Immunotoxin Research Articles

Two Saporin-Containing Immunotoxins Specific for CD20 and CD22 Show Different Behavior in Killing Lymphoma Cells.

Immunotoxins (ITs) are hybrid proteins combining the binding specificity of antibodies with the cytocidal properties of toxins. They represent a promising approach to lymphoma therapy. The cytotoxicity of two immunotoxins obtained by chemical conjugation of the plant toxin saporin-S6 with the anti-CD20 chimeric antibody rituximab and the anti-CD22 murine antibody OM124 were evaluated on the CD20-/CD22-positive cell line Raji. Both ITs showed strong cytotoxicity for Raji cells, but the anti-CD22 IT was two logs more efficient in killing, probably because of its faster internalization. The anti-CD22 IT gave slower but greater caspase activation than the anti-CD20 IT. The cytotoxic effect of both immunotoxins can be partially prevented by either the pan-caspase inhibitor Z-VAD or the necroptosis inhibitor necrostatin-1. Oxidative stress seems to be involved in the cell killing activity of anti-CD20 IT, as demonstrated by the protective role of the H2O2 scavenger catalase, but not in that of anti-CD22 IT. Moreover, the IT toxicity can be augmented by the contemporary administration of other chemotherapeutic drugs, such as PS-341, MG-132, and fludarabine. These results contribute to the understanding of the immunotoxin mechanism of action that is required for their clinical use, either alone or in combination with other drugs.

Immunotoxin and bcl-2 inhibitor combination therapy targeting chondroitin sulfate proteoglycan 4.

74 Background: Immunotoxins (ITs) are a class of bifunctional chimeric proteins composed of an antibody fragment linked to a toxin. When ITs internalize into target cells, they induce protein synthesis inhibition and apoptosis. While ITs are highly specific and potent, the efficacy of IT-based therapies in some tumor cells is limited by hyperactive anti-apoptotic pathways and inefficient translocation of ITs from the endoplasmic reticulum to the cytosol. Therefore, to improve the efficacy of IT-based therapies, we evaluated a dual-pathway therapy that combines an IT with the ABT-737, ABT-263, or ABT-199 small molecule Bcl-2 inhibitor. Methods: The immunotoxin 9.2.27-PE38KDEL (9.2.27-IT) was generated by fusing a truncated mutant form of Pseudomonas exotoxin A to a single-chain variable fragment antibody. It targets human chondroitin sulfate proteoglycan 4 (CSPG4), an antigen highly expressed in a variety of cancer cells. We screened and identified 3 human glioblastoma xenografts, 3 human melanoma cell lines, and 5 human breast cancer cell lines resistant to the 9.2.27-IT despite their high levels of cell surface expression of CSPG4 (IC50 of IT alone was >100 ng/ml in all cell lines except for one melanoma cell line). In vitro cytotoxicity of the 9.2.27-IT —alone or in combination with the individual Bcl-2 inhibitors ABT-737, ABT-263, or ABT199—was assessed. Concentrations of ABT analogues were chosen so that ABT alone did not induce cytotoxicity. Results: The treatment groups that responded to the combination therapy yielded IC50 values ranging from 0.04 – 9 ng/ml for glioblastoma xenografts, 0.21-15 ng/ml for melanoma cell lines, and 4.5-50 ng/ml for breast cancer cell lines. The most potent combination group showed >1000 fold improvement of IC50 compared to using the immunotoxin alone. ABT-737 produced the strongest synergistic effects among the ABT analogues. Preliminary results from in vivo studies further demonstrated that this approach engendered a synergistic response and delayed tumor growth in immunotoxin-resistant mouse tumor models. Conclusions: This new combinatorial approach will potentially help to overcome immunotoxin resistance in cancer patients and provide better therapeutic outcomes.

