Oxaliplatin, tetraplatin, cisplatin, and carboplatin: spectrum of activity in drug-resistant cell lines and in the cell lines of the National Cancer Institute's Anticancer Drug Screen panel

Chemoradiation with novel agents for rectal cancer

Surgery remains the mainstay of treatment for colorectal cancer. Although the role of radiation therapy in colon cancer is unclear, its role in the management of locally advanced rectal cancer has been extensively studied in clinical trials. The use of postoperative chemoradiotherapy has been shown to improve local control and disease-free survival in patients with locally advanced disease over surgery alone; however, an overall survival advantage remains unproven. Clinical trials evaluating preoperative radiotherapy have demonstrated an improved local control as well as a survival advantage. Randomized studies comparing preoperative versus postoperative combined-modality approaches have failed in the United States, mainly due to the perceived advantages of preoperative treatment: improved patient tolerance, tumor downstaging, and fewer treatment-related complications. While 5-fluorouracil-based chemotherapy remains the standard systemic agent used along with radiation, other novel agents and strategies have recently been developed and are under investigation. In this review, we discuss the use of novel anticancer agents in combination with radiation therapy for the treatment of locally advanced rectal cancer.

Oxaliplatin (L-OHP) treatment of human myeloma cells induces in vitro growth inhibition and apoptotic cell death

Oxaliplatin (L-OHP), a diaminocyclohexane platinum derivative, is an active and well tolerated anticancer drug which is presently used in the treatment of gastrointestinal tumours. Since the efficacy of L-OHP in the treatment of multiple myeloma (MM) has not yet been evaluated, we studied the antiproliferative activity of this compound in vitro in a panel of MM cell lines (XG1, XG1a, U266 and IM-9). We found that L-OHP inhibited the growth of MM cells at therapeutically achievable concentrations (IC(50): 5-10 microM after 24 h of exposure) and was more active than Cisplatin (CDDP) or Carboplatin (CBDCA). The activity of L-OHP was apparently not affected by interleukin-6 (IL-6), the major growth and survival factor of MM cells. We also found that L-OHP induced apoptotic cell death. We demonstrated that the combination of L-OHP with Dexamethasone (Dex) resulted in the enhancement of the anti-myeloma effects. L-OHP and Dex both induced poly adenosine diphosphate (ADP)-ribose polymerase (PARP) cleavage and this induction was enhanced by the combined treatment. L-OHP-induced apoptosis correlated with caspase-3 cleavage, but this correlation could not be demonstrated in Dex-treated cells. Taken together, these in vitro results provide a rationale for the experimental use of L-OHP in the treatment of MM patients and suggest therapeutic combinations of potential value.

Activity of oxaliplatin in patients with relapsed or cisplatin-refractory germ cell cancer: a study of the German Testicular Cancer Study Group

PURPOSE

To investigate the efficacy and toxicity of oxaliplatin, a diaminocyclohaxane platinum derivative with incomplete cross-resistance to cisplatin in patients with relapsed or cisplatin-refractory germ cell cancer.

PATIENTS AND METHODS

Thirty-two patients with nonseminomatous cisplatin-refractory germ cell cancer or relapsed disease after high-dose chemotherapy (HDCT) plus autologous stem-cell support were treated with single-agent oxaliplatin 60 mg/m(2) on days 1, 8, and 15 repeated every 4 weeks (group 1; n = 16) or oxaliplatin 130 mg/m(2) given on days 1 and 15 of a 4-week cycle (group 2; n = 16). Patients were pretreated with a median of seven (range, three to 13) cisplatin-containing treatment cycles; 78% had received carboplatin/etoposide-based HDCT before oxaliplatin therapy. Twenty-seven patients (84%) were considered refractory (n = 20; 63%) or absolutely refractory (n = 7; 22%) to cisplatin therapy.

RESULTS

Overall, four patients achieved a partial remission (13%; 95% confidence interval, 1% to 24%). Two additional patients achieved disease stabilization. All responses were observed in cisplatin-refractory patients, including three who had not responded to previous HDCT. Patients received a median two cycles of oxaliplatin with a median cumulative dose of 350 mg/m(2). Hematologic toxicity was generally mild, with five patients developing grade 3/4 thrombocytopenia. Nonhematologic side effects consisted mainly of nausea/vomiting. One patient developed grade 3 neurotoxicity.

CONCLUSION

Considering the particularly unfavorable prognostic characteristics of this patient population compared with patients from previous trials for new drugs in germ cell cancer, eg, paclitaxel and gemcitabine, a 13% overall response rate and a 19% response rate in the group treated with oxaliplatin 130 mg/m(2) seems to be of interest. Oxaliplatin may be a palliative treatment option for this patient population, and evaluation in combination regimens is warranted.

Sensitivity of p53-deficient cells to oxaliplatin and thio-TEPA (N, N', N" triethylenethiophosphoramide)

P53 is known as a determinant of cellular responses to DNA damage, including apoptosis, cell cycle arrest, and DNA repair. Its role is most easily understood in the context of Burkitt lymphoma and other apoptosis-prone cell types. A number of epithelial cancer cell types, by contrast, exhibit a higher threshold for apoptosis induction in response to DNA damage. In fact, p53 mediates DNA repair and protective responses in the latter cell types, in some cases p53-deficient cells being more sensitive to DNA damage, antithetical to the situation in Burkitt lymphoma and other apoptosis-prone cell types. Ultraviolet light, cisplatin, and nitrogen mustards produce damage that is repaired by a p53-regulated pathway. Here, we explore the sensitivity of the platinum compound oxaliplatin and thio-TEPA (N, N', N", triethylenethiophosphoramide), a cancer chemotherapeutic agent that produces largely base damage, in p53-defective cells. This work demonstrates that the contribution of p53 temporally correlates with DNA repair pathways to produce a resistant phenotype, while the p53-defective cells are more sensitive to certain DNA-damaging chemotherapeutic agents.

Acute oxaliplatin-induced peripheral nerve hyperexcitability

PURPOSE

Oxaliplatin is a novel platinum compound with clinical activity in several malignancies. Neurotoxicity is dose-limiting and occurs in two distinct forms, an acute neurologic symptom complex that occurs within hours or days of therapy and a chronic, cumulative sensory neuropathy.

PATIENTS AND METHODS

Patients were treated in a phase I study designed to establish the maximum-tolerated dose of capecitabine given with oxaliplatin. Because of the unusual neurosensory toxicity of oxaliplatin, detailed neurologic examination, needle electromyography (EMG), and nerve conduction studies (NCS) were performed before and the day after oxaliplatin in a subset of 13 patients. Carbamazepine therapy was tried in 12 additional patients to determine whether the neurologic effects might be relieved.

RESULTS

All patients experienced acute, reversible neurotoxicities with oxaliplatin. Symptoms included paresthesias, dysesthesias, cold hypersensitivity, jaw pain, eye pain, pain in the arm used for drug infusion, ptosis, leg cramps, and visual and voice changes. Serial EMG and NCS revealed striking signs of hyperexcitability in motor nerves after oxaliplatin. In patients who achieved therapeutic levels, carbamazepine did not alter the clinical or electromyographic abnormalities.

