CLINICAL PHARMACOLOGY
PROLEUKIN® (aldesleukin) has been shown to possess the biological activities of human native interleukin-2.1,2 In vitro studies performed on human cell lines demonstrate the immunoregulatory properties of PROLEUKIN, including: a) enhancement of lymphocyte mitogenesis and stimulation of long-term growth of human interleukin-2 dependent cell lines; b) enhancement of lymphocyte cytotoxicity; c) induction of killer cell (lymphokine-activated (LAK) and natural (NK)) activity; and d) induction of interferon-gamma production.
The in vivo administration of PROLEUKIN in animals and humans produces multiple immunological effects in a dose dependent manner. These effects include activation of cellular immunity with profound lymphocytosis, eosinophilia, and thrombocytopenia, and the production of cytokines including tumor necrosis factor, IL-1 and gamma interferon.
3 In vivo experiments in murine tumor models have shown inhibition of tumor growth.4 The exact mechanism by which PROLEUKIN mediates its antitumor activity in animals and humans is unknown.
Pharmacokinetics
PROLEUKIN exists as biologically active, non-covalently bound microaggregates with an average size of 27 recombinant interleukin-2 molecules. The solubilizing agent, sodium dodecyl sulfate, may have an effect on the kinetic properties of this product.
The pharmacokinetic profile of PROLEUKIN is characterized by high plasma concentrations following a short IV infusion, rapid distribution into the extravascular space and elimination from the body by metabolism in the kidneys with little or no bioactive protein excreted in the urine. Studies of IV PROLEUKIN in sheep and humans indicate that upon completion of infusion, approximately 30% of the administered dose is detectable in plasma. This finding is consistent with studies in rats using radiolabeled PROLEUKIN, which demonstrate a rapid (<1 min) uptake of the majority of the label into the lungs, liver, kidney, and spleen.
The serum half-life (T 1/2) curves of PROLEUKIN remaining in the plasma are derived from studies done in 52 cancer patients following a 5-minute IV infusion. These patients were shown to have a distribution and elimination T 1/2 of 13 and 85 minutes, respectively.
Following the initial rapid organ distribution, the primary route of clearance of circulating PROLEUKIN is the kidney. In humans and animals, PROLEUKIN is cleared from the circulation by both glomerular filtration and peritubular extraction in the kidney.5-8 This dual mechanism for delivery of PROLEUKIN to the proximal tubule may account for the preservation of clearance in patients with rising serum creatinine values. Greater than 80% of the amount of PROLEUKIN distributed to plasma, cleared from the circulation and presented to the kidney is metabolized to amino acids in the cells lining the proximal convoluted tubules. In humans, the mean clearance rate in cancer patients is 268 mL/min.
The relatively rapid clearance of PROLEUKIN has led to dosage schedules characterized by frequent, short infusions. Observed serum levels are proportional to the dose of PROLEUKIN.
Immunogenicity
Fifty-seven of 77 (74%) metastatic renal cell carcinoma patients treated with an every 8-hour PROLEUKIN regimen and 33 of 50 (66%) metastatic melanoma patients treated with a variety of IV regimens developed low titers of non-neutralizing anti-PROLEUKIN antibodies. Neutralizing antibodies were not detected in this group of patients, but have been detected in 1/106 (<1%) patients treated with IV PROLEUKIN using a wide variety of schedules and doses. The clinical significance of anti-PROLEUKIN antibodies is unknown.
Clinical Experience
Two hundred fifty-five patients with metastatic renal cell cancer (metastatic RCC) were treated with single agent PROLEUKIN in 7 clinical studies conducted at 21 institutions. Two hundred seventy patients with metastatic melanoma were treated with single agent PROLEUKIN in 8 clinical studies conducted at 22 institutions. Patients enrolled in trials of single agent PROLEUKIN were required to have an Eastern Cooperative Oncology Group (ECOG) Performance Status (PS) of 0 or 1 and normal organ function as determined by cardiac stress test, pulmonary function tests, and creatinine ≤1.5 mg/dL. Patients with brain metastases, active infections, organ allografts and diseases requiring steroid treatment were excluded.
PROLEUKIN was given by 15 min IV infusion every 8 hours for up to 5 days (maximum of 14 doses). No treatment was given on days 6 to 14 and then dosing was repeated for up to 5 days on days 15 to 19 (maximum of 14 doses). These 2 cycles constituted 1 course of therapy. Patients could receive a maximum of 28 doses during a course of therapy. In practice >90% of patients had doses withheld. Metastatic RCC patients received a median of 20 of 28 scheduled doses of PROLEUKIN. Metastatic melanoma patients received a median of 18 of 28 scheduled doses of PROLEUKIN during the first course of therapy. Doses were withheld for specific toxicities (see “DOSAGE AND ADMINISTRATION” section, “Dose Modifications” subsection and “ADVERSE REACTIONS” section).
In the renal cell cancer studies (n=255), objective response was seen in 37 (15%) patients, with 17 (7%) complete and 20 (8%) partial responders (see Table I). The 95% confidence interval for objective response was 11% to 20%. Onset of tumor regression was observed as early as 4 weeks after completion of the first course of treatment, and in some cases, tumor regression continued for up to 12 months after the start of treatment. Responses were observed in both lung and non-lung sites (e.g., liver, lymph node, renal bed occurrences, soft tissue). Responses were also observed in patients with individual bulky lesions and high tumor burden.
In the metastatic melanoma studies (n=270), objective response was seen in 43 (16%) patients, with 17 (6%) complete and 26 (10%) partial responders (see Table I). The 95% confidence interval for objective response was 12% to 21%. Responses in metastatic melanoma patients were observed in both visceral and non-visceral sites (e.g., lung, liver, lymph node, soft tissue, adrenal, subcutaneous). Responses were also observed in patients with individual bulky lesions and large cumulative tumor burden.
TABLE I
PROLEUKIN CLINICAL RESPONSE DATA
|
|
Number of
Responding Patients
(response rate)
|
Median Response
Duration in Months
(range)
|
|
Metastatic RCC
|
|
|
| CR’s |
17 (7%) |
80+* (7 to 131+) |
| PR’s |
20 (8%) |
20 (3 to 126+) |
| PR’s + CR’s |
37 (15%) |
54 (3 to 131+) |
|
Metastatic Melanoma
|
|
|
| CR’s |
17 (6%) |
59+* (3 to 122+) |
| PR’s |
26 (10%) |
6 (1 to 111+) |
| PR’s + CR’s |
43 (16%) |
9 (1 to 122+) |
(+) sign means ongoing
* Median duration not yet observed; a conservative value is presented which represents the minimum median duration of response. |
An analysis of prognostic factors showed that a better ECOG performance status (see Table II) was significantly associated with response.
TABLE II
PROLEUKIN CLINICAL RESPONSE BY ECOG PERFORMANCE STATUS (PS)
|
Pretreatment
|
METASTATIC RCC
|
METASTATIC MELANOMA
|
|
ECOG PS
|
CR
|
PR
|
CR
|
PR
|
| 0 |
14/166 (8%) |
16/166 (10%) |
14/191 (7%) |
22/191 (12%) |
| ≥1 |
3/89 (3%) |
4/89 (4%) |
3/79 (4%) |
4/79 (5%) |
|
