Pancratistatin Selectively Targets Cancer Cell Mitochondria and Reduces Growth of Human Colon Tumor Xenografts

Abstract

The naturally occurring Amaryllidaceae alkaloid pancratistatin exhibits potent apoptotic activity against a large panel of cancer cells lines and has an insignificant effect on noncancerous cell lines, although with an elusive cellular target. Many current chemotherapeutics induce apoptosis via genotoxic mechanisms and thus have low selectivity. The observed selectivity of pancratistatin for cancer cells promoted us to consider the hypothesis that this alkaloid targets cancer cell mitochondria rather than DNA or its replicative machinery. In this study, we report that pancratistatin decreased mitochondrial membrane potential and induced apoptotic nuclear morphology in p53-mutant (HT-29) and wild-type p53 (HCT116) colorectal carcinoma cell lines, but not in noncancerous colon fibroblast (CCD-18Co) cells. Interestingly, pancratistatin was found to be ineffective against mtDNA-depleted (r 0 ) cancer cells. Moreover, pancratistatin induced cell death in a manner independent of Bax and caspase activation, and did not alter b-tubulin polymerization rate nor cause double-stranded DNA breaks. For the first time we report the efficacy of pancratistatin in vivo against human colorectal adenocarcinoma xenografts. Intratumor administration of pancratistatin (3 mg/kg) caused significant reduction in the growth of subcutaneous HT-29 tumors in Nu/Nu mice (n ¼ 6), with no apparent toxicity to the liver or kidneys as indicated by histopathologic analysis and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling. Altogether, this work suggests that pancratistatin may be a novel mitochondria-targeting compound that selectively induces apoptosis in cancer cells and significantly reduces tumor growth.

A novel synthetic C-1 analogue of 7-deoxypancratistatin induces apoptosis in p53 positive and negative human colorectal cancer cells by targeting the mitochondria: enhancement of activity by tamoxifen

“…We have previously stably transfected and expressed anti-Bax single-domain antibodies (sdAbs) [30]. These sdAbs however, were unable to prevent PST-induced apoptosis in the SH-SY5Y cells [18]. Moreover, the tumor suppressor p53 functions as a transcription factor for the pro-apoptotic proteins Bax, Noxa, and PUMA and also indirectly activates Bim, which all act to permeabilize the mitochondrial membrane to induce apoptosis [31][32][33][34].…”

“…1a) has been shown to induce apoptosis selectively in cancers cells [15,16,18]. As there are insufficient quantities of PST available for preclinical and clinical work, various synthetic analogues of PST were synthesized and screened for similar specific apoptosis inducing activity on both p53 positive HCT-116 and p53 negative HT-29 human CRC cell lines.…”

Induction of Apoptosis and Autophagy in Human Pancreatic Cancer Cells by a Novel Synthetic C-1 Analogue of 7-deoxypancratistatin

“…Furthermore, PST was able to decrease the volume of human tumor xenografts in vivo and was nontoxic to mice [21,22]. PST however, is only present in parts per million quantities in the buds of the Hymenocallis littoralis plant and many difficulties have burdened its chemical synthesis.…”

“…In previous reports, we have attributed the apoptosis-inducing capabilities of PST to mitochondrial targeting [17][18][19][20][21][22]. Subsequent to mitochondrial membrane permeabilization, various apoptogenic factors are released from the mitochondria into the cytosol which can then directly or indirectly execute apoptosis [2].…”

“…In preceding studies, we have reported the Amaryllidaceae alkaloid pancratistatin (PST) to induce apoptosis selectively in a variety of cancer cell types at low doses and decrease the volume of human tumors in vivo; PST is well tolerated in mice and non-cancerous cells are drastically less sensitive to this compound [16][17][18][19][20][21][22]. Nevertheless, the availability of this compound has impeded its preclinical and clinical work; PST is present in only minuscule quantities in the Hymenocallis littoralis plant and many difficulties have been encountered with its chemical synthesis.…”