Lee, Shing Mirn

11526 Background: There are no FDA-approved treatments for advanced cCS. Chemotherapy provides limited benefit. IDH1/2 mutations (m) occur in 50% of cCS. Both IDHm and wild-type cCS harbor epigenetic dysregulation. In preclinical models, HDAC + DNMT inhibition (i) suppressed growth by inducing apoptosis, reversing the hypermethylated state, and upregulating expression of interferon (IFN) response genes including PDL1(1). This prompted a phase 2 study of HDACi + DNMTi in cCS, which failed to meet the 1° endpoint of ORR. The majority of pts had a best response of stable disease, with a trend towards improved mPFS in IDHm (2). Here we report correlative analysis of NCI 10330. Methods: NCI 10330 is a single-arm, multicenter, phase 2 study of belinostat with SGI-110 or ASTX727 in advanced cCS. All pts were required to have pre- and on-treatment (tx) biopsies (Cycle 2, Day 3-5). Tissue was evaluated with whole exome sequencing (WES) and RNA sequencing (RNAseq). From RNAseq, Tumor Inflammation Signature Scores (TISS) and Tumor Microenvironment functional Gene Set Enrichment Analysis scores (TME GSEA) were calculated as the mean of the log2 normalized counts of 18 signature genes (Danaher et al. J Imm Can 2018) and pre-defined gene sets (3), respectively. Wilcoxon rank sum test was used to analyze TME GSEA between pre- and on-tx samples. Differential expression was significant if |FC| > 1.33, adjusted P <0.01. Results: 19 pts were treated; all received paired biopsies. WES was adequate in 7/19 (37%) pts, with IDHm identified in 3/7 (43%) pts. All pts were MSI-stable, TMB: 1.01-3.57 mut/Mb. RNAseq was adequate in 7/19 (37%) pts at pre-tx and 5/19 (26%) pts at on-tx. TISS ranges trended higher for pre-tx (8.77-10.14) vs on-tx (7.36-9.51) samples. TME GSEA identified significantly enriched tumor immune infiltration (p < 0.05) in pre- vs on-tx samples. Differential analysis identified several gene sets related to inflammation overexpressed in pre-tx samples only, including IFN response. On-tx samples were enriched in myogenesis and coagulation gene sets. Conclusions: This is the first study to describe transcriptomic changes following epigenetic tx in cCS. Contradictory to our preclinical data, HDACi + DNTMi resulted in low expression of inflammation. Prior studies reported that the immune infiltrate of CS at progression is immunosuppressive; higher immune infiltrate is correlated with worse outcomes (4). Loss of inflammation may have implications for disease stability experienced by most pts on NCI 10330. Further analyses are planned to correlate TME (pro- vs anti-inflammatory infiltrates) and outcomes. Analyses are limited by small sample size, highlighting the challenges in collecting adequate CS specimens. 1. Sheikh, Schwartz et al. Mol Cancer Ther 2021. 2. Lacuna et al. ASCO 2023: #11531. 3. Bagaev et al. Can Cell 2021. 4. Richert et al. J Bone Onc 2020. Clinical trial information: NCT04340843 .

