Low-dose Temozolomide Research Articles

Abstract 7207: Targeting hippo signaling pathway to overcome chemoresistance in glioblastoma

Abstract The study aims to investigate whether the Hippo signaling pathway contributes to temozolomide chemoresistance in glioblastoma, and to validate whether the combinational treatment of temozolomide and YAP inhibitor is effective against glioblastoma. Temozolomide-sensitive and temozolomide-resistant U87 and U251 GBM human cell lines were previously established. Temozolomide-resistant cells were maintained in low-dose temozolomide. Here, we investigate whether Hippo signaling contributes to temozolomide chemoresistance. By modulating the Hippo signaling pathway through YAP gene knockdown, the outcome on cell proliferation was studied by cell viability assay (in vitro) and mouse orthotopic xenograft (in vivo). Finally, the therapeutic effect of YAP inhibitor is studied in vitro and in vivo respectively. Our data showed that YAP is overexpressed in temozolomide-resistant glioblastoma cells. Nuclear translocation of YAP (which becomes its active state) is increased in temozolomide-resistant cells. In fact, YAP inhibition show decreased cell viability and higher susceptibility to temozolomide. In addition, mice with tumor injection of the YAP knockdown cells reduced tumor size with temozolomide treatment. Similarly, YAP inhibitor resensitizes temozolomide-resistant cells to temozolomide. Combinational treatment of YAP inhibitor and temozolomide is effective in shrinking tumor size in mouse xenograft models. In conclusion, our data suggest dysregulated Hippo signaling pathway contributes to temozolomide chemoresistance, thus targeting the Hippo signaling pathway resensitizes GBM cells to temozolomide. This research provides pre-clinical evidence on using YAP inhibitor for combinational therapy with temozolomide for the treatment of glioblastoma. Citation Format: Cheuk Lun Ethan Wong, Mei Yee Karrie Kiang, Ka Kit Gilberto Leung. Targeting hippo signaling pathway to overcome chemoresistance in glioblastoma [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 7207.

CTNI-26. EFFICACY AND SAFETY OF METFORMIN PLUS LOW-DOSE TEMOZOLOMIDE IN PATIENTS WITH RECURRENT OR REFRACTORY GLIOBLASTOMA: A RANDOMIZED, PROSPECTIVE, MULTICENTER, DOUBLE-BLIND, CONTROLLED, PHASE 2 TRIAL

Abstract Glioblastoma(GBM) has a poor prognosis after standard treatment. Recently, metformin has been shown to have an antitumor effect on glioma cells. We performed the first randomized prospective phase II clinical trial to investigate the clinical efficacy and safety of meformin in patients with recurrent or refractory GBM treated with low-dose temozolomide (TMZ). Included patients were randomly assigned to a control group [placebo plus low-dose TMZ (50mg/m2, daily) or and experimental group [metformin (1,000mg, 1,500mg, and 2,000mg per day during the 1st, 2nd, and 3rd week until disease progression, respectively) plus low-dose TMZ]. The primary endpoint was progression-free survival (PFS). Secondary endpoints were overall survival (OS), disease control rate, overall response rate, health-related quality of life, and safety. Among the 92 patients screened, 81 were randomly assigned to the control group (43 patients) or the experimental group (38 patients). Although the control group showed a longer median PFS, the difference between the two groups was not statistically significant (2.66 versus 2.3 months, p = 0.679). The median OS was 17.22 months (95% CI:12.19-21.68 months) in the experimental group and 7.69 months (95% CI: 5.16-22.67 months) in the control group, showing no significant difference by the log-rank test (HR:0.78; 95% CI:0.39-1.58; p = 0.473). The overall response rate and disease control rate were 9.3% and 46.5% in the control group and 5.3% and 47.3% in the experimental group, respectively. Although the metformin plus TMZ regimen was well tolerated, it did not confer a clinical benefit in patients with recurrent or refractory GBM.

Efficacy and safety of metformin plus low-dose temozolomide in patients with recurrent or refractory glioblastoma: a randomized, prospective, multicenter, double-blind, controlled, phase 2 trial (KNOG-1501 study)

PurposeGlioblastoma (GBM) has a poor prognosis after standard treatment. Recently, metformin has been shown to have an antitumor effect on glioma cells. We performed the first randomized prospective phase II clinical trial to investigate the clinical efficacy and safety of metformin in patients with recurrent or refractory GBM treated with low-dose temozolomide.MethodsIncluded patients were randomly assigned to a control group [placebo plus low-dose temozolomide (50 mg/m2, daily)] or an experimental group [metformin (1000 mg, 1500 mg, and 2000 mg per day during the 1st, 2nd, and 3rd week until disease progression, respectively) plus low-dose temozolomide]. The primary endpoint was progression-free survival (PFS). Secondary endpoints were overall survival (OS), disease control rate, overall response rate, health-related quality of life, and safety.ResultsAmong the 92 patients screened, 81 were randomly assigned to the control group (43 patients) or the experimental group (38 patients). Although the control group showed a longer median PFS, the difference between the two groups was not statistically significant (2.66 versus 2.3 months, p = 0.679). The median OS was 17.22 months (95% CI 12.19–21.68 months) in the experimental group and 7.69 months (95% CI 5.16–22.67 months) in the control group, showing no significant difference by the log-rank test (HR: 0.78; 95% CI 0.39–1.58; p = 0.473). The overall response rate and disease control rate were 9.3% and 46.5% in the control group and 5.3% and 47.4% in the experimental group, respectively.ConclusionsAlthough the metformin plus temozolomide regimen was well tolerated, it did not confer a clinical benefit in patients with recurrent or refractory GBM.Trial registration NCT03243851, registered August 4, 2017.

