Cytoprotective agent troxipide-cyanine dye conjugate with cytotoxic and antiproliferative activity in patient-derived glioblastoma cell lines

Involvement of the tumour necrosis factor receptor system in glioblastoma cell death induced by palbociclib-heptamethine cyanine dye conjugate

Glioblastoma is the most common and aggressive primary brain tumour in adults. The development of anti-brain cancer agents are challenged by the blood-brain barrier and the resistance conferred by the local tumour microenvironment. Heptamethine cyanine dyes (HMCDs) are a class of near-infrared fluorescence compounds that have recently emerged as promising agents for drug delivery. We conjugated palbociclib, a cyclin-dependent kinase (CDK) 4/6 inhibitor, to an HMCD, MHI-148, and conducted drug activity analysis on primary patient-derived glioblastoma cell lines. In addition to the expected cytostatic activity, our in vitro studies revealed that palbociclib-MHI-148 conjugate resulted in an almost 100-fold increase in cytotoxicity compared to palbociclib alone. This shift of palbociclib from cytostatic to cytotoxic when conjugated to MHI-148 was due to increased DNA damage, as indicated by an increase in γH2AX foci, followed by an increased expression of key extrinsic apoptosis genes, including TP53, TNFR1, TRAIL, FADD and caspase 8. In addition, we observed a time-dependent increase in the cell surface expression of TNFR1, consistent with an observed increase in the secretion TNFα, followed by TNFR1 endocytosis at 48 h. The treatment of patient GBM cells with the palbociclib-MHI-148 conjugate prevented TNFα-induced NFκB translocation, suggesting conjugate-induced TNFR1 signalling favoured the TNFR1-mediated apoptotic response rather than the pro-inflammatory response pathway. Notably, pharmacological inhibition of endocytosis of TNFR1, and siRNA-knockdown of TNFR1 reversed the palbociclib-MHI-148-induced cell death. These results show a novel susceptibility of glioblastoma cells to TNFR1-dependent apoptosis, dependent on inhibition of canonical NFκB signalling using our previously reported palbociclib-HMCD conjugate. Video Abstract.

Cytotoxicities of Tumor-Seeking Dyes: Impact on Future Clinical Trials

Heptamethine (Cy7) dyes with meso-Cl substituents injected intravenously (iv) into mice accumulate in tumors and persist there over several days. We believe this occurs via meso-Cl displacement by the only free cysteine residues of albumin; therefore, conjugating tumor-seeking dyes with fragments can increase selective therapeutic delivery to tumors and drug residence. This strategy has elevated significance recently because the first tumor-seeking dye-drug conjugate has moved into clinical trials. Options for further clinical research include modifying the dye, and use of preformed albumin adducts instead of dyes alone. Herein we show correlations of cytotoxicities, lipophilicities, organelle localization, apoptosis, cell-cycle arrest, wound healing/migration assays, and reactivities/affinities with human serum albumin are difficult to observe. However, our studies arrived at an important conclusion: preformed dye-drug-HSA adducts are less cytotoxic, and therefore preferable for subsequent clinical work, relative to direct injection of meso-Cl-containing forms.

Elucidating the cellular uptake mechanisms of heptamethine cyanine dye analogues for their use as an anticancer drug-carrier molecule for the treatment of glioblastoma

The development of chemotherapies for glioblastoma is hindered by their limited bioavailability and toxicity on normal brain function. To overcome these limitations, we investigated the structure-dependent activity of heptamethine cyanine dyes (HMCD), a group of tumour-specific and BBB permeable near-infrared fluorescent dyes, in both commercial (U87MG) and patient-derived GBM cell lines. HMCD analogues with strongly ionisable sulphonic acid groups were not taken up by patient-derived GBM cells, but were taken up by the U87MG cell line. HMCD uptake relies on a combination of transporter uptake through organic anion-transporting polypeptides (OATPs) and endocytosis into GBM cells. The uptake of HMCDs was not affected by p-glycoprotein efflux in GBM cells. Finally, we demonstrate structure-dependent cytotoxic activity at high concentrations (EC₅₀ : 1-100 μM), likely due to mitochondrial damage-induced apoptosis. An in vivo orthotopic glioblastoma model highlights tumour-specific accumulation of our lead HMCD, MHI-148, for up to 7 days following a single intraperitoneal injection. These studies suggest that strongly ionisable groups like sulphonic acids hamper the cellular uptake of HMCDs in patient-derived GBM cell lines, highlighting cell line-specific differences in HMCD uptake. We envisage these findings will help in the design and structural modifications of HMCDs for drug-delivery applications for glioblastoma.

Probing tricarbocyanine dyes for targeted delivery of anthracyclines

Along with bright fluorescence in the near-IR range, heptamethine carbocyanine dyes possess affinity to cancer cells. Thus, these dyes could be utilized as fluorescent labels and vectors for drug delivery as covalent conjugates with cytotoxic compounds. To test the properties, structure-activity relationship, and scope of such conjugates, we synthesized drug-dye dyads of tricarbocyanine dyes with anthracycline drug daunorubicin. We used hydrophilic zwitterionic and hydrophobic positively charged benzoindoline-benzothiazole-based heptamethine dyes as terminal alkyne derivatives and N-acylated or oxime-linked daunorubicin as azido-derivatives. These two alkynes and two azides were coupled to each other by Cu-catalyzed Huisgen-Meldal-Sharpless cycloaddition (click reaction) to afford four conjugates. Molecules based on hydrophobic dyes possess submicromolar cytotoxicity to HCT116 cells. Cytotoxicity, cell penetration, intracellular distribution, apoptosis induction and the effect of antioxidants on toxicity were evaluated. The results show that the structure of the cyanine-anthracycline conjugate (hydrophilicity/hydrophobicity, charge, linker, attachment site) is important for its biological activity, thus, expansion of the chemical space of such conjugates could provide new molecular research tools for diagnostics and therapy.

Near-Infrared Fluorescent Heptamethine Cyanine Dyes for COX-2 Targeted Photodynamic Cancer Therapy

We designed and synthesized two heptamethine cyanine based theranostic probes that aimed to target COX-2 in cancer cells. One is I-IR799-CXB which I-IR799 was conjugated to COX-2 specific inhibitor, celecoxib, and another is I-IR799-IMC , where the non-selective COX inhibitor, indomethacin, was used. I-IR799 is a heptamethine cyanine derivative that can be activated by near infrared light for photodynamic therapy (PDT) purposes. I-IR799-CXB and I-IR799-IMC were tested for their cancer targeting and photodynamic efficiency towards liver hepatocellular carcinoma cells (HepG2) compared to normal liver cell, alpha mouse liver 12 cells (AML12). Interestingly, after conjugation, I-IR799-IMC exhibited superior tumour targetability and PDT efficiency than I-IR799-CXB .