Influence of the tumor mass on the valine rate constants and on valine incorporation into proteins in an experimental brain tumor model

Radiolabelled-tyrosine for the measurement of protein synthesis rate in vivo by positron emission tomography

The amino acid incorporation rate, generally described as protein synthesis rate or PSR, can be assessed in vivo using carboxylic-labelled amino acids such as L-[1-11C]tyrosine and PET. In animals, labelled tissue metabolites are below 4% of total tissue radioactivity and are therefore neglected in the model. Labelled plasma metabolites on the other hand rise continuously to 50% of total plasma radioactivity at 40 minutes. After correction of the total plasma radioactivity for the metabolite fraction, a Patlak analysis may be performed to calculate the PSR. A number of applications in the field of oncology were presented. The use of L-[1-11C]tyrosine in the study of metabolic disease was also discussed. It is concluded that the application of [11C]tyrosine-PET in a clinical setting is of interest for an increasing number of diseases.

The sequential changes in DNA synthesis, glucose utilization, protein synthesis, and peripheral benzodiazepine receptor density in C6 brain tumors after chemotherapy to predict the response of tumors to chemotherapy

BACKGROUND

Monitoring therapy in patients with brain tumors is very difficult and unreliable. It has been shown that there is no good correlation between tumor sensitivity measured in vitro and in situ tumor response to therapies.

METHODS

Sequential changes in tumor size, number of DNA synthesizing cells (labelling index [LI]), glucose utilization (LCGU), protein synthesis (LCPS), and peripheral benzodiazepine receptor (PBR) density were examined after chemotherapy for seven days. This was done using antibromodeoxyuridine immunohistochemical stain and multiple tracer quantitative autoradiography in a C6 rat brain with an implanted glioma. On Day 10 after inoculation, the rats were divided into 5 experimental groups: (1) a nontreatment group (control Group 1); (2) a group received 5% dextrose intraarterial (IA) administration (control Group 2); (3) a group received 1,3-bis-(2-chloroethyl) nitrosourea (BCNU) intravenous (i.v.) administration (Group 3) (5% dextrose was solvent); (4) a group received BCNU IA administration (Group 4) (5% dextrose was solvent); and (5) a group received sarcosinamide chloroethyl nitrosourea (SarCNU) IA administration (Group 5) (solvent as for the BCNU group).

RESULTS

Three treatments showed a significant decrease (P < 0.003) in tumor growth. The most effective treatment was BCNU IA and SarCNU IA was moderately effective. BCNU i.v. showed no effect on tumor growth when compared with the two control groups. The change in the peak LI correlated well with the peak LCGU. These parameters decreased markedly and significantly in both Group 4 and Group 5 from Day 1 after treatment. The rates of the decrease in these biologic factors also correlated well with a decrease in the tumor growth. The LCPS did not correlate with a decrease in the LI or LCGU. The dissociation constant (Kd) and densities of the receptors PBR (B max) did not change significantly in any of the treatment groups during the observation period.

CONCLUSIONS

From the results presented, we concluded that changes in the LI and LCGU represent the most reliable parameters with which to predict the response or sensitivity of this glial tumor to the treatments applied. These data suggest that if changes in peak LCGU were measured in tumors using positron emission tomography, they might be instrumental in providing in vivo information about the sensitivity of a tumor to a given treatment without the need for repeated tumor biopsy.