Platinum-DNA adducts in leukocyte DNA correlate with disease response in ovarian cancer patients receiving platinum-based chemotherapy

Aphidicolin markedly increases the platinum sensitivity of cells from primary ovarian tumours

Enhanced DNA repair has been observed in cisplatin-resistant ovarian cancer cell lines. This resistance can be modulated, on co-incubation with aphidicolin in established cell lines and animal tumour models, by inhibiting DNA polymerases. We describe a study of the in vitro modulation effect of aphidicolin on cisplatin and carboplatin using fresh cells harvested from biopsy samples or ascitic fluids from 25 patients with ovarian adenocarcinoma. The MTT assay was used to measure cell survival after drug exposure. Aphidicolin (up to 30 microM) showed no cytotoxicity when tested alone. Forty-seven comparisons were made between drug with and without aphidicolin, and 37 (79%) cases demonstrated a significant increase in sensitivity to the platinum agents on co-incubation. Overall, there was a median 10-fold (range 1.64- to 58.5-fold) increase in sensitivity. When patients were grouped according to in vitro sensitivity to platinum, aphidicolin had a significantly greater effect in the "resistant' group, causing a median 13.5-fold increase in sensitivity compared with 2.4-fold in the "sensitive' group. Furthermore, a positive correlation between the LC50 for platinum and the corresponding fold increase in sensitivity suggests that aphidicolin overcomes platinum resistance in fresh cells from primary tumours. These results encourage the further development of this interesting compound.

Relationship between the exposure to cisplatin, DNA-adduct formation in leucocytes and tumour response in patients with solid tumours

The study was designed to investigate possible relationships between tumour response and exposure to cisplatin (area under the curve of unbound cisplatin in plasma, AUC) and DNA-adduct formation in leucocytes (WBC) in patients with solid tumours. Patients were treated with six weekly courses of cisplatin at a dose of 70 or 80 mg m-2. The AUC was determined during the first course and DNA-adduct levels in WBC during all courses at baseline, 1 h (A(max)) and 15 h after a 3 h infusion of cisplatin. The area under the DNA-adduct-time curve (AUA) was calculated. The tumour response was determined after six courses. Forty-five evaluable patients received 237 courses of cisplatin. Sixteen patients with head and neck cancer received a dose of 80 mg m-2 and 29 with various other tumour types received 70 mg m-2 plus daily 50 mg oral etoposide. There were 20 responders (partial and complete) and 25 non-responders (stable and progressive disease). The AUC was highly variable (mean +/- s.d. = 2.48 +/- 0.51 micrograms h-1 ml-1; range 1.10-3.82) and was closely correlated with the AUA (r = 0.78, P < 0.0001) and A(max) (r = 0.73, P < 0.0001). The AUC, AUA and A(max) were significantly higher in responders than in non-responders in the total population (P < 0.0001) and in the two subgroups treated at 70 or 80 mg m-2. In logistic regression analysis AUC, AUA and A(max) were important predictors of response. The magnitude of exposure to cisplatin is, through DNA-adduct formation, the major determinant of the response rate in this population. Hence, individualised dosing of cisplatin using AUC or DNA-adducts should lead to increased response rates.

Kinetic Analysis of the Reactions between GG-Containing Oligonucleotides and Platinum Complexes. 1. Reactions of Single-Stranded Oligonucleotides with cis-[Pt(NH(3))(2)(H(2)O)(2)](2+) and [Pt(NH(3))(3)(H(2)O)](2+)

Using concentration measurements based on high performance liquid chromatography, we have investigated the kinetics of reaction between single-stranded oligonucleotides containing a d(GpG) sequence, i.e., d(GG), d(TGG), d(TTGG), and d(CTGGCTCA), and the platinum complexes cis-[Pt(NH(3))(2)(H(2)O)(2)](2+) (1) and [Pt(NH(3))(3)(H(2)O)](2+) (2). The rate constants for the substitution of one aqua ligand of platinum in 1 or 2 by each guanine of the oligonucleotides were individually measured, as well as, for 1, those for the subsequent conversion of the monoadducts to the diadduct. For the platination of d(GG) and d(TGG), the rate constants are similar for the 5'- and 3'-guanines. The longer oligonucleotides d(TTGG) and d(CTGGCTCA) are platinated slightly faster on the 5'-G than on the 3'-G. 2 shows a similar slight preference for the 5'-guanine, but it reacts by a factor of 4-10 more slowly than 1. For both complexes, the platination rate constants increase with increasing oligonucleotide length. Platination of the 5'-G by 1 is 1 order of magnitude faster on d(CTGGCTCA) than on d(GG). Concerning the chelation step giving the GG diadduct of 1, the longer the oligonucleotide, the larger is the ratio between the rates of the cyclization of the 3'- and 5'-monoadducts k(3)(')(c) and k(5)(')(c): k(3)(')(c)/k(5)(')(c) equals 1.4 for d(GG) and 3.3 for d(CTGGCTCA).

