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PubMed1997

Immunoconjugates made of an anti-EGF receptor monoclonal antibody and type 1 ribosome-inactivating proteins from Saponaria ocymoides or Vaccaria pyramidata.

The present paper describes two immunoconjugates consisting of an anti-epidermal growth factor receptor (EGFR) monoclonal antibody (MAb), named Mint5, covalently linked to the type 1 ribosome-inactivating proteins (RIPs) ocymoidine (Ocy) and pyramidatine (Pyra) from Saponaria ocymoides and Vaccaria pyramidata respectively. Both antibody and toxins are shown to retain their respective biological properties upon chemical conjugation. The immunoconjugates exert specific inhibition of EGFR expressing target cell proliferation and protein synthesis in in vitro assays and also inhibit the growth of grafted human tumour cells in nude mice.

Animals↗
PubMed1993

Potent anti-CD5 ricin A chain immunoconjugates from bacterially produced Fab' and F(ab')2.

We have used genetic engineering to obtain secretion of anti-human CD5 antibody fragments from Escherichia coli for conjugation to the 30-kDa form of ricin A chain (RTA30). This was accomplished by introducing stop codons at two positions in the hinge region of the human IgG1 gene so that coexpression of the truncated heavy-chain genes (Fd') with a light chain would result in Fab' and/or F(ab')2 proteins containing either one or two interheavy-chain cysteines. An Fd' gene encoding both interheavy-chain cysteines yielded a mixture of F(ab')2 and Fab', which could be separated by size-exclusion chromatography. An Fd' gene encoding only one interheavy-chain cysteine yielded primarily Fab'. Purified F(ab')2 protein was equivalent to unlabeled chimeric IgG in competing for binding of IgG with CD5 antigen, while the molar concentration of the monovalent Fab' required for 50% binding inhibition was 4- to 5-fold higher than IgG. An immunoconjugate was prepared with Fab' by direct coupling to the unique free cysteine on RTA30. The bivalent F(ab')2 was conjugated to RTA30 after derivatization with the crosslinking agent 5-methyl-2-iminothiolane. These immunoconjugates efficiently killed a CD5+ T-cell line and human peripheral blood T cells.

Amino Acid Sequence↗
PubMed1999

Stability of monoclonal antibodies, Lym-1 and ChL6, and 2IT-BAD-Lym-1 immunoconjugate with ultra freezer storage.

UNLABELLED: Use of a single lot of monoclonal antibody (MoAb) or immunoconjugate for clinical studies provides efficiency of scale and consistent characteristics for MoAb-based pharmaceuticals. Lym-1, an anti-lymphoma mouse IgG2 alpha chimeric L6 (ChL6), an anti-adenocarcinoma mouse IgG2 alpha-human IgG1 chimera, and the immunoconjugate 2IT-BAD-Lym-1 were examined for stability following storage. METHODS: Lym-1, ChL6, and 2IT-BAD-Lym-1 were aliquotted with filtration and stored at -70 degrees C for up to 8.5 years. 2IT-BAD-Lym-1 stored for 6.3 years (lot A) was compared to freshly prepared 2IT-BAD-Lym-1 (lot B). MoAbs were thawed and examined yearly by gel filtration high performance liquid chromatography (HPLC), polyacrylamide gel electrophoresis (PAGE), cellulose acetate electrophoresis (CAE), and Scatchard analysis of antigen binding. 2IT-BAD-Lym-1 was evaluated by HPLC, CAE, and radioimmunoassay. To assure the in vivo significance of the in vitro studies, 2IT-BAD-Lym-1 lots A and B were labeled with 111In and their pharmacokinetics in BALB/c mice were compared. RESULTS: Lym-1 demonstrated stability over 8.5 years, providing the following ranges of data over the interval: 98-100% chemical purity (HPLC), 96-100% monomeric fraction (CAE), 8.18-8.46 antigen binding pKa (Scatchard). Similar results were obtained for ChL6 for 7.4 years. HPLC and PAGE of Lym-1 and ChL6 have not changed from original manufacturer specifications, and both MoAbs remain sterile and apyrogenic. No significant differences between 2IT-BAD-Lym-1 lots A and B were observed by in vitro evaluation or pharmacokinetics in mice. CONCLUSIONS: Lym-1, ChL6, and 2IT-BAD-Lym-1 as manufactured and stored for 8.5, 7.4, and 6.3 years, respectively, demonstrated retention of structural and functional integrity.

