Activity of the hypoxia-activated pro-drug TH-302 in hypoxic and perivascular regions of solid tumors and its potential to enhance therapeutic effects of chemotherapy

Hypoxia-activated prodrug and antiangiogenic therapies cooperatively treat pancreatic cancer but elicit immunosuppressive G-MDSC infiltration

We previously showed that ablation of tumor hypoxia can sensitize tumors to immune checkpoint blockade (ICB). Here, we used a Kras+/G12D TP53+/R172H Pdx1-Cre-derived (KPC-derived) model of pancreatic adenocarcinoma to examine the tumor response and adaptive resistance mechanisms involved in response to 2 established methods of hypoxia-reducing therapy: the hypoxia-activated prodrug TH-302 and vascular endothelial growth factor receptor 2 (VEGFR-2) blockade. The combination of both modalities normalized tumor vasculature, increased DNA damage and cell death, and delayed tumor growth. In contrast with prior cancer models, the combination did not alleviate overall tissue hypoxia or sensitize these KPC tumors to ICB therapy despite qualitative improvements to the CD8+ T cell response. Bulk tumor RNA sequencing, flow cytometry, and adoptive myeloid cell transfer suggested that treated tumor cells increased their capacity to recruit granulocytic myeloid-derived suppressor cells (G-MDSCs) through CCL9 secretion. Blockade of the CCL9/CCR1 axis could limit G-MDSC migration, and depletion of Ly6G-positive cells could sensitize tumors to the combination of TH-302, anti-VEGFR-2, and ICB. Together, these data suggest that pancreatic tumors modulate G-MDSC migration as an adaptive response to vascular normalization and that these immunosuppressive myeloid cells act in a setting of persistent hypoxia to maintain adaptive immune resistance.

Design and synthesis of silver nanoparticle anchored poly(ionic liquid)s mesoporous for controlled anticancer drug delivery with antimicrobial effect

Owing to the importance of drug delivery, the synthesis of advanced nanomaterials for targeted drug delivery plays a considerable role in medical treatment. One of the most prominent nanomaterials is PIL, which is used as controlled anticancer drug delivery and significantly improves the half-life and antitumor effect. In this study, a stable and effective drug carrier containing silver nanoparticles was reported for the drug delivery with an antimicrobial effect, and the capability of the drug carrier . PILP was synthesized by radical polymerization, and silver nanoparticles were anchored into PIL voids by in-situ reduction, which developed the adsorption antimicrobial effect and capability of the drug carrier. The synthesized nanocomposite was characterized. The Ag-PILP nanocomposite showed antibacterial activityagainst both E. coli and S. aureus with a MIC of 256 μg/mL, and bactericidal activity against E. coli and S. aureus strains with a MBC of 256 and 512 μg/mL, respectively.

Cell proliferation, drug distribution and therapeutic effects in relation to the vascular system of solid tumours

In this perspective, the authors summarise some properties of the solid tumour micro-environment that have been explored during the last 55 years. It is well established that the concentrations of nutrients, including oxygen, decrease with increasing distance from tumour blood vessels, and that low extracellular pH is found in nutrient-poor regions. Cell proliferation is dependent on nutrient metabolites and decreases in regions distal from patent blood vessels. Proliferating cells cause migration of neighbouring cells further from blood vessels where they may die, and their breakdown products pass into regions of necrosis. Anticancer drugs reach solid tumours via the vascular system and establish concentration gradients such that drug concentration within tumours may be quite variable. Treatment with chemotherapy such as doxorubicin or docetaxel can kill well-nourished proliferating cells close to blood vessels, thereby interrupting migration toward necrotic regions and lead to re-oxygenation and renewed proliferation of distal cells, as can occur with radiotherapy. This effect leads to the paradox that cancer treatment can rescue cells that were destined to die in the untreated tumour. Renewed and sometimes accelerated repopulation of surviving tumour cells can counter the effects of cell killing from repeated treatments, leading to tumour shrinkage and regrowth without changes in the intrinsic sensitivity of cells to the administered treatment. Strategies to prevent these effects include the combined use of chemotherapy with agents that selectively kill hypoxic tumour cells, including inhibitors of autophagy, since this is a process that may allow recycling of cellular macromolecules from dying cells and improve their survival.

The Tumor Microenvironment in Tumorigenesis and Therapy Resistance Revisited

Tumorigenesis is a complex and dynamic process involving cell-cell and cell-extracellular matrix (ECM) interactions that allow tumor cell growth, drug resistance and metastasis. This review provides an updated summary of the role played by the tumor microenvironment (TME) components and hypoxia in tumorigenesis, and highlight various ways through which tumor cells reprogram normal cells into phenotypes that are pro-tumorigenic, including cancer associated- fibroblasts, -macrophages and -endothelial cells. Tumor cells secrete numerous factors leading to the transformation of a previously anti-tumorigenic environment into a pro-tumorigenic environment. Once formed, solid tumors continue to interact with various stromal cells, including local and infiltrating fibroblasts, macrophages, mesenchymal stem cells, endothelial cells, pericytes, and secreted factors and the ECM within the tumor microenvironment (TME). The TME is key to tumorigenesis, drug response and treatment outcome. Importantly, stromal cells and secreted factors can initially be anti-tumorigenic, but over time promote tumorigenesis and induce therapy resistance. To counter hypoxia, increased angiogenesis leads to the formation of new vascular networks in order to actively promote and sustain tumor growth via the supply of oxygen and nutrients, whilst removing metabolic waste. Angiogenic vascular network formation aid in tumor cell metastatic dissemination. Successful tumor treatment and novel drug development require the identification and therapeutic targeting of pro-tumorigenic components of the TME including cancer-associated- fibroblasts (CAFs) and -macrophages (CAMs), hypoxia, blocking ECM-receptor interactions, in addition to the targeting of tumor cells. The reprogramming of stromal cells and the immune response to be anti-tumorigenic is key to therapeutic success. Lastly, this review highlights potential TME- and hypoxia-centered therapies under investigation.

Assessing the therapeutic response of tumors to hypoxia-targeted prodrugs with an in silico approach

Tumor hypoxia is commonly recognized as a condition stimulating the progress of the aggressive phenotype of tumor cells. Hypoxic tumor cells inhibit the delivery of cytotoxic drugs, causing hypoxic areas to receive insufficient amounts of anticancer agents, which results in adverse treatment responses. Being such an obstruction to conventional therapies for cancer, hypoxia might be considered a target to facilitate the efficacy of treatments in the resistive environment of tumor sites. In this regard, benefiting from prodrugs that selectively target hypoxic regions remains an effective approach. Additionally, combining hypoxia-activated prodrugs (HAPs) with conventional chemotherapeutic drugs has been used as a promising strategy to eradicate hypoxic cells. However, determining the appropriate sequencing and scheduling of the combination therapy is also of great importance in obtaining favorable results in anticancer therapy. Here, benefiting from a modeling approach, we study the efficacy of HAPs in combination with chemotherapeutic drugs on tumor growth and the treatment response. Different treatment schedules have been investigated to see the importance of determining the optimal schedule in combination therapy. The effectiveness of HAPs in varying hypoxic conditions has also been explored in the study. The model provides qualitative conclusions about the treatment response, as the maximal benefit is obtained from combination therapy with greater cell death for highly hypoxic tumors. It has also been observed that the antitumor effects of HAPs show a hypoxia-dependent profile.

