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UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

Form 10-K

ANNUAL REPORT

PURSUANT TO SECTIONS 13 OR 15(d)

OF THE SECURITIES EXCHANGE ACT OF 1934

(Mark One)

For the fiscal year ended: December 31, 2006

For the transition period from                      to                     

Commission file number: 000-50676

Icagen, Inc.

(Exact name of registrant as specified in its charter)

4222 Emperor Boulevard, Suite 350

Durham, North Carolina 27703

(Address of principal executive offices, including zip code)

Registrant’s telephone number, including area code: (919) 941-5206

Securities registered pursuant to Section 12(b) of the Act:

Common Stock, $0.001 par value per share

(Title of class)

Securities registered pursuant to Section 12(g) of the Act: None

Indicate by check mark if the registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act of 1933, or the Securities Act.    Yes  ¨    No  x.

Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or 15(d) of the Securities Act.    Yes  ¨    No  x.

Indicate by check mark whether the registrant: (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934, as amended, or the Exchange Act, during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days.    Yes  x    No  ¨

Indicate by check mark if disclosure of delinquent filers pursuant to Item 405 of Regulation S-K is not contained herein, and will not be contained, to the best of registrant’s knowledge, in definitive proxy or information statements incorporated by reference in Part III of this Form 10-K or any amendment to this Form 10-K.    x

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, or a non-accelerated filer. See definitions of “accelerated filer and large accelerated filer” in Rule 12b-2 of the Exchange Act. (Check One).

Indicate by check mark whether the registrant is a shell company (as defined in Exchange Act Rule 12b-2 of the Exchange Act).    Yes  ¨    No  x

The aggregate market value of voting and non-voting common equity held by non-affiliates of the registrant, as of June 30, 2006, was approximately $95,297,665 based on the closing sale price of the common stock on such date as reported on the Nasdaq Global Market. For purposes of the immediately preceding sentence, the term “affiliate” consists of each director and executive officer of the registrant.

The number of shares of the registrant’s common stock, $0.001 par value per share, outstanding on February 28, 2007 was 37,782,857.

DOCUMENTS INCORPORATED BY REFERENCE

Portions of the registrant’s Definitive Proxy Statement for its 2007 Annual Meeting of Stockholders scheduled to be held on June 26, 2007, or the 2007 Proxy Statement, which will be filed with the Securities and Exchange Commission, or SEC, not later than 120 days after December 31, 2006, are incorporated by reference into Part III of this Annual Report on Form 10-K. With the exception of the portions of the 2007 Proxy Statement expressly incorporated into this Annual Report on Form 10-K by reference, such document shall not be deemed filed as part of this Annual Report on Form 10-K.

Icagen and our logo are our trademarks. Each of the other trademarks, trade names or service marks appearing in this prospectus belongs to its respective holder.

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ICAGEN, INC.

INDEX TO ANNUAL REPORT ON FORM 10-K

FOR THE FISCAL YEAR ENDED DECEMBER 31, 2006

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SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS

This Annual Report on Form 10-K and the documents incorporated by reference in this Annual Report on Form 10-K contain forward-looking statements that involve substantial risks and uncertainties. In some cases you can identify these statements by forward-looking words such as “anticipate,” “believe,” “could,” “estimate,” “expect,” “intend,” “may,” “should,” “will,” and “would,” or similar words. You should read statements that contain these words carefully because they discuss future expectations, contain projections of future results of operations or of financial position or state other “forward-looking” information. The important factors listed below, as well as any cautionary language elsewhere in this Annual Report on Form 10-K, provide examples of risks, uncertainties and events that may cause our actual results to differ materially from the expectations described in these forward-looking statements. You should be aware that the occurrence of the events described in the “Risk Factors” section below and elsewhere in this Annual Report on Form 10-K could have an adverse effect on our business, results of operations and financial position.

Any forward-looking statements in this Annual Report on Form 10-K are not guarantees of future performance, and actual results, developments and business decisions may differ from those envisaged by such forward-looking statements, possibly materially. We disclaim any duty to update any forward-looking statements.

