Of a series of newly synthesized derivatives of the pyrrolo[2,3-d]
pyrimidine nucleosides tubercidin,
toyocamycin, and
sangivamycin, the xylosyl analog of
tubercidin,
xylotubercidin, exhibited the greatest potency and selectivity against herpes simplex virus type 2 (HSV-2) in vitro. At dosage regimens that were not toxic for the host,
xylotubercidin proved efficacious in various HSV-2 animal model
infections. When applied topically at 0.25, 0.5, or 1% in
dimethyl sulfoxide or when administered systemically (intraperitoneally) at 12.5 or 25 mg/kg per day,
xylotubercidin suppressed the development of herpetic skin lesions and the
paralysis and mortality associated therewith in hairless mice inoculated intracutaneously with HSV-2. In this model,
acyclovir was effective only if administered topically at 5 or 10% in
dimethyl sulfoxide. When administered intraperitoneally over a dosage range of 10 to 50 mg/kg per day,
xylotubercidin achieved a significant reduction in the mortality rate of mice infected intraperitoneally with HSV-2. Under the same conditions,
acyclovir did not offer any protection even when administered at doses up to 250 mg/kg per day.
Xylotubercidin thus appears to have considerable potential for both topical and systemic treatment of HSV-2
infections.