Evaluation of novel highly specific antibodies to cancer testis antigen Centrin-1 for radioimmunoimaging and radioimmunotherapy of pancreatic cancer

Background

Pancreatic ductal adenocarcinoma (PDAC) accounts for >90% of pancreatic malignancies, and has median survival of <6 months. There is an urgent need for diagnostic and therapeutic options for PDAC. Centrin1 (CETN1) is a novel member of Cancer/Testis Antigens, with a 25‐fold increase of CETN1 gene expression in PDX from PDAC patients. The absence of selective anti‐CETN1 antibodies is hampering CETN1 use for diagnosis and therapy. Here we report the generation of highly specific for CETN1 antibodies and their evaluation for radioimmunoimaging and radioimmunotherapy (RIT) of experimental PDAC.

Methods

The antibodies to CETN1 were generated via mice immunization with immunogenic peptide distinguishing CETN1 from CETN2. Patient tumor microarrays were used to evaluate the binding of the immune serum to PDAC versus normal pancreas. The antibodies were tested for their preferential binding to CETN1 over CETN2 by ELISA. Mice bearing PDAC MiaPaCa2 xenografts were imaged with microSPECT/CT and treated with ²¹³Bi‐ and ¹⁷⁷Lu‐labeled antibodies to CETN1.

Results

Immune serum bind to 50% PDAC cases on patient tumor microarrays with no specific binding to normal pancreas. Antibodies demonstrated preferential binding to CETN1 versus CETN2. Antibody 69‐11 localized to PDAC xenografts in mice in vivo and ex vivo. RIT of PDAC xenografts with ²¹³Bi‐labeled antibodies was effective, safe, and CETN1‐specific.

Conclusions

The results demonstrate the ability of these novel antibodies to detect CETN1 both in vitro and in vivo; as well, the RIT treatment of experimental PDAC when radiolabeled with ²¹³Bi is highly efficient and safe. Further evaluation of these novel reagents for diagnosis and treatment of PDAC is warranted.

Survival and redox activity of Friedmanniomyces endolithicus, an Antarctic endemic black meristematic fungus, after gamma rays exposure

Despite living organisms are not exposed to acute ionizing radiation under natural conditions, some exhibit a high radiation resistance. Understanding this phenomenon is important for assessing the impact of radiation-related accidents, occupational exposures and space missions. In this context, in this study we analyzed the effect of gamma rays on the Antarctic cryptoendolithic melanized fungus Friedmanniomyces endolithicus CCFEE 5208 and demonstrated its resistance to acute doses of gamma radiation (up to 400 Gy), accompanied by increase in metabolic activity.

The effect of protracted X-ray exposure on cell survival and metabolic activity of fast and slow growing fungi capable of melanogenesis

The aim of this study was to analyse how protracted exposure to X-rays delivered at low dose rates of 0.0032-0.052 kGy h^-1 affects the survival and metabolic activity of two microfungi capable of melanogenesis: fast-growing Cryptococcus neoformans (CN) and slow-growing Cryomyces antarcticus (CA). Melanized CN and CA cells survived the protracted exposure better than non-melanized ones, which was consistent with previous reports on the radioprotective role of melanin in these fungi after high dose rate exposures. The survival data were described by the linear quadratic dose response model. The XTT metabolic profiles were practically identical for melanized CN and CA with activity dose-dependent increasing: no changes in the activity of the non-melanized CN and CA were recorded by this assay. In contrast, the MTT assay, which measures the intracellular energy-related processes, recorded an increase in activity of non-melanized CN and CA cells, but not in their melanized counterparts. This could reflect intensive repair processes initiated by the non-melanized cells post exposure. This study suggests that differences in radiation responses between melanized and non-melanized fungal cells occur over a wide range of radiation dose rates.

Structure-function analysis and therapeutic efficacy of antibodies to fungal melanin for melanoma radioimmunotherapy

Metastatic melanoma remains difficult to treat despite recent approvals of several new drugs. Recently we reported encouraging results of Phase I clinical trial of radiolabeled with 188Re murine monoclonal IgM 6D2 to melanin in patients with Stage III/IV melanoma. Subsequently we generated a novel murine IgG 8C3 to melanin. IgGs are more amenable to humanization and cGMP (current Good Manufacturing Practice) manufacturing than IgMs. We performed comparative structural analysis of melanin-binding IgM 6D2 and IgG 8C3. The therapeutic efficacy of 213Bi- and 188Re-labeled 8C3 and its comparison with anti-CTLA4 immunotherapy was performed in B16-F10 murine melanoma model. The primary structures of these antibodies revealed significant homology, with the CDRs containing a high percentage of positively charged amino acids. The 8C3 model has a negatively charged binding surface and significant number of aromatic residues in its H3 domain, suggesting that hydrophobic interactions contribute to the antibody-melanin interaction. Radiolabeled IgG 8C3 showed significant therapeutic efficacy in murine melanoma, safety towards healthy melanin-containing tissues and favorable comparison with the anti-CTLA4 antibody. We have demonstrated that antibody binding to melanin relies on both charge and hydrophobic interactions while the in vivo data supports further development of 8C3 IgG as radioimmunotherapy reagent for metastatic melanoma.

Effects of radiation type and delivery mode on a radioresistant eukaryote Cryptococcus neoformans

INTRODUCTION

Most research on radioresistant fungi, particularly on human pathogens such as Cryptococcus neoformans, involves sparsely-ionizing radiation. Consequently, fungal responses to densely-ionizing radiation, which can be harnessed to treat life-threatening fungal infections, remain incompletely understood.

METHODS

We addressed this issue by quantifying and comparing the effects of densely-ionizing α-particles (delivered either by external beam or by (213)Bi-labeled monoclonal antibodies), and sparsely-ionizing (137)Cs γ-rays, on Cryptococcus neoformans.

