Rapid humanization of the Fv of monoclonal antibody B3 by using framework exchange of the recombinant immunotoxin B3(Fv)-PE38

B3(Fv)-PE38 is a recombinant single-chain immunotoxin in which the Fv region of carcinoma-specific antibody B3 is fused to a truncated form of Pseudomonas exotoxin (PE). The efficacy of monoclonal antibody B3 and B3 immunotoxins in cancer therapy and diagnosis may be limited by the human anti-mouse response. Here we describe the humanization of the Fv of B3(Fv)-PE38 by "framework exchange." The variable domains of the heavy (VH) and light (VL) chains were aligned with their best human homologs to identify framework residues that differ. Initially, 11 framework residues in VH and six in VL were changed by site-specific mutagenesis to human residues and introduced simultaneously into a preassembled single-chain Fv expression cassette. Six VH and five VL residues that differ were not changed because they were buried, in the interdomain interface, or previously found to result in decreased affinity when mutated. This basic design resulted in some 20-fold loss of activity. Changing VL residues at the interdomain interfacial position 100 and at the buried position 104 to the human sequence increased the activity 8-fold. Changing VH residue at position 82b from the human sequence back to that of the mouse restored the activity 2- to 3-fold to the full binding and cytotoxic activity of the mouse sequence. Humanized B3(Fv)-PE38 lost immunogenic epitopes recognized by sera from monkeys that had been immunized with B3(Fv)-PE38.

Primate antibody response to immunotoxin: serological and computer-aided analysis of epitopes on a truncated form of Pseudomonas exotoxin

NLysPE38 is a 38-kDa derivative of Pseudomonas exotoxin (PE) in which domain Ia (amino acids 1 to 252) and part of domain Ib (365 to 380) are deleted and an 11-amino-acid N-terminal peptide is added. LMB-1 is an immunotoxin in which the monoclonal antibody B3 is coupled to NLysPE38 near its N terminus. LMB-7 is a single-chain immunotoxin in which the Fv fragment of B3 is fused to PE38. To identify the antigenic regions of PE38, 12 polyclonal serum samples from monkeys immunized with the immunotoxins LMB-1 (six monkeys) and LMB-7 (six monkeys) were tested for their reactivity to a panel of 120 synthetic, overlapping peptides representing the amino acid sequence of NLysPE38. The antibody responses to peptides were similar among the 12 serum specimens, identifying several major immunodominant B-cell epitopes. Predominant reactivity was seen in six locations: amino acids 272 to 287, 341 to 359, 504 to 516, 540 to 564, and 573 to 591 and the C-terminal amino acids 591 to 613. The sera did not react with approximately 75% of the peptides. Furthermore, a computer-aided analysis was done to predict the immunologically relevant areas and revealed the same antigenic regions defined by serum reactivity to peptides. Competition enzyme-linked immunosorbent assays and neutralization assays were performed with domain II, III, or III plus Ib of PE38 and confirmed the immunodominance of domain III. To analyze the role of specific amino acids in antibody binding, individual amino acids of PE38 with large accessible surface areas were altered by site-directed mutagenesis. These results also show that the predicted areas of immunogenicity agree with the reactivity of the anti-PE38 antibodies to peptides and to the mutants of PE.

Evaluation of piroxantrone in women with metastatic breast cancer and failure on nonanthracycline chemotherapy

BACKGROUND

Doxorubicin generally is considered to be the most effective single chemotherapeutic agent for the treatment of breast cancer. The major cumulative dose-limiting toxicity is cardiac toxicity, which may be related to the formation of free radicals with subsequent lipid peroxidation, leading to membrane damage. The anthrapyrazoles, of which piroxantrone is a member, were synthesized in an attempt to eliminate this toxicity.

METHODS

A Phase II clinical trial was conducted in 30 women with metastatic breast cancer in whom piroxantrone was administered at a dose of 160 mg/m2 by 1-hour infusion. The planned cycle length for retreatment was 3 weeks. Measurable metastatic disease and failure on one prior chemotherapy regimen, but no prior anthracycline exposure, were required for response evaluation.

RESULTS

Twenty-nine patients were evaluable for response, and 6 (21% and 95% confidence intervals: 10-43%) achieved an objective response (1 complete, 5 partial responses), with a median response duration of 244 days. The median time-to-disease progression for all patients was 124 days. Eight patients received cumulative doses of piroxantrone approaching or exceeding 1000 mg/m2, and all had reductions in the resting left ventricular ejection fraction (LVEF). The estimated median decrease in LVEF at 1000 mg/m2 was 16%, with a range of 10-28%. Clinical findings of congestive heart failure developed in two patients.

