Phase II study of sphingosomal vincristine in patients with recurrent or refractory adult acute lymphocytic leukemia
Outcomes with salvage therapy for patients with recurrent or refractory acute lymphocytic leukemia (ALL) are poor, with complete response (CR) rates reported to be 20–30% and a median survival ranging from 2–6 months. New agents are needed to reduce the recurrence rate after frontline chemotherapy. Vincristine is an important component of ALL therapy. In animal models, the encapsulation of vincristine into sphingomyelin liposomes or “sphingosomes” for injection (SV) has improved efficacy compared with conventional vincristine.
A Phase II clinical trial of single-agent SV given at a dose of 2.0 mg/m2 every 2 weeks was conducted in patients with recurrent or refractory ALL. Approximately half of the 16 patients who received SV had a first CR duration of less than 1 year, 19% had failed standard induction chemotherapy, and 50% had Philadelphia chromosome-positive disease. SV was the first salvage attempt in 69% of the patients.
The overall response rate in the 14 evaluable patients was 14% (1 CR and 1 partial response). Five patients (36%) had transient reductions in bone marrow leukemia infiltrate with subsequent regrowth of the leukemia between SV infusions. Toxicity with limited treatment (median number of doses was two; range, one to five doses) was minimal with expected peripheral neuropathy.
Further study of SV in patients with ALL is warranted. A Phase I-II clinical trial of weekly SV with pulse dexamethasone currently is ongoing. Cancer 2006. © 2005 American Cancer Society.
The vinca alkaloid vincristine has significant activity against lymphomas and acute lymphocytic leukemia (ALL).1 Vincristine induces cytotoxicity by binding to tubulin, resulting in microtubule depolymerization and metaphase arrest.2, 3 These events lead to apoptosis of cells undergoing mitosis.4 In human leukemia cell lines, vincristine induced apoptosis in vitro in proportion to the concentration and time of exposure of the drug.4–6 The dose intensity and delivery of conventional vincristine is limited by the disruption of axonal microtubules after vincristine binds to neuronal tubulin. This results in significant neurotoxicity at doses higher than the “capped” dose of 2.0 mg.7
In most experimental models, the resistance of leukemia cells to vincristine is associated with decreased drug accumulation and retention, a phenomenon usually associated with the cellular expression of P-glycoprotein and the multidrug resistance (MDR) phenotype.8 The in vitro sensitivity of lymphoblasts to vincristine (determined by the methyl-thiazole-tetrazolium bromide [MTT] assay) has been correlated with clinical outcome in pediatric ALL patients.9 Many of the same clinical characteristics associated with a poor early response in pediatric ALL patients have also been identified in children with resistance to vincristine by in vitro testing of primary ALL cells.
The pharmacokinetics of conventional vincristine given by bolus infusion are characterized by large interpatient and intrapatient variations in drug clearance, volume of distribution, and elimination half-life (t½).10–12 The cellular pharmacology of vincristine is characterized by rapid intracellular uptake. Peak plasma concentrations of 100 ± 400 nM are achieved only briefly after an intravenous bolus of vincristine; the initial t½α of approximately 8 minutes reflects the rapid cellular uptake and extensive tissue binding of the drug. The long terminal elimination t½β of approximately 14 hours results in lower maintenance plasma levels of 1 ± 2 nM.
Liposomes are vesicular microscopic structures with one or more concentric lipid bilayers surrounding aqueous compartments. When administered intravenously, liposomes are sequestered by the reticuloendothelial system. Liposomal preparations of anticancer agents are reported to have increased plasma drug concentrations, improved tumor delivery, improved efficacy, and reduced toxicity (e.g., liposomal doxorubicin or daunorubicin).13, 14
Sphingosomal vincristine (vincristine encapsulated in sphingomyelin liposomes or “sphingosomes” for injection [SV]) has demonstrated significantly greater antitumor activity in vitro and in animal models when compared with conventional vincristine.15–18 SV was more likely than vincristine to be curative in murine systems against L1210 or P388 leukemia cell lines.19–24 Pharmacokinetic studies in animals demonstrated that SV given intravenously had a significantly longer t½ (approximately 12-fold longer) than conventional vincristine, which was attributed to the protection afforded by the liposome in abrogating the rapid initial elimination phase. A reduction in neurotoxicity compared with conventional vincristine was attributed to lower systemic levels of free vincristine with SV.25 Dermatologic toxicity also was found to be decreased with the liposomal formulation, without the skin necrosis or ulceration that occurs with the extravasation of free vincristine.26
An initial Phase I clinical trial with dose escalation of SV from 0.5 mg/m2 to 2.8 mg/m2 every 3 weeks was conducted in 25 patients with previously treated solid tumors.27 The dose-limiting toxicities (DLT) were observed at the 2.8 mg/m2-dose level (3 patients treated, with 1 patient receiving only 1 infusion) including myalgias, peripheral neuropathy, and constipation. The maximum tolerated dose was determined to be 2.4 mg/m2, although review of the toxicity profiles revealed a similar distribution of toxicity with the 2 dose levels of 2.0 mg/m2 and 2.4 mg/m2 (6 patients treated at each dose level). The most frequent Grade 3-4 toxicities observed over all dose levels were constipation (12%), fatigue (8%), alopecia (8%), and anemia (8%). Other toxicities occurring at an incidence of 4% each were neuropathy, nausea, fever without infection, pain, myalgia, granulocytopenia, and thrombopenia.
