Pegylated Liposomal Doxorubicin: Antitumor Activity in Epithelial Ovarian Cancer or Cancers of Peritoneal Origin

Introduction

Systemic chemotherapy has saved the lives of many patients with cancer, but the maximum efficacy of cytotoxic agents is severely limited by their adverse effects. Thus, the main goal in designing new chemotherapeutic regimens is to achieve the greatest benefit while minimizing the drugs’ concomitant side effects.

Liposomal encapsulation provides a mechanism by which high concentrations of cytotoxic drugs can be delivered to tumor sites where they may be able to exert their greatest effect. Kruskal et al demonstrated that after intraportal or intra-arterial injection of doxorubicin(Drug information on doxorubicin)-containing Stealth liposomes (Doxil) into mice with tumor-bearing livers, a higher proportion of doxorubicin autofluorescence was seen in the colorectal cancer cells (85%) than in the surrounding Kupffer cells, without the necessity of tumor embolization.[1] Other studies have shown that when mice bearing a variety of other tumors (colon, prostate, Kaposi’s sarcoma, ovarian) were treated with doxorubicin encapsulated in pegylated liposomes, the drug concentration in tumor sites was higher and the antitumor activity was greater than in animals receiving comparable amounts of the free drug.[2-6]

Based upon the activity of pegylated liposomal doxorubicin (PEG-LD) in ovarian tumors, a series of studies have been conducted at the University of Southern California (USC) since August 1993 in patients with gynecological malignancies or peritoneal cancers (Table 1). A phase I study (A) was conducted in 56 patients with solid tumors, 8 of whom had epithelial ovarian cancer.[7] We also conducted a phase II study (B) in 35 women, 22 from USC, with platinum- and paclitaxel(Drug information on paclitaxel)-refractory epithelial ovarian cancer.[8] Six women were treated with PEG-LD on a compassionate basis (C) while we awaited the opening of the second phase II study. This second phase II study (D) is being performed in similarly refractory patients and includes women with other peritoneal and gynecological cancers and patients with various degrees of pretreatment, including autologous bone marrow support and whole abdominal radiation. We have thus far analyzed 20 of the women with ovarian cancer. Two other studies are ongoing: one is a phase I study of combination paclitaxel (Taxol) and PEG-LD (E) based on the activity of both of these agents in breast and ovarian cancer; four women with papillary serous cancers have been entered to date. The other is a phase I/II study of PEG-LD combined with local hyperthermia (F) based on preclinical models showing enhancement of PEG-LD’s effects by local hyperthermia;[9] three patients have been entered to date.

This article will summarize our treatment methods, pharmacokinetic observations, the antitumor activity of PEG-LD, its impact on progression-free and overall survival rates, and the toxicity profile of PEG-LD alone and in combination.

Methods

Entry Criteria, Treatment, and Assessment Methods

Except for the formal phase II study (B), which limited the number of prior treatments and was confined to primary ovarian carcinoma, criteria for entry into the other trials were liberalized to include any patients with platinum-refractory cancer, as well as patients with primary peritoneal tumors or tumors from other gynecologic sites of origin. Patients were generally refractory to taxane treatment as well, except for rare patients refusing treatment with paclitaxel because of its associated alopecia.

In the USC phase I study (A), PEG-LD was administered at doses ranging from 20 to 60 mg/m^2. The dose of single-agent PEG-LD selected for the subsequent phase II study (B) was 50 mg/m² repeated every 3 weeks. However, all patients required dose reductions to 40 mg/m² after a median of three doses; the dosing interval was also routinely increased from every 3 weeks to every 4 weeks if patients failed to recover from skin or mucosal toxicities. In the compassionate use study (C) and the second phase II study (D), the dosing interval was automatically increased to every 4 weeks in all patients after the second dose; the initial dose was also lowered from 50 to 40 mg/m² when patients had been heavily pretreated. In the combination study (E), the initial PEG-LD dose was 40 mg/m² every 4 weeks and paclitaxel was given as a 1-hour infusion, just after PEG-LD, and repeated 1 week later, at a starting dose of 110 mg/m². In the phase I/II study combining PEG-LD with hyperthermia (F), PEG-LD was administered at a dose of 20 mg/m² every 2 weeks for three cycles, and the heating to 40° C was achieved by microwave devices.

