Characterization of CC-531 as a Rat Model of Colorectal Liver Metastases

Distinguishing metabolic signals of liver tumors from surrounding liver cells using hyperpolarized 13 C MRI and gadoxetate

PURPOSE

To use the hepatocyte-specific gadolinium-based contrast agent gadoxetate combined with hyperpolarized (HP) [1-13 C]pyruvate MRI to selectively suppress metabolic signals from normal hepatocytes while preserving the signals arising from tumors.

METHODS

Simulations were performed to determine the expected changes in HP 13 C MR signal in liver and tumor under the influence of gadoxetate. CC531 colon cancer cells were implanted into the livers of five Wag/Rij rats. Liver and tumor metabolism were imaged at 3 T using HP [1-13 C] pyruvate chemical shift imaging before and 15 min after injection of gadoxetate. Area under the curve for pyruvate and lactate were measured from voxels containing at least 75% of normal-appearing liver or tumor.

RESULTS

Numerical simulations predicted a 36% decrease in lactate-to-pyruvate (L/P) ratio in liver and 16% decrease in tumor. In vivo, baseline L/P ratio was 0.44 ± 0.25 in tumors versus 0.21 ± 0.08 in liver (p = 0.09). Following administration of gadoxetate, mean L/P ratio decreased by an average of 0.11 ± 0.06 (p < 0.01) in normal-appearing liver. In tumors, mean L/P ratio post-gadoxetate did not show a statistically significant change from baseline. Compared to baseline levels, the relative decrease in L/P ratio was significantly greater in liver than in tumors (-0.52 ± 0.16 vs. -0.19 ± 0.25, p < 0.05).

CONCLUSIONS

The intracellular hepatobiliary contrast agent showed a greater effect suppressing HP 13 C MRI metabolic signals (through T1 shortening) in normal-appearing liver when compared to tumors. The combined use of HP MRI with selective gadolinium contrast agents may allow more selective imaging in HP 13 C MRI.

Enhanced Therapeutic Efficacy of the Nanoscale Fluoropyrimidine Polymer CF10 in a Rat Colorectal Cancer Liver Metastasis Model

Combination chemotherapy regimens that include fluoropyrimidine (FP) drugs, e.g., 5-fluorouracil (5-FU), are central to the treatment of colorectal cancer liver metastases (CRLMs), a major cause of cancer mortality. We tested a second-generation FP polymer, CF10, in a CC531/WAGRij syngeneic orthotopic rat model of liver metastasis to determine if CF10 improved response relative to 5-FU. CF10 displayed increased potency relative to 5-FU in CC531 rat colorectal cancer cells based on clonogenic assay results and caused increased apoptosis, as shown using a live/dead assay. The increased potency of CF10 to CC531 cells was associated with increased replication stress, as assessed by Western blot for biomarkers of ATR/Chk1 and ATM/Chk2 pathway activation. CF10 dosed to deliver equivalent FP content as an established dose of 5-FU in rats (50 mg/kg) did not cause weight loss in WAGRij rats even when combined with ethynyl uracil (EU), an inhibitor of dihydropyrimidine dehydrogenase, the enzyme primarily responsible for 5-FU degradation in the liver. In contrast, 5-FU caused significant weight loss that was exacerbated in combination with EU. Importantly, CF10 was significantly more effective than 5-FU at inhibiting tumor progression (~90% reduction) in the CC531/WAG/Rij CRLM model. Our results reveal strong potential for CF10 to be used for CRLM treatment.

Hepatic arterial infusion with nanoliposomal irinotecan leads to significant regression of tumor size of colorectal liver metastases in a CC531 rat model

