An Evaluation of Bioactive, Sponge-Derived, Marine Natural Products Used Against Triple Negative Breast Cancer and the Malaria Parasite, Plasmodium falciparum
Authors:   , Odron Sophia 
Published: January 2025

Marine natural products from sponges of the Indo-Pacific have proven to be a source of structurally diverse secondary metabolites that are biologically active against a variety of targets. In the first chapter of this thesis, the stability of the nanomolar-potent, irreversible microtubule stabilizer, (-)-zampanolide (1), the cytotoxicity of its N-acyl hemiaminal side chain (2), and the activity of the more stable related compound (-)-dactylolide (3) were investigated. Following the discovery of 1 from extracts of Cacospongia mycofijiensis, in a previous study, the first in vivo evaluation of 1 in MDA-MB-231 tumor bearing mice was performed, demonstrating it had potent and persistent antitumor efficacy but only when targeted to the tumor site due to a narrow therapeutic index. It was hypothesized that 1 is thermally unstable at body temperature (37°C, 98°F) and may decompose into the toxicant Michael acceptor, 2, and covalent microtubule stabilizing agent, 3. Thermolysis at 80°C of 1 reveals the decomposition of 1 into 2 and 3 as keto (3k)/enol (3e) tautomers shown by HPLC and NMR. HR-LCMS analysis revealed incubation at 37°C (body temperature) of 1 for 24 hrs generated 2 and 3 similar to 80°C thermolysis. Antiproliferative and biochemical assays reveal low micromolar cytotoxicity of 2 against selected triple negative breast cancer (TNBC) cell lines HCC1806, MDA-MB-453, BT-549, HCC70, and MDA- MB-231 (IC50 = 1.9 ~ 10.6 μM) and no microtubule binding affinity. Compound 3k displayed nanomolar potency against BT-549 (IC50 = 0.37 μM), MDA-MB-231 (IC50 = 0.62 μM), HCC70 (IC50 = 0.65 μM), with selectivity for MDA-MB-453 (IC50 = 0.054 μM) and HCC1806 (IC50 = 0.080 μM) and delayed binding mode to microtubules compared to 1. These results show that 1 is thermally unstable at body temperature, that 2 may be responsible, at least partially, for the in vivo toxicity of 1 in MDA-MB-231 tumor bearing mice, and that 3 may serve as a more stable and selective therapeutic lead against MDA-MB-453 and HCC1806 cell lines.

In the second chapter of this thesis, a panel of secondary metabolites from the marine sponges C. mycofijiensis, Jaspis splendens, and Jaspis coriacea were evaluated against the most notorious malaria parasite Plasmodium falciparum in a drug response assay. Due to the rise in resistance to standard antimalarials such as chloroquine (1), dihydroartemisinin (2), and lumefantrine (3), there is a critical need to determine novel lead therapeutics with unique mechanisms of action (MOA) that can circumvent forms of drug resistance. Scale-up isolation by HPLC was conducted to purify latrunculin A (4), fijianolide A/isolaulimalide (5), fijianolide B/laulimalide (6), (-)-zampanolide (7), (-)-dactylolide (8), (+)-(5Z)-(8S)-(14Z)-mycothiazole (9), (+)-(5Z)-(8S)-8-O-acetyl-(14Z)- mycothiazole (10), (-)-(5E)-(8R)-(14Z)-mycothiazole (11), jasplakinolide (12), bengamide B (13), and fascaplysin (14). Both microtubule stabilizing agents, 6 and 7, from C. mycofijiensis displayed the greatest efficacy against P. falciparum proliferation on par with standard antimalarials (1-3). To identify the importance of the C-15 and C-20 chiral centers of 6, semi-synthesis was performed to produce the di-oxo fijianolide L (15). The malaria parasite drug response assay demonstrated a 2000-fold reduction in potency in 15 compared to 6, suggesting C-15 and C-20 to be key functional groups in the activity of 6. Overall, these results revealed that 41% of the selected sponge-derived secondary metabolites were comparable to frontline standard antimalarials used today, suggesting there is potential in developing marine natural products as antimalarial therapeutics.