Selected Articles from This Issue

Shoushtari and colleagues report a pilot trial of ONCOS-102, a novel oncolytic adenovirus encoding GM-CSF, administered intratumorally either sequentially or in combination with pembrolizumab in patients with melanoma resistant to prior PD-1 blockade. Treatment was well tolerated. Objective responses were seen in 7 of 20 patients, and size reductions in noninjected lesions suggested local delivery of ONCOS-102 can drive a systemic anti-tumor effect. Serial biopsies of injected tumors at baseline, Week 3 (following ONCOS-102 and prior to pembrolizumab), and Week 9 (following ONCOS-102 and pembrolizumab) indicated that while most tumors experience CD8+ and CD4+ infiltration after ONCOS-102 injection, sustained infiltration at Week 9 was associated with clinical benefit. Future trials of ONCOS-102 and checkpoint inhibition are warranted in anti-PD-1-resistant melanoma. These findings suggest trials using viral agents in anti-PD-1-resistant disease should not solely rely on early onset of cytotoxicity to predict clinical response.Wainberg and colleagues report on the combination of very low doses of chemotherapy (10% of the usual dose) with a full dose of talazoparib (TAL). The study design reports preferentially increasing the dose of TAL before increasing the chemotherapy to improve the hematologic profile as well as exploring efficacy signals among non-BRCA patients. This phase I study demonstrates that TAL with low-dose temozolomide or irinotecan shows an improved hematologic toxicity profile than most prior chemo/PARP inhibitor combinations and has signals of clinical activity in small cell lung cancer and ovarian cancer. The results of this phase I study are supportive of ongoing trials with this combination.Obesity has been unexpectedly associated with improved outcomes with immune checkpoint inhibitors and BRAF-targeted therapies in metastatic melanoma; however, the biology underlying this observation is unknown. Hahn and colleagues examined associations between body mass index (BMI) and molecular, immune, and metabolic features of melanoma tumors as well as host microbiome in 782 patient specimens. Host BMI was associated with altered tumor metabolism, with downregulation of oxidative phosphorylation (OXPHOS) and other metabolic pathways in tumors from high BMI patients. OXPHOS has been associated with resistance to targeted and immune therapies, suggesting a potential mechanism underlying the “obesity paradox” in metastatic melanoma.Circulating tumor DNA (ctDNA) levels are associated with tumor volume and minimal residual disease in lymphoid malignancies. Fernández-Miranda and colleagues suggest that pre-treatment ctDNA levels in follicular lymphoma patients could be useful to predict response to treatment and early progression as an independent predictive biomarker or in combination with clinical variables. Circulating tumor DNA levels and cell-free DNA genotyping at mid-treatment and end-of-treatment are associated with treatment response and early progression follicular lymphoma. Circulating tumor DNA measurement at diagnosis and follow-up is a valuable tool that might feasibly be used in clinical trials and, eventually, in daily clinical practice.

The efficacy and safety of low-dose temozolomide maintenance therapy in elderly patients with glioblastoma: a retrospective cohort study.

Radiotherapy combined with temozolomide chemotherapy (STUPP regimen) is the standard treatment regimen for newly diagnosed glioblastoma (GBM). It is considered feasible to prolong the treatment cycle of temozolomide (TMZ), however, the efficacy and safety of prolonging the treatment cycle of TMZ are still lacking in elderly patients with glioblastoma. This study observed the efficacy and safety of low dose TMZ maintenance therapy in elderly patients with glioblastoma after receiving standard STUPP regimen. The clinical data were retrospectively analyzed in 34 patients with glioblastoma aged ≥65 years from April 2017 to April 2021 in Ningbo First Hospital. The patients received conventional radiotherapy (59.4 Gy/28 F/5.5 weeks) and TMZ (75 mg/m2·d) concurrent chemotherapy, followed by sequential TMZ (150-200 mg/m2·d, d1-5, q28d) adjuvant treatment for 6 cycles, and patients with no disease progress or intolerable side effects received low dose TMZ (100 mg/m2·d, d1-5, q28d) maintenance treatment. The patient's progression free survival time (PFS), total survival time (OS) and adverse reactions were observed by telephone, outpatient reexamination and other follow-up methods. Kaplan-Meier method was used to calculate and draw the survival curve for survival analysis. Twenty-four of 34 patients were finally included in the analysis, including 13 males and 11 females (65-74 years old), with a median of 14 cycles (8-38 cycles) of adjuvant TMZ chemotherapy. The median PFS was 11.0 months [95% confidence interval (CI): 8.67-13.33 months] and the median OS was 17.4 months (95% CI: 12.49-22.31 months). The main adverse reactions were digestive tract reactions and hematological toxicity. Three cases of grade III granulocytopenia occurred during the adjuvant treatment, while no grade III or above related adverse reactions occurred during the follow-up TMZ reduction maintenance treatment: leukopenia (5/24), anemia (2/24), decreased blood platelets (2/24), asthenia (5/24), nausea (4/24), and abnormal liver function (3/24). In general, for elderly patients with good Karnofsky Performance Scale (KPS) scores, further reducing TMZ to maintain chemotherapy after the standard STUPP regimen may improve the PFS and OS to a certain extent, with tolerable adverse reactions and reduced cost. However, prospective randomized grouping study is still needed to determine whether clinical benefits will be achieved.

