Multiple Sclerosis (1996) 1, 343-347
`© 1996 Stockton Press All rights reserved 1352~4585/06 $12.00
`
`Developmentof cladribine treatment in multiple sclerosis
`
`JC Sipe, JS Romine, JA Koziol, R McMillan, J Zyroff and E Beutler
`Department of Molecular and Experimental Medicine, The Scripps Research Institute and the Divisions of Neurology
`and Radiology, Scripps Clinic and Research Foundation, La Jolla, California, USA
`
`Cladribine is a new type of drug with properties of selective lymphocyte suppression that appearto favorably alter the clinical course of progressive
`multiple sclerosis (MS). The history of the development of cladribine treatment in chronic progressive MSis discussed, and the application of
`dadribine treatment to progressive multiple sclerosis in a doubfe-blind, placebo crossover study is reviewed. Cladribine selectively targets bath
`resting and dividing lymphocytes and may be able to destroy the activated lymphocytes that induce CNS demyelination, thus producing stabilization
`or improvement in chronic MS. Although the role of cladribine has not yet been fully defined, additional studies are underway to evaluate the
`efficacy and safety of cladribine in both progressive MS and relapsing-remitting MS.
`
`Keywords: multiple sclerosis; cladribine; immunosuppression
`
`Introduction
`
`Cladribine [2-chlorodeoxyadenosine (2-CdA), Leusta-
`tin®]
`is a relatively new type of selective immuno-
`suppressive drug that was synthesized by Carson"to
`mimic the immunodeficiency state seen in hereditary
`adenosine deaminase deficiency. This compoundis a
`purine nucleoside that contains substitution of a
`chlorine atom for hydrogen at the two position of the
`purine ring. This change in the structure of deoxya-
`denosine
`to
`2-chlorodeoxyadenosine
`renders
`the
`molecule resistant to the effects of adenosine -deami-
`nase and produces
`a phenomenon of
`selective
`lymphocyte killing with relatively low toxicity toward
`othertissues.'?
`The history of the developmentof cladribine for use
`in clinical medicine begins with the discovery of
`hereditary adenosine deaminase (ADA) deficiency by
`Giblett
`in 1972" in patients with severe combined
`immunodeficiency syndrome. However, the cause of
`the
`severe
`lymphocyte depletion seen in ADA
`deficiency was not clearly understood until 1977,
`when Carson’ showed that degradation of deoxynu-
`cleotides in lymphocytes is entirely dependent upon
`the activity of ADA. Carson proposed that the very
`high levels of
`lymphocyte deoxycytidine kinase
`‘specifically predisposes these cells to accumulate
`lethal levels of deoxyribonucleotides.’° Indeed, extra-
`ordinarily high levels of deoxyribonucleotides were
`subsequently found in ADA-deficient lymphocytes.®
`The mechanism of cell death in lymphocytes
`exposed to cladribine is
`as
`follows: nicks and
`Standbreaks
`appear
`spontaneously in lymphocyte
`double-stranded DNA. Repair of
`these nicks
`is
`inhibited by high levels of deoxyribonucleotides and
`eads to excessive activation of the enzyme poly-
`ADPribose polymerase. This in turn exhausts cellular
`NAD and leads to lymphocyte death (apoptosis).*
`With this
`insight
`into lymphocyte metabolism,
`Carson and colleagues synthesized some 25 com-
`
`Correspondence: JC Sipe
`
`pounds, andof these, 2-CdA (or cladribine) was found
`to have the most favorable therapeutic ratio. In vitro
`studies demonstrated that the selectivity of cladribine
`is related to the cellular level of deoxycytidine kinase
`and that T and non-T, non-B lymphocytes are the most
`susceptible to killing, with B lymphocytes being less
`susceptible and monolayer cell lines being the most
`resistant.*®
`:
`Phase I andII clinical trials were begun in patients
`with advanced lymphoid neoplasms undergoing bone
`marrow transplantation, in chronic lymphocytic leu-
`kemia and in cutaneous T-cell lymphomas.**"*-*" The
`most notable results were seen in patients with hairy
`cell leukemia.’*” By 1993 at Scripps Clinic, a total of
`350 hairy cell leukemia patients had been treated with
`cladribine and 97% respondedto treatment, 86% with
`a complete and durable remission. Cladribine is now
`licensed in the United States for treatmentof hairy cell
`leukemia. Thus, cladribine was designed, synthesized,
`tested in vitro and in vivo, and introducedinto clinical
`medicine at Scripps Clinic and Research Foundation.
