The potential of positron-emission tomography to study anticancer-drug resistance

Current Advances and Outlook in Gastric Cancer Chemoresistance: A Review

BACKGROUND

Surgical resection of the lesion is the standard primary treatment of gastric cancer. Unfortunately, most patients are already in the advanced stage of the disease when they are diagnosed with gastric cancer. Alternative therapies, such as radiation therapy and chemotherapy, can achieve only very limited benefits. The emergence of cancer drug resistance has always been the major obstacle to the cure of tumors. The main goal of modern cancer pharmacology is to determine the underlying mechanism of anticancer drugs.

OBJECTIVE

Here, we mainly review the latest research results related to the mechanism of chemotherapy resistance in gastric cancer, the application of natural products in overcoming the chemotherapy resistance of gastric cancer, and the new strategies currently being developed to treat tumors based on immunotherapy and gene therapy.

CONCLUSION

The emergence of cancer drug resistance is the main obstacle in achieving alleviation and final cure for gastric cancer. Mixed therapies are considered to be a possible way to overcome chemoresistance. Natural products are the main resource for discovering new drugs specific for treating chemoresistance, and further research is needed to clarify the mechanism of natural product activity in patients. .

Intratumor dihydropyrimidine dehydrogenase mRNA expression levels are decreased in extramammary Paget's disease

S-1, a 5-fluorouracil (5-FU)-based anti-cancer agent, is an important drug for treating metastatic extramammary Paget's disease (EMPD). Although intratumor expression levels of 5-FU metabolism enzymes have been studied widely in many solid tumors, no studies have examined on the expression levels of thymidylate synthase (TS), orotate phosphoribosyl-transferase (OPRT) or dihydropyrimidine dehydrogenase (DPD) in skin cancers. The aim of this study was to estimate the intratumoral mRNA expression levels of these genes in EMPD by real time PCR. Intratumoral DPD mRNA levels were decreased in EMPD compared to those in normal skin, but its intratumoral DPD mRNA expression levels were not correlated with clinical manifestations. Intratumoral DPD mRNA levels were positively correlated with OPRT mRNA levels in EMPD. Based on these results, low expression of intratumoral DPD mRNA in EMPD may contribute to the pathogenesis of this disease.

Approaches and genetic determinants in predicting response to neoadjuvant chemotherapy in locally advanced gastric cancer

Gastric cancer remains a major health burden worldwide. There is near-universal agreement that neoadjuvant chemotherapy (NAC) is a preferred management for locally advanced gastric cancer (LAGC). However, the optimal approach for an individual patient is still not clear and remains controversial, which could be at least partly explained by the lack of predictive tools. The ability to predict chemosensitivity from NAC in routine clinical practice is difficult and is an area of intense investigation, especially in the Precision-Medicine Era. Available consistent evidence suggests that a favorable tumor histopathological response to NAC may be a useful positive prognostic marker in gastric cancer. Hence, it is reasonable to speculate that making the histopathological response from NAC predictable will dramatically facility the NAC and improve patients' outcome. This review provides an overview on the current status of predictive biomarkers for histopathological response from NAC in LAGC, including clinicopathological variables, imaging and molecular testing. Furthermore, limitations and future perspectives are also discussed.

Radiosynthesis and pharmacokinetics of [18F]fluoroethyl bufalin in hepatocellular carcinoma-bearing mice

Purpose

Bufalin, the main component of a Chinese traditional medicine chansu, shows convincing anticancer effects in a lot of tumor cell lines. However, its in vivo behavior is still unclear. This research aimed to evaluate how bufalin was dynamically absorbed after intravenous injection in animal models. We developed a radiosynthesis method of [¹⁸F]fluoroethyl bufalin to noninvasively evaluate the tissue biodistribution and pharmacokinetics in hepatocellular carcinoma-bearing mice.

Methods

[¹⁸F]fluoroethyl bufalin was synthesized with conjugation of 18F-CH₂CH₂OTs and bufalin. The radiochemical purity was proved by the radio-high-performance liquid chromatography (HPLC). The pharmacokinetic studies of [¹⁸F]fluoroethyl bufalin were then performed in Institute of Cancer Research (ICR) mice. Furthermore, the biodistribution and metabolism of [¹⁸F]fluoroethyl bufalin in HepG2 and SMMC-7721 tumor-bearing nude mice were studied in vivo by micro-positron emission tomography (micro-PET).