Targeting Krebs-cycle-deficient renal cell carcinoma with Poly ADP-ribose polymerase inhibitors and low-dose alkylating chemotherapy.

Loss-of-function mutations in genes encoding the Krebs cycle enzymes Fumarate Hydratase (FH) and Succinate Dehydrogenase (SDH) induce accumulation of fumarate and succinate, respectively and predispose patients to hereditary cancer syndromes including the development of aggressive renal cell carcinoma (RCC). Fumarate and succinate competitively inhibit αKG-dependent dioxygenases, including Lysine-specific demethylase 4A/B (KDM4A/B), leading to suppression of the homologous recombination (HR) DNA repair pathway. In this study, we have developed new syngeneic Fh1- and Sdhb-deficient murine models of RCC, which demonstrate the expected accumulation of fumarate and succinate, alterations in the transcriptomic and methylation profile, and an increase in unresolved DNA double-strand breaks (DSBs). The efficacy of poly ADP-ribose polymerase inhibitors (PARPis) and temozolomide (TMZ), alone and in combination, was evaluated both in vitro and in vivo. Combination treatment with PARPi and TMZ results in marked in vitro cytotoxicity in Fh1- and Sdhb-deficient cells. In vivo, treatment with standard dosing of the PARP inhibitor BGB-290 and low-dose TMZ significantly inhibits tumor growth without a significant increase in toxicity. These findings provide the basis for a novel therapeutic strategy exploiting HR deficiency in FH and SDH-deficient RCC with combined PARP inhibition and low-dose alkylating chemotherapy.

Abstract 1051: Combination of senaparib with temozolomide for the treatment of cancer

Abstract Poly (ADP-ribose) polymerase (PARP) is a critical enzyme for DNA repair and PARP inhibitors have been found to be efficacious against cancers with defects in DNA repair pathways such as with BRCA mutations. In addition, in vitro and in vivo studies have found that for PARP inhibitors with good trapping activity, combination with temozolomide (TMZ) produced the best synergetic effects among different types of chemotherapies. Several clinical combination studies of PARP inhibitors with TMZ have been reported, such as the combination of olaparib with TMZ in small cell lung cancer (SCLC). In this presentation, we will report in vitro and in vivo studies of PARP inhibitor senaparib (IMP4297) in combination with TMZ. Synergetic effects were observed when senaparib was combined with TMZ in vitro against human SCLC NCI-H209 cells. In vivo studies of high-dose senaparib in combination with low-dose TMZ once a day continuously in human SCLC NCI-H209 xenograft model was found to be highly synergetic and well tolerated. A clinical study of senaparib in combination with TMZ in patients with advanced solid tumors and SCLC is ongoing (ClinicalTrials.gov Identifier: NCT04434482). Citation Format: Sui Xiong Cai, Ning Ma, Xiaozhu Wang, Jie Ma, Mingchuan Guo, Ruiyu Zhou, Lan Liu, Chih-Yi Hsieh, Ye Edward Tian. Combination of senaparib with temozolomide for the treatment of cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1051.

MODL-27. An organotypic brain slice culture platform as a novel pre-clinical model for diffuse intrinsic pontine glioma and diffuse midline glioma

High-grade pediatric brain tumors (PBTs) such as diffuse intrinsic pontine glioma (DIPG) and diffuse midline glioma (DMG) are devastating diseases with a median survival of just 11 months. Little progress has been made in identifying effective treatments due to the lack of effective pre-clinical models to accurately assess drug sensitivity. Historically, models of DIPG and DMG have been limited due to the low availability of surgical biopsies and small patient populations. Existing in vitro models are often unable to recapitulate growth and migration patterns seen in patients, while in vivo work is costly, time intensive, and many biopsies fail to establish in mice. We have developed an ex vivo organotypic brain slice culture (OBSC) platform to model DIPG and DMG. Through our partnership with the Ian’s Friends Foundation and Children’s Healthcare of Atlanta Biobank, we have seeded, grown, and treated several low-passage patient-derived PBT lines such as DIPG and DMG. Additionally, we can assess treatment response to a variety of agents used in clinical patient care. Viability assays revealed differences in the sensitivity of cell lines to individual agents, indicating that OBSCs have the potential to capture minute differences in efficacy between cell lines and drugs. When we assessed combination treatments, we found low doses of radiation with low doses of temozolomide were synergistic, but using higher doses of radiation was antagonistic, suggesting the OBSC platform has the potential to guide dosing strategies to maximize therapeutic synergy. Overall, these results suggest that OBSC PBT models have the potential to effectively model PBTs, including DIPG and DMG, to accelerate preclinical evaluation of therapeutics and guide drug development towards more effective treatment strategies.

A study of senaparib in combination with temozolomide for the treatment of patients with advanced solid tumors and extensive-stage small cell lung cancer.

