1,9-Dideoxyforskolin

Synthetic transformation of ptychantin into forskolin and 1,9-dideoxyforskolin.[Pubmed:16749796]

J Org Chem. 2006 Jun 9;71(12):4619-24.

Forskolin (1), a highly oxygenated labdane diterpenoid and an activator of adenylate cyclase, has been synthesized in 12 steps and 12% overall yield from ptychantin A (4), which has been isolated from liverwort Ptychanthus striatus in good yield. The 1alpha-hydroxy group was furnished by stereoselective reduction of the corresponding carbonyl group by sodium in t-BuOH. The 9alpha-hydroxy group was introduced stereoselectively by epoxidation of delta(9.11)-enolether. 1,9-Dideoxyforskolin (2), an inhibitor of glucose transporter, has been synthesized in 8 steps and 37% overall yield. The hydroxy group at C-1 was removed by solid-state thicarbonylimidazolation and subsequent radical cleavage.

Adenylate cyclase and potassium channels are involved in forskolin- and 1,9-dideoxyforskolin-induced inhibition of pregnant rat uterus contractility.[Pubmed:10739518]

Am J Obstet Gynecol. 2000 Mar;182(3):620-4.

OBJECTIVE: We sought to study the contribution of potassium channels in the effect of forskolin and 1,9-Dideoxyforskolin on uterine contractility in the pregnant rat. STUDY DESIGN: Rings taken from the middle portions of uterine horns from rats at 16 days of gestation were positioned in organ chambers containing physiologic salt solution bubbled with 5% carbon dioxide in air (37 degrees C, pH approximately 7.4) for isometric tension recording under 2 g passive tension. The effects of cumulative concentrations of forskolin and 1,9-Dideoxyforskolin in the absence or presence of an adenylate cyclase inhibitor (MDL-12,330A, 10(-5) mol/L), a nonselective potassium channel blocker (tetrabutylammonium, 10(-4) mol/L), or an adenosine triphosphate-dependent potassium channel blocker (glibenclamide 10(-5) mol/L) were studied. RESULTS: Both forskolin and, to a lesser extent, 1,9-Dideoxyforskolin inhibit uterine contractions. Tetrabutylammonium, glibenclamide, and MDL-12, 330A attenuated the effects of forskolin, whereas glibenclamide was less effective against 1,9-Dideoxyforskolin. CONCLUSION: Activation of adenylate cyclases, as well as adenosine triphosphate-dependent potassium channels and, to a greater extent, calcium-dependent potassium channels, is involved in the inhibitory effect of forskolin in uterine rings from rats at 16 days of gestation. Inhibition of uterine contractions by 1,9-Dideoxyforskolin is less than that by forskolin and involves activation of adenylate cyclase and calcium-dependent potassium channels. Whether activation of guanylate cyclase is involved in the effect of the agents on calcium-dependent potassium channels needs further investigation. 1, 9-Dideoxyforskolin is not an inactive isomer of forskolin in rat uterine rings.

Selective modulation of vinblastine sensitivity by 1,9-dideoxyforskolin and related diterpenes in multidrug resistant tumour cells.[Pubmed:8094975]

Br J Cancer. 1993 Mar;67(3):471-9.

The ability of 1,9-Dideoxyforskolin (DDF), 1-deoxyforskolin (DF) and forskolin to modulate cellular sensitivity to vinblastine (VBL) was examined in drug-sensitive parental KB-3-1 cells and a multidrug-resistant subline, KB-GRC1, derived by transfection of mdr1. Fifty microM DF and forskolin enhanced the 1 h uptake of VBL by 8.0 +/- 0.7 (s.d.) and 4.7 +/- 2.5-fold, respectively, with 50 microM DDF producing a 13.6 +/- 1.9-fold increase. The greater effect of DDF relative to forskolin indicated that the effect was independent of activation of cAMP, and this was supported by a lack of effect of dibutyryl cAMP on the uptake. The effect of these agents on uptake were < or = 1.4-fold in KB-3-1 cells. DDF selectively inhibited initial efflux in cells expressing a functional P-glycoprotein (PGP), but both forskolin and DDF inhibited the terminal phase of efflux irrespective of PGP expression. Neither agent affected membrane permeability of polarisation and forskolin did not enhance the uptake of VBL in protein-free liposomes. At a non-toxic concentration of 20 microM, DDF and forskolin decreased the IC50 of VBL from 18.9 to 2.7 and 13 nM in KB-GRC1 cells, respectively, and DDF acted synergistically with VBL as shown by median effect analysis [combination index = 0.20 +/- 0.05 (s.d.)]. In contrast, these diterpenes did not affect VBL sensitivity in KB-3-1 cells. These results indicate that the diterpenes modulate VBL sensitivity predominantly by inhibiting PGP-mediated efflux activity.

Forskolin's structural analogue 1,9-dideoxyforskolin has Ca2+ channel blocker-like action in rat cerebellar granule cells.[Pubmed:8804917]

Eur J Pharmacol. 1996 May 6;303(1-2):101-8.

