Seaport Therapeutics and Hemab filed simultaneous S-1 amendments this week, pricing initial public offerings worth a combined $180 million to advance depression and clotting disorder programs into late-stage trials. Seaport's offering accounts for $100 million, targeting a valuation near $500 million pre-money, while Hemab pursues $80 million at a $320 million pre-money mark. Both companies plan to list on Nasdaq within fourteen days, according to Renaissance Capital's IPO calendar.

Seaport's lead candidate, SPI-62, is a GABA-A receptor modulator in Phase 2b trials for major depressive disorder with 240 patients enrolled across 32 U.S. sites. Topline data is scheduled for Q3 2025. The company holds exclusive licenses from Genentech covering five neuropsychiatric indications, with milestone payments capped at $450 million plus mid-single-digit royalties. Hemab's core asset, HMB-001, is a monoclonal antibody targeting Factor XI for venous thromboembolism prevention, currently in Phase 2 with 180 patients across European and North American centers. Results are expected Q4 2025. Hemab's IP portfolio includes 14 issued patents expiring between 2038 and 2041.

The timing reflects capital-market positioning ahead of a crowded biotech IPO window. Twelve healthcare offerings are queued for Q2 2025, the largest cohort since Q1 2021, when 19 biotechs priced within a single quarter. Institutional pre-marketing for both companies began March 17, with books closing April 2. Lead underwriters are JPMorgan for Seaport and Jefferies for Hemab. Seaport's offering includes a 15% greenshoe, potentially raising the total to $115 million. Hemab's structure is fixed at $80 million with no overallotment provision. Both companies entered quiet periods with burn rates near $18 million quarterly, implying eighteen-month runways at midpoint pricing.

Allocators should note three factors. First, Seaport's Genentech relationship provides both validation and cap-table complexity—Roche holds a 12% pre-IPO stake with pro-rata rights through Series C, limiting future financing flexibility. Second, Hemab's Factor XI mechanism competes with Bristol Myers Squibb's milvexian, now in Phase 3 with 8,000-patient enrollment, establishing both proof-of-concept and competitive pressure. Third, both companies carry preclinical pipeline assets—Seaport's anxiety program SPI-81 and Hemab's stroke-prevention candidate HMB-003—that are unfunded beyond animal studies but appear in valuation discussions. The risk is execution. Seaport's depression trial uses a 16-week endpoint, longer than typical antidepressant studies, raising trial-failure risk if dropout rates exceed 25%. Hemab's coagulation pathway requires bleeding-event monitoring across 52 weeks, extending cash-burn duration.

Watch for three signals. First, book-building results by April 1—any downward pricing revision below the $12-$14 midpoint for Seaport or $10-$12 for Hemab indicates weak institutional demand. Second, topline data readouts: Seaport's MDD trial in Q3 and Hemab's VTE study in Q4 will validate or crater these bets within nine months. Third, the Form 4 filings post-lockup—both companies impose standard 180-day lockups, with expiration mid-October, when founder and VC selling pressure typically emerges. Seaport's insider ownership sits at 68% pre-offering, Hemab's at 71%, both high enough to trigger meaningful supply at unlock.

The dual offering arrives as biotech IPO returns have averaged negative 18% from pricing through twelve months over the past three years, per Renaissance Capital. Seaport and Hemab are betting that late-stage assets and clear catalysts justify entry before that window closes again.