Combination effect of inavolisib and FGFR inhibitors in FGFR2-expressing cell lines

FGFR2 controls HER3 to induce p85β binding and signaling in FGFR2 high-expressing cell lines

RNA-seq gene set enrichment analysis for siRNA KDM4 A, B, C, A-C, and non-targeting control in WiT49 cells

Data collection and refinement statistics of the dCK/UDP/EdC crystal structure.

Proposed mechanistic model of FGFR2-mediated inavolisib sensitivity

PURPOSE:PIK3CA mutations frequently drive solid tumors, particularly hormone receptor-positive breast cancer. Inavolisib, an ATP-competitive p110α inhibitor, also promotes the degradation of mutated p110α. PI3K inhibitors have generally shown modest single-agent activity and have safety concerns. PATIENTS AND METHODS:A first-in-human phase 1 study (NCT03006172) evaluated oral inavolisib in patients with PIK3CA-mutated solid tumors to determine the maximum tolerated dose and safety. Correlative analyses included ctDNA. Preclinical studies in cell lines and xenografts elucidated the role of FGFR2. RESULTS:The maximum tolerated dose was 9 mg daily, with a manageable safety profile (e.g., hyperglycemia and diarrhea). Inavolisib showed linear pharmacokinetics, consistent pharmacodynamic modulation, and antitumor activity in hormone receptor-positive PIK3CA-mutated breast cancer (26% objective response rate and 45% clinical benefit rate). FGFR2 hotspot mutations in ctDNA were strongly associated with clinical benefit. Preclinically, oncogenic FGFR2 signaling enhanced inavolisib sensitivity by engaging HER3, RAS, and p85β, that facilitated mutated p110α degradation, surpassing nondegrading inhibitors. Combination therapy with FGFR2 inhibitors showed synergy and delayed resistance. CONCLUSIONS:These findings highlight a novel cooperativity between FGFR2 and p110α that boosts the effectiveness of inavolisib. The data support advancing precision oncology beyond single biomarkers to complex algorithms utilizing co-occurring alterations, suggesting that combining inavolisib with FGFR2 inhibitors may offer enhanced and more durable responses in PIK3CA/FGFR2-altered tumors.

Mechanism of action of compounds identified in PRISM screen as top hits with similar efficacy and sensitivity profile as EdC.

Representativeness of study participants

ADME and PK properties of 1µM EdC in vitro.

Gene set enrichment analysis demonstrated significant alteration of the GO_CHROMATIN_SILENCING_AT_RDNA pathways in WiT49 and HEK293 cells treated with QC6352.

Evaluation of the anti-tumor activity of FGFR2 inhibitor in combination with inavolisib in MFM223x2.2 xenograft model

GI50 values for OSUMMER-derived cell lines in response to RMC-7977.

Additional CYPA M136R, MEK1 P124L K57N Q56P.

The 26S proteasome is an essential regulator of protein homeostasis and a clinically validated therapeutic target in multiple myeloma (MM). Rapaprotin, a novel macrocycle identified from a rapamycin-inspired rapafucin library, disrupts 26S proteasome function by inducing disassembly of the 19S regulatory particle in the 26S proteasome, leading to apoptosis in MM cells. Its bioactivation requires prolyl endopeptidase (PREP)-mediated cleavage to generate Rapaprotin-L, a negatively charged, linear metabolite with potent proteasome-disassembly activity. Using the PRISM cancer cell line profiling platform, we identified high P-glycoprotein (P-gp/ABCB1) expression as a major determinant of Rapaprotin resistance in solid tumor cell lines. Efflux assays confirmed Rapaprotin-L, but not its parent Rapaprotin, as a high-efficiency P-gp substrate. Co-treatment with the third-generation P-gp inhibitor tariquidar restored the intracellular accumulation of Rapaprotin-L, reinstating proteasome inhibition and consequent apoptosis in Rapaprotin-resistant colorectal cancer cell lines. Strong synergy between Rapaprotin and tariquidar was observed in a 3D spheroid model. These results establish P-gp as a key mediator of resistance to Rapaprotin and identify a rare example of a negatively charged Rapaprotin-L as a P-gp substrate. Together, these findings expand the potential therapeutic scope of Rapaprotin beyond hematologic malignancies to a broader range of solid tumors.

