Bronchioalveolar organoids: A preclinical tool to screen toxicity associated with antibody-drug conjugates

Despite extensive preclinical testing, cancer therapeutics can result in unanticipated toxicity to non-tumor tissue in patients. These toxicities may pass undetected in preclinical experiments due to modeling limitations involving poor biomimicry of 2-dimensional in vitro cell cultures and due to lack of interspecies translatability in in vivo studies. Instead, primary cells can be grown into miniature 3-dimensional structures that recapitulate morphological and functional aspects of native tissue, termed "organoids." Here, human bronchioalveolar organoids grown from primary alveolar epithelial cells were employed to model lung epithelium and investigate off-target toxicities associated with antibody-drug conjugates (ADCs). ADCs with three different linker-payload combinations (mafodotin, vedotin, and deruxtecan) were tested in bronchioalveolar organoids generated from human, rat, and nonhuman primate lung cells. Organoids demonstrated antibody uptake and changes in viability in response to ADC exposure that model in vivo drug sensitivity. RNA sequencing identified inflammatory activation in bronchioalveolar cells in response to deruxtecan. Future studies will explore specific cell populations involved in interstitial lung disease and incorporate immune cells to the culture.

A CD45-targeted antibody-drug conjugate successfully conditions for allogeneic hematopoietic stem cell transplantation in mice

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is a potentially curative treatment of patients with nonmalignant or malignant blood disorders. Its success has been limited by graft-versus-host disease (GVHD). Current systemic nontargeted conditioning regimens mediate tissue injury and potentially incite and amplify GVHD, limiting the use of this potentially curative treatment beyond malignant disorders. Minimizing systemic nontargeted conditioning while achieving alloengraftment without global immune suppression is highly desirable. Antibody-drug-conjugates (ADCs) targeting hematopoietic cells can specifically deplete host stem and immune cells and enable alloengraftment. We report an anti-mouse CD45-targeted-ADC (CD45-ADC) that facilitates stable murine multilineage donor cell engraftment. Conditioning with CD45-ADC (3 mg/kg) was effective as a single agent in both congenic and minor-mismatch transplant models resulting in full donor chimerism comparable to lethal total body irradiation (TBI). In an MHC-disparate allo-HSCT model, pretransplant CD45-ADC (3 mg/kg) combined with low-dose TBI (150 cGy) and a short course of costimulatory blockade with anti-CD40 ligand antibody enabled 89% of recipients to achieve stable alloengraftment (mean value: 72%). When CD45-ADC was combined with pretransplant TBI (50 cGy) and posttransplant rapamycin, cyclophosphamide (Cytoxan), or a JAK inhibitor, 90% to 100% of recipients achieved stable chimerism (mean: 77%, 59%, 78%, respectively). At a higher dose (5 mg/kg), CD45-ADC as a single agent was sufficient for rapid, high-level multilineage chimerism sustained through the 22 weeks observation period. Therefore, CD45-ADC has the potential utility to confer the benefit of fully myeloablative conditioning but with substantially reduced toxicity when given as a single agent or at lower doses in conjunction with reduced-intensity conditioning.

Antibody-drug conjugates with dual payloads for combating breast tumor heterogeneity and drug resistance

Breast tumors generally consist of a diverse population of cells with varying gene expression profiles. Breast tumor heterogeneity is a major factor contributing to drug resistance, recurrence, and metastasis after chemotherapy. Antibody-drug conjugates (ADCs) are emerging chemotherapeutic agents with striking clinical success, including T-DM1 for HER2-positive breast cancer. However, these ADCs often suffer from issues associated with intratumor heterogeneity. Here, we show that homogeneous ADCs containing two distinct payloads are a promising drug class for addressing this clinical challenge. Our conjugates show HER2-specific cell killing potency, desirable pharmacokinetic profiles, minimal inflammatory response, and marginal toxicity at therapeutic doses. Notably, a dual-drug ADC exerts greater treatment effect and survival benefit than does co-administration of two single-drug variants in xenograft mouse models representing intratumor HER2 heterogeneity and elevated drug resistance. Our findings highlight the therapeutic potential of the dual-drug ADC format for treating refractory breast cancer and perhaps other cancers.

N-terminal selective conjugation method widens the therapeutic window of antibody-drug conjugates by improving tolerability and stability

Antibody-drug conjugates (ADCs) are targeted therapeutic agents that treat cancers by selective delivery of highly potent cytotoxic drugs to tumor cells via cancer-specific antibodies. However, their clinical benefit is limited by off-target toxicity and narrow therapeutic windows. To overcome these limitations, we have applied reductive alkylation to develop a new type of ADC that has cytotoxic drugs conjugated to the N-terminal of an antibody through amine bonds introduced via reductive alkylation reactions (NTERM). To test whether the NTERM-conjugated ADCs can widen therapeutic windows, we synthesized three different ADCs by conjugating trastuzumab and monomethyl auristatin-F using three different methods, and compared their stability, efficacy, and toxicity. The NTERM-conjugated ADC was more stable in vitro and in vivo than the thiol-conjugated and the lysine-conjugated ADCs. The NTERM-conjugated ADC showed lower toxicity compared to other ADCs, whereas its efficacy was comparable to that of the thiol-conjugated ADC and better than that of the lysine-conjugated ADC. These results suggest that the NTERM conjugation method could widen the therapeutic window of ADCs by enhancing its stability and reducing toxicity.

Robust Strategy for Antibody-Polymer-Drug Conjugation: Significance of Conjugating Orientation and Linker Charge on Targeting Ability

Antibody-drug conjugates have shown great promise in active targeting for cancer therapy. The existing chemical techniques for antibody conjugation generally lack efficiency or universality. In this article, a site-specific antibody conjugation was developed by using a mild reaction between a benzoboroxole (BB) functionality and cis-diol moiety of sugar units in the antibody fragment crystallizable region under neutral pH conditions. A BB/PEG/ICG-grafted poly(aspartic acid) comb-like functional polymer was first synthesized and conjugated with transferrin (Tf) to form a transferrin-polymer-drug conjugate [Tf-P(BB)], which showed 120% increase in HepG2 hepatoma (Tf receptor overexpression) cell uptake compared to a nontargeting protein-polymer-drug conjugate [HRP-P(BB)]. The universality of this method was further demonstrated by the enhanced uptake of trastuzumab (anti-Her2 antibody)-polymer-drug conjugates in MCF-7 (295%) and MDA-MB-435S (66.4%) (Her2 positive) cells. The positive charge of the linker had great influence on the targeting ability of the antibody-polymer-drug conjugates. The in vivo studies demonstrated the distinct targeting ability of Tf-P(BB) in the HepG2 xenograft tumor, and the tumor accumulation of the Tf-P(BB) testing group increased by 92% with respect to the control group [HRP-P(BB)]. More significantly, the HepG2 cell uptake amount of the antibody-oriented conjugate [Tf-P'(BB)] was 2.4-fold higher than that of the controlled group [Tf-P'(Hex)]. On the basis of this facile site-specific conjugation method, the conjugates are able to change the antibody species easily against various cancers, while maintaining the antibody integrity and targeting ability.

