Hypoxia-activated Prodrug Research Articles

Abstract 2803: Distinct roles of intracellular ROS in cisplatin and evofosfamide cytotoxicity

Abstract Cisplatin is one of the most widely used anticancer agents for the treatment of an array of malignancies. Although multiple mechanisms are involved in cisplatin efficacy, the most prominent and best understood modes of action are the generation of DNA lesions and induction of apoptosis and mitochondrial reactive oxygen species (ROS)-dependent effects on mitochondrial integrity. However, intrinsic or acquired cisplatin resistance can become a limiting factor in cisplatin-based therapy. Evofosfamide is a hypoxia-activated prodrug that is reduced at its nitroimidazole group and preferentially under hypoxic conditions releases Br-IPM, a DNA cross-linker. Evofosfamide is currently being investigated in multiple clinical trials for the treatment of cancer including indications and settings where resistance to cisplatin is observed (e.g. second-line non-small cell lung cancer; NCT01403610). We have previously demonstrated both shared and distinct DNA repair pathways involved with evofosfamide and cisplatin DNA damage. In the current study, we have conducted comparative studies to identify any distinctions in the relative role of ROS underlying cell sensitivity to cisplatin and evofosfamide to help evaluate the potential of evofosfamide to treat cisplatin-resistant tumors. The cisplatin-sensitive cervical cancer cell line ME180, the intermediate cisplatin-resistant human ovarian cancer cell line SK-OV-3, and cisplatin-resistant human lung cancer cell line A549 were investigated with respect to their chemosensitivity to evofosfamide. Unlike cisplatin, evofosfamide exhibited similar potency across all three cell lines. Addition of the ROS scavenger N-acetyl-L-cysteine (NAC) reduced the potency of cisplatin- but not evofosfamide-mediated cytotoxicity, indicating ROS plays a role in cytotoxicity mediated by cisplatin, but not evofosfamide. ROS levels were investigated using the dye H2DCFDA. Cisplatin induced a concentration-dependent and NAC-inhibitable increase of cellular ROS in cisplatin-sensitive ME-180 cells but not in cisplatin-resistant A549 cells. In contrast, ROS levels were not affected by the addition of evofosfamide under normoxia and hypoxia in both ME180 and A549 cells. In order to ascertain whether mitochondrial pathway-mediated apoptosis was involved in cytotoxicity mediated by evofosfamide and cisplatin, mitochondrial membrane depolarization was investigated with the dye JC-1. Cisplatin induced a concentration-dependent JC-1 polarization and these effects were abolished by NAC. In contrast, evofosfamide did not affect mitochondrial membrane potential. In conclusion, this data demonstrates that ROS is an essential factor in cisplatin-mediated cytotoxicity, but not in evofosfamide-mediated cytotoxicity. Citation Format: Fanying Meng, Deepthi Bhupathi, Geraldine Chan, Charles P. Hart. Distinct roles of intracellular ROS in cisplatin and evofosfamide cytotoxicity. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2803.

Role and treatment strategy of hypoxia in the pathogenesis of multiple myeloma

Hypoxia environment plays an important role in the pathogenesis of multiple myeloma such as stimulating angiogenesis, increasing bone destructiong, epithelial-mesenchymal transition and drug resis-tance. Thus, there are many therapeutic strategies targeting the hypoxic environment of multiple myeloma, such as hypoxia-activated prodrug and molecular targeting inhibitors. Targeting the hypoxic environment is a promising therapy for multiple myeloma in the future. Key words: Hypoxia-inducible factor 1; Multiple myeloma; Neoplasms; Metabolism

Combined Antitumor Therapy with Metronomic Topotecan and Hypoxia-Activated Prodrug, Evofosfamide, in Neuroblastoma and Rhabdomyosarcoma Preclinical Models.