RESULTS

The best-fit linear-quadratic parameters for clonogenic survival were the following: α = 0.24 × 10(-2) Gy(-1) for γ-rays and 1.07 × 10(-2) Gy(-1) for external-beam α-particles, and β = 1.44 × 10(-5) Gy(-2) for both radiation types. Fungal cell killing by radiolabeled antibodies was consistent with predictions based on the α-particle dose to the cell nucleus and the linear-quadratic parameters for external-beam α-particles. The estimated RBE (for α-particles vs. γ-rays) at low doses was 4.47 for the initial portion of the α-particle track, and 7.66 for the Bragg peak. Non-radiological antibody effects accounted for up to 23% of cell death.

CONCLUSIONS

These results quantify the degree of C. neoformans resistance to densely-ionizing radiations, and show how this resistance can be overcome with fungus-specific radiolabeled antibodies.

Treatment of experimental pancreatic cancer with 213-Bismuth-labeled chimeric antibody to single-strand DNA

BACKGROUND

Novel approaches to treatment of pancreatic cancer (PCa) are urgently needed. A chimeric monoclonal antibody (mAb) chTNT3 binds to single-strand DNA (ssDNA) and RNA released from the non-viable cells in fast growing tumors. Here the authors investigated whether radioimmunotherapy (RIT) using chTNT3 mAb radiolabeled with 213-Bismuth ((213)Bi) could be effective in treatment of experimental PCa.

METHODS

Two human PCa cell lines, Panc1 and MiaPaCa-2, were used for in vitro experiments. The xenografts in mice were established using MiaPaCa-2 cells. Therapy compared (213)Bi-chTNT3 (700 μCi) to gemcitabine or cisplatin, untreated controls and 'cold' chTNT3.

RESULTS

RIT abrogated the tumors growth while tumors in control groups grew aggressively. Chemotherapy was less effective than RIT and toxic to mice while RIT did not have any side effects.

CONCLUSIONS

RIT with (213)Bi-chTNT3 was safe and effective in the treatment of experimental PCa in comparison with chemotherapy. This makes α-RIT targeting ssDNA a promising modality for further development.

Radioimmunotherapy of Cryptococcus neoformans spares bystander mammalian cells

AIM

Previously, we showed that radioimmunotherapy (RIT) for cryptococcal infections using radioactively labeled antibodies recognizing the cryptococcal capsule reduced fungal burden and prolonged survival of mice infected with Cryptococcus neoformans. Here, we investigate the effects of RIT on bystander mammalian cells.

MATERIALS & METHODS

Heat-killed C. neoformans bound to anticapsular antibodies, unlabeled or labeled with the β-emitter rhenium-188 (16.9-h half-life) or the α-emitter bismuth-213 (46-min half-life), was incubated with macrophage-like J774.16 cells or epithelial-like Chinese hamster ovary cells. Lactate dehydrogenase activity, crystal violet uptake, reduction of tetrazolium dye (2,3)-bis-(2-methoxy-4-nitro-5-sulfenyl)-(2H)-terazolium-5-carboxanilide and nitric oxide production were measured.

RESULTS

The J774.16 and Chinese hamster ovary cells maintained membrane integrity, viability and metabolic activity following exposure to radiolabeled C. neoformans.

CONCLUSION

RIT of C. neoformans is a selective therapy with minimal effects on host cells and these results are consistent with observations that RIT-treated mice with cryptococcal infection lacked RIT-related pathological changes in lungs and brain tissues.

Mathematical modeling predicts enhanced growth of X-ray irradiated pigmented fungi

Ionizing radiation is known for its cytotoxic and mutagenic properties. However, recent evidence suggests that chronic sub-lethal irradiation stimulates the growth of melanin-pigmented (melanized) fungi, supporting the hypothesis that interactions between melanin and ionizing photons generate energy useful for fungal growth, and/or regulate growth-promoting genes. There are no quantitative models of how fungal proliferation is affected by ionizing photon energy, dose rate, and presence versus absence of melanin on the same genetic background. Here we present such a model, which we test using experimental data on melanin-modulated radiation-induced proliferation enhancement in the fungus Cryptococcus neoformans, exposed to two different peak energies (150 and 320 kVp) over a wide range of X-ray dose rates. Our analysis demonstrates that radiation-induced proliferation enhancement in C. neoformans behaves as a binary “on/off” phenomenon, which is triggered by dose rates <0.002 mGy/h, and stays in the “on” position. A competing dose rate-dependent growth inhibition becomes apparent at dose rates >5000 mGy/h. Proliferation enhancement of irradiated cells compared with unirradiated controls occurs at both X-ray peak energies, but its magnitude is modulated by X-ray peak energy and cell melanization. At dose rates <5000 mGy/h, both melanized and non-melanized cells exposed to 150 kVp X-rays, and non-melanized cells exposed to 320 kVp X-rays, all exhibit the same proliferation enhancement: on average, chronic irradiation stimulates each founder cell to produce 100 (95% CI: 83, 116) extra descendants over 48 hours. Interactions between melanin and 320 kVp X-rays result in a significant (2-tailed p-value = 4.8×10⁻⁵) additional increase in the number of radiation-induced descendants per founder cell: by 55 (95% CI: 29, 81). These results show that both melanin-dependent and melanin-independent mechanisms are involved in radiation-induced fungal growth enhancement, and implicate direct and/or indirect interactions of melanin with high energy ionizing photons as an important pro-proliferative factor.

Compton scattering by internal shields based on melanin-containing mushrooms provides protection of gastrointestinal tract from ionizing radiation

There is a need for radioprotectors that protect normal tissues from ionizing radiation in patients receiving high doses of radiation and during nuclear emergencies. We investigated the possibility of creating an efficient oral radioprotector based on the natural pigment melanin that would act as an internal shield and protect the tissues via Compton scattering followed by free radical scavenging. CD-1 mice were fed melanin-containing black edible mushrooms Auricularia auricila-judae before 9 Gy total body irradiation. The location of the mushrooms in the body before irradiation was determined by in vivo fluorescent imaging. Black mushrooms protected 80% of mice from the lethal dose, while control mice or those given melanin-devoid mushrooms died from gastrointestinal syndrome. The crypts of mice given black mushrooms showed less apoptosis and more cell division than those in control mice, and their white blood cell and platelet counts were restored at 45 days to preradiation levels. The role of melanin in radioprotection was proven by the fact that mice given white mushrooms supplemented with melanin survived at the same rate as mice given black mushrooms. The ability of melanin-containing mushrooms to provide remarkable protection against radiation suggests that they could be developed into oral radioprotectors.

