Hoff, Daniel D. Von

Abstract Triptolide, which was initially extracted from a Chinese medicinal herb, demonstrates potent antitumor, anti-inflammatory, and immunosuppressive properties, yet it is clinically limited due to its poor solubility, bioavailability, and toxicity. Minnelide, a water-soluble analog of triptolide, has potent antiproliferative activity. It is currently in Phase I/II clinical trials for Acute Myeloid Leukemia (AML) and 7 solid tumor indications, including advanced gastrointestinal tumors, pancreatic cancer, and colorectal cancer. To overcome the potential drug resistance and to improve the drug potency as well as to minimize the drug toxicity, we conducted a high throughput screening (HTS) for drug synergy, combining Minnelide with compounds from the LOPAC and/or Prestwick libraries in 3 different cancer cell lines: BxPC3 (pancreatic), HT29 (colon) and SNU5 (gastric). LOPAC and Prestwick libraries consist of drugs approved by FDA and/or drugs that have reached clinical trial stages, representing 2,274 unique compounds in total. After quality control evaluation and data normalization, hits were selected if greater than 20% inhibition was achieved when combined compared with Minnelide alone. A total of 43, 54, and 47 hits were identified for each cell line, representing an average hit rate of 2.1%. We further prioritized the hits by selecting those that were common in two or more cell lines, which resulted in 9 compounds from Prestwick library and 20 compounds from LOPAC library (Harmane is in common between the two libraries). Only 17 compounds were available for purchase for hits confirmation, which was conducted in a similar manner as in primary HTS, except that drugs were tested in a dose-dependent manner instead of a single concentration done in HTS, a duplicated biological run was performed, and a total of 9 cell lines were screened, with 3 cell lines for each tumor type (pancreatic, colon and gastric). IC50 and Combination Index (CI) values for each drug combination were calculated for each cell line. A fold change of 2 or more for the IC50 values and CI value < 1.0 were used for hit selection. In general, colon lines had the most synergistic combinations and gastric had the least. A total of 15 drug candidates were confirmed to have synergistic effect, representing a confirmation rate of 88%, among which 12 drugs demonstrated synergy in >50% of the cell lines tested, with Harmane and Harmine demonstrating synergy in all 9 cell lines tested. In addition, CGS-15943, Amiloride, Naphthalimide, and Idazoxan indicated good synergy with Minnelide in at least 6 out of 9 cell lines. Interestingly, Phenamil, an irreversible inhibitor of amiloride-sensitive Na+ channels, showed synergy in all cell lines tested for pancreatic and colon cancers, but not in gastric cancer cell lines. Overall, our study shed light on potential drug combinations with Minnlide for clinical use. Citation Format: Nanyun Tang, Chris Sereduk, Ashok Saluja, Mohana Velagapudi, Haiyong Han, Daniel D Von Hoff, Hongwei Holly Yin. Drug combination screen to identify novel synergy with Minnelide [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr A142. doi:10.1158/1535-7163.TARG-19-A142

3082 Background: CX-3543 is a novel small molecule specifically designed to target three dimensional nucleic acid motifs, and thus induce apoptosis in cancer cells. Preclinically, CX-3543 demonstrated potency in suppressing xenograft tumor growth with a broad therapeutic window. The objectives of this phase I study are: to determine the maximum tolerated dose (MTD) and dose limiting toxicities (DLTs), to establish the pharmacokinetics (PKs), and to determine the recommended dose for further clinical development of CX-3543. Methods: Eligible patients with advanced solid tumors or lymphomas whose tumors progressed on standard therapy or for whom there are no standard therapies receive CX-3543 in successive dose cohorts at: 10, 20, 40, 80 and 160 mg/m2. Dosing is by one hour intravenous infusion daily for five consecutive days repeated on a three week cycle. Therapy is continued until the patient shows signs of intolerance to CX-3543 or evidence of advancing disease. Response by RECIST criteria is determined after every 2 cycles. Results: Ten patients with solid tumors (3–4 per cohort) have received intravenous CX-3543. Doses have been well tolerated. Seven grade 3 adverse events have been reported during the study, but none of these are related to CX-3543. To date no objective responses have been observed. One patient with advanced refractory prostate cancer has stable disease of longer than 4 months duration. CX-3543 has demonstrated good linearity in PK parameters between the dose cohorts with a terminal half life of approximately 12 hours following the first dose. Conclusions: To date, CX-3543 has shown no drug related toxicity and has predictable PKs. No DLTs have yet been observed, and the MTD remains to be defined in this Phase I study. Further enrollment to the planned dose escalation cohorts is ongoing. [Table: see text]

