Metastatic castration-resistant prostate cancer (mCRPC) is a uniformly fatal disease which has displayed resistance to many single-agent therapies, underscoring the need for novel combination therapies. Histone acetyltransferases CBP/p300, which act as androgen receptor (AR) coactivators, are often upregulated in mCRPC. Elevated CBP/p300 levels correlate with reduced overall and progression-free survival in prostate cancer patients. Our recent work has demonstrated that CBP/p300 have important roles in regulating DNA repair, particularly homologous recombination, and that inhibition of CBP/p300 may sensitize mCRPC to existing therapeutics. A Phase 1/2a study investigating a CBP/p300 inhibitor, CCS1477, alone and in combination regimens is currently underway. However, research into CCS1477 combination treatments is highly limited, necessitating further investigation into combination therapies and markers of sensitivity to improve outcomes for mCRPC patients. We hypothesized that combination treatment using CBP/p300 inhibitors (CBP/p300i) with PARP inhibitors (PARPi) would enhance anticancer effects by synergistically impairing DNA damage repair in cancer cells. Using preclinical 2D and 3D models, including patient-derived explants, we evaluated the mechanistic and functional impacts of targeting CBP/p300 and PARP pathways in combination. We found that this combination therapy was significantly more effective than either monotherapy at reducing cell growth both in vitro and ex vivo. Importantly, a comprehensive screen with clinically relevant PARPi revealed that combination of CBP/300 and PARP inhibition demonstrate synergy across several PCa cell lines. In mechanistic studies, increased expression of DNA damage markers in mCRPC cells treated with CCS1477 alongside a PARPi (olaparib) indicated delayed DNA damage repair. Cell cycle analysis revealed G1 arrest induced by combination treatment and an increase in cell size consistent with this finding. To assess the utility of CBP/p300 and PARP combination therapy in patients, we treated PCa tissues from a racially diverse cohort with CBP/p300i and PARPi. Ki67 staining revealed decreased proliferation in combination therapy-treated tissue, supporting the findings from 2D models. Spatial transcriptomics will identify molecular signatures distinguishing responders from non-responders, advancing precision medicine in diverse populations. Our findings indicate that CBP/p300 inhibition in combination with PARPi may have stronger anti-tumor effects than single-agent therapies, offering a promising novel therapeutic option to improve outcomes for mCRPC patients. Orly I. Richter, Sumaira Sardar, Xiaohu Zhang, Jessica D. Kindrick, Lakshmi Ravindranath, Cindy H. Chau, Craig J. Thomas, Christopher McNair, Xiaofeng A. Su, Adam Sharp, Johann de Bono, Kris Frese, William D. Figg, Karen Knudsen, Ayesha A. Shafi. Combining CBP/p300 and PARP inhibitors to enhance anti-tumor efficacy in lethal prostate cancer [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Innovations in Prostate Cancer Research and Treatment; 2026 Jan 20-22; Philadelphia PA. Philadelphia (PA): AACR; Cancer Res 2026;86(2_Suppl):Abstract nr PR019.

Histone modifications, including Nε-lysine acetylation and methylation, play critical roles in the regulation of eukaryotic transcription. The addition of acetyl and methyl groups and removal of acetyl groups to histones involve redox-neutral reactions. Demethylation is O2-dependent, as reported for reactions catalysed by the 2-oxoglutarate-dependent hypoxia-inducible factor (HIF) hydroxylases, one of which is structurally related to the Jumonji-C (JmjC) histone demethylases. We screened for substrates of the HIF-regulated JmjC lysine demethylase KDM3A and unexpectedly observed that purified recombinant KDM3A catalyses oxidation of the Nε-acetyl group of the Lys-9 of histone H3 (H3K9ac) giving an Nε-hydroxyacetylated product (H3K9acOH). Here we show that Nε-hydroxyacetyl-lysine is recognized by proteins known to bind to H3K9ac, including histone deacetylases and the YEATS domain-containing AF9. Studies employing an Nε-hydroxyacetyl-lysine selective antibody and mass spectrometry support the cellular relevance of Nε-hydroxyacetyl-lysine. Our combined biochemical and cellular results provide evidence for an unanticipated O2-mediated link between histone lysine Nε-acetylation and JmjC catalysis.