A novel in vivo model using immunotoxin in the absence of p-glycoprotein to achieve ultra selective depletion of target cells: Applications in trogocytosis and beyond

A commonly employed method to determine the function of a particular cell population and to assess its contribution to the overall system in vivo is to selectively deplete that population and observe the effects. Using monoclonal antibodies to deliver toxins to target cells can achieve this with a high degree of efficiency. Here, we describe an in vivo model combining the use of immunotoxins and multidrug resistant (MDR) gene deficient mice so that only MDR deficient cells expressing the target molecule would be depleted while target molecule expressing, but MDR sufficient, cells are spared. This allows targeted depletion at a higher degree of specificity than has been previously achieved. We have applied this technique to study trogocytosis, the intercellular transfer of cell surface molecules, but this principle could also be adapted using technology already available for use in other fields of study.

SHR-A1403, a novel c-Met antibody-drug conjugate, exerts encouraging anti-tumor activity in c-Met-overexpressing models

Emerging evidence demonstrates that a c-Met antibody-drug conjugate (ADC) has superior efficacy and safety profiles compared with those of currently available small molecules or antibody inhibitors for the treatment of c-Met-overexpressing cancers. Here we described both the in vitro and in vivo efficacies of SHR-A1403, a novel c-Met ADC composed of a humanized IgG2 monoclonal antibody against c-Met conjugated to a novel cytotoxic microtubule inhibitor. SHR-A1403 showed high affinity to c-Met proteins derived from human or monkey and potent inhibitory effects in cancer cell lines with high c-Met protein expression. In mice bearing tumors derived from cancer cell lines or patient HCC tissues with confirmed c-Met overexpression, SHR-A1403 showed excellent anti-tumor efficacy. Antibody binding with c-Met contributed to SHR-A1403 endocytosis; the subsequent translocation to lysosomes and cytotoxicity of the released toxin are speculated to be predominant mechanisms underlying the anti-tumor activity of SHR-A1403. In conclusion, SHR-A1403 showed significant anti-tumor activity in cancer cell lines, xenograft mouse models and an HCC PDX model, which all have high c-Met levels. These data provide references for SHR-A1403 as a potential therapy for the treatment of cancers with c-Met overexpression.

Ontak-like human IL-2 fusion toxin

Ontak® is a FDA-approved diphtheria toxin-based recombinant fusion toxin for treatment of human CD25⁺ cutaneous T cell lymphoma (CTCL). However, it has been discontinued clinically due to the production issue related to the bacterial expression system with difficult purification. Recently we have developed monovalent and bivalent human IL-2 fusion toxins targeting human CD25⁺ cells using advanced unique diphtheria toxin resistant yeast Pichia Pastoris expression system. In vitro efficacy characterization using human CD25⁺ HUT102/6TG cells demonstrated that both monovalent and bivalent isoforms are potent and the bivalent isoform is approximately two logs more potent than the monovalent isoform. In this study, we further assessed the in vivo efficacy of the human IL-2 fusion toxins using human CD25⁺ HUT102/6TG tumor-bearing NSG mouse model. The data demonstrated that both monovalent and bivalent human IL-2 fusion toxins significantly prolonged the survival of the human CD25⁺ tumor-bearing NSG mice in a dose-dependent manner. Then we further assessed the residual tumor cells from the HUT102/6TG tumor-bearing NSG mice using the residual tumor cell bearing NSG mouse model. The results demonstrated that the residual tumor cells were still sensitive to the continual treatment with the human IL-2 fusion toxin. This yeast-expressed human IL-2 fusion toxin will be a promising candidate to replace the clinically discontinued Ontak®.

Peripheral neuropathy with microtubule inhibitor containing antibody drug conjugates: Challenges and perspectives in translatability from nonclinical toxicology studies to the clinic

Antibody drug conjugates (ADC) consist of potent cytotoxic drugs conjugated to antibodies via chemical linkers, which enables specific targeting of tumor cells while reducing systemic exposure to the cytotoxic drug and improving the therapeutic window. The valine citrulline monomethyl auristatin E (vcMMAE, conventional linker-drug) ADC platform has shown promising clinical activity in several cancers, but peripheral neuropathy (PN) is a frequent adverse event leading to treatment discontinuation and dose reduction. This was not predicted based on nonclinical toxicology studies in monkeys or rats treated with vcMMAE ADCs. We evaluated four hypotheses for the lack of translatability of PN with vcMMAE ADCs: 1) species differences in exposure; 2) insensitivity of animal models; 3) species differences in target biology and other vcMMAE ADC properties in peripheral nerves and 4) increased susceptibility of patient population. The result of this hypothesis-based approach identified opportunities to improve the predictivity of PN in our animal models by increasing duration of exposure and adding an expanded neurohistopathology assessment of peripheral nerves. The utility of a predictive animal model would be to provide possible mitigation strategies in the clinic with vcMMAE ADCs and help to screen the next generation microtubule inhibitor (MTI) ADCs for reduced PN.

Antibody Drug Conjugates: Nonclinical Safety Considerations

Antibody drug conjugates (ADCs) are biopharmaceutical molecules consisting of a cytotoxic small molecule covalently linked to a targeted protein carrier via a stable cleavable or noncleavable linker. The process of conjugation yields a highly complex molecule with biochemical properties that are distinct from those of the unconjugated components. The impact of these biochemical differences on the safety and pharmacokinetic (PK) profile of the conjugate must be considered when determining the types of nonclinical safety studies required to support clinical development of ADCs. The hybrid nature of ADCs highlights the need for a science-based approach to safety assessment that incorporates relevant aspects of small and large molecule testing paradigms. This thinking is reflected in current regulatory guidelines, where sections pertaining to conjugates allow for a flexible approach to nonclinical safety testing. The aim of this article is to review regulatory expectations regarding early assessment of nonclinical safety considerations and discuss how recent advances in our understanding of ADC-mediated toxicity can be used to guide the types of nonclinical safety studies needed to support ADC clinical development. The review will also explore nonclinical testing strategies that can be used to streamline ADC development by assessing the safety and efficacy of next generation ADC constructs using a rodent screen approach.

Evaluation of oxygen dependence on in vitro and in vivo cytotoxicity of photoimmunotherapy using IR-700-antibody conjugates

Photoimmunotherapy (PIT) using the near-infrared-absorbing photosensitizing phthalocyanine dye, IRDye 700DX (IR-700), conjugated with a tumor-targeting antibody such as panitumumab (Pan) has shown efficacy in in vitro studies and several preclinical models in mice with promise for clinical translation. PIT results in rapid necrotic cell death in vitro and tumor shrinkage in vivo. Photochemical studies with the Pan-IR-700 conjugate showed that this agent can support generation of singlet oxygen and also generate reactive oxygen species after exposure to near-infrared (NIR) light. Moreover, in vitro studies using A431 cells, singlet oxygen scavengers abrogated the efficacy of PIT with Pan-IR-700, while oxygen depletion to undetectable levels in the exposure chamber almost completely inhibited the cellular cytotoxicity of PIT. Survival of tumor bearing mice was prolonged in PIT-treated animals but mice whose tumors were made transiently hypoxic prior to PIT had no benefit from the treatment. The results from this study support a central role for molecular oxygen-derived species in cell death caused by PIT.

