Targeting TRIP13 in favorable histology Wilms tumor with nuclear export inhibitors synergizes with doxorubicin

Wilms tumor (WT) is the most common renal malignancy of childhood. Despite improvements in the overall survival, relapse occurs in ~15% of patients with favorable histology WT (FHWT). Half of these patients will succumb to their disease. Identifying novel targeted therapies remains challenging in part due to the lack of faithful preclinical in vitro models. Here we establish twelve patient-derived WT cell lines and demonstrate that these models faithfully recapitulate WT biology using genomic and transcriptomic techniques. We then perform loss-of-function screens to identify the nuclear export gene, XPO1, as a vulnerability. We find that the FDA approved XPO1 inhibitor, KPT-330, suppresses TRIP13 expression, which is required for survival. We further identify synergy between KPT-330 and doxorubicin, a chemotherapy used in high-risk FHWT. Taken together, we identify XPO1 inhibition with KPT-330 as a potential therapeutic option to treat FHWTs and in combination with doxorubicin, leads to durable remissions in vivo.

The yes-associated protein (YAP) is associated with resistance to anti-GD2 immunotherapy in neuroblastoma through downregulation of ST8SIA1

Pediatric patients with high-risk neuroblastoma often relapse with chemotherapy-resistant, incurable disease. Relapsed neuroblastomas harbor chemo-resistant mesenchymal tumor cells and increased expression/activity of the transcriptional co-regulator, the Yes-Associated Protein (YAP). Patients with relapsed neuroblastoma are often treated with immunotherapy such as the anti-GD2 antibody, dinutuximab, in combination with chemotherapy. We have previously shown that YAP mediates both chemotherapy and MEK inhibitor resistance in relapsed RAS mutated neuroblastoma and so posited that YAP might also be involved in anti-GD2 antibody resistance. We now show that YAP genetic inhibition significantly enhances sensitivity of mesenchymal neuroblastomas to dinutuximab and gamma delta (γδ) T cells both in vitro and in vivo. Mechanistically, YAP inhibition induces increased GD2 cell surface expression through upregulation of ST8SIA1, the gene encoding GD3 synthase and the rate-limiting enzyme in GD2 biosynthesis. The mechanism of ST8SIA1 suppression by YAP is independent of PRRX1 expression, a mesenchymal master transcription factor, suggesting YAP may be the downstream effector of mesenchymal GD2 resistance. These results therefore identify YAP as a therapeutic target to augment GD2 immunotherapy responses in patients with neuroblastoma.

Identification and targeting of protein tyrosine kinase 7 (PTK7) as an immunotherapy candidate for neuroblastoma

GD2-targeting immunotherapies have improved survival in children with neuroblastoma, yet on-target, off-tumor toxicities can occur and a subset of patients cease to respond. The majority of neuroblastoma patients who receive immunotherapy have been previously treated with cytotoxic chemotherapy, making it paramount to identify neuroblastoma-specific antigens that remain stable throughout standard treatment. Cell surface glycoproteomics performed on human-derived neuroblastoma tumors in mice following chemotherapy treatment identified protein tyrosine kinase 7 (PTK7) to be abundantly expressed. Furthermore, PTK7 shows minimal expression on pediatric-specific normal tissues. We developed an anti-PTK7 chimeric antigen receptor (CAR) and find PTK7 CAR T cells specifically target and kill PTK7-expressing neuroblastoma in vitro. In vivo, human/murine binding PTK7 CAR T cells regress aggressive neuroblastoma metastatic mouse models and prolong survival with no toxicity. Together, these data demonstrate preclinical efficacy and tolerability for targeting PTK7 and support ongoing investigations to optimize PTK7-targeting CAR T cells for neuroblastoma.

A phase 1 study of simvastatin in combination with topotecan and cyclophosphamide in pediatric patients with relapsed and/or refractory solid and CNS tumors

BACKGROUND

3-Hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitors (statins) can inhibit tumor proliferation, angiogenesis, and restore apoptosis in preclinical pediatric solid tumor models. We conducted a phase 1 trial to determine the maximum tolerated dose (MTD) of simvastatin with topotecan and cyclophosphamide in children with relapsed/refractory solid and central nervous system (CNS) tumors.

