Intratumoral Implantation Research Articles

Abstract B50: An innovative technique for preventing telomere elongation and its associated immortalization of cancer cells

Abstract B50: An innovative technique for preventing telomere elongation and its associated immortalization of cancer cells

Intratumorally implanted mesenchymal stromal cells potentiate peripheral immunotherapy against malignant rat gliomas

Bone marrow-derived mesenchymal stromal cells (MSCs) target glioma extensions and micro-satellites efficiently when implanted intratumorally. Here, we report that intratumoral implantation of MSCs and peripheral immunotherapy with interferon-gamma (IFNγ) producing tumor cells improve the survival of glioma-bearing rats (54% cure rate) compared to MSC alone (0% cure rate) or immunotherapy alone (21% cure rate) by enforcing an intratumoral CD8+ T cell response. Further analysis revealed that the MSCs up-regulate MHC classes I and II in response to IFNγ treatment in vitro and secrete low amounts of immunosuppressive molecules prostaglandin E2 and interleukin-10.

Promoted antitumor activities of acid-labile electrospun fibers loaded with hydroxycamptothecin via intratumoral implantation

The acidosis of tumor microenvironments is one of the universal phenomena of solid tumors, and the increased acidity may be in fact essential intermediates in the progression of tumor growth and several lethal phenotypic traits of tumors, such as invasion and metastasis. Acid-labile polymers PBELA with incorporating acetal groups into biodegradable backbone of poly(d,l-lactide)–poly(ethylene glycol) (PELA) were utilized to load hydroxycamptothecin (HCPT) into electrospun fibers for intratumoral chemotherapy. Compared with that under a simulated physiological condition of pH 7.4, the incubation of PBELA fibers in acidic media resulted in larger mass loss and molecular weight reduction of fiber matrices and enhanced HCPT release from fibers. In vitro cytotoxicity assay of HCPT-loaded PBELA fibers indicated 6-fold higher inhibitory activity against HepG2 cells after incubation in pH 6.8 media than that of pH 7.4, while there was no significant difference for free HCPT and HCPT-loaded PELA fibers. The tumor growth, tumor cell apoptosis, and animal survival rate after intratumoral implantation of HCPT-loaded PBELA fibers indicated a superior in vivo antitumor activity and fewer side effects than other treatment. Therefore, acid-labile electrospun fibers may be promising implants for localized therapy of inoperable tumors and for prevention of post-surgical tumor recurrence.

Antitumor activities of emulsion electrospun fibers with core loading of hydroxycamptothecin via intratumoral implantation

Emulsion electrospinning was used in the present study to prepare core–sheath structured fibers with core-loading of hydroxycamptothecin (HCPT), and their antitumor activities were evaluated both in vitro on cancer cell lines and in vivo on tumor bearing mice via intratumoral implantation. Compared with our previous investigation on blend electrospun fibers, the addition of 2-hydroxypropyl-β-cyclodextrin (HPCD) and the preferential formation of HPCT/HPCD inclusion complexes resulted in significantly faster HCPT release from and higher degradation rate of emulsion electrospun fibers. The core–sheath structure led to around 93% of lactone form remaining after emulsion electrospinning and incubation in buffer solutions for over one month. In vitro cytotoxicity tests on HCPT-loaded electrospun fibers indicated over 20 times higher inhibitory activity against HepG2 cells than free HCPT during 72h incubation. Hepatoma H22 cells were subcutaneously injected into Kunming mice to form solid tumors for in vivo tests on the antitumor efficacy. Based on the tumor volume, survival rate and body weight changes, HCPT-loaded fibers indicated superior in vivo antitumor activities to and fewer side effects than free HCPT. The histopathological staining and immunohistochemical examinations of caspase-3 expression indicated more necrosis and apoptosis induced by HCPT-loaded fibers. The above results demonstrate the potential use of emulsion electrospun fibers as drug carriers for local treatment of solid tumors.

Pilot trial of endoscopic ultrasound-guided interstitial chemoradiation of UICC-T4 pancreatic cancer.