Animals↗
PubMed1991

Expression of genetically engineered immunoconjugates of lymphotoxin and a chimeric anti-ganglioside GD2 antibody.

Human lymphotoxin was genetically conjugated to the constant region of a human gamma 1 immunoglobulin gene at the end of either the second (CH2-LT) or third (CH3-LT) constant region domain. The altered heavy chain constant regions were combined in a plasmid vector together with the variable regions of a mouse anti-ganglioside GD2 antibody 14.18 and the human kappa constant region. The resulting immunoconjugate constructs were expressed in transfected hybridoma cells and tested for both their antibody and lymphotoxin activities. The two constructs were assembled to varying degrees depending on whether the third heavy chain constant region was present. Both forms retained their ability to bind antigen and mediate ADCC but only CH3-LT was able to mediate the lysis of melanoma target cells in the presence of human complement. Lymphotoxin activity, as defined in a cytolytic assay with mouse fibroblasts, was found to increase significantly as a function of heavy chain assembly and to be equivalent to unconjugated lymphotoxin. Neither of the constructs were cytotoxic for antigen-bearing melanoma cells that are normally resistant to lymphotoxin and tumor necrosis factor alpha. Such immunoconjugates may prove useful in targeting cytokines to the site of antigen-bearing cells in vivo. In this case, as a means of eliciting an inflammatory response at the site of a solid tumor.

Animals↗
PubMed1993

Anti-human immunodeficiency virus type 1 activity of an anti-CD4 immunoconjugate containing pokeweed antiviral protein.

The ability of an alpha CD4-pokeweed antiviral protein (PAP) immunoconjugate to inhibit replication of human immunodeficiency virus type 1 (HIV-1) was evaluated in vitro with 22 clinical HIV-1 strains obtained from four seropositive asymptomatic individuals, three patients with AIDS-related complex, and four patients with AIDS. Fifteen isolates were from zidovudine-untreated individuals, whereas seven isolates were obtained after 24 to 104 weeks of therapy with zidovudine, alone or alternating with zalcitabine. Mean zidovudine 50% inhibitory concentrations (IC50s) were 126 nM (range, 1 to 607 nM) for isolates from zidovudine-untreated individuals and 2,498 nM (range, 14 to 6,497 nM) for strains from patients treated with antiretroviral agents. Mean alpha CD4-PAP IC50s were 48 x 10(-3) nM (range, 0.02 x 10(-3) to 212 x 10(-3) nM) for isolates from zidovudine-untreated individuals, and 16 x 10(-3) nM (range, 2 x 10(-3) to 28 x 10(-3) nM) for isolates from treated patients. Overall, higher concentrations of alpha CD4-PAP were necessary to inhibit HIV-1 strains from untreated individuals at more advanced stages of disease. Seventeen isolates were susceptible to zidovudine (mean IC50, 117 nM), and five were resistant to zidovudine (mean IC50, 3,724 nM). Mean alpha CD4-PAP IC50s were 43 x 10(-3) nM for zidovudine-susceptible isolates and 19 x 10(-3) nM for isolates resistant to zidovudine. All HIV-1 strains had IC50s greater than 0.5 nM for unconjugated PAP, the alpha CD19-PAP immunoconjugate, and monoclonal antibody alpha CD4. At concentrations as high as 5,000 nM, alphaCD4-PAP did not inhibit colony formation by normal bone marrow progenitor cells(BFU-E, CFU-GM , and CFU-GEMM) or myeloid cell lines (KG-1 and HL-60) and did not decrease cell viabilities of T-cell (Jurkat) or B-cell (FL-112 and Raji) precursor lines. Overall, alphaCD4-PAP demonstrated more potent anti-HIV-1 activity than zidovudine and inhibited replication of zidovudine-susceptible and zidovudine-resistant viruses at concentrations that were not toxic to lymphohematopoietic cell populations.