Persistence of cisplatin-induced DNA interstrand crosslinking in peripheral blood mononuclear cells from elderly and young individuals

DNA interstrand crosslinks (ISCL) produced by the incubation of human peripheral blood mononuclear cells (PBMs) with cisplatin (CDDP) were measured in two populations of volunteers, one aged less than 25 years and the other, greater than 72 years. The technique of fluorometric alkaline elution was used to measure DNA interstrand crosslinking with time after a 1-h exposure to drug. The samples from the young group showed a more consistent pattern of crosslink formation and removal, with extensive, or in some cases complete, repair at 48 h. Those from the elderly group showed considerable inter-individual variation and significantly higher mean levels of crosslinking at 24 and 48 h. No samples showed complete repair at 48 h in this population. These results indicate an impaired DNA repair capacity in the cells from the elderly group. This may be a factor in the poor tolerance of chemotherapy in the ageing population.

Current sample handling methods for measurement of platinum-DNA adducts in leucocytes in man lead to discrepant results in DNA adduct levels and DNA repair

DNA adduct levels were measured with atomic spectroscopy in white blood cells (WBCs) from patients with solid tumours who were treated with six weekly courses of cisplatin. In 21 patients (I) the WBCs were collected after thawing frozen whole-blood samples according to a previously described method. In 32 other patients (II) WBCs were collected immediately after blood sample collection. The two methods for WBC collection were also compared in vitro. The maximal DNA adduct levels in vivo after the first course were in I 2.48 +/- 1.14 and in II 1.28 +/- 0.40 pg of platinum per microgram of DNA (P < 0.0001). The DNA 'repair' in the first course (DNA adduct level at the end of the infusion minus the level 15 h post infusion) was in I 40% +/- 29% and in II 18% +/- 29% (P = 0.009). These differences were consistent in all measured courses. In vitro, the DNA adduct levels in the freshly prepared WBCs were significantly lower at 0, 1 and 4, but not 24 h, after start of the incubation with cisplatin than in the WBCs collected after freezing and thawing the blood sample. The same experiment with carboplatin in vitro also resulted in significantly lower adducts in freshly isolated WBCs. The higher DNA adduct levels and DNA 'repair' in I are caused by remaining unbound cisplatin in the sample tubes, which can form DNA adducts ex vivo. The same results in vivo can be anticipated when carboplatin is used.

Correlation of gene-specific damage with cisplatin between human adenocarcinoma cells and peripheral blood mononuclear cells analyzed by polymerase chain reaction-stop assay

We investigated gene-specific damage in adenocarcinoma cells, obtained from pleural effusions of 9 primary lung cancer patients, induced by incubation with cisplatin for 3 h in vitro. The 2.7 kb fragment of the hypoxanthine phosphoribosyltransferase (HPRT) gene was amplified by the polymerase chain reaction (PCR) to quantify the DNA damage. A 7-fold difference in the extent of gene-specific damage among the patients was observed. Mononuclear cells (MNC) were obtained from freshly isolated blood from the same patients before they received chemotherapy. These cells were also incubated with cisplatin in vitro, and PCR amplification of the HPRT gene was carried out. A 4-fold variation of DNA damage among the patients was observed. Moreover, there was a linear correlation between the extents of the DNA damage in the tumor cells and MNCs (R2 = 0.676, P = 0.0016). These results suggest that the PCR-stop assay could be used to detect interindividual variations in the extent of gene-specific damage in both tumor cells and MNC from the same patients induced by cisplatin treatment. In conclusion, MNC could be used to analyze cisplatin-induced gene-specific damage in cancer patients whose tumor cells are inaccessible.

Rapid polymerase chain reaction assay to detect variation in the extent of gene-specific damage between cisplatin- or VP-16-resistant and sensitive lung cancer cell lines

We previously established a rapid and facile polymerase chain reaction (PCR)-stop assay for quantitation of specific gene damage in very small numbers of cells. The present study investigated whether the PCR-stop assay was able to detect variation in the extent of DNA damage in transcribed active genes between cisplatin- or VP-16-resistant and sensitive cells. The assay demonstrated that about twice as much genetic damage occurs in PC-9 cells than in cisplatin-resistant PC-9/CDDP cells following cisplatin exposure and about 4.6 times more damage occurs in H69 than in VP-16-resistant H69/VP cells following VP-16 exposure. These results show that DNA damage, as detected by PCR-stop assay, correlates with cytotoxicity. In conclusion, the PCR-stop assay could be useful in detecting variation in DNA damage in specific genes.

Platinum-DNA adducts assayed in leukocytes of patients with germ cell tumors measured by atomic absorbance spectrometry and enzyme-linked immunosorbent assay

BACKGROUND

Platinum-DNA adducts can be measured in peripheral blood cells, and high adduct levels have previously been correlated with favorable clinical response to platinum-based therapy in patients with germ cell tumors and ovarian cancer.

METHODS

To evaluate the relationship between platinum-DNA adducts and clinical response to chemotherapy, 36 patients with germ cell tumors treated with cisplatin-based chemotherapy had platinum-DNA adducts assayed in leukocytes by atomic absorption spectrometry (AAS) and cisplatin-DNA enzyme-linked immunosorbent assay (ELISA). Three chemotherapy regimens were involved: cisplatin and etoposide (Regimen A); carboplatin and etoposide (Regimen B); and cyclophosphamide, vinblastine, dactinomycin, bleomycin, and cisplatin [VAB-6] with or without high dose carboplatin plus etoposide plus autologous bone marrow rescue (Regimen C). Blood samples were drawn before and after each cycle of chemotherapy.

