Nat Rev Drug Discov. 2008 Jan;7(1):21-39.

Protein therapeutics: a summary and pharmacological classification.

Leader B, Baca QJ, Golan DE.

Pharmaceutical Industry• Research based companies spent ≈20% of their

sales on R&D• Since 1980 US based companies have doubled

spending on R&D every 5 years• Steady decline in number of drugs introduced

for clinical use each year– 70-100 in the 60s– 60-70 in the 70s– ≈50 in the 80s– ≈40 in the 90s

• New drug costs ≈$1billion & takes 16 years to develop

• ≈90% of all drug candidates fail to make it to market!

Drug Target Identification

• 25K-40K different genes in the human genome– with splicing & post-translational modification the

number of functional proteins is likely greater

• Estimated that up to 10 genes contribute to a multifactorial disease– Typically these are linked to 5-10 gene products in

physiological circuits which are targetable

• ~5000-10000 potential drug targets!

How are we doing?

• Current therapy based upon <500 molecular targets– 45% are G-protein coupled receptors– 28% are enzymes– 11% are hormones and factors– 5% are ion channels– 2% nuclear receptors

• At present ~130 different proteins or peptides are approved for clinical use!

Pro’s over SMDs• Proteins serve highly specific and complex

functions not mimicked by chemical compounds• Due to specificity, less likely to interfere with

normal biological processes• “natural” and hence often better tolerated & less

likely to elicit an immune response• Effective replacement therapy for certain genetic

diseases, alternative to gene therapy• Clinical development and FDA approval faster

than for SMD (typically 1 year)• Due to uniqueness of protein, better patent

protection

Case 1Robert H, a 55 year old travelling sales man presents to the A&E of a

small rural hospital with left chest pain & lightheadedness. The pain started 1 hr a go when he was carrying a large box & his symptoms improved at rest a resolved after 20min. He has no notable past medical history. On physical exam, he is afebrile with a HR of 100bpm, BP 150/90 & resp of 16breaths/min. Remainder of exam is normal except for a S4 heart sound. ECG demonstrates sinus tachycardia with no ST elevation. Chest X-ray and blood biochemistries are normal. Cardiac biomarkers & coagulation studies are pending. RH is given aspirin, metoprolol & sublinqual nitroglycerine upon arrival in A&E. On admission to hospital his troponin T returns at 1.34ng/ml (N, 1-0.1ng/ml) & develops 2mm ST segment depression when he has chest pain. At this time he is given heparin, abciximab & clopidogrel, chest pain resolves. Next day RH develops crushing substernal chest pain and diaphoresis, his ECG shows 4mm change in ST segment. As no cardiac catheterisation is available at a regional centre for 4hr, he is given tenecteplas in the CCU, other meds are continued. He stabilises and uneventful 5 days in hospital. Transferred to regional cardiac centre for catheterisation and diagnosed with unstable angina. Outpatient plans include rehab tx with aspirin, metoprolol, enalapril, spironolactone as nitroglycerine as needed.

Questions

• By what mechanism does abciximab act?

• How could abciximab augment the function of

clopidogrel and aspirin in this case?

• By what mechanism does tenecteplase act?

• How does the action of tenecteplase differ

from that of heparin?

Functional Classification of Protein Based Therapies

• Group 1: Protein therapeutics with enzymatic or regulatory activity

• Group 2: Protein therapeutics with special targeting activity

• Group 3: Protein vaccines• Group 4: Protein diagnostics

Group 1: Protein Therapeutics with Enzymatic or Regulatory Activity

• Group 1a: Replace a protein which is deficient or abnormal– Factor VIII– Insulin and its analogues– Growth Hormone

• Group 1b: Augment an existing pathway– Erythropoietin– Pegylated interferon– Tenecteplase

• Group 1c: Provide a novel function or activity– Collagenase– L-asparaginase– Etanercept

Tenecteplase

• Use in thrombolysis• Genetically engineered derivative of tissue

plasminogen activator (tPA)• Greater specificity than tPA for binding to

plasminogen• Causes more efficacious lysis of fibrin in blood

clots

Group 2: Protein Therapeutics with Special Targeting Activity

• Group 2a: Interfering with a molecule or organism by binding to it and blocking its function or targeting it for degradation– Abciximab– Enfuviritide– Infliximab

• Group 2b: Stimulating a signalling pathway– Trastuzumab

• Group 2c: Delivering other compounds or proteins– Gemtuzumab ozagamicin

Abciximab

• Chimeric mouse-human Mab against human GPIIb-IIIa receptor– Prevents activation

• Reduces platelet aggregation• Essentially irreversible

– Dissociation t1/2 ~18-24 hr

• Clincal trial:– Adding abciximab to conventional antithrombotic

therapy reduces both long-term and short-term ischaemic events in pts undergoing percutaneous coronary intervention

Trastuzumab (Herceptin)

• Chimeric mouse/human IgG Mab directed against ErbB2 (HER2)

• ~ 25-30% of breast cancers are associated with amplification and overexpression of Her2/neu– Tend to be aggressive cancers

• HER2 amplifies signals generated by ErbB family members by forming heterodimers

