Dorothea E. Myers

Engagement of the CD19 receptor on human B-lineage leukemia cells activates LCK tyrosine kinase and facilitates radiation-induced apoptosis.

As presently reported, both ionizing radiation and engagement of the CD19 receptor are capable of inducing apoptosis in B-lineage acute lymphoblastic leukemia (ALL) cells. In both instances, activation of tyrosine kinases appears to be a proximal and mandatory step, since it can be prevented by the tyrosine kinase inhibitor genistein. This common biochemical signaling pathway involves the rapid activation of the Src family tyrosine kinase LCK (p56lck), which is physically associated with the CD19 receptor, and enhanced tyrosine phosphorylation of multiple substrates leading to stimulation of phosphoinositide turnover, and activation of protein kinase C. Importantly, engagement of the CD19 receptor promoted radiation-induced apoptosis in radiation-resistant B-lineage ALL cells in a cell type-specific fashion. Our results prompt the hypothesis that clonogenic B-lineage ALL blasts with an inherent or acquired resistance to radiation could be radiosensitized in clinical settings using anti-CD19 MoAb B43 or its homoconjugate as adjuncts.

EGF-genistein inhibits neointimal hyperplasia after vascular injury in an experimental restenosis model.

A murine model of vascular injury-induced neointimal hyperplasia was developed by using a photoactive dye, rose bengal. Photoactivation of rose bengal induced vascular injury to the femoral arteries of C57B1/6 mice and resulted in an occlusive neointimal hyperplasia after 4 weeks. The cellular elements of the hyperplastic neointima were found to be alpha-actin-positive vascular smooth muscle cells expressing epidermal growth factor (EGF) receptor at high levels. EGF-Gen, an EGF-R-specific inhibitor with potent anticancer activity, suppressed the formation of hyperplastic neointima. Morphometric analysis of serial tissue sections at 4 weeks after vascular injury showed that in 75% of the EGF-Gen-treated mice, the maximal stenosis index was only 0.44 +/- 0.13, whereas in 75% of phosphate-buffered saline (PBS)-treated mice, the maximal stenosis index was 1.20 +/- 0.25. The mean neointima/media ratios for areas of maximum neointimal hyperplasia were 0.59 +/- 0.16 (n = 24) for the EGF-Gen-treated group, 0.99 +/- 16 (n = 45) for the PBS group (EGF-Gen vs. PBS, p = 0.0017), and 1.03 +/- 18 (n = 8) for group treated with unconjugated genistein (EGF-Gen vs. Gen, p = 0.0088). EGF-Gen treatment of mice with vascular injury to the left femoral artery was not associated with any clinical signs of toxicity or histopathologic lesions in any of the organs, including the uninjured right femoral artery. EGF-Gen also inhibited VSMC migration in vitro, without affecting VSMC proliferation and viability, suggesting that EGF-Gen is blocking neointima formation by inhibiting cellular migration to vascular injury sites. In conclusion, EGF-Gen may be useful as a nontoxic prophylactic agent for prevention of restenosis in clinical settings.

Clinical Pharmacokinetics of the CD19 Receptor-Directed Tyrosine Kinase Inhibitor B43-Genistein in Patients with B-Lineage Lymphoid Malignancies

The authors examined the pharmacokinetics of the CD 19 receptor‐directed tyrosine kinase inhibitor B43‐Genistein in 17 patients (4 children, 13 adults) with B‐lineage lymphoid malignancies, including 12 patients with acute lymphoblastic leukemia (ALL) and 5patients with non‐Hodgkins lymphoma (NHL). The immune conjugate was administered intravenously as a 1‐hour continuous infusion at a dose level of either 0.1 mg/kg (N = 12) or 0.18 mg/kg (N = 5), and the plasma concentration‐time data were modeled by using the WinNonlin program to estimate the pharmacokinetic parameters. Pharmacokinetic analyses revealed a plasma half‐life of 19 ± 4 hours, mean residence time of 22 ± 4 hours, and a systemic clearance of 18 ± 2 mL/h/kg. The average (mean ± SEM) values for the maximum plasma concentration Cmax, volume of distribution at steady state (Vss), and area under curve (AUC) were 1092 ± 225ng/ml, 291 ± 37mL/kg, and 9987 ± 2021 μg × h/L, respectively The AUC values were higher at the 0.18 mg/kg dose level than at the 0.1 mg/kg dose level (16,848 ± 5118 μg × h/L vs. 7128 ± 1156 μg × h/L, p = 0.009). Patients with ALL had a significantly larger volume of distribution at steady state (332 ± 47 mL/kg vs. 191 ± 12 mL/kg, p = 0.04), faster clearance (21 ± 3 mL/h/kg vs. 11 ± 2 mL/h/kg, p = 0.03), and lower dose‐corrected AUC than patients with NHL (6010 ± 836 μg × h/L vs. 12,044 ± 2707 μg × h/L, p = 0.006). There was a trend toward faster clearance rates (23 ± 4 mL/h/kg vs. 16 ± 3 mL/h/kg, p = 0.1), shorter elimination half‐lives (5.7 ± 3.6 hours vs. 13 ± 8.8 hours, p = 0.1), and shorter mean residence times (11 ± 3 hours vs. 25 ± 5 hours, p = 0.08) for non‐Caucasian patients as compared to Caucasian patients. When compared to adult patients, pediatric patients showed a significantly larger volume of distribution at steady state (418 ± 82 mL/kg vs. 252 ± 34 mL/kg, p = 0.02) and a longer elimination half‐lives (18.4 ± 13.6 hours vs. 8.7 ± 6.7 hours, p = 0.04). The pharmacokinetics of B43‐Genistein was not affected by the gender of the patients or by bone marrow transplantation in past medical history. Overall, B43‐Genistein showed favorable pharmacokinetics in this heavily pretreated leukemia/lymphoma patient population, which is reminiscent of its recently reported favorable pharmacokinetics in cynomolgus monkeys. To our knowledge, this is the first clinical pharmacokinetics study of a tyrosine kinase inhibitor containing immunoconjugate.

