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

Evofosfamide and Gemcitabine Act Synergistically in Pancreatic Cancer Xenografts by Dual Action on Tumor Vasculature and Inhibition of Homologous Recombination DNA Repair

Aims: Pancreatic ductal adenocarcinomas (PDACs) form hypovascular and hypoxic tumors, which are difficult to treat with current chemotherapy regimens. Gemcitabine (GEM) is often used as a first-line treatment for PDACs but has issues with chemoresistance and penetration in the interior of the tumor. Evofosfamide, a hypoxia-activated prodrug, has been shown to be effective in combination with GEM, although the mechanism of each drug on the other has not been established. We used mouse xenografts from two cell lines (MIA Paca-2 and SU.86.86) with different tumor microenvironmental characteristics to probe the action of each drug on the other. Results: GEM treatment enhanced survival times in mice with SU.86.86 leg xenografts (hazard ratio [HR] = 0.35, p = 0.03) but had no effect on MIA Paca-2 mice (HR = 0.91, 95% confidence interval = 0.37-2.25, p = 0.84). Conversely, evofosfamide did not improve survival times in SU.86.86 mice to a statistically significant degree (HR = 0.57, p = 0.22). Electron paramagnetic resonance imaging showed that oxygenation worsened in MIA Paca-2 tumors when treated with GEM, providing a direct mechanism for the activation of the hypoxia-activated prodrug evofosfamide by GEM. Sublethal amounts of either treatment enhanced the toxicity of other treatment in vitro in SU.86.86 but not in MIA Paca-2. By the biomarker γH2AX, combination treatment increased the number of double-stranded DNA lesions in vitro for SU.86.86 but not MIA Paca-2. Innovation and Conclusion: The synergy between GEM and evofosfamide appears to stem from the dual action of GEMs effect on tumor vasculature and inhibition by GEM of the homologous recombination DNA repair process. Antioxid. Redox Signal. 39, 432-444.

Hypoxia, a Targetable Culprit to Counter Pancreatic Cancer Resistance to Therapy

Pancreatic ductal adenocarcinoma (PDAC) is the most common type of pancreatic cancer, and it is a disease of dismal prognosis. While immunotherapy has revolutionized the treatment of various solid tumors, it has achieved little success in PDAC. Hypoxia within the stroma-rich tumor microenvironment is associated with resistance to therapies and promotes angiogenesis, giving rise to a chaotic and leaky vasculature that is inefficient at shuttling oxygen and nutrients. Hypoxia and its downstream effectors have been implicated in immune resistance and could be contributing to the lack of response to immunotherapy experienced by patients with PDAC. Paradoxically, increasing evidence has shown hypoxia to augment genomic instability and mutagenesis in cancer, suggesting that hypoxic tumor cells could have increased production of neoantigens that can potentially enable their clearance by cytotoxic immune cells. Strategies aimed at relieving this condition have been on the rise, and one such approach opts for normalizing the tumor vasculature to reverse hypoxia and its downstream support of tumor pathogenesis. An important consideration for the successful implementation of such strategies in the clinic is that not all PDACs are equally hypoxic, therefore hypoxia-detection approaches should be integrated to enable optimal patient selection for achieving improved patient outcomes.

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.

The Role of Imaging Biomarkers to Guide Pharmacological Interventions Targeting Tumor Hypoxia

Hypoxia is a common feature of solid tumors that contributes to angiogenesis, invasiveness, metastasis, altered metabolism and genomic instability. As hypoxia is a major actor in tumor progression and resistance to radiotherapy, chemotherapy and immunotherapy, multiple approaches have emerged to target tumor hypoxia. It includes among others pharmacological interventions designed to alleviate tumor hypoxia at the time of radiation therapy, prodrugs that are selectively activated in hypoxic cells or inhibitors of molecular targets involved in hypoxic cell survival (i.e., hypoxia inducible factors HIFs, PI3K/AKT/mTOR pathway, unfolded protein response). While numerous strategies were successful in pre-clinical models, their translation in the clinical practice has been disappointing so far. This therapeutic failure often results from the absence of appropriate stratification of patients that could benefit from targeted interventions. Companion diagnostics may help at different levels of the research and development, and in matching a patient to a specific intervention targeting hypoxia. In this review, we discuss the relative merits of the existing hypoxia biomarkers, their current status and the challenges for their future validation as companion diagnostics adapted to the nature of the intervention.

