Therapeutic strategies with monoclonal antibodies and immunoconjugates.
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Antibodies, Monoclonal↗
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Monoclonal antibodies and immunoconjugates for cancer treatment.
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Animals↗
Monoclonal antibodies and immunoconjugates for cancer treatment.
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Antibodies, Monoclonal↗
Increased antitumor effect of immunoconjugates and tumor necrosis factor in vivo.
The potential of specifically targeting antineoplastic drugs and toxins to tumors with the use of monoclonal antibodies (MoAbs) reactive with tumor-associated antigens is currently being examined. N-Acetyl-melphalan-MoAb (N-AcMEL-MoAb) conjugates have previously been shown to have greater antitumor activity than N-AcMEL, melphalan, or MoAb alone against both subcutaneous and ascites murine thymomas in mice (1). Although this conjugate is also a highly selective tumor inhibitor in vitro, it may not reach all the tumor cells in a high concentration, and consequently larger tumors (greater than 0.4 cm2) cannot be eradicated. This conjugate is representative of many drug-MoAb conjugates in that they are unable to gain adequate access to the tumor site to exert their cytotoxic effect. To potentiate the antitumor effect of the N-AcMEL-MoAb conjugate, studies were undertaken to analyze its action in combination with recombinant human tumor necrosis factor alpha (rTNF-alpha), a monokine, capable of causing acute necrosis of syngeneic tumor transplants in mice. Treatment of mice with murine thymomas (0.4 to 0.6 cm2 in size) demonstrated that 30% of the tumors in mice receiving conjugate and rTNF-alpha partially or completely regressed, while no regressions were observed in the tumors of mice receiving N-AcMEL-anti-Ly-2.1 conjugate or rTNF-alpha alone. This and other experiments indicated that the antitumor effect and tumor localization of N-AcMEL-MoAb conjugates can be enhanced in vivo by rTNF-alpha, thereby enabling successful eradication of larger established subcutaneous murine tumors.
Animals↗
Enhancement of the selectivity and antitumor efficacy of a CC-1065 analogue through immunoconjugate formation.
Bis-indolyl-(seco)-1,2,9a-tetrahydrocyclopropa[c]benz[e]indol-4-on e compounds are synthetic analogues of CC-1065 that are highly cytotoxic toward a broad spectrum of tumor cell lines. One of these compounds, called DC1, was conjugated to antibodies via novel cleavable disulfide linkers. Conjugates of DC1 with murine mAbs anti-B4 and N901 directed against tumor-associated antigens CD19 and CD56, respectively, proved to be extremely potent and antigen selective in killing target cells in culture. DC1 conjugates with humanized versions of anti-B4 and N901 antibodies were also constructed and demonstrated to be as cytotoxic and selective as the respective murine antibody conjugates. The anti-B4-DC1 conjugate showed antitumor efficacy in an aggressive metastatic human B-cell lymphoma survival model in SCID mice and completely cured animals hearing large tumors. Anti-B4-DC1 was considerably more effective in this tumor model than doxorubicin, cyclophosphamide, etoposide, or vincristine at their maximum tolerated doses.
Animals↗
Differential patterns of response in patients with rheumatoid arthritis following administration of an anti-CD 5 immunoconjugate.
As part of the clinical investigation of a new biologic agent in the treatment of rheumatoid arthritis (RA) various outcome measures were utilized to evaluate clinical activity in two multicenter open label protocols. These measures included the single criteria of joint tenderness and swelling counts and scores and composite criteria based on the Paulus analysis of four placebo-controlled CSSRD studies of second line agents in RA. Findings suggest a difference in the pattern of response between early and long-standing RA. Changes in both the swollen and tender joint counts should be utilized, especially in a population with sustained disease.
Antibodies, Monoclonal↗
Anti-chelate antibodies after intraperitoneal yttrium-90-labeled monoclonal antibody immunoconjugates for ovarian cancer therapy.