AIDS-Related Complex↗
PubMed1992

Thrombolytic and pharmacokinetic properties of an immunoconjugate of single-chain urokinase-type plasminogen activator (u-PA) and a bispecific monoclonal antibody against fibrin and against u-PA in baboons.

Targeting of plasminogen activators to the fibrin component of a thrombus with the use of monoclonal antibodies (MA) directed against human fibrin may enhance their thrombolytic potency and fibrin-specificity. The thrombolytic and pharmacokinetic properties of rscu-PA/MA-FU1-74, an immunoconjugate of recombinant single-chain urokinase-type plasminogen activator (rscu-PA) and a bispecific MA directed against u-PA and against the beta-chain of human fibrin (MA-FU1-74), were investigated in baboons with a [125I]fibrin-labeled autologous blood clot in the femoral vein. Continuous intravenous infusion of rscu-PA/MA-FU1-74 (1:1.2 molar ratio) over 2 hours showed a fivefold increased thrombolytic potency (lysis per unit dose) over that of unconjugated rscu-PA, as evidenced both by a higher maximal rate of lysis (380% +/- 68% v 78% +/- 25% lysis per mg u-PA equivalent of compound administered per kg body weight, P less than .001), and by a lower dose at which the maximal rate of lysis occurs (0.19 +/- 0.03 v 0.82 +/- 0.10 mg compound per kg body weight, P less than .001). The specific thrombolytic activity (percent lysis per unit steady-state plasma u-PA antigen level) was lower for rscu-PA/MA-FU1-74 than for rscu-PA, as shown by both a lower maximal rate of lysis (60% +/- 13% v 220% +/- 22% lysis per microgram/mL u-PA antigen level in plasma, P less than .001) and a higher plasma antigen level at which maximal lysis is achieved (1.2 +/- 0.17 v 0.20 +/- 0.01 microgram/mL, P less than .001). The thrombolytic potency of rscu-PA/MA-UK1-3, an immunoconjugate of rscu-PA with the parental anti-u-PA antibody was similar to that of unconjugated rscu-PA. Clot lysis was achieved without systemic fibrinogen or alpha 2-antiplasmin consumption, and with a minor transient prolongation of the bleeding time. After the end of the infusions, u-PA-related antigen disappeared from plasma in a biphasic manner, with an initial half-life of 3.3 +/- 0.4 minutes for rscu-PA, 13 +/- 1 minutes for rscu-PA/MA-FU1-74, and 13 +/- 1 minutes for rscu-PA/MA-UK1-3, with corresponding plasma clearances of 340 +/- 28, 10 +/- 1, and 37 +/- 4 mL/min, respectively (mean +/- SEM). rscu-PA/MA-FU1-74 has a fivefold higher thrombolytic potency than unconjugated rscu-PA, as a result both of fibrin targeting by the specific idiotype of the antibody and of a slower plasma clearance.

Animals↗
PubMed1992

Monoclonal antibody immunoconjugates in the diagnosis and treatment of advanced melanoma.

It appears that monoclonal antibody immunoconjugates may have a role in the radioimmunodiagnosis of melanoma. The precise method of administering the immunoconjugate still remains to be defined. Also evident is the possibility of treating patients with metastatic melanoma with repeated doses of a monoclonal antibody ricin A-chain immunotoxin, but appropriate dosing schedules of the immunotoxin need to be explored further. The agents selected for suppressing the immune response need further study.

Antibodies, Monoclonal↗
PubMed1992

Activity of recombinant mitogillin and mitogillin immunoconjugates.

