Validation of a new experimental model of colon cancer

Colonoscopic injection for murine solid cecal cancer model

BACKGROUND

The validity of current animal colon cancer models is questionable. This study was performed to evaluate whether colonoscopic injection of a murine colon cancer cell line into the cecal wall of immunocompetent rats leads to a solid tumor.

METHODS

A bolus of bowel prep was given to BD-IX rats. Anesthesia was injected intraperitoneally. Video fiberscope allowed for irrigation and suction. Failure was inability to reach/inject cecum. Procedure was performed by four surgeons; 100 μl of colon tumor cell suspension (DHD/K12TRb; 10 million cells in 0.1 ml) was injected into cecal wall with 23-gauge needle placed on 3 mm wire resulting in a blister. Rats were allowed to recover. Solid tumor growth was measured at scheduled necropsy at 4 weeks. Sample size (107 rats: type I error 0.05; power 80%) was based on a pilot study. Data were presented as median (range).

RESULTS

A total of 107 male BD-IX retired breeders weighing 356 g (range 256-432 g) underwent colonoscopy with submucosal injection of cecal wall. A single solid cecal cancer was identified in 98 (91.5%) rats at scheduled necropsy. Histology confirmed adenocarcinoma with tumor size of 4 mm (range 2.6-8.4 mm). Peritoneal carcinomatosis was found in ten (9.3%) rats. Distant metastases were found in three (2.8%) rats. Complications occurred in four (3.8%) rats: two aspirations and two colon perforations.

CONCLUSIONS

A solid cecal tumor without carcinomatosis or metastasis has been developed by colonoscopic injection of a rat colon cancer cell line in 79% of immunocompetent rats.

Application of a solid tumor model to evaluate tumor recurrence after an open or laparoscopic rectal resection in rats

PURPOSE

We used a solid tumor model to evaluate the influence of laparotomy versus laparoscopy on tumor growth after curative resection for rectal cancer in rats.

METHODS

Colon tumor cells (DHD/K12/TRb) were administered intraperitoneally in 15 rats, which were used as solid tumor donors. Twenty-one days later, a 20-mg piece was then implanted in the rectal submucosa of the study rats (n=45). Animals were randomized into 3 groups for rectal resection either open or laparoscopic using either carbon dioxide (CO2) or helium for pneumoperitoneum. Autopsy took place 21 days after resection and tumor recurrence was evaluated.

RESULTS

Port-site metastasis was observed after laparoscopy with CO2 (1 animal) and helium (1), whereas intraperitoneal tumor growth was detected in 2 and 3 animals of these groups. No tumor recurrence was observed after open surgery.

CONCLUSIONS

Our solid tumor model is a novel neoplastic model that might simulate the clinical situation of an upper rectal carcinoma. It might be helpful to develop new protocols in studying solid tumor biology and different surgical procedures for cancer to address problematic issues in oncologic research.

First surgical tumour reduction of peritoneal surface malignancy in a rat's model

Surgical therapy of peritoneal surface malignancy from colorectal origin in combination with Hyperthermic Intraoperative Peritoneal Chemotherapy (HIPEC) has now become an established treatment approach in very few specialised centres. A peritonectomy procedure is possible to perform with additional HIPEC in patients. An experimental model to simulate peritonectomy procedure and HIPEC does not exist so far in rats. Nevertheless, animal models seem to be very important for evaluation of new therapeutic opportunities and toxicity of different multimodal therapies. In a first step we analysed the surgical tumour debulking of peritoneal surface malignancy in rats. A peritoneal surface malignancy from colonic origin was induced in 75 male BD IX rats. Twenty one days after induction of peritoneal surface malignancy rats were randomised and animals intend to create an operation with surgical tumour debulking. There was no tumour growth in two animals. The aim of the peritonectomy procedure was the complete tumour reduction. In this study the results of the surgical approach will be described. A complete tumour reduction (R0) was achieved in 34 animals. In 39 rats a macroscopic tumour deposit was left behind (R2). The intraoperative experimental Peritoneal Cancer Index (ePCI) was used to describe tumour weight and number of tumour inoculations. Both parameters were found to be dependent factors of complete tumour reduction. Six animals died due to therapeutical interventions. Surgical tumour debulking in rats with peritoneal surface malignancy is possible with high reliability and a low mortality rate. This animal model could be an important step for investigation of multimodal treatment options and toxicity in treatment regimens of peritoneal surface malignancy.

Development of a total colonoscopy rat model with endoscopic submucosal injection of the cecal wall

BACKGROUND

Experimental models of colorectal tumor require either laparotomy for induction or anastomosis following resection. The long murine cecum avoids the need for an anastomosis, making the cecum the preferred site for induction. This study aimed to evaluate total colonoscopy with submucosal injection of cecal wall (TCWI) in rats in terms of failure rate (FR), complication rate (CR), and reproducibility (R).