Functional native disulfide bridging enables delivery of a potent, stable and targeted antibody-drug conjugate (ADC)

Herein we report the use of next generation maleimides (NGMs) for the construction of a potent antibody-drug conjugate (ADC) via functional disulfide bridging. The linker has excellent stability in blood serum and the ADC, armed with monomethyl auristatin E (MMAE), shows excellent potency and cancer cell selectivity in vitro.

177Lu-DOTA-HH1, a novel anti-CD37 radio-immunoconjugate: a study of toxicity in nude mice

BACKGROUND

CD37 is an internalizing B-cell antigen expressed on Non-Hodgkin lymphoma (NHL) and chronic lymphocytic leukemia cells (CLL). The anti-CD37 monoclonal antibody HH1 was conjugated to the bifunctional chelator p-SCN-Bn-DOTA and labelled with the beta-particle emitting radionuclide 177Lu creating the radio-immunoconjugate (RIC) 177Lu-DOTA-HH1 (177Lu-HH1, trade name Betalutin). The present toxicity study was performed prior to initiation of clinical studies with 177Lu-HH1.

METHODOLOGY/PRINCIPAL FINDINGS

Nude mice with or without tumor xenografts were treated with 50 to 1000 MBq/kg 177Lu- HH1 and followed for clinical signs of toxicity up to ten months. Acute, life threatening bone marrow toxicity was observed in animals receiving 800 and 1000 MBq/kg 177Lu-HH1. Significant changes in serum concentrations of liver enzymes were evident for treatment with 1000 MBq/kg 177Lu-HH1. Lymphoid depletion, liver necrosis and atrophy, and interstitial cell hyperplasia of the ovaries were also observed for mice in this dose group.

CONCLUSIONS/SIGNIFICANCE

177Lu-DOTA-HH1 was well tolerated at dosages about 10 times above those considered relevant for radioimmunotherapy in patients with B-cell derived malignancies.The toxicity profile was as expected for RICs. Our experimental results have paved the way for clinical evaluation of 177Lu-HH1 in NHL patients.

Reduced myelotoxicity with sustained tumor concentration of radioimmunoconjugates in rats after extracorporeal depletion

The aim of this study was to evaluate the possibility of decreasing the myelotoxicity associated with radioimmunotherapy (RIT) by extracorporeal depletion of radioimmunoconjugates (RIC) from the circulation. The optimal combination of radionuclide and the time interval between injection of the RIC and the subsequent extracorporeal depletion procedure was assessed in immunocompetent rats, with respect to both myelotoxicity and tumor concentration of RIC.

METHODS

Rats were injected with 177Lu- or 90Y-labeled antibody conjugate (mAb-DOTA-biotin) (mAb is monoclonal antibody; DOTA is 1,4,7,10-tetraazacyclododecane-N,N',N'',N'''-tetraacetic acid) and subjected to removal of the conjugate from the circulation by extracorporeal affinity adsorption treatment (ECAT) 12, 24, or 48 h after injection. Myelotoxicity was assessed by analysis of blood parameters for 10 wk. The effect of ECAT on the tumor concentration of RIC was evaluated in parallel by scintillation camera imaging in rats injected with 111In-labeled RIC.

RESULTS

ECAT reduced the blood content of RIC by 95%. Thus, myelotoxicity was significantly milder in animals subjected to ECAT than that in controls. The timing of ECAT influenced the rate and level of bone marrow recovery, with an earlier recovery in animals subjected to ECAT early after injection. The toxicity-reducing effect of ECAT was more distinct in animals injected with 177Lu-labeled RIC than in animals injected with 90Y-labeled RIC. Scintillation camera imaging of tumors before and after ECAT revealed that subjecting animals to ECAT at 12 h after injection considerably reduced the total activity in tumors (34%), whereas the effect was lower at both 24 h (18%) and 48 h (18%) after injection.

CONCLUSION

ECAT can efficiently reduce myelotoxicity associated with RIT, and the concentration of RIC in tumor can be sustained, provided ECAT is performed at an optimal time after antibody administration. The choice of radionuclide for RIT in combination with ECAT is important, as the physical half-life is crucial for the toxicity-reducing potential of ECAT at a specific time.

A new procedure for experimental autoimmune uveitis with small uveitogenic peptides

PURPOSE

Demonstration of experimental autoimmune uveitis (EAU) with extremely small, fragmented peptides (12-30 amino acid residues) of interphotoreceptor retinoid-binding protein (IRPB).

METHOD

Very small fragmented peptides (no. 854, 888, 907, and 1057) were conjugated to heat-killed Group A Streptococcus cells and administered as a single intravenous injection to Lewis rats. A non-uveitogenic peptide 950 was also conjugated to heat-killed Streptococcus and administered. Administration of a mixture of small peptides and Streptococcus was a control for the peptides conjugated with Streptococcus.

RESULTS

The uveitogenic peptide/Streptococcus conjugates produced uveitis inflammatory responses in the uvea, retina and pineal gland. Administration of mixtures of small peptides and Streptococcus cells, and a non-uveitogenic peptide 950 conjugated with Streptococcus did not produce autoimmune uveitis.

CONCLUSIONS

Since mixtures of small uveitogenic peptides and Streptococcal cells did not develop autoimmune uveitis, conjugated Streptococcal cells provided a vehicle for macrophage phagocytosos of very small uveitogenic IRBP peptides. Subsequent antigen presentation from macrophages to lymphocytes developed autoimmune uveitis. Peptide 888, one of four IRBP peptides that encompass the major uveitogenic domain, proved to be the most effective in development of uveitis.

In vitro cytotoxicity of 211At-labeled trastuzumab in human breast cancer cell lines: effect of specific activity and HER2 receptor heterogeneity on survival fraction

INTRODUCTION

Radioimmunotherapy with anti-HER2 monoclonal antibodies (mAbs) such as trastuzumab is a promising strategy for treating HER2-positive breast and ovarian carcinoma patients. The objective of this study was to determine the cytotoxic effectiveness of trastuzumab labeled with the 7.2-h half-life alpha-particle emitter 211At.

METHODS

Experiments were performed on SKBr-3, BT-474 and the transfected MCF7/HER2-18 human breast carcinoma cell lines. Intrinsic radiosensitivity was determined after exposure to external beam irradiation. The cytotoxicity of 211At-labeled trastuzumab was measured by clonogenic assays. The distribution of HER2 receptor expression on the cell lines was measured using fluorescence-activated cell sorting. A pharmacokinetic (PK)/microdosimetric model was established to assess the effects of specific activity (SA), HER2 receptor expression and absorbed dose on survival fraction (SF).

RESULTS

With external beam irradiation, the 2-Gy SF for BT-474, SKBr-3 and MCF7/HER2-18 cells was 0.78, 0.53 and 0.64 Gy, respectively. Heterogeneous HER2 expression was observed, with a subpopulation of cells lacking measurable receptor (14.5%, SKBr-3; 0.34%, MCF-7/HER2; 1.73%, BT-474). When plotted as a function of activity concentration, SF curves were biphasic and inversely proportional to SA; however, when the model was applied and absorbed doses calculated, the SF curve was monoexponential independent of SA. Thus, the PK model was able to demonstrate the effects of competition between cold and labeled mAb. These studies showed that the relative biological effectiveness of 211At-labeled trastuzaumab was about 10 times higher than that of external beam therapy.