PART I

ITEM 1—BUSINESS

Overview

We are a biopharmaceutical company focused on the discovery, development and commercialization of novel orally-administered small molecule drugs that modulate ion channel targets. Ions are charged particles, such as sodium, potassium, calcium and chloride. Ion channels are protein structures found in virtually every cell of the human body. Ion channels span the cell membrane and regulate the flow of ions into and out of cells. There are currently over 35 drugs marketed by third parties for multiple indications that modulate ion channels according to data from IMS Health. We believe this demonstrates that ion channels are attractive drug targets.

Utilizing our proprietary know-how and integrated scientific and drug development capabilities, we have identified multiple drug candidates that modulate ion channels. Our four most advanced programs are:

We are also conducting ongoing drug discovery programs focused on new therapeutics for pain and inflammatory disorders. In each of these programs, we have identified small molecule compounds that have

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demonstrated activity on specific ion channels. When we tested these compounds in preclinical studies, including in some cases animal models, they showed desired activities and profiles, validating these ion channels as potential therapeutic targets for the particular indication. In addition to our internal programs, we have established collaborations with McNeil, Bristol-Myers Squibb and Astellas to further capitalize on our ion channel capabilities. We plan to generate revenue from any product candidates that we successfully develop either through direct sales, collaboration arrangements with leading pharmaceutical and biotechnology companies or a combination of these approaches.

Scientific Background

Ion Channels as Drug Targets

Ions generally cannot move freely across cell membranes, but must enter or exit a cell through pores created by ion channels. Ion channels open and close, or gate, in response to particular stimuli, including ions, other cellular factors, changes in electrical voltage or drugs.

The concentration of specific ions in particular cells in the body is critically important to many vital physiological functions. Consequently, ion channels play a key role in a wide variety of processes in the human body, which can be broadly grouped into three categories:

Small molecule compounds have been shown to both activate and inhibit ion channels. As a result, ion channels represent an important class of targets for pharmaceutical intervention in a broad range of disease areas. Examples of currently marketed drugs that exert their effects through ion channel modulation include:

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Despite the number of successful ion channel drugs on the market today, the majority of these drugs were developed without prior knowledge of their mechanism of action. Only recently have drug researchers identified and cloned a substantial number of ion channel genes, enabling integration of genetic information with the drug discovery process and allowing for a more methodical and scientific approach to the identification and selection of both the ion channel target and potential drug.

We believe that many pharmaceutical and biotechnology companies historically have avoided drug discovery programs targeting ion channels due to significant technical challenges and complexities associated with the structure and function of ion channels. Ion channel drug discovery is a complex endeavor that requires a comprehensive understanding of ion channel function. Ion channel drug discovery also requires specialized functional assays to characterize the interaction between a drug and an ion channel and determine the ability of a compound to modify the activity of an ion channel target, often across a range of physiologic conditions. Functional assays are difficult and time-consuming to develop, tend to be low throughput and require significant technical expertise. Ion channel drug discovery also requires expertise in electrophysiology to determine the effects of drugs on ion channel activity. Electrophysiology is the study of ion channel function and involves the measurement of the electrical current generated when ions flow through ion channel pores. For these reasons, we believe that the majority of the promising ion channel targets remain unexploited and that a significant opportunity exists for an integrated approach to ion channel drug discovery that can be applied across a wide spectrum of therapeutic areas.

Ion Channel Complexity

Ion channels are complex protein structures typically comprised of two or more subunits, or building blocks. These subunits associate to form a pore through which ions are able to pass when the channel is in the open state. Other subunits are important in determining whether an ion channel is gated open or closed or whether the specific ion channel is expressed in a specific cell, tissue or organ. Subunits are capable of associating with each other in multiple combinations, allowing for the number of ion channel drug targets to be substantially greater than the number of ion channel genes. We have identified and cloned over 300 human ion channel genes coding for these subunits.

Ion channels possess gating mechanisms which may cause the channel to undergo changes in shape or molecular arrangement, called conformational changes. These conformational changes may occur in response to particular stimuli, including ions, other cellular factors, and changes in electrical voltage or drugs. Conformational changes may expose additional sites on the channels that can be targeted for drug interactions. In studying the function of ion channels, it is important to understand the different channel conformational states so that potential drugs can be discovered and appropriately characterized.

