Treatment of human B-cell precursor leukemia in SCID mice by using a combination of the anti-CD19 immunotoxin B43-PAP with the standard chemotherapeutic drugs vincristine, methylprednisolone, and L-asparaginase

The anti-CD19 antibody-drug conjugate SAR3419 prevents hematolymphoid relapse postinduction therapy in preclinical models of pediatric acute lymphoblastic leukemia

PURPOSE

Relapsed or refractory pediatric acute lymphoblastic leukemia (ALL) remains a major cause of death from cancer in children. In this study, we evaluated the efficacy of SAR3419, an antibody-drug conjugate of the maytansinoid DM4 and a humanized anti-CD19 antibody, against B-cell precursor (BCP)-ALL and infant mixed lineage leukemia (MLL) xenografts.

EXPERIMENTAL DESIGN

ALL xenografts were established as systemic disease in immunodeficient (NOD/SCID) mice from direct patient explants. SAR3419 was administered as a single agent and in combination with an induction-type regimen of vincristine/dexamethasone/l-asparaginase (VXL). Leukemia progression and response to treatment were assessed in real-time, and responses were evaluated using strict criteria modeled after the clinical setting.

RESULTS

SAR3419 significantly delayed the progression of 4 of 4 CD19(+) BCP-ALL and 3 of 3 MLL-ALL xenografts, induced objective responses in all but one xenograft but was ineffective against T-lineage ALL xenografts. Relative surface CD19 expression across the xenograft panel significantly correlated with leukemia progression delay and objective response measure scores. SAR3419 also exerted significant efficacy against chemoresistant BCP-ALL xenografts over a large (10-fold) dose range and significantly enhanced VXL-induced leukemia progression delay in two highly chemoresistant xenografts by up to 82 days. When administered as protracted therapy following remission induction with VXL, SAR3419 prevented disease recurrence into hematolymphoid and other major organs with the notable exception of central nervous system involvement.

CONCLUSION

These results suggest that incorporation of SAR3419 into remission induction protocols may improve the outcome for high-risk pediatric and adult CD19(+) ALL.

Pharmacokinetic modeling of an induction regimen for in vivo combined testing of novel drugs against pediatric acute lymphoblastic leukemia xenografts

Current regimens for induction therapy of pediatric acute lymphoblastic leukemia (ALL), or for re-induction post relapse, use a combination of vincristine (VCR), a glucocorticoid, and L-asparaginase (ASP) with or without an anthracycline. With cure rates now approximately 80%, robust pre-clinical models are necessary to prioritize active new drugs for clinical trials in relapsed/refractory patients, and the ability of these models to predict synergy/antagonism with established therapy is an essential attribute. In this study, we report optimization of an induction-type regimen by combining VCR, dexamethasone (DEX) and ASP (VXL) against ALL xenograft models established from patient biopsies in immune-deficient mice. We demonstrate that the VXL combination was synergistic in vitro against leukemia cell lines as well as in vivo against ALL xenografts. In vivo, VXL treatment caused delays in progression of individual xenografts ranging from 22 to >146 days. The median progression delay of xenografts derived from long-term surviving patients was 2-fold greater than that of xenografts derived from patients who died of their disease. Pharmacokinetic analysis revealed that systemic DEX exposure in mice increased 2-fold when administered in combination with VCR and ASP, consistent with clinical findings, which may contribute to the observed synergy between the 3 drugs. Finally, as proof-of-principle we tested the in vivo efficacy of combining VXL with either the Bcl-2/Bcl-xL/Bcl-w inhibitor, ABT-737, or arsenic trioxide to provide evidence of a robust in vivo platform to prioritize new drugs for clinical trials in children with relapsed/refractory ALL.