Abstract Metastatic castration-resistant prostate cancer (mCRPC) is a uniformly fatal disease which has displayed resistance to many single-agent therapies, underscoring the need for novel combination therapies. Histone acetyltransferases CBP/p300, which act as androgen receptor (AR) coactivators, are often upregulated in mCRPC. Elevated CBP/p300 levels are associated with reduced progression-free and overall survival in prostate cancer patients. Our recent work has demonstrated that CBP/p300 play important roles in regulating DNA repair, particularly homologous recombination, and that inhibition of CBP/p300 may sensitize mCRPC to existing therapeutics. A Phase 1/2a study investigating a CBP/p300 inhibitor, CCS1477, alone and in combination regimens is currently underway. However, research into CCS1477 combination treatments is highly limited, necessitating further investigation into combination therapies and markers of sensitivity to improve outcomes for mCRPC patients. We hypothesized that combination treatment using CBP/p300 inhibitors (CBP/p300i) with PARP inhibitors (PARPi) would enhance anticancer effects by synergistically impairing DNA damage repair in cancer cells. Using preclinical 2D and 3D models, including patient-derived explants, we evaluated the functional impacts of targeting CBP/p300 and PARP pathways in combination. We found that this combination therapy was significantly more effective than either monotherapy at reducing cell growth both in vitro and ex vivo. Importantly, a comprehensive screen with clinically relevant PARPi revealed that combination of CBP/300 and PARP inhibition demonstrate synergy across several PCa cell lines. To assess the utility of CBP/p300 and PARP combination therapy in patients, we treated PCa patient-derived explants (PDEs) from a racially diverse cohort with CBP/p300i and PARPi. Ki67 staining revealed decreased proliferation in combination therapy-treated tissue, supporting the findings from 2D models. To investigate genomic alterations that may underlie differential treatment responses, we performed whole-exome sequencing (WES) on tissues from our PDE cohort. This analysis identified distinct germline and somatic variants that segregated with treatment responders versus non-responders. Spatial transcriptomics will identify molecular signatures distinguishing responders from non-responders, advancing precision medicine in diverse populations. Our findings indicate that CBP/p300 inhibition in combination with PARPi may have stronger anti-tumor effects than single-agent therapies. Analysis of patient-derived models provides insight into the patient subsets most likely to benefit from this combination therapy, supporting its potential as a novel therapeutic approach to improve outcomes for mCRPC patients. Citation Format: Orly I. Richter, Sumaira Sardar, Xiaohu Zhang, Jessica D. Kindrick, Lakshmi Ravindranath, Cindy H. Chau, Craig J. Thomas, Christopher McNair, Xiaofeng A. Su, Adam Sharp, Johann de Bono, Kris Frese, William D. Figg, Karen E. Knudsen, Ayesha A. Shafi. CBP/p300 and PARP inhibitor combination treatment synergistically enhances anti-tumor efficacy in models of advanced prostate cancer [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 4047.

Metastatic castration-resistant prostate cancer (mCRPC) exhibits high mortality due to the emergence of therapy resistance phenotypes. We recently tested a novel combination therapy in patients with mCRPC who had progressed on androgen receptor (AR)-targeted therapies, targeting PD-L1 and PARP1 with durvalumab and olaparib, respectively. While a subset of patients exhibited partial responses, most patients experienced disease progression within a year. The goal of the current study is to perform comprehensive profiling of circulating tumor DNA (ctDNA) and buffy coat to assess the molecular characteristics of progressive vs. responsive prostate tumors. We obtained plasma cell-free DNA (cfDNA), a mixture of ctDNA and other tissue-derived DNA, from 38 individuals treated with the PD-L1/PARP1-targeted combination therapy (NCT02484404) at baseline, after two months of treatment, and upon disease progression. Whole-genome sequencing (WGS, median coverage: 139×) was performed using cfDNA and buffy coat DNA as germline control. Germline and somatic mutations including small mutations and structural rearrangements were individually curated to determine cfDNA tumor fraction. To infer epigenetic regulation, whole-genome 5-hydroxymethylcytosine and 5-methylcytosine (5hmC and 5mC, respectively) sequencing was performed using the Biomodal evoC platform. T/B cell receptor repertoire was inferred from buffy coat sequencing using MiXCR. A negative association between baseline cfDNA tumor fraction and progression-free survival (PFS) was observed. BRCA2 alterations were associated with durable responses, whereas oncogenic mutations in TP53 and MAPK signaling pathway were associated with intrinsic resistance or rapid progression. Using cfDNA methylation sequencing, we identified disease-specific AR signaling genes depleted for promoter/early intronic 5mCs and enriched for 5hmCs in ctDNA-positive plasma. Similarly, AR-associated transcription factor binding sites were depleted for 5mCs and enriched for 5hmCs. Given the association between 5mC depletion and gene expression from matched tissues, we inferred gene expression and evaluated genes that correlate with drug response. Longer PFS was associated with greater activities of interferon signaling and inflammation at baseline, consistent with greater diversity of inferred T cell clonotypes. Comparing pre- and post-treatment plasma samples, distinct genetic programs were identified from patients with longer vs shorter PFS, suggesting different mechanisms of adaptive vs intrinsic treatment resistance. Baseline genomic deficiencies associated with DNA damage repair were differentially correlated with PD-L1/PARP1-targeted therapy response. Epigenetic alterations associated with inflammatory genes and baseline T lymphocyte clonal complexity inform better therapy outcomes. Time-course evaluation of global patterns of 5hmCs and 5mCs identified distinct epigenetic mechanisms associated with therapy response or failure. Chennan Li, Anna Baj, Clara C. Y. Seo, Nicholas T. Terrigino, John B. Bright, S. Thomas Hennigan, Isaiah M. King, Scott Wilkinson, Shana Y. Trostel, William D. Figg, William L. Dahut, Jung-Min Lee, David Y. Takeda, Fatima Karzai, Adam G. Sowalsky. Mechanisms of resistance to PD-L1/PARP1-targeted therapy in metastatic castration-resistant prostate cancer inferred by liquid biopsy [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Innovations in Prostate Cancer Research and Treatment; 2026 Jan 20-22; Philadelphia PA. Philadelphia (PA): AACR; Cancer Res 2026;86(2_Suppl):Abstract nr A038.

