In cancer drug resistance, germline matters too

Understanding of Immune Escape Mechanisms and Advances in Cancer Immunotherapy

Tumor immune escape has emerged as the most significant barrier to cancer therapy. A thorough understanding of tumor immune escape therapy mechanisms is critical for further improving clinical treatment strategies. Currently, research indicates that combining several immunotherapies can boost antitumor efficacy and encourage T cells to play a more active part in the immune assault. To generate a more substantial therapeutic impact, it can establish an ideal tumor microenvironment (TME), encourage T cells to play a role, prevent T cell immune function reversal, and minimize tumor immune tolerance. In this review, we will examine the mechanisms of tumor immune escape and the limits of tumor immune escape therapy, focusing on the current development of immunotherapy based on tumor immune escape mechanisms. Individualized tumor treatment is becoming increasingly apparent as future treatment strategies. In addition, we forecast the future research direction of cancer and the clinical approach for cancer immunotherapy. It will serve as a better reference for researchers working in cancer therapy research.

Pharmacogenetics and the treatment of chronic myeloid leukemia: how relevant clinically? An update

Despite the excellent efficacy and improved clinical responses obtained with imatinib mesylate (IM), development of resistance in a significant proportion of chronic myeloid leukemia (CML) patients on IM therapy have emerged as a challenging problem in clinical practice. Resistance to imatinib can be due to heterogeneous array of factors involving BCR/ABL-dependent and BCR/ABL-independent pathways. Although BCR/ABL mutation is the major contributory factor for IM resistance, reduced bio-availability of IM in leukemic cells is also an important pharmacokinetic factor that contributes to development of resistance to IM in CML patients. The contribution of polymorphisms of the pharmacogenes in relation to IM disposition and treatment outcomes have been studied by various research groups in numerous population cohorts. However, the conclusions arising from these studies have been highly inconsistent. This review encompasses an updated insight into the impact of pharmacogenetic variability on treatment response of IM in CML patients.

The pharmacogenomics of drug resistance to protein kinase inhibitors

Dysregulation of growth factor cell signaling is a major driver of most human cancers. This has led to development of numerous drugs targeting protein kinases, with demonstrated efficacy in the treatment of a wide spectrum of cancers. Despite their high initial response rates and survival benefits, the majority of patients eventually develop resistance to these targeted therapies. This review article discusses examples of established mechanisms of drug resistance to anticancer therapies, including drug target mutations or gene amplifications, emergence of alternate signaling pathways, and pharmacokinetic variation. This reveals a role for pharmacogenomic analysis to identify and monitor for resistance, with possible therapeutic strategies to combat chemoresistance.

NF-κB-driven suppression of FOXO3a contributes to EGFR mutation-independent gefitinib resistance

Therapy with epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (EGFR-TKIs, such as gefitinib or erlotinib) significantly prolongs survival time for patients with tumors harboring an activated mutation on EGFR; however, up to 40% of lung cancer patients exhibit acquired resistance to EGFR-TKIs with an unknown mechanism. FOXO3a, a transcription factor of the forkhead family, triggers apoptosis, but the mechanistic details involved in EGFR-TKI resistance and cancer stemness remain largely unclear. Here, we observed that a high level of FOXO3a was correlated with EGFR mutation-independent EGFR-TKI sensitivity, the suppression of cancer stemness, and better progression-free survival in lung cancer patients. The suppression of FOXO3a obviously increased gefitinib resistance and enhanced the stem-like properties of lung cancer cells; consistent overexpression of FOXO3a in gefitinib-resistant lung cancer cells reduced these effects. Moreover, we identified that miR-155 targeted the 3'UTR of FOXO3a and was transcriptionally regulated by NF-κB, leading to repressed FOXO3a expression and increased gefitinib resistance, as well as enhanced cancer stemness of lung cancer in vitro and in vivo. Our findings indicate that FOXO3a is a significant factor in EGFR mutation-independent gefitinib resistance and the stemness of lung cancer, and suggest that targeting the NF-κB/miR-155/FOXO3a pathway has potential therapeutic value in lung cancer with the acquisition of resistance to EGFR-TKIs.

Overcoming Resistance to Targeted Therapies in Cancer

The recent discovery of oncogenic drivers and subsequent development of novel targeted strategies has significantly added to the therapeutic armamentarium of anti-cancer therapies. Targeting BCR-ABL in chronic myeloid leukemia (CML) or HER2 in breast cancer has led to practice-changing clinical benefits, while promising therapeutic responses have been achieved by precision medicine approaches in EGFR mutant lung cancer, colorectal cancer and BRAF mutant melanoma. However, although initial therapeutic responses to targeted therapies can be substantial, many patients will develop disease progression within 6-12 months. An increasing application of powerful omics-based approaches and improving preclinical models have enabled the rapid identification of secondary resistance mechanisms. Herein, we discuss how this knowledge has translated into rational, novel treatment strategies for relapsed patients in genomically selected cancer populations.

