Doxil (Doxorubicin Hydrochloride Liposome Injection) - Description and Clinical Pharmacology

DESCRIPTION

DOXIL (doxorubicin HCl liposome injection) is doxorubicin hydrochloride (HCl) encapsulated in STEALTH^® liposomes for intravenous administration.

Doxorubicin is an anthracycline topoisomerase inhibitor isolated from Streptomyces peucetius var. caesius.

Doxorubicin HCl, which is the established name for (8S,10S)-10-[(3-amino-2,3,6-trideoxy-α-L-lyxo-hexopyranosyl)oxy]-8-glycolyl-7,8,9,10-tetrahydro-6,8,11-trihydroxy-1-methoxy-5,12-naphthacenedione hydrochloride, has the following structure:

The molecular formula of the drug is C27 H29 NO11•HCl; its molecular weight is 579.99.

DOXIL is provided as a sterile, translucent, red liposomal dispersion in 10-mL or 30-mL glass, single use vials. Each vial contains 20 mg or 50 mg doxorubicin HCl at a concentration of 2 mg/mL and a pH of 6.5. The STEALTH^® liposome carriers are composed of N-(carbonyl-methoxypolyethylene glycol 2000)-1,2-distearoyl-sn-glycero-3-phosphoethanolamine sodium salt (MPEG-DSPE), 3.19 mg/mL; fully hydrogenated soy phosphatidylcholine (HSPC), 9.58 mg/mL; and cholesterol, 3.19 mg/mL. Each mL also contains ammonium sulfate, approximately 2 mg; histidine as a buffer; hydrochloric acid and/or sodium hydroxide for pH control; and sucrose to maintain isotonicity. Greater than 90% of the drug is encapsulated in the STEALTH^® liposomes.

MPEG-DSPE has the following structural formula:

HSPC has the following structural formula:

CLINICAL PHARMACOLOGY

Mechanism of Action

The active ingredient of DOXIL is doxorubicin HCl. The mechanism of action of doxorubicin HCl is thought to be related to its ability to bind DNA and inhibit nucleic acid synthesis. Cell structure studies have demonstrated rapid cell penetration and perinuclear chromatin binding, rapid inhibition of mitotic activity and nucleic acid synthesis, and induction of mutagenesis and chromosomal aberrations.

DOXIL is doxorubicin HCl encapsulated in long-circulating STEALTH^® liposomes. Liposomes are microscopic vesicles composed of a phospholipid bilayer that are capable of encapsulating active drugs. The STEALTH^® liposomes of DOXIL are formulated with surface-bound methoxypolyethylene glycol (MPEG), a process often referred to as pegylation, to protect liposomes from detection by the mononuclear phagocyte system (MPS) and to increase blood circulation time.

Representation of a STEALTH^® liposome:

STEALTH^® liposomes have a half-life of approximately 55 hours in humans. They are stable in blood, and direct measurement of liposomal doxorubicin shows that at least 90% of the drug (the assay used cannot quantify less than 5–10% free doxorubicin) remains liposome-encapsulated during circulation.

It is hypothesized that because of their small size (ca. 100 nm) and persistence in the circulation, the pegylated DOXIL liposomes are able to penetrate the altered and often compromised vasculature of tumors. This hypothesis is supported by studies using colloidal gold-containing STEALTH^® liposomes, which can be visualized microscopically. Evidence of penetration of STEALTH^® liposomes from blood vessels and their entry and accumulation in tumors has been seen in mice with C-26 colon carcinoma tumors and in transgenic mice with Kaposi's sarcoma-like lesions. Once the STEALTH^® liposomes distribute to the tissue compartment, the encapsulated doxorubicin HCl becomes available. The exact mechanism of release is not understood.

Pharmacokinetics

The plasma pharmacokinetics of DOXIL were evaluated in 42 patients with AIDS-related Kaposi's sarcoma (KS) who received single doses of 10 or 20 mg/m² administered by a 30-minute infusion. Twenty-three of these patients received single doses of both 10 and 20 mg/m² with a 3-week wash-out period between doses. The pharmacokinetic parameter values of DOXIL, given for total doxorubicin (mostly liposomally bound), are presented in Table 11.