Complement-dependent cytotoxicity of an antibody to melanin in radioimmunotherapy of metastatic melanoma

Aim: Novel treatments for metastatic melanoma are urgently needed. Materials & methods: We developed radioimmunotherapy of metastatic melanoma using 6D2 monoclonal antibody (mAb) to melanin with encouraging therapeutic results, preclinically and in patients. Results: We observed tumor suppression with the unlabeled 6D2 mAb and investigated its tumoricidal mechanisms. In melanoma tumor-bearing mice, we detected more complement-C3 deposition in the tumors from 188-rhenium-labeled 6D2 mAb-treated mice when compared with untreated controls. 6D2 and isotype-control mAb TEPC caused suppression of tumor growth in A2058 melanoma tumor-bearing mice. Tumors of mice treated with the unlabeled 6D2 mAb were infiltrated with more lymphocytes compared with controls. In vitro antibody-dependent cell-mediated cytotoxicity did not contribute to the tumor-suppressive effect of 6D2 mAb, while 6D2 mAb demonstrated a strong effect on initiating complement-dependent cytotoxicity. Conclusion: We concluded that 6D2 mAb mediated complement-dependent cytotoxicity, resulting in killing of the tumor cells and suppression of tumor growth. These observations will help to improve the treatment protocols of radioimmunotherapy, as well as immunotherapy.

Toward developing a universal treatment for fungal disease using radioimmunotherapy targeting common fungal antigens

BACKGROUND

Previously, we demonstrated the ability of radiolabeled antibodies recognizing the cryptococcal polysaccharide capsule to kill Cryptococcus neoformans both in vitro and in infected mice. This approach, known as radioimmunotherapy (RIT), uses the exquisite ability of antibodies to bind antigens to deliver microbicidal radiation. To create RIT reagents which would be efficacious against all major medically important fungi, we have selected monoclonal antibodies (mAbs) to common surface fungal antigens such as heat shock protein 60 (HSP60), which is found on the surface of diverse fungi; beta (1,3)-glucan, which is a major constituent of fungal cell walls; ceramide which is found at the cell surface, and melanin, a polymer present in the fungal cell wall.

METHODS

MAbs 4E12, an IgG2a to fungal HSP60; 2G8, an IgG2b to beta-(1,3)-glucan; and 6D2, an IgM to melanin, were labeled with the alpha particle emitting radionuclide 213-Bismuth ((213)Bi) using the chelator CHXA". B11, an IgM antibody to glucosylceramide, was labeled with the beta emitter 188-Rhenium ((188)Re). Model organisms Cryptococcus neoformans and Candida albicans were used to assess the cytotoxicity of these compounds after exposure to either radiolabeled mAbs or controls.

RESULTS

(213)Bi-mAbs to HSP60 and to the beta-(1,3)-glucan each reduced the viability of both fungi by 80-100%. The (213)Bi-6D2 mAb to melanin killed 22% of C. neoformans, but did not kill C. albicans. B11 mAb against fungal ceramide was effective against wild-type C. neoformans, but was unable to kill a mutant lacking the ceramide target. Unlabeled mAbs and radiolabeled irrelevant control mAbs caused no killing.

CONCLUSION

Our results suggest that it is feasible to develop RIT against fungal pathogens by targeting common antigens and such an approach could be developed against fungal diseases for which existing therapy is unsatisfactory.

Protection of melanized Cryptococcus neoformans from lethal dose gamma irradiation involves changes in melanin's chemical structure and paramagnetism

Certain fungi thrive in highly radioactive environments including the defunct Chernobyl nuclear reactor. Cryptococcus neoformans (C. neoformans), which uses L-3,4-dihydroxyphenylalanine (L-DOPA) to produce melanin, was used here to investigate how gamma radiation under aqueous aerobic conditions affects the properties of melanin, with the aim of gaining insight into its radioprotective role. Exposure of melanized fungal cell in aqueous suspensions to doses of γ-radiation capable of killing 50 to 80% of the cells did not lead to a detectable loss of melanin integrity according to EPR spectra of melanin radicals. Moreover, upon UV-visible (Xe-lamp) illumination of melanized cells, the increase in radical population was unchanged after γ-irradiation. Gamma-irradiation of frozen cell suspensions and storage of samples for several days at 77 K however, produced melanin modification noted by a reduced radical population and reduced photoresponse. More direct evidence for structural modification of melanin came from the detection of soluble products with absorbance maxima near 260 nm in supernatants collected after γ-irradiation of cells and cell-free melanin. These products, which include thiobarbituric acid (TBA)-reactive aldehydes, were also generated by Fenton reagent treatment of cells and cell-free melanin. In an assay of melanin integrity based on the metal (Bi⁺³) binding capacity of cells, no detectable loss in binding was detected after γ-irradiation. Our results show that melanin in C. neoformans cells is susceptible to some damage by hydroxyl radical formed in lethal radioactive aqueous environments and serves a protective role in melanized fungi that involves sacrificial breakdown.

Radioimmunotherapy is more effective than antifungal treatment in experimental cryptococcal infection

Radioimmunotherapy (RIT) prolongs the survival of mice infected with Cryptococcus neoformans. To compare the efficacy of RIT with that of amphotericin B, we infected AJ/Cr mice intravenously with either nonmelanized or melanized C. neoformans cells. Infected mice were either left untreated or treated 24 h after infection with (213)Bi-18B7 antibody, amphotericin B, or both. Melanization before infection did not increase resistance of C. neoformans to RIT in vivo. (213)Bi-18B7 treatment almost completely eliminated colony-forming units from the lung and brain, whereas amphotericin B did not decrease the number of colony-forming units. We conclude that RIT is more effective than amphotericin B against systemic infection with C. neoformans.