`Evenat this time the therapeutic range of cladribine is
`being expandedinto other clinical disorders including
`neoplasms, autoimmune disorders, particularly auto-
`immune hemolytic anemia, rheumatoid arthritis, and
`inflammatory bowel disease.
`Wefirst proposed to test cladribine in MS with the
`background of 10 years experience in dose-escalation
`studies
`in treatment of
`lymphoid neoplasms and
`autoimmune disorders.??”" It was apparent that cla-
`dribine has a very favorable toxicity profile relative to
`other lymphotoxic drugs. Patients treated with cladri-
`bine hadvirutally no sensation of adverse effects since
`deviations from normal occurred only in the blood
`counts.
`for
`Because there is no satisfactory treatment
`progressive multiple sclerosis and there is consider-
`able evidence that CNS demyelination in MS is
`mediated by immunopathologic mechanisms, the use
`of cladribine was considered in view of the long-
`lasting lymphopenia it produces, andits relatively low
`Merck 2040
`TWi v Merck
`
`IPR2023-00049
`
`Merck 2040
`TWi v Merck
`IPR2023-00049
`
`

`

`Cladribine in MS
`JC Sipe et al
`
`Initial Cladribine
`
`50
`
`0
`
`3
`
`6
`
`9
`
`12
`
`15
`
`18
`
`21
`
`24
`
`Month
`
`Initial Placebo
`
`Initial Placebo
`
`Initial Cladribine
`
`Month
`
`a
`
`=g
`
`nn
`wn
`fa
`Zzwn
`
`b
`
`2oNa
`wm
`Ww
`wn
`QeS}
`
`Month
`Month
`Figure 1 Tiventy-fifth, fiftieth (median), and seventy-fifth percentiles of neurologic scores, separately by treatment
`group, over the course ofclinicaltrial. (a) SNRS. (b) EDSS. In the initial cladribine group, scores tend to improve
`during the first 12 months, then stabilize over the second year. In the initial placebo group, scores decline during the
`first 12 months, then tend to stabilize or improve
`
`toxicity: An open-label feasibility study was begun in
`1990 with a small numberofpatients. The results were
`favorable
`in terms of apparent
`improvement
`in
`neurologic function and lack of toxicity. We were
`encouraged to proceed with a double-blind, placebo-
`controlled crossover study of cladribine in progressive
`MS. The first year results demonstrated improvement
`in the clinical course of progressive MS and have been
`published.?? We nowhave data on the complete 2-year
`study with an additional 6 months of unblinded data.®
`
`Methods
`
`The study subjects were 51 patients with clinically
`definite MS (mostly secondary progressive). Three
`patients dropped from the study in the first year, and
`four patients dropped from the study in the second
`year, but the data of all patients has been retained on
`an intent-to-treat basis. Patients were paired by ag@
`sex, duration and severity of MS, and each gave
`informed consent to participate in the study. Study
`
`

`

`A 3
`
`45
`
`Cladribine in MS
`JC Sipe et al
`
`subjects were raridomized to cladribine treatment ar
`was maintained for 24 months of follow-up, even
`Jacebo by the statistician using a random number
`though thefirst year treatment group had received no
`table. At baseline, both groups were equivalent
`in
`therapy after the first 4 months of the study (Figure
`terms of neurologic rating scale scores, disability and
`1A). SNRS scores of patients initially on placebo and
`MRI
`lesion activity. In the first year of the study,
`then treated with half-dose cladribine (1.4 mg/kg)
`atients on the cladribine arm were given 4 monthly,
`seemed also to stabilize or improve but for a shorter
`7-day infusions of cladribine 0.1 mg/kg/day (0.7 mg
`period of time with peak at approximately 8 months,
`cladribine per course), for a total of four courses (total
`After 2 years, unblinded observations revealed a
`dose=2.8 mg/kg). During the second year,blinding was
`decline in the average scores. These findings suggest
`maintained but patients who had received placebo