CONCLUSION

The acute neurotoxicity seen with oxaliplatin is characterized by peripheral-nerve hyperexcitability, and the findings are similar to the clinical manifestations of neuromyotonia. Carbamezepine, which provides symptomatic relief in acquired neuromytonia, did not seem to be beneficial. Efforts to identify a successful neuroprotectant strategy would have a major impact on improving patient quality of life and the ability to deliver full doses of oxaliplatin.

Radiosensitization by oxaliplatin in a mouse adenocarcinoma: influence of treatment schedule

PURPOSE

The aim of our study was to investigate if oxaliplatin (1-OHP) could be used as a radiosensitizer in vivo.

MATERIALS AND METHODS

Experiments were performed in mice (C3D2F1) bearing a transplanted mammary carcinoma in a foot. Drugs, 1-OHP and cis-diammine-dichloro-platinum (CDDP), were administered i.p. Results were analyzed in terms of tumor growth delay (TGD).

RESULTS

1-OHP and CDDP were tested in single doses of 6 and 10 mg/kg body weight. Administration of either 1-OHP or CDDP produced a significant TGD but only with the dose of 10 mg/kg. Single dose combined X-ray (10 Gy) and 1-OHP (6 and 10 mg/kg) treatments were performed with different sequences and time intervals (1 h, 4 h, and 24 h). All TGDs of these combined treatments were uniform among themselves (indicating that sequence and time interval did not influence the results), and did not depend on the drug dose. In X-ray (10 and 20 Gy) and 1-OHP (6 and 10 mg/kg) combined treatment, the TGDs increased only with X-ray dose. Different 1-OHP administration schedules were performed for fractionated experiments: two treatments every 4 days. The least toxic protocol (1-OHP total dose from 6 to 14 mg/kg) was selected for combined treatments with 10 daily X-ray treatments of 2 Gy. A clear drug dose-effect relationship was observed in those treatments with 1-OHP doses from 10 to 14 mg/kg.

CONCLUSION

Although low-dose 1-OHP did not induce a TGD when administered alone, in combined protocols it increased X-ray efficacy.

An oxaliplatin-based chemotherapy in patients with relapsed or refractory intermediate and high-grade non-Hodgkin's lymphoma

This study was designed to assess the efficacy and safety of substituting cisplatin with oxaliplatin in the DHAP (dexamethasone, cytarabine and cisplatin) regimen for patients with relapsed or refractory non-Hodgkin's lymphoma. Twenty-four evaluable patients with intermediate or high-grade non-Hodgkin's lymphoma were treated at 3-weekly intervals with oxaliplatin (130 mg/m2, d 1), cytarabine (2 g/m2 for two doses, d 2) and dexamethasone (40 mg, d 1-4). The median age of the patients was 58 (range 18-70). Histological subtypes were diffuse large B cell, 20; mantle cell, two; anaplastic large cell, one; and peripheral T cell, one. The overall objective response rate (RR) was 50% [95% confidence interval (CI) = 29-71%] including four complete responses and eight partial responses. RR for those patients treated at first relapse was higher than those treated at second and subsequent relapse (77% versus 29%). Grade 3 and 4 toxicity was mainly haematological: anaemia 17%, neutropenia 75% and thrombocytopenia 75%. No grade 4 non-haematological toxicity was reported. No significant renal and neurotoxicity was demonstrated. Median survival was 10.6 months. Probabilities of 1-year progression-free survival and overall survival were 47% (95% CI = 26-66%) and 50% (95% CI = 23-72%) respectively. In conclusion, dexamethasone, cytarabine and oxaliplatin (DHAX) is a novel combination in salvage therapy for relapsed or refractory non-Hodgkin's lymphoma. It has clinically significant activity with an acceptable toxicity profile. Lack of renal toxicity makes DHAX an attractive cytoreductive regimen before high-dose chemotherapy.

Oxaliplatin: available data in non-colorectal gastrointestinal malignancies

Oxaliplatin is a third-generation platinum compound which has proven its efficacy alone or in combination with 5-fluorouracil (5-FU) and/or new anticancer drugs in advanced colorectal cancer. Compared to the amount of available data in this cancer, little is known about the use of oxaliplatin in non-colorectal gastrointestinal malignancies. (1) The preclinical activity of the drug alone or in combination; (2) the phase I studies (oxaliplatin alone or in combination with irinotecan, raltitrexed, gemcitabine, folinic acid and 5-FU); (3) the phase II studies developed in gastric, pancreatic, biliary tract, hepatocellular carcinoma and malignant mesothelioma; and (4) some of the ongoing trials with regard to non-colorectal gastrointestinal malignancies are reviewed in this paper. To date, oxaliplatin appears as a real candidate for clinical development in this field.

Multicenter phase II-III study of oxaliplatin plus cyclophosphamide vs. cisplatin plus cyclophosphamide in chemonaive advanced ovarian cancer patients

PURPOSE

A phase II-III randomised study to compare safety and efficacy of an oxaliplatin/cyclophosphamide (OXAC) combination, vs. the reference combination of cisplatin/cyclophosphamide (CPC), in untreated advanced ovarian cancer patients.

PATIENTS AND METHODS

182 patients were enrolled, of whom 177 were treated: 86 with OXAC (130 mg/m2 oxaliplatin two-hour intravenous (i.v.) infusion, 1,000 mg/m2 cyclophosphamide two-hour i.v. infusion), and 91 with CPC (100 mg/m2 cisplatin one-hour i.v. infusion. 1,000 mg/m2 cyclophosphamide two-hour i.v. infusion). Treatment cycles were repeated every three weeks (maximum of six cycles).

RESULTS

The main toxicities, which were significantly less severe in the OXAC arm, were myelosuppression and vomiting, including (OXAC vs CPC, % patients): grade 3-4 leukopenia (37% vs. 56%), and anaemia (7% vs. 32%), with blood transfusions in 8% vs. 21%. In the OXAC arm, 64% of surgically assessable patients and 33% of clinically assessable patients achieved an objective response. In the CPC arm, 67% patients achieved a surgical response and 42% achieved an objective clinical response. In the OXAC and CPC arms, median progression free-survival was 13.0 and 13.3 months, and overall survival was 36.0 and 25.1 months respectively, without statistically significant difference.

CONCLUSION

The activity and time-related parameters of the OXAC and CPC combinations in advanced ovarian cancer patients, are comparable. Combined with the better safety profile of the oxaliplatin-containing regimen, this confirms the interest of oxaliplatin combined with active new agents in this indication.

