DPM-1001 inhibits the short form of PTP1B reversibly, whereas PTP1B(1–405) remained inactive over an extended period of time. DPM-1001 is against PTP1B(1–405) with no pre-incubation, the IC50 value for PTP1B(1–405) is 600 nM. However, after a 30-min pre-incubation, the potency is improved to 100 nM. In contrast, there is no obvious time-dependent change in the IC50 value for PTP1B(1–321).