Introduction

In 1992, arsenic trioxide (As₂O₃, ATO) was reported by Chinese investigators to have a substantial activity in acute promyelocytic leukaemia (APL).¹ This observation, that was confirmed by various investigators,^{2, 3, 4} prompted screening of ATO as a new biologic agent in various haematological malignancies.

Despite the use of intensive chemotherapeutic regimens, multiple myeloma (MM) remains an incurable disease with a median survival still limited to 3 years. Patients usually respond to treatment but experience recurrences featured by the emergence of resistant plasma cells.⁵

We and others have previously investigated the biological activity of ATO in MM.^{6, 7, 8, 9} We found that arsenic derivatives such as melarsoprol and ATO induced apoptosis in myeloma cell lines and in plasma cells derived from MM patients in vitro. In an attempt to further document the interest of the arsenicals in vivo, we treated SCID mice transplanted with human myeloma cells by melarsoprol or ATO and observed significant responses, including apparent complete remission persisting up to 5 months after ATO discontinuation.¹⁰ After these encouraging results, we decided to evaluate the efficacy and the safety of ATO administration in patients with refractory MM.

Patients and methods

Patients

Patients aged 18 years or more with secretory MM in failure after at least two lines of treatment were eligible. Patients may have been previously treated by conventional chemotherapy (using repeated courses of akylating agents, anthracycline and/or corticosteroids) and by an intensive strategy including a high-dose therapeutic regimen supported with autologous bone marrow transplantation. The study was approved by the Ethics Committee of Hôpital Pitié-Salpétrière (Paris, France) and Ministère de l'Emploi et de la Solidarité. All patients gave signed informed consent.

Treatments

Study design consisted of allocating 10 patients to continuous ATO and 10 patients to melarsoprol. In order to avoid patients' selection, we decided to randomize treatment arm. ATO was manufactured by the Pharmacie Centrale des Hôpitaux de Paris (Paris, France). The formulation process was validated as previously described.⁴ ATO was administrated at the dosage of 0.15 mg/kg/day by a 3-h intravenous infusion. Melarsoprol was obtained from manufacturer as Arsobal^® (Aventis, Paris, France) and administered in three intravenous perfusions at the dosage of 1 mg/kg at day 1 and 2.2 mg/kg/day thereafter. To prevent potential arsenic-related neurotoxicity, all patients received vitamin B1 (250 mg/day) and clobazam (10–30 mg/day) during treatment. ATO and melarsoprol were maintained for a maximum of 56 days and stopped in case of severe toxicity (OMS grade 2–4, depending of the organ concerned) or if the arsenic serum concentration was 10^-5 M or greater. For the last two patients in the ATO group, the trial was amended and patients received ATO during 14 days, one cycle every month, using an increased daily dosage (0.2 mg/kg/day) as compared to the continuous ATO regimen. The melarsoprol arm of treatment was stopped because of the occurrence of serious, grade III–IV adverse events in the two first treated patients. Subsequently, all included patients received ATO.

The study was initiated in September 1998 and terminated in May 1999 after the inclusion of 10 patients in the ATO arm, as initially planned.

Response criteria

Complete response (CR) was defined as no monoclonal immunoglobulins (M protein) in serum and/or 100 times concentrated urine by immunofixation analysis and less than 5% plasma cells in bone marrow aspiration when evaluated. Partial response (PR) was defined as a 50% or more reduction of M protein in serum and/or a 75% or more reduction of the Bence–Jones (BJ) proteinuria. Minor response (MR) was defined as a 25–49% reduction M protein in serum and/or a 50–74% reduction of the BJ proteinuria.

Failure to treatment was defined by less than a 25% reduction in M-protein serum level and/or by less than a 50% reduction of BJ proteinuria. Progressive disease was defined by any of the following criteria: increase of 25% or more in serum M-protein level on two successive dosages, increase of 50% or more in BJ proteinuria, onset of hypercalcemia, plasmocytoma or new bone lesions.

