Triapine® is a novel RR inhibitor that inhibits the M2 unit and has been shown to act synergistically with DNA damaging agents in vitro. This phase I study was designed to evaluate the safety and tolerability of Triapine® in combination with doxorubicin and to determine the MTD and examine pharmacokinetic and exploratory pharmacodynamic analysis.
The MTD in this study was established at doxorubicin 60 mg/m2 IV on day 1 and Triapine® 25 mg/m2 IV over 2 hours on days 1 through 4. The dose of Triapine® in this combination was not able to be increased above 25 mg/m2 due to excessive toxicity. Dose limiting toxicities (febrile neutropenia and grade 4 thrombocytopenia) were experienced in 2 of 3 patients at dose level 2 (doxorubicin 60 mg/m2 and Triapine® 45 mg/m2) early in the first treatment course. When Triapine® was increased to 45 mg/m2 in dose level 2a, with a decreased dose of doxorubicin (45 mg/m2), the first two patients enrolled also had DLTs (diarrhea, CVA). No DLTs were noted at dose level 1a when doxorubicin was administered at 45 mg/m2 with Triapine® at 25 mg/m2. Examination of the twelve evaluable patients enrolled to dose level 1 shows that only one who experienced a treatment-related DLT after the second course of therapy. Otherwise, treatment was fairly well-tolerated with 83% (10/12) experiencing grade 3 or 4 neutropenia, and one each (8%) having grade 3/4 anemia, fatigue or hypokalemia during the first cycle. These symptoms were transient and tolerable and did not result in significant dose-delays, and there were no episode of febrile neutropenia. The average number of cycles completed per patient at the MTD level was 3.1.
Previous studies have documented the myelosuppressive effects of Triapine®
. In the phase 1 study with Triapine®
given by 2 hour IV infusions for 5 days of every 28 day cycle, the major hematologic toxicities were transient leucopenia (grade 4 in 93% of the patients in at least one course) and anemia (grade 2 in 73% and grade 3 in 22%) (14
). Thrombocytopenia was less common, and was grade 3 or 4 in 22% of patients. In a phase II study of Triapine®
in combination with gemcitabine in patients with advanced pancreatic cancer, Triapine®
was initially given as a 4 hour infusion weekly prior to gemcitabine (20
). Treatment with the 4 hour infusion was well tolerated with little additional myeolosuppression. However, the protocol was subsequently amended to give Triapine®
over a 24 hour continuous infusion weekly prior to gemcitabine to enhance the synergistic effect between the two agents. Excessive myelosuppression was seen in the first continuous infusion cohort necessitating a reduction in the Triapine®
dose. All subsequent patients also experienced excessive myelosuppression necessitating a dose reduction in gemcitabine. Taken together, these studies suggest that the myelosuppressive effects of Triapine®
may be related to dose intensity over a given period of time.
dose in this study was well below the single-agent MTD identified by Murren et al. (14
). In that trial, the MTD was 96 mg/m2
administered by 2 hour IV infusions for 5 days of every 28 day cycle (14
); however, the recommended phase II dose was 96 mg/m2 daily for 4 days since that schedule had a lower incidence of leucopenia. Our finding that that Triapine®
in combination with doxorubicin yielded significant hematologic toxicity is not surprising since severe myelosuppression is one of the DLTs of doxorubicin, and leucopenia occurs in approximately 75% of patients treated with 60 mg/m2
every 21 days (21
). Anemia and thrombocytopenia are less common with single-agent doxorubicin. The myelosuppressive effects of Triapine®
may limit the dose schedules and chemotherapy agents that may be chosen when considering other combination studies.