CONCLUSION

These in vitro studies showed that 211At-labeled trastuzumab mAb is an effective cytotoxic agent for the treatment of HER2-positive tumor cells. The SA of the labeled mAb and the homogeneity of HER2 receptor expression are important variables influencing the efficiency of cell killing.

Synergistic therapeutic effects of a tumor targeting antibody fragment, fused to interleukin 12 and to tumor necrosis factor alpha

The potent antitumor activity of certain cytokines is often achieved at the expense of unacceptable toxicity. One avenue to improve the therapeutic index of cytokines in cancer therapy consists of fusing them to monoclonal antibodies capable of a selective localization at the tumor site. We have constructed fusion proteins of interleukin-12 (IL-12) and tumor necrosis factor (TNF-alpha) with L19, an antibody fragment specific to the extradomain B of fibronectin which has been shown to target tumors in animal models and in patients with cancer. These fusions display a potent antitumor activity in several immunocompetent murine models of cancer but do not lead to complete remissions of established aggressive tumors. In this article, we have evaluated the tumor-targeting properties and the anticancer activities of combinations of the two antibody-cytokine fusion proteins, as well as of a triple fusion protein between IL-12, L19, and TNF-alpha. Although all fusion proteins were active in vitro, the triple fusion protein failed to localize to tumors in vivo and to show significant therapeutic effects. By contrast, the combination of IL-12-L19 and L19-TNF-alpha displayed potent synergistic anticancer activity and led to the eradication of F9 teratocarcinomas grafted in immunocompetent mice. When cured mice were rechallenged with tumor cells, a delayed onset of tumor growth was observed, indicating the induction of a partial antitumor vaccination effect. Potent anticancer effects were achieved at doses of IL-12-L19 and L19-TNF-alpha (2 micro g + 2 micro g/mouse), which were at least 5-fold lower than the maximal-tolerated dose. The combined administration of the two fusion proteins showed only a modest increase in toxicity, compared with treatments performed with the individual fusion proteins. These results show that the targeted delivery of cytokines to the tumor environment strongly potentiates their antitumor activity and that the combination treatment with IL-12-L19 and L19-TNF-alpha appears to be synergistic in vivo.

Nuclear delivery of p53 C-terminal peptides into cancer cells using scFv fragments of a monoclonal antibody that penetrates living cells

scFv fragments of a monoclonal antibody that penetrates living cells and localizes in nuclei were designed as fusion proteins with C-terminal p53 peptides and tested for restoring p53 function in p53 mutant cancer cells. scFv fragments transported a 30-mer C-terminal peptide of p53 into cancer cells and induced cellular cytotoxicity in contrast to scFv fragments alone and other scFv-p53 fusion peptides. Cellular toxicity was not observed with scFv fragments containing a single mutation in VH that prevented antibody penetration. Our results demonstrate the potential efficacy of antibody scFv fragments as a nuclear delivery system in cancer cells.

Targeting colon cancer cells with genistein-17.1A immunoconjugate

We have shown that genistein, a major component of soy, has anti-colon cancer effects in vitro. These effects are attainable at high concentrations that are difficult to achieve in the serum. The purpose of this study was to enhance the activity of genistein against colon cancer cells by coupling it to 17.1A. The monoclonal antibody 17.1A recognizes an epithelial membrane antigen that is overexpressed in colon cancer. Synthesis of Gen-17.1A was achieved by photochemical conjugation using sulfa-SANPAH. Its purity was evaluated by SDS-PAGE. Binding of Gen-17.1A to SW-620 and HT-29 cells was shown using flow cytometry. Internalization was demonstrated by FITC-labeling. Gen-17.1A induced apoptosis in colon cancer cells as evidenced by the acridine orange/ethidium bromide staining method. Gen-17.1A significantly inhibited colon cancer cell growth in vitro and in vivo. Our findings suggest that conjugating genistein to 17.1A monoclonal antibody enhances its effects against colon cancer cells.

Comparison of immunoscintigraphy, efficacy, and toxicity of conventional and pretargeted radioimmunotherapy in CD20-expressing human lymphoma xenografts

Pretargeted radioimmunotherapy (RIT) using streptavidin (sAv)-conjugated antibodies before radiolabeled-biotin is a promising approach to improve absorbed dose ratios and achieve high durable remission rates with diminished systemic toxicity. This study compared the immunoscintigraphy, toxicity, and therapeutic efficacy of pretargeted RIT with conventional RIT using an anti-CD20 antibody.

METHODS

Athymic mice bearing Ramos human Burkitt's lymphoma xenografts were injected intraperitoneally with a 1F5-sAv conjugate followed 24 h later by a galactosylated, biotinylated clearing agent (CA) and, finally, 3 h later by (111)In- or (90)Y-labeled 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA)-biotin. The comparison groups consisted of mice injected with conventional, directly labeled (111)In- or (90)Y-1F5.

RESULTS

Rapid tumor uptake of radioactivity within 2 h was observed with the pretargeting approach, resulting in high-contrast tumor images at 24 h with minimal blood-pool radioactivity. Although conventional radiolabeled antibodies produced clear tumor images at 24 h, a large amount of radioactivity was present in the blood pool. The tumor-to-blood ratio was 3.5:1 with pretargeting compared with 0.4:1 with conventional (111)In-1F5. Pretargeted RIT with 29.6 MBq (800 micro Ci) (90)Y-DOTA-biotin cured 100% of mice with tolerable toxicity, whereas conventional RIT with (90)Y-1F5 at a dose of 14.8 MBq (400 micro Ci) produced no cures, induced profound pancytopenia, and was lethal to all mice.

CONCLUSION

These results suggest that anti-CD20 pretargeted RIT may be superior to conventional radiolabeled antibodies in terms of radioimmunoscintigraphy, toxicity, and therapeutic efficacy for treatment of B-cell lymphomas.

188Re-labeled anti-CD66 monoclonal antibody in stem cell transplantation for patients with high-risk acute myeloid leukemia

We have intensified the conditioning regimen prior to stem cell transplantation in 57 patients with high-risk AML and MDS by treating patients with a 188Re-labeled anti-CD66 monoclonal antibody. Dosimetry was performed prior to therapy and a favorable dosimetry was observed in all cases. Radioimmunotherapy with the labeled antibody provided a mean of 15.5 Gy of additional radiation to the marrow, the kidney was the normal organ receiving the highest dose of supplemental radiation (mean 7.4 Gy): Radioimmunotherapy was followed by standard full-dose conditioning with total body irradiation (12 Gy) (n = 30) or busulfan (n = 27) and high-dose cyclophosphamide +/- thiotepa. Patients subsequently received a T cell depleted allogeneic graft from a HLA-compatible family donor (n = 24), a matched unrelated donor (n = 23) or a haploidentical family donor (n = 6). In four patients, an unmanipulated autologous graft was used. Infusion-related toxicity due to the labeled antibody was minimal and no increase in treatment-related mortality due to the radioimmunoconjugate was observed. Day +30 and day +100 mortalities were 3 and 7%, respectively, and after a median follow-up of 26 months treatment-related mortality was 30%. Late renal toxicity was observed in 14% of patients. The disease-free survival rate for 44 patients in 1 or 2 CR or in very good PR (< 15% blasts in the marrow at transplant) is 64% with only 8% disease-free survival for those with > 15% blasts in the marrow at transplant.