PEG-LD was prepared by dilution in 250 mL of a 5% dextrose solution, and was delivered through a peripheral intravenous route. Except for the first dose, infusion took place over a 1-hour period; for the first dose, patients were premedicated with intravenously delivered hydrocortisone(Drug information on hydrocortisone) (100 mg), diphenhydramine(Drug information on diphenhydramine) (25 mg), and cimetidine(Drug information on cimetidine) (300 mg) (Tagamet), and PEG-LD was infused during the first half-hour at a rate of 1 mg/mL. These precautions were taken to minimize acute flushing reactions and discomfort occasionally observed during the first few minutes of infusion. This reaction always resolved by retreating at slower infusion rates.

Methods for assessing response and toxicity were those of the Southwest Oncology Group.[10] In addition, a CA-125 assay was used for patients whose responses were not yet assessable by computerized tomography (CT) or whose responses were initially nonmeasurable. Responses were defined by a fall in CA-125 level to the normal range, or a decrease of greater than or equal to 50% that was confirmed 4 or more weeks later in accordance with the method of Rustin et al.[11] Confirmation of partial response by CT scan 4 weeks after initial documentation was generally not possible because of practical considerations. Therefore, the response rates may include some responses that were “unconfirmed” and others that were defined by markers only. Nevertheless, the correlation between objective responses and CA-125-defined responses was generally excellent,[8] confirming the experience of Rustin et al.[11]

Results

Pharmacokinetics

Over the dosage range studied (40 to 50 mg/m²), PEG-LD pharmacokinetics are best described by an open, two-compartment structural model with linear distribution between the central and peripheral compartments and a nonlinear elimination from the central compartment. Pharmacokinetic parameters for nine patients in the completed phase II study (B) are estimated in Table 2.

Noteworthy are the low volume of distribution (V_ss) and the predicted area under the concentration-time curve (AUC) after a dose of 50 mg/m². The high AUC values reflect the prolonged elimination half-life, in excess of 52 hours. The faster clearances, exceeding 0.10 L/h/m², were recorded in two patients with large, palpable abdominal masses, declining performance status, and low serum albumin levels. Of the nine patients, only one had ascites. This patient, and two other patients (without accompanying pharmacokinetic data), did not experience PEG-LD toxicity, suggesting that patients with ascites also have fast clearances.

Antitumor Activity

Objective responses were seen in all trials. In the phase I study (A), one patient of the eight with epithelial ovarian cancer experienced a partial response that lasted 6 months after the onset of therapy. Two additional patients with epithelial ovarian cancer had responses defined by the normalization of their CA-125 levels, or by a decrease in CA-125 to less than or equal to 50% of their previous levels. One of these patients had a minor response for 27 months and was alive with disease 39 months after study entry. The other patient’s tumor was nondetectable and her CA-125 declined by 50% to 75% for 30 months. This patient’s CA-125 rose again coincident with the detection of a new lesion in her spleen. This patient is still alive 36 months after entry.

In the completed phase II study (B), 9 of 35 patients (25.7%) were documented to have objective tumor responses (Table 3). The patient who achieved the complete response did so after 10 months of treatment. She remains in complete remission at 21 months and has now been off PEG-LD for 5 months. Her CA-125 level normalized at cycle 2 and has remained normal. Almost all of the other patients who responded to treatment manifested their objective response at their second or third reassessment. Of the nine patients who responded, eight have progressed after 8 to 21 months on therapy, and one is still receiving treatment at 21 months. The median time of response (first evidence of partial response) was 5.5 months (range, 2 to 8) and the median duration of response was 6 months (range, 3.6+ to 16). The median progression-free survival was 5.7 months, and the median overall survival was 11 months (range, 1.5 to 21+).