Nkx2.8 promotes chemosensitivity in bladder urothelial carcinoma via transcriptional repression of MDR1

Multidrug resistance gene 1 (MDR1), a key factor contributing to drug insensitivity, has been associated with treatment failure and poor prognoses in various cancers, including bladder urothelial carcinoma (UC). Here we show that positive Nkx2.8 expression was associated with better prognosis of UC patients received chemotherapy. Patients with positive Nkx2.8 expression had promising prognosis from adjuvant chemotherapy. Enforced expression of Nkx2.8 promotes drug sensitivity of UC cells. Mechanistic investigations showed that Nkx2.8 negatively regulated expression of MDR1 by binds directly to the MDR1 promoter and transcriptionally represses MDR1 expression. P-gp inhibitor reversed chemosensitivity inhibition by Nkx2.8 scilencing. In clinical UC specimens, expression of Nkx2.8 inversely correlated with P-gp expression, and UC patients with Nkx2.8 positivity and low P-gp expression displayed the best prognosis. Our findings uncovered a new mechanism of chemosensitivity in UC cells and proposing Nkx2.8-MDR1 axis as a novel candidate target for therapeutic intervention of UC.

Targeting HIF-1α/NOTCH1 pathway eliminates CD44+ cancer stem-like cell phenotypes, malignancy, and resistance to therapy in head and neck squamous cell carcinoma

Poor prognosis of head and neck squamous cell carcinomas (HNSCCs) results from resistance to chemotherapy and radiotherapy. To uncover the drivers of HNSCC resistance, including stemness and hypoxia, in this study, we compared the gene expression between CD44+ and CD44- HNSCC cells and assessed the correlation of CD44 and hypoxia-inducible factor 1α (HIF-1α) expression with mouse features and outcomes of patients with HNSCC. We combined the knockdown or activation of HIF-1α with in vitro and in vivo assays to evaluate effects on stemness and resistance of HNSCC cells. Analysis of clinical data showed that activation of HIF-1α in CD44+ patients with HNSCC was correlated with worse prognosis. Functional assays showed that HIF-1α promoted stemness, resistance, and epithelial-mesenchymal transition in HNSCC CD44+ cells. HIF-1α activated NOTCH1 signaling in HNSCC stem-like cells characterized by CD44 expression. Moreover, inhibition of these signaling proteins using shRNA or Evofosfamide (Evo) development for cancer treatment, reversed chemoresistance in vitro and in vivo. Taken together, our results indicated that targeting HIF-1α attenuated NOTCH1-induced stemness, which regulates responses to chemotherapy or radiotherapy and malignancy in CD44+ HNSCCs. HIF-1α/NOTCH1 signaling may represent a target for HNSCC treatment.

The Hypoxia-Activated Prodrug TH-302: Exploiting Hypoxia in Cancer Therapy

Hypoxia is an important feature of most solid tumors, conferring resistance to radiation and many forms of chemotherapy. However, it is possible to exploit the presence of tumor hypoxia with hypoxia-activated prodrugs (HAPs), agents that in low oxygen conditions undergo bioreduction to yield cytotoxic metabolites. Although many such agents have been developed, we will focus here on TH-302. TH-302 has been extensively studied, and we discuss its mechanism of action, as well as its efficacy in preclinical and clinical studies, with the aim of identifying future research directions.

Mechanisms of Taxane Resistance

The taxane family of chemotherapy drugs has been used to treat a variety of mostly epithelial-derived tumors and remain the first-line treatment for some cancers. Despite the improved survival time and reduction of tumor size observed in some patients, many have no response to the drugs or develop resistance over time. Taxane resistance is multi-faceted and involves multiple pathways in proliferation, apoptosis, metabolism, and the transport of foreign substances. In this review, we dive deeper into hypothesized resistance mechanisms from research during the last decade, with a focus on the cancer types that use taxanes as first-line treatment but frequently develop resistance to them. Furthermore, we will discuss current clinical inhibitors and those yet to be approved that target key pathways or proteins and aim to reverse resistance in combination with taxanes or individually. Lastly, we will highlight taxane response biomarkers, specific genes with monitored expression and correlated with response to taxanes, mentioning those currently being used and those that should be adopted. The future directions of taxanes involve more personalized approaches to treatment by tailoring drug-inhibitor combinations or alternatives depending on levels of resistance biomarkers. We hope that this review will identify gaps in knowledge surrounding taxane resistance that future research or clinical trials can overcome.

Doxorubicin uptake in ascitic lymphoma model: resistance or curability is governed by tumor cell density and prolonged drug retention

Background/Aims: Chemotherapy resistance of malignancies is a universal phenomenon which unfavorably affects therapeutic results. Genetic adaptations as well as epigenetic factors can play an important role in the development of multidrug resistance. Cytotoxic drug content in plasma of cancer patients is known to variate up to one hundred-fold regardless of the same dose injected per m² body surface. The relationship between plasma concentrations, tissue uptake, and chemotherapy response is not completely understood. The main objective of this study was to investigate how the identical dose of Doxorubicin (Dox) can result in a different therapeutic response pattern depending on tumor size. Study Design: The study was performed on ascitic EL4 lymphoma in an exponential growth phase focusing on the rapidly changing tumor susceptibility to the Dox treatment. Well distinguishable tumor response patterns (curability, remission-relapse, resistance) were selected to unveil Dox intratumoral uptake and drug tissue persistence. Intratumoral Dox content within peritoneal cavity (PerC) in conjunction with systemic toxicity and plasma pharmacokinetics, were monitored at several time points following Dox injection in tumor bearing mice (TBM) with differing patterns of response. Results: Following intraperitoneal (i.p.) transplantation of 5x10⁴ EL4 lymphoma cells rapid exponential proliferation with ascites volume and animal mass increase resulted in median survival of 14.5 days. The increase in tumor cell mass in PerC between day 3 and day 9 was 112.5-fold (0.2±0.03 mg vs 22.5±0.31 mg respectively). However, tumors at this time interval (day 3 to day 9 post-transplantation) were relatively small and constituted less than 0.05% of animal weight. An identical dose of Dox (15 mg/kg) injected intravenously (i.v.) on Day 3 lead to a cure whereas a TBM injected on day 9 exhibited resistance with a median survival time no different from the untreated TBM control. Injection of Dox resulted in noticeable differences of cellular uptake in PerC between all three groups of TBM ("cure", relapse", "resistance"). Larger tumors were consistently taking up less Dox 60 min after the 15 mg/kg i.v. bolus injection. Higher initial uptake resulted also in longer retention of drug in PerC cells. The area under the concentration curve in PerC cells AUC_0-10d was 8.2±0.57 µg/g x h, 4.6±0.27 µg/g x h and 1.6±0.02 µg/g x h in "cure", "relapse" and "resistance" TBM respectively (p<0.05 "relapse" vs "cure" and p<0.001 "resistance" vs "cure"). No differences in plasma Dox pharmacokinetics or systemic hematological effects were observed in TBM following a single i.v. Dox push. Hematologic nadir was tested on day 2 and subsequent hematologic recovery was evaluated on day 10 following Dox administration. Hematologic recovery on day 10 coincided with complete drug efflux from PerC and rising tumor cell numbers in PerC of "relapse" TBM. Myelosuppression and hematological recovery patterns were identical in all surviving animal groups regardless of the tumor size on the day of Dox injection. Conclusions: Within a few days of exponential tumor growth, an identical dose of Dox produced dramatically different responses in the TBM with increasing resistance. Systemic toxicity and plasma pharmacokinetics were indistinguishable between all TBM groups. Initial uptake in tumor cells was found to be consistently lower in larger tumors. Drug uptake in tumor cells was regulated locally - a phenomenon known as inoculum effect in vitro. The duration of drug retention in cells was directly related to initial cellular uptake. The magnitude of Dox cellular retention could potentially play a role in determining tumor remission and relapse.