Novel immunotherapies and their role in the treatment of acute lymphoblastic leukemia

Acute lymphoblastic leukemia (ALL) remains incurable for many adult patients. The success observed in the pediatric population with intensive combination chemotherapy regimens is not matched in older populations due to inability to tolerate treatment and biological differences in the disease. The development of immune therapies has ushered in a new much needed approach to treat ALL in the adult population as well as in the pediatric population with relapsed or refractory disease. While not heavily studied in the upfront setting, immune therapies have demonstrated astounding results in patients with minimal residual disease (MRD) and those with relapsed and refractory disease. The wide array of immunotherapy available consists of simple unconjugated monoclonal antibodies, immunotoxins or drug conjugated monoclonal antibodies, bispecific T cell engagers, and chimeric antigen receptor (CAR) T cells. In this article, we review the clinical data, efficacy, toxicity, and future direction of these therapies.

Membrane cholesterol is essential for triterpenoid saponin augmentation of a saporin-based immunotoxin directed against CD19 on human lymphoma cells

Triterpenoid saponins from Saponinum Album (SA) exert potent lytic effects on eukaryotic cell plasma membranes and, when used at sub-lytic concentrations, significantly augment the cytotoxicity of saporin-based immunotoxins (IT). To help elucidate the mechanism(s) behind these two phenomena we investigated the role of cholesterol to both.Human Daudi lymphoma cells were lipid deprived using a combination of three different approaches. Following treatment, the total cellular lipid content was analyzed by electrospray ionization mass spectrometry (ESI-MS) and plasma membrane (PM) cholesterol content measured using the lipophilic fluorescent probe NR12S. Maximal lipid deprivation of cells resulted in a complete loss of sensitivity to lysis by SA. Similarly augmentation of the anti-CD19 immunotoxin (IT) BU12-SAPORIN by SA was lost but without a concomitant loss of intrinsic IT cytotoxicity. The lytic activity of SA was restored following incubation of lipid deprived Daudi cells with Synthecol or LDL. The augmentative effect of SA on IT cytotoxicity for Daudi cells was restored following repletion of PM cholesterol levels with LDL. NR12S fluorescence and ESI-MS analysis of cellular lipids demonstrated that restoration of SA lytic activity by Synthecol was entirely due to increased PM cholesterol levels. Restoration of cellular and PM cholesterol levels by LDL also restored the augmentative effect of SA for IT, an effect associated with repletion of PM cholesterol with minor changes in some phospholipid species. These results indicate that the lytic and IT augmentative properties of SA are cholesterol-dependent in contrast to intrinsic IT cytotoxicity that is at least partially cholesterol independent.

Identification of Human Anti-HIV gp160 Monoclonal Antibodies That Make Effective Immunotoxins.

There is increased interest in using antibodies to treat and cure HIV infection. Antibodies can neutralize free virus and kill cells already carrying the virus. The virus envelope (Env) is the only HIV protein expressed on the surfaces of virions and infected cells. In this study, we examined a panel of human anti-Env antibodies for their ability to deliver cell-killing toxins to HIV-infected cells and to perform other antiviral functions. The ability of an antibody to make an effective immunotoxin could not be predicted from its other functional characteristics, such as its neutralizing activity. Anti-HIV immunotoxins could be used to eliminate virus reservoirs that persist despite effective antiretroviral therapy.

Enhancement of Anti-Robo1 Immunotoxin Cytotoxicity to Head and Neck Squamous Cell Carcinoma via Photochemical Internalization

Background: Head and neck squamous cell carcinoma (HNSCC) is the sixth most common cancer worldwide. The long-term complications arising from standard therapy with surgery, chemotherapy and radiotherapy lower the quality of life (QOL) due to eating disorders, speech problems and cosmetic issues. Recently the importance of antibody therapy has increasingly come to be recognized for its capacity to enhance QOL. Robo1, an axon guidance receptor, has been received considerable attention as a monoclonal antibody target in various cancers. Methods and findings: We checked the expression of Robo1 and the cytotoxic effect of saporin-conjugated anti- Robo1 immunotoxin (IT) against several HNSCC cell lines. The Robo1 cell surface expression level estimated by flow cytometry using the antibody B5209B was approximately 220,000 copies in Robo1 over-expressed CHO (Robo1/ CHO) cells, and in HNSCCs, 22,000 copies in HSQ-89 cells, 3,000 copies in Sa3 cells, and few copies inSAS cells. Conventional IT treatment exhibited an inadequate cytotoxic effect even in HSQ-89 cells. When we added a photosensitizer and LED light illumination (650 nm), the cytotoxic effect was remarkably improved in HSQ89. With longer exposure, significant cytotoxicity was observed, even in Sa3 cells. Conclusion: These results suggest that the photochemical internalization (PCI) is a promising method for augmenting the cytotoxicity of IT against tumors. The drug delivery system shown in this study should be applicable to other targets with low level expression on cancer cells, thus widening the therapeutic window in rare cancers.