One 71 year-old male with metastatic bladder cancer with lung metastases who was enrolled at the MTD level experienced grade 5 CHF following the second course of chemotherapy (cumulative doses of Triapine®
= 385 mg and doxorubicin = 228 mg). The patient was otherwise healthy and had previously undergone transurethral resection of the tumor and was treated with mitomycin-C and gemcitabine in combination with pemetrexed for Metastatic disease. While reversible hypotension, hypoxia, dyspnea, cough, and EKG changes, including ST-T wave changes and prolongation of the QT interval, were observed in a prior phase I study with Triapine®
), CHF has not been observed in single-agent studies. Congestive heart failure related to chronic cardiomyopathy is a well-documented toxicity attributed to doxorubicin; however, the incidence of CHF is typically related to the cumulative dose administered, occurring in 1% in patients treated with up to 300 mg/m2
and 4% of patients who receive 450 mg/m2
). Acute cardiac toxicity has also been observed with doxorubicin, but this is usually characterized by transient arrhythmias or other EKG changes. Three cases of severe and fatal (2 cases) doxorubicin-induced cardiotoxicity have been reported at cumulative doses below 400 mg/m2
). In all 3 cases, the patients were receiving multi-agent chemotherapy with bleomycin, cyclophosphamide, dactinomycin, high-dose methotrexate and cisplatin, and the risk of this toxicity appeared to be enhanced with concurrent administration of other cardiotoxic or hepatotoxic agents. It is unclear whether there may be any synergistic effects between Triapine®
and doxorubicin in terms of cardiac toxicity but this may be a consideration for patient selection if this combination is used in other clinical studies.
The plasma concentrations of Triapine®
) and doxorubicin (17
) in this study were similar to previously reported values, suggesting no interaction between the agents. Our observed half-life of doxorubicin was shorter than previous reports, which is most likely explained by our limited sampling schedule. The dose-adjusted AUC and Cmax for Triapine®
in plasma were significantly lower than the corresponding values in erythrocytes (AUC: p = 0.01; Cmax: p = 0.02, non-parametric Wilcoxon Signed Rank test (two-sided)) which suggests an accumulation of Triapine®
in the erythrocytes and could be related to the development of methemoglobinemia. Additionally, the Tmax occurred in the erythrocytes at 0.04 ± 0.11 hours compared to 0.22 ± 0.11 hours in plasma. This may indicate that Triapine®
preferentially enters the erythrocyte and that the accumulation of Triapine®
may be the result of decreased diffusion out of the erythrocyte.
Despite lack of objective tumor responses in this study, two patients with melanoma and another two patients with prostate cancer derived clinical benefit with this combination. While antitumor activity with Triapine®
has been shown in melanoma in preclinical models (12
) and in a patient with prostate cancer in a single-agent phase I study (13
), there are no in vitro
data showing activity of this combination in either of these malignancies. Since preclinical data and the findings from this study support a synergistic interaction between Triapine®
and doxorubicin, we believe that further clinical development of this combination in these two tumor types is warranted.
A growing body of evidence suggests that RR expression may influence survival and response in a number of malignancies. Studies examining RRM1 expression in lung tumors have shown that higher levels of this subunit may be associated with growth suppression and a less malignant phenotype, particularly in patients with resectable disease (25
). However, patients with metastatic NSCLC who have increased RRM1 levels are potentially less responsive to cytotoxic therapy with gemcitabine and a platinum (26
). Likewise, overexpression of RRM2 resulted in increased in resistance to gemcitabine chemoresistance in lung (27
) and pancreatic (28
) cancer cells in vitro
. In cell lines selected for resistance to hydroxyurea, increased RRM2 protein levels and ribonucleotide reductase activity were detected (29
). Taken together, these findings suggest that alterations in RRM1 and RRM2 expression may confer resistance to chemotherapy and may be useful biomarkers for predicting and monitoring responses to various therapies including Triapine®
). Pooled analyses from 40 different tumor samples obtained at baseline in 3 studies evaluating Triapine®
at our institution showed that RRM2 protein and gene expression varied by tumor type following treatment with Triapine®
(data not shown) (18
). Although the number of samples was too small to determine whether the level of RRM2 protein correlated with response or resistance to Triapine®
in specific tumor types, evaluation of RRM1 and RRM2 expression should be considered in future studies with Triapine®
Based on the clinical activity observed in this study, the combination of Triapine® and doxorubicin may be considered for use in future studies in melanoma and prostate cancer. While this combination was fairly well tolerated at the MTD, it was associated with significant myelosuppression. It is possible that the hematologic effects would be less pronounced in patients with adequate marrow reserve who have not received multiple prior therapies. In addition, liberal us of growth factors could minimize treatment-related neutropenia and associated sequelae. The recommended phase II combination dose based on our data would be Triapine® 25 mg/m2 administered as a 2 hour infusion on days 1-4 and doxorubicin 60 mg/m2 given by IV bolus on day 1 immediately following Triapine®.