Results

The radiochemical purity (RCP) of [¹⁸F]fluoroethyl bufalin confirmed by radio-HPLC was 99%±0.18%, and [¹⁸F]fluoroethyl bufalin showed good in vitro and in vivo stabilities. Blood dynamics of [¹⁸F]fluoroethyl bufalin conformed to the two compartments in the ICR mice model. The pharmacokinetic parameters of [¹⁸F]fluoroethyl bufalin were calculated by DAS 2.0 software. The area under concentration–time curve (AUC_0–t) and the values of clearance (CL) were 540.137 μg/L·min and 0.001 L/min/kg, respectively. The half-life of distribution (t_1/2α) and half-life of elimination (t_1/2β) were 0.693 and 510.223 min, respectively. Micro-PET imaging showed that [¹⁸F]fluoroethyl bufalin was quickly distributed via the blood circulation; the major tissue biodistribution of [¹⁸F]fluoroethyl bufalin in HepG2 and SMMC-7721 tumor-bearing mice was liver and bladder.

Conclusion

[¹⁸F]fluoroethyl bufalin was accumulated rapidly in the liver at an early time point (5 min) post injection (pi) and then declined slowly, mainly through both the hepatic pathway and the renal pathway. Our study showed the biodistribution of [¹⁸F]fluoroethyl bufalin in micro-PET images and provided visible information for demonstrating the bioactivities of bufalin.

Assessment of the biodistribution of an [(18) F]FDG-loaded perfluorocarbon double emulsion using dynamic micro-PET in rats

Perfluorocarbon (PFC) double emulsions loaded with a water-soluble, therapeutic agent can be triggered by ultrasound in a process known as acoustic droplet vaporization. Elucidating the stability and biodistribution of these sonosensitive vehicles and encapsulated agents is critical in developing targeted drug delivery strategies using ultrasound. [(18) F]fluorodeoxyglucose (FDG) was encapsulated in a PFC double emulsion and the in vitro diffusion of FDG was assessed using a Franz diffusion cell. Using dynamic micro-positron emission tomography and direct tissue sampling, the biodistribution of FDG administered as a solution (i.e. non-emulsified) or as an emulsion was studied in Fisher 344 rats (n = 6) bearing subcutaneous 9L gliosarcoma. Standardized uptake values (SUVs) and area under the curve of the SUV (AUCSUV ) of FDG were calculated for various tissues. The FDG flux from the emulsion decreased by up to a factor of 6.9 compared with the FDG solution. FDG uptake, calculated from the AUCSUV , decreased by 36% and 44% for brain and tumor, respectively, when comparing FDG solution vs FDG emulsion (p < 0.01). Decreases in AUCSUV in highly metabolic tissues such as brain and tumor demonstrated retention of FDG within the double emulsion. No statistically significant differences in lung AUCSUV were observed, suggesting minimal accumulation of the emulsion in the pulmonary capillary bed. The liver AUCSUV increased by 356% for the FDG emulsion, thus indicating significant hepatic retention of the emulsion.

Development and experimental medicine applications of PET in oncology: a historical perspective

Nearly 90 years of scientific research have led to the use of PET and the ability to forge advances in the field of oncology. In this Historial Review we outline the key developments made with this imaging technique, including the evolution of cyclotrons and scanners, together with the associated advances made in image reconstruction, presentation, analysis of data, and radiochemistry. The applications of PET to experimental medicine are summarised, and we cover how these are related to the use and development of PET, especially in the assessment of tumour biology and pharmacology. The use of PET in clinical oncology and for tissue pharmacokinetic and pharmacodynamic studies as a means of supporting drug development is detailed. The current limitations of the technology are also discussed.