Improving the synergistic combination of programmed death‐1/programmed death ligand‐1 blockade and radiotherapy by targeting the hypoxic tumour microenvironment

Immune checkpoint inhibition with PD‐1/PD‐L1 blockade is a promising area in the field of anti‐cancer therapy. Although clinical data have revealed success of PD‐1/PD‐L1 blockade as monotherapy or in combination with CTLA‐4 or chemotherapy, the combination with radiotherapy could further boost anti‐tumour immunity and enhance clinical outcomes due to the immunostimulatory effects of radiation. However, the synergistic combination of PD‐1/PD‐L1 blockade and radiotherapy can be challenged by the complex nature of the tumour microenvironment (TME), including the presence of tumour hypoxia. Hypoxia is a major barrier to the effectiveness of both radiotherapy and PD‐1/PD‐L1 blockade immunotherapy. Thus, targeting the hypoxic TME is an attractive strategy to enhance the efficacy of the combination. Addition of compounds that directly or indirectly reduce hypoxia, to the combination of PD‐1/PD‐L1 inhibitors and radiotherapy may optimize the success of the combination and improve therapeutic outcomes. In this review, we will discuss the synergistic combination of PD‐1/PD‐L1 blockade and radiotherapy and highlight the role of hypoxic TME in impeding the success of both therapies. In addition, we will address the potential approaches for targeting tumour hypoxia and how exploiting these strategies could benefit the combination of PD‐1/PD‐L1 blockade and radiotherapy.

On the Evaluation of a Novel Hypoxic 3D Pancreatic Cancer Model as a Tool for Radiotherapy Treatment Screening

Tissue engineering is evolving to mimic intricate ecosystems of tumour microenvironments (TME) to more readily map realistic in vivo niches of cancerous tissues. Such advanced cancer tissue models enable more accurate preclinical assessment of treatment strategies. Pancreatic cancer is a dangerous disease with high treatment resistance that is directly associated with a highly complex TME. More specifically, the pancreatic cancer TME includes (i) complex structure and complex extracellular matrix (ECM) protein composition; (ii) diverse cell populations (e.g., stellate cells), cancer associated fibroblasts, endothelial cells, which interact with the cancer cells and promote resistance to treatment and metastasis; (iii) accumulation of high amounts of (ECM), which leads to the creation of a fibrotic/desmoplastic reaction around the tumour; and (iv) heterogeneous environmental gradients such as hypoxia, which result from vessel collapse and stiffness increase in the fibrotic/desmoplastic area of the TME. These unique hallmarks are not effectively recapitulated in traditional preclinical research despite radiotherapeutic resistance being largely connected to them. Herein, we investigate, for the first time, the impact of in vitro hypoxia (5% O2) on the radiotherapy treatment response of pancreatic cancer cells (PANC-1) in a novel polymer (polyurethane) based highly macroporous scaffold that was surface modified with proteins (fibronectin) for ECM mimicry. More specifically, PANC-1 cells were seeded in fibronectin coated macroporous scaffolds and were cultured for four weeks in in vitro normoxia (21% O2), followed by a two day exposure to either in vitro hypoxia (5% O2) or maintenance in in vitro normoxia. Thereafter, in situ post-radiation monitoring (one day, three days, seven days post-irradiation) of the 3D cell cultures took place via quantification of (i) live/dead and apoptotic profiles and (ii) ECM (collagen-I) and HIF-1a secretion by the cancer cells. Our results showed increased post-radiation viability, reduced apoptosis, and increased collagen-I and HIF-1a secretion in in vitro hypoxia compared to normoxic cultures, revealing hypoxia-induced radioprotection. Overall, this study employed a low cost, animal free model enabling (i) the possibility of long-term in vitro hypoxic 3D cell culture for pancreatic cancer, and (ii) in vitro hypoxia associated PDAC radio-protection development. Our novel platform for radiation treatment screening can be used for long-term in vitro post-treatment observations as well as for fractionated radiotherapy treatment.

Hypoxia-Activated Prodrug Evofosfamide Treatment in Pancreatic Ductal Adenocarcinoma Xenografts Alters the Tumor Redox Status to Potentiate Radiotherapy

Aims: In hypoxic tumor microenvironments, the strongly reducing redox environment reduces evofosfamide (TH-302) to release a cytotoxic bromo-isophosphoramide (Br-IPM) moiety. This drug therefore preferentially attacks hypoxic regions in tumors where other standard anticancer treatments such as chemotherapy and radiation therapy are often ineffective. Various combination therapies with evofosfamide have been proposed and tested in preclinical and clinical settings. However, the treatment effect of evofosfamide monotherapy on tumor hypoxia has not been fully understood, partly due to the lack of quantitative methods to assess tumor pO₂in vivo. Here, we use quantitative pO₂ imaging by electron paramagnetic resonance (EPR) to evaluate the change in tumor hypoxia in response to evofosfamide treatment using two pancreatic ductal adenocarcinoma xenograft models: MIA Paca-2 tumors responding to evofosfamide and Su.86.86 tumors that do not respond. Results: EPR imaging showed that oxygenation improved globally after evofosfamide treatment in hypoxic MIA Paca-2 tumors, in agreement with the ex vivo results obtained from hypoxia staining by pimonidazole and in apparent contrast to the decrease in K^trans observed in dynamic contrast-enhanced magnetic resonance imaging (DCE MRI). Innovations: The observation that evofosfamide not only kills the hypoxic region of the tumor but also improves oxygenation in the residual tumor regions provides a rationale for combination therapies using radiation and antiproliferatives post evofosfamide for improved outcomes. Conclusion: This study suggests that reoxygenation after evofosfamide treatment is due to decreased oxygen demand rather than improved perfusion. Following the change in pO₂ after treatment may therefore yield a way of monitoring treatment response. Antioxid. Redox Signal. 35, 904-915.

