Solanki, M. H.

Abstract Background: Fatty Acid Synthase (FASN) is a key lipogenic enzyme co-regulated with HER2 and highly expressed in ER+ and HER2+ BC. Its targeting downregulates HER2 expression. Our preclinical studies revealed that FASN inhibition can sensitize or restore sensitivity to trastuzumab, paclitaxel and ET in HER2+ BC models. Denifanstat (deni, formerly TVB-2640) is a novel FASN inhibitor that demonstrated promising clinical activity and safety in a prior phase I trial as either monotherapy or in combination with paclitaxel. The primary objective of this study was to evaluate the objective tumor response rate (ORR) of deni plus trastuzumab (H) in combination with paclitaxel (T) or ET. Methods: Two independent, phase II clinical trials were initiated to assess the efficacy and safety of deni plus H in combination with T (Cohort A) or ET (Cohort B). Key inclusion criteria included HER2+ MBC resistant to HER2-directed therapy, measurable disease, unlimited ET, ≤6 prior chemotherapy or antibody drug conjugate regimens, and confirmation of HER2+ MBC on a pre-registration biopsy. Deni was administered 100 mg/m2 orally once daily. HP or H plus ET (fulvestrant or aromatase inhibitor) was administered at standard dose and schedule. Blood was collected on Cycle 1 Day 1 (C1D1), C1D8 and C2D1 for serum FASN analysis. An additional MBC tumor biopsy was collected on C2D1 for correlative studies. A 2-stage Simon design with a safety-run in was used to test the null hypothesis that the true ORR is at most 5% against the alternative it is at least 20%. With a sample size of 32 patients (pts) per cohort, if ≥4 responses are seen, this design has a 90% chance of rejecting the true ORR is <5% when the true ORR is ≥20% at a 0.10 level of significance. The decision to close both trials to enrollment early was multifactorial. Results: From August 2017 - February 2024, 33 pts with HER2+ MBC pre-registered, among which 17 were eligible and 16 were evaluable (15 pts in Cohort A and 1 pt in Cohort B). The most common reason for ineligibility was HER2-negative status on central review of the pre-registration biopsy. Median age was 57 years (range 35-80). All pts were non-Hispanic and 13 (81.3%) were White. Median prior lines of therapy was 5 (range 0 - 11). In Cohort A, there were 5 partial responses; thus, the primary endpoint was met with the ORR estimated to be 33.3% (90% CI: 14.2-57.7%). The median PFS time was 7.0 months (95 %CI: 3.7 - 11.3), and median OS was 25.7 months (95%CI: 10.2 - NE). No dose limiting toxicities were observed during the C1 safety run-in (6 pts). In Cohort A, 7 (46.7%) developed a grade 3 or 4 adverse event (AE) attributed to combination therapy. Grade ≥2 AEs regardless of attribution occurring in ≥20% of all pts included anemia, fatigue, neutropenia, palmar plantar erythrodysesthesia (PPE), and peripheral neuropathy. Treatment was discontinued due to progression (12; 80%) or AE (3; 20% - pneumonitis; neuropathy; PPE). In Cohort B, the pt maintained stable disease through 8 cycles with grade 3 ALT increase, and she remained alive 31.2 months post-registration. Median C1D1 FASN level was 32.7 ng/mL (IQR: 18.7 - 49.6 ng/mL). There was minimal association between C1D8 and C2D1 FASN levels and time to disease progression (C1D8 n=9, Spearman rank correlation coefficient (r s) = 0.040; C2D1 n=13, r s = -0.019). Analyses of changes in MBC tumor expression of FASN, phospho-AKT, and phospho-S6 are in progress. Conclusion: Deni combined with HP provided clinical antitumor activity in pts with HER2+ MBC resistant to trastuzumab. Expected paclitaxel-associated AEs were observed. Nearly half of pts experienced a grade 3 or 4 AE attributed to the combination therapy, and 20% stopped treatment due to AE. Further study of deni, H plus ET is necessary to draw safety and efficacy conclusions. Citation Format: T. C. Haddad, V. J. Suman, R. R. Roa, B. J. Ernst, R. Lupu, T. Vander Steen, M. H. Solanki, M. Keeney, D. W. Northfelt, K. S. Anderson, T. J. Hobday, S. Chumsri, J. E. Hoppenworth, J. L. Carroll, K. V. Giridhar, C. C. O’Sullivan, R. A. Leon-Ferre, M. P. Goetz. Phase II Trial of the FASN Inhibitor, Denifanstat (TVB-2640), Plus Trastuzumab in Combination with Paclitaxel or Endocrine Therapy (ET) in Patients with HER2+ Metastatic Breast Cancer (MBC) Resistant to Trastuzumab [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS5-01-16.

