Potent aromatase inhibitors through fungal transformation of anti-cancer drug testolactone: an approach towards treatment of breast cancer

Abstract

Biotransformation of an aromatase inhibitor, testolactone (1), yielded four metabolites, 7?-hydroxy-3-oxo-13,17-seco-5?-androsta-1-eno-17,13?-lactone (2), 3?,11?-dihydroxy-13,17-seco-5?-androsta-17,13?-lactone (3), 4?,5?-epoxy-3?-hydroxy-13,17-secoandrosta-1-eno-17,13?-lactone (4), and 4?,5?-epoxy-3?-hydroxy-13,17-secoandrosta-1-eno-17,13?-lactone (5). Aromatase (estrogen synthase) involves in the synthesis of estrogen, and promotes the growth of breast cancerous cells. It is a key target for the discovery of chemotherapeutic agents against ER+(estrogen-positive) breast-cancers. Metabolites 2 (IC.sub.50=8.63?0.402 nM), and 3 (IC.sub.50=9.23?1.31 nM) were identified as potent inhibitors against human aromatase enzyme, in comparison to 1 (IC.sub.50=0.716?0.031 ?M), and the standard aromatase inhibiting drug, exemestane (IC.sub.50=0.232?0.031 ?M). Derivatives 4 (IC.sub.50=10.37?0.50 ?M) and 5 (IC.sub.50=0.82?0.059 ?M) also showed a good inhibition against aromatase enzyme. Therefore, metabolites 2-5 have the potential to serve as therapeutic agents against ER+ (estrogen-positive) breast-cancers.

Claims

1. A testolactone derivative selected from the group consisting of 7?-hydroxy-3-oxo-13,17-seco-5?-androsta-1-eno-17,13?-lactone (2), 3?,11?-dihydroxy-13,17-seco-5?-androsta-17,13?-lactone (3), 4?,5?-epoxy-3?-hydroxy-13,17-secoandrosta-1-eno-17,13?-lactone (4), and 4?,5?-epoxy-3?-hydroxy-13,17-secoandrosta-1-eno-17,13?-lactone (5) and a pharmaceutically acceptable salt thereof.

2. A method of treating estrogen-responsive (ER+) breast cancer, the method comprising on administration of effective amount of testolactone derivative selected from the group consisting of 7?-hydroxy-3-oxo-13,17-seco-5?-androsta-1-eno-17,13?-lactone (2), 3?,11?-dihydroxy-13,17-seco-5?-androsta-17,13?-lactone (3), 4?,5?-epoxy-3?-hydroxy-13,17-secoandrosta-1-eno-17,13?-lactone (4), and 4?,5?-epoxy-3?-hydroxy-13,17-secoandrosta-1-eno-17,13?-lactone (5) or their salts in suitable pharmaceutical excipients, adjuvant, carrier, or diluent to subject in need thereof.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 depicts the structures of testolactone (1) and its metabolites, 7?-hydroxy-3-oxo-13,17-seco-5?-androsta-1-eno-17,13?-lactone (2) 3?,11?-dihydroxy-13,17-seco-5?-androsta-17,13?-lactone (3), 4?,5?-epoxy-3?-hydroxy-13,17-secoandrosta-1-eno-17,13?-lactone (4), and 4?,5?-epoxy-3?-hydroxy-13,17-secoandrosta-1-eno-17,13?-lactone (5) via M. phaseolina-mediated transformation of drug 1, along with their aromatase inhibition and cytotoxic activities against human fibroblast (BJ) and mouse fibroblast (3T3) cell lines.

(2) FIG. 2 depicts the computer-generated ORTEP drawing of final X-ray models of derivatives 3-5.

DETAILED DESCRIPTION OF THE INVENTION

Experimental

(3) Media Preparation

(4) One-liter media for the maximum growth of fungus (Macrophomina phaseolina, KUCC 730 (Karachi University Culture Collection, Pakistan), was prepared by mixing 10 g glucose, 5 g NaCl, 5 g peptone, 5 g KH.sub.2PO.sub.4, and 10 mL glycerol in 1 L distilled water, and autoclaved for their maximum, and mature growth.

