A Phase 1 Open-label, Multicenter, Dose-Ranging Study to Investigate Safety and Tolerability, Efficacy, Pharmacokinetics, Pharmacodynamics, and Immunogenicity of MT-6402 in Subjects with Advanced Solid Cancer That Expresses PD-L1

MT-6402 may bind and kill both tumor and immune PD-L1 expressing cells in a manner consistent with SLTA mediated cellular cytotoxicity through ribosomal inactivation, independent of checkpoint inhibition.

In this study, the sponsor and investigators want to learn:

• How much of the study drug can be given with an acceptable level of side effects
• The effects of the study drug (good and bad)
• How much of the study drug is absorbed into the blood and how fast it is removed
• How the study drug is acting on your body

The study will be divided into two parts: Part A (dose-escalation) and Part B (expansion).

The aim of Part A is to determine the highest tolerable dose (also known as the maximum tolerated dose) and the best dosing schedule of the study drug, with the goal of choosing the recommended dose to be used in Part B.

The highest tolerable dose is the highest dose with acceptable side effects, which lowers the risk of having a side effect that would cause you to stop receiving the study drug at that dose level (known as a dose-limiting toxicity).

The aim of Part B is to confirm the safety and tolerability of the recommended dose and dosing schedule from Part A, and to start to test whether the study drug is a useful treatment for subjects with certain types of advanced PD-L1-positive solid tumors.

For subjects who take part in Part A of the study, at the time of joining this study, your study doctor will assign the dose level of study drug you will receive. At least 3 subjects will receive study drug at each dose level. The first group of subjects will receive the lowest dose level. The next groups may then receive a higher or lower dose than the group before, or a different dosing schedule based on how the study drug is tolerated. Once you begin receiving the study drug, you will always receive the same dose level of study drug in the same schedule, unless you have side effects that require the dose to be reduced.

For subjects who take part in Part B of the study, you will receive study drug at the highest dose found tolerable during Part A of the study. You will always receive this dose level unless you have side effects that require the dose to be reduced.