Sarkaria, Jann N.

Glioblastoma (GBM), a highly invasive and vascular malignancy is shown to rapidly develop resistance and evolve to a more invasive phenotype following bevacizumab (Bev) therapy. Rho Guanine Nucleotide Exchange Factor proteins (RhoGEFs) are mediators of key components in Bev resistance pathways, GBM and Bev-induced invasion. To identify GEFs with enhanced mRNA expression in the leading edge of GBM tumours, a cohort of GEFs was assessed using a clinical dataset. The GEF βPix/COOL-1 was identified, and the functional effect of gene depletion assessed using 3D-boyden chamber, proliferation, and colony formation assays in GBM cells. Anti-angiogenic effects were assessed in endothelial cells using tube formation and wound healing assays. In vivo effects of βPix/COOL-1-siRNA delivered via RGD-Nanoparticle in combination with Bev was studied in an invasive model of GBM. We found that siRNA-mediated knockdown of βPix/COOL-1 in vitro decreased cell invasion, proliferation and increased apoptosis in GBM cell lines. Moreover βPix/COOL-1 mediated endothelial cell migration in vitro. Mice treated with βPix/COOL-1 siRNA-loaded RGD-Nanoparticle and Bev demonstrated a trend towards improved median survival compared with Bev monotherapy. Our hypothesis generating study suggests that the RhoGEF βPix/COOL-1 may represent a target of vulnerability in GBM, in particular to improve Bev efficacy.

Chromosome region maintenance protein1 (CRM1) mediates protein export from the nucleus and is a new target for anti-cancer therapeutics. Broader application of KPT-330 (selinexor), a first in class CRM1 inhibitor recently approved for multiple myeloma and diffuse large B-cell lymphoma (DLBCL), has been limited by substantial adverse effects (AEs). To address this clinical problem, we focused on identifying novel strategies to boost the potency, reduce toxicity, and broaden the applicability of CRM1 inhibitors to a wider range of malignancies. We discovered that salicylates could markedly enhance the anti-tumor activity of CRM1 inhibitors by extending the mechanisms of action beyond CRM1 inhibition. KPT-330 was chosen as the prototypical CRM1 inhibitor given its current FDA approval status and characterized pharmacokinetics; and choline salicylate (CS) was chosen as the prototypical salicylate given its favorable pharmacokinetics and reduced antiplatelet, renal, neurological and gastrointestinal AEs in humans compared to other salicylates. By using cell lines belonging to different hematologic malignancies and solid tumors, we demonstrated ex vivo that the combination of KPT-330 and CS (K+CS) could induce unique and significant antitumor effect at much lower dose of KPT-330 (at 25% of the dose used in the clinic), thereby potentially mitigating prohibitive clinical AEs (Figure 1a-d, and e-g). This significant synergetic antitumor effect observed with K+CS ex vivo was also validated in vivo by using an NSG mouse model of mantle cell lymphoma (Figure 1h). Moreover, the K+CS combination did not show this potent toxic effect on non-malignant cells in vivo and was safe without inducing toxicity to normal organs in NSG mice. Mechanistically, protein profiling through mass spectroscopy revealed that K+CS uniquely affects the cellular pathways of DNA damage repair, DNA synthesis and cell cycle progression. Studies involving immunoblotting, cell cycle analysis, immunofluorescence microscopy assessing nucleocytoplasmic molecular export and DNA damage, reporter assay to assess homologous recombination repair proficiency and immunohistochemistry showed that, compared to KPT-330 treatment alone, K+CS decreased the expression of CRM1, Rad51 and thymidylate synthase proteins in vitro and in vivo, leading to more efficient inhibition of CRM1-mediated nuclear export, impairment of DNA-damage repair, reduced pyrimidine synthesis, and importantly a unique cell cycle arrest in S-phase, thus leading to cell apoptosis. These effects on cellular proteins and pathways were unique to K+CS treatment and were not observed with KPT-330 or CS single agent treatment. Pathway analyses through RNA sequencing also paralleled the findings of proteomic studies thus further validating the unique effect of K+CS treatment on the aforementioned