# Presentation: 071078

## RAID Investigator Training – Clinical Trial Section II May 2007

**Hong Zhao, Ph.D.**
- Office of Clinical Pharmacology
- Office of Translational Science
- Center for Drug Evaluation and Research
- FDA

## Topics

**Exploratory IND (ExIND) Guidance**
**Clinical Pharmacology Considerations for Therapeutic Biologic Products (TBPs) Review**

## Exploratory IND (ExIND) Guidance

## Exploratory IND Guidance

**Overview**
**Ideas and Concepts**
**Basic Outline of the ExIND**
**Projects as Outlined in ExIND Guidance**
- Clinical investigation of biodistribution (pharmacokinetics) characteristics or imaging
- Clinical investigation of mechanisms of action (MOAs) related to efficacy
- Clinical investigation of pharmacological effects
**Summary**

## Overview

**Existing regulations (21 CFR 321) allow for a great deal of flexibility in the amount of data to be submitted with IND applications depending on the intended goals of clinical study and the expected risks. **
**Exploratory IND (ExIND) is intended to clarify what**
- chemistry, manufacturing and control (CMC) standards,
- pre-clinical testing and
- clinical approaches
**	****are needed when planning limited, early studies in humans.**
**This presentation concerns pre-clinical testing and clinical studies. **

## Ideas and Concepts (1)

**Not follow the typical or conventional mode of drug development. Addressed need to:**
- Characterize new therapeutic targets
- Identify lead candidates from a portfolio to interact with a specific therapeutic target
- Examine biodistribution using various imaging technologies
- Perform ‘scouting’ studies of pharmacokinetics and/or pharmacodynamics in humans
**Not intended to provide means of selecting a therapeutic dose, e.g., not an MTD study **

## Ideas and Concepts (2)

**Not intended to supplant a conventional IND**
**Upon completion of an ExIND**
- ExIND is withdrawn
- If appropriate, investigative studies may be continued under a traditional IND supported by a full appropriate preclinical studies.
- Results should be discussed with the review division after closing the ExIND and prior to submission of a conventional IND.

## Ideas and Concepts (3)

**Benefits to the public health**
**Increase understanding of MOA associated with candidate selection**
**Emphasize and increase the contribution of science to the selection of drug candidates**
**Promote efficient and effective use of resources**
**Increase the number and rate of NME developed for patient use**
**Protect human subjects**

## Basic Outline of the ExIND (1)

**Clinical Studies in ExINDs**
**Limited human exposure with no therapeutic or diagnostic intent (e.g., screening studies, micro dose studies)**
**Administration of either sub-pharmacologic doses or doses expected to produce a pharmacologic, but not a toxic effect**
**Limited number of human subjects with a limited dose range for a limited period of time **
**Less risk to human subjects than traditional Phase 1 studies that look for dose-limiting toxicities**

## Basic Outline of the ExIND (2)

**Preclinical studies supporting ExINDs**
**Preclinical safety data required for ExIND will need to meet the proposed clinical study.**
**Reduction in safety data requirements will match the limited goals, duration and scope of the proposed clinical study.**
**Imaging studies can be initiated with much less preclinical support than is typically required for conventional IND studies.  **

## Basic Outline of the ExIND (3)

**Goals of preclinical studies**
**Qualitative (identification of target organs) and quantitative characterization of pharmacology and toxicology**
**Specific outcomes**
- Initial starting dose
- High dose
- Tentative therapeutic index
- Dose escalation scheme
- Monitoring scheme

**Clinical investigation of biodistribution (pharmacokinetics) or imaging**
**Clinical investigation of mechanisms of action (MOAs) related to efficacy**
**Clinical investigation of pharmacological effects**

**Projects as Outlined in the ****ExIND Guidance**

## Clinical Investigation of Biodistribution or Imaging (1)

**Clinical Studies**
**Use micro dosing concept for safety**
-  	(at 1/100th of pharmacological dose)
- Not designed to induce pharmacological effects
- Collect biodistribution (PK) information in human subjects
- Investigate specific targets of imaging agents
- Select compounds for further development
**Involve single dose administration**

## Clinical Investigation of Biodistribution or Imaging (2)

**Supporting Preclinical Studies **
**Traditional IND**
- Safety pharmacology studies
- Expanded acute toxicity studies in **two** mammalian species
- Standard battery of genotoxicity tests
**ExIND**
- Expanded acute toxicity studies in **one** mammalian species
- Conducted using intended route of clinical administration
- Single dose study in relevant species with a 14-day observation and interim sacrifice, full clinical and histopathology evaluation
- No need to establish MTD

