The heterogeneous distribution of hypoxic regions within solid tumors renders them refractive to chemo- and radio-therapies and contributes positively to tumor invasion and metastasis. Moreover, hypoxia favors the enrichment of cancer stem cells by interacting with differentiation signals via the maintenance of stem cell properties of undifferentiated cells or via the induction of cellular dedifferentiation. The discovery of the hypoxia inducible factor 1alpha (HIF-1α) has led to the current extensive interest in the signal molecules related to tumor hypoxia and the major regulatory pathways that control the family of hypoxia-inducible factors as potential molecular targets for cancer therapeutics. Multiple approaches have been developed to circumvent hypoxia-induced resistance, such as oxygenating tumors, using radio-sensitizers and more recently using bio-reductively activated pro-drugs. Recent evidence suggests that radio-sensitization has undergone a paradigm shift from compounds that enhance the effect of radiation via mimicking oxygen, to compounds that target HIF-mediated signaling pathways eventually reducing radio-resistance. In this paper, we give an overview of our recent understandings in hypoxia research, discuss the mechanisms of resistance of hypoxic tumors and of hypoxia-induced cancer stem cells and highlight the latest advances in cancer treatments that target tumor hypoxia and the resistant populations of cancer stem cells. Classical and novel radio-sensitization methods, mainly the molecular inhibition of HIFs and downstream targets and the use of hypoxia-activated drugs are compared and contrasted. Such multi-faceted targeted therapies ultimately enhance treatment outcomes and reduce normal tissue toxicity by the selective targeting of solid tumors.

The hedgehog (Hh) signaling pathway is an important therapeutic target in cancer; involvement of the Hh pathway has been shown in a variety of cancers including basal cell carcinoma, medulloblastoma, leukemia, and gastrointestinal, breast, prostate, lung, and pancreatic cancers.Currently, several Hh pathway inhibitory drugs are in clinical development, and the FDA recently approved Erivedge (vismodegib) from Curis/Genentech.These new drugs are effective in many, but not all patients. In fact there are documented reports of tumors developing mutations that confer resistance to the drugs.This highlights the importance of finding second generation drugs that can be used on cancers that develop resistance to the first generation Hh inhibitors. Botanicals may serve as the backbone for such research. The gold-standard pathway inhibitor, cyclopamine, is itself a naturally occurring alkaloid found in Veratrum californicum. In this review we will summarize the available literature on botanical compounds in Hh-related studies. In particular we will look at curcumin, genistein, EGCG, resveratrol, quercetin, baicalen, and apigenin along with novel compounds isolated from Southeast Asian plants, such as the potent sub-micromolar gitoxigenin derivatives. Due to the nature of the pathway, most of the research published has focused on functional Gli-transcriptional assays, which we will describe and summarize.

Ovarian cancer (OC) carries a poor prognosis; however, accumulating molecular data for the major histologic subtypes may lead to subtype-specific treatment paradigms. The present review discusses what is currently understood about the major molecular and histologic subgroups of OC. Areas specifically addressed include hormonal pathways, tumor protein p53 (TP53) and AT rich interactive domain 1A (SWI-like; ARID1A) mutation, and the breast cancer 1/2, early onset (BRCA1/2) mutation/poly (ADP-ribose) polymerase 1 (PARP1), phosphatidylinositol-4,5-bisphosphate 3-kinase, catalytic subunit alpha (PI3KCA)/v-akt murine thymoma viral oncogene homolog 1 (AKT1)/mechanistic target of rapamycin (MTOR), and mitogen-activated protein kinase kinase 1and 2 (MAP2K1/2) pathways. This molecular characterization only very recently has impacted clinical research efforts to develop targeted therapies for both common and rare OC subtypes. This targeted strategy is illustrated by ongoing low-grade serous, clear-cell, and mucinous subtype-exclusive clinical trials evaluating agents based on common molecular abnormalities among patients (ie, PARP1 inhibitors for BRCA1/2 mutation-positive OC). This report also reviews the published clinical trial efficacy data for investigational therapies within specific subgroups, and summarizes the currently active clinical trials evaluating these agents (eg, temsirolimus, sunitinib, TP53 immunotherapy, olaparib, iniparib, veliparib). Available data suggest that histologic profiles and molecular tumor markers are valuable resources for identifying patients who may benefit from these specific agents, and future research should focus on targeting molecules and signaling pathways that are most commonly altered in each subtype.

