Alpha Lipoic Acid (ALA) Inhibits the Anti-Myeloma Effects of Bortezomib.

ALA is an antioxidant often used in the management of peripheral neuropathy (PN) for patients with multiple myeloma (MM). A clinical trial evaluating ALA in diabetic neuropathy showed this drug to be effective for patients with both somatic and autonomic neuropathies. It also normalized the endoneural blood flow, reduced oxidative stress and improved vascular dysfunction. Bortezomib (Velcade^®), the first-in-class proteasome inhibitor (PI), which is approved for the treatment of patients with MM, may cause PN. As a result, patients are often treated empirically with ALA. In this study, we investigated whether ALA has any impact on the anti-MM effects of bortezomib.

First, cells from the MM cell lines RPMI8226 and MM1S (1×10⁵ cells per 100μl) were treated with ALA alone to determine whether ALA had any effects on their growth as determined with an MTS assay. MM cells were plated in a 96-well plate using serum-free media. The cells were treated with either media alone or ALA at concentrations ranging from 1 to 1000 μM for 48 hours. The acidity of ALA at these doses was determined and if the pH was less than 7, we neutralized it using NaOH. Second, we measured the proliferation of cells exposed to bortezomib alone and combinations of a fixed concentration of bortezomib and escalating concentrations of ALA.

The exposure of cells to ALA alone had a stimulatory effect on the growth of both MM cell lines in vitro. ALA alone at 1000 μM resulted in an increase in cell viability of MM1S cells by approximately 10% when compared to the control group. ALA alone also stimulated the growth of RPMI8226 cells but at much lower concentrations than observed for MM1S. Compared to untreated cells, there was an increase in cell viability with ALA at concentrations as low as 1 μM and a concentration dependent increase at concentrations of 1, 10, 100, and 1000 μM in RPMI8226 cells. At the highest concentration (1000 μM) of ALA, cell viability increased 150% when compared to RPMI8226 cells incubated with media alone. Next, we evaluated the effect of ALA on bortezomib's anti-MM activity. As a single agent, bortezomib reduced MM1S (20 nM) and RPMI8226 (5 nM) cell viability by 93% and 70% respectively. When ALA was added at a clinically achievable concentration (100 μM) to bortezomib (RPMI8226, 5 nM; MM1S, 20 nM), a reduction in the anti-MM effects of bortezomib on these cell lines was observed when compared to bortezomib treatment alone. Compared to bortezomib alone, the combination of ALA plus bortezomib doubled cell viability (increased RPMI8226 and MM1S cell viability from 32.5% to 65% and 7.5% to 15%, respectively). These negative effects of ALA on bortezomib's anti-MM activity were consistently observed in multiple experiments involving both of these cell lines evaluating concentrations of ALA ranging from 100 to 1000 μM and bortezomib ranging from 5 to 20 nM.

Our data suggest that ALA has the potential to antagonize the anti-MM effects of bortezomib based on our in vitro results using MM cell lines. Thus, it is possible that ALA could negatively impact the therapeutic benefit of bortezomib for MM patients and this requires further study especially if ALA is accepted as an intervention in bortezomib-related neuropathy. We are currently completing studies evaluating primary MM patients' tumor cells in vitro and our human MM xenograft models in vivo to further validate this impact of ALA on bortezomib's anti-MM activity and whether changes in treatment schedule of these drugs may prevent this inhibitory effect from occurring. In addition, because part of bortezomib's anti-tumor effects are related to reactive oxygen species (ROS) levels, we are evaluating whether the inhibitory effects of ALA on this PI may be overcome by increasing intracellular ROS levels.

Hilger:Millennium Pharmaceutcals: Employment. Berenson:Millennium Pharmaceuticals, Inc.: Consultancy, Honoraria, Research Funding, Speakers Bureau.