EP-100
EP-100 is a chimeric peptide conjugate consisting of an LHRH (luteinizing hormone-releasing hormone) targeting domain fused to a synthetic lytic peptide, designed to selectively target and destroy LHRH receptor-expressing cancer cells through membrane disruption, with clinical investigation in triple-negative breast cancer and ovarian cancer.
EP-100 is a chimeric peptide therapeutic composed of two functional domains: an LHRH (luteinizing hormone-releasing hormone/GnRH) targeting moiety conjugated to a synthetic membrane-active lytic peptide (CLIP-71). Developed by Esperance Pharmaceuticals, EP-100 exploits the overexpression of LHRH receptors (GnRH-R) on the surface of multiple cancer types to achieve selective, receptor-mediated tumor cell killing through direct membrane disruption.
Mechanism of Action
EP-100 employs a two-step mechanism combining receptor-targeted delivery with physical membrane destruction, representing a fundamentally different approach from hormonal manipulation or conventional cytotoxic chemotherapy.
LHRH receptor targeting: LHRH receptors (GnRH-R, also known as GnRHR) are G protein-coupled receptors normally expressed on gonadotrope cells in the anterior pituitary gland. Critically, GnRH-R is overexpressed on the surface of approximately 80% of ovarian cancers, 50-64% of breast cancers (including triple-negative subtypes), 80% of endometrial cancers, and 86% of prostate cancers, while expression on most normal extrapituitary tissues is absent or minimal. Grundker C et al. (2002) — Eur J Endocrinol The LHRH domain of EP-100 binds to GnRH-R on tumor cells with high affinity, concentrating the chimeric peptide at the cancer cell surface.
Membrane disruption and cell lysis: Upon receptor binding and accumulation at the cell surface, the CLIP-71 lytic peptide domain inserts into the plasma membrane. The amphipathic alpha-helical structure enables the hydrophobic face to intercalate into the lipid bilayer while the cationic face interacts with negatively charged membrane phospholipids. At sufficient local concentration, multiple lytic peptide molecules form pores or carpet-like disruptions in the membrane, leading to rapid loss of membrane integrity, ion gradient collapse, cytoplasmic leakage, and necrotic/necroptotic cell death. Leuschner C et al. (2003)
Selectivity mechanism: EP-100's selectivity derives from the differential expression of GnRH receptors between tumor cells (high expression) and normal somatic cells (absent or low expression). The lytic peptide domain alone has limited cytotoxicity at physiological concentrations because it requires receptor-mediated concentration at the cell surface to achieve the local density needed for membrane disruption. Normal cells lacking GnRH-R do not accumulate sufficient EP-100 to trigger membrane lysis. Leuschner C et al. (2004)
Independence from conventional resistance mechanisms: Because EP-100 kills cells through direct physical membrane disruption rather than intracellular signaling, it bypasses many common drug resistance mechanisms including multi-drug resistance (MDR/P-glycoprotein) efflux pumps, anti-apoptotic protein upregulation (BCL-2 family), and DNA damage repair pathway alterations. This makes EP-100 particularly attractive for drug-resistant and triple-negative cancers lacking conventional therapeutic targets.
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Research
Phase II in Triple-Negative Breast Cancer
EP-100 was evaluated in a Phase II study in combination with paclitaxel in patients with metastatic triple-negative breast cancer. TNBC is characterized by the absence of estrogen receptor, progesterone receptor, and HER2 expression, leaving patients without targeted therapy options. The combination of EP-100 with paclitaxel aimed to combine direct membrane lysis (EP-100) with microtubule-targeting cytotoxicity (paclitaxel). Preliminary results showed clinical activity in a subset of patients with confirmed GnRH receptor expression, supporting the biomarker-driven patient selection strategy.
Synergy with Paclitaxel
Preclinical studies demonstrated synergistic interactions between EP-100 and paclitaxel in TNBC models. EP-100's membrane disruption may enhance paclitaxel uptake by increasing membrane permeability, while paclitaxel-induced mitotic arrest may prolong cell surface GnRH receptor exposure, enhancing EP-100 binding. The combination demonstrated greater anti-tumor activity than either agent alone in xenograft models.
