Figure 9. Periodic analysis (every 24 h) of the effects of 1.0 μ g/mL of bullatacin against MCF-7/wt cells with refeeding of fresh media in half of the plates. Values are expressed as average absorbances (n = 6 for both control and drug treated wells), and the error bars represent the standard deviation about each average. The “R” indicates when refeeding was initiated.

Figure 10. Comparison of the cell growth inhibition potential of bullatacin vs the standard antineoplastic compounds adriamycin, vinblastine, and vincristine against multidrug-resistant MCF-7/Adr cells. Values are expressed as percentages of the vehicle-treated controls with each point representing the normalized average of four values and the error bars representing the standard deviation about each average. The concentration values are log dose units in μg/mL.

conducted with 14 structurally diverse acetogenins (seven bis-adjacent, two bis-nonadjacent, and five mono-THF ring compounds).[21] All compounds were tested with adriamycin, vincristine, and vinblastine, as standard chemotherapeutic agents (Figure 1O). Thirteen of the 14 acetogenins were generally more potent than all three of the standard drugs. Bullatacin is 258 times more cytotoxic against MCF-7/Adr than adriamycin. Acetogenins with the stereochemistry threo-trans-threo-trans-erythro (from C-15 to C-24) were the most potent among the bis-adjacent acetogenins.[21] The most potent compound, gigantetrocin A (a mono-THF ring acetogenin), was two times as potent as bullatacin.[21] The optimal length of the alkyl chain between the THF ring and the γ-lactone was 15 carbons as recently corroborated by Miyoshi et al.[45] with the purified mitochondrial enzyme. Shortening the length of the alkyl chain decreased the potency significantly in this particular cell line. While Oberlies et al.[21] have observed slight differences in potency between stereoisomeric acetogenins, all previous studies, based on cellfree systems, i.e., electron-transport inhibition in rat liver mitochondrial suspensions[98,99] and with the purified enzyme,[45] did not. As previously mentioned, this might be attributed to such factors such as, but not restricted to, membrane transport, intracellular transport, or metabolic inactivation in the whole cell assay systems, which are better mimics of in vivo effects.

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in rat liver mitochondrial suspensions98,99 and with the purified enzyme,45 did not. As previously mentioned, this might be attributed to such factors such as, but not restricted to, membrane transport, intracellular transport, or metabolic inactivation in the whole cell assay systems, which are better mimics of in vivo effects.

Adriamycin has been reported to us to accumulate in bullatacin-treated MDR tumor cells, but we have not evaluated the original data (personal communication).106 Concurrent therapy of acetogenins with the traditional antitumor agents would, thus, potentially extend patient survival times, and in addition, those patients who have already developed MDR would be expected to benefit substantially by acetogenin treatment.

Annonaceous Acetogenins vs Resistant and Susceptible Insects and Pests. Six compounds, representing the mono-THF (gigantetrocin A, annomontacin), adjacent bis-THF (asimicin, parviflorin), and nonadjacent bis-THF (sylvaticin, bullatalicin) classes of Annonaceous acetogenins, were compared with technical grades of synthetic amidinohydrazone (hydramethylnon), carbamate (propoxur, bendiocarb), organophosphate (chlorpyrifos), and pyrethroid (cypermethrin) insecticides to determine their dietary toxicities to insecticide-resistant and insecticide-susceptible strains of the German cockroach, Blattella germanica.[22] As a widespread urban insect, cockroaches are controlled primarily by the use of conventional synthetic insecticides that provide a relatively rapid and efficient means of reducing cockroach populations.[22] Most of these insecticides interfere with the proper functioning of the cockroach nervous system or other physiological processes after entering the body following direct contact, exposure to vapor, or ingestion. Repeated applications of these insecticides have resulted in the development of resistance to the chlorinated hydrocarbon, organophosphate, carbamate, and pyrethroid classes of synthetic insecticides. The development of novel insecticide classes with new biochemical mechanisms as targets is needed to help to overcome this resistance problem.

Acetogenins have been frequently described in the literature as being toxic to mosquito larvae, European corn borers, spider mites, melon aphids, Mexican bean beetles, bean leaf beetles, striped cucumber beetles, blowfly larvae, Colorado potato beetles, and free-living nematodes.[15,97,107] The acetogenins typically occur as complex mixtures of over 4O different compounds within the plant extract; thus, application as mixtures in crude extracts has been suggested.[107]

On the basis of our preliminary testing (topical bioassays), acetogenins are more toxic by ingestion than by contact to cockroaches.[22] Thus, tests were conducted at $ 1000 $ ppm of all test compounds in the diet (bait). Differential susceptibility occurred among B. germanica nymphs of both strains to this variety of the acetogenins and to the five conventional synthetic insecticides. The speed of killing values (LT50) against insecticide-susceptible (Jwax) and insecticide-resistant (Muncie), second and fifth instars, permitted ranking of all 11 compounds. The adjacent bis-THF acetogenins showed the highest potency among the three acetogenin classes (Tables 1 and 2). The acetogenins caused high percentages of mortality and delays in development of the fifth instars of both strains (Figure 11). In the Jwax-susceptible German cockroach strain, nymphal development was mainly affected by gigantetrocin A and annomontacin, whereas in Muncie, a resistant German cockroach strain, nymphal development was mainly affected by gigantetrocin A and bullatalicin.