(5) Fermentation

(6) On the basis of small-scale screening results, 4 L of media for fungus was prepared by mixing aforementioned ingredients. Media (4 L) was distributed into 20 Erlenmeyer flasks of 500 mL (200 mL in each), cotton plugged, and autoclaved at 121? C. The sterilized media was then cooled at room temperature, and inoculated with seed flasks of Macrophomina phaseolina cell culture under sterilized conditions. Fungal cell cultures containing flasks were placed for 3-4 days on rotary shaker (121 rpm). After the mature growth of M. phaseolina in each flask, 1 g of testolactone (1) (C.sub.19H.sub.24O.sub.3) ((Cas No. 968-93-4) was procured from Fartop Limited, China) was dissolved in 10 mL of DMSO and dispensed (2 mL) in each fungal culture containing flasks. The flasks were then again placed on rotary shaker (121 rpm) at 25? C. for twelve days.

(7) Extraction

(8) After incubation, the reaction was stopped by addition of DCM (dichloromethane) in each flask, and filtered to separate fungal masses. Each filtrate (aqueous and organic phases) was separated by extracting with 20 L of DCM. Anhydrous Na.sub.2SO.sub.4 (sodium sulfate) was added in each organic layer to make them moisture free, filtered, and concentrated under reduced pressure.

(9) Isolation and Purification

(10) The resulting crude (2 g) was fractionated by column chromatography (CC) with a mobile phase of hexanes-acetone. The polarity of mobile phase was increased by increasing 5-100% gradients of acetone. As a result, four main fractions, i.e., 1-4 were obtained, which were analyzed by thin layer chromatography (TLCs). The fractions were further purified through recycling reverse phase HPLC (LC-908; equipped with YMC M-80; 20-250 mm i.d. 4-5 ?m). Compounds 2 (methanol-water; 7/3, R.sub.T=32 min, 22.3 mg), 3 (methanol-water; 6/4, R.sub.T=36 min, 24.2 mg), 4 (methanol-water; 7/3, R.sub.T=36 min, 8.1 mg), and 5 (methanol-water; 7/3, R T=31 min, 7.1 mg) were purified from fractions 1-4, respectively. Substrate 1 was also recovered.

7?-Hydroxy-3-oxo-13,17-seco-5?-androsta-1-eno-17,13?-lactone (2)

(11) White solid; m. p. 197-199? C.; [?].sub.D.sup.25=+231.3 (c 0.001, MeOH); IR (CH.sub.3Cl): ?.sub.max (cm.sup.?1) 3455 (OH), 2942 (CH), 1675 (?,?-unsaturated ketone), 1714 (6-membered lactone carbonyl); HREI-MS m/z 318.1844 [M.sup.+] (C.sub.19H.sub.26O.sub.4) (calcd. 318.1831); EI-MS m/z: 318.3 [M.sup.+]; .sup.1H-NMR (?) (CDCl.sub.3), H-1 (6.81, d, J.sub.1,2=10.2 Hz), H-2 (5.96, d, J.sub.2,1=10.2 Hz), H.sub.2-4 (2.60, overlap; 2.35, dd, J.sub.4a,4b=17.2 Hz; J.sub.4,5=4.4 Hz), H-5 (2.20, m), H.sub.2-6 (1.86, overlap; 1.76, overlap), H-7 (3.79, m), H-8 (? 1.35, overlap), H-9 (1.62, m), H.sub.2-11 (1.74, overlap; 1.51, m), H.sub.2-12 (2.08, dt, J.sub.12,12=12.6 Hz; J.sub.12,11=3.1 Hz), H-14 (? 1.69, overlap), H.sub.2-15 (? 2.61, overlap; 1.85, overlap), H.sub.2-16 (? 2.68, overlap; 2.52, overlap), H.sub.3-18 (1.36, s), H.sub.3-19 (1.21, s); .sup.13C-NMR (?) (CDCl.sub.3), C-1 (159.2), C-2 (127.9), C-3 (198.6), C-4 (39.4), C-5 (40.7), C-6 (37.4), C-7 (70.1), C-8 (44.6), C-9 (46.8), C-10 (37.9), C-11 (23.5), C-12 (39.4), C-13 (83.2), C-14 (44.0), C-15 (21.9), C-16 (29.0), C-17 (171.2), C-18 (20.4), C-19 (20.7).