METHODS

Simvastatin was administered orally twice daily on days 1-21, with topotecan and cyclophosphamide intravenously on days 1-5 of a 21-day cycle. Four simvastatin dose levels (DLs) were planned, 140 (DL1), 180 (DL2), 225 (DL3), 290 (DL4) mg/m² /dose, with a de-escalation DL of 100 mg/m² /dose (DL0) if needed. Pharmacokinetic and pharmacodynamic analyses were performed during cycle 1.

RESULTS

The median age of 14 eligible patients was 11.5 years (range: 1-23). The most common diagnoses were neuroblastoma (N = 4) and Ewing sarcoma (N = 3). Eleven dose-limiting toxicity (DLT)-evaluable patients received a median of four cycles (range: 1-6). There were three cycle 1 DLTs: one each grade 3 diarrhea and grade 4 creatine phosphokinase (CPK) elevations at DL1, and one grade 4 CPK elevation at DL0. All patients experienced at least one grade 3/4 hematologic toxicity. Best overall response was partial response in one patient with Ewing sarcoma (DL0) and stable disease for four or more cycles in four patients. Simvastatin exposure increased with higher doses and may have correlated with toxicity. Plasma interleukin 6 (IL-6) concentrations (N = 6) showed sustained IL-6 reductions with decrease to normal values by day 21 in all patients, indicating potential on-target effects.

CONCLUSIONS

The MTD of simvastatin with topotecan and cyclophosphamide was determined to be 100 mg/m² /dose.

Abstract 3545: The Yes-associated protein (YAP) regulates GD2 immunotherapy response in high-risk neuroblastoma

Background Patients with the pediatric solid tumor high-risk neuroblastoma (HR NB) receive intense multimodal therapy yet 50% still relapse with chemotherapy-resistant disease. Relapsed NBs harbor increased RAS/MAPK pathway mutations and increased expression and downstream activity of the transcriptional co-regulator YAP. We have previously shown that YAP mediates resistance to chemotherapy and MEK inhibitors in RAS mutant NBs (Shim et al., Cancer Res 2020). Patients with relapsed NB are treated with the GD2-targeting monoclonal antibody dinutuximab in combination with chemotherapy. Given the increased expression and activity of YAP in relapsed HR NB, we posited that YAP might also play a role in GD2 immunotherapy response.

Methods/Results We stably knocked down YAP in the human derived NRAS mutant SK-N-AS NB cell line with a scrambled short hairpin (sh) control or 2 YAP-targeting shRNAs to generate 3 distinct cell lines. Dinutuximab requires antibody-dependent cellular cytotoxicity (ADCC) and we have shown that gamma delta (γδ) T cells augment dinutuximab in aggressive NB models. We exposed the shYAP1, shYAP2, and control SK-N-AS cells to γδ T cells with/without dinutuximab. YAP knockdown sensitized both SK-N-AS shYAP cell lines to γδ T cell killing both in the presence and absence of dinutuximab. To investigate the mechanism of increased dinutuximab sensitivity, we evaluated a panel of NB cell lines (MYCN amplified and MYCN single copy) for YAP protein and GD2 cell surface expression and noted an inverse relationship. That same inverse correlation was found for GD2 and YAP gene expression in primary HR NB tumor datasets. We therefore evaluated GD2 expression following YAP knockdown in SK-N-AS and show that GD2 significantly increased on the cell surface following YAP inhibition. PRRX1 is a master transcription factor that induces a mesenchymal NB phenotype which is one of high YAP expression with very low to no GD2 surface expression. Interestingly, PRRX1 expression increased in YAP knockdown cells yet GD2 expression also increased, suggesting YAP regulates GD2 expression more directly than PRRX1. In the GD2 biosynthesis pathway, GM3 is converted into GD3 by GD3 synthase (GD3S). GD2 synthase then catalyzes GD3 into GD2. GD3S gene (ST8SIA1) expression significantly increased (>100-fold) upon YAP knockdown. Furthermore, shRNA stable inhibition of GD3S in shYAP NB cells reverted the phenotype and decreased GD2 cell surface expression back to baseline. We then treated established SK-N-AS control or shYAP xenografts with an 18-day course of human γδ T cells, dinutuximab, and cyclophosphamide. Pilot results show significantly extended survival in mice harboring SK-N-AS shYAP tumors.

