The equine herpes virus 4 thymidine kinase is a better suicide gene than the human herpes virus 1 thymidine kinase.

The herpes simplex virus type 1 thymidine kinase suicide gene (HSV1tk) together with ganciclovir (GCV) have been successfully used for in vivo treatment of various experimental tumors, and many clinical trials using this system have been launched. With the aim to improve this therapeutic system, we compared the potential efficacy of different herpes virus derived thymidine kinases (HSV1, varicella-zoster virus, equine herpes virus type-4 and Epstein-Barr virus) as suicide genes in association with the nucleoside analogs acyclovir, ganciclovir and bromovinyldeoxyur- idine. Using various murine and human cell lines expressing these viral tk, we show that HSV1- and EHV4tk are the more efficient suicide genes for the different nucleoside analogs tested. Moreover, EHV4tk expressing murine and human cells were three- to 12-fold more sensitive to GCV than HSV1tk expressing cells. This was correlated with the presence of five-fold higher amounts of the toxic triphosphated-GCV in EHV4- versus HSV1tk expressing cells. Altogether, these experiments underline the potential advantages of the EHV4tk as a suicide gene.     

Optimizing prostate cancer suicide gene therapy using herpes simplex virus thymidine kinase active site variants

The herpes simplex virus (HSV) thymidine kinase gene (tk) forms the basis of a widely used strategy for suicide gene therapy. A library of HSV thymidine kinase enzyme (TK) active site mutants having different affinities for guanosine analog prodrugs was developed. We sought to determine the optimal combination of tk variant and prodrug specifically for prostate cancer gene therapy, using in vitro and in vivo studies of adenovirally infected CL1, DU-145, and LNCaP tumor lines carrying wild-type tk, tk30, tk75, and sr39tk mutants expressed by a strong, constitutive cytomegalovirus promoter and treated with ganciclovir and acyclovir. In vitro experiments involving prostate cancer (CaP) cell line infection were carried out with a broad range of prodrug concentrations, and cell killing was determined by limiting dilution (colony-forming), MTT, and propidium iodide assays. In vivo studies based on CL1-GFP xenograft experiments were carried out to examine the ability of each TK variant to prevent tumor formation and to inhibit tumor growth and development of metastases in established orthotopic and subcutaneous tumors in SCID mice. Both in vitro and in vivo studies suggest improved killing with the sr39tk variant. Thus, the results suggest that the use of sr39tk in future trials of prostate cancer tk suicide gene therapy may be beneficial.     

Specific inhibitors of herpes simplex virus thymidine kinase diminish reactivation of latent virus from explanted murine ganglia.

Two specific inhibitors of herpes simplex virus thymidine kinase, N2-phenyl-2'-deoxyguanosine and N2-(m-trifluoromethylphenyl)guanine, were tested for their ability to inhibit the reactivation of virus from explant cultures of latently infected murine trigeminal ganglia. Both compounds significantly diminished the frequency of reactivation compared with that of untreated controls.     

Hydroxyurea significantly enhances tumor growth delay in vivo with herpes simplex virus thymidine kinase/ganciclovir gene therapy

We have previously demonstrated with several cell lines in vitro that hydroxyurea (HU) synergistically enhances ganciclovir (GCV)-mediated cytotoxicity in bystander cells. In this study, we evaluated the role of DNA synthesis inhibition on enhanced bystander killing and assessed whether addition of HU would improve the efficacy of the HSV-TK/GCV system in vivo. Compared with GCV treatment alone, addition of HU resulted in increased DNA synthesis inhibition and delayed progression through S phase following removal of drug. In a xenograft tumor model, 1:10 and 1:1 mixtures of HSVtk- and LacZ-expressing SW620 cells were injected s.c. in the flanks of nude mice and treated i.p. (100 mg/kg GCV, 1500 mg/kg HU) daily for 5 days. Tumors from mice treated with GCV alone grew rapidly and increased to 10 times their initial size in 15.7 +/- 1.8 and 16.0 +/- 0.9 days for 1:10 and 1:1 mixtures, respectively. However, when both GCV and HU were administered in combination, a single complete tumor regression was observed in both the 1:10 and 1:1 groups. In the remaining mice treated with GCV/HU, it took 23.2 +/- 2.1 (1:10) and 26.4 +/- 3.8 days (1:1) to obtain a similar 10-fold increase in tumor size.     

Complete cure of established murine hepatocellular carcinoma is achievable by repeated injections of retroviruses carrying the herpes simplex virus thymidine kinase gene.