10572 Background: Adrenocortical carcinoma (ACC) is a rare and lethal cancer with an average incidence of 1 in 1.4 million. Response to current standard therapy including mitotane is approximately 22%. Herein we use gene expression profiling to identify novel targets for therapeutic intervention. Methods: The transcriptomes of 29 ACC tumors and 4 normal adrenal glands were profiled on Affymetrix Human Genome and Agilent 22K element expression arrays in order to identify genes that could represent potential therapeutic targets. Agents known to inhibit the selected targets were tested in comparison with mitotane in two ACC cell lines (H295R and SW-13) in vitro and are currently being tested in a Scid mouse xenograft system. Results: Expression of numerous kinesin family members is dysregulated within the ACC tumor population. Of interest in the ACC cells EG5 (KIF11, KSP), a kinesin important for mitotic spindle formation, is up-regulated 5.81+ 4.42 (μ+SD) and 6.48 + 0.99 fold on the Agilent and Affymetrix platforms respectively. In addition, SPARC, an albumin binding matrix associated protein is up-regulated in ACC tumors by 3.69 + 2.37 (μ+SD) and 1.56 + 0.44 on the two platforms. The anti-microtubular drugs paclitaxel and albumin bound paclitaxel (abraxane) exhibited in vitro inhibition of H295R and SW-13 cells at IC50 concentrations of 0.33 μM and 0.0078 μM for paclitaxel and 0.35 μM and 0.0087 μM for Abraxane compared to mitotane concentrations of 15.9 μM and 46.4 μM. Treatment effects of monastrol, paclitaxel, and Abraxane are currently being tested in xenograft murine models. Testing of the EG5 inhibitor S-trityl-L- cysteine is ongoing in the in vitro system. Conclusions: KIF11 inhibitors have been proposed in the treatment of cancer. These compounds may offer better anti-mitotic activity than other tubulin interacting agents with less neurotoxic side effects. Based on biological insight garnered through expression profiling of ACC tumors, the current ongoing research is investigating the use of abraxane and EG5 inhibitors in the in vitro and in vivo treatment of ACC. No significant financial relationships to disclose.

3585 Background: CX-3543 inhibits over-expressed ribosomal RNA synthesis in cancer cells by disrupting an essential protein-rDNA quadruplex complex, thereby inducing selective apoptosis. A phase I clinical trial for CX-3543 was undertaken to determine the dose limiting toxicities (DLTs), maximum tolerated dose (MTD), and pharmacokinetics (PK) of this agent. Methods: Eligible patients with advanced solid tumors received CX-3543 in successive dose cohorts at: 10, 20, 40, 80, 160, 240, 360 and 480 mg/m2. Drug is administered by daily intravenous infusion on the first five consecutive days of a three week cycle, and the infusion duration has varied from one hour to six hours. Response by RECIST is determined after every 2 cycles. Results: Thirty-three patients (M/F:19/14; median age 69, range 44–83) with advanced solid tumors were treated with intravenous CX-3543. No drug related serious adverse events (SAEs) were encountered. DLTs of infusion-related cough and headache were identified at 480 mg/m2 (The MTD was 360 mg/m2). These adverse events were fully and rapidly reversible upon slowing or interrupting the infusion. Other drug-related adverse events were of mild to moderate intensity. Four patients had stable disease for longer than 4 months and one patient, with stable disease for over one year, currently continues on study. CX-3543 demonstrated an increasing plasma terminal half life at the higher dose levels due to a ‘reservoir‘ effect from CX-3543 reversibly binding to blood cells. Conclusions: CX-3543 administered as a 6 hour infusion for five consecutive days of a three week cycle is well tolerated and has stabilized disease in a number of patients enrolled in this phase I study. This trial is now in an expanded enrollment phase at 360 mg/m2 and pharmacodynamic measures, specifically FDG-PET scans and circulating tumor cells, have been included to detect biological activity at this dose level. No significant financial relationships to disclose.

