Different effect of paclitaxel on primary tumor mass, tumor cell contents, and metastases for four experimental human prostate tumors expressing luciferase.

PURPOSE: Primary tumor growth is usually assessed by measuring tumor mass or volume, under the assumption that such variables correlate with the contents of tumor cells. However, tumors are complex interacting mixtures of tumor cells and host components. The different sensitivity of such components to cytostatic agents should be taken into consideration when evaluating the effectiveness of antineoplastic agents. We evaluate the effect of the antineoplastic agent paclitaxel on primary tumors expressing luciferase and their metastases using a sensitive luminescence-based procedure to directly asses the number tumor cells, in comparison with traditionally used tumor mass measurement. EXPERIMENTAL DESIGN: Nude mice bearing human prostate tumors expressing the luciferase gene, LNCaP.Sluc, DU 145.Sluc, and PC-3.Sluc, i.m. inoculated, and PC-3M.Sluc, orthotopically inoculated, were subjected to a 10-day treatment with either 10 mg/kg/d paclitaxel or saline solution. At the end of the treatment period, primary tumors as well as metastasis target organs were harvested, weighed, and homogenized. The presence of tumor cells in the tissue homogenates was evaluated using a luminometer, following the addition of luciferin. Tumor cell equivalent is defined as the amount of light produced by a single tumor cell in culture. RESULTS: Paclitaxel had a different effect on the primary tumor mass and the contents of tumor cells for each tumor type. Whereas LNCaP.Sluc, PC-3.Sluc, and PC-3M.Sluc primary tumor masses were significantly reduced by the action of paclitaxel, their contents in tumor cell equivalents were not significantly affected. In contrast, paclitaxel only reduced significantly the number of tumor cell equivalents in DU 145 primary tumors. In the lymph nodes, paclitaxel reduced the number of DU 145.Sluc metastases significantly, by a factor of 10(3), but had no significant effect on the rest of tumor cells. However, in lungs and muscle, paclitaxel treatment reduced significantly the number of metastatic PC-3.Sluc and PC-3M.Sluc tumor cell equivalents. In the bones, no tumor cell type was significantly affected by paclitaxel. CONCLUSIONS: Some components of tumor stroma seem to be more sensitive to antineoplastic agents than the tumor cells themselves and may also contribute to modulate the response to therapy. Our results caution against the use of a single general variable, such as tumor mass, to evaluate the effectiveness of antineoplastic agents and emphasize the effect of the tumor cell environment in their sensitivity to treatment.

Noninvasive in vivo whole body luminescent analysis of luciferase labelled orthotopic prostate tumours.

Light photons refracted through living tissues can be used to noninvasively monitor the proliferation of cells expressing bioluminescent markers. We demonstrate the use of a luminometer for noninvasive in vivo whole body luminometric analysis (in vivo WBLA) of luciferase-expressing prostate tumours growing orthotopically in nude mice, and thus hidden from visual inspection. In this procedure, the intraperitoneally (i.p.) inoculated luciferin, the luciferase substrate, reaches the tumours rapidly and the light photons generated by the tumour are recorded by placing the anaesthetised mice in the detection chamber of a luminometer, over the detector slot. We show that the number of recorded light photons is proportional to the tumour mass and to the luciferase activity recorded in vitro. The procedure is applied to demonstrate the use of paclitaxel as an antineoplasic agent with its well characterised antiproliferative activity.

Combined noninvasive imaging and luminometric quantification of luciferase-labeled human prostate tumors and metastases.

Noninvasive imaging should facilitate the analysis of changes in experimental tumors and metastases-expressing photoproteins and result in improved data consistency and experimental animal welfare. We analyzed quantitative aspects of noninvasive imaging of luciferase-labeled tumors by comparing the efficiency of noninvasive light detection with in vitro quantification of luciferase activity. An intensified charge coupled device video camera was used to noninvasively image luciferase-expressing human prostate tumors and metastases in nude mice, after ip inoculation of luciferin. Repeated imaging of anesthetized animals after intervening growth periods allowed monitoring of tumor and metastases development. Comparison of photon events recorded in tumor images with the number of relative light units from luminometric quantification of homogenates from the same tumors, revealed that the efficiency with which light escapes tumors is inversely related to tumor size and that intensified charge coupled device images alone are not sufficient for quantitative evaluation of tumor growth. However, a combined videometric and luminometric approach did allow quantification and was used to show the cytostatic effects of paclitaxel in three different human prostate tumors growing in nude mice.