Significant interpatient variability in SV pharmacokinetics (similar to prior studies with conventional vincristine) was identified, but overall, the area under the curve (AUC) and Cmax values were significantly increased with SV (with as much as a 150-fold higher exposure than for free vincristine).27 Clinical activity also was observed. A partial response (PR) was achieved in one patient with pancreatic carcinoma. Five patients had stable disease, including two patients with PRs lasting fewer than the 4 weeks required for the classification of response. In the final analysis, the increasing severity and frequency of the toxicities observed with each dose level of 2.0 mg/m2 or higher led the investigators to recommend the dosing schema of SV to be 2.0 mg/m2 over 1 hour every 21 days for Phase II studies.
Given the activity of vincristine in lymphoproliferative disorders, Sarris et al.28 conducted a trial of SV in patients with recurrent intermediate or low-grade non-Hodgkin lymphoma (NHL). The interval of SV dosing was decreased to every 14 days, given the aggressive nature of the disease entities and the conservative dose selection based on the Phase I trial. In the current study, we report the outcome of what, to our knowledge, is the first Phase II study of single-agent SV in adults with recurrent or refractory ALL published to date.
MATERIALS AND METHODS
Patients age ≥ 16 years with documented diagnoses of recurrent or refractory ALL (including Burkitt or lymphoblastic lymphoma) with measurable disease and a Zubrod performance status of ≥ 3 were eligible. Adequate hepatic (total bilirubin ≤ 1.5 mg/dL and an alanine aminotransferase level ≤ 4 × the upper limit of normal) and renal functions (creatinine ≤ 1.5 mg/dL) were required. Patients could have neuropathy except for Grade 3 or 4 sensory or motor dysfunction related to the prior use of vinca alkaloids. At least 3 weeks must have elapsed from the previous anticancer therapy. No prior bone marrow transplantation was permitted. No serious intercurrent illnesses or active infections (including human immunodeficiency virus) could be present at the time of study entry.
Preparation of SV
SV (at a dose of 0.16 mg/mL) is a 3-part formulation comprised of sphingomyelin and cholesterol liposomes for injection (100 mg/mL), sodium phosphate for injection (14.2 mg/mL), and vincristine sulfate for injection (Vincasar PFS®; Pharmacia and Upjohn, Columbus, OH, which was used without further modification). The liposomes and sodium phosphate used in the current study were provided by INEX Pharmaceuticals (Burnaby, British Columbia, Canada) and were prepared by the ProPharma Pharmaceutical Clean Room, British Columbia Cancer Agency (Vancouver, British Columbia, Canada). The encapsulation procedure involved adding 1 mL of vincristine sulfate for injection (100 mg/mL) to a sterile liposome vial and mixing. Sodium phosphate for injection (14.2 mg/mL) buffer solution (5 mL) was then added. The mixture was heated for 10 minutes at 63 °C (range, 60–65 °C) in a water bath with gentle shaking. The incubation step is crucial for the proper loading of vincristine into liposomes, and was performed by trained pharmacists at the M. D. Anderson Cancer Center (MDACC). The reconstituted drug was administered within 8 hours of preparation.
Informed consent was obtained according to MDACC guidelines after approval by the Institutional Review Board. SV was infused intravenously over 60 minutes at a dose of 2.0 mg/m2 with the body surface area calculated based on the patient's actual body weight. All therapy was administered at MDACC because of the requirements of the reconstitution process. Premedications included either prochlorperazine (10 mg) or ondansetron (8 mg orally or intravenously) and were given approximately 30 minutes prior to the infusion. Counseling regarding the use of appropriate stool softeners and/or laxatives (e.g., docusate sodium, bisacodyl, lactulose, or others) was provided to minimize the occurrence of obstipation.