Ion channels are classified into families based upon the type of ion or ions that pass through the channel and the gating mechanism. Within a given family, ion channels share similarities in structure and functional properties, facilitating the study of multiple channels within a family. Across different ion channel families, there may also be similarities in structure and functional properties, although to a lesser degree than within the same family. Despite the potential similarities, there are key areas on ion channels that allow for potent and selective drug interactions.

A comprehensive knowledge base that spans multiple ion channels and ion channel families enhances ion channel drug discovery because it enables identification of similarities and differences among ion channels. Similarities among channels are important because they can lead to the identification of related chemical structures that have activity against many related ion channels. These related chemical structures can then be modified to provide for the desired specificity against a particular ion channel target. Similarities among ion channels are also important because they can lead to side effects if a small molecule modulator is not appropriately targeted. Differences among ion channels are important because they provide the opportunity to develop specific, targeted therapies.

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Our Approach to Ion Channel Drug Discovery and Development

Over the past decade, we have established an interdisciplinary environment that is designed to meet the challenges and complexities faced in ion channel drug discovery. Our capabilities include molecular biology and the use of complex functional assays, electrophysiology, medicinal and computational chemistry, bioanalytics, pharmacology and clinical development. We believe that this integrated set of capabilities enhances our ability to develop drug candidates that modulate ion channels for the treatment of a range of diseases with significant unmet medical need and commercial opportunity.

We utilize a target class approach to drug discovery. Whereas traditional drug discovery starts with the disease and seeks to identify potential intervention points, or drug targets, our target class approach starts with all potential ion channel targets and seeks to identify applications to the treatment of various diseases. We believe that our understanding of the ion channel genome and ability to apply this knowledge in a target class approach to drug discovery facilitates our identification of small molecule drug candidates with novel mechanisms of action and enhanced selectivity and specificity profiles. Moreover, because our drug discovery and development process screens for potential side effects at an earlier stage than some alternative approaches, we believe that this process enables us to identify small molecule drug candidates that may have a reduced risk of clinical failure and may shorten clinical development timelines.

Complementary to our target class approach is our expertise across the therapeutic areas that are the focus of our current research efforts. Not only do we have a deep understanding of the functional activity of our ion channel targets, but we also understand the role that these targets play in the relevant physiologic system. For example, much of our current research efforts are focused on disorders of the central and peripheral nervous system. To understand the role of ion channels in these systems and in the disease areas of interest to us, we have developed the capability to study our targets in a variety of in vitro and in vivo models. These models include cell-based assays, tissue-based assays, and complex animal models of seizure, memory and pain disorders. We combine our expertise in ion channel targets with our capabilities in systems-based biology and understanding of physiologic systems to identify attractive opportunities for therapeutic intervention.

Using our drug discovery and development approach, we have:

Our Strategy

Our goal is to become a fully-integrated biopharmaceutical company and a leader in the discovery, development and commercialization of novel small molecule drugs that modulate ion channel targets and address disease areas with significant unmet medical need and commercial potential. We intend to achieve this goal through the execution of our strategy, key elements of which are as follows:

Maximize the commercial potential of senicapoc. We are focusing a significant portion of our business efforts on completing clinical trials of senicapoc for the treatment of sickle cell disease. We initiated a pivotal Phase III clinical trial of this drug candidate in the first quarter of 2005. If we are successful in developing and obtaining regulatory approval for the marketing of this product, we and McNeil have agreed to copromote senicapoc in the United States and share equally in the profits and losses from the commercialization of senicapoc in the United States and, if we elect to copromote in Canada, from the commercialization of senicapoc in Canada. McNeil is entitled to commercialize senicapoc outside the United States, including in Canada if we do not elect to copromote in that country, pursuant to an exclusive license and is required to pay us a royalty on net product sales.