11531 Background: Conventional chondrosarcoma (cCS) is the 2nd most common primary bone tumor and is resistant to chemotherapy and radiation. IDH1/2 mutations (m) occur in 50% of cCS. Both IDHm and wild-type (wt) cCS harbor epigenetic dysregulation. In preclinical models of IDHm and wt cCS, combination treatment with HDAC and DNMT inhibitors (i) suppressed growth in vitro and in vivo by reversing the hypermethylated state and inducing tumor suppressors, interferon response genes and apoptosis (Sheikh T, Schwartz G. Mol Cancer Ther 2021;20). Methods: NCI 10330 is a single-arm, multicenter, phase 2 study evaluating the HDACi belinostat (B) with the DNMTi SGI-110 (S) or ASTX727 (A). A replaced S due to drug availability (pts were replaced). Pts had advanced cCS, ECOG PS ≤ 2 and could be treatment naïve. Progression was required for grade 1 cCS. Pts received B 1000mg/m2 IV + S 45mg/m2 SC both days 1-5 or B (same dosing) + A (cedazuridine 100mg/decitabine 35mg) PO both days 1-5, in 28-day cycles. 1° endpoint was objective response. A Simon 2-stage design was used. If ≥ 2/13 responses occurred in stage 1, the study would proceed to full accrual. Design had 85% power with α = 0.05 to test ORR 8% vs 28%. 2° endpoints included safety, PFS and OS. A safety lead-in was performed. Paired biopsies were collected. Results: Stage 1 is complete. 19 pts were treated: 6 on B+S and 13 on B+A. Median age was 50 and 67 years, respectively. All pts had prior surgery. 17% (B+S) and 38% (B+A) had prior radiation. 33% (B+S) and 55% (B+A) were IDHm. 67% (B+S) and 75% (B+A) were histologic grade ≥ 2. There were no objective responses. Best response (at 8 weeks) was stable disease (SD) in 4/6 pts (67%) on B+S and 6/10 pts (60%) on B+A. mPFS was 4.2 mos (95% CI 1.97-NR) for B+S and 3.8 mos (95% CI 2.17-NR) for B+A. mOS has not been reached. For B+A, mPFS for IDHm vs wt pts was 4.7 and 3.1 mos, respectively (p=0.21). One pt with IDHm grade 2 cCS who progressed on FT-2102 (IDH1i) remains on B+A > 1 year. There were no DLTs during either safety lead-in. Grade 3/4 treatment-related adverse events (TRAEs) occurred in 17% (B+S) and 69% (B+A). For B+A, the most common grade 3/4 TRAE was neutropenia (54%) and the most common all-grade TRAEs were nausea (69%), leukopenia (61%), neutropenia (54%), anemia (46%) and fatigue (46%). Paired tumor biopsies are being evaluated with whole exome sequencing, RNAseq, methylation array and multiplex IHC with results forthcoming. Conclusions: Combination HDACi + DNMTi was well-tolerated in advanced cCS. There were no objective responses; however, a subset of pts experienced prolonged SD with a trend towards improved mPFS in IDHm pts. Correlative work is ongoing with a focus on differential effects on IDHm tumors and whether modulation of the immune microenvironment might support combinations with immunotherapy. Support: UM1CA186689. Clinical trial information: NCT04340843 .

TPS11578 Background: Conventional chondrosarcoma (cCS) accounts for ̃25% of primary bone cancers and is the second most common primary bone tumor after osteosarcoma. Surgical resection is the primary treatment for localized disease. No FDA approved therapy exists for advanced disease and chemotherapy has marginal efficacy with ORR < 12%. IDH1/2 mutation is seen in 50% of cases. Epigenetic dysregulation is central to oncogenesis in both IDH1/2 mutant and wild-type CS. Pre-clinical studies from our group show that combination treatment with HDAC and DNMT inhibitors is significantly more effective at suppressing the growth of CS models in vitro and in vivo compared to either therapy alone. The combination regimen mediates anti-tumor effects on CS by induction of apoptosis, induction of tumor suppressor genes (eg. E-cadherin), the induction of interferon responsive genes (eg. IRF7, OASL, ISG15, DDX58) and reversal of global hypomethylated state. Based on these findings we have designed a phase 2 clinical trial with an HDAC inhibitor (belinostat) and a DNMT inhibitor (guadecitabine) in patients with advanced cCS. Methods: NCI # 10330 is a single-arm, multi-center, Simon 2-stage, phase 2 clinical trial evaluating belinostat and guadecitabine in patients with advanced cCS. Eligible patients will have biopsy proven cCS which is measurable by RECIST v1.1 and amenable to biopsy, ECOG PS ≤ 2, any number of prior treatments (including none). Patients will receive guadecitabine 45 mg/m2 SC followed by belinostat 1000 mg/m2 IV once daily on days 1-5 of a 28-day cycle. A safety lead-in and continuous toxicity monitoring rule will be applied. The primary endpoint will be ORR. Since chemotherapy is associated with an ORR of 8-12% and targeted agents have shown an ORR of 0% in cCS, we will consider an ORR of 8% as inactive while an ORR of 28% will suggest promising activity. A Simon 2-stage design is employed. The design calls for 26 patients. If ≥ 2 responses are observed among 13 patients in stage I, the study will proceed to full accrual. If ≥ 5 responses are seen among 26 patients, the study treatment is considered promising. This design has 85% power with α of 0.054 to test for a response rate of 8% vs 28%. Secondary objectives include safety, tolerability and PFS. All patients will undergo pre-treatment and on-treatment tumor biopsies. Paired tissue will be used for correlative analysis including: 1) whole exome sequencing/RNAseq to evaluate changes in gene expression in response to treatment, 2) multiplex IHC to interrogate the effect of combination therapy on tumor immune microenvironment and 3) a global DNA methylation assay to better understand the changes in epigenetic landscape in response to treatment. This study is open throughout the ETCTN (NCT04340843). Six of the planned 26 patients in the safety lead-in have been enrolled without DLT. Further accrual is on hold pending completion of the safety lead-in. Clinical trial information: 04340843.