Metastatic castration-resistant prostate cancer (mCRPC) remains lethal as adaptive resistance to standard-of-care therapy develops, often driven by AR splice variants alongside transcriptional and translational reprogramming. To identify strategies capable of overcoming these mechanisms, we performed an unbiased high-throughput screen of 2,480 mechanistically annotated compounds across advanced prostate cancer models. Exportin-1 (XPO1)-mediated nuclear export emerged as a critical dependency, and matrix-based combination screening uncovered robust synergy between inhibitors of XPO1 and the translation initiation factor EIF4A1. Dual inhibition induced coordinated disruption of oncogenic protein networks, including AR/AR-V7, triggering apoptosis and suppressing cell-cycle and metabolic programs. These effects extended to genetically diverse patient-derived organoids and in vivo xenografts at low doses, approximately 8-fold (Eltanexor) and 12-fold (Zotatifin) below established human single-agent regimens. Together, these findings reveal concurrent control of nuclear export and protein translation as a therapeutic vulnerability in mCRPC, providing a strong rationale for clinical evaluation of XPO1-EIF4A1 co-inhibition to overcome AR-driven resistance.

BACKGROUND:Poly(ADP-ribose) polymerase (PARP) inhibition (PARPi) is a precision medicine strategy in advanced prostate cancer, with the greatest benefit seen in a subset of patients with homologous recombination repair (HRR) gene alterations. Combination approaches may expand activity beyond HRR-altered disease. We conducted a phase 2 study of the PARP inhibitor olaparib in combination with the anti-PD-L1 antibody durvalumab in an HRR-unselected population of men with metastatic castration-resistant prostate cancer (mCRPC). METHODS:This is a single-arm, open-label phase 2 trial of olaparib plus durvalumab in men with mCRPC previously treated with abiraterone and/or enzalutamide. Pretreatment biopsies of metastatic lesions were attempted for tumor sequencing. Peripheral blood was collected longitudinally for immune profiling of cell subsets and soluble factors, circulating tumor DNA (ctDNA) analyses, and peripheral blood mononuclear cell (PBMC) gene expression profiling. RESULTS:61 patients were enrolled; 60 were evaluable. Median age was 65 years (45-88). Median radiographic progression-free survival (rPFS) was 5.0 months (95% CI 4.6 to 7.6) and median overall survival (OS) was 19.1 months (95% CI 15.0 to 29.3 months). 10 patients achieved partial responses, and 17 (28%) had ≥50% prostate-specific antigen declines. Patients with BRCA2 variants experienced longer rPFS (13.2 months; 95% CI 7.7 to 20.2 months) than patients without BRCA2 variants (4.8 months; 95% CI 4.5 to 6.4 months, p=0.0026). Baseline ctDNA fraction was higher in patients with radiographic progression than in those with partial response (p=0.022) and inversely correlated with time-to-progression (ρ=-0.51). Treatment- induced early peripheral immune perturbations included transient inflammatory cytokine increases and expansion of activated/proliferating T cells with concurrent regulatory features. Exploratory PBMC profiling identified IL1R2 as a response-associated transcript, and lower IL1R2 expression was associated with longer OS. CONCLUSIONS:Olaparib plus durvalumab demonstrated modest activity in HRR-unselected mCRPC, with clinical benefit enriched in BRCA2-variant disease. Integrated ctDNA and peripheral immune analyses support ongoing efforts to refine molecular and immune selection strategies and to better define mechanisms of benefit and resistance for combination approaches in mCRPC. TRIAL REGISTRATION NUMBER:NCT02484404.

