Abstract 5484: Preclinical evaluation of CAP-0121 for multidrug resistant cancers

CAP-0121 is a second generation illudofulvene agent that produces an unusual type of DNA damage and is being developed to treat ovarian cancer by Califia Pharma. CAP-0121 DNA damage, like other illudofulvenes, can only be recognized and repaired by the Transcription-Coupled Repair pathway, and is ignored by the Global Genome Repair Pathway. The first generation illudofulvene, irofulven, displayed significant activity in clinical trials against ovarian, prostate and hepatocellular tumors. While irofulven has proven to be a potent antitumor agent against drug-resistant tumors, its efficacy is limited by hematologic toxicity that reduced the maximum dosage that can be administered to patients. CAP-0121 is as cytotoxic, or even more cytotoxic, than irofulven when tested in the NCI 60 cell line panel. Despite this increased cytotoxicity noted in vitro, CAP-0121 is less toxic to animals and the maximum tolerated dose is approximately 3 times higher than irofulven (mg/kg basis). CAP-0121 also retains activity against multidrug resistant cell lines including MRP1 and MDR1 expressing variants. As a result CAP-0121 is capable of inducing tumor remission in MDR xenograft models that are unresponsive to 35 conventional and experimental agents, and in which irofulven is only capable of slowing the rate of tumor growth. This response of CAP-0121 in drug resistant xenografts is observed at nontoxic doses. Synergistic action is observed when CAP-0121 is administered in combination with traditional drugs used for treating ovarian cancer, including taxanes, platinum agents, and PARP inhibitors.

Citation Format: Michael J. Kelner, Venkata R. Kotamraju. Preclinical evaluation of CAP-0121 for multidrug resistant cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5484.

Abstract 385: iRGD mediated delivery of neoantigens to enable immunotherapy in integrin b5-rich tumors

Pancreatic duct adenocarcinomas are known for their abundant desmoplastic stroma that acts as a barrier for drug penetration and reduces treatment efficacy. iRGD is a tumor-penetrating peptide that initially targets αv integrins expressed on tumor vasculature with its RGD motif and then is proteolytically processed to expose a CendR motif (R/KXXR/K) that interacts with neuropilin-1 (NRP-1), leading to extravasation. We investigated the mechanism of iRGD tissue penetration and found that iRGD initially targets Carcinoma Associated Fibroblasts (CAFs) and then spreads to the tumor cells in a time dependent manner. CAF targeting was dependent on integrin β5 expression and CAFs induced upregulation of integrin β5 in the adjacent tumor cells in a TGF- β dependent manner. Drugs conjugated or co-administered with iRGD can penetrate deep into tumor tissue, significantly increasing the efficacy of chemotherapeutic agents in a variety of solid tumors. Our recent data shows that KrasLSL-G12D/+ Trp53LSL-R172H/+ Pdx1-Cre (KPC) mice treated with iRGD co-administered with Gemcitabine increased survival compared to drug alone. In addition, we are using iRGD to deliver neoantigens to breast and pancreatic cancers to enable immunotherapy. These tumors have a low mutational burden and a very immunosuppressive microenvironment, rendering them resistant to such therapies. We have used iRGD, to deliver the ovalbumin 257-264 (OVAI) peptide to triple negative breast tumors, followed by adoptive T cell transfer of OT1 CD8 T cells, in order to elicit an antitumor immune response. Our preliminary data showed tumor regression in 70%, and complete response in 42% of the mice treated with iRGD plus OVA1. We are now working on adapting this strategy to pancreatic cancer.

Citation Format: Tatiana Hurtado de Mendoza, Evangeline S. Mose, Gregory P. Botta, Gary B. Braun, Venkata R. Kotamraju, Randall P. French, Kodai Suzuki, Norio Miyamura, Siming Sun, Jay Patel, Tambet Teesalu, Erkki Ruoslahti, Kazuki N. Sugahara, Andrew M. Lowy. iRGD mediated delivery of neoantigens to enable immunotherapy in integrin b5-rich tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 385.

