This is a two-part study. The first part is a single-dose open label design. The second part employs a multiple dose, randomized, placebo controlled study design. Studies have demonstrated that GRFT is highly potent for HIV prevention and is effective at very low concentrations. One 4 mL dose of PC-6500, designed to provide an adequate vaginal concentration of GRFT for the prevention of HIV, based on preclinical data, will be evaluated. Rising dose tolerance is not the goal of this study because GRFT is likely to be minimally absorbed systemically, if at all.

Inclusion Criteria:

• 1) Between 18 and 49 years of age (at screening), inclusive.
• 2) Willing and able to provide written informed consent.
• 3) Healthy, based on medical history, vital signs, physical examination, urinalysis, laboratory evaluations for genital infections and laboratory evaluations for hematology, liver and renal function.
• 4) HIV-negative as determined by HIV ELISA test at screening.
• 5) In the absence of the use of exogenous hormone(s), have a self-reported regular menstrual cycle, defined as having a minimum of 21 days and a maximum of 35 days between menses.
• 6) Normal Pap test at screening. (Documentation of normal Pap test results within 12 months prior to screening is also acceptable.)
• 7) Agrees to use effective contraception for the duration of the trial. If hormonal contraception or intrauterine device (IUD)/ Intrauterine system (IUS) is being used, it must be have been used for at least 30 days prior to screening, with no planned change in method during the study. The following forms of contraception (per self-report) are permitted: same-sex relationship, male or female sterilization, oral contraceptives, contraceptive implant, contraceptive patch, IUS, IUD depo-medroxyprogesterone acetate (DMPA; Depo-Provera®).
• 8) Willing to abstain from sexual intercourse/activity including receptive vaginal, oral, digital, and anal intercourse, and the use of any vaginal products including tampons, male and female condoms, contraceptive sponges, diaphragms, cervical caps, douches, lubricants, and vibrators/dildos; starting the Screening Visit (Visit 0) through the final safety visit (Visit 3/Day 8) in the OL period; and starting 48 hours before enrollment through the final safety visit (Visit 8/Day 21) in the randomized period
• 9) Agrees to not participate in any other clinical research for the duration of this trial.

Exclusion Criteria:

• 1) History of or known sensitivity/allergy to any component of either study product.
• 2) Currently pregnant or breast-feeding, or within 3 months of last pregnancy outcome.
• 3) Participation in any other clinical research trial involving investigational or marketed products currently or within two months of participation prior to screening, including any trial of a spermicide, microbicide and/or drug.
• 4) Known bleeding disorder that could lead to prolonged or continuous bleeding with biopsy.
• 5) Diagnosed with or treated for any STI or pelvic inflammatory disease in the last 3 months. Note: Women with a history of condylomata or genital herpes who have been asymptomatic for at least six months may be considered for eligibility.
• 6) Positive test for Neisseria gonorrhea (NG), Chlamydia trachomatis (CT), or Trichomonas vaginalis (TV) at screening.
• 7) Symptomatic vulvovaginal candidiasis, bacterial vaginosis (BV), or urinary tract infection (UTI) at screening. (Participants who test positive at initial screening may be treated and re-tested once, and reconsidered for screening).
• 8) Presence of any clinically significant genital epithelial findings (e.g. abrasions, ulcerations, or lacerations, or vesicles) suspicious for STIs at screening.
• 9) History of hysterectomy or menopause.
• 10) Use of excluded contraceptive methods including Nuvaring®, condoms (male or female), contraceptive sponge, diaphragm, or cervical cap.
• 11) History of gynecological surgery or procedure within past 2 months.
• 12) History of uterine prolapse, undiagnosed vaginal bleeding or urethral obstruction within the last 3 months, including unexplained break-through bleeding requiring sanitary protection.
• 13) Known current drug abuse, including illicit drugs, or alcohol abuse.
• 14) Abnormal finding on laboratory or physical examination or a social or medical condition which, in the opinion of the investigator, would make participation in the study unsafe or would complicate interpretation of data.
• 15) Unable to comply with study requirements, including but not limited to, attending all study visits, using the gel as directed, observing abstinence throughout the study and use of allowable effective contraceptives.
• 16) History of latex allergy.