Immunotoxin therapy of small-cell lung cancer: a phase I study of N901-blocked ricin

PURPOSE

Immunotoxins could improve outcome in small-cell lung cancer (SCLC) by targeting tumor cells that are resistant to chemotherapy and radiation. N901 is a murine monoclonal antibody that binds to the CD56 (neural cell adhesion molecule [NCAM]) antigen found on cells of neuroendocrine origin, including SCLC. N901-bR is an immunoconjugate of N901 antibody with blocked ricin (bR) as the cytotoxic effector moiety. N901-bR has more than 700-fold greater selectivity in vitro for killing the CD56+ SCLC cell line SW-2 than for an antigen-negative lymphoma cell line. Preclinical studies suggested the potential for clinically significant cardiac and neurologic toxicity. We present a phase I study of N901-bR in relapsed SCLC.

PATIENTS AND METHODS

Twenty-one patients (18 relapsed, three primary refractory) with SCLC were entered onto this study. Successive cohorts of at least three patients were treated at doses from 5 to 40 microg/kg/d for 7 days. The initial three cohorts received the first day's dose (one seventh of planned dose) as a bolus infusion before they began the continuous infusion on the second day to observe acute toxicity and determine bolus pharmacokinetics. Toxicity assessment included nerve-conduction studies (NCS) and radionuclide assessment of left ventricular ejection fraction (LVEF) before and after N901-bR administration to fully assess potential neurologic and cardiac toxicity.

RESULTS

The dose-limiting toxicity (DLT) of N901-bR given by 7-day continuous infusion is capillary leak syndrome, which occurred in two of three patients at the dose of 40 microg/kg (lean body weight [LBW])/d. Detectable serum drug levels equivalent to effective in vitro drug levels were achieved at the 20-, 30-, and 40-microg/kg(LBW)/d dose levels. Specific binding of the immunotoxin to tumor cells in bone marrow, liver, and lung was observed. Cardiac function remained normal in 15 of 16 patients. No patient developed clinically significant neuropathy. However, a trend was noted for amplitude decline in serial NCS of both sensory and motor neurons. One patient with refractory SCLC achieved a partial response.

CONCLUSION

N901-bR is an immunotoxin with potential clinical activity in SCLC. N901-bR is well tolerated when given by 7-day continuous infusion at the dose of 30 microg/kg(LBW)/d. Neurologic and cardiac toxicity were acceptable when given to patients with refractory SCLC. A second study to evaluate this agent after induction chemoradiotherapy in both limited- and extensive-stage disease was started following completion of this study.

Decreases in levels of serum fibronectin predict the severity of vascular leak syndrome in patients treated with ricin A chain-containing immunotoxins

The major dose-limiting adverse effect of ricin A chain-containing immunotoxin (IT) therapy is vascular leak syndrome (VLS). Since plasma fibronectin (Fn) plays a role in maintaining microcirculatory integrity and since the gradient between plasma and tissue Fn can be altered in various pathological situations, we determined whether the administration of IT-ricin A chain to patients resulted in changes in the levels of serum Fn and, if so, whether these changes correlated with the severity of VLS. We also measured the serum levels of tumor necrosis factor alpha (TNFalpha), a proinflammatory cytokine which has been implicated in tissue damage and in interleukin 2-mediated VLS. Our results indicate that the most severe manifestations of VLS were associated with the highest pretreatment levels of Fn, the largest decreases in Fn immediately after starting IT therapy, increases in the levels of serum TNFalpha, higher concentrations of circulating IT, and the lowest numbers of circulating tumor cells. These parameters should, therefore, be useful for predicting which patients will have severe VLS.

Combination immunotoxin treatment and chemotherapy in SCID mice with advanced, disseminated Daudi lymphoma

We describe the use of an immunotoxin (IT) cocktail (anti-CD22- and anti-CD19-ricin A chain) and any 1 of 3 chemotherapeutic drugs (doxorubicin, cytoxan or camptothecin) to treat advanced disseminated Daudi lymphoma in SCID mice (SCID/Daudi). In a previous report, we demonstrated that this regimen was curative when given the day following tumor cell inoculation. Here, we show that combination therapy in mice with advanced tumor significantly increased their survival, although it was not curative. Importantly, the outcome of therapy was dependent upon the temporal order in which IT and chemotherapy were administered. Thus, the best anti-tumor effect was achieved when an IT cocktail was given before or at the same time as chemotherapy. When the IT was given after chemotherapy, there was no additional therapeutic benefit. Our results confirm the rationale of using combination therapy in the treatment of advanced B-cell neoplasia and suggest that ITs should be administered prior to or during chemotherapy.