While pharmacogenetic testing has traditionally relied on array-based genotyping platforms, these methods are limited by incomplete variant coverage and inability to detect novel alleles. We hypothesize that the performance of genome sequencing (GS) is superior to that of an array-based genotyping method for gene-drug pairs that are clinically implemented at the NIH Clinical Center. DNA was collected from a cohort of 293 patients from a single-center prospective cohort study at the National Institutes of Health, Bethesda, MD. Post hoc analysis was conducted in probands with genetically inferred ancestry: European, African, African American, and Asian. The primary endpoint was to determine concordance between GS, exome sequencing (ES), and a commercial genotyping array while assessing accuracy of non-concordant alleles using orthogonal sequencing. In a cohort of 293 individuals genotyped with a commonly used array, GS (n = 120) and/or ES (n = 185) was conducted. GS demonstrated superior accuracy, resolving unknown or ambiguous array-based allele calls in 5% of cases, ultimately achieving 99% baseline accuracy. Moreover, we confirmed discordances between array-based calls and GS in favor of GS through validation by orthogonal sequencing methods such as long-read sequencing. We highlight clinically significant inaccuracies that include critical variants missed by arrays and ES. From a cost perspective, GS proved comparable or superior to array-based methods, with significantly greater clinical applicability and flexibility. Our findings underscore the feasibility and superiority of integrating GS-based pharmacogenetics testing into clinical settings, demonstrating robust analytical performance, improved patient management potential, and a pathway toward broader, lifetime utility of genomic data.

Prostate cancer remains a major therapeutic challenge, as resistance to androgen deprivation therapy (ADT) frequently develops and leads to castration-resistant prostate cancer (CRPC). This transition is driven in part by metabolic reprogramming that sustains growth under androgen suppression. While the classical Warburg model emphasizes increased glycolysis and reduced oxidative phosphorylation (OXPHOS), emerging evidence indicates that advanced prostate cancers can exhibit both elevated glycolytic and mitochondrial activity, underscoring metabolic flexibility as a hallmark of resistance. However, the influence of androgen sensitivity on these metabolic pathways remains poorly understood. To address this, we characterized the metabolic features of the paired androgen-sensitive (VCaP) and castration-resistant (VCaP-CR) prostate cancer cell models. Extracellular flux analysis revealed that VCaP cells had higher basal glycolytic and respiratory activity, whereas VCaP-CR cells displayed greater spare respiratory capacity, suggesting enhanced mitochondrial adaptability. These findings highlight that CRPC cells rely more heavily on mitochondrial plasticity to sustain energy production. Utilizing a publicly available transcriptomic dataset, we performed gene set enrichment analysis and found VCaP-CR cells exhibit increased expression of genes involved in glucose uptake and glycolysis. Given these metabolic vulnerabilities, we performed a high-throughput combination screen in two CRPC models to identify agents that synergize with either glucose uptake or mitochondrial complex I inhibition. Using the GLUT1 inhibitor BAY-876 and the complex I inhibitor IACS-010759 as anchor compounds, we combined each inhibitor with a panel of 40 prostate cancer-relevant compounds. Notably, the most striking synergy emerged from the dual combination of BAY-876 and IACS-010759 themselves. Combined treatment rapidly depleted mitochondrial membrane potential and induced apoptosis in both models, revealing co-dependence on glycolytic and oxidative metabolism. To assess nutrient utilization, we quantified glutamine consumption and glutamate secretion under basal and drug-treated conditions. VCaP-CR cells exhibited increased glutamine consumption under dual drug treatment, while VCaP cells secreted more glutamate, suggesting divergent routes of glutamine metabolism. Furthermore, combined inhibition suppressed the lactate accumulation typically observed with complex I inhibitors, indicating that glucose uptake blockade is capable of preventing compensatory glycolysis. These results demonstrate that metabolic adaptation accompanying androgen independence creates a therapeutic vulnerability that can be exploited through dual targeting of glucose and mitochondrial metabolism. Together, these findings provide a mechanistic rationale for combined GLUT1 and complex I inhibition as a strategy to overcome metabolic resilience in CRPC. Spencer S. Gaut, Giulia C. Napoli, Jessica D. Kindrick, Cindy H. Chau, Choh Yeung, Christine M. Heske, Craig J. Thomas, William D. Figg. Dual inhibition of mitochondrial complex I and GLUT-1 exerts a synergistic effect in advanced prostate cancer models [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Innovations in Prostate Cancer Research and Treatment; 2026 Jan 20-22; Philadelphia PA. Philadelphia (PA): AACR; Cancer Res 2026;86(2_Suppl):Abstract nr B026.