Abstract 5344: The contribution of unlabeled antibodies to intracellular antigens to efficacy of radioimmunotherapy in experimental metastatic melanoma and cervical cancer

Introduction: Radioimmunotherapy (RIT) targeting intracellular antigens released in rapidly growing tumors as a result of a cellular turnover is an attractive modality for treatment of aggressive solid tumors. We are developing RIT for metastatic melanoma and HPV-related cervical cancer by targeting the intracellular antigens melanin and E6 oncoprotein, respectively, with radiolabeled specific antibodies (mAbs). In prior studies we observed that administration of unlabeled mAbs to melanin and E6 alone to tumor-bearing mice caused retardation of tumor growth.

Objective: To investigate the immunological mechanisms by which unlabeled mAbs to intracellular antigens melanin and E6 oncoprotein contribute to the efficacy of RIT of melanoma and cervical cancer.

Methods: The CasKi human cervical tumors and A2058 human metastatic melanoma tumors were induced in female nude mice and when the tumors diameter reached 0.5-0.7 cm, the mice with cervical tumors were treated with C1P5 mAb (IgG1 isotype) to E6 or isotype-matching control mAbs, or left untreated; and mice with melanoma tumors were given 6D2 mAb (IgM isotype) to melanin or isotype matching control mAbs; or left untreated. The tumor growth was monitored for 30 days. On day 5 and 10 post-treatment 4 mice out of each group were sacrificed and their tumors analyzed for C3 complement by Western blot and immunohistochemistry (IHC). On day 10 the tumors were analyzed by flow cytometry for the infiltration by inflammatory cells.

Results: There was significant retardation of melanoma and cervical tumor growth during the observation period by 6D2 mAb to melanin and C1P5 mAb to E6 compared with untreated controls (P&lt;0.05). For both types of tumors the isotype-matching control mAbs had the same in magnitude effect on the tumor growth as specific mAbs (P&gt;0.05). On days 5 and 10 C3 complement deposition was observed by Western blot and IHC in specific and non-specific mAbs-treated tumors but not in the untreated controls. The expression of C3 was more prominent on day 10. On day 10 there was infiltration of mAb-treated melanoma and cervical tumors by CD45+, CD4+ and CD8+ inflammatory cells with their levels being 30-100% greater than in untreated tumors.

Conclusions: Our results of the treatment of melanoma and cervical tumors with unlabeled mAbs to intracellular antigens suggest that these mAbs can initiate complement dependent toxicity (CDC) and antibody dependent cellular toxicity (ADCC). The effect of mAbs did not depend on a mAb specificity for a particular antigen. It appeared to be dependent on the affinity of the Fc portion of mAbs for C1q molecule (CDC case) or for the Fc receptors on inflammatory cells (ADCC case). Further investigation of the contribution of unlabeled mAbs to efficacy of RIT will help to design effective treatment regiments for patients with metastatic melanoma and cervical cancer.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5344.

Physico-chemical evaluation of rationally designed melanins as novel nature-inspired radioprotectors

Background

Melanin, a high-molecular weight pigment that is ubiquitous in nature, protects melanized microorganisms against high doses of ionizing radiation. However, the physics of melanin interaction with ionizing radiation is unknown.

Methodology/Principal Findings

We rationally designed melanins from either 5-S-cysteinyl-DOPA, L-cysteine/L-DOPA, or L-DOPA with diverse structures as shown by elemental analysis and HPLC. Sulfur-containing melanins had higher predicted attenuation coefficients than non-sulfur-containing melanins. All synthetic melanins displayed strong electron paramagnetic resonance (2.14·10¹⁸, 7.09·10¹⁸, and 9.05·10¹⁷ spins/g, respectively), with sulfur-containing melanins demonstrating more complex spectra and higher numbers of stable free radicals. There was no change in the quality or quantity of the stable free radicals after high-dose (30,000 cGy), high-energy (¹³⁷Cs, 661.6 keV) irradiation, indicating a high degree of radical stability as well as a robust resistance to the ionizing effects of gamma irradiation. The rationally designed melanins protected mammalian cells against ionizing radiation of different energies.

Conclusions/Significance

We propose that due to melanin's numerous aromatic oligomers containing multiple π-electron system, a generated Compton recoil electron gradually loses energy while passing through the pigment, until its energy is sufficiently low that it can be trapped by stable free radicals present in the pigment. Controlled dissipation of high-energy recoil electrons by melanin prevents secondary ionizations and the generation of damaging free radical species.

The radioprotective properties of fungal melanin are a function of its chemical composition, stable radical presence and spatial arrangement

Melanized microorganisms are often found in environments with very high background radiation levels such as in nuclear reactor cooling pools and the destroyed reactor in Chernobyl. These findings and the laboratory observations of the resistance of melanized fungi to ionizing radiation suggest a role for this pigment in radioprotection. We hypothesized that the radioprotective properties of melanin in microorganisms result from a combination of physical shielding and quenching of cytotoxic free radicals. We have investigated the radioprotective properties of melanin by subjecting the human pathogenic fungi Cryptococcus neoformans and Histoplasma capsulatum in their melanized and non-melanized forms to sublethal and lethal doses of radiation of up to 8 kGy. The contribution of chemical composition, free radical presence, spatial arrangement, and Compton scattering to the radioprotective properties of melanin was investigated by high-performance liquid chromatography, electron spin resonance, transmission electron microscopy, and autoradiographic techniques. Melanin protected fungi against ionizing radiation and its radioprotective properties were a function of its chemical composition, free radical quenching, and spherical spatial arrangement.