## Clinical Investigation of MOAs Related to Efficacy

**Preclinical safety established by **
**Alternative or modified pharmacological and toxicological studies**
**Used to determine starting and ending clinical doses**
**Driven by MOA, e.g., degree of receptor saturation, but include endpoints used to assess toxicity**
**Incorporate documentation and procedures to allow an independent review of the data, e.g., protocol, SOPs and study report**

## Clinical Investigation of Pharmacological Effects (1)

**Starting dose would be no greater than 1/50 the NOAEL from the 2-week toxicity study using the most sensitive species; extrapolated by body surface area conversion**
**Stopping dose would be whichever is lowest:**
- Dose that induces pharmacological effect or target modulation
- 1⁄4 of rat NOAEL as determined in the 2-week toxicity study
- 1⁄2 of AUC at the NOAEL for in rat 2-week study or 1⁄2 of dog AUC at the rat NOAEL (assume ‘real time’ measurement of plasma drug levels during clinical studies)

## Clinical Investigation of Pharmacological Effects (2)

_**Example**_** **
**(starting and stopping doses) **
**Drug tested in rats and dog 2-week p.o.**
**NOAEL **
- Rat: 6 mg/kg, HED 1 mg/kg
- Dog: 20 mg/kg, HED 11 mg/kg
**Actual clinical start dose: 0.02 mg/kg (1/50th rat NOAEL = 0.02 mg/kg)**
**Highest clinical dose tested: 1 mg/kg (1/4th rat NOAEL  = 1.25 mg/kg)**

## Summary (1)

**CDER sees implementation of the ExIND guidance as vital part of FDA’s commitment to improving the “critical path” to new medical products.**
**Projects as outlined in the ExIND Guidance include clinical investigation of biodistribution (pharmacokinetics) or imaging, mechanisms of action (MOAs) related to efficacy, and pharmacological effects.**

## Summary (2)

**The preclinical safety data requirements for ExIND studies are less extensive than for conventional INDs. **
**Reduction in preclinical safety data requirements will be scaled to the goals, duration and scope of the proposed clinical studies.**
**Upon completion, ExIND is withdrawn.**
**If appropriate, studies may be continued under a conventional IND that is supported by a full appropriate battery of preclinical studies.**

## Clinical Pharmacology Considerations for Therapeutic Biologic Products (TBPs) Review

## Clinical Pharmacology Considerations for Therapeutic Biologic Products (TBPs) Review

**General Differences between Biologics and Small Molecule Drugs**
**Pharmacokinetic Characteristics of TBPs**
- 	Species specificity
- 	Assay-dependent PK
- 	Route, site and rate of administration
- 	Volume of distribution and binding proteins
- 	Receptor-mediated and/or immune-mediated 	clearance
- 	Immunogenicity
- 	Structure modifications (pegylation and glycosylation)
- 	TBP-drug interactions
**Summary**

## General Differences between Biologics and Small Molecules (1)

**Drug Substance (DS) and Drug Product (PD)**

## General Differences between Biologics and Small Molecules (2)

**Pharmacology***

## Well-known TBPs

**Examples include but not limited to:**
- Cytokines
- Plasminogen activators
- Recombinant plasma factors
- Growth factors
- Fusion proteins
- Enzymes
- Receptors
- Hormones
- Monoclonal antibodies

## Species Specificity and Receptor Related Disposition

**Many TBPs are species specific and receptor(s) may be a factor in disposition.**
- Antigen specificity limits ADME studies of humanized monoclonal antibodies in rodents.
- Animals may rapidly develop an immune response to recombinant human (rh)-proteins.

## Limitations of Assay Methodologies

## Route of Administration

_**Route of Administration**_
**Oral:**
**Denaturation in acid pH of the stomach**
**Proteolytic degradation within GI**
**Minimal rates of diffusion through the GI epithelial due to large molecular size and high polarity**
**IV:  ****	**
**Complete systemic availability**
**Rapid delivery to achieve high concentrations**
**Allowing administration of larger volumes**
**Less possibility of immunogenicity**
**Inconvenient, increasing cost, precipitating AEs with rapid infusion**

## Route of Administration

_**Route of Administration**_
**SC, IM: ****	**** **
**Large doses **_**may not be**_** feasible due to the relatively limited solubility of IgG (********100 mg/mL), and pain associated with administration of volumes >2.5mL (SC) or 5mL (IM)**
**Large dose can be given by multiple injections **
**Viable for therapeutic antibodies that rapid absorption is not necessary and dose is not greater than 500 mg**

