Buhrow, Sarah A.

BET bromodomain inhibitors are efficacious as anti-inflammatory compounds, but clinical translation is hampered by dose-limiting toxicities from non-selective inhibition. We herein report compounds 16 and 26, based on previously reported 4-methyl-1,2,3-triazole-based inhibitor, DW34. 16 has a BRD4 BD1 Ki of 10 nM, and up to 13–38-fold selectivity for BRD4 BD1 over other BD2 domains, and an improved hERG affinity of 4.24 µM over DW34. 26, A biscyclopropyl analog of 16 showed further enhancement of BD1 selectivity over BD2 (26–203-fold), but exhibited more potent hERG inhibition. Compound 16 had improved liver and plasma clearance over DW34, with good biodistribution to the liver, and had an intracellular target-engagement affinity Ki of 92 nM, with reduction of Ccl2, Cxcl1, AST, and ALT in in vitro and in vivo mouse models of liver inflammation. 16 represents a useful lead for treating inflammatory liver diseases, with improved specificity, drug-like properties, and reduced hERG affinity.

Abstract Introduction: We aimed to characterize the preclinical pharmacokinetics (PK) of a series of 20 anticancer agents in highly immunodeficient female NOD scid gamma (NSG) mice to provide clearance and exposure data for agents under investigation by the NCI PDX Development and Trial Centers Research Network (PDXNet). Methods: The series of 20 anticancer agents (inhibitors of CDK4/6, PI3K-β/PI3K-δ, ATR, MEK1/2, PI3K, microtubule, EZH2, BCL-2, PARP, histone deacetylase, γ-secretase, FGFR, SHP2, and ERK1/2, as well as a SMAC mimetic) were administered to female NSG mice via IV, PO, or IP routes to characterize plasma exposures under conditions used for PDX efficacy testing. Serial plasma samples were collected 15, 30, 60, 120, 240, 360, 480, and 1440 minutes after dosing. Drug concentrations were quantified using validated LC-MS/MS assays. PK parameters were calculated using non-compartmental analysis. Results: The PK for each agent was determined, and the clearance and half-life values are listed in the table below. The PK metrics for Navitoclax could not be calculated. Due to higher metabolic rates, mice show faster PK processes. They generally had shorter half-lives and higher weight-normalized clearance than humans. Copanlisib, Navitoclax, and Trametinib were exceptions. Conclusion: These PK data are critical for understanding the antitumor activities of agents studied by the PDXNet and will aid investigators in developing new approach methodologies for preclinical safety studies in preparation for human clinical trials. Citation Format: Mohd Beshr Chama, Emily J. Koubek, Sarah A. Buhrow, Renee A. Schoon, Joel M. Reid. Pharmacokinetics of a series of anticancer agents in immunodeficient female NOD scid gamma mice [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 3156.