Simulated dose painting of hypoxic sub-volumes in pancreatic cancer stereotactic body radiotherapy

Dose painting of hypoxic tumour sub-volumes using positron-emission tomography (PET) has been shown to improve tumour controlin silicoin several sites, predominantly head and neck and lung cancers. Pancreatic cancer presents a more stringent challenge, given its proximity to critical gastro-intestinal organs-at-risk (OARs), anatomic motion, and impediments to reliable PET hypoxia quantification. A radiobiological model was developed to estimate clonogen survival fraction (SF), using¹⁸F-fluoroazomycin arabinoside PET (FAZA PET) images from ten patients with unresectable pancreatic ductal adenocarcinoma to quantify oxygen enhancement effects. For each patient, four simulated five-fraction stereotactic body radiotherapy (SBRT) plans were generated: (1) a standard SBRT plan aiming to cover the planning target volume with 40 Gy, (2) dose painting plans delivering escalated doses to a maximum of three FAZA-avid hypoxic sub-volumes, (3) dose painting plans with simulated spacer separating the duodenum and pancreatic head, and (4), plans with integrated boosts to geometric contractions of the gross tumour volume (GTV). All plans saturated at least one OAR dose limit. SF was calculated for each plan and sensitivity of SF to simulated hypoxia quantification errors was evaluated. Dose painting resulted in a 55% reduction in SF as compared to standard SBRT; 78% with spacer. Integrated boosts to hypoxia-blind geometric contractions resulted in a 41% reduction in SF. The reduction in SF for dose-painting plans persisted for all hypoxia quantification parameters studied, including registration and rigid motion errors that resulted in shifts and rotations of the GTV and hypoxic sub-volumes by as much as 1 cm and 10 degrees. Although proximity to OARs ultimately limited dose escalation, with estimated SFs (∼10^-5) well above levels required to completely ablate a ∼10 cm³tumour, dose painting robustly reduced clonogen survival when accounting for expected treatment and imaging uncertainties and thus, may improve local response and associated morbidity.

Targeting Hypoxia: Hypoxia-Activated Prodrugs in Cancer Therapy

Hypoxia is an important characteristic of most solid malignancies, and is closely related to tumor prognosis and therapeutic resistance. Hypoxia is one of the most important factors associated with resistance to conventional radiotherapy and chemotherapy. Therapies targeting tumor hypoxia have attracted considerable attention. Hypoxia-activated prodrugs (HAPs) are bioreductive drugs that are selectively activated under hypoxic conditions and that can accurately target the hypoxic regions of solid tumors. Both single-agent and combined use with other drugs have shown promising antitumor effects. In this review, we discuss the mechanism of action and the current preclinical and clinical progress of several of the most widely used HAPs, summarize their existing problems and shortcomings, and discuss future research prospects.

Sunitinib and Evofosfamide (TH-302) in Systemic Treatment-Naïve Patients with Grade 1/2 Metastatic Pancreatic Neuroendocrine Tumors: The GETNE-1408 Trial

BACKGROUND

Sunitinib (SUN)-induced hypoxia within the tumor could promote the activation of the prodrug evofosfamide (EVO), locally releasing the cytotoxic DNA alkylator bromo-isophosphoramide mustard. SUNEVO, a phase II, open-label, single-arm trial, investigated the potential synergy of SUN plus EVO in advanced progressive pancreatic neuroendocrine tumors (panNETs).

METHODS

Systemic treatment-naïve patients with advanced or metastatic, unresectable, grade 1/2 panNETs with a Ki67 ≤20%, received EVO 340 mg/m² on days 8, 15, and 22 every 4 weeks and sunitinib 37.5 mg/day continuously. The primary endpoint was objective response rate, measured every 8 weeks by RECIST version 1.1.