Tumor Hypoxia As an Enhancer of Inflammation-Mediated Metastasis: Emerging Therapeutic Strategies

Metastasis is the leading cause of cancer-related deaths. Recent research has implicated tumor inflammation as a promoter of metastasis. Myeloid, lymphoid, and mesenchymal cells in the tumor microenvironment promote inflammatory signaling amongst each other and together with cancer cells to modulate sustained inflammation, which may enhance cancer invasiveness. Tumor hypoxia, a state of reduced available oxygen present in the majority of solid tumors, acts as a prognostic factor for a worse outcome and is known to have a role in tumor inflammation through the regulation of inflammatory mediator signals in both cancer and neighboring cells in the microenvironment. Multiple methods to target tumor hypoxia have been developed and tested in clinical trials, and still more are emerging as the impacts of hypoxia become better understood. These strategies include mechanistic inhibition of the hypoxia inducible factor signaling pathway and hypoxia activated pro-drugs, leading to both anti-tumor and anti-inflammatory effects. This prompts a need for further research on the prevention of hypoxia-mediated inflammation in cancer. Hypoxia-targeting strategies seem to have the most potential for therapeutic benefit when combined with traditional chemotherapy agents. This paper will serve to summarize the role of the inflammatory response in metastasis, to discuss how hypoxia can enable or enhance inflammatory signaling, and to review established and emerging strategies to target the hypoxia-inflammation-metastasis axis.

Evofosfamide sensitizes esophageal carcinomas to radiation without increasing normal tissue toxicity

BACKGROUND AND PURPOSE

Esophageal cancer incidence is increasing and is rarely curable. Hypoxic tumor areas cause resistance to conventional therapies, making them susceptible for treatment with hypoxia-activated prodrugs (HAPs). We investigated in vivo whether the HAP evofosfamide (TH-302) could increase the therapeutic ratio by sensitizing esophageal carcinomas to radiotherapy without increasing normal tissue toxicity.

MATERIALS AND METHODS

To assess therapeutic efficacy, growth of xenografted esophageal squamous cell (OE21) or adeno (OE19) carcinomas was monitored after treatment with TH-302 (50 mg/kg, QD5) and irradiation (sham or 10 Gy). Short- and long-term toxicity was assessed in a gut mucosa and lung fibrosis irradiation model, sensitive to acute and late radiation injury respectively. Mice were injected with TH-302 (50 mg/kg, QD5) and the abdominal area (sham, 8 or 10 Gy) or the upper part of the right lung (sham, 20 Gy) was irradiated. Damage to normal tissues was assessed 84 hours later by histology and blood plasma citrulline levels (gut) and for up to 1 year by non-invasive micro CT imaging (lung).

RESULTS

The combination treatment of TH-302 with radiotherapy resulted in significant tumor growth delay in OE19 (P = 0.02) and OE21 (P = 0.03) carcinomas, compared to radiotherapy only. Irradiation resulted in a dose-dependent decrease of crypt survival (P < 0.001), mucosal surface area (P < 0.01) and citrulline levels (P < 0.001) in both tumor and non-tumor bearing animals. On the long-term, irradiation increased CT density in the lung, indicating fibrosis, over time. TH-302 did not influence the radiation-induced short-term and long-term toxicity, confirmed by histological evaluation.

CONCLUSION

The combination of TH-302 and radiotherapy might be a promising approach to improve the therapeutic index for esophageal cancer patients.

Schedule-dependent potentiation of chemotherapy drugs by the hypoxia-activated prodrug SN30000

Hypoxia-activated prodrugs (HAPs) are hypothesized to improve the therapeutic index of chemotherapy drugs that are ineffective against tumor cells in hypoxic microenvironments. SN30000 (CEN-209) is a benzotriazine di-N-oxide HAP that potentiates radiotherapy in preclinical models, but its combination with chemotherapy has not been explored. Here we apply multiple models (monolayers, multicellular spheroids and tumor xenografts) to identify promising SN30000/chemotherapy combinations (with chemotherapy drugs before, during or after SN30000 exposure). SN30000, unlike doxorubicin, cisplatin, gemcitabine or paclitaxel, was more active against cells in spheroids than monolayers by clonogenic assay. Combinations of SN30000 and chemotherapy drugs in HCT116/GFP and SiHa spheroids demonstrated hypoxia-and schedule-dependent potentiation of gemcitabine or doxorubicin in growth inhibition and clonogenic assays. Co-administration with SN30000 suppressed clearance of gemcitabine in NIH-III mice, likely due to SN30000-induced hypothermia which also modulated extravascular transport of gemcitabine in tumor tissue as assessed from its diffusion through HCT116 multicellular layer cultures. Despite these systemic effects, the same schedules that gave therapeutic synergy in spheroids (SN30000 3 h before or during gemcitabine, but not gemcitabine 3 h before SN30000) enhanced growth delay of HCT116 xenografts without increasing host toxicity. Identification of hypoxic and S-phase cells by immunohistochemistry and flow cytometry established that hypoxic cells initially spared by gemcitabine subsequently reoxygenate and re-enter the cell cycle, and that this repopulation is prevented by SN30000 only when administered with or before gemcitabine. This illustrates the value of spheroids in modeling tumor microenvironment-dependent drug interactions, and the potential of HAPs for overcoming hypoxia-mediated drug resistance.

Hypoxia-targeted drug delivery

Hypoxia is a state of low oxygen tension found in numerous solid tumours. It is typically associated with abnormal vasculature, which results in a reduced supply of oxygen and nutrients, as well as impaired delivery of drugs. The hypoxic nature of tumours often leads to the development of localized heterogeneous environments characterized by variable oxygen concentrations, relatively low pH, and increased levels of reactive oxygen species (ROS). The hypoxic heterogeneity promotes tumour invasiveness, metastasis, angiogenesis, and an increase in multidrug-resistant proteins. These factors decrease the therapeutic efficacy of anticancer drugs and can provide a barrier to advancing drug leads beyond the early stages of preclinical development. This review highlights various hypoxia-targeted and activated design strategies for the formulation of drugs or prodrugs and their mechanism of action for tumour diagnosis and treatment.

An Intratumor Pharmacokinetic/Pharmacodynamic Model for the Hypoxia-Activated Prodrug Evofosfamide (TH-302): Monotherapy Activity is Not Dependent on a Bystander Effect

Tumor hypoxia contributes to resistance to anticancer therapies. Hypoxia-activated prodrugs (HAPs) selectively target hypoxic cells and their activity can extend to well-oxygenated areas of tumors via diffusion of active metabolites. This type of bystander effect has been suggested to be responsible for the single agent activity of the clinical-stage HAP evofosfamide (TH-302) but direct evidence is lacking. To dissect the contribution of bystander effects to TH-302 activity, we implemented a Green's function pharmacokinetic (PK) model to simulate the spatial distribution of O₂, TH-302 and its cytotoxic metabolites, bromo-isophosphoramide mustard (Br-IPM) and its dichloro derivative isophosphoramide mustard (IPM), in two digitized tumor microvascular networks. The model was parameterized from literature and experimentally, including measurement of diffusion coefficients of TH-302 and its metabolites in multicellular layer cultures. The latter studies demonstrate that Br-IPM and IPM cannot diffuse significantly from the cells in which they are generated, although evidence was obtained for diffusion of the hydroxylamine metabolite of TH-302. The spatially resolved PK model was linked to a pharmacodynamic (PD) model that describes cell killing probability at each point in the tumor microregion as a function of Br-IPM and IPM exposure. The resulting PK/PD model accurately predicted previously reported monotherapy activity of TH-302 in H460 tumors, without invoking a bystander effect, demonstrating that the notable single agent activity of TH-302 in tumors can be accounted for by significant bioreductive activation of TH-302 even in oxic regions, driven by the high plasma concentrations achievable with this well-tolerated prodrug.