Comparative evaluation of capsular polysaccharide-specific IgM and IgG antibodies and F(ab')2 and Fab fragments as delivery vehicles for radioimmunotherapy of fungal infection

PURPOSE

The applicability of radioimmunotherapy with organism-specific monoclonal antibodies to treatment of infectious disease in experimental models has been recently shown for fungal, bacterial, and viral infections. To identify the best delivery vehicle for radioimmunotherapy of human pathogenic fungus Cryptococcus neoformans (CN), we have done comparative evaluation of capsular polysaccharide-specific antibodies with IgG1 and IgM isotypes and F(ab')2 and Fab fragments.

EXPERIMENTAL DESIGN

18B7 IgG1 and 13F1 IgM and their isotype-matching controls were radiolabeled with 188Re, and their binding to 24067 and H99 CN strains was evaluated by doing Scatchard and kinetics analyses. The doses delivered during in vitro radioimmunotherapy were estimated using a cellular dosimetry algorithm. The biodistribution of 188Re-labeled 18B7 and 13F1 and of 111In-labeled 18B7 and its F(ab')2 and Fab fragments was done in A/JCr mice systemically infected with 24067 CN strain.

RESULTS

18B7 IgG1 showed superior to 13F1 IgM binding to 24067 CN (Ka=1.7x10(9) mol/L(-1) and 5.4x10(7) mol/L(-1), respectively). Substantial killing of 24067 and H99 CN cells was achieved with 1 microCi 188Re-18B7 (55 cGy dose), whereas no killing was observed for 1 microCi 188Re-13F1 (2 cGy dose). In vivo 188Re-18B7 localized specifically in the lungs of CN-infected mice, whereas uptake of 188Re-13F1 was nonspecific. 111In-F(ab')2 fragments showed higher uptake in the lungs and lower in the liver at the 48-h time point in comparison with intact 111In-18B7.

CONCLUSIONS

Comparative evaluation of IgG and IgM and of F(ab')2 and Fab fragments as potential delivery vehicles for radioimmunotherapy of cryptococcal infection strongly suggests that affinity for the target antigen is an important prerequisite for successful targeting of infection in vivo and that in vitro affinity measurements may predict the in vivo efficacy of candidate monoclonal antibodies.

Treating cancer as an infectious disease--viral antigens as novel targets for treatment and potential prevention of tumors of viral etiology

Background

Nearly 20% of human cancers worldwide have an infectious etiology with the most prominent examples being hepatitis B and C virus-associated hepatocellular carcinoma and human papilloma virus-associated cervical cancer. There is an urgent need to find new approaches to treatment and prevention of virus-associated cancers.

Methodology/Principal Findings

Viral antigens have not been previously considered as targets for treatment or prevention of virus-associated cancers. We hypothesized that it was possible to treat experimental HPV16-associated cervical cancer (CC) and Hepatitis B-associated hepatocellular carcinoma (HCC) by targeting viral antigens expressed on cancer cells with radiolabeled antibodies to viral antigens. Treatment of experimental CC and HCC tumors with ¹⁸⁸Re-labeled mAbs to E6 and HBx viral proteins, respectively, resulted in significant and dose-dependent retardation of tumor growth in comparison with untreated mice or mice treated with unlabeled antibodies.

Conclusions/Significance

This strategy is fundamentally different from the prior uses of radioimmunotherapy in oncology, which targeted tumor-associated human antigens and promises increased specificity and minimal toxicity of treatment. It also raises an exciting possibility to prevent virus-associated cancers in chronically infected patients by eliminating cells infected with oncogenic viruses before they transform into cancer.

Ionizing radiation changes the electronic properties of melanin and enhances the growth of melanized fungi

Background

Melanin pigments are ubiquitous in nature. Melanized microorganisms are often the dominating species in certain extreme environments, such as soils contaminated with radionuclides, suggesting that the presence of melanin is beneficial in their life cycle. We hypothesized that ionizing radiation could change the electronic properties of melanin and might enhance the growth of melanized microorganisms.

Methodology/Principal Findings

Ionizing irradiation changed the electron spin resonance (ESR) signal of melanin, consistent with changes in electronic structure. Irradiated melanin manifested a 4-fold increase in its capacity to reduce NADH relative to non-irradiated melanin. HPLC analysis of melanin from fungi grown on different substrates revealed chemical complexity, dependence of melanin composition on the growth substrate and possible influence of melanin composition on its interaction with ionizing radiation. XTT/MTT assays showed increased metabolic activity of melanized C. neoformans cells relative to non-melanized cells, and exposure to ionizing radiation enhanced the electron-transfer properties of melanin in melanized cells. Melanized Wangiella dermatitidis and Cryptococcus neoformans cells exposed to ionizing radiation approximately 500 times higher than background grew significantly faster as indicated by higher CFUs, more dry weight biomass and 3-fold greater incorporation of ¹⁴C-acetate than non-irradiated melanized cells or irradiated albino mutants. In addition, radiation enhanced the growth of melanized Cladosporium sphaerospermum cells under limited nutrients conditions.

Conclusions/Significance

Exposure of melanin to ionizing radiation, and possibly other forms of electromagnetic radiation, changes its electronic properties. Melanized fungal cells manifested increased growth relative to non-melanized cells after exposure to ionizing radiation, raising intriguing questions about a potential role for melanin in energy capture and utilization.