RESULTS

From 2015 to 2018, 17 patients were enrolled. The median age was 62.4 years, 47% had a Ki67 >10%, and 70.6% had liver metastasis. Patients received a median of five and four cycles of SUN and EVO, respectively. After a median follow-up of 15.7 months, 17.6% of patients achieved a complete (n = 1) or partial response (n = 2), and 11 patients had stable disease (64.7%). The median progression-free survival was 10.4 months (95% confidence interval, 2.6-18.0). Treatment-related adverse events (grade ≥3) were observed in 64.7% of the patients, the most frequent being neutropenia (35.3%), fatigue (17.6%), and thrombopenia (11.8%). Treatment discontinuation due to toxicity was reported in 88.2% of the patients. No correlation was found between treatment response and DAXX, ATRX, MEN1, SETD2, and PTEN gene mutations.

CONCLUSION

SUN plus EVO had a negative toxicity profile that should be taken into account for further clinical research in advanced panNETs. The combination showed moderate activity in terms of treatment response that did not correlate with somatic mutations. (Clinical trial identification number: NCT02402062) IMPLICATIONS FOR PRACTICE: Addition of hypoxia-activated prodrugs has been proposed as a potential mechanism to overcome tumor resistance to antiangiogenic agents. Sunitinib and evofosfamide, which were widely proposed as a potential synergistic option, showed modest efficacy in pancreatic neuroendocrine tumors (panNETs), reaching a median objective response rate of 17.6% and median progression-free survival of 10.4 months. Treatment response does not correlate with the biomarkers analyzed. The high systemic toxicity, with 88.2% of patients discontinuing the treatment, makes this therapeutic approach unfeasible and encourages future research to overcome panNETs' resistance to antiangiogenic agents with other therapies with a safer profile.

Interfering with Tumor Hypoxia for Radiotherapy Optimization

Hypoxia in solid tumors is an important predictor of treatment resistance and poor clinical outcome. The significance of hypoxia in the development of resistance to radiotherapy has been recognized for decades and the search for hypoxia-targeting, radiosensitizing agents continues. This review summarizes the main hypoxia-related processes relevant for radiotherapy on the subcellular, cellular and tissue level and discusses the significance of hypoxia in radiation oncology, especially with regard to the current shift towards hypofractionated treatment regimens. Furthermore, we discuss the strategies to interfere with hypoxia for radiotherapy optimization, and we highlight novel insights into the molecular pathways involved in hypoxia that might be utilized to increase the efficacy of radiotherapy.

Overcoming the Tumor Microenvironmental Barriers of Pancreatic Ductal Adenocarcinomas for Achieving Better Treatment Outcomes

Pancreatic ductal adenocarcinoma (PDAC) is a highly aggressive disease with the lowest survival rate among all solid tumors. The lethality of PDAC arises from late detection and propensity of the tumor to metastasize and develop resistance against chemo and radiation therapy. A highly complex tumor microenvironment composed of dense stroma, immune cells, fibroblast, and disorganized blood vessels, is the main obstacle to current PDAC therapy. Despite the tremendous success of immune checkpoint inhibitors (ICIs) in cancers, PDAC remains one of the poorest responders of ICIs therapy. The immunologically "cold" phenotype of PDAC is attributed to the low mutational burden, high infiltration of myeloid-derived suppressor cells and T-regs, contributing to a significant immunotherapy resistance mechanism. Thus, the development of innovative strategies for turning immunologically "cold" tumor into "hot" ones is an unmet need to improve the outcome of PDAC ICIs therapies. Other smart strategies, such as nanomedicines, sonic Hedgehog inhibitor, or smoothened inhibitor, are discussed to enhance chemotherapeutic agents' efficiency by disrupting the PDAC stroma. This review highlights the current challenges and various preclinical and clinical strategies to overcome current PDAC therapy difficulties, thus significantly advancing PDAC research knowledge.

An Eight-Gene Hypoxia Signature Predicts Survival in Pancreatic Cancer and Is Associated With an Immunosuppressed Tumor Microenvironment

Intratumoral hypoxia is a widely established element of the pancreatic tumor microenvironment (TME) promoting immune escape, tumor invasion, and progression, while contributing to treatment resistance and poor survival. Despite this critical role, hypoxia is underrepresented in molecular signatures of pancreatic ductal adenocarcinoma (PDA) and concurrent investigations into the hypoxia-immune status are lacking. In this work a literature-based approach was applied to derive an eight-gene hypoxia signature that was validated in fourteen cancer cell lines and in a cohort of PDA. The eight-gene hypoxia signature was significantly associated with overall survival in two distinct PDA datasets and showed independent prognostic value in multivariate analysis. Comparative analysis of tumors according to their hypoxia score (high versus low) determined that tumors with high hypoxia were significantly less enriched in cytotoxic T-cells, and cytolytic activity. In addition, they had lower expression of cytokines and tumor inflammatory markers, pointing to the signature’s ability to discern an immune “cold”, hypoxic TME. Combining the signature with an immune metric highlighted a worse survival probability in patients with high hypoxia and low immune reactivity, indicating that this approach could further refine survival estimates. Hypoxia as determined by our signature, was significantly associated with certain immune checkpoint inhibitors (ICI) biomarkers, suggesting that the signature reflects an aspect of the TME that is worth pursuing in future clinical trials. This is the first work of its kind in PDA, and our findings on the hypoxia-immune tumor contexture are not only relevant for ICI but could also guide combinatorial hypoxia-mediated therapeutic strategies in this cancer type.