Platinum compounds in the treatment of advanced breast cancer

Interest in platinum compounds for the treatment of breast cancer has been reawakened because of preclinical studies indicating synergy of platinum salts with the monoclonal antibody trastuzumab in human breast cancer cell lines that overexpress HER2/neu. Cisplatin, carboplatin, and iproplatin are not very active as single agents in patients with previously treated metastatic breast cancer (MBC). The activity of oxaliplatin has not been adequately tested in refractory MBC. On the other hand, cisplatin is very active as first-line chemotherapy, with response rates (RR) of 50%; carboplatin appears to be moderately active in patients without prior chemotherapy (RR around 30%). The clinical effectiveness of the other platinum compounds (iproplatin, oxaliplatin, and others) has not yet been fully tested as first-line chemotherapy. Platinum compounds have been extensively tested in combination with other antitumoral agents. Cisplatin combinations have been employed as neoadjuvant chemotherapy in women with locally advanced breast cancer. These combinations are very active, although the precise contribution of cisplatin to the overall activity is not known. Combinations with cisplatin have been investigated, essentially, as salvage therapy for patients with previously treated MBC. The combinations of cisplatin with older pharmacological agents (5-fluorouracil, etoposide) have moderate activity, while the combinations of cisplatin with the newer agents (vinorelbine, paclitaxel, docetaxel, gemcitabine) appear to be more active. The combinations of carboplatin with the classical agents (5-fluorouracil, etoposide) are poorly active in previously treated MBC; however, the combination of carboplatin with the taxanes (docetaxel, paclitaxel) is more active. Of greatest interest is the synergy between the platinum derivatives and the monoclonal antibody trastuzumab demonstrated in vitro in breast cancer cell lines overexpressing HER2/neu. Currently, several combinations of platinum compounds (either cisplatin or carboplatin) with docetaxel and trastuzumab are under clinical testing in patients with MBC who overexpress HER2/neu. The preliminary results are very promising, and these combinations will soon be tested in the adjuvant setting. Cisplatin, carboplatin, and perhaps, oxaliplatin appear to have some antitumor activity in MBC and can be combined safely with other agents that are active in this disease. However, the precise role that platinum compounds play in the treatment of breast cancer remains to be defined.

Elevated expression of vacuolar proton pump genes and cellular PH in cisplatin resistance

V-ATPases are proton-translocating enzymes, which are found not only in numerous intracellular organelles but also in the plasma membranes of many eukaryotic cells. Using differential display, we have identified one of the proton pump subunit genes, ATP6C, as a cisplatin-inducible gene. Northern blot analysis demonstrated that expression of other members of the subunit is inducible by cisplatin treatment. Proton pump gene expression is also upregulated in 3 independent cisplatin-resistant cell lines but not in vincristine- or etoposide-resistant cell lines. Cellular pH was significantly higher in cisplatin-resistant cells than in sensitive parental cells. In vitro DNA-binding activity of cisplatin was markedly increased in acidic conditions, suggesting that the cytotoxicity of cisplatin is modulated by cellular pH. Furthermore, the proton pump inhibitor bafilomycin can synergistically potentiate the cytotoxicity of cisplatin but not of etoposide or camptothecin. These results indicate that cellular pH is one of the critical parameters for effective cancer chemotherapy with cisplatin.

Advances in the treatment of metastatic colorectal cancer

Colorectal cancer represents the third leading cause of cancer mortality in the United States. During the past four decades, 5-fluorouracil (5-FU) has served as the cornerstone of therapy for individuals with advanced colorectal cancer (ACRC). Despite numerous attempts at maximizing efficacy of 5-FU through biochemical modulation, a significant benefit in terms of survival has never been realized. The recent emergence of novel chemotherapeutic drugs employing different mechanisms of action than 5-FU has led to the incorporation of irinotecan (CPT-11) with 5-FU/leucovorin as the new standard first-line regimen for future trials. This review outlines emerging data utilizing oral fluoropyrimidines and other new agents including oxaliplatin, raltitrexed, and eniluracil. Randomized clinical trials are currently underway in an effort to define optimal combination chemotherapy regimens, scheduling of agents, duration of therapy, and choice of therapy using a variety of prognostic molecular markers.

Oxaliplatin: a new agent for colorectal cancer

For nearly 40 years, the medical treatment of colorectal cancer had been limited to the fluoropyrimidines until the recent development of irinotecan (CPT-11). In the past decade, a new agent has appeared, oxaliplatin. This third-generation platinum compound has synergistic activity with 5-fluorouracil and is non-cross-resistant with 5-fluorouracil, CPT-11, and other platinum agents. Numerous clinical trials in Europe have demonstrated the activity of oxaliplatin in patients with untreated and refractory metastatic colorectal cancer. Nevertheless, the US Food and Drug Administration recently denied approval for oxaliplatin as first-line treatment of colorectal cancer because of a lack of clear-cut survival advantage in clinical trials. Additional clinical trials in patients with colorectal cancer are ongoing in the United States and will test the activity of oxaliplatin in the metastatic and adjuvant setting. These studies will define the role for what appears to be a very useful and important agent.

Comparison of the reactivity of oxaliplatin, pt(diaminocyclohexane)Cl2 and pt(diaminocyclohexane1)(OH2)2(2+) with guanosine and L-methionine

The initial rates of reactivity of oxaliplatin, its metabolites Pt(dach)Cl2 and Pt(dach)(OH2)2(2+) with guanosine and L-met in water, NaCl and phosphate were compared. Versus guanosine, the most reactive molecule was Pt(dach)(OH2)2(2+), about 40 fold that of oxaliplatin, the least reactive was Pt(dach)Cl2, Versus L-met, Pt(dach)(OH2)2(2+), was also the most reactive species but only about 2 fold more reactive than Pt(dach)Cl2 and oxaliplatin. Pt(dach)(OH2)2(2+) was approximately 3 fold less reactive versus methionine than guanosine whereas oxaliplatin and Pt(dach)Cl2 were about seven fold more reactive versus methionine than guanosine. Thus, the three platinum compounds oxaliplatin, Pt(dach)Cl2 and Pt(dach)(OH2)2(2+) react with L-met but only the Pt(dach)(OH2)2(2+) has a high reactivity with guanosine. Oxaliplatin, which is stable in water, has to be transformed in the presence of chloride in chloro-derivatives which are aquated to become active particularly versus guanosine. These data demonstrate that oxaliplatin has similarities with cisplatin in terms of chloride versus water coordination and in terms of dependence on chloride concentration for transformations.

Highlights in ovarian cancer

The ovarian cancer presentations at the 2000 ASCO meeting did not yield any major paradigm shifts in the treatment of women with epithelial ovarian cancer. Emphasis at this year's meeting focused on the potential incorporation of drugs such as topotecan, oxaliplatin, doxil, and gemcitabine into the initial treatment strategies of women with advanced ovarian cancer. These studies included the introduction of several active and tolerable regimens that are potentially worthy of direct comparison to the carboplatin and paclitaxel combination. In the woman with recurrent or persistent ovarian cancer there was a greater focus on phase III studies directly comparing various chemotherapy strategies in the treatment of women with recurrent disease. This included the comparisons of single-versus two-drug salvage regimens, alternate salvage schedules, and direct comparison of agents active in taxane- and platinum-resistant disease. Finally, several early studies of novel non-chemotherapeutic strategies were presented.