Table 11: Pharmacokinetic Parameters of DOXIL in Patients With AIDS-Related Kaposi's Sarcoma

	Dose
Parameter (units)	10 mg/m2	20 mg/m2
N = 23
Mean ± Standard Error
Peak Plasma Concentration (µg/mL)	4.12 ± 0.215	8.34 ± 0.49
Plasma Clearance (L/h/m2)	0.056 ± 0.01	0.041 ± 0.004
Steady State Volume of Distribution (L/m2)	2.83 ± 0.145	2.72 ± 0.120
AUC (µg/mL∙h)	277 ± 32.9	590 ± 58.7
First Phase (λ1) Half-Life (h)	4.7 ± 1.1	5.2 ± 1.4
Second Phase (λ1) Half-Life (h)	52.3 ± 5.6	55.0 ± 4.8

DOXIL displayed linear pharmacokinetics over the range of 10 to 20 mg/m². Disposition occurred in two phases after DOXIL administration, with a relatively short first phase (

The pharmacokinetics of DOXIL at a 50 mg/m² dose is reported to be nonlinear. At this dose, the elimination half-life of DOXIL is expected to be longer and the clearance lower compared to a 20 mg/m² dose. The exposure (AUC) is thus expected to be more than proportional at a 50 mg/m² dose when compared with the lower doses.

Distribution:

In contrast to the pharmacokinetics of doxorubicin, which displays a large volume of distribution, ranging from 700 to 1100 L/m², the small steady state volume of distribution of DOXIL shows that DOXIL is confined mostly to the vascular fluid volume. Plasma protein binding of DOXIL has not been determined; the plasma protein binding of doxorubicin is approximately 70%.

Metabolism:

Doxorubicinol, the major metabolite of doxorubicin, was detected at very low levels (range: of 0.8 to 26.2 ng/mL) in the plasma of patients who received 10 or 20 mg/m² DOXIL.

Excretion:

The plasma clearance of DOXIL was slow, with a mean clearance value of 0.041 L/h/m² at a dose of 20 mg/m². This is in contrast to doxorubicin, which displays a plasma clearance value ranging from 24 to 35 L/h/m².

Because of its slower clearance, the AUC of DOXIL, primarily representing the circulation of liposome-encapsulated doxorubicin, is approximately two to three orders of magnitude larger than the AUC for a similar dose of conventional doxorubicin HCl as reported in the literature.

Special Populations:

The pharmacokinetics of DOXIL have not been separately evaluated in women, in members of different ethnic groups, or in individuals with renal or hepatic insufficiency.

Drug-Drug Interactions:

Drug-drug interactions between DOXIL and other drugs, including antiviral agents, have not been adequately evaluated in patients with ovarian cancer, AIDS-related Kaposi's sarcoma or multiple myeloma.

Tissue Distribution in Patients with Kaposi's Sarcoma:

Kaposi's sarcoma lesions and normal skin biopsies were obtained at 48 and 96 hours post infusion of 20 mg/m² DOXIL in 11 patients. The concentration of DOXIL in KS lesions was a median of 19 (range, 3-53) times higher than in normal skin at 48 hours post treatment; however, this was not corrected for likely differences in blood content between KS lesions and normal skin. The corrected ratio may lie between 1 and 22 times. Thus, higher concentrations of DOXIL are delivered to KS lesions than to normal skin.

NON-CLINICAL TOXICOLOGY

Carcinogenesis, Mutagenesis, and Impairment of Fertility

Although no studies have been conducted with DOXIL, doxorubicin HCl and related compounds have been shown to have mutagenic and carcinogenic properties when tested in experimental models.

STEALTH^® liposomes without drug were negative when tested in Ames, mouse lymphoma and chromosomal aberration assays in vitro, and mammalian micronucleus assay in vivo.

The possible adverse effects on fertility in males and females in humans or experimental animals have not been adequately evaluated. However, DOXIL resulted in mild to moderate ovarian and testicular atrophy in mice after a single dose of 36 mg/kg (about twice the 50 mg/m² human dose on a mg/m² basis). Decreased testicular weights and hypospermia were present in rats after repeat doses ≥ 0.25 mg/kg/day (about one thirtieth the 50 mg/m² human dose on a mg/m² basis), and diffuse degeneration of the seminiferous tubules and a marked decrease in spermatogenesis were observed in dogs after repeat doses of 1 mg/kg/day (about one half the 50 mg/m² human dose on a mg/m² basis).

CLINICAL STUDIES

Ovarian Cancer

DOXIL (doxorubicin HCl liposome injection) was studied in three open-label, single-arm, clinical studies of 176 patients with metastatic ovarian cancer. One hundred forty-five (145) of these patients were refractory to both paclitaxel- and platinum-based chemotherapy regimens. Refractory ovarian cancer is defined as disease progression while on treatment, or relapse within 6 months of completing treatment. Patients in these studies received DOXIL at 50 mg/m² infused over one hour every 3 or 4 weeks for 3–6 cycles or longer in the absence of dose-limiting toxicity or progression of disease.

