Sarkaria, Jann N.

2071 Background: Brigimadlin (BI 907828) is a potent small molecule inhibitor of the p53-MDM2 pathway currently in a phase 0/1 clinical trial in combination with radiotherapy in newly diagnosed MGMTunmethylated glioblastoma (GBM). To inform development of brigimadlin for GBM, we developed a pharmacokinetic (PK)/ pharmacodynamic (PD)/ efficacy model using GBM patient derived xenografts (PDXs). Methods: Brigimadlin PK parameters were evaluated in FVB wild-type and knockout (Mdr1a/b-/-Bcrp1-/-) mice and in athymic nude mice. Drug binding was measured by rapid equilibrium dialysis, and drug levels quantified by LC/MS-MS. Dose-response relationships were evaluated in subcutaneous and orthotopic PDXs across a range of doses. Response to brigimadlin (2 mg/kg weekly) +/- RT (2 Gy x 10 fractions) was evaluated in orthotopic PDXs. Results: Brigimadlin significantly delayed median time to regrowth of GBM108 ( MDM2amplified) subcutaneous tumors (vs. placebo; p<0.05) at dose levels of 0.25 mg/kg (1.3-fold), 0.5 mg/kg (1.5-fold), 1 mg/kg (2.6-fold), and 2 mg/kg (5.3-fold). A single dose of brigimadlin resulted in corresponding intra-tumoral drug levels 24 hours post-dose: 84 nM (0.25 mg/kg), 175 nM (0.5 mg/kg), 398 nM (1 mg/kg) and 924 nM (2 mg/kg) and dose-dependent upregulation of p53 target genes (p21 and PUMA). In contrast, GBM14 ( MDM2non-amplified) showed regrowth delay (1.6-fold) only at 2 mg/kg (p=0.008). Brigimadlin was highly bound (fraction unbound = 0.0006 in brain; 0.0017 in GBM tumor tissue), and CNS distribution was limited by efflux; in wild-type mice Kp,uu_brain = 0.002 ± 0.003; in Mdr1a/b-/-Bcrp1-/- mice Kp,uu = 0.043 ± 0.025. Efficacy of brigimadlin was compared in orthotopic GBM108 PDXs grown in athymic nude mice vs. immuno/efflux-deficient (Rag2-/-Mdr1a-/-Bcrp1-/-) mice. In nude mice, median survival was extended at 2 mg/kg brigimadlin (1.4-fold, p=0.009), with corresponding intra-tumoral drug levels of 29 nM. In efflux deficient mice, median survival was extended (p<0.05) at 0.25 mg/kg (1.5-fold), 0.5 mg/kg (1.5-fold), 1 mg/kg (1.8-fold), and 2 mg/kg (>4-fold). Measurement of intra-tumoral drug levels is in progress. In combination with RT in GBM108, brigimadlin (2 mg/kg x 2 weeks) extended median survival vs. vehicle (66 vs. 50 days; p=0.012) and enhanced median survival following RT (128.5 vs. 82 days; p=0.009). In GBM14, 2 mg/kg brigimadlin (2 mg/kg x 12 weeks) extended median survival (39.5 vs. 32.5 days; p=0.0004) and enhanced survival following RT (97 vs. 81 days; p<0.0001). Conclusions: Efficacy of brigimadlin is dependent on adequate CNS delivery. Studies in subcutaneous PDX demonstrated intra-tumoral total drug levels in the mid-nanomolar range provide meaningful tumor effects in a highly sensitive, MDM2 amplified PDX. In orthotopic PDXs with and without MDM2 amplification, brigimadlin provided further benefit in combination with RT. These data support ongoing clinical evaluation of brigimadlin in GBM.