Doses were repeated every 14 days in the absence of DLT or rapid disease progression. Dose modifications could be implemented for nonhematologic toxicities of Grade 3-4 severity with dose level decrements of 0.2 mg/m2 (unless serious life-threatening toxicity related to SV was observed, which resulted in consideration for removal from the study). No dose modifications were implemented for changes in hematologic parameters.
Pretreatment evaluations included history and physical examination; complete blood count with differential; Sequential Multiple Analysis-12 including lactate dehydrogenase; and bone marrow aspiration for histology, flow cytometry, and cytogenetic studies. Cytogenetic analysis was performed by standard techniques, with bone marrow specimens examined on direct or short-term (24-hour) cultures.29 Karyotypic categories were established according to previously reported, nonrandom chromosomal abnormalities of defined significance in ALL.30
Hematologic profiles were obtained at least weekly or more frequently depending on the clinical situation. Chemistry profiles were repeated at least every 2 weeks, usually just prior to the administration of each dose of SV. Neurologic assessments were performed prior to each dose of SV. Bone marrow aspirations were performed prior to the second infusion to determine early response, and repeated prior to the third infusion unless there was clear evidence of circulating leukemia. Bone marrow assessments were performed as indicated thereafter.
Appropriate transfusion support was provided with packed red blood cells given for symptomatic and/or severe anemia. Platelet transfusions were given prophylactically for platelet counts of < 10–15 × 109/L or therapeutically for a platelet count < 30–50 × 109/L with hemorrhage. All blood products were irradiated. Prophylactic antibiotic therapy included either a quinolone (ciprofloxacin or levofloxacin) or trimethoprim-sulfamethoxazole for antibacterial coverage; fluconazole for antifungal coverage; and acyclovir or valacyclovir for antiviral coverage. Neutropenic febrile episodes generally resulted in hospitalization and the initiation of broad-spectrum parenteral antibiotics.
A complete response (CR) was defined as 5% or fewer blasts in a normocellular or hypercellular bone marrow specimen with a granulocyte count ≥ 1.0 × 109/L and a platelet count ≥ 100 × 109/L. Complete resolution of extramedullary disease was required for CR. A PR was defined as above with the exception of the presence of 6–25% bone marrow blasts. Other response outcomes were considered failures. Relapse was defined as disease recurrence at any site after the patient achieved a CR. Progressive disease (PD) was defined as at least a 50% increase in either leukemia peripheral blood involvement (absolute counts), bone marrow leukemia infiltrate (MLI) (calculated as cellularity × % blasts), or extramedullary sites of disease, if applicable.
Differences in response rates or pretreatment characteristics among subgroups were analyzed using the chi-square or Fisher exact tests.31 Survival was measured from the date of initiation of therapy until death from any cause. Disease-free survival (DFS) was measured from the date of CR until documented disease progression or recurrence. Survival and DFS curves were plotted according to the methods of Kaplan and Meier, with differences among them analyzed using the log-rank test.32 Toxicity was evaluated according to the National Cancer Institute Expanded Common Toxicity Criteria (version 2.0).
Between December 1998 and November 1999, 17 adults with previously treated recurrent or refractory ALL were considered for SV therapy. One patient subsequently withdrew informed consent. Details regarding the 16 patients who received at least 1 dose of SV are provided in Table 1. Their median age was 35 years (range, 23–64 yrs). The median duration of the first disease remission in those patients who achieved a CR with their initial induction chemotherapy was 6 months (range, 2 mos to 3 yrs); 19% were refractory to initial induction chemotherapy. Therapy with SV was the first salvage attempt in 11 patients (69%). A poor-risk karyotype was observed in 11 patients, 8 of whom had the Philadelphia (Ph) chromosome and 3 of whom had chromosome 5 or 7 aberrations. All patients had bone marrow disease (median 60% blasts), and 4 patients (25%) had involvement of other sites (bone, mediastinum, lymph nodes, and spleen, respectively).
