CEND-1: a game changer for pancreatic cancer chemotherapy?

Tumor-penetrating iRGD facilitates penetration of poly(floxuridine-ketal)-based nanomedicine for enhanced pancreatic cancer therapy

Efficient intratumoral penetration is essential for nanomedicine to eradicate pancreatic tumors. Although nanomedicine can enter the perivascular space of pancreatic tumors, their access to distal tumor cells, aloof from the vessels, remains a formidable challenge. Here, we synthesized an acid-activatable macromolecular prodrug of floxuridine (FUDR)-poly(FUDR-ketal), engineered a micellar nanomedicine of FUDR, and intravenously co-administered the nanomedicine with the tumor-penetrating peptide iRGD for enhanced treatment of pancreatic tumor. A FUDR-derived mono-isopropenyl ether was synthesized and underwent self-addition polymerization to afford the hydrophobic poly(FUDR-ketal), which was subsequently co-assembled with amphiphilic DSPE-mPEG into the micellar nanomedicine with size of 12 nm and drug content of 56.8 wt% using nanoprecipitation technique. The acetone-based ketal-linked poly(FUDR-ketal) was triggered by acid to release FUDR to inhibit cell proliferation. In an orthotopic pancreatic tumor model derived from KPC (KrasLSL-G12D/+; Trp53LSL-R172H/+; Pdx1-Cre) cells that overexpress neuropilin-1 (NRP-1) receptor, iRGD improved penetration of FUDR nanomedicine into tumor parenchyma and potentiated the therapeutic efficacy. Our nanoplatform, along with iRGD, thus appears to be promising for efficient penetration and activation of acid-responsive nanomedicines for enhanced pancreatic cancer therapy.

Clinical advances in TNC delivery vectors and their conjugate agents

Tenascin C (TNC), a glycoprotein that is abundant in the tumor extracellular matrix (ECM), is strongly overexpressed in tumor tissues but virtually undetectable in most normal tissues. Many TNC antibodies, peptides, aptamers, and nanobodies have been investigated as delivery vectors, including 20A1, α-A2, α-A3, α-IIIB, α-D, BC-2, BC-4 BC-8, 81C6, ch81C6, F16, FHK, Ft, Ft-NP, G11, G11-iRGD, GBI-10, 19H12, J1/TN1, J1/TN2, J1/TN3, J1/TN4, J1/TN5, NJT3, NJT4, NJT6, P12, PL1, PL3, R6N, SMART, ST2146, ST2485, TN11, TN12, TNFnA1A2-Fc, TNfnA1D-Fc, TNfnBD-Fc, TNFnCD-Fc, TNfnD6-Fc, TNfn78-Fc, TTA1, TTA1.1, and TTA1.2. In particular, BC-2, BC-4, 81C6, ch81C6, F16, FHK, G11, PL1, PL3, R6N, ST2146, TN11, and TN12 have been tested in human tissues. G11-iRGD and simultaneous multiple aptamers and arginine-glycine-aspartic acid (RGD) targeting (SMART) may be assessed in clinical trials because G11, iRGD and AS1411 (SMART components) are already in clinical trials. Many TNC-conjugate agents, including antibody-drug conjugates (ADCs), antibody fragment-drug conjugates (FDCs), immune-stimulating antibody conjugates (ISACs), and radionuclide-drug conjugates (RDCs), have been investigated in preclinical and clinical trials. RDCs investigated in clinical trials include 111In-DTPA-BC-2, 131I-BC-2, 131I-BC-4, 90Y-BC4, 131I81C6, 131I-ch81C6, 211At-ch81C6, F16124I, 131I-tenatumomab, ST2146biot, FDC 131I-F16S1PF(ab')2, and ISAC F16IL2. ADCs (including FHK-SSL-Nav, FHK-NB-DOX, Ft-NP-PTX, and F16*-MMAE) and ISACs (IL12-R6N and 125I-G11-IL2) may enter clinical trials because they contain components of marketed treatments or agents that were investigated in previous clinical studies. This comprehensive review presents historical perspectives on clinical advances in TNC-conjugate agents to provide timely information to facilitate tumor-targeting drug development using TNC.

Molecular View on the iRGD Peptide Binding Mechanism: Implications for Integrin Activity and Selectivity Profiles

Receptor-selective peptides are widely used as smart carriers for specific tumor-targeted delivery. A remarkable example is the cyclic nonapeptide iRGD (CRGDKPGDC, 1) that couples intrinsic cytotoxic effects with striking tumor-homing properties. These peculiar features are based on a rather complex multistep mechanism of action, where the primary event is the recognition of RGD integrins. Despite the high number of preclinical studies and the recent success of a phase I trial for the treatment of pancreatic ductal adenocarcinoma (PDAC), there is little information available about the iRGD three-dimensional (3D) structure and integrin binding properties. Here, we re-evaluate the peptide's affinity for cancer-related integrins including not only the previously known targets αvβ3 and αvβ5 but also the αvβ6 isoform, which is known to drive cell growth, migration, and invasion in many malignancies including PDAC. Furthermore, we use parallel tempering in the well-tempered ensemble (PT-WTE) metadynamics simulations to characterize the in-solution conformation of iRGD and extensive molecular dynamics calculations to fully investigate its binding mechanism to integrin partners. Finally, we provide clues for fine-tuning the peptide's potency and selectivity profile, which, in turn, may further improve its tumor-homing properties.

Assessment of the Pharmacokinetics, Disposition, and Duration of Action of the Tumour-Targeting Peptide CEND-1

CEND-1 (iRGD) is a bifunctional cyclic peptide that can modulate the solid tumour microenvironment, enhancing the delivery and therapeutic index of co-administered anti-cancer agents. This study explored CEND-1’s pharmacokinetic (PK) properties pre-clinically and clinically, and assessed CEND-1 distribution, tumour selectivity and duration of action in pre-clinical tumour models. Its PK properties were assessed after intravenous infusion of CEND-1 at various doses in animals (mice, rats, dogs and monkeys) and patients with metastatic pancreatic cancer. To assess tissue disposition, [3H]-CEND-1 radioligand was administered intravenously to mice bearing orthotopic 4T1 mammary carcinoma, followed by tissue measurement using quantitative whole-body autoradiography or quantitative radioactivity analysis. The duration of the tumour-penetrating effect of CEND-1 was evaluated by assessing tumour accumulation of Evans blue and gadolinium-based contrast agents in hepatocellular carcinoma (HCC) mouse models. The plasma half-life was approximately 25 min in mice and 2 h in patients following intravenous administration of CEND-1. [3H]-CEND-1 localised to the tumour and several healthy tissues shortly after administration but was cleared from most healthy tissues by 3 h. Despite the rapid systemic clearance, tumours retained significant [3H]-CEND-1 several hours post-administration. In mice with HCC, the tumour penetration activity remained elevated for at least 24 h after the injection of a single dose of CEND-1. These results indicate a favourable in vivo PK profile of CEND-1 and a specific and sustained tumour homing and tumour penetrability. Taken together, these data suggest that even single injections of CEND-1 may elicit long-lasting tumour PK improvements for co-administered anti-cancer agents.