3?,11?-Dihydroxy-13,17-seco-5?-androstano-17,13?-lactone (3)

(12) White solid; m. p. 188-191? C.; [?].sub.D.sup.25=+11.6 (c 0.001, MeOH); IR (CH.sub.3Cl): ?.sub.max (cm.sup.?1) 3431 (OH), 2931 (CH), 1702 (6-membered lactone carbonyl); HRFAB-MS (+ve) m/z 323.2233 [M+H].sup.+ (C.sub.19H.sub.34O.sub.4) (calcd. 323.2222); FAB-MS (+ve) m/z 323.1 [M+H].sup.+; FAB-MS (?ve) m/z 321.2 [M?H].sup.+; .sup.1H-NMR (?) (CDCl.sub.3), H.sub.2-1 (1.89, overlap; 1.22, overlap), H.sub.2-2 (1.71, overlap; 1.29, overlap), H-3 (3.64, m), H.sub.2-4 (1.68, overlap; 1.53, overlap), H-5 (1.66, overlap), H.sub.2-6 (1.73, overlap; 1.28, overlap), H.sub.2-7 (1.83, overlap; 1.12, overlap), H-8 (1.69, overlap), H-9 (1.51, overlap), H-11 (4.32, br. d, J.sub.e,?=1.7 Hz), H.sub.2-12 (2.08, dd, J.sub.12,12=13.8 Hz; J.sub.12,11e=3.1 Hz; 1.81, overlap), H-14 (1.30, overlap), H.sub.2-15 (1.99, overlap; 1.50, overlap), H.sub.2-16 (2.66, ddd, J.sub.16,16=19.1 Hz; J.sub.16a,15a=8.9; J.sub.16a,15b=2.1 Hz; 2.53, m), H.sub.3-18 (1.46, s), H.sub.3-19 (1.09, s); .sup.13C-NMR (?) (CDCl.sub.3), C-1 (35.0), C-2 (30.7), C-3 (71.4), C-4 (36.0), C-5 (42.4), C-6 (25.8), C-7 (26.0), C-8 (33.1), C-9 (48.0), C-10 (34.8), C-11 (66.6), C-12 (47.4), C-13 (82.6), C-14 (43.7), C-15 (19.6), C-16 (28.7), C-17 (171.5), C-18 (23.2), C-19 (26.4); Single-crystal X-ray Data: crystal system, orthorhombic; space group, P2.sub.12.sub.12.sub.1; unit cell dimensions, a=6.4517 (2) ?, ?=90, b=12.2365 (3) ?, ?=90, c=21.1261 (5) ?, ?=90; volume, 1667.83 (8) ?.sup.3; crystal size, 0.11?0.10?0.05 mm; density, 1.284 mg/m.sup.3; ? range, 4.18 to 68.22.

4?,5?-Epoxy-3?-hydroxy-13,17-secoandrosta-1-eno-17,13?-lactone (4)

(13) White solid; m. p. 192-193? C.; [?].sub.D.sup.25=+302.0 (c 0.001, MeOH); IR (CH.sub.3Cl): ?.sub.max (cm.sup.?1) 3434 (OH), 2944 (CH), 1720 (6-membered lactone carbonyl); HR-EIMS m/z 318.1832 [M.sup.+] (C.sub.19H.sub.26O.sub.4) (calcd. 318.1831); EI-MS m/z: 318.1 [M.sup.+]: .sup.1H-NMR (?) (CDCl.sub.3), H-1 (5.43, overlap), H-2 (5.41, overlap), H-3 (4.44, br. d, J.sub.3,2=J.sub.3,4=2.5 Hz), H-4 (3.29, br. d, J.sub.4,3=1.5 Hz), H.sub.2-6 (2.12, td, J.sub.6a,6b=13.7; J.sub.6,7=4.4 Hz; 1.21, m), H.sub.2-7 (1.99, overlap; 1.08, overlap), H-8 (1.26, m), H-9 (1.04, m), H.sub.2-11 (1.73, m; 1.37, overlap), H.sub.2-12 (1.92, m; 1.59, m), H-14 (1.38, m), H.sub.2-15 (1.99, m; 1.51, m), H.sub.2-16 (2.67, m; 2.57, m), H.sub.3-18 (1.31, s), H.sub.3-19 (1.09, s); .sup.13C-NMR (?) (CDCl.sub.3), C-1 (134.9), C-2 (124.2), C-3 (65.5), C-4 (63.5), C-5 (65.2), C-6 (30.4), C-7 (28.9), C-8 (37.5), C-9 (51.7), C-10 (39.2), C-11 (23.0), C-12 (39.0), C-13 (82.8), C-14 (45.6), C-15 (19.9), C-16 (28.5), C-17 (171.1); C-18 (20.0); C-19 (16.3); Single-crystal X-ray Data: crystal system, orthorhombic; space group, P2.sub.12.sub.12.sub.1; unit cell dimensions, a=7.0877 (2) ?, ?=90, b=11.0304 (3) ?, ?=90, c=20.3492 (5) ?, ?=90; volume, 1590.90 (7) ?.sup.3; crystal size, 0.24?0.15?0.11 mm; density, 1.329 mg/m.sup.3; ? range, 4.35 to 68.15.