The baseline demographics and clinical characteristics of the patients with refractory ovarian cancer are provided in Table 12 below.

Table 12: Patient Demographics for Patients With Refractory Ovarian Cancer From Single Arm Ovarian Cancer Studies

	Study 1 (U.S.) (n = 27)	Study 2 (U.S.) (n = 82)	Study 3 (non-U.S.) (n = 36)
Age at Diagnosis (Years)
Median	64	61.5	51.5
Range	46 – 75	34 – 85	22 – 80
Drug-Free Interval (Months)
Median	1.8	1.7	2.6
Range	0.5 – 15.6	0.6 – 7.0	0.7 – 15.2
Sum of Lesions at Baseline (cm2)
Median	25	18.3	32.4
Range	1.2 – 230.0	1.3 – 285.0	0.3 – 114.0
FIGO Staging
I	1 (3.7%)	3 (3.7%)	4 (11.1%)
II	3 (11.1%)	3 (3.7%)	1 (2.8%)
III	15 (55.6%)	60 (73.2%)	24 (66.7%)
IV	8 (29.6%)	16 (19.5%)	6 (16.7%)
Not Specified	—	—	1 (2.8%)
CA-125 at Baseline
Median	123.5	199.0	1004.5
Range	20 – 14,012	7 – 46,594	20 – 12,089
Number of Prior Chemotherapy Regimens
1	7 (25.9%)	13 (15.9%)	9 (25.0%)
2	11 (40.7%)	44 (53.7%)	19 (52.8%)
3	6 (22.2%)	25 (30.5%)	8 (22.8%)
4	3 (11.1%)	—	—

The primary efficacy parameter was response rate for the population of patients refractory to both paclitaxel- and a platinum-containing regimen. Assessment of response was based on Southwest Oncology Group (SWOG) criteria, and required confirmation four weeks after the initial observation. Secondary efficacy parameters were time to response, duration of response, and time to progression.

The response rates for the individual single arm studies are given in Table 13 below.

Table 13: Response Rates in Patients With Refractory Ovarian Cancer From Single Arm Ovarian Cancer Studies

	Study 1 (U.S.)	Study 2 (U.S.)	Study 3 (non-U.S.)
Response Rate	22.2% (6/27)	17.1% (14/82)	0% (0/36)
95% Confidence Interval	8.6% – 42.3%	9.7% – 27.0%	0.0% – 9.7%

When the data from the single arm studies are combined, the response rate for all patients refractory to paclitaxel and platinum agents was 13.8% (20/145) (95% CI 8.1% to 19.3%). The median time to progression was 15.9 weeks, the median time to response was 17.6 weeks, and the duration of response was 39.4 weeks.

DOXIL (doxorubicin HCl liposome injection) was also studied in a randomized, multicenter, open-label, study in 474 patients with epithelial ovarian cancer after platinum-based chemotherapy. Patients in this study received an initial dose of either DOXIL 50 mg/m² infused over one hour every 4 weeks or topotecan 1.5 mg/m² infused daily for 5 consecutive days every 3 weeks. Patients were stratified according to platinum sensitivity and the presence of bulky disease (presence of tumor mass greater than 5 cm in size). Platinum sensitivity is defined by response to initial platinum-based therapy and a progression-free interval of greater than 6 months off treatment. The primary efficacy endpoint for this study was time to progression (TTP). Other efficacy endpoints included overall survival and objective response rate.

The baseline patient demographic and clinical characteristics are provided in Table 14 below.

Table 14: Ovarian Cancer Randomized Study Baseline Demographic and Clinical Characteristics

	DOXIL (n = 239)	Topotecan (n = 235)
Age at Diagnosis (Years)
Median	60.0	60.0
Range	27 – 87	25 – 85
Drug-Free Interval (Months)
Median	7.0	6.7
Range	0.9 – 82.1	0.5 – 109.6
FIGO Staging
I	11 (4.6%)	15 (6.4%)
II	13 (5.4%)	8 (3.4%)
III	175 (73.2%)	164 (69.8%)
IV	40 (16.7%)	48 (20.4%)
Platinum Sensitivity
Sensitive	109 (45.6%)	110 (46.8%)
Refractory	130 (54.4%)	125 (53.2%)
Bulky Disease
Present	108 (45.2%)	105 (44.7%)
Absent	131 (54.8%)	130 (55.3%)

Study results are provided in Table 15.

