Largazole is a potent and class I-selective histone deacetylase (HDAC) inhibitor purified from marine cyanobacteria and was demonstrated to possess antitumor activity. Largazole employs a unique prodrug strategy, via a thioester moiety, to liberate the bioactive species largazole thiol. Here we report alternate prodrug strategies to modulate the pharmacokinetic and pharmacodynamics profiles of new largazole-based compounds. The in vitro effects of largazole analogues on cancer cell proliferation and enzymatic activities of purified HDACs were comparable to the natural product. However, in vitro and in vivo histone hyperacetylation in HCT116 cells and implanted tumors, respectively, showed differences, particularly in the onset of action and oral bioavailability. These results indicate that, by employing a different approach to disguise the “warhead” moiety, the functional consequence of these prodrugs can be significantly modulated. Our data corroborate the role of the pharmacokinetic properties of this class of compounds to elicit the desired and timely functional response.

Kempopeptin C, a novel chlorinated analogue of kempopeptin B, was discovered from a marine cyanobacterium collected from Kemp Channel in Florida. The structure was elucidated using NMR spectroscopy and mass spectrometry (MS). The presence of the basic Lys residue adjacent to the N-terminus of the 3-amino-6-hydroxy-2-piperidone (Ahp) moiety contributed to its selectivity towards trypsin and related proteases. The antiproteolytic activity of kempopeptin C was evaluated against trypsin, plasmin and matriptase and found to inhibit these enzymes with IC₅₀ values of 0.19, 0.36 and 0.28 μM, respectively. Due to the significance of these proteases in cancer progression and metastasis, as well as their functional redundancy with respect to targeting overlapping substrates, we examined the effect of kempopeptin C on the downstream cellular substrates of matriptase: CDCP1 and desmoglein-2 (Dsg-2). Kempopeptin C was shown to inhibit the cleavage of both substrates in vitro. Additionally, kempopeptin C reduced the cleavage of CDCP1 in MDA-MB-231 cells up to 10 µM. The functional relevance of targeting matriptase and related proteases was investigated by assessing the effect of kempopeptin C on the migration of breast cancer cells. Kempopeptin C inhibited the migration of the invasive MDA-MB-231 cells by 37 and 60% at 10 and 20 µM, respectively.