Production and quality control assessment of a GLP-grade immunotoxin, D2C7-(scdsFv)-PE38KDEL, for a phase I/II clinical trial.

D2C7-(scdsFv)-PE38KDEL (D2C7-IT) is a novel recombinant Pseudomonas exotoxin A-based immunotoxin (IT), targeting both wild-type epidermal growth factor receptor (EGFRwt) and mutant EGFR variant III (EGFRvIII) proteins overexpressed in glioblastomas. Initial pre-clinical testing demonstrated the anti-tumor efficacy of D2C7-IT against orthotopic glioblastoma xenograft models expressing EGFRwt, EGFRvIII, or both EGFRwt and EGFRvIII. A good laboratory practice (GLP) manufacturing process was developed to produce sufficient material for a phase I/II clinical trial. D2C7-IT was expressed under the control of the T7 promoter in Escherichia coli BLR (λ DE3). D2C7-IT was produced by a 10-L batch fermentation process and was then purified from inclusion bodies using anion exchange, size exclusion, and an endotoxin removal process that achieved a yield of over 300mg of purified protein. The final vialed batch of D2C7-IT for clinical testing was at a concentration of 0.12±0.1mg/mL, the pH was at 7.4±0.4, and endotoxin levels were below the detection limit of 10EU/mL (1.26EU/mL). The stability of the vialed D2C7-IT has been monitored over a period of 42months through protein concentration, sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), isoelectric focusing, size exclusion chromatography, cytotoxicity, sterility, and pH measurements. The vialed D2C7-IT is currently being tested in a phase I/II clinical trial by intratumoral convection-enhanced delivery for 72h in patients with recurrent glioblastoma (NCT02303678, D2C7 for Adult Patients with Recurrent Malignant Glioma; clinicaltrials.gov ).

Chemo-radiotherapy free conditioning regimen: immunotoxin at its magical best

In the June, 2016 issue of Nature Biotechnology , Palchaudhury and colleagues report a novel immunotoxin-based preparative regimen that efficiently conditions immunocompetent mice for autologous hematopoietic stem cell transplantation (HSCT) (1). In comparison with total body irradiation (TBI), there was equivalent endogenous HSC depletion with similar donor chimerism, avoided neutropenia and anemia, enabled rapid immune reconstitution, better preservation of bone marrow architecture and had minimal overall toxicity.

Epidermal growth factor receptor is overexpressed in neuroblastoma tissues and cells.

Neuroblastoma is the most common abdominal malignant tumor in childhood. Immunotoxin (IT) that targets the tumor cell surface receptor is a new supplementary therapeutic treatment approach. The purpose of this study is to detect the expression of epidermal growth factor receptor (EGFR) in neuroblastoma cell lines and tissues, and to explore if IT therapy can be used to treat refractory neuroblastoma. The EGFR expression in human neuroblastoma tissue samples was detected by immunohistochemistrystaining. The positive rate of EGFR expression was 81.0% in neuroblastoma tissue and 50.0% in gangliocytoma, respectively, but without statistical significance between them (P>0.05). The positive rate of EGFR expression in favorable type and unfavorable type was 62.5% and 92.3%, respectively, but they were not statistically different (P>0.05). Results from pre-chemotherapy and post-chemotherapy samples showed that there was no significant statistical difference (P>0.05) between them in the EGFR expression. Furthermore, the EGFR expression levels in five neuroblastoma cell lines were measured using cell-based ELISA assay and western blot analysis. The results showed that the expression of EGFR was higher in KP-N-NS and BE(2)-C than those in other cell lines. Our results revealed that there are consistent and widespread expressions of EGFR in neuroblastoma tissues as well as in neuroblastoma cell lines, suggesting that it is possible to develop future treatment strategies of neuroblastoma by targeting at the EGFR.

