by Elise Kohn and Eddie Reed (EK, Section Head, Laboratory of Pathology, NCI; ER, Acting Chief, Clinical Pharmacology, NCI)

Identification and characterization of effective, novel treatment modalities is a critical mission for the Clinical Oncology Program (COP) of the National Cancer Institute. Within the Clinical Pharmacology Branch of COP, the Medical Ovarian Cancer Section has two arms: basic science research and clinical investigation. Our clinical focus has been on developing novel approaches to the treatment of epithelial ovarian cancer with emphasis on the treatment of newly diagnosed ovarian cancer patients and the subsequent treatment of patients with recurrent ovarian cancer or disease that is refractory to standard therapy. The unique integration of laboratory observations into clinical practice at NIH has allowed the development of novel treatment approaches for patients with newly diagnosed, advanced-stage epithelial ovarian cancer and patients with advanced and recurrent ovarian cancer. The new concepts in the use of Taxol identified in the Intramural Research Program have spurred further clinical investigation into 1) the use of dose-intense Taxol in an ongoing phase III study and 2) a three-drug combination for newly diagnosed patients in a phase II study.

Epithelial ovarian cancer, arising from the surface epithelial lining of the ovary, is the fourth leading cause of cancer deaths in women, accounting for approximately 15,000 deaths per year. Unfortunately, in over 80% of women, diagnosis is late, usually occurring after the cancer has spread throughout the abdominal cavity. The lack of early detection capability and the extensive disease at diagnosis result in a high mortality rate for this disease, with an average 5-year survival of 40%. The lack of successful screening techniques for the general population has heightened the importance of improved therapeutic and surgical interventions.

The treatment approach to advanced-stage (abdominal-spread) ovarian cancer involves initial surgical debulking followed by chemotherapy. The addition of cisplatin to the therapeutic armamentarium and the advent of combination chemotherapy led to improvements in disease-free survival and overall survival for ovarian cancer patients. The standard chemotherapy treatment for newly diagnosed patients after surgery now consists of the combination of a platinum compound, cisplatin or carboplatin, with a DNA-alkylating agent such as cyclophosphamide. This combination has been shown to have synergy in vitro and to prolong disease-free survival and overall survival for ovarian cancer patients.

Over the past two decades, our ovarian cancer effort has defined the use and toxicities of platinum compounds and now has spearheaded the use of paclitaxel (Taxol) in high doses for patients with advanced ovarian cancer. The hypothesis under investigation is that more therapy, through either more intense doses or drug-combination therapy, might improve time to recurrent disease, disease-free survival, or overall survival.

Our first goal was the ability to intensify doses of therapeutic agents without unacceptable toxicity. In the 1980s, a dose-intense regimen of cisplatin was tested (1) This regimen, which doubled the administered dose of cisplatin, was profoundly toxic, resulting in significant and lasting neurotoxicity. With the identification of Taxol as a novel agent with a different spectrum of toxicity, we again addressed the possibility of increasing the administered drug dose to improve the therapeutic outcome.

William McGuire and colleagues at the Johns Hopkins Oncology Center in Baltimore generated excitement over Taxol's potential in 1989 with publication of their phase I/II study of continuous-infusion Taxol (2). This trial used a dose-escalation scheme, followed by expansion of a cohort that received the maximally tolerated dose that the researchers had identified in phase I. Because efficacy in patients with relapsed epithelial ovarian cancer was observed during the phase I component of the study, this disease was chosen for the phase II efficacy portion of the trial. The dose-limiting toxicity in this trial was myelosuppression -- marked lowering of the white blood cell counts.

The advent of cytokine administration to obviate myelosuppression (3) suggested that it would be possible to increase the administered dose of Taxol with a white blood cell - stimulating agent, such as granulocyte colony-stimulating factor (G-CSF). We began our studies of dose-intense Taxol in 1990 with 18 patients in a Taxol dose-escalation study in which G-CSF was used to block bone marrow suppression. G-CSF administration was successful in preventing the dangerous myelosuppression, and sensory peripheral neuropathy emerged as the new dose-limiting toxicity in our trial (4). By using G-CSF, we were able to administer Taxol safely at a dose of nearly twice that recommended by the trial of McGuire and colleague (250 mg/m[2] vs. 135 mg/m[2] every 21 days).

