1. Small activating RNA (saRNA) in regulating CRMP4 expression in prostate cancer
Rapid biochemical recurrence with distal metastasis are often found in high-risk prostate cancers include locally advanced such as positive surgical margin and high grade like Gleason sum score > 8 tumors. Although prostate specific antigen (PSA) screening has led to earlier diagnosis of the disease, it has failed to save many lives because the death rate did not change significantly. One plausible reason is that prostate cancer cells migrate to extra-prostatic surrounding tissue and that micro-metastasis already exists even in clinically high-risk cancers.
Collapsin response mediator protein-4 (CRMP4, also termed as dihydropyrimidinase-like 3, DPYSL3) belongs to the CRMP family of cytosolic phosphoproteins, which are involved in semaphorin/collapsin-induced cellular events. So far, five members of the CRMP gene family (CRMP1-5) have been cloned and they have 50-70% sequence homology. Recent studies indicated that CRMP1 is an invasion suppressor in human glioma and lung cancer cells, and its reduced expression correlates with poor clinical outcomes in non-small cell lung cancer. CRMP-2 and CRMP-5 were found to be extensively expressed in colorectal cancers and high-grade lung neuro-endocrine carcinomas, respectively. In our preliminary studies, we identified CRMP4 as a metastasis suppressor in prostate cancers, since its expression is inversely associated with lymph node metastasis and its over-expression in prostate cancer cells not only suppressed cell motility/invasion in vitro but also strongly inhibited tumor metastasis in animal xenograft model. Thus it is feasibly to suppress tumor metastasis by enhancing CRMP4 expression in high-risk prostate cancers.
Recent emerging evidence shows that small double-stranded RNAs (saRNA) targeting gene promoters are potent in inducing prolonged gene activation at the transcriptional level. Several reports have demonstrated the potential usage of double-stranded RNAs targeting tumor suppressor genes in inhibiting tumor cell growth in vitro and in vivo. The objective of this proposal is to develop and validate double-stranded activating RNAs targeting CRMP4 promoter for suppressing metastasis of prostate cancer. The rationale is based on our recent publication and preliminary studies, as well as previous reports from other groups. It is conceivable that distal metastatic tumor begin with a micro-metastatic cell that can be targeted to prevent the development of metastatic disease. If micro-metastatic cells are taken off the table, then most of prostate cancers will be manageable and severe side effects due to extensive therapies can be avoided. We believe that its successful completion of this project would lead to a novel preventive therapy for prostate cancers.
This project was supported by a grant from NIH/NCI R21 project and KUMC Masonic Foundation.
2. Novel macrocyclic tetrapeptides targeting oncogenic c-Myc protein for degradation as a potential therapeutic approach to treating advanced prostate cancer.
Oncogenic c-Myc protein is a transcription factor and a powerful regulator of various cellular functions including the transcription of numerous genes, cell growth and proliferation, cell cycle control, apoptosis, differentiation and angiogenesis. The tight regulation of c-Myc expression is very important to maintain normal cellular function, and deregulation of c-Myc protein levels or dysfunction in cells is often associated with disease. Overexpression of c-Myc is observed in many cancers including prostate cancer due at least partially to increased stability of c-Myc in these cells.
Small molecules that decrease c-Myc stability and induce apoptosis through this pathway have been identified recently. We recently have been studying macrocyclic tetrapeptides based on the natural product CJ-15,208 (cyclo[Phe-D-Pro-Phe-Trp]. Since c-Myc is often overexpressed in PC, we examined whether these peptides decreased c-Myc levels in PC-3 cells. Our preliminary data showed that the macrocyclic tetrapeptides can down regulate c-Myc levels and induce PC-3 cell death. Based on our preliminary data we hypothesize that macrocyclic peptide treatment will induce PC cell death by inhibiting c-Myc protein accumulation in cells, which in turn will prevent tumor cell proliferation. To test this hypothesis and to identify more potent analogs for further study, the following three specific aims will be explored:
Specific Aim 1: To examine the regulation of c-Myc levels and cell growth in PC cell lines by the lead compound [DTrp] CJ-15,208.
Specific Aim 2: To explore the structure-activity-relationships (SAR) of CJ-15,208 and [D-Trp]-CJ- 15,208 for anti-proliferative activity in PC cells.
Specific Aim 3: To examine selected macrocyclic peptides for inhibition of tumor growth and metastasis in vivo in a mice tumor model. This project was supported by a grant from DOD PCRP PC130736.
3. PI3K/p110beta in Prostate Cancer Progression
The combination of androgen ablation (hormone therapy) along with early detection and surgery has made prostate cancer highly treatable at the initial stage. However, this cancer remains the second leading cause of cancer death among American men. Recently, we demonstrated that PI3K p110beta isoform, a major cellular signaling molecule, is critical for prostate cancer progression in cell culture model and mouse xenograft model. In addition, p110beta-specific inhibitor TGX-221 significantly suppressed tumor growth of prostate cancer xenografts in our preliminary studies. Therefore, with the help of novel nanocarrier that targets prostate specific membrane antigen (PSMA) present in all clinical prostate cancers, cancer cell specific delivery of TGX-221 will be a potent therapy for late-stage prostate cancer patients.
Our hypothesis is PSMA-targeted nanocarrier delivery of the PI3K-p110beta inhibitor TGX-221 will eliminate prostate cancer cells that are dependent on p110beta for proliferation and survival. This hypothesis has been based on our recent publications and preliminary data, as well as previous reports from other groups. The rational is that its successful completion would lead to a novel therapy for prostate cancer. The objective of the proposed study is to establish that a nanocarrier-approach for targeted p110beta-specific inhibition in prostate cancer cells. This cancer cell-targeted nanocarrier approach will be effective in blocking xenograft tumor growth with few or no side-effects, which fits into our long term goal of developing novel therapeutic strategies for prostate cancer treatment.
Ideally, a functionalized nanocarrier targeting prostate cancer cells for clinical use should have high tissue/cell selectivity, molecular target specificity and long blood stream circulating time to increase the efficiency of delivered therapeutic molecules. The nanocarrier should not have a broad range of tissue distribution to avoid systemic side effects. Therefore, in this proposal, we plan to develop such a nanocarrier with components that are biocompatible, biodegradable and FDA-approved.
This project was supported by a grant from DOD PCRP.
4. Novel small molecule Alternol for Prostate Cancer Therapy
Prostate cancer at the castration-resistant stage is a life-threatening disease without means to cure in clinic. Although few new drugs such as Enzalutamide (marketed as XtandiTM) and Abiraterone Acetate (Zytiga®), as well as the first prostate cancer vaccine PROVENGE (Sipuleucel-T) were introduced in clinic recently for this patient population, the benefit for them was only a few month extension of survival. Obviously, there is an urgent need to develop more effective therapies. Ideally, any cancer therapy should be able to selectively kill cancer cells without harming benign tissues. With this idea in mind, after several years of hard working, we recently identified a novel small molecule Alternol that preferentially kills malignant prostate cancer cells over benign prostate-derived epithelial cells. Alternol is produced by a mutant micro-organism isolated from the bark of a yew tree, similar to the source of Paclitaxel. Both our very recent publication (Tang et al. Mol Cancer Therapeutics 2014) and works from others demonstrated that Alternol triggers apoptotic cell death in cancer cells. Our initial analyses revealed that Alternol-induced apoptotic cell death depends on reactive oxygen species (ROS)-mediated activation of pro-apoptotic Bax protein in prostate cancer cells. We are now working on the mechanisms of molecule's action on cancer cells and benign cells to develop it as a novel anti-cancer therapy.