Hodgkin's disease. Future treatment strategies: fact or fiction?

Many new approaches involving biological agents have given promising results in experimental HD models. Clinical trials with immunotoxins, IL-2, Bi-Moabs or radioimmunoconjugates have demonstrated some clinical efficacy in patients with advanced refractory HD. Although it looks very unlikely to cure patients with larger tumour masses by either of these approaches, it might be feasible to treat bulky disease by conventional therapy first and then administer biological drugs to kill residual H-RS cells. Future phase-III trials will have to prove a possible superior effect of this combined immuno-/chemotherapy. In the meantime, the search for the most promising approach continues.

Elimination of neuroblastoma and small-cell lung cancer cells with an anti-neural cell adhesion molecule immunotoxin

BACKGROUND

The development of immunotoxins has been hampered by difficulties, particularly in solid tumors, of finding appropriate target antigens and of linking sufficiently potent toxins.

PURPOSE

We evaluated the tissue specificity of an immunotoxin, N901-blocked ricin (N901-bR), and assessed its potential for eliminating neural cell adhesion molecule (NCAM)-positive tumor cells in conditions appropriate for in vitro purging, prior to autologous stem cell transplantation, and its potential for myelosuppression. N901-bR consists of a monoclonal antibody (MAb), N901, directed against CD56, an antigen of the family of NCAMs, covalently linked to blocked ricin as the cytotoxic effector moiety.

METHODS

The tissue specificity of the N901 MAb and the N901-bR immunotoxin was tested against a wide array of human tumor tissues and normal human tissues by immunohistochemical staining. The cytotoxic activity of N901-bR was tested against both small-cell lung cancer (SCLC) cells and neuroblastoma cells, either alone or among normal bone marrow mononuclear cells, and the efficacy of this treatment to specifically eliminate these cells was evaluated in a limiting dilution assay. In addition, normal bone marrow mononuclear cells were incubated with N901-bR, and the toxic effects of the immunotoxin on normal hematopoietic progenitors was evaluated.

RESULTS

N901 and N901-bR exhibited specificity for several neoplasms of neuroectodermal origin, including SCLC and neuroblastoma. Staining of normal tissues was essentially limited to various neuroendocrine cells, cardiac muscle cells, and cells in peripheral nerve tissue. We observed a time- and dose-dependent elimination of tumor cells in vitro, with three logs (i.e., > 99.9%) of malignant cells being killed following only 5 hours of exposure to 10 nM N901-bR. Unconjugated N901 MAb specifically blocked the elimination of NCAM-positive cells by N901-bR, whereas neither an isotype-matched control MAb nor galactose (the ligand of native ricin) had any effect on the activity of the immunotoxin, confirming the specificity of its cytotoxic activity. Importantly, N901-bR used under optimal conditions for in vitro tumor cell depletion was not toxic to hematopoietic precursors.

CONCLUSIONS

N901-bR has the properties required to target CD56, an antigen present not only on cells from a large number of cancers of neuroendocrine origin, but also on some important normal tissues. In addition, treatment with this immunotoxin results in the highly effective and specific elimination of neuroblastoma and SCLC cells and does not affect normal hematopoietic progenitors.

IMPLICATIONS

N901-bR may have clinical utility for purging of neuroblastoma cells and SCLC cells before autologous stem cell transplantation. Further toxicology studies are warranted to assess the potential of N901-bR for in vivo administration.

Evaluation of a CD5-specific immunotoxin for treatment of acute graft-versus-host disease after allogeneic marrow transplantation

Acute graft-versus-host disease (GVHD) is most often treated with high dose glucocorticoids, but less than half of patients have durable overall improvement. Previous phase I and phase II studies suggested that treatment with a CD5-specific immunotoxin (XomaZyme-CD5 Plus) could ameliorate symptoms of GVHD. In a randomized, double-blind trial, we compared XomaZyme-CD5 Plus and glucocorticoids versus placebo and glucocorticoids as initial therapy for 243 patients who developed acute GVHD after allogeneic marrow transplantation. The study drug (XomaZyme. CD5-Plus or an identical appearing placebo) was administered at a dose of 0.1 mg/kg body weight on each of 14 consecutive days. All patients were treated concomitantly with a standard regimen of methylprednisolone. At the time of entry on study, 94% of patients had a rash, 56% had hyperbilirubinemia, 61% had diarrhea, and 84% had nausea and vomiting. At 3, 4, and 5 weeks after starting treatment, symptom severity was less in the CD5 group than in the placebo group. At 4 weeks, 40% of patients assigned to the CD5 group had complete response compared with 25% of those assigned to the control group (P = .019). At 6 weeks, 44% of patients assigned to the CD5 group had complete response as compared with 38% in the placebo group (P = .36). Clinical extensive chronic GVHD developed in 65% of patients in the CD5 group compared with 72% in the control group (P = .35). Survival at 1 year after treatment was 49% in the CD5 group and 45% in the control group (P = .68). Side effects required close monitoring and appropriate adjustment of treatment. The combined administration of a CD5-specific immunotoxin and glucocorticoids controls GVHD manifestations more effectively than treatment with glucocorticoids alone during the first 5 weeks after starting treatment. Use of this immunotoxin does not result in any long-term clinical benefit for patients with acute GVHD.

