Molecular imaging of tumor metabolism: Insight from pyruvate- and glucose-based deuterium MRI studies

Cancer diagnosis by metabolic MRI proposes to follow the fate of glycolytic precursors such as pyruvate or glucose, and their in vivo conversion into lactate. This study compares the 2H MRI outlooks afforded by these metabolites when targeting a pancreatic cancer model. Exogenously injected [3,3',3″-2H3]-pyruvate was visible only briefly; it generated a deuterated lactate signal throughout the body that faded after ~5 min, showing a minor concentration bias at the rims of the tumors. [6,6'-2H2]-glucose by contrast originated a lactate signal that localized clearly within the tumors, persisting for over an hour. Investigations alternating deuterated and nondeuterated glucose injections revealed correlations between the lactate generation and the glucose available at the tumor, evidencing a continuous and avid glucose consumption generating well-localized lactate signatures as driven by the Warburg effect. This is by contrast to the transient and more promiscuous pyruvate-to-lactate transformation, which seemed subject to transporter and kinetics effects. The consequences of these observations within metabolic MRI are briefly discussed.

High-sensitivity deuterium metabolic MRI differentiates acute pancreatitis from pancreatic cancers in murine models

Deuterium metabolic imaging (DMI) is a promising tool for investigating a tumor's biology, and eventually contribute in cancer diagnosis and prognosis. In DMI, [6,6'-2H2]-glucose is taken up and metabolized by different tissues, resulting in the formation of HDO but also in an enhanced formation of [3,3'-2H2]-lactate at the tumor site as a result of the Warburg effect. Recent studies have shown DMI's suitability to highlight pancreatic cancer in murine models by [3,3'-2H2]-lactate formation; an important question is whether DMI can also differentiate between these tumors and pancreatitis. This differentiation is critical, as these two diseases are hard to distinguish today radiologically, but have very different prognoses requiring distinctive treatments. Recent studies have shown the limitations that hyperpolarized MRI faces when trying to distinguish these pancreatic diseases by monitoring the [1-13C1]-pyruvate→[1-13C1]-lactate conversion. In this work, we explore DMI's capability to achieve such differentiation. Initial tests used a multi-echo (ME) SSFP sequence, to identify any metabolic differences between tumor and acute pancreatitis models that had been previously elicited very similar [1-13C1]-pyruvate→[1-13C1]-lactate conversion rates. Although ME-SSFP provides approximately 5 times greater signal-to-noise ratio (SNR) than the standard chemical shift imaging (CSI) experiment used in DMI, no lactate signal was observed in the pancreatitis model. To enhance lactate sensitivity further, we developed a new, weighted-average, CSI-SSFP approach for DMI. Weighted-average CSI-SSFP improved DMI's SNR by another factor of 4 over ME-SSFP-a sensitivity enhancement that sufficed to evidence natural abundance 2H fat in abdominal images, something that had escaped the previous approaches even at ultrahigh (15.2 T) MRI fields. Despite these efforts to enhance DMI's sensitivity, no lactate signal could be detected in acute pancreatitis models (n = 10; [3,3'-2H2]-lactate limit of detection < 100 µM; 15.2 T). This leads to the conclusion that pancreatic tumors and acute pancreatitis may be clearly distinguished by DMI, based on their different abilities to generate deuterated lactate.

Deuterium imaging of the Warburg effect at sub-millimolar concentrations by joint processing of the kinetic and spectral dimensions

Deuterium metabolic imaging (DMI) is a promising molecular MRI approach, which follows the administration of deuterated substrates and their metabolization. [6,6'-2 H2 ]-glucose for instance is preferentially converted in tumors to [3,3'-2 H2 ]-lactate as a result of the Warburg effect, providing a distinct resonance whose mapping using time-resolved spectroscopic imaging can diagnose cancer. The MR detection of low-concentration metabolites such as lactate, however, is challenging. It has been recently shown that multi-echo balanced steady-state free precession (ME-bSSFP) increases the signal-to-noise ratio (SNR) of these experiments approximately threefold over regular chemical shift imaging; the present study examines how DMI's sensitivity can be increased further by advanced processing methods. Some of these, such as compressed sensing multiplicative denoising and block-matching/3D filtering, can be applied to any spectroscopic/imaging methods. Sensitivity-enhancing approaches were also specifically tailored to ME-bSSFP DMI, by relying on priors related to the resonances' positions and to features of the metabolic kinetics. Two new methods are thus proposed that use these constraints for enhancing the sensitivity of both the spectral images and the metabolic kinetics. The ability of these methods to improve DMI is evidenced in pancreatic cancer studies carried at 15.2 T, where suitable implementations of the proposals imparted eightfold or more SNR improvement over the original ME-bSSFP data, at no informational cost. Comparisons with other propositions in the literature are briefly discussed.