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Build and advance our product candidate pipeline. Through our ion channel drug discovery and development programs, we have created a pipeline of drug candidates that address diseases with significant unmet medical need and commercial potential across a range of therapeutic areas. We plan to aggressively pursue the development and commercialization of these drug candidates, including the lead compounds that we are developing for the treatment of epilepsy and neuropathic pain. We believe that the breadth of our capabilities in ion channel drug discovery technology will enable us to continue to identify and develop additional drug candidates on an efficient and rapid basis. In addition to developing drug candidates internally, we continue to evaluate opportunities to in-license promising compounds and technologies.

Strengthen and expand our core ion channel drug discovery technologies and development capabilities. All of our drug candidates and research programs have resulted from our core ion channel drug discovery technologies. We have steadily built these technologies, which span the key disciplines of biology, chemistry and pharmacology, over a number of years. We intend to continue to invest in these core technologies, including our ion channel focused compound library, as the key to our future research programs and drug candidates. We also plan to augment our existing development team by adding personnel with experience in drug safety, regulatory affairs, statistical methods, project management and medical affairs.

Establish strategic alliances with leading pharmaceutical and biotechnology companies. We plan to selectively enter into new strategic alliances with leading pharmaceutical and biotechnology companies to assist us in advancing our drug discovery and development programs. We expect that these alliances will provide us with access to the therapeutic area expertise and research, development and commercialization resources of our collaborators as well as augment our financial resources. We believe that our expertise in ion channel drug discovery and development helps us to secure collaborations, such as our current collaborations with McNeil, Bristol-Myers Squibb and Astellas, on attractive terms. We expect that in some of these alliances we will seek to maintain rights in the development of drug candidates and the commercialization of drugs as part of our effort to build our internal clinical development and sales and marketing capabilities.

Establish specialized sales and marketing capabilities. We plan to retain United States marketing and sales rights or copromotion rights for our product candidates for which we receive marketing approvals in situations in which we believe it is possible to access the market through a focused, specialized sales force. For example, for senicapoc we believe that the community of hematologists who are the key specialists in treating sickle cell disease, and the medical facilities in which they practice, are sufficiently concentrated to enable us to effectively copromote to this market together with McNeil with a small internal sales force. For situations in which a large sales force is required to access the market and with respect to markets outside of the United States, we generally plan to commercialize our drug candidates through a variety of types of collaboration arrangements with leading pharmaceutical and biotechnology companies.

Clinical and Preclinical Programs

The following table summarizes key information about our and our collaborators’ product candidates that are in clinical trials and our principal preclinical programs. All of the compounds in these programs are the result of our internal or collaborative research efforts. In all of these programs, we or our collaborators are developing small molecule drugs that target specific ion channels.

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Senicapoc for Sickle Cell Disease

Our most advanced drug candidate, senicapoc, is a novel small molecule ion channel inhibitor that targets a particular potassium channel, called the Gardos channel, that is located on the membrane of red blood cells. We are developing senicapoc for the chronic prophylactic treatment of sickle cell disease. Senicapoc is taken orally and is being developed for once-a-day dosing. Senicapoc has received fast track designation and orphan drug designation from the U.S. Food and Drug Administration, or FDA. Fast track designation may allow for expedited review by the FDA and is granted to those proposed products that the FDA believes address life threatening conditions and that demonstrate the potential to address unmet medical needs. Orphan drug designation would preclude the FDA, subject to some exceptions, from approving another application to market the same drug for the same indication for seven years if senicapoc is the first drug that the FDA approves for this indication in the United States. We have retained the right to copromote and share equally in profits from the commercialization of senicapoc together with McNeil in the United States and, at our option, Canada.

Disease overview. Sickle cell disease is a chronic and debilitating genetic blood disorder, primarily affecting individuals of African descent, resulting in a variety of disease complications and a significantly shortened lifespan in the majority of patients. The genetic defect in sickle cell disease is a single point mutation in the DNA sequence coding for hemoglobin, the oxygen-carrying protein found in red blood cells. This genetic defect predisposes the hemoglobin molecules to polymerize into long chain-like structures under particular conditions, creating abnormal red blood cells. These abnormal red blood cells lose potassium ions along with chloride ions and water. These processes lead to the formation of dense and dehydrated red blood cells that may assume a characteristic “sickle” shape. There are also a variety of other abnormalities that occur in sickle cell disease, including damage to the red blood cell membrane, increased viscosity of the blood and abnormalities of blood vessels, which contribute to the disease.

