Conjugates of Alantolactone with Anthracycline Antibiotics

Abstract

Natural anthracycline antibiotics exhibit high antitumor activity. Their mechanism of action is based on inhibition of nucleic acid synthesis by intercalation between pairs of nitrogenous bases and binding to topoisomerase II [1]. This results in not only high antitumor activity but also low selectivity and side effects [2]. The selectivity can be increased and the side effects decreased by modifying anthracycline antibiotics with natural sesquiterpene lactones. We demonstrated that the Michael reaction [3] can be used to combine into one molecule fragments of the antitumor anthracycline antibiotics daunorubicin (1a) and doxorubicin (1b) and natural alantolactone (2).The antiproliferative activity of the obtained conjugates in vitro in human tumor-cell cultures showed that the conjugate of alantolactone with daunorubicin (3a) was 3-5 times more active with equal toxicity for normal renal epithelium cells. Our results suggested that the new conjugates of sesquiterpene lactones with anthracycline antibiotics were promising for producing more active and less toxic drugs.High-resolution mass spectra were recorded on a Thermo Fisher Exactive Orbitrap mass spectrometer with a mass analyzer using orthogonal ion injection and electrospray ionization. Solutions in MeCN at concentration ~10 5 M were ionized. The resulting m/z value corresponded to a peak for the protonated molecular ion. PMR and 13 C NMR spectra were recorded using TMS as an internal standard on a Bruker Avance III instrument (500.13 and 125.78 MHz). The symbols D and E in the interpreted spectra denoted non-equivalent protons on the same C atom. Equipment of the CCU, IPAC, RAS was used (Contract No. 14.621.21.0008, identifier RFMEFI62114X0008).Preparation of Daunorubicin Base. Daunorubicin hydrochloride (1 g) was dissolved in H 2 O (200 mL) in a separatory funnel and treated with CHCl 3 (100 mL) and NaHCO 3 to transfer the colored anthracycline base into the organic (lower) layer, which was drained off and evaporated. Daunorubicin remaining in the aqueous phase was extracted (3u) with CHCl 3 (50 mL each time).Compound 3a. Alantolactone (100 mg, 0.431 mmol) was dissolved in MeOH (3 mL) and treated with daunorubicin base (250 mg, 0.474 mmol). The course of the reaction was monitored by TLC on Silufol plates using CHCl 3 -MeOH (4:1, R f of 3a, 0.77). When the reaction was finished, the mixture was evaporated at reduced pressure. The residue was rinsed with MeOH and purified by column chromatography over silica gel (15 g) with elution first by CHCl 3 and then by a mixture with

N-Alkylation of Anthracycline Antibiotics by Natural Sesquiterpene Lactones as a Way to Obtain Antitumor Agents with Reduced Side Effects

“…The signals and their multiplicity of the remaining protons of both the initial lactone and daunorubicin or doxorubicin are retained, which corresponds to the proposed structures, as well as the configuration of all asymmetric centers of the initial molecules. In addition, a new chiral center with a certain configuration is formed in the conjugates [ 20 ]. The stereoconfiguration of the new asymmetric center (atom C-29) was established based on two-dimensional experiments H—H COZY and NOESY ( Figure 4 ).…”

“…Anthracycline antibiotics conjugates ( 1a ), ( 2a ), ( 4a) , ( 5a ), ( 6a ), ( 1b ), ( 3b ), ( 4b ), ( 5b ), ( 6b ) were obtained as described earlier; the spectral characteristics corresponded to the literature data [ 20 , 21 , 22 ].…”

“…The anthracycline antibiotics doxorubicin ( a ) and daunorubicin ( b ) were modified with sesquiterpene lactones—isoalantholactone ( 1 ), alantolactone ( 2 ), alloalantholactone ( 3 ), epoxy-isoalantholactone ( 4 ), epoxyalantholactolactone ( 5 ), epoxyalloalantholactone ( 6 ), 6-hydroxyxanthanodiene ( 7 ), alanthodiene ( 8 ). Conjugates 1-6a-b were obtained in our previous works [ 20 , 21 , 22 ]; compounds 7a , b and 8a , b were first obtained and studied. Their cytotoxic and antiproliferative properties in relation to tumor cell lines were evaluated and their influence on key aspects of formation of cytotoxicity—mitochondrial functional characteristics (mitochondrial swelling, membrane potential, and mitochondrial respiratory chain complexes) as well as the glycolytic function parameters of HeLa tumor cells— was studied.…”

New Conjugates of Daunorubicin with Sesquiterpene Lactones and Their Biological Activity

“…Before the synthesis, DAU was converted into the free amine form from commercially available DAU hydrochloride in the same way as [13] , since the latter is not active in the Michael addition reaction.…”