Radiolabeled nucleoside analogs in cancer diagnosis and therapy

Radiolabeled nucleosides, specifically 5-iodo-2'-deoxyuridine (IUdR) radioiodinated with the Auger-electronemitting 123I or 125I, have been shown to produce extensive DNA damage in mammalian cell systems in vitro. Such nucleosides are cycle-dependent agents that are taken up by mitotically dividing cells in the S phase of the cell cycle. The degree of damage that occurs is related to the fact that these nucleosides bind covalently to DNA bringing the decaying Augerelectron-emitting radionuclide in close proximity to the genome. The use of these radiohalogenated nucleosides in vivo is associated with several problems. The first relates to their extremely short biologic half-life in blood (T1/2 of minutes in humans). The second involves achieving therapeutic ratios in tumor cells in the face of efficient hepatic dehalogenation. The third concerns the uptake of these radiopharmaceuticals by actively proliferating normal cell renewal systems, thus potentially causing toxic side effects. The fourth, one shared with other cycle-dependent drugs, relates to the matter of labeling the whole tumor cell population. To facilitate targeting to tumors, investigators have been examining the direct introduction of these agents into the targeted area or into an arterial blood supply that immediately precedes the target. For example, radiopharmaceutical administration could be intracavitary (bladder, spinal fluid, peritoneum), intralesional (brain tumor, breast mass) or intra-arterial (liver, pancreas). In all these situations, the following conditions must be met: (a) once within the vicinity of the tumor the agent can freely diffuse through the tissues and is selectively taken up by cancerous cells; (b) once the agent has left the target area it is converted quickly into a nontoxic form and/or excreted from the body; and finally, (c) the biologic behavior of the agent is not altered by repeated injections. We report herein our experience and that of others with [123I/125I/131I]IUdR in cultured cells, animal tumor-model systems, and patients. In vitro, DNA incorporation of 123I- and 125I-labeled IUdR leads to an exponential decrease in cell survival (no shoulder on the survival curve). However, the total number of decays needed to produce a given lethal effect with [123I]IUdR is approximately twice that required with [125I]IUdR. In vivo, the scintigraphic and antineoplastic capabilities of radioiodinated IUdR have been demonstrated in an intraperitoneal murine ovarian tumor model following intraperitoneal injection; in an intracerebral rat gliosarcoma model after intracranial administration; in an intrathecal rat gliosarcoma model after intrathecal infusion; and in a rat transitional cell bladder cancer model following intravesicular infusion. [123I]IUdR, [125I]IUdR, and/or [131I]IUdR have been administered to patients with brain, breast, colorectal, or gastrointestinal cancers (intratumorally); ovarian cancer (intraperitoneally); bladder cancer (intravesically); liver metastases from colorectal cancer (through the hepatic artery, permanent intra-arterial catheter). These studies have confirmed the observations made in animal models. The data indicate that 5-iodo-2'-deoxyuridine radiolabeled with an Auger electron emitter (123I or 125I) may be a useful agent for the scintigraphic diagnosis and/or therapy of neoplastic diseases that are accessible to direct radiopharmaceutical administration. This radiopharmaceutical should serve as a prototype for, and facilitate the development of, other radiolabeled nucleoside analogs. Further investigations are certainly warranted.

Biochemical modulation in the treatment of advanced cancer: a study of combined leucovorin, fluorouracil, and iododeoxyuridine

Multiple studies have shown that leucovorin-fluorouracil regimens are modestly superior to fluorouracil alone in the treatment of advanced colorectal cancer. Laboratory data suggest that iododeoxyuridine could further enhance the efficacy of leucovorin-fluorouracil regimens. This report describes the Phase I clinical evaluation of a leucovorin-fluorouracil-iododeoxyuridine chemotherapy regimen. Twenty-four patients received treatment with leucovorin (500 mg/m2), fluorouracil (500 mg/m2), and iododeoxyuridine (escalating doses) on days 1 and 8 of a 21-day cycle. The maximum tolerated dose of iododeoxyuridine was 1200 mg/m2, with a recommended Phase II dose of 1000 mg/m2. Myelosuppression (leukopenia) was dose limiting; other commonly observed treatment toxicities were nausea/vomiting, mucositis, and hyperlacrimation. Although the 1200 mg/m2 dose was tolerated during the initial few cycles of therapy, chronic administration could not be maintained secondary to dose-limiting neutropenia. Since neutropenia was dose limiting, in a follow-up study, 10 patients received a modified regimen (treatment on days 1 and 6 instead of days 1 and 8) with the addition of granulocyte colony-stimulating factor (days 8-19). The addition of granulocyte colony-stimulating factor, however, did not permit further escalation of the iododeoxyuridine dose. Three partial responses and six minor responses were observed. Phase II studies of this regimen are ongoing in advanced colorectal and advanced pancreatic cancer to determine response rates in these diseases.

Clinical characteristics of acyclovir-resistant herpetic keratitis and experimental studies of isolates

BACKGROUND

We treated two patients with dendritic keratitis that did not respond to acyclovir (ACV) ointment therapy. Their systemic immune status was normal: however, one patient had a long history of atopic disease and the other had previously undergone topical corticosteroid treatment. HSV-1 was isolated from the patients and inoculated into animals to investigate its viral pathogenicity and latent infection.