Abstract C016: New treatment modality for pancreatic cancer-Vascular Targeted Photodynamic therapy with WST11 (Padeliporfin) combined with endovascular light delivery

Background: Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal human malignancies. Early detection and surgical removal of PDAC, when the cancer is localized with no clinical evidence for systemic spread, may be curative but tumor spread into the vicinity of major blood vessels, e.g. superior mesenteric artery (SMA), can be lethal and therefore avoid surgery. Here we show that Vascular Targeted Photodynamic therapy (VTP) with WST11 in combination with immune modulating chemotherapeutic agents allows PDAC tumors ablation while preserving large normal vessels and tissues in animal models. New endovascular illumination system recently developed by our group (1) provides the light needed for such ablation with no damage to the SMA and complete remodeling of the surrounding normal tissue. Methods: Two orthotopic models of pancreatic cancer (KPC-Luc-mcherry and non-labeled KPC tumors (NL-KPC)) in C57B mice were subjected to VTP, alongside intraperitoneal gemzar (GEM) or cyclophosphamide (CTX) treatment. multiplex immunohistochemistry (mIHC) and single analyses using 10X Genomics platform of tumor were performed for resolving the key factors in the therapeutic process. Results: Comparing the KPC-Luc-mcherry with the NL-KPC tumor, we found that non labeled KPC has the typical morphology of human PDAC, immunologically cold and is highly aggressive compared with KPC-Luc-mcherry. WST11-VTP results in high cure rate (~50%) of animals bearing small KPC-Luc-mcherry tumors, larger tumors required combinations with metronomic administration of GEM. High rate of complete necrosis (95-100%) was achieved also with the non-labled PDAC tumors but prolonged disease- free survival required combination with CTX. The mechanism of action for both tumor models involves co-generation of oxygen and NO radicals through local photoexcitation of WST11, followed by iNOS consumption and vascular break down. Infiltration of immune cells alarmed by HMGB1 and other DAMPs leads to annihilation of residual cancer cells and prolonged anticancer immunity. The administration of CTX amplifies and prolonged the VTP oxidative stress. Conclusion: WST11-VTP combination with immune modulating chemotherapeutic agents administrations, activated by endovascular illumination through the SMA, may provide solution to the unmet need of early stage diagnosed PDAC patients. (1) Franz E. Boas et al, “Downstaging Locally Advanced Pancreatic Cancer To Resectability: Perivascular Ablation Using An Intra-arterial Balloon Laser Catheter In Pigs”, Abstract Archives of the RSNA, RSNA 2021,SDR-IR-13- “Redefining radiology” 11/29-12/4, 2021

Citation Format: Lilach Agemy, Keren Sasson, Tamar Yechezkel, Dina Priese, Yaniv Cohen, Zachary Zacks, Gil Stelzer, David P. Kelsen, Hooman Yarmohammadi, Alice C. Wei, Stephen B. Solomon, Avidgor Scherz. New treatment modality for pancreatic cancer-Vascular Targeted Photodynamic therapy with WST11 (Padeliporfin) combined with endovascular light delivery [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer; 2022 Sep 13-16; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2022;82(22 Suppl):Abstract nr C016.

Deuterium MRSI characterizations of glucose metabolism in orthotopic pancreatic cancer mouse models

Detecting and mapping metabolism in tissues represents a major step in detecting, characterizing, treating and understanding cancers. Recently introduced deuterium metabolic imaging techniques could offer a noninvasive route for the metabolic imaging of animals and humans, based on using ² H magnetic resonance spectroscopic imaging (MRSI) to detect the uptake of deuterated glucose and the fate of its metabolic products. In this study, ² H_6,6' -glucose was administered to mice cohorts that had been orthotopically implanted with two different models of pancreatic ductal adenocarcinoma (PDAC), involving PAN-02 and KPC cell lines. As the tumors grew, ² H_6,6' -glucose was administered as bolii into the animals' tail veins, and ² H MRSI images were recorded at 15.2 T. 2D phase-encoded chemical shift imaging experiments could detect a signal from this deuterated glucose immediately after the bolus injection for both the PDAC models, reaching a maximum in the animals' tumors ~ 20 min following administration, and nearly total decay after ~ 40 min. The main metabolic reporter of the cancers was the ² H_3,3' -lactate signal, which MRSI could detect and localize on the tumors when these were 5 mm or more in diameter. Lactate production time traces varied slightly with the animal and tumor model, but in general lactate peaked at times of 60 min or longer following injection, reaching concentrations that were ~ 10-fold lower than those of the initial glucose injection. This ² H_3,3' -lactate signal was only visible inside the tumors. ² H-water could also be detected as deuterated glucose's metabolic product, increasing throughout the entire time course of the experiment from its ≈10 mM natural abundance background. This water resonance could be imaged throughout the entire abdomen of the animals, including an enhanced presence in the tumor, but also in other organs like the kidney and bladder. These results suggest that deuterium MRSI may serve as a robust, minimally invasive tool for the monitoring of metabolic activity in pancreatic tumors, capable of undergoing clinical translation and supporting decisions concerning treatment strategies. Comparisons with in vivo metabolic MRI experiments that have been carried out in other animal models are presented and their differences/similarities are discussed.