Transferrin-ricin A chain toxin limits the development of experimental proliferative vitreoretinopathy

This study was designed to determine the safety and efficacy of transferrin-ricin A chain toxin (Tfr-rRA) at preventing retinal detachment in a rabbit model of proliferative vitreoretinopathy (PVR). The toxicity of intravitreal Tfr-rRA (1000-5000 ng) was determined by indirect ophthalmoscopy and electroretinography on days 1, 5, 8, 16, 26 and 48 post-injection, and by light and transmission electron microscopy conducted on eyes enucleated 48 days after drug exposure. PVR was created by injecting 25,000 homologous fibroblasts into the vitreous cavity of eyes which had previously undergone a gas compression vitrectomy. Eyes then received intravitreal Tfr-rRA (2000 ng) or vehicle. Animals were examined on days 1, 4, 7, 10, 14, 21 and 28 post-injection. Intravitreal injection of 1000 and 2000 ng Tfr-rRA did not show ophthalmoscopic or electroretinographic toxicity. Injection of 5000 ng Tfr-rRA showed mild retinal whitening, retinal arteriolar narrowing, and electroretinographic toxicity, but no morphologic damage, such as photoreceptor loss, nuclear layer vacuolation, or inflammatory cell infiltration, to the retina. Tfr-rRA (2000 ng) injected intravitreally 3 days after fibroblast injection prevented traction retinal detachment in 90% of eyes compared to 22% of sham treated eyes (P < 0.001). The data from this study suggest that transferrin-ricin A chain toxin (2000 ng) safely and effectively limits retinal detachment in experimental PVR.

Cure of multidrug-resistant human B-cell lymphoma xenografts by combinations of anti-B4-blocked ricin and chemotherapeutic drugs

The CD-19-directed immunotoxin anti-B4-blocked ricin (anti-B4-bR) is currently in clinical trials for the treatment of B-cell malignancies. To explore the potential of using anti-B4-bR with chemotherapy protocols we tested the in vivo efficacy of the immunotoxin in combination with two multi-drug chemotherapeutic regimens in severe combined immunodeficient (SCID) mice bearing disseminated tumors of the multidrug-resistant human B-cell lymphoma Namalwa/mdr-1. In cytotoxicity studies in vitro, combinations of the immunotoxin with cisplatin produced supra-additive killing effects on both Namalwa and Namalwa/mdr-1 cells, whereas anti-B4-bR combined with 4-hydroperoxy-cyclophosphamide caused additive killing of both cell lines. In vivo cyclophosphamide, cisplatin, vincristine, doxorubicin, and etoposide as single agents, were effective in prolonging the survival of SCID mice burdened with the Namalwa tumor, whereas only cyclophosphamide and cisplatin were effective on Namalwa/mdr-1 tumors. Treatment of Namalwa/mdr-1-bearing mice with anti-B4-bR alone or with the drug combination CHOE (consisting of cyclophosphamide, vincristine, doxorubicin, and etoposide) alone increased the lifespan of the tumor-burdened mice by 58% and 73%, respectively. However, treatment with five daily bolus intravenous injections of anti-B4-bR followed by CHOE increased the lifespan by 173%, and 20% of the mice were cured. The drug combination CCE (cyclophosphamide, cisplatin, and etoposide) alone could increase the lifespan of the Namalwa/mdr-1 tumor-burdened mice by 129% compared with untreated controls. Combination therapy with anti-B4-bR and CCE produced long-term cures in 50% of the tumor-burdened mice. These results suggest that anti-B4-bR in combination with current multidrug regimens may constitute a highly efficacious modality for the treatment of drug-resistant B-cell malignancies.