Evofosfamide for the treatment of human papillomavirus-negative head and neck squamous cell carcinoma

Evofosfamide (TH-302) is a clinical-stage hypoxia-activated prodrug of a DNA-crosslinking nitrogen mustard that has potential utility for human papillomavirus (HPV) negative head and neck squamous cell carcinoma (HNSCC), in which tumor hypoxia limits treatment outcome. We report the preclinical efficacy, target engagement, preliminary predictive biomarkers and initial clinical activity of evofosfamide for HPV-negative HNSCC. Evofosfamide was assessed in 22 genomically characterized cell lines and 7 cell line-derived xenograft (CDX), patient-derived xenograft (PDX), orthotopic, and syngeneic tumor models. Biomarker analysis used RNA sequencing, whole-exome sequencing, and whole-genome CRISPR knockout screens. Five advanced/metastatic HNSCC patients received evofosfamide monotherapy (480 mg/m2 qw × 3 each month) in a phase 2 study. Evofosfamide was potent and highly selective for hypoxic HNSCC cells. Proliferative rate was a predominant evofosfamide sensitivity determinant and a proliferation metagene correlated with activity in CDX models. Evofosfamide showed efficacy as monotherapy and with radiotherapy in PDX models, augmented CTLA-4 blockade in syngeneic tumors, and reduced hypoxia in nodes disseminated from an orthotopic model. Of 5 advanced HNSCC patients treated with evofosfamide, 2 showed partial responses while 3 had stable disease. In conclusion, evofosfamide shows promising efficacy in aggressive HPV-negative HNSCC, with predictive biomarkers in development to support further clinical evaluation in this indication.

Cellular pharmacology of evofosfamide (TH-302): A critical re-evaluation of its bystander effects

Evofosfamide (TH-302) is a clinical-stage hypoxia-activated prodrug with proven efficacy against hypoxic cells in preclinical tumour models. TH-302 is designed to release the DNA crosslinking agent bromo-isophosphoramide mustard (Br-IPM) when reduced in hypoxic tissue. Br-IPM is considered to diffuse locally from hypoxic regions, eliciting additional tumour cell killing, but the latter 'bystander effect' has not been demonstrated directly. Previous studies with multicellular co-cultures that included cells expressing the E. coli nitroreductase NfsA as a model TH-302 reductase have provided clear evidence of a bystander effect (which we confirm in the present study). However, NfsA is an oxygen-insensitive two-electron reductase that is not expected to generate the nitro radical intermediate that has been demonstrated to fragment to release Br-IPM. Here, we use mass spectrometry methods to characterise TH-302 metabolites generated by one-electron reduction (steady-state radiolysis by ionising radiation and cellular metabolism under hypoxia, including HCT116 cells that overexpress P450 oxidoreductase, POR) or by NfsA expressed in HCT116 cells under oxic conditions, and investigate the stability and cytotoxicity of these products. Br-IPM is shown to have very low cytotoxic potency when added to extracellular culture medium and to be rapidly converted to other hydrophilic products including dichloro-isophosphoramide mustard (IPM). Only traces of Br-IPM or IPM were detected in the extracellular medium when generated by cellular metabolism of TH-302. We identify, in NfsA-expressing cells, the hydroxylamine metabolite of TH-302, and downstream products resulting from rearrangement or hydration of the imidazole ring, and demonstrate that formation of these candidate bystander effect mediators is suppressed by hypoxia. This characterisation of the cellular pharmacology of TH-302 implies that bystander effects from hypoxic activation of TH-302 are unlikely to contribute to its anticancer activity.

Administration of Hypoxia-Activated Prodrug Evofosfamide after Conventional Adjuvant Therapy Enhances Therapeutic Outcome and Targets Cancer-Initiating Cells in Preclinical Models of Colorectal Cancer

Purpose: Cancer-initiating cells (C-IC) have been described in multiple cancer types, including colorectal cancer. C-ICs are defined by their capacity to self-renew, thereby driving tumor growth. C-ICs were initially thought to be static entities; however, recent studies have determined these cells to be dynamic and influenced by microenvironmental cues such as hypoxia. If hypoxia drives the formation of C-ICs, then therapeutic targeting of hypoxia could represent a novel means to target C-ICs.Experimental Design: Patient-derived colorectal cancer xenografts were treated with evofosfamide, a hypoxia-activated prodrug (HAP), in combination with 5-fluorouracil (5-FU) or chemoradiotherapy (5-FU and radiation; CRT). Treatment groups included both concurrent and sequential dosing regimens. Effects on the colorectal cancer-initiating cell (CC-IC) fraction were assessed by serial passage in vivo limiting dilution assays. FAZA-PET imaging was utilized as a noninvasive method to assess intratumoral hypoxia.Results: Hypoxia was sufficient to drive the formation of CC-ICs and colorectal cancer cells surviving conventional therapy were more hypoxic and C-IC-like. Using a novel approach to combination therapy, we show that sequential treatment with 5-FU or CRT followed by evofosfamide not only inhibits tumor growth of xenografts compared with 5-FU or CRT alone, but also significantly decreases the CC-IC fraction. Furthermore, noninvasive FAZA-PET hypoxia imaging was predictive of a tumor's response to evofosfamide.Conclusions: Our data demonstrate a novel means to target the CC-IC fraction by adding a HAP sequentially after conventional adjuvant therapy, as well as the use of FAZA-PET as a biomarker for hypoxia to identify tumors that will benefit most from this approach. Clin Cancer Res; 24(9); 2116-27. ©2018 AACR.

Established Models and New Paradigms for Hypoxia-Driven Cancer-Associated Bone Disease

The five-year survival rate for primary bone cancers is ~ 70% while almost all cases of secondary metastatic bone cancer are terminal. Hypoxia, the deficiency of oxygen which occurs as the rate of tumour growth exceeds the supply of vascularisation, is a key promoter of tumour progression. Hypoxia-driven effects in the primary tumour are wide ranging including changes in gene expression, dysregulation of signalling pathways, resistance to chemotherapy, neovascularisation, increased tumour cell proliferation and migration. Paget's seed and soil theory states that for a metastasising tumour cell 'the seed' it requires the correct microenvironment 'soil' to colonise. Why and how metastasising tumour cells colonise the bone is a complex and intriguing problem. However, once present tumour cells are able to disrupt bone homeostasis through increasing osteoclast activity and downregulating osteoblast function. Osteoclast resorption releases growth factors from the bone matrix that subsequently contribute to the proliferation of invasive tumour cells creating the vicious cycle of bone loss and metastatic cancer progression. Recently, we have shown that hypoxia increases expression and release of lysyl oxidase (LOX) from primary mammary tumours, which in turn disrupts bone homeostasis to favour osteolytic degradation to create pre-metastatic niches in the bone microenvironment. We also demonstrated how treatment with bisphosphonates could block this cancer-induced bone remodelling and reduce secondary bone metastases. This review describes the roles of hypoxia in primary tumour progression to metastasis, with a focus on key signalling pathways and treatment options to reduce patient morbidity and increase survival.