CTLA-4-Ig regulates tryptophan catabolism in vivo

Cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) plays a critical role in peripheral tolerance. However, regulatory pathways initiated by the interactions of CTLA-4 with B7 counterligands expressed on antigen-presenting cells are not completely understood. We show here that long-term survival of pancreatic islet allografts induced by the soluble fusion protein CTLA-4-immunoglobulin (CTLA-4-Ig) is contingent upon effective tryptophan catabolism in the host. In vitro, we show that CTLA-4-Ig regulates cytokine-dependent tryptophan catabolism in B7-expressing dendritic cells. These data suggest that modulation of tryptophan catabolism is a means by which CTLA-4 functions in vivo and that CTLA-4 acts as a ligand for B7 receptor molecules that transduce intracellular signals.

Targeted sonodynamic therapy of cancer using a photosensitizer conjugated with antibody against carcinoembryonic antigen

The goal of this study was to develop a strategy for the selective destruction of cancer cells by ultrasonic irradiation in the presence of an antibody-conjugated photosensitizer. To this end, a photoimmunoconjugate (PIC) was prepared between ATX-70, a photosensitizer of a gallium-porphyrin analogue, and F11-39, a high affinity monoclonal antibody (MAb) against carcinoembryonic antigen (CEA), which is often overexpressed in various carcinoma cells. This conjugate, designated F39/ATX-70, retained immunoreactivity against purified CEA and CEA-expressing cells as determined by enzyme-linked immunosorbent assay, flow cytometry and immunofluorescence microscopic analysis. The cytotoxicity of F39/ATX-70 against CEA-expressing human gastric carcinoma cells in vitro was found to be greater than that of ATX-70 when applied in combination with ultrasound irradiation. When in vivo anti-tumor effects in a mouse xenograft model were assessed, intravenous administration of F39/ATX-70 followed by ultrasonic irradiation produced a marked growth inhibition of tumor compared with irradiation alone or irradiation after administration of ATX-70. These results suggest that the PIC between anti-CEA MAb and ATX-70 may have applications in sonodynamic therapy where destruction of CEA-expressing tumor is required.

Size-dependent intracellular immunotargeting of therapeutic cargoes into endothelial cells

Cell-selective intracellular targeting is a key element of more specific and safe enzyme, toxin, and gene therapies. Endothelium poorly internalizes certain candidate carriers for vascular immunotargeting, such as antibodies to platelet endothelial cell adhesion molecule 1 (PECAM-1). Conjugation of poorly internalizable antibodies with streptavidin (SA) facilitates the intracellular uptake. Although both small and large (100-nm versus 1000-nm diameter) anti-PECAM/SA-beta galactosidase (SA-beta-gal) conjugates bound selectively to PECAM-expressing cells, only small conjugates showed intracellular accumulation of active beta-gal. To study whether size of the conjugates controls the uptake, a series of anti-PECAM/SA and anti-PECAM/bead conjugates ranging from 80 nm to 5 microm in diameter were produced. Human umbilical vein endothelial cells and PECAM-transfected mesothelioma cells internalized 80- to 350-nm anti-PECAM conjugates, but not conjugates larger than 500 nm. Further, size controls intracellular targeting of active therapeutic cargoes in vitro and in vivo. Small anti-PECAM/DNA conjugates transfected target cells in culture 5-fold more effectively than their large counterpart (350- versus 4200-nm diameter). To evaluate the practical significance of the size-controlled subcellular addressing, we coupled glucose oxidase (GOX) to anti-PECAM and antithrombomodulin. Both types of conjugates had equally high pulmonary uptake after intravenous injection in mice, yet only small (200- to 250-nm), not large (600- to 700-nm), GOX conjugates caused profound oxidative vascular injury in the lungs, presumably owing to intracellular generation of H(2)O(2). Thus, engineering of affinity carriers of specific size permits intracellular delivery of active cargoes to endothelium in vitro and in vivo, a paradigm useful for the targeting of drugs, genes, and toxins.

Evaluation of the safety of recombinant P-selectin glycoprotein ligand-immunoglobulin G fusion protein in experimental models of localized and systemic infection

P-selectin is a major component in the early interaction between platelets, endothelial cells, and inflammatory cells in the initial phases of the innate immune response. The major ligand for P-selectin is P-selectin glycoprotein ligand-1 (PSGL-1) and this ligand is expressed on the surface of monocyte, lymphocyte, and neutrophil membranes. A truncated form of recombinant human P-selectin glycoprotein ligand-1 has been covalently linked to immunoglobulin G (rPSGL-Ig) and this fusion peptide functions as a competitive inhibitor of PSGL-1. As an inhibitor of neutrophil-endothelial cell adherence, rPSGL-Ig is in early clinical development for the treatment of ischemia reperfusion injury. To determine the potential for deleterious effects from inhibition in P-selectin-mediated neutrophil attachment in the presence of bacterial infection, the effects of therapeutic doses of rPSGL-Ig were tested in three standard laboratory sepsis models. The experimental models included: the murine systemic Listeria monocytogenes infection model, the Pseudomonas aeruginosa bacteremia model in neutropenic rats, and the cecal ligation and puncture (CLP)-induced peritonitis model in rats. Recombinant human PSGL-Ig had no adverse effects on mortality or immune clearance in systemic bacterial infection in any of the three infection models. The PSGL-1 inhibitor did significantly decrease local neutrophil infiltration and bacterial clearance in the peritoneum following CLP, but this did not increase the systemic levels of proinflammatory cytokines, the quantitative levels of bacteremia, or the overall mortality rate following CLP. The results indicate that rPSGL-Ig did not exacerbate infection in these experimental sepsis models.

Idarubicin-145-2C11-F(ab')2 promotes peripheral tolerance and reduces chronic vascular disease in mouse cardiac allografts

In order to reduce the toxic effects of the T cell activating anti-CD3 monoclonal antibody, 145-2C11, F(ab')2 fragments were prepared by pepsin digestion. These fragments were then used as non-immunosuppressive carriers for the cytotoxic drug idarubicin (IDA), to reduce toxicity of both the monodonal antibodies (mAb) and the drug and to increase the specificity of drug delivery. The IDA-145-2C11 F(ab')2 immunoconjugate was tested for specificity by fluorometry. 145-2C11 intact antibody, 145-2C11 F(ab')2 and IDA conjugates of the antibody and F(ab')2 were used to treat CBA recipients of BALB/c vascularized cardiac allografts. Mice with hearts surviving >100 days were challenged with donor and third party (C57BL/6) skin grafts. Although both antibody and F(ab')2 blocked the binding of 145-2C11-FITC to CBA spleen cells, only the intact antibody caused sustained depletion of CD3 cells in vivo. 145-2C11 F(ab')2 blocked cell surface CD3 within 30 min, but was cleared in 24 h without depletion of CD3 cells from the spleen. In BALB/c to CBA cardiac allografts (rejected in 12-17 days), IDA-145-2C11 F(ab')2 (0.2 mg/20 g mouse i.p. at the time of transplantation) induced >100 days' allograft survival and specific tolerance, in contrast to the equivalent dose of 145-2C11 F(ab')2 (mean survival 25 days). Hearts from IDA-145-2C11 F(ab')2-treated mice at >100 days showed decreased cellular infiltration and less chronic vascular disease than long-surviving hearts from mice treated with an alternative antibody, KT3. Thus, F(ab')2 prepared from 145-2C11 provided a suitable CD3-specific, nonimmunosuppressive carrier for IDA. This immunoconjugate was more effective against both acute and chronic rejection than other conjugates or whole antibody. IDA-145-2C11 F(ab')2 is an effective, nontoxic tolerogen in the mouse cardiac allograft model.