UNLABELLED: The development of stable chelating agents for metal isotopes (e.g., 90Y) such as CITC-DTPA, a benzyl-analog of DTPA, allowed us to evaluate the efficacy of 90Y-labeled HMFG1 MAb administered intraperitoneally in patients with ovarian cancer. Our previous studies of 90Y-HMFG1 antibody, however, showed that all patients developed anti-chelate antibody responses (to the macrocycle benzyl-DOTA), resulting in clinical side effects in a significant percentage of this group. METHODS: We evaluated the immunogenicity of CITC-DTPA (administered to 12 patients as 90Y-HMFG1-CITC-DTPA after coupling it to HSA using solid-phase ELISA. RESULTS: Eleven of 12 evaluable patients developed anti-CITC-DTPA antibodies. Five patients (approximately 40%) developed hypersensitivity syndrome, most likely due to a type III immune reaction (serum sickness). Most patients had a low titer of pre-existing anti-chelate response which correlated positively with post-therapy response levels (p = 0.001). IgM anti-CITC-DTPA antibodies developed 2 wk while IgG antibodies developed 3 wk after treatment. Western blot analysis of post-therapy sera revealed a reaction with HSA-CITC-DTPA (60 kDa band) and no reaction with HSA or HSA-DTPA, whereas pre-therapy sera of the same patients were negative to all antigens. CONCLUSION: CITC-DTPA is immunogenic in patients after intraperitoneal administration of 90Y-CITC-DTPA labeled MAbs. Self-limiting clinical side effects consistent with a serum sickness-like immune reaction were observed in 5 of 12 patients.
Antibodies↗
[Effect of targeting treatment of mitomycin C immunoconjugate on stomach neoplasm].
An anti-gastric cancer monoclonal antibody MGb2-mitomycin C conjugate via dextran T-70 as intermediate (MGb2-PAD-MMC) was produced, and 28-30 g molecules of MMC were introduced into 1 g molecule of MGb2. Ninety-six hours after ip of 125I-MGb2-PAD-MMC (1.48 MBq/22 micrograms MGb2 per mouse) to nude mice bearing human gastric cancer SGC-7901, the tumor tissue:blood (T/NT) radioactivity ratio was 2.6, very much higher than that of the control 125I-normal IgG-PAD-MMC group (T/NT = 0.20). Single photo computed tomography imaging confirmed the results of biodistribution study. MGb2-PAD-MMC exhibited selective killing action on the SGC-7901 cells in vitro, which was considered to be mediated by monoclonal antibody MGb2. Nude mice inoculated with SGC-7901 xenograft in bilateral subrenal capsule were treated by MMC (ip), human recombinant interferon-alpha (Hu-IFN-alpha im), MGb2-PAD-MMC (ip) and MGb2-PAD-MMC+Hu-IFN-alpha daily for 5 d beginning 4 h after inoculation. The efficacy of the reagents estimated by the reduction of tumor size and calculated by T/C (%), was 28.3%, 16.4%, 47.8%, and 83.1%, respectively. These results demonstrated that the antitumor effect of MGb2-PAD-MMC was superior to free MMC, and that the Hu-IFN-alpha might further enhance the action of MGb2-PAD-MMC.
Adenocarcinoma↗
[Anticancer immunoconjugates: current status and prospects].
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Animals↗
[Antitumor effect of the immunoconjugate composed of antibiotic C1027 and Fab fragment from a monoclonal antibody directed against human hepatoma].
Antibiotic C1027, a macromolecular peptide with highly potent cytotoxicity to cultured cancer cells, was conjugated to monoclonal antibody 3A5 and its Fab fragment separately using SPDP as the linker agent. McAb 3A5, identified as IgG1, was directed against human hepatoma BEL-7402 cells. By ELISA, McAb 3A5 and the Fab fragment were strongly reactive with hepatoma cells and weakly reactive with KB cells. Determined by clonogenic assay against hepatoma BEL-7402 cells, the IC50 values for McAb-C1027, Fab-C1027 and C1027 were 4.2 x 10(-14), 8.6 x 10(-16) and 6.5 x 10(-16) mol.L-1, respectively. Fab-C1027 was 49-fold more potent than McAb-C1027 in cytotoxicity. Moreover, Fab-C1027 was 160-fold more potent in cytotoxicity to hepatoma cells than to KB cells, indicating selective cytotoxicity of Fab-C1027 conjugate to the target cells. Therapeutic effect of the conjugate was evaluated with hepatoma BEL-7402 xenograft in nude mice. After subcutaneous transplantation of the tumor, treatment started on day 3, iv, with equivalent dose of C1027, 0.1 mg.kg-1 x 6. Fab-C1027 and free C1027 inhibited tumor growth by 85% and 59%, respectively. Fab-C1027 conjugate showed more marked antitumor effect in vivo than free C1027.
Aminoglycosides↗
An immunotoxin composed of a monoclonal antitransferrin receptor antibody linked by a disulfide bond to the ribosome-inactivating protein gelonin: potent in vitro and in vivo effects against human tumors.
