Current Pharmaceutical Design - Volume 20, Issue 24, 2014

The disappointing results in long-term survival of patients affected by non-small cell lung cancer (NSCLC) may be attributed, at least in part, to the lack of knowledge on the way by which genetic characteristics in normal and neoplastic cells affect responsiveness as well as metabolism of chemotherapy and new targeted agents. This issue deserves further pharmacogenetics studies, in order to identify patients who are most likely to benefit from specific therapies selected on the base of the individual and tumor genetic features, thus improving the efficacy/toxicity profile of the treatment strategy. Even if most meta-analyses in NSCLC yielded contradictory results, a number of candidate biomarkers for response/resistance to conventional chemotherapeutic agents such as gemcitabine, platinumcompounds, pemetrexed and taxanes have been proposed. Similarly, recent studies suggested the key role of polymorphisms in the prediction of toxicity to EGFR-targeted agents. However, larger prospective randomized trials of personalized therapy to validate these biomarkers are still needed. The unification of the technical procedures, as well as additional investigation to unravel pivotal factors influencing genotype-phenotype relationships, represent other crucial issues. From this perspective, functional studies aiming at unravel eventual pharmacokinetics/pharmacodynamics interactions are critical for the pharmacogenetic optimization of anti-cancer regimens. With the development of high-throughput technologies, including whole exome analyses, the traditional pharmacogenetic approach that till present has relied only on candidate genes suspected of influencing drug response/metabolism can be fulfilled with further lists of potential predictive alleles. The clinical implementation of such pharmacogenetics/genomics studies as well as of therapeutic drug monitoring could enable clinicians to personalize treatment to enhance efficacy and/or limit toxicity.

Treatment of lung cancer is improving, also based on the identification of molecular characteristics of the tumor, of which some already constitute promising targets. One of the molecular characteristics thought to play an important role in lung cancer is DNA repair dysfunctionality. Deregulated expression of DNA repair proteins, such as PARP, has been studied in lung cancer as a possible biomarker and clinically useful target, but the literature remains relatively poor. Pharmacological inactivation of PARP has allowed the identification of a synthetic lethality with a second DNA repair protein such as BRCA1, but has also shown the potential to sensitize tumors to commonly used cytotoxic agents. The current manuscript reviews data regarding PARP in the context of DNA repair and its different pathways, as well as the clinical data generated until now with PARP inhibitors. A deeper understanding of the DNA damage response in lung malignancies, and particularly a clarification of the crosstalk between DNA repair functionality and genetic stability, is the key to optimize the development of PARP inhibitors in the setting of NSCLC.

A new era in lung cancer targeted therapy arrived with the discovery of a subset of lung adenocarcinomas harboring activating mutations of the epidermal growth factor receptor (EGFR), whose tyrosine kinase activity can be selectively blocked by small molecule pharmaceuticals referred as tyrosine kinase inhibitors (TKIs). This was the starting point for a less toxic and more effective treatment strategy for a disease that has historically presented as chemorefractory and highly lethal. In spite of this progress, only 80% of the patients treated with this class of compounds will obtain a clinical benefit, of variable magnitude and duration, with remaining patients being primarily refractory to the treatment. Moreover, responding tumors will eventually develop acquired resistance to TKIs and progress to more advanced stages. In this review we summarize the current knowledge with regard to the mechanisms leading to tumor regression and the modifiers of this primary response that determine significant variability in sensitivity of tumors harboring EGFR activating mutations, ranging from complete remission to primary refractoriness. We also analyze the mechanisms of secondary resistance and the strategies the scientific community is exploring in order to overcome these barriers.

The epidermal growth factor receptor (EGFR) is among the most important targets in the treatment of advanced non-small cell lung cancer (NSCLC). Erlotinib and gefitinib, two small molecules, are reversible EGFR tyrosine kinase inhibitors (TKIs). Non-small cell lung cancers with EGFR mutations, are characterized by excellent responses when treated with the EGFR-TKIs gefitinib and erlotinib. However, all the patients with tumors harbouring EGFR mutations experience disease progression after a median of 10 to 14 months of treatment with gefitinib or erlotinib. A group of new generation EGFR-TKIs irreversibly inhibit EGFR-TK and represent one of the strategies that may potentially overcome the acquired resistance to gefitinib and erlotinib or achieve better outcomes than reversible inhibitors in the first-line treatment of EGFR mutant lung cancers. Afatinib (BIBW 2992) and PF299804 are the irreversible EGFR-TKIs with the most relevant data in the treatment of advanced NSCLC, as primary EGFR-targeted therapy and after resistance to reversible EGFR-TKIs. However, to date, the role of irreversible EGFR inhibitors remains to be defined.