Although xenotransplantation of retrovirus-producing cells into a tumor has been shown to be effective for the treatment of cancer, injections of recombinant retroviruses are much more feasible for clinical applications. We established a clone producing retroviruses carrying the herpes simplex virus thymidine kinase (HSVtk) gene with titers of up to 4 x 10(7) colony-forming units/ml, and examined the effectiveness of in vivo gene therapy against cancer. Syngeneic mice were inoculated subcutaneously with murine hepatocellular carcinoma (HCC) cells, BNL1ME A.7R.1, and the treatment was initiated after tumors were established. When mice were given an intratumoral injection of HSVtk-carrying retroviruses or their producing cells followed by ganciclovir (GCV) treatment, significantly prolonged survival periods were observed. When mice were treated with repeated intratumoral injections of HSVtk-carrying retrovirus-producing cells, significant antitumor responses and some cures were induced by GCV treatment. Furthermore, repeated intratumoral injections of HSVtk-carrying retroviruses and GCV treatment resulted in complete regression of established HCC tumors in all animals used in the experiment. Mice that completely eradicated tumors exhibited protective immunity against wild-type HCC tumors. These results suggest that repeated injections of HSVtk-carrying retroviruses followed by GCV treatment is a potent modality for the treatment of solid tumors.     

Liposomal encapsulation of ganciclovir enhances the efficacy of herpes simplex virus type 1 thymidine kinase suicide gene therapy against hepatic tumors in rats.

Suicide gene therapy based on ganciclovir (GCV) metabolism by transgene herpes simplex thymidine kinase (HSV-1 TK) has been used to selectively kill proliferating cells in clinical settings such as cancer, vascular restenosis, and immunological disorders. We investigated whether encapsulation of ganciclovir (GCV) into liposomes would improve its efficacy, especially against hepatic tumors. Large unilamellar liposomes containing GCV were prepared by reversed-phase evaporation. Pharmacokinetic studies in rats showed that, compared with free GCV, the intravenous injection of liposome-encapsulated GCV (lip-GCV) led to a faster decrease in GCV plasma concentrations, but higher liver-blood ratios. After treatment of syngeneic HSV-1 TK+ liver metastases in rats, histologically active tumors were found in 95% of the transplanted lesions when physiological saline had been given and in 50% when free GCV had been given at 90.2 microM/kg twice daily. This dose is known to be insufficient for the eradication of HSV-1 TK+ tumors. In contrast, only 5% viable tumors were found in rats receiving lip-GCV at this same concentration. Average tumor volumes were 19 +/- 15, 7 +/- 9, and <1 mm3 for the control, free GCV, and lip-GCV groups, respectively. GCV-related toxicity was no longer observed. The results demonstrate that liposomal encapsulation of GCV is feasible and significantly enhances its efficacy against HSV-1 TK+ hepatic tumors.     

Liver failure caused by herpes simplex virus thymidine kinase plus ganciclovir therapy is associated with mitochondrial dysfunction and mitochondrial DNA depletion

Herpes simplex virus thymidine kinase (HSV-tk) converts ganciclovir (GCV) into an active compound, which can be incorporated into DNA molecules and terminate DNA synthesis. Gene transfer of HSV-tk followed by GCV administration has been used with success to treat experimental cancer and this strategy has entered into clinical trials. Although it is thought that the cytotoxic effect occurs mainly in tumoral dividing cells, where mitotic activity favors integration of the genotoxic compound into nuclear DNA, there are concerns of potential damage to normal nondividing cells. In the present work we have explored the mechanisms of HSV-tk/GCV toxicity and in particular whether this therapy may cause lesions of mitochondrial DNA (mtDNA) and mitochondrial dysfunction. We found that the administration of GCV to rats injected with adenovirus encoding HSV-tk induced hepatocellular damage characterized by the presence of apoptotic bodies, ballooning of hepatocytes, and severe hepatic steatosis with mitochondria enlargement and cristae dissolution at the ultrastructural level. Remarkably, Southern blot analysis showed substantial reduction in the amount of mtDNA in the liver. Using radiolabeled GCV we could demonstrate incorporation of this compound into both nuclear and mtDNA in HSV-tk-transduced rat hepatocytic cell line MCA-RH7777 and subsequent alteration of mitochondrial function. Our observations confirm that GCV can damage both nuclear and mtDNA in cells transduced with HSV-tk and that this effect could be responsible for severe mitochondrial dysfunction and toxicity in normal nondividing cells. These data are relevant for the design of clinical trials using adenoviral vectors encoding HSV-tk.     