Tumor cells residing in tumor hypoxic zones are a major cause of drug resistance and tumor relapse. In this study, we investigated the efficacy of evofosfamide, a hypoxia-activated prodrug, and its combination with topotecan in neuroblastoma and rhabdomyosarcoma preclinical models. Neuroblastoma and rhabdomyosarcoma cells were tested in vitro to assess the effect of evofosfamide on cell proliferation, both as a single agent and in combination with topotecan. In vivo antitumor activity was evaluated in different xenograft models. Animal survival was studied with the neuroblastoma metastatic tumor model. All tested cell lines showed response to evofosfamide under normoxic conditions, but when exposed to hypoxia overnight, a 2- to 65-fold decrease of IC50 was observed. Adding topotecan to the evofosfamide treatment significantly increased cytotoxicity in vitro In neuroblastoma xenograft models, single-agent evofosfamide treatment delayed tumor growth. Complete tumor regression was observed in the combined topotecan/evofosfamide treatment group after 2-week treatment. Combined treatment also improved survival in a neuroblastoma metastatic model, compared to single-agent treatments. In rhabdomyosarcoma xenograft models, combined treatment was more effective than single agents. We also showed that evofosfamide mostly targeted tumor cells within hypoxic regions while topotecan was more effective to tumor cells in normoxic regions. Combined treatment induced tumor cell apoptosis in both normoxic and hypoxic regions. Evofosfamide shows antitumor effects in neuroblastoma and rhabdomyosarcoma xenografts. Compared with single-agent, evofosfamide/topotecan, combined therapy improves tumor response, delays tumor relapse, and enhances animal survival in preclinical tumor models. Clin Cancer Res; 22(11); 2697-708. ©2015 AACR.

Targeting and Treatment of Tumor Hypoxia by Newly Designed Prodrug Possessing High Permeability in Solid Tumors.

Tumor hypoxia, which is associated with poor prognosis in cancer, is known to lead to resistance to radiotherapy and anticancer chemotherapy. Impaired drug penetration in hypoxic regions has been recognized as an essential barrier to drug development in solid tumors. Here, we propose novel hypoxia-activated prodrugs, which drastically improved the penetration property of commonly used anticancer drugs in the hypoxic region. In this design, conventional anticancer drugs were modified with 2-nitroimidazole derivatives. The most important point of this study was that the prodrug designed formed a 6-membered cyclic structure to allow liberation of the active drug in the hypoxic region. This design markedly increased the selectivity of the hypoxia-targeted prodrug, resulting in significant reduction of adverse effects in the normoxic region. In vitro studies confirmed the selective activation under hypoxic conditions. In vivo studies showed drastic reduction of adverse effects associated with conventional anticancer drugs and improvement of the survival rate of mice. Immunofluorescence analyses confirmed that the designed prodrug had a tendency to localize at the hypoxic region, in contrast to conventional anticancer drugs, which localize only at the normoxic region.

Highlights of This Issue

Resistance to aromatase inhibitors (AIs) is an ongoing clinical challenge in the treatment of breast cancer. To investigate the role of the estrogen receptor in AI resistance, Varešlija and colleagues conducted global ChIP-sequencing analysis in AI-resistant breast cancer cells and profiled patient tumor samples before, during, and after AI therapy. The estrogen receptor rapidly adapted to AI therapy, developing estrogen-independent transcriptional activity; however, during later stages of resistant disease progression, activity and even expression of the estrogen receptor was frequently lost. This study highlights the need to reassess tumor status during disease progression.Current multiparametric magnetic resonance imaging (MP-MRI) techniques for detecting prostate cancer are limited regarding tumor conspicuity assessment, in vivo characterization, and localization. Yamin and colleagues demonstrated that restriction spectrum imaging (RSI-MRI), a novel diffusion-based technique, differentiates among benign, low-grade, and high-grade prostate cancer within tumors. The RSI-MRI cellularity index used in this study may help to improve and refine diagnosis and staging of prostate cancer. Additionally, because it can detect intratumor variation, RSI-MRI may facilitate the targeting of most aggressive portions of tumors with interventions such as focal radiotherapy, magnetic resonance (MR)-guided focused ultrasound surgery, and MR-guided targeted biopsy.Tumor cells residing in tumor hypoxic zones are a major cause of drug resistance and tumor relapse. Targeting tumor hypoxia may improve cancer therapy and should be integrated in personalized medicine strategies. Zhang and colleagues investigated the efficacy of evofosfamide, a hypoxia-activated prodrug, and its combination with topotecan in neuroblastoma and rhabdomyosarcoma preclinical models. They demonstrated that targeting tumor hypoxia with evofosfamide improves antitumor effects of topotecan, including tumor growth inhibition, delayed tumor relapse, and enhanced animal survival in preclinical tumor models, which provides a new therapeutic approach for the treatment of pediatric solid tumors.The antifungal drug itraconazole has been found to possess potent antiangiogenic and anti-hedgehog activity. A major limitation of itraconazole, however, is its hepatotoxicity. In this study, each of the four stereoisomers of itraconazole was separated and assessed for their antiangiogenic activity and hepatotoxicity. It was found that one of the four stereoisomers possesses slightly higher antiangiogenic and anticancer activity without significantly decreased hepatotoxicity, making the specific stereoisomer an attractive candidate for development as a novel antiangiogenic and anticancer drug.