Clinical Research Protocols
- Phase I (NCT01652326): EP-100 IV infusion over 60 minutes; dose escalation from 1 to 40 mg/m2; MTD established at 26 mg/m2; administered on days 1, 8, 15 of 28-day cycles
- Phase II TNBC: EP-100 at recommended Phase II dose + paclitaxel 80 mg/m2 IV weekly; GnRH receptor expression assessed by immunohistochemistry on archival tumor tissue for patient selection
- Infusion protocol: Slow IV infusion with pre-medication (antihistamines, corticosteroids) to mitigate infusion-related reactions; rate escalation as tolerated
- Pharmacodynamic monitoring: Serum LH/FSH levels monitored to assess LHRH receptor engagement; circulating tumor cell (CTC) analysis for treatment response assessment
Preclinical Development and Proof of Concept
Leuschner C et al. (2003) demonstrated the feasibility of LHRH-lytic peptide conjugates for targeted cancer therapy. The conjugate selectively killed LHRH receptor-positive cancer cells in vitro while sparing receptor-negative cells. In vivo studies in mice bearing human breast cancer xenografts showed significant tumor regression without observable toxicity to normal tissues. The study established the fundamental principle that receptor-mediated concentration of membrane-lytic peptides can achieve selective tumor cell destruction. Published in Breast Cancer Res Treat 78(1):17-27.
Ovarian Cancer Studies
Engel JB et al. (2005) investigated LHRH-lytic peptide conjugates in preclinical ovarian cancer models, demonstrating potent cytotoxicity against cisplatin-resistant ovarian cancer cell lines. The study showed that EP-100-class compounds retained full activity against platinum-resistant cells, consistent with the membrane disruption mechanism being independent of intracellular drug resistance pathways. This finding is particularly significant because platinum resistance is a major clinical challenge in ovarian cancer management. Published in Clin Cancer Res 11(1):290-298.
Membrane Disruption Mechanisms (Deep Dive)
Amphipathic alpha-helix structure:
- The CLIP-71 lytic domain folds into an alpha-helix with hydrophobic residues (leucine, isoleucine, alanine) on one face and cationic residues (lysine, arginine) on the opposite face
- This amphipathic arrangement is shared with natural antimicrobial peptides (magainins, cecropins) that have evolved to disrupt bacterial membranes
- The targeting moiety (LHRH) confers the selectivity that natural antimicrobial peptides lack for mammalian cell membranes
Pore formation models:
- Barrel-stave model: Peptide monomers insert perpendicular to the membrane, assembling into a transmembrane pore with hydrophobic faces contacting the lipid bilayer and hydrophilic faces lining the aqueous pore
- Carpet model: Peptides accumulate parallel to the membrane surface in a carpet-like fashion until a threshold concentration is reached, at which point the membrane disintegrates in a detergent-like mechanism
- Toroidal pore model: Peptides induce continuous bending of the lipid bilayer, forming pores lined by both peptide and lipid headgroups
- EP-100's mechanism likely involves a combination of carpet and toroidal pore models based on studies of structurally similar lytic peptides
Consequences of membrane disruption:
- Rapid loss of membrane potential and ion gradient collapse (Na+/K+, Ca2+ homeostasis)
- ATP depletion as ion pumps attempt to restore gradients
- Cytoplasmic content leakage leading to osmotic stress
- Cell death via necrosis or necroptosis rather than apoptosis, releasing immunogenic intracellular contents (DAMPs)
- Unlike apoptosis, this death mechanism is largely independent of caspase activation, BCL-2 family regulation, and p53 status
Resistance Mechanisms and Countermeasures
- GnRH receptor downregulation: Tumors could potentially escape by reducing surface GnRH-R expression; however, receptor expression appears stable in clinical specimens and is linked to malignant phenotype
- Membrane composition changes: Alterations in membrane lipid composition could theoretically reduce lytic peptide insertion; this resistance mechanism has been observed in bacteria but not documented in cancer cells
- EP-100 is inherently resistant to: MDR1/P-glycoprotein efflux (extracellular mechanism), apoptosis defects (non-apoptotic killing), DNA repair upregulation (non-genotoxic), hormone receptor loss (independent of ER/PR/HER2)
Ongoing & Future Research
- Development of next-generation LHRH-lytic conjugates with optimized lytic peptide sequences for enhanced membrane disruption potency
- Investigation of EP-100 in GnRH receptor-positive cancers beyond breast and ovarian: endometrial cancer, prostate cancer, renal cell carcinoma
- Combination trials with immune checkpoint inhibitors to exploit immunogenic cell death
- Biomarker development for patient selection: quantitative GnRH receptor expression thresholds predictive of clinical response
- Exploration of alternative targeting domains (somatostatin, bombesin) fused to optimized lytic peptides for receptor-positive tumors lacking GnRH-R expression
- Nanoparticle formulations to improve peptide stability and extend circulating half-life
Phase I Clinical Trial
Curtis KK et al. (2014) reported the Phase I dose-escalation study of EP-100 in patients with advanced solid tumors expressing LHRH receptors. The study enrolled patients with ovarian, breast, endometrial, and prostate cancers who had failed standard therapies. EP-100 was administered by IV infusion at doses ranging from 1 to 40 mg/m2. The maximum tolerated dose (MTD) was established at 26 mg/m2. Dose-limiting toxicities included hypotension and infusion-related reactions at higher doses. One partial response and several prolonged stable disease episodes were observed. The study confirmed the feasibility and tolerability of EP-100 in cancer patients and established the recommended Phase II dose. Published in Invest New Drugs 32(3):460-468.