METHODS

HSV-1 isolates from the patients were tested for drug sensitivity to acyclovir, ganciclovir, idoxuridine, trifluridine, foscarnet and interferon-beta in vitro. In in vivo studies, bilateral corneas of two New Zealand white rabbits and 10 BALB/c mice in each of four groups were infected by the respective viral isolates. The extent of corneal epithelial and/or stromal lesions produced by the viruses was evaluated. The trigeminal ganglial tissues of the mice were examined for viral latent infection by co-culture with Vero cells.

RESULTS

Herpetic keratitis in both patients was characterized by prolonged clinical course, succeeded by various types of corneal lesions and ocular complications. In in vitro studies, the two HSV-1 isolates demonstrated cross-resistance to ACV, ganciclovir and/or idoxuridine. Both strains demonstrated weakly virulent corneal epithelial and/or stromal lesions in rabbits and mice. One isolate displayed delayed advent but prolonged course of epithelial lesions in rabbits. The latent infection incidences of the isolates in mice trigeminal ganglia were 6.25% (1/16) and 0% (0/18) respectively.

CONCLUSION

Topical immune depression may induce ACV-resistant HSV-1 infection in the cornea, with a prolonged course in association with ocular complications. The prolonged infectious course of the viral isolates in the animal study partially supported the clinical demonstrations in the patient. The existence of latent infection by one ACV-resistant HSV-1 in its animals may indicate the possibility of its recurrence. Trifluridine may be an alternative choice for treating corneal epithelial lesions caused by ACV-resistant HSV-1.

Modulation of [5-125I]iododeoxyuridine incorporation into tumour and normal tissue DNA by methotrexate and thymidylate synthase inhibitors

A potentially useful method for imaging of micrometastases and in situ radiotherapy, would be the incorporation of radioactive labelled iododeoxyuridine (IdU) into tumour DNA. However, there are two main problems: incorporation of the radioactive IdU into normal cells and low incorporation into tumour cells. The aim of this study was to attempt to augment the incorporation of [5-125I]iododeoxyuridine (125IdU) into tumour DNA and to improve the tumour/normal tissue ratio by the use of inhibitors (methotrexate, 5-fluorouracil, AG337, ZD 1694, benzyloxybenzyl uracil) which would prolong the metabolic half-life of the compound. Mammary tumours were induced in GR mice, which were then treated with the inhibitors and the 125IdU. The tumours and representative normal tissue were removed following sacrifice of the animals, and radioactivity within the tissues measured. Pretreatment of mammary carcinoma-bearing GR mice with methotrexate caused approximately a 3-fold increase in the incorporation of 125IdU into tumour DNA, and approximately a > or = 10-fold increase in the tumour/small intestine ratio of incorporated radioactivity. Inhibition of thymidylate synthase, the enzyme involved in IdU dehalogenation, by 5-fluorouracil plus folic acid, or by novel inhibitors AG337 and ZD1694 led to a 3- to 5-fold increase in the 125IdU incorporation. Benzyloxybenzyl uracil, an inhibitor of dihydrouracil dehydrogenase, had little effect. Treatment of tumour-bearing mice with methotrexate plus ZD1694 significantly reduced the rate of tumour growth, but addition of 125IdU (70 microCi/mouse, three daily injections) had no additional antitumour activity. In conclusion, these results do not support the hypothesis that systemic administration of 125IdU can be used for cancer therapy or for imaging purposes unless better methods are found to boost its incorporation into tumour DNA.

Tumor targeting by intra-arterial infusion of 5-[123I]iodo-2'-deoxyuridine in patients with liver metastases from colorectal cancer

We previously showed the tumor-targeting potential of the 125I-labeled thymidine analog 5-iodo-2'-deoxyuridine (IUdR) injected intratumorally in patients with high tumor-cell kinetics. In this study, we evaluated the tumor incorporation of [123I]IUdR infused intra-arterially in patients with liver metastases from colorectal cancer.

METHODS

Iodine-123-IUdR (110-300 MBq, 3-8 mCi, specific activity, 150-200 Ci/mumole) was infused into the hepatic artery of 16 patients with inoperable liver metastases over 30-45 min through a permanent intra-arterial catheter. A dynamic sequence during infusion, spot images, whole-body scans and SPECT acquisitions were recorded up to 42 hr. Blood and urine samples were obtained for biodistribution and HPLC analyses.

RESULTS

In the 14 patients with adequate tumor perfusion patterns, tumor uptake reached 2%-17.6% ID at the end of infusion. After a washout phase that lasted 18-20 hr, incorporated radioactivity remained steadily associated with the tumor lesions until at least 42 hr after infusion (about 1.4%-11.1% ID). HPLC analysis indicated a virtually 100% first-pass hepatic deiodination of unincorporated [123I]IUdR (about 80%-95% ID recovered in the 42-hr urine). No significant uptake was detected in the bone marrow or in other normal dividing tissues.

CONCLUSION

These results encourage further studies to enable dosimetric estimates, optimization of dose regimens, and examination of the therapeutic potential of Auger-electron-emitter-labeled IUdR in cancer therapy utilizing this type of approach.