Anti-Human Endoglin (hCD105) Immunotoxin-Containing Recombinant Single Chain Ribosome-Inactivating Protein Musarmin 1.

Endoglin (CD105) is an accessory component of the TGF-β receptor complex, which is expressed in a number of tissues and over-expressed in the endothelial cells of tumor neovasculature. Targeting endoglin with immunotoxins containing type 2 ribosome-inactivating proteins has proved an effective tool to reduce blood supply to B16 mice tumor xenografts. We prepared anti-endoglin immunotoxin (IT)—containing recombinant musarmin 1 (single chain ribosome-inactivating proteins) linked to the mouse anti-human CD105 44G4 mouse monoclonal antibody via N-succinimidyl 3-(2-pyridyldithio) propionate (SPDP). The immunotoxin specifically killed L929 fibroblast mouse cells transfected with the short form of human endoglin with IC50 values in the range of 5 × 10−10 to 10−9 M.

Engineered human angiogenin mutations in the placental ribonuclease inhibitor complex for anticancer therapy: Insights from enhanced sampling simulations.

Targeted human cytolytic fusion proteins (hCFPs) represent a new generation of immunotoxins (ITs) for the specific targeting and elimination of malignant cell populations. Unlike conventional ITs, hCFPs comprise a human/humanized target cell-specific binding moiety (e.g., an antibody or a fragment thereof) fused to a human proapoptotic protein as the cytotoxic domain (effector domain). Therefore, hCFPs are humanized ITs expected to have low immunogenicity. This reduces side effects and allows long-term application. The human ribonuclease angiogenin (Ang) has been shown to be a promising effector domain candidate. However, the application of Ang-based hCFPs is largely hampered by the intracellular placental ribonuclease inhibitor (RNH1). It rapidly binds and inactivates Ang. Mutations altering Ang's affinity for RNH1 modulate the cytotoxicity of Ang-based hCFPs. Here we perform in total 2.7 µs replica-exchange molecular dynamics simulations to investigate some of these mutations-G85R/G86R (GGRRmut ), Q117G (QGmut ), and G85R/G86R/Q117G (GGRR/QGmut ). GGRRmut turns out to perturb greatly the overall Ang-RNH1 interactions, whereas QGmut optimizes them. Combining QGmut with GGRRmut compensates the effects of the latter. Our results explain the in vitro finding that, while Ang GGRRmut -based hCFPs resist RNH1 inhibition remarkably, Ang WT- and Ang QGmut -based ones are similarly sensitive to RNH1 inhibition, whereas Ang GGRR/QGmut -based ones are only slightly resistant. This work may help design novel Ang mutants with reduced affinity for RNH1 and improved cytotoxicity.

EGFR/EGFRvIII-targeted immunotoxin therapy for the treatment of glioblastomas via convection-enhanced delivery.

Glioblastoma is the most aggressive malignant brain tumor among all primary brain and central nervous system tumors. The median survival time for glioblastoma patients given the current standard of care treatment (surgery, radiation, and chemotherapy) is less than 15 months. Thus, there is an urgent need to develop more efficient therapeutics to improve the poor survival rates of patients with glioblastoma. To address this need, we have developed a novel tumor-targeted immunotoxin (IT), D2C7-(scdsFv)-PE38KDEL (D2C7-IT), by fusing the single chain variable fragment (scFv) from the D2C7 monoclonal antibody (mAb) with the Pseudomonas Exotoxin (PE38KDEL). D2C7-IT reacts with both the wild-type epidermal growth factor receptor (EGFRwt) and EGFR variant III (EGFRvIII), two onco-proteins frequently amplified or overexpressed in glioblastomas. Surface plasmon resonance and flow cytometry analyses demonstrated a significant binding capacity of D2C7-IT to both EGFRwt and EGFRvIII proteins. In vitro cytotoxicity data showed that D2C7-IT can effectively inhibit protein synthesis and kill a variety of EGFRwt-, EGFRvIII-, and both EGFRwt- and EGFRvIII-expressing glioblastoma xenograft cells and human tumor cell lines. Furthermore, D2C7-IT exhibited a robust anti-tumor efficacy in orthotopic mouse glioma models when administered via intracerebral convection-enhanced delivery (CED). A preclinical toxicity study was therefore conducted to determine the maximum tolerated dose (MTD) and no-observed-adverse-effect-level (NOAEL) of D2C7-IT via intracerebral CED for 72 hours in rats. Based on this successful rat toxicity study, an Investigational New Drug (IND) application (#116855) was approved by the Food and Drug Administration (FDA), and is now in effect for a Phase I/II D2C7-IT clinical trial (D2C7 for Adult Patients with Recurrent Malignant Glioma, https://clinicaltrials.gov/ct2/show/NCT02303678). While it is still too early to draw conclusions from the trial, results thus far are promising.

