Clinical and toxicological aspects of the antineoplastic drug cladribine: a review

Reynoutria Japonica from Traditional Chinese Medicine: A Source of Competitive Adenosine Deaminase Inhibitors for Anticancer

BACKGROUND

Adenosine deaminase (ADA) is an important enzyme in purine metabolism and is known as a potential therapeutic target for the treatment of lymphoproliferative disorders and cancer. Traditional Chinese Herbal Medicine (TCHM) is widely used alone or in combination with chemotherapy to treat cancer, due to its ability to deliver a broad variety of bioactive secondary metabolites as promising sources of novel organic natural agents.

OBJECTIVE

In the present study, 29 varieties of medicinal plants were screened for the presence of ADA inhibitors.

RESULTS

Extracts from Reynoutria japonica, Glycyrrhiza uralensis, Lithospermum erythrorhizon, Magnolia officinalis, Gardenia jasminoides, Stephania tetrandra, Commiphora myrrha, Raphanus sativus and Corydalis yanhusuo demonstrated strong ADA inhibition with rates greater than 50%. However, Reynoutria japonica possessed the highest ADA inhibitory activity at 95.26% and so was used in our study for isolating the ADA inhibitor to be further studied. Eight compounds were obtained and their structures were identified. The compound H1 had strong ADA inhibitory activity and was deduced to be emodin by 1H and 13C-NMR spectroscopic analysis with an IC50 of 0.629 mM. The molecular docking data showed that emodin could bind tightly to the active site of ADA. Our results demonstrated that emodin displayed a new biological activity which is ADA inhibitory activity with high cytotoxic activity against K562 leukemia cells. The bioactivity of cordycepin was significantly increased when used in combination with emodin.

CONCLUSION

Emodin may represent a good candidate anti-cancer therapy and adenosine protective agent.

Development of oral cladribine for the treatment of multiple sclerosis

Multiple sclerosis (MS) is a chronic immune-mediated disorder of the CNS in which autoreactive CD4+ and CD8+ T lymphocytes, B lymphocytes, antibodies, macrophages and cytokines synergize to attack myelin sheaths and injure underlying axons. Current disease-modifying drugs (DMDs) for MS require regular and frequent parenteral administration and are associated with limited long-term treatment adherence. Of all the potential new oral MS agents in development, cladribine is the only therapy with the potential for short-course dosing. Cladribine is an immunosuppressant that offers targeted, sustained regulation of the immune system and that has a well-characterized safety profile, derived from more than 15 years of use of the parenteral formulation in oncology indications and MS. This paper discusses the need for new MS therapies to improve treatment adherence, and reviews the mechanism of action, existing efficacy and safety data, and the clinical development of oral cladribine. The need for continuous risk monitoring for all new potent immunoactive drugs under development is emphasized. Preliminary results of the 96-week, double-blind, randomized, placebo-controlled, multicenter CLARITY (CLAdRIbine Tablets Treating MS OrallY) study are encouraging and provide the first complete phase III data on an oral DMD for MS.

[Cladribin. Development of an oral formulation for the treatment of multiple sclerosis]

Multiple sclerosis (MS) is a chronic, immune-mediated disease of the central nervous system in which autoreactive CD4(+) and CD8(+) T lymphocytes, B lymphocytes, macrophages, antibodies, and cytokines attack the myelin sheaths and damage the axons. The basic therapeutic agents and disease-modifying drugs that are currently available for MS require regular and frequent parenteral administration and therefore long-term compliance is unsatisfactory. Among all of the new oral MS agents presently under development, cladribine is the only substance that appears able to achieve long treatment-free intervals after only short-term administration. Cladribine is an immunomodulator with a long-lasting effect and a well-characterized safety profile based on over 15 years of experience with the parenteral route for MS and other indications. This contribution addresses the need for novel MS treatment approaches to improve compliance and describes the mechanism of action of cladribine, the available data on effectivity and safety, and the clinical development of the oral formulation of cladribine. The results from the recently published 96-week, double-blind, randomized, placebo-controlled, multicenter study CLARITY (CLAdRIbine Tablets Treating MS OrallY) are very promising. They clearly show that oral cladribine reduces relapse rate, disability progression and disease activity and burden as evidenced by MRI.

