Paul Klausmeyer

Histone Deacetylase Inhibitors from Burkholderia thailandensis

Bioactivity-guided fractionation of an extract of Burkholderia thailandensis led to the isolation and identification of a new cytotoxic depsipeptide and its dimer. Both compounds potently inhibited the function of histone deacetylases 1 and 4. The monomer, spiruchostatin C (2), was tested side by side with the clinical depsipeptide FK228 (1, Istodax, romidepsin) in a murine hollow fiber assay consisting of 12 implanted tumor cell lines. Spiruchostatin C (2) showed good activity toward LOX IMVI melanoma cells and NCI-H522 non small cell lung cancer cells. Overall, however, FK228 (1) showed a superior in vivo antitumor profile in comparison to the new compound.

Schweinfurthins I and J from Macaranga schweinfurthii.

Demand for the experimental antineoplastic agent schweinfurthin A, for developmental testing, prompted a re-collection of leaf material of Macaranga schweinfurthii from the original collection site in Cameroon. During chromatographic purification of the organic solvent extract, analytical UPLC-PDA-TOFMS of stilbene-enriched fractions revealed the presence of six known schweinfurthins and two previously unknown stilbenes. The structures of these new compounds, schweinfurthins I and J (1 and 2), were elucidated by 1D- and 2D-NMR techniques.

Cytotoxic and HIF-1α inhibitory compounds from Crossosoma bigelovii.

Cytotoxicity-guided fractionation of an organic solvent extract of the plant Crossosoma bigelovii led to the discovery of a new strophanthidin glycoside (1) and two new 2-methylchromone glycosides (2 and 3). Also isolated were the known chromones eugenin and noreugenin, the indole alkaloid ajmalicine, the dibenzylbutane lignan secoisolariciresinol, the dibenzylbutyrolactone lignan matairesinol, and the furanone 5-tetradec-5-enyldihydrofuran-2-one. Further investigation into the biological properties of strophanthidin glycosides revealed a connection between inhibition of HIF-1 activation and the glycosylation of the genin. This work is the first published study of the bioactive phytochemicals of the family Crossosomataceae.

An Inhibitor of CCL2-Induced Chemotaxis from the Fungus Leptoxyphium sp.

A biological screen used to identify inhibitors of monocyte chemotactic protein-1 (CCL2)-induced chemotaxis was applied in the activity-guided fractionation of an extract from a fungus of the genus Leptoxyphium sp. Inhibition of CCL2-induced chemotaxis was traced to a new dichlorinated diketopiperazine, cyclo(13,15-dichloro-L-Pro-L-Tyr). A structure-activity relationship (SAR) study evaluating relative activities of cyclo(13,15-dichloro-L-Pro-L-Tyr) and a nonchlorinated homologue cyclo(L-Pro-L-Tyr) showed that the dichlorinated molecule was 10- to 20-fold more active than the nonchlorinated form, while no activity was observed for cyclo(D-N-methylLeu-L-Trp).

Separation and SAR Study of HIF-1α Inhibitory Tubulosines from Alangium cf. longiflorum

A crude organic solvent extract of Alangium cf. longiflorum exhibited potent inhibition of hypoxia-induced HIF-1 transcriptional activity in human U251 glioma cells. Dereplication and bioactivity-guided fractionation, including Sephadex LH-20 and chiral HPLC chromatographies, led to the isolation of tubulosine ( 1), 9-desmethyltubulosine ( 2), and isotubulosine ( 3). Structures were verified by complete (1)H and (13)C assignments using 1D- and 2D-NMR techniques. Tubulosine strongly inhibited HIF-1 transcriptional activity, isotubulosine was devoid of activity, and 9-desmethyltubulosine possessed 6-fold less potency than tubulosine.

Discovery and Preliminary SAR of Bisbenzylisoquinoline Alkaloids as Inducers of C/EBPα

A high throughput in vitro screen has been developed to identify substances that induce expression of C/EBPα in tumor cells. An extract of the fruit of Gyrocarpus jacquinii showed induction of C/EBPα activity that was attributed to the bisbenzylisoquinoline (BBIQ) alkaloid pheanthine (13) by dereplication analysis. The research project was broadened to assess the effect of other natural BBIQ structural types occurring outside the genus Gyrocarpus. Several of the 28 compounds assayed showed enhancement of C/EBPα induction in U937 cells. The results of this study should encourage future efforts toward obtaining and screening a larger set of both natural and synthetic analogs of this interesting group of alkaloids.