cellular pathways. Importantly, K+CS treatment exerted unique and significant antitumor effect ex vivo on primary malignant cells obtained from patient's with high-risk hematologic malignancies such as double hit DLBCL, BTK and BCL2 inhibitor resistant mantle cell lymphoma, TP53 deleted/mutated chronic lymphocytic leukemia and high-risk multiple myeloma thus signifying its broader applicability as a treatment option for these aggressive hematologic malignancies where there is a dire need to find new treatment strategies (Figure 1i). In summary, we describe a unique all-oral drug combination with a novel constellation of mechanisms of action on cellular pathways that are exploited by cancer cells. K+CS represents a new class of therapy for multiple cancer types and will stimulate future investigations to exploit DNA-damage repair and nucleocytoplasmic transport for therapy of blood cancers. Disclosures Witzig: Karyopharm Therapeutics: Research Funding; Acerta: Research Funding; Incyte: Consultancy; AbbVie: Consultancy; Celgene: Consultancy, Research Funding; MorphSys: Consultancy; Immune Design: Research Funding; Spectrum: Consultancy.

Abstract Chromosome region maintenance protein 1 (CRM1) mediates protein export from the nucleus and is a new target for anticancer therapeutics. Broader application of KPT-330 (selinexor), a first-in-class CRM1 inhibitor recently approved for relapsed multiple myeloma and diffuse large B-cell lymphoma, have been limited by substantial toxicity. We discovered that salicylates markedly enhance the antitumor activity of CRM1 inhibitors by extending the mechanisms of action beyond CRM1 inhibition. Using salicylates in combination enables targeting of a range of blood cancers with a much lower dose of selinexor, thereby potentially mitigating prohibitive clinical adverse effects. Choline salicylate (CS) with low-dose KPT-330 (K+CS) had potent, broad activity across high-risk hematological malignancies and solid-organ cancers ex vivo and in vivo. The K+CS combination was not toxic to nonmalignant cells as compared with malignant cells and was safe without inducing toxicity to normal organs in mice. Mechanistically, compared with KPT-330 alone, K+CS suppresses the expression of CRM1, Rad51, and thymidylate synthase proteins, leading to more efficient inhibition of CRM1-mediated nuclear export, impairment of DNA-damage repair, reduced pyrimidine synthesis, cell-cycle arrest in S-phase, and cell apoptosis. Moreover, the addition of poly (ADP-ribose) polymerase inhibitors further potentiates the K+CS antitumor effect. K+CS represents a new class of therapy for multiple types of blood cancers and will stimulate future investigations to exploit DNA-damage repair and nucleocytoplasmic transport for cancer therapy in general.

Abstract The efficacy of standard radiation therapy (RT) in glioblastoma (GBM) is limited, and there is a strong rationale to develop effective radiosensitizing agents. ATM is a key regulator of DNA damage induced by RT, and small molecule ATM inhibitors have shown radio-sensitizing effects in cancer cells, and may improve radio-sensitivity in GBM. Here, we evaluated the brain penetrant ATM inhibitor AZD1390 in combination with RT in GBM cell lines and patient derived xenografts (PDXs). AZD1390 (30 nM and higher) suppressed ionizing radiation-(5 Gy, IR) induced phosphorylation of ATM-Serine1981 and downstream signaling proteins Kap1, Chk2 and H2AX in GBM established cell lines (U251 and U87) and PDX lines (GBM12, GBM39 and GBM43). In cell cycle analysis, 30nM AZD1390 enhanced the IR induced G2/M arrest in U251 (80.6% with AZD1390/IR vs. 64.6% with IR alone, p= 0.01) and PDX lines GBM43 (61.9% vs. 25.7%, p= 0.01) and GBM39 (40.9% vs. 25.4%, p= 0.01). Moreover, in a U251 clonogenic survival assay, AZD1390 sensitized cells to IR-(5 Gy) induced killing (0.24% survival with AZD1390/RT vs. 2.3% with IR alone, P=0.01). For in vivo radiation combination studies, mice with established orthotopic tumors were irradiated to the cerebrum through opposed laterals with a 225 kVp stereotactic animal irradiator. While the hard palate and upper tongue were in the radiation target, the oropharynx and hypopharynx were spared with this radiation set up. A pilot study