3102 Background: Senaparib (or IMP4297) is a PARP inhibitor with a novel chemical structure. Preliminary data demonstrate senaparib has significant anti-tumor activity with good tolerability in some patients with advanced solid tumors. DNA damage caused by temozolomide, a non-classic oral alkylating agent, can sensitize tumors to the effects of PARP inhibitors. In a xenograft model, synergistic antitumor effect was observed with the combination of senaparib and temozolomide, supporting this trial (NCT04434482). Methods: This is a phase Ⅰb/Ⅱ dose-escalation and dose-expansion study. Patients with advanced solid tumors were enrolled for dose escalation to evaluate the safety, tolerability using a modified “3+3” design. Low dose temozolomide (20 to 30 mg, once daily, days 1 to 21) in combination with continuous senaparib (40 to 80 mg, once daily, days 1 to 28) of each 28-day cycle was evaluated. Dose expansion will establish anti-tumor activity and safety of the combination in patients with extensive stage small cell lung cancer (ES-SCLC). Results: A total of 14 patients were enrolled for dose escalation as follows: Cohort 1 (1 patient; senaparib 40 mg plus temozolomide 20 mg), Cohort 2 (3 patients; senaparib 60 mg plus temozolomide 20 mg), Cohort 3 (7 patients; senaparib 80 mg plus temozolomide 20 mg), Cohort 4 (3 patients; senaparib 80 mg plus temozolomide 30 mg). One DLT (Grade 4 thrombocytopenia) was observed in Cohorts 3 and 4. The MTD and RP2D were determined as: senaparib 80 mg plus temozolomide 20 mg. Anaemia, neutropenia and thrombocytopenia were the only Grade ≥3 TEAEs occurring in > 1 patient. All AEs were manageable, and no treatment related deaths were reported. The ORR was observed in 3 of 12 (25.0%) evaluable patients, including 2 confirmed PR and 1 unconfirmed PR. The DCR was 83.3% (10 of 12 evaluable patients). Two patients remain on treatment for more than 1 year. Conclusions: Preliminary results suggest that low dose temozolomide (D1-21 of a 28-day cycle) in combination with continuous senaparib is generally well tolerated with encouraging anti-tumor activity. Recruitment for dose expansion for ES-ECLC patients has commenced (Sep 2021). Clinical trial information: NCT04434482.

Primary analysis from the phase 2 study of continuous talazoparib (TALA) plus intermittent low-dose temozolomide (TMZ) in patients with relapsed or refractory extensive-stage small cell lung cancer (ES-SCLC).

8517 Background: TALA exhibits cytotoxic effects by inhibiting poly (ADP-ribose) polymerase (PARP) proteins 1 and 2 in addition to “trapping” PARP on DNA. TMZ has been shown to increase antitumor response when combined with TALA in SCLC models (Wainberg AACR 2016). TALA plus TMZ as second-line therapy for ES-SCLC may improve disease-related outcomes. Methods: This is a phase 2, open-label, single-arm study of the safety and efficacy of TALA plus TMZ in patients with ES-SCLC, relapsed or refractory to a first-line platinum-based regimen. Participants receive TALA 0.75 mg (or 0.5 mg if creatinine clearance < 60 mL/min) po daily on 28-day cycles with TMZ 37.5 mg/m2 po on days 1-5. The primary endpoint is objective response rate (ORR) based on RECIST 1.1 criteria, versus a historical control of 15% ORR in second-line topotecan, with the null hypothesis rejected for 8 or more confirmed responses among 28 evaluable subjects (29% ORR). Secondary endpoints include progression-free survival, overall survival, duration of response, and time to response. Exploratory endpoints include biomarker studies such as status of DNA damage response genes (DDR) and patient reported outcomes. A Simon two-stage design was utilized to reach a total accrual of 28 evaluable patients. Results: Thirty-one subjects were enrolled, of which 3 were non-evaluable due to ineligibility (1) or early withdrawal of consent prior to first disease assessment (2). Eleven of 28 evaluable subjects (39.3%) achieved a confirmed partial response. The ORR was similar among platinum-refractory (3/6), -resistant (4/9), and -sensitive subgroups (4/13). The median time to response was 1.8 months (m), duration of response 5.8 m, progression free survival 4.5 m, and overall survival 11.9 m. Adverse events (AEs) were manageable, with grade ≥ 3 AEs being thrombocytopenia (61.3%), anemia (54.8%), neutropenia (41.9%), and atypical pneumonia (3.2%), which responded well to dose-hold or dose-reduction and transfusion or growth factor support as needed. Cell free DNA and tissue analysis demonstrated no germline DDR mutations among the trial subjects, but somatic DDR mutations at baseline and acquired during treatment were common. Three subjects remain on study treatment. Conclusions: The study exceeded its target response rate. This is the second trial to demonstrate a benefit of PARP inhibition with low-dose TMZ in SCLC (see Farago Cancer Discovery 2019). A phase 3 study is appropriate to confirm the benefit of this approach compared to currently approved options. Clinical trial information: NCT03672773.

Abstract P1-21-06: Phase I study of T-DM1 and metronomic temozolomide in secondary prevention of HER2+ breast cancer brain metastases following local radiation therapy