RESULTS

One hundred ninety-two blood samples were assayed by AAS and 137 by ELISA: DNA adducts measured by AAS and ELISA increased immediately after treatment and decreased during the intervening time before the next treatment. DNA adducts were measurable by both methods 4-8 weeks after the last cycle of therapy. The peak and mean adduct levels measured in samples drawn immediately after Cycles 1 and 2 and after all cycles were analyzed in terms of their relationship to clinical response. In contrast to numerous prior studies, a positive correlation was not observed between DNA adduct formation as determined by either AAS or ELISA and favorable clinical responses.

CONCLUSIONS

This study demonstrated that peak and mean platinum-DNA adduct levels were influenced by the dose and schedule of the platinum analogue. For example, treatment with VAB-6 with or without high dose carboplatin and etoposide (Regimen C) resulted in significantly higher adduct levels when measured by AAS compared with Regimen A or B. Inconsistencies between studies regarding observed correlations of DNA adducts and treatment outcome may be attributable to differences in platinum analogue, dose, schedule, and timing of sample procurement. These factors must be considered in future studies.

Pharmacokinetic and biotransformation studies of ormaplatin in conjunction with a phase I clinical trial

Ormaplatin is a second-generation platinum (Pt) analogue with in vitro activity against some cisplatin-resistant malignant cell lines. We have evaluated the pharmacokinetics and biotransformations of ormaplatin during a phase I trial in which ormaplatin was administered by daily 30-min infusions on 5 consecutive days every 28 days. Sixteen patients received 25 courses at doses ranging from 5.0 to 11.6 mg/m2 per day. Pharmacokinetic parameters determined for ultrafilterable Pt measured by atomic absorption spectrophotometry revealed a short half-life (t1/2 16 min), moderate volume of distribution (Vd 12 l/m2), and relatively fast systemic clearance (Cls 544 ml/min per m2). Cls and percentage of drug unbound decreased during the 5-day administration period. Average systemic exposure increased with dose; however, inter-individual variability in Cls produced overlap in systemic exposure between the dose levels. The major active biotransformation product [PtCl2(dach)] was evaluated at the highest dose level by HPLC. This product decayed monoexponentially with a mean t1/2 of 13 min and a higher degree of pharmacokinetic variability than that of ultrafilterable Pt at this dose. No unreacted ormaplatin was detected; however, several inactive biotransformation products persisted for at least 120 min. Approximately 32% of the dose was excreted in the urine during the first day, one-third of this during the initial 1.5 h. The human pharmacokinetic characteristics of ormaplatin resemble those of cisplatin; however, additional study will be required to discern which analyte of ormaplatin correlates best with clinical effects.

Enhanced repair of a cisplatin-damaged reporter chloramphenicol-O-acetyltransferase gene and altered activities of DNA polymerases alpha and beta, and DNA ligase in cells of a human malignant glioma following in vivo cisplatin therapy

Current evidence suggest an important role for increased repair of drug-induced DNA damage as one of the major mechanisms involved in tumor cell resistance to cis-DDP. In this study, we examined the DNA repair capacity and the activities of three DNA repair related proteins, namely, DNA polymerases alpha and beta, and total DNA ligase in cells of a malignant oligodendroglioma obtained from a patient before therapy and compared it with those of a specimen of the tumor acquired after the patient had failed cis-DDP therapy. DNA repair capacity was quantitated as the extent of reactivation of the chloramphenicol-O-acetyltransferase (CAT) gene in a eukaryotic expression vector that had been damaged and inactivated by prior treatment with cis-DDP and then transfected into the tumor cells. The extent of DNA-platinum adduct formation in the expression vector was determined by flameless atomic absorption spectrometry. The level of cis-DDP resistance of cells of the two tumors was determined with the capillary tumor stem cell assay. We observed a 2.8-fold increased capacity to repair Pt-DNA adducts and reactivate the CAT gene in cells of the tumor obtained after cis-DDP therapy, compared to cells of the untreated tumor. This was associated with increases of 9.4-fold and a 2.3-fold, respectively, in DNA polymerase beta and total DNA ligase activities in cells of the treated tumor. At 5 microM cis-DDP, there was a 5.9-fold increase in the in vitro cis-DDP resistance of post-therapy tumor cells relative to cells of the untreated tumor.(ABSTRACT TRUNCATED AT 250 WORDS)

Quantitation of cell-associated doxorubicin by high-performance liquid chromatography after enzymatic desequestration

A method for measuring cellular concentrations of the anthracycline doxorubicin was developed. The assay involves cell lysis and protein degradation by detergent and proteinase K treatment followed by DNA hydrolysis using DNase I. Prior to high-performance liquid chromatography, samples are deproteinized by the addition of ZnSO4 and methanol. The assay is linear with respect to both the cellular drug content and the number of cells assayed over the ranges tested, and drug recovery is close to 100%. The method has a limit of detection of 50 fmol injected doxorubicin. Within run and between-day coefficients of variation have consistently been found to be in the 5% and 10% range, respectively, in different cell lines exposed to doxorubicin in vitro. The method has been evaluated in analyses of doxorubicin levels in mononuclear blood cells of patients. The assay offers several advantages over commonly used organic extraction techniques and may improve cellular drug monitoring during anthracycline therapy in patients.