Antibody-guided alpha radiation effectively damages fungal biofilms

The use of indwelling medical devices--pacemakers, prosthetic joints, catheters--is rapidly growing and is often complicated by infections with biofilm-forming microbes that are resistant to antimicrobial agents and host defense mechanisms. We investigated for the first time the use of microbe-specific monoclonal antibodies (MAbs) as delivery vehicles for targeting biofilms with cytocidal radiation. MAb 18B7 (immunoglobulin G1 [IgG1]), which binds to capsular polysaccharides of the human pathogenic fungus Cryptococcus neoformans, penetrated cryptococcal biofilms, as shown by confocal microscopy. When the alpha radiation-emitter 213-Bismuth ((213)Bi) was attached to MAb 18B7 and the radiolabeled MAb was added to C. neoformans biofilms, there was a 50% reduction in biofilm metabolic activity. In contrast, when the IgM MAb 13F1 labeled with (213)Bi was used there was no penetration of the fungal biofilm and no damage. Unlabeled 18B7, (213)Bi-labeled nonspecific MAbs, and gamma and beta types of radiation did not have an effect on biofilms. The lack of efficacy of gamma and beta radiation probably reflects the radioprotective properties of polysaccharide biofilm matrix. Our results indicate that C. neoformans biofilms are susceptible to treatment with antibody-targeted alpha radiation, suggesting a novel option for the prevention or treatment of microbial biofilms on indwelling medical devices.

Interaction of radiolabeled antibodies with fungal cells and components of the immune system in vitro and during radioimmunotherapy for experimental fungal infection

BACKGROUND

The usefulness of radioimmunotherapy (RIT) for infectious diseases was recently demonstrated for several fungal and bacterial infections, but the mechanisms by which RIT is effective against microbes are uncertain.

METHODS

We investigated the interaction between polysaccharide capsule-binding 18B7 monoclonal antibodies (MAbs) labeled with alpha-emitter 213Bi and Cryptococcus neoformans cells as well as between 213Bi-18B7 and components of immune system, both in vitro and in vivo.

RESULTS

For 213Bi-18B7, the microbicidal effect was predominantly due to "direct-hit" killing, with some contribution from the "crossfire" effect. The efficacy of cell killing correlated with the binding capacity of the MAb to the capsule and was dependent on the MAb isotype. RIT also promoted the apoptosis-like death of fungal cells. Cooperation was observed in vitro between the antifungal activity of macrophages and RIT, suggesting the potential for synergistic action in vivo. RIT was associated with changes in concentration of the cytokines interleukin (IL)-2, IL-4, IL-10, tumor necrosis factor-alpha, and interferon-gamma, suggesting that the therapeutic effects of RIT may result from changes in the inflammatory response.

CONCLUSIONS

The present results suggest that the antimicrobial efficacy of RIT involves killing through promotion of fungal cell apoptosis-like death, reduction in yeast capsule size, cooperation with macrophages, and modulation of the inflammatory response.

The polysaccharide capsule of the pathogenic fungus Cryptococcus neoformans enlarges by distal growth and is rearranged during budding

The capsule of Cryptococcus neoformans can undergo dramatic enlargement, a phenomenon associated with virulence. A prior study that used Ab to the capsule as a marker for older capsular material concluded that capsule growth involved the intermixing of new and old capsular material with displacement of older capsular polysaccharide towards the surface. Here we have revisited that question using complement (C), which binds to capsular polysaccharide covalently, and cannot redistribute by dissociation and binding at different sites. The experimental approach involved binding of C to cells with small capsules, inducing capsule growth, and following the location of C relative to the cell wall as the capsule enlarged. C remained close to the cell wall during capsule growth, indicating that capsule enlargement occurred by addition of new polysaccharide near the capsule edge. This conclusion was confirmed by an independent method that employed radioactive metabolic labelling of newly synthesized capsule with 3H-mannose followed by gradual capsular stripping with gamma-radiation. Capsule growth proceeded to a certain size, which was a function of cell size, and was not degraded when the cells were transferred to a non-inducing medium. During budding, an opening appeared in the capsule of the mother cell that permitted the nascent bud to separate. Scanning EM suggested that a physical separation formed between the capsules of the mother and daughter cells during budding, which may avoid mixture between both capsules. Our results indicate that C. neoformans capsular enlargement also occurs by apical growth and that budding results in capsular rearrangements.

Radiolabeled Melanin-Binding Peptides Are Safe and Effective in Treatment of Human Pigmented Melanoma in a Mouse Model of Disease

The incidence of melanoma is rising, and therapeutic options for metastatic melanoma are limited. We report the results of experimental melanoma therapy with 188-Rhenium-labeled melanin-binding decapeptide ((188)RE-HYNIC-4B4) and a comprehensive safety evaluation of this treatment. (188)RE-HYNIC- 4B4 bound only to nonviable eumelanotic MNT1 and pheomelanotic SK-28-MEL human melanoma cells in vitro, as determined by immunofluorescence, which is consistent with the inaccessibility of intracellular melanin in live cells, and suggests specificity for tumors with a significant amount of extracellular melanin. Administration of 1 mCi (188)RE-HYNIC-4B4 to MNT1 tumor-bearing mice significantly slowed tumor growth, with the therapeutic effect being a result of specific binding to tumor melanin, as irrelevant (188)RE-labeled decapeptide did not produce therapeutic gain. Repeated doses of (188)RE-HYNIC-4B4 had a more profound effect on tumor growth than a single dose. Treatment of tumors with 0.3-0.4 cm diameter was more effective than of larger ones (0.5-0.7 cm). There was no difference in uptake of (188)REHYNIC- 4B4 in melanized tissues of black C57BL6 mice and no histologically apparent damage to these tissues in comparison with white BALB/C mice. Treatment of C57BL6 mice with (188)RE-HYNIC-4B4 did not change their behavior, as established by SHIRPA protocol, and did not cause damage to neurons and glial cells. These results indicate that radiolabeled melanin-binding peptides are efficient and safe in treatment of melanoma and could be potentially useful against this tumor.