There was no statistically significant difference in TTP between the two treatment arms.

Table 15: Results of Efficacy AnalysesAnalysis based on investigators' strata for protocol defined ITT population.

	Protocol Defined ITT Population
	DOXIL (n = 239)	Topotecan (n = 235)
TTP (Protocol Specified Primary Endpoint)
Median (Months) 1	4.1	4.2
p-valuep-value is based on the stratified log-rank test.	0.617
Hazard Ratio 2	0.955
95% CI for Hazard Ratio	(0.762, 1.196)
Overall Survival
Median (Months)	14.4	13.7
p-valuep-value not adjusted for multiple comparisons.	0.05
Hazard Ratio	0.822
95% CI for Hazard Ratio	(0.676, 1.000)
Response Rate
Overall Response n (%)	47 (19.7)	40 (17.0)
Complete Response n (%)	9 (3.8)	11 (4.7)
Partial Response n (%)	38 (15.9)	29 (12.3)
Median Duration of Response (Months)	6.9	5.9

AIDS-Related Kaposi's Sarcoma

DOXIL was studied in an open-label, single-arm, multicenter study utilizing DOXIL at 20 mg/m² by intravenous infusion every three weeks, generally until progression or intolerance occurred. In an interim analysis, the treatment history of 383 patients was reviewed, and a cohort of 77 patients was retrospectively identified as having disease progression on prior systemic combination chemotherapy (at least 2 cycles of a regimen containing at least two of three treatments: bleomycin, vincristine or vinblastine, or doxorubicin) or as being intolerant to such therapy. Forty-nine of the 77 (64%) patients had received prior doxorubicin HCl.

These 77 patients were predominantly Caucasian, homosexual males with a median CD4 count of 10 cells/mm³. Their age ranged from 24 to 54 years, with a mean age of 38 years. Using the ACTG staging criteria, 78% of the patients were at poor risk for tumor burden, 96% at poor risk for immune system, and 58% at poor risk for systemic illness at baseline. Their mean Karnofsky status score was 74%. All 77 patients had cutaneous or subcutaneous lesions, 40% also had oral lesions, 26% pulmonary lesions, and 14% of patients had lesions of the stomach/intestine.

The majority of these patients had disease progression on prior systemic combination chemotherapy.

The median time on study for these 77 patients was 155 days and ranged from 1 to 456 days. The median cumulative dose was 154 mg/m² and ranged from 20 to 620 mg/m².

Two analyses of tumor response were used to evaluate the effectiveness of DOXIL: one analysis based on investigator assessment of changes in lesions over the entire body, and one analysis based on changes in indicator lesions.

Investigator Assessment

Investigator response was based on modified ACTG criteria. Partial response was defined as no new lesions, sites of disease, or worsening edema; flattening of ≥50% of previously raised lesions or area of indicator lesions decreasing by ≥50%; and response lasting at least 21 days with no prior progression.

Indicator Lesion Assessment

A retrospectively defined analysis was conducted based on assessment of the response of up to five prospectively identified representative indicator lesions. A partial response was defined as flattening of ≥50% of previously raised indicator lesions, or >50% decrease in the area of indicator lesions and lasting at least 21 days with no prior progression.

Only patients with adequate documentation of baseline status and follow-up assessments were considered evaluable for response. Patients who received concomitant KS treatment during study, who completed local radiotherapy to sites encompassing one or more of the indicator lesions within two months of study entry, who had less than four indicator lesions, or who had less than three raised indicator lesions at baseline (the latter applies solely to indicator lesion assessment) were considered nonevaluable for response. Of the 77 patients who had disease progression on prior systemic combination chemotherapy or who were intolerant to such therapy, 34 were evaluable for investigator assessment and 42 were evaluable for indicator lesion assessment.