Targeting hypoxic microenvironment of pancreatic xenografts with the hypoxia-activated prodrug TH-302.

Previous reports have suggested that the hypoxic microenvironment provides a niche that supports tumor stem cells, and that this might explain clinical observations linking hypoxia to metastasis. To test this, we examined the effects of a hypoxia-activated prodrug, TH-302, on the tumor-initiating cell (TIC) frequency of patient-derived pancreatic xenografts (PDX).The frequencies of TIC, measured by limiting dilution assay, varied widely in 11 PDX models, and were correlated with rapid growth but not with the levels of hypoxia. Treatment with either TH-302 or ionizing radiation (IR), to target hypoxic and well-oxygenated regions, respectively, reduced TIC frequency, and the combination of TH-302 and IR was much more effective in all models tested. The combination was also more effective than TH-302 or IR alone controlling tumor growth, particularly treating the more rapidly-growing/hypoxic models. These findings support the clinical utility of hypoxia targeting in combination with radiotherapy to treat pancreatic cancers, but do not provide strong evidence for a hypoxic stem cell niche.

MR Imaging Biomarkers to Monitor Early Response to Hypoxia-Activated Prodrug TH-302 in Pancreatic Cancer Xenografts.

TH-302 is a hypoxia-activated prodrug known to activate selectively under the hypoxic conditions commonly found in solid tumors. It is currently being evaluated in clinical trials, including two trials in Pancreatic Ductal Adenocarcinomas (PDAC). The current study was undertaken to evaluate imaging biomarkers for prediction and response monitoring of TH-302 efficacy in xenograft models of PDAC. Dynamic contrast-enhanced (DCE) and diffusion weighted (DW) magnetic resonance imaging (MRI) were used to monitor acute effects on tumor vasculature and cellularity, respectively. Three human PDAC xenografts with known differential responses to TH-302 were imaged prior to, and at 24 h and 48 hours following a single dose of TH-302 or vehicle to determine if imaging changes presaged changes in tumor volumes. DW-MRI was performed at five b-values to generate apparent diffusion coefficient of water (ADC) maps. For DCE-MRI, a standard clinically available contrast reagent, Gd-DTPA, was used to determine blood flow into the tumor region of interest. TH-302 induced a dramatic decrease in the DCE transfer constant (Ktrans) within 48 hours after treatment in the sensitive tumors, Hs766t and Mia PaCa-2, whereas TH-302 had no effect on the perfusion behavior of resistant SU.86.86 tumors. Tumor cellularity, estimated from ADC, was significantly increased 24 and 48 hours after treatment in Hs766t, but was not observed in the Mia PaCa-2 and SU.86.86 groups. Notably, growth inhibition of Hs766t was observed immediately (day 3) following initiation of treatment, but was not observed in MiaPaCa-2 tumors until 8 days after initiation of treatment. Based on these preclinical findings, DCE-MRI measures of vascular perfusion dynamics and ADC measures of cell density are suggested as potential TH-302 response biomarkers in clinical trials.

Development of biomarkers to guide the clinical development of tarloxotinib bromide, a hypoxia-activated irreversible EGFR/HER2 inhibitor.

e17521Background: Tarloxotinib is a hypoxia-activated prodrug that releases an irreversible inhibitor of EGFR/HER2. A Phase 2 clinical study (NCT02449681) is ongoing in squamous cell carcinoma of t...

Randomized, double-blind, placebo-controlled trial of evofosfamide (Evo) and pemetrexed (Pem) in advanced non-squamous non-small cell lung cancer (n-s NSCLC).

9075Background: Tumor hypoxia is associated with chemo- and radioresistance. Evo is a hypoxia-activated prodrug that releases the bis-alkylating DNA crosslinker Br-IPM when reduced in severe hypoxi...

MAESTRO: A randomized, double-blind phase III study of evofosfamide (Evo) in combination with gemcitabine (Gem) in previously untreated patients (pts) with metastatic or locally advanced unresectable pancreatic ductal adenocarcinoma (PDAC).

4007Background: Hypoxia in PDAC is associated with disease progression and poor prognosis. Evo is a hypoxia-activated prodrug of Br-IPM that is preferentially activated under hypoxic conditions. Th...