A synthetic gene for the Aspergillus protein toxin mitogillin has been synthesized and expressed in Escherichia coli. The recombinant mitogillin is a potent inhibitor of protein synthesis in vitro with an IC50 of 9.7 pM. Immunoconjugates of recombinant mitogillin derivatized with S-acetylmercaptosuccinic anhydride and 5-methyl-2-iminothiolane modified H65 antibody kill T cell lines and peripheral blood mononuclear cells expressing the human CD5 surface antigen. Native mitogillin contains 4 cysteine residues which form two disulfide pairs (Fernandez-Luna, J. L., Lopez-Otin, C., Soriano, F., and Mendez, E. (1985) Biochemistry 24, 861-867). Three derivatives of mitogillin have been assembled which substitute alanine residues for cysteine residues 5, 147, or 5 and 147. Each of these molecules retains the ability to inhibit protein synthesis in vitro with at most a 2-fold reduction in activity. The derivative mitogillinC147A can be conjugated to 5-methyl-2-iminothiolane- modified H65 antibody directly without pretreatment with S-acetylmercaptosuccinic anhydride, and the immunoconjugate is active against HSB2 cells. Genetic manipulation of toxin genes to expose an accessible cysteine residue into a recombinant product can thus be used to generate immunotoxins without initial derivatization by nonspecific cross-linking reagents.

Adult↗
PubMed1991

Custom-tailored drug immunoconjugates in cancer therapy.

Forty-three patients with disseminated refractory malignancies each received an individually specified combination of either Adriamycin (n = 24) or mitomycin-C (n = 19) conjugated to a cocktail of murine monoclonal antibodies (mAb). Cancers were typed with both immunohistochemistry and flow cytometry using a panel of antibodies. Cocktails of up to six antibodies were selected based on total binding of greater than 80% of the malignant cells in the biopsy specimen. These mAb cocktails were then drug conjugated, safety tested, and administered intravenously. The Adriamycin immunoconjugates were well tolerated in 22/24 patients, with 17/24 having significant side effects. Fever, chills, pruritus, and skin rash were by far the most common transitory reactions. All were well controlled with premedication. A total of up to 1 g Adriamycin and 5 g mAb were administered to each patient. The limiting factor appeared to be a variable dissociation of active Adriamycin from the antibody that unpredictably caused hemopoietic depression. Similar findings were noted among 19 patients treated with mitomycin-C conjugates. Thrombocytopenia at a 60-mg dose of mitomycin-C in this schedule was dose limiting. Serological evidence suggested that the development of an immunoglobulin M antibody specific against the mouse mAb had the specificity and sensitivity to predict clinical reactions. These antibodies were quantitatively less in mitomycin-C-treated patients. Selected patients were retreated. One patient with chronic lymphocytic leukemia was treated on three occasions with regression of peripheral lymph nodes. Two patients with breast carcinoma had definite improvement in ulcerating skin lesions, and two patients with tongue carcinoma had shrinkage of their lesions. No responses were seen with mitomycin-C conjugates but binding was noted to tumors. Drug-induced colitis was seen at higher doses with some binding of these conjugates to normal colon epithelium. This study demonstrated the feasibility of preparing individually specified drug immunoconjugate cocktails for patients with refractory malignancies. Cocktail formulation and antibody delivery to the tumor in vivo was accomplished. There was limited antigenic drift among various biopsies within the same patient over time. The major technical hurdle continues to be the selection of effective drug conjugation methods to optimally bind drugs to mAbs for targeted cancer therapy.

Antibodies, Monoclonal↗
PubMed1991

Monoclonal antibody-based therapy of a human tumor xenograft with a 177lutetium-labeled immunoconjugate.