Conclusion These results support YAP regulation of GD2 expression through transcriptional suppression of GD3 synthase and identify YAP as a therapeutic target to augment GD2 immunotherapy responses in HR and relapsed NB.

Citation Format: Adeiye A. Pilgrim, Hunter C. Jonus, Andrew Ho, Anna Cole, Jenny Shim, Kelly C. Goldsmith. The Yes-associated protein (YAP) regulates GD2 immunotherapy response in high-risk neuroblastoma. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3545.

Abstract 1790: Exploring the efficacy of allogeneic gamma delta T cell adoptive cell therapy against the pediatric brain tumor medulloblastoma

Antigenic heterogeneity and limited immune cell infiltration has historically hindered immunotherapy approaches to treat the pediatric brain tumor medulloblastoma (MB). Therefore, modern MB treatment modalities rely on broadly cytotoxic chemotherapy and/or radiation, leaving survivors with side effects that diminish quality of life, stressing an urgent need for novel approaches. Gamma delta (γδ) T cells represent an emerging class of cellular immunotherapy with preclinical potency against the CNS tumor glioblastoma and pediatric solid tumors. The ability of γδ T cells to recognize tumor stress antigens, alongside their MHC independence, supports γδ T cell usage as an off-the-shelf allogeneic cellular immunotherapy for MB and other immunologically cold cancers. Our team recently identified protein tyrosine kinase 7 (PTK7) as a novel immunotherapy target highly expressed in neuroblastoma, with low pediatric healthy tissue expression. Alpha beta T cells engineered with CARs targeting PTK7 demonstrated impressive antitumor efficacy against PTK7+ neuroblastoma xenografts. In that study, we also noted MB and other pediatric solid tumors express elevated levels of PTK7 mRNA. This work therefore serves to test the susceptibility of MB to γδ T cell immunotherapy and validate if targeting PTK7 can further enhance γδ T cell potency.

Six MB cell lines representing three out of the four MB molecular subgroups were chosen: DAOY, ONS-76, UW228, D341, D425 and D283. Western blot analysis showed five of six MB cell lines express PTK7 protein, and flow cytometry confirmed PTK7 membrane localization. PTK7high (DAOY) and PTK7low (ONS-76) cells were chosen to test for the antigen-specific killing potential of PTK7-targeted CAR γδ T cells against MB. To generate PTK7-targeted γδ T cells, previously cryopreserved γδ T cells were electroporated with mRNA encoding a PTK7-targeted CAR construct containing the CD28 co-stimulatory domain. After a four hour co-culture, both ONS-76 and DAOY showed moderate rates of apoptosis from exposure to mock electroporated or naïve γδ T cells at 1:1, 2:1 and 5:1 effector:target (E:T) ratios, with approximately 30-40% cell death at 5:1. There was no change in susceptibility of ONS-76 cells to PTK7-CAR γδ T cells when compared to mock electroporated or naïve γδ T cell controls. However, co-culture of DAOY cells with PTK7-CAR γδ T cells markedly increased tumor cell death by as much as 40% compared to the mock controls at E:T ratios as low as 1:1.

In summary, naïve expanded γδ T cells induce pronounced MB tumor cell death. Cytotoxicity is further increased against PTK7high MB cells following the introduction of an anti-PTK7 CAR. These results provide a strong rationale for additional preclinical studies regarding the feasibility of γδ T cell-based immunotherapy against MB.