MYC overexpression, often associated with chromosome 8q24 amplification, is a well identified genetic alteration in aggressive prostate cancer, especially in metastatic castration-resistant prostate cancer (mCRPC). It has been reported that MYC amplification counteracts with androgen receptor (AR) signaling, which has significant impacts on androgen deprivation therapy efficacy. In this study, we developed a prostate cancer mouse model in which MYC overexpression is initially induced by AR but AR-independent during tumorigenesis and progression. We employed the Multiome technology integrating single-cell RNA-sequencing (scRNA-seq) and ATAC-sequencing (scATAC-seq) to profile late-stage MYC-driven non-metastatic and metastatic prostate cancers. Consistent with previous studies using AR-dependent MYC-driven models, we identified that primary tumors are composed of a large quantity of luminal cells. We have also observed a higher proportion of luminal cells in the tumors that developed metastasis, while localized primary tumors were more abundant in basal cells, and transitional cell types. Interestingly, we uncovered heterogeneous transitional populations featured by different cell cycle profiles and cell-type gene signatures. With gene set enrichment analysis (GSEA), we identified differential enrichment of inflammatory pathways in luminal cells in metastatic primary tumors relative to localized primary tumors. By integrating with scATAC-seq analysis, we also identified new differential transcriptional and epigenetic regulators that may drive the aggressiveness of these MYC-driven cancers in a tissue specific manner. In addition, we applied inferred copy number variation (CNV) analysis and showed that aggressive tumors and metastasis harbor higher levels of CNVs. Together, these findings reveal how MYC overexpression reshapes prostate epithelial lineage, chromatin landscape and genomic instability to promote AR-independent aggressiveness, providing mechanistic insights and a foundation for future therapeutic targeting of MYC-driven malignancies. Kathryn Echandía-Monroe, Sofia Hu, Daniel R. Schmidt, Kun-Lin Ho, Duanduan Ma, Elise G. DeArment, Faith Kim, Chloe Springer, Savannah Washburn, Madeline M. Wong, Kate Lu, Marianna Trakala, William D. Figg, Matthew G. Vander Heiden, Xiaofeng A. Su. Multiomic single-cell profiling of a novel MYC-driven mouse prostate cancer model [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Innovations in Prostate Cancer Research and Treatment; 2026 Jan 20-22; Philadelphia PA. Philadelphia (PA): AACR; Cancer Res 2026;86(2_Suppl):Abstract nr B017.

OBJECTIVE:Ghrelin and liver-expressed antimicrobial peptide 2 (LEAP2) act via the growth hormone secretagogue receptor (GHSR), which modulates feeding, alcohol use, and endocrine and immune system function. The GHSR blocker PF-5190457 has potential as a novel pharmacotherapy for alcohol use disorder (AUD). This study aimed to characterize the effects of PF-5190457 on endocrine and immune markers in individuals with AUD. METHODS:Pre-planned analyses used data from a randomized, double-blind, placebo-controlled, crossover human laboratory study in recently abstinent inpatients with AUD (N = 29; 8 females). Participants received PF-5190457 (100 mg twice daily) or matched placebo for 5+ days, separated by 2+ washout days. Blood was collected daily prior to dosing (T1). On days 4+, behavioral testing occurred post-dosing, followed by an additional blood collection ~2 hours post dosing (T2). Pharmacokinetic (PK: PF-5190457 and its active metabolite PF-6870961) and pharmacodynamic (PD: comprehensive panel of endocrine and immune markers) parameters were assessed over the course of dosing days. Additional exploratory analyses examined relationships between PK, PD, and behavioral measures. RESULTS:PF-5190457 and PF-6870961 concentrations peaked at T2 and were elevated at T1 under drug vs placebo. LEAP2 levels were reduced under drug vs placebo but rebounded on the first washout day. PF-5190457 dramatically reduced growth hormone (GH) at T2, followed by an elevation of GH at T1 the following day. No other endocrine or immune markers differed significantly between drug and placebo. GH at T1 negatively correlated with the number of calories selected during a cafeteria-like virtual reality buffet experiment under drug, but not placebo conditions. CONCLUSIONS:GHSR blockade with repeated dosing of PF-5190457 changed LEAP2 and GH concentrations but produced overall negligible effects on the endocrine and immune systems. These results further characterize the ghrelin system in AUD and its potential as a therapeutic target. TRIAL REGISTRATION:ClinicalTrials.gov Identifier: NCT02707055; registered November 3, 2016.