Tumor-penetrating therapy for β5 integrin-rich pancreas cancer

Pancreatic ductal adenocarcinoma (PDAC) is characterized by marked desmoplasia and drug resistance due, in part, to poor drug delivery to extravascular tumor tissue. Here, we report that carcinoma-associated fibroblasts (CAFs) induce β5 integrin expression in tumor cells in a TGF-β dependent manner, making them an efficient drug delivery target for the tumor-penetrating peptide iRGD. The capacity of iRGD to deliver conjugated and co-injected payloads is markedly suppressed when β5 integrins are knocked out in the tumor cells. Of note, β5 integrin knock-out in tumor cells leads to reduced disease burden and prolonged survival of the mice, demonstrating its contribution to PDAC progression. iRGD significantly potentiates co-injected chemotherapy in KPC mice with high β5 integrin expression and may be a powerful strategy to target an aggressive PDAC subpopulation.

Selective Targeting of a Novel Vasodilator to the Uterine Vasculature to Treat Impaired Uteroplacental Perfusion in Pregnancy

Fetal growth restriction (FGR) in pregnancy is commonly caused by impaired uteroplacental blood flow. Vasodilators enhance uteroplacental perfusion and fetal growth in humans and animal models; however, detrimental maternal and fetal side effects have been reported. We hypothesised that targeted uteroplacental delivery of a vasodilator would enhance drug efficacy and reduce the risks associated with drug administration in pregnancy. Phage screening identified novel peptides that selectively accumulated in the uteroplacental vasculature of pregnant mice. Following intravenous injection, the synthetic peptide CNKGLRNK selectively bound to the endothelium of the uterine spiral arteries and placental labyrinth in vivo; CNKGLRNK-decorated liposomes also selectively bound to these regions. The nitric oxide donor 2-[[4-[(nitrooxy)methyl]benzoyl]thio]-benzoic acid methyl ester (SE175) induced significant relaxation of mouse uterine arteries and human placental arteries in vitro; thus, SE175 was encapsulated into these targeted liposomes and administered to healthy pregnant C57BL/6J mice or endothelial nitric oxide synthase knockout (eNOS-/-) mice, which exhibit impaired uteroplacental blood flow and FGR. Liposomes containing SE175 (0.44mg/kg) or PBS were administered on embryonic (E) days 11.5, 13.5, 15.5 and 17.5; fetal and placental weights were recorded at term and compared to mice injected with free PBS or SE175. Targeted uteroplacental delivery of SE175 had no effect on fetal weight in C57BL/6J mice, but significantly increased fetal weight and mean spiral artery diameter, and decreased placental weight, indicative of improved placental efficiency, in eNOS-/- mice; free SE175 had no effect on fetal weight or spiral artery diameter. Targeted, but not free SE175 also significantly reduced placental expression of 4-hydroxynonenal, cyclooxygenase-1 and cyclooxygenase-2, indicating a reduction in placental oxidative stress. These data suggest that exploiting vascular targeting peptides to selectively deliver SE175 to the uteroplacental vasculature may represent a novel treatment for FGR resulting from impaired uteroplacental perfusion.

Tumor-homing peptides as tools for targeted delivery of payloads to the placenta

The availability of therapeutics to treat pregnancy complications is severely lacking mainly because of the risk of causing harm to the fetus. As enhancement of placental growth and function can alleviate maternal symptoms and improve fetal growth in animal models, we have developed a method for targeted delivery of payloads to the placenta. We show that the tumor-homing peptide sequences CGKRK and iRGD bind selectively to the placental surface of humans and mice and do not interfere with normal development. Peptide-coated nanoparticles intravenously injected into pregnant mice accumulated within the mouse placenta, whereas control nanoparticles exhibited reduced binding and/or fetal transfer. We used targeted liposomes to efficiently deliver cargoes of carboxyfluorescein and insulin-like growth factor 2 to the mouse placenta; the latter significantly increased mean placental weight when administered to healthy animals and significantly improved fetal weight distribution in a well-characterized model of fetal growth restriction. These data provide proof of principle for targeted delivery of drugs to the placenta and provide a novel platform for the development of placenta-specific therapeutics.