2017 Background: MDM2 inhibits tumor suppressor p53. Brigimadlin, a potent MDM2–p53 antagonist, restores wild-type (wt) p53 function and has shown early efficacy in pts with solid tumors (LoRusso et al Cancer Disc 2023). GBM is an area of unmet need with 5-year survival <10%. In p53 wt GBM pt-derived xenograft models, brigimadlin promotes tumor cell apoptosis and extends survival in combination with RT. Methods: NCT05376800 is a Ph 0/Ia open-label, single-arm trial that aims to measure brigimadlin concentration in brain tumor tissue in pts with histologically or radiologically newly diagnosed GBM eligible for resection (Ph 0) and determine the maximum tolerated dose of brigimadlin plus RT in pts with TP53wt, IDH wt, MGMT promoter unmethylated GBM (Ph Ia). In Ph 0, pts received one brigimadlin dose (30 mg or 45 mg) ~12–24 h before resection. Ph 0 primary endpoints are the measured total concentration and the calculated unbound concentration of brigimadlin in brain tissue homogenate from non-contrast enhancing (NCE) and contrast enhancing (CE) regions. The predefined threshold for trial continuation is 0.5 nmol/L (corresponding to IC50 in GBM cell lines) unbound brigimadlin in CE samples in ≥50% of pts. Brigimadlin concentration was measured using LC/MS and corrected for amount of brigimadlin in residual blood. Unbound concentration was calculated using an in vitro estimate of unbound fraction (fu): 0.654% (rat brain slice). fu in human plasma was 0.22%. Kp,uu (ratio of unbound concentration in brain vs plasma) was calculated. Biomarker testing was performed. Results: Data are available for 11 pts (brigimadlin 30 mg: n=6; 45 mg: n=5). In the 30 mg group, median total brigimadlin concentration in NCE samples was 267 nmol/L (4 samples, range 86–316 nmol/L) and 332 nmol/L (6 samples, range 272–952 nmol/L) in CE samples. In the 45 mg group, median total brigimadlin concentration in NCE samples was 197 nmol/L (5 samples, range 140–347 nmol/L) and 603 nmol/L (5 samples, range 441–905 nmol/L) in CE samples. Unbound concentration exceeded the 0.5 nmol/L threshold in most cases (Table). Post-brigimadlin, an increase in selected p53 target gene expression was observed in CE vs NCE tissue. Conclusions: Unbound brigimadlin concentrations in CE regions in all pts receiving the low dose of 30 mg brigimadlin exceeded the 0.5 nmol/L threshold. Kp,uu in most patients was close to 1 in CE regions. Biomarker data support target engagement in brain tissue. Our findings support continued investigation of brigimadlin in GBM. Recruitment is ongoing. Updated data will be presented. Clinical trial information: NCT05376800 . [Table: see text]

2012 Background: Navtemadlin (nvtm) is a potent, selective, orally available small molecule inhibitor of murine double minute 2 homologue (MDM2), which has completed a Ph 0 surgical window of opportunity study in glioblastoma, IDH-wildtype (GBM; Lee SNO 2022). To optimally interpret the clinical data, an extensive evaluation of nvtm PK, PD, and efficacy was performed in GBM patient derived xenografts (PDXs). Methods: Response to nvtm +/- radiotherapy (RT) was characterized in vitro and in vivo across a panel of GBM PDXs with various TP53 and MDM2 alterations. Efficacy, PK, and PD were evaluated in flank or orthotopic PDX models. p53 pathway activation was evaluated by qPCR, Western blot, and IHC. Nvtm brain penetration was evaluated in immunodeficient abcb1a/b-/- (P-glycoprotein; P-gp), abcg2-/- (BCRP), or double-knockout mice. Binding was assessed by rapid equilibrium dialysis, and nvtm concentrations by LC/MS-MS and MALDI-MSI. Results: Nvtm decreased in vitro viability of TP53WT GBM PDX explant cultures with IC50s <100 nM, but was ineffective in TP53-mutant GBM. In flank PDX models, nvtm (100 mg/kg daily for 4 weeks) delayed tumor regrowth by 1.9 to 4.8-fold in TP53 WT PDXs without MDM2amplification (n=9 models), and more markedly by 20.1 to 29.4-fold in MDM2amplified models (n=4; 2 PDXs did not recur). In a flank PDX dose-response study, nvtm delayed the growth