An immunoconjugate was prepared containing a disulfide linker between a murine monoclonal antibody (5E9), which recognized the human transferrin receptor, and the ribosome-inactivating protein gelonin. This immunoconjugate was found to consist of two major species, 5E9-gelonin2 and 5E9-gelonin1, and a minor species of 5E9-gelonin3 and less than 10% of either free antibody or gelonin. 5E9-gelonin was extremely toxic in vitro to human tumor cell lines expressing the 5E9 antigen, including a Burkitt's lymphoma, an adult T-cell acute lymphocytic leukemia, an acute myelogenous leukemia, a promyelocytic leukemia, and a cervical carcinoma line. A 24-hour exposure to 10(-9) M immunoconjugate killed 90-99.9% of tumor cells, depending on the cell line. A 5E9-negative murine leukemia was not sensitive to this conjugate. Pharmacokinetic analysis of the disappearance of this immunoconjugate from the murine circulation revealed that it had a biphasic clearance, with an initial rapid phase with a half-life (t1/2) of 3 hours and a later, slower phase with a t1/2 of about 1 day. Analysis of blood samples by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis revealed that a substantial degree of disulfide-linker breakdown occurred in vivo and that the 5E9-gelonin2 species was cleared more rapidly than the 5E9-gelonin1. With use of the same clonogenic assays used to measure in vitro toxicity, biologically active immunoconjugate could be detected in murine plasma for up to 24 hours after iv administration, but the concentration of immunoconjugate by this measure was considerably less than that predicted by SDS-gel electrophoresis. The ability to deliver immunoconjugate to tumor cells in vivo was studied with use of the Burkitt's lymphoma Namalwa as a xenograft in nude mice. It was possible to deliver substantial amounts of immunoconjugate to Namalwa cells in xenografted ascites with direct ip inoculation; lower but significant amounts of immunoconjugate could be delivered to this xenograft after systemic iv administration, provided the tumor burden was low. The 5E9-gelonin conjugate, when administered iv at the time of ip tumor inoculation, prolonged survival of nude mice bearing Namalwa or other human tumors as ascites xenografts and delayed or prevented the growth of subcutaneous nodules of Namalwa in an antigen-specific fashion after a single iv injection. Direct intratumoral administration also inhibited the growth of visible subcutaneous nodules of Namalwa. This immunoconjugate may be useful in the treatment of human cancer.
Animals↗
Antibody immunoglobulin G (IgG) against human prostatic specific antigen (PSA) as a carrier protein for chemotherapeutic drugs to human prostate tumors: Part 1. A double immunofluorescence analysis.
BACKGROUND: Adenocarcinoma of the prostate (CaP) is the the second highest cause of cancer deaths in U.S. males. Current chemotherapeutic and/or endocrine treatments do not specifically and selectively target tumor cells of prostate cancer and benign prostatic hyperplasia (BPH). We hypothesized that because of the specific binding characteristics of antibody immunoglobulin G (IgG) to human prostatic-specific antigen (PSA), PSA-IgG could function as a carrier protein for conjugated chemotherapeutic drugs and that the immunoconjugate would selectively bind to prostatic epithelial cells and their tumors, but not to epithelial cells of unrelated organs. Our objective was to test the hypothesis using human prostatectomy specimens. METHODS: WE used several derivatives of 5'-fluorouracil, namely, 5'-fluoro- 2'-deoxyuridine (5'-Fu-2'-d), 5'-fluoro-2'-deoxyuridine-5' monophosphate (5'-Fu-2'-d-5'-mp), 5'-fluoro-2'-deoxyuridine-5'-(p-aminophenyl) monophosphate (5'-Fu-2'-d'-5'-amp), to conjugate with rabbit anti-PSA-IgG together with fluorescent markers (such as rhodamine and fluorescein or fluorescein isothiocyanate: FITC). Prostate specimens were obtained from prostatectomy patients who had not been treated with cytotoxic drugs before surgery. We evaluated formalin-fixed and paraffin-embedded sections as well as cryostat sections of frozen specimens for localization of PSA-IgG alone and PSA-IgG-drug immunoconjugate using immunoperoxidase (IP) and single and/or double