Differentiation of antiinflammatory and antitumorigenic properties of stabilized enantiomers of thalidomide analogs

Abstract

Therapeutics developed and sold as racemates can exhibit a limited therapeutic index because of side effects resulting from the undesired enantiomer (distomer) and/or its metabolites, which at times, forces researchers to abandon valuable scaffolds. Therefore, most chiral drugs are developed as single enantiomers. Unfortunately, the development of some chirally pure drug molecules is hampered by rapid in vivo racemization. The class of compounds known as immunomodulatory drugs derived from thalidomide is developed and sold as racemates because of racemization at the chiral center of the 3-aminoglutarimide moiety. Herein, we show that replacement of the exchangeable hydrogen at the chiral center with deuterium allows the stabilization and testing of individual enantiomers for two thalidomide analogs, including CC-122, a compound currently in human clinical trials for hematological cancers and solid tumors. Using "deuterium-enabled chiral switching" (DECS), in vitro antiinflammatory differences of up to 20-fold are observed between the deuterium-stabilized enantiomers. In vivo, the exposure is dramatically increased for each enantiomer while they retain similar pharmacokinetics. Furthermore, the single deuterated enantiomers related to CC-122 exhibit profoundly different in vivo responses in an NCI-H929 myeloma xenograft model. The (-)-deuterated enantiomer is antitumorigenic, whereas the (+)-deuterated enantiomer has little to no effect on tumor growth. The ability to stabilize and differentiate enantiomers by DECS opens up a vast window of opportunity to characterize the class effects of thalidomide analogs and improve on the therapeutic promise of other racemic compounds, including the development of safer therapeutics and the discovery of new mechanisms and clinical applications for existing therapeutics.

Keywords: CC-122; cancer; deuterium; enantiomer; thalidomide.

Fig. 1.

Structures of thalidomide, pomalidomide, lenalidomide, and protonated and deuterated enantiomers of compound 1 [CC-11006; i.e., (S)-H-1, (R)-H-1, (S)-D-1, and (R)-D-1] as well as protonated and deuterated enantiomers of compound 2 [CC-122; (S)-H-2, (R)-H-2, (S)-D-2, and (R)-D-2 (absolute configuration was not established for compound 2; enantiomers are referred to by the sign of their optical rotation; i.e., (+) or (−); details in the text)].

Fig. 2.

Synthesis of rac-H-1 and isotopomeric enantiomers (R)-D-1 and (S)-D-1: (i) maleic anhydride, trifluoroacetic acid, 50 °C; (ii) rac-3-amino-2,3-dioxopiperidine, imidazole, acetic acid, 77 °C (for rac-H-1); (R)- or (S)-(3-²H)-3-amino-2,3-dioxopiperidine, diisopropylethylamine, 70 °C [for (R)-D-1 or (S)-D-1, respectively]; (iii) H₂, palladium on carbon (Pd/C); and (iv) cyclopropanecarbonyl chloride, diisopropylethylamine.

Fig. 3.

Synthesis of rac-D-2: (i) acetic anhydride, 120 °C; (ii) water, reflux; (iii) rac-3-amino-2,6-piperidinedione hydrochloride, diisopropylethylamine, hydroxybenzotriazole, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide, N,N-dimethylformamide; (iv) chlorotrimethylsilane, triethylamine, acetonitrile, 75 °C and then deuterium oxide, room temperature; and (v) H₂, Pd(OH)₂, N,N-dimethylformamide.

Fig. 4.

Semilogarithmic plot of the pharmacokinetics of (−)-2 (blue circles) and (+)-2 (red diamonds; sum of isotopomers) in female CB.17 SCID mice dosed orally with (A) protonated racemate rac-H-2 (30 mg/kg), (B) (−)-D-2 (15 mg/kg), or (C) (+)-D-2 (15 mg/kg).

Fig. 5.

H929 xenograft model. Average tumor volume (± SEM) as function of time in female CB.17 SCID mice (n = 10 per group) treated daily by oral gavage with vehicle (black circles), rac-H-2 (3 mg/kg; green diamonds), and (A) (−)-D-2 [1.5 (open blue squares) or 15 mg/kg (filled blue squares)] or (B) (+)-D-2 [1.5 (open red triangles) or 15 mg/kg (filled red triangles)]. Two-way ANOVA of tumor volume vs. time with Bonferroni’s multiple comparisons posttest against vehicle group. *P < 0.05; **P < 0.01; ***P < 0.001; ****P < 0.0001. (C) Average tumor volume (± SD) on the last day of dosing for the two repeats (n = 20 per group). One-way ANOVA of tumor volume with Tukey posttest against vehicle group. ****P < 0.0001.