Novel molecular and cellular therapeutic targets in acute lymphoblastic leukemia and lymphoproliferative disease

While the outcome for pediatric patients with lymphoproliferative disorders (LPD) or lymphoid malignancies, such as acute lymphoblastic leukemia (ALL), has improved dramatically, patients often suffer from therapeutic sequelae. Additionally, despite intensified treatment, the prognosis remains dismal for patients with refractory or relapsed disease. Thus, novel biologically targeted treatment approaches are needed. These targets can be identified by understanding how a loss of lymphocyte homeostasis can result in LPD or ALL. Herein, we review potential molecular and cellular therapeutic strategies that (i) target key signaling networks (e.g., PI3K/AKT/mTOR, JAK/STAT, Notch1, and SRC kinase family-containing pathways) which regulate lymphocyte growth, survival, and function; (ii) block the interaction of ALL cells with stromal cells or lymphoid growth factors secreted by the bone marrow microenvironment; or (iii) stimulate innate and adaptive immune responses.

Anti-CD19 immunotoxin enhances the activity of chemotherapy in severe combined immunodeficient mice with human pre-B acute lymphoblastic leukemia

The anti-CD19 immunotoxin (IT) (HD37-dgRTA) is effective in killing B-lineage leukemia cells and in curing severe combined immunodeficient mice with acute lymphoblastic leukemia. The present study aimed to identify effective combinations of HD37-dgRTA and chemotherapeutic agents. The in-vitro cytotoxicity assays demonstrate that the combination of HD37-dgRTA and either daunorubicin or vincristine is effective. The in-vivo experiments using HD37-dgRTA with vincristine prolonged the survival of mice compared to the chemotherapeutic agent or IT (90.7 vs. 147.1 days). Also, 80% of the mice treated with IT plus vincristine were long-term survivors.

The mTOR inhibitor CCI-779 induces apoptosis and inhibits growth in preclinical models of primary adult human ALL

Acute lymphoblastic leukemia (ALL) in adult patients is often resistant to current therapy, making the development of novel therapeutic agents paramount. We investigated whether mTOR inhibitors (MTIs), a class of signal transduction inhibitors, would be effective in primary human ALL. Lymphoblasts from adult patients with precursor B ALL were cultured on bone marrow stroma and were treated with CCI-779, a second generation MTI. Treated cells showed a dramatic decrease in cell proliferation and an increase in apoptotic cells, compared to untreated cells. We also assessed the effect of CCI-779 in a NOD/SCID xenograft model. We treated a total of 68 mice generated from the same patient samples with CCI-779 after establishment of disease. Animals treated with CCI-779 showed a decrease in peripheral-blood blasts and in splenomegaly. In dramatic contrast, untreated animals continued to show expansion of human ALL. We performed immunoblots to validate the inhibition of the mTOR signaling intermediate phospho-S6 in human ALL, finding down-regulation of this target in xenografted human ALL exposed to CCI-779. We conclude that MTIs can inhibit the growth of adult human ALL and deserve close examination as therapeutic agents against a disease that is often not curable with current therapy.

Characterization of childhood acute lymphoblastic leukemia xenograft models for the preclinical evaluation of new therapies

Continuous xenografts from 10 children with acute lymphoblastic leukemia (ALL) were established in nonobese diabetic/severe combined immunodeficient (NOD/SCID) mice. Relative to primary engrafted cells, negligible changes in growth rates and immunophenotype were observed at second and third passage. Analysis of clonal antigen receptor gene rearrangements in 2 xenografts from patients at diagnosis showed that the pattern of clonal variation observed following tertiary transplantation in mice exactly reflected that in bone marrow samples at the time of clinical relapse. Patients experienced diverse treatment outcomes, including 5 who died of disease (median, 13 months; range, 11-76 months, from date of diagnosis), and 5 who remain alive (median, 103 months; range, 56-131 months, following diagnosis). When stratified according to patient outcome, the in vivo sensitivity of xenografts to vincristine and dexamethasone, but not methotrexate, differed significantly (P = .028, P = .029, and P = .56, respectively). The in vitro sensitivity of xenografts to dexamethasone, but not vincristine, correlated significantly with in vivo responses and patient outcome. This study shows, for the first time, that the biologic and genetic characteristics, and patterns of chemosensitivity, of childhood ALL xenografts accurately reflect the clinical disease. As such, they provide powerful experimental models to prioritize new therapeutic strategies for future clinical trials.