Cisplatin-DNA damage recognition proteins in human tumour extracts

Enhanced repair of DNA adducts may be a cause of cis-diamminedichloroplatinum(II) resistance in solid malignancies. Binding of specific damage recognition proteins to the sites of DNA damage may be involved in the initial steps of DNA repair, or alternatively may block access of repair proteins to damaged DNA. Proteins which bind specifically to CDDP-modified DNA were identified in cell extracts from human ovarian carcinoma cell lines by two assays, the gel mobility shift assay and the southwestern blot. In the first assay, proteins complexed with CDDP-modified oligonucleotide and produced two retarded bands, B1 and B2. The B2 complex was partially purified from an ovarian cell extract by anion exchange FPLC, and was shown to bind to DNA damaged by CDDP but not by transDDP or UV irradiation. Using the southwestern blot, proteins of 97, 48, and 25 kD were identified; each of these bound to CDDP-modified but not undamaged oligonucleotide. The partially purified B2 protein fraction contained both the 97 and the 25 kD damage recognition proteins. A human ovarian carcinoma cell line selected in vitro for CDDP-resistance (OV1P/DDP), which is 5-fold more resistant to CDDP than the parental line (OV1P), showed an increase in binding of the 97 and 48 kD damage recognition proteins compared with the parental line. Twelve ovarian cell lines differed by up to 3-fold in their expression of these proteins, but there was no correlation between the amount of damage recognition protein in a cell extract and the cellular sensitivity to CDDP. Damage recognition proteins were also demonstrated in extracts prepared from biopsies of human ovarian, cervical, and testicular malignancies, but there was no apparent difference in the binding activity in extracts from tumours of different CDDP-sensitivity. The functional role of these damage recognition proteins remains to be established.

WR2721 as a modulator of cisplatin- and carboplatin-induced side effects in comparison with other chemoprotective agents: a molecular approach

Cisplatin is an active cytostatic that became successful in the treatment of several types of solid tumours after its nephrotoxic potential was controlled by hydration and diuresis. Thiol compounds were tested to reduce further cisplatin-induced nephrotoxicity. Thiosulphate is rapidly excreted by the kidneys and protects against cisplatin-induced nephrotoxicity by inactivating reactive platinum species in the kidney. Due to inactivation of cisplatin in the circulation, thiosulphate also interferes with its antitumour activity. Therefore, it is mainly used in two-route schedules, whereby cisplatin is delivered locally to the tumour (i.p. or i.a.) while systemic (i.v.) thiosulphate protects the kidneys. Diethyldithiocarbamate was shown to protect against cisplatin-induced nephrotoxicity in several animal models by reversing cellular damage. However, in the clinic it has been less successful, partly due to its central nervous system toxicity. The endogenous thiol compounds glutathione and metallothionein have been shown to reduce cisplatin-induced toxicity both in animal models and in clinical trials. However, the results are rather preliminary and a reduction in therapeutic efficacy may be expected, for both glutathione and metallothionein have been reported to be involved in platinum resistance. The thioether methionine has been shown to reduce cisplatin-induced nephrotoxicity in animal models but it has not yet been tested in the clinic. Cisplatin-induced acute emesis can be sufficiently controlled with a new class of 5-hydroxytryptamine-3 (5HT3)-receptor blockers, but delayed emesis remains a problem. High-dose cisplatin regimens with protection of the kidneys induces ototoxicity, peripheral neuropathy and myelotoxicity, which become dose-limiting. Neurotoxicity was partly reversed by the neurogenerative agent ORG2766, but this agent does not reduce other cisplatin-induced toxicities. Therefore, an agent capable of protecting multiple non-tumour tissues is needed. Carboplatin is a second-generation analogue of cisplatin with less nephro-, neuro- and ototoxicity. Carboplatin is at least as active as cisplatin at its maximum tolerated dose, which is defined by its myelotoxicity. Protection from carboplatin-induced myelotoxicity may be controlled by autologous bone marrow transplantation and/or hematopoietic growth factor infusions. High-dose carboplatin schedules may cause nephrotoxicity, neurotoxicity and ototoxicity. Again, the protection of multiple non-tumour tissues is needed. WR2721 appears to be such a modulating agent capable of protecting multiple non-tumour tissues. It was shown to be preferentially metabolized and taken up as the thiol metabolite WR1065 by non-tumour tissues as compared with (hypoxic) solid tumours. It was shown to protect mice from cisplatin-induced nephrotoxicity and from cisplatin- and carboplatin-induced myelotoxicity without interfering with the antitumour activity.(ABSTRACT TRUNCATED AT 400 WORDS)

Platinum drug-DNA interactions in human tissues measured by cisplatin-DNA enzyme-linked immunosorbent assay and atomic absorbance spectroscopy