CONCLUSIONS

Piroxantrone had definite antitumor activity in women who had metastatic breast cancer and failure on prior chemotherapy that did not include an anthracycline. The 95% confidence interval for response probability was broad, but the level of activity observed was relatively low. The clear association with cardiac toxicity combined with the relatively low efficacy led to the conclusion that piroxantrone cannot be recommended for further development as therapy for women with breast cancer. Further study of other anthrapyrazoles is necessary to determine if the promise of this new class of agents can be fulfilled.

Clear cell sarcoma of the kidney--immunohistochemical study and flow cytometric DNA analysis of 7 cases

Immunohistochemical study and flow cytometric DNA analysis were done on seven cases of clear cell sarcoma of the kidney (CCSK) to speculate its histogenesis and to access the diagnostic usefulness of these methods in the differential diagnosis of Wilm's tumor. Clinically, CCSK is a rare malignant renal tumor of children with a propensity to metastasize to bone. Arborizing vascular pattern surrounding the tumor cells which have clear cytoplasm is characteristic histologic finding. Immunohistochemically, only vimentin was diffusely demonstrated in the tumor cell membrane and cytoplasm. In flow cytometric DNA analysis, four cases showed diploidy and two cases near diploidy. CCSK is a separate disease entity with characteristic clinicopathologic, immunohistochemical and flow cytometric findings in distinction from Wilms' tumor. Considering the histologic and immunohistochemical findings, the possible histogenetic mechanism of CCSK seems to be in common with congenital mesoblastic nephroma (CMN), that is primitive mesenchymal cells which committed early stromagenic activity.

Improved binding and antitumor activity of a recombinant anti-erbB2 immunotoxin by disulfide stabilization of the Fv fragment

e23(dsFv)-PE38KDEL is a recombinant immunotoxin composed of the Fv region of anti-erbB2 monoclonal antibody e23 connected to a truncated form of Pseudomonas exotoxin (PE38KDEL), in which the inherently unstable Fv heterodimer (composed of VH and VL) is stabilized by a disulfide bond engineered between structurally conserved framework positions of VH and VL. We have now found that e23(dsFv)-PE38KDEL is considerably more cytotoxic to antigen-positive cell lines than the corresponding single-chain immunotoxin. The basis for the enhanced cytotoxic activity is that the e23 dsFv-immunotoxin binds to erbB2 with greater affinity than the single-chain counterpart. The dsFv-immunotoxin had 4-fold increased binding compared to the scFv and almost identical to the binding affinity of e23 Fab. e23(dsFv)-PE38KDEL was also considerably more stable at 37 degrees C than the single-chain immunotoxin. The therapeutic potential of the disulfide-stabilized immunotoxin was compared with its single-chain counterpart using two animal models of immunodeficient mice bearing subcutaneous tumor xenografts of human gastric tumor N87 cells or human A431 epidermoid carcinoma cells. The antitumor effect of e23(dsFv)-PE38KDEL was significantly better than that of the single-chain immunotoxin. e23(dsFv)-PE38KDEL caused complete regression of tumors at doses which caused no toxic effects in mice, whereas the single-chain immunotoxin did not cause complete regressions at the same doses.

Stabilization of the Fv fragments in recombinant immunotoxins by disulfide bonds engineered into conserved framework regions

Disulfide-stabilized Fv's (dsFv's) are recombinant Fv fragments of antibodies in which the unstable variable heavy (VH) and variable light (VL) heterodimers are stabilized by disulfide bonds engineered at specific sites that lie between structurally conserved framework positions of VH and VL. We have recently described one example of a recombinant immunotoxin, B3(dsFv)-PE38KDEL, that is composed of such a dsFv connected to a truncated form of Pseudomonas exotoxin [Brinkmann, U., Reiter, Y., Jung, S.-H., Lee, B., & Pastan, I. (1993) Proc. Natl. Acad. Sci. U.S.A. 90, 7538-7542]. This disulfide-stabilized immunotoxin has the same cytotoxic activity and specificity as its single-chain immunotoxin counterpart. To determine whether the stabilization of Fv's by disulfides at these positions is generally applicable, we made and analyzed two other dsFv-containing immunotoxins. One is made from the e23 antibody, which binds to the carcinoma-associated antigen erbB2; the other is made from the anti-Tac antibody, which binds to the p55 subunit of the IL-2 receptor. Comparison of the specificity and activity of these immunotoxins with those of their scFv counterparts revealed that e23(dsFv)-PE38KDEL was considerably more active than e23(Fv)-PE38KDEL, whereas anti-Tac(dsFv)-PE38KDEL was only somewhat more active than its single-chain counterpart. These results suggest that dsFv's have at least the same binding properties as scFv's, and in some cases they may have better binding. Thus, it should be feasible to use the positions we have identified in the conserved framework region to disulfide-stabilize many different Fv's.(ABSTRACT TRUNCATED AT 250 WORDS)