Forskolin, routinely used as a specific activator of the cAMP pathway, is also a blocker of various ionic channels in a cAMP-independent way. We investigated, in rat cerebellar granule cells in culture, the effects of forskolin and its structural analogue 1,9-Dideoxyforskolin on Ca2+ entry. Changes in cytosolic free Ca2+ concentration ([Ca]i) were monitored using fura-2 microfluorimetry. The increase in [Ca]i observed in response to membrane depolarization by 30 mM KCI was reduced by 20% in the presence of 100 microM forskolin, and by 71% with the same concentration of 1,9-Dideoxyforskolin. A dose-response curve for 1,9-Dideoxyforskolin gave an estimated IC50 of 54 microM. Additional experiments using the patch-clamp technique showed that 100 microM 1,9-Dideoxyforskolin inhibit voltage-activated Ca2+ currents by 63%, although forskolin had no significant effect in the same conditions. This blocking effect of 1,9-Dideoxyforskolin is not specific of a given Ca2+ channel type.

Partial reversal of doxorubicin resistance by forskolin and 1,9-dideoxyforskolin in murine sarcoma S180 variants.[Pubmed:2825978]

Cancer Res. 1988 Feb 1;48(3):539-43.

Acquired resistance to chemotherapeutic agents is an important clinical problem. One preclinical model, termed multidrug resistance (MDR), is characterized by a complex phenotype of cross-resistance to biochemically unrelated antineoplastic agents, the presence of a high-molecular-weight membrane glycoprotein, and impaired accumulation of drug. To determine whether MDR is mediated in part by altered cyclic 3',5'-adenosine monophosphate (cAMP) levels, the effect of incubation with the adenylate cyclase agonist, forskolin, was investigated in the murine sarcoma S180 cell line and two MDR variants (A5-.8, A5-2.5). Basal cAMP levels in sensitive and MDR lines were not significantly different (range, 0.15 +/- 0.05 to 0.31 +/- 0.09 pmol/mg protein); however, 1-h incubation with forskolin, 10 microM, elevated intracellular cAMP 2-fold in the parent line and 43- and 35-fold in the variants. The adenylate cyclase agonists, prostaglandin E2 and cholera toxin, and the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine had no significant effect on cAMP levels. To determine the effect of forskolin on doxorubicin-induced cell lethality, S180 and MDR lines were incubated with doxorubicin plus forskolin for 1 h and cloned in soft agar. Coincubation with forskolin partially reversed doxorubicin resistance in the MDR lines in a dose-dependent fashion. To determine whether this effect was mediated solely by elevation of intracellular cAMP, the inactive 1,9-dideoxy analogue of forskolin (DF) was used. Incubation with DF resulted in no elevation of cAMP levels in the sensitive or resistant cell lines; however, DF also partially reversed doxorubicin resistance in the MDR variants. Furthermore, coincubation of the A5-2.5 cell line with doxorubicin and 8-bromo cAMP, 1 mM, did not result in reversal of resistance to doxorubicin. To determine whether the reversal of resistance by the diterpenes was associated with alteration of doxorubicin transport, uptake and efflux of [14C]doxorubicin were measured. Coincubation with both forskolin and DF, 10 microM, enhanced [14C]doxorubicin uptake in the resistant cells, while drug efflux was significantly affected only in the cell line exhibiting intermediate resistance. Since both forskolin and its inactive analogue are effective in partially reversing resistance to doxorubicin and augmenting anthracycline uptake, a mechanism other than elevation of cAMP is most likely responsible.

Direct anesthetic-like effects of forskolin on the nicotinic acetylcholine receptors of PC12 cells.[Pubmed:3005280]

J Biol Chem. 1986 Mar 5;261(7):3103-6.

Forskolin is thought to be a highly specific activator of adenyl cyclase. However, when applied to rat pheochromocytoma (PC12) cells at concentrations of 1 microM or higher it caused an immediate, concentration-dependent inhibition of carbachol-stimulated uptake of 86Rb+ through the nicotinic receptors, which did not appear to be related to activation of adenyl cyclase. The inhibition of receptor activation occurred instantaneously whereas cellular cAMP content did not increase for a measureable period of time. Normal receptor function was recovered rapidly upon removal of forskolin. Additional evidence that this effect of forskolin was not related to cAMP was obtained when 1,9-Dideoxyforskolin (an analog of forskolin which does not activate adenyl cyclase) also caused a rapid, concentration-dependent, rapidly reversible inhibition of receptor-mediated influx of 86Rb+ into the cells. An examination of the effect of forskolin on 86Rb+ uptake at various concentrations of carbachol showed that forskolin was not acting by competing with carbachol for the receptor activation site. Given the lipophilic nature of forskolin, it probably acts like a general anesthetic to perturb the plasma membrane lipid structure and alter the function of the nicotinic acetylcholine receptors, possibly by increasing the rate of closure of open channels.