`a dose-response effect with cladribine and a wearing
`were given active drug at one-half the total dose given
`off of improvement and resumption of progressive MS
`during the first year (total dose=1.4 mg/kg). Patients
`symptoms in somepatients after 2 years. Analysis of
`who had received cladribine in the first year were
`variance based on the two-period crossover design
`given 4 monthly saline infusions from the start of the
`with primary endpoints, the absolute EDSS and SNRS
`revealed no significant carryover effects between
`second year. Throughoutthe study, patients, neurolo-
`gists, nurses and neuroradiologists had no knowledge
`subjects or period effects within subjects. Highly
`of
`the
`treatment protocol or
`laboratory studies.
`significant
`treatment effects using F-statistics were
`found.
`Monthly examinations were carried out
`to monitor
`adverse events and to determine the patients’ Ex-
`Kaplan-Meier time-to-failure analyses also indi-
`tended Disability Status Scale (EDSS) and Scripps
`cated positive
`treatment
`effects with cladribine.
`Neurologic Rating Scale (SNRS). Laboratory blood
`Whether time-to-failure is defined as a gain of 0.5,
`studies were carried out at
`least montly and MRI
`1.0 or 1.5 points on the EDSSscale, or a reduction of
`brain scans with and without contrast enhancement
`5, 10 or 15 points on the SNRS scale, patients
`receiving cladribine fared much better than placebo.
`were completed at 0, 6, 12, 18 and 24 monthsof the
`study. All patients had a portacath central venous
`Time-to-improvement plots also showeda statistically
`access device implanted for drug or placebo adminis-
`significant advantage for patients on cladribine.
`Analysis of MRI data showed a highly significant
`
`tration. MRI scans and_statistical analyses were
`performed using methods previously described.”
`difference in the number of enhancing lesions, a
`The results of clinical performance (SNRS) and
`measure of current disease activity (Figure 2). In this
`disability (EDSS) score during the first and second
`analysis, enhancing lesions were differentiated by
`years of the cladribine study have been previously
`designating the complete disappearance or continued
`reported.*”In the first year of the study, average EDSS
`absence of enhancement as ‘absent’, and the emer-
`and SNRSscores of patients on full dose cladribine
`gence or continued presence of enhancement as
`improved modestly while patients on placebo con-
`‘present’. As noted in Figure 2, there is no significant
`tinued to deteriorate. Differences at 1 year were highly
`difference in the proportion of individuals in the
`significant in both scoring systems (Figure 1A and B):
`initial placebo group with enhancing lesions over the
`P=0.001 for SNRS, P=0.02 for EDSS. Improvementin
`first year. In contrast, there was a dramatic fall in the
`SNRSscores appeared to peak at about 18 months and
`proportion of
`individuals with enhancing lesions
`
`Initial Cladribine
`
`Enhancing
`
`Volumes
`
`Baseline
`
`6
`
`12
`
`18
`
`24
`
`Initial Placebo
`
`
`
`Baseline
`
`6
`
`12
`
`18
`
`24
`
`
`
`SUOTSa]IMsjuanedJoagequaoIayoe
`
`Month
`
`Month
`
`Figure 2. Percentages of patients with enhancing lesions over the course of the clinical trial; and, mean volumes
`(+5.e.) of the enhancing lesions, in cubic millimeters. Means are taken solely over those patients with enhancing
`lesions, at each of the specific time points
`
`

`

`Cladribine in MS
`JC Sipe et al
`
`present in the cladribine group during the same time
`interval (P=0.001). Analysis after the crossover at 1
`year showed complete absence of enhancing lesions at
`2 years in the group first treated with cladribine and
`near-complete absence in the group treated with
`placebo first and cladribine second.