Abstract Uptake of tamoxifen is limited to 5-15% of all eligible women due to concerns regarding medication side effects combined with the lack of ability to predict which women will benefit from the therapies. We used a unique retrospective sample of n=92 high-risk women with paired benign biopsies obtained before (PreTam) and during tamoxifen (OnTam) to discover tissue gene expression biomarkers of biologic response, defined as change (Δ) in lobular Ki67. Ki67 was digitally quantified in normal lobules from PreTam and OnTam benign tissue samples and samples with PreTam Ki67 = 0 were excluded. Data were analyzed from 51 women with both PreTam and OnTam Ki67 (median age = 49 years and median BMI = 25.5 kg/m2 at PreTam biopsy). OnTam biopsies were collected a median of 11.5 months after PreTam biopsy (median 6.5 months after starting tamoxifen; dose 20 mg/day in 86%). Median Ki67 significantly decreased overall (Δ Ki67 = -0.29%, p=0.003), but the effect was restricted to women with baseline Ki67 ≥ 0.5% (n=38, Δ Ki67 = -0.78%, p=0.0002); no significant change occurred with baseline Ki67 < 0.5 (Δ Ki67 = 0.19%, p=0.23). Δ Ki67 was inversely proportional to baseline Ki67. RNA-seq was successful for 171 benign tissue samples (including 53 PreTam-OnTam pairs). After edgeR normalization (>14,600 genes), PreTam vs OnTam comparison across 33 pairs with baseline Ki67 ≥ 0.5% yielded 66 differentially expressed genes (fold-change > 2 and p<0.01). At p<0.01, ranked gene set enrichment analysis revealed 27 gene sets enriched for reduced expression with Tam (with top-ranked gene set related to steroid hormone biosynthesis) and 59 gene sets enriched for increased expression with Tam (with top-ranking gene sets related to B cell and T cell receptor signaling, regulation of cell cycle, and other immune-related pathways). To identify predictors of response, we correlated baseline PreTam gene expression with Δ Ki67 in 37 women with available baseline PreTam RNAseq and Δ Ki67 data. Partial correlation analysis (via ‘ppcor’ package, adjusted for library qubit) revealed 73 genes with significant positive correlation (rho > 0.50) and 14 genes with significant negative correlation (rho < -0.50) with Δ Ki67 (p<0.01). At p<0.01, ranked gene set enrichment analysis yielded 67 gene sets enriched with negative correlation (i.e. increased expression associated with a reduction in Ki67), including pathways related to ribosome biogenesis, DNA recombination, and nucleic acid metabolic processes; there were 62 gene sets enriched for positive correlation (i.e. decreased expression associated with a reduction in Ki67), including pathways such as VEGF and ERBB signaling. Our data support (i) baseline Ki67 ≥ 0.5 % and (ii) an 87-gene baseline signature as complementary biomarkers of tamoxifen response. Prospective validation of this combined assay could target tamoxifen to the women most likely to benefit, potentially overcoming a major barrier to chemoprevention uptake. Citation Format: S. J. Winham, C. Wang, Y. Liu, B. M. McCauley, D. J. Tabrizi, D. L. Gehling, J. L. Fischer, L. R. Seymour, M. H. Solanki, M. E. Sherman, K. R. Lohani, T. L. Hoskin, D. C. Radisky, A. C. Degnim. Gene expression signatures of beneficial response to tamoxifen for breast cancer prevention [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS3-01-18.