Abstract 1170: Anti-tumor effects of p53-pathway restoring compound Prodigiosin in colorectal cancer involve effects on apoptotic signaling, angiogenesis and cancer stem cells
Authors: Varun Vijay Prabhu, Bo Hong, Joshua E. Allen, David T. Dicker, Arunasalam Navaraj, Levy Kopelovich, Wafik S. El-Deiry
Journal: Cancer Research (2012)

Abstract Colorectal cancer (CRC) is the third leading cause of death due to cancer in USA. Restoration of wild-type (wt) p53 function alone has been shown to cause tumor regression in mice with minimal toxicity. p53-restoration compounds may provide a tumor-specific therapeutic regimen to overcome the resistance and toxicity associated with current CRC therapy. Utilizing a p53-responsive luciferase reporter-based screen we identified the fluorescent red bacterial pigment Prodigiosin as a potent p53 family transcriptional activator. Anti-tumoral properties of Prodigiosin have been reported for various types of cancer both in vitro and in vivo with minimal toxicity to normal tissues but the p53 mechanism has not been previously recognized. Prodigiosin has been shown to induce mitochondria-dependent apoptosis in cancer cells, but the role of the pro-apoptotic protein Bax in anti-tumor efficacy of Prodigiosin in CRC has not been clearly defined. Using fluorescence microscopy we determined that Prodigiosin localizes to the mitochondria in CRC cells. Results of trypan-blue dye exclusion tests reveal that HCT116 wild-type and Bax-null cells were equally sensitive to Prodigiosin-induced cell death. Thus, Bax played a minor role in Prodigiosin-induced cell death. The p53 family transcriptional activation by Prodigiosin is independent of the p53 status of the CRC cells. In vivo Prodigiosin induced p53 transcriptional activity and reduced tumor volume in subcutaneous xenografts of CRC cells. Prodigiosin induced apoptosis, inhibited cell proliferation and suppressed angiogenesis in vivo in CRC cells. Emerging evidence suggests that CRC tumors contain a rare population of CRC stem cells (CSCs) capable of self-renewal that are responsible for long-term sustenance of the tumor, local tumor recurrence and metastatic relapse. CSCs are therapy resistant since they are dormant and possess various efflux mechanisms. We hypothesize that anti-tumor effects of Prodigiosin involve targeting of the CSC population by p53 restoration in CSCs. With flow cytometric analysis for Prodigiosin fluorescence we determined that Prodigiosin is not effluxed from CRC cells. We have previously demonstrated that efflux of calcein AM is a marker for the cancer stem cell population. Here, we report that Prodigiosin is retained by the calcein low population (CloP) and induced apoptosis in CloP, as determined by fluorescence microscopy. Prodigiosin suppressed the ability of CRC cells to be serially passaged in vitro. Ongoing work involves determination of: mechanism of anti-angiogenic effect of Prodigiosin; effect of Prodigiosin on CSC frequency, self renewal and tumorigenicity; synergy of Prodigiosin with chemotherapeutic drugs for CRC in targeting CSCs. This work was supported by the NCI Developmental Therapeutics Program through NCI Contract N01-CN-43302. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1170. doi:1538-7445.AM2012-1170