One of the key pathways by which dehydration of red blood cells occurs in patients with sickle cell disease involves the Gardos ion channel. Although this channel is normally closed, in patients with sickle cell disease, the Gardos channel is open in some circumstances. The opening of the Gardos channel allows the outward flow of potassium ions from the cell, which is followed by an outward flow of chloride ions and water, contributing to the dehydration of the red blood cell. This dehydration contributes to an increase in the rate of polymerization of hemoglobin, leading to the formation of dense and, ultimately, sickled cells.

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There are several clinical manifestations of sickle cell disease, including chronic anemia, the effects of chronic hemolysis, vaso-occlusive crises and chronic organ damage.

In addition, chronic anemia is believed to lead to long-term complications that contribute to the difficult clinical course experienced by many patients. In particular, since each unit of blood in a sickle cell patient delivers less oxygen than in a normal person, chronic anemia places abnormal stress on the heart to pump more blood through the body. Over a period of years, this added stress on the heart can lead to heart failure. In addition, if the anemia is sufficiently severe, oxygen delivery to vital cells, tissues and organs can be compromised, a condition called chronic hypoxia. Chronic hypoxia causes a generalized impairment of growth and development as well as damage to multiple organs.

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Market opportunity and current treatment. Sickle cell disease is the most common genetic disease among individuals of African descent and is prevalent worldwide according to information on the Washington University Physicians website. According to market research conducted on our behalf, there are approximately 120,000 patients with sickle cell disease in the United States. In the United States, sickle cell disease affects approximately one in every 500 African-American births and one in every 1,000 to 1,400 Hispanic-American births according to the National Institutes of Health. Approximately 1,000 children are born with sickle cell disease in the United States each year according to the Sickle Cell Disease Association of America. Screening programs have been established in most states to ensure that a child born with sickle cell disease receives prompt medical attention and parents receive counseling on caring for their child according to the Georgia Comprehensive Sickle Cell Center at Grady Health System.

Treatment options for patients with sickle cell disease are currently extremely limited. For patients with particularly severe disease, hydroxyurea, a cancer chemotherapeutic agent, is used on a chronic basis to reduce the incidence of vaso-occlusive crises. The mechanism of action of hydroxyurea is believed to include an increase in the production of a form of hemoglobin that is normally found in fetal life and that does not contain the sickle cell disease-causing genetic mutation. Although hydroxyurea has been shown to be effective in the treatment of some patients, many patients continue to have frequent vaso-occlusive crises even while on hydroxyurea therapy. Hydroxyurea is also associated with several potentially serious side effects, including suppression of the bone marrow and the immune system. As a result, physicians generally prescribe hydroxyurea only for those patients with frequent vaso-occlusive crises. While the use of hydroxyurea has historically been limited as a result of these side effects, its use has increased due to increasing patient and physician acceptance of the benefits of hydroxyurea therapy. Nevertheless, there is a need for additional therapeutic agents which may be used either in combination with hydroxyurea or as monotherapy. Physicians may also consider the use of blood transfusions in some situations, either on an acute or a chronic basis. However, there are significant risks associated with frequent transfusions, including iron-overload, the transmission of blood-borne diseases and the development of antibodies to the transfused blood, all of which are potentially lethal. Physicians may consider bone marrow transplantation to treat sickle cell disease patients in select cases in which a suitable donor is available, but this treatment option carries a significant risk of morbidity or mortality.

Senicapoc

We are developing senicapoc, which is an inhibitor of the Gardos channel, for the chronic treatment of sickle cell disease. We have evaluated senicapoc in multiple preclinical and clinical studies.