Pharmacokinetics and dosimetry of iodine-125-IUdR in the treatment of colorectal cancer metastatic to liver

The radiotoxicity of 125I is highly sensitive to the site of decay relative to nuclear DNA. This paper describes a new approach, based upon pharmacokinetic clearance of radioactivity from the tumor, with which to quantify the fraction of [125I]IUdR incorporated within the DNA of tumor cells.

METHODS

Patients were injected with [125I]IUdR through the hepatic artery. Iodine-131-IUdR was used as a tracer for imaging and quantitation. Both conventional and DNA-level dosimetry were performed.

RESULTS

We calculated that if 15% of the tumor cells were in S phase at the time of injection, there would be 250 decays of 125I in the DNA per tumor cell after an infusion of 5 mCi [125I]IUdR. According to in vitro data based on 5 x 10(8) cells per g tumor, 99% of these cells in S phase would be killed.

CONCLUSION

The estimate of cell inactivation is strongly dependent on the number of cells per gram and the fraction of cells in S phase at the time of injection, which indicates that repeat injections would be necessary to achieve a therapeutic effect.

Radiolabeled iododeoxyuridine: safety evaluation

The emphasis of radiolabeled iododeoxyuridine (*IUdR) research at our institution to date has been to assess its safety as a potential therapeutic agent. Toward this goal, we have performed preclinical and clinical studies, using various routes of administration, to detect adverse changes in normal tissues in both humans and animals. As IUdR is rapidly dehalogenated by the liver, the intravenous route is unlikely to be successful in therapeutic efforts. We have therefore focused our attention on more "protected" routes: intra-arterial and intravesicular administration.

METHODS

Studies were performed in farm pigs after multiple administrations of [125I]IUdR into the aorta, carotid artery and bladder. IUdR and metabolites were measured in venous blood samples at appropriate time intervals after administration, after which histologic examination of tissues was performed. Studies in human have been performed after intra-arterial administration of [123I]IUdR in patients with liver metastases and intravesicular administration in patients with bladder carcinoma, initially using [123I]IUdR and currently using both [123I]IUdR and [125I]IUdR. Blood samples for pharmacokinetics and metabolite analysis and tissue for autoradiography (when feasible) have been obtained.

RESULTS

To date, no evidence of adverse effects on normal tissue or alteration of hematologic or metabolic indices have been seen in pigs or humans. When instilled in the bladder, there is little leakage of IUdR in the circulation.

CONCLUSION

When [125I]IUdR is used as a therapeutic agent, we anticipate little or no effect on normal tissues.

Radioiododeoxyuridine in cancer therapy: an in vitro approach to developing in vivo strategies

Studies were undertaken to determine the relationship between IUdR concentration and the duration of radiolabeled IUdR treatment required to incorporate the equivalent of a D(o) dose in vitro and to estimate the treatment parameters necessary to incorporate a killing dose in vivo.

METHODS

W138 (normal human) and HeLa (human cancer) cells were grown axenically or in co-culture. The three cultures were treated for 5 days with 18.5 kBq/ml [125I]IUdR. After treatment, the cells were subcultured and grown for 7 days in medium without [125I]IUdR. In separate experiments, Chinese hamster ovary cells (CHO) were labeled with various ratios of radiolabeled (125I) and nonradiolabeled IUdR and the mole rate of IUdR incorporation in double-stranded DNA was measured. Mitotically selected CHO cells were incubated without treatment until > 98% were in S phase. At this time, the cells were labeled for 15 min with several concentrations of either [123I]IUdR or [125I]IUdR and their colony survival was measured.

RESULTS

After incubation with [125I]IUdR, selective eradication of HeLa cells from a co-culture of W138 and HeLa cells was achieved. The incorporation of IUdR into DNA of CHO cells, although the sum of a series of enzymatic steps, has the appearance of and can be analyzed as a Michaelis-Menton type curve. The maximum rate of IUdR incorporation (Vmax) is 4.424 x 10(-18) mol/min and the substrate concentration at 1/2 Vmax (K) is 3.717 x 10(-6) M IUdR. The Do dose rates for [123I]IUdR and [125I]IUdR, respectively, are 18.78 and 1.88 initial decays/cell/hr.

CONCLUSION

The D(o) dose for *IUdR can be determined from survival curves versus the mole amount of *IUdR incorporated in DNA. To be effective as an in vivo treatment it will be necessary to manipulate the IUdR delivery time, concentration and volume in a manner that assures that the target cells incorporate a cytocidal dose of *IUdR.

Pilot clinical trial of 5-[125I]iodo-2'-deoxyuridine in the treatment of colorectal cancer metastatic to the liver

The thymidine analog, 5-iodo-2'-deoxyuridine (IUdR), is incorporated in the DNA of cells in the S phase. When incorporated into DNA, short-range Auger electrons emitted by 125I-labeled IUdR can cause double-strand breaks, delivering a lethal radiation dose to the cell. We conducted therapeutic trial to evaluate[125I/131I]IUdR pharmacokinetics in liver metastases from colorectal cancer. Dosimetry, safety, and therapeutic potential were assessed.