Background and aims:Both interstitial brachytherapy and interstitial chemotherapy are effective in improving local control in patients with local UICC-T4 pancreatic cancer. In this study, we report the results of endoscopic ultrasound (EUS)-guided interstitial chemoradiation (EUS-ICR) in patients with advanced pancreatic cancer, with respect to tumor response, clinical response, safety, and complications.Patients and methods:A total of 8 patients (3 men, 5 women; median age of 69) with T4 pancreatic adenocarcinoma were the subjects of this study. A mean of 18 radioactive seeds and 36 intratumoral implants for sustained delivery of 5-fluorouracil in each patient were implanted into the tumors using EUS-guided needle puncture. The mean total implanted radioactive activity was 13.68 mCi, the mean total dose of intratumoral 5-fluorouracil was 3.6 g, and the mean volume of implants was 28 cm3. The conditions of the patients were followed-up by examination and imaging tests every two months. Clinical endpoints included the Karnofsky performance status, pain response, tumor response (assessed by computed tomography and/or EUS), and survival.Results:During a median follow-up period of 8.3 months, the objective tumor response was classified as “partial” in 1 of 8 patients (with a median duration of partial response of 3 months), “minimal” in 2 patients, and indicative of “stable disease”, in 3 of 8 patients. Clinical benefit was shown in 4 of 8 patients, which was mostly due to pain reduction, and lasted for 3.5 months. No local complications or hematologic toxicity occurred.Conclusions:EUS-ICR had a moderate local anti-tumor effect, showed some clinical benefits in 4 of the 8 patients, and was well tolerated by all the patients in this study.

Pilot trial of endoscopic ultrasound-guided interstitial chemoradiation of UICC-T4 pancreatic cancer

Background and aims: Both interstitial brachytherapy and interstitial chemotherapy are effective in improving local control in patients with local UICC-T4 pancreatic cancer. In this study, we report the results of endoscopic ultrasound (EUS)-guided interstitial chemoradiation (EUS-ICR) in patients with advanced pancreatic cancer, with respect to tumor response, clinical response, safety, and complications. Patients and methods: A total of 8 patients (3 men, 5 women; median age of 69) with T4 pancreatic adenocarcinoma were the subjects of this study. A mean of 18 radioactive seeds and 36 intratumoral implants for sustained delivery of 5-fluorouracil in each patient were implanted into the tumors using EUS-guided needle puncture. The mean total implanted radioactive activity was 13.68 mCi, the mean total dose of intratumoral 5-fluorouracil was 3.6 g, and the mean volume of implants was 28 cm3. The conditions of the patients were followed-up by examination and imaging tests every two months. Clinical endpoints included the Karnofsky performance status, pain response, tumor response (assessed by computed tomography and/or EUS), and survival. Results: During a median follow-up period of 8.3 months, the objective tumor response was classified as 'partial' in 1 of 8 patients (with a median duration of partial response of 3 months), 'minimal' in 2 patients, and indicative of 'stable disease, in 3 of 8 patients. Clinical benefit was shown in 4 of 8 patients, which was mostly due to pain reduction, and lasted for 3.5 months. No local complications or hematologic toxicity occurred. Conclusions: EUS-ICR had a moderate local anti-tumor effect, showed some clinical benefits in 4 of the 8 patients, and was well tolerated by all the patients in this study.

32P-chromic phosphate-poly (L-lactide) implantation brachytherapy on prostatic carcinoma with lymphatic metastasis