Detection of herpes simplex virus thymidine kinase polypeptides in cells labeled with 35S-methionine.

To investigate the size of herpes simplex virus (HSV) thymidine kinase (TK) polypeptides, procedures have been devised to purify the enzyme from infected cells labeled with 35S-methionine by (i) affinity chromatography on Sepharose-5'-amino-5'-deoxythymidine; (ii) preparative isoelectric focusing or preparative PAGE; and (iii) glycerol gradient centrifugation. Portions of enzyme fractions, at each purification step, were also treated with an immunoadsorbent, Sepharose-anti-HSV-1 TK immunoglobulin (IgG). Labeled polypeptides eluted from the immunoadsorbent were analyzed by electrophoresis in SDS slab gels and autoradiography. The results demonstrate that the molecular weights of HSV TK polypeptides are about 40,000. TK-negative HSV-1 mutant B2006 failed to induce the 40 K dalton polypeptide.     

Assessment of a selective inhibitor of herpes simplex virus thymidine kinase (L-653,180) as therapy for experimental recurrent genital herpes.

Herpes simplex virus (HSV)-coded thymidine kinase (TK) is important in efficient reactivation of latent infection. These studies were designed to investigate whether treatment of latently infected animals with a TK inhibitor altered the natural history of recurrent HSV disease. 9-([(Z)-2-(hydroxymethyl)cyclohexyl]methyl) guanine (L-653,180) is a potent and selective nonsubstrate inhibitor of HSV TK which can suppress or delay reactivation of HSV-1 from latently infected cells in vitro without affecting viral replication. In an initial study, six female Hartley guinea pigs were treated with L-653,180 in their diet (25 mg/30 g of food) and water (300 mg/liter) for 7 days. Blood, urine, kidney, liver, spinal cord, and cerebral cortex specimens were collected. L-653,180 was detected in all specimens at concentrations which, although low, were higher than the in vitro 50% inhibitory concentration of the drug against HSV TK. In the second study, 20 female Hartley guinea pigs were randomized into two groups following recovery from primary genital HSV-2 infection. One group received L-653,180 in diet and water for 4 weeks beginning 21 days postinoculation. Animals were examined daily for recurrent lesions for 10 weeks. Treated animals experienced fewer recurrences during the treatment period but the results were not significantly different from results with controls. During the first 2-week posttreatment period, L-653,180-treated animals had significantly fewer recurrences than control animals (P = 0.02). Over the entire 10-week observation period, treated animals experienced fewer recurrences (P = 0.06). These results suggest that inhibitors of viral TK may be useful in limiting reactivation of latent virus and thus recurrent infections. In these experiments, the amount of drug that could be administered to the animals was limited by its poor solubility. Further studies with more potent and soluble inhibitors of HSV TK appear to be warranted.     

Safety of interleukin-12 gene therapy against cancer: a murine biodistribution and toxicity study

As a prerequisite for a human clinical trial using interleukin (IL)-12 gene therapy, the biodistribution and safety of IL-12, administered as an intradermal naked DNA injection, was evaluated in mice. The pNGVL3-mIL12 plasmid used in this study is a nonviral vector designed to induce a high level of IL-12 protein expression during a transient transfection of the host cell. The biodistribution was evaluated by a polymerase chain reaction (PCR) assay that is capable of detecting less than 100 copies of the plasmid in the context of host DNA. Twenty-four hours after three intradermal injections of 0.5 microg or 5 microg of pNGVL3-mIL12 plasmid, the plasmid was detectable in various internal organs, the blood, and the injection site. The plasmid was detectable in the gonads of only one animal at the high-dose treatment 24 hr after the injections. In the majority of the organs the plasmid was undetectable throughout the study. Possible side effects were monitored by histology and clinical chemistry, and the level of IL-12 protein expression was assessed by enzyme-linked immunosorbent assay (ELISA). No treatment-related histologic abnormalities were detected and the blood chemistry parameters showed no toxicity. The IL-12 protein was undetectable at all times at the injection site and interferon (IFN)-gamma levels at the injection site and in the serum were at background levels. The results of this murine safety study indicate that based on the distribution pattern of the plasmid in the body and the undetectable toxicities in the tissues, the use of the pNGVL3-hIL12 plasmid in cancer gene therapy clinical trials can be considered as safe.     