`
`recurrence of worsening, usually 2 or more years afte;
`initial
`treatment. A multicenter US and Canadian
`study of subcutaneously administered cladribine jin
`chronic progressive MS is also now underway.It is
`notable that subcutaneous cladribine has been used in
`relapsing-remitting MS patients by Grieb ef al." who
`report preliminary evidence of benefit. Although the
`role of cladribine has not been fully delineated,it ig
`our hope that this new drug will prove to be a useful
`therapeutic option for patients with all formsofactive
`MS.
`
`References
`
`Toxicity and adverse events
`Analysis of the laboratory studies during the first
`study year have previously been reported.’ There
`were noside effects or adverse events that could have
`systematically affected the double-blind protocol
`status. However, a few problems were encountered
`in the study. More thrombocytopenia than expected
`was seen with the higher dose of cladribine. Two of
`24 patients on the full dose developedplatelet counts
`1 Beutler E. (1992) Cladribine (2-chlorodeoxyadenosine),
`Lancet 340: 952 — 956.
`of under 50 000 yl. One patient who was receiving
`high doses of Dilantin® and Tegretol® developed
`2 Beutler E.
`(1994) New chemotherapeutic agent: 2-
`chlorodeoxyadenosine. Semin Hematol 31: 40-45.
`marrow suppression but completely recovered in 6
`3 Beutler E et al. (1994) Marrow suppression produced by
`months. In this study, there were five cases of mild
`repeated doses of cladribine. Acta Haematol 91: 10-15,
`dermatomal herpes
`zoster;
`four
`after
`full dose
`4 Beutler E et al. (1991) 2-Chlorodeoxyadenosine (2-CdA);
`cladribine
`and one
`after half-dose. One patient
`A potent chemotherapeutic and immunosuppressive
`developed acute fatal newly acquired hepatitis B
`nucleotide. Leuk Lymphoma5: 1-8.
`shortly after
`the second dose of cladribine. As
`5 Beutler E et al.
`(1996) The treatment of chronic
`previously discussed,” experts in hepatitis B immu-
`progressive multiple sclerosis with cladribine. Proc Nat!
`Acad Sci USA 93: 1716-1720,
`nopathogenesis who completely reviewed the post-
`mortem data from this patient consider it unlikely
`the
`6 Carson DA ef al.
`(1979) Biochemical basis for
`that cladribine played a role in the patient’s illness.
`enhanced toxicity of deoxyribonucleosides toward ma-
`lignant humanTcell lines. Proe Nat] Acad Sci USA 76:
`Some additional patients who were treated in an
`2430—2433.
`open-label protocol and were not part of this study
`7 Carson DA,KayeJ, SeegmillerJE. (1977) Lymphospecific
`also developed adverse
`events
`that have been
`toxicity in adenosine deaminase deficiency and purine
`discussed in detail elsewhere.”
`nucleoside phosphorylase deficiency: Possible role of
`nucleoside kinase(s). Proc Natl Acad Sci USA 74: 5677-
`5681.
`8 Carson DA, Seto S, Wasson DB, Carrera CJ. (1986) DNA
`The data analysis from this study has shown that
`strand breaks, NAD metabolism, and programmed cell
`cladribine favorably alters
`the clinical course of
`death. Exp Cell Res 164: 273-281.
`9 Carson DA, WassonDB, Beutler E. (1984) Antileukemic
`progressive MS. There was proloned suppression of
`and immunosuppressive activity of 2-chloro-2’-de-
`CD4 cells but no associated opportunistic infections
`oxyadenosine. Proc Nail Acad Sci USA 81: 2232-2236.