Malignant melanoma is an extremely aggressive and metastatic cancer, highly resistant to conventional treatment modalities. Understanding of fundamental mechanisms responsible for its genesis and progression is critical for development of successful chemotherapeutic treatment. It is becoming clear that melanoma results from complex changes in multiple signaling pathways that control cell proliferation and ability to evade the cell death processes. Impairment or hyper-activation of some components of these pathways may lead to malignant transformation and cancer development. In the present review we consider the current data on involvement of such signaling pathways as cyclin/CDK, Ras/Raf/MEK/MAPK, JNK/c-Jun/AP-1, PI3K/Akt/PTEN/mTOR, IKK/I-κB/NF-κB, Wnt/β-catenin, Notch, Jak/STAT, MITF and some growth factors in regulation of the cell cycle progression and apoptosis and development of human cutaneous melanoma. Understanding of molecular aberrations that underlie melanoma oncogenesis is essential for improvement of diagnosis, accurate prognosis assessment, and rational design of effective therapeutics. Inhibitors of these pathways may serve as promising tools for anti-melanoma targeted therapy. Some novel anti-melanoma target drugs are characterized.

Pancreas cancer is the fourth leading cause of cancer death due to the limited treatment success rate. The wide number of signalling pathway aberrations contributing to tumorigenesis, progression and drug resistance, is the main reason for unsuccessful treatments in pancreatic cancer. An additional and still under-investigated intracellular cancer target is the peroxisome proliferator activated receptor gamma (PPAR-γ). Several studies have shown the in vitro antitumor activity of PPAR-γ agonists in cancer cells but, if used in monotherapy, they were poorly effective in cancer treatment. The present review will focus on the potential therapeutic role of PPAR-γ agonists in combination with other drugs (type I interferons, gemcitabine and COX-2 inhibitors), highlighting molecular interactions and signalling pathways involved in pancreatic cancer cells. Understanding of the underlying molecular mechanisms and survival pathways activated in cancer cells should promote the development of more successful strategies based on the specific targeting of molecular pathways involved in the resistance to anti-cancer agents.

Tumor microenvironment (TME) refers to the dynamic cellular and extra-cellular components surrounding tumor cells at each stage of the carcinogenesis. TME has now emerged as an integral and inseparable part of the carcinogenesis that plays a critical role in tumor growth, angiogenesis, epithelial to mesenchymal transition (EMT), invasion, migration and metastasis. Besides its vital role in carcinogenesis, TME is also a better drug target because of its relative genetic stability with lesser probability for the development of drug-resistance. Several drugs targeting the TME (endothelial cells, macrophages, cancer-associated fibroblasts, or extra-cellular matrix) have either been approved or are in clinical trials.Recently, non-steroidal anti-inflammatory drugs targeting inflammationwere reported to also prevent several cancers. These exciting developments suggest that cancer chemopreventive strategies targeting both tumor and TME would be better and effective towards preventing, retarding or reversing the process of carcinogenesis. Here, we have reviewed the effect of a well established hepatoprotective and chemopreventive agent silibinin on cellular (endothelial, fibroblast and immune cells) and non-cellular components (cytokines, growth factors, proteinases etc.) of theTME. Silibinin targets TME constituents as well as their interaction with cancer cells, thereby inhibiting tumor growth, angiogenesis, inflammation, EMT, and metastasis.Silibinin is already in clinical trials, and based upon completed studies we suggest that its chemopreventive effectiveness should be verified through its effect on biological end points in both tumor and TME. Overall, we believe that the chemopreventive strategies targeting both tumor and TMEhave practical and translational utility in lowering the cancer burden.