Use of the ratio of time to progression following first- and second-line therapy to document the activity of the combination of oxaliplatin with 5-fluorouracil in the treatment of colorectal carcinoma

BACKGROUND

It has been proposed that the activity of a second-line treatment regimen can be documented by showing that the time to progression (TTP) following second-line therapy is longer than the TTP following first-line therapy in the same patients.

PATIENTS AND METHODS

The ratio of TTP during first and second-line therapy, identified as the growth modulation index (GMI), was determined in 34 patients with advanced colorectal cancer. First-line chemotherapy consisted of one of several schedules of leucovorin (LV)-modulated 5-fluorouracil (5-FU) or raltitrexed. Second-line therapy consisted of the combination of LV-modulated 5-FU and oxaliplatin (1-OHP). Patients were switched to second-line therapy upon evidence of progressive disease following first-line therapy.

RESULTS

Median TTP following first-line therapy was 13 weeks (95% confidence interval (CI): 7.6-18.7), while median TTP following second-line therapy was 31 weeks (95% CI: 21.3-41.0). Sixteen patients (47%; 95% CI: 35%-59%), showed a GMI > or = 1.33, while the remaining 18 patients (53%; 95% CI: 40%-66%) had a GMI < 1.33. Log-rank analysis of the Kaplan-Meier curves of TTP following first- versus second-line therapy demonstrated a statistically significant difference in favour of second-line therapy (P = 0.0081).

CONCLUSIONS

This study demonstrates the utility of the GMI as a tool for assessing the activity of novel second-line therapeutic programs.

Oxaliplatin-induced damage of cellular DNA

Damage to cellular DNA is believed to determine the antiproliferative properties of platinum (Pt) drugs. This study characterized DNA damage by oxaliplatin, a diaminocyclohexane Pt drug with clinical antitumor activity. Compared with cisplatin, oxaliplatin formed significantly fewer Pt-DNA adducts (e.g., 0.86+/-0.04 versus 1.36+/- 0.01 adducts/10(6) base pairs/10 microM drug/1 h, respectively, in CEM cells, P<.01). Oxaliplatin was found to induce potentially lethal bifunctional lesions, such as interstrand DNA cross-links (ISC) and DNA-protein cross-links (DPC) in CEM cells. As with total adducts, however, oxaliplatin produced fewer (P<.05) bifunctional lesions than did cisplatin: 0.7+/-0.2 and 1.8+/-0.3 ISC and 0.8+/-0.1 and 1.5+/-0.3 DPC/10(6) base pairs/10 microM drug, respectively, after a 4-h treatment. Extended postincubation (up to 12 h) did not compensate the lower DPC and ISC levels by oxaliplatin. ISC and DPC determinations in isolated CEM nuclei unequivocally verified that oxaliplatin is inherently less able than cisplatin to form these lesions. Reactivation of drug-treated plasmids, observed in four cell lines, suggests that oxaliplatin adducts are repaired with similar kinetics as cisplatin adducts. Oxaliplatin, however, was more efficient than cisplatin per equal number of DNA adducts in inhibiting DNA chain elongation ( approximately 7-fold in CEM cells). Despite lower DNA reactivity, oxaliplatin exhibited similar or greater cytotoxicity in several other human tumor cell lines (50% growth inhibition in CEM cells at 1.1/1.2 microM, respectively). The results demonstrate that oxaliplatin-induced DNA lesions, including ISC and DPC, are likely to contribute to the drug's biological properties. However, oxaliplatin requires fewer DNA lesions than does cisplatin to achieve cell growth inhibition.

Oxaliplatin is active in vitro against human melanoma cell lines: comparison with cisplatin and carboplatin

We have previously confirmed the in vitro activity of cisplatin and carboplatin against human melanoma cell lines. Both drugs are important components in the chemotherapy used in our service for advanced metastatic melanoma. In this communication we report the in vitro activity of oxaliplatin against human melanoma cell lines in comparison with cisplatin and carboplatin. Oxaliplatin was found to be active against C32 and G361 cell lines with IC50 values of 49.48 and 9.07 microM (1 h exposure), 9.47 and 1.30 microM (4 h exposure), and 0.98 and 0.14 microM (24 h exposure), respectively. The cytotoxic activity of oxaliplatin in this in vitro system appears to be significantly superior to that of carboplatin. Its activity becomes comparatively closer to that of cisplatin as exposure time increases. Indeed at a 24 h exposure oxaliplatin appears to be significantly more active than cisplatin against the G361 cell line (p=0.0343). Oxaliplatin merits evaluation in the clinic both as a single agent and in combination with other drugs active against melanoma.

Preclinical perspectives on platinum resistance

In the 30 years since the introduction of cisplatin into the clinic, laboratory studies have provided considerable information as to both how the drug exerts its antitumour effects and how some tumours are, or become, resistant. Once inside a cell, the chlorine groups of cisplatin are exchanged for water (aqua) species, which are more chemically reactive. The intracellular target for cisplatin is DNA, where a variety of adducts are formed, some on the same strand of DNA (intrastrand adducts) and others between strands (interstrand adducts). Of the 4 bases, guanine is the preferred site for binding and the most common adduct involves linkages on 2 adjacent guanines on the same strand of DNA. It remains uncertain which of the various types of adduct is the most important in terms of producing antitumour effects. Resistance to cisplatin has been studied extensively using tumour cells repeatedly exposed to the drug in vitro. In these cell models, resistance is generally due to a combination of mechanisms, some resulting in reduced damage to DNA and others following DNA damage. Resistance due to inadequate binding to DNA has been shown to be caused by reduced drug uptake (influx rather than efflux) and inactivation by thiol-containing species such as glutathione and metallothioneins. Resistance occurring post-DNA binding may be due to changes in DNA repair pathways [an increase in nucleotide excision repair (NER) or a loss of DNA mismatch repair (MMR)]. Conversely, the hypersensitivity of some cell lines to cisplatin has been shown to be due to defective NER, through loss or reduced expression of NER proteins such as XPG and XPA. Resistance may also be mediated through alterations in proteins involved in programmed cell death (apoptosis) such as p53 and the BCL2 family. A basic understanding of cisplatin resistance pathways has made a major impact in the development of new platinum analogues capable of circumventing resistance. Examples (which are now undergoing clinical trial) include ZD0473 (which, relative to cisplatin, possesses a reduced reactivity towards inactivating thiol-containing molecules) and the trinuclear platinum BBR3464 (which has markedly different DNA binding properties compared with cisplatin).

