As the company reaps $180 million in a stock sale to advance its handful of phase I and phase II candidates, success by competitors with anti-myostatin therapies could bode well for Atara Biotherapeutics Inc.’s proof-of-concept phase II with Pinta 745.

The South San Francisco-based firm is selling about 3.4 million shares of stock at $52 each in the deal expected to close Wednesday, and granting underwriters a 30-day option to buy as many as 519,320 more shares at the offering price. CEO Isaac Ciechanover was traveling and unavailable for comment, a spokesperson said.

Spun out from Amgen Inc., of Thousand Oaks, Calif., the firm is doing research in oncology and muscle wasting, with several T-cell therapy candidates in phase I and phase II trials. Pinta 745 is undergoing tests in patients with end-stage renal disease (ESRD) to find out if the compound can reverse protein-energy wasting (PEW).

As many as half of ESRD patients suffer from PEW, and existing treatment is limited, mostly consisting of nutritional supplements, though the effects of those often are hampered by dialysis. Inhibiting myostatin, however, has been proven to increase muscle mass and muscle strength and activity.

In April, among the firms to offer positive data at the International Conference on Frailty & Sarcopenia Research (ICFSR) in Boston was Martinsried, Germany-based Morphosys AG collaborator Novartis AG, of Basel, Switzerland, which detailed results with the HucAL-derived antibody bimagrumab (BYM338) for pathological muscle loss and weakness. Tarrytown, N.Y.-based Regeneron Pharmaceuticals Inc. brought data from tests of REGN1033, and Eli Lilly and Co., of Indianapolis, talked up LY2495655 at the scientific meeting.

All of these candidates at ICFSR, moving their ways through the clinic in phase I and phase II trials, affirm Pinta 745’s mechanism of action. Jefferies analyst Chris Howerton upped his odds of success for Pinta 745, which he called the company’s main value driver, from 40 percent to 50 percent, based on the bolstering outcomes with other would-be therapies. He set at half-and-half the chances for approval in 2019, and projected worldwide sales of about $870 million.

Atara made news last month by exercising its option with Memorial Sloan Kettering Cancer Center (MSK) in New York to license several allogeneic T-cell therapies for cancers and persistent viral infections, including T cells activated against Epstein-Barr virus (EBV, at the phase II stage), cytomegalovirus (CMV, in phase II), and Wilms tumor 1 (phase I). “Each program is an ‘off-the-shelf’ T-cell therapeutic, which is derived from third-party donors and then partially human leukocyte antigen-matched to each patient using a proprietary algorithm,” noted Howerton in a research report. “Based upon impressive data for EBV cytotoxic T lymphocytes [CTL] in cancers following bone marrow transplants that are refractory to rituximab [Rituxan, Biogen Inc./Roche AG], the FDA granted breakthrough designation.” The deal with MSK doesn’t block collaborative work for the development of other cellular immunotherapies, such as chimeric antigen receptor T cells.

Having gone public to the tune of $55 million in the fall of 2014, the company has five compounds in phase II experiments and three in phase I. Howerton saw particular promise in the EBV-CTL program, with a 65 percent probability of approval. He likes the CMV-CTL effort somewhat less, pegging its chances of reaching the market at 45 percent, and setting the combined peak-adjusted sales estimate for the two products at around $312 million. (See BioWorld Today, Dec. 17, 2013, and June 24, 2014.)

In May, Howerton upped his price target for Atara to $43, citing data from a plenary presentation at the American Association for Cancer Research meeting highlighting the efficacy of the EBV-CTL program in the Rituxan-refractory patients with EBV-associated lymphoproliferative disorders following a bone marrow transplant, who gained about a 63 percent complete response and partial response rate.

Another molecular-targeting prospect in Atara’s pipeline is STM 434, a soluble receptor that is fused to part of an antibody that is designed to block the growth factor activin A. STM 434 is being studied in patients with ovarian cancer and other advanced solid tumors. The phase I experiment under way is examining the effects of the compound alone or in combination with liposomal doxorubicin.

Muscle-wasting disease is a popular indication, according to Cortellis Clinical Trials Intelligence, which lists 149 studies, most with the phase not disclosed (65), with 33 phase II trials. Along with myostatin, the androgen receptor has been seen as a promising target in muscle wasting, although Memphis, Tenn.-based Gtx Inc.’s enobosarm blew up in phase III trials in 2013. The company said in April that it remained focused on targeting the androgen receptor in women with advanced breast cancer using enobosarm, an oral nonsteroidal selective modulator. (See BioWorld Today, Aug. 20, 2013.)

Goldman, Sachs & Co. and Citigroup Global Markets Inc. are acting as joint book-running managers for Atara’s proposed offering, with William Blair & Co. LLC, Canaccord Genuity Inc., and JMP Securities LLC serving as co-managers.

Shares of Atara (NASDAQ:ATRA) closed Friday at $54.17, up 76 cents.