This observation led to our recent phase II efficacy trial of Taxol at this maximal dose for patients with chemotherapy-resistant ovarian cancer. The use of G-CSF allowed maintenance of intended dose intensity within 90% of the planned dose, per cycle, of 250 mg/m[2]. The frequency of response, defined as greater than 50% reduction in the measurable tumor mass in response to high-dose Taxol, was 48% (4). Notably, this response rate was observed in a cohort of patients who were resistant to platinum and, thus, were also resistant to other chemotherapeutic interventions (5). The result is also in striking contrast to the 24% response rate for platinum-resistant patients reported by McGuire and co-workers when they administered doses of Taxol in the range of 117 to 135 mg/m[2] (see figure 1). Our doubled response rate in heavily pretreated patients has been confirmed by Kavanaugh and colleagues at the M. D. Anderson Cancer Center (6) and collectively, the findings have sparked a controversy in Taxol-dosing recommendations.

The striking efficacy of dose-intense Taxol administration for patients with advanced relapsed and drug-refractory ovarian cancer was the basis for the development of a phase II randomized clinical trial of Taxol by the multi-institutional Gynecologic Oncology Group. The objective of this trial is to determine whether there is a dose-response relationship for the administered dose of Taxol. Patients will be assigned randomly to one of three groups to receive doses, per cycle, of 135 mg/m[2], 175 mg/m[2], or 250 mg/m[2]. Shortly after initiation of the trial, the low-dose arm was terminated due to early evidence of a dose-response relationship between the lower two arms. The two higher-dose arms of the trial are now accruing patients and G-CSF is being used at the highest dose level of 250 mg/m[2] per cycle to ameliorate the myelosuppression we saw in our trial. The phase II clinical trial should definitively address the issue of Taxol-dosing recommendations for patients with advanced epithelial ovarian cancer.

A second issue in the treatment of epithelial ovarian cancer is what the optimal combination regimen should be for the initial treatment of newly diagnosed patients after debulking surgery. Previous clinical trials, many initiated in the Clinical Oncology Program, have identified the utility of combination chemotherapy in the treatment of such patients. The current standard regimen is the combination of cisplatin with cyclophosphamide; however, it is currently unclear whether this is the best therapy. Is the combination of cisplatin with cyclophosphamide is equivalent or superior to the combination of cisplatin with Taxol? Points of comparison include the response rate to initial therapy, durable responses to treatment (prolonged disease-free intervals or long-term disease-free status), and toxicity pattern. The combination of cisplatin with cyclophosphamide has a high response rate--in the range of 70 - 80% clinical complete responses--but only 20 - 25% of patients will have no evidence of disease at surgical restaging and half of those patients will relapse. In addition, the higher recommended doses of cisplatin and cyclophosphamide can have serious and lasting side effects.

On the basis of the preliminary report from a prospective, randomized study conducted and reported by the Gynecologic Oncology Group (7) cisplatin used in combination with Taxol may have clinical benefits over standard cisplatin with cyclophosphamide. This clinical benefit is small and has lessened with further follow-up. Thus, the next question became, if cisplatin with Taxol is similar to or slightly better than cisplatin with cyclophosphamide, is the combination of all three drugs potentially better than either combination alone? Several bodies of data collectively suggest that the combination of all three drugs may be preferable.

Our clinical team has been conducting a trial of the combination of Taxol and cyclophosphamide in patients with recurrent, platinum-refractory epithelial ovarian cancer. In preliminary analysis presented in April, we reported that this two-drug combination is better than either drug alone (8), with improved disease-response rate, frequency of complete clinical remissions, and median duration of response. These data suggest that, clinically, in tumor cells that are refractory to platinum-based therapy in a cohort of patients for whom effective choices are very limited, Taxol in combination with a bifunctional DNA alkylating agent may be very effective.

Recent basic research on DNA repair may shed light on the possible molecular mechanisms that underlie these clinical observations. The mechanism of antitumor activity of the platinum family drugs is the formation of platinum-DNA cross-links or adducts. In mammalian cells, platinum-DNA adduct repairs are made via the nucleotide-excision-repair pathway (9, 10). Taxol inhibits the repair of platinum-DNA adducts by up to 90%, and this is associated with markedly enhanced cell kill that is specific to the sequence of drug administration (10). The leading hypothesis for this effect of Taxol is that Taxol dissociates high-energy phosphates from energy-requiring reactions during the process of nucleotide-excision repair (9)..

The DNA damage of bifunctional alkylator-DNA binding, on the other hand, is probably repaired by the mismatch-DNA-repair system (11), also an energy-requiring system. We hypothesize that the enhanced effect of Taxol with cyclophosphamide is related to inhibition of alkylator-DNA adduct repair, similar to that demonstrated for cisplatin.

The reliance on different cellular-DNA-repair pathways by cisplatin and cyclophosphamide would explain why the administration of the combination of cisplatin and cyclophosphamide has been shown to be better than either drug alone, and the ability of Taxol to inhibit both DNA-repair pathways supports the hypothesis that the combination of all three agents should result in superior clinical efficacy. This hypothesis is now being tested in a dose-escalation phase I clinical trial in the Medical Ovarian Cancer Section.

