Sequence-dependent antitumor effects of differentiation agents in combination with cell cycle-dependent cytotoxic drugs

Epigenetics of colorectal cancer: biomarker and therapeutic potential

Colorectal cancer (CRC), a leading cause of cancer-related death worldwide, evolves as a result of the stepwise accumulation of a series of genetic and epigenetic alterations in the normal colonic epithelium, leading to the development of colorectal adenomas and invasive adenocarcinomas. Although genetic alterations have a major role in a subset of CRCs, the pathophysiological contribution of epigenetic aberrations in this malignancy has attracted considerable attention. Data from the past couple of decades has unequivocally illustrated that epigenetic marks are important molecular hallmarks of cancer, as they occur very early in disease pathogenesis, involve virtually all key cancer-associated pathways and, most importantly, can be exploited as clinically relevant disease biomarkers for diagnosis, prognostication and prediction of treatment response. In this Review, we summarize the current knowledge on the best-studied epigenetic modifications in CRC, including DNA methylation and histone modifications, as well as the role of non-coding RNAs as epigenetic regulators. We focus on the emerging potential for the bench-to-bedside translation of some of these epigenetic alterations into clinical practice and discuss the burgeoning evidence supporting the potential of emerging epigenetic therapies in CRC as we usher in the era of precision medicine.

Multifunctional Compounds for Activation of the p53-Y220C Mutant in Cancer

The p53 protein plays a major role in cancer prevention, and over 50 % of cancer diagnoses can be attributed to p53 malfunction. The common p53 mutation Y220C causes local protein unfolding, aggregation, and can result in a loss of Zn in the DNA-binding domain. Structural analysis has shown that this mutant creates a surface site that can be stabilized using small molecules, and herein a multifunctional approach to restore function to p53-Y220C is reported. A series of compounds has been designed that contain iodinated phenols aimed for interaction and stabilization of the p53-Y220C surface cavity, and Zn-binding fragments for metallochaperone activity. Their Zn-binding affinity was characterized using spectroscopic methods and demonstrate the ability of compounds L4 and L5 to increase intracellular levels of Zn²⁺ in a p53-Y220C-mutant cell line. The in vitro cytotoxicity of our compounds was initially screened by the National Cancer Institute (NCI-60), followed by testing in three stomach cancer cell lines with varying p53 status', including AGS (WTp53), MKN1 (V143A), and NUGC3 (Y220C). Our most promising ligand, L5, is nearly 3-fold more cytotoxic than cisplatin in a large number of cell lines. The impressive cytotoxicity of L5 is further maintained in a NUGC3 3D spheroid model. L5 also induces Y220C-specific apoptosis in a cleaved caspase-3 assay, reduces levels of unfolded mutant p53, and recovers p53 transcriptional function in the NUGC3 cell line. These results show that these multifunctional scaffolds have the potential to restore wild-type function in mutant p53-Y220C.

The role of cell cycle progression for the apoptosis of cancer cells induced by palladium(II)-saccharinate complexes of terpyridine

OBJECTIVES

Palladium complexes are potent and less toxic molecules in comparison to other metal based agents. Here, we characterized two palladium(II) saccharinate complexes with terpyridine for their cell cycle specificity.

MATERIALS AND METHODS

Cells were arrested at G1, G1/S boundary or mitosis using mimosine, double-Thymidine block, aphidicolin, nocodazole or colcemid, and evaluated based on morphology and flow cytometry. Synchronized cells were treated with the Pd(II) complexes, and viability was measured via MTT assay.

RESULTS

While treatment of arrested cells with the Pd(II) complexes resulted in no significant change in cell death in HCT-116 and MDA-MB-231 cells, HeLa cells were more sensitive in S/G1. The main form of cell death was found to be apoptosis.

CONCLUSIONS

Pd(II) complexes appear to be cell-cycle non-specific, while cell line dependent differences may be observed. Cells die through apoptosis regardless of the cell cycle stage, which makes these complexes more promising as anti-cancer agents.

