In Vitro and In Vivo Comparison of Gemcitabine and the Gemcitabine Analog 1-(2'-deoxy-2'-fluoroarabinofuranosyl) Cytosine (FAC) in Human Orthotopic and Genetically Modified Mouse Pancreatic Cancer Models

Analysis of capecitabine metabolites in conjunction with digital autoradiography in a murine model of pancreatic cancer suggests extensive drug penetration through the tumor

Previously published digital autoradiography of 3 H-labeled capecitabine reveals a near-uniform distribution of activity throughout a murine pancreatic model. This is in contrast both to 14 C-labeled gemcitabine, and established expectations, as the dense stroma of pancreatic cancer is understood to inhibit drug penetration. Capecitabine is a pro-drug for 5 FU. The positioning of the radiolabel on capecitabine leaves open the possibility that much of the autoradiographic signal is generated by nontoxic compounds. Studies were performed on tumors derived via organoid culture from a murine KPC tumor. As before, we performed autoradiography comparing 3 H capecitabine to the gemcitabine analog 18 F-FAC. The metabolism of capecitabine in this model was studied through LC-MS of tumor tissue. The autoradiographs confirmed that the 3 H label from capecitabine was much more uniformly distributed through the tumor than the 18 F from the gemcitabine analog. LC-MS revealed that approximately 75% of the molar mass of capecitabine had been converted into 5 FU or pre-5 FU compounds. The remainder had been converted into nontoxic species. Therapeutically relevant capecitabine metabolites achieve a relatively even distribution in this pancreatic cancer model, in contrast to the gemcitabine analog 18 F-FAC. In a human xenograft model, (BxPC3), the 3 H label from capecitabine was also uniformly spread across the tumor autoradiographs. However, at 2 h post-administration the metabolism of capecitabine had proceeded further and the bulk of the agent was in the form of nontoxic species.

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.

A Liposomal Gemcitabine, FF-10832, Improves Plasma Stability, Tumor Targeting, and Antitumor Efficacy of Gemcitabine in Pancreatic Cancer Xenograft Models

Purpose

The clinical application of gemcitabine (GEM) is limited by its pharmacokinetic properties. The aim of this study was to characterize the stability in circulating plasma, tumor targeting, and payload release of liposome-encapsulated GEM, FF-10832.

Methods

Antitumor activity was assessed in xenograft mouse models of human pancreatic cancer. The pharmacokinetics of GEM and its active metabolite dFdCTP were also evaluated.

Results

In mice with Capan-1 tumors, the dose-normalized areas under the curve (AUCs) after FF-10832 administration in plasma and tumor were 672 and 1047 times higher, respectively, than after using unencapsulated GEM. The tumor-to-bone marrow AUC ratio of dFdCTP was approximately eight times higher after FF-10832 administration than after GEM administration. These results indicated that liposomal encapsulation produced long-term stability in circulating plasma and tumor-selective targeting of GEM. In mice with Capan-1, SUIT-2, and BxPC-3 tumors, FF-10832 had better antitumor activity and tolerability than GEM. Internalization of FF-10832 in tumor-associated macrophages (TAMs) was revealed by flow cytometry and confocal laser scanning microscopy, and GEM was efficiently released from isolated macrophages of mice treated with FF-10832. These results suggest that TAMs are one of the potential reservoirs of GEM in tumors.

Conclusion

This study found that FF-10832 had favorable pharmacokinetic properties. The liposomal formulation was more effective and tolerable than unencapsulated GEM in mouse xenograft tumor models. Hence, FF-10832 is a promising candidate for the treatment of pancreatic cancer.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11095-021-03045-5.

Modeling pancreatic cancer in mice for experimental therapeutics

Pancreatic ductal adenocarcinoma (PDAC) is a highly aggressive malignancy that is characterized by early metastasis, low resectability, high recurrence, and therapy resistance. The experimental mouse models have played a central role in understanding the pathobiology of PDAC and in the preclinical evaluation of various therapeutic modalities. Different mouse models with targetable pathological hallmarks have been developed and employed to address the unique challenges associated with PDAC progression, metastasis, and stromal heterogeneity. Over the years, mouse models have evolved from simple cell line-based heterotopic and orthotopic xenografts in immunocompromised mice to more complex and realistic genetically engineered mouse models (GEMMs) involving multi-gene manipulations. The GEMMs, mostly driven by KRAS mutation(s), have been widely accepted for therapeutic optimization due to their high penetrance and ability to recapitulate the histological, molecular, and pathological hallmarks of human PDAC, including comparable precursor lesions, extensive metastasis, desmoplasia, perineural invasion, and immunosuppressive tumor microenvironment. Advanced GEMMs modified to express fluorescent proteins have allowed cell lineage tracing to provide novel insights and a new understanding about the origin and contribution of various cell types in PDAC pathobiology. The syngeneic mouse models, GEMMs, and target-specific transgenic mice have been extensively used to evaluate immunotherapies and study therapy-induced immune modulation in PDAC yielding meaningful results to guide various clinical trials. The emerging mouse models for parabiosis, hepatic metastasis, cachexia, and image-guided implantation, are increasingly appreciated for their high translational significance. In this article, we describe the contribution of various experimental mouse models to the current understanding of PDAC pathobiology and their utility in evaluating and optimizing therapeutic modalities for this lethal malignancy.