## Impact of Route of Administration on PK

_**Route of Administration**_** (IV, IM, SC)  **
**Molecular weight may play a role in absorption process. **
**Absolute bioavailability may be 50-100% depending on the extent of presystemic degradation by proteolytic enzymes.**
**Proteolytic degradation may be saturable leading to increases in bioavailability with increasing doses.**
**Absolute bioavailability may appear to be >100% (assay artifacts, formation of antibodies).**
**Different routes may produce different biological activity and adverse effects. **

## Impact of Site and Rate of Administration on PK

_**Site of Administration **_
**(arm, abdomen, thigh)**
**	**rh-erythropoietin absorption: thigh > arm > abdomen**  **
- 		GH Cmax: abdomen > thigh, similar AUC
_**Rate of Administration **_
**(Intermittent, pulsed delivery, continuous infusion) **
- Effectiveness of GH, parathyroid hormone, tPA:
- 	intermittent or pulsed delivery > continuous infusion
- Tumor inhibition of IL-2 in mice:
- 	12 injections of 1,500 units > 2 doses of 9,000 units

## Volume of Distribution

_**Distribution**_
**After reaching the blood stream, a protein molecule is distributed intracellularly through the vascular space transporting**
- across the microvascular wall
- through the interstitial space
- across cell membranes
_**Volume of Distribution**_
**For most TBP Vss is small and approximates the plasma volume (3-5% of TBW).**
**For TBP with higher affinity and higher capacity binding to cellular binding sites, Vd may be greater than plasma volume.**
**In case where binding capacity is limited, nonlinear distribution may be expected.**

## Impact of Binding Proteins on PK

_**Binding Proteins**_** (Endothelial binding sites, free or shed receptors, macroglobulins, and other circulating molecules) may**
**  ****have inhibitory or stimulatory effects**
**  ****serve as transporters and activators**
**  ****affect protein drug elimination**

## Clearance

**Clearance Pathways **
**Internalization**
**Formation of endosomes and lysosomes**
**Proteolytic degradation **
**Fc receptor (FcRn, Fc****γ****)-mediated **
**Cleavage to activate for blood coagulation cascade **
**No metabolites (amino acids recycled)**
**Non-cytochrome P450 substrates**

## Elimination

- Hepatocytes uptake (for large MW)
- Receptor-mediated endocytosis: specific and saturable
- Nonselective pinocytosis: nonsaturable, noncarrier-mediated
- Biliary excretion, spleen, lymphatic
- Renal excretion (for MW<69kDa)
- Filtered by the glomerulus and excreted (for MW<30kDa), reabsorbed back as intact or catabolic
- Peritubular extraction and hydrolysis

**Major form of elimination from circulation is binding to receptor/antigen and internalization**

## Impact of Receptor-Mediated Clearance on PK

**Receptor-mediated clearance may result in nonlinear PK due to receptor saturation.**
**Anti-TBP antibodies may alter PK of TBPs.**
** **

## Example:An MAb – Nonlinear PK with Dose

## Immunogenicity

**Anti-TBP antibody formation depends on**
**State of the host immune system (disease state)**
**Characteristics of the antigen**
- 	(nonhuman sources, molecular size, structural complexity) Immunogenicity  with the extent of IgG humanization: “fully humanized” IgG < CDR-grafted IgG < chimeric IgG < rodent IgG
**Dose, frequency and duration**
- 	Immunogenicity  with  dose,  frequency,  duration
**Route of administration**
- 	SC > IM > IV, due to precipitation and aggregation
**Complex and difficult to predict**
- *Exceptions exist.

## Impact of Immunogenicity on PK, Efficacy and Safety

- decrease pharmacological response through ‘neutralizing’ the TBP’s activity or increase its clearance (↑ CL)
- sustain activity through decrease TBP’s clearance (↓CL)
- cause adverse effects not directly related to the TBP (e.g., immune complex deposition)
- cross-react with endogenous proteins
- mask TBP’s detection

**Anti-TBP antibody formation may**

## Impact of Anti-lenercept Antibodies on Lenercept PK

## Impact of Pegylation on PK, Efficacy and Safety (1)

- Pegylation may
-  t1/2
-  CL
-  Toxicity
-  Immunogenicity
-  Drug stability and solubility
-  Biological activity
- *Exceptions exist: e.g., albumin’s t1/2 is not changed by Pegylation

