these fourteen clinical trial sites if the patients qualify. The first tranche of this program has been activated with seventeen of our clinical trial sites and any further increases, if any, will follow after the review by IDMC of interim data from the Phase 2b clinical trial.
We believe the Referring Physician Program, which has a number of other supportive elements, will enhance the rate of enrollment potentially mitigating or partially mitigating the countervailing enrollment disruption caused by the COVID-19 pandemic.
Additionally, in July 2022, we increased the number of clinical trial sites participating in our Phase 2b clinical trial from the original twelve clinical trial sites to twenty eight.
Registered Direct Offering
On July 25, 2022, we entered into securities purchase agreements (the “Purchase Agreements”) with David P. Luci, our President and Chief Executive Officer, Robert J. DeLuccia, our Executive Chairman, Carl V. Sailer, a member of our board of directors (collectively, the “Affiliate Investors”), and a single U.S. institutional investor (the “Investor”) pursuant to which we issued and sold in a registered direct offering an aggregate of 1,159,211 shares of our common stock, par value $0.001 per share and pre-funded warrants to purchase an aggregate of 130,769 shares of our common stock. The Affiliate Investors purchased an aggregate of 59,211 shares of common stock at a purchase price of $3.80 per share. The Investor purchased an aggregate of 1,100,000 shares of common stock at a purchase price of $3.25 per share and an aggregate of 130,769 pre-funded warrants at a purchase price of $3.2499 per pre-funded warrant. The pre-funded warrants sold to the Investor have an exercise price of $0.0001, were immediately exercisable and may be exercised at any time until fully exercised. As of December 31, 2022, all of the pre-funded warrants were exercised.
The gross proceeds to us from the registered direct offering were $4.2 million and net proceeds after deducting the placement agents’ fees and other offering expenses payable by us were approximately $3.7 million. The securities were offered by the Company pursuant to an effective shelf registration statement on Form S-3 (File No. 333-265956) previously filed with the SEC on July 1, 2022, and which was declared effective by the SEC on July 11, 2022.
In a concurrent private placement, we issued to the Affiliate Investors and the Investor, series A warrants to purchase 1,289,980 shares of our common stock and series B warrants to purchase 1,289,980 shares of our common stock, all of which are deemed equity classified. We issued an aggregate of 59,211 series A warrants and an aggregate of 59,211 series B warrants to the Affiliate Investors with an exercise price per share of $3.55. Additionally, we issued an aggregate of 1,230,769 series A warrants and an aggregate of 1,230,769 series B warrants to the Investor with an exercise price per share of $3.25. The series A warrants are exercisable commencing on January 27, 2023 and will expire on January 27, 2028. The series B warrants are exercisable commencing on January 27, 2023 and will expire on January 27, 2024. The registered direct offering and concurrent private placement closed on July 27, 2022.
On July 25, 2022, we entered into a co-placement agent agreement (the “Placement Agent Agreement”), with A.G.P./Alliance Global Partners (“AGP”) and Maxim Group LLC (“Maxim”, and together with AGP, the “Placement Agents”) in connection with the registered direct offering pursuant to which we paid the Placement Agents a cash fee of $287,874 and issued to the Placement Agents an aggregate of 63,018 warrants to purchase shares of common stock (which is 5% of the aggregate number of shares of common stock and pre-funded warrants sold in the registered direct offering to the Investor and 2.5% of the aggregate number of shares of common stock sold to the Affiliate Investors). The warrants will have an exercise price of $3.60 per share (representing 110% of the weighted average public offering price of the aggregate number of shares of common stock sold in the registered direct offering to the Investor and Affiliate Investors), are exercisable beginning January 27, 2023, and will expire on July 27, 2027.
Initial Public Offering
On June 29, 2021, we completed our IPO, in which we issued and sold 2,875,000 shares of our common stock, including the full exercise by the underwriters of their option to purchase 375,000 additional shares of our common stock, at a public offering price of $6.00 per share, which resulted in net cash proceeds of $14.8 million after deducting underwriting discounts and commissions and offering expenses. The proceeds from the IPO are being used (i) to