Background: Primary DLBCL of the CNS (PCNSL) relies on chronic active B-cell receptor (BCR) signaling. Ibrutinib targets BCR signaling through BTK inhibition (BTKi), which may also impair innate immunity. We showed that ibrutinib and temozolomide, etoposide, liposomal doxorubicin, dexamethasone, rituximab (TEDDI-R) induces durable remissions in relapsed/refractory PCNSL but 7 (39%) pts developed Aspergillus infections without fungal prophylaxis. Newer triazoles are effective against Aspergillus but inhibit ibrutinib clearance through CYP3A4. Isavuconazole has less effect on CYP3A4 and less hepatotoxicity than voriconazole. We hypothesized that ibrutinib and isavuconazole could be safely co-administered in TEDDI-R and ameliorate the risk of Aspergillus while maintaining efficacy. We studied escalating doses of ibrutinib in TEDDI-R with isavuconazole to determine the safety profile, ibrutinib PK, and clinical activity in relapsed/refractory PCNSL.
Methods: Pts with relapsed/refractory PCNSL, age ≥18, ECOG PS ≤2, and adequate organ function were enrolled. Previous BTKi, HIV, EBV+, and pregnancy were excluded. Pts had baseline MRI brain, FDG-PET brain and body, Ommaya placed, CSF with flow cytometry, and eye exam. Isavuconazole 200mg BID x 3d started prior to ibrutinib then 200mg daily. Three dose levels of ibrutinib (280mg, 420mg, 560mg) were given continuously through each cycle. Pts received up to 6 cycles of TEDDI-R with IT cytarabine. No one received maintenance or consolidation. If a DLT occurred in the first 3 pts at a given ibrutinib dose level, 3 more pts were treated before escalating. Full safety and PK data was reviewed after two dose levels prior to escalating. An expansion of 10 pts was planned at the highest ibrutinib dose level to confirm safety and clinical activity. Surveillance for fungal infections included chest CT mid-cycle 1 and after each cycle along with Beta-D glucan and aspergillus galactomannan in blood and CSF. Brain MRI was performed after cycles 1, 2, 4, and 6 to determine response and screen for CNS Aspergillus. All remissions by MRI were confirmed with FDG-PET and CSF analysis. Surveillance brain MRI were q3m for 1y, q4m x 1y, q6m x 1y, then annually. Primary objective was to identify the highest dose of ibrutinib safely co-administered with isavuconazole in TEDDI-R that achieves adequate PK concentrations.
Results: 13 relapsed/refractory PCNSL pts enrolled between 11/2018 and 06/2020. 10 (77%) pts were male and the median age was 65 (range 46-77), including 3 pts ≥age 70. 13 (100%) pts had prior high-dose MTX, and 2 (15%) pts had prior autologous stem cell transplant (ASCT). Three evaluable pts received ibrutinib 280mg, 3 pts received ibrutinib 420mg, and 6 pts received ibrutinib 560mg. One pt in the 280mg cohort was not evaluable. Toxicity was evaluated in 13 pts across 49 cycles and the toxicity was mainly hematologic. G3 and G4 neutropenia occurred in 45% and 37% of cycles, respectively, while febrile neutropenia occurred in 8% of cycles. The median (range) duration of neutropenia was 4.5 (1-12) days. One pt with prior ASCT stopped after 4 cycles due to myelosuppression. Four (8%) cycles were complicated by ≥G3 infection, but no opportunistic infections (including Aspergillus) were observed. G3 and G4 thrombocytopenia occurred in 22% and 8% of cycles, respectively, and 1 pt developed melena with no overt GI bleeding. ≥G3 mucositis occurred in 6% of cycles and 1 patient stopped therapy after 5 cycles due to recurrent mucositis. Palmar-plantar-erythrodysesthesia led to dose reductions of liposomal doxorubicin in 9 (69%) pts, but only 1 G3 event occurred. Twelve pts were evaluable for response, and 11 (92%) pts have responded and all after receiving only 1 cycle (Figure 1). All 8 (100%) pts who have completed at least 4 cycles have achieved CR and the other 4 remain on therapy. Six (75%) pts who achieved CR remain in remission while 2 (25%) pts relapsed within 3 months of stopping therapy. After a median potential f/u of 5.2 months, the 1-year PFS is estimated at 60.0% (95% CI, 12.6-88.2) and the OS is 100%.
Conclusions: Ibrutinib 560mg was safely co-administered with isavuconazole in TEDDI-R for relapsed/refractory PCNSL. No DLTs were observed, no cases of Aspergillus occurred, and no new safety signals. The first 8 (100%) patients who have completed therapy achieved complete response. Updated clinical results from this ongoing study (NCT02203526) will be presented at the meeting.
Lai:Abbvie: Consultancy; Agios: Consultancy; Jazz: Speakers Bureau; Macrogenics: Consultancy; Astellas: Speakers Bureau.
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