Timed, sequential administration of paclitaxel improves its cytotoxic effectiveness in a cell culture model

Paclitaxel (taxol) is a chemotherapeutic agent frequently used in combination with other anti-neoplastic drugs. It is most effective during the M phase of the cell-cycle and tends to cause synchronization in malignant cells lines. In this study, we investigated whether timed, sequential treatment based on the cell-cycle characteristics could be exploited to enhance the cytotoxic effect of paclitaxel. We characterized the cell-cycle properties of a rapidly multiplying cell line (Sp2, mouse myeloma cells) by propidium-iodide DNA staining such as the lengths of various cell cycle phases and population duplication time. Based on this we designed a paclitaxel treatment protocol that comprised a primary and a secondary, timed treatment. We found that the first paclitaxel treatment synchronized the cells at the G2/M phase but releasing the block by stopping the treatment allowed a large number of cells to enter the next cell-cycle by a synchronized manner. The second treatment was most effective during the time when these cells approached the next G2/M phase and was least effective when it occurred after the peak time of this next G2/M phase. Moreover, we found that after mixing Sp2 cells with another, significantly slower multiplying cell type (Jurkat human T-cell leukemia) at an initial ratio of 1:1, the ratio of the two different cell types could be influenced by timed sequential paclitaxel treatment at will. Our results demonstrate that knowledge of the cell-cycle parameters of a specific malignant cell type could improve the effectivity of the chemotherapy. Implementing timed chemotherapeutic treatments could increase the cytotoxicity on the malignant cells but also decrease the side-effects since other, non-malignant cell types will have different cell-cycle characteristic and be out of synch during the treatment.

Novel therapies for the treatment of advanced prostate cancer

In recent years, great success has been achieved on many fronts in the treatment of men with metastatic castration-resistant prostate cancer (CRPC), including novel chemotherapeutics, immunotherapies, bone microenvironment-targeted agents, and hormonal therapies. Numerous agents are currently in early-phase clinical trial development for the treatment of advanced prostate cancer. These novel therapies target several areas of prostate tumor biology, including the upregulation of androgen signaling and biosynthesis, critical oncogenic intracellular pathways, epigenetic alterations, and cancer immunology. Importantly, the characterization of the prostate cancer genome offers the potential to exploit conserved genetic alterations, which may increase the efficacy of these targeted therapies. Predictive and prognostic biomarkers are urgently needed to maximize therapeutic efficacy and safety of these promising new treatments options in prostate cancer.

Scheduling of paclitaxel and gefitinib to inhibit repopulation for optimal treatment of human cancer cells and xenografts that overexpress the epidermal growth factor receptor

PURPOSE

In clinical studies, evaluating the combination of chemotherapy and the epidermal growth factor receptor (EGFR) inhibitor gefitinib, treatments were administered concurrently, despite it being counter-intuitive to give a cytostatic agent concurrent with cycle-active chemotherapy. One strategy to enhance efficacy might be to give the agents sequentially, thus allowing selective inhibition of repopulation of cancer cells between doses of chemotherapy. Here, we evaluate the hypothesis that sequential administration might allow inhibition of repopulation by gefitinib, with tumor cells re-entering cycle to allow sensitivity to subsequent chemotherapy.

METHODS

Sequential and concurrent administration of paclitaxel and gefitinib were studied in vitro and in xenografts using EGFR over-expressing, EGFR-mutant, and EGFR wild-type human cancer cell lines. We evaluated cell cycle distribution and repopulation during treatment.

RESULTS

The sequential use of gefitinib and paclitaxel to treat EGFR over-expressing A431 cells in vitro decreased repopulation compared to chemotherapy alone, and there was greater cell kill compared to concurrent treatment. In contrast, combined treatment led to greater growth delay than use of gefitinib alone for concurrent but not for sequential treatment of mice bearing A431 xenografts; concurrent treatment had greater effects to reduce functional vasculature in the tumors. Conversely, sequential treatment led to greater growth delay than concurrent treatment of EGFR-mutant HCC-827 xenografts that are sensitive to lower doses of gefitinib.

CONCLUSIONS

These studies highlight the importance of considering effects on the cell cycle, and on the solid tumor microenvironment, including tumor vasculature, when scheduling cytostatic and cytotoxic agents in combination.

Promise and challenges in drug discovery and development of hybrid anticancer drugs

BACKGROUND

Because cancer is a complex disease, it is unlikely that a single mono functional 'targeted' drug will be effective for treating this most advanced disease. Combined drugs that impact multiple targets simultaneously are better at controlling complex disease systems, are less prone to drug resistance and are the standard of care in cancer treatment. In order to improve the efficiency of using a two-drug cocktail, one approach involves the use of the so-called hybrid drugs, which comprises the incorporation of two drugs in a single molecule with the intention of exerting dual drug action.

