Protein engineering of DAB-IL-2 fusion toxins to increase biologic potency

An electrochemiluminescence assay for quantification of Denileukin Diftitox and its anti-drug antibodies in rat serum

Denileukin Diftitox (DD), comprising fragments of diphtheria toxin (DT) and interleukin-2 (IL2), was developed for the treatment of lymphoma and has been approved for marketing in Japan. Toxicological evaluation including pharmacokinetics and immunogenicity in preclinical animals is important for drug development and thus the assays of DD and anti-drug antibody (ADA) were developed by electrochemiluminescence (ECL) detection. For the DD assay, ruthenium-labeled anti-DT Ab and biotinylated anti-IL2 Ab were mixed with serum samples and the mixture was captured by streptavidin-coated wells for ECL detection. For the ADA assay, signals of immuno-complex of biotinylated DD, ruthenium-labeled DD, and ADA, bound to streptavidin plate were determined. DD was quantifiable from 10 ng/mL. Accuracy and precision of quality control samples were within ±20% and 20%, respectively, and stability of DD in rat serum was successfully assessed. Precision of positive control samples of ADA was within the acceptance criteria and cut point values for ADA detection in the screening and confirmatory assay were determined by statistical analysis. Drug-induced ADA was detected by screening assay followed by confirmatory assay. The developed method was successfully applied to assess pharmacokinetics and immunogenicity to support toxicity studies in rats.

Immunogenic and tolerogenic effects of the chimeric IL-2-diphtheria toxin cytocidal agent Ontak® on CD25+ cells

Ontak^®, a conjugate between IL-2 and a diphtheria toxin fragment, was recently investigated in cancer clinical trials aiming to kill CD25⁺ regulatory T cells (T_regs). We found that the activity of Ontak^® was more complex on T_regs and conventional T cells (T_convs) than anticipated, including a novel strong influence on dendritic cells (DCs).

Phase II study of denileukin diftitox for previously treated indolent non-Hodgkin lymphoma: final results of E1497

Denileukin diftitox (DD) is approved for treatment of CD-25 expressing cutaneous T-cell lymphomas (CTCL). Initial studies of DD demonstrated responses in patients with B-cell non-Hodgkin lymphoma (NHL). This phase II trial evaluated response rate (RR) and tolerability of DD in this population. Patients were stratified into two arms: those with NHL expressing > or =20% IL-2R (IL-2R+) or <20% IL-2R (IL-2R-). DD was dosed at 18 microg/kg/day for 5 days every 21 days. Corticosteroid pre-medication was not allowed. Thirty-five patients of a planned 77 accrued due to closure for slow accrual. This report is on 29 patients (18 males) with indolent B-cell NHL (11 IL-2R+ and 18 IL-2R-). Histologic subtypes included small lymphocytic (SLL) (8 patients) and follicular grade I/II lymphoma (21 patients). Patients received a median of three prior regimens, including rituximab in 76%. Three partial responses were observed (RR 10%). The RR for the IL-2R- and IL-2R+ patients was 11% and 9%, respectively. Of 8 patients with SLL, 2 responded. Toxicities were generally grade I - II and transient but 1 patient experienced a fatal thrombo-embolism. Therapy with DD is tolerable and modest efficacy was observed in SLL subtype. Measured IL-2R status did not correlate with efficacy.

Phase II trial of the combination of denileukin diftitox and rituximab for relapsed/refractory B-cell non-Hodgkin lymphoma

Denileukin diftitox plus rituximab was evaluated in relapsed/refractory B-cell non-Hodgkin lymphoma patients. Of the 38 evaluable patients, 30 (80%) were rituximab-refractory. The overall response rate (ORR) was 32%, with six complete responses (CR) and six partial responses (PR). The median time to progression for responders was 8 months (range: 2-36+); two patients with rituximab-refractory follicular lymphoma were in CR at 25 and 36+ months. The ORR was 55% (4 CRs, 2 PRs) in 11/14 patients with rituximab-refractory follicular lymphoma, and 100% in the three patients with rituximab-sensitive tumour. Most toxicities were low grade and transient, and myelotoxicity was uncommon.

Denileukin diftitox: a concise clinical review

Denileukin diftitox (DAB389IL-2; Ontak) is a novel recombinant fusion protein approved by the US Food and Drug Administration for the treatment of relapsed or refractory cutaneous T-cell lymphoma. It consists of fragments of diphtheria toxin linked to human interleukin-2 and works by targeting the high-affinity interleukin-2 receptor expressed on malignant cells. This article will review the clinical trials leading to the approval of denileukin diftitox for cutaneous T-cell lymphoma, and discuss the potential future role of this novel drug in patients with both malignant and nonmalignant diseases, including non-Hodgkin's lymphoma, chronic lymphocytic leukemia, solid tumors, psoriasis and graft-versus-host disease.