Multimodal targeting of tumor vasculature and cancer stem-like cells in sarcomas with VEGF-A inhibition, HIF-1α inhibition, and hypoxia-activated chemotherapy

Vascular endothelial growth factor A (VEGF-A) inhibition with pazopanib is an approved therapy for sarcomas, but likely results in compensatory pathways such as upregulation of hypoxia inducible factor 1α (HIF-1α). In addition, cancer stem-like cells can preferentially reside in hypoxic regions of tumors and be resistant to standard chemotherapies. In this study, we hypothesized that the combination of VEGF-A inhibition, HIF-1α inhibition, and hypoxia-activated chemotherapy with evofosfamide would be an effective multimodal strategy. Multimodal therapy was examined in one genetically engineered and two xenograft mouse models of sarcoma. In all three models, multimodal therapy showed greater efficacy than any single agent therapy or bimodality therapy in blocking tumor growth. Even after cessation of therapy, tumors treated with multimodal therapy remained relatively dormant for up to 2 months. Compared to the next best bimodality therapy, multimodal therapy caused 2.8-3.3 fold more DNA damage, 1.5-2.7 fold more overall apoptosis, and 2.3-3.6 fold more endothelial cell-specific apoptosis. Multimodal therapy also decreased microvessel density and HIF-1α activity by 85-90% and 79-89%, respectively, compared to controls. Sarcomas treated with multimodal therapy had 95-96% depletion of CD133(+) cancer stem-like ells compared to control tumors. Sarcoma cells grown as spheroids to enrich for CD133(+) cancer stem-like cells were more sensitive than monolayer cells to multimodal therapy in terms of DNA damage and apoptosis, especially under hypoxic conditions. Thus multimodal therapy of sarcomas with VEGF-A inhibition, HIF-1α inhibition, and hypoxia-activated chemotherapy effectively blocks sarcoma growth through inhibition of tumor vasculature and cancer stem-like cells.

Antagonism in effectiveness of evofosfamide and doxorubicin through intermolecular electron transfer

Hypoxic cells pose a problem in anticancer chemotherapy, in which often drugs require oxygen as an electron acceptor to bring about the death of actively cycling cells. Bioreductive anticancer drugs, which are selectively activated in the hypoxic regions of tumours through enzymatic one-electron reduction, are being developed for combination with chemotherapy-, radiotherapy- and immunotherapy-containing regimens to kill treatment-resistant hypoxic cells. The most clinically-advanced bioreductive drug, evofosfamide (TH-302), which acts by releasing a DNA-crosslinking mustard, failed to extend overall survival in combination with doxorubicin, a topoisomerase II inhibitor, for advanced soft tissue sarcoma in a pivotal clinical trial. However, the reasons for the lack of additive efficacy with this combination are unknown. Here, we show that the radical anion of evofosfamide undergoes electron transfer to doxorubicin in kinetic competition to fragmentation of the radical anion, thus suppressing the release the cytotoxic mustard. This electron transfer process may account, at least in part, for the lack of overall survival improvement in the recent clinical trial. This study underlines the need to consider both redox and electron transfer chemistry when combining bioreductive prodrugs with other redox-active drugs in cancer treatment.

A Combination of Radiation and the Hypoxia-Activated Prodrug Evofosfamide (TH-302) is Efficacious against a Human Orthotopic Pancreatic Tumor Model

This study was designed to investigate the effect of single-dose radiation therapy (RT) in combination with evofosfamide (TH-302), a hypoxia-activated prodrug, in a pre-clinical model of pancreatic cancer. AsPC1 tumors were implanted orthotopically in the pancreas of nude mice. Tumors were treated with 15 Gy of RT, using a 1 cm diameter field, and delivered as a continuous arc. Image-guidance to center the field on the tumor was based on CT imaging with intraperitoneal contrast. Evofosfamide (100 mg/kg, i.p.) was administered 3 hours before RT. Tumor volumes were measured using ultrasound, and regrowth curves were plotted. Tumor hypoxia and cell proliferation were measured using pimonidazole and the thymidine analog EdU, respectively. In vitro clonogenic assays were performed. Tumors were shown to contain substantial areas of hypoxia, as calculated by percent pimonidazole staining. Evofosfamide was active in these tumors, as demonstrated by a significant reduction in uptake of the thymidine analog EdU. This effect was visible in oxygenated tissue, consistent with the previously reported bystander effects of evofosfamide. RT produced significant regrowth delay, as did evofosfamide. The combination of both agents produced a growth delay that was at least equal to the sum of the two treatments given separately. The improvement in tumor response when evofosfamide is combined with RT supports the hypothesis that hypoxia is a cause of radioresistance in high dose RT for pancreatic cancer. Assessing the efficacy and safety of stereotactic radiation treatment and evofosfamide is warranted in patients with locally advanced pancreatic cancer.

Proteoglycan-targeting applied to hypoxia-activated prodrug therapy in chondrosarcoma: first proof-of-concept

Due to its abundant chondrogenic matrix and hypoxic tissue, chondrosarcoma is chemo- and radio-resistant. Our group has developed a proteoglycan targeting strategy by using a quaternary ammonium (QA) function as a carrier of DNA alkylating agents to chondrosarcoma environment. Here, we assessed the relevance of this strategy applied to hypoxia-activated prodrugs, by conjugating a QA to 2-nitroimidazole phosphoramidate. This derivative, named as 8-QA, was evaluated respectively to its non-QA equivalent and to a QA-conjugated but non-hypoxia activated. Firstly binding to aggrecan was confirmed from dissociation constant determined by Surface Plasmon Resonance. In vitro, in HEMC-SS chondrosarcoma cells cultured in monolayer and in spheroids, 8-QA showed higher cytotoxic activity in hypoxia versus normoxia, and led to a strong accumulation of cells in S phase and apoptosis. In vivo, a HEMC-SS xenograft model was implanted on SCID mice and characterized for hypoxia by photoacoustic imaging as well as proteoglycan content. When HEMC-SS bearing mice were given 8-QA at 47 μmol/kg according to a q4d x 6 schedule, a significant 62.1% inhibition of tumor growth was observed, without associated hematological side effects. Mechanistic studies of treated tumors highlighted decrease in mitotic index associated to increase in both p21 and p53S15 markers. Interestingly, 8-QA treatment induced an increase of DNA damages as measured by γH2AX predominantly found in pimonidazole-positive hypoxic areas. These preclinical results are the first to demonstrate the interest of addressing hypoxia-activated prodrugs selectively to proteoglycan of chondrogenic tumor tissue, as a promising therapeutic strategy.

Leveraging Hypoxia-Activated Prodrugs to Prevent Drug Resistance in Solid Tumors

Experimental studies have shown that one key factor in driving the emergence of drug resistance in solid tumors is tumor hypoxia, which leads to the formation of localized environmental niches where drug-resistant cell populations can evolve and survive. Hypoxia-activated prodrugs (HAPs) are compounds designed to penetrate to hypoxic regions of a tumor and release cytotoxic or cytostatic agents; several of these HAPs are currently in clinical trial. However, preliminary results have not shown a survival benefit in several of these trials. We hypothesize that the efficacy of treatments involving these prodrugs depends heavily on identifying the correct treatment schedule, and that mathematical modeling can be used to help design potential therapeutic strategies combining HAPs with standard therapies to achieve long-term tumor control or eradication. We develop this framework in the specific context of EGFR-driven non-small cell lung cancer, which is commonly treated with the tyrosine kinase inhibitor erlotinib. We develop a stochastic mathematical model, parametrized using clinical and experimental data, to explore a spectrum of treatment regimens combining a HAP, evofosfamide, with erlotinib. We design combination toxicity constraint models and optimize treatment strategies over the space of tolerated schedules to identify specific combination schedules that lead to optimal tumor control. We find that (i) combining these therapies delays resistance longer than any monotherapy schedule with either evofosfamide or erlotinib alone, (ii) sequentially alternating single doses of each drug leads to minimal tumor burden and maximal reduction in probability of developing resistance, and (iii) strategies minimizing the length of time after an evofosfamide dose and before erlotinib confer further benefits in reduction of tumor burden. These results provide insights into how hypoxia-activated prodrugs may be used to enhance therapeutic effectiveness in the clinic.

