A Phase 1a/1b, Multicenter, Open-Label, First-in-Human Study to Assess the Safety, Tolerability, Pharmacokinetics, and Preliminary Antitumor Activity of DB-1317 in Participants With Selected Advanced/Metastatic Solid Tumors

Phase 1a (Dose Escalation and Backfilling)

Approximately 5 increasing dose levels of DB-1317 dosing every 3 weeks (Q3W) will be evaluated using an accelerated titration design at the first dose level, followed by a BOIN design at subsequent dose levels with the oversight of a Safety Monitoring Committee (SMC). For safety reasons, in any dose level of the dose escalation where a number of participants ≥ 2, a staggered dosing is required. The second participant in each dose level should start dosing no sooner than at least 24 hours after the initial dosing of the first participant. If no safety concerns arise during these 24 hours, the remaining participants can be enrolled into the same dose level with no additional staggering required. Each dose level will be subject to the DLT assessment. After completing the 21-day DLT observation period (Cycle 1), participants will continue to the next treatment cycle and receive DB-1317 on Day 1 of each cycle in the same dose level cohort. Participants who complete the DLT observation period are not allowed to switch to a higher dose level (i.e., intra-participant escalation is not allowed) unless it is deemed necessary and strongly recommended by the investigator with a written approval by the Sponsor.

Upon confirmation of MTD or MAD of DB-1317 based on data from the completed dose-escalation phase, the safety dose range of DB-1317 may be defined based on cumulative data. Following confirmation by the SMC, alternative dosing regimens, such as Q2W may be explored within the established safety dose range.

Phase 1b (Dose Expansion)

Upon completion of the Phase 1a dose escalation, following determination of MTD or MAD, and at the Sponsor's discretion, -one randomized expansion cohort and two single arm expansion cohorts will be opened each enrolling one of the selected solid tumor types, if preliminary anti-tumor activities in these tumor types are observed in Phase 1a part. GC is the tumor type pre-selected for the randomized expansion cohort CRC and PDAC are the two tumor types pre-selected for the single arm expansion cohorts based on ADAM9 expressing data, in vivo anti-tumor activities in non-clinical tumor models, and consideration of unmet medical needs. The final selection of tumor type(s) to be enrolled in the Phase 1b cohorts will be determined by Sponsor based on emerging data from Phase 1a part. Approximately 80 participants will be enrolled in the randomized expansion cohort and randomly assigned in a 1:1 ratio to two dose levels (approximately 40 each) . Approximately 40 participants will be enrolled in each single arm expansion cohort at a selected dose level, and 160 participants will be enrolled in Phase 1b. Dose levels used in Phase 1b part will be determined by Sponsor and SMC based on Phase 1a data. Based on new emerging data from the study, Sponsor may explore other randomized cohorts with other tumor types.