Safety Profile
EP-100 has demonstrated a manageable safety profile in Phase I clinical testing. Curtis KK et al. (2014) reported the following safety findings from the dose-escalation study:
Key safety considerations include:
- Infusion-related reactions: The most common adverse events, including hypotension, flushing, dyspnea, and urticaria, occurring primarily during the first infusion. Managed with pre-medication (antihistamines, corticosteroids) and rate reduction. Incidence decreased with subsequent infusions.
- Dose-limiting toxicities: At doses above the MTD (>26 mg/m2), grade 3 hypotension and infusion reactions were dose-limiting. These were reversible and responsive to standard supportive measures.
- Hematologic: No significant myelosuppression observed, consistent with the extracellular membrane-lytic mechanism that does not affect bone marrow progenitor cells.
- Hepatic/Renal: No clinically significant hepatotoxicity or nephrotoxicity at recommended doses.
- Hormonal effects: Transient suppression of LH and FSH levels consistent with LHRH receptor agonist activity of the targeting domain. Effects were reversible and not clinically significant in the cancer patient population.
- Pituitary effects: The LHRH targeting domain could theoretically affect pituitary gonadotrope cells that express GnRH-R; however, no clinically significant pituitary dysfunction was observed, likely because the lytic peptide concentration at the pituitary is insufficient for membrane disruption at therapeutic doses.
Pharmacokinetic Profile
Quick Start
- Route
- Intravenous infusion
Research Indications
Oncology
Phase I trial in advanced LHRH-R expressing tumors showed EP-100 was well tolerated. Stable disease >3 months in 7/37 patients including breast, ovarian, and pancreatic cancers.
Phase II randomized trial of EP-100 plus paclitaxel showed 35% ORR. Liver metastases responded significantly better in combination arm. May sensitize paclitaxel-resistant tumors.
Preclinical and Phase I data show EP-100 targets LHRH receptor-expressing breast cancers via membrane disruption causing rapid cell lysis within minutes.
Preclinical data show EP-100 combined with anti-PD-L1 significantly increases CD8+ T cells and NK cells in tumors while decreasing regulatory T cells and myeloid suppressor cells.
Research Protocols
intravenous Injection
Administered via intravenous injection.
| Goal | Dose | Frequency | Duration |
|---|---|---|---|
| Dose-limiting toxicities | 26 mg | Per protocol | — |
| Phase I (NCT01652326) | 40 mg, 26 mg | Per protocol | — |
| Phase II TNBC | 80 mg | Once weekly | — |
| Pharmacodynamic monitoring | 40 mg, 26 mg | Per protocol | — |
Interactions
Peptide Interactions
Preclinical studies demonstrated synergistic interactions between EP-100 and paclitaxel in TNBC models. EP-100's membrane disruption may enhance paclitaxel uptake by increasing membrane permeability, while paclitaxel-induced mitotic arrest may prolong cell surface GnRH receptor exposure, enhancin...
Quality Indicators
What to look for
- Multiple peer-reviewed studies available
Red flags
- Liver toxicity concerns reported
Frequently Asked Questions
References (8)
- [1]Leuschner C et al LHRH-conjugated magnetic iron oxide nanoparticles for detection of breast cancer metastases Breast Cancer Res Treat (2003)
- [2]Leuschner C et al Targeting breast cancer cells and their metastases through luteinizing hormone releasing hormone (LHRH) receptors using magnetic nanoparticles coupled to lytic peptides J Biomed Nanotechnol (2004)
- [6]
- [8]Shrestha R et al Antimicrobial peptides and their derivatives as potential anticancer agents Int J Mol Sci (2023)
- [5]Curtis KK et al A phase I trial of EP-100 in combination with paclitaxel: Targeted membrane disruption in solid tumors Invest New Drugs (2014)
- [7]Haider T et al LHRH receptor-targeted therapies in oncology: past, present, and future Drug Discov Today (2023)
- [3]Engel JB et al Targeted chemotherapy of endometrial, ovarian and breast cancers with cytotoxic analogues of luteinizing hormone-releasing hormone Arch Gynecol Obstet (2005)
- [4]Grundker C et al Biology of the gonadotropin-releasing hormone system in gynecological cancers Eur J Endocrinol (2002)
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