Background: ACT001, an orally-available parthenolide derivative targeting NF-κB and STAT3 signaling pathways, has immunomodulatory effects and showed promising activity in preclinical models of glioblastoma (GBM). The updated data in this report summarizes clinical findings from this first-in-human clinical trial of ACT001 in patients with advanced solid tumors, including GBM. Methods: Eligible patients were adults with ECOG PS 0-1 and satisfactory hematologic, renal and hepatic function. Additionally, GBM patients had progressive disease despite initial radiation and temozolomide, measurable tumor and no radiation treatment within 3 months prior to enrollment. ACT001 was given orally BID until intolerance or disease progression. Dose escalation followed a standard 3+3 design. Gliomas were imaged with MRI every 8 weeks and responses assessed using RANO criteria. Results: A total of 24 patients were enrolled as of this report: 14 with primary GBM, 2 with secondary GBM, 2 with anaplastic astrocytoma, 2 with colorectal cancer and 1 with each of anaplastic oligioastrocytoma, diffuse intrinsic pontine glioma, non-small cell lung cancer and pleural epithelioid mesothelioma. Median age was 49 years old (range 32-72). ACT001 dose levels were 100 mg BID, 200 mg BID, 400 mg BID, 600 mg BID, 900 mg BID and 1200 mg BID. Study drug treatment was well tolerated with no dose-limiting toxicity or ACT001-related SAE observed. The originally-planned maximum dose of 600 mg BID and the 1200 mg BID dose were expanded to 7 and 5 patients, respectively. The plasma half life of ACT001 was approximately 3-4 hours and no accumulation was observed after multiple dosing. Cmax and AUC_0-last were approximately dose linear across the evaluated dose range. Of the 19 patients with recurrent malignant gliomas, a complete remission was observed in 1 patient with GBM (ongoing 27 months from starting ACT001) and stable disease lasting ≥ 6 months was seen in 3 patients. Preliminary biomarker analysis of PBMC samples revealed a post-treatment reduction in CD4+ Treg cells at some dose levels. Conclusions: In this first-in-human phase 1 study, ACT001 was well tolerated and showed satisfactory bioavailability and preliminary evidence of anti-tumor activity in malignant glioma patients dosed at 400 mg BID or lower. A phase 1b trial in recurrent GBM patients of ACT001 at 200-400 mg BID in combination with anti-PD-1 therapy is planned. Clinical trial information: ACTRN12616000228482.