Table 1. Pretreatment Characteristics of 16 Patients with Recurrent or Refractory ALL
|Age in yrs|| || |
| ||< 40||8 (50)|
| ||40–59||4 (25)|
| ||≥ 60||4 (25)|
|Duration of first CR in mos|| || |
| ||0||3 (19)|
| ||1–5.9||6 (38)|
| ||6–11.9||3 (19)|
| ||≥ 12||4 (25)|
|Circulating blasts (%)|| || |
| ||Yes||11 (69)|
| ||No||5 (31)|
|Karyotype|| || |
| ||Philadelphia||8 (50)|
| ||−5, −7||3 (19)|
| ||Diploid||2 (12)|
| ||Insufficient metaphases||3 (19)|
|Leukocyte count (× 109/L)|| || |
| ||< 25||10 (63)|
| ||25–49.9||4 (25)|
| ||≥ 50||2 (12)|
|Hemoglobin (g/dL)|| || |
| ||< 10||7 (44)|
| ||≥ 10||9 (56)|
|Platelet count (× 109/L)|| || |
| ||< 100||13 (81)|
| ||≥ 100||3 (19)|
|Induction therapy|| || |
| ||Hyper-CVAD42 ± rituximab||13 (81)|
| ||Hyper-CVXD + rituximab||1 (6)|
| ||MTX + L-asparaginase||1 (6)|
| ||Idarubicin and cytarabine||1 (6)|
|Salvage attempt no.|| || |
| ||1||11 (69)|
| ||2||3 (19)|
| ||3||2 (12)|
Based on a prognostic model designed to provide a risk analysis of adults with primary refractory or first recurrence of ALL,33 the expectation of achieving a CR was 30–40% (favorable) for only 3 of the 11 patients in this category, and was < 10% (unfavorable) for the remainder of the patients (including those patients undergoing SV therapy as their second or later salvage attempt) (Table 2).
Table 2. Outcome of Treatment with SV
|3||2||Idarubicin, ara-C; hyper-CVAD||RES; CR||0c||Ph||4||3||CR|
|4||3||Hyper-CVAD; hyper-CVXD; CAT||CR; CR RES||39||Diploid||—||2||RES (49% to 6%)|
|5||1||Hyper-CVXD plus R||CR||5||Ph||3||1||RES|
|6||1||Hyper-CVAD||CR||5||Ph||4||4||RES (65% to 18%)|
|7||1||Hyper-CVAD||RES||0||Ph||4||2||PR (33% to 10%)|
|8||2||MTX, L-asp; hyper-CVXD + R||RES; RES||0||−5, −7||—||1||Inevaluabled|
|9||1||Hyper-CVAD||CR||6||Ph||1||3||RES (38% to 5%)|
|10||1||Hyper-CVAD + R||CR||8||−7||1||1||RES|
|11||2||Hyper-CVAD; Hyper-CVAD||CR; RES||18||Ph||—||2||RES|
|12||3||Hyper-CVAD; hyper-CVXD; imatinib mesylate||CR; RES RES||54||Ph||—||1||RES|
|14||1||Hyper-CVAD||CR||9||ND||4||5||RES (25% to 15%)|
|16||2||Hyper-CVAD; hyper-CVXD||CR; RES||17||IM||—||3||RES|
Two patients were inevaluable for response to single-agent SV because of the coadministration of other chemotherapy agents. One patient (Patient 2) was removed from the study after the administration of intravenous L-asparaginase on Day 9 (given because of the absence of a reduction in leukocytosis after one dose of SV without definitive PD). The other patient (Patient 8) underwent leukopheresis (allowed by protocol) for an elevated leukocyte count and received a single dose of intravenous cytarabine (the administration of which was prohibited by protocol) concurrently on Day 0 and therefore was removed from study after the first dose of SV.
Details of patient responses to SV are provided in Table 2. Among the 14 evaluable patients, 1 patient (Patient 3) achieved a CR after 3 doses with subsequent relapse after 2 months. Another patient with primary refractory Ph-positive ALL (Patient 7) achieved a PR after two doses, and proceeded to undergo matched-related sibling allogeneic stem cell transplantation (SCT). The overall objective response rate was 14% in all evaluable patients (22% in those patients receiving more than 1 dose of SV). An additional 5 patients (36%) had reductions in the MLI after 1–2 doses, but subsequently developed PD (Table 2).
The median number of SV doses was 2 (range, 1–5 doses) and the median dose of SV administered was 3.8 mg (range, 2.9–4.2 mg). Neurotoxicity was minimal in this group, with two patients developing Grade 1 peripheral neuropathy (prior peripheral neuropathy with vincristine) after two doses and four doses, respectively. One patient (Patient 5) with a history of brain hematomas had a Grade 3 seizure that was not attributed to SV. Other neurologic toxicities included Grade 2 orthostasis and intermittent headaches (Patient 6), and transient visual field defect attributed to leukostasis at the time of presentation (Patient 8). Other events included catheter-related subclavian venous thrombosis and bone pain related to PD. Expected infectious complications during study participation (all related to preexisting neutropenia) included pneumonia (three episodes); catheter-related gram-positive bacteremia (two episodes); and fever of unknown origin (two episodes).
Patient outcome after therapy with SV is detailed in Table 3. Three patients received supportive care only and subsequently died of disease within 2–5 months. The remaining 13 patients received subsequent salvage therapy for either persistent or recurrent disease. Twelve of the 13 patients died of complications related to either infections, graft-versus-host disease, or PD. One patient achieved a CR after allogeneic SCT and was alive at the time of last follow-up.
