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e20609 Background: ACSS2 catalyzes the ligation of acetate with Co-enzyme A to generate Acetyl-CoA. Selection to an acetate dependent state has been demonstrated and is associated with the induction of ACSS2 gene expression in certain human cancers. The ACSS2 gene is amplified in human breast cancers, and its expression is up-regulated in human colorectal, breast, ovarian and lung cancers. MTB-9655 is a potent (IC50 = 0.15nM in biochemical, and EC50 = 3nM in cellular assays) oral inhibitor of ACSS2 and induces anti-tumor effects in xenograft mouse models of human colorectal, breast and lung cancers that express high levels of ACSS2. Methods: Using a combined accelerated (single patient for the first two dose levels) and 3+3 dose escalation and dose expansion design, MTB-9655 was administered on a once daily (QD) schedule in 21-day cycles in a Phase 1 trial to assess safety, tolerability, PK and potential anti-tumor activity in patients with advanced solid tumors. Re-staging was performed every 2 cycles. Results: To-date, 10 subjects have received MTB-9655 at doses up to 225mg. MTB-9655 was absorbed rapidly post oral dosing with a half-life of 6-12 hours. Dose proportional exposure was observed on day 1 of the first dosing cycle, and steady-state exposure was noted between day 8 and day 1 of the second dosing cycle. Dose limiting toxicities or Grade 3 treatment-related adverse events (AEs) have not been observed up to the 225mg dose level. The most common AE was nausea (29%). Low grade increase in bilirubin levels was observed in 1 patient at 225mg dose, without changes in other liver enzyme levels. Increased bilirubin levels were readily reversed with dose interruption. As MTB-9655 is a 729nM inhibitor of the UGT1A1 enzyme, the increase in bilirubin levels is likely attributed to off-target UGT1A1 inhibitory activity. Conclusions: MTB-9655 has been well tolerated, and the safety profile was predictable based on preclinical studies in rodents and non-human primates. Dose proportional plasma drug levels were observed and predicted to have reached biologically active levels. Expected increase in bilirubin levels was observed in 1 patient, which may be used as a marker of significant drug exposure. MTD has not reached up to the 225mg dose and the dose escalation is continuing. Development of MTB-9655 is planned as a single agent, and based on animal model studies, in combination with standard of care platinum-based agents and gemcitabine. Clinical trial information: NCT04990739.

276 Background: BL-8040 is a novel CXCR4 antagonist being developed for multiple oncology indications. Preclinical studies demonstrated that BL-8040 increases the number of immune cells in peripheral blood and promotes CD8+ T cell infiltration into orthotropic pancreatic mouse tumors, reducing tumor load. BL-8040 is being evaluated in a Phase 2a, multicenter, open label trial in patients with metastatic pancreatic cancer (the COMBAT study). Patients are undergoing a 5-day period of monotherapy in which they receive daily doses of BL-8040, followed by 21-day cycles in which patients receive one dose of pembrolizumab and 3 doses/week of BL-8040 until disease progression or discontinuation. To date, 32 patients have been enrolled. Methods: On Day 1 and Day 5, blood samples were taken at pre- and post-dosing, to evaluate peripheral immune cell subset frequency by flow cytometry. In addition, core biopsies were taken from liver metastases, where possible, to assess immune cell infiltration into tumors and the tumor microenvironment (TME). Results: Here we present interim PD biomarker data from the BL-8040 monotherapy portion of the trial. Flow cytometry shows that BL-8040 monotherapy caused an approximately two-fold reduction in frequency of peripheral T regulatory cells, but had no effect on the frequency of T cells, NKT cells or cell populations that contain B cells (CD3- CD56-). Additionally, BL-8040 remained bound to CXCR4 on peripheral immune cells throughout the period of monotherapy. Analysis of available biopsies (N = 7) shows an up to 15-fold increase in the CD3+ population, and up to two-fold increase of CD8+ cells, in the tumor periphery and TME of 43% (3/7) of the patients after five days of BL-8040 monotherapy compared to baseline. Conclusions: In summary, the PD biomarker results in humans support the proposed mechanism of action for BL-8040 that was based on preclinical mouse models. Analysis of tumor biopsies is ongoing, with an emphasis on investigating the effects of BL-8040 on tumor-resident immune cells and the TME. Clinical trial information: NCT02826486.

162 Background: 30% of patients with localized PC will have a biochemical relapse post local therapy. Their optimal treatment remains elusive. While androgen deprivation therapy is effective in reducing PSA level, its long-term benefit remains undefined, and it is toxic. Thus, evaluation of new nontoxic compounds in these patients is warranted. PectaSol-C modified citrus pectin (P-MCP) is an inhibitor of galectin-3 protein, which is involved in prostate cancer pathogenesis. We herein report the final long-term results of a multi-center phase 2 study of P-MCP treatment in BRPC-M0. Methods: Patients with BRPC-M0 were enrolled and treated with P-MCP, 4.8 grams X 3/day, for 6 months (first phase of trial). Patients without PSA progression and/or with improvement of PSA doubling time (PSADT), and with negative scans, were treated for an additional 12 months (second phase of trial). Results: 59 patients were initially enrolled. After initial 6 months of therapy, 46 patients (78%) without disease progression entered the second phase of additional 12 months therapy. Among them, 7 patients withdrew consent and chose to continue therapy out of pocket. Of the remaining 39 patients, after another year of therapy (total of 18 months), 85% (n=33) had an overall long-term response, with a decreased/stable PSA (62 %, n=24), and improvement of PSADT (90 %, n=35), and with negative scans. No patient had grade 3/4 toxicity. Conclusions: P-MCP may have a durable long-term efficacy in patients with BRPC-M0. Clinical trial information: NCT01681823 .