Effect of recombinant interleukin-12 on murine skin regeneration and cell dynamics using in vivo multimodal microscopy

Interleukin-12 (IL-12) is a pro-inflammatory cytokine known for its role in immunity, and previous studies have shown that IL-12 provides mitigation of radiation injury. In this study, we utilize a multimodal microscopy system equipped with second harmonic generation (SHG) and fluorescence lifetime imaging microscopy (FLIM) to examine the effect of IL-12 on collagen structure and cellular metabolic activity in vivo during skin wound healing. This preliminary study illustrates the highly dynamic and heterogeneous in vivo microenvironment of the wounded skin. In addition, results suggest that IL-12 triggers a significantly more rapid and greater cellular metabolic response in the wounded animals. These results can elucidate insights into the response mechanism of IL-12 in both wound healing and acute radiation syndrome.OCIS codes: (180.4315) Nonlinear microscopy, (170.2520) Fluorescence microscopy, (170.6920) Time-resolved imaging, (190.1900) Diagnostic applications of nonlinear optics, (170.3880) Medical and biological imaging     

单纯疱疹病毒胸苷激酶基因重组真核表达载体的构建及在烫伤大鼠皮肤组织中的表达

目的:构建单纯疱疹病毒胸苷激酶(HSV-tk)基因重组真核表达载体pcDNA3.1/HSV-tk,并观察其在烫伤大鼠皮肤中的表达。方法:实验于2003-07/12在解放军第一军医大学热带卫生学系实验室进行。在原核表达质粒pUChHyTk基础上,利用分子克隆技术,构建重组真核表达质粒pcDNA3.1/HSV-tk。取20只Wistar大鼠,全麻后背部浸入95℃水浴锅中,烫伤12s,造成30%Ⅲ度烫伤,烫伤后随机分为两组(n=10):①pcDNA3.1/tk组:烫伤后当天及第1,2,3,4周后于大鼠左后背部创面边缘(距创面边缘0.5cm)皮下注射脂质体和重组质粒的混合物192μL眼3.6μgpcDNA3.1/tk(2μL) 10μL脂质体 180μL生理盐水演。②pcDNA3.1组:注射时间和方法同前,脂质体和质粒混合物为3.0μgpcDNA3.1(2μL) 10μL脂质体 180μL生理盐水。伤后5周断头处死大鼠,取注射点附近皮肤,用反转录-聚合酶链反应法检测HSV-tk基因的表达。结果:20只大鼠全部进入结果分析。大鼠重组质粒经酶切鉴定与预期结果一致,DNA测序结果表明tk基因已正确插入到pcDNA3.1质粒,说明了重组真核表达载体pcDNA3.1/HSV-tk已成功构建。反转录-聚合酶链反应结果显示脂质体介导的HSV-tk基因转移可在创面成纤维细胞中出现阳性表达。结论:应用分子克隆技术成功地构建了重组真核表达载体pcDNA3.1/HSV-tk,并在烫伤大鼠皮肤中得到了阳性表达。     

单纯疱疹病毒胸苷激酶基因重组真核表达载体的构建及在烫伤大鼠皮肤组织中的表达

目的：构建单纯疱疹病毒胸苷激酶（HSV—tk）基因重组真核表达载体pcDNA3．1／HSV—tk，并观察其在烫伤大鼠皮肤中的表达。方法：实验于2003～07／12在解放军第一军医大学热带卫生学系实验室进行。在原核表达质粒pUChHyTk基础上，利用分子克隆技术，构建重组真核表达质粒pcDNA3．1／HSV—tk。取20只Wistar大鼠，全麻后背部浸入95℃水浴锅中，烫伤12s，造成30％Ⅲ度烫伤，烫伤后随机分为两组（n=10）：①pcDNA3．1／tk组：烫伤后当天及第1，2，3，4周后于大鼠左后背部创面边缘（距创面边缘0．5cm）皮下注射脂质体和重组质粒的混合物192μL[3．6μg pcDNA3．1／tk（2μL）＋10μL脂质体＋180μL生理盐水】。②pcDNA3．1组：注射时间和方法同前，脂质体和质粒混合物为3．0μg pcDNA3．1（2μL）＋10μL脂质体＋180μL生理盐水。伤后5周断头处死大鼠，取注射点附近皮肤，用反转录-聚合酶链反应法检测HSV—tk基因的表达。结果：20只大鼠全部进入结果分析。大鼠重组质粒经酶切鉴定与预期结果一致，DNA测序结果表明tk基因已正确插入到pcDNA3．1质粒，说明了重组真核表达载体pcDNA3.1／HSV—tk已成功构建。反转录-聚合酶链反应结果显示脂质体介导的HSV—tk基因转移可在创面成纤维细胞中出现阳性表达。结论：应用分子克隆技术成功地构建了重组真核表达载体pcDNA3．1／HSV—tk，并在烫伤大鼠皮肤中得到了阳性表达。     