Objective To study the anticancer effects of 32P-chromic phosphate-poly ( L-lactide) (32P-CP-PLI^A) in nude mice with lymphatic metastasis of prostatic carcinoma after implantation brachytherapy. Methods The nude mice were intratumorally implanted with 32P-CP-PLLA of 3.7, 7.4, 14.8 MBq after prostatic carcinoma solid tumor model was established for four weeks. The distribution of 32P in body was observed. The morphology of the tumor and regional lymph nodes was examined. White blood cells and platelets were counted in peripheral blood. Results 32P mainly remained in the tumor and regional lymph nodes. Morphological examination demonstrated that the solid tumor foci necrosed thoroughly, normal structure of regional lymph nodes disappeared, which was replaced by necrotic tissue and hemorrhage. The tumor growth inhibition rate was positively correlated to administration doses. When the doses were 3.7, 7.4, 14.8 MBq, the tumor growth inhibition rate was (70.16 ±5.48)% , (80.18 ±5.84)% , (84.97 ±4.79)% , respectively. No obvious bone marrow depressions were detected. Conclusion The intratumoral implantation with 32P-CP-PLLA can produce anticancer effects on the solid tumor foci and regional lymph nodes. Key words: 32P-chromic phosphate; Prostatic carcinoma; Lymphatic metastasis; Implantation brachytherapy

Phase Ib Trial of Oncolytic Herpes Virus G207 Shows Safety of Multiple Injections and Documents Viral Replication

The prognosis for patients with glioblastoma remains poor despite numerous phase I–II clinical trials on systemic chemotherapies such as the vascular endothelial growth factor–neutralizing antibody bevacizumab.1 Indeed, only two chemotherapies—implantable carmustine-containing Gliadel wafers and temozolomide2—have been approved for glioblastoma by the Food and Drug Administration, because these two agents showed benefit in phase III clinical trials by prolonging median survival by approximately 8 weeks. Therefore, there is a continued need to explore new treatments or to further refine and optimize older treatments for this type of brain cancer.

Modeling doxorubicin transport to improve intratumoral drug delivery to RF ablated tumors

A mathematical model of drug transport provides an ideal strategy to optimize intratumoral drug delivery implants to supplement radiofrequency (RF) ablation for tumor treatment. To simulate doxorubicin transport in non-ablated and ablated liver tumors, a one-dimensional, cylindrically symmetric transport model was generated using a finite element method (FEM). Parameters of this model, the diffusion ( D) and elimination (γ) coefficients for doxorubicin, were estimated using drug distributions measured 4 and 8 days after placing biodegradable implants in non-ablated and ablated rabbit VX2 liver carcinomas. In non-ablated tumor, values of diffusion and elimination parameters were 25% and 94% lower than normal liver tissue, respectively. In ablated tumor, diffusion near the ablation center was 75% higher than non-ablated tumor but decreased to the non-ablated tumor value at the ablation periphery. Drug elimination in ablated tumor was zero for the first four days, but by day 8 returned to 98% of the value for non-ablated tumor. Three-dimensional (3-D) simulations of drug delivery from implants with and without RF thermal ablation underscore the benefit of using RF ablation to facilitate local drug distribution. This study demonstrates the use of computational modeling and optimal parameter estimation to predict local drug pharmacokinetics from intratumoral implants after ablation.

Carrier Cell–mediated Delivery of a Replication-competent Adenovirus for Cancer Gene Therapy

Carrier Cell–mediated Delivery of a Replication-competent Adenovirus for Cancer Gene Therapy

New approaches to primary brain tumor treatment

Primary brain tumors represent over 100 different tumor types with widely divergent biologies and clinical outcomes, but these neoplasms frequently pose similar challenges to neuro-oncologists. Malignant gliomas are the most common type of primary intrinsic brain tumor in adults and remain extremely lethal. Current standard-of-care therapies for these cancers include surgery, radiation and palliative cytotoxics, which have significant side-effects and limited efficacy. Advances in our understanding of the molecular underpinnings of cancer have led to targeted molecular therapies that may permit improvement in therapeutic efficacy and reduced toxicity; these therapies, however, still face many challenges. Signal transduction pathways that are inappropriately regulated in brain cancers include growth factors and their receptors (e.g. epidermal growth factor receptor, vascular endothelial growth factor receptor and platelet-derived growth factor receptor), which regulate cellular interactions with the microenvironment and intracellular oncogenic pathways. Low-molecular-weight inhibitors have been developed to target many kinases and may have advantages in terms of delivery. Monoclonal antibodies may have greater specificity, but face delivery restrictions. Preferential tumor delivery of chemotherapies, conjugated toxins and radioisotopes has been achieved through convection-enhanced delivery, intratumoral implants and intra-arterial infusion. Despite these advances, few molecularly targeted therapies have demonstrated significant antineoplastic activity for a broad range of patients, possibly due to tumor and patient heterogeneity. Improved functional neuropathology and imaging may permit identification of patient subgroups for which clinical responses may be enriched. It is probable, however, that targeted therapies will be most effective in combination either with one another or with cytotoxic therapies. In this study, we review the current state of new therapies for malignant gliomas.