of RT combined with AZD1390 was evaluated in mice with established U251 orthotopic tumors using cohorts of 5 mice per arm. AZD1390 was given concurrently with conventionally fractionated radiation (2 Gy x 5 fractions) at a dose of 20 mg/kg PO delivered either daily or twice daily, with or without the efflux inhibitor elacridar. RT alone was well tolerated with minimal weight loss but was ineffective (median survival 30 days vs. 33 days in control group, p=0.5). In contrast, all of the RT/AZD1390 treatment arms exhibited enhanced but tolerable weight loss and had significant extension in symptom-free survival that currently extends beyond 65 days (median survival no reached). In conclusion, AZD1390 is an effective radio-sensitizer in vitro, and survival benefit from AZD1390 combined with conventionally fractionated RT in U251 models is encouraging. Further evaluation of efficacy across additional PDX models and careful analysis of the pharmacodynamic effects in tumor vs. normal tissues will be important to understand the therapeutic window for this agent in combination with RT. Citation Format: Jiajia Chen, Shiv K. Gupta, Gaspar J. Kitange, Ann C. Mladek, Brett L. Carlson, Lihong He, Zeng Hu, Katrina K. Bakken, Danielle M. Burgenske, Margaret A. Connors, Jann N. Sarkaria. Targeting ATM with AZD1390 for radio-sensitization of glioblastoma patient derived xenografts [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 6506.

Abstract Despite aggressive treatment that involves surgery, radiation and temozolomide therapy, a significant morbidity from glioblastoma (GBM) recurrence highlights the pressing unmet medical need to develop effective novel therapies for GBM. Murine Double Minute 2 (MDM2) is an important regulator of the p53 tumor suppressor, which promotes cell cycle arrest and apoptosis in response to DNA damage. Here we have assessed the efficacy of RG7388, a purported brain penetrant MDM2-inhibitor, alone or combined with radiation therapy (RT) in patient-derived xenograft (PDX) models of GBM. In vitro, RG7388 suppressed viability of GBM PDX short-term stem cell cultures of p53 wildtype lines with MDM2-amplification (GBM46 and 108, IC50 25 and 11 nM, respectively) or without MDM2-amplification (GBM10 and 14, IC50 43.5 and 9.1 nM, respectively). Serum proteins appear to reduce efficacy of RG7388, which is supported by the notion that adding 2.5% bovine serum albumin to a serum free stem cell cultures increased the IC50 by 3 to 5 fold. At the molecular level, both RG7388 and RT could induce p53 signaling in GBM10, but a more robust induction was observed with the combination. In athymic nude mice, RG7388 readily distributes into normal brain as measured by LCMS-MS at 1 hour after five daily oral doses (70 mg/kg) the average RG7388 concentrations in brain and plasma were 2167 ng/g and 4423 ng/ml, respectively. In an initial efficacy study using flank tumors established from GBM10, one week of dosing at 70 mg/kg/day RG7388 alone was ineffective, while combining RG7388 with focal radiation (4 daily doses of 5 Gy each) had a moderate 15 day delay in tumor progression. However, in an MDM2-amplified GBM108 line with a relatively intact blood-brain barrier, one week of daily RG7388 dosing, either alone or in combination with RT was remarkably effective (median survival 71 days with RG7388 alone vs. 29 days with vehicle, p<0.0001; and 262 days for RG7388/RT vs. 74 days with RT, p=0.017). Taken together, RG7388 alone or in combination with RT is highly effective in an MDM2-amplified pre-clinical model of GBM. Determining impact of serum protein binding on drug pharmacokinetics and further evaluation of pharmacodynamic effects and orthotopic therapy in additional p53 wildtype PDX lines will help to increase our understanding if RG7388/RT therapy can be used in a larger population of GBM tumors. Citation Format: Shiv K. Gupta, Ann C. Mladek, Surabhi Telele, Afroz S. Mohammad, Lihong He, Zeng Hu, Katrina K. Bakken, Danielle M. Burgenske, Brett L. Carlson, William F. Elmquist, Jann N. Sarkaria. Brain penetrant MDM2 inhibitor RG7388 extends survival benefit of radiation treatment in select glioblastoma patient-derived xenograft models [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 6276.