Randomized trial of cyclophosphamide, methotrexate, and 5-fluorouracil with or without estrogenic recruitment in women with metastatic breast cancer

BACKGROUND

The fraction of breast cancer cells undergoing DNA synthesis at any one time is relatively low, which is problematic because most chemotherapeutic agents are most effective against dividing cells. Estrogens administered in vitro and in vivo can increase breast cancer cell proliferation. A randomized clinical trial was performed to determine if estrogenic recruitment could increase the effectiveness of combination chemotherapy.

METHODS

One hundred sixty-five women were randomized, with two excluded from these analyses, to either an intravenous cyclophosphamide, methotrexate, and 5-fluorouracil (CMF) regimen alone (cyclophosphamide, 600 mg/m2; methotrexate, 40 mg/m2; 5-fluorouracil, 600 mg/m2) or CMF preceded by 3 days of diethylstilbestrol (DES) at a dose of 1 mg orally per day. The planned cycle length was 3 weeks.

RESULTS

Objective responses were seen in 20 of 80 patients (25%) treated with CMF and 32 of 83 patients (39%) treated with DES-CMF, and this difference almost achieved statistical significance (chi-square, two-sided P = 0.06). However, duration of response, time to disease progression, and survival time were similar for the two regimens.

CONCLUSIONS

Estrogenic recruitment with DES as used in this study does not substantially increase the efficacy of a CMF regimen administered intravenously every 3 weeks.

Engineering interchain disulfide bonds into conserved framework regions of Fv fragments: improved biochemical characteristics of recombinant immunotoxins containing disulfide-stabilized Fv

Using molecular modeling technology, we have recently identified two positions in conserved framework regions of antibody Fv fragments (Fvs) that are distant from CDRs, and potentially can be used to make recombinant Fv fragments in which the unstable VH and VL heterodimer is stabilized by an interchain disulfide bond inserted between structurally conserved framework positions. A disulfide bond has been introduced at one of these positions, VH44-VL105, and shown to stabilize various Fvs that retain full binding and specificity. Recombinant immunotoxins, e.g. B3(dsFv)-PE38KDEL in which this disulfide-stabilized Fv moiety is connected to a truncated form of Pseudomonas exotoxin (PE; PE38KDEL) which contains the translocation and ADP ribosylation domains, are indistinguishable in binding and specificity from its single-chain immunotoxin counterparts. We have now analyzed the alternative position, (VH111-VL48), predicted by the modeling methodology, for disulfide stabilization of mAb B3(Fv) by producing a recombinant immunotoxin with such disulfide-stabilized (ds) Fv. This immunotoxin was also very active and retained full specificity to B3 antigen-positive cells. However, it was 2- to 3-fold less active than the VH44-VL105 dsFv-molecule. We also tested various biochemical features of VH44-VL105 and VH111-VL48 dsFv immunotoxins and compared them with the corresponding single-chain immunotoxin. We found the dsFv immunotoxins were more stable in human serum and more resistant to thermal and chemical denaturation than the single chain (sc) Fv immunotoxin. Because dsFv immunotoxins and dsFvs have full activity and specificity and improved stability, they may be more useful than scFv immunotoxins as therapeutic and diagnostic agents.

Design of interchain disulfide bonds in the framework region of the Fv fragment of the monoclonal antibody B3

The Fv fragments are the smallest units of antibodies that retain the specific antigen binding characteristics of the whole molecule and are being used for the diagnosis and therapy of human diseases. These are noncovalently associated heterodimers of the heavy (VH) and the light (VL) chain variable domains, which, without modification, tend to dissociate, unfold, and/or nonspecifically aggregate. The fragment is usually stabilized by producing it as a single chain recombinant molecule in which the two chains are linked by means of a short polypeptide linker. An alternative strategy is to connect the two chains by means of an interchain disulfide bond. We used molecular graphics and other modeling tools to identify two possible interchain disulfide bond sites in the framework region of the Fv fragment of the monoclonal mouse antibody (mAb) B3. The mAb B3 binds to many human cancer cells and is being used in the development of a new anticancer agent. The two sites identified are VH44-VL105 and VH111-VL48. (VH44-VL100 and VH105-VL43 in the numbering scheme of Kabat et al., "Sequence of Proteins of Immunological Interest," U.S. DHHS, NIH publication No. 91-3242, 1991). This design was recently tested using the chimeric protein composed of a truncated form of Pseudomonas exotoxin and the Fv fragment of mAb B3 with the engineered disulfide bond at VH44-VL105 (Brinkmann et al., Proc. Natl. Acad. Sci. U.S.A. 90:7538, 1993). The chimeric toxin was found to be just as active as the corresponding single chain counterpart and considerably more stable. Because these disulfide bond sites are in the framework region, they can be located from sequence alignment alone. We expect that the disulfide bond at these sites will stabilize the Fv fragment of most antibodies and the antigen-specific portion of the T-cell receptors, which are homologous.