Evofosfamide combined with gemcitabine/nab-paclitaxel in patients with previously untreated locally advanced or metastatic pancreatic adenocarcinoma (PAC): Results of a phase I trial.

4114Background: Gemcitabine + nab-paclitaxel (G/nab-P) is a standard first-line option for advanced PAC. Evofosfamide (Evo, previously known as TH-302) is a hypoxia-activated prodrug of bromo-isoph...

Tirapazamine has no Effect on Hepatotoxicity of Cisplatin and 5-fluorouracil but Interacts with Doxorubicin Leading to Side Changes in Redox Equilibrium.

Tirapazamine is a hypoxia-activated prodrug which was shown to exhibit up to 300 times greater cytotoxicity under anoxic in comparison with aerobic conditions. Thus, the combined anticancer therapy of tirapazamine with a routinely used anticancer drug seems to be a promising solution. Because tirapazamine undergoes redox cycle transformation in this study, the effect of tirapazamine on redox hepatic equilibrium, lipid status and liver morphology was evaluated in rats exposed to cisplatin, doxorubicin and 5-fluorouracil. Rats were intraperitoneally injected with tirapazamine and a particular cytostatic. The animals were killed, and blood and liver were collected. Hepatic glucose, total cholesterol, triglycerides, NADH, NADPH glutathione and the activity of glucose-6-phosphate dehydrogenase were determined. Liver morphology and the immune expression of HMG-CoA-reductase were also assessed. Glucose, total cholesterol, triglycerides, bilirubin concentrations and the activity of aspartate and alanine aminotransferases were determined in the plasma. Tirapazamine displayed insignificant interactions with cisplatin and 5-fluorouracil referring to hepatic morphology and biochemical parameters. However, tirapazamine interacts with doxorubicin, thus leading to side changes in redox equilibrium and lipid peroxidation, but those effects are not severe enough to exclude that drug combination from further studies. Thus, tirapazamine seems to be a promising agent in successive studies on anticancer activity in similar schedules.

Therapeutic targeting of hypoxia and hypoxia-inducible factors in cancer.

Insufficient tissue oxygenation, or hypoxia, contributes to tumor aggressiveness and has a profound impact on clinical outcomes in cancer patients. At decreased oxygen tensions, hypoxia-inducible factors (HIFs) 1 and 2 are stabilized and mediate a hypoxic response, primarily by acting as transcription factors. HIFs exert differential effects on tumor growth and affect important cancer hallmarks including cell proliferation, apoptosis, differentiation, vascularization/angiogenesis, genetic instability, tumor metabolism, tumor immune responses, and invasion and metastasis. As a consequence, HIFs mediate resistance to chemo- and radiotherapy and are associated with poor prognosis in cancer patients. Intriguingly, perivascular tumor cells can also express HIF-2α, thereby forming a "pseudohypoxic" phenotype that further contributes to tumor aggressiveness. Therefore, therapeutic targeting of HIFs in cancer has the potential to improve treatment efficacy. Different strategies to target hypoxic cancer cells and/or HIFs include hypoxia-activated prodrugs and inhibition of HIF dimerization, mRNA or protein expression, DNA binding capacity, and transcriptional activity. Here we review the functions of HIFs in the progression and treatment of malignant solid tumors. We also highlight how HIFs may be targeted to improve the management of patients with therapy-resistant and metastatic cancer.

Hypoxia-activated prodrugs: paths forward in the era of personalised medicine.

Tumour hypoxia has been pursued as a cancer drug target for over 30 years, most notably using bioreductive (hypoxia-activated) prodrugs that target antineoplastic agents to low-oxygen tumour compartments. Despite compelling evidence linking hypoxia with treatment resistance and adverse prognosis, a number of such prodrugs have recently failed to demonstrate efficacy in pivotal clinical trials; an outcome that demands reflection on the discovery and development of these compounds. In this review, we discuss a clear disconnect between the pathobiology of tumour hypoxia, the pharmacology of hypoxia-activated prodrugs and the manner in which they have been taken into clinical development. Hypoxia-activated prodrugs have been evaluated in the manner of broad-spectrum cytotoxic agents, yet a growing body of evidence suggests that their activity is likely to be dependent on the coincidence of tumour hypoxia, expression of specific prodrug-activating reductases and intrinsic sensitivity of malignant clones to the cytotoxic effector. Hypoxia itself is highly variable between and within individual tumours and is not treatment-limiting in all cancer subtypes. Defining predictive biomarkers for hypoxia-activated prodrugs and overcoming the technical challenges of assaying them in clinical settings will be essential to deploying these agents in the era of personalised cancer medicine.