Radiological studies reveal radial differences in the architecture of the polysaccharide capsule of Cryptococcus neoformans

The polysaccharide capsule of the pathogenic fungus Cryptococcus neoformans is an important virulence factor, but relatively little is known about its architecture. We applied a combination of radiological, chemical, and serological methods to investigate the structure of this polysaccharide capsule. Exposure of C. neoformans cells to gamma radiation, dimethyl sulfoxide, or radiolabeled monoclonal antibody removed a significant part of the capsule. Short intervals of gamma irradiation removed the outer portion of the cryptococcal capsule without killing cells, which could subsequently repair their capsules. Survival analysis of irradiated wild-type, acapsular mutant, and complemented mutant strains demonstrated that the capsule contributed to radioprotection and had a linear attenuation coefficient higher than that of lead. The capsule portions remaining after dimethyl sulfoxide or gamma radiation treatment were comparable in size, 65 to 66 microm3, and retained immunoreactivity for a monoclonal antibody to glucuronoxylomannan. Simultaneous or sequential treatment of the cells with dimethyl sulfoxide and radiation removed the remaining capsule so that it was not visible by light microscopy. The capsule could be protected against radiation by either of the free radical scavengers ascorbic acid and sorbitol. Sugar composition analysis of polysaccharide removed from the outer and inner parts of the capsule revealed significant differences in glucuronic acid and xylose molar ratios, implying differences in the chemical structure of the constituent polysaccharides. Our results provide compelling evidence for the existence of two zones in the C. neoformans capsule that differ in susceptibility to dimethyl sulfoxide and radiation and, possibly, in packing and composition.

Retrospective analysis of factors influencing the eruption of delayed permanent incisors after supernumerary tooth removal

AIM

This was to assess the predictability of eruption of delayed permanent incisors after supernumerary removal and creation of adequate space, in relation to: root maturity, degree of vertical impaction, and degree of angulation of impaction.

METHODS

The dental records of children with supernumerary teeth delaying the eruption of permanent incisors were analysed. The type of a supernumerary tooth, its location and position were recorded, along with the stage of root maturation, angulation and vertical distance of impaction of the permanent incisor. At the initial surgery, the unerupted supernumerary tooth and any retained primary incisors were removed. The unerupted permanent incisor was not exposed. If necessary, the maxillary primary canines were removed to create sufficient space for eruption of the delayed permanent tooth. A secondary surgical procedure was planned after 18 months if there was no significant progress of the permanent tooth towards eruption.

STATISTICS

All data were entered onto a Microsoft Excel spread sheet and analysed using Fisher's Exact Tests throughout due to the small numbers.

RESULTS

Sixty-six supernumerary teeth were removed, 22 from boys and 44 from girls with ages ranging from 6 to 10 years 6 months at the time of surgery. Primary canines were extracted in 59.1% of cases. Spontaneous eruption occurred in 89.4% of delayed permanent teeth. The mean time to eruption was 9.2 months (median = 7 months). There was no statistically significant association between tooth eruption and root maturity or the degree of vertical impaction. There was an association between eruption and the degree of the angle of impaction of the permanent incisor (p<0.05).

CONCLUSION

The majority of delayed permanent teeth erupt spontaneously if sufficient space is available or created at the time of removal of the unerupted supernumerary. The angulation of impaction of the permanent incisor is associated with a delay in eruption.

Feasibility of radioimmunotherapy of experimental pneumococcal infection

Streptococcus pneumoniae is an important cause of community-acquired pneumonia, meningitis, and bacteremia. The problem of pneumococcal disease is exacerbated by increasing drug resistance. Furthermore, patients with impaired immunity are at high risk for invasive pneumococcal infections. Thus, there is an urgent need for new approaches to antimicrobial therapy. Antibody therapies take advantage of the specificity and high affinity of the antigen-antibody interaction to deliver antibacterial compounds to a site of infection in the form of naked or conjugated antibodies. We have recently established that radioimmunotherapy (RIT) can be used to treat experimental fungal infections in mice. In the present study, we investigated the feasibility of applying a RIT approach to the treatment of S. pneumoniae infection by evaluating the susceptibility of S. pneumoniae to radiolabeled antibody in vitro and in an animal infection model. For the specific antibody carrier, we used human monoclonal antibody D11, which binds to pneumococcal capsular polysaccharide 8. We have selected the alpha particle emitter (213)Bi as the radionuclide for conjugation to the antibody. Incubation of serotype 8 S. pneumoniae with (213)Bi-D11 resulted in dose-dependent killing of bacteria. RIT of S. pneumoniae infection in C57BL/6 mice showed that 60% more mice survived in the (213)Bi-D11-treated group (80 micro Ci) than in the untreated group (P < 0.01). The treatment did not cause hematological toxicity, as demonstrated by platelet counts. This feasibility study establishes that RIT can be applied to the treatment of bacterial infections.

Evaluation of acute hematologic and long-term pulmonary toxicities of radioimmunotherapy of Cryptococcus neoformans infection in murine models

We evaluated acute hematological and long-term pulmonary toxicity of radioimmunotherapy in murine models of Cryptococcus neoformans infection. Activities up to 250 microCi were well tolerated by healthy A/JCr mice for (213)Bi-18B7 and (188)Re-18B7 monoclonal antibodies. In infected mice, doses up to 150 microCi produced only transient toxicity. The lungs of treated mice had no evidence of radiation fibrosis.

Susceptibility of the human pathogenic fungi Cryptococcus neoformans and Histoplasma capsulatum to gamma-radiation versus radioimmunotherapy with alpha- and beta-emitting radioisotopes

Fungal diseases are difficult to treat in immunosuppressed patients and, consequently, new approaches to therapy are urgently needed. One novel strategy is to use radioimmunotherapy (RIT) with fungal-binding monoclonal antibodies (mAbs) labeled with radionuclides. However, many fungi manifest extreme resistance to gamma-radiation, such that the doses of several thousand gray are required for 90% cell killing, whereas for mammalian cells the lethal dose is only a few gray. We compared the susceptibility of human pathogenic fungi Cryptococcus neoformans (CN) and Histoplasma capsulatum (HC) to external gamma-radiation and to the organism-specific mAbs 18B7 and 9C7, respectively, conjugated to (213)Bi and (188)Re radionuclides.