of MDM2amplified GBM108 at 25 mg/kg vs. placebo (61 vs. 11 days; p=0.014; mean intra-tumoral nvtm = 590 nM). In contrast, growth of MDM2 non-amplified GBM14 was delayed only at 100 mg/kg (37 vs. 15 days; p=0.082; mean intra-tumoral nvtm = 2990 nM). In both flank models, p53 target gene upregulation was similar between 25 and 100 mg/kg and did not correlate with regrowth. Nvtm was highly bound (fraction unbound = 0.090 in culture media and 0.014 in GBM tissue homogenate). In mice after oral dosing, distribution to CNS was limited by P-gp, with a brain to plasma ratio of 0.009 and unbound ratio of 0.005, whereas BCRP deficiency did not affect CNS distribution. With orthotopic GBM108, nvtm efficacy was evaluated in nude vs. efflux-deficient mice. In nude mice, nvtm was ineffective at doses up to 100 mg/kg; however, in efflux deficient mice, the mean intra-tumoral nvtm level at 25 mg/kg was similar to flank tumors (690 nM) and survival was significantly extended (134 vs. 62 days, p=0.0002) with additional benefit at 100 mg/kg (>300 vs. 62 days, p=0.002). Conclusions: Nvtm showed significant efficacy in TP53 WT GBM flank PDX models but efficacy in orthotopic PDX was highly dependent on CNS penetration. Targeting nvtm levels based on the in vitroIC50 may significantly underestimate the in vivo effective concentration . In vivo studies showed lower intra-tumoral nvtm levels are required to significantly inhibit growth of MDM2amplified compared with non-amplified tumors.

Abstract Purpose: Antibody-drug conjugates (ADC) are targeted therapies with robust efficacy in solid cancers, and there is intense interest in using EGFR-specific ADCs to target EGFR-amplified glioblastoma (GBM). Given GBM’s molecular heterogeneity, the bystander activity of ADCs may be important for determining treatment efficacy. In this study, the activity and toxicity of two EGFR-targeted ADCs with similar auristatin toxins, Losatuxizumab vedotin (ABBV-221) and Depatuxizumab mafodotin (Depatux-M), were compared in GBM patient-derived xenografts (PDX) and normal murine brain following direct infusion by convection-enhanced delivery (CED). Experimental Design: EGFRviii-amplified and non-amplified GBM PDXs were used to determine in vitro cytotoxicity, in vivo efficacy, and bystander activities of ABBV-221 and Depatux-M. Nontumor-bearing mice were used to evaluate the pharmacokinetics (PK) and toxicity of ADCs using LC-MS/MS and immunohistochemistry. Results: CED improved intracranial efficacy of Depatux-M and ABBV-221 in three EGFRviii-amplified GBM PDX models (Median survival: 125 to &gt;300 days vs. 20–49 days with isotype control AB095). Both ADCs had comparable in vitro and in vivo efficacy. However, neuronal toxicity and CD68+ microglia/macrophage infiltration were significantly higher in brains infused with ABBV-221 with the cell-permeable monomethyl auristatin E (MMAE), compared with Depatux-M with the cell-impermeant monomethyl auristatin F. CED infusion of ABBV-221 into the brain or incubation of ABBV-221 with normal brain homogenate resulted in a significant release of MMAE, consistent with linker instability in the brain microenvironment. Conclusions: EGFR-targeting ADCs are promising therapeutic options for GBM when delivered intratumorally by CED. However, the linker and payload for the ADC must be carefully considered to maximize the therapeutic window.

Abstract DNA damage response (DDR) mechanisms are critical to maintenance of overall genomic stability, and their dysfunction can contribute to oncogenesis. Significant advances in our understanding of DDR pathways have raised the possibility of developing therapies that exploit these processes. In this expert-driven consensus review, we examine mechanisms of response to DNA damage, progress in development of DDR inhibitors in IDH-wild-type glioblastoma and IDH-mutant gliomas, and other important considerations such as biomarker development, preclinical models, combination therapies, mechanisms of resistance and clinical trial design considerations.