Cladribine: not just another purine analogue?

Cladribine was synthesized as a purine analogue drug that inhibited adenosine deaminase. It received FDA approval in the 1980s for treatment of hairy cell leukemia. Given its toxicity towards lymphocytes and its corresponding immunosuppressive effects, it has been studied and found efficacious in a variety of hematologic malignancies and autoimmune conditions, most recently multiple sclerosis. This review highlights pharmacological, toxicological and clinical data for the use of cladribine. It also discusses existing and new mechanisms that may contribute to its unique clinical activity. Emerging data show that in addition to its known purine nucleoside analogue activity, cladribine possesses epigenetic properties, inhibiting S-adenosylhomocysteine hydrolase and DNA methylation. This may contribute to its efficacy and highlights the importance of studying combination therapy with other epigenetic or targeted agents. Clinical trials are underway in a variety of malignant and nonmalignant conditions.

Sinus histiocytosis with massive lymphadenopathy (Rosai-Dorfman disease) treated with 2-chlorodeoxyadenosine

Sinus histiocytosis with massive lymphadenopathy (SHML) or Rosai-Dorfman disease (RDD) is a rare but well-defined histiocytic proliferative disorder of unknown etiology that usually presents with cervical lymphadenopathy, fever, leukocytosis, and hypergammaglobulinemia in an otherwise healthy child. Although many patients undergo spontaneous remission, a subset of patients with systemic disease has a more serious course. For those patients with a poor outcome, steroids and chemotherapeutic agents such as etoposide or 6-mercaptopurine plus low dose methotrexate have been used. We present a child with a massive cervical lymphadenopathy treated with 2-chlorodeoxyadenosine (2-CdA, cladribine) after other approaches failed.

Treatment of children with Langerhans cell histiocytosis with 2-chlorodeoxyadenosine

Langerhans cell histiocytosis (LCH) is a disorder characterized by proliferation of activated Langerhans cells. Immune dysregulation is believed to be part of the pathogenesis. Although current therapies are very effective at inducing remission, multiple recurrences and long-term sequelae are common for patients with low-risk disease, and a significant proportion of young patients die of their disease. More effective therapies based on the pathogenesis of LCH are needed. We investigated the use of 2-chloro-deoxyadenosine (2-CdA), a purine analogue with an antiproliferative effect on histiocytes and lymphocytes, in patients with recurrent or high-risk LCH. Six patients with recurrent LCH received 2-CdA (5-7 mg/m(2)/day for 5 days, repeated every 21-28 days). All patients achieved remission. With a median follow-up of 15 months (range, 3-25 months), 5 patients remain in remission. A patient with multisystem disease who recurred after 13 months, achieved a second remission with 2-CdA. Hematologic toxicity was minimal, and no infectious complications were documented. 2-CdA is among the most effective drugs for the treatment of LCH, and this is probably due to both its anti-proliferative and immunomodulatory effects. 2-CdA needs to be considered for the treatment of recurrent LCH. However, its incorporation into front-line treatment of patients with multi-system LCH needs further study.

Novel approaches in the treatment of lupus nephritis

In systemic lupus erythematosus hyperactive helper T-cells drive polyclonal B-cell activation and secretion of pathogenic auto-antibodies. The auto-antibodies form immune complexes with their respective auto-antigens, which in turn deposit in sites such as the kidney and initiate a destructive inflammatory reaction. Lupus nephritis can be managed successfully in the majority of cases; however, the most widely used immunosuppressive therapies, notably corticosteroids and cyclophosphamide are non-specific and are associated with substantial toxicities. Novel treatments for lupus nephritis have to be at least as effective and less toxic than existing therapies. The ultimate aim is to develop treatments that target specific steps in the disease process. Novel therapeutic strategies in the short-term more likely will focus on refining regimens of drugs that are already in use (mycophenolate mofetil, adenosine analogues) and combinations of existing chemotherapeutic agents, as well as attempts to achieve immunological reconstitution using immunoablative chemotherapy with or without haematopoietic stem cell rescue. Several new agents targeting specific steps in the pathogenesis of lupus are in various phases of clinical development. Interrupting the interactions between T-lymphocytes and other cells by blocking co-stimulatory molecules, such as CD40 ligand or CTLA4-Ig, may interfere with the early steps of pathogenesis. Blocking IL-10 may decrease auto-antibody production and help normalise T-cell function. Treating patients with DNase or interfering with the complement cascade by blocking C5, or neutralising pathogenic antibodies by administering specific binding peptides or inducing specific anti-idiotype antibodies may prevent immune complex formation and/or deposition.

