This is a two-part, multi-center first in human study of ION251 in up to 80 participants. Part 1 will use a 3+3 dose-escalation scheme in sequential cohorts to determine the MTD and RP2D during repeated 28-day treatment cycles. MTD will be determined by the number of participants with AEs meeting the dose-limiting toxicity (DLT) criteria during Cycle 1. The MTD determined in Part 1 will be used with other variables to inform a RP2D for participants proceeding to Part 2 for further assessments in the safety, tolerability and anti-myeloma activity.