Abstract The selectivity of the blood-brain-barrier (BBB) can prevent therapeutics from reaching the brain, and this may contribute to the high failure rate of new drugs for tumors like glioblastoma (GBM) and brain metastasis. The capacity to detect BBB penetrance in real-time in a noninvasive manner would arguably aid the rate of therapeutic development. Extracellular vesicles, which are membrane bound particles secreted by all cell types in the body, have potential as a neuro pharmacodynamic reporter given that their protein and RNA cargo reflect the originating cell population. We hypothesized that the exposure of GBM cells to therapy results in altered EV cargo, and that the detection of this shift can be leveraged as a liquid biopsy from patients during early clinical trials to determine BBB penetrance and tumor engagement. To identify cargo shifts indicative of treatment, we exposed four short-term patient derived glioma cell lines to arsenic trioxide (an idiopathic toxin), MLN4924 (a neddylation inhibitor), and the alkylating agent temozolomide, then harvested EVs for unbiased mass spectrometry and RNA sequencing. Interestingly, we identified conserved upregulated and downregulated protein and RNA species across cell lines and across drug treatments, despite the diverse mechanisms of action. Candidate proteins were further validated by mesoscale immunoassays and exoview evaluation of tetraspanin-captured EVs. RNA species were validated by qRT-PCR. Overall, we demonstrate that GBM-derived EV cargo changes in response to therapy, supporting the development of EVs as a reporter of drug delivery in GBM. Ongoing and future work is focused on identifying enrichment handles in order to selectively evaluate GBM-derived EV cargo from patient biofluids. Thus far, B7H3, PTPRZ1, EGFRvII and IL13Ra2 have been screened as putative handles. Success in this pursuit could substantially enhance findings and accelerate drug testing in early-stage clinical trials in brain tumor patients by reporting drug accessibility to the tumor and engagement with drug targets. Citation Format: Valerie DeLuca, Nanyun Tang, Nathaniel Hansen, Anjali Raju, Charles Shaffer, Yue Hao, Terry C. Burns, Jann N. Sarkaria, Ian Parney, Patrick Pirrotte, Kendall Van Keuren-Jensen, Michael E. Berens. Glioblastoma-derived extracellular vesicle cargo as a reporter of drug delivery and effect [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2130.

Abstract Radiation therapy (RT) is a cornerstone of oncologic therapy for the majority of solid malignancies, and unrepaired DNA double-strand breaks are responsible for radiation-induced cytotoxicity. RT-induced DNA lesions can be repaired by multiple mechanisms including homologous recombination (HR) and non-homologous end joining (NHEJ), and disruption of either of these pathways can enhance cytotoxicity. A key component of the NHEJ pathway is the catalytic subunit of DNA-dependent protein kinase (DNA-PKcs), and loss of kinase activity can significantly increase radiosensitivity. Herein we describe the results of our medicinal chemistry campaign to develop a potent and selective DNA-PKcs inhibitor, WNC0901. WNC0901 inhibits DNA-PKcs kinase activity in a cell free system with an IC50 of 0.071 nM and demonstrated at least 30-fold higher sensitivity than other family members (ATM, ATR, mTOR, PI3K). WNC0901 has limited aldehyde oxidase (AO) liability with a T1/2 &gt;2000 min in liver cytosol and is stable for over 120 minutes in the presence and absence of an AO inhibitor. A preliminary pharmacokinetic analysis in wista han rat (IV=2mg/kg, PO=20mg/kg) demonstrated 116% apparent absolute oral bioavailability, 2.6 hour terminal half-life, 33.0 mL/min/kg clearance, and a 2.6% unbound brain-to-plasma partition coefficient (Kpuu). WNC0901 also had favorable pharmacokinetic properties in beagle dog (IV=2mg/kg, PO=20mg/kg) with moderate clearance (8.5 mL/min/kg), high apparent absolute oral bioavailability (131%) with good exposure (AUC=36092 h*ng/mL), moderate half-life (4.28 h), and low protein binding (74.3% fraction unbound). The volume of distribution was moderate in both species (Vss = 1.32 L/kg in wistar han rat and 1.87 L/kg in beagle dog). In cell culture, WNC0901 inhibited autophosphorylation of DNA-PKcs in HT29 cells irradiated with 10 Gy with an IC50 of 