Radiopharmaceutical chemistry for positron emission tomography

Molecular imaging is an emerging technology that allows the visualization of interactions between molecular probes and biological targets. Molecules that either direct or are subject to homeostatic controls in biological systems could be labeled with the appropriate radioisotopes for the quantitative measurement of selected molecular interactions during normal tissue homeostasis and again after perturbations of the normal state. In particular, positron emission tomography (PET) offers picomolar sensitivity and is a fully translational technique that requires specific probes radiolabeled with a usually short-lived positron-emitting radionuclide. PET has provided the capability of measuring biological processes at the molecular and metabolic levels in vivo by the detection of the gamma rays formed as a result of the annihilation of the positrons emitted. Despite the great wealth of information that such probes can provide, the potential of PET strongly depends on the availability of suitable PET radiotracers. However, the development of new imaging probes for PET is far from trivial and radiochemistry is a major limiting factor for the field of PET. In this review, we provided an overview of the most common chemical approaches for the synthesis of PET-labeled molecules and highlighted the most recent developments and trends. The discussed PET radionuclides include ¹¹C (t₁(/)₂=20.4min), ¹³N (t₁(/)₂=9.9min), ¹⁵O (t₁(/)₂=2min), ⁶⁸Ga (t₁(/)₂=68min), ¹⁸F (t₁(/)₂=109.8min), ⁶⁴Cu (t₁(/)₂=12.7h), and ¹²⁴I (t₁(/)₂=4.12d).

Synthesis, functionalization, and biomedical applications of multifunctional magnetic nanoparticles

Synthesis of multifunctional magnetic nanoparticles (MFMNPs) is one of the most active research areas in advanced materials. MFMNPs that have magnetic properties and other functionalities have been demonstrated to show great promise as multimodality imaging probes. Their multifunctional surfaces also allow rational conjugations of biological and drug molecules,making it possible to achieve target-specific diagnostics and therapeutics.This review fi rst outlines the synthesis of MNPs of metal oxides and alloy sand then focuses on recent developments in the fabrication of MFMNPs of core/shell, dumbbell, and composite hybrid type. It also summarizes the general strategies applied for NP surface functionalization. The review further highlights some exciting examples of these MFMNPs for multimodality imaging and for target-specific drug/gene delivery applications.

Fluorinase: a tool for the synthesis of 18F-labeled sugars and nucleosides for PET

There is an increasing interest in the preparation of 18F-labeled radiopharmaceuticals with potential applications in PET for medicinal imaging. Appropriate synthetic methods require a quick and efficient route in which to incorporate the 18F into a ligand, due to the relatively short half-life of the 18F isotope. Enzymatic methods are rare in this area; however, the discovery of a fluorinating enzyme from Streptomyces cattleya (EC 2.5.1.63) has opened up the possibility of the enzymatic synthesis and formation of C-18F bonds from the [18F]fluoride ion. In this article, the development of enzymatic preparations of 18F-labeled sugars and nucleosides as potential radiotracers using the fluorinase from S. cattleya for PET applications is reviewed. Enzymatic reactions are not traditional in PET synthesis, but this enzyme has some attractive features. The enzyme is available in an overexpressed form from Escherichia coli and it is relatively stable and can be easily purified and manipulated. Most notably, it utilizes [18F] fluoride, the form of the isotope normally generated by the cyclotron and usually in very high specific radioactivity. The disadvantage with the enzyme is that it is substrate specific; however, when the fluorinase is used in combination biotransformations with a second or third enzyme, then a range of radiolabeled nucleosides and ribose sugars can be prepared. The fluorinase enzyme has emerged as a curiosity from biosynthesis studies, but it now has some potential as a new catalyst for 18F incorporation for PET syntheses. The focus is now on delivering a user-friendly catalyst to the PET synthesis community and establishing a clinical role for some of the 18F-labeled molecules available using this technology.

Sleep and recovery from critical illness and injury: a review of theory, current practice, and future directions

OBJECTIVE

The objectives of this article were to describe the deleterious effects of sleep deprivation, characterize sleep in patients cared for in an intensive care unit (ICU) environment, and propose an integrated strategy to improve sleep in critical care units.

STUDY SELECTION

Clinical trials and review articles assessing sleep deprivation, sleep in a critical care setting, and interventions to improve sleep in the critical care environment were identified through an in depth PubMed search.

CONCLUSIONS

Sleep deprivation and disruption are particularly prevalent in patients cared for in the critical care environment. Although numerous observational studies during the past several decades have demonstrated that sleep in patients cared for in ICUs is highly abnormal, little is known about the effects of poor sleep quality on outcomes from critical illness or injury. Reasons for sleep deprivation during recovery from illness and injury in the ICU are multifactorial. Major contributing factors in this patient population are type and severity of underlying illness, the pathophysiology of acute illness/injury, pain from surgical procedures, and perhaps most importantly, the ICU environment itself. Sleep in ICU patients is characterized by prolonged sleep latencies, sleep fragmentation, decreased sleep efficiency, frequent arousals, a predominance of stage 1 and 2 nonrapid eye movement sleep, decreased or absent stage 3 and 4 nonrapid eye movement sleep, and decreased or absent rapid eye movement sleep. Optimizing patient comfort and ensuring that patients achieve adequate restorative sleep while cared for in the ICU is an arduous task. However, environmental alterations in the ICU may reliably improve sleep quality and subsequently alter outcomes during recovery from critical illness and injury.