Quantitation of cytokine mRNA expression as an endpoint for prediction and diagnosis of xenobiotic-induced hypersensitivity reactions

Xenobiotic-induced hypersensitivity reactions are immune-mediated effects that involve specific antibodies and/or effector and regulatory T lymphocytes. Cytokines are key mediators of such responses and must be considered as possible endpoints for predicting sensitizing potency of drugs and chemicals, as well as for helping diagnosis of allergy. Detecting cytokine production at the protein level has been shown to not be always sensitive enough. This paper describes three examples of the utilization of semiquantitative or competitive reverse transcription polymerase chain reaction analysis of interleukin-4, interferon gamma, and interleukin-1beta mRNAs as endpoints for assessing T-cell or dendritic cell responses to sensitizing drugs (beta-lactam antibiotics) or chemicals (dinitrochlorobenzene).

Biorecognition of HPMA copolymer-adriamycin conjugates by lymphocytes mediated by synthetic receptor binding epitopes

PURPOSE

The EDPGFFNVE nonapeptide (NP) was recognized as the CD21 (CR2) binding epitope of the Epstein-Barr virus (EBV) gp350/ 220 envelope glycoprotein which mediates the virus attachment to human B lymphocytes (Nemerow et al., Cell 56:369-377, 1989). Here we evaluated the targeting potential of a synthetic receptor binding epitope (NP) covalently attached to a water-soluble polymeric drug carrier. In particular, the biorecognition of N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer-NP conjugates by B- and T-cells and the cytotoxicity of HPMA copolymer-NP-adriamycin (ADR) conjugates toward B-cells, T-cells, and peripheral blood lymphocytes (PBL) were evaluated.

METHODS

HPMA copolymer-NP and optionally ADR conjugates varying in the NP density and mode of NP attachment were incubated with Raji B-cells (human Burkitt's lymphoma), CCRF-CEM T-cells (acute human lymphoblastic leukemia), and CCRF-HSB-2 T-cells (human lymphoblastic leukemia). The kinetics of binding was studied, the Langmuir adsorption isotherms analyzed, binding constants calculated, and IC50 doses determined.

RESULTS

Flow cytometry studies revealed that binding was homogeneous to both cell types. The apparent binding constants to T-cells were about two times higher when compared to B-cells. The binding and cytotoxicity increased with increased amount of epitopes per polymer chain. Attachment of the NP via a GFLG spacer resulted in increased biorecognition when compared with conjugates containing NP bound via a GG spacer. HPMA copolymer-NP-ADR conjugates possessed specific cytotoxicity to T- and B-malignant cells. Concentrations, which were lethal to the latter, were not toxic for PBL.

CONCLUSIONS

The data obtained seem to indicate the potential of the HPMA copolymer-NP conjugates as polymer anticancer drug carriers targetable to immunocompetent cells.

Preparation and in vitro studies of [125I]IUDR-T101 antibody conjugate

Idoxuridine labeled with 125I was conjugated to polylysine. This conjugate was then coupled to the carbohydrate side chains of T101 monoclonal antibody (anti-CD5). The immunoreactivity, cell retention, cytotoxicity, and intracellular localization of this conjugate was tested in CCRF-CEM cells (CD5 positive). The conjugate had 68% immunoreactivity. The retention of 125I by CCRF-CEM cells was higher for the conjugate than for T101 directly labeled with 125I and more of it localized in the nucleus than did the 125I-labeled T101. The 125I IUDR-polylysine-T101 conjugate was more cytotoxic than the 125I-labeled T101. In conclusion, the conjugation of [125I]IUDR to T101 is feasible, and preferential targeting of the 125I to the nucleus is obtained.

Monoclonal antibody conjugates of doxorubicin prepared with branched linkers: A novel method for increasing the potency of doxorubicin immunoconjugates

Immunoconjugates of monoclonal antibody BR96 and Doxorubicin have been prepared using a novel series of branched hydrazone linkers. Since each linker bound to the mAb carries two DOX molecules, the DOX/mAb molar ratios of these conjugates were approximately 16, twice that of those previously prepared with single-chain hydrazone linkers. The conjugates were stable at a physiological pH of 7, but released DOX rapidly at lysosomal pH 5. The branched series of BR96 conjugates demonstrated antigen-specific cytotoxicity, and were more potent in vitro than the single-chain conjugate on both a DOX (4-14-fold) and mAb (7-23-fold) basis. The results suggest that, by using the branched linker methodology, it is possible to significantly reduce the amount of mAb required to achieve antigen-specific cytotoxic activity. In this paper, the synthesis and in vitro biology of branched chain immunoconjugates are described.

Human single-chain Fv immunoconjugates targeted to a melanoma-associated chondroitin sulfate proteoglycan mediate specific lysis of human melanoma cells by natural killer cells and complement

Two antimelanoma immunoconjugates containing a human single-chain Fv (scFv) targeting domain conjugated to the Fc effector domain of human IgG1 were synthesized as secreted two-chain molecules in Chinese hamster ovary and Drosophila S2 cells, and purified by affinity chromatography on protein A. The scFv targeting domains originally were isolated as melanoma-specific clones from a scFv fusion-phage library, derived from the antibody repertoire of a vaccinated melanoma patient. The purified immunoconjugates showed similar binding specificity as did the fusion-phage clones. Binding occurred to human melanoma cells but not to human melanocytes or to several other types of normal cells and tumor cells. A 250-kDa melanoma protein was immunoprecipitated by the immunoconjugates and analyzed by mass spectrometry, using two independent procedures. A screen of protein sequence databases showed an exact match of several peptide masses between the immunoprecipitated protein and the core protein of a chondroitin sulfate proteoglycan, which is expressed on the surface of most human melanoma cells. The Fc effector domain of the immunoconjugates binds natural killer (NK) cells and also the C1q protein that initiates the complement cascade; both NK cells and complement can activate powerful cytolytic responses against the targeted tumor cells. An in vitro cytolysis assay was used to test for an immunoconjugate-dependent specific cytolytic response against cultured human melanoma cells by NK cells and complement. The melanoma cells, but not the human fibroblast cells used as the control, were efficiently lysed by both NK cells and complement in the presence of the immunoconjugates. The in vitro results suggest that the immunoconjugates also could activate a specific cytolytic immune response against melanoma tumors in vivo.