OBJECTIVE

In the present article, we discuss the design, synthesis and various applications of anticancer hybrid agents and the developments in this field during the last few decades. Additionally, we describe different types of linkers and their role in contributing towards biological effects and the in vivo mechanism of drug release. We also depict some challenges from scientific and regulatory perspectives in the hybrid drug development process.

CONCLUSION

In the era of increasing drug resistance in cancer patients, the discovery of hybrid drugs could provide an effective strategy to create chemical entities likely to be more efficacious and less prone to resistance. However, some technical and regulatory challenges will have to be surmounted before hybrid drugs succeed in the clinical settings and justify the considerable promise of this novel concept.

Clinical and experimental applications of sodium phenylbutyrate

Histone acetyltransferase and histone deacetylase are enzymes responsible for histone acetylation and deacetylation, respectively, in which the histones are acetylated and deacetylated on lysine residues in the N-terminal tail and on the surface of the nucleosome core. These processes are considered the most important epigenetic mechanisms for remodeling the chromatin structure and controlling the gene expression. Histone acetylation is associated with gene activation. Sodium phenylbutyrate is a histone deacetylase inhibitor that has been approved for treatement of urea cycle disorders and is under investigation in cancer, hemoglobinopathies, motor neuron diseases, and cystic fibrosis clinical trials. Due to its characteristics, not only of histone deacetylase inhibitor, but also of ammonia sink and chemical chaperone, the interest towards this molecule is growing worldwide. This review aims to update the current literature, involving the use of sodium phenylbutyrate in experimental studies and clinical trials.

ID1 enhances docetaxel cytotoxicity in prostate cancer cells through inhibition of p21

To identify potential mechanisms underlying prostate cancer chemotherapy response and resistance, we compared the gene expression profiles in high-risk human prostate cancer specimens before and after neoadjuvant chemotherapy and radical prostatectomy. Among the molecular signatures associated with chemotherapy, transcripts encoding inhibitor of DNA binding 1 (ID1) were significantly upregulated. The patient biochemical relapse status was monitored in a long-term follow-up. Patients with ID1 upregulation were found to be associated with longer relapse-free survival than patients without ID1 increase. This in vivo clinical association was mechanistically investigated. The chemotherapy-induced ID1 upregulation was recapitulated in the prostate cancer cell line LNCaP. Docetaxel dose-dependently induced ID1 transcription, which was mediated by ID1 promoter E-box chromatin modification and c-Myc binding. Stable ID1 overexpression in LNCaP increased cell proliferation, promoted G(1) cell cycle progression, and enhanced docetaxel-induced cytotoxicity. These changes were accompanied by a decrease in cellular mitochondria content, an increase in BCL2 phosphorylation at serine 70, caspase-3 activation, and poly(ADP-ribose) polymerase cleavage. In contrast, ID1 siRNA in the LNCaP and C42B cell lines reduced cell proliferation and decreased docetaxel-induced cytotoxicity by inhibiting cell death. ID1-mediated chemosensitivity enhancement was in part due to ID1 suppression of p21. Overexpression of p21 in LNCaP-ID1-overexpressing cells restored the p21 level and reversed ID1-enhanced chemosensitivity. These molecular data provide a mechanistic rationale for the observed in vivo clinical association between ID1 upregulation and relapse-free survival. Taken together, it shows that ID1 expression has a novel therapeutic role in prostate cancer chemotherapy and prognosis.

Understanding the causes of multidrug resistance in cancer: a comparison of doxorubicin and sunitinib

Multiple molecular, cellular, micro-environmental and systemic causes of anticancer drug resistance have been identified during the last 25 years. At the same time, genome-wide analysis of human tumor tissues has made it possible in principle to assess the expression of critical genes or mutations that determine the response of an individual patient's tumor to drug treatment. Why then do we, with a few exceptions, such as mutation analysis of the EGFR to guide the use of EGFR inhibitors, have no predictive tests to assess a patient's drug sensitivity profile. The problem urges the more with the expanding choice of drugs, which may be beneficial for a fraction of patients only. In this review we discuss recent studies and insights on mechanisms of anticancer drug resistance and try to answer the question: do we understand why a patient responds or fails to respond to therapy? We focus on doxorubicin as example of a classical cytotoxic, DNA damaging agent and on sunitinib, as example of the new generation of (receptor) tyrosine kinase-targeted agents. For both drugs, classical tumor cell autonomous resistance mechanisms, such as drug efflux transporters and mutations in the tumor cell's survival signaling pathways, as well as micro-environment-related resistance mechanisms, such as changes in tumor stromal cell composition, matrix proteins, vascularity, oxygenation and energy metabolism may play a role. Novel agents that target specific mutations in the tumor cell's damage repair (e.g. PARP inhibitors) or that target tumor survival pathways, such as Akt inhibitors, glycolysis inhibitors or mTOR inhibitors, are of high interest. In order to increase the therapeutic index of treatments, fine-tuned synergistic combinations of new and/or classical cytotoxic agents will be designed. More quantitative assessment of potential resistance mechanisms in real tumors and in real time, such as by kinase profiling methodology, will be developed to allow more precise prediction of the optimal drug combination to treat each patient.

