1. Alpharadin® (Xofigo®) in the treatment of skeletal metastasis secondary to metastatic prostate cancer:
an educational exhibit.
Duong E, Orquiza M, Khorjekar G, Van Nostrand D
MedStar Washington Hospital Center, Div of Nuclear Medicine, Washington, D.C.
Abstract
References
Summary
Learning Objectives: The objectives of this educational
exhibit are to:
(1) Describe what Alpharadin® (Xofigo®) is,
(2) Discuss its mechanism of action,
(3) List the advantages of Alpharadin® (Xofigo®) and
(4) Review the results of initial trials.
Alpharadin® is presently not approved for use by the
Food and Drug Administration, but Xofigo® has recently
been approved, and this brand name will be used
through the remainder of the educational exhibit.
Summary: Prostate cancer is one of the most prevalent
cancers in the world, and frequently, prostate cancer may
metastasize to the bone. In order to remove the
stimulatory affects of testosterone on prostate
metastases, such as in bone, castration is an important
management option. However, some patients may
advance to a more serious phase called castration
resistant prostate cancer (CRPC). Currently, the
therapies that target CRPC bone metastases primarily
help alleviate pain and do not improve overall survival
(OS), thus new treatment modalities are needed to treat
this group of patients. One new treatment option under
study for patients with CRPC bone metastases is the
radiopharmaceutical Xofigo®, which targets the bone
and delivers alpha-radiation. Following treatment with
Xofigo®, recent clinical trials exhibited a significant
decrease in bone alkaline phosphatase levels, time
to PSA progression, pain tolerance, and an increase in
OS. Regarding safety profile, no significant
hematological adverse events have been observed. As
noted above, the objective of this educational exhibit is to
present an overview of Xofigo® in the treatment of CRPC
bone metastases.
Xofigo® holds promise in improving the outlook for
patients with metastatic bone cancer. The characteristic
properties of Xofigo® has less side effects then
chemotherapy while being just as effective, if not more
effective in improving overall survival.
Introduction
Prostate cancer is one of the most prevalent cancers
in the world. Often times it will advance to a more
serious phase called castration resistant prostate cancer
(CRPC). Patients with CRPC have a 90% chance of
showing signs of bone metastases, which are major
factors in decreased quality of life, and even death.
Currently, the bone-targeting therapies that are primarily
in use focus on alleviating pain and not improving overall
survival (OS). New pharmaceuticals are being
developed with the aims of decreasing the morbidity of
bone metastases and OS. Xofigo® is the first alpha
particle approved by the Food and Drug Administration
for the treatment of CRPC bone metastases. The
Overall Survival Improvement
What is Alpharadin® (Xofigo®) ?
Beta-Radiation vs. Alpha-Radiation: (See Table 1.)
•Most of the radiation used in therapy today is in the
form of beta and gamma radiation.
•Beta-radiation produces a low-energy radiation with
a larger effective range,--up to a few mm-- when
compared to alpha-radiation.
•Alpha-radiation has a very high linear energy
transfer (LET) with a range of less than 100 µm.
Xofigo® is an alpha-emitting radium-223 isotope with
a half-life of 11.4 days.
Usage:
•Aimed at treating bone metastases resulting from
advanced cancers—usually prostate or breast
cancer (most common).
•Mechanisms of Action:
•Radium-223’s nature as a calcium mimic makes it
effective in targeting bone metastases.
•Radium is in the same family as calcium on the
periodic table so it is able to be taken up by bones in
a similar fashion as calcium.
•Once absorbed by the bone, radium-223 is able to
irradiate cancerous tissue by inducing double-strand
breaks in the DNA of the tumor cells.
Status:
• FDA approved for CRPC bone metastases.
All 3 phases of clinical testing have been completed
with some phase 3 trials still ongoing.
Phase 1:
According to Cheetham et al. [1], who conducted a
phase I & II study, the drug was found to be safe and
tolerable in the vast majority of patients and the
efficacy results were beneficial as overall survival as
well as related biomarkers, such as bone-alkaline
phosphatase were shown to improve significantly, in
patients with CRPC and bone disease.
Phase 2:
Similarly, a phase II study conducted by Nilsson et
al. concluded that there was a significant (p=.017)
improvement in overall survival and consistent
improvement in the reduction of prostate-specific
antigen (PSA) levels in patients with CRPC and
bone metastases when compared to the placebo
group [2].
Phase 3:
In the ALSYMPCA trial conducted by Parker et al.
[4], phase III studies met the primary overall survival
endpoints.
Advantages Safety
Safety Profile:
•Xofigo® has been successfully proven to be a safe drug.
•The primary reason that Xofigo® is safe is because the alpha
particles travel 2-10 cell diameters. This short distance spares
the healthy neighboring tissue, which in the case of bone
metastases is the bone marrow.
Pharmacokinetics:
•Xofigo® that is not taken up by the bones briefly resides in the
blood, which is quickly eliminated through the intestines.