Combined in vitro and in vivo T lymphocyte depletion for the control of graft-versus-host disease following haploidentical marrow transplant

Most patients requiring allogeneic bone marrow transplantation (BMT) lack a human leukocyte antigen genotypically identical sibling and require an alternative donor. This carries an increased risk of graft failure and acute graft-versus-host disease (GVHD). We sought to overcome these problems with transplants by using grafts obtained from the most readily available source: the haploidentical, partially mismatched, related donor. This study of 40 patients used a novel approach combining in vitro and in vivo T cell depletion with T lymphocyte targeted monoclonal antibodies (mAb) and intensified conditioning therapy, including fractionated total body irradiation before etoposide, cytoside arabinoside, cyclophosphamide, and methylprednisolone. Grafts were treated with T10B9.1A-31 mAb, directed against the alpha-beta heterodimer of the T cell receptor, and rabbit complement. In vivo depletion was attempted with an anti-CD5 mAb-Ricin A-chain (H65-RTA) immunotoxin (IT). Study patients were compared with a historical control group of 17 patients not given H65-RTA. Rates of engraftment were not significantly different (93% vs. 100%, P=0.12), although patients receiving IT engrafted more rapidly. The incidence of > grade I GVHD was significantly lower in the study group (36% vs. 100%, P=0.0001), as well as for severe grade III-IV GVHD (19% vs. 92%, P=0.0001). Five-year survival tended to be improved in the study group (40% vs. 18%, P=0.21). Transplant from haploidentical family members is indicated for patients without a matched sibling in whom allogeneic BMT offers the best opportunity to achieve cure.

Prolonged inhibition of IgE production in mice following treatment with an IgE-specific immunotoxin

The synthesis of IgE antibodies by B cells is the first in a series of steps resulting in an allergic response. To eliminate IgE-bearing B cells and thereby prevent IgE production, we have developed an immunotoxin (ITA) composed of the non-anaphylactic 84.1c anti-mouse IgE mAb and the A chain of ricin (ricin A). This ITA specifically inhibited the induction of IgE synthesis by lipopolysaccharide plus interleukin-4 (LPS + IL-4) in vitro, and antigen-specific IgE production in vivo in adult mice. A single dose of anti-IgE ITA, given within a week (either before or after) of antigen challenge completely abolished antigen-specific primary IgE responses. No IgE production was seen for 2 months after ITA treatment. Following antigenic re-challenge, a suppressed secondary response (over 50% reduction) was still seen in the ITA-treated mice, 100 days after immunization. The results of this study demonstrate the potential use of anti-IgE toxin conjugates for the suppression of periodic (seasonal) allergic outbreaks.

Therapy for ongoing graft-versus-host disease induced across the major or minor histocompatibility barrier in mice with anti-CD3F(ab')2-ricin toxin A chain immunotoxin

A new pharmacologic agent, anti-CD3F(ab')2-ricin toxin A chain (RTA), was synthesized for the purpose of targeting T cells and as a means of treating established graft-versus-host disease (GVHD). The Fc region of anti-CD3 monoclonal antibody (MoAb) was removed to prevent its ability to activate T cells. The resulting F(ab')2 fragments were conjugated to deglycosylated RTA (dgRTA), a catalytic and potent phytotoxin. The resulting immunotoxin (IT) was potent (greater than 95% inhibition) and selective in inhibiting T-cell mitogenesis in vitro. In vivo, the IT depleted 80% of T cells in mice receiving bone marrow (BM) transplants. Transplantation in an aggressive acute GVHD model using C57BL/6 donor cells and H-2 disparate B10.BR recipients resulted in an infiltration of CD3-expressing cells and a median survival time (MST) of 20 to 30 days. A 5-day course of anti-CD3F(ab')2-RTA (30 micrograms/d intraperitoneally) beginning 7 days after GVHD induction was beneficial in treating established GVHD in these mice, as evidenced by significantly prolonged survival (MST, greater than 80 days), superior mean weight values, and improved clinical appearance. Neither intact anti-CD3, unconjugated anti-CD3 F(ab')2 fragments, nor a mixture of anti-CD4 and anti-CD8 MoAbs (which are highly effective in prophylactic models) were as effective. F(ab')2 fragments made from anti-Lyt-1 (the murine homologue of human anti-CD5) linked to RTA were also not effective, despite the fact that both anti-CD3F(ab')2-RTA and anti-Lyt-1F(ab')2-RTA had similar half-lives of about 9 hours. The IT also increased MST in two aggressive models of GVHD across non-H-2 minor histocompatibility barriers, indicating that the usefulness of anti-CD3F(ab')2-dgRTA is not limited to a single-strain combination. This agent should be further investigated as an alternative to current strategies for treating steroid refractory GVHD.

