Interstitial Release of Cisplatin from Triggerable Liposomes Enhances Efficacy against Triple Negative Breast Cancer Solid Tumor Analogues

Low-dose temozolomide selectively increases glioblastoma's vascular permeability, tumor microenvironment penetration and the killing potential of systemic actinium-225 α-particle dendrimer-radioconjugates improving treatment efficacy

PURPOSE

The poor prognosis of glioblastoma is mostly due to the relatively low tumor vascular permeability to therapeutics, the tumor's vicinity to the brain, that limits treatment aggressiveness, and/or drug resistance.

METHODS

In this study, the efficacy of systemically injected actinium-225 dendrimer-radioconjugates was evaluated in an immune-competent orthotopic GL261-C57BL/6 mouse model after administration of low-dose, standard-of-care temozolomide, that selectively increased the tumor vascular permeability to dendrimer-radioconjugates. Alpha-particles' short range in tissue combined with the dendrimers' selective uptake by glioblastomas, could limit the irradiation of the neighboring brain, while the complex double-strand DNA breaks caused by α-particles were expected to be largely impervious to resistance by cancer cells.

RESULTS

On mice bearing 9.7 ± 5.7mm3 brain tumors, at activities that did not cause long-term (11-months) toxicities, dendrimer-radioconjugates, that were systemically-administered 24-hours after injection of temozolomide, significantly improved survival compared to dendrimer-radioconjugates alone (44 vs. 39 days mean survival, p = 0.0017) and/or compared to temozolomide alone and/or to non-treated animals (31 and 30 days, p < 0.001). This was attributed to: (1) the noteworthy increase (by 33%) in tumor absorbed doses delivered by dendrimer-radioconjugates when injected after chemotherapy, without altering normal organ (including the brain's) dosimetry; (2) the potentially deeper tumor penetration of dendrimer-radioconjugates, suggested by the enhanced dendrimer penetration within GL261-spheroids, employed as model tumor-avascular regions; and/or (3) the formation of a more lethal cocktail when both modalities acted on same cancer cells.

CONCLUSIONS

This study demonstrates the potential and safety of actinium-225 dendrimer-radioconjugates as a systemic α-particle radiotherapy for glioblastoma enhanced by low-dose temozolomide.

MIRD Pamphlet No. 31: MIRDcell V4-Artificial Intelligence Tools to Formulate Optimized Radiopharmaceutical Cocktails for Therapy

Radiopharmaceutical cocktails have been developed over the years to treat cancer. Cocktails of agents are attractive because 1 radiopharmaceutical is unlikely to have the desired therapeutic effect because of nonuniform uptake by the targeted cells. Therefore, multiple radiopharmaceuticals targeting different receptors on a cell is warranted. However, past implementations in vivo have not met with convincing results because of the absence of optimization strategies. Here we present artificial intelligence (AI) tools housed in a new version of our software platform, MIRDcell V4, that optimize a cocktail of radiopharmaceuticals by minimizing the total disintegrations needed to achieve a given surviving fraction (SF) of tumor cells. Methods: AI tools are developed within MIRDcell V4 using an optimizer based on the sequential least-squares programming algorithm. The algorithm determines the molar activities for each drug in the cocktail that minimize the total disintegrations required to achieve a specified SF. Tools are provided for populations of cells that do not cross-irradiate (e.g., circulating or disseminated tumor cells) and for multicellular clusters (e.g., micrometastases). The tools were tested using model data, flow cytometry data for suspensions of single cells labeled with fluorochrome-labeled antibodies, and 3-dimensional spatiotemporal kinetics in spheroids for fluorochrome-loaded liposomes. Results: Experimental binding distributions of 4 211At-antibodies were considered for treating suspensions of MDA-MB-231 human breast cancer cells. A 2-drug combination reduced the number of 211At decays required by a factor of 1.6 relative to the best single antibody. In another study, 2 radiopharmaceuticals radiolabeled with 195mPt were each distributed lognormally in a hypothetical multicellular cluster. Here, the 2-drug combination required 1.7-fold fewer decays than did either drug alone. Finally, 2 225Ac-labeled drugs that provide different radial distributions within a spheroid require about one half of the disintegrations required by the best single agent. Conclusion: The MIRDcell AI tools determine optimized drug combinations and corresponding molar activities needed to achieve a given SF. This approach could be used to analyze a sample of cells obtained from cell culture, animal, or patient to predict the best combination of drugs for maximum therapeutic effect with the least total disintegrations.