Similar information on responders from the compassionate use study (C), the 20 patients thus far enrolled in the ongoing phase II study (D), and patients treated with PEG-LD combined with either paclitaxel (E) or hyperthermia (F) is provided in Table 4. None of the responding patients had bulky masses (less than 5 cm), or a hemoglobin level less than 10 g%. A more formal analysis of responders from the phase I and phase II studies is underway.[12]

The longest duration of objective response was recorded for a patient who received PEG-LD on a compassionate basis (Patient DL, Table 4). It is noteworthy that this patient failed treatment with cyclophosphamide(Drug information on cyclophosphamide) (Cytoxan, Neosar), doxorubicin (Adriamycin) and cisplatin(Drug information on cisplatin) (Platinol) 3 years previously, with disease returning before the completion of six treatment cycles (total cumulative doxorubicin dose of 300 mg/m²⁾ and involving both the abdominal cavity and the pleura. The response to PEG-LD followed an equally lengthy response to paclitaxel, but terminated when the disease progressed in the pleura and axillary lymph nodes.

The combination of PEG-LD and local hyperthermia was tried on three occasions. One patient, who initially responded to PEG-LD alone, subsequently developed an ulcerating mass at the site of a palliative gastric resection (Patient SM, Table 4) and was treated with PEG-LD but showed no response. Two other patients with subcutaneous masses (one with an abdominal wall mass from pseudomyxoma, and another with an enlarged supraclavicular node secondary to a Mullerian tumor of the tunica vaginalis testis) had minor responses (regression of the mass size on palpation).

Two of the three patients with epithelial ovarian cancer treated with paclitaxel and PEG-LD experienced either a partial response and a decrease in CA-125 level, or a decrease in CA-125 level only. One patient (patient CJ) who had received carboplatin(Drug information on carboplatin) (Paraplatin) and paclitaxel in both standard and high doses with cytokine support after a positive “second-look” laparotomy, was treated with paclitaxel and PEG-LD upon detection of a rising CA-125 level a few months later. She failed to respond despite receiving two cycles of PEG-LD at doses high enough to cause skin and mucosal toxicities. A fourth patient (patient BR), with a primary peritoneal cancer and an accumulation of ascites, failed initial therapy with paclitaxel and carboplatin and two courses of ifosfamide(Drug information on ifosfamide) (Ifex). Treatment with paclitaxel and PEG-LD resulted in a decline in this patient’s CA-125 level without toxicity, but she did not achieve an obvious clinical benefit. Two patients, begun on PEG-LD alone on a compassionate basis, subsequently received cisplatin and carboplatin when their CA-125 levels showed no further decline. One of these patients experienced a reduction to normal of her slightly elevated CA-125 level and had a near-complete response as judged by para-aortic lymph node enlargement; this response has continued for more than 12 months since cessation of all treatment. Whether this patient responded to PEG-LD or to the combination cannot be stated since the objective response could have been secondary to the platinums.

Survival

In the completed phase II study (B), progression-free survival ranged from 2 months to greater than 21 months, with a median overall survival time of 11 months. When the eight patients from the phase I study (A) are included in the analysis, the median progression-free survival time is 7 months and overall survival time for the 29 evaluable (of 31) patients is 13 months (Figure 1 and Figure 2).

Single-Agent Toxicity

No patients in the initial phase II study (B) were dropped due to toxicity and PEG-LD was tolerated at a dose of 50 mg/m² for a median of three cycles (range, one to nine). Among the 35 patients entered into the study, dose reduction to 40 mg/m² was required during the first three cycles for World Health Organization (WHO) grade 3 stomatitis (five patients), and for grade 3 skin changes (10 patients with palmar-plantar erythrodysesthesia, occasional skin rashes in intertriginous areas, or punctate lesions in other areas) (Table 5). Grade 3 or grade 4 myelosuppression occurred in only three patients concomitant with stomatitis. Additional dose modifications were eventually instituted for grade 2 stomatitis. Some patients experienced esophageal and gastric discomfort but nausea and vomiting were absent. Two patients experienced both sacroiliac pain and pain suggestive of cervical spine radiculitis, however the relationship between this pain syndrome and PEG-LD is uncertain. Neither cardiac toxicity nor multiple-gated acqusition scan (MUGA) abnormalities were recorded despite the large number of patients now exceeding a cumulative PEG-LD doses of 550 mg/m². Following transplant or whole abdomen radiation, patients who were begun on 40 mg/m2 PEG-LD had their dosage reduced to 30 mg/m² because of thrombocytopenia.