Nanoparticles coated with the tumor-penetrating peptide iRGD reduce experimental breast cancer metastasis in the brain

Metastasis is the main killer in cancer; consequently, there is great interest in novel approaches to prevent and treat metastatic disease. Brain metastases are particularly deadly, as the protection of the blood-brain barrier obstructs the passage of common anticancer drugs. This study used magnetic resonance imaging (MRI) to investigate the therapeutic effects of nanoparticles coated with a tumor-penetrating peptide (iRGD) against a preclinical model of breast cancer brain metastasis. Single doses of iRGD nanoparticle were administered intravenously, and the effect on tumor growth was observed over time. iRGD nanoparticles, when applied in the early stages of metastasis development, strongly inhibited tumor progression. Overall, this study demonstrated for the first time that a single dose of iRGD nanoparticle can have a significant effect on metastatic tumor progression and nonproliferative cancer cell retention when applied early in course of tumor development. These data suggest that iRGD nanoparticles may be useful in preventatively reducing metastasis after a cancer diagnosis has been established.

KEY MESSAGES

bSSFP MRI can be used to track nonproliferative iron-labeled cells and tumor development over time. iRGD-NW, when applied early, has a significant effect on metastatic tumor progression. Retained signal voids represent a subpopulation of nonproliferating tumor cells. Reduced cell retention and tumor burden show a role for iRGD-NW in metastasis prevention. iRGD target is universally expressed; thus, iRGD-NW should be clinically translatable.

Clot-targeted micellar formulation improves anticoagulation efficacy of bivalirudin

Application of anticoagulants remains the primary strategy for prevention and treatment of thrombosis. However, high rate of bleeding complications limits their use. The peptide anticoagulant bivalirudin has been reported to exhibit a lower rate of bleeding complications than heparin, and it also has the advantage of not causing thrombocytopenia, which is a problem with heparin. Nonetheless, hemorrhage is the most common complication of bivalirudin therapy, and there is no effective antidote. Here we use a thrombus-binding peptide, CR(NMe)EKA, to accomplish selective delivery of the bivalirudin-carrying micellar nanocarrier to sites of thrombosis. Bivalirudin and CR(NMe)EKA, each with a PEG-lipid tail, spontaneously assembled into 30 nm micelles, which almost completely retained the anticoagulant activity of bivalirudin. The micellar formulations exhibited high stability both in vitro and in vivo. In a thromboplastin-induced mouse thrombosis model, the targeted micelles accumulated in lung thrombi 10-fold more than nontargeted micelles. Moreover, the micellar formulation significantly prolonged the half-life and thereby increased the bioavailability of bivalirudin. The micellar bivalirudin had significantly higher anticoagulant activity than free bivalirudin in both the lung thrombosis model and a ferric chloride-induced carotid artery thrombosis model. The specific targeting of thrombi demonstrated here makes it possible to increase the efficacy of bivalirudin as an anticoagulant. Alternatively, the dose could be reduced without loss of efficacy to lower the systemic exposure and improve safety.

A free cysteine prolongs the half-life of a homing peptide and improves its tumor-penetrating activity

The accessibility of extravascular tumor tissue to drugs is critical for therapeutic efficacy. We previously described a tumor-targeting peptide (iRGD) that elicits active transport of drugs and macromolecules (covalently coupled or co-administered) across the vascular wall into tumor tissue. Short peptides (iRGD is a 9-amino acid cyclic peptide) generally have a plasma half-life measured in minutes. Since short half-life limits the window of activity obtained with a bolus injection of iRGD, we explored to extend the half-life of the peptide. We show here that addition of a cysteine residue prolongs the plasma half-life of iRGD and increases the accumulation of the peptide in tumors. This modification prolongs the activity of iRGD in inducing macromolecular extravasation and leads to greater drug accumulation in tumors than is obtained with the unmodified peptide. This effect is mediated by covalent binding of iRGD to plasma albumin through a disulfide bond. Our study provides a simple strategy to improve peptide pharmacokinetics and activity. Applied to RGD, it provides a means to increase the entry of therapeutic agents into tumors.