Abstract Background: Endocrine therapy (ET) with aromatase inhibitors (AI) plus ovarian function suppression (OFS) is standard for premenopausal women with ER+/HER2- breast cancer. However, many premenopausal women are intolerant of AI + OFS, leaving tamoxifen (with or without OFS) as their only option. Extensive studies have demonstrated that premenopausal women treated with neoadjuvant ET whose tumors exhibit Ki-67 ≤ 10% following 4 weeks of therapy (defined as endocrine sensitive disease (ESD)) achieve 5-year distant disease-free survival > 96%. Problematically, only 41% of patients reach this ESD threshold with tamoxifen compared to 78% with AI+OFS (Nitz JCO 2022). (Z)-endoxifen (ENDX) is a potent selective estrogen receptor modulator (SERM) that inhibits ERα at plasma concentrations of 3-5 ng/ml and dually targets PKCβ1, a suspected oncogene in breast tumors, at concentrations ≥ 500 ng/ml. We therefore developed the EVANGELINE study (NCT05607004) is an open label, randomized neoadjuvant phase II study that includes a pharmacokinetic (PK) Run-in, aiming to evaluate whether ENDX +/- goserelin is non-inferior to exemestane plus goserelin with respect to ESD rate. Following the completed PK run-in portion of the study, where 40mg/day or 80mg/day ENDX were assessed, the 40 mg/day dose was selected for further evaluation in the second part of the trial. The second part is comprised of a randomized treatment cohort, for patients with a Ki-67% >10% at preregistration randomized to either 40mg (Z)-endoxifen + goserelin or exemestane + goserelin neoadjuvant treatment and a Single Arm Treatment Cohort for patients who have a Ki-67 ≤ 10% at pre-registration assigned to 40mg/day (Z)-endoxifen monotherapy neoadjuvant treatment. Methods: To investigate ENDX further in premenopausal women, a multicenter study in the United States, was designed(EVANGELINE; NCT05607004). This phase 2, open-label, randomized, neoadjuvant trial includes a PK run-in phase designed to assess whether the 4-week ESD rate with (Z)-endoxifen + goserelin is non-inferior to that of exemestane + goserelin in premenopausal women with Stage IIA or IIB ER+/HER2- breast cancer with diagnostic Ki67 > 10%. Additionally, a single arm Phase 2, open-label neoadjuvant Cohort was designed to assess the 4-week ESD rate with ENDX monotherapy in premenopausal women with Stage IIA or IIB ER+/HER2- BC with diagnostic Ki67 ≤10%. Subjects will undergo neoadjuvant treatment for six months before receiving surgical treatment in the involved breast. This study will additionally assess safety, tolerability, response rates, surgical outcomes, and monitor disease progression. Comprehensive biomarker evaluations will be conducted using paired tumor biopsies and blood samples collected at baseline and week four, as well as 6 month surgical specimens. Enrollment in the PK run-in phase (n-22) was completed in Fall 2024 with the second portion of the trial slated to begin early in 2025. Citation Format: Matthew P. Goetz, Vera J. Suman, Claudia Lopez, Hayley Erickson, Lonnissa Nguyen, Sandra S. Hammer, Lida Mina, Pooja Advani, Roberto Leon-Ferre, Karthik Giridhar, Felipe Batalini, Daniel Flora, Jason M. Jones, Nusayba A. Bagegni, Katie N. Hunt, Mara Piltin, Amy Degnim, James N. Ingle, Judy C. Boughey, Sarah A. Buhrow, Joel M. Reid, Matthew Schellenberg, John R. Hawse, Steven C. Quay. A randomized phase 2 non-inferiority trial of (Z)-endoxifen + goserelin and exemestane + goserelin as neoadjuvant treatment for premenopausal women with ER+/HER2- breast cancer (EVANGELINE) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_2):Abstract nr CT237.

Abstract HER2+ breast cancer is an aggressive subtype of cancer that often develops resistance to the current first-line therapy, Trastuzumab. In our previous work, we demonstrated that HER2 signaling activates mitochondrial creatine kinase 1 (MtCK1), which enhances mitochondrial energy metabolism for rapid proliferation of breast cancer cells. However, pharmacological blockage of MtCK1 with a creatine analog, Cyclo-Creatine (CCr), requires millimolar concentration to inhibit breast cancer cell proliferation and is associated with brain toxicity, limiting its clinical application. This brain toxicity may result from the inhibition of the creatine transporter SLC6A8 by CCr, which decreases to transport creatine into brain. In this study, we took a prodrug development approach to identify and optimize protection groups for CCr, designed to bypass the SLC6A8 transporter, enhancing bioavailability and reducing toxicity. Liquid chromatography-mass spectrometry (LC-MS) was utilized to analyze drug uptake and creatine metabolites in cells treated with the prodrugs. Prodrug C, which is our lead prodrug candidate, demonstrated a seven-fold increase in cellular uptake and more than a hundred-fold improvement in cell-killing effects as compared to CCr in an MtCK1 specific manner in breast cancer cells. This approach offers a promising therapeutic strategy to inhibit HER2+ breast cancer cell by disrupting mitochondrial energy metabolism. Future investigations will focus on validating this prodrug’s pharmacokinetics (PK) and pharmacodynamics (PD) through further preclinical studies. Citation Format: Ya Li, Yetong Huang, Puja Dey, Sadae Hitosugi, Sarah A. Buhrow, Joel M. Reid, Taro Hitosugi. Prodrug development of Cyclo-Creatine: Enhancing permeability and reducing toxicity for HER2+ breast cancer treatment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 4157.