Exploring the longitudinal glioma microenvironment landscape uncovers reprogrammed pro-tumorigenic neutrophils in the bone marrow

Recent multi-omics studies show different immune tumor microenvironment (TME) compositions in glioblastoma (GBM). However, temporal comprehensive knowledge of the TME from initiation of the disease remains sparse. We use Cre recombinase (Cre)-inducible lentiviral murine GBM models to compare the cellular evolution of the immune TME in tumors initiated from different oncogenic drivers. We show that neutrophils infiltrate early during tumor progression primarily in the mesenchymal GBM model. Depleting neutrophils in vivo at the onset of disease accelerates tumor growth and reduces the median overall survival time of mice. We show that, as a tumor progresses, bone marrow-derived neutrophils are skewed toward a phenotype associated with pro-tumorigenic processes. Our findings suggest that GBM can remotely regulate systemic myeloid differentiation in the bone marrow to generate neutrophils pre-committed to a tumor-supportive phenotype. This work reveals plasticity in the systemic immune host microenvironment, suggesting an additional point of intervention in GBM treatment.

Tumour irradiation combined with vascular-targeted photodynamic therapy enhances antitumour effects in pre-clinical prostate cancer

BACKGROUND

There is a need to improve the treatment of prostate cancer (PCa) and reduce treatment side effects. Vascular-targeted photodynamic therapy (VTP) is a focal therapy for low-risk low-volume localised PCa, which rapidly disrupts targeted tumour vessels. There is interest in expanding the use of VTP to higher-risk disease. Tumour vasculature is characterised by vessel immaturity, increased permeability, aberrant branching and inefficient flow. FRT alters the tumour microenvironment and promotes transient 'vascular normalisation'. We hypothesised that multimodality therapy combining fractionated radiotherapy (FRT) and VTP could improve PCa tumour control compared against monotherapy with FRT or VTP.

METHODS

We investigated whether sequential delivery of FRT followed by VTP 7 days later improves flank TRAMP-C1 PCa tumour allograft control compared to monotherapy with FRT or VTP.

RESULTS

FRT induced 'vascular normalisation' changes in PCa flank tumour allografts, improving vascular function as demonstrated using dynamic contrast-enhanced magnetic resonance imaging. FRT followed by VTP significantly delayed tumour growth in flank PCa allograft pre-clinical models, compared with monotherapy with FRT or VTP, and improved overall survival.

CONCLUSION

Combining FRT and VTP may be a promising multimodal approach in PCa therapy. This provides proof-of-concept for this multimodality treatment to inform early phase clinical trials.

Improving deuterium metabolic imaging (DMI) signal-to-noise ratio by spectroscopic multi-echo bSSFP: A pancreatic cancer investigation

PURPOSE

Deuterium metabolic imaging (DMI) maps the uptake of deuterated precursors and their conversion into lactate and other markers of tumor metabolism. Even after leveraging ² H's short T₁ s, DMI's signal-to-noise ratio (SNR) is limited. We hypothesize that a multi-echo balanced steady-state free precession (ME-bSSFP) approach would increase SNR compared to chemical shift imaging (CSI), while achieving spectral isolation of the metabolic precursors and products.

METHODS

Suitably tuned ² H ME-bSSFP (five echo times [TEs], ΔTE = 2.2 ms, repetition time [TR]/flip-angle = 12 ms/60°) was implemented at 15.2T and compared to CSI (TR/flip-angle = 95 ms/90°) regarding SNR and spectral isolation, in simulations, in deuterated phantoms and for the in vivo diagnosis of a mouse tumor model of pancreatic adenocarcinoma (N = 10).

RESULTS

Simulations predicted an SNR increase vs. CSI of 3-5, and that the peaks of ² H-water, ² H_6,6' -glucose, and ² H_3,3' -lactate can be well isolated by ME-bSSFP; phantoms confirmed this. In vivo, at equal spatial resolution (1.25 × 1.25 mm² ) and scan time (10 min), ² H_6,6' -glucose's and ² H_3,3' -lactate's SNR were indeed higher for bSSFP than for CSI, three-fold for glucose (57 ± 30 vs. 19 ± 11, P < .001), doubled for water (13 ± 5 vs. 7 ± 3, P = .005). The time courses and overall localization of all metabolites agreed well, comparing CSI against ME-bSSFP. However, a clearer localization of glucose in kidneys and bladder, the detection of glucose-avid rims in certain tumors, and a heterogeneous pattern of intra-tumor lactate production could only be observed using ME-bSSFP's higher resolution.

CONCLUSIONS

ME-bSSFP provides greater SNR per unit time than CSI, providing for higher spatial resolution mapping of glucose uptake and lactate production in tumors.