Induction of Potent Antitumor Immunity by Intratumoral Injection of Interleukin 23–Transduced Dendritic Cells

Dendritic cells (DCs) are potent antigen-presenting cells that play a critical role in priming immune responses to tumor. Interleukin (IL)-23 can act directly on DC to promote immunogenic presentation of tumor peptide in vitro. Here, we evaluated the combination of bone marrow-derived DC and IL-23 on the induction of antitumor immunity in a mouse intracranial glioma model. DCs can be transduced by an adenoviral vector coding single-chain mouse IL-23 to express high levels of bioactive IL-23. Intratumoral implantation of IL-23-expressing DCs produced a protective effect on intracranial tumor-bearing mice. The mice consequently gained systemic immunity against the same tumor rechallenge. The protective effect of IL-23-expressing DCs was comparable with or even better than that of IL-12-expressing DCs. IL-23-transduced DC (DC-IL-23) treatment resulted in robust intratumoral CD8(+) and CD4(+) T-cell infiltration and induced a specific TH1-type response to the tumor in regional lymph nodes and spleen at levels greater than those of nontransduced DCs. Moreover, splenocytes from animals treated with DC-IL-23 showed heightened levels of specific CTL activity. In vivo lymphocyte depletion experiments showed that the antitumor immunity induced by DC-IL-23 was mainly dependent on CD8(+) T cells and that CD4(+) T cells and natural killer cells were also involved. In summary, i.t. injection of DC-IL-23 resulted in significant and effective systemic antitumor immunity in intracranial tumor-bearing mice. These findings suggest a new approach to induce potent tumor-specific immunity to intracranial tumors. This approach may have therapeutic potential for treating human glioma.

The Development and Characterization of an HEK293-Derived Cell Line for Use in an Intratumoral Cytokine Delivery System.

As part of ongoing work to develop a method of cytokine delivery for use as an intratumoral depot, we noted that HEK293 cells, encapsulated in alginate, died within 24-48 h after in vivo, intratumoral implantation. We hypothesized that the highly hypoxic and acidic conditions found inside the tumor was the cause of the cells' premature demise. Therefore, we set out to develop a cell line, derived from HEK293, that would survive these hostile conditions. The HEK293 line was selected in 0.3-0.5% oxygen conditions over several weeks, followed by a further 6-week period of culture in alternating hypoxic and normoxic conditions. The most rapidly growing clones were selected and grown in normoxic conditions for several weeks to ensure their stability. The clones were then compared to the original line in terms of cell proliferation in normoxia and hypoxia, colony-forming efficiency, and morphological characteristics. The resulting line was able to proliferate in the harshest of conditions and continues to release its biological payload after alginate microencapsulation.

Thymidine kinase activation of ganciclovir in recurrent malignant gliomas: a gene-marking and neuropathological study

