Plant cell cultures: Chemical factories of secondary metabolites

Medical imaging technologies have undergone explosive growth over the past few decades and now play a central role in clinical oncology. But the truly transformative power of imaging in the clinical management of cancer patients lies ahead. Today, imaging is at a crossroads, with molecularly targeted imaging agents expected to broadly expand the capabilities of conventional anatomical imaging methods. Molecular imaging will allow clinicians to not only see where a tumor is located in the body, but also to visualize the expression and activity of specific molecules (e.g., proteases and protein kinases) and biological processes (e.g., apoptosis, angiogenesis, and metastasis) that influence tumor behavior and/or response to therapy. This information is expected to have a major impact on cancer detection, individualized treatment, and drug development, as well as our understanding of how cancer arises.

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Molecular Imaging in Cancer

Monoclonal antibodies (mAbs) are now established as targeted therapies for malignancies, transplant rejection, autoimmune and infectious diseases, as well as a range of new indications. However, administration of mAbs carries the risk of immune reactions such as acute anaphylaxis, serum sickness and the generation of antibodies. In addition, there are numerous adverse effects of mAbs that are related to their specific targets, including infections and cancer, autoimmune disease, and organ-specific adverse events such as cardiotoxicity. In March 2006, a life-threatening cytokine release syndrome occurred during a first-in-human study with TGN1412 (a CD28-specific superagonist mAb), resulting in a range of recommendations to improve the safety of initial human clinical studies with mAbs. Here, we review some of the adverse effects encountered with mAb therapies, and discuss advances in preclinical testing and antibody technology aimed at minimizing the risk of these events.

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The safety and side effects of monoclonal antibodies

The consumption of cruciferous vegetables has long been associated with a reduced risk in the occurrence of cancer at various sites, including the prostate, lung, breast and colon. This protective effect is attributed to isothiocyanates present in these vegetables, and sulforaphane (SF), present in broccoli, is by far the most extensively studied to uncover the mechanisms behind this chemoprotection. The major mechanism by which SF protects cells was traditionally thought to be through Nrf2-mediated induction of phase 2 detoxification enzymes that elevate cell defense against oxidative damage and promote the removal of carcinogens. However, it is becoming clear that there are multiple mechanisms activated in response to SF, including suppression of cytochrome P450 enzymes, induction of apoptotic pathways, suppression of cell cycle progression, inhibition of angiogenesis and anti-inflammatory activity. Moreover, these mechanisms seem to have some degree of interaction to synergistically afford chemoprevention.

Molecular basis for chemoprevention by sulforaphane: a comprehensive review.

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1016/j.molonc.2008.04.001

Imaging and cancer: A review

The process of early clinical drug development has changed little over the past 20 years despite an up to 40% failure rate associated with inappropriate drug metabolism and pharmacokinetics of candidate molecules. A new method of obtaining human metabolism data known as microdosing has been developed which will permit smarter candidate selection by taking investigational drugs into humans earlier. Microdosing depends on the availability of two ultrasensitive 'big-physics' techniques: positron emission tomography (PET) can provide pharmacodynamic information, whereas accelerator mass spectrometry (AMS) provides pharmacokinetic information. Microdosing allows safer human studies as well as reducing the use of animals in preclinical toxicology.

Big physics, small doses: the use of AMS and PET in human microdosing of development drugs.

Objectives: A volunteer trial was performed to compare the pharmacokinetics of 5 drugs-warfarin, ZK253 (Schering), diazepam, midazolam, and erythromycin-when administered at a microdose or pharmacologic dose. Each compound was chosen to represent a situation in which prediction of pharmacokinetics from either animal or in vitro studies (or both) was or is likely to be problematic. Methods: In a crossover design volunteers received (1) 1 of the 5 compounds as a microdose labeled with radioactive carbon (carbon 14) (100 I¼g), (2) the corresponding 14C-labeled therapeutic dose on a separate occasion, and (3) simultaneous administration of an intravenous 14C-labeled microdose and an oral therapeutic dose for ZK253, midazolam, and erythromycin. Analysis of 14C-labeled drugs in plasma was done by use of HPLC followed by accelerator mass spectrometry. Liquid chromatography-tandem mass spectrometry was used to measure plasma concentrations of ZK253, midazolam, and erythromycin at therapeutic concentrations, whereas HPLC-accelerator mass spectrometry was used to measure warfarin and diazepam concentrations. Results: Good concordance between microdose and therapeutic dose pharmacokinetics was observed for diazepam (half-life t1/2 of 45.1 hours, clearance CL of 1.38 L/h, and volume of distribution V of 90.1 L for 100 I¼g and t1/2 of 35.7 hours, CL of 1.3 L/h, and V of 123 L for 10 mg), midazolam (t1/2 of 4.87 hours, CL of 21.2 L/h, V of 145 L, and oral bioavailability F of 0.23 for 100 I¼g and t1/2 of 3.31 hours, CL of 20.4 L/h, V of 75 L, and F of 0.22 for 7.5 mg), and development compound ZK253 (F = <1% for both 100 I¼g and 50 mg). For warfarin, clearance was reasonably well predicted (0.17 L/h for 100 I¼g and 0.26 L/h for 5 mg), but the discrepancy observed in distribution (67 L for 100 I¼g and 17.9 L for 5 mg) was probably a result of high-affinity, low-capacity tissue binding. The oral microdose of erythromycin failed to provide detectable plasma levels as a result of possible acid lability in the stomach. Absolute bioavailability for the 3 compounds examined yielded excellent concordance with data from the literature or data generated in house. Conclusion: Overall, when used appropriately, microdosing offers the potential to aid in early drug candidate selection. Â© 2006 American Society for Clinical Pharmacology and Therapeutics.