Identification of variable stages in murine pancreatic tumors by a multiparametric approach employing hyperpolarized 13 C MRSI, 1 H diffusivity and 1 H T1 MRI

This study explored the usefulness of multiple quantitative MRI approaches to detect pancreatic ductal adenocarcinomas in two murine models, PAN-02 and KPC. Methods assayed included 1 H T1 and T2 measurements, quantitative diffusivity mapping, magnetization transfer (MT) 1 H MRI throughout the abdomen and hyperpolarized 13 C spectroscopic imaging. The progress of the disease was followed as a function of its development; studies were also conducted for wildtype control mice and for mice with induced mild acute pancreatitis. Customized methods developed for scanning the motion- and artifact-prone mice abdomens allowed us to obtain quality 1 H images for these targeted regions. Contrasts between tumors and surrounding tissues, however, were significantly different. Anatomical images, T2 maps and MT did not yield significant contrast unless tumors were large. By contrast, tumors showed statistically lower diffusivities than their surroundings (≈8.3 ± 0.4 x 10-4 for PAN-02 and ≈10.2 ± 0.6 x 10-4 for KPC vs 13 ± 1 x 10-3 mm2 s-1 for surroundings), longer T1 relaxation times (≈1.44 ± 0.05 for PAN-02 and ≈1.45 ± 0.05 for KPC vs 0.95 ± 0.10 seconds for surroundings) and significantly higher lactate/pyruvate ratios by hyperpolarized 13 C MR (0.53 ± 0.2 for PAN-02 and 0.78 ± 0.2 for KPC vs 0.11 ± 0.04 for control and 0.31 ± 0.04 for pancreatitis-bearing mice). Although the latter could also distinguish early-stage tumors from healthy animal controls, their response was similar to that in our pancreatitis model. Still, this ambiguity could be lifted using the 1 H-based reporters. If confirmed for other kinds of pancreatic tumors this means that these approaches, combined, can provide a route to an early detection of pancreatic cancer.

Immune microenvironment landscape and the role of neutrophils in glioblastoma

Glioblastoma (GBM) is an aggressive, highly invasive primary brain tumor with near total fatality. Using a Cre-inducible lentiviral GBM mouse model we previously showed that gliomas can originate from terminally differentiated neurons and astrocytes, which can dedifferentiate to a stem cell-like state upon transformation. We believe that the tumor microenvironment (TME) may contribute to the process of tumor reprogramming. Although the majority of infiltrating cells in the tumor are peripheral macrophages and microglia, recent appreciation of the effects of neutrophils in cancer directed our efforts in understanding their role in GBM.

Flow cytometry analysis revealed differences in the brain TME of both the innate and adaptive immune populations compared to healthy brain tissue, changes were also seen in spleen and bone marrow even at early stages of GBM development. The neutrophils population varies not only at different time-points but also between tumor subtypes. We believe neutrophils switch from anti-tumor to pro-tumor phenotype. Depletion of neutrophils right before tumor initiation accelerated the onset of the disease while co-transplantation of equal ratio of glioma cells and naïve neutrophils delayed the initiation of tumors lesions. In-vitro assays showed higher migration and formation of neutrophils extracellular traps (NETs) on exposure to glioma cells condition media or glioma derived exosomes. Our findings suggest neutrophils play a role in tumor initiation and progression, and further understanding the transition of neutrophils from anti-tumor to pro-tumor phenotype will shed light into new strategies to treat GBM.

Abstract A69: Mutagenicity of urea cycle dysregulation and its implications for cancer immunotherapy

Immune checkpoint therapy leads to durable clinical responses in many cancer patients, but fails in others. To improve the clinical response to immunotherapy, it is highly important to identify predictive biomarkers. While checkpoint genes’ expression levels, tumor neo-antigen load and microsatellite instability (MSI) have been associated with enhanced response to checkpoint immunotherapies, they yet provide only a modest predictive signal and hence there is a need to identify additional predictive factors. Specifically, while there is growing evidence that metabolic alterations can affect the tumor and modulate the immune response, the potential effects of altered cancer metabolism on tumor mutagenesis and immunotherapy remain unexplored.

The urea cycle (UC) converts excess nitrogen derived from the breakdown of nitrogen-containing molecules (e.g., ammonia) to urea, a relatively non-toxic and disposable nitrogenous compound. We and others have shown that silencing of the UC enzyme ASS1 promotes cancer proliferation by diverting its substrate aspartate toward CAD enzyme, which mediates the first three reactions in the pyrimidine synthesis pathway. We now demonstrate, by analysis of the TCGA data, tumor samples and cancer cell line experiments, that UC dysregulation (UCD) is a much wider common metabolic phenomenon that maximizes nitrogen utilization in cancer, favoring pyrimidine synthesis over urea disposal. Of note, while UCD is significantly associated with decreased cancer patient survival, the overall mutational load is not.

Remarkably, we find that the UCD changes the 1:1 purine (R)-to-pyrimidine (Y) ratio in favor of pyrimidine in cancer cells. Moreover, in analysis of both TCGA data and UC perturbed cancer cells we find that: (a) UCD is significantly associated with a novel and unique pattern of purine-to-pyrimidine transversion mutational bias across many cancer types at the DNA coding (sense) strand, and (b) this trend becomes stronger and more significant at both the mRNA and protein levels, testifying to its functional implications. Notably, the overall mutational load in cancer is negatively correlated with UCD, testifying to their independence.

To test whether the mutational bias is associated with better immunotherapy response, we analyze published data of three large melanoma cohorts. We find that responders of both anti-PD1 and anti-CTLA4 therapy exhibit significantly higher UCD and R-&gt;Y mutational bias than non-responders. We further observe that the peptides carrying transverse R-&gt;Y mutations are preferentially presented as neoantigens in responders independent of mutational load, and this trend becomes significant for more clonal neoantigens, promoting UCD as a potential biomarker for the success of immunotherapy.