The gene therapy paradigm of intratumoral activation of ganciclovir (GCV) following transduction of tumor cells by retroviral vectors bearing the thymidine kinase (tk) gene has produced dramatic remissions of malignant gliomas in animal models. In human trials, although the technique has been deemed safe, little antitumor effect has been demonstrated. To evaluate the basis of this inefficacy in human gliomas, the authors conducted a gene-marking trial involving neuropathological and biochemical studies of treated tumor specimens. Five patients with malignant recurrent gliomas underwent stereotactic biopsy sampling and intratumoral implantation procedures with three aliquots of 10(6) vector-producing cells (VPCs) in columns. After 5 days, the tumor was resected and the tumor bed reimplanted with VPCs, and a course of GCV was given. Patients received clinical and radiological follow up for 6 months. Tumor specimens were analyzed neuropathologically and for tk gene expression by anti-TK immunohistochemistry and TK enzymatic activity. Four patients tolerated the treatment well but experienced tumor progression. The other developed an abscess after the second operation and died. Increased TK enzymatic activity was demonstrated in the one tumor specimen analyzed. Immunohistochemical evidence of tk gene expression was limited to VPCs. Transduction of tumor cells was not seen. Viable tumor cells were seen near VPCs containing TK. The lymphocytic immune response was mild. Except for the risk of infection inherent in reoperation, this tk-GCV paradigm was both feasible and safe. Pathological studies indicated that limited dissemination of VPCs and vector from the infusion site and failure to transduce tumor cells with the tk gene are major barriers to efficacy.

Effect on Regrowth Delay in a Murine Tumor of Scheduling Split-Dose Irradiation Based on Direct pO 2 Measurements by Electron Paramagnetic Resonance Oximetry

Tumor reoxygenation after irradiation may contribute to a tumor's response to subsequent doses of radiation. The timing of reoxygenation in RIF-1 murine tumors was determined using electron paramagnetic resonance (EPR) oximetry with intratumoral implantation of an oxygen-sensitive paramagnetic material (India ink) to monitor the pO2 in individual murine tumors before, during and after three different irradiation schemes. Radiation was given as a single 20-Gy dose or was split into two 10-Gy doses where the second dose of radiation was delivered at the minimum postirradiation tumor pO2 (24-h interval, hypoxic group) or where the second dose of radiation was delivered after reoxygenation had occurred (72-h interval, oxygenated group). The end point for tumor response was time taken to reach double the volume at the time of treatment. There were significantly longer tumor doubling times in the oxygenated compared to the hypoxic group, indicating that the measured changes in pO2 reflected changes in tumor radiosensitivity. A 24-h interval between doses resulted in a delay of reoxygenation in the tumors, while a 72-h interval resulted in a second cycle of hypoxia/reoxygenation. Our results suggest that repeated direct measurements of pO2 in tumors by EPR oximetry could be useful in timing radiation doses to achieve improved local control of tumors.

Complete regression of established murine hepatocellular carcinoma by in vivo tumor necrosis factor alpha gene transfer

BACKGROUND & AIMS: Although tumor necrosis factor (TNF)-alpha possesses a potent antitumor activity, systemic administration of TNF-alpha causes severe side effects. To circumvent this, the efficacy of tumor cell-targeted TNF-alpha gene therapy was investigated.METHODS: Murine hepatocellular carcinoma (HCC) cells were infected with MNSM-Alb e/p- TNF-alpha retroviruses carrying the murine TNF-alpha gene under the transcriptional control of the murine albumin gene promoter, and antitumor effects induced by TNF-alpha gene transfer were examined in vitro and in vivo.RESULTS: Although MNSM-Alb e/p-TNF-alpha retrovirally infected HCC cells showed the same in vitro cell growth as parental HCC cells, they lost their tumorigenicity when implanted in syngeneic mice and induced tumor immunity against parental HCCs. The retrovirally infected HCC cells also significantly inhibited the tumorigenicity of previously implanted parental HCCs. Furthermore, intratumoral administration of MNSM-Alb e/p-TNF-alpha retroviruses showed the antitumor effect against established HCCs, resulting in significantly prolonged survival periods. Most importantly, intratumoral implantation of MNSM-Alb e/p-TNF-alpha retroviral- producing cells completely abrogated established HCCs in mice.CONCLUSIONS: These results indicate the potential efficacy of transferring the TNF-alpha gene via retroviral vectors directly into tumors for gene therapy against HCCs.(Gastroenterology 1997 Feb;112(2):501-10)

Implantable biodegradable polymers for IUdR radiosensitization of experimental human malignant glioma.