Abstract New approaches are needed to overcome intrinsic therapy resistance in glioblastoma (GBM). Because GBMs exhibit sexual dimorphism and are reported to express steroid hormone receptors, we reasoned that signaling through the androgen receptor (AR) could mediate therapy resistance in GBM, as it does in AR-positive prostate and breast cancers. Using RNAseq, immunoblot and immunohistochemistry, we found that nearly half of GBM cell lines, patient-derived xenografts and human tumors express AR transcript and protein with levels that overlap those of primary prostate cancer. AR expression in GBM did not vary by sex, age or common molecular alterations. We identified two cell line models of GBM that expressed AR protein (LN18 and T98G: termed “AR positive”) and two that did not (8MGBA and AM38: termed “AR negative”). Seviteronel, a blood-brain barrier permeable CYP17 lyase inhibitor and antiandrogen slowed growth in AR positive GBM cell lines (GI50 3-4 µM) but not AR negative lines (GI50 > 500 µM) as measured by the colony formation assay. The antiandrogen enzalutamide, which also penetrates the blood brain barrier, similarly preferentially slowed growth in AR positive GBM cell lines. Seviteronel and enzalutamide sensitized AR positive GBM cell lines to radiation with enhancement ratios of 1.3-1.6 as measured by the clonogenic survival assay. Antiandrogens had no effect on the radiosensitivity of AR negative GBM cell lines. Seviteronel treatment did not affect the growth of AR positive T98G xenografts grown in vivo, but did sensitize these tumors to radiation (median time to tripling: 15 d with radiation alone and not reached with radiation combined with seviteronel). Enzalutamide similarly had modest single agent effects on an AR positive GBM patient-derived xenograft (GBM26 from the Mayo Clinic GBM PDX national resource) grown in vivo but sensitized these tumors to radiation (median time to tripling: 25.5 d with radiation alone and 39 d with radiation combined with enzalutamide). RNAseq performed on GBM26 tumors grown in vivo revealed that enzalutamide treatment caused minimal transcriptional changes when given as monotherapy but, when given in combination with radiation, blocked the ability of AR-positive GBMs to engage adaptive transcriptional programs related to multiple DNA repair pathways. We confirmed these mechanistic findings in vitro, as antiandrogens selectively impaired the repair of radiation-induced double strand DNA breaks in AR positive GBM cell lines. These results suggest that AR signaling may mediate therapy resistance in AR positive GBMs, and patients with these tumors could derive clinical benefit from combination therapies involving radiation and blood-brain-barrier permeable antiandrogens. Citation Format: Christian K. Werner, Uchechi Nna, Hanshi Sun, Kari Wilder-Romans, Joseph Dresser, Ayesha Kothari, Weihua Zhou, Yangyang Yao, Arvind Rao, Stefanie Stallard, Carl Koschmann, Tarik Bor, Waldemar Debinski, Alexander Hegedus, Meredith Morgan, Sriram Venneti, Edwina Baskin-Bey, Daniel Spratt, Howard Colman, Jann Sarkaria, Arul Chinnayain, Joel Eisner, Corey Speers, Theodore S. Lawrence, Roy Strowd, Daniel R. Wahl. Repurposing antiandrogens to overcome therapy resistance in androgen receptor-positive glioblastoma [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 6267.