Pharmacogenomics in oncology care

Cancer pharmacogenomics have contributed a number of important discoveries to current cancer treatment, changing the paradigm of treatment decisions. Both somatic and germline mutations are utilized to better understand the underlying biology of cancer growth and treatment response. The level of evidence required to fully translate pharmacogenomic discoveries into the clinic has relied heavily on randomized control trials. In this review, the use of observational studies, as well as, the use of adaptive trials and next generation sequencing to develop the required level of evidence for clinical implementation are discussed.

Epidermal growth factor receptor mutations in lung adenocarcinoma

Despite tremendous progress in the last decade, lung adenocarcinoma still represents a tumor with unfavorable prognosis when detected at advanced clinical stage. High-stage tumors are not amenable to surgical resection, and therefore systemic therapies are needed to control these tumors to prolong patient survival. In the era of molecular and personalized therapeutics, the discovery of mutations in epidermal growth factor receptor (EGFR) in 15-20% of lung adenocarcinomas and the associated response to EGFR-targeting tyrosine kinase (TK) inhibitors have provided a successful avenue of attack in high-stage adenocarcinomas. In this review, we will provide an overview of the EGFR pathway, review the significant somatic EGFR alterations in lung adenocarcinoma and highlight their implications for treatment. In addition, we will examine pathways by which tumors resist EGFR TK therapy, both as primary nonresponders and by acquired resistance. In doing so, we will examine other oncogenic pathways whose status in tumor samples may impact therapeutic responses despite presence of activating EGFR mutations.

The EphB4 receptor tyrosine kinase promotes lung cancer growth: a potential novel therapeutic target

Despite progress in locoregional and systemic therapies, patient survival from lung cancer remains a challenge. Receptor tyrosine kinases are frequently implicated in lung cancer pathogenesis, and some tyrosine kinase inhibition strategies have been effective clinically. The EphB4 receptor tyrosine kinase has recently emerged as a potential target in several other cancers. We sought to systematically study the role of EphB4 in lung cancer. Here, we demonstrate that EphB4 is overexpressed 3-fold in lung tumors compared to paired normal tissues and frequently exhibits gene copy number increases in lung cancer. We also show that overexpression of EphB4 promotes cellular proliferation, colony formation, and motility, while EphB4 inhibition reduces cellular viability in vitro, halts the growth of established tumors in mouse xenograft models when used as a single-target strategy, and causes near-complete regression of established tumors when used in combination with paclitaxel. Taken together, these data suggest an important role for EphB4 as a potential novel therapeutic target in lung cancer. Clinical trials investigating the efficacy of anti-EphB4 therapies as well as combination therapy involving EphB4 inhibition may be warranted.

PUMA and BIM are required for oncogene inactivation-induced apoptosis

The clinical efficacy of tyrosine kinase inhibitors supports the dependence of distinct subsets of cancers on specific driver mutations for survival, a phenomenon called "oncogene addiction." We demonstrate that PUMA and BIM are the key apoptotic effectors of tyrosine kinase inhibitors in breast cancers with amplification of the gene encoding human epidermal growth factor receptor 2 (HER2) and lung cancers with epidermal growth factor receptor (EGFR) mutants. The BH3 domain containing proteins BIM and PUMA can directly activate the proapoptotic proteins BAX and BAK to permeabilize mitochondria, leading to caspase activation and apoptosis. We delineated the signal transduction pathways leading to the induction of BIM and PUMA by tyrosine kinase inhibitors. Inhibition of the mitogen-activated or extracellular signal-regulated protein kinase kinase (MEK)-extracellular signal-regulated kinase (ERK) pathway caused increased abundance of BIM, whereas antagonizing the phosphoinositide 3-kinase (PI3K)-AKT pathway triggered nuclear translocation of the FOXO transcription factors, which directly activated the PUMA promoter. In a mouse breast tumor model, the abundance of PUMA and BIM was increased after inactivation of HER2. Moreover, deficiency of Bim or Puma impaired caspase activation and reduced tumor regression caused by inactivation of HER2. Similarly, deficiency of Puma impeded the regression of EGFR(L858R)-driven mouse lung tumors upon inactivation of the EGFR-activating mutant. Overall, our study identified PUMA and BIM as the sentinels that interconnect kinase signaling networks and the mitochondrion-dependent apoptotic program, which offers therapeutic insights for designing novel cell death mechanism-based anticancer strategies.

