Diethylstilbestrol (DES) General Information

Transcription

1 Use of the DES Paradigm to Inform Risk Assessment for Weakly Estrogenic Chemicals Robert Golden PhD ToxLogic Potomac, MD Diethylstilbestrol (DES) General Information DES ranges from slightly less to several times more potent than 17β-estradiol (E2) depending on assay 100s 1000s X more potent than most weakly estrogenic naturally occurring or environmental chemicals Effects in animals & humans following in utero exposure show dose-response & no-effect maternal intake doses DES a worst case scenario, i.e., E2 typically bound to sex hormone binding globulin (SHGB) which decreases free E2 available to fetus ToxLogic 2

2 Use of DES in Humans Widely prescribed to 4-5,000,000 pregnant women until 1972 in mistaken belief that it would prevent miscarriage Large numbers of males & females exposed in utero to widely differing dosing protocols Use discontinued in 1972 with discovery that small number of women developed vaginal adenocarcinoma 100s of clinical studies on DES-exposed men and women Ongoing investigations of DES-exposed cohorts; documentation/verification of exposure a critical element Most exposures during 1 st trimester during critical window of sensitivity ToxLogic 3 Human Dosing With DES During peak years of use, in different centers, dosing regimens varied widely; in utero exposure to vastly different total maternal DES doses Institution Estimated Mean Total Maternal Dose (g) Mayo Clinic 1.4 Stanford Univ. 3.5 Boston Univ. 6.4 DES Efficacy trial 10+ Univ. Chicago 12 British Medical Res. Council 18 ToxLogic 4

3 Human DES Data and Specific Health Endpoints Human studies of potential associations with in utero/maternal exposure to DES Breast cancer Endometriosis Adverse effects on male & female reproductive tract Alterations in sexual behavior Testicular cancer Prostate cancer Immune system effects ToxLogic 5 Effects of DES in Animals DES extensively studied in animals; effects on offspring following in utero exposure to sufficient doses well characterized Spectrum of effects; mainly on reproductive tract Effects in Mice Following in utero Exposure to DES Effects in males Sperm abnormalities Decrease sperm counts Epididymal cysts Cryptorchid testes Microphallus Hypospadias Testicular tumors Prostatic tumors Infertility Immune dysfunction Effects in females Ovarian cysts Ovarian tumors Structural abnor. uterus Malformations cervical canal Vaginal adenocarcinoma Vaginal adenosis Salpingitis of oviduct Uterine tumors Infertility ToxLogic Immune dysfunction 6

4 Extrapolation from Animals to Humans Experimental mouse model qualitatively predicts or confirms many adverse effects in humans from in utero exposure to DES Quantitative aspects of extrapolating from rodents to humans far less certain Qualitative & quantitative differences between rodents & humans for hormonally-mediated effects Animals appear more sensitive to DES-induced effects Vaginal adenosis Cryptorchidism Epidymal cysts Impaired fertility ToxLogic 7 Hypothetical Potency Comparison of DES with Weakly Estrogenic Chemicals Mayo Clinic study: total median maternal dose of DES=720 mg & median exposure duration=101 days not associated with any male reproductive tract effects, i.e., 7 mg/day 7 mg/day may represent approximate no-effect level for in utero DES effects on male reproductive tract (other endpoints may have different no-effect levels) Assume DES 1000 x more potent than a weakly estrogenic chemical Approximate no-effect daily intake dose; 7 mg/day x mg/day or 7 g/day Need to compare with actual intake to assess MOE ToxLogic 8

5 In Utero Exposure to DES & Effects on Sperm Quality Mice exposed in utero to DES show sperm production & abnormal morphology as adults Univ. Chicago mean maternal DES dose 12,000 mg associated with decreased sperm counts and abnormal morphology in some adults; average sperm counts from 115 to 91 million/ml Mayo Clinic mean maternal DES dose 1400 mg; no differences between exposed and controls in sperm count, motility or abnormal sperm ToxLogic 9 In Utero Exposure to DES & Adult Breast Cancer Risks Estrogen-related factors associated with breast cancer risk, e.g., late age of 1 st childbirth, nulliparity, late age of menopause, lactation, OC or HRT Latest update; 4817 exposed, 2073 unexposed; multiple cohorts with known DES exposures: Chicago, Boston & California cohorts with median DES doses of 12,442, 8,675 & 7,550 mg (high dose) Texas, Minnesota & Wisconsin cohorts with median DES doses of 2,572, 1,520 & 3,175 mg (low dose) ToxLogic 10

6 In Utero Exposure to DES & Adult Breast Cancer Risks Dose in Cohort P-Y follow-up No. Cases RR (95% CI) Low dose 12, ( ) High dose 16, ( ) Unknown ( ) Highest relative risk was observed for the cohorts receiving the highest cumulative dose of DES exposure (Palmer et al. 2006) ToxLogic 11 In Utero Exposure to DES & Adult Male Cancer Risks Cancer site or type Observed Expected SIR (95% CI) Digestive ( ) Lung ( ) Germ cell ( ) Testicular ( ) Melanoma ( ) Thyroid ( ) Bone ( ) Lymphatic/hematopoietic ( ) 1365 DES exposed & 1394 non DES exposed men; no statistically significant findings for testicular cancer based on cohort treatment location It is still uncertain as to whether prenatal DES exposure is associated with testicular cancer risk. (Strohsnitter et al. 2001) ToxLogic 12

7 Use of TEF Approach for Assessing Cumulative Risk TEF/TEQ concept based on dioxin & dioxin-like PCBs Large amount of key data based on differential CYP1A1 (EROD) induction Other endpoints now used, but most also involve MFO induction Assumption that rodent-based TEFs relevant for humans Data now demonstrate that this is not correct ToxLogic 13 Humans Are Far Less Sensitive to PCBs PCB 126 Aroclor Rhesus 300 Rhesus EROD Rat HepG2 Donors human Rat HepG2 Donors human Concentration (Log M) Concentration (Log M) AhR- mediated CYP1A enzyme induction assay: If species equally sensitive, all lines should overlap. Humans are far less sensitive to PCBs than rats or monkeys. ToxLogic 14 Silkworth et al., Tox. Sci., 2005

8 DES Paradigm Avoid and/or account for issues now apparent with dioxin TEF/TEQ approach Species differences in responsiveness to estrogen Can t assume that rodent data quantitatively apply to humans Critical need to ground risk assessment with human data Comparison of rodent/human DES (or E2) NOELs ToxLogic 15