32.7 nM and robustly inhibited autophosphorylation in both U251 glioma and A549 lung cancer cell lines at 300 nM in combination with 5Gy. In a clonogenic assay, 5Gy irradiation (10% survival) combined with 100nM WNC0901 demonstrated modestly enhanced cell killing (1.5% survival), and maximal effects were seen at 300nM (0.04% survival, p&lt;0.01). Similar radiosensitizing effects with 300 nM WNC0901 were seen in the A549 cell line (0.2% survival with combination compared to 19% with 5Gy alone, p&lt;0.01). In summary, WNC0901 inhibits DNA-PK kinase activity and provides potent radiosensitization in a GBM and lung cancer cell line. Future studies will assess the combination of WNC0901 and RT in GBM patient-derived xenograft models in vivo. Citation Format: Ann C. Mladek, Danielle L. Burgenske, William F. Elmquist, Wei Zhong, Jann N. Sarkaria. Preclinical data of a novel DNA-PK inhibitor in combination with radiation therapy shows promise in the treatment of established GBM and lung carcinoma cell lines [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 701.

Abstract Mayo Clinic has developed 111 GBM PDXs from newly diagnosed (72 PDX) and recurrent (39 PDX) patients. This large collection of PDXs provides a broad representation of genetic heterogeneity seen in patients. GBM PDXs that perform well in both in vitro and in vivo settings can be extensively utilized in the preclinical setting for downstream analysis. Based on 20 years of experience, we have defined the attributes that best enable preclinical use of our GBM PDX models. Among them are short-term in vitro culturing performance, large scale genomic evaluation data, benchmarked responses to standards of care, and median time to moribund for untreated orthotopic tumors. PDXs with prolonged survival timelines delay study readouts and, in some situations, confound efficacy results due to age-related animal decline. Setting median survival thresholds as part of the upfront experimental design allows for more timely study readouts that are unaffected by these confounding variables. Our preferred cutoff for the Mayo GBM PDX collection is 70 days median survival (n=64). Using this 64 PDX line panel, regimens expected to double survival would produce results within 4-5 months. This timeframe is well within the range of robust health for athymic nude mice. This 64-line collection features both newly diagnosed (nGBM; n=42) and recurrent (rGBM; n=22) tumors. MGMT promoter methylation status was determined by qMS-PCR (25 methylated, 37 unmethylated, 2 indeterminate). Available WES (n=62) and RNAseq (n=42) data, along with our tissue microarray (n=42), are critical resources for biomarker-based evaluations aimed at defining patient populations that are most likely to benefit from a given therapeutic. From these data, the molecular subtypes available include 26 classical, 14 proneural, and 3 mesenchymal. Twenty-seven of these 64 PDX models have also been successfully cultured from fresh as well as cryopreserved cell stocks to further expand their experimental value. Correlative clinical data including diagnosis and treatments are also available (n=61). Current standards of care for GBM include radiation, temozolomide, and bevacizumab. Defining sensitivity to these therapies is an important first step for evaluating the integration of novel therapeutics with these standards. Since the creation of our GBM PDX collection, efficacy of these therapies has been evaluated as follows: RT 26 PDXs, TMZ 20 PDXs, and Avastin 23 PDXs. The Mayo Clinic GBM PDX collection provides an important platform for preclinical evaluation of novel therapeutics. Through careful selection of PDX lines with favorable growth characteristics and known genetic features, researchers can select the most relevant models for their study. This approach will enable more meaningful preclinical work in the hopes of providing more tangible clinical benefits for GBM patients. Citation Format: Danielle M. Burgenske, Ann C. Mladek, Katrina K. Bakken, Zeng Hu, Brett L. Carlson, Paul A. Decker, Jeanette E. Eckel-Passow, Jann N. Sarkaria. Defining critical features for successful preclinical use of glioblastoma patient-derived xenografts (PDX) models for therapeutic assessment and clinical trial development [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6897.