Prevention of graft-versus-host disease with anti-CD5 ricin A chain immunotoxin after CD3-depleted HLA-nonidentical marrow transplantation in pediatric leukemia patients

To determine if partial T cell depletion and intensive post-transplant immunosuppression is effective for the prevention of graft-versus-host disease (GVHD) in pediatric recipients of HLA-non-identical marrow transplants, 10 children with leukemia received high-dose thiotepa, cyclophosphamide and total body irradiation followed by transplantation of CD3-depleted marrow from matched unrelated or one-antigen mismatched related adult donors. To maximize the number of stem cells infused, a large volume (1-1.51) of marrow was harvested from the donors. After immunopurging, the marrow infused contained a median of 3.7 x 10(6) CD34+ cells/kg, 1.4 x 10(6) CD3+ cells/kg, and 1.6 x 10(6) CD5+ cells/kg as assessed by flow cytometry. Cyclosporine, methylprednisolone and anti-CD4 ricin A chain immunotoxin (XZ-CD5) were used for prevention of GVHD post-transplant. All patients achieved an ANC > 0.5 x 10(9)/l. No patient developed capillary leak syndrome or renal failure from XZ-CD5. Five developed grade 2-4 acute GVHD, and all responded to treatment with steroids. Five of nine evaluable patients developed chronic GVHD. Two patients relapsed, but the most common cause of death was infection with or without chronic GVHD. Four patients survive 10+ to 27+ months post-transplant. XZ-CD5 is well-tolerated in T cell-depleted marrow transplant recipients. However, partial T cell depletion and intensive post-transplant immunosuppression did not prevent moderate acute GVHD or chronic GVHD. This may have been due to the high number of T cells infused with the marrow.

The in vivo anti-tumor activity of immunotoxins containing two versus one deglycosylated ricin A chains

We have compared the in vitro and in vivo activities of three deglycosylated ricin A chain (dgA)-containing immunotoxins (ITs) with one versus two molecules of dgA per molecule of IgG. Two of the ITs (anti-CD19-dgA2 and anti-CD25-dgA2) had 3-0-fold improvements over their dgA1 counterparts in vitro. However, the in vivo anti-tumor activity of both constructs of each IT was the same. In contrast, anti-CD22-dgA2 was 7-fold more potent in vitro and significantly more potent in vivo than its dgA1 counterpart. These studies suggest that monoclonal antibodies must be individually tested to determine whether the addition of two versus one dgA will improve cytotoxic activity in vivo.

IL2-ricin fusion toxin is selectively cytotoxic in vitro to IL2 receptor-bearing tumor cells

Fusion toxins consist of peptide ligands linked through amide bonds to polypeptide toxins. The ligand directs the molecule to the surface of target cells and the toxin enters the cytosol and induces cell death. Ricin toxin is an excellent candidate for use in fusion toxins because of its extreme potency, the extensive knowledge of its atomic structure, and the years of experience with RTA chemical conjugates in clinical trials. We synthesized a baculovirus transfer vector with the polyhedrin promoter followed sequentially from the 5' end with DNA encoding the gp67A leader sequence, the tripeptide ADP, IL2, another ADP tripeptide, and RTB. Recombinant baculovirus was generated in Sf9 insect cells and used to infect Sf9 cells. Recombinant IL2-RTB protein was recovered at high yields from day 5 insect cell supernatants, partially purified by affinity chromatography, and characterized. The recombinant product was soluble and immunoreactive with antibodies to RTB and IL2, bound asialofetuin and lactose, and reassociated with RTA. In the presence of lactose to block galactose-binding sites on RTB, the IL2-RTB-RTA heterodimer was selectively cytotoxic to IL2 receptor, bearing cells. Specific cytotoxicity could be blocked with IL2. Thus, we report a novel targeted plant toxin fusion protein with full biological activity.

Phase I trial of an anti-CD19 deglycosylated ricin A chain immunotoxin in non-Hodgkin's lymphoma: effect of an intensive schedule of administration

In a phase I trial, eight patients with non-Hodgkin's B-cell lymphoma received mouse IgG1k monoclonal antibody HD37 specific for CD19 conjugated to deglycosylated ricin A chain (dgA) administered in four doses at 4-h intervals with total doses ranging from 4-12 mg/m2. This schedule generated serum levels of immunotoxin which were sustained over 36 h. The plasma half-life of HD37-dgA was 17 +/- 4 (SD) h. The HD37-dgA conjugate was stable in vivo as demonstrated by serum levels of HD37-dgA conjugate comparable to those of total HD37 antibody. Peak serum levels attained after the fourth dose ranged from 0.36 to 5.63 micrograms/ml. Two of seven evaluable patients developed modest human anti-immunotoxin antibody responses. Toxicity in patients 1-7 consisted of dose-dependent capillary leak syndrome with hypoalbuminemia, orthostatic hypotension, and weight gain. Patient 8 died on day 8 with severe capillary leak, bronchopneumonia, and rhabdomyolysis. All patients had progressive disease at 4 weeks except patient 8, who exhibited a near-complete remission before his death. This intensive schedule appears to produce inordinate toxicity with a maximal tolerated total dose of 8 mg/m2.