It has been suggested that one key factor driving the emergence of drug resistance is the spatial heterogeneity in the distribution of drug and oxygen throughout a tumor due to disorganized tumor vasculatures. Researchers have developed a class of novel drugs that penetrate to hypoxic regions where they are activated to kill tumor cells. The inclusion of these drugs, called hypoxia-activated prodrugs (HAPs) alongside standard therapies in combination may be the key to long-term tumor control or eradication. However, identifying the right timing and administration sequence of combination therapies is an extremely difficult task, and the time and human costs of clinical trials to investigate even a few options is often prohibitive. In this work we design a mathematical model based upon evolutionary principles to investigate the potential of combining HAPs with standard targeted therapy for a specific example in non-small cell lung cancer. We formulate novel toxicity constraints from existing clinical data to estimate the shape of the tolerated drug combination treatment space. We find that (i) combining these therapies delays resistance longer than any monotherapy schedule with either evofosfamide or erlotinib alone, and (ii) the best strategy for combination involves single doses of each drug sequentially administered in an alternating sequence. These model predictions of tumor dynamics during treatment provide insight into the role of the tumor microenvironment in combination therapy and identify treatment hypotheses for further experimental and clinical testing.

A phase 1 'window-of-opportunity' trial testing evofosfamide (TH-302), a tumour-selective hypoxia-activated cytotoxic prodrug, with preoperative chemoradiotherapy in oesophageal adenocarcinoma patients

Background

Neo-adjuvant chemoradiotherapy followed by surgery is the standard treatment with curative intent for oesophageal cancer patients, with 5-year overall survival rates up to 50 %. However, patients’ quality of life is severely compromised by oesophagectomy, and eventually many patients die due to metastatic disease.

Most solid tumours, including oesophageal cancer, contain hypoxic regions that are more resistant to chemoradiotherapy. The hypoxia-activated prodrug evofosfamide works as a DNA-alkylating agent under these hypoxic conditions, which directly kills hypoxic cancer cells and potentially minimizes resistance to conventional therapy. This drug has shown promising results in several clinical studies when combined with chemotherapy. Therefore, in this phase I study we investigate the safety of evofosfamide added to the chemoradiotherapy treatment of oesophageal cancer.

Methods/Design

A phase I, non-randomized, single-centre, open-label, 3 + 3 trial with repeated hypoxia PET imaging, will test the safety of evofosfamide in combination with neo-adjuvant chemoradiotherapy in potentially resectable oesophageal adenocarcinoma patients. Investigated dose levels range from 120 mg/m2 to 340 mg/m2. Evofosfamide will be administered one week before the start of chemoradiotherapy (CROSS-regimen) and repeated weekly up to a total of six doses. PET/CT acquisitions with hypoxia tracer ¹⁸F-HX4 will be made before and after the first administration of evofosfamide, allowing early assessment of changes in hypoxia, accompanied with blood sampling to measure hypoxia blood biomarkers. Oesophagectomy will be performed according to standard clinical practice.

Higher grade and uncommon non-haematological, haematological, and post-operative toxicities are the primary endpoints according to the CTCAEv4.0 and Clavien-Dindo classifications. Secondary endpoints are reduction in hypoxic fraction based on ¹⁸F-HX4 imaging, pathological complete response, histopathological negative circumferential resection margin (R0) rate, local and distant recurrence rate, and progression free and overall survival.

Discussion

This is the first clinical trial testing evofosfamide in combination with chemoradiotherapy. The primary objective is to determine the dose limiting toxicity of this combined treatment and herewith to define the maximum tolerated dose and recommended phase 2 dose for future clinical studies. The addition of non-invasive repeated hypoxia imaging (‘window-of-opportunity’) enables us to identify the biologically effective dose. We believe this approach could also be used for other hypoxia targeted drugs.

Trial registration

ClinicalTrials.gov Identifier: NCT02598687.

Preclinical Benefit of Hypoxia-Activated Intra-arterial Therapy with Evofosfamide in Liver Cancer

PURPOSE

To evaluate safety and characterize anticancer efficacy of hepatic hypoxia-activated intra-arterial therapy (HAIAT) with evofosfamide in a rabbit model.

EXPERIMENTAL DESIGN

VX2-tumor-bearing rabbits were assigned to 4 intra-arterial therapy (IAT) groups (n = 7/group): (i) saline (control); (ii) evofosfamide (Evo); (iii) doxorubicin-lipiodol emulsion followed by embolization with 100-300 μm beads (conventional, cTACE); or (iv) cTACE and evofosfamide (cTACE + Evo). Blood samples were collected pre-IAT and 1, 2, 7, and 14 days post-IAT. A semiquantitative scoring system assessed hepatocellular damage. Tumor volumes were segmented on multidetector CT (baseline, 7/14 days post-IAT). Pathologic tumor necrosis was quantified using manual segmentation on whole-slide images. Hypoxic fraction (HF) and compartment (HC) were determined by pimonidazole staining. Tumor DNA damage, apoptosis, cell proliferation, endogenous hypoxia, and metabolism were quantified (γ-H2AX, Annexin V, caspase-3, Ki-67, HIF1α, VEGF, GAPDH, MCT4, and LDH).

RESULTS

cTACE + Evo showed a similar profile of liver enzymes elevation and pathologic scores compared with cTACE. Neither hematologic nor renal toxicity were observed. Animals treated with cTACE + Evo demonstrated smaller tumor volumes, lower tumor growth rates, and higher necrotic fractions compared with cTACE. cTACE + Evo resulted in a marked reduction in the HF and HC. Correlation was observed between decreases in HF or HC and tumor necrosis. cTACE + Evo promoted antitumor effects as evidenced by increased expression of γ-H2AX, apoptotic biomarkers, and decreased cell proliferation. Increased HIF1α/VEGF expression and tumor glycolysis supported HAIAT.

CONCLUSIONS

HAIAT achieved a promising step towards the locoregional targeting of tumor hypoxia. The favorable toxicity profile and enhanced anticancer effects of evofosfamide in combination with cTACE pave the way towards clinical trials in patients with liver cancer. Clin Cancer Res; 23(2); 536-48. ©2016 AACR.

Mechanisms of Drug Resistance Related to the Microenvironment of Solid Tumors and Possible Strategies to Inhibit Them

Drug resistance can occur at the individual cellular level or as a result of properties of the tumor microenvironment. The convoluted vasculature within tumors results in robustly proliferating well-nourished cells located proximal to functional blood vessels and regions of slowly proliferating (often hypoxic) cells located distal to functional blood vessels. Irregular blood flow and large distances between functional blood vessels in solid tumors lead to poor drug distribution within them such that cells distal from functional blood vessels are exposed to ineffective concentrations of drug, resulting in therapeutic resistance. Strategies to improve or complement the distribution of anticancer drugs within tumors hold promise for increasing antitumor effects without corresponding increases in normal tissue toxicity. In particular, use of hypoxia-targeted agents and modulation of autophagy have shown promising results in enhancing the distribution of drug activity within solid tumors and hence antitumor efficacy. In this review, we describe causes of resistance to chemotherapy that relate to the microenvironment of solid tumors and the potential to improve antitumor effects by countering such mechanisms of resistance.