immunofluorescence (IF) localization techniques. RESULTS: Our study showed that the immunoconjugate (PSA-IgG-5'-Fu-2'-d) bound to PSA (molecular size of approximately 34 KDa) on nitrocellulose sheets in Western immunoblots of extracts of BPH and CaP tissues. This binding of immunoconjugate to PSA on immunoblots was similar to that of the unconjugated PSA-IgG. Immunostaining patterns for rabbit anti-PSA-IgG and PSA-IgG-5'-Fu-2'-d immunoconjugate were similar and specific for prostate epithelial cells and their tumors, as revealed by IP techniques. To demonstrate that both the antibody and drug localized in the same group of prostatic epithelial cells, we used an immunoconjugate in which the PSA-IgG was labeled with rhodamine and 5'-Fu-2'-d-5'-amp with FITC. Our study showed that fluorescence for rhodamine and FITC was present in the same group of prostatic epithelial cells. Phase contrast microscopy demonstrated details of prostatic glandular epithelium and connective tissues. Our study showed that fluorescence for rhodamine and FITC and immunostaining by IP techniques were not observed in prostate sections incubated with normal rabbit serum. CONCLUSIONS: We have shown that conjugation of 5'-Fu derivatives to PSA-IgG did not affect either the selectivity or specificity of the antibody for prostatic epithelial cells. Differential immunofluorescence study has shown that PSA-IgG may function as a carrier protein for chemotherapeutic drugs to prostate epithelial cells and their tumors. Furthermore, FITC-labeled 5'-Fu-2'-d did not specifically localize in prostatic glands, kidney, lungs, bladder, or colon. Because of the specificity and selectivity of the immunoconjugate for prostatic epithelial cells and their tumors, the immunoconjugate could be used in small dosages to treat prostatic tumors and such treatment would greatly reduce many unpleasant side effects in patients. This is the first report to show that PSA-IgG can function as an organ specific carrier protein for chemotherapeutic drugs to human prostate epithelium and its tumors.
Antibodies↗
Enhanced antitumour effects using a combination of two antibodies conjugated to different drugs.
The heterogeneity of tumour antigen expression, the differential sensitivity of individual cells to drugs and the use drug--antibody immunoconjugates with limited potency can limit the antitumour effects of immunoconjugate therapy. In this study we have used two different antibodies linked to two different drugs Melphalan (Mel) and Idarubicin (Ida), each with a different site action, to evaluate the potential of using cocktails of immunoconjugates. A series of drug combinations were screened for their synergistic activity in vitro using the inhibition of [3H]-thyrmidine uptake by E3 cells, and constructing isobolagrams: Mel plus Ida was the only combination found to be synergistic in vitro and this synergism extended to the drugs after conjugation to antibodies. In addition, in vivo studies in mice bearing E3 tumours showed that synergy between both free drugs and between Ida-anti-Ly-2.1 and N-AcMEL-anti-Ly-3.1 immunoconjugates was time dependent, requiring treatment with Ida or Ida-MoAb conjugates prior to the addition of the second melphalan containing immunoconjugate. The use of two different antibodies, anti-Ly-2.1 and anti-Ly-3.1 against E3 (Ly-2.1+ve, Ly-3.1+ve) gave greater synergy in vitro compared to using only one antibody. Again a cocktail of two antibody immunoconjugates provided significantly greater antitumour efficacy when given to tumour bearing mice, provided that the Ida-anti-Ly-2.1 was given 24 h before injection of N-AcMEL-anti-Ly-3.1. The enhanced antitumour effect was not observed when the immunoconjugates were given simultaneously, or if the same antibody was used in each conjugate. Of importance was the finding that although the anti-tumour effect was synergistic, there was no increase in toxicity noted. The increased therapeutic index observed by using a double cocktail (2 antibodies + 2 drugs) could have major implications for immunoconjugate therapy.
Animals↗
The antileukemic efficacy of an immunotoxin composed of a monoclonal anti-Thy-1 antibody disulfide linked to the ribosome-inactivating protein gelonin.