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.

Molecular Immunotherapy: Promising Approach to Treat Metastatic Colorectal Cancer by Targeting Resistant Cancer Cells or Cancer Stem Cells

The immune system is able to recognize and eliminate tumor cells. Some tumors, including colorectal cancer (CRC), induce immune tolerance via different mechanisms of “immunoediting” and “immune evasion” and can thus escape immune surveillance. The impact of immunotherapy on cancer has been investigated for many years, but so far, the application was limited to few cancer types. Immuno-oncological therapeutic strategies against metastatic colorectal cancer (mCRC), the adaptive immune system activating approaches, offer a high potential for adaptation to the great heterogeneity of CRC. Moreover, novel treatment approaches are currently being tested that might specifically target the disease initiating and maintaining population of colorectal cancer stem cells (CSCs). In this review, we aim to summarize the current state of immune-oncology and tumor immunotherapy of patients with mCRC and discuss different therapeutic modalities that focus on the activation of tumor-specific T-cells and their perspectives such as tumor vaccination, checkpoint inhibition, and adoptive T-cell transfer or on the eradication of colorectal CSCs.

Relevance of the combination of external beam radiotherapy with the hypoxia-activated prodrug ICF05016 in an experimental model of extraskeletal myxoid chondrosarcoma

Currently, there is no gold standard treatment for Extraskeletal Myxoid Chondrosarcomas (EMC) making wide margin surgical resection the most effective alternative treatment. Nevertheless, in previous preclinical studies our lab demonstrated the potential of the hypoxia-activated prodrug (HAP) ICF05016 on EMC murine model inoculated with the H-EMC-SS human cell line. The aim of this study was to assess, in vivo, the relevance of the combination of this HAP with External Beam Radiotherapy (EBR). Firstly EMC-bearing mice were treated with 6 Gy or 12 Gy of EBR (single 6 MV photon). Then for combination of HAP and EBR, animals received 6 doses of ICF05016 (46.8 μmol/kg, intravenously) at 4-day intervals, with 6 Gy EBR performed 24 h after the 3rd dose of HAP. Animals were monitored throughout the study for clinical observations (tumour growth, side effects) and survival studies were performed. From tumour samples, PCNA, Ki-67 and p21 expressions were used as markers of proliferation and cell cycle arrest. Statistical significances were determined using Kruskall-Wallis and log rank tests. The radiosensitivity of the EMC model was demonstrated at 12 Gy with significant inhibition of tumour growth. Then, the HAP strategy potentiated EBR efficacy at a lower dose (6 Gy) by improving survival without generating side effects. Thus, results of this study showed the potential interest of ICF05016 for the combination with EBR in the management of EMC.

Combining hypoxia-activated prodrugs and radiotherapy in silico: Impact of treatment scheduling and the intra-tumoural oxygen landscape

Hypoxia-activated prodrugs (HAPs) present a conceptually elegant approach to not only overcome, but better yet, exploit intra-tumoural hypoxia. Despite being successful in vitro and in vivo, HAPs are yet to achieve successful results in clinical settings. It has been hypothesised that this lack of clinical success can, in part, be explained by the insufficiently stringent clinical screening selection of determining which tumours are suitable for HAP treatments. Taking a mathematical modelling approach, we investigate how tumour properties and HAP-radiation scheduling influence treatment outcomes in simulated tumours. The following key results are demonstrated in silico: (i) HAP and ionising radiation (IR) monotherapies may attack tumours in dissimilar, and complementary, ways. (ii) HAP-IR scheduling may impact treatment efficacy. (iii) HAPs may function as IR treatment intensifiers. (iv) The spatio-temporal intra-tumoural oxygen landscape may impact HAP efficacy. Our in silico framework is based on an on-lattice, hybrid, multiscale cellular automaton spanning three spatial dimensions. The mathematical model for tumour spheroid growth is parameterised by multicellular tumour spheroid (MCTS) data.