Predicting Gemcitabine Delivery by 18F-FAC PET in Murine Models of Pancreatic Cancer

¹⁸F-FAC (2'-deoxy-2'-¹⁸F-fluoro-β-d-arabinofuranosylcytosine) has close structural similarity to gemcitabine and thus offers the potential to image drug delivery to tumors. We compared tumor ¹⁸F-FAC PET images with ¹⁴C-gemcitabine levels, established ex vivo, in 3 mouse models of pancreatic cancer. We further modified tumor gemcitabine levels with injectable PEGylated recombinant human hyaluronidase (PEGPH20) to test whether changes in gemcitabine would be tracked by ¹⁸F-FAC. Methods: ¹⁸F-FAC was synthesized as described previously. Three patient-derived xenograft (PDX) models were grown in the flanks of NSG mice. Mice were given PEGPH20 or vehicle intravenously 24 h before coinjection of ¹⁸F-FAC and ¹⁴C-gemcitabine. Animals were euthanized and imaged 1 h after tracer administration. Tumor and muscle uptake of both ¹⁸F-FAC and ¹⁴C-gemcitabine was obtained ex vivo. The efficacy of PEPGPH20 was validated through staining with hyaluronic acid binding protein. Additionally, an organoid culture, initiated from a KPC (Pdx-1 Cre LSL-Kras^G12D LSL-p53^R172H) tumor, was used to generate orthotopically growing tumors in C57BL/6J mice, and these tumors were then serially transplanted. Animals were injected with PEGPH20 and ¹⁴C-gemcitabine as described above to validate increased drug uptake by ex vivo assay. PET/MR images were obtained using a PET insert on a 7-T MR scanner. Animals were imaged immediately before injection with PEGPH20 and again 24 h later. Results: Tumor-to-muscle ratios of ¹⁴C-gemcitabine and ¹⁸F-FAC correlated well across all PDX models and treatments (R ² = 0.78). There was a significant increase in the tumor PET signal in PEGPH20-treated PDX animals, and this signal was matched in ex vivo counts for 2 of 3 models. In KPC-derived tumors, PEGPH20 raised ¹⁴C-gemcitabine levels (tumor-to-muscle ratio of 1.9 vs. 2.4, control vs. treated, P = 0.013). PET/MR ¹⁸F-FAC images showed a 12% increase in tumor ¹⁸F-FAC uptake after PEGPH20 treatment (P = 0.023). PEGPH20-treated animals uniformly displayed clear reductions in hyaluronic acid staining. Conclusion: ¹⁸F-FAC PET was shown to be a good surrogate for gemcitabine uptake and, when combined with MR, to successfully determine drug uptake in tumors growing in the pancreas. PEGPH20 had moderate effects on tumor uptake of gemcitabine.

Comparing the intra-tumoral distribution of Gemcitabine, 5-Fluorouracil, and Capecitabine in a murine model of pancreatic ductal adenocarcinoma

PURPOSE

To develop a technique to compare the intra-tumoral distribution of the drug gemcitabine, its surrogate [18F]-fluoroarabinocytosine ([18F]-FAC) and related chemotherapeutics 5-FU and capecitabine in a pre-clinical model of pancreatic ductal adenocarcinoma (PDAC).

EXPERIMENTAL DESIGN

Using a KPC-organoid derived model of PDAC, we obtained autoradiographic images of the tumor distribution of, [14C]-gemcitabine, [14C]-5-FU, [3H]-capecitabine. These were compared indirectly by co-administering [18F]-FAC, a close analog of gemcitabine with a proven equivalent intra-tumor distribution. The short half-life of 18F allows for clean separation of 3H/14C labeled drugs in specimens by dual isotope digital autoradiography. Autoradiographic images of [14C]-gemcitabine, [3H]-capecitabine and [14C]-5-FU were each correlated to [18F]-FAC on a pixel-by-pixel basis. The tumor drug penetration was compared using cumulative histograms.

RESULTS

Gemcitabine distribution correlated strongly with FAC as expected. 5-FU also gave a similar microdistribution to that of FAC, whereas no correlation was found between capecitabine or its metabolic products and FAC distribution. Accumulation of Gemcitabine and 5-FU was lower in hypoxic regions of the tumor, whereas no such correlation was observed for capecitabine and its metabolites.

CONCLUSIONS

Gemcitabine and 5-FU target the same regions of the tumor, leaving hypoxic cells untreated. Capecitabine metabolites penetrate further into the tumor but it is yet to be determined whether these metabolites are the active form of the drug.