Abstract Robust function of the p53 tumor suppressor pathway is critical when treating with DNA-damage inducing agents such as radiation therapy (RT), which is a key component of standard care for GBM. MDM2 is an important negative regulator of p53 stability and MDM2 is amplified in approximately 14% of GBM. Based on the concept that suppression of MDM2 can reactivate p53 function and potentially have single agent or combinatorial effects, multiple MDM2 inhibitors have been developed. Here we report in vitro and in vivo efficacy and pharmacodynamic (PD) effects of a BBB-penetrant MDM2-p53 antagonist, BI-MDM2, in GBM patient-derived xenograft (PDX) models. In vitro studies in p53 wild-type (WT) lines with or without MDM2 amplification demonstrate IC50 values in cell viability assays of 2-12 nM in serum-free culture and 5-35 nM in serum-containing culture after seven days of treatment. In vivo studies were performed in p53 WT lines: the MDM2-amplified GBM108, and the non-amplified GBM14, grown as orthotopic tumors in nude mice. Weekly oral treatment at 2 mg/kg of BI-MDM2 doubled median survival (placebo, 28 days (d) vs 2 mg/kg BI-MDM2, 57 d. p<0.0001) while weekly dosing at 10 mg/kg extended the median over 5 fold (176 d. p<0.0001) with half of the mice still living at 223 days post-inoculation. To assess the PD properties of this compound, mice bearing orthotopic GBM108 were treated three weeks after inoculation with a single dose of 2 or 10 mg/kg BI-MDM2. Normal brain, tumor, and plasma were collected at 24 and 48 hours (h) after dosing and downstream p53 transcriptional targets, p21 and PUMA were evaluated by qRT-PCR. p21 mRNA relative quantification detection at 24h increased by 1.5-10.5-fold in the 2 mg/kg group of animals compared to vehicle while the 10 mg/kg dose led to an increase by 2-25 fold compared to vehicle. PUMA was minimally affected by the 2 mg/kg dose but increased 1.2-17-fold over vehicle in the 10 mg/kg group at 24h. The observed increases in p21 and PUMA varied little between the 24 and 48h timepoints. In an orthotopic GBM14 PDX efficacy study, BI-MDM2 was combined with 20 Gy RT delivered in 10 fractions over 2 weeks with dosing limited to 2 weeks of therapy or until mice reached a moribund state. While two doses of 10 mg/kg BI-MDM2 alone had a modest effect on survival (41 d vs 31 d with placebo; p=0.002), continued dosing until moribund further extended median survival (82 d with BI-MDM2; p=0.001). The combination of two doses of BI-MDM2 with 2 weeks of RT extended survival as compared to RT alone (107 d vs. 69 d, respectively; p=0.019), while with extended drug dosing combined with 2 weeks of RT, median survival has not yet been reached (>125 d). Taken together, these results suggest that BI-MDM2 is a promising therapeutic agent that may provide significant anti-tumor efficacy either alone or in combination with RT in both MDM2 amplified and non-amplified p53 WT patients. Citation Format: Ann C. Mladek Tuma, Shiv Gupta, Surabhi Talele, Afroz Shareef Mohammad, Katrina K. Bakken, Helen He, Zeng Hu, Margaret A. Connors, Danielle M. Burgenske, Brett L. Carlson, William F. Elmquist, Ulrike Weyer-Czernilofsky, Jann N. Sarkaria. A promising blood-brain-barrier penetrant MDM2-p53 antagonist, BI-MDM2, increases survival in orthotopic, glioblastoma patient-derived xenograft models [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 4190.