We have shown previously that withaferin A (WA), which is a highly promising anticancer constituent of Ayurvedic medicine plant Withania somnifera, inhibits viability of cultured breast cancer cells in association with reactive oxygen species (ROS)-dependent apoptosis induction. Because ROS production is implicated in induction of autophagy, which is an evolutionary conserved process for bulk degradation of cellular components including organelles (e.g., mitochondria) and considered a valid cancer chemotherapeutic target, we questioned whether WA treatment resulted in autophagy induction. Indeed exposure of MDA-MB-231 and MCF-7 human breast cancer cells as well as a spontaneously immortalized and non-tumorigenic normal human mammary epithelial cell line (MCF-10A) to pharmacologic concentration of WA resulted in autophagy as evidenced by transmission electron microscopy, cleavage of microtubule-associated protein 1 light chain 3 isoform B (LC3B-II), and/or acridine orange staining. Inhibition of MDA-MB-231 xenograft growth in vivo by WA administration was also associated with a significant increase in level of total LC3 protein in the tumor. However, WA-mediated inhibition of MDA-MB-231 and MCF-7 cell viability was not compromised either by pharmacological suppression of autophagy using 3-methyl adenine or genetic repression of autophagy by RNA interference of Atg5, a critical component of the autophagic machinery. Finally, Beclin1 was dispensable for WA-mediated autophagy as well as inhibition of MDA-MB-231 cell viability. Based on these observations we conclude that autophagy induction fails to have any meaningful impact on WA-mediated lethality in breast cancer cells, which may be a therapeutic advantage because autophagy serves to protect against apoptosis by several anticancer agents.

Identification and validation of molecular targets are considered as a key element in new drug discovery and development. We have recently demonstrated that a novel synthetic iminoquinone analog, termed [7-(benzylamino)-1,3,4,8-tetrahydropyrrolo [4,3, 2-de]quinolin-8(1H)-one] (BA-TPQ), has significant anti-breast cancer activity both in vitro and in vivo, but the underlying molecular mechanisms are not fully understood. Herein, we report the molecular studies for BA-TPQ's effects on JNK and its upstream and downstream signaling pathways. The compound up-regulates the JNK protein levels by increasing its phosphorylation and decreasing its polyubiquitination-mediated degradation. It activates ZAK at the MAPKKK level and MKK4 at the MAPKK level. It also up-regulates the TGFβ2 mRNA level, which can be abolished by the JNK-specific inhibitor SP600125, but not TGFβ pathway-specific inhibitor SD-208, indicating that both JNK and TGFβ signaling pathways are activated by BA-TPQ and that the JNK pathway activation precedes TGFβ activation. The pro-apoptotic and anti-growth effects of BA-TPQ are significantly blocked by both the JNK and TGFβ pathway inhibitors. In addition, BA-TPQ activates the ZAK-MKK4-JNK pathway in MCF7 cells, but not normal MCF10A cells, demonstrating its cancer-specific activities. In conclusion, our results demonstrate that BA-TPQ activates the ZAK-MKK4-JNK-TGFβ signaling cascade as a molecular target for its anticancer activity.

Aberrant expression of the RON receptor tyrosine kinase contributes to breast cancer malignancy. Although clinical trials of RON targeting are underway, the intriguing issue is the diversity of RON expression as evident by cancer cells expressing different variants including oncogenic RON160. The current study determines aberrant RON160 expression in breast cancer and its potential as a target for breast cancer therapy. Using mouse monoclonal antibody Zt/h12 in immunohistochemical staining of breast cancer tissue microarray, we observed that RON160 was expressed in high frequency in primary invasive ductal (77.2%, 61/79 cases), lobular (42.5%, 34/80 cases), and lymph node-involved (63.9%, 26/36 cases) breast cancer samples. Moreover, RON160 overexpression was predominantly observed in invasive ductal (26.6%, 21/79 cases) and lymph node-involved (33.3%, 12/36) cases. Among a panel of breast cancer cell lines analyzed, Du4475 cells naturally expressing RON160. Silencing RON160 expression by siRNA reduces Du4475 cell viability. Inhibition of RON160 signaling by tyrosine kinase inhibitor PHA665752 also suppressed Du4475 cell anchorage-independent growth and induced apoptotic cell death. Studies in vivo revealed that PHA665752 inhibited 3T3-RON160 and Du4475 cell-mediated tumor growth in mouse mammary fat pad. A 60% reduction in tumor volume compared to controls was achieved after a 13-day treatment. We conclude from these studies that RON160 is highly expressed in breast cancer and its signaling is integrated into cellular signaling network for tumor cell growth and survival. Experimental treatment by PHA665752 in Du4475 breast cancer xenograft model highlights the significance of RON160 as a drug target in molecular-targeted breast cancer therapy.