Preclinical Results. In preclinical studies, including in vitro assays using human red blood cells and in a mouse model of sickle cell anemia, senicapoc:

Phase I Trials. We conducted a Phase I clinical trial program for senicapoc that involved a total of over 200 study participants, including both healthy volunteers and sickle cell disease patients. In addition, we are currently conducting a pediatric pharmacokinetic, safety and pharmacodynamic Phase I study in 28 pediatric sickle cell disease patients. The Phase I program was designed to study senicapoc with regard to safety, dose, pharmacokinetics, metabolism, bioavailability, interaction with oral contraceptives and Gardos channel inhibition. Pharmacokinetics refers to the absorption into, distribution within and excretion from the body of a drug. Pharmacodynamics refers to the effect of a drug upon measurable physiologic parameters. We conducted seven separate Phase I studies, including single-dose escalation studies in both patients and healthy volunteers, as well as multiple dose, food effect, bioavailability, drug metabolism and drug interaction studies in healthy

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volunteers. In blood samples taken from both healthy volunteers and patients, senicapoc achieved dose-dependent Gardos channel inhibition. Senicapoc demonstrated pharmacokinetic properties suitable for chronic therapy. The half-life of senicapoc in these trials was approximately 12 to 14 days. The drug was shown to have a favorable safety profile, with no drug-related serious adverse events. There was, however, a mild increase in the activity of a liver enzyme that is responsible for the metabolism of some other drugs. A mild increase in this enzyme could decrease somewhat the blood levels of other drugs, such as some contraceptives, erythromycin-type antibiotics and some cholesterol lowering drugs, when taken concurrently with senicapoc. A similar, but more marked, effect is seen in other currently marketed drugs, and we do not consider this finding to be a concern with regard to the further development of senicapoc. However, no assessment of the efficacy or safety of a product candidate can be considered definitive until all clinical trials needed to support a submission for marketing approval are complete. Success in earlier clinical trials does not mean that subsequent trials will confirm the earlier findings.

Phase II Trial. In 2004, we completed a randomized, double-blind, placebo-controlled dose-range-finding Phase II clinical trial of the efficacy and safety of senicapoc in 90 patients with sickle cell anemia. The study was conducted at 19 academic medical centers across the United States. Male and female patients, 18 to 60 years of age, with a confirmed diagnosis of sickle cell anemia and a history of at least one vaso-occlusive crisis requiring hospitalization in the past were eligible for the study.

The study was comprised of three arms, consisting of approximately 30 patients each:

In each arm of the study, eight of the approximately 30 patients were also receiving hydroxyurea therapy.

Efficacy assessments included changes in hemoglobin level, which was the primary study endpoint, red blood cell count, hematocrit, reticulocytes, dense red blood cells and two biochemical markers of hemolysis, bilirubin and lactate dehydrogenase, or LDH. Clinical assessments included rates of painful crises, time to painful crisis, chronic pain intensity score, maximum crisis morbidity rank and quality of life as measured by the SF-36 health status survey. We included these clinical parameters to help us assess the feasibility and logistics of these endpoints for use in our planned Phase III trial. However, this study was not powered to demonstrate statistical significance with respect to these clinical parameters. We also determined plasma concentrations of senicapoc and hydroxyurea and Gardos channel inhibition.

Our analyses of hemoglobin and other laboratory parameters compared baseline values with values measured at the end of the study period in each of the two active treatment arms and in the placebo arm. The efficacy assessments at the end of the study period were the average of the values measured at weeks 10 and 12, the last two weeks of the treatment period of the study. For the analysis, we used the placebo adjusted difference, which is the difference between the effect measured in the relevant active treatment arm and the effect measured in the placebo arm. In connection with our analysis of the data, we determined statistical significance based on a widely used, conventional statistical method that establishes the p-value of clinical results. A p-value indicates the likelihood that the measured result was obtained purely by chance. Under this method, a p-value of 0.05 or less is considered to indicate statistical significance.