We have just completed a study of the sequential use of cyclophosphamide, Taxol, and cisplatin, used with G-CSF for bone marrow support for newly diagnosed, advanced-stage epithelial ovarian cancer patients. Our preliminary results, reported last year, have shown that these agents can be administered together safely (12). Optimal doses result in acceptable neurologic toxicity, minimal bone marrow toxicity, and antitumor activity that is greater than seen with other regimens. A multi-institutional phase II study of this regimen is planned.

Because the presence of platinum-DNA adducts in the circulating white blood cells of patients accurately mirrors the drug effect on tumor cells, these studies offer an opportunity to observe clinical-laboratory correlations. We have initiated laboratory studies of the levels of DNA-adduct formation in the white blood cells of patients undergoing treatment with the three-drug combination of cisplatin, cyclophosphamide, and Taxol. This will allow testing of the hypothesis that Taxol is favorably altering DNA repair and will help to establish a basic science foundation for understanding the interactions of these drugs.

Patients or referring physicians seeking information regarding these trials may contact the Medical Ovarian Cancer Section at (301) 402-1357 or the PDQ database available through the National Library of Medicine.

References

1. M.C. Rothenberg, R.F. Ozols, R.C. Robert, E.J. Glatspein, S.M. Steinberg, E. Reed, et al. "Dose-intensive induction therapy with cyclophosphamide, cisplatin, and consolidative abdominal radiation in advance-stage epithelial ovarian cancer."J. of Clini. Oncol. 10, 727 - 34 (1992).

2. W.P. McGuire, B. Reichman, T. Hacks, and W. Jones. "Taxol: a unique antineoplastic agent with significant activity in advanced ovarian epithelial neoplasms." Ann. Int. Med., 1989. 111, 273 - 9 (1989).

3. J. Gabrilove, L. Jakubowski, and H. Sher. "Effect of granulocyte colony-stimulating factor on neutropenia and associated morbidity due to chemotherapy for transitional cell carcinoma of the urothelium." New Engl. J. Med. 318, 1414 - 22 (1988).

4. G.A. Sarosy, E.C. Kohn, D.A. Stone, M. Rothenberg, J. Jacob, and D.O. Adamo. "Phase I study of taxol and granulocyte colony-stimulating factor in patients with refractory ovarian cancer." J. Clin. Oncol. 10, 1165 - 70 (1992)..

5. M. Markman, B. Reichman, T. Hacks, W. Jones, J.L. Louis, S. Reuben, et al. "Responses to second-line cisplatin-based intraperitoneal therapy in ovarian cancer: influence of a prior response to intravenous cisplatin." J. Clin. Oncol. 9, 1801 - 5 (1991).

6. J.J. Kavanaugh, A.T. Kudelka, C.L. Edwards, R.S. Freedman, C. Gonzalez-DeLeon, et al. "A randomized crossover trial of parenteral hydroxyurea v. high dose taxol in cisplatin/carboplatin resistant epithelial ovarian cancer." Proc. of the Am. Soc. for Clin. Oncol. 12, 259 (19930.

7. W. McGuire, W. Hoskins, M.F. Brady, P.R. Kucera, K.Y. Luke, E.E. Partridge, et al. "A Phase III trial comparing cisplatin/cytoxan (PC) and cisplatin/Taxol (PT) in advanced ovarian cancer." Proc. of the Am. Soc. for Clin. Oncol. 12, 255 (1993).

8. E. Reed, G. Sarosy, E. Kohn, M. Christian, C. Link, and P. Davis. "Phase I study of paclitaxel "TAX" and cyclophosthamide "CTX" in reccurrence adenocarcinoma of the ovary." Proc. of the Am. Assoc. for Cancer Res. 35, 234 (1994).

9. P.B. Schiff, et al. "Taxol assembles tubulin in the absence of exogenous guanosine 5'-triphosphate or microtubule-associated protein." Biochem. 20, 3247 - 52 (1981).

10. R.J. Parker, M.D. Dabholkar, K.B. Lee, F. Bostick-Bruton, and E. Reed. "Taxol effects on cisplasin sensitivity and cis cellular accumulation in human ovarian cancer cells." Monogr. of the Natl. Cancer Inst. 15, 83 - 8 (1993).

11. J.E. Cleaver. "It was a very good year for DNA repair." Cell 76, 1 - 4 (1994).

12. E.C. Kohn, E Reed, C. Link, M. Christian, P. Davis, and G. Sarosy. "A pilot study of cyclophosphamide, cisplatin, taxol, and G-CSF in newly diagnosed stage III/IV ovarian cancer patients." Proc. of the Am. Soc. for Clin. Oncol. 12, 1993.