Breast biopsy: a comparative study of stereotaxically guided core and excisional techniques

OBJECTIVE

The major objectives of this prospective study were to compare pathologic findings from stereotaxic core and excisional biopsies performed on patients with impalpable breast lesions and to compare the initial mammographic impression with the final histologic diagnosis.

SUBJECTS AND METHODS

All patients referred for preoperative localization of impalpable breast lesions between October 29, 1991, and January 15, 1993, were eligible for the study. If the patient and the lesion, on the basis of mammography, were considered suitable for core biopsy, the patient was asked to participate. Four hundred forty-five excisional biopsies were performed. One hundred sixty lesions were evaluated by core biopsy; for 104 of these lesions, five or more core samples were removed. Core biopsies were done with 14-gauge biopsy needles and were followed by a localization procedure. The pathologic features of core and excisional specimens were compared.

RESULTS

Biopsy results were compared for 93 (58%) benign and 67 (42%) malignant lesions. Of 104 lesions evaluated with at least five core specimens, 56 (54%) were benign and 48 (46%) were malignant. Results of core biopsy corresponded to those of excisional biopsy for 96% of benign lesions, 83% of malignant lesions, and 90% overall; sensitivity of core biopsy for malignant lesions was 85%. Of 56 lesions for which fewer than five core specimens were obtained, 37 (66%) were benign and 19 (34%) were malignant. Results of core biopsy corresponded to those of excisional biopsy for 81% of benign lesions, 79% of malignant lesions, and 80% overall; sensitivity of core biopsy for malignant lesions was 84%. Specificity of core biopsy for the entire series of benign lesions was 100%.

CONCLUSION

For mammographic lesions that are believed to be not malignant or not very likely malignant, stereotaxic core biopsy decreases the need for excisional biopsy.

Flow cytometric analysis of DNA ploidy in childhood rhabdomyosarcoma

Flow cytometric DNA analysis was performed on 17 rhabdomyosarcomas in conjunction with a histopathological review to determine the usefulness of this technique to predict the biologic behavior of the tumor and to establish the characteristic ploidy pattern of rhabdomyosarcoma compared to other small round cell tumors occurring in childhood. Aneuploidy including near-tetraploidy is the most common ploidy pattern encountered, followed by multiploidy and diploidy, and the presence of multiploidy in this tumor is useful for differentiating rhabdomyosarcoma from other kinds of small round cell tumors in which there are rare previous reports on occurrence of multiploidy. Even though there is no significant correlation between ploidy pattern and histologic type of rhabdomyosarcoma, patients with multiploid tumors or aneuploid tumors with a DNA index of 1.10-1.80 tend to have a high risk of treatment failure. Therefore, the ploidy pattern seems to be useful for predicting the patient's survival in concert with other variables.

A recombinant immunotoxin containing a disulfide-stabilized Fv fragment

B3(dsFv)-PE38KDEL is a recombinant immunotoxin composed of the Fv region of monoclonal antibody B3 connected to a truncated form of Pseudomonas exotoxin (PE38KDEL), in which the unstable Fv heterodimer (composed of heavy- and light-chain variable regions) is held together and stabilized by a disulfide bond [termed disulfide-stabilized Fv (dsFV)]. A computer modeled structure of the B3(Fv), made by mutating and energy minimizing the amino acid sequence and structure of McPC603, enabled us to identify positions in conserved framework regions that "hypothetically" could be used for disulfide stabilization without changing the structure or affecting antigen binding. This prediction was evaluated experimentally by constructing a disulfide-linked two-chain dsFv-immunotoxin that was produced in Escherichia coli. The activity and specificity of this immunotoxin was indistinguishable from its single-chain Fv (scFv) counterpart, indicating that, as in B3(scFv), the structure of the binding region is retained in B3(dsFv). Because we introduced the stabilizing disulfide bond in between two framework residues in a position that is conserved in most Fv molecules, this method of linkage between the heavy- and light-chain variable regions should be generally applicable to construct immunotoxins and dsFv molecules using other antibodies. Furthermore, the finding that B3(dsFv) was much more stable at 37 degrees C in human plasma than B3(scFv) indicates that dsFvs are possibly more versatile for therapeutic application than scFvs.