Abstract Radio-resistant properties of melanomas undermine benefit of radiation therapy (RT). DNA-dependent protein kinase (DNA-PKcs) is essential for the non-homologous end joining (NHEJ) mediated repair DNA double-strand break (DSB). We evaluated radio-sensitizing effects of M3814, a selective oral inhibitor of DNA-PKcs, in patient-derived xenografts (PDXs) of melanoma brain metastases. M3814 (≥300 nM) inhibited RT-induced (5 Gy) auto-phosphorylation of serine-2056 of DNA-PKcs in primary cultures of M12, M15 and M27 PDX lines. Interestingly, inhibition of RT-induced DNA-PKcs by M3814 coincided with increased KAP1 phosphorylation, a DNA damage signaling regulated via ATM. As a measure of lasting DNA damage, persistent γH2AX foci were observed in 28% cells 24 hours after co-treatment with M3814 and RT as compared to RT controls, where only 12% cells had persistent γH2AX foci. In a clonogenic survival assay, M3841 augmented RT-induced killing of M12 cells in a dose dependent manner. However, a minimal 16 h exposure with ~300 nM M3814 was most effective treatment. Pharmacokinetics (PK) after single oral dose of 20 mg/kg M3814, showed considerably short half-life (~2.44 hours) and poor brain distribution in wildtype (WT) FBV mice (Kpuu, 0.027). Suggesting liability to efflux transporters, brain distribution of M3814 in TKO mice (triple knockouts for efflux transporters Mdr1a, Mdr1b and BCRP1) was ~11 fold higher than WT animals (kpuu, 0.215). Using this preliminary PK data, simulations were performed using simBiology software to define dosing regimen and schedule to maximize drug exposures in brain. Based on this in silico modeling, two regimens- (A: 125 mg/kg twice a day (at 0 and 7 hours), and B: 50 mg/kg dose followed by three additional doses of 35 mg/kg per day at 4 hour intervals), combined with a single fraction RT (3 Gy) delivered 10 min after the first M3814 dose in each regimen, were tested in athymic nude mice carrying M12 flank tumors. In this study, drug levels achieved in brain and plasma (121±95, 1914±1661 nM with regimens A and 79±51, 1205±664 nM with regimen B, respectively at 24 h), exceeded predictions. Consistent with a much higher accumulation of M3814 in flank tumor tissues (1.5 to 3.4 fold higher than plasma), therapy with M3814/RT had robust pharmacodynamics effects on DNA damage signaling both at 6 and 24 hours of treatment as compared to RT alone. In summary, M3814 is a promising radio-sensitizer in melanoma brain metastases. Further studies will determine efficacy and pharmacodynamics effects of M3814/RT regimens in relevant orthotopic models of brain metastases and address potential concerns of normal tissue toxicity. Citation Format: Jianxiong Ji, Emily J. Smith, Paige Sarkaria, Ann C. Mladek, Surabhi Talele, Katelyn Swanson, Afroz S. Mohammad, Lihong He, Zeng Hu, Katrina K. Bakken, Shiv K. Gupta, Danielle M. Burgenske, Gaspar J. Kitange, William F. Elmquist, Jann N. Sarkaria. Inhibition of DNA-PKcs by M3814 potentiates efficacy of ionizing radiation in patient derived xenografts of melanoma brain metastases [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 1381.