Abstract Background: Ovarian function suppression (OFS) combined with tamoxifen (TAM) or an aromatase inhibitor (AI) is standard for premenopausal (PM) ER+, HER2- breast cancer (BC). However, > 40% PM patients (pts) are intolerant of OFS. For these pts, TAM is the only FDA approved option. In the neoadjuvant endocrine setting, pts with endocrine sensitive disease (ESD) (Ki-67 ≤ 10% at 4 weeks) have 5yr dDFS > 97%; however, only 45% of TAM pts vs >75% with AI+OFS achieve 4 wk ESD (Nitz JCO 2022). (Z)-endoxifen (ENDX) is a potent anti-estrogen superior to TAM and AI in xenograft models and with antitumor activity in endocrine-resistant postmenopausal pts. ENDX additionally targets protein kinase C beta 1 (PKCβ1) at concentrations >500 ng/mL, resulting in AKT inhibition and apoptosis (Jayaraman npj Breast Cancer 2023). We hypothesize that ENDX dual targeting of ERα and PKCβ1 will obviate the need for OFS and be non-inferior to AI plus OFS for PM pts with ER+/HER2- BC. Methods: EVANGELINE (NCT05607004) is an ongoing phase 2 multicenter neoadjuvant study with pharmacokinetic (PK) run-in assessing ENDX in PM women with ER+/HER2- BC. The primary objective for the PK run-in is to identify a dose (40 or 80 mg/day) resulting in ENDX steady state concentrations (Css) of 500-1000 ng/mL (to target both ERα and PKCβ1) without significant toxicity. Following PK run-in, the randomized phase II goal is to assess whether the ESD rate with ENDX is non-inferior to exemestane plus goserelin. Women with ESD at wk4 continue treatment for 24 weeks followed by surgery. Here we report the results from the 40 mg/day PK run-in. Results: Seven PM women (6 White, 1 Asian) aged 28-51 (median 46) received ENDX 40 mg/day. Pt characteristics on study were: ER > 90% (all pts), median Ki-67 = 13 (range 4-33%), cTstage (cT2: 6 pts, cT3: 1 pt), and tumor grade (G1: 1 pt, G2: 6 pts). The median ENDX 28 day Css (ng/mL) was 263.6 (range 180.3-376.6). One pt discontinued due to wk4 Ki-67 remaining > 10%. The remaining 6 had ESD, with either wk4 Ki-67 remaining ≤ 10% (3 pts) or decreasing to ≤ 10% (3 pts) and after 24 wks underwent surgery with surgical Ki-67 ≤ 3% (range 0-3%). MRI central review (wk12 and wk24) demonstrated target lesion decreases in all pts with 1 CR, 1 PR and 4 SD (RECIST). Treatment related toxicities included grade 3 headache (n=1), grade 2 amenorrhea (n=1), and grade 2 hot flashes (n=1). The median (range) baseline estrone (n=5) was 54 pg/mL (19-114) with median (range) fold increase from baseline of 9.0 (1.3-23.2) at wk4 and 4.7 (0.4 - 25.9) at wk24. The median baseline estradiol level (n=5) was 29 pg/mL (19-209) with median fold increases from baseline of 17.9 (0.4-57.0) at wk4 and 8.1 (0.04 - 56.6) at wk24. Additional surgical and blood biomarker data will be presented at the meeting. Conclusions: ENDX (40 mg/day) exhibits promising antitumor activity for PM ER+/HER2- BC but with ENDX Css below target. Enrollment is ongoing to the 80 mg/day dose level. Citation Format: Matthew P. Goetz, Vera J. Suman, Heather Fraser, Lida Mina, Pooja Advani, Roberto Leon-Ferre, Karthik Giridhar, Felipe Batalini, Katie N. Hunt, Swaathi Jayaraman, James Jakub, Patricia Cronin, Mara Piltin, Amy Degnim, James N. Ingle, Judy C. Boughey, Sarah Buhrow, Joel Reid, Matthew Schellenberg, John Hawse, Steven Quay. Neoadjuvant (Z)-endoxifen in premenopausal ER+, HER2- breast cancer: Evaluation of the first pharmacokinetic cohort of the EVANGELINE trial [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr CT205.