177Lutetium (177Lu) is a member of the family of elements known as lanthanides or rare earths. Monoclonal antibody (MAb) CC49, a murine IgG1, which is reactive with the tumor-associated antigen, TAG-72, has been shown previously to react with a wide range of human carcinomas; CC49 reacts to a different epitope on the TAG-72 molecule than MAb B72.3 and has a higher binding affinity. We report here the first use of a 177Lu-labeled immunoconjugate, 177Lu-CC49, in an experimental therapy model for human carcinoma. 177Lu-CC49 was shown to delay the growth of established LS-174T human colon carcinomas in athymic mice at a single dose of 50 microCi. Overt toxicity was observed with the administration of approximately 500 microCi of 177Lu-CC49 in which 5 of 9 mice died of apparent marrow toxicity. A single administration of 200 or 350 microCi of 177Lu-CC49, however, was shown to eliminate established tumors through the 77-day observation period after MAb administration. Dose fractionation experiments revealed that at least 750 microCi of 177Lu-CC49 (250 microCi/week for 3 consecutive weeks) was well tolerated in that 9 of 10 mice survived. Moreover, this dose schedule was able to eliminate the growth of relatively large (300 mm3) human colon tumor xenografts in 90% of the animals treated. Single-dose and dose fractionation studies were also carried out with an isotype-matched control MAb, 177Lu-MOPC-21. In all dose schedules, a large differential was seen between the therapeutic effects of the 177Lu-CC49 versus that of the 177Lu-control MAb. The merits and limitations of the use of 177Lu-labeled immunoconjugates (in particular, 177Lu-CC49) are discussed in terms of potential novel therapeutics for human carcinoma.

Adenocarcinoma, Mucinous↗
PubMed1991

Anthracycline immunoconjugates prepared by a site-specific linkage via an amino-dextran intermediate carrier.

Anthracycline, either daunomycin or doxorubicin, was site specifically attached to the carbohydrate moiety of a monoclonal anticarcinoembryonic antigen antibody by using amino-dextran as the intermediate carrier. The reaction resulted in an immunoconjugate that contains approximately 20 to 25 molecules of drug per molecule of immunoglobulin G. Flow-cytometric studies revealed the retention of the antibody-binding activity. The immunoconjugate was cytotoxic to the target cells, as examined by the 75selenomethionine incorporation studies, and remained efficient for targeting a human colonic tumor (GW-39) in the nude mouse model. The conjugate possessed a greater antitumor activity against the subcutaneous tumor than either the free drug or an irrelevant antibody conjugate, and it was well tolerated by the animals at a much higher dose level than was the unconjugated drug.

Animals↗
PubMed1991

Preclinical assessments of 90Y-labeled C110 anti-carcinoembryonic antigen immunotoxin: a therapeutic immunoconjugate for human colon cancer.

We have synthesized 90Y-labeled immunotoxin (IT) containing ricin A chain and C110 anti-carcinoembryonic antigen monoclonal antibody (MAb) to produce a therapeutic immunoconjugate for human colon cancer. The C110 IT was labeled with 90Y via a benzylisothiocyanate derivative of diethylenetriaminepentaacetic acid. The efficiency of 90Y labeling was consistently 90 to 98%, with a specific activity of about 1 microCi/microgram. In in vitro stability studies, more than 80% of 90Y remained bound to the C110 IT for up to 5 days after incubation. The percentage of binding of 90Y-labeled C110 IT to carcinoembryonic antigen-coated microbeads was 86%, indicating good retention of the initial immunoreactivity of the C110 MAb. In in vitro protein synthesis inhibition assays, 90Y-labeled C110 IT was approximately 3.7-fold more toxic to the LS174T human colon carcinoma cell line than unmodified C110 IT and 1380-fold more toxic than 90Y-labeled C110 MAb. Biodistribution studies of 90Y-labeled C110 IT in LS174T tumor-bearing mice showed that, at 24 h following i.p. injection, high accumulation of radioactivity was seen in the i.p. tumor and liver and, thereafter, high accumulation in these tissues remained almost unchanged until up to 168 h, with percentage of injected dose/g ranging from 15 to 18% in the tumor and 10 to 15% in the liver. The radioactivity in the spleen and bone gradually increased with time and reached their highest levels (approximately 8% of injected dose/g) at 168 h. Estimation of absorbed radiation doses to the tissues showed that i.p. tumor would have received an approximately 1.5 to 7 times higher radiation dose than normal organs. In in vivo therapeutic trials, 90Y-labeled C110 IT provided survival prolongation of LS174T tumor-bearing mice superior to that with either unmodified C110 IT or 90Y-labeled C110 MAb (4 less than 0.01; Mann-Whitney U test). These results indicate that 90Y-labeled C110 anti-carcinoembryonic antigen IT may be a potent therapeutic immunoconjugate for human colon cancer and that it may have direct relevance for i.p. treatment of peritoneal carcinomatosis from colon cancers.