Clinical trials of targeted toxins

Immunotoxins (monoclonal antibodies chemically coupled to peptide toxins) and fusion toxins (peptide ligands fused genetically to peptide toxins) have been used to treat a variety of malignancies over the last 20 years. Problems with normal tissue toxicities (vascular leak syndrome, hepatotoxicity, and neurotoxicities), poor penetration to tumor interstitum, and humoral immune responses have limited clinical efficacy. Higher response rates were observed with systemic therapy of leukemias and lymphomas and regional therapy of primary brain tumors. Ongoing studies are examining the role of targeted toxins in combination with chemoradiotherapy and in minimal residual disease settings.

Prospects for immunotoxin therapy of non-Hodgkin's lymphoma

The use of unconjugated monoclonal antibodies to treat patients with non-Hodgkin's lymphoma by targeting specific antigenic determinants on malignant cells has been an area of intense laboratory and clinical research. Although occasional clinical successes have been seen, many limitations of such therapy have been identified, including the low endogenous cytotoxicity of most of the antibodies. More recently, investigators have attempted to employ monoclonal antibody-toxin conjugates (immunotoxins) to deliver specific cytotoxins to the lymphoma cell surface. This article describes the preclinical development of immunotoxin therapy as well as the initial results from selected Phase I and II clinical trials in patients with NHL. In addition, future directions are suggested for the use of these agents as adjuvant therapy and as treatment for patients with human immunodeficiency virus-related NHL.

Phase I study of monoclonal antibody-ricin A chain immunoconjugate Xomazyme-791 in patients with metastatic colon cancer

The immunoconjugate XMMCO-791/RTA consists of ricin A chain bound to a murine monoclonal antibody MoAb 791T. This monoclonal antibody (MoAb) binds to a glycoprotein of 72 kD, which is expressed on human colorectal carcinoma, ovarian carcinoma, and osteogenic sarcoma. XMMCO-791/RTA was tested in a Phase I trial with proposed dose escalation steps of 0.02, 0.04, 0.15, and 0.2 mg/kg per day. Twelve patients with metastatic colorectal carcinoma were treated at 0.02, 0.03, and 0.04 mg/kg per day dose levels administered over 1 hour on days 1-5. Study-related toxicities were hypotension (6 patients); greater than 10% weight gain (6 patients); peripheral edema (9 patients); fever (4 patients); confusion (3 patients); diarrhea (3 patients); proteinuria, as identified by dipstick (3 patients), greater than 0.6 mg/dl decrease in serum albumin (11 patients); greater than 25% decrease in oncotic pressure (10 patients), and a decrease in ionized calcium (8 patients). Six patients received a second course of treatment. HAMA levels developed in 9 patients and titers increased with number of courses administered. Decreased overall toxicity, in comparison to the first course, was noted, but one patient had an allergic-type response (hypotension, crushing chest pain, diaphoresis) after the test dose of the second course (HAMA level > 10,000 IgG). Life-threatening toxicity in the form of fluid shift, resulting in noncardiac pulmonary edema and third-spacing occurred after course 1 in 1 of 3 patients at the 0.04 mg/kg per day level. No further dose escalation was attempted and no antitumor activity was seen.

Escape mechanisms of human leukemic cells to long-term immunotoxin treatment in an in vitro experimental model

In kinetic assays, an anti-CD5-ricin A chain (ST.I-RTA) immunoconjugate (immunotoxins, IT) specifically inhibited up to 40% the protein synthesis of Jurkat target cells within the first 40 hr. Longer exposures of leukemia cells to ST.I-RTA resulted in a progressively higher number of target cells escaping IT treatment and becoming resistant to further treatment with ST.I-RTA even in the presence of the RTA-IT enhancer monensin. Resistant Jurkat cells proliferated at the same rate as control untreated cells, and were as sensitive as control cells to a transferrin-RTA IT, indicating that the ST.I-RTA-resistant tumor-cell population did not become insensitive to the enzymatic activity of RTA. Binding studies revealed that the anti-CD5 IT treatment induced a transient modulation of CD5 antigens but not of the functionally related CD3 antigens. The CD5 antigens were re-expressed at the cell surface following removal of the IT molecules from the culture medium with 1.1% of the total CD5 Ag being re-expressed per hr. When our experimental data on the kinetics of cell intoxication by the IT were corrected for the proliferative potential of the resistant and of the sensitive tumor-cell populations, it appeared that the effect of ST.I-RTA treatment on Jurkat cells was only to delay cell growth for a limited time period (20 hr) without reducing effectively the tumor-cell burden. Our results may have implications for the long-term treatment of target tumor cells with IT.

