Assessing Tumor Growth and Distribution in a Model of Prostate Cancer Metastasis using Bioluminescence Imaging

Abstract

Bioluminescence imaging (BLI) has greatly facilitated the development of animal models of cancer, allowing sensitive detection of luciferase-expressing cancer cells in living mice. Previous efforts characterizing such models have involved small numbers of animals, limiting understanding of their performance features. We employed BLI to serially image the growth and distribution of a prostate cancer cell line, 22Rv1, after intracardiac injection into scid mice (n = 85). This approach models hematogenous dissemination of cancer cells and allows inquiry of the process of metastatic colonization at various organ sites, although accurately injecting cancer cells into the left ventricle remains challenging. Therefore, to predict injection success we measured the ratio of the thoracic bioluminescence signal to the whole body bioluminescence signal (T/WB ratio) immediately following intracardiac injection. A T/WB ratio less than 0.50 predicted the development of tumors outside of the thoracic cavity while a T/WB greater than 0.50 predicted the development of tumors entirely within the thoracic cavity, suggestive of a failed injection. Progressive tumor growth was quantified using BLI. Tumors colonized multiple organ sites including bone, liver, and adrenal glands resembling the spectrum of metastases in autopsy studies of patients with prostate cancer. Tumors growing in bone exhibited mixed osteolytic and osteoblastic features, eliciting a spiculated periosteal response. With the ability to more accurately predict injection success, we can now monitor efficacy of intracardiac injections facilitating the performance of this model.

Bone-specific growth inhibition of prostate cancer metastasis by Atrasentan

“…Bioluminescence imaging immediately following injections was used to estimate injection success by measuring the ratio of signal in the thoracic cavity to that in the whole body (T/WB ratio) as described previously. 38 There were no significant differences in the T/WB ratio between the treatment groups indicating an equivalent level of injection success (Fig. 1B).…”

“…To evaluate the efficacy of atrasentan in a mouse model of prostate cancer metastasis we employed a model involving 22Rv1-luciferase cells previously developed in our lab. 38 We first determined whether atrasentan had any direct cytotoxic effects on 22Rv1-luciferase cells in vitro and determined that at doses up to 10 µM, well above pharmacologically relevant levels in vivo, there was no significant toxicity noted with up to 5 d of exposure (Fig. 1A).…”

“…Moreover, an important difference from the previously cited study involving ZR-75-1 breast cancer cells is that 22Rv1-luciferase cells elicit a mixed osteolytic/ osteoblastic phenotype in bone, with the lytic phenotype predominating. 38,39 Therefore, the efficacy of atrasentan treatment in prostate cancer may not depend strictly on its effects disrupting an overtly osteoblastic phenotype. An alternative possibility is that ETA inhibition in osteoblasts results in a blockade of tumor angiogenesis in bone such that initial tumor growth proceeds to a point where it depends on angiogenesis and then collapses.…”

“…Mice were injected blinded to treatment group with 10 5 22Rv1-luciferase cells as described previously. 38 Bioluminescence signal distribution was recorded immediately post-injection to calculate thoracic cavity/whole body (T/WB) ratios as an indicator of injection success and was followed weekly using bioluminescence imaging on an IVIS100 (Caliper Life Sciences, Mountain View, CA) as described previously.…”

“…We previously developed the model based on intracardiac injection of luciferase-expressing 22Rv1 luciferase cells which form tumors in bone as well as soft tissue sites, such as liver and adrenal gland. 38 We administered atrasentan via an oral route just prior to injection of tumor cells. Atrasentan did not significantly affect whole body tumor burden as judged by bioluminescence imaging.…”