New developments and approaches in the platinum arena

Following the introduction of cisplatin and the demonstration of its importance in the treatment of testicular and ovarian cancer, there was a need to develop less toxic analogues. Compared with cisplatin, carboplatin proved markedly less toxic to the kidneys and nervous system and caused less nausea and vomiting, while generally (and certainly for ovarian cancer) retaining equivalent antitumour activity. In many situations, carboplatin is now the drug of choice in view of the improved quality of life it offers patients. Many drug combinations involving platinum complexes have been explored, but those with taxanes are particularly noteworthy. Paclitaxel in combination with a platinum agent is now accepted as a standard component of first-line treatment for ovarian cancer, and produces improved survival. Preclinical studies suggested that drugs containing the diaminocyclohexane ligand would be capable of overcoming intrinsic or acquired resistance. However, this outcome was not realised in the clinic until the development of oxaliplatin, which appears to have a different spectrum of activity compared with cisplatin and carboplatin. Oxaliplatin improves the response rate and progression-free survival when given with fluorouracil for the treatment of advanced colorectal cancer, and its activity in other tumour types is under investigation. ZD0473 is a platinum analogue that relies on steric hindrance to overcome thiol-mediated detoxification. It has a good tolerability profile, is currently undergoing phase II testing, and its activity in combination with other agents is being explored. The trinuclear platinum complex BBR3464 also looks promising in preclinical studies and will shortly be evaluated in phase II trials. Although much research remains to be done, these new developments in platinum-based chemotherapy should translate into significant improvements in treatment for patients with a broad range of tumour types.

Clinical pharmacokinetics and administration of established platinum drugs

We review the pharmacology and clinical administration of the commonly used platinum-based anticancer drugs cisplatin and carboplatin, and the more recently approved diamminocyclohexane-based oxaliplatin. The development of analogues of cisplatin has been focused upon identifying compounds with less toxicity and with a different spectrum of activity. Carboplatin exemplifies the former, while the initial data with oxaliplatin support its activity in cisplatin-resistant tumours. The clinical pharmacokinetics of the drugs are reviewed. Incorporation of these data into the design of clinical regimens has permitted individualised therapy with carboplatin, and has enhanced safety. Additional investigation of the pharmacodynamics of all of these agents is expected to result in their selective application. The clinical effects of these analogues are discussed.

Oxaliplatin. A review of its pharmacological properties and clinical efficacy in metastatic colorectal cancer and its potential in other malignancies

Oxaliplatin is a platinum compound that inhibits DNA synthesis, primarily by causing intrastrand cross-links in DNA. Oxaliplatin has a broad spectrum of antineoplastic activity and has demonstrated a lack of cross-resistance with other platinum compounds. In patients with metastatic colorectal cancer, intravenous oxaliplatin has been trialled as a monotherapy and in combination with other agents. The highest response rates were achieved when oxaliplatin was used in combination with fluorouracil/folinic acid (leucovorin; calcium folinate), typically > or = 50% in the first-line setting and 13 to 45% as a second-line therapy. First-line triple therapy with oxaliplatin and fuorouracil/folinic acid achieved significantly higher response rates and longer median progression-free survival than fluorouracil/folinic acid therapy alone. However, no significant difference in the median duration of overall survival was found. This may be a consequence of the subsequent use of oxaliplatin and/or surgery after disease progression in patients who relapsed after fluorouracil/folinic acid therapy alone. Neoadjuvant therapy with oxaliplatin/fluorouracil/folinic acid has proven beneficial in enabling surgical removal of previously unresectable liver metastases. In 2 studies, surgery with curative intent was performed in 16 and 51% of patients with initially unresectable liver metastases following oxaliplatin/fluorouracil/folinic acid therapy; the 5-year survival rates were 40 and 50%, respectively. In patients with advanced ovarian cancer, first-line therapy with oxaliplatin/cyclophosphamide achieved an objective response rate which did not differ significantly from that of cisplatin/cyclophosphamide (33 vs 42%). In addition, oxaliplatin has shown efficacy in patients with platinum-pretreated ovarian cancer and achieved objective response rates similar to paclitaxel in this setting (16 vs 17%). Promising results have also been found with oxaliplatin in patients with non-Hodgkin's lymphoma, breast cancer, mesothelioma and non-small cell lung cancer. Reversible, cumulative, peripheral sensory neuropathy is the principle dose-limiting factor of oxaliplatin therapy. Haematological and gastrointestinal toxicities occur frequently but are generally mild to moderate in intensity.

CONCLUSION

Oxaliplatin in combination with fluorouracil/folinic acid is an effective treatment option for patients with metastatic colorectal cancer, both as a first-line therapy and in patients refractory to previous chemotherapy. Although preliminary results failed to show any overall survival advantage of this regimen over fluorouracil/folinic acid alone, this may be a consequence of trial design and requires further examination. Additional clinical investigation of oxaliplatin in patients with other cancers is warranted given the promising results achieved in early trials, most notably in patients with platinum-pretreated ovarian cancer.

Oxaliplatin clinical activity: a review

Oxaliplatin (Eloxatin), a recently developed third-generation cisplatin analogue with a 1,2-diaminocyclohexane (DACH) carrier ligand, has displayed preclinical and clinical activity in a wide variety of tumour types. Synergistic with 5-FU in colorectal cancer (CRC), the combination has proven efficacy in 5-FU-resistant advanced disease and in previously untreated CRC, as demonstrated in controlled phase III trials, while evaluation in the adjuvant setting is ongoing. Due to its excellent safety profile, its unique mechanism of action and lack of cross-resistance with other active agents in CRC, oxaliplatin has also been combined with CPT-11 and Raltitrexed with promising results. Trials in pretreated and untreated advanced ovarian cancer (AOC), as a single agent or in combination with cisplatin, cyclophosphamide or paclitaxel, indicate a yet to be defined role in AOC and confirm its lack of cross-resistance with cis/carboplatin. Clinical investigations of single agent and combination therapies in breast, lung, prostate and germ-cell carcinomas, non-Hodgkin's lymphoma and malignant mesothelioma are being pursued. While the role of oxaliplatin in medical oncology is yet to be fully defined, it appears to be an important new anticancer agent.

Combination raltitrexed (Tomudex(R))-oxaliplatin: a step forward in the struggle against mesothelioma? The Institut Gustave Roussy experience with chemotherapy and chemo-immunotherapy in mesothelioma

The aim of this study was to review the experience of the Institut Gustave Roussy in 163 patients with malignant mesothelioma over a 9-year period. Data from seven consecutive prospective trials, four of chemo-immunotherapy and three of chemotherapy were reviewed. The rationale, methods and results of these trials are summarised and discussed. 98 patients were included in four phase II trials of chemo-immunotherapy whose common denominator was a combination of cisplatin and alpha-interferon. The response rate ranged from 15% to 40%. High-dose weekly cisplatin combined with alpha-interferon yielded the highest response rate but the toxicity of this regimen was considered unacceptable. Neither higher doses of alpha-interferon or the addition of mitomycin C or interleukin-2 to the regimen were able to enhance the activity of this combination. 18 patients were included in a paclitaxel-cisplatin phase II trial. The response rate was only 6% (95% confidence interval (CI): 0-24) and toxicity was also significant. This regimen was, therefore, considered ineffective. Of 17 patients with mesothelioma included in a phase I trial that combined raltitrexed and oxaliplatin, 6 (35%) obtained a partial response. Responses were seen even in cisplatin-refractory mesothelioma. Preliminary results of a subsequent ongoing phase II trial using raltitrexed (3 mg/m(2)) and oxaliplatin (130 mg/m(2)) have confirmed this promising activity with a 30% (9/30) response rate (95% CI: 15-49). The tolerance of this outpatient regimen is acceptable (no significant haematological toxicity and no alopecia) and compares favourably with that of our previous regimens. The final results concerning response and survival are required to confirm the efficacy of this combination. The preliminary results of two studies suggest promising activity with the combination of raltitrexed-oxaliplatin in malignant mesothelioma. The efficacy/toxicity ratio of this combination compares favourably with that of our previous chemotherapy and chemo-immunotherapy regimens.