• Trastuzumab down-regulates HER2 and disrupts signalling– In vitro: Ab-dependent cytotoxicity and inhibits

angiogenesis– Adjuvant setting: following resection enhances efficacy

of chemotherapy and reduces rate recurance by 50%

Gemtuzumab ozagamicin

• Links the binding region of a Mab directed against CD33 with calicheamicin – small molecule chemotherapeutic agent

• Used to treat CD33 positive acute myeloid leukaemia (AML) cells– Guided delivery of cytotoxic agent– Selective toxicity

Group 3: Protein Vaccines

• Group 3a: Protecting against a deleterious foreign agent– HBsAg– Lyme disease (Borrelia burgdorfei)

• Outer surface protein A (OspA)

• Group 3b: Treating an autoimmune disease– Anti-Rh IgG

• Group 3c: Treating cancer– Currently in clinical trials

Anti-Rh IgG

• Prevents sensitisation of a Rh-negative mother at time of delivery of a Rh-positive neonate

• As mother fails to develop Ab against foetal antigent immune reactions and loss of pregnancy do not occur in subsequent pregnancies

Group 4: Protein Diagnostics

• HIV antigens• Hepatitis C antigens• Thyroid stimulating hormone (TSH)• Glucagon

Case 1: Questions

• By what mechanism does abciximab act?

• How could abciximab augment the function of

clopidogrel and aspirin in this case?

• By what mechanism does tenecteplase act?

• How does the action of tenecteplase differ

from that of heparin?

Case 2You are working in the A&E when a 32 year-old woman, KO, is

brought by ambulance after a car crash. Her car was struck on its side and rolled over once down a shallow embankment. She had no loss of consciousness and was easily extricated. She arrives on a backboard in spinal immobilisation to protect her cervical spine. She is crying and very upset. She tells you that she is 10 weeks’ pregnant and wants to know if there may be any injury to the baby. A trauma evaluation is performed, including routine lab tests and imaging. Mrs KO reports that she feels a small amount of spotting on her underwear, and a pelvic examination releases a small amount of pink discharge coming from the closed uterine os. A pelvic ultrasound demonstrates and intact uterus with a normal appearing intrauterine pregnancy and normal foetal heart activity. Remainder of evaluation reveals no other injury. Her lab evaluation is also reassuring. However, you find that her blood type is type A, Rh(D) antigen negative. You confirm with her that this is her first pregnancy. Based on Mrs KO’s presentation, you cannot exclude the possiblility of a small degree of foetomaternal haemorrhage as a result of this trauma.

Case 2 – MCQ 1

If Mrs KO is Rh(D) antigen negative and her foetus is Rh(D) antigen positive and there has been some mixing of foetal and maternal blood as a result of this trauma, what could be the result in Mrs KO?

1. Mrs O could develop antibodies to her own erythrocytes2. Mrs O could develop antibodies to her foetus’s erythrocytes3. Mrs O could suffer an anaphylactic reaction4. Mrs O could suffer a transfusion reaction to rh(D)5. Mrs O could develop an autoimmune disease

Case 2 – MCQ 2

If Mrs KO is Rh(D) antigen negative and her foetus is Rh(D) antigen positive and there has been some mixing of foetal and maternal blood as a result of this trauma, what could be the results in the foetus:

1. The foetus could develop antibodies to the Rh(D) antigen2. The foetus could develop antibodies to maternal proteins and

be unable to nurse after birth3. The foetus could suffer haemolysis as a result of maternal

anti-Rh antibodies4. The foetus could suffer bone marrow aplasia as a result of

maternal anti-Rh antibodies5. The foetus could suffer a transfusion reaction to Rh(D)

erythrocytes in the future

Case 2 – MCQ 3

You explain to Mrs KO that based on her Rh typing, she should have therapy to prevent future harm to the foetus. This therapy and its intended effects are:

1. Exchange transfusion to exchange any Rh(D) positive blood for Rh(D) negative blood

2. Transfusion with Rh(D) positive blood to induce desensitization to foreign Rh antigens

3. Hepatitis D vaccine to prevent sensitisation to all D antigens4. Anti-Rh(D) immunoglobulin to prevent sensitisaton to Rh(D)

antigens5. Vitamin D to prevent the formation of antibodies against all

D antigens

Case 2 – MCQ 4

Administration of the above therapy is a form of:

1. Protein replacement therapy2. Vaccination3. Enzyme inhibition4. Immmuno-adhesion5. Antigenic neutralisation

Case 2 – MCQ 5

Which of the following is a protein derived vaccine?

1. Purified protein derivative (PDD)2. Etanercept3. OspA4. Secretin5. L-asparaginase

Six men in intensive care after drug trial goes wrong

• Company: TeGenero Immuno Therapeutics• Drug: TGN1412 (also known as CD28-SuperMAB)• Use: Tx of B cell chronic lymphocytic leukaemia

and rheumatoid arthritis• “In its first human clinical trials in March 2006, it

caused catastrophic systemic organ failure in the subjects, despite being administered at a supposed sub-clinical dose of 0.1 mg per kg; some 500 times lower than the dose found safe in animals. Six volunteers were hospitalized on 13 March 2006, at least four of these suffering from multiple organ dysfunction, and one trial volunteer is said to show signs of developing cancer”.

“Elephant man” drug trial victim set to win £2m payout for horrific

injuries