Kosan's Lead Hsp90 Inhibitor, Tanespimycin, Shows High Level of Activity in Trastuzumab Resistant/Refractory HER2-Positive Breas
03 Juin 2008 - 4:00PM
PR Newswire (US)
Data Presented at ASCO Show 26% Partial Response, 63% Clinical
Benefit Incidence HAYWARD, Calif., June 3 /PRNewswire-FirstCall/ --
Kosan Biosciences Incorporated (NASDAQ:KOSN) today announced that
its lead Hsp90 inhibitor, tanespimycin, demonstrated a high level
of antitumor activity in a Phase 2 trial when administered in
combination with trastuzumab (Herceptin(R)) to patients with
HER2-positive metastatic breast cancer whose disease had either
progressed after, or did not respond to, treatment with trastuzumab
immediately prior to entering the trial. Of 27 evaluable patients,
17 patients showed clinical benefit including 7 patients with
partial response (PR), 5 patients with tumor regression (minor
response or MR) and 5 patients with extended stable disease (SD,
greater than 4 cycles), yielding an overall clinical benefit
incidence of 63%. Common toxicities were mainly mild to moderate
and included fatigue and gastrointestinal symptoms. Updated data
from the Phase 2 trial were presented in a poster titled, "Phase 2
trial of the Hsp90 inhibitor tanespimycin (Tan) + trastuzumab (T)
in patients (pts) with HER2-positive metastatic breast cancer
(MBC)," by Shanu Modi, M.D., of Memorial Sloan-Kettering Cancer
Center, at the 44th American Society of Clinical Oncology (ASCO)
Annual Meeting being held in Chicago, IL. "The response data from
this Phase 2 trial of tanespimycin plus trastuzumab have grown
stronger as more patients have been treated, underscoring our
observation that tanespimycin is a highly active and tolerable
agent in patients whose disease is refractory to trastuzumab," said
Clifford A. Hudis, M.D., Chief, Breast Cancer Medicine Service,
Memorial Sloan-Kettering Cancer Center, and senior author on the
poster. "We look forward to seeing tanespimycin advance into its
next set of clinical trials with the goal of elucidating its
potential role in the metastatic breast cancer treatment paradigm."
"Tanespimycin is the most advanced Hsp90 inhibitor in development
for HER2-positive breast cancer and has generated what we believe
is highly promising data in this indication," said Pamela Cohen,
M.D., Kosan's Chief Medical Officer. "We believe that Hsp90
inhibition is among the most novel and broadly applicable
anticancer targets being explored today, and that it may have broad
applicability in breast cancer and other cancer indications." Phase
2 Tanespimycin Data Tanespimycin is an Hsp90 inhibitor that has
demonstrated the potential to disrupt the activity of multiple
oncogenes and cell signaling pathways implicated in tumor growth,
including HER2, a key pathway in breast cancer. The objective of
the Phase 2 trial is to determine the objective response rate by
RECIST in patients with HER2-positive metastatic breast cancer. To
be eligible for the trial, patients must have had either
progressive disease within 3 months following last dose of adjuvant
treatment with trastuzumab or have progressive disease following
initial therapy for metastatic disease with trastuzumab
(trastuzumab may have been administered with cytotoxic chemotherapy
or as a single agent). Tanespimycin was administered at a dose of
450 mg/m2 following administration of the standard dose of
trastuzumab. Of 31 patients enrolled in the trial, 27 were
evaluable for efficacy (as of May 15, 2008). -- Of the 27 patients
evaluable for efficacy, 17 (63%) showed evidence of clinical
benefit, including: -- 7 patients or 26% had PR (including 1
patient with an unconfirmed PR who remains on study) -- 5 patients
or 19% had tumor regressions (20-29% decrease) -- 5 patients or 19%
had SD of 4 or more cycles (4 week cycle) Antitumor activity and
toxicity were similar between the Injection and Injectable
Suspension products. -- Of the 31 patients enrolled, 21 were
treated with Kosan's Injection product (Cremophor(R)-containing
formulation and 10 were treated with Kosan's Injectable Suspension
product (contains no Cremophor). In addition, 4 of the patients
treated initially with the Injection formulation crossed over to
receive the Injectable Suspension formulation. -- For the Injection
product: 18 were evaluable and 11 responded (4 PR, 4 tumor
regressions, 3 SD), yielding a PR response rate of 22% and a
clinical benefit incidence of 61%. -- For the Injectable Suspension
product: 9 were evaluable and 6 responded (3 PR, 1 tumor
regression, 2 SD), yielding a PR response rate of 33% and a
clinical benefit incidence of 67%. -- Patients with an objective
response on the Injection product maintained their objective
response after crossover to the Injectable Suspension product.