METHODS

Four patients were each infused with 5 mCi [125I]IUdR and 10 mCi [131I]IUdR through the sideport of a hepatic artery pump. Iodine-131 images were quantitated and used for pharmacokinetic studies. The radioactivity in the DNA of biopsy samples of tumor, normal liver and bone marrow, obtained 24 or 48 hr after injection, was counted.

RESULTS

All patients had [125I]IUdR and [131I]IUdR uptake in tumor, with a biexponential clearance. Repeat injections in individual patients showed little variation in tumor uptake, especially in the slow clearance component. On planar images, no long-term retention was seen in bone marrow or other actively dividing normal tissues. Radioactivity in all tumor DNA samples was greater than background, while that in normal liver cell DNA was at background levels. Radioactivity in the DNA of one marrow sample taken at 24 hr was above background, but in another taken at 48 hr it was equal to background levels. No side effects were noted, no hematologic toxicity was observed in any patients and no tumor responses were seen.

CONCLUSION

There is persistent uptake of [125I]IUdR in hepatic tumors, thereby making hepatic artery infusion a suitable mode of delivery for therapy. Repeat injections will be needed because only 15%-50% of tumor cells are in the S phase. Based on results from this pilot study, a therapeutic regimen is being planned.

Tumor uptake and mitotic activity pattern of 5-[125I]iodo-2'- deoxyuridine after intravesical infusion in patients with bladder cancer

In patients with bladder cancer, little is known about diffusion in the tumor mass of 5-iodo-2'-deoxyuridine (IUdR) administered intraluminally, although previous studies based on external scanning have shown promising tumor-targeting properties of IUdR instilled intravesically. This study compared the pattern of IUdR uptake by bladder cancer cells with the actual distribution of mitotic activity, as evaluated by incubation of ex vivo tumor specimens with tritiated thymidine.

METHODS

The [125I]IUdR (2-13 MBq) was instilled over 1-3 hr in the bladder of four patients with bladder cancer scheduled for ablative surgery. Twenty-four hours later, surgical samples were assayed for radioactivity and processed for microautoradiography, while fresh tumor specimens were fragmented, incubated with [3H]thymidine and further processed for microautoradiography. The diffusion of labeled IUdR across the bladder wall was evaluated by blood sampling.

RESULTS

Tumor incorporation of [125I]IUdR 24 hr after intravesical instillation was 0.002%-0.05% ID/g, while the average tumor-to-normal bladder ratio was about 20. Microautoradiography showed that [125I]IUdR incorporation was confined to tumor cells in the most superficial layers of the bladder, while incubation of the tumor fragments with [3H]thymidine demonstrated the presence of diffuse mitotic activity also in the deeper tumor mass. Diffusion of labeled IUdR in the general circulation was minimal.

CONCLUSION

Poor diffusion in the tumor mass makes *IUdR unsuitable for intracavitary therapy of bladder cancer, but the role of such an approach in the postsurgical "sterilization" of cancer remnants floating in the bladder lumen after partial cystectomy should be explored.

Strategies for selective targeting of Auger electron emitters to tumor cells

Strategies based on the use of Auger-emitting radionuclides require the targeting of genomic DNA. Iododeoxyuridine and its analogs, which target the process of DNA synthesis, are incorporated randomly in the genome. Alternative targeting agents are likely to assume a greater role in the future. One possibility is the use of triplex-forming oligonucleotides to target genomic DNA on a sequence-specific basis.

METHODS

A model oligonucleotide-targeting system has been developed using a synthetic DNA target sequence based on the N-myc gene. This has been used to examine the ability of alternative oligonucleotides to form DNA triplexes with homopurine-homopyrimidine tract of the target sequence.

RESULTS

Oligonucleotides consisting of G and A or G and T that were designed to bind in an antiparallel orientation to the homopurine strand of the target sequence formed triplexes.

CONCLUSION

Triplex-forming oligonucleotides have potential as therapeutic agents for cytotoxic therapy. They may also have applications in the study of microradiobiological questions, such as the radiosensitivity of individual genes. Methods of synthesizing high specific activity triplex-forming oligonucleotides, probably using short half-life radionuclides such as 123I, are required.

Intratumoral administration of 5-[123I]iodo-2'-deoxyuridine in a patient with a brain tumor

We have initiated a study in which patients suspected of having primary gliomas are given a single intracerebral injection of the thymidine analog 5-[123I]iodo-2'-deoxyuridine ([123I]IUdR). The purpose of the study is to determine the biodistribution of the radiopharmaceutical and to calculate dose estimates to the tumor and normal tissues.

METHODS

A patient with a cystic glioma was injected with [123I]IUdR. Whole-body scans and brain scans were obtained at various times after injection, and blood, urine and stools were collected and assayed for radioactivity to assess its biodistribution and clearance.

RESULTS

Scintigraphic imaging demonstrated that the distribution of radiolabeled IUdR was mainly confined to the tumor (injection site), stomach and bladder. Disappearance from the tumor site and blood clearance were delayed probably due to collection in the cystic lesion. Eighty percent of the injected dose was recovered in the urine.

CONCLUSION

The pharmacokinetics of [123I]IUdR locoregionally administered to a human glioma in situ resembled those observed in a rat glioma model where administration of the radiopharmaceutical radiolabeled with the Auger electron emitter 125I was therapeutically effective.