Citation Format: Benjamin S. Lowry, Hunter C. Jonus, Jasmine Lee, Trent H. Spencer, Anna M. Kenney, Kelly Goldsmith. Exploring the efficacy of allogeneic gamma delta T cell adoptive cell therapy against the pediatric brain tumor medulloblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1790.

Abstract 3552: YAP-TEAD2 binding mediates therapy resistance in RAS-driven neuroblastoma

Background/Objectives: Despite intensive multimodal therapy, greater than 50% of children with high-risk neuroblastoma (HR NB) relapse with incurable disease. Next generation sequencing of primary HR NB tumors identified an increase in activating mutations in the RAS/RAF/MAPK pathway. Moreover, gene set enrichment analyses showed a significant decrease in expression of genes suppressed by the Yes-Associated Protein (YAP) at relapse, suggesting increased YAP transcriptional repression. YAP binds with TEAD family transcription factors to regulate gene expression. We have shown that YAP promotes chemotherapy and MEK inhibitor resistance in RAS-mutated NB tumors in vivo by suppressing the expression of Harakiri (HRK), a BH3-only pro-apoptotic protein activated in response to tumor environmental stress such as serum starvation. Our overall objective is to elucidate how YAP represses HRK and tumor suppressor genes globally, and to enhance MEK inhibitor potency by combining MEK inhibition with agents that inhibit YAP or induce HRK to restore the tumor environmental stress response and apoptosis in RAS-mutated NB.

Design/Methods: We used publicly available databases to identify TEAD binding sites on the HRK gene locus in NB. To assess the global state of methylation, we treated NB cells, SK-N-AS (NRASQ61K mutation, MYCN non-amplified) and NLF (NF1 deletion, MYCN amplified), with demethylating agent azacitidine and evaluated HRK expression. To identify the specific TEAD (1-4) binding partner to YAP, we performed siRNA and co-immunoprecipitation studies. We further tested novel YAP-TEAD small molecule inhibitors with varying TEAD1-4 inhibition specificity in SK-N-AS and NLF cells in vitro.

Results: We observed that TEAD binds near cis-regulatory regions on the HRK gene locus in NB. We found that HRK expression is restored when SK-N-AS and NLF cells are treated with azacitidine despite YAP expression increasing. We also identified TEAD2 as the specific binding partner to YAP in NB and found that TEAD2 is necessary for HRK regulation. Novel YAP-TEAD small molecule inhibitors affect NB cell viability under serum-deprived conditions in vitro, especially the inhibitor with highest specificity against TEAD2, and affect YAP-TEAD downstream targets.

Conclusions: YAP-TEAD2 binding is essential for HRK regulation in RAS-mutated NB and thus is a logical therapeutic target to restore therapy response. Further studies are ongoing to test YAP-TEAD small molecule inhibitors in combination with MEK inhibitors and in vivo.

Citation Format: Jenny Shim, Andrew Ho, Hunter C. Jonus, Adeiye A. Pilgrim, Benjamin G. Barwick, Tracy T. Tang, Lawrence H. Boise, Kelly C. Goldsmith. YAP-TEAD2 binding mediates therapy resistance in RAS-driven neuroblastoma. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3552.

Abstract 4093: Dual targeted CAR immunotherapy for neuroblastoma using γδ T cells

Cellular immunotherapy for aggressive pediatric solid tumors like neuroblastoma (NB) has focused on autologous products of αβ T cells, that so far, have been uniformly unsuccessful. γδ T cells offer a potentially superior, off-the-shelf therapy that is directly cytotoxic towards tumors without alloreactivity. Furthermore, γδ T cell infiltration of the hostile, solid tumor microenvironment is a prognostic marker of favorable disease outcome. Our team recently opened a first-in-child evaluation of unengineered allogeneic γδ T cells in combination with dinutuximab, an anti-GD2 antibody, and chemotherapy (NCT05400603). Our focus now is to optimize a second-generation γδ T-cell therapy by engineering the expression of tumor targeting chimeric antigen receptors (CAR). We hypothesize that CAR-targeting will further enhance γδ T-cell homing and antitumor potency. While anti-GD2 antibodies have been clinically successful immunotherapies for NB, GD2-targeted cell therapies need improvement. Our team recently validated a novel immunotherapy target for NB, protein tyrosine kinase 7 (PTK7), an inactive tyrosine kinase expressed highly amongst all NBs with low to no normal pediatric tissue expression.

