Phase I first-in-human trial of ABT-301, an oral pan-HDAC inhibitor, in patients with advanced solid tumors.
Authors: Lin Chia-Chi , Chen Tom Wei-Wu , Shiah Her-Shyong , Tan Kien Thiam , Lin Chien-Ting , Hsu Tzu-An , Lin Meng-Chieh , Liou Jing-Ping , Pan Shiow-Lin , Huang Han-Li , Sung Ting-Yi , Lai Mei-Jung , Chen Chun-Han 
Published: June 2023

e15137 Background: ABT-301 (previously known as MPT0E028) is a novel, oral pan-histone deacetylases (HDAC) inhibitor with potent inhibitory activity for HDAC 1, 2, 3 (class I), HDAC 6, 10 (class IIb), modest activity for HDAC 8 (class I) and HDAC 11 (class IV), but no activity for HDAC 4, 5, 7, 9 (class IIa). Preclinical studies showed that ABT-301 had a stronger apoptotic activity and inhibited HDAC activity more potently than vorinostat. ABT-301 exerts antitumor activity as a monotherapy in human colorectal cancer and B-cell lymphoma xenografts and synergistic antitumor activity with immune checkpoint inhibitor in CT26 syngeneic tumor model. Methods: This was a 3+3 Phase 1 dose escalation study to determine the safety, dose-limiting toxicities (DLTs), maximum tolerated dose (MTD), and pharmacokinetic (PK) /pharmacodynamic (PD) profiles for the ABT-301 in patients with locally advanced or metastatic solid cancers. 5 cohorts of 3 or 6 patients received ABT-301 once daily at gradually escalating doses starting from 50 mg. Results: 23 subjects (6 sarcomas and 17 carcinomas) were treated at 5 dose levels (3 at 50, 100, and 250 mg respectively, 6 at 150 mg, and 8 at 200 mg). Cycle 1 DLTs occurred in 5 subjects: 1 at 50 mg (G3 mucositis); 2 at 200 mg (G3 abdominal pain and G4 thrombocytopenia); 2 at 250 mg (G3 vomiting and G4 thrombocytopenia). The MTD was 150 mg. The most common treatment-related adverse events were thrombocytopenia (44%), anemia (18%), nausea (61%), vomiting (44%), anorexia (22%), hyperglycemia (22%), fatigue (18%), and mucositis (18%), which were generally G1 to G2 in severity. No cardiac abnormalities were observed. 1 had a partial response (PR), and 8 achieved SD, resulting in a disease control rate (DCR) of 39%. The PR (a patient with eccrine ductal carcinoma) lasted 24 weeks whereas 5/8 SD patients achieved a sustained condition of 16 to 53 weeks (hepatocellular carcinoma, 53 w; thymic cancer, 49 w; salivary gland carcinoma, 27 w; endometrial stromal carcinoma, 25 w; renal cell carcinoma, 16 w). DCR for 9 patients at MTD was 78% (7/9; 1 PR and 6 SD). Plasma PK showed a dose-dependent increase in ABT-301 exposure. Cmax is 5.5 µM and AUC0-inf is 11.5 µM*h at 150 mg. Increased acetylated histone 3 was observed across all cohorts. Conclusions: ABT-301 was well-tolerated at a daily dose of up to 150 mg and demonstrated objective responses and long-term SD across multiple tumor types at MTD. The safety profile of ABT-301 was superior to known HDAC inhibitors with only predictable HDAC inhibitor-related toxicities observed but no cardiac toxicity, neutropenia, nor lymphopenia elicited. Non-clinical and clinical results suggested the potential clinical development of ABT-301 in combination with myelosuppressive agents and immunotherapies. Phase 2 studies combining PD-1/PD-L1 blockade are being designed. Clinical trial information: NCT02350868 .