Preclinical animal studies with radioiododeoxyuridine

We examined the diagnostic and therapeutic potential of 5-iodo-2'- deoxyuridine (IUdR) radiolabeled with the Auger electron emitters 123I and 125I in several animal tumor models.

METHODS

Experiments were conducted using mice bearing an intraperitoneal ovarian tumor (*IUdR by intracavitary injection), and rats bearing either bladder cancer (*IUdR by intravesical injection), brain gliosarcomas (intratumoral injection), or intrathecal gliosarcomas (intrathecal injection).

RESULTS

After locoregional administration, [123I]IUdR and [125I]IUdR localize within tumor, clear rapidly from the rest of the body and are therapeutically effective.

CONCLUSION

When labeled with the Auger electron emitter 123I or 125I, IUdR demonstrates therapeutic efficacy. In addition, [123I]IUdR has a potential role in the scintigraphic detection of cancer.

5-[211 At]astato-2'-deoxyuridine, an alpha particle-emitting endoradiotherapeutic agent undergoing DNA incorporation

When labeled with the subcellular range Auger electron emitters 125I and 123I, the thymidine analogue 5-iodo-2'deoxyuridine (IUdR) is highly cytotoxic but only to cells going through S-phase during exposure to these radiopharmaceuticals. Since 211 At emits alpha-particles of high linear energy transfer, but with a range of a few cell diameters, an IUdR analogue labeled with 211At could markedly improve the homogeneity of tumor dose deposition. Herein we describe the synthesis of 5-[211 At]astato-2'-deoxyuridine ([211 At]AUdR) in 85-90% radiochemical yield via the astatodestannylation of 5-(trimethylstannyl)-2'-deoxyuridine. In vitro studies using the human glioma cell line D-247 MG demonstrated that [211 At]AUdR was virtually identical to [131I]IUdr; both exhibited a linear increase in cell uptake with activity concentration, an inhibition of uptake by 10 micrometers IUdR, and the incorporation of about 50% of cell-bound activity into DNA. In a clonogenic assay, [211 At]AUdR exhibited a high cytotoxicity for D-247 MG cells, with a D(0) equivalent to less than 3 211At atoms/cell.

Tumor-targeting potential of radioiodinated iododeoxyuridine in bladder cancer

Since bladder cancer arises in the superficial lining of the urothelium, it is a likely candidate for site-directed administration of 5-iodo-2'-deoxyuridine radiolabeled with the Auger electron emitter 123I or 125I (*IUdR).

METHODS

We instilled *IUdR for 2 hr directly within the bladder lumen of rats bearing N-methyl-N-nitrosourea (NMU)-induced bladder cancer and conducted scintigraphic, biodistribution and autoradiography (ARG) studies 48 hr and 1 wk later. Control animals were not subjected to the carcinogen but were instilled with *IUdR.

RESULTS

Two groups of animals were identified after instillation of MNU: Group A consisted of rats with hyperplasia and Group B of rats with papillary carcinoma (stages Ta and T1). Scintigraphic detection of carcinomas was achieved with high sensitivity and specificity, and increased tumor-to-normal tissue ratios were obtained in both groups. Moreover, ARG demonstrated that (1) the uptake of *IUdR was observed in the hyperplastic and carcinomatous urothelium but not in the normal urothelium; (2) uptake was detected at a very early stage of tumor development (hyperplasia stage); (3) *IUdR was able to penetrate deep within the bladder wall; and (4) other normal dividing tissues, such as the bone marrow, the small intestine and the large intestine, were free of silver grains (i.e., no DNA-incorporated *IUdR).

CONCLUSION

Since this carrier of Auger electron emitters has antineoplastic effects ([123I]IUdR and [125I]IUdR) in addition to its scintigraphic potential ([123I]IUdR and [131I]IUdR), it holds promise for therapy and early diagnosis of bladder cancer.

5-[125]iodo-2'-deoxyuridine in the radiotherapy of solid CNS tumors in rats

We have been investigating the therapeutic efficacy of the thymidine analog 5-iodo-2'-deoxyuridine (IUdR) when radiolabeled with the Auger electron emitter 125I in rats bearing intrathecal (i.t.) or intracerebral (i.c.) 9L gliosarcoma solid tumors. [125I]IUdR was infused i.t. (via subarachnoid catheters) or intracerebrally over a 5- or 2-day period; equimolar concentrations of [127I]IUdR were infused into control animals. Hind-leg paralysis and/or survival were followed over time. The results indicate that compared with [127I]IUdR, rats bearing intrathecal tumors and infused i.t. with [125I]IUdR showed significant prolongation of the onset of median paralysis (15.2 versus 9 days). Similarly, the median survival of rats bearing intracerebral tumors and infused i.c. with [125I]IUdR was significantly increased (24 versus 17 days). The data substantiate the antineoplastic potential of [125I]IUdR and indicate a promising role for this radiopharmaceutical in the treatment of CNS cancers.