METHODS

CN and HC cells were irradiated with up to 8,000 Gy ((137)Cs source, 30 Gy/min). RIT of CN with (213)Bi- and (188)Re-labeled specific mAb and of HC with (188)Re-labeled specific mAb used 0-1.2 MBq per 10(5) microbial cells. After irradiation or RIT, the cells were plated for colony-forming units (CFUs). Cellular dosimetry calculations were performed, and the pathway of cell death after irradiation was evaluated by flow cytometry.

RESULTS

Both CN and HC proved to be extremely resistant to gamma-radiation such that significant killing was observed only for doses of >4,000 Gy. In contrast, these cells were much more susceptible to killing by radiation delivered with a specific mAb, such that a 2-logarithm reduction in colony numbers was achieved by incubating them with (213)Bi- and (188)Re-labeled mAb 18B7 or with (188)Re-9C7 mAb. Dosimetry calculations showed that RIT was approximately 1,000-fold more efficient in killing CN and approximately 100-fold more efficient in killing HC than gamma-radiation. Both gamma-radiation and RIT caused cell death via an apoptotic-like pathway with a higher percentage of apoptosis observed in RIT-treated cells.

CONCLUSION

Conjugating a radioactive isotope to a fungal-specific antibody converted an immunoglobulin with no antifungal activity into a microbicidal molecule. RIT of fungal cells using specific antibodies labeled with alpha- and beta-emitting radioisotopes was significantly more efficient in killing CN and HC than gamma-radiation when based on the mean absorbed dose to the cell. These results strongly support the concept of using RIT as an antimicrobial modality.

Ionizing radiation delivered by specific antibody is therapeutic against a fungal infection

There is an urgent need for new antimicrobial therapies to combat drug resistance, new pathogens, and the relative inefficacy of current therapy in compromised hosts. Ionizing radiation can kill microorganisms quickly and efficiently, but this modality has not been exploited as a therapeutic antimicrobial strategy. We have developed methods to target ionizing radiation to a fungal cell by labeling a specific mAb with the therapeutic radioisotopes Rhenium-188 and Bismuth-213. Radiolabeled antibody killed cells of human pathogenic fungus Cryptococcus neoformans in vitro, thus converting an antibody with no inherent antifungal activity into a microbicidal molecule. Administration of radiolabeled antibody to mice with C. neoformans infection delivered 213Bi and 188Re to the sites of infection, reduced their organ fungal burden, and significantly prolonged their survival without apparent toxicity. This study establishes the principle that targeted radiation can be used for the therapy of an infectious disease, and suggests that it may have wide applicability as an antimicrobial strategy.

Dental disease and caries related microflora in children with dystrophic epidermolysis bullosa

PURPOSE

The purpose of this study was to investigate dental caries, bacterial dental plaque, gingivitis and caries related oral microflora in children with predominantly autosomal recessive Dystrophic Epidermolysis Bullosa (DEB).

METHODS

Thirty children with DEB from The Great Ormond Street Hospital for Children and 31 control children matched for age, gender and ethnicity were included in the study.

RESULTS

The main findings were: 1. A significantly greater mean dmft in the DEB children (p < 0.05). 2. A significantly greater mean plaque score for the DEB children for both the primary (p < 0.001) and permanent teeth (p < 0.02) compared with the control children. 3. A significantly greater mean gingivitis score for the DEB children for both the primary (p < 0.002) and permanent teeth (p < 0.0001) compared with the control children. 4. A significantly greater salivary total anaerobic count for the control children compared with the DEB children (p < 0.001).

CONCLUSIONS

The results reflect the difficulties that children with DEB have with basic oral hygiene procedures combined with slow oral clearance.

Control of synthesis and positioning of a Caulobacter crescentus flagellar protein

The Caulobacter crescentus flagellum is assembled during a defined time period in the cell cycle. Two genes encoding the major components of the flagellar filament, the 25K and the 27.5K flagellins, are expressed coincident with flagellar assembly. A third gene, flgJ, is also temporally regulated. The synthesis of the product of flgJ, the 29K flagellin, occurs prior to the synthesis of the other flagellin proteins. We demonstrate here that the time of initiation of flgJ expression is independent of chromosomal location but is dependent upon cis-acting sequences present upstream of the flgJ structural gene. Evidence that there is transcriptional control of flgJ expression includes the following: (1) The initial appearance of flgJ message was coincident with the onset of 29K flagellin protein synthesis, and (2) expression of an NPT II reporter gene driven by the flgJ promoter was temporally correct. Post-transcriptional regulation might contribute to the control of expression, because the flgJ mRNA persisted for a longer period of time than did the synthesis of the 29K protein. The 29K flagellin was found only in the progeny swarmer cell after cell division. In a mutant strain that failed to assemble a flagellum, the 29K flagellin still segregated to the presumptive swarmer cell, demonstrating that positioning of the protein is independent of filament assembly. Analysis of a chimeric flgJ-NPT II transcriptional fusion showed that the flgJ regulatory sequences do not control the segregation of the 29K flagellin to the swarmer cell progeny, suggesting that correct segregation depends on the protein product.

Effect of 2, 3-diphosphoglycerate on the solubility of deoxy-sickle hemoglobin

We have examined the effect of 2, 3-diphosphoglycerate (DPG) on the solubility of deoxy-sickle hemoglobin (deoxy-Hb S) under conditions such that concentration, pH, and osmolarity of deoxy-Hb S solutions approached physiological. The range of DPG/Hb molar ratios encompassed the extremes found for this ratio in erythrocytes from individuals with sickle cell anemia. After monomer-polyer equilibrium had been established, the phases were separated by centrifugation and assayed for concentrations of Hb and DPG. DPG had no effect on the solubility of deoxy-Hb S. Furthermore, at DPG/Hb molar ratios less than one, there was no preferential incorporation of deoxy-Hb S containing bound DPG into polymers. At DPG/Hb molar ratios greater than one, concentrations of free DPG in monomer and polymer phases were virtually identical. Thus, under the specified equilibrium conditions, DPG is not a determining factor in the polymerization of deoxy-Hb S.