Abstract Background: The incidence of breast cancer brain metastases is rising, and, these lesions in the central nervous system (CNS) and their treatments cause physical and neurocognitive impairment. Only modest incremental advances in progression free survival have been achieved with drugs to treat CNS lesions, while nearly half of the patients who receive SRS will develop new brain metastases within 1 year. In murine models of breast cancer, we demonstrated that low doses of temozolomide (TMZ) administered in a prophylactic, metronomic fashion significantly prevented development of brain metastases. No effect, however, was seen in established brain metastases or systemic breast cancer metastases. We hypothesize that low dose, metronomic TMZ will prevent the outgrowth of brain lesions in HER2+ patients, when added to an active anti-HER2 treatment. We present here the results of the phase I trial combining T-DM1 to TMZ for the prevention of additional brain metastases after their first occurrence and local treatment. Methods: Eligible patients had HER2+ breast cancer with brain metastases and were within 12 weeks of local brain metastases therapy (WBRT, SRS and or surgery), with PS 0-2 and adequate end organ function. Standard doses of T-DM1 were administered IV every 21 days (3.6 mg/kg) and TMZ was given PO daily in a 3+3 design at 30, 40 or 50 mg/m2, continuously. The DLT period was one 21d cycle. Safety was assessed by CTCAEv4.0 and response by RECISTv1.1 and RANO-BM. Brain MRI and systemic CT scans were performed every 6 weeks. Blood samples for correlatives evaluation were collected at baseline and every cycle while on trial. CSF was collected at baseline and C3D1 for all patients. Questionnaires (MDASI-BT and PROMIS®) for evaluation of symptoms and quality of life were completed every 6 weeks. Results: Twelve women with median age 55.5yr (44-67) were enrolled. Only 3 (25%) patients had HR+/HER2+ tumors at initial diagnosis. Nine (75%) patients presented stages II and III disease at initial diagnosis, and developed brain metastases at the diagnosis of first recurrence. Nine (75%) patients received SRS therapy and 3 (25%) received WBRT prior to trial enrollment. Grade 3 or 4 AEs included thrombocytopenia (1/12), neutropenia (1/12), lymphopenia (6/12) and decreased CD4 (6/12), requiring pentamidine for PCP prophylaxis. No DLT was observed. Four patients underwent dose reductions (thrombocytopenia, fatigue and peripheral neuropathy), all of them enrolled on the highest TMZ dose. Median follow-up on study is now 9.6m (1.2-32) and no patient developed new parenchymal brain metastases. Five patients remain on study, while 7 are off study due to progression at previously irradiated CNS lesion (2), progression of systemic disease (2), focal leptomeningeal involvement (1), new cancer (1) and persistent thrombocytopenia (1). Completion rates for the questionnaires were 99% by Cycle 15 (81 completed out of expected 82) and 90% by Cycle 41 (123/137), and will be reported at presentation. Conclusion: Metronomic TMZ in combination with standard dose T-DM1 is tolerable and shows promising activity in secondary prevention of HER2+ brain metastases. Systematic longitudinal symptom assessments in breast cancer patients with brain metastasis are feasible. A randomized phase II expansion of this trial with T-DM1 or T-Dxd +/- TMZ is planned. Citation Format: Alexandra S Zimmer, Seth Steinberg, Mark Gilbert, Terri Armstrong, Eric Burton, Nicole Houston, Dee Dee Smart, Nadia Biassou, John Butman, Priscilla K Brastianos, Carey K Anders, Stanley Lipkowitz, Patricia S Steeg. Phase I study of T-DM1 and metronomic temozolomide in secondary prevention of HER2+ breast cancer brain metastases following local radiation therapy [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P1-21-06.

Overcoming chemoresistance in glioblastoma by fluvastatin via prenylation-dependent inhibition of Ras signaling.

The resistance of glioblastoma to chemotherapy remains a significant clinical problem. Targeting alternative pathways such as protein prenylation is known to be effective against many cancers. Fluvastatin is a potent competitive inhibitor of 3-hydroxy-3-methylglutaryl- CoA (HMG-CoA) reductase, thereby inhibits prenylation. We demonstrate that fluvastatin alone effectively inhibits proliferation and induces apoptosis in multiple human glioblastoma cell lines. The combination index analysis shows that fluvastatin acts synergistically with common chemotherapy drugs for glioblastoma: temozolomide and irinotecan. We further show that fluvastatin acts on glioblastoma through inhibiting prenylation-dependent Ras activation. The combination of fluvastatin and low dose temozolomide resulted in remarkable inhibition of glioblastoma tumor in mice throughout the whole treatment duration without causing toxicity. Such combinatorial effects provide the basis for utilizing these FDA-approved drugs as a potential clinical approach in overcoming resistance and improving glioblastoma treatment.

Abstract P055: Targeting Krebs-cycle-deficient renal cell carcinoma with PARP inhibitor and low-dose alkylating chemotherapy

Abstract Loss-of-function mutations in genes encoding the Krebs cycle enzymes fumarate hydratase (FH) and succinate dehydrogenase (SDH) lead to excess accumulation of fumarate and succinate, respectively. Germline mutations in FH lead to a genetic predisposition to hereditary leiomyomatosis and renal cell cancer (HLRCC)-associated RCC. Similarly, loss-of-function alterations of SDH, most commonly SDHB, are associated with SDH-deficient neoplasms, including RCC. FH and SDHB deficient RCC tends to be aggressive and metastasize early with very limited treatment options. The oncometablites produced by these mutations, fumarate and succinate, competitively inhibit αKG-dependent dioxygenases, resulting in dysregulated DNA methylation and histone modification. We have previously demonstrated that elevated levels of fumarate and succinate both suppress the homologous recombination (HR) DNA-repair pathway through inhibition of the lysine demethylase KDM4B, resulting in aberrant hypermethylation of histone 3 lysine 9 (H3K9) at loci surrounding DNA breaks and masking a local H3K9 trimethylation signal that is essential for the proper execution of HR. In this study, we sought to identify novel treatment approaches that exploit genomic instability in FH- and SDHB-deficient RCC. Temozolomide (TMZ), an alkylating agent, mediates its cytotoxic effect by attaching methyl groups to DNA (O6-guanine, N7-guanine and N3-adenine). 16 N3-MetA and N7-MetG repair are mediated by the base excision repair (BER) in a process involving PARP. While the combination of PARP inhibitors with TMZ has been shown to increase TMZ-induced cytotoxicity, clinical trials investigating combination therapy have been hampered by significant toxicity. Using CRISPR/Cas9, we developed new syngeneic FH- and SDHB-deficient murine models of RCC. We demonstrate that FH- and SDHB-deficient cells have accumulation of fumarate and succinate leading to an increase in unresolved DNA double-strand breaks (DSBs). Treatment with PARP inhibition and temozolomide results in marked in vitro cytotoxicity in FH- and SDHB-deficient cells, even at low concentrations of TMZ (50 µM). In vivo, the combination of standard dose BGB-290 and low-dose TMZ (3mg/kg/dose) results in significantly delayed tumor progression in an SDHB deficient RENCA model without any significant increase in toxicity. Notably, the TMZ dose of 3mg/kg/dose is significantly lower than the 50mg/kg/dose that is commonly used for in vivo studies. Taken together, these findings provide the basis for a novel therapeutic strategy exploiting HR deficiency in FH and SDHB-deficient RCC with combined PARP inhibition and low-dose alkylating chemotherapy. Furthermore, the development of a new syngeneic mouse model provides a tool for the future study of immunotherapy in Krebs-cycle-deficient RCC. Citation Format: Daiki Ueno, Amrita Sule, Jiayu Liang, Jinny van Doorn, Ranjini Sundaram, Randy Caliliw, Huihui Ye, Rong Rong Huang, Jing Li, Karla Boyd, Ranjit S. Bindra, Juan C. Vasquez, Brian M. Shuch. Targeting Krebs-cycle-deficient renal cell carcinoma with PARP inhibitor and low-dose alkylating chemotherapy [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2021 Oct 7-10. Philadelphia (PA): AACR; Mol Cancer Ther 2021;20(12 Suppl):Abstract nr P055.

