Background: Investigational agent APG-2449 is a novel, orally active FAK inhibitor and a third-generation ALK/ROS1 TKI that has shown potent activity against a range of ALK-resistant mutations, including G1202R, L1196M, V1180L, E1210K, S1206F, G1269A, F1174L, I1171S, and C1156Y in preclinical NSCLC, mesothelioma, and other solid tumor models. Methods: This dose escalation and dose expansion study evaluated APG-2449 in patients with second-generation TKI-resistant ALK/ROS1⁺ NSCLC or mesothelioma. APG-2449 was administered orally once daily at the assigned doses on a 28-day cycle using a “3+3” dose escalation design under fasted/fed conditions. Study aims were to assess safety/tolerability, recommended phase 2 dose (RP2D), pharmacokinetics (PK), pharmacodynamics (PD), and efficacy. Results: As of the data cutoff date of December 30, 2021, 84 pts (median age 52 [range 21-78] years; 42% female) with NSCLC or mesothelioma enrolled were treated with APG-2449 at doses ranging from 150 to 1,500 mg. PK analyses indicated an approximately dose-proportional increase in plasma exposure under fed conditions across dose levels tested. Cerebrospinal fluid PK analyses showed that APG-2449 was brain-penetrant. Low-fat meals increased APG-2449 C_max and AUC by approximately 40% to 80% compared to fasting conditions. Based on PK, biomarker, efficacy, and safety results, the RP2D was determined to be 1,200 mg. Four partial responses (PRs) were observed in 14 ALK⁺ pts resistant to second-generation TKIs treated at the RP2D. Another pt with the G1202R mutation following alectinib treatment had tumor shrinkage of 27.9%. Among 8 pts with brain metastases, 1 complete response and 3 PRs were observed intracranially. In 10 TKI-naïve pts, the overall response rate was 80% (ALK⁺, 6/8; ROS1⁺, 2/2) and the disease control rate (DCR) was 100%. Preliminary biomarker data showed decreased FAK phosphorylation in peripheral blood mononuclear cells and increased IFN-γ levels in serum after multiple doses of APG-2449. No dose-limiting toxicity was observed. A total of 66 (78.6%) pts experienced treatment-related adverse events (TRAEs). The most frequent TRAEs included elevated blood creatinine (33.3%), ALT (25.0%), and AST (19.0%) levels and gastrointestinal disorders: nausea (22.6%), vomiting (17.9%), and diarrhea (13.1%). Only 6 (7.1%) TRAEs were grade ≥ 3. Conclusions: APG-2449 has a favorable safety and PK profile and was well tolerated in 84 subjects. Preliminary efficacy was observed in pts whose disease was resistant to second-generation TKIs, especially among those with brain metastases, and in TKI-naïve pts. Biomarker data indicated potential target engagement on FAK and immunomodulatory effects of APG-2449. Clinical trial information: NCT03917043.