CC-122 Is a Cereblon Modulating Agent That Is Active in Lenalidomide-Resistant and Lenalidomide/Dexamethasone-Double-Resistant Multiple Myeloma Pre-Clinical Models

Background: CC-122 is a Cereblon (CRBN)-dependent Cul4 E3-ligase complex modulating compound currently being investigated in several hematologic malignancies, including relapsed/refractory multiple myeloma (MM). CC-122 binding to Cereblon results in the selective ubiquitination and subsequent proteasomal degradation of the hematopoietic transcription factors Ikaros (IKZF1) and Aiolos (IKZF3), accounting for its cytotoxic and immunomodulatory effects in diffuse large B-cell lymphoma.⁽¹⁾ In a phase I study CC-122-ST-001 (clintrial.gov trial #NCT01421524), CC-122 showed single agent overall response rates of ~18% in heavily pre-treated (median 6 lines prior therapy) relapsed/refractory MM. CC-122 is currently being explored as a single agent or in combination with dexamethasone in patients who previously failed lenalidomide.⁽²⁾ Here, we examine the effects of CC-122 in pre-clinical models of MM with varying degrees of sensitivity to lenalidomide and dexamethasone.

Results: We established lenalidomide-resistant and lenalidomide/dexamethasone dual-resistant cell lines according to a previously reported protocol.⁽³⁾ A broad panel of MM cell lines (57) consisting of lenalidomide-sensitive (LS; n=26), intrinsically lenalidomide-resistant (ILR; n=7), acquired lenalidomide-resistant (ALR; n=12), and acquired lenalidomide/dexamethasone-dual-resistant (ALDR; n=12) MM cell lines were investigated for the effects of either lenalidomide or CC-122, with and without dexamethasone. Proliferation analysis by ³H-thymidine incorporation at similar concentrations (0.01-100 μM), showed a greater reduction over the averaged area under the curve (AUC) for CC-122 compared to lenalidomide of 53% to 34% (p<0.01) in LS, 22% to 3% (p<0.05) in ILR, 21% to 7% (p<0.01) in ALR, and 13% to 3% (p<0.05) in ALDR cells, respectively. In combination with dexamethasone (0.001-1 μM), CC-122 also exhibited greater reduction in the AUC compared to lenalidomide at the clinically relevant doses of either compound (~0.1 and 1 μM respectively). CC-122 (1 μM) significantly (p<0.01) induced apoptosis by more than 2-fold over lenalidomide (10 μM) across the entire cell line panel by flow cytometry and AnnexinV+/ToPro3+ staining. Additionally, when incubated with isolated peripheral blood mononuclear cells for 72 hrs, CC-122 induced the killing of all MM cell line types irrespective of their cell-autonomous response when co-cultured for 4 hrs. The anti-MM effect observed in the co-culture assay also correlated well with IL-2 and Granzyme B release, which was significantly (p<0.01) higher for CC-122 than lenalidomide, regardless of Cereblon levels in the MM cell lines.

Next we compared the mechanism of action of CC-122 in MM cells by analyzing Ikaros, Aiolos, c-Myc, IRF4 protein expression and Cereblon-dependency. In the presence of CC-122, both Ikaros and Aiolos are targeted for proteasomal degradation within 6 hrs of treatment, where maximal reduction approaches 100% within 10-12 hrs and is sustained over 72 hrs, a previously reported requirement for the anti-proliferative effects of lenalidomide.⁽⁴⁾ Half maximal reduction of Ikaros and Aiolos proteins was kinetically accelerated for CC-122 (1 μM) compared to lenalidomide (10 μM) with a time span of 2.7-4 hrs compared to 3.2-8.5 hrs, respectively. Also, the key c-Myc/IRF4 axis is disrupted faster and at 10-fold lower dose for CC-122 compared to lenalidomide. Finally, we evaluated the effects of CC-122 on interferon response genes (ISGs) since Aiolos has previously been shown to act as a repressor of ISGs.⁽⁵⁾ Following exposure to CC-122, ISGs including IFIT1/3 and XAF were shown to be stimulated in MM cells, which may also account for some of the anti-MM effects in vitro and in vivo.

Conclusions: CC-122 is a Cereblon-dependent Cul4 E3-ligase complex modulating compound that displays superior pre-clinical activity compared to lenalidomide, and is active in a wide range of resistance models. In addition to its direct anti-tumor effects, CC-122 displays anti-MM activity through stimulation of tumor cell killing by co-cultured PBMCs, which tightly correlates with Granzyme B and IL-2 release, regardless of Cereblon expression in MM cells. Together, these data support the clinical rationale to study CC-122 in relapsed/refractory MM patients, who previously failed lenalidomide.