Studies of platinum drug-DNA adduct formation in tissues of cancer patients have involved both atomic absorbance spectroscopy (AAS), which measures total DNA-bound platinum, and anti-cisplatin-DNA enzyme-linked immunosorbent assay (ELISA), which detects a fraction of the AAS-measurable adduct. These studies were designed to explore mechanisms of drug-DNA interactions, to make correlations with clinical outcome, and possibly to validate DNA adduct measurements for use in occupational and environmental biomonitoring. The results, determined by both ELISA and AAS, demonstrate that cisplatin and its analog carboplatin bind to DNA in many human organs, including kidney, brain, peripheral nerve, and bone marrow, which are sites for drug toxicity. Platinum was also observed bound to ovarian tumor DNA. The adducts were highly persistent, being measurable in tissues obtained at autopsy up to 15 months after the last administration of platinum chemotherapy. A comparison of blood cell DNA adduct levels, determined by ELISA, and the clinical response of 139 patients with ovarian, testicular, colon, or breast cancer demonstrated a strong correlation between failure to form DNA adducts and failure of therapy. Conversely, patients who formed high levels of DNA adduct were most likely to respond favorably. A similar correlation was not observed for adducts determined by AAS; that is, the average total DNA-bound platinum levels were the same for patients who did not respond to therapy and for patients who had any kind of response. Thus, in this study, human blood cell DNA adducts measured by ELISA correlate with tumor remission, while those measured by AAS do not.

Synergism between alkylating agent and cis-platin with moderate local hyperthermia: the effect of multidrug chemotherapy in an animal system

The combined effect of multidrug chemotherapy given in combination with hyperthermia was investigated using early-generation isotransplants of a spontaneous fibrosarcoma, FSa-II in C3Hf/Sed mice. Combinations of various types of chemotherapeutic agents, including alkylating agents, cyclophosphamide (CY) and 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU); antibiotics, bleomycin (BLM) and mitomycin C (MMC); an antimetabolite, 5-fluorouracil (5FU); and a platinum complex, cis-diamminedichloroplatinum(II) (cDDP), were examined using the tumour growth (TG) time assay. Simultaneously, the effect of glucose on the response to thermochemotherapy was investigated. Graded doses of the multidrugs were given i.p. immediately before hyperthermia with or without a glucose dose of 5 g/kg given i.p. 60 min before hyperthermia. Hyperthermia was given by immersing the tumour-bearing murine feet into a water bath set at 41.5 +/- 0.05 degrees C for 60 min. Dose-response curves were obtained between the TG time and drug dose. The thermal enhancement ratio (TER) was expressed as a ratio of the slope of the dose-response curve obtained at 41.5 degrees C to that obtained at room temperature. To evaluate normal tissue damage, the number of white blood cells (WBC) was counted from a day before treatment to the 21st day after treatment. A substantial thermal enhancement of the anti-tumour effect was observed in all five multidrug regimens tested. Glucose administered prior to thermochemotherapy further enhanced the antitumour effect. The TER was largest for the combination of CY+cDDP (TER was 5 without glucose). The second largest TER was obtained for a combination of CY+cDDP+MMC (TER was 4.1 without glucose and 6.5 with glucose). The antitumour effects of these two combinations were synergistic at a test elevated temperature only. No synergistic effect was found at room temperature for any of the drug combinations tested. The smaller TERs were observed in the treatment regimens that included 5FU. In general, a decrease in the number of WBC following multidrug chemotherapy was slightly less than that following the individual drugs.

Mutagenicity and genotoxicity of the major DNA adduct of the antitumor drug cis-diamminedichloroplatinum(II)

The mutagenicity and genotoxicity of cis-[Pt(NH3)2[d(GpG)-N7(1),-N7(2)]] (G*G*), the major DNA adduct of the antitumor drug cisplatin, has been investigated in Escherichia coli. A duplex bacteriophage M13 genome was constructed to contain the G*G* adduct at a specific site in the (-) strand. The singly platinated duplex genome exhibited a survival of 22% relative to that of the unplatinated control genomes, and this value rose to 38% in cells treated with ultraviolet light to induce the SOS response. Singly platinated single-stranded genomes were also produced. Replication of the single- and double-stranded genomes in vivo yielded SOS-dependent, targeted mutations at frequencies of 1.3% and 0.16%, respectively. The mutagenic specificity of G*G* in both single- and double-stranded DNA was striking in that 80-90% of the mutations occurred at the 5'-platinated G. Approximately 80% of the mutations were G-->T transversions at that site. A model of mutagenesis is presented to explain this mutational specificity with respect to current understanding of platinum-DNA adduct structure.

