Selective MEK Inhibition with AZD-6244 (selumetinib) in Patients with Relapsed/Refractory Diffuse Large B-Cell Lymphoma (DLBCL): A University of Chicago Phase II Consortium Trial

Introduction: The biology of DLBCL is complex, with a number of clinicopathologic and molecular features impacting outcome. MCT-1 is an oncogene that promotes lymphomagenesis via enhanced cell survival signaling, increased G1 cyclin/CDK activity and overriding cell cycle checkpoints; its expression is substantially elevated in DLBCL without a clear difference in germinal center versus non-germinal center subtypes. Our preliminary studies showed that 1) 85% of DLBCL samples have strong or increased expression of MCT-1via IHC, 2) MCT-1 knockdown induces apoptosis in cell lines, and 3) mutant MCT-1 protein expression attenuates the malignant phenotype via translational changes. (Dai Ca Res 2009 69(19): p. 7835-43) MCT-1 levels are directly regulated by MEK/ERK signaling, providing a rationale to test MEK pathway inhibition as a therapeutic target in DLBCL. AZD-6244 (ARRY-142886, selumetinib) is a novel second generation oral small molecule MEK inhibitor that induces dose dependent apoptosis in DLBCL cell lines and attenuates tumor growth in xenograft models. (Bhalla Blood 2011 118(4): p. 1052-61) In patients with solid tumors, AZD-6244 75mg twice daily has been established as the recommended phase II dose (RP2D). (Adjei JCO 2008 26(13): p. 2139-46)

Methods: Eligible relapsed/refractory (R/R) DLBCL patients received AZD6244 hydrogen sulfate at a dose of 75 mg by mouth twice daily continuously for up to eight 28-day cycles or until disease progression or unacceptable toxicity. The primary objective of the study was overall response rate (ORR) with secondary objectives including safety, progression free survival (PFS), overall survival (OS) and pharmacodynamic (PD) analyses. The statistical design used a Simon two-stage design. Due to excessive early toxicity, the protocol was amended to reduce the dose to 50mg twice daily.

Results: Sixteen R/R DLBCL pts (9 male, 7 female) with a median age of 70 years (range, 29-86 yrs), median 3 prior regimens (range, 0-6) were enrolled. Cell-of-origin was not prospectively determined, but only 3/10 pts were CD10 positive and 5/9 were MUM1 positive. The median Lactate Dehydrogenase (LDH) at study entry was 483 (range, 194-1128). Two patients withdrew consent prior to treatment exposure. Of 14 patients receiving at least one dose of selumetinib, two had stable disease and the remainder progressed. The median number of treatment cycles was one (range, 1-5). This was partly due to toxicity causing frequent dose interruptions of AZD-6244. Grade ³3 toxicities were observed in 37.5% (15.2 - 64.6%) and included anemia (44%), thrombocytopenia (25%), diarrhea (31%), transaminitis 44%), fatigue (44%); other infrequent toxicities included AV block, LV dysfunction, anorexia and rash. Median progression-free survival (PFS) in all patients was 34 days [95% CI 14-73 days]. Median overall survival (OS) was 129 days [CI 58-134 days]; all but 3 patients (including one patient lost to follow-up) have expired.

Conclusion: Despite excellent preclinical rationale to test selective MEK antagonism as a means of modulating MCT-1 and MEK/ERK in DLBCL, AZD-6244 was not well tolerated and had limited clinical activity. Other MEK/ERK inhibitors with a more favorable toxicity profile and/or use of rational synergistic combination therapy should be considered to further evaluate the role of MEC inhibition in this heavily pretreated patient population. (Patel Cancer 2014 19(4): p. 799-805 (Supported by NCI contract N01-CM-2011-00071C)

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