Enhancement of retention and cytotoxicity of 2-chlorodeoxyadenosine in cultured human leukemic lymphoblasts by nitrobenzylthioinosine, an inhibitor of equilibrative nucleoside transport

In leukemic cells exposed to 2-chlorodeoxyadenosine (2-CdA), levels of the nucleoside drug and its phosphate metabolites decay with time in the absence of external 2-CdA; an intrinsic part of this process is the efflux of 2-CdA. The effects of nitrobenzylthioinosine (NBMPR) and of dipyridamole (DPM), both potent inhibitors of es (e, equilibrative; s, sensitive to NBMPR) nucleoside transport processes, were studied in four lines of cultured leukemic lymphoblasts. Suspensions of 2-CdA-loaded cells were diluted 10-fold with 2-CdA-free medium to initiate the cellular 2-CdA decay processes, which followed a biexponential time course. When diluting media contained NBMPR or DPM, intracellular levels of 2-CdA and its metabolites were substantially increased (P < 0.001) compared with cells in media lacking the transport inhibitors, and 2-CdA loss followed a monoexponential time course. As a consequence, the AUCs (area under time-course plots of intracellular 2-CdA and its metabolites) were significantly (P < 0.001) lower in untreated control cells compared to inhibitor-treated cells. These results suggest that nucleoside transport processes contribute to the efflux of 2-CdA from the cultured lymphoblasts. The cytotoxicity of 1-h exposure to 2-CdA of Reh-A2 and CCRF-CEM cells was enhanced three-fold by subsequent exposure to 0.5 microM NBMPR relative to that of control cells subjected to the same manipulations without NBMPR exposure. However, before such a strategy may be considered to have a therapeutic application, careful examination of effects in normal lymphocytes and ex vivo leukemic lymphoblasts must first be undertaken. Leukemia (2000) 14, 52-60.

Novel approaches in the treatment of lupus nephritis

Lupus nephritis can be managed successfully in the majority of cases; most therapies, however, are associated with significant side-effects. Several new agents aiming at specific stages in the pathogenesis of lupus are in different phases of clinical trials. The central role of lymphocytes makes them targets of various therapeutic approaches. Lymphocyte depletion can be achieved by high-dose chemotherapy with or without bone marrow transplantation. Nucleoside analogs selectively deplete mononuclear cells; antibodies against T or B cell surface antigens target specific subsets of lymphocytes. Synchronized plasmapheresis has been used in an attempt to delete pathogenic lymphocyte clones activated by plasmapheresis. Treating patients with DNase or neutralizing pathogenic antibodies by administering specific binding peptides or inducing specific anti-idiotype antibodies may prevent immune complex formation and/or deposition. Blocking the complement cascade or some of the inflammatory mediators like thromboxane A2 may be efficacious even if immune complex deposition could not be prevented. Inducing antigen-specific tolerance or interfering with important interactions between T-lymphocytes and other cells by blocking CD40 ligand or decreasing the level of interleukin-10 are some of the other approaches currently under clinical investigation.

Safety and tolerability of subcutaneous cladribine therapy in progressive multiple sclerosis

OBJECTIVE

To evaluate the safety and tolerability of subcutaneous (s.c.) cladribine therapy in patients with chronic progressive multiple sclerosis (CPMS), and to evaluate the effects on lymphocyte subsets.

BACKGROUND

Cladribine, a synthetic antineoplastic agent with immunosuppressive effects, may favourably affect the course of CPMS. However results of a previous reported clinical trial showed significant myelosuppression in some patients.

DESIGN/METHODS

19 patients with severe (mean extended disability status score [EDSS] = 6.7) CPMS were treated on a compassionate basis with cladribine 0.07 mg/kg/day s.c. for 5 days per cycle, repeated every 4 weeks for a total of 6 cycles. Patients underwent clinical evaluation, EDSS, and hematologic analysis before, during, and following therapy.