OC-0236: DTP-006: a novel, orally bioavailable hypoxia-activated prodrug

OC-0236: DTP-006: a novel, orally bioavailable hypoxia-activated prodrug

Hypoxia-Activated Prodrug TH-302 Targets Hypoxic Bone Marrow Niches in Preclinical Leukemia Models.

To characterize the prevalence of hypoxia in the leukemic bone marrow, its association with metabolic and transcriptional changes in the leukemic blasts and the utility of hypoxia-activated prodrug TH-302 in leukemia models. Hyperpolarized magnetic resonance spectroscopy was utilized to interrogate the pyruvate metabolism of the bone marrow in the murine acute myeloid leukemia (AML) model. Nanostring technology was used to evaluate a gene set defining a hypoxia signature in leukemic blasts and normal donors. The efficacy of the hypoxia-activated prodrug TH-302 was examined in the in vitro and in vivo leukemia models. Metabolic imaging has demonstrated increased glycolysis in the femur of leukemic mice compared with healthy control mice, suggesting metabolic reprogramming of hypoxic bone marrow niches. Primary leukemic blasts in samples from AML patients overexpressed genes defining a "hypoxia index" compared with samples from normal donors. TH-302 depleted hypoxic cells, prolonged survival of xenograft leukemia models, and reduced the leukemia stem cell pool in vivo In the aggressive FLT3/ITD MOLM-13 model, combination of TH-302 with tyrosine kinase inhibitor sorafenib had greater antileukemia effects than either drug alone. Importantly, residual leukemic bone marrow cells in a syngeneic AML model remain hypoxic after chemotherapy. In turn, administration of TH-302 following chemotherapy treatment to mice with residual disease prolonged survival, suggesting that this approach may be suitable for eliminating chemotherapy-resistant leukemia cells. These findings implicate a pathogenic role of hypoxia in leukemia maintenance and chemoresistance and demonstrate the feasibility of targeting hypoxic cells by hypoxia cytotoxins.

Design, synthesis and evaluation of molecularly targeted hypoxia-activated prodrugs.

Regions of insufficient oxygen supply-hypoxia-occur in diverse contexts across biology in both healthy and diseased organisms. The difference in the chemical environment between a hypoxic biological system and one with normal oxygen levels provides an opportunity for targeting compound delivery to hypoxic regions by using bioreductive prodrugs. Here we detail a protocol for the efficient synthesis of (1-methyl-2-nitro-1H-imidazol-5-yl)methanol, which is a key intermediate that can be converted into a range of 1-methyl-2-nitro-1H-imidazole-based precursors of bioreductive prodrugs. We outline methods for attaching the bioreductive group to a range of functionalities, and we discuss the strategy for positioning of the group on the biologically active parent compound. We have used two parent checkpoint kinase 1 (Chk1) inhibitors to exemplify the protocol. The PROCEDURE also describes a suite of reduction assays, of increasing biological relevance, to validate the bioreductive prodrug. These assays are applied to an exemplar compound, CH-01, which is a bioreductive Chk1 inhibitor. This protocol has broad applications to the development of hypoxia-targeted compounds.

Hypoxia, Epithelial-Mesenchymal Transition, and TET-Mediated Epigenetic Changes.

Tumor hypoxia is a pathophysiologic outcome of disrupted microcirculation with inadequate supply of oxygen, leading to enhanced proliferation, epithelial-mesenchymal transition (EMT), metastasis, and chemo-resistance. Epigenetic changes induced by hypoxia are well documented, and they lead to tumor progression. Recent advances show that DNA demethylation mediated by the Ten-eleven translocation (TET) proteins induces major epigenetic changes and controls key steps of cancer development. TET enzymes serve as 5mC (5-methylcytosine)-specific dioxygenases and cause DNA demethylation. Hypoxia activates the expression of TET1, which also serves as a co-activator of HIF-1α transcriptional regulation to modulate HIF-1α downstream target genes and promote epithelial-mesenchymal transition. As HIF is a negative prognostic factor for tumor progression, hypoxia-activated prodrugs (HAPs) may provide a favorable therapeutic approach to lessen hypoxia-induced malignancy.

Evofosfamide (TH-302) in combination with gemcitabine in previously untreated patients with metastatic or locally advanced unresectable pancreatic ductal adenocarcinoma: Primary analysis of the randomized, double-blind phase III MAESTRO study.