Transactivation of the metallothionein promoter in cisplatin-resistant cancer cells: a specific gene therapy strategy

BACKGROUND

Cisplatin (cis-diamminedichloroplatinum) is one of the most active agents against a broad range of malignancies, including ovarian cancer. Cisplatin resistance appears to be associated with several molecular alterations, including overexpression of metallothionein, a metal-binding protein. In the present study, we attempted to take advantage of metallothionein overexpression to overcome cisplatin resistance.

METHODS

Using a virus-free system (liposomes), we sought to express the suicide gene, thymidine kinase (TK), driven by the promoter of the human metallothionein IIa (hMTIIa) gene using the pMT-TK plasmid. We used cisplatin-resistant human ovarian carcinoma cells as a model.

RESULTS

We first analyzed metallothionein expression using a ribonuclease protection assay. In comparison to parental cells, the cisplatin-resistant cells were found to have increased expression of metallothionein messenger RNA (mRNA). Metallothionein overexpression in these cells was not associated with an increased copy number of the hMTIIa gene or with different transfection efficiencies. Furthermore, we showed by reverse transcription-polymerase chain reaction analysis that transfection of the pMT-TK plasmid results in a 56-fold higher expression of thymidine kinase mRNA in cisplatin-resistant cells compared with parental cells, consistent with increased metallothionein promoter-mediated transactivation in the cisplatin-resistant cells. Transfection of resistant cells with pMT-TK or a control plasmid (pCD3-TK) resulted in a marked sensitization to ganciclovir, with a 50% cell growth-inhibitory concentration (IC(50)) of 20 microg/mL and 9 microg/mL, respectively. Transfections of the cisplatin-sensitive cells resulted in no sensitization to ganciclovir with pMT-TK (IC(50) 200 microg/mL) and a high sensitization with pCD3-TK (IC(50) = 6 microg/mL).

CONCLUSION

These studies suggest that pMT-TK gene therapy may provide an alternative treatment for cisplatin-refractory ovarian tumors.

Decreased accumulation of [14C]carboplatin in human cisplatin-resistant cells results from reduced energy-dependent uptake

We have isolated cisplatin-resistant human liver carcinoma (7404-CP20) cells with reduced accumulation of cisplatin and other drugs (methotrexate, arsenate, and arsenite) to which these cells are cross-resistant. To determine whether the reduction of drug accumulation in cisplatin-resistant cells results from impaired uptake or from active efflux, [(14)C]carboplatin was used for kinetic analysis of drug uptake and efflux. We demonstrate here that the uptake of [(14)C]carboplatin in 7404 parental cells is time, temperature, and energy dependent, and that the rate of uptake is reduced in 7404-CP20 cells. Efflux of [(14)C]carboplatin in cisplatin-resistant cells was comparable to efflux in the parental cisplatin-sensitive cells. There was little effect of temperature (between 37 degrees C and 4 degrees C) on efflux in cisplatin-resistant cells. Immunoblotting with specific antibodies directed to MRP1 and MRP2 (cMOAT) also showed that expression of these two ABC transporter genes was considerably reduced in 7404-CP20 cells and another cisplatin-resistant cell line KB-CP20, in contradistinction to previous studies suggesting that MRP might be responsible for cisplatin efflux. To rule out a generalized defect in uptake of small molecules, fluorescence-activated cell sorter (FACS) analysis of rhodamine 123 uptake showed that there was no difference between cisplatin-sensitive and -resistant cells. The presence of a pleiotropic defect in uptake of [(14)C]carboplatin, [(3)H]methotrexate, [(73)As]arsenate, and [(73)As]arsenite in cisplatin-resistant cells, in association with reduced expression of related cell surface proteins as demonstrated in our previous work, suggests a novel mechanism for acquisition of resistance to cisplatin associated with reduced activity of many different specific uptake systems.

Oxaliplatin or paclitaxel in patients with platinum-pretreated advanced ovarian cancer: A randomized phase II study of the European Organization for Research and Treatment of Cancer Gynecology Group

PURPOSE

This was a multicentric, open, randomized, phase II study of single-agent paclitaxel and oxaliplatin to evaluate the efficacy of oxaliplatin in a relapsing progressive ovarian cancer patient population and to analyze the safety profile and impact of both agents on quality of life, time to progression, and survival.

PATIENTS AND METHODS

Eighty-six patients with platinum-pretreated advanced ovarian cancer were randomly assigned to two arms: 41 received paclitaxel at 175 mg/m(2) over 3 hours every 3 weeks, and 45 received oxaliplatin at 130 mg/m(2) over 2 hours every 3 weeks. For inclusion, patients had to have a performance status of 0 to 2 and to have received at least one and no more than two prior cisplatin- and/or carboplatin-containing chemotherapy regimens within the last 12 months.

RESULTS

Seven confirmed responses were observed in each arm, for an overall response rate in the total treated population of 17% (95% confidence interval [CI], 7% to 32%) in the paclitaxel arm and 16% (95% CI, 7% to 29%) in the oxaliplatin arm. Median time to progression was 14 weeks and 12 weeks, and overall survival was 37 weeks and 42 weeks in the paclitaxel and oxaliplatin arms, respectively. Among 63 patients with a 0- to 6-month progression-free, platinum-free interval, there were five objective responses with paclitaxel in 31 patients and two objective responses with oxaliplatin in 32 patients. Nine patients (22%) in the paclitaxel arm had grade 3 or 4 neutropenia (National Cancer Institute of Canada [NCIC] Common Toxicity Criteria). Two patients (4%) experienced grade 3 thrombocytopenia in the oxaliplatin arm. Maximum grade (grade 3) NCIC neurosensory toxicity was experienced by three patients (7%) in the paclitaxel arm and by four patients (9%) in the oxaliplatin arm.

CONCLUSION

Single-agent oxaliplatin at 130 mg/m(2) every 3 weeks is active with moderate toxicity in patients with cisplatin-/carboplatin-pretreated advanced ovarian cancer.

