KPT-330 Combined with Radiation Therapy: Effective Central Nervous System Lymphoma Treatment with Reduced Neurotoxicity

Whole brain radiation therapy was once the cornerstone of central nervous system lymphomas (CNSL) treatment, but the delayed neurotoxicity caused by radiotherapy has become a major obstacle. This study aims to find drug combinations that enhance CNSL radiosensitivity, reducing irradiation (IR) dose and neurotoxicity.

CNSL include primary and secondary types, with most secondary CNSLs originating from the MCD subtype (MYD88 (L265P) and CD79B (Y196) mutations) and a minority from non-MCD subtypes. Here, we utilized the primary CNSL cell line HKBML, the MCD subtype cell line HBL, and non-MCD subtype cell lines SU-DHL-2, SU-DHL-8, and Farage. We assessed the combination of radiotherapy with five small molecule drugs: lenalidomide, ibrutinib, orelabrutinib, zanubrutinib, and the XPO1 inhibitor KPT-330. Only KPT-330 showed synergistic effects when combined with IR across the five cell lines, as indicated by the calculated Combination Index. This synergistic effect significantly inhibited lymphoma cells with radiation doses as low as 4Gy, whereas achieving the same level of inhibition required radiation doses exceeding 10Gy when used alone. In intracranial orthotopic CNSL models, magnetic resonance imaging analysis showed significantly reduced disease burden with KPT-330 combined with IR compared to double-dose IR, and prolonged overall survival. The combined treatment also led to less cachexia, with minimal body weight loss. Histological examinations of vital organs (heart, liver, spleen, lung, kidneys) found no significant damage, affirming the safety of this combination therapy.

To assess the effects of different treatments on neurotoxicity, mice underwent cognitive testing one month after initial treatment. The novel object recognition (NOR) task was used to evaluate memory skills associated with cortical function. Untreated mice showed no decline in the discrimination index (DI), indicating no tumor-induced cognitive impairment. In contrast, a significant decrease in DI was observed in the 8 Gy dose-rate irradiated group compared to controls. Remarkably, mice treated with the combination therapy did not exhibit such declines and showed DI levels statistically similar to controls.

We conducted RNA-seq to explore how KPT-330 enhances radiation sensitivity. GO, KEGG, and GSEA analyses revealed that KPT-330 affected genes involved in the DNA repair pathway. Post KPT-330 treatment, DNA damage repair-related genes showed a general decrease. The combination of IR and KPT-330 worsened DNA damage and reduced lymphoma cell DNA repair capacity. Using Western blot to detect γ-H2AX and RAD51, we confirmed that KPT-330 combined with IR exacerbated DNA damage and hindered DNA repair. The BRCA1 pathway was notably enriched in the KPT-330 group, suggesting KPT-330 inhibited BRCA1 function in lymphoma cells. Further studies found KPT-330 blocked IRF3 nuclear export, leading to increased IRF3 nuclear retention. As a transcriptional repressor, IRF3 inhibited BARD1 expression, thereby reducing the BARD1-BRCA1 complex's role in DNA repair.

Overall, current normal tissue tolerances restrict the dose delivered to the CNSL bed. Our findings demonstrate that combining KPT-330 with IR can lower radiation doses while more effectively suppressing central nervous system lymphoma compared to higher dose-rate irradiation, and with reduced risk of normal tissue toxicities. This presents an encouraging clinical prospect that is poised to stimulate further investigation into CNSL radiation therapy.