5-Flourouracil
5-fluorouracil (5-FU) is an antimetabolite analogue of the pyrimidine uracil, with a fluorine atom at the C-5 position in place of hydrogen79. Intracellularly, the fluoropyrimidine is converted into fluorodeoxyuridine monophosphate (FdUMP), fluorodeoxyuridine triphosphate (FdUTP) and fluorouridine triphosphate (FUTP) which become mis-incorporated into RNA and DNA 80. Furthermore, FdUMP inhibits the enzyme thymidylate synthase by competitively binding to its active site thereby blocking binding of the normal substrate dUMP and inhibiting dTMP synthesis 81,82. Because of its cytotoxicity, 5-FU is used widely as a chemotherapeutic agent in cancer treatment. Topical 5-FU cream is used for treatment of intraepithelial neoplasia of the skin and off-license treatment of HPV related lesions including genital warts, vulvar intraepithelial neoplasia and vaginal intraepithelial neoplasia 83,84.
The safety profile of 5-FU was established in a randomized controlled study involving 90 women with HPV-associated vaginal and vulval lesions. Women who used prophylactic topical 5–FU at a dosage of 2 g once every two weeks after ablative therapy, were significantly less likely to develop recurrent lesions than controls 85. In a later study where the drug was used for vaginal HPV-associated lesions continuously over five to seven days, or periodically once a week for 10 weeks, dose and duration dependent chronic mucosal ulceration developed in 8.2% of subjects 86. In a separate study, 5-FU was used as an adjunctive treatment following excisional therapy for CIN 2-3 in HIV positive patients in order to prevent recurrence50. A dosage of 2 g of 5% 5-FU cream was self-administered using vaginal applicators at bedtime once every two weeks for six months. The recurrence rate in the treatment arm was 28% compared to 47% in the observation arm and there was a statistically significant prolonged time to recurrence in the treatment arm compared to the observation group. Once again vaginal 5-FU at this dosage and interval was extremely well tolerated, with minimal morbidity in HIV-infected women with CIN 50.
Another trial investigated intravaginal 5% 5-FU vs standard-of-care observation in young women aged 18 – 29 years with CIN 2 with the primary outcome of disease regression at six months after the diagnosis of CIN 2 51. Dual contraception with condoms plus one either oral, intravaginal, injectable, implantable, or intrauterine device was required for the 5-FU group because of its potential teratogenic effects. The established dosage of 2 g of topical 5% 5-FU cream was applied once every two weeks for a period of 16 weeks (a total of eight doses) which is standard with other studies87–90. This was inserted into the vagina at night using a vaginal applicator, and a tampon placed per vagina overnight to keep the cream in-situ, and then removed in the morning. Disease regression was demonstrated in 84% of women in the 5-FU group compared to 52% of women in the observation group, and after six months and the treated group was twice as likely to be both HPV negative and clear of neoplasia 51.
As described above, one of the drawbacks of using a vaginal cream based locoregional therapy is the inability to control the precise site of application and the duration of drug action, resulting in local and systematic side effects 91,92. In an effort to circumvent this problem, 5‐FU was incorporated into a one-way release bilaminar bio-adhesive drug delivery system 93 which was placed directly on the cervix using a device applicator, and keptin situ for 24 hours, after which time it was removed using threads that were attached to it for that purpose, releasing a once only dose of 20 mg. This study involved 104 patients with CIN 1 and 2, where the control arm received the delivery system loaded with a placebo. The device was spontaneously expelled in four patients before the 24 hours was up, and 41% of patients in the drug arm developed erythema of the cervix compared to only 8% in the placebo group. More importantly, there was no difference in remission of CIN between drug and placebo groups 93. The authors concluded that despite the effectiveness of the delivery system, one application of 5‐FU was not effective in the treatment of CIN due to inadequate dosage.
In a separate bid to achieve better therapeutic efficacy and increased patient compliance, 5-FU was formulated in a vaginal gel with thermosensitive and muco-adhesive properties in order to increase residence time at the cervix 94. The drug was incorporated as its inclusion complex in a 1:1 molar ratio with either b-cyclodextrin or hydroxypropyl-b-cyclodextrin in order to increase its aqueous solubility and to achieve the complete release of 5-FU from the gel and this did not affect the gelling temperature significantly94. The muco-adhesive polymer HPMC conferred favorable thermosensitive in situ gelling properties and complexation to cyclodextrins resulted in a ten-fold increase in cytotoxicity against HeLa cells 94. This was also confirmed by the enhanced release profile of 5-FU through complexation 94. All this suggesting that formulating an anticancer drug in a muco-adhesive, thermosensitive gel in complexation with cyclodextrins can increase its anticancer activity resulting in lower doses and reduced unwanted side effects through controlled release and prolonged residence time at the administration site. The disadvantages of 5-FU are its potential for teratogenic effects in its intravenous form in women of child-bearing age and for causing cervical mucosal ulceration 86thereby potentially placing women at increased risk of sexually transmitted infections 51.