Abstract Purpose: AB160 is a 160-nm nano-immunoconjugate consisting of nab-paclitaxel (ABX) nanoparticles noncovalently coated with bevacizumab (BEV) for targeted delivery into tissues expressing high levels of VEGF. Preclinical data showed that AB160 resulted in greater tumor targeting and tumor inhibition compared with sequential treatment with ABX then BEV. Given individual drug activity, we investigated the safety and toxicity of AB160 in patients with gynecologic cancers. Patients and Methods: A 3+3 phase I trial was conducted with three potential dose levels in patients with previously treated endometrial, cervical, and platinum-resistant ovarian cancer to ascertain the recommended phase II dose (RP2D). AB160 was administered intravenously on days 1, 8, and 15 of a 28-day cycle (ABX 75–175 mg/m2, BEV 30–70 mg/m2). Pharmacokinetic analyses were performed. Results: No dose-limiting toxicities (DLT) were seen among the three dose levels tested. Grade 3/4 toxicities included neutropenia, thromboembolic events, and leukopenia. DL2 (ABX 150 mg/m2, BEV 60 mg/m2) was chosen as the RP2D. Seven of the 19 patients with measurable disease (36.8%) had confirmed partial responses (95% confidence interval, 16.3%–61.6%). Pharmacokinetic analyses demonstrated that AB160 allowed 50% higher paclitaxel dosing and that paclitaxel clearance mirrored that of therapeutic antibodies. Conclusions: The safety profile and clinical activity of AB160 supports further clinical testing in patients with gynecologic cancers; the RP2D is DL2 (ABX 150 mg/m2, BEV 60 mg/m2).

Upamostat is an orally available small-molecule serine protease inhibitor that is a highly potent inhibitor of trypsin 1, trypsin 2, trypsin 3 (PRSS1/2/3), and the urokinase-type plasminogen activator (uPA). These enzymes are expressed in many cancers, especially during tissue remodeling and subsequent tumor cell invasion. Opaganib (ABC294640), a novel, orally available small molecule is a selective inhibitor of the phosphorylation of sphingosine to sphingosine-1-phosphate (S-1-P) by sphingosine kinase 2 (SPHK2). Both sphingosine kinase 1 (SPHK1) and SPHK2 are known to regulate the proliferation-inducing compound S-1-P. However, SPHK2 is more critical in cancer pathogenesis. The goal of this project was to investigate the potential antitumor effects of upamostat and opaganib, individually and in combination, on cholangiocarcinoma (CCA) xenografts in nude mice. PAX165, a patient-derived xenograft (PDX) from a surgically resected CCA, expresses substantial levels of SPHK2, PRSS1, PRSS2, and PRSS3. Four groups of 18 mice each were treated with upamostat, opaganib, both, or vehicle. Mouse weights and PAX165 tumor volumes were measured. Tumor volumes in the upamostat, opaganib, and upamostat plus opaganib groups were significantly decreased compared to the control group.

AbstractBackgroundDespite recent approval of several new agents, relapsed acute lymphoblastic leukemia (ALL) remains challenging to treat. Sapanisertib (MLN0128/TAK‐228) is an oral TORC1/2 inhibitor that exhibited preclinical activity against ALL.MethodsWe conducted a single‐arm multi‐center Phase II study of sapanisertib monotherapy (3 mg orally daily of the milled formulation for 21 days every 28 days) in patients with ALL through the Experimental Therapeutics Clinical Trials Network (NCI‐9775).ResultsSixteen patients, 15 of whom were previously treated (median 3 prior lines of therapy), were enrolled. Major grade 3–4 non‐hematologic toxicities included mucositis (3 patients) and hyperglycemia (2 patients) as well as hepatic failure, seizures, confusion, pneumonitis, and anorexia (1 patient each). Grade >2 hematological toxicity included leukopenia (3), lymphopenia (2), thrombocytopenia, and neutropenia (1). The best response was stable disease in 2 patients (12.5%), while only 3 patients (19%) were able to proceed to Cycle 2. Pharmacokinetic analysis demonstrated drug exposures similar to those observed in solid tumor patients. Immunoblotting in serially collected samples indicated limited impact of treatment on phosphorylation of mTOR pathway substrates such as 4EBP1, S6, and AKT.ConclusionIn summary, single‐agent sapanisertib had a good safety profile but limited target inhibition or efficacy in ALL as a single agent. This trial was registered at ClinicalTrials.gov as NCT02484430.