Novel EGFR-specific immunotoxins based on panitumumab and cetuximab show in vitro and ex vivo activity against different tumor entities.

The epidermal growth factor receptor (EGFR) is overexpressed in many solid tumors. EGFR-specific monoclonal antibodies (mAbs), such as cetuximab and panitumumab, have been approved for the treatment of colorectal and head and neck cancer. To increase tissue penetration, we constructed single-chain fragment variable (scFv) antibodies derived from these mAbs and evaluated their potential for targeted cancer therapy. The resulting scFv-based EGFR-specific immunotoxins (ITs) combine target specificity of the full-size mAb with the cell-killing activity of a toxic effector domain, a truncated version of Pseudomonas exotoxin A (ETA'). The ITs and corresponding imaging probes were tested in vitro against four solid tumor entities (rhabdomyosarcoma, breast, prostate and pancreatic cancer). Specific binding and internalization of the ITs scFv2112-ETA' (from cetuximab) and scFv1711-ETA' (from panitumumab) were demonstrated by flow cytometry and for the scFv-SNAP-tag imaging probes by live cell imaging. Cytotoxic potential of the ITs was analyzed in cell viability and apoptosis assays. Binding of the ITs was proofed ex vivo on rhabdomyosarcoma, prostate and breast cancer formalin-fixed paraffin-embedded biopsies. Both novel ITs showed significant pro-apoptotic and anti-proliferative effects toward the target cells, achieving IC50 values of 4 pM (high EGFR expression) to 460 pM (moderate EGFR expression). Additionally, rapid internalization and specific in vitro and ex vivo binding on patient tissue were confirmed. These data demonstrate the potent therapeutic activity of two novel EGFR-specific ETA'-based ITs. Both molecules are promising candidates for further development toward clinical use in the treatment of various solid tumors to supplement the existing therapeutic regimes.

A novel immunotoxin – rCCK8PE38 targeting of CCK-R overexpressed colon cancers

Background: Cholecystokinin (CCK) receptors are overexpressed in numerous human cancers, such as pancreatic, colon and gastric cancers. Previous studies have shown that the specific receptor-binding property of CCK for CCK receptors (CCKRs) can be exploited to produce immunotoxins (ITs) that target cancer cells overexpressing CCK receptors.Purpose: Construct a new IT-targeting CCKR-overexpressing colon cancers.Methods: To construct the CCKR-targeted IT, a reverse CCK8 peptide was fused with a modified 38-kDa truncated form of the Pseudomonas exotoxin (PE38KDEL). An efficient immunoaffinity purification procedure was used to produce a PE38-based IT. Several analyses, including CCK8 competition and indirect immunofluorescence assays, were performed to confirm the interaction between rCCK8 and CCKR. After cytotoxic assays on several cell lines, the anti-tumor activity of the new IT was detected in nude mice.Results: The rCCK8PE38 IT showed specific cytotoxicity for two colon cancer cell lines and one gastric cancer cell line. After purification, 18–26 mg of pure rCCK8PE38 per 1 L of culture was obtained. Purified rCCK8PE38 showed high cytotoxicity in colon cancer cell lines with IC50 values of 0.8–3.5 ng/mL. The results of the CCK8 competition and indirect immunofluorescence assays showed that rCCK8 had a specific interaction with CCKR. Nude mice inoculated with HCT-8 tumor xenografts were treated with rCCK8PE38, which efficiently decreased the tumor size in those mice.Conclusions and discussion: All of these data suggest that rCCK8PE38 has potential as a new immunotherapy agent. Furthermore, the results of this study further support the high value of the immunoaffinity method for IT purification procedures.

