Early detection and measurement of urothelial tumors in mice

Animal models for bladder cancer: The model establishment and evaluation (Review)

Bladder cancer is the most common type of tumor in the urogenital system. Approximately 75% of patients with bladder cancer present with non-muscle-invasive cancer, which is generally treated by transurethral resection and intravesical chemotherapy. In spite of different therapeutic options, there remains a very variable risk of recurrence and progression. Novel therapeutic methods of treating bladder cancer are urgently required. The exploration and preclinical evaluation of new treatments requires an animal tumor model that mimics the human counterpart. Animal models are key in bladder cancer research and provide a bridge to the clinic. Various animal bladder cancer models have been described to date, but the tumor take rate is reported to be 30-100%. Establishment of reliable, simple, practicable and reproducible animal models remains an ongoing challenge. The present review summarizes the latest developments with regard to the establishment of animal models and tumor evaluation.

Decreased tumorigenesis and mortality from bladder cancer in mice lacking urothelial androgen receptor

Much fewer mice lacking androgen receptor (AR) in the entire body develop bladder cancer (BCa). However, the role of urothelial AR (Uro-AR) in BCa development remains unclear. In the present study, we generated mice that lacked only Uro-AR (Uro-AR(-/y)) to develop BCa by using the carcinogen BBN [N-butyl-N-(4-hydroxybutyl)-nitrosamine] and found that Uro-AR(-/y) mice had a lower incidence of BCa and a higher survival rate than did their wild-type (WT; Uro-AR(+/y)) littermates. In vitro assay also demonstrated that Uro-AR facilitates the neoplastic transformation of normal urothelial cells to carcinoma. IHC staining exhibited less DNA damage, with much higher expression of p53 and its downstream target protein PNCA in Uro-AR(-/y) than that found in WT urothelium, which suggests that Uro-AR may modulate bladder tumorigenesis through p53-PCNA DNA repair signaling. Indeed, Uro-AR(-/y) mice with the transgene, simian vacuolating virus 40 T (SV40T), in the urothelium (Uro-SV40T-AR(-/y)) had a similar incidence of BCa as did their WT littermates (Uro-SV40T-AR(+/y)), and p53 was inactivated by SV40T in both genotypes. Use of the AR degradation enhancer ASC-J9 led to suppression of bladder tumorigenesis, with few adverse effects in the BBN-induced BCa mouse model. Together, these results provide the first direct in vivo evidence that Uro-AR has an important role in promoting bladder tumorigenesis and BCa progression. Targeting AR with ASC-J9 may provide a novel approach to suppress BCa initiation.

Inherited pelvic organ prolapse in the mouse: preliminary evaluation of a new murine model

The objective of this study was to report the initial anatomic, radiographic, and genetic evaluations of a novel form of spontaneous pelvic organ prolapse (S-POP) in mice. We observed S-POP in a colony of UPII-SV40T transgenic mice developed for studies on bladder cancer. We utilized magnetic resonance imaging and necropsy to characterize this finding. We have established a breeding colony to identify inheritance patterns and for future studies. Selective breeding isolated the S-POP phenotype from the transgene. In contrast to other animal models, the S-POP mouse does not require an obligatory antecedent event to manifest pelvic organ prolapse. Necropsy and imaging demonstrate significant displacement of the pelvic organs distal to the pelvic floor in both sexes. The appearance of the POP is similar to that seen in the human female phenotype. Preliminary breeding studies indicate an autosomal dominant inheritance pattern. This mouse may be an effective animal model for the study of POP in humans.

Contrast-enhanced microcomputed tomography using intraperitoneal contrast injection for the assessment of tumor-burden in liver metastasis models

OBJECTIVES

To determine if intraperitoneally (IP) administered contrast (iohexol), used in conjunction with a liver-specific agent (Fenestra), can improve measurement precision and accuracy when quantifying tumor volume from micro-CT images of a liver metastasis model.

MATERIALS AND METHODS

We compared images acquired with Fenestra alone to images acquired with the combination of Fenestra and IP iohexol. The variability in tumor volume and tumor-burden measurement was evaluated for both techniques. The tumor-burden measurement accuracy of both in vivo techniques was determined by comparison with tumor-burden quantified from ex vivo images.

RESULTS

: The addition of IP iohexol decreased measurement variability for individual tumors and overall tumor-burden by 4-8 fold and 2-3 fold, respectively. IP iohexol significantly improved the accuracy of tumor-burden measurement for both low and high tumor-burdened animals.

CONCLUSIONS

The combination of IP iohexol with Fenestra provides superior delineation of liver tumors, in comparison to Fenestra alone. The complete tumor delineation provided by this imaging strategy allows for noninvasive quantification of liver tumor-burden.

Decreased bladder cancer growth in parous mice

OBJECTIVES

To investigate the association between parity and exophytic bladder cancer growth in the UPII-SV40T transgenic mouse model of bladder cancer.

METHODS

The UPII-SV40T transgenic mice express the simian virus 40 large T antigen specifically in the urothelium (driven by uroplakin II promoter) and reliably develop bladder cancer. UPII-SV40T transgenic female mice were either never bred (nulliparous; n = 6) or placed in breeding pairs and allowed full-term pregnancies and lactation. Multiparous animals (n = 5) had between 2 and 4 litters. UPII-SV40T transgenic male mice were sham-operated (intact; n = 9) or castrated (n = 8) at 24 weeks of age. Noninvasive, contrast-enhanced, flat panel detector-based, cone beam computed tomographic imaging of animals at 32 weeks of age permitted quantification of bladder cancer volumes.