Finally, as nitrogen metabolites are excreted in the urine, we hypothesize that these changes may be detectable in urine of UCD-cancers. We observe increased levels of pyrimidine derived metabolites in the urine of mice bearing colon tumors associated with UCD in the tumors compared to normal intestine. In an analogous manner, we find significantly higher levels pyrimidine derived metabolites in the urine of human patients with prostate cancer compared to controls.

Collectively, these results support our hypothesis that UCD is a prevalent metabolic phenomenon in cancer, generating mutational biased neo-peptides, worsening patients’ prognosis and yet enhancing the response to immune therapy independent of mutational load and MSI. Taken together, our findings point to the important role of UCD in a broad spectrum of cancers, to the potential use of UCD related metabolites as cancer biomarkers, and last but not least, to the role of UCD in predicting response to immune check point therapy. Broadly, our results suggest future therapeutic interventions aiming to increase UCD levels to enhance the coverage and efficiency of cancer immunotherapy.

Citation Format: Joo Sang Lee, Narin Carmel, Hiren Karathia, Noam Auslander, Shiran Rabinovich, Rom Keshet, Noa Stettner, Alon Silberman, Lilach Agemy, Daniel Helbling, Raya Eilam, Qin Sun, Alexander Brandis, Hila Weiss, David Dimmock, Noam Stern-Ginossar, Avigdor Scherz, Igor Ulitsky, Sandesh CS Nagamani, Ronit Elhasid, Sridhar Hannenhalli, Eytan Ruppin, Ayelet Erez. Mutagenicity of urea cycle dysregulation and its implications for cancer immunotherapy [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2017 Oct 1-4; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2018;6(9 Suppl):Abstract nr A69.

Urea Cycle Dysregulation Generates Clinically Relevant Genomic and Biochemical Signatures

The urea cycle (UC) is the main pathway by which mammals dispose of waste nitrogen. We find that specific alterations in the expression of most UC enzymes occur in many tumors, leading to a general metabolic hallmark termed "UC dysregulation" (UCD). UCD elicits nitrogen diversion toward carbamoyl-phosphate synthetase2, aspartate transcarbamylase, and dihydrooratase (CAD) activation and enhances pyrimidine synthesis, resulting in detectable changes in nitrogen metabolites in both patient tumors and their bio-fluids. The accompanying excess of pyrimidine versus purine nucleotides results in a genomic signature consisting of transversion mutations at the DNA, RNA, and protein levels. This mutational bias is associated with increased numbers of hydrophobic tumor antigens and a better response to immune checkpoint inhibitors independent of mutational load. Taken together, our findings demonstrate that UCD is a common feature of tumors that profoundly affects carcinogenesis, mutagenesis, and immunotherapy response.

Tumor-homing peptides as tools for targeted delivery of payloads to the placenta

The availability of therapeutics to treat pregnancy complications is severely lacking mainly because of the risk of causing harm to the fetus. As enhancement of placental growth and function can alleviate maternal symptoms and improve fetal growth in animal models, we have developed a method for targeted delivery of payloads to the placenta. We show that the tumor-homing peptide sequences CGKRK and iRGD bind selectively to the placental surface of humans and mice and do not interfere with normal development. Peptide-coated nanoparticles intravenously injected into pregnant mice accumulated within the mouse placenta, whereas control nanoparticles exhibited reduced binding and/or fetal transfer. We used targeted liposomes to efficiently deliver cargoes of carboxyfluorescein and insulin-like growth factor 2 to the mouse placenta; the latter significantly increased mean placental weight when administered to healthy animals and significantly improved fetal weight distribution in a well-characterized model of fetal growth restriction. These data provide proof of principle for targeted delivery of drugs to the placenta and provide a novel platform for the development of placenta-specific therapeutics.

Palliative treatment of obstructive esophageal cancer by vascular targeted photodynamic therapy (VTP): Preclinical study in orthotopic rat model

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Background: Vascular targeted photodynamic therapy (VTP) based on local sensitization of circulating WST11 (Pd-bacteriochlorophyll), enables effective focal ablation of solid tumors. WST11 clears from the circulation with t1/2 ~40 min (in humans) and does not accumulate in tissues which assures high level of safety and minimal adverse effects. Here we evaluate WST11-VTP for the treatment of obstructive esophageal cancer aiming at developing clinically relevant protocol. Methods: Using endoscopy guided procedure rat esophageal cancer cells (JA) were implanted in the mid esophagus. Following intravenous infusion of WST11, established tumors were illuminated by cylindrical fiber using the same endoscope sleeve. Safety and efficacy were evaluated by monitoring animal weight shift and histology of treated esophageal tissues. Treated animals included control (light/no WST11 or WST11/no light), WST11-VTP and WST11-VTP following treatment with bevacizumab at day -3. Results: WST11-VTP on esophageal tissues resulted in coagulative necrosis of the tumor graft and prolonged survival as evident by Kaplan—Meyer curves. The impact was confined to the illuminated site without signs of perforation or death. Following Bevacizumab, WST11-VTP showed similar results while control groups showed no effect. All treated animals started to regain weight at day 7 after VTP. Esophageal tissue and function was completely restored. Conclusions: WST11-VTP could be safely applied for the treatment of esophageal tumors, with only transient and mild adverse effect that are not affected by previous, clinically relevant treatment such as Bevacizumab application. Importantly, VTP effectively eradicated established esophageal tumors and could be translated into a clinical treatment protocol.