In vivo toxicity and pharmacokinetic features of B43(Anti-CD19)-Genistein immunoconjugate

B43(anti-CD19)-Genistein immunoconjugate targets genistein, a naturally occurring protein tyrosine kinase inhibitory isoflavone to the membrane-associated anti-apoptotic CD19-LYN complexes and triggers apoptotic cell death. In this preclinical study, the toxicity profiles of B43-Genistein as well as unconjugated genistein were evaluated in mice. B43-Genistein and genistein were administered either as single bolus injections or daily injections for 10 consecutive days via the intraperitoneal route to mice. Genistein was not toxic to mice at the highest dose of 40 mg/kg and no test article-related histopathological lesions were found in any of the 64 genistein-treated mice. B43-Genistein had a significantly longer elimination half-life and slower plasma and tissue clearance than unconjugated genistein. B43-Genistein was not toxic to mice at the highest single dose of 40 mg/kg or highest cumulative dose of 100 mg/kg and no test article-related histopathological lesions were found in any of the 108 mice treated with B43-genistein. To our knowledge, this is the first preclinical toxicity and pharmacokinetic study of a tyrosine kinase inhibitor-containing immunoconjugate.

Immunobiology of lipopolysaccharide (LPS) and LPS-derived immunoconjugates vaccinate mice against Salmonella typhimurium

The immunobiology of lipopolysaccharide (LPS) of Salmonella typhimurium LT2-71 was studied in its native, modified and conjugated states using mice as the experimental model. An alkali-treated detoxified fraction of LPS (D-LPS) was found to be not only non-toxic but also equally immunogenic, like LPS. In addition D-LPS alone or conjugated with enterotoxin or hemolysin was also non-pyrogenic and non-indurogenic. The immunoprophylactic activity of D-LPS conjugates to a 100 ID50 challenge dose of S. typhimurium was also higher than that of detoxified LPS or native LPS.

In vivo toxicity and pharmacokinetic features of B43 (anti-CD19)-genistein immunoconjugate in nonhuman primates

B43 (anti-CD19)-genistein immunoconjugate targets genistein, a naturally occurring protein tyrosine kinase-inhibitory isoflavone to the membrane-associated antiapoptotic CD19-LYN complexes and triggers apoptotic cell death. In this preclinical study, the toxicity profiles of B43-genistein as well as unconjugated genistein were evaluated in cynomolgus monkeys. B43-genistein and genistein were administered either as single bolus injections or daily injections for 5-10 consecutive days via the i.v. route to monkeys. Neither genistein nor B43-genistein was toxic to cynomolgus monkeys, and no test article-related histopathological lesions were found in any of the two genistein-treated or five B43-genistein-treated cynomolgus monkeys. B43-genistein showed a favorable pharmacokinetics in monkeys, with a plasma half-life of 10-23 h. Plasma samples from B43-genistein-treated monkeys elicited potent and CD19 antigenspecific antileukemic activity against human CD19+ leukemia cells in vitro. To our knowledge, this is the first preclinical toxicity and pharmacokinetic study of a tyrosine kinase inhibitor-containing immunoconjugate in nonhuman primates.

In vivo toxicity, pharmacokinetics, and antileukemic activity of TXU (anti-CD7)-pokeweed antiviral protein immunotoxin

We evaluated the TXU (anti-CD7)-pokeweed antiviral protein (PAP) immunotoxin in both murine and nonhuman primate models. TXU-PAP caused dose-limiting cardiac toxicity in BALB/c mice. In a SCID mouse model of invariably fatal human T-lineage acute lymphoblastic leukemia (ALL), TXU-PAP therapy resulted in a marked improvement of leukemia-free survival without any side effects. Whereas 100% of control mice treated with PBS, unconjugated TXU antibody, or B43-PAP (an immunotoxin that does not react with T-lineage ALL cells) died of disseminated human leukemia within 80 days (median survival, 37 days), 80 +/- 13% of SCID mice treated with 15 microgram of TXU-PAP (median survival, >120 days) and 100% of mice treated with 30 microgram of TXU-PAP (median survival, > 120 days) remained alive and free of leukemia for >120 days. In cynomolgus monkeys, TXU-PAP showed favorable pharmacokinetics with an elimination half-life of 8.1-8.7 h. The monkeys treated with TXU-PAP at dose levels of 0.05 mg/kg/day x 5 days and 0.10 mg/kg/day x 5 days tolerated the therapy very well, without any significant clinical compromise or side effects, and at necropsy, no gross or microscopic lesions were found. This study provides a basis for further evaluation of TXU-PAP as an investigational biotherapeutic agent in the treatment of T-lineage ALL.

Efficacy and toxicity of 67Cu-2IT-BAT-Lym-1 radioimmunoconjugate in mice implanted with human Burkitt's lymphoma (Raji)

Radioimmunotherapy has shown promising results for treatment of radiosensitive malignancies such as lymphoma. Positive responses have been reported in patients with non-Hodgkin's lymphoma treated with 131I-radiolabeled Lym-1, a mouse anti-lymphoma monoclonal antibody. In this study, the efficacy of 67Cu-radiolabeled Lym-1 was examined. Nude mice bearing human Burkitt's lymphoma (Raji) tumors (20-524 mm3) were treated with 12.4, 14.8, 18.5, and 23.3 MBq of 67Cu-2IT-BAT-Lym-1. Tumor size was measured to assess efficacy, and mouse weight, blood counts, and mortality were monitored to assess toxicity. In mice treated with 12.4, 14.8, and 18.5 MBq of 67Cu-2IT-BAT-Lym-1, 50% (9 of 18), 42% (5 of 12), and 50% (3 of 6) of tumors achieved remission or cure; 33% of tumors were cured overall; and significant regrowth delay was observed. The 23.3 MBq dose group did not yield meaningful efficacy data because of high mortality. In control groups receiving 14.8 and 18.5 MBq of the isotype-matched nonspecific monoclonal antibody radioimmunoconjugate, 67Cu-2IT-BAT-L6, 0% (0 of 15) and 17% (2 of 12) of tumors achieved a response; hence, targeted delivery of radiation was the dominant antitumor mechanism of 67Cu-2IT-BAT-Lym-1. LD50/30 for mice treated with 67Cu-2IT-BAT-Lym-1 and -L6 were 21.6 and 20.6 MBq, respectively. In conclusion, 67Cu-2IT-BAT-Lym-1 provided a therapeutic and frequently curative dose of radiation to tumored mice with modest toxicity.

Morphology of rat kidney and thymus after native and antibody-coupled cyclosporin A application (reduced toxicity of targeted drug)

This study compares the toxic effects of native cyclosporia A (CyA) with those of targeted CyA that is conjugated with the anti-rat-thymocyte antibody of rabbit origin via the N-(2-hydroxypropyl)methacrylamide (HPMA) carrier bearing digestible, reactive oligopeptide side chains. Ten toxic doses of native CyA (50 mg/kg i.p.) given to young adult rats in the course of 14 d produced a severe renal lesion-diffuse microvacuolization of the proximal tubules in the deep cortex, and hypergranulation of juxtaglomerular regions. Severe atrophy of the thymic medulla was documented by morphometry. In the cortex the epithelial reticular (but not deep interdigitating) cells showed ultrastructural signs of severe degeneration and lysis. The immature CD4+8+ double-positive cortical lymphocytes were preserved whereas the single-positive medullary thymocytes were greatly depleted; there was also a restriction of MHC class II antigen expression in the medulla. The number of medullary B cells was increased. The cytokeratin net was focally shrunken in the cortex and almost negative in the medulla, with loss of Hassall's corpuscles. After ten corresponding doses of antibody-targeted conjugated CyA no damage to the renal tubules and arterioles appeared and the antiGBM or immune-complex deposition was absent. The thymus had a normal medulla with numerous mature thymocytes and the cortical epithelial reticulum remained well preserved. Thus, the main toxic effects of CyA could be eliminated by targeting. The T-cell-targeted drug was tested for preserved immunosuppressive properties and non-toxic character of HPMA copolymer carrier.