Large scale manufacturing of TXU(anti-CD7)-pokeweed antiviral protein (PAP) immunoconjugate for clinical trials.

We have conjugated the murine monoclonal anti-CD7 antibody TXU to the plant hemitoxin pokeweed antiviral protein (PAP) to construct an effective immunotoxin against CD7 antigen positive hematologic malignancies. The scaled-up production and purification of TXU antibody, PAP toxin, and TXU-PAP immunotoxin permitted the manufacturing of a highly purified clinical-grade TXU-PAP preparation. In clonogenic assays, TXU-PAP elicited selective and potent cytotoxicity against CD7 antigen positive human leukemia cells and killed primary clonogenic leukemic cells from T-lineage acute lymphoblastic leukemia (ALL) patients. To our knowledge, this pre-IND work represents the first effort of producing a clinical-grade PAP immunotoxin for treatment of T-lineage ALL. Since the CD7 antigen is also expressed on AML cells, TXU-PAP could also be useful for the treatment of CD7 positive acute myeloid leukemia (AML) patients.

In Vivo., Toxicity and Pharmacokinetic Features of B43(Anti-CD19)-Genistein Immunoconjugate

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

Effects of the Intermolecular Toxin-Monoclonal Antibody Linkage on the In Vivo Stability, Immunogenicity and Anti-Leukemic Activity of B43 (Anti-CD19) Pokeweed Antiviral Protein Immunotoxin

We have successfully constructed highly potent and selective anti-CD19 PAP immunotoxins using each of the three crosslinking agents, SPDP, LC-SPDP, or SMPT, to generate an intermolecular bridge between the B43 MoAb and PAP toxin moieties. These immunotoxins were selectively immunoreactive with and cytotoxic against CD19+ B-lineage ALL cells. In this report, we compared (a) in vivo chemical, immunological, and biological stability, (b) in vivo immunogenicity, and (c) in vivo anti-leukemic activity of various B43-PAP immunotoxin constructs. Our data recommend the use of SPDP and SMPT rather than LC-SPDP for generation of B43(anti-CD19)-PAP immunotoxins as clinical anti-leukemic agents. To our knowledge, this is the first comparative analysis of the in vivo pharmacokinetic features, immunogenicity, and anti-leukemic activity of anti-CD19 PAP immunotoxins that were prepared with different heterobifunctional crosslinking agents.

Combined Therapeutic Efficacy of the Thymidylate Synthase Inhibitor ZD1694 (TOMUDEX) and the Immunotoxin B43(Anti-CD19)-PAP in a SCID Mouse Model of Human B-Lineage Acute Lymphoblastic Leukemia