Drugs directed against Epidermal Growth Factor Receptor (EGFR), namely tyrosine kinase inhibitors erlotinib and gefitinib, and anti-angiogenic agents, namely the anti-Vascular Endothelial Growth Factor (VEGF) antibody bevacizumab, have independently demonstrated clinical benefit in the treatment of patients with advanced non-small cell lung cancer (NSCLC), and are currently approved for use in clinical practice. Pre-clinical studies have shown promising results with the combination of anti-EGFR and anti-angiogenesis drugs in different tumor models, including NSCLC. Several clinical trials have been conducted to verify if the combination of the two therapeutic strategies could improve the outcome in the setting of advanced NSCLC. The largest body of evidence has been produced testing the combination of erlotinib plus bevacizumab, or erlotinib plus a multi-targeted receptor tyrosine kinase inhibitor, namely sunitinib or sorafenib. Furthermore, several dual inhibitors, targeting both EGFR and VEGFR, have been tested in advanced NSCLC, with the greatest body of evidence produced with vandetanib. However, despite an intriguing pre-clinical background, the combination strategy has not yet produced clinically relevant results. Several phase III trials showed an improvement in progression-free survival, underlining some activity of targeting both pathways concurrently, but no trial has demonstrated an impact on overall survival to date. Unfortunately, the vast majority of trials conducted in this setting have been performed without any selection criteria based on molecular characteristics, compromising the chance of detecting a potentially relevant benefit in selected subgroup of patients. In recent years, the important interaction between the efficacy of EGFR inhibitors and the presence of EGFR activating mutations in tumor cells has been repeatedly demonstrated. On the other hand, we still have no clear idea about predictive factors of efficacy for bevacizumab and other anti-angiogenic drugs. This is probably the real challenge to optimize the use of these drugs and to fully evaluate the real clinical potential of a combination strategy.

Cell proliferation, survival, differentiation, migration and metabolism are some of the fundamental cellular processes tightly controlled by the activity of tyrosine-kinase receptors (RTKs). The aberrant signaling of RTKs contributes to cancer growth and survival and has become important target for therapeutic approaches. Well-characterized kinase molecular target in lung cancer, in particular in non-small cell lung cancer (NSCLC), is the activated epidermal growth factor receptor (EGFR) pathway. More recently, the oncogenic role of other two tyrosine-kinases, the hepatocyte growth factor receptor (MET) and the anaplastic lymphoma kinase (ALK), has been recognized. Many different therapeutic strategies have been investigated with the goal to inhibit these receptors, subsequent downstream signaling cascades and arrest tumor growth. This review will discuss the MET and ALK pathways, the different strategies of their inhibition and the potential approaches to overcome acquired resistance to kinase inhibitors in these two genes.

RAS family proteins are important signaling molecules that regulate cell growth, survival and differentiation by coupling receptor activation to downstream effector pathways. Three distinct genes encode for the three different proteins H-, K-, and N- RAS. These proteins share high sequence homology, particularly at the N-Terminal domain. Among them, K-RAS is one of the most frequently mutated in human cancer. The majority of the mutations present in K-RAS are at codon 12 (from 80 to 100%) followed by codon 13 and 61. In all cases, aminoacid change leads to a constitutively activated protein. K-RAS mutations have a role in tumor development as well as in tumor progression and resistance. Despite the various studies which have been published, the prognostic and predictive role of K-RAS mutations is still under debate. Keeping in mind that the glycine present at position 12 can be substituted by valine, aspartic acid or cysteine, it could be well understood that each different substitution plays a different role in K-RAS-dependent processes. The present article focuses on the molecular and biological characteristics of K-RAS protein, its role in NSCLC tumor development and progression. We also present an overview of the preclinical models both in vitro and in vivo available to determine the role of K-RAS in tumor progression and response to treatment and on the recent results obtained in this field. Finally, we have considered the impact of KRAS mutations in clinical practice, analyzing the different recent trials that have taken into consideration K-RAS.