The potential of halogenated pyrimidines for the radiosensitization of human malignant gliomas remains unrealized. To assess the role of local delivery for radiosensitization, we tested a synthetic, implantable biodegradable polymer for the controlled release of 5-iodo-2'-deoxyuridine (IUdR) both in vitro and in vivo and the resultant radiosensitization of human malignant glioma xenografts in vivo. In vitro: To measure release, increasing (10%, 30%, 50%) proportions (weight/weight) of IUdR in the polyanhydride [(poly(bis(p-carboxyphenoxy)-propane) (PCPP): sebacic acid (SA) (PCPP : SA ratio 20:80)] polymer discs were incubated (1 ml phosphate-buffered saline, 37 degrees C). The supernatant fractions were serially assayed using high performance liquid chromatography. To measure modulation of release, polymer discs were co-loaded with 20 microCi 5-125-iodo-2'-deoxyuridine (125-IUdR) and increasing (10%, 30%, or 50%) proportions of D-glucose. To test radiosensitization, cells (U251 human malignant glioma) were sequentially exposed to increasing (0 or 10 microM) concentrations of IUdR and increasing (0, 2.5, 5.0, or 10 Gy) doses of acute radiation. In vivo. To measure release, PCPP : SA polymer discs having 200 microCi 125-IUdR were surgically placed in U251 xenografts (0.1-0.2 cc) growing in the flanks of nude mice. The flanks were reproducibly positioned over a collimated scintillation detector and counted. To measure radiosensitization, PCPP : SA polymer discs having 0% (empty) or 50% IUdR were placed in the tumor or contralateral flank. After five days, the tumors were acutely irradiated (500 cGy x 2 daily fractions). In vitro: Intact IUdR was released from the PCPP : SA polymer discs in proportion to the percentage loading. After 4 days the cumulative percentages of loaded IUdR that were released were 43.7 +/- 0.1, 70.0 +/- 0.2, and 90.2 +/- 0.2 (p < 0.001 ANOVA) for the 10, 30, and 50% loadings. With 0, 10, 30, or 50% D-glucose co-loading, the cumulative release of 125-IUdR from PCPP : SA polymers was 21, 70, 92, or 97% (p < 0.001), respectively, measured 26 days after incubation. IUdR radiosensitized U251 cells in vitro. Cell survival (log10) was -2.02 +/- 0.02 and -3.68 +/- 0.11 (p < 0.001) after the 10 Gy treatment and no (control) or 10 microM IUdR exposures, respectively. In vivo: 125-IUdR Release: The average counts (log10 cpm +/- SEM) (hours after implant) were 5.2 +/- 0.05 (0.5), 4.3 +/- 0.07 (17), 3.9 +/- 0.08 (64), and 2.8 +/- 0.06 (284). Radiosensitization: After intratumoral implantation of empty polymer or intratumoral 50% IUdR polymer, or implantation of 50% IUdR polymers contralateral to tumors the average growth delays of tumors to 4 times the initial volumes were 15.4 +/- 1.8, 20.1 + 0.1, and 20.3 + 3.6 (mean + SEM) days, respectively (p = 0.488 one-way ANOVA). After empty polymer and radiation treatments, no tumors regressed and the growth delay was 31.1 + 2.1 (p = 0.046 vs. empty polymer alone) days. After implantation of 50% IUdR polymers either contralateral to the tumors or inside the tumors, followed by radiation, tumors regressed; growth delays to return to the initial average volumes of 14.0 + 3.6 or 24.2 + 0.2 (p < 0.01) days, respectively. Synthetic, implantable biodegradable polymers hold promise for the controlled release and local delivery of IUdR for radiosensitization of gliomas.

Effect of stereotactic implantation of biodegradable 5-fluorouracil-loaded microspheres in healthy and C6 glioma-bearing rats.