Abstract Background: Currently, intravenous atezolizumab has 3 FDA-approved dosing regimens; 840 mg every 2 weeks or 1,200 mg every 3 weeks or 1,680 mg every 4 weeks which yield steady-state concentrations > 10-fold above the stated minimum effective concentration (MEC) of 6 µg/mL, to ensure adequate exposure for all patients, including patients that may experience lower exposure due to the incidence of anti-drug-antibodies (ADA). Atezolizumab exhibits a flat exposure-response relationship. Exposure-safety analysis showed a trend of a slight increase in adverse events of special interest (AESIs) with increasing exposure. To test the feasibility of reducing drug exposure while maintaining plasma drug concentration at or above MEC, a clinical study was developed. Methods: This is an open-label, single-arm, Phase 1 feasibility study of a therapeutic drug monitoring (TDM)-based method for atezolizumab dosing (NCT06066138). The study will enroll up to 20 evaluable participants with an accrual ceiling of 30. Treatment Plan The participants will start with one of the FDA-approved Atezolizumab dosing for Cycle 1 (C1) and C2. A trough level will be checked on C2D1 using a validated immunoassay and incorporated into a validated population pharmacokinetics (PK) simulation model replicated from a model described in the FDA Center for Drug Evaluation and Research (CDER) review for the NSCLC indication via NONMEM v7.6. Covariate variables (sex, weight, albumin, tumor burden, presence of anti-drug antibodies) will be used to estimate the clearance rate of atezolizumab. From C3D1, all participants will use 840mg. The timing will be determined based on the clearance rate simulated using the C2D1 trough. The timing of subsequent cycles will be determined based on the simulated clearance rate for each cycle in the first 16 weeks. Afterward, the trough will be checked every 3 months. The participants will remain on study for up to 2 years or until unacceptable toxicity or disease progression. Restaging will be done every 12 weeks. Major Eligibility Criteria All participants must be able to provide a written informed consent. Participants who are 18 or older with an advanced or metastatic cancer who are candidates for treatment with atezolizumab, either alone or in combination with other drug(s), are eligible. Participants with chronic viral infection who are well-controlled are eligible. Participants must not have received an immune checkpoint blockade within 28 days prior to the study treatment. Active autoimmune disease or immune stimulatory or immune suppressive medications within 1 month prior to study treatment will result in exclusion.PK measurements will be obtained using an investigator-developed assay and not the manufacturer-validated assay. Assay methodological differences should be considered when interpreting pharmacokinetic comparisons with previously published manufacturer data. Two of the planned 30 patients have been enrolled. Citation Format: Hoyoung M. Maeng, Keith T. Schmidt, Michele Reed, Michell Manu, Katherine Lee-Wisdom, Manuk Manukyan, Jennifer L. Marte, Charalampos S. Floudas, Isaac Brownell, Nicholas Tschernia, Fatima Karzai, Hyoyoung Choo-Wosoba, Evrim Turkbey, Ruchi Patel, Lisa Cordes, William D. Figg, James L. Gulley. Toward personalized atezolizumab dosing by therapeutic drug monitoring [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(8_Suppl):Abstract nr CT286.

We compare our experience with three pharmacometric modeling workflows for simulating alternative dosing regimens of atezolizumab: (1) the gold-standard, NONMEM software used in combination with R, (2) the R-based package RxODE, and (3) the recently developed Julia-based software Pumas, discussing the advantages and limitations of each. Our prior work demonstrated that an extended-interval dosing regimen (840 mg q6w) following two standard loading doses maintained efficacy while having a nonsignificant exposure-response relationship with adverse events. In the original analysis, the virtual population was generated in R, simulations performed using NONMEM, and data analysis and visualization then conducted in R. In the present study, we perform the full workflow within R using RxODE for simulation and also recreate this workflow using Pumas in Julia. Pharmacokinetic parameters and graphical output, as well as the processing speed for each method were compared. All three approaches generated comparable virtual populations, key exposure metrics of CMAX, CMIN, and Weekly AUC, and data visualizations of the simulated serum concentrations. However, there were differences in how quickly each software simulated the entire seven cycle dataset, with Pumas simulating 33,273 obs/second, NONMEM 4,782 obs/sec, and RxODE 251 obs/sec. Due to this large difference, the dataset was broken into individual cycles, where NONMEM and RxODE performed comparably at 2041-3337 obs/sec, while Pumas simulated 48,122-69,168 obs/sec. All three software produced comparable results. Ultimately, the choice should be based on the modeler’s specific needs and limitations.