Long-term therapy for unresectable colorectal liver metastases remains challenging. Intraarterial treatments aim to avoid systemic adverse effects of chemotherapy. Nanoliposomal cytotoxic drugs manage to increase the drug concentration within the tumor while reducing toxicity in healthy tissue.  In this study we analyzed the effect of hepatic arterial infusion (HAI) with nanoliposomal irinotecan with or without the combination of embolization particles in a rat model for colorectal liver metastases. For the study 32 WAG/Rij rats received subcapsular tumor implantation with CC531 rat colonic adenocarcinoma cells. After ten days tumor size was assessed via ultrasound and animals underwent HAI. One group served as control receiving NaCl 0.9 % (Sham), the three treatment groups received either nanoliposomal irinotecan (HAI nal iri), Embocept® S (HAI Embo) or Embocept® S and nanoliposomal irinotecan (HAI Embo+nal iri). Three days after treatment animals were sacrificed after assessment of tumor size. As a result all treatment groups showed a significant reduction in tumor growth compared to Sham (p<0.05). Expression of the apoptosis marker caspase-3 was enhanced in HAI nal iri and HAI Embo+nal iri compared to Sham and HAI Embo and  even significantly enhanced after HAI Embo+nal iri in comparison to Sham (p<0.05). We were able to show that HAI with Embocept® S led to significantly reduced tumor growth while HAI with nanoliposomal irinotecan alone or in combination with Embocept® S even led to a reduction of tumor size. Thus, we demonstrate that intraarterial treatment with nanoliposomal irinotecan effectively inhibits tumor growth in a rat model of colorectal liver metastases and demands further investigation.

Curcumin Reduces Colorectal Cancer Cell Proliferation and Migration and Slows In Vivo Growth of Liver Metastases in Rats

Background: New therapeutic approaches are an essential need for patients suffering from colorectal cancer liver metastases. Curcumin, a well-known plant-derived polyphenol, has been shown to play a role in the modulation of multiple signaling pathways involved in the development and progression of certain cancer cells in vitro. This study aims to assess the anti-tumor effect of curcumin on CC531 colorectal cancer cells, both in vitro and in vivo. Methods: On CC531 cultures, the cell viability and cell migration capacity were analyzed (wound healing test) 24, 48, and 72 h after treatment with curcumin (15, 20, 25, or 30 µM). Additionally, in WAG/RijHsd tumor-bearing rats, the total and individual liver lobe tumor volume was quantified in untreated and curcumin-treated animals (200 mg/kg/day, oral). Furthermore, serum enzyme measurements (GOT, GPT, glucose, bilirubin, etc.) were carried out to assess the possible effects on the liver function. Results: In vitro studies showed curcumin’s greatest effects 48h after application, when all of the tested doses reduced cell proliferation by more than 30%. At 72 h, the highest doses of curcumin (25 and 30 µM) reduced cell viability to less than 50%. The wound healing test also showed that curcumin inhibits migration capacity. In vivo, curcumin slowed down the tumor volume of liver implants by 5.6-fold (7.98 ± 1.45 vs. 1.41 ± 1.33; p > 0.0001). Conclusions: Curcumin has shown an anti-tumor effect against liver implants from colorectal cancer, both in vitro and in vivo, in this experimental model.

A novel irinotecan-lipiodol nanoemulsion for intravascular administration: pharmacokinetics and biodistribution in the normal and tumor bearing rat liver

Colorectal cancer is one of the most common cancers in the United States and treatment options are limited for patients who develop liver metastases. Several chemotherapeutic regimens have been used for transvascular liver-directed therapy in the treatment of colorectal liver metastases without clear evidence of superiority of one therapy over another. We describe the development of a novel nanoemulsion through combining irinotecan (IRI), a first line systemic agent used for the treatment of colon cancer, with lipiodol, an oily contrast medium derived from poppy seed oil, and evaluated its pharmacokinetic and biodistribution profile as a function of portal venous chemoembolization (PVCE) versus transarterial chemoembolization (TACE) delivery. The Tessari technique was used to create a stable emulsion (20 mg IRI mixed with 2 mL lipiodol) with resultant particle size ranging from 28.9 nm to 56.4 nm. Pharmacokinetic profile established through venous sampling in Buffalo rats demonstrate that the area under the curve (AUC_0−∞) of IRI was significantly less after PVCE with IRI-lipiodol as compared to IRI alone (131 vs. 316 µg*min/mL, p-value = .023), suggesting significantly higher amounts of IRI retention in the liver with the IRI-lipiodol nanoemulsion via first-pass extraction. Subseqent biodistribution studies in tumor-bearing WAG/Rjj rats revealed more IRI present in the tumor following TACE versus PVCE (29.19 ± 12.33 µg/g versus 3.42 ± 1.62; p-value = .0033) or IV (29.19 ± 12.33 µg/g versus 1.05 ± 0.47; p-value = .0035). The IRI-lipiodol nanoemulsion demonstrated an acceptable hepatotoxicity profile in all routes of administration. In conclusion, the IRI-lipiodol nanoemulsion via TACE showed promise and warrants further investigation as an option for the treatment of metastatic colorectal cancer.

