No abstract

Fluoropyrimidines, such as 5-fluorouracil (5-FU), are used extensively in cancer therapy. In the cell, 5-FU is metabolized to 5-fluorodeoxyuridylate (5-FdUMP), a tight binding covalent inhibitor of thymidylate synthase (TS). In order to create 5-FdUMP resistant enzymes to protect chemosensitive normal cells and further understand mechanisms of 5-FdUMP resistance, we have randomized four residues within the active site of TS. Our previous studies identified alterations in residues which produce active TS with enhanced resistance to 5-fluorouridine (5-FdUR). By remutagenizing a subset of the 13 previously targeted residues (A197, L198, C199 and V204), an unbiased random library can be created allowing for extensive testing of all possible amino acid substitutions at each of the sites. Using genetic complementation and selection in Escherichia coli, we identified the spectrum of substitutions that yield active TS as well as those that resulted in 5-FdUR resistant mutants of TS. The 5-FdUR resistant TS were found to share several structural features including hydrophobic substitutions at residue 197, retention of the wild-type leucine 198, the alteration C199L (present in 64% of the drug-resistant library), and polar alterations of valine 204. The catalytic activity of mutants with these features was approximately equal to that of the wild-type TS.

Granulocytic sarcoma (chloroma) is a rare solid tumor resulting from the proliferation of myelogenous leukemia cells. Chloromas usually present as soft tissue or bony masses of the head and neck in patients with acute myelogenous leukemia (AML) of the French-American-British M2 subtype. Occasionally chloromas may occur in patients with myelodysplasia and other myeloproliferative disorders and rarely precede the development of systemic disease. It is distinctly rare for such tumors to cause epidural compression as a first manifestation of disease. Herein, we report the case of a man with a thoracic extradural chloroma whose presentation of progressive lumbar pain ultimately led to the diagnosis of M2 AML. Surgical intervention prior to the onset of paraplegia and the prompt initiation of chemotherapy resulted in an excellent neurological and hematological outcome. We also review the literature of previously reported cases of spinal cord-associated chloroma and focus on the clinical presentation and treatment of this disorder.