Table 3. Subsequent Therapy after SV
| ||Imatinib mesylate||RES|| |
| ||Compound 506U7844||RES|| |
| ||Rituximab||RES|| |
|3||Imatinib mesylate||CR (relapse at 2 mos)||Dead (31)|
|4||Supportive care||—||Dead (24)|
| ||Clofarabine45||RES|| |
| ||Alemtuzumab||RES|| |
|6||Supportive care||—||Dead (9)|
|7||MRS allogeneic SCTb||CR (relapse at 2 mos)||Dead (57)|
| ||MOAD||RES|| |
| ||MUD allogeneic SCT||Death|| |
| ||DX-8951f46||RES|| |
| ||Troxacitabine47||RES|| |
| ||L-asparaginase||RES|| |
|11||MRS allogeneic SCT||CR||Alive (67)|
| ||Clofarabine45||CR|| |
| ||MUD allogeneic SCT in CR||—|| |
|14||Supportive care||—||Dead (15)|
Outcome with salvage chemotherapy in adult ALL patients remains unsatisfactory. Although a CR can be achieved in 20–40% of patients depending on patient characteristics (e.g., age and duration of first disease remission), the median DFS is reported to be only 2–6 months.33, 34 The development of novel agents is needed to alter the natural history of the disease and to reduce the disease recurrence rate after frontline therapy.35 An example of a single agent that may alter the traditional course of ALL includes imatinib mesylate, a tyrosine kinase inhibitor targeting the bcr-abl fusion protein, which was initially used as a single agent in the treatment of recurrent/refractory Ph-positive ALL or chronic myelogenous leukemia in the lymphoid blast phase. The overall CR rate was approximately 20% in patients treated with single-agent imatinib mesylate (at a dose of 600 mg daily), with short response durations of 2–4 months.36 Imatinib mesylate has now been incorporated into several frontline programs for the treatment of adult ALL, including the hyper-CVAD (hyperfractionated cyclophosphamide, vincristine, doxorubicin, and dexamethasone) regimen.37 Preliminary results with the hyper-CVAD and imatinib mesylate regimen appear promising, with improvements reported in the 2-year DFS rates for previously untreated patients compared with outcome after hyper-CVAD alone.37
The results of single-agent SV in this poor prognostic group was similarly encouraging. Activity with SV was observed in 2 of 14 evaluable patients (14%) or in 7 of 9 patients (78%) who received more than 1 dose of SV therapy. Two patients achieved objective responses (one with a CR and one with a PR) and five patients had transient reductions in the MLI (calculated to account for variations in cellularity between bone marrow assessments). No significant, unexpected toxicity was observed with SV therapy, although long-term cumulative toxicity could not be evaluated because the dose intensity of SV was limited by the schedule originally chosen for the Phase II clinical trial initiated for NHL (2.0 mg/m2 every 2 weeks). Several patients received only one dose of SV for reasons other than toxicity (usually because of the lack of significant clinical improvement resulting in the commencement of alternative salvage therapy by treating physicians), limiting the potential to achieve a response owing to limited drug exposure.
Conventional vincristine has been given safely on a weekly basis in combination with other agents in adult ALL patients.38 However, dose-intensive delivery has been limited by the development of peripheral neuropathy. To achieve further dose intensity in the salvage setting, a Phase I-II clinical trial of weekly SV (with planned dose escalation from 1.5 mg/m2 to 2.8 mg/m2) and pulse dexamethasone was designed to determine the optimal dosing regimen for future clinical trials. Preliminary results have demonstrated both tolerance to the weekly administration of SV and clinical activity of the combination regimen, with accrual to the study currently ongoing.39
Rodriguez et al.40, 41 have explored the incorporation of SV into frontline combination therapy for patients with previously untreated, aggressive NHL. Patients received cyclophosphamide, doxorubicin, vincristine, and prednisone (CHOP) ± rituximab with the substitution of SV (at a dose of 2.0 mg/m2 without capping) for conventional vincristine. Therapy was administered every 21 days for 6–8 courses. The overall response rate was 93% in 68 evaluable patients, with 80% achieving a CR (10% CRμ;). After a median follow-up of 22 months, the median progression-free survival had not been reached, with 9 patients developing disease recurrence (no difference was noted between elderly patients [older than 60 years] and their younger counterparts). The preliminary results of these studies suggest that the incorporation of SV into frontline chemotherapy regimens for ALL could improve outcome by improving drug delivery with reduced toxicity.