3501 Background: PXD101 is a hydroxamate HDAC inhibitor that has broad anti-neoplastic activity in vivo and in vitro. Preclinical data showing PXD101 down-regulation of thymidylate synthase (TS), an in vivo target of 5-fluorouracil (5-FU) provide a rationale for combination of PXD101 with 5-FU. Methods: This is a phase Ib/II trial of PXD101 plus 5-FU in patients with advanced solid tumors, with dose escalation to establish the maximum tolerated dose (MTD) and an expansion at the MTD in colorectal cancer (CRC) patients. Patients (pts) must be = 18 yrs, have measurable disease, and had disease progression after standard chemotherapy. PXD101 was administered as a 30-min IV infusion on Days 1–5 of a 3-wk cycle. 5-FU was administered from cycle 2 on, as a continuous 96-hr IV infusion starting on Day 2 of the same 3-wk cycle. The primary endpoints were safety, and effect of belinostat on TS expression in patients’ tumors. Dose-limiting toxicities (DLTs) were PXD101-related = Gr 3 non-hematologic or Gr 4 hematologic toxicities. Expression of TS mRNA was measured by RTQ-PCR. Results: Twenty pts have been treated for a median of 2 cycles (range 1–8). Cohorts of 3–6 pts were tested at 5 dose levels of PXD101/5-FU (mg/m2/d): 300/250, 600/250, 1,000/250, 1,000/500, and 1,000/1,000. Two pts did not complete cycle 2, and one pt at the 600/250 dose level received 1,000 mg/m2/d 5-FU. There were no DLTs in the first 4 dose cohorts; the 5th cohort is ongoing. In the first 4 dose cohorts (17 pts), the most frequent AEs were fatigue, nausea/vomiting, dysgeusia, dehydration, constipation, edema, anorexia and anemia. There were 2 Gr 4 AEs (pulmonary embolism, bacteremia); Gr 3 AEs in = 2 pts were fatigue and dehydration. All Gr 3/4 events were assessed as not related to PXD101. One pt with stage IV CRC treated at 600/1,000 mg/m2/d PXD101/5-FU had stable disease (SD) for 8 cycles, and one pt with stage IV esophageal cancer treated at the 1,000/250 mg/m2/d dose had SD for 4 cycles. Conclusions: PXD101 in combination with 5-FU has been well tolerated up to 1,000/500 mg/m2/d PXD101/5-FU. The study is ongoing and data from the MTD expansion part, including effect of PXD101 on tumor TS expression, will be presented. No significant financial relationships to disclose.

358 Background: Effective therapy for the treatment of PDAC remains one of the greatest unmet oncology clinical needs. The addition of C to G and AP has shown promising clinical data in a previously reported study [J Clin Oncol 35, 2017 (suppl 4S; abstract 341)]. In preclinical work, vitamin D (Vit D) analog therapy decreases myeloid derived suppressor cells and regulatory T cells, turning PDAC into a more immune-friendly microenvironment. This trial combines AP/C/G with Vit D analog P and the anti-PD-1 antibody N as a combination therapy for patients with previously untreated metastatic PDAC. This trial evaluates the efficacy and safety of NAPPCG in that patient population (NCT02754726). Methods: Eligibility criteria include Stage IV PDAC, no prior chemotherapy for systemic disease, KPS ≥ 70, and measurable disease. Doses are AP 125 mg/m2 undiluted, G 1000 mg/m2 in 250 ml of normal saline (NS), each infused over 30 minutes with C 25 mg/ m2 in 500 ml of NS infused over 60 minutes on days 1, 8, 22, and 29 of a 42-day cycle. N is given at a fixed dose of 240 mg as a 60 minute infusion on days 1, 15, and 29. P is given at a fixed dose of 25 µg IV twice weekly. Primary objective is to determine the efficacy of the combination for patients with previously untreated metastatic PDAC through determining CR, ORR, PFS, and OS. The secondary objective is to evaluate safety in patients with previously untreated metastatic PDAC. Results: Trial was initiated May 2016 and10 patients have been enrolled in the initial phase of the study and are evaluable (baseline and ≥1 follow up CT scan). Most common drug-related grade (Gr) 3-4 adverse events (AE’s), n = 10, are thrombocytopenia 100% (gr 3 = 50%, gr 4 = 50%) with no serious bleeding events, anemia 50% (gr 3 = 50%, gr 4 = 0%), and colitis 20% (gr 3 = 20%, gr 4 = 0%). By RECIST 1.1 criteria, the best response is 8 PR and 2 SD, yielding an 80% ORR. Median PFS is 8.2 months. Median OS has not been reached. Conclusions: Although a small study, the high response rate is encouraging. This regimen is being expanded to 25 patients with plans to include exploratory inflammatory biomarkers. Clinical trial information: NCT02754726.