Predicting response of micrometastases with MIRDcell V3: proof of principle with 225Ac-DOTA encapsulating liposomes that produce different activity distributions in tumor spheroids

PURPOSE

The spatial distribution of radiopharmaceuticals within multicellular clusters is known to have a significant effect on their biological response. Most therapeutic radiopharmaceuticals distribute nonuniformly in tissues which makes predicting responses of micrometastases challenging. The work presented here analyzes published temporally dependent nonuniform activity distributions within tumor spheroids treated with actinium-225-DOTA encapsulating liposomes (225Ac-liposomes) and uses these data in MIRDcell V3.11 to calculate absorbed dose distributions and predict biological response. The predicted responses are compared with experimental responses.

METHODS

Four types of liposomes were prepared having membranes with different combinations of release (R) and adhesion (A) properties. The combinations were R-A-, R-A+, R+A-, and R+A+. These afford different penetrating properties into tissue. The liposomes were loaded with either carboxyfluorescein diacetate succinimidyl ester (CFDA-SE) or 225Ac. MDA-MB-231 spheroids were treated with the CFDA-SE-liposomes, harvested at different times, and the time-integrated CFDA-SE concentration at each radial position within the spheroid was determined. This was translated into mean 225Ac decays/cell versus radial position, uploaded to MIRDcell, and the surviving fraction of cells in spherical multicellular clusters was simulated. The MIRDcell-predicted surviving fractions were compared with experimental fractional-outgrowths of the spheroids following treatment with 225Ac-liposomes.

RESULTS

The biological responses of the multicellular clusters treated with 225Ac-liposomes with physicochemical properties R+A+, R-A+, and R-A- were predicted by MIRDcell with statistically significant accuracy. The prediction for R+A- was not predicted accurately.

CONCLUSION

In most instances, MIRDcell predicts responses of spheroids treated with 225Ac-liposomes that result in different tissue-penetrating profiles of the delivered radionuclides.

Antitumor Effects of Ir(III)-2H-Indazole Complexes for Triple Negative Breast Cancer

In this work, we have synthesized a series of novel C,N-cyclometalated 2H-indazole-ruthenium(II) and -iridium(III) complexes with varying substituents (H, CH₃, isopropyl, and CF₃) in the R₄ position of the phenyl ring of the 2H-indazole chelating ligand. All of the complexes were characterized by ¹H, ¹³C, high-resolution mass spectrometry, and elemental analysis. The methyl-substituted 2H-indazole-Ir(III) complex was further characterized by single-crystal X-ray analysis. The cytotoxic activity of new ruthenium(II) and iridium(III) compounds has been evaluated in a panel of triple negative breast cancer (TNBC) cell lines (MDA-MB-231 and MDA-MB-468) and colon cancer cell line HCT-116 to investigate their structure-activity relationships. Most of these new complexes have shown appreciable activity, comparable to or significantly better than that of cisplatin in TNBC cell lines. R₄ substitution of the phenyl ring of the 2H-indazole ligand with methyl and isopropyl substituents showed increased potency in ruthenium(II) and iridium(III) complexes compared to that of their parent compounds in all cell lines. These novel transition metal-based complexes exhibited high specificity toward cancer cells by inducing alterations in the metabolism and proliferation of cancer cells. In general, iridium complexes are more active than the corresponding ruthenium complexes. The new Ir(III)-2H-indazole complex with an isopropyl substituent induced mitochondrial damage by generating large amounts of reactive oxygen species (ROS), which triggered mitochondrion-mediated apoptosis in TNBC cell line MDA-MB-468. Moreover, this complex also induced G2/M phase cell cycle arrest and inhibited cellular migration of TNBC cells. Our findings reveal the key roles of the novel C-N-cyclometalated 2H-indazole-Ir(III) complex to specifically induce toxicity in cancer cell lines through contributing effects of ROS-induced mitochondrial disruption along with chromosomal and mitochondrial DNA target inhibition.