Immunologic responses to gene transfer into mice via the polymeric immunoglobulin receptor

The respiratory epithelium is the primary target tissue for gene therapy of cystic fibrosis, and several methods of gene transfer permit the introduction of the gene encoding the normal cystic fibrosis transmembrane conductance regulator into cells of the respiratory tract in animals. DNA complexes based on Fab antibodies to secretory component have been used to mediate the delivery and uptake of expression plasmids into the respiratory tract via the polymeric immunoglobulin receptor both in vitro and in vivo. We evaluated the efficacy of gene transfer after several administrations of the DNA complexes, and examined the immunogenicity and toxicity of repetitive administration of anti-secretory component Fab-based complexes. Mice received single or multiple injections of the DNA complexes containing the plasmid pGL2 every 21 days after the initial treatment, and lysates from the lung and liver were assayed for luciferase expression. Luciferase activity was detected in the lungs of mice that received a single injection of the DNA complexes, whereas transgene expression was significantly lower in the mice that received three injections of the DNA complexes (17338 +/- 5469 integrated light units/mg and 3771 +/- 1778 integrated light units/mg, respectively). Serum samples from animals that underwent single or multiple injections were analyzed for a serologic response against the conjugate-DNA complexes by ELISA. No anticomplex antibodies were detected in the mice after a single injection. An escalating antibody response was noted with increasing number of treatments with the conjugate-DNA complexes. This serologic response was directed exclusively against the rabbit-derived, anti-secretory component (anti-SC) Fab antibody, and not against either the plasmid DNA or poly-L-lysine. Single injection of the conjugate-DNA complexes did not result in the consumption of circulating complement. Using direct immunofluorescence, perivascular deposits of immunoglobulin G were found in the liver of animals that received three treatments; no such deposition was detected in the lungs or kidneys. No increase in inflammatory cell infiltrates was observed in tissues after single and repeated injections of the DNA complexes. Thus, we conclude that repeated injections of the anti-SC Fab-based complexes evoked a humoral immune response against the heterologous Fab portion of the complex that was associated with reduced efficiency of gene transfer.

Specific targeting of phototoxic haptenated liposomes to a hapten-specific B cell lymphoma

A method is reported to eliminate B lymphocytes specific for a haptenated lipid by using the lipid hapten to target a photosensitive drug to them. The photosensitizer eosin was coupled to a phospholipid and incorporated into trinitrophenol (TNP)-bearing small unilamellar vesicles of egg phosphatidylcholine (PC) and cholesterol in order to target the photosensitizer to B lymphoma cells (A20-HL) with TNP-specific membrane IgM receptors in vitro. Exposure of the treated cells to visible light led to an antigen-specific toxic effect indicated by inhibition of cell proliferation. A significantly higher concentration of liposomal eosin was required to inhibit control B cells. These were genetically identical B lymphoma cells (A20-2J) which lack only the DNA for the surface antigen receptor. Furthermore, pretreatment with TNP-conjugated keyhole limpet hemocyanin or anti-IgM antibody abolished the antigen-specific toxic effect, confirming that the TNP-targeted liposomal eosin mediates its effect by binding to the Ig antigen receptors on TNP-specific B cells. Incubation of cells with the TNP-bearing phototoxic liposomes at 4 degrees C instead of 37 degrees C did not alter the antigen-specific targeting effect, suggesting that uptake of the liposomal drug into the cells is not necessary for its toxic effect. Replacement of the liposomal phospholipid (egg PC) with saturated species of PC having higher phase transition temperatures or with sphingomyelin caused a decrease of the antigen-specific effect. These results demonstrate the potential use of antigen-bearing liposomal phototoxic drugs for the purpose of targeting and eliminating B cells with antigen-specific surface Ig receptors.

Cytotoxicity of 213Bi- and 225Ac-immunoconjugates

This paper describes in vitro cytotoxicity experiments with 213Bi- and 225Ac-immunoconjugates on the human epidermoid tumour cell line A431 using a blood group A-reactive murine IgG (2D11) as the specific antibody and MOPC 21 as the control antibody. With both radionuclides, specific cell-killing was achieved. The observed cytotoxicity of 213Bi (T1/2 - 47 min) indicates that this radionuclide is a useful alternative for the alpha-emitter 212Bi in the treatment of blood-borne malignancies. 225Ac-immunoconjugates (T1/2 of 225Ac is 10 days) may be applicable for the treatment of solid tumours, since the daughter radionuclides of 225Ac contribute to the cytotoxic efficacy by a field effect (i.e. toxicity in an area distal from the antibody-binding site). The lack of an adequate chelator for 225Ac is a major drawback.

Biochemical and cytotoxic properties of conjugates of transferrin with equinatoxin II, a cytolysin from a sea anemone

Transferrin, a serum glycoprotein, is a major regulator of cellular growth via its cellular receptor. Because transferrin receptors are absent from the plasma membranes of most normal adult resting cells, but are present on transformed, activated, and malignant cells, it can be used to address a toxin toward these cells. The cytolysin equinatoxin II, isolated from the sea anemone Actinia equina L., was coupled to human apo or diferric transferrin by using a heterobifunctional cross-linking reagent, N-succinimidyl 3-(2-pyridyldithio)propionate (SPDP). The conjugates were separated by column chromatography, and their composition was demonstrated by electrophoresis, antibody staining, and determination of the hemolytic activity in the absence or presence of a reducing agent. The average molar ratio of equinatoxin II to transferrin for the studied conjugates was found to be approximately 3.4. The activity of the conjugates against human erythrocytes and human tumor cells (Raji and Jurkat) was assessed. The conjugate is very active on tumor cells in vitro; however, the hybrid molecule maintains an unspecific hemolytic activity. This unspecific toxicity is due to the fact that transferrin-bound toxin partially retains its original ability to bind to the cell membrane directly. It could be strongly reduced (and even eliminated) by pretreating the conjugates with sphingomyelin, the natural ligand of sea anemone cytolysins. These conjugates were stable versus temperature (up to at least 40 degrees C), versus time (up to several weeks at 4 degrees C and at least 1 year at -80 degrees C), and versus repeated freeze-thaw cycles with liquid nitrogen (but not with -80 degrees C).

Antibody-targeted drugs for the therapy of cancer

The advent of monoclonal antibodies has revitalised the concept of magic bullets and various agents (eg. drugs, toxins and isotopes) have been conjugated to monoclonal antibodies for selective delivery to tumours. Preclinical studies in mouse tumour models have been impressive and have lead to several clinical trials. These phase I trials have been less impressive. However, keeping in mind the aim of Phase I trials, the safety of using these conjugates in humans have been established. Several, major problems still remain to be overcome before these agents may be useful for the treatment of cancer. These problems stem from the nature of tumour vasculature, cytotoxic activity of the moiety linked to antibody and the targeted tumour antigen expressed on the cell surface. This review will deal with these various aspects described above and possible approaches to overcome these obstacles with a definite bias towards drug-monoclonal antibody conjugates. However, these concepts are equally applicable for improved targeting of other agents.