We performed analyses on both an intent-to-treat basis and a per-protocol basis. The intent-to-treat analysis was based on the 88 patients from whom we collected any efficacy data with respect to the effect of treatment with senicapoc. The per-protocol analysis was based on the 70 patients who completed the study and who took at least 80% of the study medication as determined by investigator pill count. The results from our analyses of efficacy assessments were similar between the intent-to-treat and per-protocol populations. We have presented

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data on our primary efficacy endpoint using the results of data from both the intent-to-treat and the per-protocol populations. All other data uses the results of data from only the intent-to-treat population.

The findings presented below with respect to hemoglobin and other laboratory parameters were dose-dependent. We have focused on describing the results obtained in the 10 mg treatment arm because patients in this arm obtained levels of senicapoc in the bloodstream that achieved near-complete Gardos channel inhibition and that we believe provide optimal therapeutic benefit. Our Phase III clinical trial calls for dosing study patients with a 10 mg daily dose of senicapoc following an initial loading dose of 160 mg administered over a four-day period. The results described below with regard to hemoglobin and other laboratory parameters were generally similar within treatment arms across patients who were both on and off hydroxyurea therapy. We believe that this finding suggests that senicapoc may have benefits both as a standalone therapy and when used in combination with hydroxyurea.

Primary Efficacy Endpoint

The primary endpoint was change in hemoglobin level. Hemoglobin level is a measure of the amount of hemoglobin per unit volume of blood and provides a measure of the ability of blood to transport oxygen to the tissues. Hemoglobin level is commonly used in clinical practice to assess the severity of anemic disorders and is one of the factors considered by physicians in determining whether to prescribe treatment, such as a blood transfusion, to patients with anemia, including sickle cell anemia. Senicapoc demonstrated a dose-dependent and, in the 10 mg treatment arm, statistically significant increase in hemoglobin level as compared to the placebo arm.

The time course for the mean changes in hemoglobin from baseline for the three treatment arms is depicted in the following chart. The maximal change in hemoglobin was not seen until near the end of the 12-week treatment period in the 10 mg arm. Grams per deciliter (g/dL) is a commonly accepted laboratory measurement of hemoglobin level. The vertical bars at each point on the chart indicate the degree of variability, as measured by standard error, a commonly used statistical parameter, in the measurements of hemoglobin level associated with each point.

Mean Changes in Hemoglobin From Baseline During

12 Week Treatment Period Intent-to-Treat Population

The following tables set forth an analysis of hemoglobin changes on an intent-to-treat and per-protocol basis in patients in the 10 mg treatment arm divided into three groups: (1) all patients; (2) patients receiving senicapoc with hydroxyurea; and (3) patients receiving senicapoc without hydroxyurea. The magnitude of the hemoglobin

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change was similar in all three groups for both analyses, with median changes somewhat higher, in general, than mean changes. The mean changes in both the group of all patients and the group of patients receiving senicapoc without hydroxyurea were statistically significant. We did not test statistical significance in the group of patients receiving senicapoc with hydroxyurea because of the small sample size. Increasing values are indicated with an upwards arrow.

Placebo Adjusted Difference in Hemoglobin Level in the 10 mg Treatment Arm (g/dL)

For purposes of comparison, an increase in hemoglobin level of approximately 1.0 g/dL is generally consistent with the hemoglobin change resulting from the transfusion of one unit of blood. Based upon this metric, we believe that the increase in hemoglobin level seen in patients in the 10 mg treatment arm was clinically meaningful. We further believe that this increase in hemoglobin level is consistent with the predicted activity of senicapoc to decrease hemolysis and thereby improve anemia.

Secondary Efficacy Endpoints

We also measured other laboratory parameters as secondary efficacy endpoints to further evaluate the effect of senicapoc upon hemolytic anemia. The following table sets forth the placebo-adjusted results for patients in the 10 mg treatment arm. With respect to each of these parameters, senicapoc demonstrated a dose-dependent and, in the 10 mg treatment arm, statistically significant effect as compared to the placebo arm. With regard to most of these measurements, these effects were also statistically significant in the 6 mg treatment arm. In making each of these measurements, we applied the laboratory units commonly employed in measuring these parameters. Decreasing values are indicated with a downwards arrow; increasing values are indicated with an upwards arrow.

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Placebo Adjusted Difference in the 10 mg Treatment Arm