Threshold Pharmaceuticals Presents Encouraging Data From Clinical Trials of TH-302...

Threshold Pharmaceuticals Presents Encouraging Data From Clinical Trials of
TH-302 for Solid Tumors

REDWOOD CITY, Calif., June 1, 2009 (GLOBE NEWSWIRE) -- Threshold
Pharmaceuticals, Inc. (Nasdaq:THLD) previously announced on May 30, 2009,
clinical trial results related to its clinical stage hypoxia-activated prodrug,
TH-302. The results were presented at the American Society for Clinical Oncology
(ASCO) being held May 29 to June 2, 2009, at the Orange County Convention Center
in Orlando, FL.

"The results from these studies are encouraging to us and to our advisors. The
monotherapy trial demonstrated an attractive safety profile for TH-302 with
minimal evidence of myelosuppression and, as previously reported, signs of
therapeutic activity in small cell lung cancer and metastatic melanoma. In the
combination therapy trials, TH-302 appears to be safely combined with labeled
doses and schedules of gemcitabine, docetaxel, pemetrexed, and doxorubicin.
Additionally, we have observed partial responses in combination with all four
chemotherapies with some patients experiencing durable responses extending out
over six months," said John Curd, M.D., Threshold's president and chief medical
officer. "Though these clinical trials are in an early stage of development with
a relatively small number of patients, we remain hopeful that TH-302 may provide
an additional treatment option for patients living with cancer."

Monotherapy Results

Results from thirty-one patients in a Phase 1 clinical trial evaluating the
safety and preliminary efficacy of TH-302 in patients with advanced solid tumors
were presented at a poster session on May 30, 2009. The clinical trial was
designed with an initial accelerated titration design followed by a standard
dose escalation schema. The trial has completed the dose escalation component,
reached the maximum tolerated dose (MTD) and is currently enrolling patients in
the expansion phase of the trial at the MTD.

As previously reported, efficacy signals have been observed in two patients
enrolled in this Phase 1 trial. One patient with refractory small cell lung
cancer metastatic to the liver had a partial response (PR), as judged by RECIST
(Response Evaluation Criteria In Solid Tumors), at their initial response
assessment. The patient had received two cycles of TH-302 at 480 mg/m2 and
discontinued from the trial after treatment delay, unrelated to therapy, and
disease progression. An additional patient with melanoma metastatic to the lung
and liver had a RECIST PR after two cycles of TH-302 at 670 mg/m2. Fifty-eight
percent of these 31 patients, who had previously failed a median of 3 prior
therapies, achieved stable disease (SD) or better.

The first dose limiting toxicities for TH-302 were reported in the 670 mg/m2
cohort: one patient developed grade 3 perianal and rectal ulcers that were
considered related to study drug and a second patient developed grade 3 oral
mucositis with dehydration. An intermediate dose of 575 mg/m2 was evaluated and
determined to be the MTD. Since nausea and vomiting increased at higher doses of
TH-302, standard anti-emetic prophylaxis was recommended at doses that exceed
240 mg/m2. Skin and mucosal adverse events increased with dose, therefore there
was an increase in dose delays or reductions at higher doses. Adverse events of
grade 3 or greater were reported in 17 (55%) patients. Hematologic toxicity has
been minimal with grade 2 neutropenia reported in two patients, grade 2
thrombocytopenia reported in one patient, and worsening anemia and lymphopenia
in 14 (45%) and 20 (65%) patients, respectively.

In the expansion phase of the trial, which includes weekly doses of TH-302 at
the MTD of 575 mg/m2 the drug continues to be tolerated. There have been no new
unexpected adverse events, with one of the 9 additional patients treated at the
MTD of 575 mg/m2 having a dose limiting toxicity (DLT) of grade 3 cheilitis
(inflammation of the lips). The initial activity seen in small cell lung cancer
and malignant melanoma was further supported by an additional PR in each
indication in the initial patients treated in the dose expansion. Thus far, 2 of
5 patients with small cell lung cancer and 2 of 2 patients with metastatic
melanoma in the monotherapy trial have achieved a RECIST criteria PR. Dosing
once every three weeks is also being evaluated in this trial and dose escalation
is ongoing. To date there has been one case of pancytopenia (a reduction in the
number of red and white blood cells, as well as platelets) at 670 mg/m2 and one
DLT of grade 3 fatigue in the initial patient dosed at 940 mg/m2.

Combination Therapy Results

The combination therapy results refer to two clinical trials, 402 and 403, that
are investigating TH-302 in combination with four different chemotherapy
regimens.

The 402 trial is a Phase 1/2, three arm, multicenter, dose escalation and dose
expansion trial to determine the safety, efficacy and pharmacokinetics of TH-302
in combination with gemcitabine or docetaxel or pemetrexed in patients with
advanced solid tumors. The trial was initiated in August 2008. The trial is
expected to include up to 102 patients. The trial will include a dose escalation
phase followed by expansion at the MTD within four specific indications with 12
patients treated in each indication. To date, 30 patients in the dose-escalation
phase have been assessed for response.