We designed a dual-targeting platform directed against both GD2 and PTK7 using γδ T cells, where CARs are separately encoded and dually expressed. Previously optimized transgenes containing GD2 or PTK7 scFv targeting domains followed by a CD8 hinge region, CD28 co-stim/trans-membrane domain, and CD3ζ signalling domain were inserted under the T7 promoter for mRNA production. Purified mRNA was electroporated into γδ T cells following their thaw from cryopreservation. Electroporation titrations were performed to optimize CAR expression to be detected up to 72 hours post-modification, which is compatible with the approximate in vivo lifespan γδ T cells in mice. Simultaneous expression of both CARs appears highest 24 h after electroporation, with ~70% of the target γδ T cell population modified. Anti-GD2/PTK7 γδ T cells are potent against the NB cell line IMR5 (GD2+PTK7+) in a 4 h cytotoxicity assay at effector:target ratios as low as 0.5:1. Importantly, specificity is also shown against NB cell lines genetically engineered to represent the clinical heterogeneity of GD2 and PTK7 expression that may be observed, where the dual CAR therapy is effective against GD2+PTK7+, GD2+PTK7−, and GD2−PTK7+, but not GD2−PTK7− NBs.

In conclusion, we developed a dual CAR-based cellular therapy for NB using γδ T cells as an effector population in place of classical αβ T cells. Early studies demonstrate feasibility for innovative dual CAR expression and show promise for strong anti-NB potency. Future work will optimize CAR signaling domains for maximal efficacy in solid tumors, as well as confirm efficacy and safety in vivo with results rapidly translatable into our established γδ T cell clinical trial pipeline.

Citation Format: Hunter C. Jonus, Jasmine Y. Lee, Jordan A. Silva, H. Trent Spencer, Kelly C. Goldsmith. Dual targeted CAR immunotherapy for neuroblastoma using γδ T cells. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4093.

Dissecting the cellular components of ex vivo γδ T cell expansions to optimize selection of potent cell therapy donors for neuroblastoma immunotherapy trials

γδ T lymphocytes represent an emerging class of cellular immunotherapy with preclinical promise to treat cancer, notably neuroblastoma. The innate-like immune cell subset demonstrates inherent cytoxicity toward tumor cells independent of MHC recognition, enabling allogeneic administration of healthy donor-derived γδ T cell therapies. A current limitation is the substantial interindividual γδ T cell expansion variation among leukocyte collections. Overcoming this limitation will enable realization of the full potential of allogeneic γδ T-based cellular therapy. Here, we characterize γδ T cell expansions from healthy adult donors and observe that highly potent natural killer (NK) lymphocytes expand with γδ T cells under zoledronate and IL-2 stimulation. The presence of NK cells correlates with both the expansion potential of γδ T cells and the overall potency of the γδ T cell therapy. However, the potency of the cell therapy in combination with an antibody-based immunotherapeutic, dinutuximab, appears to be independent of γδ T/NK cell content both in vitro and in vivo, which minimizes the implication of interindividual expansion differences toward efficacy. Collectively, these studies highlight the utility of maintaining the NK cell population within expanded γδ T cell therapies and suggest a synergistic action of combined innate cell immunotherapy toward neuroblastoma.