180 Background: BCR pts have a rising PSA after definitive surgery or radiation, but negative CT/Tc99 scans. While ADT-based strategies are commonly used, they can be associated with life-altering toxicities and have not been shown to improve survival. Radium 223 is an alpha-emitting radiopharmaceutical that accumulates in areas of high bone turnover and has demonstrated a survival benefit in metastatic prostate cancer, but its benefits as a monotherapy in BCR without ADT have not been explored prior to this study. This strategy may be important as bone metastasis drives morbidity/mortality in prostate cancer. Methods: Eligible pts in this study (NCT04206319) have BCR following definitive therapy, testosterone (T) >100ng/dL, normal organ and marrow function, and negative CT/Tc99 imaging. Pts must have findings on a NaF or PSMA PET suspicious for metastatic bone disease not seen on Tc99. Pts are treated with Radium 223 at the approved dosing of 55 kBq/kg for 6 cycles. PSA declines were defined as 2 or more confirmed declines from an intra-study apex PSA (ISAP; Madan ASCO GU 2018). All pts have pre- and post-treatment PSMA and NaF imaging. Immune responses (primary endpoint) are to be evaluated at study completion. Results: 18 pts have enrolled with 16 currently evaluable for response, with a median age of 67 yrs (58-80) and PSA of 1.75 ng/ml (0.2-49.5). 14/16 pts had PSMA+ scans. 13/16 pts had NaF+ scans. There have been no missed cycles for toxicity and no grade >3 toxicities. Grade 2 toxicities have been rare and no Grade 1 or 2 changes in hemoglobin or platelets have occurred. 2 pts with rapid PSA doubling times came off for progression and were not evaluable for follow up imaging. Five pts (31%) had confirmed ISAP PSA declines of 14%, 21%, 24%, 33%, and 57% lasting 84, 173, 292, 246+, and 661+ days, respectively. 8/11 evaluable pts had evidence of decreased standard uptake value (SUV) on NaF PET imaging after treatment. Two pts had resolution of multiple PSMA+ bone findings, and one of them remains with negative bone findings on PET after 2+ years and with a stable PSA. Conclusions: Radium 223 in BCR is safe and associated with rare grade 1/2 toxicities. Decreases in SUV seen on most NaF scans suggest Radium 223 targeting of suspicious lesions. Substantial improvements in PSMA imaging have been observed. Delayed but confirmed PSA declines have been seen in 31% of pts. Radium 223 monotherapy may have a therapeutic activity in BCR and further studies are needed to define its potential role in PET+ BCR. Clinical trial information: NCT04206319 .

Adaptation to reduced levels of oxygen (hypoxia) is an essential feature of eukaryotic life. Within the animal kingdom, cellular responses are orchestrated by the transcription factor HIF (Hypoxia Inducible Factor) which is regulated by specific 2-oxoglutarate-dependent oxygenases. This family of enzymes also includes histone demethylases, and histone methylation has also been observed to increase in hypoxia. Since histone methylation is associated with gene expression, this has raised questions about whether this also contributes to transcriptional regulation in hypoxia. However, to date pangenomic studies have not been normalised in a way that preserves these bulk changes. Using drosophila chromatin spike-in normalisation, we have shown widespread increases in histone H3K4/9/27/36me3 in hypoxia at almost all gene loci that occur irrespective of whether gene expression is increased or reduced. However, methylation of H3K4me3 and H3K36me3 increases most at direct transcriptional targets of HIF and this is abrogated by inactivation of HIF. Taken together this suggests that global H3 trimethylation increases in hypoxia are widespread and not sufficient to predict transcriptional direction, whereas enhanced H3K4me3/H3K36me3 at direct HIF targets appears consequent to HIF binding and transcriptional engagement.