Two diverse carriers are better than one: A case study in α‐particle therapy for prostate specific membrane antigen‐expressing prostate cancers

Partial and/or heterogeneous irradiation of established (i.e., large, vascularized) tumors by α‐particles that exhibit only a 4–5 cell‐diameter range in tissue, limits the therapeutic effect, since regions not being hit by the high energy α‐particles are likely not to be killed. This study aims to mechanistically understand a delivery strategy to uniformly distribute α‐particles within established solid tumors by simultaneously delivering the same α‐particle emitter by two diverse carriers, each killing a different region of the tumor: (1) the cancer‐agnostic, but also tumor‐responsive, liposomes engineered to best irradiate tumor regions far from the vasculature, and (2) a separately administered, antibody, targeting any cancer‐cell's surface marker, to best irradiate the tumor perivascular regions. We demonstrate that on a prostate specific membrane antigen (PSMA)‐expressing prostate cancer xenograft mouse model, for the same total injected radioactivity of the α‐particle emitter Actinium‐225, any radioactivity split ratio between the two carriers resulted in better tumor growth inhibition compared to the tumor inhibition when the total radioactivity was delivered by any of the two carriers alone. This finding was due to more uniform tumor irradiation for the same total injected radioactivity. The killing efficacy was improved even though the tumor‐absorbed dose delivered by the combined carriers was lower than the tumor‐absorbed dose delivered by the antibody alone. Studies on spheroids with different receptor‐expression, used as surrogates of the tumors' avascular regions, demonstrated that our delivery strategy is valid even for as low as 1+ (ImmunoHistoChemistry score) PSMA‐levels. The findings presented herein may hold clinical promise for those established tumors not being effectively eradicated by current α‐particle radiotherapies.

Growth Inhibition of Triple-Negative Breast Cancer: The Role of Spatiotemporal Delivery of Neoadjuvant Doxorubicin and Cisplatin

Combinations of platinum-based compounds with doxorubicin in free and/or in liposomal form for improved safety are currently being evaluated in the neoadjuvant setting on patients with advanced triple-negative breast cancer (TNBC). However, TNBC may likely be driven by chemotherapy-resistant cells. Additionally, established TNBC tumors may also exhibit diffusion-limited transport, resulting in heterogeneous intratumoral delivery of the administered therapeutics; this limits therapeutic efficacy in vivo. We studied TNBC cells with variable chemosensitivities, in the absence (on monolayers) and presence (in 3D multicellular spheroids) of transport barriers; we compared the combined killing effect of free doxorubicin and free cisplatin to the killing effect (1) of conventional liposomal forms of the two chemotherapeutics, and (2) of tumor-responsive lipid nanoparticles (NP), specifically engineered to result in more uniform spatiotemporal microdistributions of the agents within solid tumors. This was enabled by the NP properties of interstitial release, cell binding/internalization, and/or adhesion to the tumors’ extracellular matrix. The synergistic cell kill by combinations of the agents (in all forms), compared to the killing effect of each agent alone, was validated on monolayers of cells. Especially for spheroids formed by cells exhibiting resistance to doxorubicin combination treatments with both agents in free and/or in tumor-responsive NP-forms were comparably effective; we not only observed greater inhibition of outgrowth compared to the single agent(s) but also compared to the conventional liposome forms of the combined agents. We correlated this finding to more uniform spatiotemporal microdistributions of agents by the tumor-responsive NP. Our study shows that combinations of NP with properties specifically optimized to improve the spatiotemporal uniformity of the delivery of their corresponding therapeutic cargo can improve treatment efficacy while keeping favorable safety profiles.

Co-Encapsulation of Fisetin and Cisplatin into Liposomes for Glioma Therapy: From Formulation to Cell Evaluation

(1) Background: Glioblastoma (GBM) is the most frequent cerebral tumor. It almost always relapses and there is no validated treatment for second-line GBM. We proposed the coencapsulation of fisetin and cisplatin into liposomes, aiming to (i) obtain a synergistic effect by combining the anti-angiogenic effect of fisetin with the cytotoxic effect of cisplatin, and (ii) administrate fisetin, highly insoluble in water. The design of a liposomal formulation able to encapsulate, retain and deliver both drugs appeared a challenge. (2) Methods: Liposomes with increasing ratios of cholesterol/DOPC were prepared and characterized in term of size, PDI and stability. The incorporation of fisetin was explored using DSC. The antiangiogneic and cytotoxic activities of the selected formulation were assayed in vitro. (3) Results: We successfully developed an optimized liposomal formulation incorporating both drugs, composed by DOPC/cholesterol/DODA-GLY-PEG2000 at a molar ratio of 75.3/20.8/3.9, with a diameter of 173 ± 8 nm (PDI = 0.12 ± 0.01) and a fisetin and cisplatin drug loading of 1.7 ± 0.3% and 0.8 ± 0.1%, respectively, with a relative stability over time. The maximum incorporation of fisetin into the bilayer was determined at 3.2% w/w. Then, the antiangiogenic activity of fisetin was maintained after encapsulation. The formulation showed an additive effect of cisplatin and fisetin on GBM cells; (4) Conclusions: The developed co-loaded formulation was able to retain the activity of fisetin, was effective against GBM cells and is promising for further in vivo experimentations.