High-Throughput Screening Identifies Idasanutlin as a Resensitizing Drug for Venetoclax-Resistant Neuroblastoma Cells

Neuroblastoma tumors frequently overexpress the anti-apoptotic protein B-cell lymphoma/leukemia 2 (BCL-2). We previously showed that treating BCL-2-dependent neuroblastoma cells with the BCL-2 inhibitor venetoclax results in apoptosis, but unfortunately partial therapy resistance is observed. The current study describes the identification of drugs capable of resensitizing venetoclax-resistant neuroblastoma cells to venetoclax. To examine these effects, venetoclax resistance was induced in BCL-2-dependent neuroblastoma cell lines KCNR and SJNB12 by continuous exposure to high venetoclax concentrations. Non-resistant and venetoclax-resistant neuroblastoma cell lines were exposed to a 209-compound library in the absence and presence of venetoclax to identify compounds that were more effective in the venetoclax-resistant cell lines under venetoclax pressure. Top hits were further validated in combination with venetoclax using BCL-2-dependent neuroblastoma model systems. Overall, high-throughput drug screening identified the MDM2 inhibitor idasanutlin as a promising resensitizing agent for venetoclax-resistant neuroblastoma cell lines. Idasanutlin treatment induced BAX-mediated apoptosis in venetoclax-resistant neuroblastoma cells in the presence of venetoclax, whereas it caused p21-mediated growth arrest in control cells. In vivo combination treatment showed tumor regression and superior efficacy over single-agent therapies in a BCL-2-dependent neuroblastoma cell line xenograft and a patient-derived xenograft. However, xenografts less dependent on BCL-2 were not sensitive to venetoclax-idasanutlin combination therapy. This study demonstrates that idasanutlin can overcome resistance to the BCL-2 inhibitor venetoclax in preclinical neuroblastoma model systems, which supports clinical development of a treatment strategy combining the two therapies.

YAP-Mediated Repression of HRK Regulates Tumor Growth, Therapy Response, and Survival Under Tumor Environmental Stress in Neuroblastoma

Following chemotherapy and relapse, high-risk neuroblastoma tumors harbor more genomic alterations than at diagnosis, including increased transcriptional activity of the Yes-associated protein (YAP), a key downstream component of the Hippo signaling network. Although YAP has been implicated in many cancer types, its functional role in the aggressive pediatric cancer neuroblastoma is not well-characterized. In this study, we performed genetic manipulation of YAP in human-derived neuroblastoma cell lines to investigate YAP function in key aspects of the malignant phenotype, including mesenchymal properties, tumor growth, chemotherapy response, and MEK inhibitor response. Standard cytotoxic therapy induced YAP expression and transcriptional activity in patient-derived xenografts treated in vivo, which may contribute to neuroblastoma recurrence. Moreover, YAP promoted a mesenchymal phenotype in high-risk neuroblastoma that modulated tumor growth and therapy resistance in vivo. Finally, the BH3-only protein, Harakiri (HRK), was identified as a novel target inhibited by YAP, which, when suppressed, prevented apoptosis in response to nutrient deprivation in vitro and promoted tumor aggression, chemotherapy resistance, and MEK inhibitor resistance in vivo. Collectively, these findings suggest that YAP inhibition may improve chemotherapy response in patients with neuroblastoma via its regulation of HRK, thus providing a critical strategic complement to MEK inhibitor therapy. SIGNIFICANCE: This study identifies HRK as a novel tumor suppressor in neuroblastoma and suggests dual MEK and YAP inhibition as a potential therapeutic strategy in RAS-hyperactivated neuroblastomas.

A phase I study of simvastatin in combination with topotecan and cyclophosphamide in pediatric patients with relapsed and/or refractory solid and CNS tumors