Animals↗
PubMed1990

Antitumor activity of adriamycin (hydrazone-linked) immunoconjugates compared with free adriamycin and specificity of tumor cell killing.

Adriamycin (ADM) was chemically coupled to two monoclonal antibodies (MAb) expressed on human B-cell lymphomas. Immunoconjugates were prepared by linking to the MAb an ADM derivative, Adriamycin 13-[3-(2-pyridyldithio)propionyl]hydrazone (ADM-HZN), which releases ADM under mild acidic conditions (see preceding article). The (ADM-HZN) conjugates were tested for antitumor activity on two human B-lymphoma xenografts, Daudi and Ramos, which were growing as solid tumors in athymic mice. The conjugates, injected i.p., significantly inhibited tumor growth when antibody protein doses were greater than or equal to 500 mg/kg (approximately 10 mg/mouse). At these input antibody doses, (ADM-HZN) conjugates were more potent and had greater antitumor activity than free ADM given at an optimized dose and schedule. MAb-conjugated ADM was also tolerated to much higher levels than unconjugated drug. Antitumor activity was not obtained using mixtures of MAb plus free drug or with MAb-drug conjugates that did not bind to the tumor target cell. Thus, the antitumor activity of the immunoconjugate was directed by binding of the MAb portion of the conjugate to target tumor cells.

Animals↗
PubMed1990

Antimelanoma monoclonal antibody-ricin A chain immunoconjugate (XMMME-001-RTA) plus cyclophosphamide in the treatment of metastatic malignant melanoma: results of a phase II trial.

Prior studies with the XMMME-001-RTA immunoconjugate composed of an antimelanoma monoclonal antibody and ricin A chain demonstrated some antitumor activity. However, almost all patients studied developed human antimurine antibodies and antiricin antibodies. In an effort to abrogate these host anti-immunotoxin immune responses and thus enhance antitumor activity, we treated 20 patients with the immunoconjugate plus a single dose of intravenous cyclophosphamide. An overall response rate of 20% was observed-predominantly in pulmonary and soft tissue nodules. There was no diminution in antibody responses against either the murine antibody or the ricin moiety. Further studies to elucidate the role of cyclophosphamide in monoclonal antibody therapy are planned.

Adult↗
PubMedDate not supplied

Individually specified drug immunoconjugates in cancer treatment.

Forty-three patients with disseminated refractory malignancies each received an individually-specified combination of either Adriamycin (24 patients) or mitomycin-C (19 patients) conjugated murine monoclonal antibodies. Tumors were typed using a panel of antibodies with both immunohistochemistry and flow cytometry. Cocktails of up to six antibodies were selected based on binding greater than 80% of the malignant cells in the biopsy specimen. These monoclonal antibody cocktails were drug conjugated and administered intravenously. Seventeen out of twenty-four patients had reactions to the administration of Adriamycin immunoconjugates, but these were tolerable in all but two patients. Fever, chills, pruritus and skin rash were by far the most common transitory reactions. All were well controlled with premedication. In several patients it was demonstrated that there was limited antigenic drift among various biopsies within the same patient over time. Up to 1 gram of Adriamycin and up to 5 grams of monoclonal antibody were administered. The limiting factor appeared to be a variable dissociation of active Adriamycin from the antibody which unpredictably caused hemopoietic depression. Similar findings were noted in 19 patients with mitomycin-C conjugates. Thrombocytopenia at a 60mg dose of mitomycin-C in this schedule was dose limiting. Preliminary serological evidence suggests that the development of an IgM antibody which is specific against the mouse monoclonal antibody has the specificity and sensitivity to predict clinical reactions. These antibodies were quantitatively less in mitomycin-C patients. Selected patients were re-treated. One patient with chronic lymphocytic leukemia had re-treatment on three occasions and demonstrated regression of peripheral lymph nodes. Two patients with breast carcinoma had definite improvement in ulcerating skin lesions and two patients with tongue carcinoma had shrinkage of their lesions. No responses were seen with mitomycin-C conjugates but binding was noted to tumors and colon with likely drug induced colitis seen after colon binding. This study demonstrates the feasibility and illustrates technical considerations in preparing drug immunoconjugate cocktails for patients with refractory malignancies. Cocktail formulation and antibody delivery was accomplished. The major technical hurdle appears to be the selection of effective conjugation methods that can be used to optimally bind drugs to monoclonal antibodies for targeted cancer therapy.