Abstract Glioblastoma (GBM) is one of the most malignant central nervous system (CNS) tumors and accounts for more than 60% of primary brain tumors in adults [1]. While chemotherapy is a frequently employed treatment for GBM, its lack of specificity towards tumor cells leads to toxicity in healthy tissues. Antibody-drug conjugates (ADCs) are a prevalent targeted-drug delivery strategy that may enhance the therapeutic window. ADC development for GBM has progressed in recent years, yet recent clinical trials have thus far failed to demonstrate drug efficacy [2]. This is likely attributed to poor brain penetration and heterogeneous drug distribution within GBM [3]. Convection-enhanced delivery (CED) is an invasive delivery method that can achieve direct administration of therapeutics to brain tumors and potentially could be used to enhance the delivery and efficacy of ADCs. This study investigates the CNS and systemic pharmacokinetics and distribution of similar payload molecules following CED administration of two GBM-targeting ADCs, ABBV-221 and ABT-414. The ADC payloads are monomethyl auristatin E (MMAE) and monomethyl auristatin F (MMAF), respectively, and both are potent anti-tubulin toxins commonly used as warheads for ADCs. Both ADCs and free MMAE were administered as single doses to FVB mice via CED infusion or intraperitoneal (IP) injection. Plasma and brain samples were collected over 24 hours for ABBV-221 and 96 hours for ABT-414, and unconjugated payload molecules were quantified via LC-MS/MS analysis. The results showed that free (i.e., not bound to the targeting antibody) MMAE has a significantly higher exposure in brain compared to plasma when delivered via CED, and exposure in the right hemisphere was 10-fold higher than the left hemisphere, as the site of CED infusion was located in the right hemisphere for all trials. Similar results for MMAE payload were observed after the CED of ABBV-221. Systemic administration of ABBV-221 resulted in a nearly 100-fold decrease in unconjugated MMAE concentration in brain, indicating the poor brain penetration of the ADC. Similarly, following the CED of ABT-414, unconjugated payload concentration was the highest in right anterior brain among all brain regions, and plasma concentration was below the limit of quantification. Systemic injection of ABT-414 resulted in non-quantifiable payload concentrations in either brain or plasma samples. Taking these results as a whole, this study demonstrated significantly enhanced brain distribution of payload molecules from GBM-targeting ADCs following CED compared to systemic administration. The consistent payload delivery pattern observed in both ADCs further supports the potential of CED as an effective drug delivery method for the treatment of GBM. These findings highlight the promise of CED as a means to address the limitations of conventional chemotherapy and improve therapeutic outcomes in GBM treatment. 1. Sarkaria JN et al. Neuro Oncol. 2018; 20:184–91. 2. Lassman AB et al. Neuro Oncol. 2023; 25:339–50. 3. Marin B-M, et al. Neuro Oncol. 2021; 23:2042–53. Citation Format: Jessica I. Griffith, Jiayan Le, Kendra A. Porath, Sonia Jain, Katrina K. Bakken, Jann N. Sarkaria, William F. Elmquist. CNS and systemic pharmacokinetics of antibody-drug conjugate payloads through convection-enhanced delivery [abstract]. In: Proceedings of the AACR Special Conference on Brain Cancer; 2023 Oct 19-22; Minneapolis, Minnesota. Philadelphia (PA): AACR; Cancer Res 2024;84(5 Suppl_1):Abstract nr B023.