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

Abstract

To develop a technique to compare the intra-tumoral distribution of the drug gemcitabine, its surrogate [ 18 F]-fluoroarabinocytosine ([ 18 F]-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, [ 14 C]-gemcitabine, [ 14 C]-5-FU, [ 3 H]-capecitabine. These were compared indirectly by co-administering [ 18 F]-FAC, a close analog of gemcitabine with a proven equivalent intra-tumor distribution. The short half-life of 18 F allows for clean separation of 3 H/ 14 C labeled drugs in specimens by dual isotope digital autoradiography. Autoradiographic images of [ 14 C]-gemcitabine, [ 3 H]-capecitabine and [ 14 C]-5-FU were each correlated to [ 18 F]-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.

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

“…For the murine model we examined, 75% of the drug in the tumor is still in the form of either 5 FU or a 5 FU precursor. Previously we showed that directly injected 14 C-5 FU had a heterogeneous autoradiographic distribution more closely resembling gemcitabine and FAC than capecitabine, 9 and this supports our proposal that the additional delay required for activation of the capecitabine pro-drug improves its intra-tumoral distribution. These results are encouraging for capecitabine in pancreatic therapy, as it may have the ability to overcome the pen- of capecitabine radiolabel but as this is accompanied by a more extensive metabolism of capecitabine, it is not clear whether the active species are also evenly distributed through the tumor.…”

“…The H&E image was matched to the brightfield image, based on tumor outline, and the autoradiographs were matched to the image based on the markers. To reduce noise in the 3 H images, adjacent sections were registered in ImageJ with the StackReg plugin, and a median image obtained, as described previously 9 . The H&E images were used to exclude nonviable tissue from the autoradiographs; histograms of pixel intensity values were constructed, comparing 18 F‐FAC to 3 H capecitabine.…”

“…In this context, we recently published observations showing that when autoradiography of radiolabeled drug was employed, gemcitabine and 5 FU—both mainstays of pancreatic chemotherapy—were very nonuniformly distributed through tumor mass in KPC‐derived tumors 9 . However, capecitabine, which is a 5 FU prodrug, yielded autoradiograph images that were essentially uniform across the tumor area.…”

“…In this context, we recently published observations showing that when autoradiography of radiolabeled drug was employed, gemcitabine and 5 FU-both mainstays of pancreatic chemotherapy-were very nonuniformly distributed through tumor mass in KPC-derived tumors. 9 However, capecitabine, which is a 5 FU prodrug, yielded autoradiograph images that were essentially uniform across the tumor area. A significant caveat of such results is that as the autoradiographs report on the radiolabel, and considering capecitabine's extensive metabolic fates, it is challenging to characterize whether signal originates from active or inactive metabolites.…”

Modeling pancreatic cancer in mice for experimental therapeutics

“…The optimization of chemotherapy and radiotherapy regimen in preclinical PDAC models is highly challenging because the small size animals differ in body weight, organ size, and basal metabolic rate (BMR), which are critical parameters for the chemotherapy dose optimization and for the delivery of radiotherapy. Despite that, major chemotherapies including gemcitabine, FOLFIRINOX, nab-paclitaxel, and capecitabine, have been optimized in mouse PDAC models [114,[227][228][229][230][231]. Earlier preclinical evaluations of chemotherapies and radiotherapy were intended to assess their effects on tumor growth, metastasis, and therapeutic resistance [18,[232][233][234][235][236].…”