A Phase I/II Trial Evaluating the Combination of Arsenic Trioxide, Bortezomib and Ascorbic Acid for Patients with Relapsed or Refractory Multiple Myeloma.

Background: Both arsenic trioxide and bortezomib as single agents have shown efficacy for patients with relapsed/refractory multiple myeloma (MM). Recently, we have demonstrated synergistic anti-MM effects when these two agents are combined to treat human MM in SCID mice and evaluated in in vitro studies. In addition, we and others have also shown that the addition of ascorbic acid (AA) sensitizes MM cells to the cytotoxic effects of arsenic trioxide both through in vitro and in vivo studies. Thus, the objective of the current Phase I clinical trial was to assess the safety and tolerability of bortezomib + arsenic trioxide + AA treatment for patients with refractory/relapsed MM.

Methods: A treatment cycle comprised of intravenous injections of arsenic trioxide, bortezomib and AA on days 1, 4, 8, and 11 followed by a 10-day rest period every three weeks. Bortezomib was given at one of three dose levels (0.7, 1.0, or 1.3 mg/m²), followed by arsenic trioxide at one of two doses (0.125 or 0.25 mg/kg) intravenously followed by AA (1000 mg). Patients were treated for a maximum of eight cycles and were eligible for maintenance therapy with the same treatments given once every other week.

Results: Eighteen patients have been enrolled to date, with three patients enrolled in each of the six cohorts. Patients had received a median of three prior therapies (range, 1–6), and five patients had received prior bortezomib therapy. Fifteen patients are evaluable for efficacy to date, and response data are summarized in Table 1. Overall, among the 15 evaluable patients, seven patients responded (2 PR, 5 MR), three patients showed stable disease, and five patients progressed. Among the six patients (in cohorts 1 and 4) enrolled at the lowest (0.7 mg/m²) bortezomib dose level, only one achieved a MR whereas among the nine evaluable patients enrolled at the higher (1.0 and 1.3 mg/m²) bortezomib dose levels six patients responded (2 PR, 4 MR). In general, the regimen was well tolerated. One patient in cohort 3 was removed from study during the first cycle because of the development of an asymptomatic arrhythmia which resolved spontaneously. Other serious adverse events included pneumonia in two patients, chest pain, and abdominal pain (one patient each).

Conclusion: These early results from this Phase I/II study indicate that the combination of bortezomib, arsenic trioxide and ascorbic acid has efficacy and is well tolerated in a heavily pretreated population of patients with relapsed or refractory MM. Because of these encouraging clinical results, we plan to further evaluate this combination in a larger group of patients with relapsed/refractory myeloma.