Antidisialoganglioside ricin A-chain immunotoxins show potent antitumor effects in vitro and in a disseminated human neuroblastoma severe combined immunodeficiency mouse model

Several monoclonal antibodies (mAbs) were screened on different neuroblastoma cell lines to evaluate ricin A-chain immunotoxins for possible use against human neuroblastoma. Four mAbs were identified that exhibited high antitumor activity against neuroblastoma cell lines as measured in an indirect cytotoxicity assay. These mAbs, including 14G2a (antidisialoganglioside), ch14.18 (a humanized switch variant), BW704 (antidisialoganglioside), and chCE7 (anti-glycoprotein of M(r) 190,000), were subsequently linked via the bivalent linker N-succinimidyloxycarbonyl-alpha-methyl-alpha-(2-piridyldithio++ +)toluene to deglycosylated ricin A chain. The most potent immunotoxin, 14G2a.dgA, inhibited the protein synthesis of neuroblastoma cell lines IMR5 and NMB by 50% at concentrations of 6 x 10(-12) M. To test the antitumor efficacy of these immunotoxins in vivo, we developed a disseminated human neuroblastoma model in severe combined immunodeficiency mice. Treatment of tumor-bearing mice with 14G2a.dgA 12 days after tumor challenge resulted in a significant prolongation of survival as compared with phosphate-buffered saline-treated controls (16.8 versus 6.5 weeks). We conclude that ricin A-chain immunotoxins might be of potential use in the treatment of human neuroblastoma.

A pilot study of anti-CD5 ricin A chain immunoconjugate in systemic lupus erythematosus

OBJECTIVE

To determine the safety and clinical and biological effects of a murine monoclonal anti-CD5 ricin A chain immunoconjugate (CD5 Plus) in patients with systemic lupus erythematosus (SLE).

METHODS

An open label phase I study of CD5 Plus. A dose of 0.1 mg/kg was administered intravenously on 5 consecutive days. A second course of immunoconjugate was given to patients who failed to show any clinical response one to 2 months later.

RESULTS

Six patients (4 with glomerulonephritis and 2 with thrombocytopenia) were studied. Improvement was documented in 2 patients with nephritis; no effect on thrombocytopenia was observed. Adverse effects were mild and transient. Relative to pretreatment lymphocyte counts, the mean reduction in CD3+ T cell count was 69% at 2 weeks, 32% at one month, and 34% at 6 months following initial treatment. A comparable decrease in all subpopulations of mature T cells was noted, using a variety of surface markers, including CD4 and CD8. The mean percentage of T cells expressing the activation markers HLA-DR and interleukin 2R (IL-2R) was high before treatment, and remained so. There was a transient decrease in CD5+ B cells, but no persistent depletion of total B cell numbers. There was no consistent change in natural killer cell populations.

CONCLUSION

Anti-CD5 ricin A chain immunoconjugate is well tolerated in patients with SLE, causes modest T cell depletion which may persist for months, and may have some clinical efficacy in lupus nephritis.

In vitro and in vivo antitumor activity of ZENECA ZD0490, a recombinant ricin A-chain immunotoxin for the treatment of colorectal cancer

ZENECA ZD0490 is a recombinant ricin A-chain-containing immunotoxin that recognizes an antigen that is expressed on approximately 65% of colorectal tumors. The antigen CA242 is recognized by a mouse monoclonal antibody designated C242. C242 antibody was conjugated to recombinant ricin A-chain via a methyl-hindred disulfide linker which confers in vivo stability. ZD0490 was extremely potent against colorectal cell lines CoLo201 and CoLo205, which express the CA242 antigen. ZD0490 activity was determined in vitro by both protein synthesis inhibition (50% inhibitory concentrations of 1-20 ng/ml after 24-h exposure) and clonogenic assay (76-95% cell kill after 24-h exposure to a 50% inhibitory concentration for protein synthesis inhibition; > 99.99% cell kill at 1000 ng/ml). This in vitro activity was translated to in vivo efficacy where single dose i.v. administration of 2.5 mg/kg of ZD0490 was sufficient to induce substantial growth delays of both CoLo201 and CoLo205 s.c. tumors in nude mice. This growth delay equates to between 40 and 60% inhibition of tumor protein synthesis as quantified by an in vivo [14C]leucine incorporation assay. Using this technique, it was shown that protein synthesis inhibition persisted for at least 96 h after a single dose of ZD0490. Administration of the same total dose given as daily doses over 5 days did not alter the antitumor efficacy of ZD0490 in either the growth delay or the protein synthesis inhibition assays. The in vitro and in vivo activity of ZD0490 detailed in this paper show that this novel immunotoxin is worthy of clinical evaluation, which is currently under way in the United Kingdom.