We prepared an immunoconjugate consisting of a monoclonal antibody recognizing the Thy-1 antigen and the ribosome-inactivating protein gelonin linked by a disulfide bond. This immunotoxin preparation was judged to contain less than 5% free antibody or gelonin. It was highly toxic in vitro in an antigen-specific fashion to the Thy-1 expressing RADA leukemia of A/J mice. The IC50 of this preparation on RADA in vitro was 10(-12) M, while the IC50 on the Thy-1 negative S1509a fibrosarcoma of A/J mice was 10(-7) M. The toxicity of this immunoconjugate was also measured in a direct proliferation and it was found that a 4-h exposure and a 24-h exposure of RADA cells to a 1 nM concentration of immunotoxin killed 90% and 99.9% of cells, respectively. Furthermore, efficacy in vitro was not due to the intrinsic susceptibility of RADA cells to tis type of immunotoxin, as one prepared with gelonin and an antibody recognizing the TLa determinant on this leukemia had no efficacy in vitro. Clearance of the anti-Thy-1-gelonin immunoconjugate from the circulation of A/J mice after i.v. injection was rapid, especially during the first 8 h after injection, possibly because of binding to Thy-1 expressing tissue. Delivery of immunoconjugate to ascitic tumor in vivo was substantially better if the immunoconjugate was given by i.p. injection, rather than by the i.v. route. When given either i.v. or i.p. at the time of i.p. tumor inoculation in vivo, the anti-Thy-1-gelonin immunotoxin showed potency in an antigen-specific fashion; while this immunoconjugate prolonged survival and frequently cured RADA-inoculated mice, neither anti-Thy-1 antibody, gelonin, a combination of the two, nor immunotoxin of irrelevant specificity had any significant effect on survival. Anti-Thy-1-gelonin also had no effect on survival of A/J mice inoculated i.p. with S1509a. Furthermore, it was determined that a single i.p. dose of anti-Thy-1-gelonin killed 90% to 99% cells in vivo, and that the immunoconjugate was about as effective in this model as either adriamycin or cytoxan.
Animals↗
The use of natural interferon alpha conjugated to a monoclonal antibody anti mammary epithelial mucin (Mc5) for the treatment of human breast cancer xenografts.
An immunoconjugate composed of natural interferon alpha (nIFN alpha) bound in a noncleavable fashion to a monoclonal antibody (MoAb) recognizing a breast epithelial membrane mucin (Mc5) was used to to treat xenografts of a human mammary carcinoma cell line (MCF-7) growing in nude mice. The immunoconjugate (nIFN alpha/Mc5) was administered as 20 intralesional (i.l.) injections to 1 of 2 xenografts in each animal. It was found that nIFN alpha/Mc5 produced a significant enhancement of the growth inhibitory actions of nIFN alpha on the injected tumors. Further enhancement was obtained when nIFN gamma or nIFN gamma together with Mc5 (at a dose 10 times larger than that present in nIFN alpha/Mc5) were added to the immunoconjugate. Biodistribution experiments showed that the uptake of 125I-nIFN alpha/Mc5 by the tumors was greater and its elimination slower than for 125I-nIFN alpha alone or conjugated to irrelevant mouse IgG1. In addition, the immunoconjugate up-regulated the antigenic expression of a breast epithelial membrane mucin by the carcinoma cells, an up-regulation which was not significantly different from that produced by nIFN alpha alone. The contralateral noninjected tumors exposed to systemic levels of the immunoconjugate showed an enhancement of antitumor effects, but to a lesser extent than the injected tumors. These findings suggest that the enhancement of the growth inhibitory action of the immunoconjugate was related to the specific binding of Mc5 which targeted the IFN to the carcinoma cells and impeded its elimination. It is likely that the targeting was favored by the IFN-mediated up-regulation of antigenic expression by the carcinoma cells, thereby producing a cascade of interrelated effects. The results of this study point out the feasibility and potential usefulness of IFN treatment by means of immunoconjugates as well as the worth of pursuing and improving this form of therapy.
Animals↗
Antibody conjugates with cobra venom factor. Synthesis and biochemical characterization.