Use of microdosing to predict pharmacokinetics at the therapeutic dose: Experience with 5 drugs

The formation of DNA adducts in human HepG2 cells and human hepatocytes exposed to 14C-labelled 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) was examined using Accelerator Mass Spectrometry (AMS). PhIP generated DNA adducts in a linear dose-dependent manner between 100 pM and 20 micro M. Co-treatment with the dietary isothiocyanate, sulforaphane (SFN, 1-10 micro M), or the flavonoid, quercetin (5-20 micro M), significantly reduced the level of PhIP-DNA adducts in a dose-dependent manner. The degree of protection was dependent on PhIP concentration, i.e. after 100 pM PhIP exposure, SFN or quercetin reduced adduct levels to below the limit of detection (0.15 amol PhIP/ micro g DNA) but at higher PhIP exposure (10 nM and 1 micro M), the protection was 60 and 10%, respectively. The involvement of phase I, phase II and DNA repair enzymes in this protection against PhIP-DNA adduct formation was investigated using real-time RT-PCR and enzyme activity assays. In intact HepG2 cells, quercetin inhibited cytochrome P450 (CYP)1A2, the main phase I enzyme responsible for PhIP bioactivation. In contrast, SFN induced phase II detoxification enzymes, UDP-glucuronosyltransferase 1A1 and glutathione S-transferase A1 mRNA expression. SFN and quercetin showed no effect on DNA repair, neither in terms of the level of PhIP-DNA adducts, when cells were treated with phytochemicals after the carcinogen exposure, nor the regulation of mRNA expression of two DNA repair enzymes, apurinic endonuclease and DNA polymerase beta. This study indicates that dietary isothiocyanates and flavonoids modulate phase I and phase II enzyme expression, hence increasing the rate of detoxification of the dietary carcinogen PhIP in human HepG2 cells but do not affect the rate of PhIP-DNA adduct repair. The formation of PhIP-DNA adducts in human hepatocytes was also dose-dependent with PhIP-concentration and the levels of protection by SFN or quercetin were up to 60% after 10 nM PhIP treatment, but showed large inter-individual variation with no observed protection in some individuals.

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Sulforaphane and quercetin modulate PhIP-DNA adduct formation in human HepG2 cells and hepatocytes

Pharmacokinetics of fexofenadine: evaluation of a microdose and assessment of absolute oral bioavailability.

Background: Microdosing studies (human Phase 0) are used to select drug candidates for Phase I clinical trials on the basis of their pharmacokinetic properties, using subpharmacologic doses (maximum 100 μg). There are questions as to whether pharmacokinetic data obtained at these low doses will predict those at the clinically relevant dose. Objective: To review the current literature on microdosing and assess how well microdose data have predicted the pharmacokinetics obtained at a therapeutic dose. Methods: All data published in the peer reviewed literature comparing pharmacokinetics at a microdose with a therapeutic dose were reviewed, excluding those studies aimed at imaging. Conclusions: Of the 18 drugs reported, 15 demonstrated linear pharmacokinetics within a factor of 2 between a microdose and a therapeutic dose. Therefore, data that support the utility of microdosing are beginning to emerge.

Graham Lappin

Papers

Big physics, small doses: the use of AMS and PET in human microdosing of development drugs.

Use of microdosing to predict pharmacokinetics at the therapeutic dose: Experience with 5 drugs

Sulforaphane and quercetin modulate PhIP-DNA adduct formation in human HepG2 cells and hepatocytes

Pharmacokinetics of fexofenadine: evaluation of a microdose and assessment of absolute oral bioavailability.

The utility of microdosing over the past 5 years.