Abstract The Mayo Clinic collection of patient-derived xenograft (PDX) models has been developed from the direct implantation of fresh glioblastoma samples into immunodeficient mice. Over 95 models have been extensively characterized with regards to histology, invasion, flank and orthotopic growth rates, and molecular profiling. Evaluation of orthotopic tumors demonstrated clear infiltration of tumor cells into the brain parenchymal in 90% of PDXs with contralateral hemisphere involvement in 64%. Extensive molecular profiling confirmed that our collection of PDXs captures the genetic heterogeneity of GBM, with the majority of known alterations represented at a frequency similar to the TCGA including gain of chromosome 7 and loss of chromosome 10. TERT promoter mutations were the most frequent overall (86%) followed by homozygous deletion of CDKN2A (70%). Multiple alterations were identified in the p53 pathway, including TP53 mutations (36%) and MDM2/4 (10%/2%) amplification. PI3-kinase pathway alterations mainly involved PTEN (48%) while MAP kinase pathway alterations were present in a subset of PDXs (NF1 alterations 17%, BRAF 4%). IDH mutations were found in only two models. Gene expression analysis revealed that our PDX collection includes all GBM subtypes with classical being the most represented (46% vs mesenchymal 31% and proneural 23%). MGMT promoter methylation was also observed in 45% of PDXs. The high fidelity of PDX models to their human counterpart makes these models ideal for testing standard of care and novel targeted therapies. To assess if PDXs are predictive of patient treatment response, 37 orthotopic PDX lines were treated with radiation (RT), temozolomide (TMZ), or concurrent RT/TMZ. Across all PDXs, RT and TMZ demonstrated median survival extension of 90 and 46 days relative to vehicle. Concurrent RT/TMZ further extended survival by 146 days. MGMT promoter methylation was strongly associated with response to TMZ-based strategies but not RT alone.This observation suggests that our PDX collection possesses clinically relevant predictive value. To date, we have characterized treatment responses to over 135 regimens including both GBM standards of care and targeted strategies in our PDX models. Recent lab efforts strive to define the effect of blood brain barrier disruption on drug delivery. With over 20 years of experience, our group has extensive expertise in the development of clinically relevant study designs focused on examining efficacy, tolerability, and pharmacokinetic/pharmacodynamic assessments. Since 2016, we have shared over 5200 individual samples (tumor tissue, cells, DNA/RNA, protein extracts, tissue microarray slides) in both internal and external collaborators. Our models have been utilized in over 41 NIH funded grants, including 33 funded RO1s, as well as by the pharmaceutical community with 50 working relationships to date (20 contracts, 30 collaborations). Finally, our PDX collection has been used in over 120 peer-reviewed published manuscripts. Citation Format: Danielle Burgenske, Ann C. Mladek, Rachael A. Vaubel, Shulan Tian, Mark A. Schroeder, Zeng Hu, Brett L. Carlson, Paul A. Decker, Jeanette E. Eckel-Passow, Jann N. Sarkaria. Evaluation of novel therapeutics using models from the Mayo Clinic GBM patient-derived xenograft (PDX) collection [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 1113.

2019 Background: The mammalian target of rapamycin (mTOR) functions within the PI3K/Akt signaling pathway as a critical modulator of cell survival. We previously demonstrated significant synergy of the mTOR inhibitor sirolimus with RT in glioma xenografts. Methods: The standard cohorts of 3 design was applied with dose escalation of weekly IV CCI-779 in combination with standard TMZ/RT. CCI-779 was given during both RT (60 Gy)/TMZ (75 mg/m2 daily) and adjuvant TMZ (200 mg/m2 daily x 5 every 28 days). Results: A total of 17 patients were enrolled. CCI-779 therapy during RT/TMZ was well tolerated at dose level 0 (25 mg CCI-779, n = 3) and dose level 1 (50 mg CCI-779, n = 6) with 1 of 9 patients experiencing a DLT (Gr 3 fatigue). Dose level 2 (75 mg CCI-779) exceeded the maximally tolerated dose with two of six patients with DLT (<75% CCI-779 delivered; Gr 4 dyspnea). Despite reasonable tolerance during RT/TMZ, the overall regimen was associated with a high rate of infection associated with lymphopenia. After a patient died from PCP on cycle 2 of adjuvant TMZ/CCI-779, antibiotic prophylaxis was mandated. Two other patients died of gram-negative sepsis despite prophylaxis: one after their first dose of CCI-779 and one during cycle 4 of adjuvant therapy. In contrast to our 18% grade 5 infection rate, only 4% grade 3 (no grade 4/5) infections were observed in 26 other CTEP-sponsored clinical trials involving 1,006 patients treated with CCI-779. Results from translational studies evaluating the effects of treatment on immune function will be presented. Further infections were avoided on this trial after CCI-779 therapy was limited to RT/TMZ. Conclusions: Although CCI-779 in combination with RT/TMZ was well-tolerated, adjuvant therapy with TMZ/CCI-779 was associated with an increased risk of opportunistic infections. [Table: see text]