The quinazoline antifolate N-(5-[N-(3,4-dihydro-2-methyl-4-oxoquinazolin-6-ylmethyl)-N- methylamino]-2-thenoyl)-L-glutamic acid (ZD1694; Tomudex) is a potent inhibitor of thymidylate synthase and causes cell death through disruption of DNA synthesis and repair by blocking the obligatory thymidine nucleotide synthesis. B43(anti-CD19)-PAP immunotoxin is a potent inhibitor of protein synthesis in CD19+ B-lineage acute lymphoblastic leukemia (ALL) cells and causes apoptosis. In this model, 100% of SCID mice challenged with 1 x 10(6) human NALM-6 B-lineage ALL cells develop overt and invariably fatal leukemia. All of the 22 control SCID mice treated with phosphate-buffered saline died of disseminated human leukemia between 31 and 61 days with a median survival of 41.2 days. Treatment with ZD 1694 resulted in improved leukemia-free survival with a median survival of 69.2 days (P < 0.001, log-rank test). B43-PAP treatment was more effective than ZD1694 (P=0.026) and resulted in 51.0% long-term leukemia-free survival with a median survival of 187.5 days (P < 0.0001. log-rank test). The combination of ZD1694 and B43-PAP was more effective than either agent alone and resulted in 100% long-term leukemia-free survival. To our knowledge, this preclinical study is the first to demonstrate the feasibility and therapeutic advantage of combining an anti-leukemia immunotoxin with a thymidylate synthase inhibitor.

LARGE SCALE MANUFACTURING OF B43(ANTI-CD19)-GENISTEIN FOR CLINICAL TRIALS IN LEUKEMIA AND LYMPHOMA

We have conjugated the murine monoclonal anti-CD19 antibody B43 to the tyrosine kinase inhibitor genistein to construct an effective immunoconjugate against CD19 antigen positive hematologic malignancies. The scaled-up production and purification of B43 antibody, genistein, and B43-Genistein immunoconjugate permitted the manufacturing of a highly purified clinical-grade B43-Genistein preparation. In clonogenic assays, B43-Genistein elicited selective and potent cytotoxicity against CD19 antigen positive human leukemia cells. To our knowledge, this work represents the first effort of producing a clinical-grade genistein immunoconjugate for treatment of B-lineage leukemia and lymphoma.

Favorable Pharmacodynamic Features and Superior Anti-Leukemic Activity of B43 (Anti-CD 19) Immunotoxins Containing Two Pokeweed Antiviral Protein Molecules Covalently Linked to each Monoclonal Antibody Molecule

Standard immunotoxin production procedures using whole IgG as the MoAb moiety yield a heterogeneous mixture of 180 kDa, 210 kDa, and 240 kDa immunotoxin species with 1 to 1, 1 to 2, and 1 to 3 MoAb to toxin ratios. This heterogeneity makes it impossible to precisely deliver a predetermined immunotoxin dose to target cells and impairs the accuracy of pharmacologic studies. In this report, we describe the preparation and characterization of B43(anti-CD19)-pokeweed antiviral protein (PAP) immunotoxins containing either one or two 30 kDa PAP toxin molecules covalently linked to each 150 kDa B43 monoclonal antibody molecule. Compared to the 180 kDa immunotoxin, the 210 kDa immunotoxin displayed greater in vitro chemical stability, resulted in higher systemic exposure levels in vivo, and was a more effective anti-leukemic agent in a SCID mouse model of human B-lineage acute lymphoblastic leukemia. Taken together, the results of this study recommend the clinical evaluation of 210 kDa B43-PAP as a potentially more effective immunotoxin against relapsed B-lineage ALL.

Recombinant human CD19L-sTRAIL effectively targets B cell precursor acute lymphoblastic leukemia

Patients with B cell precursor acute lymphoblastic leukemia (BPL) respond well to chemotherapy at initial diagnosis; however, therapeutic options are limited for individuals with BPL who relapse. Almost all BPL cells express CD19, and we recently cloned the gene encoding a natural ligand of the human CD19 receptor (CD19L). We hypothesized that fusion of CD19L to the soluble extracellular domain of proapoptotic TNF-related apoptosis-inducing ligand (sTRAIL) would markedly enhance the potency of sTRAIL and specifically induce BPL cell apoptosis due to membrane anchoring of sTRAIL and simultaneous activation of the CD19 and TRAIL receptor (TRAIL-R) apoptosis signaling pathways. Here, we demonstrate that recombinant human CD19L-sTRAIL was substantially more potent than sTRAIL and induced apoptosis in primary leukemia cells taken directly from BPL patients. CD19L-sTRAIL effectively targeted and eliminated in vivo clonogenic BPL xenograft cells, even at femtomolar-picomolar concentrations. In mice, CD19L-sTRAIL exhibited a more favorable pharmacokinetic (PK) profile than sTRAIL and was nontoxic at doses ranging from 32 fmol/kg to 3.2 pmol/kg. CD19L-sTRAIL showed potent in vivo antileukemic activity in NOD/SCID mouse xenograft models of relapsed and chemotherapy-resistant BPL at nontoxic fmol/kg dose levels. Together, these results suggest that recombinant human CD19L-sTRAIL has clinical potential as a biotherapeutic agent against BPL.