In Vitro and Clinical Compassionate Use Experiences with the Drug-Repurposing Approach CUSP9v3 in Glioblastoma.

Background: Glioblastoma represents the most common primary brain tumor in adults. Despite technological advances, patients with this disease typically die within 1–2 years after diagnosis. In the search for novel therapeutics, drug repurposing has emerged as an alternative to traditional drug development pipelines, potentially facilitating and expediting the transition from drug discovery to clinical application. In a drug repurposing effort, the original CUSP9 and its derivatives CUSP9* and CUSP9v3 were developed as combinations of nine non-oncological drugs combined with metronomic low-dose temozolomide. Methods: In this work, we performed pre-clinical testing of CUSP9v3 in different established, primary cultured and stem-like glioblastoma models. In addition, eight patients with heavily pre-treated recurrent glioblastoma received the CUSP9v3 regime on a compassionate use basis in a last-ditch effort. Results: CUSP9v3 had profound antiproliferative and pro-apoptotic effects across all tested glioblastoma models. Moreover, the cells’ migratory capacity and ability to form tumor spheres was drastically reduced. In vitro, additional treatment with temozolomide did not significantly enhance the antineoplastic activity of CUSP9v3. CUSP9v3 was well-tolerated with the most frequent grade 3 or 4 adverse events being increased hepatic enzyme levels. Conclusions: CUSP9v3 displays a strong anti-proliferative and anti-migratory activity in vitro and seems to be safe to apply to patients. These data have prompted further investigation of CUSP9v3 in a phase Ib/IIa clinical trial (NCT02770378).

CTNI-04. RECURRENT GLIOBLASTOMA LONG-TERM SURVIVORS TREATED WITH CUSP9v3

Abstract CUSP9v3 is a new treatment regimen for glioblastoma. It consists of continuous daily use of 9 drugs repurposed from general medicine. Their primary non-oncology uses are given in parentheses: aprepitant (nausea), auranofin (rheumatoid arthritis), celecoxib (pain), captopril (hypertension), disulfiram (alcohol abuse), itraconazole (fungal infection), minocycline (bacterial infection), ritonavir (viral infection) and sertraline (depression). All drugs have preclinical or clinical data indicating that they can retard glioblastoma growth, as reviewed in the published background papers. In CUSP9v3 all 9 medicines are given daily with added metronomic, low-dose (20 mg/m2 BSA twice daily) temozolomide. After 3 years of daily, uninterrupted use of CUSP9v3, of an initial cohort of 10 recurrent glioblastoma patients, as of May 2021, 3 are alive, functioning well, progression-free at 44, 44, and 57 months after recurrence and CUSP9v3 started. We report now that there were no unexpected toxicities from this combination of 10 daily drugs, although all patients required dose reduction of one or more of the drugs. CUSP9v3 was reasonably well-tolerated. Ritonavir, temozolomide, captopril and itraconazole were the drugs most frequently requiring dose reduction or pausing. The most common adverse events were nausea, headache, fatigue, diarrhea and ataxia. There were no treatment-related deaths. In the 3 long-term survivors, the median neutrophil-to-lymphocyte ratio decreased from 2.5 to 1.5 during CUSP9v3 treatment. In the group of the 3 shortest-term survivors that ratio increased from 4.7 to 14.3. CUSP9v3 follows the injunction of Palmer et al. that cancer therapy can be constructed using drug combinations that are independently effective, with non-overlapping mechanisms of action, and non-overlapping resistance pathways. We interpret the data accrued over the last few decades on the ever-shifting spatial and temporal growth drives active at any given moment in glioblastoma as requiring a complex pharmacological approach like CUSP9v3.