Targeting the hypoxic fraction of tumours using hypoxia-activated prodrugs

The presence of a microenvironment within most tumours containing regions of low oxygen tension or hypoxia has profound biological and therapeutic implications. Tumour hypoxia is known to promote the development of an aggressive phenotype, resistance to both chemotherapy and radiotherapy and is strongly associated with poor clinical outcome. Paradoxically, it is recognised as a high-priority target and one of the therapeutic strategies designed to eradicate hypoxic cells in tumours is a group of compounds known collectively as hypoxia-activated prodrugs (HAPs) or bioreductive drugs. These drugs are inactive prodrugs that require enzymatic activation (typically by 1 or 2 electron oxidoreductases) to generate cytotoxic species with selectivity for hypoxic cells being determined by (1) the ability of oxygen to either reverse or inhibit the activation process and (2) the presence of elevated expression of oxidoreductases in tumours. The concepts underpinning HAP development were established over 40 years ago and have been refined over the years to produce a new generation of HAPs that are under preclinical and clinical development. The purpose of this article is to describe current progress in the development of HAPs focusing on the mechanisms of action, preclinical properties and clinical progress of leading examples.

Targeting the hypoxic fraction of tumours using hypoxia-activated prodrugs

The presence of a microenvironment within most tumours containing regions of low oxygen tension or hypoxia has profound biological and therapeutic implications. Tumour hypoxia is known to promote the development of an aggressive phenotype, resistance to both chemotherapy and radiotherapy and is strongly associated with poor clinical outcome. Paradoxically, it is recognised as a high-priority target and one of the therapeutic strategies designed to eradicate hypoxic cells in tumours is a group of compounds known collectively as hypoxia-activated prodrugs (HAPs) or bioreductive drugs. These drugs are inactive prodrugs that require enzymatic activation (typically by 1 or 2 electron oxidoreductases) to generate cytotoxic species with selectivity for hypoxic cells being determined by (1) the ability of oxygen to either reverse or inhibit the activation process and (2) the presence of elevated expression of oxidoreductases in tumours. The concepts underpinning HAP development were established over 40 years ago and have been refined over the years to produce a new generation of HAPs that are under preclinical and clinical development. The purpose of this article is to describe current progress in the development of HAPs focusing on the mechanisms of action, preclinical properties and clinical progress of leading examples.

Hypoxia-Targeted Drug Q6 Induces G2-M Arrest and Apoptosis via Poisoning Topoisomerase II under Hypoxia

In spite of the tremendous efforts dedicated to developing hypoxia-activated prodrugs, no agents yet have been approved for clinical therapy. In the present study, the hypoxic selective anti-cancer activity as well as the cellular target of a novel tirapazamine (TPZ) analogue, 7-methyl-3-(3-chlorophenyl)-quinoxaline-2-carbonitrile 1,4-dioxide (Q6) were investigated. Q6 implemented anti-cancer effects via poisoning topoisomerase II (topo II) under hypoxia. Modified trapped in agarose DNA immunostaining (TARDIS) assay showed more topo II-DNA cleavage complexes trapped by Q6 than TPZ at even lower concentration. In addition, by introducing ataxia-telangiectasia-mutated (ATM) kinase inhibitors caffeine and KU-60019, we displayed that Q6-triggered apoptosis was attributed, at least partially, to DNA double-strand breaks generated by the topo II-targeting effect. Collectively, Q6 stood out for its better hypoxia-selectivity and topo II-poisoning than the parental compound TPZ. All these data shed light on the research of Q6 as a promising hypoxia-activated prodrug candidate for human hepatocellular carcinoma therapy.

Hypoxia-Targeted Drug Q6 Induces G2-M Arrest and Apoptosis via Poisoning Topoisomerase II under Hypoxia

In spite of the tremendous efforts dedicated to developing hypoxia-activated prodrugs, no agents yet have been approved for clinical therapy. In the present study, the hypoxic selective anti-cancer activity as well as the cellular target of a novel tirapazamine (TPZ) analogue, 7-methyl-3-(3-chlorophenyl)-quinoxaline-2-carbonitrile 1,4-dioxide (Q6) were investigated. Q6 implemented anti-cancer effects via poisoning topoisomerase II (topo II) under hypoxia. Modified trapped in agarose DNA immunostaining (TARDIS) assay showed more topo II–DNA cleavage complexes trapped by Q6 than TPZ at even lower concentration. In addition, by introducing ataxia-telangiectasia-mutated (ATM) kinase inhibitors caffeine and KU-60019, we displayed that Q6-triggered apoptosis was attributed, at least partially, to DNA double-strand breaks generated by the topo II-targeting effect. Collectively, Q6 stood out for its better hypoxia-selectivity and topo II-poisoning than the parental compound TPZ. All these data shed light on the research of Q6 as a promising hypoxia-activated prodrug candidate for human hepatocellular carcinoma therapy.

F-18 fluoromisonidazole for imaging tumor hypoxia: imaging the microenvironment for personalized cancer therapy

Hypoxia in solid tumors is one of the seminal mechanisms for developing aggressive trait and treatment resistance in solid tumors. This evolutionarily conserved biological mechanism along with derepression of cellular functions in cancer, although resulting in many challenges, provide us with opportunities to use these adversities to our advantage. Our ability to use molecular imaging to characterize therapeutic targets such as hypoxia and apply this information for therapeutic interventions is growing rapidly. Evaluation of hypoxia and its biological ramifications to effectively plan appropriate therapy that can overcome the cure-limiting effects of hypoxia provides an objective means for treatment selection and planning. Fluoromisonidazole (FMISO) continues to be the lead radiopharmaceutical in PET imaging for the evaluation, prognostication, and quantification of tumor hypoxia, one of the key elements of the tumor microenvironment. FMISO is less confounded by blood flow, and although the images have less contrast than FDG-PET, its uptake after 2 hours is an accurate reflection of inadequate regional oxygen partial pressure at the time of radiopharmaceutical administration. By virtue of extensive clinical utilization, FMISO remains the lead candidate for imaging and quantifying hypoxia. The past decade has seen significant technological advances in investigating hypoxia imaging in radiation treatment planning and in providing us with the ability to individualize radiation delivery and target volume coverage. The presence of widespread hypoxia in the tumor can be effectively targeted with a systemic hypoxic cell cytotoxin or other agents that are more effective with diminished oxygen partial pressure, either alone or in combination. Molecular imaging in general and hypoxia imaging in particular will likely become an important in vivo imaging biomarker of the future, complementing the traditional direct tissue sampling methods by providing a snap shot of a primary tumor and metastatic disease and in following treatment response and will serve as adjuncts to personalized therapy.

Guttiferone K induces autophagy and sensitizes cancer cells to nutrient stress-induced cell death

BACKGROUND

Medicinal plants have long been an excellent source of pharmaceutical agents. Autophagy, a catabolic degradation process through lysosomes, plays an important role in tumorigenesis and cancer therapy.

PURPOSE

Through a screen designed to identify autophagic regulators from a library of natural compounds, we found that Guttiferone K (GUTK) can activate autophagy in several cancer cell lines. The objective of this study is to investigate the mechanism by which GUTK sensitizes cancer cells to cell death in nutrient starvation condition.

METHODS

Cell death analysis was performed by propidium iodide staining with flow cytometry or Annexin V-FITC/PI staining assay. DCFH-DA staining was used for intracellular ROS measurement. Protein levels were analyzed by western blot analysis. Cell viability was measured by MTT assay.

RESULTS

Exposure to GUTK was observed to markedly induce GFP-LC3 puncta formation and activate the accumulation of LC3-II and the degradation of p62 in HeLa cells, suggesting that GUTK is an autophagy inducer. Importantly, hydroxychloroquine, an autophagy inhibitor, was found to significantly prevent GUTK-induced cell death in nutrient starvation conditions, suggesting that the cell death observed is largely dependent on autophagy. We further provide evidence that GUTK inhibits Akt phosphorylation, thereby inhibiting the mTOR pathway in cancer cells during nutrient starvation. In addition, GUTK causes the accumulation of reactive oxygen species (ROS) and the phosphorylation of JNK in EBSS, which may mediate both autophagy and apoptosis.

