CUDC-907: An Oral HDAC/PI3K Dual Inhibitor with Strong Preclinical Efficacy in MCL Model

Introduction

Mantle cell lymphoma (MCL) is an aggressive lymphoma with elevated B-cell receptor activity. Ibrutinib (IBN), a Bruton's tyrosine kinase (BTK) inhibitor, has been shown to have a response rate of 68% in relapsed or refractory MCL patients. However, with the emergence of IBN-resistant lymphomas, new therapies are needed. It is suspected that upregulation of the PI3K-Akt-mTOR pathway allows survival in the presence of IBN. CUDC-907 is a next generation PI3K and HDAC dual-inhibitor currently in phase II clinical trials. Our objective is to investigate the effects of CUDC-907 in IBN-resistant MCL cells in vitro and in PDX model.

Methods

MCL cells were seeded at 10,000 cells per well in 96-well plate and were treated with various doses of compounds at the following concentrations: CUDC-907/Ibrutinib 0.015, 0.05, 0.15, 0.5, 1.5, 5, and 15 uM. Cell viability was tested by CellTiter-Glo luminescent cell viability assay (Promega) after a 72-hour incubation. Next, MCL cells were incubated with IBN at varying doses (0.39 uM, 1.56 uM, 6.25 uM), CUDC-907 (0.39 uM, 1.56 uM, 6.25 uM), and IBN+CUDC-907 (0.39 uM, 1.56 M, 6.25 uM) for 24 hours. Apoptosis was detected by Annexin V-binding assay. In patient derived xenograft (PDX) model: CUDC-907 was administered at a dose of 50 mg/kg in ibrutinib-resistant MCL-bearing PDX mice daily. Tumor volumes were measured as the length X width² X 0.5 weekly. Toxicity was also observed every week. Mice were sacrificed once diameter of tumor mass reached 15 mm size.

Results

CUDC-907 inhibited the growth of both ibrutinib-sensitive and resistant MCL cells in vitro. Sensitive cell lines include: Rec-1, Mino, and JVM-13 with IC⁵⁰ values of 1.1 nM, 1.0 nM, and 5 nM respectively. Resistant cell lines include: Granta-519, Maver-1, and Z-138 with IC⁵⁰ values of 2 nM, 3 nM, and 1.5 nM respectively. All tested cell lines were more sensitive to CUDC-907 than to ibrutinib. In addition, combination treatments of CUDC-907 and IBN increased cell death in comparison to single agent treatments. Next, one pair of MCL cell lines, Jeko-1 (sensitive to IBN) and Jeko-R (resistant to IBN) were treated for 24 hours with varying doses of CUDC-907 or ibrutinib either as single agent inhibitors or in combination therapies. The results demonstrated that CUDC-907 induced apoptosis in both Jeko-1 and Jeko-R cell lines in a dose-dependent manner. Combination therapies increased cell death in a dose-dependent manner as well. In PDX model, tumor volume in treated mice of ibrutinib-resistant PDX decreased significantly compared with vehicle control (pvalue = 0.032). Control mice also weighed considerably more than treated mice (p value = 0.073). Common toxicities included a decrease in body mass for first 28 days of treatment.

Conclusion

CUDC-907, a dual inhibitor of PI3K-Akt-mTOR and HDAC, inhibits tumor growth of ibrutinib-resistant MCL in vitro and in PDX model. It would be a potential drug for the patients with ibrutinib-resistant/relapsed MCL.