Selected Articles from This Issue

Relapse to MAp. pathway inhibitors (such as BRAF, MEK, and KRAS inhibitors) is common due to the reactivation of ERK and MAPK signaling. In this First Disclosure, Wallis, Munck, and colleagues outline the ERK inhibitor ASTX029. ASTX029 inhibits both the phosphorylation of ERK by MEK as well as its catalytic activity and, therefore, is categorized as a dual-mechanism inhibitor by the authors. The dual-mechanism ERK inhibitor demonstrated anti-tumor activity to MAPK inhibitor-resistant cancers in vitro and in vivo. Their work supports the continued clinical development of ASTX029 in advanced solid tumors.The specific DNA damage O6-methylguanine induced by temozolomide was quantified and set in relation to double-strand breaks, apoptosis and senescence. The findings challenged the model of DNA damage thresholding as O6-methylguanine induced these endpoints in glioblastoma cells without a no-effect threshold. Interestingly, senescence appears to occur at a much lower number of O6-methylguanine molecules than cell death, indicating that low dose temozolomide impedes cytotoxicity by increasing the quiescent population. The data indicate a) need of inhibiting selectively senescence in order to ameliorate the killing effects and b) quantification of O6-methylguanine could serve as a potential biomarker of temozolomide intratumoral dose.Although imatinib can target KIT mutations in gastrointestinal stomach tumor, 40% of localized tumors recur within 5 years. In this study, Sicklick and colleagues report a population of CD34+KITlow GIST cells with a cancer stem cell-like expression profile and were enriched by imatinib treatment. Tumors with low KIT expression had activated Gas6/AXL and NF-κB pathways which could be targeted by bemcentinib (AXL inhibitor) or bardoxolone (NF-κB inhibitor) alone or in combination with imatinib. Their findings present a new population of resistant cells that can be overcome in recurrent GIST disease.Despite advances in experimental therapeutics for refractory acute myeloid leukemia (AML), it remains incurable. The success of CD19 CAR T cells in hematologic malignancies has led to their development in expanding indications. In this manuscript, Rennert and colleagues describe the preclinical development of a CD19-anti-CLEC12A bridge-protein secreting CAR T cell targeting CLEC12A in AML. The CAR19 cells secrete the biparatopic bridging protein to increase the cytotoxicity against CLEC12A-positive AML cells in vitro and in vivo. The efficacy of these cells demonstrates a means to thwart resistance by enhancing CD19-based CAR T cells.

Abstract IA-006: Enhancing the therapeutic ratio for glioblastoma by combining radiation therapy with PARP inhibitors

Abstract PARP inhibitors (PARPi) enhance radiation sensitivity in multiple cancer models, both in vitro and in vivo. Our observation that the radiosensitizing properties of PARPi are most pronounced in rapidly proliferating cells is reflected in early phase clinical trial data showing exacerbation of acute radiation toxicity in rapidly proliferating tissues such as oropharyngeal and esophageal mucosa. Lack of radiosensitization in late responding, slowly proliferating normal tissues indicates that PARPi may be more effectively combined with radiation therapy (RT) in patients with brain tumors. We are therefore evaluating the oral PARPi olaparib in combination with RT and/or temozolomide (TMZ) in the treatment of glioblastoma (GBM), the most prevalent and most aggressive primary brain tumor. Patients with GBM experience very poor outcomes in terms of median survival (c.1 year) and neurocognitive decline caused primarily by RT. Olaparib was initially evaluated in combination with daily low-dose TMZ in patients with recurrent GBM in the OPARATIC trial. Pharmacokinetic studies revealed that olaparib penetrates both core and margin regions of GBM, indicating that the BBB is significantly disrupted throughout these tumors. Olaparib could be safely combined with daily TMZ (75 mg/m2), but intermittent olaparib dosing (150 mg three days per week) was required to avoid dose-limiting hematological toxicity. Early phase testing of the olaparib-radiotherapy combination is now underway in three populations of patients with newly diagnosed GBM. Patients aged >65 with MGMT unmethylated GBM are being recruited to a randomized, placebo-controlled phase II study (PARADIGM) after a phase I dose escalation study showed that olaparib (200 mg twice daily) was extremely well tolerated when combined with brain irradiation (40 Gray in 15#). Good performance status patients aged <70 are being recruited to two parallel phase I dose escalation studies: patients with MGMT unmethylated tumors are receiving daily olaparib with RT (60 Gy in 30#) without TMZ, while patients with MGMT methylated tumors are receiving intermittent olaparib with standard chemoradiation (60 Gy). The impact of PARPi on RT induced neurotoxicity is being investigated in preclinical studies. In vitro data show that PARPi reduce proliferation of neural stem cells and protect them against RT induced apoptosis, while in vivo studies support the emerging concept that RT induced neuroinflammation is important in the pathogenesis of neurotoxicity. Importantly, preliminary PET and immunohistochemical studies have shown robust anti-neuroinflammatory effects of PARPi in this context. Ongoing experiments are defining the roles of microglia, astrocytes and neurogenesis in this phenomenon. These diverse data sets provide support for our hypothesis that combining PARPi with RT has potential to improve outcomes for GBM patients by enhancing tumor control while simultaneously suppressing neuroinflammation and alleviating RT related neurocognitive decline. Citation Format: Anthony J. Chalmers, Rodrigo Gutierrez-Quintana, David J. Walker, Karin Williams, Duncan Forster, Mark R. Jackson, Sarah Derby, Jon Stobo, Lorna Sweeting, Caroline Kelly, Stephen Durant, Kaye J. Williams. Enhancing the therapeutic ratio for glioblastoma by combining radiation therapy with PARP inhibitors [abstract]. In: Proceedings of the AACR Virtual Special Conference on Radiation Science and Medicine; 2021 Mar 2-3. Philadelphia (PA): AACR; Clin Cancer Res 2021;27(8_Suppl):Abstract nr IA-006.