Clinical pharmacokinetics of carboplatin

Carboplatin [diammine(1,1-cyclobutanedicarboxylato)platinum(II)] is one of the most promising second generation platinum compounds. Its greater chemical stability in comparison with cisplatin accounts for its lower reactivity with nucleophilic sites of DNA, and may therefore be related to the higher dose necessary to obtain an antitumour effect similar to that of cisplatin. The lower reactivity with proteins may be related to the observed reduction in nephrotoxicity. Its dose-limiting toxicity is myelosuppression, especially thrombocytopenia. Total and ultrafilterable platinum are detected by flameless atomic absorption spectrophotometry, and high performance liquid chromatography with either UV or electrochemical detection is used for the quantification of carboplatin. These 3 species have been measured as a function of time in biological fluids and tissues to determine their pharmacokinetics. Carboplatin has high stability in infusion fluids in the absence of chloride, but it is less stable in plasma and urine. Protein binding is limited, while the low uptake in red blood cells appears to be species dependent. Commonly, carboplatin is administered intravenously, and its pharmacokinetics are linear up to a dose of 2400 mg/m2. In comparison with cisplatin, carboplatin has longer half-lives of ultrafilterable platinum (23 and 120 min versus 6 and 36 min for distribution and initial elimination half-lives, respectively) and a higher cumulative urinary platinum excretion (77 versus 28% of the dose in 24 h), both due to the lower protein binding of carboplatin. The terminal half-life of total platinum is comparable between the 2 compounds (5.8 versus 5.4 days). This value most probably represents the breakdown of proteins to which both compounds are irreversibly bound. Relationships between pharmacokinetics (area under the curve) and pharmacodynamics (extent of myelosuppression or extent of existing kidney failure) have allowed the development of equations for rational dosage reduction. Intraperitoneal administration has been used in cases of residual ovarian cancer: as a result of its higher hydrophilicity and higher molecular weight, carboplatin is cleared more slowly from the peritoneal cavity than cisplatin (6 vs 15 ml/min). The low bioavailability (4 to 12%) and the gastrointestinal side effects observed did not warrant further studies with oral administration. In contrast to results from animal studies, the modulation of carboplatin-induced myelosuppression by diethyldithiocarbamate (DDTC) was not clinically successful. Valuable alternatives may be the combination with WR2721 or colony-stimulating factors.

Measures of renal function in patients with cisplatin-related chronic renal disease

Twenty-seven patients with advanced stage refractory ovarian cancer were studied to determine if chronic stable cisplatin-related renal dysfunction was present. Medical histories were examined to determine the types of therapy previously received as well as the total previous platinum doses received that ranged from 200 to 2,100 mg/m2. Standard assessments of renal function were made prior to administering current chemotherapy or immunotherapy to the patient, which included 24-hour creatinine clearance, serum creatinine, and blood urea nitrogen (BUN). For patients with a 24-hour creatinine clearance of less than 60 mL/minute, serum creatinine was highly variable (range: 0.9 to 2.0 mg/dL) and was not related to the degree of diminution in the 24-hour creatinine clearance value. Conversely, for patients with a serum creatinine of less than 1.5, the 24-hour creatinine clearance values varied by almost three-fold, ranging between 46 and 120 mL/minute. Two patients with serum creatinines of less than 1 had creatinine clearances of less than 50 mL per minute. Similarly, BUN measurements did not correlate with 24-hour creatinine clearance values, and the 24-hour creatinine clearance value was not related to the total cumulative platinum dose. We conclude that patients who receive substantive doses of cisplatin may experience chronic stable cisplatin-related renal dysfunction and that serum creatinine cannot be relied on to assess the degree of renal compromise. In such patients, we recommended that the 24-hour creatinine clearance value should be used when medical management is influenced by renal function.

Antineoplastic drug resistance and DNA repair

Important aspects of the DNA repair mechanisms in mammalian, and especially human, cells are reviewed. The DNA repair processes are essential in the maintenance of the integrity of the DNA and in the defense against cancer. It has recently been discovered that the DNA repair efficiency differs in different regions of the genome and that active genes are preferentially repaired. There is mounting evidence that DNA repair processes play a role in the development of drug resistance by tumor cells. We will discuss such data as well as further approaches to clarify the relationship between DNA repair and antineoplastic drug resistance. Specifically, there is an increasing need to investigate the intragenomic heterogeneity of DNA repair and correlate the repair efficiency in specific genes to aspects of drug resistance. We also discuss the therapeutic potential of inhibiting the DNA repair processes and thereby possibly overcoming drug resistance.

Antibodies against cisplatin-modified DNA and cisplatin-modified (di)nucleotides

Cytotoxic effects of cis-diamminedichloroplatinum-(II) (cis-DDP) are thought to be mediated by binding to DNA. Studies on binding of cis-DDP to cellular DNA rely heavily on the availability of specific antibodies. We therefore raised and characterized four rabbit antisera: one against cis-DDP-modified DNA (antiserum NKI-A59) and three others against the cis-DDP-modified (di)nucleotides cis-Pt(NH3)2d(pApG) (NKI-A68), cis-Pt(NH3)2d(GMP)2 (NKI-A10), and Pt(NH3)3dGMP (NKI-A39). Reactivities to platinum compounds were determined in an enzyme-linked immunosorbent assay (ELISA) and in a quantitative immunocytochemical assay. In the ELISA, NKI-A59 showed a high affinity for DNA heavily substituted with either cis-DDP or CBDCA [cis-diammine(1,1-cyclobutanedicarboxylato)platinum(II)]; amounts of platinum per well giving 50% inhibition (IA50) were as low as 15 and 76 fmol, respectively. NKI-A59 also showed affinity to cis-DDP-modified poly[d(G-C)].poly[d(G-C)], poly(dC), and poly(dG). No affinity was found for trans-DDP [trans-diamminedichloro-platinum(II)]-modified DNA, enzymatically digested cis-DDP-DNA, or cis-DDP-DNA, or cis-DDP-modified poly(dA).poly(dT), oligo(dA)15.oligo(dT)15, oligo(dG)21, oligo(dG)42, or oligo(dAAAG)10. The efficiency of binding to cis-DDP-DNA decreased with decreasing DNA modification levels. Although other cis-DDP-DNA- and cis-DDP-(di)nucleotide-specific antisera have been identified, NKI-A59 is the first antiserum described that is suitable for the in situ detection of cis-DDP-DNA adducts at clinically relevant platinum levels. Adduct-specific immunostaining signals in cultured RIF-1 cells or rat liver paralleled platinum-DNA binding as measured by atomic absorption spectroscopy. The antisera NKI-A68, NKI-A10, and NKI-A39 showed high affinity for their corresponding haptens and varying affinity for non-hapten cis-DDP-DNA adducts. Their affinity for digested cis-DDP-modified DNA was up to 30 times that for intact cis-DDP-DNA. Neither NKI-A68 nor NKI-A10 resulted in specific immunocytochemical staining of cis-DDP-DNA adducts. We conclude that NKI-A68, NKI-A10, and NKI-A39 are suitable for platinum-DNA adduct analysis of digested DNA in ELISA and that NKI-A59 is suitable for platinum-DNA adduct detection at the single-cell level using immunocytochemical methods.