Harnessing Extracellular Matrix Biology for Tumor Drug Delivery

The extracellular matrix (ECM) plays an active role in cell life through a tightly controlled reciprocal relationship maintained by several fibrous proteins, enzymes, receptors, and other components. It is also highly involved in cancer progression. Because of its role in cancer etiology, the ECM holds opportunities for cancer therapy on several fronts. There are targets in the tumor-associated ECM at the level of signaling molecules, enzyme expression, protein structure, receptor interactions, and others. In particular, the ECM is implicated in invasiveness of tumors through its signaling interactions with cells. By capitalizing on the biology of the tumor microenvironment and the opportunities it presents for intervention, the ECM has been investigated as a therapeutic target, to facilitate drug delivery, and as a prognostic or diagnostic marker for tumor progression and therapeutic intervention. This review summarizes the tumor ECM biology as it relates to drug delivery with emphasis on design parameters targeting the ECM.

Enhanced cytotoxicity of a redox-sensitive hyaluronic acid-based nanomedicine toward different oncocytes via various internalization mechanisms

Receptor-mediated active targeting and tumor microenvironment responsive systems from polymeric micelles have been studied for rapid cellular internalization and triggered drug release. Previously we have constructed redox-responsive polymeric micelles composed of vitamin E succinate conjugated hyaluronic acid (HA-ss-TOS), which are able to actively target CD44 proteins and quickly release loaded drugs upon exposure to high levels of glutathione (GSH) in tumor cells. In the present study, we found that despite different cellular internalization mechanisms, micelles showed strong antineoplastic effects on 4T1 and B16F10 cells due to redox responsiveness. HA-ss-TOS-PTX micelles exhibited an excellent tumor targeting ability and prolonged retention time compared to Taxol in vivo. In addition, a superior antitumor effect was achieved compared to PTX-loaded insensitive micelles (HA-TOS-PTX) and Taxol. Our results revealed that PTX-loaded HA-ss-TOS micelles could enhance the antineoplastic efficacy of PTX for breast cancer and melanoma treatment and, thus, deserve further attention.

Designing Aptamer-Gold Nanoparticle-Loaded pH-Sensitive Liposomes Encapsulate Morin for Treating Cancer

This study proposes the synthesis of a type of anticancer nanoparticle, aptamers and Au nanoparticle (Apt-Au)-modified Morin pH-sensitive liposome (MSL), which exhibits targeting properties. Tumors are difficult to cure because their microenvironment varies from that of normal tissue; its pH is lower than that of normal tissue, which generally impedes the effectiveness of drugs. Thus, pH-responsive drugs have attracted extensive attention. Gold nanoparticles (AuNPs) show potential as drug carriers because of their small size, good biocompatibility, easy surface modification, and strong cell penetration. Apt-Au@MSL exhibits excellent monodispersity and tumor-targeting properties and can be released in partly acidic environment via dialysis. We screened our model cancer cell by MTT assay and found that SGC-7901 cells can effectively suppress proliferation. In vivo results demonstrate that the administration of Apt-Au@MSL could inhibit tumor growth in xenograft mouse models. H&E staining and TUNEL assay further confirmed that Apt-Au@MSL can promote tumor apoptosis. Apt-Au@MSL may induce apoptosis by triggering overproduction of reactive oxygen species (ROS) and regulating multiple signal crosstalk. Both blood biochemistry tests and H&E staining suggested that these materials exhibit negligible acute toxicity and good biocompatibility in vivo. With its powerful function, Apt-Au@MSL can be used as a target-based anticancer material for future clinical cancer treatment.

