Co-targeting driver pathways in prostate cancer: two birds with one stone

Review On Documented Medicinal Plants Used For The Treatment Of Cancer

Background:

Cancer is a frightful disease and it is the second leading cause of death worldwide. Naturally derived compounds are gaining interest of research workers as they have less toxic side effects as compared to currently used treatments such as chemotherapy. Plants are the pool of chemical compounds which provides a promising future for research on cancer.

Objective:

This review paper provides updated information gathered on medicinal plants and isolated phytoconstituents used as anticancer agents and summarises the plant extracts and their isolated chemical constituents exhibiting anticancer potential on clinical trials.

Methods:

An extensive bibliographic investigation was carried out by analysing worldwide established scientific databases like SCOPUS, PUBMED, SCIELO, ScienceDirect, Springerlink, Web of Science, Wiley, SciFinder and Google Scholar etc. In next few decades, herbal medicine may become a new epoch of medical system.

Results:

Many researches are going on medicinal plants for the treatment of cancer but it is a time to increase further experimental studies on plant extracts and their chemical constituents to find out their mechanism of action at molecular level.

Conclusion:

The article may help many researchers to start off further experimentation that might lead to the drugs for the cancer treatment.

Signaling Pathways That Control Apoptosis in Prostate Cancer

Prostate cancer is the second most common malignancy and the fifth leading cancer-caused death in men worldwide. Therapies that target the androgen receptor axis induce apoptosis in normal prostates and provide temporary relief for advanced disease, yet prostate cancer that acquired androgen independence (so called castration-resistant prostate cancer, CRPC) invariably progresses to lethal disease. There is accumulating evidence that androgen receptor signaling do not regulate apoptosis and proliferation in prostate epithelial cells in a cell-autonomous fashion. Instead, androgen receptor activation in stroma compartments induces expression of unknown paracrine factors that maintain homeostasis of the prostate epithelium. This paradigm calls for new studies to identify paracrine factors and signaling pathways that control the survival of normal epithelial cells and to determine which apoptosis regulatory molecules are targeted by these pathways. This review summarizes the recent progress in understanding the mechanism of apoptosis induced by androgen ablation in prostate epithelial cells with emphasis on the roles of BCL-2 family proteins and "druggable" signaling pathways that control these proteins. A summary of the clinical trials of inhibitors of anti-apoptotic signaling pathways is also provided. Evidently, better knowledge of the apoptosis regulation in prostate epithelial cells is needed to understand mechanisms of androgen-independence and implement life-extending therapies for CRPC.

Novel Therapeutic Strategies for CDK4/6 Inhibitors in Metastatic Castrate-Resistant Prostate Cancer

The majority of patients with castrate-resistant prostate cancer will have metastatic disease at the time of diagnosis. Investigative efforts on new therapeutics for this patient population have improved with the development of androgen signaling inhibitors, such as abiraterone and enzalutamide, and PARP inhibitors, such as rucaparib and olaparib, to accompany the previously FDA-approved docetaxel, cabazitaxel, sipuleucel-T, and Radium 223. However, new therapeutic strategies are necessary to prolong survival as progression after these agents is inevitable. CDK4/6 inhibitors have advanced the field of estrogen receptor positive breast cancer treatment and are being investigated in prostate cancer given the role of androgen receptor signaling effects on the cell cycle. Response to CDK4/6 inhibitors may be predicted by the tumors' genomic profile and may provide insight into combinatory therapy with CDK4/6 inhibitors in order to delay resistance or provide synergistic effects. Here, we review the use of CDK4/6 inhibitors in prostate cancer and potential combinations based on known resistance mechanisms to CDK4/6 inhibitors, prostate cancer regulatory pathways, and prostate-cancer-specific genomic alterations.

Negative cross talk between LIMK2 and PTEN promotes castration resistant prostate cancer pathogenesis in cells and in vivo

Androgen deprivation therapy (ADT) and androgen receptor (AR) signaling inhibitors are front-line treatments for highly aggressive prostate cancer. However, prolonged inhibition of AR triggers a compensatory activation of PI3K pathway, most often due to the genomic loss of tumor suppressor PTEN, driving progression to the castration-resistant prostate cancer (CRPC) stage, which has very poor prognosis. We uncovered a novel mechanism of PTEN downregulation triggered by LIMK2, which contributes significantly to CRPC pathogenesis. LIMK2 is a CRPC-specific target. Its depletion fully reverses tumorigenesis in vivo. LIMK2 phosphorylates PTEN at five sites, degrading and inhibiting its activity, thereby driving highly aggressive oncogenic phenotypes in cells and in vivo. PTEN also degrades LIMK2 in a feedback loop, which was confirmed in prostates from PTEN^-/- and PTEN^+/+ mice. LIMK2 is also the missing link between hypoxia and PTEN degradation in CRPC. This is the first study to show a feedback loop between PTEN and its regulator. Uncovering the LIMK2-PTEN loop provides a powerful therapeutic opportunity to retain the activity and stability of PTEN protein by inhibiting LIMK2, thereby halting the progression to CRPC, ADT-resistance and drug-resistance.

The PI3K-AKT-mTOR Pathway and Prostate Cancer: At the Crossroads of AR, MAPK, and WNT Signaling

Oncogenic activation of the phosphatidylinositol-3-kinase (PI3K), protein kinase B (PKB/AKT), and mammalian target of rapamycin (mTOR) pathway is a frequent event in prostate cancer that facilitates tumor formation, disease progression and therapeutic resistance. Recent discoveries indicate that the complex crosstalk between the PI3K-AKT-mTOR pathway and multiple interacting cell signaling cascades can further promote prostate cancer progression and influence the sensitivity of prostate cancer cells to PI3K-AKT-mTOR-targeted therapies being explored in the clinic, as well as standard treatment approaches such as androgen-deprivation therapy (ADT). However, the full extent of the PI3K-AKT-mTOR signaling network during prostate tumorigenesis, invasive progression and disease recurrence remains to be determined. In this review, we outline the emerging diversity of the genetic alterations that lead to activated PI3K-AKT-mTOR signaling in prostate cancer, and discuss new mechanistic insights into the interplay between the PI3K-AKT-mTOR pathway and several key interacting oncogenic signaling cascades that can cooperate to facilitate prostate cancer growth and drug-resistance, specifically the androgen receptor (AR), mitogen-activated protein kinase (MAPK), and WNT signaling cascades. Ultimately, deepening our understanding of the broader PI3K-AKT-mTOR signaling network is crucial to aid patient stratification for PI3K-AKT-mTOR pathway-directed therapies, and to discover new therapeutic approaches for prostate cancer that improve patient outcome.