N-(4-Hydroxyphenyl) retinamide potentiated paclitaxel for cell cycle arrest and apoptosis in glioblastoma C6 and RG2 cells

Glioblastoma grows aggressively due to its ability to maintain abnormally high potentials for cell proliferation. The present study examines the synergistic actions of N-(4-hydroxyphenyl) retinamide (4-HPR) and paclitaxel (PTX) to control the growth of rat glioblastoma C6 and RG2 cell lines. 4-HPR induced astrocytic differentiation that was accompanied by increased expression of the tight junction protein e-cadherin and sustained down regulation of Id2 (member of inhibitor of differentiation family), catalytic subunit of rat telomerase reverse transcriptase (rTERT), and proliferating cell nuclear antigen (PCNA). Flow cytometric analysis showed that the microtubule stabilizer PTX caused cell cycle deregulation due to G2/M arrest. This in turn could alter the fate of kinetochore-spindle tube dynamics thereby halting cell cycle progression. An interesting observation was the induction of G1/S arrest by a combination of 4-HPR and PTX, altering the G2/M arrest induced by PTX alone. This was further ratified by the upregulation of tumor suppressor protein retinoblastoma, which repressed the expression of the key signaling moieties to induce G1/S arrest. Collectively, the combination of 4-HPR and PTX diminished the survival factors (e.g., rTERT, PCNA, and Bcl-2) to make glioblastoma cells highly prone to apoptosis with activation of cysteine proteases (e.g., calpain, cathepsins, caspase-8, caspase-3). Hence, the combination of 4-HPR and PTX can be considered as an effective therapeutic strategy for controlling the growth of heterogeneous glioblastoma cell populations.

MS-275 synergistically enhances the growth inhibitory effects of RAMBA VN/66-1 in hormone-insensitive PC-3 prostate cancer cells and tumours

Combining drugs, which target different signalling pathways, often decreases adverse side effects while increasing the efficacy of treatment. The objective of our study was to determine if the combination of our novel atypical retinoic acid metabolism-blocking agent (RAMBA) VN/66-1 and a promising histone deacetylase inhibitor N-(2-aminophenyl)4-[N-(pyridine-3-yl-methoxy-carbonyl)aminomethyl]benzamide (MS-275) would show enhanced antineoplastic activity on human PC-3 prostate cancer cells/tumours and also to decipher the molecular mechanisms of action. The combination of VN/66-1+MS-275 was found to be synergistic in inhibiting PC-3 cell growth, caused cell cytostaticity/cytotoxicity and induced marked G2/M phase arrest and apoptosis. In mice with well-established PC-3 tumours, VN/66-1 (5 and 10 mg kg⁻¹ day⁻¹) caused significant suppression of tumour growth compared with mice receiving vehicle alone. Furthermore, treatment with VN/66-1 (10 mg kg⁻¹ day⁻¹)+MS-275 (2.5 mg kg⁻¹ day⁻¹) for 18 days resulted in an 85% reduction in final mean tumour volume compared with control and was more effective than either agent alone. Mechanistic studies indicated that treatment of PC-3 cells/tumours with VN/66-1+MS-275 caused DNA damage (upregulation of γH2AX), hyperacetylation of histones H3 and H4, upregulation of retinoic acid receptor-β, p21^WAF1/CIP1, E-cadherin, and Bad and downregulation of Bcl-2. These data suggest that the mechanism of action of the combination of agents is DNA damage-induced p21 activation, resulting in inhibition of the Cdc2/cyclin B complex and accumulation of cells in G2/M phase. In addition, the combination caused modulation and induction of apoptosis. These results suggest that VN/66-1 or its combination with MS-275 may be a novel therapy for the treatment of prostate carcinoma.