A Phase II Study of the MEK 1/2 Inhibitor AZD6244 (Selumetinib, ARRY-142866) in Relapsed or Refractory Multiple Myeloma

Abstract 2931

AZD6244 is a potent, selective, oral, non-ATP competitive small molecule inhibitor of the mitogen-activated protein kinase, MEK 1/2 that has shown significant pre-clinical activity in multiple myeloma (MM) cells, both in vitro and in vivo, as well as a favorable clinical profile. The present phase II study was designed to determine the response rate for AZD6244 in patients with relapsed or refractory MM.

The study utilized a two-stage Simon design to allow for early termination if there was strong evidence of regimen inactivity. Eligible patients were restricted to those with MM who have had at least 2 prior regimens. AZD6244 capsules (75 mg) were administered orally twice daily continuously for 28 day cycles. Response was evaluated after 3 cycles.

To date, 37 patients have been enrolled (13 in the 1^st stage and 24 in the 2^nd stage). One subject enrolled in the 1^st stage was not treated. Gender enrollment was balanced (male/female 18/19). The median age of treated patients was 65 years [range 43–81]. ECOG performance scores ranged from 0–2. The median number of prior therapies was 5 [range 2–11].

The most common treatment-related adverse events (occurring in 10–50% of patients) were leukopenia, acneiform rash and other skin/subcutaneous tissue manifestations, fatigue, limb edema, increased aspartate aminotransferase (AST), neutropenia, nausea, facial edema, vomiting, thrombocytopenia, increased creatine phosphokinase, and diarrhea. The most common grade 3 and 4 toxicities (CTCAE v4) included fatigue, peripheral sensory neuropathy, increased AST, neutropenia, nausea, hypotension, thrombocytopenia, increased alanine aminotransferase, and diarrhea. Five deaths have occurred: 2 associated with sepsis, 1 associated with acute kidney injury, all deemed possibly related to AZD6244; and 2 due to disease progression after discontinuation of study treatment.

Two objective partial responses have been reported, the first of which justified expansion of the study to the 2^nd stage. Twelve patients have had a best response of stable disease, 11 patients have had progressive disease, 1 patient withdrew after cycle 1 (unrelated to toxicity) and did not have response assessed, 3 patients died before response was assessed, and 7 patients are too early to evaluate. Accrual is ongoing to determine if the response threshold in the 2^nd stage can be met.

Correlative studies are ongoing and are designed to identify potential mechanisms of response/resistance to AZD6244, and to determine the effect of AZD6244 on the bone marrow microenvironment. These include, among others, assessment of pre- and post-treatment expression of phospho-MEK 1/2 and -ERK 1/2, and total levels of Bim. Fifteen patients consented to correlative sampling of bone marrow, blood and/or urine. Results and sample analysis are pending.

It is concluded that AZD6244 has modest activity as a single agent in relapsed or refractory MM. This trial also provides a foundation for successor studies employing the MEK 1/2 inhibitor AZD6244 in combination with other agents in patients with MM.