Current Cancer Drug Targets - Volume 16, Issue 4, 2016

The evolutionarily conserved mechanistic target of rapamycin (mTOR) forms two functionally distinct complexes, mTORC1 and mTORC2. mTORC1, consisting of mTOR, raptor, and mLST8 (GβL), is sensitive to rapamycin and thought to control autonomous cell growth in response to nutrient availability and growth factors. mTORC2, containing the core components mTOR, mLST8, Rictor, mSIN1, and Protor1/2 is largely insensitive to rapamycin. mTORC2 specifically senses growth factors and regulates cell proliferation, metabolism, actin rearrangement, and survival. Dysregulation of mTOR signaling often occurs in a variety of human malignant diseases, rendering it a crucial and validated target in cancer treatment. However, the effectiveness of rapamycin as single-agent therapy is suppressed, in part, by the numerous strong mTORC1-dependent negative feedback loops. Although preclinical and clinical studies of ATP-competitive mTOR inhibitors that target both mTORC1 and mTORC2 have shown greater effectiveness than rapalogs for cancer treatment, the mTORC1 inhibition-induced negative feedback activation of PI3- K/PDK1 and Akt (Thr308) may be sufficient to promote cell survival. Recent cancer biology studies indicated that mTORC2 is a promising target, since its activity is essential for the development of a number of cancers. These studies provide a rationale for developing inhibitors specifically targeting mTORC2, which do not perturb the mTORC1- dependent negative feedback loops and have a more acceptable therapeutic window. This review summarizes the present understanding of mTORC2 signaling and functions, especially tumorigenic functions, highlighting the current status and future perspectives for targeting mTORC2 in cancer treatment.

In the past 15 years, advances in molecular biology have exposed the genetic and physiopathologic heterogeneity of diffuse large B-cell lymphoma (DLBCL). Subsets of patients have been identified in which current chemoimmunotherapies may not be as efficacious, such as the activated B-cell subtype (ABC). In this review, we present an in-depth study of the differences between the two main DLBCL subsets (germinal center B cell [GCB] and ABC), focusing specifically on their different genetic features, active tumoral pathways, and pathologic features. We also discuss the bridges that have been built from the bench to the forefront of patient care through translational research, including the use of immunohistochemistry versus gene profiling to categorize patients with DLBCL and current clinical trial data pertaining to new possible targeted therapies for patients with these two subtypes of DLBCL. We hope that clinicians use this review as a tool to better understand the complexity of the two more prevalent DLBCL subtypes seen in the day to day practice and update their knowledge in both current and upcoming novel treatment options that can potentially change the outcomes of this population.

Chronic myeloid leukemia (CML) is a myeloproliferative neoplasm characterized by the causative oncoprotein BCR-ABL1 (Breakpoint-cluster region/Abelson kinase), which is a fusion protein with constitutive tyrosine kinase activity. The first tyrosine kinase inhibitor (TKI), imatinib, revolutionized the treatment of CML. Despite the spectacular effects of imatinib, primary and acquired resistance as well as intolerance to imatinib still exist. The mechanisms of BCR-ABL1 point mutations, amplification of the BCR-ABL1 gene and increased expression of efflux drug transporters, which play important roles in resistance, have been extensively described. Consequently, second- and third-generation TKIs have been explored to overcome resistance. However, some CML patients are refractory to all available TKIs. In addition, most patients relapse after discontinuing TKI therapy, due to the existence of CML stem cells, which have been demonstrated to be primarily resistant to TKIs. Thus, TKIs alone are not sufficient to cure CML, and it is necessary to further investigate the molecular resistance mechanisms in both the bulk and stem cells of CML to identify new targets to overcome resistance and eradicate the residual CML stem cells. This article reviews new insights into the various molecular resistance mechanisms of CML and discusses treatment strategies based on the targets that have recently been found to play an important role in the molecular mechanisms of resistance.

The complex pathology of cancer development requires correspondingly complex treatments. The traditional application of individual single-target drugs fails to sufficiently treat cancer with durable therapeutic effects and tolerable adverse events. Therefore, synergistic combinations of drugs represent a promising way to enhance efficacy, overcome toxicity and optimize safety. Chinese Herbal Medicines (CHMs) have long been used as such synergistic combinations. Therefore, we summarized the synergistic combinations of CHMs used in the treatment of cancer and their roles in chemotherapy in terms of enhancing efficacy, reducing side effects, immune modulation, as well as abrogating drug resistance. Our conclusions support the development of further science-based holistic modalities for cancer care.

Among the various drug delivery devices, nanoliposome is an emerging formulation in the treatment of cancer. Here we have developed tamoxifen citrate (TC) loaded nanoliposome conjugated with phosphoethanolamine (PE) by thin film hydration method. Various physicochemical and biopharmaceutical characterization studies such as drug-excipients interaction, surface morphology, energy dispersive X-ray analysis, zeta potential, in vitro drug release, cellular uptake, in vitro cytotoxicity assay and in vivo pharmacokinetic profiles were conducted. TC-loaded nanoliposome (TNL1) and PE-conjugated TC-loaded nanoliposome (TNL-PE) showed 3.23±0.26% and 3.07±0.05% drug loading values, respectively. Average diameters (z-average) of the nanoliposomes were within 100 nm, with negative zeta potentials and cumulative percentages of drug release were 75.77±12.21% and 61.04±10.53% at 30 h for TNL1 and TNL-PE respectively. Predominant uptake of both the types of nanoliposomes was visualized in MCF-7 breast cancer cells. TNL1 and TNL-PE decreased the cell viability from 95.95±0.37 to 12.22±0.64% and from 96.51±0.24 to 13.49±0.08% respectively. In vivo pharmacokinetic study showed that AUC 0-∞, AUMC0-∞, MRT, and t1/2 value of TNL-PE increased (22%, 100%, 2.66 fold and 60% respectively) as compared to the free drug. Administration of TNL-PE decreased the renal clearance value (about 38%) as compared to the free drug. TNL1 and TNL-PE released the drug in a sustained manner. Further, TNL-PE may be used for active targeting for breast cancer cells when it is tagged with specific antibodies to PE, a linker molecule.

Molecules with synergistic effects often enhance the benefits of cancer therapy. We observed that the major catechin of green tea, (-)-Epigallocatechin-3-gallate (EGCG), induced retinoid X receptor-γ (RXRγ) expression in the SK-Ch-A1 cholangiocarcinoma cell line and in two colon carcinoma cell lines (LoVo and the derivative multi-drug resistant LoVoMDR). On this basis, we analyzed the effects of EGCG in combination with an RXRγ ligand, 6-OH-11-O-hydroxyphenantrene (IIF), or with a ligand of retinoic acid receptor, all-trans-retinoic acid (RA). IIF alone and in combination with EGCG activated the retinoic X response elements and induced the germ cell nuclear factor. In parallel, EGCG induced 67 kDa laminin receptor expression alone and in combination with IIF. We observed a synergistic growth inhibition with EGCG and IIF in combination at lower doses. These effects were accompanied by apoptosis activation through the mitochondrial pathway. Moreover, in LoVo cell line we observed an induction of Forkhead box O3 expression, another molecule involved in apoptosis activation. Finally, metalloproteinase activity and extracellular matrix metalloproteinase inducer (EMMPRIN) expression were inhibited and tumor cell invasion was strongly reduced in the SK-Ch-A1 cell line after treatment with EGCG and IIF. In conclusion, the use of specific RXR ligands in combination with catechins could open a new perspective in gastrointestinal tumor chemoprevention.