193 Background: Pancreatic ductal adenocarcinoma (PDAC) is invariably diagnosed at an advanced stage and has poor clinical outcome. Hypoxia is a significant prognostic factor in PDAC progression and is associated with poor prognosis. Evofosfamide (Evo, previously known as TH-302) is a hypoxia-activated prodrug of bromo-isophosphoramide mustard (Br-IPM) that is preferentially activated under hypoxic conditions. The addition of Evo to gemcitabine (Gem) significantly improved progression-free survival (PFS) in a randomized phase II trial in advanced PDAC (NCT01144455). Methods: MAESTRO is an international, randomized, double-blind, placebo-controlled phase III trial of Evo/Gem vs Placebo/Gem in patients (pts) with measurable, locally advanced unresectable or metastatic PDAC (NCT01746979). Evo and Gem were administered intravenously at a dose of 340 mg/m2 and 1,000 mg/m2, respectively, on days 1, 8, and 15 of a 28-day cycle. Treatment continued until disease progression. Key eligibility criteria included ECOG PS 0/1 and no neoadjuvant or adjuvant chemotherapy <6 months prior to entry. The primary endpoint was overall survival (OS) with the study designed to detect a HR of 0.75 with 90% power. Secondary endpoints included PFS and objective response rate (ORR), employing a hierarchical testing procedure with a 2-sided α=0.05 at each level. Results: A total of 693 pts were randomized to treatment with Evo/Gem (n=xxx) or Placebo/Gem (n=yyy). Baseline pt characteristics were similar between treatment arms. The OS HR was X.XX (95% CI: Y.YY, Z.ZZ; p=A.AAA). Median OS was AA.A months (m) for Evo/Gem vs BB.B m for Placebo/Gem. Median PFS was C.C m and D.D m, respectively (HR E.EE [95% CI: F.FF, G.GG; p = H.HHH). ORR was JJ.J% with Evo/Gem vs KK.K% with Placebo/Gem (p = L.LLL). Grade ≥3 adverse events (AEs) occurring in >5% of pts in treated with Evo/Gem were: TBC. Conclusions: The data from the MAESTRO trial will make an important contribution to our understanding of PDAC treatment. Clinical trial information: NCT01746979.

A phase II trial to assess the activity and safety of the hypoxia-activated prodrug evofosfamide (TH-302) in combination with sunitinib in patients with disseminated grade 1 and 2 pancreatic neuroendocrine tumors (pNET) as a first-line approach: The GETNE-1408 trial.

TPS479 Background: Pancreatic-NETs are highly vascular tumors. The anti-angiogenetic sunitinib was approved in advanced pNETs based on prolongation of progression-free survival. Upregulation of several proangiogenic factors that reflects intratumor hypoxia conditions might drive resistance to sunitinib in pNETs. Evofosfamide is a prodrug that under hypoxic conditions preferentially releases a brominated version of isophosphoramide mustard and has shown activity in cell lines from neural crest derived tumors such as melanoma and glioblastoma/astrocytoma. We hypothesize that evofosfamide may have activity in the pathologic hypoxic conditions present in the tumor environment of neuroendocrine tumors inducing responses that may be consolidated and prolonged with sunitinib in patients with advanced pNETs that are naïve for systemic treatment. Methods: This is a prospective, non randomized, open-label, phase II study that is being conducted in 10 university sites belonging to the Spanish Task Force Group for NETs (GETNE) in Spain. Patients with histologically proven diagnosis of progressive unresectable or metastatic pNET with Ki67 < 20% and grade 1 or 2 will receive sunitinib orally at 37.5 mg PO daily on days 1 to 28 of a 28-day cycle (4 weeks) plus evofosfamide administered at 340 mg/m2 by IV infusion over 30-60 minutes on Days 8, 15 and 22 of a 28-day cycle (4 weeks). Hypoxia-related tumor markers, single nucleotide polymorphisms related to activity and metabolism of antiangiogenic agents (VEGFR2, VEGFR3, PDGFR-α, VEGF-A, IL8, CYP3A4, CYP3A5, ABCB1-2) will be correlated with clinical outcome. In this study it is planned to include 43 patientsbased on a two-stage Simon’s phase II design (α = 0.05, β = 80%). If the trial shows 8 responses or more among 43 patients, the treatment will be considered for further investigation. EudraCT number: 2014-004072-30 Clinical trial information: NCT02402062.