Intraductal administration of N-methyl-N-nitrosourea as a novel rodent mammary tumor model

Abstract

Background: Chemically induced animal models of breast cancer (BC) using N-methyl-N-nitrosourea (MNU) have been widely used in preclinical research. The conventional approach entails intraperitoneal (i.p) or intravenous injection of a carcinogen, leading to tumor induction at unpredictable locations. This study aimed to establish a modified MNU-induced rat mammary tumor model using intraductal (i.duc) administration and to evaluate its biological behavior, morphology, and response to chemotherapy drugs.Methods: In a pilot experiment, female Sprague-Dawley (SD) rats were injected with either i.duc MNU or vehicle to test the feasibility of this approach. We explored the appropriate dosage for stable tumor formation in pubescent female SD rats by testing a single i.duc dose of MNU (0.5, 1.0 and 2.0 mg) or vehicle.Results: An i.duc injection of 20 μL (1 mg/per duct) MNU in the fourth rat mammary gland induced stable carcinomas in situ. Immunohistochemical (IHC) analysis showed positive expression of estrogen receptor (ER), negative expression of human epidermal growth factor receptor 2 (Her-2), and low expression of Ki-67. Histopathology revealed atypical hyperplasia in the mammary gland 4 weeks after carcinogen injection, developing into carcinoma in situ 5-6 weeks after treatment, with loss of α-SMA and calponin expressions during tumor progression. Albumin-bound paclitaxel (nab-PTX) was injected i.duc and intravenously (i.v) 5 weeks after administration of MNU. The tumor growth rate of the nab-PTX i.duc-treated group was lower than in the i.v and control groups. The number of TUNEL-positive apoptotic cells was significantly higher in the nab-PTX i.duc-treated group.Conclusions: Using i.duc MNU (20 μL, 1 mg) to establish a rat mammary tumor model resulted in a predictable location in the rat mammary gland and exhibited better consistency; i.duc administration of nab-PTX permitted a smaller drug dose, but produced a better drug response, than i.v injection.

Distinct invasive patterns in situ between estrogen receptor‐positive and triple‐negative breast cancer through the intraductal tracking of carbon nanoparticles

“…During the injection, animals were maintained under anesthesia using continuous 2% isoflurane inhalation (1% oxygen). Carcinoma in situ with positive expression of ER, and negative expression of Her‐2 developed 28 to 42 days after the first intraductal injection of MNU and eventually progressed to invasive ductal carcinoma 23,43 . The animals were randomized to three groups of three to five rats each.…”

“…[24][25][26][27] In previous work, we developed the rat model by intraductal injection of MNU with a fully predictable tumor location. 23 By gene expression profiles, tumors in this model cluster with the ER-positive subtype of human BC. Likewise, the MIND model based on 4T1 cells has the advantage of presenting disease progression from DCIS to invasive carcinoma compared to the traditional fat pad model.…”

“…Rats administrated with N ‐methyl‐ N ‐nitrosourea (MNU) have been widely used to study breast carcinogenesis due to the ability to replicate the occurrence of human breast cancer 24‐27 . In previous work, we developed the rat model by intraductal injection of MNU with a fully predictable tumor location 23 . By gene expression profiles, tumors in this model cluster with the ER‐positive subtype of human BC.…”

“…[18][19][20][21][22] We combined the ER-positive BC model previously established by our lab and a mouse intraductal (MIND) model representing the TNBC with intraductal administration of specific nanomaterials as a tracer to understand the distinct invasion pattern. 23 Rats administrated with N-methyl-N-nitrosourea (MNU) have been widely used to study breast carcinogenesis due to the ability to replicate the occurrence of human breast cancer. [24][25][26][27] In previous work, we developed the rat model by intraductal injection of MNU with a fully predictable tumor location.…”

Large Animal Models of Breast Cancer

“…Long term studies have shown that some rats can develop breast tumors spontaneously (118). Use of a chemical carcinogen in rats can result in a shorter latency period to tumor development (119)(120)(121)(122)(123). Recently, 17b-estradiol (E2) was used to induce breast tumors in August Copenhagen Irish-rats by modulating estrogen mediated mechanisms in breast cancer development (121).…”