Role of autoantibodies to various Ro60 epitopes in the decrease of lymphocytes seen in systemic lupus erythematosus and primary Sjögren’s syndrome

We investigated the roles of autoantibodies to different Ro60 epitopes in lymphopenia in systemic lupus erythematosus (SLE) and primary Sjögren's syndrome (pSS). We recruited 16 patients with SLE, 14 with pSS, and 10 healthy controls; all were female. Patients had active disease, had not received glucocorticoid or immunosuppressants for at least 3 months, and had positive laboratory tests for autoantibodies against Ro60. Patient peripheral blood lymphocyte (LC) counts were < 1 x 10(9)/L: (0.66 ± 0.12) x 10(9)/L and (0.70 ± 0.16) x 10(9)/L for SLE and pSS groups, respectively (P = 0.511). LCs from each group were cultured in vitro with each of the three immunotoxins (ITs) (AE1-3), which specifically combine with one of the three epitopes (aa482-493, aa310-323, and aa230-241, respectively) on Ro60. The cytotoxicity of each IT to the cultured LCs was measured by the MTT colorimetric method. The relationships between IT cytotoxicity and LC counts were analyzed, and autoantibodies against the three epitopes in patient peripheral blood were detected. All ITs showed cytotoxicity to control LCs; however, AE3 and AE2 showed greater toxicity to LCs from SLE and pSS groups, respectively, and the enhanced cytotoxicity was significantly associated with the respective LC counts (r = 0.653, P = 0.06; r = 0.594, P = 0.025). No difference was found in the prevalence of the autoantibodies between the SLE and pSS groups. These results suggest that autoantibodies to Ro60 might play a pathogenic role in lymphopenia in both SLE and pSS, but the pathogenic mechanisms might differ.

Triterpenoid saponin augmention of saporin-based immunotoxin cytotoxicity for human leukaemia and lymphoma cells is partially immunospecific and target molecule dependent

Context: Saponinum album (SA) is a complex mixture of triterpenoid saponins previously shown to augment the cytotoxicity of the type I ribosome-inactivating protein saporin and an EGF-saporin target toxin that could potentially be used to improve the therapeutic window of targeted toxins.Objective: To investigate the augmentative property of SA on saporin and saporin-based immunotoxins (IT) directed against five different cell surface target molecules on human leukemia and lymphoma cells.Materials and methods: After determining the optimum dose of SA for each cell line, the extent of SA-mediated augmentation was established for saporin and five saporin-based ITs using XTT and an annexin V apoptosis assay. Immunospecificity was investigated using three different blocking assays. Dose-scheduling was also investigated using the XTT assay.Results: Uncorrected SA-mediated augmentation ranged at best from 31.5 million-fold to, at worse, 174-fold. However, when the calculated fold-increases were adjusted for the non-immunospecific effects of SA on an off-target IT, the true augmentative effects of SA were found to be largely non-immunospecific. Antibody blocking studies demonstrated that the augmentative effect of SA was only partially immunospecific. Separate exposure of target cells to IT and SA at different times demonstrated that immunospecific augmentation of IT by SA could be achieved but only if cells were exposed to IT first and SA second.Conclusions: SA significantly, although variably, augments the cytotoxicity of saporin and saporin-based immunotoxins. Concomitant exposure to both IT and SA can result in non-immunospecific cytotoxicity that can be overcome by temporally separating exposure to each.

A CSPG4-specific immunotoxin kills rhabdomyosarcoma cells and binds to primary tumor tissues

The treatment of rhabdomyosarcoma (RMS) remains challenging, with metastatic and alveolar RMS offering a particularly poor prognosis. Therefore, the identification and evaluation of novel antigens, which are suitable targets for immunotherapy, is one attractive possibility to improve the treatment of this disease. Here we show that chondroitin sulfate proteoglycan 4 (CSPG4) is expressed on RMS cell lines and RMS patient material. We evaluated the immunotoxin (IT) αMCSP-ETA′, which specifically recognizes CSPG4 on the RMS cell lines RD, FL-OH1, TE-671 and Rh30. It is internalized rapidly, induces apoptosis and thus kills RMS cells selectively. We also demonstrate the specific binding of this IT to RMS primary tumor material from three different patients.