Pharmacokinetic (PK) studies

Arsenic concentrations were evaluated at baseline, day 4, day 7 and then once a week until the end of the treatment. Serum residual total arsenic concentrations were determined just before the following injection. Total arsenic in serum was determined as previously described.⁴

Safety evaluation

During ATO administration, physical examination was performed daily, complete blood count with differential, hepatic and renal function tests were assessed at least twice a week and an ECG was obtained weekly. Adverse events were graded on a scale of 0–4 using the World Health Organization toxicity criteria.

Results

Patient characteristics

From October 1998 to April 1999, 12 patients with relapsing or refractory secretory MM were treated. Two patients received melarsoprol and 10 patients received ATO. Patient's characteristics and previous treatments are listed in Table 1. The median time from diagnosis to inclusion was 86.2 months.

Table 1 - Characteristics of patients in ATO group.

Full table

Completion of allocated treatment

None of the eight patients allocated to the continuous ATO regimen completed the 56-day planned treatment. The median treatment duration was 35 days (range 5–44). The treatment was interrupted because of failure or progression in four patients, toxicity in three patients and total serum arsenic concentration >1 10^-5 in one patient. ATO daily dose was reduced (by 75%, during 2 weeks) in only one patient who developed grade III hepatitis.

Both two patients that received the discontinuous ATO regimen completed the planned treatment.

The first patient treated by melarsoprol experienced grade IV neurological toxicity at day 9. In the second patient, systematic monitoring of serum arsenic revealed over dosage at day 3 and the patient also experienced neurologic toxicity (see below). Accordingly, the survey committee of the protocol advised the interruption of the melarsoprol arm.

PK studies

In the eight patients who received the continuous ATO regimen (0.15 mg/kg/day), the mean residual serum total arsenic concentration progressively increased to reach a maximum of 1.110.16 mol/l at day 14 (Figure 1a). In the two patients (patient 9 and 10) treated with ATO 14 days per month (0.20 mg/kg/day), residual values of arsenic at day 1 of cycle 1, 2 and 3 were 0, 0.42 and 1 mol/l, respectively, providing evidence for arsenic accumulation. However, maximal residual serum total arsenic concentrations were not significantly different after completion of one cycle as compared to the previous one (Figure 1b). Serum arsenic concentration profiles did not differ between responding and nonresponding patients (data not shown).

Figure 1.

Pharmacokinetic studies. (a) Mean residual total arsenic concentrations.e.m. during the first 5 weeks of continuous ATO (0.15 mg/kg/day) treatment (n=8). (b) Pharmacokinetic of ATO in patients 9 and 10 who received ATO (0.20 mg/kg/day) discontinuously (14 day cycles, every month).

Full figure and legend (23K)

Patient outcome

No CR or PR was observed in any patient. A transient stabilization of the M-protein level was observed in two patients in the continuous regimen and two in the discontinuous regimen. Three patients showed a minor response (25–49% reduction of M protein in serum). In two of these, ATO must be stopped due to toxicity. The later patient developed a plasmocytoma of the clavicle while on therapy. In all patients, disease stabilization or minor responses were of 1–3 weeks duration.

After ATO administration, all surviving patients were treated by thalidomide alone or combined with dexamethasone.

Adverse events

As mentioned, the melarsoprol arm of the study was rapidly interrupted because of high toxicity for central nervous system. Indeed, the first patient experienced refractory generalized grand mal seizure during the second week of therapy, and the second patient rapidly presented with tremor and lethargy.

Treatment by ATO also produced significant toxicity. Nonhaematological adverse events were responsible for premature treatment discontinuation in three cases with encephalopathy with confusion and somnolence (grade 3, n=1) and hepatitis cytolysis (grade 3, n=2). In two cases, infections lead to a transient interruption of ATO therapy. Finally, other reported grade 1 and 2 adverse events were increased transaminase levels (n=8), herpes zoster (n=3), nausea (n=2), skin rash (n=2) and peripheral neuropathy (n=2).