Abstract Background: Primary DLBCL of CNS (PCNSL) that relapses after or is refractory to high-dose methotrexate (HD-MTX) has poor long-term survival of 20%. PCNSL biology includes chronic active BCR signaling targeted by ibrutinib. Ibrutinib with temozolomide, etoposide, liposomal doxorubicin, dexamethasone, and rituximab (TEDDI-R) induces durable remissions in relapsed or refractory PCNSL but carries Aspergillus risk (Lionakis et al. Cancer Cell 2017). We added isavuconazole prophylaxis and report outcomes with escalating ibrutinib doses. Methods: Study conduct has been described (Roschewski et al. ASH 2024). Adults with relapsed or refractory PCNSL were enrolled in a phase 1 study with expansion. Prior BTKi, HIV+, and EBV+ were excluded. Isavuconazole started 3d before ibrutinib and continued throughout therapy. In phase 1, three dose levels of ibrutinib (280/420/560mg) were tested with TEDD-R. Two expansion cohorts received ibrutinib either continuously or on a fixed schedule (d1-10/cycle). Pts received up to 6 cycles without consolidation or maintenance. Tumors were molecularly classified by LymphGen. The primary objective was to determine the highest ibrutinib dose safely given with isavuconazole. Secondary objectives included overall response rate (ORR), PFS, and OS. Results: Thirty pts enrolled, including 10 in phase 1 and 10 each in the expansion cohorts. Median age was 63y (range 40-78), with 6 (20%) ≥70y. All had prior HD-MTX and 5 (17%) had prior stem cell transplant. Nineteen (63%) pts were refractory to HD-MTX. No DLTs were observed; ibrutinib 560mg was used in expansion. Neutropenia occurred in 6% (G3) and 40% (G4) of cycles, with febrile neutropenia in 11%. Thrombocytopenia occurred in 13% (G3) and 14% (G4) of cycles. ≥G3 infections occurred in 53% of pts, most common being UTI (20%), none fungal or opportunistic. Palmar plantar erythrodysesthesia occurred in 17 (57%) pts, managed with liposomal doxorubicin dose reduction. Notable ≥G3 non-hematologic toxicities included venous thromboembolism in 20%, and fatigue, syncope, mucositis, and hypokalemia in 13% pts each. G2 supraventricular arrhythmias occurred in 2 (7%) pts. Twenty-two pts died: 16 (73%) from progression, 2 (9%) from COVID, 1 (5%) from HBV reactivation, and 3 (14%) unknown. ORR was 90% (95% CI, 74-97), including complete response (CR) in 60% (95% CI, 42-75). CRs occurred across LymphGen subtypes: MCD 5 (71%), A53 2 (100%), BN2 1 (100%), and Other 2 (40%). No pt received consolidation. With a median f/u of 5.3y, the 2y PFS was 29% (95% CI, 14-46) and the 2y OS 47% (95% CI, 28-63). Ibrutinib schedule and HD-MTX refractoriness did not affect 2y PFS (P=0.94 and 0.68, respectively). Conclusions: Ibrutinib 560mg is safe across ages in TEDDI-R, and concurrent isavuconazole substantially reduces Aspergillus risk. TEDDI-R achieves high CR rate in relapsed or refractory PCNSL, including HD-MTX refractory disease. Durable remissions occur without consolidation. Cancer Therapy Evaluation Program sponsored this trial [NCT02203526] along with NCI’s Intramural Research Program. Citation Format: Rahul Lakhotia, Christopher Melani, Tatyana Gavrilova, Jagan R. Muppidi, James D. Phelan, Michail S. Lionakis, Kieron Dunleavy, Lode J. Swinnen, Matthias Holdhoff, Catherine Lai, Sami Ibrahimi, Michael Glantz, Jan Drappatz, John A. Butman, Stefania Pittaluga, Kim Johnson, Atekelt Tadese, Hyoyoung Choo-Wosoba, John D. Heiss, William D. Figg, Elaine S. Jaffe, S. Percy Ivy, Richard F . Little, Louis M. Staudt, Mark Roschewski, Wyndham H. Wilson. Final analysis of a Phase 1 study of ibrutinib dose-escalation in TEDDI-R with isavuconazole for relapsed or refractory primary DLBCL of the CNS [abstract]. In: Proceedings of the Fifth AACR International Meeting on Advances in Malignant Lymphoma: From Discovery to Clinical Impact; 2026 Jun 24-27; Philadelphia, PA. Philadelphia (PA): AACR; Blood Cancer Discov 2026;7(3_Suppl):Abstract nr A047.

Proteus syndrome is a rare genetic disorder characterized by progressive, abnormal overgrowth that can affect any organ or tissue in the body. This abnormality is caused by a mosaic activating variant in AKT1 that encodes a key serine/threonine kinase of the phosphoinositide-3-kinase (P13K)/AKT signaling pathway and is involved in cell growth, survival, and metabolism. Miransertib (MK-7075, formerly ARQ 092) is a novel, orally bioavailable allosteric pan-AKT inhibitor that selectively targets AKT1, AKT2, and AKT3, demonstrating potent suppression of AKT signaling and tumor growth in murine xenograft models with dysregulated signaling pathways. It has also been evaluated as a potential therapeutic option for individuals with Proteus syndrome, both in pre-clinical studies and in clinical trials. In this study, we have developed and validated a sensitive, robust, and specific LC-MS/MS method for quantifying miransertib in human plasma. The calibration curve ranged from 0.5 to 500 ng/mL in human plasma with a linearity of r2 = 0.9945 ± 0.0019 across multiple days. Accuracy of assay ranged from -3.38 to 3.53% and precision was between 2.90 and 8.42%. Miransertib also showed excellent stability following multiple freeze-thaw cycles, during bench-top storage, and while on the autosampler overnight. This method enabled us to assess the pharmacokinetic parameters of participants enrolled in a phase II clinical trial (NCT04316546).

SYNTHESIS-Breast is an exploratory trial that adapts early-phase design to identify off-label therapies in metastatic breast cancer via ENLIGHT, a retrospectively validated computational algorithm, and generate preliminary data for future trials. ENLIGHT selects treatments via gene-expression-based synthetic lethality/rescue. SYNTHESIS-Breast’s design includes algorithm-specific adaptations (ex. a reproducible molecular tumor board or layered Simon two-stages for fast interim checkpoints). SYNTHESIS-Breast will not only guide ENLIGHT applications, but also future prospective algorithm trials.