Localized and triggered release of oxaliplatin for the treatment of colorectal liver metastasis

Purpose: The aim of this study was to develop and evaluate a liposome formulation that deliver oxaliplatin under magnetic field stimulus in high concentration to alleviate the off-target effects in a rat model of colorectal liver metastases (CRLM).

Materials and Methods: Hybrid liposome-magnetic nanoparticles loaded with Cy5.5 dye and oxaliplatin (L-NIR- Fe₃O₄/OX) were synthesized by using thermal decomposition method. CRLM (CC-531) cell viability was assessed and rats orthotopically implanted with CC-531 cells were treated with L-NIR-Fe₃O₄/OX or by drug alone via different routes, up to 3 cycles of alternating magnetic field (AMF). Optical and MR imaging was performed to assess the targeted delivery. Biodistribution and histology was performed to determine the distribution of oxaliplatin.

Results: L-NIR-Fe₃O₄/OX presented a significant increase of oxaliplatin release (~18%) and lower cell viability after AMF exposure (p<0.001). Optical imaging showed a significant release of oxaliplatin among mesenteric vein injected (MV) group of animals. MR imaging on MV injected animals showed R2* changes in the tumor regions at the same regions immediately after infusion compared to the surrounding liver (p<0.001). Biodistribution analysis showed significantly higher levels of oxaliplatin in liver tissues compared to lungs (p<0.001) and intestines (p<0.001) in the MV animals that received AMF after L-NIR- Fe₃O₄/OX administration. Large tumor necrotic zones and significant improvement in the survival rates were noted in the MV animals treated with AMF.

Conclusion: AMF triggers site selective delivery of oxaliplatin at high concentrations and improves survival outcomes in colorectal liver metastasis tumor bearing rats.

Spectral photon-counting CT imaging of colorectal peritoneal metastases: initial experience in rats

Computed tomography imaging plays a major role in the preoperative assessment of tumor burden by providing an accurate mapping of the distribution of peritoneal metastases (PM). Spectral Photon Counting Computed Tomography (SPCCT) is an innovative imaging modality that could overcome the current limitations of conventional CT, offering not only better spatial resolution but also better contrast resolution by allowing the discrimination of multiple contrast agents. Based on this capability, we tested the feasibility of SPCCT in the detection of PM at different time of tumor growth in 16 rats inoculated with CC531 cells using dual-contrast injection protocols in two compartments (i.e. intravenous iodine and intraperitoneal gadolinium or the reverse protocol), compared to surgery. For all peritoneal regions and for both protocols, sensitivity was 69%, specificity was 100% and accuracy was 80%, and the correlation with surgical exploration was strong (p = 0.97; p = 0.0001). No significant difference was found in terms of diagnostic performance, quality of peritoneal opacification or diagnostic quality between the 2 injection protocols. We also showed poor vascularization of peritoneal metastases by measuring low concentrations of contrast agent in the largest lesions using SPCCT, which was confirmed by immunohistochemical analyses. In conclusion, SPCCT using dual-contrast agent injection protocols in 2 compartments is a promising imaging modality to assess the extent of PM in a rat model.

Animal Models for the Evaluation of Theranostic Radiopharmaceuticals

BACKGROUND

Theranostic is a new field of medicine that combines diagnosis and patient- specific targeted treatment. In the theranostic approach, it is aimed to detect diseased cells by using targeted molecules using disease-specific biological pathways and then destroy them by cellular irradiation without damaging other tissues. Diagnostic tests guide the use of specific therapeutic agents by demonstrating the presence of the receptor/molecule on the target tissue. As the therapeutic agent is administered to patients who have a positive diagnostic test, the efficacy of treatment in these patients is largely guaranteed. As therapeutic efficacy can be predicted by therapeutic agents, it is also possible to monitor the response to treatment. Many diagnostic and therapeutic procedures in nuclear medicine are classified as theranostic. ¹³¹I treatment and scintigraphy are the best examples of the theranostic application. Likewise, ¹⁷⁷Lu / ⁹⁰Y octreotate for neuroendocrine tumors, ¹⁷⁷Lu PSMA for metastatic or treatment-resistant prostate cancer, ⁹⁰Y SIRT for metastatic liver cancer, and ²²³Ra for bone metastasis of prostate cancer are widely used. Moreover, nanoparticles are one of the most rapidly developing subjects of theranostics. Diagnostic and therapeutic agents that show fluorescent, ultrasonic, magnetic, radioactive, contrast, pharmacological drug or antibody properties are loaded into the nanoparticle to provide theranostic use.