Assessing responses to cancer therapy using molecular imaging

Tumor responses to therapy in the clinic are still evaluated primarily from non-invasive imaging measurements of reductions in tumor size. This approach, however, lacks sensitivity and can only give a delayed indication of a positive response to treatment. Major advances in our understanding of the molecular mechanisms responsible for cancer, combined with new targeted clinical imaging technologies designed to detect the molecular correlates of disease progression and response to treatment, are set to revolutionize our approach to the detection and treatment of the disease. We describe here the imaging technologies available to image tumor cell proliferation and migration, metabolism, receptor and gene expression, apoptosis and tumor angiogenesis and vascular function, and show how measurements of these parameters can be used to give early indications of positive responses to treatment or to detect drug resistance and/or disease recurrence. Special emphasis has been placed on those applications that are already used in the clinic and those that are likely to translate into clinical application in the near future or whose use in preclinical studies is likely to facilitate translation of new treatments into the clinic.

Estrogen induces death of tamoxifen-resistant MCF-7 cells: contrasting effect of the estrogen receptor downregulator fulvestrant

A common problem in breast cancer therapy is resistance to the antiestrogen tamoxifen. However, tamoxifen-resistant breast tumors can still respond to other hormonal therapies. In animal models of tamoxifen-resistant breast cancer cells, physiological levels of estrogen can induce tumor regression. Recently, the estrogen receptor downregulator fulvestrant was shown to promote tumor growth of tamoxifen-resistant cells when added in combination with physiological levels of estrogen. Here, we show, using a cell culture model, that continuous exposure of tamoxifen-resistant cells to physiological levels of estrogen leads to cell death. Addition of the estrogen receptor downregulator fulvestrant prevents estrogen-induced death in a dose-dependent manner. Our data indicate that endogenous levels of estrogen affect the response of tamoxifen-resistant cells to fulvestrant. These results suggest that failure of fulvestrant to inhibit tumor growth in some tamoxifen-resistant patients may be due to endogenous estrogen levels. Moreover, these studies support short-term treatment with estrogen as a second-line hormonal therapy for tamoxifen-resistant breast cancer.

Rapid methylation on carbon frameworks useful for the synthesis of 11CH3-incorporated PET tracers: Pd(0)-mediated rapid coupling of methyl iodide with an alkenyltributylstannane leading to a 1-methylalkene

The Pd(0)-mediated rapid coupling of methyl iodide with an excess of alkenyltributylstannane was examined with the aim of incorporating a short-lived 11C-labeled methyl group into a biologically significant organic compound with a 1-methylalkene unit for the synthesis of a PET tracer. Four sets of reaction conditions (A-D) were used, all performed in DMF at 60 degrees C for 5 min. Condition B, using CH3I/stannane/Pd2(dba)3/P(o-tolyl)3/CuCl/K2CO3 (1:40:0.5:4-6:2:5), works well in almost all cases. Condition D, using CH3I/stannane/Pd2(dba)3/P(o-tolyl)3/CuX (X = Br, Cl, or I)/CsF (1:40:0.5-5:2-20:2-20:5-50), shows the best results with regard to general applicability to tin substrates, affording the corresponding methylated product in >90% yield based on consumption of methyl iodide. P(t-Bu)2Me was less effective than P(o-tolyl)3, particularly for alpha,beta-unsaturated carbonyl substrates. No regio- or stereoisomerization occurred under these reaction conditions. The efficiency of the protocol was demonstrated by synthesis of an 11C-methylated compound.

Drug resistance in cancer

Cancer Research UK has recently sponsored a meeting, organized by the UK Medical Research Council, on cancer drug resistance. Several of the molecular mechanisms responsible for this clinical outcome, such as DNA interstrand crosslink repair, apoptosis evasion, cytochrome P450 and P-glycoprotein, were discussed. There was a special focus on leukaemia, breast and ovarian cancer, and the potential use of positron-emission tomography to study anticancer-drug resistance. The progress made in translating these findings to the clinic, like Gefitinib, P-glycoprotein phenotyping, or genome-wide analysis technology, was also discussed.