Let's take a closer look at three biotech stocks -- Achillion Pharmaceuticals (NASDAQ:ACHN), Receptos (NASDAQ: RCPT), and Dendreon (NASDAQ: DNDN) -- which could all loom large in health care headlines this Tuesday morning.

Achillion surges after the FDA lifts its clinical hold on sovaprevir
Achillion Pharmaceuticals just announced two positive developments this morning -- the FDA just lifted its clinical hold on sovaprevir, and initial dosing has started with ACH-3422. Sovaprevir and ACH-3422 are two of Achillion's four experimental hepatitis C treatments.

Sovaprevir was put on a clinical hold by the FDA last June due to abnormal liver results in patients. That ongoing hold was the main reason that shares of Achillion plunged 49% over the past 12 months. Sovaprevir is now clear to begin trials with a once-daily maximum dose of 200 mg in hepatitis C patients and healthy volunteers. A partial hold is still in effect for multiple dose studies on healthy volunteers, which will require an FDA approval of the protocol prior to initiation.

Meanwhile, results for ACH-3422, which is in a phase 1 proof-of-concept trial, are expected in the fall. Combination studies of the drug should start by the end of the year.

These two positive developments come a day after Merck's acquisition of Idenix Pharmaceuticals (which also specializes in experimental hepatitis C treatments) caused Achillion shares to rally 48% on speculation that it could also be a target. Although lifting the hold of sovaprevir certainly makes Achillion a more attractive takeover target, investors should remember that no official offers have been made yet. Shares of Achillion are currently up almost 40% in pre-market trading.

Receptos rallies on positive phase 2 results for RPC1063
Meanwhile, shares of Receptos are up 28% in pre-market trading, after the company announced that a phase 2 trial of its experimental treatment for relapsing multiple sclerosis (MS) had met its primary endpoint of reduction in MRI brain lesion activity. The trial tested Receptos' drug, RPC1063, against a placebo in 258 patients. The detailed results of the phase 2 trial are expected to be presented in the coming months.

The phase 2 trial is part of the RADIANCE trial, which also includes a phase 3 trial that was initiated under a Special Protocol Assessment (SPA) with the FDA last December. The phase 3 trial, which will test two doses of RPC1063 against Biogen's Avonex in 1,200 patients, is currently in the enrollment stage. Analysts expect RPC1063 to generate peak sales of $1.8 billion if approved.

RPC1063, which is being tested for two indications (MS and irritable bowel syndrome) is one of two experimental drugs in Receptos' pipeline. Its other drug, RPC4046, is being tested as a potential treatment for eosinophilic esophagitis (EoE), an allergic disease characterized by inflammation problems in the esophagus.

Shares of Receptos have climbed 45% over the past 12 months. The company went public at $14 per share last May.

Dendreon slides after CEO John Johnson steps down
Last but not least, Dendreon is down more than 6% in pre-market trading, after the company announced that CEO John Johnson will step down in mid-August. Johnson already resigned from Dendreon's board last week.

Johnson replaced former CEO Mitchell Gold in 2012, after Dendreon's lead drug Provenge failed to match market expectations. Analysts originally expected Provenge, an immunotherapy for late-stage prostate cancer, to generate peak sales of $3 billion to $4 billion. However, the drug only generated $213.5 million in sales in 2011, $325.3 million in 2012, and $283.7 million in 2013. Strong competition from competing oral drugs like Johnson & Johnson's Zytiga and Medivation/Astellas' Xtandi made it tough for Provenge, an infused therapy, to gain market share.

Dendreon has elected Douglas Watson, the company's lead independent director, as board chairman, and is currently looking for Johnson's successor. Meanwhile, the company needs to deal with $620 million in convertible debt that it owes in 2016, plus $27.7 million more that it must pay by June 15.

Dendreon finished last quarter with only $155 million in cash and equivalents. In an aggressive effort to cut costs, the company reduced its workforce from 2,000 employees to around 820 after several rounds of job cuts. Shares of Dendreon have fallen 45% over the past 12 months.