In silico analysis of hypoxia activated prodrugs in combination with anti angiogenic therapy through nanocell delivery

Tumour hypoxia is a well-studied phenomenon with implications in cancer progression, treatment resistance, and patient survival. While a clear adverse prognosticator, hypoxia is also a theoretically ideal target for guided drug delivery. This idea has lead to the development of hypoxia-activated prodrugs (HAPs): a class of chemotherapeutics which remain inactive in the body until metabolized within hypoxic regions. In theory, these drugs have the potential for increased tumour selectivity and have therefore been the focus of numerous preclinical studies. Unfortunately, HAPs have had mixed results in clinical trials, necessitating further study in order to harness their therapeutic potential. One possible avenue for the improvement of HAPs is through the selective application of anti angiogenic agents (AAs) to improve drug delivery. Such techniques have been used in combination with other conventional chemotherapeutics to great effect in many studies. A further benefit is theoretically achieved through nanocell administration of the combination, though this idea has not been the subject of any experimental or mathematical studies to date. In the following, a mathematical model is outlined and used to compare the predicted efficacies of separate vs. nanocell administration for AAs and HAPs in tumours. The model is experimentally motivated, both in mathematical form and parameter values. Preliminary results of the model are highlighted throughout which qualitatively agree with existing experimental evidence. The novel prediction of our model is an improvement in the efficacy of AA/HAP combination therapies when administered through nanocells as opposed to separately. While this study specifically models treatment on glioblastoma, similar analyses could be performed for other vascularized tumours, making the results potentially applicable to a range of tumour types.

Tumour hypoxia is a well-documented phenomenon with adverse effects for the progression of the cancer. Accordingly, various therapeutic strategies have emerged in recent years to combat its effects. Herein, we present an experimentally-motivated mathematical model used to assess the feasibility of the therapeutic combination of anti angiogenic agents with hypoxia-activated prodrugs. Analysis of the combination therapy shows that delivery through drug nanocells provides the optimal anticancer effect: a novel result which should inspire further examination.

Quantifying Reoxygenation in Pancreatic Cancer During Stereotactic Body Radiotherapy

Hypoxia, the state of low oxygenation that often arises in solid tumours due to their high metabolism and irregular vasculature, is a major contributor to the resistance of tumours to radiation therapy (RT) and other treatments. Conventional RT extends treatment over several weeks or more, and nominally allows time for oxygen levels to increase ("reoxygenation") as cancer cells are killed by RT, mitigating the impact of hypoxia. Recent advances in RT have led to an increase in the use stereotactic body radiotherapy (SBRT), which delivers high doses in five or fewer fractions. For cancers such as pancreatic adenocarcinoma for which hypoxia varies significantly between patients, SBRT might not be optimal, depending on the extent to which reoxygenation occurs during its short duration. We used fluoro-5-deoxy-α-D-arabinofuranosyl)-2-nitroimidazole positron-emission tomography (FAZA-PET) imaging to quantify hypoxia before and after 5-fraction SBRT delivered to patient-derived pancreatic cancer xenografts orthotopically implanted in mice. An imaging technique using only the pre-treatment FAZA-PET scan and repeat dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) scans throughout treatment was able to predict the change in hypoxia. Our results support the further testing of this technique for imaging of reoxygenation in the clinic.

Clinical Limitations of Photon, Proton and Carbon Ion Therapy for Pancreatic Cancer

Introduction: Despite improvements in radiation therapy, chemotherapy and surgical procedures over the last 30 years, pancreatic cancer 5-year survival rate remains at 9%. Reduced stroma permeability and heterogeneous blood supply to the tumour prevent chemoradiation from making a meaningful impact on overall survival. Hypoxia-activated prodrugs are the latest strategy to reintroduce oxygenation to radioresistant cells harbouring in pancreatic cancer. This paper reviews the current status of photon and particle radiation therapy for pancreatic cancer in combination with systemic therapies and hypoxia activators. Methods: The current effectiveness of management of pancreatic cancer was systematically evaluated from MEDLINE^® database search in April 2019. Results: Limited published data suggest pancreatic cancer patients undergoing carbon ion therapy and proton therapy achieve a comparable median survival time (25.1 months and 25.6 months, respectively) and 1-year overall survival rate (84% and 77.8%). Inconsistencies in methodology, recording parameters and protocols have prevented the safety and technical aspects of particle therapy to be fully defined yet. Conclusion: There is an increasing requirement to tackle unmet clinical demands of pancreatic cancer, particularly the lack of synergistic therapies in the advancing space of radiation oncology.