10541

Background: HMG-CoA reductase inhibitors (statins) can inhibit IL-6-mediated STAT3 activation, a critical pathway in pediatric CNS and solid tumors. Statins also inhibit tumor proliferation, angiogenesis, and restore apoptosis in preclinical pediatric solid tumor models. We therefore conducted a phase 1 trial of simvastatin in combination with topotecan and cyclophosphamide in children with relapsed/refractory (r/r) solid and CNS tumors. Methods: Eligible patients were 1-29 years of age with a r/r solid or CNS tumor. Simvastatin was administered orally twice daily on days 1-21, with topotecan 0.75 mg/m2/dose IV and cyclophosphamide 250 mg/m2/dose IV on days 1-5. Four dose levels (DLs) were planned: 140, 180, 225, 290 mg/m2/dose. A 3+3 design was used to determine the maximum tolerated dose (MTD). Pharmacokinetic and pharmacodynamic analyses were performed. Results: The median (range) age of 14 eligible patients was 11.5 years (1 - 23). Diagnoses included neuroblastoma (N = 4), sarcoma (N = 7), and one each of malignant rhabdoid tumor of kidney, medulloblastoma, and Wilms tumor. Eleven DLT-evaluable patients received a median of 4 cycles (range: 1-6). There were 3 cycle 1 DLTs, grade 3 diarrhea and grade 4 creatine phosphokinase (CPK) increased at DL 1, and grade 4 CPK increased at DL 0 (100 mg/m2/dose). Grade 3/4 treatment-related cycle 1 adverse events occurring in ≥ 10% patients were neutropenia (100%), leukopenia (100%), thrombocytopenia (91%), lymphopenia (91%), anemia (55%), febrile neutropenia (55%) and CPK increased (18%). Best overall response was partial response in 1 patient and stable disease in four. Simvastatin and simvastatin acid Cmax (geomean 82.5 and 12.6 ng/mL) and AUC0-6 (geomean 82.5 and 12.6 ng•h/mL) were comparable with reported pediatric literature values (Cmax 3.5 and 0.4-2.1 ng/mL; AUC0-8 10.7 and 3.8 ng•h/mL) after correction for the higher doses (3.77 vs 0.16 mg/kg) used in our study. Patient peripheral blood mononuclear cells showed maximum phospho-(p)STAT3 inhibition on Day 5, with recurrence by Day 21 despite continued simvastatin dosing. Plasma IL6 levels showed sustained IL6 inhibition with decrease to normal values by Day 21 in all patients, indicating potential on target effects. Conclusions: For this first-in-pediatrics trial of statins as anti-cancer therapy, the MTD of simvastatin with chemotherapy was 100 mg/m2/dose. This combination was well-tolerated with predominantly hematologic toxicity and predictable DLTs related to simvastatin. Clinical trial information: NCT02390843.

Thiamine mimetics sulbutiamine and benfotiamine as a nutraceutical approach to anticancer therapy

Malignant cells frequently demonstrate an oncogenic-driven reliance on glycolytic metabolism to support their highly proliferative nature. Overexpression of pyruvate dehydrogenase kinase (PDK) may promote this unique metabolic signature of tumor cells by inhibiting mitochondrial function. PDKs function to phosphorylate and inhibit pyruvate dehydrogenase (PDH) activity. Silencing of PDK expression has previously been shown to restore mitochondrial function and reduce tumor cell proliferation. High dose Vitamin B1, or thiamine, possesses antitumor properties related to its capacity to reduce PDH phosphorylation and promote its enzymatic activity, presumably through PDK inhibition. Though a promising nutraceutical approach for cancer therapy, thiamine's low bioavailability may limit clinical effectiveness. Here, we have demonstrated exploiting the commercially available lipophilic thiamine analogs sulbutiamine and benfotiamine increases thiamine's anti-cancer effect in vitro. Determined by crystal violet proliferation assays, both sulbutiamine and benfotiamine reduced thiamine's millimolar IC50 value to micromolar equivalents. HPLC analysis revealed that sulbutiamine and benfotiamine significantly increased intracellular thiamine and TPP concentrations in vitro, corresponding with reduced levels of PDH phosphorylation. Through an ex vitro kinase screen, thiamine's activated cofactor form thiamine pyrophosphate (TPP) was found to inhibit the function of multiple PDK isoforms. Attempts to maximize intracellular TPP by exploiting thiamine homeostasis gene expression resulted in enhanced apoptosis in tumor cells. Based on our in vitro evaluations, we conclude that TPP serves as the active species mediating thiamine's inhibitory effect on tumor cell proliferation. Pharmacologic administration of benfotiamine, but not sulbutiamine, reduced tumor growth in a subcutaneous xenograft mouse model. It remains unclear if benfotiamine's effects in vivo are associated with PDK inhibition or through an alternative mechanism of action. Future work will aim to define the action of lipophilic thiamine mimetics in vivo in order to translate their clinical usefulness as anticancer strategies.