Acquired cisplatin resistance in human ovarian cancer cells is associated with enhanced repair of cisplatin-DNA lesions and reduced drug accumulation

Studies were undertaken to investigate acquired resistance to cisplatin in human ovarian cancer cells. The cell lines A2780 and A2780/CP70 were studied to assess their respective characteristics of drug accumulation and efflux, cytosolic inactivation of drug, and DNA repair. All experiments were performed using 1-h drug exposures. The A2780/CP70 cell line was 13-fold more resistant to cisplatin than A2780 cells. When studied at their respective IC50 doses, drug accumulation rates were similar for the two cell lines. However, the resistant cell line was twofold more efficient at effluxing drug, which was associated with reduced total drug accumulation for equivalent micromolar drug exposures. At equivalent levels of total cellular drug accumulation, the two cell lines formed the same levels of cisplatin-DNA damage, suggesting that cytosolic inactivation of drug does not contribute to the differential in resistance between these cell lines. Resistant cells were also twofold more efficient at repairing cisplatin-DNA lesions in cellular DNA and in transfected plasmid DNA. We conclude that in these paired cell lines, alterations in drug uptake/efflux and in DNA repair are the major contributing factors to acquired resistance to cisplatin.

Formation of interaction products of carboplatin with DNA in vitro and in cancer patients

Binding of the cytostatic drug carboplatin to DNA was studied in solution, in RIF-1 and CHO cell lines and in human buccal cells after in vitro or in situ drug exposure. Results were compared with DNA adduction by cisplatin. The rate of binding in solution, determined by atomic absorption spectroscopy, was 35 times lower for carboplatin than for cisplatin. Adduct formation in cells in vitro was determined in a quantitative immunostaining assay. Staining intensities after carboplatin treatment were at least 29 times lower than after an equimolar dose of cisplatin. For RIF-1 and CHO cells, maximum levels of carboplatin-induced DNA modification were obtained 24 h after treatment; these levels correlated with cell killing. Adduct-specific staining in buccal cells from two carboplatin-treated patients increased 5-7 fold between 0 and 14 h after infusion, reaching a maximum at 10-14 h. This strongly contrasts with buccal cells from a cisplatin-treated patient, in which the adduct-specific staining signal increased by only 23% between 0 and 6 h after infusion, and then declined. This difference in the rate of adduct formation in vivo is consistent with the in vitro data.

A d(GpG)-platinated decanucleotide duplex is kinked. An extended NMR and molecular mechanics study

A conformational study of the double-stranded decanucleotide d(GCCG*G*ATCGC).d(GCGATCCGGC), with the G* guanines chelating a cis-Pt(NH3)2 moiety, has been accomplished using 1H and 31P NMR, and molecular mechanics. Correlation of the NMR data with molecular models has disclosed an equilibrium between several kinked conformations and has ruled out an unkinked structure. The deformation is localized at the CG*G*.CCG trinucleotide where the helix is kinked by approximately 60 degrees towards the major groove and unwound by 12-19 degrees. The models revealed an unexpected mobility of the cytosine complementary to the 5'-G*. This cytosine can stack on either branch of the kinked complementary strand. The energy barrier between the two positions has been calculated to be less than or equal to 12 kJ/mol. The NMR data are in support of rapid flip-flopping of this cytosine. An explanation for the strong downfield shift observed in the 31P resonance of the G*pG* phosphate is given.