Abstract Cancer cells are dependent on the control of transcription for maintenance of the malignant cell state. EP300 and CBP are paralogous, commonly expressed, master epigenetic enzymes, whose activity controls normal and malignant transcription. Here, using a cancer-wide integrative chemical-genetic analysis, we find enhanced dependency on EP300 compared to CBP in most cancer lineages, including osteosarcoma (OS). OS is a highly lethal malignancy of bone and has enhanced dependency on EP300, compared with CBP. To take advantage of selective pharmacology targeting EP300 alone that spares CBP in untransformed cells and thereby reduces toxicity, we used the EP300-targeted degrader JQAD1. We identify a specific genetic subgroup of OS, marked by dysregulation of the PI3K-AKT-mTOR pathway, that is both genetically dependent on EP300 and uniquely sensitive to EP300 degradation. Expression of constitutively active AKT in insensitive OS cells induces sensitivity to JQAD1, driven by physical relocalization of EP300, CBP and H3K27ac to genetic subtype-enriched dependency loci. Mechanistically, combinations of AKT inhibitors and JQAD1 suppress the growth of AKT-dysregulated OS. These observations extend across >850 cancer cell lines, where multiple AKT inhibitors, including the FDA-approved capivasertib, positively combine with EP300 degraders in a manner mechanistically dependent on control of protein synthesis. Finally, combination treatment is synergistic in AKT-dysregulated, orthotopic OS xenografts. These findings reveal genetic and transcriptional determinants of EP300 degrader function in high-risk OS and provide a foundation for biomarker-directed investigation of co-targeting of EP300 and AKT for therapeutic gain across cancers marked by enhanced protein translation. Citation Format: Ian Delahunty, Stephanie Nance, Yang Zhang, Francois Lamoureux, Qi Liu, W. Charlie Wright, K. Elaine Ritter, Noha A. Shendy, Benedicte Brounais, Sandra Kietlinska, Barbara De Kegel, Matthew G. Rees, Mustafa Kocak, Ashish B. George, Anoop M. Kavirayani, Paris P. Prinsen, Yousef Khashana, Melissa M. Ronan, Jennifer Roth, Alejandro Sweet-Cordero, Xiaotu Ma, Lillian M. Guenther, Paul Geeleher, Benjamin Ory, Jun Qi, Brian Abraham, Adam D. Durbin. Dysregulated AKT signaling reprograms osteosarcoma to drive selective reliance on EP300 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 4024.

Individual blood concentrations (ng/mL) and pharmacokinetic parameters for EdC after IP injection.

Supplementary Figure 7. Gastroesophageal cancers are enriched in KRAS wild-typeWT amplified tumors. Gastroesophageal cancers (n=3464) were selected from the AACR Genie MSK and DFCI cohort (version v16.0-public). Only patients with any alterations in the above listed genes are shown (1498 unaltered patients are not shown). Co-alterations are ranked by frequency. KRAS amplified samples are defined with a GISTIC score of 2 according to AACR GENIE as exact copy number thresholds are not available from the AACR GENIE cohort.

Additional EdC metabolism data.

Schematic of GEMM alleles and Cre initiation schedules, IHC, and immunoblotting on GEMM tumors.

Abstract Acute myeloid leukemia or AML encompasses diverse molecular subtypes driven by distinct transcriptional and genetic programs that influence therapeutic response. AOH1996 which is a PCNA-dependent replication stress pathway inhibitor has demonstrated preclinical activity in AML. However biomarkers that may predict sensitivity across heterogeneous AML subgroups remain undefined. We first applied integrative multiomic analysis to begin defining the molecular contexts in which AOH1996 may be most effective. Transcriptomic, genomic, and proteomic datasets from PRISM, DepMap, and other curated subtype annotations were integrated with AOH1996 response metrics also known as AUC. Initial analyses focused on quantitative assessment of MYC RNA expression relative to AOH1996 sensitivity using a quadrant based visualization framework, and ongoing multi-omic analyses incorporating mutational backgrounds. Pathway activity scores, and protein level features are being used to explore broader biomarker patterns across AML models. Guided by these computational findings we are developing complementary in vitro studies in a panel of molecularly annotated AML models to functionally probe AOH1996 response, with planned readouts broadly focused on cell growth, cell cycle behavior, and stress associated phenotypes consistent with replication stress and innate immune pathway engagement. Preliminary computational results reveal subtype dependent variation in the relationship between MYC expression and AOH1996 response which aligns with MYC’s established role in driving transcriptional load and replication stress and nominating MYC expression as a biologically plausible candidate biomarker. Together, this integrated multiomics and emerging experimental framework supports the feasibility of biomarker-guided evaluation of AOH1996 across AML subtypes and provides a foundation for future translational studies aimed at molecularly informed therapeutic stratification. Citation Format: Hamsini Kala, Dana Abou Abbas, Robert J. Hickey, Linda H. Malkas, Caroline M. Li, Robert G. Lingeman, Guido Marcucci, Le Xuan Truong Nguyen, Brian Ball, Amanda Blackmon, Melissa Ronan, Jennifer Roth, Matthew G. Rees. Integrative multiomics and functional studies to identify biomarkers of AOH1996 sensitivity across AML subtypes [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 3749.