Vandetanib: a novel targeted therapy for the treatment of metastatic or locally advanced medullary thyroid cancer.

PURPOSE: The pharmacology, pharmacokinetics, efficacy, safety and tolerability, drug and food interactions, cost, and place in therapy of vandetanib are reviewed. SUMMARY: Vandetanib is a small-molecule inhibitor of vascular endothelial growth factor receptor, epidermal growth factor receptor, and receptor tyrosine kinase signaling pathways, which are involved in the pathogenesis of medullary thyroid cancer (MTC). Vandetanib is currently approved as an alternative to local therapies for both unresectable and disseminated disease. Vandetanib was evaluated in a randomized, placebo-controlled, double-blind Phase III study comparing vandetanib with placebo in adult patients with unresectable locally advanced or metastatic hereditary or sporadic MTC. Vandetanib demonstrated a statistically significant longer progression-free survival (predicted median of 30.5 months) compared with placebo (median of 19.3 months) (hazard ratio, 0.46; 95% confidence interval, 0.31-0.69; p = 0.0001). The most commonly observed adverse effects of vandetanib include nausea, diarrhea, headache, rash, prolongation of the Q-T interval, and hypertension. Because it can prolong the Q-T interval, vandetanib is contraindicated for use in patients with serious cardiac complications, including congenital long QT syndrome, bradyarrhythmias, uncompensated heart failure, and a history of torsades de pointes. CONCLUSION: Vandetanib has been shown to be more effective than placebo in the treatment of advanced MTC; however, it has not been compared with radiation, resection, or embolization. Vandetanib also has significant and fairly common cardiac toxicities. The cost, benefits, and risks of vandetanib for patients with MTC should be weighed, as alternative treatments remain an option for most patients.

Quantification of CLR1401, a novel alkylphosphocholine anticancer agent, in rat plasma by hydrophilic interaction liquid chromatography-tandem mass spectrometric detection.

A rapid and specific LC-MS/MS based bioanalytical method was developed and validated for the determination of 18-(p-iodophenyl)octadecyl phosphocholine (CLR1401), a novel phosphocholine drug candidate, in rat plasma. The optimal chromatographic behavior of CLR1401 was achieved on a Kromasil silica column (50 mm x 3 mm, 5 microm) under hydrophilic interaction chromatography. The total LC analysis time per injection was 2.8 min with a flow rate of 1.5 mL/min under gradient elution. Liquid-liquid extraction in a 96-well format using ethyl acetate was developed and applied for method validation and sample analysis. The method validation was conducted over the curve range of 2.00-1000 ng/mL using 0.0500 mL of plasma sample. The intra- and inter-day precision and accuracy of the quality control samples at low, medium, and high concentration levels showed < or = 5.9% relative standard deviation (RSD) and -10.8 to -1.4% relative error (RE). The method was successfully applied to determine the toxicokinetics of CLR1401 in rats from three dose groups of 0.4, 4.0, and 10.0 mg/kg/day via intravenous administration.

Methoxypoly(ethylene glycol)-conjugated carboxypeptidase A for solid tumor targeting: part I: synthesis and characterization.

In vivo efficacy of novel anticancer agents has been hindered by the inability to deliver effective concentrations of drugs to tumors. The use of macromolecules such as antibodies and polymers for enzyme delivery to tumors has revealed that catalyzing the conversion of a nontoxic prodrug into its cytotoxic form can generate an effective level of cytotoxic agents at tumor sites. This study primarily focuses on the synthesis and characterization of methoxypoly(ethylene glycol)-modified carboxypeptidase A (CPA) for solid tumor targeting. The molecular weight of CPA has been successfully altered from 35 to 40-50 kDa via attachment of a defined number of mPEG moieties. Relatively pure mPEG-CPA conjugates containing one, two, and three mPEG chains were obtained at preparative scale quantities through controlled PEGylation followed by fractionation that involved size-exclusion chromatography. An enhancement in kinetic properties including k(cat) and k(cat)/K(m) towards hippuryl-L-phenylalanine (hipp-L-phe) was observed in mPEG-CPA conjugates. An increase in the V(m) appeared to be responsible for this enhancement. The attachment of mPEG to CPA substantially improved the stability of the enzyme with respect to the specific peptidase activity toward the model substrate. This finding is particularly important in the development of a novel CPA/methotrexate-alpha-peptide system in solid tumor chemotherapy.

Methoxypoly(ethylene glycol)-conjugated carboxypeptidase A for solid tumor targeting: part II: pharmacokinetics and biodistribution in normal and tumor-bearing rodents.

We have evaluated effects of mPEG modification on pharmacokinetic properties of carboxypeptidase A (CPA) in normal rats. Attachment of two or three mPEG chains to CPA resulted in the generation of mPEG2-CPA and mPEG3-CPA analogs with significantly enhanced plasma half-lives, especially during the distribution phase. Moreover, the assessment of real-time whole-body kinetics in CT26 tumor-bearing mice showed both mPEG2-CPA and mPEG3-CPA exhibited increased body retention at 48 h post-injection. In addition, tumor localization of mPEG3-CPA at 72 h was visualized and confirmed by fusion of the gamma-scintigraphy and microCT data sets. Results from the imaging studies support our hypothesis of a correlation between tumor uptake and enhanced circulatory half-life. Tissue distribution data indicated the combination of increased tumor extravasation and effective renal elimination observed with mPEG2-CPA at 48 h following administration led to the highest observed tumor-to-blood ratio of 4.8:1. Although the total concentration of mPEG3-CPA accumulated in tumor was higher than that of mPEG2-CPA and CPA at predetermined time intervals, a higher tumor-to-blood ratio was not obtained owing to a higher level of blood activity. Clearly, the attachment of an appropriate number of mPEG chains can facilitate tumor localization as effectively as can the use of a tumor-specific antibody.

Substrate specificity for 4-thiouridine modification in Escherichia coli.

The biosynthesis of 4-thiouridine (s4U) in Escherichia coli tRNA requires the action of both the thiamin pathway enzyme ThiI and the cysteine desulfurase IscS. IscS catalyzes sulfur transfer from l-cysteine to ThiI, which utilizes Mg-ATP to activate uridine 8 in tRNA and transfers sulfur to give s4U. In this work, we show through deletion analysis of unmodified E. coli tRNA(Phe) that the minimum substrate for s4U modification is a mini-helix comprising the stacked acceptor and T stems containing an internal bulged region. The size of the bulged loop must be at least 4 nucleotides and contain the target uridine as the first nucleotide. Replacement of the T loop sequence with a tetraloop in the deletion substrate increases activity and shows that the TpsiC primary sequence is not a recognition element. An unmodified tRNA(Phe) transcript in which the 3'-terminal ACCA sequence is removed to give a blunt terminus has <0.1% activity, although the addition of a single overhanging base essentially restores activity. In addition, reducing the distance of the 3' terminus relative to U8 by as little as 1 bp severely impairs activity. By dissecting a minimal RNA substrate in the T loop region, a two-piece system consisting of a substrate RNA and a "guide" RNA is efficiently modified. Our results indicate that outside of the modified U8, there is no primary sequence requirement for substrate recognition. However, the secondary and tertiary structure restrictions appear sufficient to explain why s4U modification is limited in the cell to tRNA.