The cytotoxic effect of cis-diamminedichloroplatinum(II) on cultured Chinese hamster ovary cells at elevated temperatures: Arrhenius plot analysis

The effect of cis-diamminedichroloplatinum (II) (cis-DDP) and hyperthermia on cultured Chinese hamster ovary (CHO) cells were investigated. Cells were treated with 6 microM cis-DDP for various durations of time at temperatures ranging from 37 to 43 degrees C, and cell survival curves were determined as a function of treatment time. The cytotoxic effect of cis-DDP increased with increasing temperatures, indicating that hyperthermia enhanced cytotoxicity of cis-DDP. Arrhenius analysis of surviving fraction data (6 microM cis-DDP) yielded activation energies of 61 kcal/M between 37 and 41 degrees C and 213 kcal/M between 41 and 43 degrees C. Further experiments using two different drug concentrations (3 and 12 microM) confirmed these activation energies in these two different temperature ranges. However, the activation energy for 12 microM cis-DDP given in the temperature range 33-37 degrees C was 22 kcal/M, which is smaller than those found above 37 degrees C. This activation energy appeared to be identical to that reported for the degradation or depurination of DNA. The activation energy between 37 and 41 degrees C, i.e. approximately 61 kcal/M, was twice as great as that found for alkylation of thio-TEPA, an alkylating agent. This may indicate that the mechanism of action of cis-DDP differs from that of thio-TEPA. A greater activation energy observed in the range of 41-43 degrees C is most likely attributable to the additive effect of hyperthermia and thermal enhancement for cis-DDP. Although only one data point is available at the temperature above 43 degrees C, it suggests that the activation energy is identical to that for hyperthermia alone.

How does cisplatin alter DNA structure? A molecular mechanics study on double-stranded oligonucleotides

Molecular models for two double-stranded decanucleotides, d(GCCG*G*ATCGC)-d(GCGATCCGGC) (1) and d(GCTG*G*ATCGC)-d(GCGATCCAGC) (2), with the G* guanines cross-linked by a cis-Pt(NH3)2 moiety, were calculated using molecular mechanics. Nine models for 1 and eight models for 2 are reported; in all of them, the double helix is kinked by approx. 60 degrees towards the major groove and slightly unwound. The model building has been guided by comparison with the NMR data available for duplex 1. The influence of the base at the 5'-side of the coordinated G*G* dinucleotide is discussed.

Biophysical studies of the modification of DNA by antitumour platinum coordination complexes

Cisplatin (cis-diamminedichloroplatinum(II] is widely used in the treatment of various human tumours. A large body of experimental evidence indicates that the reaction of cisplatin with DNA is responsible for the cytostatic action of this drug. Several platinum-DNA adducts have been identified and their effect on the conformation of DNA has been investigated. Structural studies of platinum-DNA adducts now permit a reasonably good explanation of the biophysical properties of platinated DNA. Antitumouractive platinum compounds induce in DNA, at low levels of binding, local conformational alterations which have the character of non-denaturing distortions. It is likely that these changes occur in DNA due to the formation of intrastrand cross-links between two adjacent purine residues. On the other hand, the modification of DNA by antitumour-inactive complexes results in the formation of more severe local denaturation changes. Conformational alterations induced in DNA by antitumour-active platinum compounds may be reparable with greater difficulty than those induced by the inactive complexes. Alternatively, non-denaturation change induced in DNA by antitumour platinum drugs could represent more significant steric hindrance against DNA replication as compared with inactive complexes.

Markers of exposure to carcinogens

Methods have been developed for the detection of exposure to carcinogens and other DNA damaging agents in experimental animals and man through the detection of carcinogens or their metabolic derivatives in body fluids, or through adducts bound covalently to DNA or hemoglobin. The successful use of urinary markers of genotoxic exposures has been reported with respect to nitrosoproline as an indicator of exposure to N-nitroso compounds. The same approach has been used to detect AFB1 and AFB1-N7-Gua as markers of exposure to aflatoxin B1; of 3-methyladenine produced as a result of exposure to methylating agents; and thymine glycol as an indicator of exposure to agents causing oxidative damage to DNA. Detection of adducts formed between genotoxic agents and hemoglobin has been reported in studies of populations occupationally exposed to ethylene oxide, in which 3-hydroxyhistidine and 3-hydroxyvaline have been measured, and in smokers, whose hemoglobin has been found to contain levels of 4-aminobiphenyl and 3-hydroxyvaline that were correlated with the frequency of cigarette smoking. Detection of DNA adducts of genotoxic agents in the cells and tissues of exposed individuals has also been accomplished through the use of several types of analytical methods. Immunoassays and physicochemical methods have been applied to detect adducts formed through the major intermediate in the activation of benzo(a)pyrene, the 7,8-diol-9,10-epoxide (BPDE). This adduct has been found in the DNA of peripheral leukocytes of workers in foundries, aluminum manufacturing plants, roofers, and coke oven plants, and also in cigarette smokers.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunochemistry of DNA

Since the first reports of anti-DNA antibodies in sera of patients with systemic lupus erythematosus (SLE) in 1957, studies of nucleic acid immunochemistry have grown in two directions. One has been the analysis of the specificity, the nature and the origins of these autoantibodies. The second has been exploration of anti-nucleic acid antibodies that can be induced experimentally, their specificities, and their application as biochemical reagents. Although the properties of autoantibodies and experimentally induced antibodies differ in certain respects, these two lines of research are complementary and provide important information for each other. For example, the production of autoantibodies by adjuvant-stimulated B cells yields a background that has to be considered in evaluating the specificity of weak responses to experimental nucleic acid immunogens: in turn, the possibilities and limitations of experimental immunization should be considered in evaluating possible stimuli for autoantibody production. Several aspects of nucleic acid immunochemistry have been described and evaluated in previous reviews. Following some general statements of historical perspective, this review will emphasize questions addressed and findings of about the last five years.