The RAS/RAF/MEK/ ERK and the PI3K/AKT/mTOR pathways govern fundamental physiological processes, such as cell proliferation, differentiation, metabolism, cytoskeleton reorganization and cell death and survival. Constitutive activation of these signal transduction pathways is a required hallmark of cancer and dysregulation, on either genetic or epigenetic grounds, of these pathways has been implicated in the initiation, progression and metastastic spread of lung cances. Targeting components of the MAPK and PI3K cascades is thus an attractive strategy in the development of novel therapeutic approaches to treat lung cancer, although the use of single pathway inhibitors has met with limited clinical success so far. Indeed, the presence of intra- and inter-pathway compensatory loops that re-activate the very same cascade, either upstream or downstream the point of pharmacological blockade, or activate the alternate pathway following the blockade of one signaling cascade has been demonstrated, potentially driving preclinical (and possibly clinical) resistance. Therefore, the blockade of both pathways with combinations of signaling inhibitors might result in a more efficient anti-tumor effect, and thus potentially overcome and/or delay clinical resistance, as compared with single agent. The current review aims at summarizing the current status of preclinical and clinical research with regard to pathway crosstalks between the MAPK and PI3K cascades in NSCLC and the rationale for combined therapeutic pathway targeting.

The discovery of specific molecular alterations (i.e. EGFR activating mutations, EML4/ALK translocation, ROS1 rearrangements) in a selected population of patients affected by non small cell lung cancer (NSCLC) translated into effective treatments for this small but well defined fraction of patients, driven by the use of predictive biomarkers of efficacy for targeted agents. Unfortunately, the same reliable predictive biomarkers are lacking for anti-angiogenic drugs. Angiogenesis plays a major role in the progression of NSCLC, however, anti-angiogenic agents provided a minimal, although significant, clinical benefit in unselected populations, burdened by a not negligible toxicities. In this context, no validated angiogenic factor or other molecular biomarker of angiogenesis can reliably predict clinical outcome, sensitivity, early response or resistance to any of the investigated anti-angiogenic therapies currently used. Moreover, the available clinical data are prevalently retrospective, underpowered, and, in many cases, contradictory, thus underscoring that the understanding of the complex architecture of angiogenic signaling is still incomplete. We here review the currently available studies on the effect of anti-angiogenic drugs in NSCLC, with a particular focus on bio-molecular factors that are regarded as potential predictors of treatment efficacy.

The advent of molecular targeted agents is changing the treatment of solid tumors. In non-small-cell lung cancer, compounds directed against oncogenic proteins offer novel therapeutic opportunities for a fraction of patients whose tumors harbor specific genetic defects. With the increased level of resolution achieved by high-throughput technologies, the taxonomy of lung cancer is rapidly changing. For instance, by cataloguing genetic abnormalities in squamous cell lung cancer the Cancer Genome Atlas Network revealed the existence of multiple molecular entities, each one characterized by specific molecular abnormalities, and by a different spectrum of activated/ inactivated molecular networks. Although this increased complexity could be perceived as a further drawback in effective anticancer therapy, on the other hand the combined interrogation of genomic and proteomic data is expected to provide the whole molecular map of each tumor, and to determine the information flow in the explored biological system. In particular, novel genetic and proteomic approaches are offering the opportunity for matching specific genetic defects and aberrant protein-protein interactions with active pathwaytargeted inhibitors. Moreover, the isolation and characterization of a cellular pool endowed with stem-like traits, and able to recapitulate the parental disease in animals, is enabling investigators to recreate the individual patient tumor in the laboratory. In this article, we discuss how novel technologies and cellular and animal models, applied to lung cancer research, hold the potential to foster a new wave of biomarker-driven clinical trials.

A biological characterization of tumor tissue is mandatory in NSCLC patients to identify cases at high risk of recurrence and to drive current targeted therapies such as EGFR and ALK inhibitors. In addition, promising results have been reported on the utility of molecular parameters for the prediction of the efficacy of systemic cytotoxic therapy. MicroRNAs (miRNAs) are small single stranded non-coding RNA molecules, which regulate gene expression at the posttranscriptional level. Growing evidence suggests that miRNAs are expressed aberrantly in many human cancers and that they play a significant role in carcinogenesis and cancer progression. There is increasing evidence that miRNA profiling may become an accurate way to differentiate tumor subtypes, determine prognosis and response to therapy. This review aims to summarize the current literature on this rapidly evolving field.