Key Points Our 5-year experience shows sustained single-agent efficacy of ibrutinib in CLL patients, with complete response rates increasing over time. Long-term ibrutinib was well tolerated with no new safety signals; rates of grade ≥3 cytopenias decreased with continued therapy.

Although promising results are achieved in ultrasound mediated drug delivery, its underlying biophysical mechanisms remain to be elucidated. Pore formation as well as endocytosis has been reported during ultrasound application. Due to the plethora of ultrasound settings used in literature, it is extremely difficult to draw conclusions on which mechanism is actually involved. To our knowledge, we are the first to show that acoustic pressure influences which route of drug uptake is addressed, by inducing different microbubble-cell interactions. To investigate this, FITC-dextrans were used as model drugs and their uptake was analyzed by flow cytometry. In fluorescence intensity plots, two subpopulations arose in cells with FITCdextran uptake after ultrasound application, corresponding to cells having either low or high uptake. Following separation of the subpopulations by FACS sorting, confocal images indicated that the low uptake population showed endocytic uptake. The high uptake population represented uptake via pores. Moreover, the distribution of the subpopulations shifted to the high uptake population with increasing acoustic pressure. Real-time confocal recordings during ultrasound revealed that membrane deformation by microbubbles may be the trigger for endocytosis via mechanostimulation of the cytoskeleton. Pore formation was shown to be caused by microbubbles propelled towards the cell. These results provide a better insight in the role of acoustic pressure in microbubble-cell interactions and the possible consequences for drug uptake. In addition, it pinpoints the need of a more rational, microbubble behavior based choice of acoustic parameters in ultrasound mediated drug delivery experiments.

The safety and efficacy of ibrutinib, a once-daily Bruton's tyrosine kinase (BTK) inhibitor, in chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL) was demonstrated in this phase Ib/II study. Extended follow-up up to 8 years is described, representing the longest follow-up for single-agent ibrutinib, or any BTK inhibitor, to date.Patients and Methods: Phase Ib/II PCYC-1102 (NCT01105247) and extension study PCYC-1103 (NCT01109069) included patients receiving single-agent ibrutinib in first-line or relapsed/refractory CLL/SLL.Results: Overall response rate was 89%, with similar rates in first-line (87%; complete response, 35%) and relapsed/refractory settings (89%; 10%). Estimated 7-year progression-free survival (PFS) rates were 83% in first-line and 34% in relapsed/refractory settings. Forty-one patients had CLL progression (n ¼ 11 with Richter's transformation). Median PFS was not reached with first-line ibrutinib. In relapsed/refractory CLL/SLL, median PFS was 52 months overall, 26 months in patients with chromosome 17p deletion, 51 months with 11q deletion, not reached with trisomy 12 or 13q deletion, and 88 months in patients without these cytogenetic abnormalities. Estimated 7-year overall survival rates were 84% in first-line and 55% in relapsed/refractory settings. Grade ≥3 adverse events (AE) in >15% of patients were hypertension (28%), pneumonia (24%), and neutropenia (18%). These grade ≥3 AEs generally declined over time, except hypertension. AEs leading to discontinuation in ≥2 patients were observed only in the relapsed/refractory setting (sepsis, diarrhea, subdural hematoma, and Richter's transformation).Conclusions: With up to 8 years of follow-up, sustained responses and long-term tolerability of single-agent ibrutinib were observed with treatment of first-line or relapsed/refractory CLL/SLL, including high-risk CLL/SLL.