Toxicity of Drug Combinations

When PEG-LD and paclitaxel were used in combination (E), stomatitis was the dose-limiting toxicity at concentrations of 40 mg/m² and 90 mg/m², respectively. The study is currently ongoing at a fixed PEG-LD dose of 30 mg/m² every 3 weeks, and a paclitaxel dose of greater than or equal to 110 mg/m² (the paclitaxel dose that proved toxic to skin, mucosa, and bone marrow in three of four patients when given with 40 mg/m² of PEG-LD).[13] (The patient not demonstrating toxicity was the previously cited patient with ascites from a primary peritoneal cancer.)

Experience with platinum compounds is limited to two patients (patients RL and the previously cited near-complete response, Table 4). Both initially received PEG-LD alone at 40 mg/m². Patient RL, who previously received radiation treatment, required platelet transfusion when receiving cisplatin and/or carboplatin with PEG-LD at 30 mg/m². The other patient, who is not included in Table 4 because her near-complete response could be attributed to the platinums, received 40 mg/m² PEG-LD, 30 to 40 mg/m² cisplatin, and carboplatin at an AUC of 3.0. She experienced prolonged grade 2 to 3 toxicities in all three blood cell elements which caused delays in redosing and necessitated blood transfusions.

Discussion

In our initial phase II study (B), 9 of the 35 patients (25.7%) with platinum- and paclitaxel-refractory epithelial ovarian cancer responded to PEG-LD therapy. Current, ongoing trials are designed to explore the role of PEG-LD in a more heterogeneous group of patients, including those with peritoneal and gynecologic cancers and various degrees of pretreatment. Early results show good response rates especially when considering that some of these patients were heavily pretreated and all patients in the tables were platinum- and paclitaxel-refractory. We plan to analyze which factors are predictive of a response, stable disease, or disease progression. Preliminary results from these studies suggest that patients with bulky masses (less than 5 cm) generally did not respond to PEG-LD. However, even nonresponders rarely manifested oral and cutaneous toxicity. The diminished toxicity may be due to the fewer courses of chemotherapy these patients received or to alterations in pharmacology, that is, patients with large tumors may show increased clearance of the drug because of egress from the vascular compartment.

Our experience with PEG-LD in combination is too limited for even preliminary conclusions. However, the relative lack of severe myelosuppression seen with PEG-LD makes it a rational candidate for combination with other active drugs in the treatment of ovarian cancer. Formal phase I studies of PEG-LD in combination with the taxanes, platinums, and topoisomerase I inhibitors are underway.

PEG-LD’s antitumor activity and mild toxicity profile make it suitable for repetitive, long-term administration, and therefore an ideal drug for maintaining a response in a palliative (salvage) setting. Its combination with platinum compounds and taxanes should be tested earlier in the disease process. In addition, the following trials should be designed to study the efficacy of PEG-LD as initial therapy for epithelial ovarian cancer:

1. The conventional combination of platinum and a taxane should be compared with therapy with three cycles of cisplatin. Responders in the latter arm of the study (probably greater than 70%) should be randomized to platinum plus either PEG-LD or paclitaxel; nonresponders would receive regimens without platinum.
2. The combination of PEG-LD and cisplatin should be compared with the standard paclitaxel and cisplatin combination regimen or to paclitaxel and carboplatin. Both of these strategies would require an initial phase I study (now in progress) to assess the tolerability of the combined drug regimens. The possibility of increased myelosuppression renders the choice of cisplatin preferable to carboplatin for such a combination study.

Finally, the durable responses observed on PEG-LD raise a number of questions leading to possible new, testable hypotheses. Beyond the ability of PEG-LD to deliver more doxorubicin to the tumor site, if the duration of response is increased beyond that which is achieved with free doxorubicin or epirubicin(Drug information on epirubicin),[14] other effects of continued exposure in relation to overcoming drug resistance or angiogenesis could be considered. Thus, comparative studies as well as correlative studies with biological markers may prove helpful in generating new hypotheses.