6 days. However, measures of the efficacy of the immunotoxin were directly related to the length of time of observation after IT exposure and were inversely related to cell concentration. M195-gelonin immunoconjugates are potential candidates for therapeutic use in in vivo or ex vivo bone marrow purging for myeloid leukemias.