Synergistic effect of vincristine with tacrolimus or sirolimus in prevention of acute heart allograft rejection in the rat

The application of multiple immunosuppressive therapy for organ transplantation could enhance therapeutic efficacy, while minimizing the toxicity of individual drugs used in the regimen. In this study, the effect of the combined therapy of vincristine (VCR) with tacrolimus (FK506) or sirolimus (rapamycin, RAPA) was tested in prevention of acute heart allograft rejection in the rat. A Brown Norway (BN, RT 1(n)) to Lewis (LEW, RT 1(1)) rat combination was used in a heart allografting model. VCR was administered intraperitoneally once daily, while FK506 and RAPA were given by gavage once daily for 14 days after transplantation. There were dose-related prolongations of mean survival time (MST) to monotherapy of VCR, FK506, or RAPA. The MST in combination therapy indicated that a synergistic interaction was produced when compared with the respective monotherapies: VCR 0.05 mg/kg/day + FK506 0.5 mg/kg/day (16.00 +/- 1.79 days, P = 0.001; combination index (CI) = 0.557); VCR 0.05 mg/kg/day + FK506 1.0 mg/kg/day (29.00 +/- 10.54 days, P = 0.001; CI = 0.598); VCR 0.05 mg/kg/day + RAPA 0.2 mg/kg/day (17.33 +/- 1.97 days, P = 0.001; CI = 0.500); and VCR 0.05 mg/kg/day + RAPA 0.4 mg/kg/day (21.17 +/- 3.19 days, P = 0.001; CI = 0.838). Combination therapy of VCR and FK506 or RAPA produced synergistic effects in prevention of acute heart allograft rejection in the rat.

New agents in the treatment of acute lymphocytic leukaemia

The overall prognosis of adult patients with acute lymphocytic leukaemia (ALL) has improved significantly over the past few decades. Combined modality strategies (e.g. chemotherapy used with targeted therapies such as monoclonal antibodies or tyrosine kinase inhibitors) may improve long-term disease-free survival. Still, most patients succumb to complications of disease progression, with current long-term disease-free survival rates of 30-45% overall. Thus, either new strategies or refinements of old ones are needed to improve the long-term prognosis. An increasing number of unique active new chemotherapeutic and biological agents are available for study. This chapter reviews new agents with the potential to be incorporated into therapeutic strategies for the treatment of ALL.

Antitumor activity of L-asparaginase from Thermus thermophilus

L-asparaginase (EC 3.5.1.1) was purified to homogeneity from Thermus thermophilus. The apparent molecular mass of L-asparaginase was found to be 33 kDa by SDS-PAGE, whereas by Sephacryl S-300 superfine column it was found to be 200 kDa, indicating that the enzyme in the native stage acts as hexamer. It is a thermostable enzyme and keeps all of its activity at 80 degrees C for 10 min. The antiproliferative activity of the purified L-asparaginase from T. thermiphilus was tested against the following human cell lines: K-562 (chronic myelogenous leukemia), Raji (Burkitt's lymphoma), SK-N-MC (primitive neuroectodermal tumor), HeLa (cervical cancer), BT20 and MCF7 (breast cancers), HT-29 (human colon cancer), and OAW-42 (ovarian cancer). The antiproliferative activity of T. thermophilus enzyme was compared with Erwinase, the commercially available L-asparaginase from Erwinia corotovora. The potency difference between the two L-asparaginases was greater in HeLa and SK-N-MC than in other cell lines. The fact that L-asparaginase from T. thermophilus does not hydrolyse L-glutamine makes it advantageous for future clinical trials.

Salvage therapy for refractory or relapsed acute lymphocytic leukemia

The overall prognosis for patients with relapsed or refractory adult ALL remains poor. Further insight into the biology of ALL is required, and novel therapeutic agents are needed to counter mechanisms of resistance. A palliative approach to the management of multiply relapsed or refractory ALL should be supplanted by enrollment into clinic trials to promote drug discovery. Monitoring of minimal residual disease may allow an earlier intervention before overt clinical relapse and improve outcome; prospective studies are needed. Attainment of a second or later CR should be followed by allogeneic BMT when feasible owing to the paucity of long-term survivors with salvage chemotherapy alone.