Growth of Metastatic Triple-Negative Breast Cancer Is Inhibited by Deep Tumor-Penetrating and Slow Tumor-Clearing Chemotherapy: The Case of Tumor-Adhering Liposomes with Interstitial Drug Release

The poor prognosis of triple-negative breast cancer (TNBC) is attributed largely to the lack of tumor-selective therapeutic modalities that effectively deliver lethal doses at the sites of metastatic disease. Tumor-selective drug delivery strategies that aim to improve uniformity in intratumoral drug microdistributions and to prolong exposure of these cancer cells to delivered therapeutics may improve therapeutic efficacy against established TNBC metastases. In this study, we present lipid carriers for selective (due to their nanometer size) tumor delivery, which are loaded with cisplatin and designed to exhibit the following properties when in the tumor interstitium: (1) interstitial drug release (for deeper tumor penetration of cisplatin) and/or (2) intratumoral/interstitial adhesion of the carriers to tumors' extracellular matrix (ECM)-not accompanied by cell internalization-for delayed tumor clearance of carriers prolonging cancer cell exposure to the cisplatin being released. We show that on large multicellular spheroids, used as surrogates of avascular solid tumor regions, greater growth inhibition was strongly correlated with spatially more uniform drug concentrations (due to interstitial drug release) and with longer exposure to the released drug (i.e., higher time-integrated drug concentrations enabled by slow clearing of adhesive nanoparticles). Lipid nanoparticles with both the release and adhesion properties were the most effective, followed by nanoparticles with only the releasing property and then by nanoparticles with only the adhering property. In vivo, cisplatin-loaded nanoparticles with releasing and/or adhering properties significantly inhibited the growth of spontaneous TNBC metastases compared to conventional liposomal cisplatin, and the efficacy of different property combinations followed the same trends as in spheroids. This study demonstrates the therapeutic potential of a general strategy to bypass treatment limitations of established TNBC metastases due to the lack of cell-targeting markers: aiming to optimize the temporal intratumoral drug microdistributions for more uniform and prolonged drug exposure.

Synergistic breast tumor cell killing achieved by intracellular co-delivery of doxorubicin and disulfiram via core-shell-corona nanoparticles

Combination therapy with different functional chemotherapeutic agents based on nano-drug delivery systems is an effective strategy for the treatment of breast cancer. However, co-delivery of drug molecules with different physicochemical properties still remains a challenge. In this study, an amphiphilic poly (ε-caprolactone)-b-poly (l-glutamic acid)-g-methoxy poly (ethylene glycol) (PCL-b-PGlu-g-mPEG) copolymer was designed and synthesized to develop a nanocarrier for the co-delivery of hydrophilic doxorubicin (DOX) and hydrophobic disulfiram (DSF). The amphiphilic copolymer self-assembled into core-shell-corona structured nanoparticles with the hydrophobic PCL core for DSF loading (hydrophobic interaction) and anionic poly (glutamic acid) shell for DOX loading (electrostatic interaction). DSF and DOX co-loaded nanoparticles (Co-NPs) resulted in high drug loading and precisely controlled DSF/DOX ratio via formulation optimization. Compared with free drug solutions, DSF and DOX delivered by the Co-NPs were found to have improved intracellular accumulation. Results of cytotoxicity assays showed that DSF/DOX delivered at the weight ratio of 0.5 and 1 could achieve a synergistic cytotoxic effect on breast cancer cell lines (MCF-7 and MDA-MB-231). In vivo imaging confirmed that the core-shell-corona nanoparticles could efficiently accumulate in tumors. In vivo anti-tumor effect results indicated that Co-NPs showed an improved drug synergistic effect on antitumor activity compared with the free drug combination. Therefore, it can be concluded that core-shell-corona nanoparticles prepared by PCL-b-PGlu-g-mPEG could be a promising co-delivery system for drug combination therapy in the treatment of breast cancer.

Roles of pH and the Na+/H+ exchanger NHE1 in cancer: From cell biology and animal models to an emerging translational perspective?

Acidosis is characteristic of the solid tumor microenvironment. Tumor cells, because they are highly proliferative and anabolic, have greatly elevated metabolic acid production. To sustain a normal cytosolic pH homeostasis they therefore need to either extrude excess protons or to neutralize them by importing HCO₃^-, in both cases causing extracellular acidification in the poorly perfused tissue microenvironment. The Na⁺/H⁺ exchanger isoform 1 (NHE1) is a ubiquitously expressed acid-extruding membrane transport protein, and upregulation of its expression and/or activity is commonly correlated with tumor malignancy. The present review discusses current evidence on how altered pH homeostasis, and in particular NHE1, contributes to tumor cell motility, invasion, proliferation, and growth and facilitates evasion of chemotherapeutic cell death. We summarize data from in vitro studies, 2D-, 3D- and organotypic cell culture, animal models and human tissue, which collectively point to pH-regulation in general, and NHE1 in particular, as potential targets in combination chemotherapy. Finally, we discuss the possible pitfalls, side effects and cellular escape mechanisms that need to be considered in the process of translating the plethora of basic research data into a clinical setting.