Abstract 892: Alterations of vitamin B1 homeostasis following oxidative stress in breast cancer and impact of supplementation on cellular redox homeostasis

Vitamin B1, or thiamine, has been demonstrated to enhance the development and growth of breast tumors in vivo. In addition, alterations in the expression of critical thiamine homeostasis genes have been extensively described in pre-clinical models of breast cancer as well as in clinical breast tumor tissue. Despite the effort that has been placed on delineating alterations to thiamine homeostasis that occur during breast cancer, there remains little evidence demonstrating a molecular advantage for supplemental thiamine in breast cancer cells. Our previous work in colorectal cancer suggests that the proliferative benefits of thiamine may be related to the maintenance of oxidative stress. This appears to be facilitated through the adaptive regulation of the thiamine activating enzyme thiamine pyrophosphokinase-1 (TPK1) for thiamine pyrophosphate production. Here, using MCF7 cells as a model of breast cancer, we also identified a relationship between thiamine homeostasis and oxidative stress. Similar to previous findings in colorectal cancer, Western blot analysis revealed that TPK1 expression was up-regulated in response to enhanced levels of ROS induced by hypoxia and chemotherapeutic treatment. TPK1 knockdown mediated by shRNA reduced the proliferation of MCF7 cells, while the presence of supplemental thiamine promoted proliferation as determined by cell counting. The effect of supplemental thiamine on MCF7 proliferation corresponded with a direct impact to the antioxidant status of tumor cells measured by reduced nuclear accumulation of the transcription factor nuclear factor- erythroid 2-related factor 2 by Western blot analysis. Molecular probes detecting intracellular ROS revealed that supplemental thiamine did not reduce the basal level of ROS in MCF7 cells. However, enhanced thiamine reduced intracellular superoxide levels following stimulation with the electron transport chain inhibitor Antimycin A. These findings support that during supplemental thiamine conditions thiamine homeostasis may be exploited in breast cancer for a redox advantage contributing to tumor progression.

Citation Format: Hunter C. Jonus, Ashley E. Ray, Jason A. Zastre. Alterations of vitamin B1 homeostasis following oxidative stress in breast cancer and impact of supplementation on cellular redox homeostasis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 892.

The adaptive regulation of thiamine pyrophosphokinase-1 facilitates malignant growth during supplemental thiamine conditions

Supplemental levels of vitamin B1 (thiamine) have been implicated in tumor progression. Tumor cells adaptively up-regulate thiamine transport during hypoxic stress. Upon uptake, thiamine pyrophosphokinase-1 (TPK1) facilitates the rapid phosphorylation of thiamine into thiamine pyrophosphate (TPP). However, the regulation of TPK1 during hypoxic stress is undefined. Understanding how thiamine homeostasis changes during hypoxia will provide critical insight into the malignant advantage supplemental thiamine may provide cancer cells. Using Western blot analysis and RT-PCR, we have demonstrated the post-transcriptional up-regulation of TPK1 in cancer cells following hypoxic exposure. TPK1 expression was also adaptively up-regulated following alterations of redox status by chemotherapeutic and antioxidant treatments. Although TPK1 was functionally up-regulated by hypoxia, HPLC analysis revealed a reduction in intracellular TPP levels. This loss was reversed by treatment with cell-permeable antioxidants and corresponded with reduced ROS production and enhanced cellular proliferation during supplemental thiamine conditions. siRNA-mediated knockdown of TPK1 directly enhanced basal ROS levels and reduced tumor cell proliferation. These findings suggest that the adaptive regulation of TPK1 may be an essential component in the cellular response to oxidative stress, and that during supplemental thiamine conditions its expression may be exploited by tumor cells for a redox advantage contributing to tumor progression.