Immunoconjugates are semi-synthetic hybrid proteins which bear great promise to become a new generation of anti-tumor agents. While many immunoconjugates have been shown to be selectively cytotoxic in in vitro model systems, dramatic in vivo anti-tumor effects have not been reported. To improve the activity of immunoconjugates, careful structure-function analyses have to be performed. We report here such an analysis for immunoconjugates consisting of a monoclonal anti-tumor antibody (MoAb) and cobra venom factor (CVF), the complement-activating glycoprotein from cobra venom, synthesized with the heterobifunctional crosslinking reagent N-succinimidyl-3-(2-pyridyldithio)propionate (SPDP). It is shown that a reaction mixture after protein coupling contains free MoAb and CVF as well as hybrid proteins of different compositions (dimers (MoAb-CVF), trimers (MoAb2-CVF, MoAb-CVF2), tetramers (MoAb-CVF3, MoAb2-CVF2, MoAb3-CVF), and some higher oligomers). While free MoAb and CVF can be removed by size exclusion chromatography, separation of different oligomeric hybrid proteins is not possible by this method. From the biochemical characterization of the hybrid proteins, which included the determination of sedimentation coefficients, recording of circular dichroism spectra with subsequent determination of secondary structure, and ultrastructural analysis by transmission electron microscopy, it was concluded that the two proteins do not undergo major structural changes upon coupling, and that the coupling of the two proteins is random with no preferential relative orientation. The functional inactivation of CVF was substantial (approximately 70%) due to both derivatization with SPDP and subsequent conjugation to the MoAb, with conjugation being relatively more inactivating than derivatization. In contrast, the binding activity of the antibody was far less susceptible to inactivation. In conclusion, our data indicate that immunoconjugate synthesis with heterobifunctional crosslinking reagents results in a mixture of heterogeneous hybrid proteins and causes substantial functional inactivation. For successful in vivo anti-tumor activity of future immunoconjugates with CVF and other protein ligands better methods for immunoconjugate synthesis will have to be developed.
Antibodies, Neoplasm↗
Time-resolved fluorescence microscopy using an improved europium chelate BHHST for the in situ detection of Cryptosporidium and Giardia.
Fluorescent immunoconjugates prepared with the europium chelate BHHCT (4,4'-bis(1'',1'',1'',2'',2'',3'',3''-heptafluoro-4'',6''-hexanedion-6''-yl)-chlorosulfo-o-terphenyl) have previously been reported as suitable labels for time-resolved fluorescence applications. BHHCT is limited by a tendency to destabilize immunoglobulins when covalently bound to the protein at moderate to high fluorophore to protein ratios (F/P). We report a new derivative of BHHCT prepared by appending a short hydrophylic tether to the chlorosulfonate activating group on BHHCT. The new derivative, BHHST (4,4'-bis-(1'',1'',1'',2'',2'',3'',3''-heptafluoro-4'',6''-hexanedion-6''-yl)sulfonylamino-propyl-ester-N-succinimide-ester-o-terphenyl), was activated to bind at the tether terminus with a succinimide leaving group that displayed less aggressive coupling activity and improved storage stability. BHHST has been used to prepare a stable and useful immunoconjugate with the anti-Cryptosporidium monoclonal antibody CRY104. The BHHST immunoconjugate provides more than a 10-fold enhancement in the signal to noise ratio (SNR) of labeled oocyst fluorescence over background when observed using TRFM techniques. An immunoconjugate was also prepared with BHHST and (goat) anti-mouse that effectively labeled Giardia cysts in situ. Detection of cysts with the TRFM was achieved with an 11-fold increase in SNR when a gate-delay of 60 micros was employed. The storage half-life of both immunoconjugates is extended more than 20-fold when compared to immunoconjugates prepared with BHHCT.
Animals↗
Targeting tumor vasculature endothelial cells and tumor cells for immunotherapy of human melanoma in a mouse xenograft model.
An immunotherapy treatment for cancer that targets both the tumor vasculature and tumor cells has shown promising results in a severe combined immunodeficient mouse xenograft model of human melanoma. The treatment involves systemic delivery of an immunoconjugate molecule composed of a tumor-targeting domain conjugated to the Fc effector domain of human IgG1. The effector domain induces a cytolytic immune response against the targeted cells by natural killer cells and complement. Two types of targeting domains were used. One targeting domain is a human single-chain Fv molecule that binds to a chondroitin sulfate proteoglycan expressed on the surface of most human melanoma cells. Another targeting domain is factor VII (fVII), a zymogen that binds with high specificity and affinity to the transmembrane receptor tissue factor (TF) to initiate the blood coagulation cascade. TF is expressed by endothelial cells lining the tumor vasculature but not the normal vasculature, and also by many types of tumor cells including melanoma. Because the binding of a fVII immunoconjugate to TF might cause disseminated intravascular coagulation, the active site of fVII was mutated to inhibit coagulation without affecting the affinity for TF. The immunoconjugates were encoded as secreted molecules in a replication-defective adenovirus vector, which was injected into the tail vein of severe combined immunodeficient mice. The results demonstrate that a mutated fVII immunoconjugate, administered separately or together with a single-chain Fv immunoconjugate that binds to the tumor cells, can inhibit the growth or cause regression of an established human tumor xenograft. This procedure could be effective in treating a broad spectrum of human solid tumors that express TF on vascular endothelial cells and tumor cells.
Adenoviridae↗