We report the case of an infant with severe combined immunodeficiency who was presented with PIV3 infection. Aerosolized ribavirin was administered for 10 months until the child gained a functional immune system through an allogeneic hematopoietic stem cell transplant and cleared PIV3 infection. No adverse effect was observed in the child and in healthcare personnel, with a follow-up of three years. Despite the burden of aerosolized administration, early and prolonged administration of aerosolized ribavirin was feasible, well tolerated, and safe for the patient and the caregivers. This is a case report and no definite conclusions can be drawn. However, our experience suggests that prolonged aerosolized ribavirin administration should be considered for the treatment of PIV3 infection in the context of primary immunodeficiency, where there is no currently available alternative treatment, until a functional immune system is gained.

Purpose: Many cancer lines are methionine dependent and decrease proliferation when methionine supply is limited. Methylenetetrahydrofolate reductase (MTHFR) generates the folate derivative for homocysteine remethylation to methionine. We investigated the effect of antisensemediated inhibition of MTHFR on survival of human cancer cells.Experimental Design: We examined the in vitro and in vivo anticancer effects of a combination of MTHFR antisense and standard cytotoxic drugs.Results: Specific antisense against MTHFR (EX5) showed significant inhibitory effects on growth of human colon, lung, breast, prostate, and neuroblastoma tumor cells in vitro compared with that of the control oligonucleotide. Cytotoxic drugs (5-fluorouracil, cisplatin, or paclitaxel) potentiated the effect of EX5. In vivo, antisense alone or in combination with cytotoxic drugs inhibited the growth of human colon and lung carcinoma xenografts. In comparison with control oligonucleotide, treatment with EX5 inhibited growth of colon tumors and lung tumors by 60% and 45%, respectively. EX5 with 5-fluorouracil decreased growth of colon tumors by an additional 30% compared with EX5 alone, and EX5 with cisplatin decreased growth of lung tumors by an additional 40% compared with cisplatin alone. Growth inhibition by EX5 was associated with decreased amounts of MTHFR protein and with increased amounts of an apoptosis marker.Conclusions: Our results confirm that MTHFR inhibition decreases tumor growth and suggest that inhibition of MTHFR by antisense or small molecules may be a novel anticancer approach.

Tumor cells have an enhanced requirement for glucose, amino acids and DNA precursors. Since folates are required for the synthesis of thymidine and purines, the metabolism of folate has been exploited as an anti-cancer target for over 6 decades, with emphasis on the inhibition of DNA synthesis. However, folate is also used to generate methionine, which is essential for proliferation by virtue of its role in protein synthesis, polyamine synthesis and transmethylation reactions. Tumor-derived cell lines and human tumor xenografts have been shown to be methionine dependent i.e., they are unable to survive without methionine and are unable to efficiently utilize homocysteine, the immediate metabolic precursor of methionine. Since non-transformed cells are methionine-independent, the targeting of methionine metabolism presents an opportunity to selectively disrupt the unique metabolic networks in cancer cells. This chapter provides an overview of the critical role of folate and methionine metabolism in tumor cells and summarizes the current anti-folate and anti-methionine strategies to inhibit growth of transformed lines and tumors. We also present our work on the development of a novel anti-cancer target, methylenetetrahydrofolate reductase (MTHFR), a key enzyme of both folate and methionine metabolism. Our data demonstrate that antisense-mediated inhibition of MTHFR is associated with increased cytotoxicity in vitro and with decreased growth of tumors in vivo. These findings warrant further investigation of this enzyme and the methionine biosynthetic pathway in exploring new strategies for cancer chemotherapy.