alanosine and Lung-Neoplasms

We conducted parallel phase II trials of cimetidine as a single agent and the combination N-phosphonacetyl-L-aspartate (PALA) plus L-alanosine among 40 previously untreated patients with biopsy-proven, measurable disseminated malignant melanoma. We did not design the trial to be a comparative assessment of the two regimens. Among 19 patients treated with cimetidine, 300 mg orally four times daily, there was one complete response of extensive pleural and pulmonary metastases for 16+ months and two partial regressions of soft tissue lesions for 7 and 21+ months, respectively. Among 21 patients treated with the combination regimen, there was only one partial response in soft tissue for 1 month. The median times to progression and death were 1.4 and 6 months, respectively, for cimetidine, and 1.3 and 4 months, respectively, from the combination of PALA plus L-alanosine. Among patients who progressed on initial treatment, there were no responses in 12 who received crossover therapy with cimetidine and 11 with the combination regimen. Two patients treated with the combination program had severe stomatitis, two developed renal failure, and one had severe leukopenia and thrombocytopenia. Recognizing the limitations of small sample size, these early observations suggest that cimetidine may have intriguing implications in the management of disseminated malignant melanoma.

Topics: Alanine; Antineoplastic Combined Chemotherapy Protocols; Aspartic Acid; Cimetidine; Drug Evaluation; Female; Humans; Lung Neoplasms; Male; Melanoma; Middle Aged; Phosphonoacetic Acid; Pleural Neoplasms; Soft Tissue Neoplasms

Methylthioadenosine phosphorylase (MTAP), an enzyme involved in purine and methionine metabolism, is present in all normal tissues but is frequently deficient in a variety of cancers. It has been suggested that this metabolic difference between normal and cancer cells may be exploited to selectively treat MTAP-negative cancers by inhibiting de novo purine synthesis and by depleting L-methionine. However, these therapeutic strategies have only been tested in naturally occurring MTAP-positive and -negative cell lines, which might have additional genetic alterations that affect chemotherapeutic sensitivity. Therefore, it is of importance to examine the feasibility of enzyme-selective treatment using paired cell lines that have an identical genotype except for MTAP status. MTAP-negative A549 lung cancer cells were transfected with eukaryotic expression vectors encoding MTAP cDNA in sense and antisense orientations. The resultant stable transfectomas were treated with inhibitors of de novo purine synthesis such as methotrexate, 5,10-dideazatetrahydrofolate, and L-alanosine and by methionine depletion. The A549 cells transfected with an antisense construct (antisense transfectoma) expressed no MTAP protein and were more sensitive to both purine and methionine depletion than were cells expressing MTAP protein (sense transfectoma). Methylthioadenosine was able to completely rescue the sense transfectoma but not the antisense transfectoma from growth inhibition by depletion of purine and methionine. These results prove that MTAP deficiency contributes directly to the sensitivity of cancer cells to purine or methionine depletion. Inhibition of de novo purine synthesis, combined with methionine depletion in the presence of methylthioadenosine, is a highly selective treatment for MTAP-negative cancers.

Topics: Alanine; Antimetabolites, Antineoplastic; Drug Resistance, Neoplasm; Feasibility Studies; Genetic Vectors; Humans; Lung Neoplasms; Methionine; Methotrexate; Neoplasm Proteins; Purine-Nucleoside Phosphorylase; Purines; Tetrahydrofolates; Transcription, Genetic; Transfection; Tumor Cells, Cultured