Tanespimycin plus trastuzumab was highly tolerable at the
recommended Phase 2 dose of 450 mg/m2 weekly. Common toxicities
were mainly mild-to-moderate diarrhea, fatigue, nausea, headache
and vomiting (limited duration and amenable to supportive care).
The few drug-related Grade 3 and 4 toxicities (including fatigue,
increased AST and headache, two patients each) were manageable and
only one patient discontinued treatment for an adverse event.
Noticeably absent were toxicities common to cytotoxic chemotherapy
including alopecia and myelosuppression. The Injectable Suspension
product provided considerable advantages over the Injection
product, including shorter time of infusion, no need for steroid or
antihistamine premedications and ease of pharmacist preparation.
Kosan anticipates conducting additional studies with tanespimycin
with the goal of further characterizing the drug candidate's safety
and efficacy profile and potentially paving the way to a
registration program. Patients currently enrolled in the ongoing
Phase 2 trial of tanespimycin plus trastuzumab will continue on
study per protocol. Kosan does not plan to enroll additional
patients in this trial. About Kosan Kosan Biosciences is a
biotechnology company advancing two new classes of anticancer
agents through clinical development -- a Hsp90 (heat shock protein
90) inhibitor and an epothilone. Hsp90 inhibitors have a novel
mechanism of action targeting multiple pathways involved in cancer
cell growth and survival. Tanespimycin (KOS-953) is being tested in
combination with Velcade(R) (bortezomib) in patients with multiple
myeloma in a clinical program called TIME. Tanespimycin is also
being studied in HER2-positive metastatic breast cancer in
combination with Herceptin(R) (trastuzumab). KOS-1584 epothilone
product candidate is in a Phase 2 clinical trial in patients with
non-small cell lung cancer. Kosan's epothilone program is licensed
to Bristol-Myers Squibb. Kosan's motilin agonist compound,
KOS-2187, licensed to Pfizer for development in gastroesophagel
reflux disease, is in a Phase 1 trial. Kosan recently agreed to be
acquired by Bristol-Meyers Squibb. For additional information on
Kosan Biosciences, please visit the company's website at
http://www.kosan.com/. This press release contains forward-looking
statements within the meaning of the "safe harbor" provisions of
the Private Securities Litigation Reform Act of 1995 (the "Act").
Such forward-looking statements include but are not limited to
statements regarding the further development and potential safety,
efficacy, regulatory status, commercial potential and other
characteristics of Kosan's product candidates; the continuation of
current clinical trials; the initiation of additional clinical
trials and the timing thereof and the use of Kosan's financial
resources. Words such as "will," "expect," "believe," "may,"
"intend," "plan," "potential" and similar expressions are intended
to identify forward-looking statements. Any statements contained in
this press release that are not statements of historical fact may
be deemed to be forward-looking statements. These forward-looking
statements are based upon Kosan's current expectations.
Forward-looking statements involve risks and uncertainties. Kosan's
actual results and the timing of events could differ materially
from those anticipated in such forward-looking statements as a
result of these risks and uncertainties, which include, without
limitation, the risk that the acquisition of Kosan by Bristol-Myers
Squibb may not be consummated as the transaction is subject to
certain closing conditions, risks related to the uncertain progress
and results of Kosan's preclinical and clinical testing, including
the risks that studies and trials may not demonstrate safety and
efficacy sufficient to initiate clinical trials on the timing
currently anticipated, or at all, continue clinical development,
obtain the requisite regulatory approvals or result in a marketable
product; the conduct of clinical trials; manufacturing; regulatory
approval requirements and process; the effort and expense necessary
for further development of Kosan's product candidates, including
the costs of bortezomib; intellectual property matters, including
Kosan's ability to obtain valid and enforceable patents covering
its product candidates; Kosan' dependence on it license with
Bristol-Myers Squibb to develop its epothilone products in order
for Kosan to receive milestones or royalties, Kosan's dependence on
its collaboration with Pfizer for development of its motilin
agonist product candidate; Kosan's need for additional financing
and Kosan's strategy to enter into partnering or licensing
arrangements. These and other risk factors are discussed under
"Risk Factors" in Kosan's Annual Report on Form 10-K for the year
ended December 31, 2007 and other periodic filings with the SEC.
Kosan expressly disclaims any obligation or undertaking to release
publicly any updates or revisions to any forward-looking statements
contained herein. Velcade(R) (bortezomib) is a registered trademark
of Millennium Pharmaceuticals, Inc. Herceptin(R) (trastuzumab) is a
registered trademark of Genentech, Inc. Cremophor(R) is a
registered trademark of BASF Corporation DATASOURCE: Kosan
Biosciences Incorporated CONTACT: Jane Green, VP, Corporate
Communications of Kosan Biosciences Incorporated, +1-510-731-5335,
mobile, +1-415-652-4819, Web site: http://www.kosan.com/
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