tas-108 tas-108 tas-108, also known as sr-16234, is a drug discovered by masato tanabe and under development by sri international and taiho pharmaceutical. it is a steroid hormone that has shown signs of treating and preventing breast cancer, even in patients where tamoxifen has failed. tas-108clinical dataother names17β--2-methoxyphenoxy]ethyl]-7α-methylestra-1,3,5(10)-trien-3-ol; 17β--2-methoxyphenoxy]ethyl]-7α-methylestradiolatc codel02ba (who) identifiers iupac name (1s,9r,10s,11s,14r,15r)-14-(2-ethyl)-9,15-dimethyltetracycloheptadeca-2(7),3,5-trien-5-ol cas number229634-97-3citrate: 229634-98-4pubchem cid9874875citrate: 9874874chemspider8050564 ycitrate: 8050563unii42u0c8volocitrate: 9b29n23k7echemical and physical dataformulac33h47no3molar mass505.743 g·mol−13d model (jsmol)interactive imagecitrate: interactive image smiles ccn(cc)cc1=cc(=c(c=c1)occ2cc32(cc43(cc5=c4c=cc(=c5)o)c)c)occitrate: ccn(cc)cc1=cc(=c(c=c1)occ2cc32(cc43(cc5=c4c=cc(=c5)o)c)c)oc.c(c(=o)o)c(cc(=o)o)(c(=o)o)o inchi inchi=1s/c33h47no3/c1-6-34(7-2)21-23-8-13-30(31(19-23)36-5)37-17-15-25-9-12-29-32-22(3)18-24-20-26(35)10-11-27(24)28(32)14-16-33(25,29)4/h8,10-11,13,19-20,22,25,28-29,32,35h,6-7,9,12,14-18,21h2,1-5h3/t22-,25-,28-,29+,32-,33-/m1/s1 ykey:ohcpnhflpcvwrg-mwsjhzltsa-n ycitrate: inchi=1s/c33h47no3.c6h8o7/c1-6-34(7-2)21-23-8-13-30(31(19-23)36-5)37-17-15-25-9-12-29-32-22(3)18-24-20-26(35)10-11-27(24)28(32)14-16-33(25,29)4;7-3(8)1-6(13,5(11)12)2-4(9)10/h8,10-11,13,19-20,22,25,28-29,32,35h,6-7,9,12,14-18,21h2,1-5h3;13h,1-2h2,(h,7,8)(h,9,10)(h,11,12)/t22-,25-,28-,29+,32-,33-;/m1./s1key:vohocsjonojosd-scidsjfvsa-n development masato tanabe's team at sri has focused on the development of steroid hormones. a compound discovered in a previous sri contract from the national institutes of health showed potential – it acted like "anti-estrogen" in the breasts and uterus but like normal estrogen elsewhere in the body, and was more "tissue-selective". a contract was proposed to taiho pharmaceutical in july 1996, and within six years and slightly under $3 million (an unusually short amount of time), two new drugs were discovered and tested on people (particularly people for which tamoxifen has failed): sr-16234 and sr-16287. the first of those, sr-16234, also inhibited the growth of blood vessels angiogenesis and accelerated the death of cancer cells apoptosis and thus was particularly well suited to be an anti-cancer drug. as of august 2010, the drug had been through five phase i and two phase ii studies, and phase iii studies are being planned.