Search

Phospholipid extracts were made of a murine mammary adenocarcinoma implanted in the dorsum of the foot of C3H/He mice before and 96 h after 17 Gy irradiation or 150 mg/kg cyclophosphamide. Extracts of untreated tumors, which had grown for a further 96 h, were also studied. Although previous studies have shown significant changes in the precursors and catabolites of phosphatidylcholine and phosphatidylethanolamine following therapy, 31P nuclear magnetic resonance analysis of extracts showed no changes in these membrane constituents and other observed phospholipid species. A significant decrease in 1-alkyl-2-acyl-sn-glycero-3-phosphocholine, however, was observed 96 h following cyclophosphamide treatment.

6-aminonicotinamide (6AN) has been shown to enhance radiosensitivity in vitro, although previous in vivo studies failed to show an effect. 31P NMR spectra were obtained by using a one-dimensional chemical shift imaging technique on a first generation transplant of the CD8FI spontaneous mammary carcinoma tumor model. Spectra were obtained both before and 10 h after treatment with 6AN (20 mg/kg). Changes in pH, nucleoside triphosphate/inorganic phosphate, and phosphocreatine/ inorganic phosphate measured at 10 h post-6AN were not significant. A new peak was detected 10 h post-6AN, which was assigned to 6-phosphogluconate (6PG), indicating inhibition of the pentose phosphate pathway (PPP). Based on the spectral data demonstrating inhibition of the PPP at 10 h post-6AN, tumor-bearing mice were irradiated (15 Gy x 3 fractions) on Days 1, 10 or 11, and 21 10 h after administration of 6-aminonicotinamide (20 mg/kg). Tumor-bearing mice receiving 6AN alone (20 mg/kg x 3), radiation alone (15 Gy x 3), or saline were also studied. Tumor growth delay studies indicated that 6AN alone induced a small but significant tumor growth delay (4.3 +/- 0.8 days). Radiation alone induced a tumor growth delay of 34.5 +/- 2.7 days. Treatment with 6AN followed by radiation induced a tumor growth delay of 57.0 +/- 3.8 days. This was significantly greater than the TGD values for treatment with 6AN alone or radiation (P < 0.01). No complete regressions were noted after treatment with 6AN or radiation alone. Concomitant therapy with 6AN plus radiation yielded 6/28 complete regressions (21%), which was significantly greater than radiation (P < 0.05) or 6AN alone (P < 0.01) on this mammary carcinoma.

The chemotherapeutic regimen of N-(phosphonacetyl)-L-aspartate (PALA) followed 17 h later by 6-methylmercaptopurine riboside (MMPR) and 6-aminonicotanamide (6AN) has been shown to be a potent sensitizer of anti-neoplastic therapy. We undertook this study to compare the therapeutic and metabolic effects of this triple drug combination vs one of its components, 6AN, in a murine mammary carcinoma. After treatment with PALA, MMPR and 6AN, a new peak was detected which was assigned to 6-phosphogluconate (6PG), which is a marker of inhibition of the pentose phosphate pathway at the 6-phosphogluconate dehydrogenase step. Treatment with PALA, MMPR and 6AN also induced a decrease in the ratios of nucleoside triphosphate/inorganic phosphate (NIP/P i ) and phosphocreatine/inorganic phosphate (PCr/P i ) similar to previous results with a different tumor model. These effects were most pronounced at 6 and 10 h. In addition, an increase in PME'/phosphocholine (PME'=downfield peak in the phosphomonoester region) was detected, which was expected because of the cytotoxic effect of this regimen. Treatment with 6AN alone also resulted in the detection of 6PG with a maximum intensity at 6 h post-6AN. Treatment with 6AN alone induced a smaller change in PME'/PC and failed to cause a decrease in PCr/P i or NTP/P i at 6 and 10 h. The enhanced response to the combination of PALA, MMPR and 6AN vs 6AN alone, both with regard to cytotoxicity and radiosensitization, may be due to energy depletion.

The effect of cyclophosphamide on the metabolic profile of a mammary carcinoma implanted on the foot of mouse was studied by 31P NMR spectroscopy both in vivo and in perchloric acid extracts. The ratio nucleotide triphosphate:P(i) was significantly elevated in cyclophosphamide treated tumours relative to untreated tumours after 96 h in vivo (p < 0.05). Phosphocreatine:P(i) was similarly elevated from 48 to 168 h (p < 0.01). Resolution of the phosphomonoester peak into two distinct resonances allowed us to estimate the ratio of PME' to phosphocholine (PC), where PME' is a composite peak consisting, in part, of phosphoethanolamine (PE). PME':PC was found to be significantly higher in treated animals relative to control animals in vivo (p < 0.01 from 48 to 168 h). Perchloric acid extract spectra suggest that the increase in PME':PC was in part due to a decrease in PC concentration and also due to an increase in a previously unidentified resonance which was coresonant with PE. Extract data show that there was a significant increase in the concentration of the phosphodiesters, glycerophosphocholine (p < 0.01) and glycerophosphoethanolamine (p < 0.05) in treated relative to control tumours. The changes in the phosphomonoester resonances are qualitatively similar to previously described changes following radiation and suggest that they may be a marker of cell kill or lack of cell growth after antineoplastic therapy.