Proapoptotic peptide-mediated cancer therapy targeted to cell surface p32

Antiangiogenic therapy is a promising new treatment modality for cancer, but it generally produces only transient tumor regression. We have previously devised a tumor-targeted nanosystem, in which a pentapeptide, CGKRK, delivers a proapoptotic peptide into the mitochondria of tumor blood vessel endothelial cells and tumor cells. The treatment was highly effective in glioblastoma mouse models completely refractory to other antiangiogenic treatments. Here, we identify p32/gC1qR/HABP, a mitochondrial protein that is also expressed at the cell surface of activated (angiogenic) endothelial cells and tumor cells, as a receptor for the CGKRK peptide. The results demonstrate the ability of p32 to cause internalization of a payload bound to p32 into the cytoplasm. We also show that nardilysin, a protease capable of cleaving CGKRK, plays a role in the internalization of a p32-bound payload. As p32 is overexpressed and surface displayed in breast cancers, we studied the efficacy of the nanosystem in this cancer. We show highly significant treatment results in an orthotopic model of breast cancer. The specificity of cell surface p32 for tumor-associated cells, its ability to carry payloads to mitochondria, and the efficacy of the system in important types of cancer make the nanosystem a promising candidate for further development.

De novo design of a tumor-penetrating peptide

Poor penetration of antitumor drugs into the extravascular tumor tissue is often a major factor limiting the efficacy of cancer treatments. Our group has recently described a strategy to enhance tumor penetration of chemotherapeutic drugs through use of iRGD peptide (CRGDK/RGPDC). This peptide comprises two sequence motifs: RGD, which binds to αvβ3/5 integrins on tumor endothelia and tumor cells, and a cryptic CendR motif (R/KXXR/K-OH). Once integrin binding has brought iRGD to the tumor, the peptide is proteolytically cleaved to expose the cryptic CendR motif. The truncated peptide loses affinity for its primary receptor and binds to neuropilin-1, activating a tissue penetration pathway that delivers the peptide along with attached or co-administered payload into the tumor mass. Here, we describe the design of a new tumor-penetrating peptide based on the current knowledge of homing sequences and internalizing receptors. The tumor-homing motif in the new peptide is the NGR sequence, which binds to endothelial CD13. The NGR sequence was placed in the context of a CendR motif (RNGR), and this sequence was embedded in the iRGD framework. The resulting peptide (CRNGRGPDC, iNGR) homed to tumor vessels and penetrated into tumor tissue more effectively than the standard NGR peptide. iNGR induced greater tumor penetration of coupled nanoparticles and co-administered compounds than NGR. Doxorubicin given together with iNGR was significantly more efficacious than the drug alone. These results show that a tumor-specific, tissue-penetrating peptide can be constructed from known sequence elements. This principle may be useful in designing tissue-penetrating peptides for other diseases.

Optimization of iron oxide nanoparticle detection using ultrashort echo time pulse sequences: comparison of T1, T2*, and synergistic T1- T2* contrast mechanisms

Iron oxide nanoparticles (IONPs) are used in various MRI applications as negative contrast agents. A major challenge is to distinguish regions of signal void due to IONPs from those due to low signal tissues or susceptibility artifacts. To overcome this limitation, several positive contrast strategies have been proposed. Relying on IONP T(1) shortening effects to generate positive contrast is a particularly appealing strategy because it should provide additional specificity when associated with the usual negative contrast from effective transverse relaxation time (T(2)*) effects. In this article, ultrashort echo time imaging is shown to be a powerful technique which can take full advantage of both contrast mechanisms. Methods of comparing T(1) and T(2)* contrast efficiency are described and general rules that allow optimizing IONP detection sensitivity are derived. Contrary to conventional wisdom, optimizing T(1) contrast is often a good strategy for imaging IONPs. Under certain conditions, subtraction of a later echo signal from the ultrashort echo time signal not only improves IONP specificity by providing long T(2)* background suppression but also increases detection sensitivity, as it enables a synergistic combination of usually antagonist T(1) and T(2)* contrasts. In vitro experiments support our theory, and a molecular imaging application is demonstrated using tumor-targeted IONPs in vivo.