3D-printed PEEK reactors and development of a complete continuous flow system for chemical synthesis

This paper presents the development of milli- and microfluidic reactors made of polyether ether ketone (PEEK) and 3D-printed equipment for a complete continuous flow system.

Translational molecular imaging in exocrine pancreatic cancer

Effective treatment for pancreatic cancer remains challenging, particularly the treatment of pancreatic ductal adenocarcinoma (PDAC), which makes up more than 95% of all pancreatic cancers. Late diagnosis and failure of chemotherapy and radiotherapy are all too common, and many patients die soon after diagnosis. Here, we make the case for the increased use of molecular imaging in PDAC preclinical research and in patient management.

Elastography Can Map the Local Inverse Relationship between Shear Modulus and Drug Delivery within the Pancreatic Ductal Adenocarcinoma Microenvironment

PURPOSE

High tissue pressure prevents chemotherapeutics from reaching the core of pancreatic tumors. Therefore, targeted therapies have been developed to reduce this pressure. While point probes have shown the effectiveness of these pressure-reducing therapies via single-location estimates, ultrasound elastography is now widely available as an imaging technique to provide real-time spatial maps of shear modulus (tissue stiffness). However, the relationship between shear modulus and the underlying tumor microenvironmental causes of high tissue pressure has not been investigated. In this work, elastography was used to investigate how shear modulus influences drug delivery in situ, and how it correlates with collagen density, hyaluronic acid content, and patent vessel density-features of the tumor microenvironment known to influence tissue pressure.

EXPERIMENTAL DESIGN

Intravenous injection of verteporfin, an approved human fluorescent drug, was used in two pancreatic cancer xenograft models [AsPC-1 (n = 25) and BxPC-3 (n = 25)].

RESULTS

Fluorescence intensity was higher in AsPC-1 tumors than in BxPC-3 tumors (P < 0.0001). Comparing drug uptake images and shear wave elastographic images with histologic images revealed that: (i) drug delivery and shear modulus were inversely related, (ii) shear modulus increased linearly with increasing collagen density, and (iii) shear modulus was marginally correlated with the local assessment of hyaluronic acid content.

CONCLUSIONS

These results demonstrate that elastography could guide targeted therapy and/or identify patients with highly elevated tissue pressure.See related commentary by Nia et al., p. 2024.

18F-fluoromisonidazole predicts evofosfamide uptake in pancreatic tumor model

Background

Quantitative imaging can facilitate patient stratification in clinical trials. The hypoxia-activated prodrug evofosfamide recently failed a phase III trial in pancreatic cancer. However, the study did not attempt to select for patients with hypoxic tumors. We tested the ability of ¹⁸F-fluoromisonidazole to predict evofosfamide uptake in an orthotopic xenograft model (BxPC3).

Methods

Two forms of evofosfamide were used: (1) labeled on the active moiety (³H) and (2) on the hypoxia targeting nitroimidazole group (¹⁴C). Tumor uptake of evofosfamide and ¹⁸F-fluoromisonidazole was counted ex vivo. Autoradiography of ¹⁴C and ¹⁸F coupled with pimonidazole immunohistochemistry revealed the spatial distributions of prodrug, radiotracer, and hypoxia.

Results

There was significant individual variation in ¹⁸F-fluoromisonidazole uptake, and a significant correlation between normalized ¹⁸F-fluoromisonidazole and both ³H-labeled and ¹⁴C-labeled evofosfamide. ¹⁸F-fluoromisonidazole and ¹⁴C-evofosfamide both localized in hypoxic regions as identified by pimonidazole.

Conclusion

¹⁸F-fluoromisonidazole predicts evofosfamide uptake in a preclinical pancreatic tumor model.

TMSOTf assisted synthesis of 2'-deoxy-2'-[18F]fluoro-β-D-arabinofuranosylcytosine ([18F]FAC)

[¹⁸F]FAC (2’-deoxy-2’-[¹⁸F]fluoro-β-D-arabinofuranosylcytosine, 1) is a versatile probe for imaging deoxycytidine kinase (dCK) expression levels in vivo. dCK is responsible for phosphorylation of deoxycytidine (dC, 2) and other nucleoside analogs, plays a key role in immune activation and has demonstrated to be one of the key enzymes in activating nucleoside based drugs including gemcitabine. Reported synthesis of [¹⁸F]FAC is high yielding but is quite challenging requiring bromination using HBr and careful drying of excess HBr which is critical for successful synthesis. Here in we report a simplified trimethylsilyl trifluoromethanesulfonate (TMSOTf) assisted synthesis of [¹⁸F]FAC eliminating the need of bromination and drying. [¹⁸F]FAC (β-anomer) was synthesized with average isolated decay corrected yield of 10.59 + 4.2% (n = 6) with radiochemical purity of >98% and total synthesis time of 158 + 19 min.