Glioblastoma stem cell (GSC)-derived PD-L1-containing exosomes activates AMPK/ULK1 pathway mediated autophagy to increase temozolomide-resistance in glioblastoma

Temozolomide (TMZ)-resistance hampers the therapeutic efficacy of this drug for glioblastoma (GBM) treatment in clinic, and emerging evidences suggested that exosomes from GBM-derived stem cells (GSCs) contributed to this process, but the detailed mechanisms are still largely unknown. In the present study, we reported that GSCs derived programmed death-ligand 1 (PD-L1) containing exosomes activated AMPK/ULK1 pathway mediated protective autophagy enhanced TMZ-resistance in GBM in vitro and in vivo. Specifically, we noticed that continuous low-dose TMZ stimulation promoted GSCs generation and PD-L1 containing exosomes (PD-L1-ex) secretion in GBM cells, and that PD-L1-ex inhibited cell apoptosis and promoted cell autophagy to increased TMZ-resistance in GBM cells, which were reversed by co-treating cells with the autophagy inhibitor 3-methyladenine (3-MA). Consistently, upregulation of PD-L1 also increased TMZ-resistance in TS-GBM cells, and silencing of PD-L1 sensitized TR-GBM cells to TMZ. In addition, PD-L1-ex activated AMPK/ULK1 pathway to induce autophagy in TMZ treated GBM cells, and the inhibitors for AMPK (compound C) and ULK1 (SBI-0206965) promoted cell apoptosis in GBM cells co-treated with PD-L1-ex and high-dose TMZ. Finally, we evidenced that PD-L1-ex promoted tumor growth and Ki67 protein expressions to increase TMZ-resistance in GBM in vivo. Collectively, we concluded that GSCs-derived PD-L1-ex activated AMPK1/ULK1 signaling cascade mediated autophagy to increase TMZ-resistance in GBM, and this study provided potential strategies to improve the therapeutic efficacy of TMZ in GBM.

Establishment of a mouse model bearing orthotopic temozolomide-resistant glioma

To establish a mouse model bearing orthotopic temozolomide (TMZ)-resistant glioma that mimics the development of drug resistance in gliomas in vivo. Seventy-eight adult C57BL/6 mice were randomly divided into 6 groups (n=13), including 3 TMZ induced groups with low, medium and high doses (5, 25, and 50 mg/kg, respectively) and 3 control groups. In each group, 5 mice were used for evaluating tumor size, 5 for observing survival, and 3 for collecting tumor tissues for primary cell culture. In low-dose TMZ induced group, 3 mice bearing orthotopic murine glioma GL261 cell xenografts received intraperitoneal injections of 5 mg/kg TMZ for 5 days followed by a 10-day washout period before collecting glioma tissues. Tumor cell suspensions were prepared and injected in the mice in the medium-dose group, which were treated with the same protocol but with an increased TMZ dose, and the tumor cells harvested from 3 mice were injected in the high-dose group. The mice bearing GL261 cell xenografts in the 3 control groups received no treatment or were injected with medium- or high-dose TMZ. Cell colony forming assay was used to assess TMZ resistance of each generation of the tumor cells; CCK8 assay was used to determine drug resistance index of the cells. The mouse models bearing TMZresistant glioma was successfully established. The cells from the high-dose induced group showed a significantly higher colony-forming rate than those from the high-dose control group (P < 0.05), and had a drug resistance 4.25 times higher than that of the cells from untreated control group. High-dose TMZ significantly reduced the tumor volume in the control group (P < 0.05) but not in the high-dose induced group (P < 0.01). The survival time of the tumor-bearing mice was significantly shortened in the high-dose induced group (P=0.0018). Progressive increase of TMZ doses in mice bearing orthotopic gliomas can effectively induce TMZ resistance of the gliomas.

A phase Ib/IIa trial of 9 repurposed drugs combined with temozolomide for the treatment of recurrent glioblastoma: CUSP9v3.

BackgroundThe dismal prognosis of glioblastoma (GBM) may be related to the ability of GBM cells to develop mechanisms of treatment resistance. We designed a protocol called Coordinated Undermining of Survival Paths combining 9 repurposed non-oncological drugs with metronomic temozolomide—version 3—(CUSP9v3) to address this issue. The aim of this phase Ib/IIa trial was to assess the safety of CUSP9v3.MethodsTen adults with histologically confirmed GBM and recurrent or progressive disease were included. Treatment consisted of aprepitant, auranofin, celecoxib, captopril, disulfiram, itraconazole, minocycline, ritonavir, and sertraline added to metronomic low-dose temozolomide. Treatment was continued until toxicity or progression. Primary endpoint was dose-limiting toxicity defined as either any unmanageable grade 3–4 toxicity or inability to receive at least 7 of the 10 drugs at ≥ 50% of the per-protocol doses at the end of the second treatment cycle.ResultsOne patient was not evaluable for the primary endpoint (safety). All 9 evaluable patients met the primary endpoint. Ritonavir, temozolomide, captopril, and itraconazole were the drugs most frequently requiring dose modification or pausing. The most common adverse events were nausea, headache, fatigue, diarrhea, and ataxia. Progression-free survival at 12 months was 50%.ConclusionsCUSP9v3 can be safely administered in patients with recurrent GBM under careful monitoring. A randomized phase II trial is in preparation to assess the efficacy of the CUSP9v3 regimen in GBM.