4?,5?-Epoxy-3?-hydroxy-13,17-secoandrosta-1-eno-17,13?-lactone (5)

(14) White solid; m. p. 194-196? C.; [?].sub.D.sup.25=+28.6 (c 0.001, MeOH); IR (CH.sub.3Cl): ?.sub.max (cm.sup.?1) 3437 (OH), 2944 (CH), 1720 (6-membered lactone carbonyl); HREI-MS m/z 318.1838 [M.sup.+] (C.sub.19H.sub.26O.sub.4) (calcd. 318.1831); EI-MS m/z (%): 318.1 [M.sup.+] (54), 300.2 (49), 227.1 (23), 199.1 (21), 147.1 (37), 121.1 (100); .sup.1H-NMR (?) (CDCl.sub.3), H-1 (5.59, overlap), H-2 (5.57, overlap), H-3 (4.50, br. t, J.sub.3,2=J.sub.3,4=1.4 Hz), H-4 (3.08, br. d, J.sub.4,3=1.6 Hz), H.sub.2-6 (2.15, overlap; 1.29, overlap), H.sub.2-7 (2.01, overlap; 1.18, overlap), H-8 (1.31, overlap), H-9 (1.33, overlap), H.sub.2-11 (1.71, overlap; 1.37, overlap), H.sub.2-12 (1.98, overlap; 1.65, overlap), H-14 (1.46, m), H.sub.2-15 (2.02, overlap; 1.55, overlap), H.sub.2-16 (2.72, ddd, J.sub.16,16=18.8 Hz; J.sub.16a,15a=8.1 Hz; J.sub.16a,15b=2.0 Hz; 2.65, m), H.sub.3-18 (1.33, s), H.sub.3-19 (1.11, s); .sup.13C-NMR (?) (CDCl.sub.3), C-1 (137.2), C-2 (122.5), C-3 (64.2), C-4 (62.0), C-5 (63.7), C-6 (30.2), C-7 (28.7), C-8 (38.0), C-9 (52.9), C-10 (39.4), C-11 (22.7), C-12 (38.9), C-13 (82.9), C-14 (45.5), C-15 (19.9), C-16 (28.6), C-17 (171.1), C-18 (20.0), C-19 (16.9). Single-crystal X-ray Data: crystal system, monoclinic; space group, P2.sub.1; unit cell dimensions, a=5.9716 (15) ?, ?=90, b=14.040 (4) ?, =100.909 (17), c=10.445 (2) ?, ?=90; volume, 860.0 (4) ?.sup.3; crystal size, 0.180?0.170?0.080 mm; density, 1.299 mg/m.sup.3; ? range, 4.310 to 68.221.

(15) Human Placental Aromatase Inhibition Assay Protocol

(16) The aromatase enzyme activity can be determined by measuring conversion of testosterone to 17?-estradiol, shown as follows:

(17) ##STR00001##

(18) The activity is determined in a 1 mL reaction mixture, containing protein (mainly aromatase enzyme) (2 mg/mL), testosterone (10 ?M), potassium phosphate buffer (0.1 M) at pH 7.4, and 101.11, of test compound (0.1 mM). The reaction mixture was pre-incubated at 37? C. for 10 min. NADPH (1 mM) was then added, and incubated for 20 min. The reaction was terminated by adding 100 ?L of trichloroacetic acid (10%, w/v). The reaction mixture was centrifuged for 10 min at 12,000 g, pellet was discarded, and the supernatant containing 17?-estradiol was extracted with 1 mL N-butylchloride. The extracted 17?-estradiol was then dried and the quantity of the product was determined by UPLC (column ACE Generix 5 ?m C.sub.18 150?4.6 mm) using isocratic elution of the mobile phase containing triethylamine (0.1%) in ACN/H.sub.2O (45:55, v/v), and pH 3.0 (adjusted by orthophosphoric acid) with a flow rate of 1.2 mL/min at 200 nm. Calculations were performed by following formula:

(19) $\%\mathrm{Inhibition}=100-\frac{\left(\mathrm{Peak}\mathrm{area}\mathrm{of}\mathrm{test}\mathrm{sample}\right)}{\left(\mathrm{Peak}\mathrm{area}\mathrm{of}\mathrm{control}\right)}?100$
Results and Discussion

(20) The HREI-MS of metabolite 2 displayed the [M.sup.+] at m/z 318.1844 (C.sub.19H.sub.26O.sub.4), indicating addition of an oxygen atom, along with two hydrogen atoms in substrate 1 (m/z 300). Reduction between C-4/C-5 was inferred via .sup.3J correlation of H.sub.2-6 and H-1 with C-4. Hydroxyl group at C-7 was supported by HMBC correlations of H-7 with C-5, C-8 and C-9, and H.sub.2-6 with C-7. The structure of compound 2 was identified as 7?-hydroxy-3-oxo-13,17-seco-5?-androsta-1-eno-17,13?-lactone.

(21) The [M+H].sup.+ of metabolite 3 was observed at m/z 323.2233 in the HRFAB-MS (high resolution fast atom bombardment spectrometry), 22 amu greater than the substrate 1 (m/z 300). Reduction in the ring A of derivative 3 was inferred through the HMBC correlations of H.sub.2-1 and H.sub.2-4 with C-2, C-3 and C-10. An OH group was placed at C-11, based on HMBC correlations of H-11 with C-9, C-10, and C-12. The structure of derivative 3 was determined as 3?,11?-dihydroxy-13,17-seco-5?-androstano-17,13?-lactone.

(22) The HREI-MS of metabolite 4 presented its [M.sup.+] at m/z 318.1832, indicating addition of oxygen, and two hydrogen atoms in substrate 1 (m/z 300). Epoxidation between C-4/C-5, along with reduction at C-3 was inferred though the .sup.2J and .sup.3J correlations of H-2 with C-3 and C-4. The structure was deduced as 4?,5?-epoxy-3?-hydroxy-13,17-secoandrosta-1-eno-17,13?-lactone (4).

(23) The [M.sup.+] of metabolite 5 in the HREI-MS was observed at m/z 318.1838, indicating the addition of an oxygen atom, along with two hydrogen atoms in substrate 1 (m/z 300). Reduction at C-3, along with epoxidation between C-4/C-5 was determined via the HMBC correlations of H-1 with C-5, and H-2 with C-3 and C-4. The structure of derivative 5 was identified as 4?,5?-epoxy-3?-hydroxy-13,17-secoandrosta-1-eno-17,13?-lactone.

(24) Placement of ?-OH at C-7, along with reduction between C-4/C-5 in compound 2 (IC.sub.50=0.00863?0.0004 ?M) has increased its anti-aromatase activity than substrate 1 (IC.sub.50=0.716?0.031 ?M). Similarly, ?-OH at C-11, and reduction of olefinic groups at C-1, C-2, C-4, and C-5, and ketonic carbonyl C-3 into secondary alcohol (?-OH) in compound 3 (IC.sub.50=0.00923?0.0013 ?M) also increased its anti-aromatase activity. While epoxidation between C-4/C-5, along with reduction of ketone into alcohol (?-OH) in compound 5 (IC.sub.50=0.82?0.059 ?M) has not much affected its inhibition potential against placental microsomal aromatase. Likewise, epoxidation between C-4/C-5, along with reduction of ketone into alcohol (?-OH) in derivative 4 (IC.sub.50=10.37?0.50 ?M) has decreased its anti-aromatase activity, as compared to parent molecule, testolactone (1), and derivatives 2, 3, and 5.

(25) Presence of hormone receptors, such as estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor (HER2) in breast cancer cell lines make them responsive towards hormonal therapies. While the breast cancer negative for these hormone receptors are more difficult to treat, as they do not respond to hormonal therapies. High amount of estrogens in the body due to overexpression of aromatase enzyme, enhances the breast tumors growth. In general, breast cancer tissues have been reported to express more aromatase enzyme than the normal tissues of breast. Estrogens and androgens stimulate the growth of MCF-7 breast cancer cells. Derivatives 2-5 were found to be inactive to breast cancer cell lines, e.g., MCF-7 (ER+, PR+, and HER.sub.2+), MDA-MB-231 (ER?, PR?, and HER.sub.2?), and BT-474 (ER+, and HER.sub.2+) in vitro. This showed structural alteration, in anti-cancer drug, testolactone (1) did not affect their cytotoxicity potential.