Animals↗
PubMedDate not supplied

Development of a human xenograft model for the evaluation of monoclonal antibody L6-mitomycin immunoconjugates.

The human lung carcinoma H2981, was characterized as a preclinical model for evaluating immunoconjugates consisting of monoclonal antibody (MAb) L6 and drugs of the mitomycin (MMC) chemotype. The H2981 tumor, implanted subcutaneously in athymic, mice grew progressively in greater than 95% of recipients. Spontaneous regressions of established tumors were not observed. The administration of tolerated doses of MMC resulted in dose-dependent delays in tumor growth. The incidence of tumor regressions was low indicating the potential to observe increased efficacy with immunoconjugates. The antitumor effects of MMC were independent of the schedule and route of administration. MAb L6 delayed the outgrowth of tumors when administered 24 h after tumor implant. Antitumor activity was not observed when MAb L6 was administered to mice bearing established tumors. The efficacy of mixtures of MAb L6 and optimal doses of MMC was not significantly better than that of optimal doses of MMC given alone.

Animals↗
PubMed1989

Immunoconjugates of doxorubicin and murine antihuman breast carcinoma monoclonal antibodies prepared via an N-hydroxysuccinimide active ester intermediate of cis-aconityl-doxorubicin: preparation and in vitro cytotoxicity.

Doxorubicin (DXR) conjugated to murine monoclonal antibodies (MoAb) raised against human breast tumor cells demonstrated a MoAb-specific, molar ratio-dependent in vitro cytotoxicity. These conjugates were prepared on a scale sufficient to allow for subsequent clinical trials (1 to 3 g of MoAb per conjugation reaction). The conjugation reaction proceeded via an N-hydroxysuccinimide (NHS) active ester intermediate of cis-aconityl-DXR (CA-DXR), resulting in a cis-aconitate acid-sensitive linker between the DXR and MoAb. Molar ratios of DXR to MoAb ranged from 40 to 45. The immunoreactivity of conjugated MoAb was only slightly decreased from naked MoAb. When immunoconjugates were incubated with MoAb-reactive tumor cells for 3 hours, specific cell-killing was observed. If the exposure time was lengthened to 18 hours, however, nonspecific killing resulted. Incubation of the immunoconjugate with the nonspecific adsorbant Amberlite XAD-2 caused an average 30% decrease in the DXR-to-MoAb molar ratio, suggesting a population of drug that is tightly but noncovalently associated with MoAb.

Adsorption↗
PubMed1988

Superiority of an acid-labile daunorubicin-monoclonal antibody immunoconjugate compared to free drug.

We conjugated the chemotherapy agent daunorubicin to the anti-T-cell monoclonal antibody T101 using an active ester intermediate of the acid-labile linker cis-aconitate anhydride. By converting carbohydrate hydroxyl groups on the antibody to amines prior to conjugation, average drug to antibody ratios of 25:1 were achieved with retention of cytotoxicity and only minimal loss of immunoreactivity. The pH sensitivity of the linkage was confirmed. The preparation was cytotoxic for antigen-bearing cells but not antigen-negative cells, even up to 48-h incubation in vitro. Specific cytotoxicity was apparently mediated through the endocytosis of the intact T101 immunoconjugate and the release of the active drug in the lysosomal compartment. Athymic mice bearing human tumor xenografts who received a single injection of the immunoconjugate had less tumor growth and more tumor regressions than animals receiving antibody alone, drug alone, or a mixture of drug plus antibody. This approach appears promising for further investigation.

Animals↗