The treatment of esophageal cancer by vascular-targeted photodynamic therapy (VTP) using orthotopic rat model

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Background: Vascular targeted photodynamic therapy (VTP) based on local sensitization of circulating WST11, a water-soluble derivative of Pd-bacteriochlorophyll, enables effective focal ablation of solid tumors. Highly toxic oxygen radicals are produced in the vascular lumen upon illumination with near infra-red light (755nm), leading to irreversible occlusion of tumor feeding arteries and veins. WST11 clears rapidly from the circulation and does not accumulate in the body, providing high level of safety and minimizing adverse effects. WST11-VTP completed Phase II clinical trials in USA and Phase III in Europe for the treatment of early localized prostate cancer as a first line monotherapy with above 80% complete response rate. Here we evaluate its’ safety and efficacy for the treatment of esophageal cancer aiming at development of clinically translatable treatment protocol. Methods: We developed an orthotopic model in which esophageal cancer cells are implanted in the mid esophagus using endoscopy guided procedure. Established tumors are illuminated with cylindrical diffuser deployed through the custom built endoscopy guided system following infusion of WST11. For assessment of treatment safety and tissue recovery normal esophagus tissue was subjected to WST11-VTP using the same treatment set up. Selectivity and efficacy were evaluated histologically by examining sections of treated tumors and normal esophageal tissues under various treatment conditions. Results: Safety control VTP procedures on healthy esophageal tissues have shown a confined destruction only at the illuminated zone while collateral damage to neighboring tissues was not observed. The impact runs as deep as the muscularis propria without signs of perforation or death as a result of the procedure. The VTP protocol was able to ablate implanted and established tumors as opposed to the control group with light illumination alone without the sensitizer (WST11). Conclusions: VTP could be safely applied to treat esophageal tumors, with transient and mild adverse effects. Importantly, VTP effectively eradicated established esophageal tumors in tested set up that could be translated into a clinical treatment protocol.

Increasing Tumor Accessibility with Conjugatable Disulfide-Bridged Tumor-Penetrating Peptides for Cancer Diagnosis and Treatment

Tumor-homing peptides with tissue-penetrating properties increase the efficacy of targeted cancer therapy by delivering an anticancer agent to the tumor interior. LyP-1 (CGNKRTRGC) and iRGD (CRGDKGPDC) are founding members of this class of peptides. The presence of the cysteines forming the cyclizing disulfide bond complicates conjugation of these peptides with other molecules, such as drugs. Here, we report the synthesis of conjugatable disulfide-bridged peptides and their conjugation to biologically important molecules. We have synthesized the LyP-1, iRGD, and CRGDC (GACRGDCLGA) peptides with a cysteine or maleimidohexanoic acid added externally at N-terminus of the sequences. Subsequent conjugation to payloads yielded stable compounds in which the tumor-homing properties of the peptide and the biological activity of the payload were retained.

Proapoptotic peptide-mediated cancer therapy targeted to cell surface p32

Antiangiogenic therapy is a promising new treatment modality for cancer, but it generally produces only transient tumor regression. We have previously devised a tumor-targeted nanosystem, in which a pentapeptide, CGKRK, delivers a proapoptotic peptide into the mitochondria of tumor blood vessel endothelial cells and tumor cells. The treatment was highly effective in glioblastoma mouse models completely refractory to other antiangiogenic treatments. Here, we identify p32/gC1qR/HABP, a mitochondrial protein that is also expressed at the cell surface of activated (angiogenic) endothelial cells and tumor cells, as a receptor for the CGKRK peptide. The results demonstrate the ability of p32 to cause internalization of a payload bound to p32 into the cytoplasm. We also show that nardilysin, a protease capable of cleaving CGKRK, plays a role in the internalization of a p32-bound payload. As p32 is overexpressed and surface displayed in breast cancers, we studied the efficacy of the nanosystem in this cancer. We show highly significant treatment results in an orthotopic model of breast cancer. The specificity of cell surface p32 for tumor-associated cells, its ability to carry payloads to mitochondria, and the efficacy of the system in important types of cancer make the nanosystem a promising candidate for further development.

Engineering strategy to improve peptide analogs: from structure-based computational design to tumor homing

We present a chemical strategy to engineer analogs of the tumor-homing peptide CREKA (Cys-Arg-Glu-Lys-Ala), which binds to fibrin and fibrin-associated clotted plasma proteins in tumor vessels (Simberg et al. in Proc Natl Acad Sci USA 104:932-936, 2007) with improved ability to inhibit tumor growth. Computer modeling using a combination of simulated annealing and molecular dynamics were carried out to design targeted replacements aimed at enhancing the stability of the bioactive conformation of CREKA. Because this conformation presents a pocket-like shape with the charged groups of Arg, Glu and Lys pointing outward, non-proteinogenic amino acids α-methyl and N-methyl derivatives of Arg, Glu and Lys were selected, rationally designed and incorporated into CREKA analogs. The stabilization of the bioactive conformation predicted by the modeling for the different CREKA analogs matched the tumor fluorescence results, with tumor accumulation increasing with stabilization. Here we report the modeling, synthetic procedures, and new biological assays used to test the efficacy and utility of the analogs. Combined, our results show how studies based on multi-disciplinary collaboration can converge and lead to useful biomedical advances.