In the TH-302 plus gemcitabine arm, TH-302 is administered intravenously for 30
to 60 minutes on days 1, 8 and 15 of a 28 day cycle. Gemcitabine is dosed
according to its package insert (1000 mg/m2 on days 1, 8 and 15 of the 28 day
cycle). Eleven patients have had tumor assessments, 3 of whom had a PR in the
following cancers: ovarian, esophageal and pancreatic. The ovarian response was
confirmed, meaning that the RECIST criteria PR was maintained through a
subsequent assessment at least 28 days later; the esophageal and pancreatic PRs
were unconfirmed. There are 6 patients with SD, 5 of whom have ongoing SD
lasting for 3 to 8 cycles of chemotherapy.

In the TH-302 plus docetaxel arm, TH-302 is administered intravenously on days 1
and 8 of a 21 day cycle. Docetaxel is dosed according to its package insert (75
mg/m2 on day 1 of the 21 day cycle). Nine patients have had tumor assessments, 2
of whom had a PR in non-small cell lung cancer and anal cancer with both
confirmed and ongoing. There are 5 patients with SD, 3 of whom have ongoing SD
lasting for 4 to 5 cycles.

In the TH-302 plus pemetrexed arm, TH-302 is administered intravenously on days
1 and 8 of a 21 day cycle. Pemetrexed is dosed according to its package insert
(500 mg/m2 on day 1 of the 21 day cycle). Ten patients have had tumor
assessments, 2 of whom had a PR, both in non small cell lung cancer with both
confirmed and ongoing after over six months on treatment. There are 5 patients
with SD, 3 of whom have ongoing SD lasting for 5 to 9 cycles.

The 403 trial is a Phase 1/2, multicenter, dose escalation trial to determine
the safety, efficacy and pharmacokinetics of TH-302 in combination with
doxorubicin in patients with advanced soft tissue sarcoma. The trial was
initiated in September 2008. The trial will include up to 36 patients (12-24 in
the dose escalation arm). TH-302 is administered intravenously on days 1 and 8
of a 21 day cycle. Doxorubicin is dosed according to its package insert (75
mg/m2 on day 1 of the 21 day cycle). Three patients have had tumor assessments,
2 of whom had a PR, one confirmed and one awaiting confirmation. The third
patient has ongoing SD for 4 cycles.

In general, hematologic toxicity was higher than might be expected if
chemotherapy was administered by itself, but was generally well tolerated and
not dose limiting. Skin and mucosal toxicities were TH-302 dose dependent with a
trend for increased frequency and greater severity at higher doses. Although
these skin and mucosal toxicities have been bothersome in some patients and
resulted in dose reductions or delays in therapy, these events have been
reversible with an improvement in symptoms between cycles and following dose
reductions. Investigations have been initiated to better understand and treat,
or prevent, these toxicities.

A copy of the monotherapy poster presented at ASCO may be obtained by calling
the Company. A copy of the Company's most recent investor presentation may be
found on the Company's website.

About Threshold Pharmaceuticals

Threshold is a biotechnology company focused on the discovery and development of
drugs targeting Tumor Hypoxia, the low oxygen condition found in
microenvironments of most solid tumors. This approach offers broad potential to
treat most solid tumors. By selectively targeting tumor cells, we are building a
pipeline of drugs that hold promise to be more effective and less toxic to
healthy tissues than conventional anticancer drugs. For additional information,
please visit our website (www.thresholdpharm.com).

Forward-Looking Statements

Except for statements of historical fact, the statements in this press release
are forward-looking statements, including statements regarding Threshold's
product candidates, clinical trial results and plans, and potential therapeutic
uses and benefits of our product candidates. These statements involve risks and
uncertainties that can cause actual results to differ materially from those in
such forward-looking statements. Potential risks and uncertainties include, but
are not limited to, Threshold's ability to enroll and complete its current and
anticipated clinical trials, the time and expense required to conduct such
clinical trials and analyze data, the possibility that results from these trials
will not be confirmed, potential adverse side effects, issues arising in the
regulatory or manufacturing process and the results of such clinical trials
(including product safety issues and efficacy results). Further information
regarding these and other risks is included under the heading "Risk Factors" in
Threshold's Quarterly Report on Form 10-Q, which was filed with the Securities
Exchange Commission on May 7, 2009 and is available from the SEC's website
(www.sec.gov) and on our website (www.thresholdpharm.com) under the heading
"Investors." We do not intend to update any forward-looking statement made in
this news release.

-0-
CONTACT: Threshold Pharmaceuticals, Inc.
Denise T. Powell, Sr. Director, Corporate Communications
650-474-8206
dpowell@thresholdpharm.com