•Hepatobiliary excretion was not present and very little of the
Xofigo® was taken up by the liver, kidneys, and various other
organs [2]. It was found that at 1, 4 and 24 hours after
administration, the levels found in the blood serum were
4.1%, 2.2% and 0.5% of the administered dose, respectively.
Adverse Events:
•Xofigo® had a very favorable tolerability profile.
•Parker et al. reported that at all grades of adverse events, the
placebo group had a higher percentage of their patients in
each grade than compared to radium-223 groups [2].
•Alpha-particles are more mutagenic than beta-particles
resulting in an increased likelihood of secondary hematologic
or solid malignancies. However, these secondary
cancers, typically do not develop for 10 to 20 years, while
CRPC patients have a mean survival of 18 to 24 months.
Most
Effective
Discussion
Those patients with advanced bone metastasis have
very few treatment options. Xofigo® is a promising new
radiopharmaceutical that has the potential to both improve
the quality of a patient’s life and increase overall survival.
The scope of Xofigo® is also expanded by the ability to
treat bone metastasis arising from different types of
cancer including breast cancer.
With the implementation of Xofigo® as a regular drug
to treat metastatic bone carcinoma, physicians and
patients will not be forced to decide between a less
morbid, shorter survival or a more morbid, longer survival.
Chemotherapy often induces adverse events in multiple
organs, but none are being seen with Xofigo®.
Published Data on Successful
Treatment (Present Literature)
Effective Range
Mutagenic
Strength
Alpha-
Radiation
Small (40-100 µm
in tissue)
High
Beta-
Radiation
Large Low
1. Cheetham P, Petrylak D. Alpha particles as radiopharmaceuticals in the
rreatment of bone metastases: mechanism of action of radium-223 chloride
(alpharadin) and radiation. Oncology. 2012;26:330-337.
2. Nilsson S, Parker C, Haugen I, et al. Alpharadin, a novel, highly targeted
alpha pharmaceutical with a good safety profile for patients with CRPC and
bone metastases: Combined safety analysis of phase I and II clinical trials.
American Society of Clinical Oncology Genitourinary Cancers Symposium
2010. Abstr 106.
3. Cook G, Parker C, Chua S, Johnson B, Aksnes A, Lewington V. 18F-flouride
PET: changes in uptake as a method to assess response in bone metastases
from castrate-resistant prostate cancer patients treated with 223 Ra-chloride
(Alpharadin). EJNMMI research. 2011;1:1-6.
4. Parker C, Heinrich D, O'Sullivan J.M, et al. Overall survival benefit of radium-
233 chloride (Alpharadin) in the treatment of patients with symptomatic bone
metastases in castration-resistant prostate cancer (CRPC): a phase III
randomized trial (ALSYMPCA). Proc Am Soc Clin Oncol 2012;30:Abstr 8.
5. Nilsson S, Parker C, Bruland O. Clinical experience and radiation safety of
the first-in-class alpha-pharmaceutical, alpharadin (radium-223) in patients
with castration-resistant prostate cancer (CRPC) and bone metastases.
International Journal of Radiation Oncology* Biology* Physics.
2010;78(suppl):375-376.
6. Nilsson S, Larsen R, Fossa S, et al. First clinical experience with alpha-
emitting radium-223 in the treatment of skeletal metastases. American
Association for cancer Research 2005;11:4451-4459.
7. Nilsson S, O'Bryan-Tear G, Bolstad B, Lokna A, Parker C. Alkaline
phosphatase (ALP) normalization and overall survival in patients with bone
metastases from castration-resistant prostate cancer (CRPC) treated with
radium-223. J Clin Oncol. 2011;29:Abstr 49.
*Nilsson et al.[7]
Graph 1.*
Overall Survival of Patients in Radium 223 Group of the BC1-
02 Study Who Had Normalized vs. Nonnormalized Baseline
ALP Values
Alpha-Radiation Advantages
Hence, alpha-radiation will then irradiate less
neighboring healthy tissue, thereby potentially sparing
bone marrow while also providing a stronger radiation
dose to the cancerous foci providing a greater chance
of killing the cancer cell.
Ease of Use:
In addition, the relative ease-of-use of Xofigo®
makes it a very attractive alternative to more arduous
methods.
•Shipping: Any institution around the world can use
Xofigo® because it is not limited by half-life.
•Handling: Handling Xofigo® requires no specific
equipment for administration. The radiation
generated from Xofigo® can be blocked by a piece
of paper or plastic tubing, which makes radiation
protection during administration of Xofigo® easier
and safer.
•Conformity: Standard radiation detection
equipment that is already present in most
institution can be used to detect for remnant traces
of radiation.
•Disposal: With an 11.4 day half life, Xofigo® can
be disposed as normal waste after 4 months of
storage.
Table 1.
Comparison of Alpha and Beta Radiation
Effective Range and Mutagenic Strength
Introduction (cont’d)
objective of this educational exhibit is to present an
overview of Xofigo® [1-6].