Efficacy of four antiviral agents in the treatment of uncomplicated herpetic keratitis

OBJECTIVE

To evaluate the efficacy of four antiviral agents--1% idoxuridine ointment (group 1), 2% trifluorothymidine ointment (group 2), 3% acyclovir ointment (group 3) and 1% bromovinyldeoxyuridine (BVDU) ointment (group 4)--in herpes simplex keratitis.

DESIGN

Randomized double-blinded clinical trial.

SETTING

Tertiary care institution in New Delhi.

PATIENTS

Eighty patients with uncomplicated herpes simplex keratitis of recent onset who had not previously received antiviral treatment.

MAIN OUTCOME MEASURES

Cure rate, frequency and severity of side effects.

RESULTS

Cure rates of 60%, 90%, 90% and 95% were obtained in groups 1, 2, 3 and 4 respectively. The average healing time was 13.4, 8.9, 8.5 and 7.5 days respectively. Side effects (follicular conjunctivitis, epithelial keratopathy and stinging) were more frequent in group 1 than in the other groups.

CONCLUSIONS

BVDU has a more pronounced therapeutic effect than idoxuridine, trifluorothymidine and acyclovir in uncomplicated epithelial herpetic disease of recent onset that has not previously been treated.

Five-chlorodeoxycytidine and biomodulators of its metabolism result in fifty to eighty percent cures of advanced EMT-6 tumors when used with fractionated radiation

PURPOSE

To extend our findings in previous radiation and biochemical studies with five rodent tumors, in which we used one and occasionally two or three irradiations. The extent of control of the EMT-6 mammary adenocarcinoma was determined using fractionated radiation (12 irradiations) over a 3-week period using the radiosensitizer 5-chloro-2'-deoxycytidine (CldC) and biomodulators of its metabolism: N-(Phosphonacetyl)-L-aspartate (PALA), tetrahydrouridine and 5-fluoro-2'-deoxycytidine (FdC).

METHODS AND MATERIALS

Mammary adenocarcinoma EMT-6 tumors implanted 1 week prior to therapy in BALB/c mice were subjected to single daily doses of focused radiation, not exceeding a total of 60 Gy, on days 2-5 of each week. N-(Phosphonacetyl)-L-aspartate (PALA) was administered on the first day of therapy. Five-fluoro-2'-deoxycytidine and CldC were administered in the morning and afternoon, respectively, of the next 2 days, and CldC was administered on the fourth day. Tetrahydrouridine was always coadministered with FdC or CldC. Drug and radiation treatments overlapped for 3 weeks.

RESULTS

Fifty to 80% cures (usually 70%) were obtained with no apparent morbidity and the same moderate weight loss that occurs with radiation alone. Neither tumor regrowth delay nor cures were obtained with drugs or radiation alone. An apparent threefold dose increase effect was obtained with the end point: "days to reach 4 times initial tumor volume." Increasing the radiation dose threefold (without drugs) resulted in four out of five deaths; increasing the dose twofold (without drugs) resulted in extensive weight loss and hair loss in the entire ventral area and no cures. Increasing the dose of drugs or radiation 1.5-fold, in the complete protocol, did not result in increased morbidity. Comparative studies with Iododeoxyuridine demonstrate the heightened efficacy of CldC.

CONCLUSIONS

One cannot achieve the same results obtained with CldC and the modulators by merely increasing the dose of radiation. There is a significant window of safety in this approach. The evidence we have obtained with EMT-6, the fifth rodent tumor we have studied with CldC, as well as the demonstrated and proposed reasons for its superior efficacy over 5-Iododeoxyuridine (and 5-Bromodeoxyuridine), drugs in current use, indicate that CldC will allow more aggressive treatment of human tumors with radiation than is now feasible.

Novel (E)-5-(2-iodovinyl)-2'-deoxyuridine derivatives as potential cytostatic agents against herpes simplex virus thymidine kinase gene transfected tumors

(E)-5-(2-Iodovinyl)-2'-deoxyuridine (IVDU), its 2'-fluoro-substituted derivatives IVFRU (with fluorine in the ribo configuration), IVFAU (with fluorine in the ara configuration), and the corresponding 3'-chemical delivery system (CDS), or 3'-O-(1-methyl-1,4-dihydropyridyl-3-carbonyl)- substituted derivatives IVDU-CDS, IVFRU-CDS and IVFAU-CDS were evaluated for their cytostatic activity against wild-type (FM3A/O), thymidine kinase (TK)-deficient (FM3A/TK-), and herpes simplex virus type 1 (HSV-1) or HSV-2 thymidine kinase (tk) gene-transfected murine mammary carcinoma FM3A cells (FM3A TK-/HSV-1 TK+ and FM3A TK-/HSV-2 TK+). The test compounds proved highly inhibitory to the proliferation of HSVtk gene-transfected FM3A cells. Their cytostatic activity was within the 0.002 to 0.80 microM range, a compound concentration that is 1000- to 10,000-fold lower than that required to inhibit proliferation of wild-type FM3A/O cells. The target for the cytostatic activity of the test compounds is the cellular thymidylate synthase. In contrast to the parent IVDU compound, IVFRU and IVFAU and their CDS-substituted derivatives proved resistant to phosphorolytic cleavage by human and bacterial thymidine phosphorylase and should be considered as promising candidate compounds for further evaluation for combined gene/chemotherapy of HSVtk gene-transfected tumor cells in animal models.