Muscle-targeted interleukin-12 gene therapy of orthotopic hepatocellular carcinoma in mice using in vivo electrosonoporation

We developed a new potent nonviral gene transfer method into mouse muscles in vivo named "electrosonoporation." We tried in this report to treat murine orthotopic hepatocellular carcinoma (HCC) by muscle-targeted mouse interleukin-12 (mIL-12) gene transfer using in vivo electrosonoporation. I.m. administration of the mIL-12 gene with electrosonoporation elevated serum IL-12 and IFN-gamma and significantly prolonged the survival periods with both growth inhibition of orthotopic HCC and inhibition of spontaneous lung metastasis. The IL-12 gene therapy reduced the number of microvessels and induced more Mac-1-positive cells into HCC. These results show that muscle-targeted mIL-12 gene therapy for orthotopic HCC using in vivo electrosonoporation is very efficient and is thus promising for further clinical trial.     

Highly efficient and specific gene transfer to Purkinje cells in vivo using a herpes simplex virus I amplicon

The transduction of cerebellar neurons in vivo with herpes simplex virus 1 (HSV-1) amplicon carrying the lacZ gene has been investigated after injection of the vector in the cerebellar cortex, ventricles, and inferior olive of adult rats. Injection into the cerebellar cortex resulted in transduction of Purkinje cells near the needle tract and injection into the ventricles yielded no transduced neurons. In contrast, high transduction efficiency was achieved by vector injection into the inferior olive, resulting in one of three positive Purkinje cells all over the ipsilateral and contralateral cerebellar hemispheres. Because neurons in the deep cerebellar nuclei are also transduced, we suggest that the vector is delivered from the inferior olive to the cerebellar nuclei and then to Purkinje cells by retrograde axonal transport. Expression of the lacZ gene within Purkinje cells was surprisingly persistent and was maintained at the same level for at least 40 days. Importantly, no signs of either toxicity or inflammation were observed in the cerebellum after vector injection, except for the borders of the needle tract where some reactive astrocytes were detected. Indeed, motor coordination of treated animals was entirely normal, as assessed by the rota-rod test. These results demonstrate that HSV-1 amplicon vectors can effect safe and stable transgene expression in Purkinje cells in vivo, raising the possibility of using these vectors for long-term gene therapy of human cerebellar disorders.     

Percutaneous gene therapy using recombinant adenoviruses encoding human herpes simplex virus thymidine kinase, human PAI-1, and human NOS3 in balloon-injured porcine coronary arteries

Local intracoronary delivery of recombinant adenoviruses expressing anti-migratory or anti-proliferative proteins including human constitutive endothelial nitric oxide synthase (NOS3), plasminogen activator inhibitor 1 (PAI-1), or herpesvirus thymidine kinase (TK) (combined with ganciclovir) was used to prevent neointimal formation in porcine coronary arteries. After balloon injury of the left anterior descending (LAD) coronary artery, animals received an intramural injection of adenovirus (1.5 X 10(9) PFU) carrying either the NOS3 cDNA (AdCMVNOS3, n = 12), the PAI-1 cDNA (AdCMVPAI-1, n = 12), the TK cDNA (AdMLPItk, n = 12), or no cDNA (AdpL+, n = 12). After 28 days, morphometric analysis was performed on coronary sections from all segments demonstrating injury. The internal elastic lamina (IEL) fracture length normalized to the IEL perimeter (initial injury) and the neointimal area normalized to the vessel area (response to injury) were used to generate linear regression lines and calculate an index of stenosis for the respective treatment groups. The response to injury was significantly smaller in AdCMVNOS3- and AdMLPItk-infected animals than in AdpL+-infected animals (slopes = 0.86 +/- 0.05 and 0.69 +/- 0.07 versus 1.11 +/- 0.06, p < 0.005 and p < 0.0001, respectively) but not in AdCMVPAI-1-infected animals (slope = 1.26 +/- 0.04, p = 0.04). No viral shedding was observed and there was no acute systemic toxicity after gene transfer. An increase in neutralizing antibody titers against Ad vectors was observed without any detectable response to the transgene products (NOS3, PAI-1). Local gene transfer of NOS3 and TK may hold promise as a safe and effective adjunctive treatment to reduce neointimal formation after percutaneous coronary intervention in humans.