METHODS

A bolus of bowel prep was given. Anesthesia was injected intraperitoneally. A video fiberscope (5.9 mm outer diameter, 180/90 degrees up/down bending, 100/100 degrees right/left bending, 103 cm working length, 120 degrees view field, and 2.0 mm channel) allowed for irrigation and suction. Saline 1 ml was injected in the cecal wall through a 4-mm-long, 23-gauge needle placed on a 3-mm wire, resulting in a blister. FR was a failure to reach and inject the cecum. Rats were allowed to recover. CR was measured at necropsy. R was assessed by comparing TCWI time, FR, and CR for three investigators. Sample size of 120 (type I error, 0.05; power, 80%) was based on a pilot study. Data are presented as median (range).

RESULTS

A total of two of 122 rats (1.6%) died after prep or anesthesia. Bowel prep resulted in 99.1% evacuation of solid feces. A total of 120 male Sprague-Dawley retired breeders weighing 592 g (range, 349-780) underwent TCWI. Scope depth was 28 cm (range, 20-36). Irrigating fluid was 290 ml (range, 100-600). TCWI time was 7 min (range, 4-28). FR was 4%. In three failed cases, the scope reached the ascending colon. CR was 2%. There were two perforations in the ascending colon. All three operators had similar TCWI time (p = 0.673), FR (p > 0.1), and CR (p > 0.1). A total of 98.3% of rats survived to planned sacrifice. At 48-h necropsy, the injection site was macroscopically identified in 118 rats.

CONCLUSIONS

A safe and reproducible TCWI rat model has been achieved, which may provide a valuable tool in the future for studies of solid colorectal tumors.

Injection of colorectal cancer cells in mesenteric and antimesenteric sides of the colon results in different patterns of metastatic diffusion: an experimental study in rats

Background

This experimental study was designed to investigate the differences in pattern of local growth and diffusion of colorectal cancer cells injected into either mesenteric (M) or antimesenteric (AM) sides of the colon.

Methods

A total of 1 × 10⁶ colonic adenocarcinoma cells (line DHD/K12-TRb) were injected into the cecal wall of BDIX syngeneic male rats at an M or AM site of the colon. At six weeks after injection, all animals were sacrificed and the presence or absence of tumor in the cecum as well as regional metastasis and peritoneal carcinomatosis were determined.

Results

Six weeks after injection, macroscopic tumor growth was observed in 27/37 (72%) animals in group M and 21/32 (65%) in group AM (P = 0.98). In group AM, diffuse peritoneal carcinomatosis was present in 19/21 rats (90.4%) versus 3/27 rats (11%) in group M; this difference was statistically significant (P = 0.025). Regional mesenteric lymph nodes were the only location in which tumor was detected in 23/27 rats (85%) in group M versus 2/21 (9.5%) in group AM; this difference too was statistically significant (P = 0.031)

Conclusion

The patterns of diffusion of tumors implanted in mesenteric and antimesenteric sites of the colon appear to be different, although the reason for this is not clear.

Validity of current experimental evidence on laparoscopic surgery for colorectal cancer

Experimental animal studies can provide crucial evidence for the evaluation and refinement of the controversial area of many areas of surgery. Recently, during the surge in interest in laparoscopic surgery, in particular for colorectal cancer, 72 animal studies have been published between 1995 and 2001. However, the question remains as to which of theses data can be suitably extrapolated to the human population. Forty-five of 47 studies, which use cell suspensions, relied on percutaneous intraperitoneal injection of cancer cells to induce peritoneal carcinomatosis. One study described a laparotomy-based model with injection of tumor cells into the cecal lumen while a different study presented the cancer cells via enema. In this study, sigmoid resection was performed before colorectal solid tumor growth.

Tumor cell dissemination during laparoscopy: prevention and therapeutic opportunities

Port-site recurrences (PSRs) are abdominal wall recurrences that occur in the subcutaneous tissue within a trocar site after cancer laparoscopy and are not associated with peritoneal carcinomatosis. In order to develop PSRs, viable tumor cells must be liberated from the primary tumor, be transported to a wound, and find there a favorable environment for growth. The short clinical delay in the occurrence of PSRs and their size suggest massive cell seeding into the abdominal wall. Traumatic handling of the tumor, slipping of trocars, liquid projection, as well as poor extraction techniques can all cause implantation of malignant cells into the subcutaneous tissue. Such contact can also occur postoperatively if the trocar channels remain open. Some histologies (e.g. gallbladder adenocarcinoma), the presence of ascites and advanced tumor stage are risk factors for PSRs. Further conditions--including the use of gas--might also play a limited role. The first preventive measure is the correct indication for a laparoscopic approach. Several techniques have been demonstrated to prevent PSRs in the animal model: (a) fixation of trocars to the abdominal wall; (b) prevention of leakage; (c) careful specimen handling; (d) reducing trauma to the abdominal wall; (e) specimen isolation before extraction from the abdominal cavity; (f) trocar-site irrigation with a cytotoxic solution, and (g) closure of peritoneum. Further innovative therapies are currently under investigation. In the clinical setting, correct indication, surgical expertise and application of prophylactic measures seem to be the best way to prevent the occurrence of PSRs.