Light-triggered, efficient cytosolic release of IM7-saporin targeting the putative cancer stem cell marker CD44 by photochemical internalization.

We have used the site specific and light-depended drug delivery method photochemical internalization (PCI) to release an immunotoxin (IT), targeting the CD44 receptor, into the cytosol of target cells. The IT consisted of a pan CD44 mAb (clone IM7) bound to the ribosome inactivating protein (RIP) saporin by a biotin-streptavidin linker named IM7-saporin. PCI is based upon photosensitizing compounds localized in the membrane of endosomes and lysosomes causing membrane rupture upon illumination followed by release of the IT into the cytosol. In this in vitro study, we have used 7 different human cancer cell lines of various origins to investigate the cytotoxic effect of PCI-based targeting of the cancer stem cell (CSC) marker CD44. Epi-fluorescence microscopy shows both specific binding and uptake of the IM7-Alexa488, after 30 min and 18 h of incubation, and colocalization with the PCI-photosensitizer TPCS2a prior to light-triggered cytosolic release of the CD44-targeting IT. PCI of IM7-saporin resulted in efficient and specific cytotoxicity in CD44-expressing but not in CD44-negative cancer cells. A higher level of reactive oxygen species (ROS) was found in untreated and photodynamic therapy (PDT)-treated LNCaP (CD44(neg)) compared to that of DU145 (CD44(pos)) prostate cancer (PC) cells. This may explain the PDT-resistance observed in the DU145 cells. PCI-based targeting of CD44-expressing cancer cells gives very potent and specific cytotoxic effects and may represent a rational strategy for achieving site-selective elimination of CSCs in aggressive androgen-independent and treatment-resistant PC cells preventing cytotoxic effects on distant normal stem cells.

The Effect of CCR5 Blockade On De Novo DSA and Long-Term Graft Survival in Non-Human Primate AMR Model.

Background: Multiple lines of evidence suggest that CCR5 blockade may reduce, delay or even prevent alloantibody production. Previously, we demonstrated that depletion using anti-CD3 immunotoxin (IT) combined with Tacrolimus and Alefacept (AMR regimen) reliably induced early DSA production with antibody-mediated injury in a nonhuman primate kidney transplant model. We hypothesize that short-term CCR5 blockade (Selzentry, maraviroc) will prevent alloantibody formation and substantially promote tolerance in our nonhuman primate model of AMR after anti-CD3 immunotoxin treatment. Methods: All rhesus macaques received the AMR regimen of CD3-IT × 4 days, alefacept × 8 weeks, and tacrolimus maintenance. Five animals were assigned as positive AMR controls, four were treated with additional CCR5 blockade maraviroc (4mg/kg PO daily) for 60 days. Results: Mean graft survival was 91.8±111.2 days (n=4), which was not prolonged compared to AMR control (n=5, 59.4±22.1d). T and B cell repopulation patterns showed no difference between treatment groups. However, B cell isotype switching measured by reduction of IgM+ B cells in peripheral blood was delayed with additional maraviroc treatment.Figure: No Caption available.Two out of 4 maraviroc recipients showed no elevation of DSA. Furthermore, one animal had tacrolimus maintenance discontinued on day 180 and maintained graft function without evidence of subclinical rejection through day 287. Conclusion: Additional CCR5 blockade did not affect peripheral T and B cell numbers but reduced the kinetics of B cell isotype switching (IgM to IgG). Half of the AMR regimen-treated animals responded to additional CCR5 blockade with suppression of DSA, and long-term graft survival was achieved. These results support the translation of selective supplementation with CCR5 blockade for AMR prevention.

Immunosupression regimen to prevent immunotoxin neutralization

Immunosupression regimen to prevent immunotoxin neutralization