C-7 Analogues of Progesterone as Potent Inhibitors of the P-Glycoprotein Efflux Pump

Abstract

The P-glycoprotein product (Pgp) of the MDR1 gene has been implicated in the multiple drug resistance phenotype expressed by many cancers. Functioning as an efflux pump, P-glycoprotein prevents the accumulation of high intracellular concentrations of substrates. We have taken a rational approach to designing inhibitors of P-glycoprotein function, selecting a natural substrate (progesterone) as our lead compound. We hypothesized that progesterone, substituted at C-7 with an aromatic moiety(s), would exhibit reduced Pgp affinity, significantly increased antiPgp activity, and reduced affinity for progesterone receptors (PGR). We synthesized 7 alpha-[4'-(aminophenyl)thio]pregna-4-ene-3,20-dione (2), which comprises a C-7 alpha thiol bridge linking an aminophenyl moiety to progesterone, from pregna-4,6-diene-3,20-dione (1). The subsequent addition reaction of 2 with the appropriate isocyanate produced an initial series of compounds (3-6). Compounds 3-5 (respectively, -CH(2)CH(2)Cl; -CH(2)CH(3); and -CH(CH(3))C(6)H(5)) exhibit a significantly increased ability to inhibit P-glycoprotein. Potency for restoring doxorubicin accumulation in MDR1-transduced human breast cancer cells is increased up to 60-fold as compared with progesterone. Compound 5 has greater potency than verapamil and is equipotent with cyclosporin A, for inhibiting P-glycoprotein function. Furthermore, 5 does not bind to PGR, implying a potential reduction in in vivo toxicity. These data identify C-7-substituted progesterone analogues and 5, in particular, as rationally designed antiPgp compounds worthy of further evaluation/development.

RU49953: a non-hormonal steroid derivative that potently inhibits P-glycoprotein and reverts cellular multidrug resistance

“…In contrast, the positioning of both the dimethylaminophenyl substituent (at position 7, instead of 11, in RU50641) and double bonds (at positions 5 and 9, instead of 4 and 10, in RU39616) appears not to be critical. This is consistent with recent results obtained with hydrophobic substitutions of progesterone at position 7 which decreased P-glycoprotein transport activity leading to intracellular drug accumulation [18]. An increased efficiency was also obtained when the dimethylaminophenyl substituent was introduced at position 21 of either dichlorisone or 17-deoxydexamethasone [40], and with 21-aminosteroid derivatives [41].…”

“…Most other steroid derivatives reported as potential MDR modulators also behaved as hormone agonists or antagonists: RU38486 [46], some C-7 progesterone derivatives [47] and 21-dimethylaminophenyl derivatives of deoxydexamethasone and dichlorisone [39] toward the GR and PR; tamoxifen [48], toremifene [49] and the pure antiestrogens ICI164,384 and ICI182,780 [29,50] toward the ER. In contrast, recently synthesized progesterone derivatives, with quite bulky substituents including two aromatic rings at position 7, were no longer able to bind to the PR [18]. RU49953, an estradiol derivative with two dimethylaminophenyl substituents at positions 11 and 17, was found here not to be able to bind to either the ER or any other hormone receptors, and may therefore constitute a powerful tool for circumventing anticancer drug efflux.…”

“…e Receptor binding of steroid derivatives was determined from the curves obtained with increasing amounts of compounds (0. and is much more efficient than cyclosporin A [31]. As stressed elsewhere [18], the use of a transfected cell line, in which P-glycoprotein alone is responsible for MDR, in contrast to drug-selected cell lines that may also exhibit increased glutathione transferase and topoisomerase II activities [42,43], is particularly well suited for studying modulators of P-glycoprotein-mediated MDR. Also worth mentioning is that such hydrophobic substitutions rendered RU49953 completely unable to bind to either the ER or any other hormone receptor.…”

ATP binding cassette transporters and drug resistance in breast cancer.

“…Moreover, several steroids and steroid derivatives appear to reverse the multidrug resistance conferred by Pgp, possibly by a competitive mechanism (Naito et al 1989, Yang et al 1989, Hu et al 1991, Abraham et al 1993, Zalcberg et al 1993, Yang et al 1994, Gruol & Bourgeois 1997, Tansan et al 1997, Leonessa et al 2002. Among steroids (and derivatives), glucocorticoids generally represent good substrates, while progesterone, medroxyprogesterone acetate, testosterone and androstenedione are poor substrates ).…”

Progestins as Anticancer Drugs and Chemosensitizers, New Targets and Applications

“…The first mention of progesterone as an MDR regulator was published in 1989 by Yang [ 65 ]. Many studies have been devoted to progesterone and its analogs as modulators of P-gp mediated resistance of tumor cells [ 66 , 67 , 68 , 69 ]. Moreover, to date, there is convincing evidence of the specific action of progesterone on P-glycoprotein [ 70 ].…”