Oxaliplatin: pharmacokinetics and chronopharmacological aspects

Oxaliplatin is the first clinically available diaminocyclohexane platinum coordination complex. The drug is non-cross-resistant with cisplatin or carboplatin and is one of the few active drugs against human colorectal cancer. Its cytotoxicity is synergistic with fluorouracil and folinic acid (leucovorin), the reference treatment for this disease. The main cumulative dose-limiting toxicity of oxaliplatin is peripheral sensory neuropathy. The drug can also produce diarrhoea, vomiting and haematological suppression. Unlike cisplatin, no renal failure or peripheral motor neuropathy have been reported and the sensory neuropathy is partly reversible. Unlike carboplatin, oxaliplatin produces only mild to moderate haematological toxicity. Oxaliplatin undergoes biotransformation into aquated forms in the blood, where 3 species can be found: total platinum, ultrafilterable or 'free' platinum and erythrocyte platinum. Flameless atomic absorption (FAAS) is used for assaying platinum concentration in various tissues. Inductively-coupled plasma mass spectrometry (ICP-MS), with a >10-fold lower sensitivity threshold than FAAS, was also used for the determination of oxaliplatin pharmacokinetics. The pharmacokinetics of oxaliplatin are described by a 3-compartment model. The drug rapidly crosses the cellular membrane as a result of its lipophilicity. Hence, at the end of a 2-hour infusion, approximately 40% of the blood platinum is found in erythrocytes. The distribution half-life of ultrafiltrated plasma platinum ranges from 10 to 25 minutes and its terminal elimination half-life is 26 hours (determined with FAAS) or 270 hours (ICP-MS). The elimination half-life of erythrocytic platinum is 12 to 50 days, close to that of erythrocytes. 30 to 50% of the platinum is recovered in the urine within 2 to 5 days, with renal clearance accounting for half of the total clearance of ultrafiltrated platinum. The total clearance of this species is correlated with the glomerular filtration rate. No pharmacokinetic-pharmacodynamic relationship has been established for oxaliplatin. Pharmacokinetic alterations produced by fluorouracil + folinic acid or irinotecan were minimal if any. The prolonged stability of oxaliplatin makes it suitable for continuous infusions over 4 to 5 days, with a delivery rate which can be either constant or chronomodulated (peak rate at 1600h), using programmable ambulatory pumps. Chronomodulation significantly reduces toxicity and improves antitumour activity as compared with constant rate infusion. These differences in pharmacodynamic properties were paralleled by differences in plasma concentration time courses. The different drug concentration profiles achieved with different infusional modalities may be useful tools for understanding the relationship between the pharmacokinetics and pharmacodynamics of oxaliplatin and may lead to further optimisation of its administration schedule and its combination with other drugs.

Antitumour activity of oxaliplatin in neuroblastoma cell lines

Oxaliplatin appears non cross-resistant with cisplatin and has a comparable antitumour effect both in preclinical and clinical studies. We compared the antitumour effect of oxaliplatin with that of cisplatin in human neuroblastoma cell lines SK-N-DZ, LAN-1 and BE(2)M17 following 24 h exposure at concentrations ranging from 0.5 to 5 microM. Oxaliplatin was less potent with IC50 values 1.08-3.4-fold higher than cisplatin. Like cisplatin, oxaliplatin induced a cell cycle block in the G2/M phase although to a lesser extent than that caused by cisplatin. The concomitant increase of DNA fragmentation and decrease of G2/G1 ratio at 72 h indicated that a fraction of blocked cells underwent apoptosis. Morphological analysis confirmed these data, although oxaliplatin appeared to be 2-3 times less potent than cisplatin in inducing apoptosis. Our results indicate that oxaliplatin is active in neuroblastoma in vitro and this finding warrants in vivo preclinical studies.

Sequence- and region-specificity of oxaliplatin adducts in naked and cellular DNA

Oxaliplatin is a clinical anticancer drug with a pharmacological profile distinct from that of cisplatin. Our studies compared site- and region-specificity of lesions induced by oxaliplatin and cisplatin in naked and intracellular DNA, respectively. Oxaliplatin adducts in naked Simian virus 40 (SV40 DNA) were mapped by repetitive primer extension. The sites of oxaliplatin adducts were nearly identical to the sites of cisplatin adducts and were focused in G clusters and GNG motifs probably reflecting intrastrand cross-links. Although alkaline agarose electrophoresis of specific SV40 fragments showed that oxaliplatin formed interstrand cross-links, the levels of this lesion type were low. Drug-induced lesions in discrete loci of cellular DNA were assessed by the polymerase chain reaction stop assay in human tumor A2780 cells. Oxaliplatin at 200 microM induced approximately 1300, approximately 1500, approximately 800, and approximately 300 lesions/10(6) bp in the human beta-globin, c-myc, and HPRT genes and in mitochondrial DNA, respectively. Cisplatin formed two to six times more lesions in the same regions. For both drugs, lesion frequencies seem to parallel the density of drug-binding motifs in the nuclear regions, whereas mitochondrial DNA was disproportionately less affected. Despite less potent induction of DNA lesions, oxaliplatin was more cytotoxic than cisplatin against A2780 cells. Because our findings clearly demonstrate that oxaliplatin forms covalent adducts with a similar sequence- and region-specificity to that of cisplatin, other properties of oxaliplatin adducts, factors other than DNA binding, or both determine the unique features of the mechanism of action of oxaliplatin.

Limitations of differential display

Since its original description, differential display PCR (DD-PCR) has been extensively used in attempts to identify novel genes under a variety of circumstances. Despite its widespread use, however, few novel genes of interest have been identified. In the present study we describe a set of experiments examining reasons for failure of differential display. Evidence is presented that aberrant priming at both the 5' and 3' ends results in competition in the PCR, precluding detection of messages other than those which are abundantly expressed. Appropriate calculations are discussed which indicate this was predictable and unlikely to be overcome. While DD may be successfully applied in some settings, the evidence indicates that only abundantly expressed messages can be detected. This limitation is emphasized.