Poly(lactic acid-co-glycolic acid) (PLAGA) microspheres are promising systems for interstitial chemotherapy of brain tumors. They can be readily implanted by stereotaxy and are biocompatible with the brain, in which they are totally biodegraded within 2 months. 5-Fluorouracil (5-FU) was selected for encapsulation, because this hydrophilic and antimetabolic drug is not directly neurotoxic and does not readily cross the blood-brain barrier. Also, its anticancer activity may be improved by sustained administration. Furthermore, it is a potent radiosensitizer. To study their fate and toxicity, two types of 5-FU-loaded PLAGA microspheres were implanted in healthy rats by stereotaxy. One type presented a fast in vitro release profile (FR), and the second exhibited a slow in vitro release pattern (SR) (100% of the encapsulated 5-FU is released within 72 hours and 18 days, respectively). Periodically, rats were killed for microscopic examination. The efficacy of these microspheres on rat glioma was then evaluated. Seven days after stereotactic implantation of C6 malignant glioma cells in the brain, the rats were treated by intratumoral injection of 5-FU solution, blank microspheres, or 5-FU-loaded microspheres (FR and SR types). The mortality of these treated groups was compared by the log-rank test with that of an untreated group. After implantation of two types of 5-FU-loaded PLAGA microspheres, no sign of clinical or histological toxicity was observed. Entrapped 5-FU crystals were observed until Days 12 and 20 postimplantation within FR and SR microspheres, respectively, which suggests a longer releasing period in vivo than in vitro. In the therapeutic evaluation, only intratumoral implantation of SR-type 5-FU-loaded microspheres significantly decreased the mortality (P = 0.017). 5-FU-loaded PLAGA microspheres were implanted in rat brains without evident toxicity. Histological examination suggested a longer sustained delivery period in vivo than in vitro. Intratumoral implantation of SR-type 5-FU-loaded microspheres decreased the mortality of C6 tumor-bearing rats. This effect can be related to the local and the sustained delivery of the drug, because 5-FU administered systemically is ineffective against brain tumors.

Toxicity studies of retroviral-mediated gene transfer for the treatment of brain tumors.

Retroviral-mediated transfer of the herpes simplex virus thymidine kinase (HSVtk) gene into malignant tumors confers drug susceptibility to the antiviral drug ganciclovir. The authors have recently shown that in situ transduction of the rat 9L brain tumor following HSVtk-producer cell implantation led to tumor regression after ganciclovir administration in treated rats. A wide spectrum of potential adverse effects may, however, be associated with the application of this approach to treat brain tumors, including dissemination of the retroviral vector to nontumoral tissues within or outside the central nervous system, proliferation of the injected murine vector-producer cells at the injection site, immune-mediated responses to the implantation of xenogeneic cells, and damage to the brain from toxic by-products of the HSVtk-ganciclovir interaction. These possibilities were investigated using intracerebral and systemic injections of retroviral vector-producer cells carrying the HSVtk or the lacZ gene in mice, rats, and nonhuman primates. Using the lacZ gene as a reporter gene, no evidence of beta-galactosidase activity consistent with vector transduction was detected in any major body organ in the treated mice or rats. Similarly, the HSVtk gene transfer did not result in toxicity, with or without ganciclovir administration. In studies using rat and monkey models, no proliferation of the vector-producer cells occurred after intracerebral injection. Vector-producer cell survival was limited to 7 to 14 days. High-dose steroid therapy did not appear to extend the survival of these xenogeneic cells in rats. No significant inflammatory response was observed in the meninges or brain parenchyma. Endothelial cells were occasionally transduced in brain capillaries adjacent to the injected site of the vector-producer cells. Injection of producer cells into brain tissue elicited mild edema and reactive gliosis surrounding the injection site, which were probably the cause of a transient toxic response arising 4 to 5 days following injection of the producer cells; short-term administration of dexamethasone eliminated that response. No neurological deficits were observed in the rats or primates treated with the HSVtk vector-producer cells, with or without ganciclovir. In primates injected with producer cells, magnetic resonance imaging before, during, and after ganciclovir administration showed minimal and localized breakdown of the blood-brain barrier without significant edema or mass effect. Similarly, histological examination of the monkeys' brains showed no damage to neurons, astroglia, or myelin. Long-term clinical (> 9 months) and radiological (3 months) assessment of the primates has revealed no evidence of toxicity.(ABSTRACT TRUNCATED AT 400 WORDS)