METHODS

This article reviewed general aspects of preclinical models for theranostic research, and presented examples from the literature.

CONCLUSION

To achieve successful results in rapidly accelerating personalized treatment research of today, the first step is to conduct appropriate preclinical studies.

The role of mouse models in colorectal cancer research-The need and the importance of the orthotopic models

Colorectal cancer is a worldwide health burden, with high incidence and mortality, especially in the advanced stages of the disease. Preclinical models are very important and valuable to discover and validate early and specific biomarkers as well as new therapeutic targets. In order to accomplish that, the animal models must replicate the clinical evolution of the disease in all of its phases. In this article, we review the existent mouse models, with their strengths and weaknesses in the replication of human cancer disease progression, with major focus on orthotopic models.

Hepatic arterial infusion of irinotecan and EmboCept® S results in high tumor concentration of SN-38 in a rat model of colorectal liver metastases

Intraarterial chemotherapy for colorectal liver metastases (CRLM) can be applied alone or together with embolization particles. It remains unclear whether different types of embolization particles lead to higher intratumoral drug concentration. Herein, we quantified the concentrations of CPT-11 and its active metabolite SN-38 in plasma, liver and tumor tissue after hepatic arterial infusion (HAI) of irinotecan, with or without further application of embolization particles, in a rat model of CRLM. Animals underwent either systemic application of irinotecan, or HAI with or without the embolization particles Embocept^® S and Tandem™. Four hours after treatment concentrations of CPT-11 and SN-38 were analyzed in plasma, tumor and liver samples by high-performance liquid chromatography. Additionally, DNA-damage and apoptosis were analyzed immunohistochemically. Tumor tissue concentrations of SN-38 were significantly increased after HAI with irinotecan and EmboCept^® S compared to the other groups. The number of apoptotic cells was significantly higher after both HAI with irinotecan and EmboCept^® S or Tandem™ loaded with irinotecan compared to the control group. HAI with irinotecan and EmboCept^® S resulted in an increased SN-38 tumor concentration. Both HAI with irinotecan and EmboCept^® S or Tandem™ loaded with irinotecan were highly effective with regard to apoptosis.

Vascular Interventional Radiology-Guided Photothermal Therapy of Colorectal Cancer Liver Metastasis with Theranostic Gold Nanorods

We report sub-100 nm optical/magnetic resonance (MR)/X-ray contrast-bearing theranostic nanoparticles (TNPs) for interventional image-guided photothermal therapy (PTT) of solid tumors. TNPs were composed of Au@Gd2O3:Ln (Ln = Yb/Er) with X-ray contrast (∼486 HU; 1014 NPs/mL, 0.167 nM) and MR contrast (∼1.1 × 108 mM-1 S-1 at 9.4 T field strength). Although TNPs are deposited in tumors following systemic administration via enhanced permeation and retention effect, the delivered dose to tumors is typically low; this can adversely impact the efficacy of PTT. To overcome this limitation, we investigated the feasibility of site-selective hepatic image-guided delivery of TNPs in rats bearing colorectal liver metastasis (CRLM). The mesenteric vein of tumor-bearing rats was catheterized, and TNPs were infused into the liver by accessing the portal vein for site-selective delivery. The uptake of TNPs with hepatic delivery was compared with systemic administration. MR imaging confirmed that delivery via the hepatic portal vein can double the CRLM tumor-to-liver contrast compared with systemic administration. Photothermal ablation was performed by inserting a 100 μm fiber-optic carrying 808 nm light via a JB1, 3-French catheter for 3 min under DynaCT image guidance. Histological analysis revealed that the thermal damage was largely confined to the tumor region with minimal damage to the adjacent liver tissue. Transmission electron microscopy imaging validated the stability of core-shell structure of TNPs in vivo pre- and post-PTT. TNPs comprising Gd-shell-coated Au nanorods can be effectively employed for the site-directed PTT of CRLM by leveraging interventional radiology methods.