A multivariate study of non Hodgkin's lymphoma involving proliferation, apoptosis, bcl-2 and the microenvironment

The study was carried out on 22 patients with non-Hodgkin's lymphoma (NHL) who had received sequential infusions of two thymidine analogues iododeoxyuridine (IUdR) and bromodeoxyuridine (BrdU). Cell cycle kinetic studies seemed to differentiate distinctly between low grade lymphoma (n = 8, LI = 2.6%) compared to that of intermediate grade (n = 9, LI = 13%, p = 0.0001) and high grade NHL (n = 5, LI = 16.3%, p = 0.0062). While the majority of 14 intermediate and high grade lymphomas had a high labeling index there were 3/14 patients with a LI of 5.5%, 5.5% and 4.1% respectively. A decrease in the rate of programmed cell death (PCD) or apoptosis due to the overexpression of bcl-2 has been implicated as the possible pathogenesis for follicular lymphoma. We determined the presence of bcl-2 protein immunohistochemically and apoptosis by in situ end labeling of DNA which detects cells in early stages of PCD not recognized morphologically. Nine NHL patients demonstrated PCD ranging from 1%-40%, while it was undetectable in 13/22 patients. Of these 13 cases, 6 showed the presence of bcl-2 expression. To understand the relationship of the microenvironment to the lymphoma cells, the presence of transforming growth factor beta (TGF-beta) was determined immunohistochemically. TGF-beta was present in all the cases where bcl-2 was present, except one. This study highlights some of the key biological features of NHL cells and their microenvironment.

Preoperative radiation therapy and iododeoxyuridine for large retroperitoneal sarcomas

PURPOSE

Local failure is frequent after conventional therapy for patients with retroperitoneal sarcomas. A Phase I/II multimodality approach was used, combining iododeoxyuridine (IdUrd) and radiation therapy, followed by attempted surgical resection, with the goal of improving local control.

METHODS AND MATERIALS

Patients with retroperitoneal sarcomas were treated with three to five consecutive cycles of treatment. Each 14-day cycle consisted of a continuous intravenous infusion of IdUrd on days 1-5, twice a day radiation therapy (1.25 Gy/fraction) on days 8-12, and a break on day 13 and 14. Surgical resection was attempted after three or five cycles. Patients resected after three cycles received an additional two cycles of treatment with radiation directed to the tumor bed. IdUrd dose was escalated in Phase I fashion (1000 mg/m2/day, 1333 mg/m2/day, and 1600 mg/m2/day). The median potential follow-up was 31 months.

RESULTS

Sixteen patients (13 with high grade tumors) were treated. The median maximum tumor size was 17 cm. Resection margins were negative in four patients, microscopically positive in four patients, and grossly positive in three patients. Five patients were not resected. The only grade 4 acute toxicity observed was vomiting which occurred in three patients receiving upper abdominal radiation. Postsurgical and long-term complications were rare. Median survival overall and for resected patients were 18 and 32 months, respectively. Local control was observed in three out of four patients with negative margins (9, 40+, and 51+ months), two out of four patients with microscopically positive margins (4 and 22 months), and one out of three patients with grossly positive margins (46+ months). The overall freedom from local progression was 45% at 24 months.

CONCLUSION

Retroperitoneal sarcomas can be resected after preoperative radiation therapy and IdUrd, with encouraging local control in patients resected with negative or microscopically positive margins. The recommended dose using this drug and radiation schedule appears to be 1600 mg/m2/day, which will form the basis for a Phase II trial.

Treatment of locally advanced cancer of the head and neck with 5'-iododeoxyuridine and hyperfractionated radiation therapy: measurement of cell labeling and thymidine replacement

BACKGROUND

The halogenated pyrimidines 5'-iododeoxyuridine (IdUrd) and 5'-bromodeoxyuridine (BrdUrd) are under active study as radiation sensitizers for a variety of malignancies. Head and neck neoplasms may also be suitable for halogenated pyrimidine-mediated sensitization; previous regimens using intra-arterial BrdUrd delivery, however, were poorly tolerated.

PURPOSE

A pilot study was undertaken with the use of intravenous IdUrd with hyperfractionated radiotherapy to assess tolerance. In addition, serial tumor biopsy specimens were obtained to determine the kinetics of IdUrd labeling and incorporation.

METHODS

Twelve patients with squamous cell carcinomas of the head and neck (one patient had stage II cancer, one had stage III, and 10 had stage IV) were treated with hyperfractionated radiation therapy at a dose of 1.2 or 1.5 Gy twice a day, to a total dose in the range of 70-76 Gy. IdUrd (1000 mg/m2 per day) was infused for a maximum of 14 days at the beginning and then again during the middle of the radiotherapy. A tumor biopsy specimen was obtained from 11 patients following initiation of treatment with IdUrd. Eight patients consented to serial biopsy to allow the study of IdUrd-labeling indices and thymidine replacement over time. Incorporation of IdUrd into tumor DNA was determined by high-performance liquid chromatography, and cell labeling was determined with the use of an anti-BrdUrd/IdUrd monoclonal antibody in conjunction with flow cytometry. Patients continue to be followed to assess local control.