AbstractThe purpose of this study was to develop and validate a population pharmacokinetic model for Z‐endoxifen in patients with advanced solid tumors and to identify clinical variables that influence pharmacokinetic parameters. Z‐endoxifen‐HCl was administered orally once a day on a 28‐day cycle (±3 days) over 11 dose levels ranging from 20 to 360 mg. A total of 1256 Z‐endoxifen plasma concentration samples from 80 patients were analyzed using nonlinear mixed‐effects modeling to develop a population pharmacokinetic model for Z‐endoxifen. A 2‐compartment model with oral depot and linear elimination adequately described the data. The estimated apparent total clearance, apparent central volume of distribution, and apparent peripheral volume of distribution were 4.89 L/h, 323 L, and 39.7 L, respectively, with weight‐effect exponents of 0.75, 1, and 1, respectively. This model was used to explore the effects of clinical and demographic variables on Z‐endoxifen pharmacokinetics. Weight, race on clearance, and aspartate aminotransferase on the absorption rate constant were identified as significant covariates in the final model. This novel population pharmacokinetic model provides insight regarding factors that may affect the pharmacokinetics of Z‐endoxifen and may assist in the design of future clinical trials.

Abstract Prior in vitro work in the human hepatoma cell lines Huh7 and HEP3B indicated that combination treatment of the BH3 mimetic, navitoclax, and the multi-kinase inhibitor, sorafenib, was more effective at inducing apoptosis than either compound alone. This current study was part of a phase I clinical trial to determine the maximum tolerated dose of concurrent navitoclax and sorafenib treatment in patients with relapsed or refractory solid organ tumors and sought to characterize the pharmacokinetics (PK) and pharmacodynamics (PD) of both agents in combination. Cleavage of cytokeratin 18 by caspase 3 was used as a biomarker for therapy-induced activation of apoptosis to determine if combination treatment results in an increase in apoptosis as previously observed in in vitro work. PK were assessed in 26 patients (ages 32 - 80) enrolled in a phase I clinical trial (NCT02143401). 150 mg of oral navitoclax was administered once daily for a seven day run-in (beginning Day -7) prior to 150 mg (Dose level 1) or 200 mg (Dose level 2) navitoclax concomitant treatment with 400 mg of twice daily oral sorafenib (Day 1). Samples for pharmacokinetic analysis were obtained on Day -7 and Day 1 prior to dosing and at 1, 2, 4, 8-12, and 24 hours post dosing. PK parameters were estimated by noncompartmental analysis using Phoenix® WinNonlin® Version 6.4. To examine the PD of both agents in combination, cytokeratin 18 cleavage was quantified by ELISA after the 7-day navitoclax run-in and on Day 2 or 4 and Day 8 of navitoclax and sorafenib combination treatment. PK estimates of maximum concentration, exposure, volume of distribution, and clearance for navitoclax on Day -7 and Day 1 were not significantly different, indicating a lack of navitoclax accumulation. Finally, no correlation was found between navitoclax exposure and apoptosis as indicated by cytokeratin-18 cleavage. This work was supported by the NCI Cancer Center Support Grant P30 CA15083 and NCI Experimental Therapeutics Phase I Grant UM1 CA186686. Citation Format: Emily J. Koubek, Brian A. Costello, Jun Yin, Renee M. McGovern, Sarah A. Buhrow, Renee A. Schoon, Carrie A. Strand, Yixing Jiang, Mitesh J. Borad, Naoko Takebe, Scott H. Kaufmann, Alex A. Adjei, Joel M. Reid. Pharmacokinetic analysis of navitoclax in combination with sorafenib in patients with relapsed or refractory solid organ tumors [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr CT114.