Bosutinib (SKI-606) exhibits clinical activity in patients with Philadelphia chromosome positive CML or ALL who failed imatinib

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Background: Bosutinib (SKI-606) is an orally available, dual Src/Abl kinase inhibitor. To assess safety and preliminary clinical activity of bosutinib, we conducted a phase 1/2 study in patients (pts) with Philadelphia chromosome positive (Ph+) chronic myelogenous leukemia (CML) or acute lymphocytic leukemia (ALL) who were imatinib resistant/intolerant. Methods: In part 1, 18 pts with imatinib- relapsed/refractory chronic phase (CP) CML received bosutinib 400 mg/day (3 pts), 500 mg/day (3 pts), or 600 mg/day (12 pts). Part 2 was an expanded cohort of 51 pts with all phases of Ph+ CML and ALL dosed at 500 mg daily. Timed blood samples were collected on days 1–3, 15 for PK analysis. Results: Of 69 pts, median age was 59 yrs; 48 were CP; 90% imatinib resistant. Drug-related grade 1/2 adverse events (AEs) occurring in =10% of CP pts: diarrhea (69%), nausea (44%), vomiting (19%), abdominal pain (13%), rash (13%). Grade 3/4 AEs occurring in =5% of CP pts: rash (6%), thrombocytopenia (6%). 17 pts required dose reductions. In evaluable imatinib-resistant CP-CML pts with no prior exposure to other Abl inhibitors, 16/19 (84%) had complete hematologic response (CHR); 4/21 had partial and 7/21 had complete cytogenetic responses for major cytogenetic response (MCyR) rate of 52%. Of 58 pts evaluable for mutations, 13 different imatinib-resistant mutations were found in 32 pts. 12/14 CP pts with non-P-loop mutations and 3/3 with P-loop mutations achieved CHR. 5/11 CP pts with non-P- loop mutations and 1/1 with P-loop mutation achieved MCyR. 4/9 evaluable advanced leukemia pts had CHR, 2 had MCyR. After oral administration, steady state exposure of bosutinib was nearly 2-fold higher than single-dose exposure. Mean elimination half-life was approximately 22–27 hours, supporting a once-daily dosing regimen. Conclusions: Bosutinib was well tolerated in pts with CML, with primarily low-grade gastrointestinal and dermatologic AEs. Bosutinib showed clinical activity in imatinib-resistant pts with cytogenetic responses and CHR across a range of mutations. Durability of response continues to be assessed.

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Alternative use of a mini exon of the L1 gene affects L1 binding to neural ligands

Neural cell adhesion molecule L1 is a cell surface glycoprotein required for the correct development of the nervous system. L1 exists as two isoforms encoded by mRNA species that either collectively incorporate or exclude exons 2 and 27. Neurons utilize only the full-length isoform, whereas Schwann cells, kidney cells, and blood lymphocytes only express the short form of L1. Still other cells, oligodendrocytes, regulate L1 isoform expression in a maturation-dependent manner. The RSLE motif encoded by exon 27 is known to have a role in clathrin-mediated endocytosis of L1, but the function of the exon 2-encoded motif (YEGHHV) is unknown. Here we show that this motif is required for the optimal binding of L1 to several neural ligands and is likely to be important for nervous system development. Thus, alternative use of exon 2 is a mechanism for regulating ligand interactions with L1.