De novo design of a tumor-penetrating peptide

Poor penetration of antitumor drugs into the extravascular tumor tissue is often a major factor limiting the efficacy of cancer treatments. Our group has recently described a strategy to enhance tumor penetration of chemotherapeutic drugs through use of iRGD peptide (CRGDK/RGPDC). This peptide comprises two sequence motifs: RGD, which binds to αvβ3/5 integrins on tumor endothelia and tumor cells, and a cryptic CendR motif (R/KXXR/K-OH). Once integrin binding has brought iRGD to the tumor, the peptide is proteolytically cleaved to expose the cryptic CendR motif. The truncated peptide loses affinity for its primary receptor and binds to neuropilin-1, activating a tissue penetration pathway that delivers the peptide along with attached or co-administered payload into the tumor mass. Here, we describe the design of a new tumor-penetrating peptide based on the current knowledge of homing sequences and internalizing receptors. The tumor-homing motif in the new peptide is the NGR sequence, which binds to endothelial CD13. The NGR sequence was placed in the context of a CendR motif (RNGR), and this sequence was embedded in the iRGD framework. The resulting peptide (CRNGRGPDC, iNGR) homed to tumor vessels and penetrated into tumor tissue more effectively than the standard NGR peptide. iNGR induced greater tumor penetration of coupled nanoparticles and co-administered compounds than NGR. Doxorubicin given together with iNGR was significantly more efficacious than the drug alone. These results show that a tumor-specific, tissue-penetrating peptide can be constructed from known sequence elements. This principle may be useful in designing tissue-penetrating peptides for other diseases.

Optimization of iron oxide nanoparticle detection using ultrashort echo time pulse sequences: comparison of T1, T2*, and synergistic T1- T2* contrast mechanisms

Iron oxide nanoparticles (IONPs) are used in various MRI applications as negative contrast agents. A major challenge is to distinguish regions of signal void due to IONPs from those due to low signal tissues or susceptibility artifacts. To overcome this limitation, several positive contrast strategies have been proposed. Relying on IONP T(1) shortening effects to generate positive contrast is a particularly appealing strategy because it should provide additional specificity when associated with the usual negative contrast from effective transverse relaxation time (T(2)*) effects. In this article, ultrashort echo time imaging is shown to be a powerful technique which can take full advantage of both contrast mechanisms. Methods of comparing T(1) and T(2)* contrast efficiency are described and general rules that allow optimizing IONP detection sensitivity are derived. Contrary to conventional wisdom, optimizing T(1) contrast is often a good strategy for imaging IONPs. Under certain conditions, subtraction of a later echo signal from the ultrashort echo time signal not only improves IONP specificity by providing long T(2)* background suppression but also increases detection sensitivity, as it enables a synergistic combination of usually antagonist T(1) and T(2)* contrasts. In vitro experiments support our theory, and a molecular imaging application is demonstrated using tumor-targeted IONPs in vivo.

Nanoparticle-induced vascular blockade in human prostate cancer

The tumor-homing pentapeptide CREKA (Cys-Arg-Glu-Lys-Ala) specifically homes to tumors by binding to fibrin and fibrin-associated clotted plasma proteins in tumor vessels. Previous results show that CREKA-coated superparamagnetic iron oxide particles can cause additional clotting in tumor vessels, which creates more binding sites for the peptide. We have used this self-amplifying homing system to develop theranostic nanoparticles that simultaneously serve as an imaging agent and inhibit tumor growth by obstructing tumor circulation through blood clotting. The CREKA nanoparticles were combined with nanoparticles coated with another tumor-homing peptide, CRKDKC, and nanoparticles with an elongated shape (nanoworms) were used for improved binding efficacy. The efficacy of the CREKA peptide was then increased by replacing some residues with nonproteinogenic counterparts, which increased the stability of the peptide in the circulation. Treatment of mice bearing orthotopic human prostate cancer tumors with the targeted nanoworms caused extensive clotting in tumor vessels, whereas no clotting was observed in the vessels of normal tissues. Optical and magnetic resonance imaging confirmed tumor-specific targeting of the nanoworms, and ultrasound imaging showed reduced blood flow in tumor vessels. Treatment of mice with prostate cancer with multiple doses of the nanoworms induced tumor necrosis and a highly significant reduction in tumor growth.