RESULTS

A plot of corrected IdUrd replacement as a function of infusion time suggests the possibility of a plateau after 5-7 days of infusion at 7.5%-8%. The average rate of replacement from days 1 to 5 was 1.3% per day and was determined by linear regression analysis. Acute toxic effects, especially mucositis, were severe enough to require delays in the radiation therapy. Eleven of 12 patients treated had complete clinical remissions. Seven of these patients remain clinically free of local disease at the time of death or most recent follow-up.

CONCLUSIONS

The level of IdUrd incorporation and cell labeling should be adequate to produce sensitization. However, the treatment as prescribed in this study (two 14-day infusions of IdUrd during radical radiotherapy with only one planned split) was not completed in a single patient because of either dose-limiting hematologic toxicity or severe mucositis necessitating treatment break. Since this particular regimen is not tolerable, future protocols will have shorter exposures to IdUrd.

IMPLICATIONS

Previous regimens using halogenated pyrimidine radiosensitizers have generally used protracted drug delivery schedules. In this study, a high level of IdUrd labeling was measured after 5-7 days of drug infusion. The halogenated pyrimidines deserve further study with the use of repetitive short courses to reduce toxicity and possibly improve efficacy.

Current experience with antiviral therapy for acute herpes zoster

Inhibition of varicella-zoster virus replication during acute herpes zoster would, theoretically, accelerate cutaneous healing and reduce the pain, both acute and chronic, associated with shingles. Early antiviral drugs were of limited efficacy, excessively toxic, or needed to be given parenterally, and were unsuitable for use in immunocompetent individuals. Acyclovir was a significant advance and remains the antiviral drug of choice for herpes zoster. There is ample evidence for its efficacy in acute illness, but its ability to influence post-herpetic neuralgia is controversial. This review also discusses the role of adjunctive therapy with steroids in acute shingles.

Preclinical and clinical aspects of biomodulation of 5-fluorouracil

Although single agent 5-FU has for many years been the standard therapy for advanced colorectal malignancies, a number of recent clinical trials show higher response rates with biomodulation of 5-FU by several different agents. In general, trials of leucovorin, methotrexate, interferon, and PALA given in biomodulatory doses and sequences with 5-FU have demonstrated comparable response rates over a broad range. However, in the absence of controlled direct comparative phase III trials, final judgement on clinical superiority of a particular regimen must be reserved. Nevertheless, on the basis of current data, certain approaches appear promising and warrant further investigation. Compared to single agent 5-FU, survival benefit has been demonstrated with both low and high dose leucovorin/5-FU regimens and response rates in the 20-50% range appear reproducibly higher than those of 5-FU alone. Low dose and either continuous infusion or repetitive dosing of leucovorin, as well as the effect of treatment sequence and intervals between drugs, require additional investigation. When given 20-24 h before 5-FU, methotrexate achieves response rates similar to leucovorin modulated 5-FU, but the potential role of rescue leucovorin used in many of the trials makes definitive interpretation difficult. Interferon/5-FU regimens attaining response rates of 30-40% are promising but need to be carefully and rationally designed. Low dose PALA with effective doses of 5-FU achieving responses in 35-45% of patients represent a marked improvement in earlier trials of high dose PALA, but additional studies with higher doses not compromising 5-FU dose intensity should be considered. Certainly, the concomitant use of multiple modulating agents also needs further investigation. While many such trials already performed attained results no better than single agent biomodulation, the preliminary results obtained by Grem and colleagues with IFN/LV/5-FU in untreated patients, and by Conti et al. using TMTX/LV/5-FU in previously treated patients are encouraging. Further understanding of the mechanisms of action and interaction of modulating agents should allow additional rational combinations to be explored clinically. Cisplatin biomodulation of 5-FU has been studied in gastrointestinal and head and neck malignancies achieving excellent results in the latter group. Preclinical evidence exists which suggests, however, that 5-FU modulation of cisplatin may be more effective, especially when 5-FU is administered 24 h or more before cisplatin. Clinical investigation of this sequence is currently lacking. Data to support the clinical promise of AZT, IdUrd, uridine, and the benzylacyclouridines are not yet available, although preclinical and preliminary clinical studies are promising.

Global comparison of radiation and chemotherapy dose-response curves with a test for interaction

In the analysis of the effects of radiation or drugs on clonogenic survival data of mammalian cells, it is often advantageous to compare entire dose-response curves generated under different experimental conditions rather than to conduct single-dose comparisons. We propose a two-stage method for the global comparison of such curves. The first stage consists of individual fits of a flexible model to the dose-response sequences. The second stage treats the fitted coefficients as data and analyzes them jointly using a multivariate analysis of variance. For dose-response models of the type commonly used in the analysis of clonogenic survival data, this method allows the definition of a statistical test for interaction among treatments. That is, a test that the combination of agents produces a dose-response curve which is not what would be expected if the agents were acting multiplicatively (additively in the log cell survival scale). Analyses of cell survival curves by this method for experiments on iododeoxyuridine-mediated radiosensitization and on chemosensitization of bleomycin cytotoxicity in a human bladder cancer cell line (647V) are presented.