Pharmacodynamic and genomic markers associated with response to the XPO1/CRM1 inhibitor selinexor (KPT-330): A report from the pediatric preclinical testing program

BACKGROUND

Selinexor (KPT-330) is an inhibitor of the major nuclear export receptor, exportin 1 (XPO1, also termed chromosome region maintenance 1, CRM1) that has demonstrated activity in preclinical models and clinical activity against several solid and hematological cancers.

PROCEDURES

Selinexor was tested against the Pediatric Preclinical Testing Program (PPTP) in vitro cell line panel at concentrations from 1.0 nM to 10 μM and against the PPTP in vivo xenograft panels administered orally at a dose of 10 mg/kg thrice weekly for 4 weeks.

RESULTS

Selinexor demonstrated cytotoxic activity in vitro, with a median relative IC50 value of 123 nM (range 13.0 nM to >10 μM). Selinexor induced significant differences in event-free survival (EFS) distribution in 29 of 38 (76%) of the evaluable solid tumor xenografts and in five of eight (63%) of the evaluable ALL xenografts. Objective responses (partial or complete responses, PR/CR) were observed for 4 of 38 solid tumor xenografts including Wilms tumor, medulloblastoma (n = 2), and ependymoma models. For the ALL panel, two of eight (25%) xenografts achieved either CR or maintained CR. Two responding xenografts had FBXW7 mutations at R465 and two had SMARCA4 mutations. Selinexor induced p53, p21, and cleaved PARP in several solid tumor models.

CONCLUSIONS

Selinexor induced regression against several solid tumor and ALL xenografts and slowed tumor growth in a larger number of models. Pharmacodynamic effects for XPO1 inhibition were noted. Defining the relationship between selinexor systemic exposures in mice and humans will be important in assessing the clinical relevance of these results.

Ribosomal Biogenesis and Translational Flux Inhibition by the Selective Inhibitor of Nuclear Export (SINE) XPO1 Antagonist KPT-185

Mantle cell lymphoma (MCL) is an aggressive B-cell lymphoma characterized by the aberrant expression of several growth-regulating, oncogenic effectors. Exportin 1 (XPO1) mediates the nucleocytoplasmic transport of numerous molecules including oncogenic growth-regulating factors, RNAs, and ribosomal subunits. In MCL cells, the small molecule KPT-185 blocks XPO1 function and exerts anti-proliferative effects. In this study, we investigated the molecular mechanisms of this putative anti-tumor effect on MCL cells using cell growth/viability assays, immunoblotting, gene expression analysis, and absolute quantification proteomics. KPT-185 exhibited a p53-independent anti-lymphoma effect on MCL cells, by suppression of oncogenic mediators (e.g., XPO1, cyclin D1, c-Myc, PIM1, and Bcl-2 family members), repression of ribosomal biogenesis, and downregulation of translation/chaperone proteins (e.g., PIM2, EEF1A1, EEF2, and HSP70) that are part of the translational/transcriptional network regulated by heat shock factor 1. These results elucidate a novel mechanism in which ribosomal biogenesis appears to be a key component through which XPO1 contributes to tumor cell survival. Thus, we propose that the blockade of XPO1 could be a promising, novel strategy for the treatment of MCL and other malignancies overexpressing XPO1.