Oxaliplatin: a review of preclinical and clinical studies

Of the new generation platinum compounds that have been evaluated, those with the 1,2-diaminocyclohexane carrier ligand-including oxaliplatin--have been focused upon in recent years. Molecular biology studies and the National Cancer Institute in vitro cytotoxic screening showed that diaminocyclohexane platinums such as oxaliplatin belong to a distinct cytotoxic family, differing from cisplatin and carboplatin, with specific intracellular target(s), mechanism(s) of action and/or mechanism(s) of resistance. In phase I trials, the dose-limiting toxicity of oxaliplatin was characterized by transient acute dysesthesias and cumulative distal neurotoxicity, which was reversible within a few months after treatment discontinuation. Moreover, oxaliplatin did not display any, auditory, renal and hematologic dose-limiting toxicity at the recommended dose of 130 mg/m2 q three weeks or 85 mg/m2 q two weeks given as a two-hour i.v. infusion. Clinical phase II experiences on the antitumoral activity of oxaliplatin have been conducted in hundreds of patients with advanced colorectal cancers (ACRC). Single agent activity reported as objective response rate in ACRC patients is 10% and 20% overall in ACRC patients with 5-fluorouracil (5-FU) pretreated/refractory and previously untreated ACRC, respectively. Synergistic cytotoxic effects in preclinical studies with thymidylate synthase inhibitors, cisplatin/carboplatin and topoisomerase I inhibitors, and the absence of hematologic dose-limiting toxicity have made oxaliplatin an attractive compound for combinations. Phase II trials combining oxaliplatin with 5-FU and folinic acid ACRC patients previously treated/refractory to 5-FU showed overall response rates ranging from 21% to 58%, and survivals ranging from 12 to 17 months. In patients with previously untreated ACRC, combinations of oxaliplatin with 5-FU and folinic acid showed response rates ranging from 34% to 67% and median survivals ranging from 15 to 19 months. Two randomized trials totaling 620 previously untreated patients with ACRC, comparing 5-FU and folinic acid to the same regimen with oxaliplatin, have shown a 34% overall response rate in the oxaliplatin group versus 12% in the 5-FU/folinic acid group for the first trial; and 51.2% vs. 22.6% in the second one. These statistically significant differences were confirmed in time to progression advantage for the oxaliplatin arm (8.7 vs. 6.1 months, and 8.7 vs. 6.1 months, respectively). A small but consistent number of histological complete responses have been reported in patients with advanced colorectal cancer treated with the combination of oxaliplatin with 5-FU/folinic acid, and secondary metastasectomy is increasingly done by oncologists familiar with the combination. Based on preclinical and clinical reports showing additive or synergistic effects between oxaliplatin and several anticancer drugs including cisplatin, irinotecan, topotecan, and paclitaxel, clinical trials of combinations with other compounds have been performed or are still ongoing in tumor types in which oxaliplatin alone showed antitumoral activity such as ovarian, non-small-cell lung, breast cancer and non-Hodgkin lymphoma. Its single agent and combination therapy data in ovarian cancer confirm its non-cross resistance with cisplatin/carboplatin. While the role of oxaliplatin in medical oncology is yet to be fully defined, it appears to be an important new anticancer agent.

Sensitivity to cisplatin and platinum-containing compounds of Schizosaccharomyces pombe rad mutants

The role of genes that affect response to radiation in determining sensitivity to platinum-containing compounds was studied using a panel of 23 strains of the yeast Schizosaccharomyces pombe. The radiation-hypersensitive mutants all had the same genetic background and most of them contained mutations that disabled either cell cycle checkpoints or DNA repair. The tested platinum compounds included cisplatin and two complexes containing diaminocyclohexane (oxaliplatin and tetraplatin), two ammine/cyclohexylamine complexes with different orientation of the leaving groups (JM216 and JM335) and a multinuclear platinum complex (BBR 3464). The cytotoxic effect of the selected platinum complexes was evaluated by using a microtiter growth inhibition assay with a 48 hr exposure to drug. The mutants fell into three groups with respect to sensitivity to cisplatin: four mutants (rad2, -7, -11, -15) exhibited minimal change in sensitivity; fifteen mutants (rad4-6, -8-10, -12-14, -16-17, -19-21, and -22) were 5.1-21.7-fold hypersensitive; only rad1 and -3 mutants, defective in checkpoints, and rad18, defective in repair, displayed a marked hypersensitivity. None of the mutants demonstrated appreciable change in sensitivity to JM216 presumably as a consequence of a lack of resistance of the wild-type strain, whereas a moderate increase in sensitivity to JM335 was observed for most of the mutants, and hypersensitivity to BBR3464 was observed only in rad1 and -3. No relevant changes in sensitivity to tetraplatin were observed. Most of the mutants, with the exception of rad2, -7, and -15, were hypersensitive to oxaliplatin. These findings demonstrate that specific mutations have disparate effects on the profile of sensitivity to different members of the same class of cytotoxic agents, which provides genetic evidence that different mechanisms are involved in differential cytotoxicity induced by Pt compounds. The results also demonstrate the utility of such a panel of mutants, constructed on the same genetic background, for detecting specific cellular response; presumably, this reflects the recognition or processing of specific DNA adducts. In conclusion, because the rad1 and rad3 gene products are determinants of cellular response to a large number of platinum-containing compounds, the present results support a critical role of genes involved in cell cycle control in cellular sensitivity to these agents.

Ongoing and unsaid on oxaliplatin: the hope

Oxaliplatin, the first available diaminocyclohexane platinum, has clinical activity in colorectal and ovarian cancers. Its mechanism of action is thought to be similar to that of cisplatin, its main mechanism being the intrastrand DNA adduct between two adjacent guanins or two adjacent guanine and adenine adducts. Ongoing molecular pharmacological studies of the mechanism of action of cisplatin suggest that platinated adducts are recognized by proteins of the mismatch repair system, including the products of the hMLH1 and hMSH2 genes. DNA mismatch repair defects occur in a wide variety of sporadic human cancers, are the main genetic factor in hereditary non-polyposis colon cancer and a frequent de novo or acquired phenomenon in ovarian cancer and other solid tumours. Moreover, they have recently been reported to be a cause of resistance to cisplatin but not to oxaliplatin, as diaminocyclohexane platinum adducts do not appear to be recognized by the mismatch repair complex. These findings explain the oxaliplatin activity in some cisplatin-resistant tumours. In addition, the good safety profile of oxaliplatin makes it a drug of choice for combination therapy, and it has been shown to be synergistic with other cytotoxic agents, including 5-fluorouracil, cisplatin, carboplatin, topotecan, gemcitabine and CPT-11. The results of several ongoing trials are awaited, but available data demonstrate that oxaliplatin is highly effective in the treatment of advanced colorectal and ovarian cancers. Promising early results suggest that it is also efficacious in non-Hodgkin's lymphoma, breast and non-small-cell lung cancers. As a result of its mechanism of action, its favourable safety profile and the differential profile of its antitumoral activity, the full potential of oxaliplatin as an active, versatile antitumoral agent is yet to be fully explored.

Oxaliplatin (L-OHP): a new reality in colorectal cancer

Oxaliplatin (trans-/-diaminocyclohexane oxalatoplatinum; L-OHP) is a new platinum derivative for the treatment of advanced colorectal cancer. Preclinical data have shown that oxaliplatin is active in a wide range of human and murine tumour cell lines, and has been found to be non-cross-resistant with cisplatin in various cisplatin-resistant cell lines and tumours. Oxaliplatin in combination with 5-fluorouracil (5-FU) leads to synergistic antiproliferative activity both in vivo and in vitro. Clinical data have shown that oxaliplatin is active and well tolerated both as monotherapy and in combination with 5-FU/folinic acid in first- or second-line treatment of patients with metastatic colorectal cancer. Oxaliplatin has a very good safety profile, and studies have confirmed that peripheral sensory neuropathy is related to the cumulative dose of oxaliplatin administered and that this neuropathy is generally reversible after discontinuation of treatment. High response rates and prolonged survival have been achieved in metastatic colorectal cancer patients, even after 5-FU failure.