Coadministration of a tumor-penetrating peptide enhances the efficacy of cancer drugs

Poor penetration of anticancer drugs into tumors can be an important factor limiting their efficacy. We studied mouse tumor models to show that a previously characterized tumor-penetrating peptide, iRGD, increased vascular and tissue permeability in a tumor-specific and neuropilin-1-dependent manner, allowing coadministered drugs to penetrate into extravascular tumor tissue. Importantly, this effect did not require the drugs to be chemically conjugated to the peptide. Systemic injection with iRGD improved the therapeutic index of drugs of various compositions, including a small molecule (doxorubicin), nanoparticles (nab-paclitaxel and doxorubicin liposomes), and a monoclonal antibody (trastuzumab). Thus, coadministration of iRGD may be a valuable way to enhance the efficacy of anticancer drugs while reducing their side effects, a primary goal of cancer therapy research.

Abstract 3703: Nanoparticle-induced targeted pro-apoptotic peptide in glioblastoma

Glioblastomas multiforme (GBM) are the most common and lethal form of intracranial tumors. They account for approximately 70% of the 22,500 new cases of malignant primary brain tumors that are diagnosed in adults in the United States each year. Although relatively uncommon, malignant gliomas are associated with disproportionately high morbidity and mortality (median survival is only 12 to 15 months). Malignant gliomas are among the most vascular of human tumors. Tumor vasculature has proven to be particularly well suited as a site for receptor-based targeting. It expresses a multitude of molecules that are not expressed in the vessels of normal tissues. Our laboratory screens phage-displayed peptide libraries in vivo and ex vivo to discover specific targets in tumor vessels. One of the peptides, CGKRK (1) binds to the blood vessels in various kinds of tumors. Initial experiments showed that intravenously injected CGKRK peptide effectively homes to lentiviral (H-RasV12-sip53)-induced glioma in mice. We coupled the CGKRK peptide to the alpha-helical amphipathic peptide D[KLAKLAK]2, which is toxic to eukaryotic cells if it internalized into the cells (2). The chimeric peptide, when added to actively growing HUVEC or U87 glioma cells colocalized with mitochondria, whereas D[KLAKLAK]2 did not. Iron oxide nanoworms (NW) coated with the chimeric D[KLAKLAK]2-CGKRK peptide were 100-200-fold more toxic to the HUVEC and U87 cells than the free peptide in vitro and specifically accumulated in the blood vessels of glioma. Treatment of lentiviral induced glioma in mice with the D[KLAKLAK]2-CGKRK-PEG-NW inhibited tumor growth and showed a significant survival increase compared to control-treated mice.

1. Hoffman, J.A., et al. Progressive vascular changes in a transgenic mouse model of squamous cell carcinoma. Cancer Cell 4, 383-391 (2003).

2. Ellerby, H.M., et al. Anti-cancer activity of targeted pro-apoptotic peptides. Nat Med 5, 1032-1038 (1999).

*These authors contributed equally to this work

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3703.

Tissue-penetrating delivery of compounds and nanoparticles into tumors

Poor penetration of drugs into tumors is a major obstacle in tumor treatment. We describe a strategy for peptide-mediated delivery of compounds deep into the tumor parenchyma that uses a tumor-homing peptide, iRGD (CRGDK/RGPD/EC). Intravenously injected compounds coupled to iRGD bound to tumor vessels and spread into the extravascular tumor parenchyma, whereas conventional RGD peptides only delivered the cargo to the blood vessels. iRGD homes to tumors through a three-step process: the RGD motif mediates binding to alphav integrins on tumor endothelium and a proteolytic cleavage then exposes a binding motif for neuropilin-1, which mediates penetration into tissue and cells. Conjugation to iRGD significantly improved the sensitivity of tumor-imaging agents and enhanced the activity of an antitumor drug.

Irradiation enhances the metastatic potential of prostatic small cell carcinoma xenografts

BACKGROUND

Small cell carcinoma of the prostate (SCCP) is a rare subset of prostate cancer (0.5-2% of all prostatic carcinomas), predominantly composed of neuroendocrine (NE) cells, with a very poor prognosis. Irradiation is one of the mainstay options for SCCP local treatment, yet, little is known about the clinical response of these aggressive tumors to radiotherapy.

METHODS

Using SCID mice, the response to fractionated ionizing radiation (IR) of two unique human NE xenografts of SCCP (WISH-PC2 and WM-4A) was investigated.

RESULTS

Fractionated irradiation of WISH-PC2 xenografts using total doses of >24 Gy induced a delay in tumor growth, while total doses of >36 Gy led to local tumor eradication. However, most of the irradiated mice suffered from disseminated metastases. Similarly, in the WM-4A xenograft, a total dose of 20 Gy led to tumor growth delay and some of the mice also developed metastases. Non-irradiated local xenografts failed to disseminate, even following surgical excision of the main tumor mass; however, tumor cells administered intravenously did form metastases. Metastases of both xenografts were located in the adrenal/kidney and inter-scapular regions, areas rich in brown adipose tissue. A correlation was found between the appearance of irradiation-induced metastases and activation of the gelatinase activity of matrix metalloproteinase-9.

CONCLUSIONS

Clinically, this study raises the possibility that radiation to SCCP may promote metastatic disease. For patients in whom prostate biopsy shows a predominance of small cell cancer, it may be necessary to deliver systemic therapy together with the radiotherapy in order to prevent the development of metastases.