The promise of pharmacogenomics: gemcitabine and pemetrexed.

Although no overall differences in survival have been observed between the many chemotherapy combinations in non-small-cell lung cancer, the clinical application ofmRNA expression levels of amplified genes may disclose many genetic influences on cytotoxic drug sensitivity and enable clinicians to tailor chemotherapy according to each individual's gene profile. Specifically, the assessment ofribonucleotide reductase subunit Ml and thymidylate synthase mRNA expression levels might select patients who benefit from gemcitabine (Gemzar) or pemetrexed (Alimta) combinations. Until recently, clinical prognostic factors such as performance status, weight loss, and lactate dehydrogenase were the only parameters used to predict chemotherapy response and survival. However, accumulated data indicate that overexpression of genes involved in cancer glycolysis pathways plays an important role, and might be an independent mechanism of chemoresistance. The dysregulation of glycolytic genes is affected by growth signals involving the PI3E/Akt pathway and downstream genes such as hypoxia-inducible factor-1-alpha. One can thus envision that substantial improvements in therapeutic outcome could benefit from the integration of tailored ribonucleotide reductase-dependent chemotherapy, ribonucleotide reductase antisense therapy, and targeted therapy.