Table 16: Response in Patients with RefractoryPatients with disease that progressed on prior combination chemotherapy or who were intolerant to such therapy. AIDS-related Kaposi's Sarcoma

Investigator Assessment	All Evaluable Patients (n = 34)	Evaluable Patients Who Received Prior Doxorubicin (n = 20)
Response 1
Partial (PR)	27%	30%
Stable	29%	40%
Progression	44%	30%
Duration of PR (Days)
Median	73	89
Range	42+ – 210+	42+ – 210+
Time to PR (Days)
Median	43	53
Range	15 – 133	15 – 109
Indicator Lesion Assessment	All Evaluable Patients (n = 42)	Evaluable Patients Who Received Prior Doxorubicin (n = 23)
Response
Partial (PR)	48%	52%
Stable	26%	30%
Progression	26%	17%
Duration of PR (Days)
Median	71	79
Range	22+ – 210+	35 – 210+
Time to PR (Days)
Median	22	48
Range	15 – 109	15 – 109

¹ There were no complete responses in this population.

Multiple Myeloma

The safety and efficacy of DOXIL in combination with bortezomib in the treatment of multiple myeloma were evaluated in a randomized, open label, international multicenter study. This study included 646 patients who have not previously received bortezomib and whose disease progressed during or after at least one prior therapy. Patients were randomized (1:1 ratio) to receive either DOXIL (30 mg/m² as a 1-hr i.v. infusion) administered on day 4 following bortezomib (1.3 mg/m² i.v. bolus on days 1, 4, 8 and 11) or bortezomib alone (1.3 mg/m² i.v. bolus on days 1, 4, 8 and 11). Treatment was administered every 3 weeks. Patients were treated for up to 8 cycles until disease progression or the occurrence of unacceptable toxicity. Patients who maintained a response were allowed to receive further treatment. The median number of cycles in each treatment arm was 5 (range 1-18). The baseline demographics and clinical characteristics of the patients with multiple myeloma are provided in Table 17 below.

Table 17 Summary of Baseline Patient and Disease Characteristics

Patient Characteristics	DOXIL + bortezomib n=324	bortezomib n=322
Median age in years (range)	61 (28, 85)	62 (34, 88)
% Male/female	58 / 42	54 / 46
% Caucasian/Black/other	90 / 6/ 4	94 / 4 / 2%
Disease Characteristics
% with IgG/IgA/Light chain	57 / 27 / 12	62 / 24 /11
% β2-microglobulin group
≤2.5 mg/L	14	14
>2.5 mg/L and ≤5.5 mg/L	56	55
>5.5 mg/L	30	31
Serum M-protein (g/dL): Median (Range)	2.5 (0-10.0)	2.7 (0-10.0)
Urine M-protein (mg/24 hours): Median (Range)	107 (0-24883)	66 (0-39657)
Median Months Since Diagnosis	35.2	37.5
% Prior Therapy
One	34	34
More than one	66	66
Prior Systemic Therapies for Multiple Myeloma
Corticosteroid (%)	99	>99
Anthracyclines	68	67
Alkylating agent (%)	92	90
Thalidomide/lenalidomide (%)	40	43
Stem cell transplantation (%)	57	54

The primary endpoint in this study was time to progression (TTP). TTP was defined as the time from randomization to the first occurrence of progressive disease or death due to progressive disease. The combination arm demonstrated significant improvement in TTP. As the prespecified primary objective was achieved at the interim analysis, patients in the bortezomib monotherapy group were then allowed to receive the DOXIL + bortezomib combination. Survival continued to be followed after the interim analysis and survival data are not mature at this time. Efficacy results are as shown in Table 18 and Figure 1.

Table 18 Efficacy of DOXIL in combination with bortezomib in the treatment of patients with multiple myeloma

Endpoint	DOXIL + bortezomib n=324	Bortezomib n=322
Time to ProgressionKaplan Meier estimate.
Progression or death due to progression (n)	99	150
Censored (n)	225	172
Median in days (months)	282 (9.3)	197 (6.5)
95% CI	250;338	170;217
Hazard ratio 1	0.55
(95% CI)	(0.43, 0.71)
p-value 2	<0.0001
Response (n) RR as per EBMT criteria	303	310
% Complete Response (CR)	5	3
% Partial Response (PR)	43	40
% CR + PR	48	43
p-valueCochran-Mantel-Haenszel test adjusted for the stratification factors.	0.251
Median Duration of Response (months)	10.2	7.0
(95% CI)	(10.2;12.9)	(5.9;8.3)

¹ Hazard ratio based on stratified Cox proportional hazards regression. A hazard ratio < 1 indicates an advantage for DOXIL+bortezomib.
² Stratified log-rank test.

Time to progression outcomes were consistent with the overall result across most subgroups defined by patient demographic and baseline characteristics. There were too few Blacks or Asian patients to adequately assess differences in effects for the race subgroup.

Figure 1 - Time to Progression Kaplan-Meier Curve