Recent clinical advances with camptothecin analogues

Topoisomerase I expression correlates to response to neoadjuvant irinotecan-based chemoradiation in rectal cancer

Biomarkers may help predict the efficacy of neoadjuvant chemoradiation in patients with rectal cancer. We hypothesized that the expression of topoisomerase I (Topo I) and thymidylate synthase (TS) may help predict the treatment response in patients undergoing irinotecan and capecitabine-based chemoradiation. Patients with rectal cancer (cT3/4Nx or Tx/N+) received neoadjuvant chemoradiotherapy within clinical studies with irinotecan and capecitabine. Samples of normal and tumour tissues were collected before the start of the treatment and during surgical resection. Topo I and TS were measured using real-time PCR. The results of gene expression levels were compared between responders (defined as ypT0-2 ypN0) and nonresponders (ypT3-4 or ypN1/2). A total of 38 patients were analysed, 18 of them were responders. The biopsies of the untreated tumour tissue of responding patients showed a significant higher expression of Topo I compared with nonresponding patients (P = 0.015). Normal tissue did not show this difference (P = 0.126). During chemoradiation, the Topo I expression in tumour tissue of responders decreased significantly. TS did not show any differences between responders and nonresponders before treatment, but a significant decrease in the tumour tissue of responders was noted at the end of the treatment. Our data suggest that Topo I expression in rectal tumour mucosa might serve as a predictor of response to the neoadjuvant irinotecan-based chemoradiation, and hence might be a factor contributing to the development of individualized treatment.

Phase II multicenter open-label study of karenitecin in previously treated epithelial ovarian and primary peritoneal cancer: a Gynecologic Oncology Group Study

The topoisomerase I agents are established as a therapy in recurrent ovarian cancer. Karenitecin, an analog of topotecan with solubility and pharmacologic advantages, was tested in a phase II trial in previously treated patients with recurrent or persistent ovarian cancer. The drug was administered intravenously over 1 h at a dose of 1.0 mg/m(2) daily for 5 days every 21 days. Patients were treated until disease progression, intolerable toxicity, or voluntary withdrawal. Response was evaluated according to modified RECIST criteria. Twenty-seven patients were entered into the study. One patient was inevaluable for not receiving any treatment. Of the 26 evaluable patients, there were two partial responses and one complete response for a total response rate of 12%. This response rate was insufficient to justify accrual to the second stage. The most common grade 3 or 4 toxicities were neutropenia (19%) and gastrointestinal (15%). Karenitecin is a well-tolerated topoisomerase compound but has minimal activity in extensively pretreated ovarian cancer with the dose-schedule employed.

Targeted prodrug treatment of HER-2-positive breast tumor cells using trastuzumab and paclitaxel linked by A-Z-CINN Linker

Targeting drugs for delivery and release has the potential to increase the efficacy of treatment. A bifunctional linker, A-Z-CINN Linker was used to create a targeted prodrug, A-Z-CINN 310. A-Z-CINN Linker links to a potent chemotherapeutic agent, paclitaxel, via an energy-reversible ester bond and also binds a targeting agent, the monoclonal antibody trastuzumab (Herceptin). This study demonstrates the effectiveness of a single-treatment use of A-Z-CINN 310 in decreasing tumor volume and tumor cell density of human HER-2-positive BT-474 mammary tumor cells implanted in scid mice, compared to treatment with simultaneously administered trastuzumab and paclitaxel and with saline control. After treatment with A-Z-CINN 310, some mice received light exposure at 6 h for 5 min adjacent to the tumor to cause light-accelerated release of paclitaxel. Changes in tumor volume were measured for 28 days following treatment; changes in histology were measured at 31 days. Animals treated with A-Z-CINN 310, then light, showed dose-dependent decreases in tumor volume and tumor cell density which were more rapid and extensive than those seen with A-Z-CINN 310 without light or a 10-fold higher concentration of co-administered trastuzumab plus paclitaxel. This suggests that targeted delivery of paclitaxel using A-Z-CINN 310 kills tumor cells by localized release of paclitaxel at the tumor site, which can be accelerated by light treatment. These results indicate that a targeted prodrug therapy containing trastuzumab as the targeting agent and A-Z-CINN-paclitaxel as the prodrug results in a conjugate that is more effective in killing tumor cells than equivalent concentrations of co-administered trastuzumab and paclitaxel. Targeting of a drug can reduce the dose needed for effective therapy and can increase local bioavailability. This makes targeted therapy using an A-Z-CINN prodrug delivery system feasible for treating both primary and metastatic tumors.

Lack of efficacy of topotecan in the treatment of metastatic or recurrent squamous carcinoma of the head and neck: an Eastern Cooperative Oncology Group Trial (E3393)

Recurrent or metastatic squamous carcinoma of the head and neck (RMSCHN) is a modestly chemoresponsive tumor; however, currently available agents have failed to improve survival. New active agents are needed for the treatment of this disease. Topotecan is a topoisomerase inhibitor that demonstrated initial promising activity in squamous carcinoma of the head and neck. The Eastern Cooperative Oncology Group conducted a phase II trial of topotecan to determine the efficacy and toxicity of a weekly treatment schedule in patients with RMSCHN. Patients with metastatic or locally recurrent squamous carcinoma of the head and neck were treated with topotecan 1.5 mg/m2 x 24 hours by continuous infusion on days 1, 8, 15, and 22 of each 35-day cycle. Patients were stratified in two cohorts: chemonaive and previously treated. Sixteen chemonaive and 16 previously treated patients were registered on study. Grade III/IV neutropenia and anemia occurred in 16% and 18% of patients, respectively. No responses were observed in either cohort. Median survival for previously untreated patients was 4.6 months and 3.2 months for previously treated patients. Topotecan failed to demonstrate efficacy in patients with RMSCHN. Further evaluation of this agent is not planned.

Clinical pharmacology of camptothecins

Camptothecins (CPTs) are a unique class of chemotherapeutic agent which inhibit DNA synthesis by inhibiting topoisomerase I activity. Structure-activity studies on the original CPT alkaloid led to the development of the new analogues irinotecan (CPT-11), topotecan, and 9-aminocamptothecin, which have improved water solubility and lower toxicity. CPT analogues exhibit interesting pharmacokinetic/pharmacodynamic and metabolic properties that are of major research and clinical interest. This review describes the clinical pharmacology of these 3 CPT analogues. Specific areas such as absorption after extravascular administration, pharmacokinetic/pharmacodynamic variability, metabolism, and administration in special populations are discussed.