Bruton's tyrosine kinase inhibitors in primary central nervous system lymphoma-evaluation of anti-tumor efficacy and brain distribution

Background: Primary central nervous system lymphoma (PCNSL) is an aggressive lymphoma confined to central nervous system. Current treatments including surgery, chemotherapy and whole-brain radiotherapy often fail to achieve satisfactory effect, especially in elderly. As a regimen in targeted therapy, Bruton's tyrosine kinase (BTK) inhibitor ibrutinib has been tested in several clinical trials against PCNSL, offering hope for patients unfit for chemotherapy. We aim to evaluate and compare the anti-PCNSL ability of three different BTK inhibitors, ibrutinib, zanubrutinib and tirabrutinib, providing direct evidence for the targeted therapy of PCNSL. Methods: Retrospective study was done on patients who received ibrutinib-based therapy in our hospital. Cerebrospinal fluid (CSF) from one patient was collected to measure the concentration of ibrutinib. Inhibition assay and apoptosis assay were done on lymphoma cells to determine the anti-tumoral effects of three inhibitors. Pharmacokinetic study was conducted to evaluate their ability in penetrating blood brain barrier and distributing in brain. Results: In retrospective study, we found three patients with PCNSL who had good clinical response to ibrutinib-based therapy (2 complete remission, 1 partial remission), which further support the use of BTK inhibitors in PCNSL. In vitro studies show that ibrutinib has the best anti-tumoral ability among three inhibitors. In vivo study on pharmacokinetic profiles indicate that both ibrutinib and tirabrutinib are good in distributing in brain parenchyma. Conclusions: In conclusion, our study results suggest that BTK inhibitors can be promising candidates for PCNSL treatment, preferring the use of ibrutinib and tirabrutinib as anti-PCNSL agents among the three inhibitors.