Pediatric Acute Lymphoblastic Leukemia: Challenges and Controversies in 2000

This article discusses ways in which pediatric patients with acute lymphoblastic leukemia (ALL) can be stratified to receive intensive and less intensive therapies in order to decrease morbidity and mortality. Specifically, the focus may shift away from current intensive therapies for ultra low-risk patients and away from transplantation for certain patients at relapse. In contrast, infants with ALL comprise an ultra high-risk population in need of specialized approaches.

In Section I Dr. Lange describes the need to identify ultra low-risk children. Groups around the world have improved the outcome of children with ALL by identifying the basic “total therapy” model of the 1970s and stratifying treatment according to risk of relapse. Current first-line treatment cures about 85% of children with standard-risk ALL and 70% of children with high-risk disease. However, all children receive anthracyclines, alkylating agents, or moderate- to high-dose antimetabolite infusions. While randomized clinical trials prove that these intensifications reduce relapses, they also show that half of all children with ALL can be cured with the modest therapy of the 1970s and early 1980s. The patients curable with lesser therapy may be considered an ultra low-risk group. Attempts to use age, gender, white count, morphology, and karyotype to identify the ultra low-risk group of patients with a 90-95% cure rate with minimal therapy have failed. An expanded repertoire of tools such as pharmacogenetic profiling, PCR measurement of minimal residual disease and microarray technology may make this goal achievable in this decade.

In section II Dr. Chessells addresses the management of children with relapsed ALL. The chance of successful re-treatment with conventional chemotherapy for relapse depends on the duration of first remission and the site of relapse. Bone marrow transplantation from a histocompatible sibling or other suitable donor, which is widely accepted as the treatment of choice for children with a first remission of < 24 months, is associated with a high risk of relapse. Bone marrow transplantation for later bone marrow relapse improves leukemia-free survival but has significant short-term and long-term toxicities. The challenges are to develop more effective treatment for early relapse and to identify those children with relapsed ALL who are curable with chemotherapy or, failing this, those children who would be candidates for bone marrow transplantation in third remission.

In Section III Dr. Felix addresses the problem of infant ALL. ALL of infancy is clinically aggressive, and infants continue to have the worst prognosis of all pediatric patients with ALL. High white blood cell count, younger age, bulky extramedullary disease, and CNS disease at diagnosis are unfavorable characteristics. These features occur with MLL gene translocations. The probability of an MLL gene translocation and the probability of poor outcome both are greatest in younger infants. Specialized intensive chemotherapy approaches and bone marrow transplantation in first remission for this disease may lead to improved survival.

Refined recognition of pediatric patients with ALL who need more and less intensive therapies is necessary to increase survival and decrease toxicities.

Pediatric Acute Lymphoblastic Leukemia: Challenges and Controversies in 2000

This article discusses ways in which pediatric patients with acute lymphoblastic leukemia (ALL) can be stratified to receive intensive and less intensive therapies in order to decrease morbidity and mortality. Specifically, the focus may shift away from current intensive therapies for ultra low-risk patients and away from transplantation for certain patients at relapse. In contrast, infants with ALL comprise an ultra high-risk population in need of specialized approaches.

In Section I Dr. Lange describes the need to identify ultra low-risk children. Groups around the world have improved the outcome of children with ALL by identifying the basic “total therapy” model of the 1970s and stratifying treatment according to risk of relapse. Current first-line treatment cures about 85% of children with standard-risk ALL and 70% of children with high-risk disease. However, all children receive anthracyclines, alkylating agents, or moderate- to high-dose antimetabolite infusions. While randomized clinical trials prove that these intensifications reduce relapses, they also show that half of all children with ALL can be cured with the modest therapy of the 1970s and early 1980s. The patients curable with lesser therapy may be considered an ultra low-risk group. Attempts to use age, gender, white count, morphology, and karyotype to identify the ultra low-risk group of patients with a 90-95% cure rate with minimal therapy have failed. An expanded repertoire of tools such as pharmacogenetic profiling, PCR measurement of minimal residual disease and microarray technology may make this goal achievable in this decade.