RESULTS

The treatment was very well tolerated with no clinically significant side effects observed. Between baseline and the end of cycle 6, mean decreases were noted in absolute lymphocyte count from 1697 to 463 (p = 0.000012), CD4 count from 865 to 187 (p = 0.0000008), CD8 from 418 to 165 (p = 0.005) and CD19 from 197 to 26 (p = 0.000002). Platelet, granulocyte and RBC counts were unaffected. Approximately one year after completion of therapy, some recovery of CD4 and CD8 counts had occurred although both counts remained suppressed compared to baseline (302 and 227 respectively); the CD19 count had recovered essentially to normal by one year. EDSS scores post-therapy revealed some deterioration in 8 patients and stable scores in the remaining 11. Global patient evaluations of the treatment were mixed.

CONCLUSIONS

Cladribine therapy, at lower doses than previously reported, was remarkably well tolerated in CPMS, with no significant myelosuppression. Profound effects occurred in total lymphocyte count and CD4, CD8 and CD19 subsets.

A pilot study of 2-chloro-2'-deoxyadenosine in the treatment of systemic lupus erythematosus-associated glomerulonephritis

OBJECTIVE

To determine the safety and tolerability, as well as the clinical and immunologic effects, of 2-chloro-2'-deoxyadenosine (2-CdA) in patients with systemic lupus erythematosus-associated glomerulonephritis.

METHODS

In a phase I study, 12 patients with proliferative lupus nephritis received 2-CdA either in weekly escalating intravenous treatments (0.15 mg/kg/week x 4, 0.1875 mg/kg/week x 4, 0.225 mg/kg/week x 4; n = 5) or in a continuous 7-day infusion (0.05 mg/kg/day; n = 7). Safety, renal improvement, and immunologic effects were evaluated for 12 months.

RESULTS

Patients treated with 2-CdA showed peripheral lymphocyte depletion without a significant reduction in neutrophil, monocyte, or platelet numbers or hematocrit levels. Naive and memory T cells were decreased, as were lymphocytes with markers of early and late activation. Peripheral B cell depletion was not associated with significant decreases in serum immunoglobulin levels. Continuous infusion induced better clinical responses than weekly infusions, as evidenced by 1) the percentage of patients showing complete response (43% versus 0%), 2) the percentage with at least 50% reduction in proteinuria (43% versus 20%), 3) the percentage with at least a 50% reduction in urinary dysmorphic red cells (57% versus 0%), and 4) the percentage in whom cellular casts disappeared (43% versus 0%). Several infections occurred; these responded to standard antibiotic therapy.

CONCLUSION

In this pilot study, 2-CdA was safely administered to 12 patients with lupus nephritis. It induced prolonged reductions in lymphocyte populations and may be efficacious in selected patients with lupus nephritis when administered as a continuous infusion.

2-chloro-2'-deoxyadenosine: clinical applications in hematology

The anticancer drug 2-chloro-2'-deoxyadenosine (CdA) belongs to the family of purine nucleoside analogs. CdA is exquisitely cytotoxic both to the dividing and to the non-dividing lymphocyte, which supports its use in lymphoproliferative disorders of low-grade malignancy. Indeed, the best clinical results with CdA are achieved in hairy-cell leukemia, in chronic lymphocytic leukemia, in Waldenström's macroglobulinemia and in low-grade malignant lymphoma. Most patients with hairy-cell leukemia achieve a complete response with a single course of CdA. However, the disease is not eradicated and a fraction of complete responders will eventually relapse. In chronic lymphocytic leukemia and in malignant lymphoma, complete or partial responses can be achieved in approximately 40% of previously treated patients, even after classical chemotherapy has failed. However, few responses sustain beyond 1 to 2 years, while longer unmaintained responses may be obtained in Waldenström's macroglobulinemia. More responses (70-80%) are achieved in patients with chronic lymphoproliferative disorders treated de novo with CdA but their impact on survival remains to be established. More than 10 years after its first use in clinical practice, late adverse consequences of the severe and sustained immunosuppression induced by CdA have not been reported but should still be closely monitored.