**Background:** Metalloaminopeptidases from the M1 and M17 families are critical regulators of physiological and pathological processes in humans, including cancer, hypertension, inflammation, and infectious diseases such as malaria. Aminopeptidase N (APN/CD13, M1 family) is upregulated in multiple malignancies (breast, lung, colon, prostate, ovarian, liver, and others) and is a target for antiangiogenic and anticancer therapy. Aminopeptidase A (APA, M1 family) participates in the renin–angiotensin system and blood pressure regulation. Thyrotropin-releasing hormone-degrading ectoenzyme (TRH-DE, M1 family) inactivates TRH in the CNS and blood, making it a target for modulating TRH activity in neurodegenerative disorders and non-thyroidal illness syndrome. The M17 leucyl aminopeptidase from Plasmodium falciparum (PfA-M17) is a validated chemotherapeutic target for antimalarial drug development. Natural inhibitors of these enzymes are scarce, with bestatin (Ubenimex) being the only FDA-approved drug inhibitor of APN. Marine invertebrates represent a promising but underexplored source of structurally diverse bioactive metabolites, including peptidase inhibitors.
**Methods:** This is a narrative review summarizing published data from the authors' own screening programs and the literature. The authors screened aqueous extracts from 26 marine invertebrate species collected from the Cuban coastline (phyla: Chlorophyta, Chlorophycota, Magnoliophyta, Chordata, Porifera, Mollusca, Cnidaria, Annelida, Echinodermata, Bryozoa) for inhibitory activity against TRH-DE, DPP-IV, porcine APN (pAPN), human APN (hAPN), porcine APA (pAPA), human LAP (hLAP), and recombinant PfA-M17 (rPfA-M17). Extracts were tested as crude aqueous extracts and after clarification with 2.5% trichloroacetic acid (TCA). Inhibitory activity was characterized by IC50 determination, pre-incubation time dependence, and reversibility. Selectivity ratios were calculated for rPfA-M17 versus hLAP. Effects on cell viability were tested in APN+ cancer cell lines (PC3, 3LL) and a chloroquine-resistant Plasmodium falciparum strain (FcB1). The review also covers the isolation and characterization of HcPI from the marine annelid Hermodice carunculata and psammaplin A from sponges Poecillastra sp. and Jaspis sp.
**Key Results:** (1) HcPI from Hermodice carunculata is a 580 Da compound that potently inhibits TRH-DE with a Ki of 70.3 nmol/L (slow, reversible). It is highly specific, showing no inhibition of serine, cysteine, aspartic, or other metalloproteases tested. Intraperitoneal injection in BalbC mice (1–50 µg/g) decreased TRH-DE activity in pituitary and brain regions (hypothalamus, cerebellum, olfactory bulb) in a dose-dependent manner, with >50% inhibition in hypophysis at <1 µg/g. In vivo, HcPI caused a transient increase in serum prolactin and TSH, indicating enhanced TRH action. (2) Psammaplin A (PsA) from sponges inhibits mammalian APN with a Ki of 15 µM (non-competitive). PsA shows antiproliferative activity against multiple cancer cell lines (TNBC MDA-MB-231, MCF-7/adr, HCT15, SK-OV-3, A549, LM4175, BoM1833, SK-MEL-2, BrM-2a, XF498, Ishikawa). (3) Screening of 10 marine invertebrate species (2015–2019) after TCA clarification revealed dose-dependent hAPN inhibition with IC50 values ranging from 11.7 µg/mL (Lissodendoryx isodictyalis) to 567.6 µg/mL (Bunodosoma granuliferum). Four species showed IC50 ≤100 µg/mL: L. isodictyalis (11.7 ± 2.7), Tripneustes ventricosus (25.0 ± 3.1), Isostichopus badionotus (69.7 ± 10.0), and Stichodactyla helianthus (103.6 ± 20.6). (4) For pAPA inhibition, IC50 values ranged from 11.03 µg/mL (T. ventricosus) to 1005.12 µg/mL (I. badionotus). Nerita versicolor showed selectivity for pAPA over hAPN. (5) For rPfA-M17 inhibition, IC50 values ranged from 15.3 µg/mL (S. helianthus) to 509.2 µg/mL (B. granuliferum). Selectivity ratios (hLAP IC50 / rPfA-M17 IC50) ranged from 1.87 (Physalia physalis) to 60.0 (Nerita versicolor). Bestatin showed a selectivity ratio of 78.86. (6) T. ventricosus extract showed potent antiplasmodial activity against the FcB1 strain (IC50 = 0.24 ± 0.01 µg/mL), 300-fold more potent than its effect on human cancer cells, and stronger than bestatin (IC50 = 1.14 ± 0.27 µg/mL). L. isodictyalis extract showed IC50 = 2.60 ± 0.60 µg/mL against FcB1. (7) Two marine natural compounds (compounds 5 and 6) were identified as new LAP3 inhibitors, showing stronger inhibition of LAP3 at 30 µM than bestatin, and stronger antiproliferative and anti-migration effects on MDA-MB-231 breast cancer cells.
**Clinical Implications:** Marine invertebrates are a promising and still underexplored source of inhibitors targeting M1 and M17 metalloaminopeptidases with potential applications in multiple human diseases. HcPI represents the first natural TRH-DE inhibitor and a tool for studying TRH physiology and potential therapeutic applications in conditions where TRH activity is beneficial (e.g., NTIS, neurodegenerative disorders). Psammaplin A and the extracts from L. isodictyalis, T. ventricosus, and I. badionotus show dual APN inhibition and anticancer activity, supporting further development as antiangiogenic and antimetastatic agents. The selectivity of several extracts (especially N. versicolor and S. helianthus) for the malarial PfA-M17 over human LAP, combined with the potent antiplasmodial activity of T. ventricosus (IC50 = 0.24 µg/mL against chloroquine-resistant P. falciparum), highlights the potential for developing new antimalarial chemotypes. The identification of LAP3 inhibitors from marine sources also opens avenues for breast cancer treatment. The authors emphasize that clarification treatments (e.g., TCA) are critical for detecting inhibitory activities masked by endogenous complexes or contaminants in crude extracts.