Hierarchical assembly of hyaluronan coated albumin nanoparticles for pancreatic cancer chemoimmunotherapy

Pancreatic cancer is a highly malignant carcinoma with limited effective treatment options, resulting in a poor patient survival rate of less than 5%. In this study, cationic albumin nanoparticles were assembled with negatively charged hyaluronic acid (HA) to achieve a hierarchical nanostructure and efficient delivery of small molecule drugs to the tumor site in the pancreas. A combination of chemotherapy with indoleamine-2,3-dioxygenase (IDO) inhibition was explored to enhance the chemotherapeutic efficacy in vivo. Hydrophobic celastrol (CLT) and hydrophilic 1-methyltryptophan (MT) were concurrently loaded in HA coated cationic albumin nanoparticles (HNPs) with an average size of ∼300 nm. The size of HNPs was reduced in the presence of hyaluronidase to facilitate penetration into deep tumor tissues. Also, the biodistribution study in the C57BL/6 mice xenograft model showed enhanced tumor accumulation and prolonged circulation of HNPs. Compared with CLT solution, the combination of CLT with MT showed significantly enhanced tumor inhibition in both xenograft and orthotopic pancreatic cancer mice models via downregulating the immunosuppressive tumor microenvironment. Taken together, the combination of CLT with MT administered via HNPs represents a highly promising strategy for targeted pancreatic cancer therapy.

Hypoxia as a barrier to immunotherapy in pancreatic adenocarcinoma

Pancreatic ductal adenocarcinoma (PDA) is a lethal disease with limited response to cytotoxic chemoradiotherapy, as well as newer immunotherapies. The PDA tumor microenvironment contains infiltrating immune cells including cytotoxic T cells; however, there is an overall immunosuppressive milieu. Hypoxia is a known element of the solid tumor microenvironment and may promote tumor survival. Through various mechanisms including, but not limited to, those mediated by HIF-1α, hypoxia also leads to increased tumor proliferation and metabolic changes. Furthermore, epithelial to mesenchymal transition is promoted through several pathways, including NOTCH and c-MET, regulated by hypoxia. Hypoxia-promoted changes also contribute to the immunosuppressive phenotype seen in many different cell types within the microenvironment and thereby may inhibit an effective immune system response to PDA. Pancreatic stellate cells (PSCs) and myofibroblasts appear to contribute to the recruitment of myeloid derived suppressor cells (MDSCs) and B cells in PDA via cytokines increased due to hypoxia. PSCs also increase collagen secretion in response to HIF-1α, which promotes a fibrotic stroma that alters T cell homing and migration. In hypoxic environments, B cells contribute to cytotoxic T cell exhaustion and produce chemokines to attract more immunosuppressive regulatory T cells. MDSCs inhibit T cell metabolism by hoarding key amino acids, modulate T cell homing by cleaving L-selectin, and prevent T cell activation by increasing PD-L1 expression. Immunosuppressive M2 phenotype macrophages promote T cell anergy via increased nitric oxide (NO) and decreased arginine in hypoxia. Increased numbers of regulatory T cells are seen in hypoxia which prevent effector T cell activation through cytokine production and increased CTLA-4. Effective immunotherapy for pancreatic adenocarcinoma and other solid tumors will need to help counteract the immunosuppressive nature of hypoxia-induced changes in the tumor microenvironment. Promising studies will look at combination therapies involving checkpoint inhibitors, chemokine inhibitors, and possible targeting of hypoxia. While no model is perfect, assuring that models incorporate the effects of hypoxia on cancer cells, stromal cells, and effector immune cells will be crucial in developing successful therapies.

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.

Fucoidan-Manganese Dioxide Nanoparticles Potentiate Radiation Therapy by Co-Targeting Tumor Hypoxia and Angiogenesis

Tumor hypoxia is a major mechanism of resistance to radiation therapy (RT), which is associated with poor prognosis in affected cancer patients. Various approaches to treat hypoxic and radioresistant cancers, including pancreatic cancer, have shown limited success. Fucoidan, a polysaccharide from brown seaweed, has antitumor and antiangiogenesis activities. Here, we discuss the development of fucoidan-coated manganese dioxide nanoparticles (Fuco-MnO₂-NPs) and testing of the therapeutic potential with RT using pancreatic cancer models. In vitro data showed that Fuco-MnO₂-NPs generated oxygen efficiently in the presence of H₂O₂ and substantially suppressed HIF-1 expression under a hypoxic condition in human pancreatic cancer cells. Fuco-MnO₂-NPs reversed hypoxia-induced radioresistance by decreasing clonogenic survival and increasing DNA damage and apoptotic cell death in response to RT. In a BxPC3 xenograft mouse model, the combination treatment with Fuco-MnO₂-NPs and RT resulted in a greater tumor growth delay than RT alone. Fucoidan-coated NPs, but not naked ones, further suppressed tumor angiogenesis, as judged by immunohistochemistry data with diminished expression of phosphorylated vascular endothelial growth factor receptor 2 (VEGFR2) and CD31. These data suggest that Fuco-MnO₂-NPs may potentiate the effects of RT via dual targeting of tumor hypoxia and angiogenesis, and they are of great clinical potential in the treatment of hypoxic, radioresistant pancreatic cancer.