In addition to its extrahaematological toxicity, ATO also produced cytopenias. Without taking into account the two patients who had grade IV neutropenia at treatment initiation, four of the eight patients who received more than 15 days of ATO presented a grade 4 neutropenia leading to a transient treatment arrest. In contrast, one patient with grade 3 neutropenia at treatment initiation improved to grade 1 during therapy. Grade 3 thrombocytopenia occurred in three patients and grade 4 in one other.

Discussion

The trial was designed to treat heavily pretreated myeloma patients either with ATO or with melarsoprol. The melarsoprol arm had to be rapidly stopped due to severe encephalitic complications, confirming the previously reported direct toxicity of the drug for the central nervous system in the treatment of trypanosomiasis.¹¹ ATO, which was initially administered continuously, according to the regimen currently used in acute promyelocytic leukaemia (0.15 mg/kg/day), was modified to a discontinuous schedule (0.20 mg/kg/day 14 days/month) because of a significant haematological toxicity. Unexpectedly, increased transaminase levels were observed in all but one patient. Thus, treatment toxicity, particularly hepatic and haematological, was relatively high, leading to a poor benefit/risk ratio. Whatever the ATO regimen used, only a minor response was noted in three out of 10 patients even in cases of prolonged administration (median cumulative duration of ATO: 37.5 days; range 5–44).

Arsenic pharmacokinetic studies in our patients showed that the mean residual arsenic serum concentrations was of 1.110.16 mol/l after 2 weeks. These concentrations were twice higher than those observed in equivalently treated APL patients⁴ and relate to the more important extrahaematological adverse events and the poorer haematological tolerance. The dose required in a myeloma cell environment for inducing cell death leads probably to an unacceptable toxicity. This effective concentration is still questioned. The serum concentration obtained should have been satisfactory as in our previous in vitro studies, a concentration of 1 mol of ATO sufficed to induce apoptosis of plasma cell from MM patients.⁶ Yet, we have also noted, in our SCID-MM model, that effective bone marrow concentrations may be difficult to achieve.¹⁰

Two other phase II trials have recently been reported in advanced-phase MM patients. In the study of Munshi et al,¹² 14 patients were treated with a similar ATO continuous protocol (0.15 mg/kg up to 60 days). In the study of Hussein et al,¹³ ATO regimen consisted in i.v. infusion of 0.25 mg/kg 5-day/week for 2 weeks followed by no therapy for 2 weeks, in repeated 4-week cycles. Objective and minor responses were observed in 3/14 and 9/21 patients in each study, respectively. In both studies, responses were of short duration. These data did not compare favourably with the results obtained with other new drugs, such as Bortezomib and Revimid, when used as single agent in highly pretreated patients.^{14, 15}

Thus, combination of ATO with other drugs may be required to enhance ATO efficacy in MM. Candidates could be conventional cytotoxic drugs, high-dose steroids or sensitizing agents, such as ascorbic acid to produce a glutathione depletion.¹⁶ Preliminary data using such combinatorial strategy showed some results. Indeed, in one study, the combination of ATO at low dosage (0.25 mg/kg twice weekly), oral melphalan and intravenously administered ascorbic acid produced four responses in 10 treated patients.¹⁷ However, all these responses were of short duration. In another study, a regimen combining ATO (0.25 mg/kg 5 days in week one and two times a week for weeks 2–10), dexamethasone and ascorbic acid was used in 16 patients, producing response and disease stabilization in one and six patients, respectively.¹⁸ Finally, in a phase I/II trial, Bahlis et al¹⁹ reported two PRs and four stable disease in patients receiving ascorbic acid 1000 mg/day in combination with two different doses of ATO (0.15 or 0.25 mg/kg/day).

In conclusion, ATO administration in MM patients is feasible but has a limited efficacy and a significant toxicity. Additional research to improve the biodistribution of the drug and its efficacy are needed.

References

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Acknowledgements

This study was supported by Grant no. P970708 and AOM 97088 from Le Programme Hospitalier de Recherche Clinique, Ministère de l'Emploi et de la Solidarité, France.