A mechanism of resistance to gefitinib mediated by cellular reprogramming and the acquisition of an FGF2-FGFR1 autocrine growth loop

Despite initial and often dramatic responses of epidermal growth factor receptor (EGFR)-addicted lung tumors to the EGFR-specific tyrosine kinase inhibitors (TKIs), gefitinib and erlotinib, nearly all develop resistance and relapse. To explore novel mechanisms mediating acquired resistance, we employed non-small-cell lung cancer (NSCLC) cell lines bearing activating mutations in EGFR and rendered them resistant to EGFR-specific TKIs through chronic adaptation in tissue culture. In addition to previously observed resistance mechanisms including EGFR-T790M ‘gate-keeper' mutations and MET amplification, a subset of the seven chronically adapted NSCLC cell lines including HCC4006, HCC2279 and H1650 cells exhibited marked induction of fibroblast growth factor (FGF) 2 and FGF receptor 1 (FGFR1) mRNA and protein. Also, adaptation to EGFR-specific TKIs was accompanied by an epithelial to mesenchymal transition (EMT) as assessed by changes in CDH1, VIM, ZEB1 and ZEB2 expression and altered growth properties in Matrigel. In adapted cell lines exhibiting increased FGF2 and FGFR1 expression, measures of growth and signaling, but not EMT, were blocked by FGFR-specific TKIs, an FGF-ligand trap and FGFR1 silencing with RNAi. In parental HCC4006 cells, cell growth was strongly inhibited by gefitinib, although drug-resistant clones progress within 10 days. Combined treatment with gefitinib and AZD4547, an FGFR-specific TKI, prevented the outgrowth of drug-resistant clones. Thus, induction of FGF2 and FGFR1 following chronic adaptation to EGFR-specific TKIs provides a novel autocrine receptor tyrosine kinase-driven bypass pathway in a subset of lung cancer cell lines that are initially sensitive to EGFR-specific TKIs. The findings support FGFR-specific TKIs as potentially valuable additions to existing targeted therapeutic strategies with EGFR-specific TKIs to prevent or delay acquired resistance in EGFR-driven NSCLC.

Bim, a proapoptotic protein, up-regulated via transcription factor E2F1-dependent mechanism, functions as a prosurvival molecule in cancer

Proapoptotic Bcl-2 homology 3-only protein Bim plays an important role in Bax/Bak-mediated cytochrome c release and apoptosis. Here, we provide evidence for a novel prosurvival function of Bim in cancer cells. Bim was constitutively overexpressed in multiple prostate and breast cancer cells as well as in primary tumor cells. Quantitative real time PCR analysis showed that Bim was transcriptionally up-regulated. We have identified eight endogenous E2F1-binding sites on the Bim promoter using in silico analysis. Luciferase assay demonstrated that Bim expression was E2F1-dependent as mutation of the E2F1-binding sites on the Bim promoter inhibited luciferase activities. In support, E2F1 silencing led to the loss of Bim expression in cancer cells. Bim primarily localized to mitochondrial and cytoskeleton-associated fractions. Bim silencing or microinjection of anti-Bim antibodies into the cell cytoplasm resulted in cell rounding, detachment, and subsequent apoptosis. We observed up-regulation of prosurvival proteins Bcl-xL and Mcl-1, which sequester Bim in cancer cells. In addition, a phosphorylated form of Bim was also elevated in cancer cells. These findings suggest that the constitutively overexpressed Bim may function as a prosurvival molecule in epithelial cancer cells, and phosphorylation and association with Bcl-xL/Mcl-1 block its proapoptotic functions.

Network-based drug discovery by integrating systems biology and computational technologies

Network-based intervention has been a trend of curing systemic diseases, but it relies on regimen optimization and valid multi-target actions of the drugs. The complex multi-component nature of medicinal herbs may serve as valuable resources for network-based multi-target drug discovery due to its potential treatment effects by synergy. Recently, robustness of multiple systems biology platforms shows powerful to uncover molecular mechanisms and connections between the drugs and their targeting dynamic network. However, optimization methods of drug combination are insufficient, owning to lacking of tighter integration across multiple '-omics' databases. The newly developed algorithm- or network-based computational models can tightly integrate '-omics' databases and optimize combinational regimens of drug development, which encourage using medicinal herbs to develop into new wave of network-based multi-target drugs. However, challenges on further integration across the databases of medicinal herbs with multiple system biology platforms for multi-target drug optimization remain to the uncertain reliability of individual data sets, width and depth and degree of standardization of herbal medicine. Standardization of the methodology and terminology of multiple system biology and herbal database would facilitate the integration. Enhance public accessible databases and the number of research using system biology platform on herbal medicine would be helpful. Further integration across various '-omics' platforms and computational tools would accelerate development of network-based drug discovery and network medicine.