Establishment of new SCID and nude mouse models of human B leukemia/lymphoma and effective therapy of the tumors with immunotoxin and monoclonal antibody: marked difference between the SCID and nude mouse models in the antitumor efficacy of monoclonal antibody

BALL-1, a human B leukemia/lymphoma cell line, was transplanted into nude and SCID mice under various conditions. The transplantation was substantially improved by preadaptation of BALL-1 by serial passages in newborn and young nude mice. We were able to establish the desirable conditions where 100% of SCID and nude mice that were inoculated i.p. with various doses of the adapted BALL-1 (termed BALL-1a) developed tumors. Tumors in SCID mice were disseminated to various tissues in a manner analogous to tumors in patients with B leukemia/lymphoma, whereas tumors in nude mice were not as widely disseminated and grew mainly as ascites. Flow cytometric analyses showed that all of the 11 tested cell surface markers of the parental BALL-1 were well maintained on the tumor cells recovered from the SCID and nude mice. The utility of the developed tumor models for the therapeutic studies was investigated by i.p. or i.v. administration of an anti-B leukemia/lymphoma monoclonal antibody, termed SN7 (IgG1 kappa), and SN7 immunotoxin (IT) that was prepared by conjugating SN7 to ricin A chain (RA) or deglycosylated RA (dgRA). In the nude mouse model study, SN7-RA that had been administered i.p. suppressed the tumor growth completely in all of the treated mice (n = 5) without any sign of tumor or undesirable side effects for as long as followed (i.e., 350 days), whereas unconjugated SN7 showed only a slight therapeutic effect. A control RA conjugate was not effective. In the SCID mouse model studies, several sets of experiments were carried out by i.p. or i.v. administration of IT, monoclonal antibody, or control IT. In the first three sets of experiments, SCID mice inoculated with 1.1 x 10(6) BALL-1a cells received an i.p. administration of phosphate-buffered saline or three different doses (i.e., 4 x 10 micrograms, 4 x 20 micrograms, and 4 x 30 micrograms) of therapeutic agents (SN7-RA and SN7). Virtually an identical result was obtained from the three experiments. All of the phosphate-buffered saline control group mice (n = 15) died within 35 days post tumor inoculation. In contrast, all of the mice that were treated with SN7-RA (n = 19) or with SN7 (n = 15) survived for as long as followed (i.e., 250 days). However, the unconjugated SN7 was less effective than SN7 IT for tumor suppression in SCID mice that were inoculated with a larger tumor burden (i.e., 4 x 10(7) BALL-1a cells).(ABSTRACT TRUNCATED AT 400 WORDS)

Experimental treatment of human Hodgkin's disease with ricin A-chain immunotoxins

In the present paper we describe the evaluation of ricin A-chain immunotoxins for clinical application in Hodgkin's disease. The immunotoxins were constructed by chemically linking deglycosylated ricin-A to monoclonal antibodies (MoAb) recognising lymphocyte activation markers CD25, CD30, or IRac, which are expressed by Hodgkin's and Reed-Sternberg (H-RS) cells. The cytotoxic effects of the immunotoxins were investigated in vitro against L540Cy Hodgkin cells and in vivo against Hodgkin's tumors in nude mice and disseminated Hodgkin's tumors in SCID mice. MoAbs were evaluated for crossreactivity with normal human tissues and staining of sections from Hodgkin's disease tissue. Of 32 MoAbs, eight showed little crossreactivity with vital human organs and produced highly active immunotoxins. The most effective immunotoxin, RFT5 gamma l.dgA (CD25), inhibits the growth of H-RS cells at concentrations of 7 x 10(-12) M. RFT5 gamma l.dgA destroys about 60% of solid Hodgkin's tumors of 0.5 cm diameter in nude mice and induces complete remissions in 95% of SCID mice with disseminated Hodgkin's tumors when administered one day after tumor challenge. This immunotoxin binds to all H-RS cells in more than 90% of patients with Hodgkin's disease. Patients with refractory Hodgkin's disease are currently being treated in a phase-I/II clinical trial.