Electron microscopic study of the cases of minimal change nephrotic syndrome with mesangial IgA deposition

Twenty-five cases of minimal change nephrotic syndrome(minimal change disease, MCD) with mesangial IgA deposition were evaluated electron microscopically. The thickness of the glomerular basement membrane(GBM) was 3875 +/- 1271 A and 3056 +/- 1201 A in adults and children, respectively. Alteration of the GBM was noted in 3 adults and eight children: splitting in 4, focal thinning in one, widening of the lamina rara interna in 10, and widening of the lamina rara externa in 4 cases. Minimal mesangial electron dense deposits were found in all but one adult, and an increase of the mesangial matrix and minimal mesangial proliferation were observed in 8 and 6 cases, respectively. Electron microscopic findings show representative findings of MCD in our cases. A relationship between the GBM alterations in these cases and frequent association of hematuria is suggested and discussed.

Subacute necrotizing lymphadenitis--a collective clinicopathological and immunohistochemical study

Subacute necrotizing lymphadenitis (SNL) is a well documented and unique clinicopathologic entity, although its etiology and pathogenesis have not been clearly established. Microscopically, cortical and paracortical necrotizing lesions with karyorrhexis, abundant nuclear debris and infiltration of large mononuclear cells are characteristic. This study analyzed the common clinical and pathological features of 118 patients with SNL and the nature of the mononuclear cells. Patients were generally young women and revealed cervical lymphadenopathy with tenderness, fever, leukopenia and elevation of the erythrocyte sedimentation rate. Features of the adjacent uninvolved area in the lymph node included a starry sky pattern, follicle centers, sinus histiocytosis or aggregation of foamy histicoytes. There was an inverse relationship between the extent of necrosis and of histocytic infiltration but not between the extent of necrosis and the duration from the onset of symptoms to the diagnosis. Immunohistochemically the infiltrated mononuclear cells of the affected foci were T lymphocytes and histiocytes. The clinical, histological and immunohistochemical features suggest that SNL represents a hypersensitivity reaction to certain infectious agent without forming granuloma.

Non-Hodgkin's lymphoma: a histopathologic and immunohistochemical study of 79 cases

Recently immunophenotyping has become a valuable tool in the diagnostic workup of malignant lymphoma. We classified 79 consecutive cases of non-Hodgkin's lymphoma experienced at our hospital during the last two years according to the Working Formulation and immunologically using MT1, UCHL1 and MB2 monoclonal antibodies. The results of this study are as follows: 1) four cases (5.1%) were low grade, 54 cases (68.4%) were intermediate grade, and 21 cases (23.3%) were high grade. The most common subtype was 'diffuse, mixed' type, 2) fifty cases (63.3%) showed T-cell phenotype and 14 cases (17.7%) showed B-cell phenotype. Immunophenotyping was impossible in 15 cases due to either double staining or negative staining. 3) the incidence of extranodal presentation was high (65.8%) and the most common extranodal site was the upper aerodigestive tract (29.1%) followed by the gastrointestinal tract (16.4%), and 4) MT1, UCHL1 and MB2 monoclonal antibodies are valuable markers of T- and B-cells in paraffin embedded tissue, enabling retrospective study. However, because these antibodies are not lineage specific, the results of immunostaining should be interpreted with caution.

Polymorphic reticulosis with colonic lesion--a case report

A 38-year-old man was admitted with a high fever, sore throat, and right upper quadrant pain. Nine months before his admission, he had undergone right hemicolectomy under the impression of intestinal lymphoma. But there had been no evidence of lymphoma on microscopic examination. Under the postoperative diagnosis of inflammatory bowel disease, corticosteroid therapy was tried without response. On the follow-up colonoscopic examination, an ovoid ulcer, with convergence of the surrounding mucosal folds at the descending colon and an irregularly shaped ulcer at the ileocolic anastomotic site, were found. The colonoscopic diagnosis was Behcet's colitis. After pathologic slides of biopsy and surgical specimens obtained from the palatine tonsil and colon were reviewed, the diagnosis of polymorphic reticulosis was made. The patient received anticancer chemotherapy, including cyclophophamide and glucocorticosteroid. To date, colonic involvement of polymorphic reticulosis has not been reported. Because of the similarity of the colonoscopic findings to those of Behcet's colitis, polymorphic reticulosis should be included in the differential diagnosis of inflammatory bowel disease. We assume that this is the first case of polymorphic reticulosis involving the colon with characteristic colonoscopic findings.