CONCLUSION

These data indicate that GUTK sensitizes cancer cells to nutrient stress-induced cell death though Akt/mTOR dependent autophagy pathway.

Hypoxia-activated chemotherapeutic TH-302 enhances the effects of VEGF-A inhibition and radiation on sarcomas

Background:

Human sarcomas with a poor response to vascular endothelial growth factor-A (VEGF-A) inhibition and radiation therapy (RT) have upregulation of hypoxia-inducible factor 1α (HIF-1α) and HIF-1α target genes. This study examines the addition of the hypoxia-activated chemotherapy TH-302 to VEGF-A inhibition and RT (a.k.a. trimodality therapy).

Methods:

Trimodality therapy was examined in two xenograft models and in vitro in tumour endothelial cells and sarcoma cell lines.

Results:

In both mouse models, VEGF-A inhibition and radiation showed greater efficacy than either therapy alone in slowing sarcoma growth. When TH-302 was added, this trimodality therapy completely blocked tumour growth with tumours remaining dormant for over 3 months after cessation of therapy. Trimodality therapy caused 2.6- to 6.2-fold more endothelial cell-specific apoptosis than bimodality therapies, and microvessel density and HIF-1α activity were reduced to 11–13% and 13–20% of control, respectively. When trimodality therapy was examined in vitro, increases in DNA damage and apoptosis were much more pronounced in tumour endothelial cells compared with that in sarcoma cells, especially under hypoxia.

Conclusions:

The combination of TH-302, VEGF-A inhibition, and RT is highly effective in preclinical models of sarcoma and is associated with increased DNA damage and apoptosis in endothelial cells and decreased HIF-1α activity.

Chemotherapy Rescues Hypoxic Tumor Cells and Induces Their Reoxygenation and Repopulation-An Effect That Is Inhibited by the Hypoxia-Activated Prodrug TH-302

PURPOSE

Chemotherapy targets rapidly proliferating tumor cells, but spares slowly proliferating hypoxic cells. We hypothesized that nutrition of hypoxic cells would improve in intervals between chemotherapy, and that hypoxic cells destined to die without treatment would survive and proliferate.

EXPERIMENTAL DESIGN

We therefore evaluated repopulation and reoxygenation following chemotherapy, and the effects of the hypoxia-activated prodrug TH-302 on these processes. Tumor-bearing mice were treated with doxorubicin or docetaxel ± TH-302. Pimonidazole (given concurrent with chemotherapy) and EF5 (given 24 to 120 hours later) identified hypoxic cells. Proliferation (Ki67) and oxygen status (EF5 uptake) of formerly hypoxic (pimo positive) cells were quantified by immunohistochemistry.

RESULTS

Chronically hypoxic cells had limited proliferation in control tumors. After chemotherapy, we observed reoxygenation and increased proliferation of previously hypoxic cells; these processes were inhibited by TH-302.

CONCLUSIONS

Chemotherapy leads to paradoxical sparing of hypoxic cells destined to die in solid tumors in absence of treatment, and their reoxygenation and proliferation: TH-302 inhibits these processes.

Drug radiotherapy combinations: review of previous failures and reasons for future optimism

Combining chemotherapy with radiotherapy has resulted in significant clinical improvements in many different tumour types. However, the non-specific mechanisms by which these drugs exert their effects mean that this is often at the expense of increased side effects. Previous attempts at using targeted drugs to induce more tumour specific radiosensitisation have been generally disappointing. Although cetuximab, an EGFR monoclonal antibody, resulted in improved overall survival in HNSCC when combined with radiotherapy, it has failed to show benefit when added to chemo-radiotherapy. In addition, our inability to successfully use drug treatments to reverse tumour hypoxia is underlined by the fact that no such treatment is currently in widespread clinical use. The reasons for these failures include the lack of robust biomarkers, and the previous use of drugs with unacceptable side-effect profiles. Despite these disappointments, there is reason for optimism. Our improved understanding of key signal transduction pathways and of tumour specific DNA repair deficiencies has produced new opportunities to specifically radiosensitise tumours. Novel strategies to reduce tumour hypoxia include the use of drugs that cause vascular normalisation and drugs that reduce tumour oxygen consumption. These new strategies, combined with better compounds at our disposal, and an ability to learn from our previous mistakes, mean that there is great promise for future drug-radiotherapy combinations to result in significant clinical benefits.

Hypoxia-activated pro-drug TH-302 exhibits potent tumor suppressive activity and cooperates with chemotherapy against osteosarcoma

Tumor hypoxia is a major cause of treatment failure for a variety of malignancies. However, tumor hypoxia also offers treatment opportunities, exemplified by the development compounds that target hypoxic regions within tumors. TH-302 is a pro-drug created by the conjugation of 2-nitroimidazole to bromo-isophosphoramide (Br-IPM). When TH-302 is delivered to regions of hypoxia, Br-IPM, the DNA cross linking toxin, is released. In this study we assessed the cytotoxic activity of TH-302 against osteosarcoma cells in vitro and evaluated its anticancer efficacy as a single agent, and in combination with doxorubicin, in an orthotopic mouse model of human osteosarcoma (OS). In vitro, TH-302 was potently cytotoxic to osteosarcoma cells selectively under hypoxic conditions, whereas primary normal human osteoblasts were protected. Animals transplanted with OS cells directly into their tibiae and left untreated developed mixed osteolytic/osteosclerotic bone lesions and subsequently developed lung metastases. TH-302 reduced tumor burden in bone and cooperated with doxorubicin to protect bone from osteosarcoma induced bone destruction, while it also reduced lung metastases. TH-302 may therefore be an attractive therapeutic agent with strong activity as a single agent and in combination with chemotherapy against OS.

In vivo quantification of hypoxic and metabolic status of NSCLC tumors using [18F]HX4 and [18F]FDG-PET/CT imaging

PURPOSE

Increased tumor metabolism and hypoxia are related to poor prognosis in solid tumors, including non-small cell lung cancer (NSCLC). PET imaging is a noninvasive technique that is frequently used to visualize and quantify tumor metabolism and hypoxia. The aim of this study was to perform an extensive comparison of tumor metabolism using 2[(18)F]fluoro-2-deoxy-d-glucose (FDG)-PET and hypoxia using HX4-PET imaging.

EXPERIMENTAL DESIGN

FDG- and HX4-PET/CT images of 25 patients with NSCLC were coregistered. At a global tumor level, HX4 and FDG parameters were extracted from the gross tumor volume (GTV). The HX4 high-fraction (HX4-HF) and HX4 high-volume (HX4-HV) were defined using a tumor-to-blood ratio > 1.4. For FDG high-fraction (FDG-HF) and FDG high-volume (FDG-HV), a standardized uptake value (SUV) > 50% of SUVmax was used. We evaluated the spatial correlation between HX4 and FDG uptake within the tumor, to quantify the (mis)match between volumes with a high FDG and high HX4 uptake.

RESULTS

At a tumor level, significant correlations were observed between FDG and HX4 parameters. For the primary GTV, the HX4-HF was three times smaller compared with the FDG-HF. In 53% of the primary lesions, less than 1 cm(3) of the HX4-HV was outside the FDG-HV; for 37%, this volume was 1.9 to 12 cm(3). Remarkably, a distinct uptake pattern was observed in 11%, with large hypoxic volumes localized outside the FDG-HV.

CONCLUSION

Hypoxic tumor volumes are smaller than metabolic active volumes. Approximately half of the lesions showed a good spatial correlation between the PET tracers. In the other cases, a (partial) mismatch was observed. The addition of HX4-PET imaging has the potential to individualize patient treatment.