In section II Dr. Chessells addresses the management of children with relapsed ALL. The chance of successful re-treatment with conventional chemotherapy for relapse depends on the duration of first remission and the site of relapse. Bone marrow transplantation from a histocompatible sibling or other suitable donor, which is widely accepted as the treatment of choice for children with a first remission of < 24 months, is associated with a high risk of relapse. Bone marrow transplantation for later bone marrow relapse improves leukemia-free survival but has significant short-term and long-term toxicities. The challenges are to develop more effective treatment for early relapse and to identify those children with relapsed ALL who are curable with chemotherapy or, failing this, those children who would be candidates for bone marrow transplantation in third remission.

In Section III Dr. Felix addresses the problem of infant ALL. ALL of infancy is clinically aggressive, and infants continue to have the worst prognosis of all pediatric patients with ALL. High white blood cell count, younger age, bulky extramedullary disease, and CNS disease at diagnosis are unfavorable characteristics. These features occur with MLL gene translocations. The probability of an MLL gene translocation and the probability of poor outcome both are greatest in younger infants. Specialized intensive chemotherapy approaches and bone marrow transplantation in first remission for this disease may lead to improved survival.

Refined recognition of pediatric patients with ALL who need more and less intensive therapies is necessary to increase survival and decrease toxicities.

Efficacy of an anti-CD138 immunotoxin and doxorubicin on drug-resistant and drug-sensitive myeloma cells

Multidrug resistance is an increasing problem in the treatment of cancer. We evaluated in vitro the effect of an anti-CD138 plasma-cell-specific immunotoxin (IT, B-B4-SO6) in combination with the chemotherapeutic drug doxorubicin on drug-sensitive and drug-resistant variants of the multiple-myeloma (MM)-derived cell line RPMI8226 and freshly isolated malignant-myeloma cells. Drug-resistant RPMI8226 cells were still sensitive to the IT, although to a lesser extent than drug-sensitive cells. In the clonogenic assay, using 10 nM B-B4-SO6, at least 5 logs kill was found for drug-sensitive RPMI8226 cells, vs. 2.5 logs kill for the drug-resistant RPMI8226 cells. When a sub-optimal dose of 1 nM IT was combined with 3 ng/ml doxorubicin, which was toxic for drug-sensitive but not for drug-resistant cells, an additive effect was found for drug-sensitive RPMI8226 cells. The IT did not influence the sensitivity of resistant cells for doxorubicin. We therefore speculate that this type of IT, may be of more value in combination with primary chemotherapy. The effect of B-B4-SO6 on malignant-myeloma cells of patients was investigated in a viability assay. Both drug-sensitive and drug-resistant cells from MM patients were sensitive to B-B4-SO6. After 2 days, a 50% kill of malignant cells was found when 10 nM IT were used. Doxorubicin was effective only on sensitive cells, and there was a tendency for an additive effect in the combination of these cells.

Evaluation of temozolomide in a SCID mouse model of human B-cell precursor leukemia

We used a SCID mouse model of human B-lineage acute lymphoblastic leukemia to examine the antileukemic activity of temozolomide in comparison to as well as in combination with B43-PAP anti-CD19 immunotoxin. One hundred percent of the 20 PBS-treated control mice died of disseminated human B-lineage ALL at 32 to 64 days after the inoculation of 1x10(6) NALM-6 cells, with a median event free survival time of 43 +/- 1 days. Temozolomide, when administered i.p. for 5 consecutive days at a dose level of 411 mg/m2 or as a single 750 mg/m2 bolus dose, elicited significant antileukemic activity and improved survival in this SCID mouse model of human B-lineage ALL. The median survival times were 43 +/- 1 days for PBS-treated mice, 56 +/- 16 days for mice injected with the 5-day temozolomide program, and 64 +/- 15 days for mice treated with a single bolus dose of temozolomide. However, temozolomide was not as effective as B43-PAP. Whereas only 40 +/- 21% of mice treated with temozolomide survived beyond 120 days, B43-PAP treatment resulted in 74 +/- 7% survival in the same model system. The combination of temozolomide with B43-PAP was well tolerated by mice but it was not significantly more effective than B43-PAP alone. Temozolomide may have very limited potential as an antileukemic agent for treatment of B-lineage ALL.