Beyond the Abstract - Regression of prostate tumors upon combination of hormone ablation therapy and Celecoxib in vivo, by Per Borgström, PhD, et al.

BERKELEY, CA (UroToday.com) - Advanced prostate cancer is normally treated by hormone therapy, i.e. withdrawal of androgens.

This treatment controls tumor growth at first, however invariably results in the development of androgen-dependent tumors and relapse. Improving the effectiveness of hormone therapy and delaying relapse is crucial, as 40,000 men still die of prostate cancer every year in the US.

Epidemiological studies have shown beneficial, potentially protective effects of anti-inflammatory COX-2 inhibitors such as FDA-approved Celecoxib (Celebrex) in various types of cancer. In addition, knock-out of the COX-2 gene in mice decreases tumor formation, whereas COX-2 overexpression promotes cancer progression. Clinical trials have demonstrated the safety of Celecoxib, but so far have shown few clinical benefits for the treatment of prostate cancer in various therapeutic settings. However, the drug has not been tested at the time of androgen therapy, despite a study showing that it suppressed the re-growth of LNCaP xenografts following androgen withdrawal.

To address this issue, we tested the efficacy of combining androgen withdrawal with Celecoxib, and we examined the respective physiological effects of Celecoxib and androgen withdrawal in vivo. To this end, we used IntraVital Microscopy (IVM) in a mouse model of prostate cancer.

IVM is used to visualize tumors in animals and analyze various aspects of cancer physiology such as tumor growth/regression, tumor vascularization, and cell migration. The main advantages of IVM include the real-time analysis of dynamic processes with single-cell resolution. Importantly, IVM offers the possibility to follow tumor growth/regression in a non-invasive, non-destructive manner. Since the application of IVM is limited to animal models that bear visually accessible tumors, we used the dorsal skinfold chamber model, in which a titanium frame with a viewing window is placed in the skin fold of the back of a mouse.

Mouse prostate tissue is grafted in the chamber and the graft develops its own vasculature and serves as orthotopic stroma for the tumor. This method emerged from early experiments showing that various syngeneic tissues grafted in rodent dorsal chambers do re-vascularize and survive over long periods of time. A small number of prostate cancer cells (TRAMP-C2 cells derived from a TRAMP mouse) are implanted on top of the prostate stroma. Indeed, it is now well known that the tumor microenvironment is crucial for the progression of almost every type of cancer, and that orthotopic implantation of cancer cells recapitulate human disease much more closely than subcutaneous implantation. Tumors grow faster and develop less leaky vasculature when the cancer cells are implanted into the relevant organ. Thus, co-implanting mouse prostate cancer cells with prostate stroma provides the tumor cells with an environment that better reflects the clinical disease compared to purely subcutaneous models. Importantly, re-vascularized stromal tissue and implanted tumors remain viable for long periods of time (up to 90 days).

Our laboratory uses tumor cells transfected with histone H2B-GFP fusion protein, which is incorporated into the chromatin without affecting cell cycle progression. Tumor cell fluorescence allows one to measure angiogenic activity, tumor cell migration, and parameters pertaining to tumor growth or regression such as mitosis, apoptosis and cell cycle arrest, all in the context of the host. The number of cancer cells in a growing tumor can be determined accurately from the fluorescence intensity by using a calibration curve. H2B-GFP makes it very simple to visualize metaphase-telophase DNA and apoptotic/pyknotic nuclei using high magnification images, and to calculate the number of cells undergoing mitosis or apoptosis. Finally, vascular parameters (vascular area, vascular length; average tumor vessel diameter and vascular density) are analyzed from video recordings using a photodensitometric computer software.

Thus, we co-implanted mouse prostate tumor cells with prostate tissue and allowed it to re-vascularize. Treatment was initiated once the prostate tissue and implanted tumors were established and vascularized. Celecoxib was administered twice daily (15mg/kg). Hormone therapy was administered in the form of surgical castration or chemical ablation, alone or in combination with Celecoxib. Four treatment groups were studied: control, untreated non-castrated mice; castration alone, Celecoxib alone, castration combined with Celecoxib.

Surgical or chemical castration inhibited angiogenesis and caused a disruption in the tumor vasculature which resulted in arrested tumor growth. The combination of androgen ablation with Celecoxib was synergistic, and was the only treatment to cause tumor regression through the combined effects of decreased angiogenesis, mitotic arrest and increased apoptosis of tumor cells. In vitro, Celecoxib inhibited the proliferation of prostate cancer cells mostly by inducing mitotic failure. In vivo, Celecoxib also caused mitotic arrest in the tumor cells and thus blocked tumor growth. Interestingly, the drug did not possess angiostatic activity.

In conclusion, the combination of hormone ablation with Celecoxib caused a profound regression of prostate tumors, and may delay progression toward androgen-independence in patients with advanced prostate cancer undergoing hormone therapy.

 

Written by:
Parisa Abedinpour, Véronique T. Baron, John Welsh and Per Borgström as part of Beyond the Abstract on UroToday.com. This initiative offers a method of publishing for the professional urology community. Authors are given an opportunity to expand on the circumstances, limitations etc... of their research by referencing the published abstract.

 

Regression of prostate tumors upon combination of hormone ablation therapy and Celecoxib in vivo - Abstract

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