RESULTS

Multiparous animals had significantly smaller bladder cancers than their nulliparous female (P < .001) and intact male (P = .007) counterparts but not different from castrated males. Bladder cancer volume in nulliparous females was significantly larger than castrated males (P < .001) but not different from intact males.

CONCLUSIONS

These results suggest that pregnancy, parity, lactation, or a combination of these may play a protective role in bladder cancer by inhibiting tumor growth. This could be an important model system for studying the effects of pregnancy/lactation hormones on bladder cancer, which could lead to identification of additional risk factors of bladder cancer.

Androgenic dependence of exophytic tumor growth in a transgenic mouse model of bladder cancer: a role for thrombospondin-1

BACKGROUND

Steroid hormones influence mitogenic signaling pathways, apoptosis, and cell cycle checkpoints, and it has long been known that incidence of bladder cancer (BC) in men is several times greater than in women, a difference that cannot be attributed to environmental or lifestyle factors alone. Castration reduces incidence of chemically-induced BC in rodents. It is unclear if this effect is due to hormonal influences on activation/deactivation of carcinogens or a direct effect on urothelial cell proliferation or other malignant processes. We examined the effect of castration on BC growth in UPII-SV40T transgenic mice, which express SV40 T antigen specifically in urothelium and reliably develop BC. Furthermore, because BC growth in UPII-SV40T mice is exophytic, we speculated BC growth was dependent on angiogenesis and angiogenesis was, in turn, androgen responsive.

METHODS

Flat panel detector-based cone beam computed tomography (FPDCT) was used to longitudinally measure exophytic BC growth in UPII-SV40T male mice sham-operated, castrated, or castrated and supplemented with dihydrotestosterone (DHT). Human normal bladder and BC biopsies and mouse bladder were examined quantitatively for thrombospondin-1 (TSP1) protein expression.

RESULTS

Mice castrated at 24 weeks of age had decreased BC volumes at 32 weeks compared to intact mice (p = 0.0071) and castrated mice administered DHT (p = 0.0233; one-way ANOVA, JMP 6.0.3, SAS Institute, Inc.). Bladder cancer cell lines responded to DHT treatment with increased proliferation, regardless of androgen receptor expression levels. TSP1, an anti-angiogenic factor whose expression is inhibited by androgens, had decreased expression in bladders of UPII-SV40T mice compared to wild-type. Castration increased TSP1 levels in UPII-SV40T mice compared to intact mice. TSP1 protein expression was higher in 8 of 10 human bladder biopsies of normal versus malignant tissue from the same patients.

CONCLUSION

FPDCT allows longitudinal monitoring of exophytic tumor growth in the UPII-SV40T model of BC that bypasses need for chemical carcinogens, which confound analysis of androgen effects. Androgens increase tumor cell growth in vitro and in vivo and decrease TSP1 expression, possibly explaining the therapeutic effect of castration. This effect may, in part, explain gender differences in BC incidence and implies anti-androgenic therapies may be effective in preventing and treating BC.

Retrospective motion gating in small animal CT of mice and rats

OBJECTIVES

Implementation and evaluation of retrospective respiratory and cardiac gating of mice and rats using a flat-panel volume-CT prototype (fpVCT).

MATERIALS AND METHODS

Respiratory and cardiac gating was implemented by equipping a fpVCT with a small animal monitoring unit. ECG and breathing excursions were recorded and 2 binary gating signals derived. Mice and rats were scanned continuously over 80 seconds after administration of blood-pool contrast media. Projections were chosen to reconstruct volumes that fall within defined phases of the cardiac/respiratory cycle.

RESULTS

Multireader analysis indicated that in gated still images motion artifacts were strongly reduced and diaphragm, tracheobronchial tract, heart, and vessels sharply delineated. From 4D series, functional data such as respiratory tidal volume and cardiac ejection fraction were calculated and matched well with values known from literature.

DISCUSSION

Implementation of retrospective gating in fpVCT improves image quality and opens new perspectives for functional cardiac and lung imaging in small animals.

The histone deacetylase inhibitor belinostat (PXD101) suppresses bladder cancer cell growth in vitro and in vivo

BACKGROUND

Treatment options for patients with recurrent superficial bladder cancer are limited, necessitating aggressive exploration of new treatment strategies that effectively prevent recurrence and progression to invasive disease. We assessed the effects of belinostat (previously PXD101), a novel histone deacetylase inhibitor, on a panel of human bladder cancer cell lines representing superficial and invasive disease, and on a transgenic mouse model of superficial bladder cancer.

METHODS

Growth inhibition and cell cycle distribution effect of belinostat on 5637, T24, J82, and RT4 urothelial lines were assessed. Ha-ras transgenic mice with established superficial bladder cancer were randomized to receive either belinostat or vehicle alone, and assessed for bladder weight, hematuria, gene expression profiling, and immunohistochemistry (IHC).

RESULTS

Belinostat had a significant linear dose-dependent growth inhibition on all cell lines (IC50 range of 1.0-10.0 microM). The 5637 cell line, which was derived from a superficial papillary tumor, was the most sensitive to treatment. Belinostat (100 mg/kg, intraperitoneal, 5 days each week for 3 weeks) treated mice had less bladder weight (p < 0.05), and no hematuria compared with 6/10 control mice that developed at least one episode. IHC of bladder tumors showed less cell proliferation and a higher expression of p21WAF1 in the belinostat-treated mice. Gene expression profile analysis revealed 56 genes significantly different in the treated group; these included the upregulation of p21WAF1, induction of core histone deacetylase (HDAC), and cell communication genes.

CONCLUSION

Our data demonstrate that belinostat inhibits bladder cancer and supports the clinical evaluation of belinostat for the treatment of patients with superficial bladder cancer.