Hypoxia-activated prodrugs and redox-responsive nanocarriers

Hypoxia is one of the marked features of malignant tumors, which is associated with several adaptation changes in the microenvironment of tumor cells. Therefore, targeting tumor hypoxia is a research hotspot for cancer therapy. In this review, we summarize the developing chemotherapeutic drugs for targeting hypoxia, including quinones, nitroaromatic/nitroimidazole, N-oxides, and transition metal complexes. In addition, redox-responsive bonds, such as nitroimidazole groups, azogroups, and disulfide bonds, are frequently used in drug delivery systems for targeting the redox environment of tumors. Both hypoxia-activated prodrugs and redox-responsive drug delivery nanocarriers have significant effects on targeting tumor hypoxia for cancer therapy. Hypoxia-activated prodrugs are commonly used in clinical trials with favorable prospects, while redox-responsive nanocarriers are currently at the experimental stage.

Metabolic and Physiologic Imaging Biomarkers of the Tumor Microenvironment Predict Treatment Outcome with Radiation or a Hypoxia-Activated Prodrug in Mice

Pancreatic ductal adenocarcinoma (PDAC) is characterized by hypoxic niches that lead to treatment resistance. Therefore, studies of tumor oxygenation and metabolic profiling should contribute to improved treatment strategies. Here, we define two imaging biomarkers that predict differences in tumor response to therapy: (i) partial oxygen pressure (pO2), measured by EPR imaging; and (ii) [1-13C] pyruvate metabolism rate, measured by hyperpolarized 13C MRI. Three human PDAC xenografts with varying treatment sensitivity (Hs766t, MiaPaCa2, and Su.86.86) were grown in mice. The median pO2 of the mature Hs766t, MiaPaCa2, and Su.86.86 tumors was 9.1 ± 1.7, 11.1 ± 2.2, and 17.6 ± 2.6 mm Hg, and the rate of pyruvate-to-lactate conversion was 2.72 ± 0.48, 2.28 ± 0.26, and 1.98 ± 0.51 per minute, respectively (n = 6, each). These results are in agreement with steady-state data of matabolites quantified by mass spectroscopy and histologic analysis, indicating glycolytic and hypoxia profile in Hs766t, MiaPaca2, and Su.86.86 tumors. Fractionated radiotherapy (5 Gy × 5) resulted in a tumor growth delay of 16.7 ± 1.6 and 18.0 ± 2.7 days in MiaPaca2 and Su.86.86 tumors, respectively, compared with 6.3 ± 2.7 days in hypoxic Hs766t tumors. Treatment with gemcitabine, a first-line chemotherapeutic agent, or the hypoxia-activated prodrug TH-302 was more effective against Hs766t tumors (20.0 ± 3.5 and 25.0 ± 7.7 days increase in survival time, respectively) than MiaPaCa2 (2.7 ± 0.4 and 6.7 ± 0.7 days) and Su.86.86 (4.7 ± 0.6 and 0.7 ± 0.6 days) tumors. Collectively, these results demonstrate the ability of molecular imaging biomarkers to predict the response of PDAC to treatment with radiotherapy and TH-302.Significance: pO2 imaging data and clinically available metabolic imaging data provide useful insight into predicting the treatment efficacy of chemotherapy, radiation, and a hypoxia-activated prodrug as monotherapies and combination therapies in PDAC tumor xenograft models. Cancer Res; 78(14); 3783-92. ©2018 AACR.

Pancreatic Ductal Adenocarcinoma: A Strong Imbalance of Good and Bad Immunological Cops in the Tumor Microenvironment

Pancreatic ductal adenocarcinoma (PDAC) is one of the most aggressive and lethal cancers with very few available treatments. For many decades, gemcitabine was the only treatment for patients with PDAC. A recent attempt to improve patient survival by combining this chemotherapy with FOLFIRINOX and nab-paclitaxel failed and instead resulted in increased toxicity. Novel therapies are urgently required to improve PDAC patient survival. New treatments in other cancers such as melanoma, non-small-cell lung cancer, and renal cancer have emerged, based on immunotherapy targeting the immune checkpoints cytotoxic T-lymphocyte-associated antigen 4 or programmed death 1 ligand. However, the first clinical trials using such immune checkpoint inhibitors in PDAC have had limited success. Resistance to immunotherapy in PDAC remains unclear but could be due to tissue components (cancer-associated fibroblasts, desmoplasia, hypoxia) and to the imbalance between immunosuppressive and effector immune populations in the tumor microenvironment. In this review, we analyzed the presence of “good and bad immunological cops” in PDAC and discussed the significance of changes in their balance.