`except for mild segmental herpes zoster in about 10%
`10 Carson DAetal. (1980) Deoxycytidine kinase-mediated
`of MS patients treated with cladribine. Analysis of the
`toxicity of deoxyadenosine analogs toward malignant
`neurologic performance and disability rating scales
`human lymphoblasts in vitro and toward murine L1210
`showed highly significant stabilization or improve-
`leukemia in vivo. Proc Natl Acad Sci USA 77: 6865-
`ment with cladribine compared to placebo in average
`6869.
`EDSS and SNRSscores, and in the time-to-failure and
`11 Carson DAet al. (1982) A potent new anti-lymphocyte
`improvement plots. Enhancing lesions on brain MRI
`agent: 2-chlorodeoxyadenosine. Blood 60(Supp! 1): 161.
`scans showed significant improvement in cladribine-
`(Abstract)
`treated patients. We conclude that cladribine is an
`12 Carson DA, Wasson DB, Taetle R, Yu A. (1983) Specific
`toxicity of 2-chlorodeoxyadenosine toward resting and
`effective agent for retarding the clinical progression of
`proliferating human lymphocytes. Blood 62: 737-743.
`chronic MS. The beneficial effect is durable but not
`13 Giblett ER et al. (1972) Adenosine deaminase deficiency
`permanent since worsening has been observed to
`in two patients with severely impaired cellulat
`eventually recur in most patients.
`immunity. Lancet 2: 1067-1069,
`Since our
`first study of cladribine in MS was
`14 Grieb P et al. (1994) Cladribine treatment of multiple
`completed, it has been recognized that subcutaneous
`sclerosis. Lancet 344: 538.
`cladribine is entirely equivalent in terms of pharma-
`15 LiliemarkJ et al. (1992) On the bioavailability of oral and
`cokineticresults compared to the intravenous route
`subcutaneous 2-chloro-2’-deoxyadenosine in humans:
`of administration. We are therefore continuing our
`Alternative routes of administration. J Clin Oncol 10
`1514-1518,
`studies of cladribine with subcutaneously adminis-
`16 Piro LD, Carrera CJ, Carson DA, Beutler E. (1990) Lasting
`tered drug. Studies presently underway at Scripps
`remissions in hairy cell leukemia induced byasingle
`Clinic include blinded, placebo-controlled evaluations
`infusion of 2-chlorodeoxyadenosine. N Engl J Med 322
`of cladribine in relapsing-remitting MS and in the
`1117-1121.
`retreatment of the chronic progressive patients with a
`
`Discussion
`
`

`

`Cladribine in MS
`JC Sipe et al
`
`17 Piro LD e# al, (1992) Prolonged complete remissions
`following 2-chlorodeoxyadenosine (2-CdA)in hairy cell
`leukemia (HCL). Proc Am Soc Clin Oncol 11: 259.
`(Abstract)
`48 Saven A et al. (1991) 2-Chlorodeoxyadenosine treatment
`of
`refractory chronic lymphocytic leukemia. Leuk
`Lymphoma 5(Suppl): 133-138.
`19 Saven A etal. (1992) 2-Chlorodeoxyadenosine: An active
`agent in the treatment of cutaneous T-cell lymphoma.
`Blood 80: 587-592.
`
`(1992)
`20 Saven A, Figueroa ML, Piro LD, Beutler E.
`Complete hematological remissions in chronic myelo-
`genous leukemia (CML) following 2-chlorodeoxyadeno-
`sine (2-CdA). Proc Am Soc Clin Oncol 11: 261. (Abstract)
`21 Saven A et al.
`(1993) 2-Chlorodeoxyadenosine dose
`escalation in non-hematologic malignancies. J Clin
`Oncol 11: 671-678.
`22 Sipe JC et al. (1994) Cladribine in treatment of chronic
`progressive multiple sclerosis. Lancet 344(No. 8914): 9—
`13.
`
`