_**Pegylation**_
- Polyethylene glycol (PEG): water soluble polymer, covalently linked to TBP, number of substitution may vary, over 40 known examples

## Impact of Pegylation on PK, Efficacy and Safety (2)

**Mechanisms of Pegylation Effects **
- Increased size above limit of glomerular filtration
- Interference with interactions of carbohydrate chains with specific receptors (adds steric hindrance, reduce proteolysis)
- Masking specific amino acids sequences which are cellular receptors (decrease biological activity)
- Masking of antigenic sites (reduce immunogenicity and toxicity)

## Impact of Glycosylation on PK, Efficacy and Safety

_**Glycosylation**_** (Addition of certain sugar to a protein moiety)**
**Glycosylation and biological function**
**Lymphocyte “homing”**
**Tumor invasiveness**
**Trophoblast implantation**
**Intracellular adhesion**
**Post-translational modification**
**may be required for biological activity**
**regulates the ligand-receptor interaction and protein secretion**
**may alter PK**
**enhances protein stability**

## TBP-Drug Interactions (1)

**ICH Topic S6 (July 1997): **
- The expected consequence of metabolism of biotechnology-derived pharmaceuticals is the degradation to small peptides and individual amino acids. Therefore, the metabolic pathways are generally understood.
- Classical biotransformation studies as performed for pharmaceuticals are not needed. (may need revisit)

## TBP-Drug Interactions (2)

- TBPs are non-P450 substrates
- TBP-drug interaction studies are usually not required unless indicated
- Some cytokines, including G-CSF may alter the PK and/or PD of other concomitant administered drugs
- Possible inhibition or stimulation of P450 system through down-regulation of P450 gene transcription and RNA modulation
- Magnitude of PK alteration relatively small and non-unidirectional
- PD interaction more important

**TBP-drug interactions are rarely observed **

## Summary

**TBPs are species specific and receptors may affect their PK. **
**PK parameter estimates are largely assay-dependent.**
**Route, site and rate of administration may have an impact on PK of a TBP and may produce different biological activity and adverse effects. **
**Binding proteins may serve as transporters and activators, may have inhibitory or stimulatory effects, and may affect elimination of TBPs. **
**Receptor-mediated and/or immune-mediated clearance may result in non-constant clearance.**

## Summary

**Immunogenicity may have an impact on PK, efficacy and safety.**
**Pegylation may decrease clearance, reduce toxicity and immunogenicity, and increase stability and solubility. **
**Glycosylation may be required for biologic activity to regulate the ligand-receptor interaction and protein secretion, to enhance protein stability, and may alter PK profile. **
**Drug interactions are rarely observed, but some cytokines may inhibit or stimulate CYP450 system.**

## Acknowledgments

**Dr. Dave Green**
**Dr. Iftekhar Mahmood**

## Quiz Questions

## Clinical Pharmacology Considerations for TBPs Review

## Question 1. (true or false)

	The expected consequence of metabolism of TBPs is the degradation to small peptides and individual amino acids; therefore, the metabolic pathways of TBPs are generally understood.

**	**The expected consequence of metabolism of TBPs is the degradation to small peptides and individual amino acids; therefore, the metabolic pathways of TBPs are generally understood.

## Answer to Question 1: True (ICH S6)

## Question 2. (multiple choice)

	Which of the following characteristics does not belong to TBPs?
		(a) high molecular weight 
		(b) highly targeted
		(c) species-specific
		(d) non-immunogenic

**	**Which of the following characteristics does not belong to TBPs?
- 		(a) high molecular weight
- 		(b) highly targeted
- 		(c) species-specific
- 		(d) non-immunogenic

## Answer to Question 2: (d)

TBPs are exogenous proteins and they are potentially immunogenic. 
Immunogenicity must be evaluated for each TBP.  

- TBPs are exogenous proteins and they are potentially immunogenic.
- Immunogenicity must be evaluated for each TBP.

## Question 3. (multiple choice)
	Which one of the following is the most appropriate statement?

	Anti-TBP antibodies may have the following effects on TBPs:
		(a) increase clearance 
		(b) decrease clearance
		(c) decrease pharmacologic effect 
		(d) increase infusion-associated reactions
		(e) all of above  
		(f) none of above

**	****Which one of the following is the most appropriate statement?**
**	**
**	****Anti-TBP antibodies may have the following effects on TBPs:**
**	****	****(a) increase clearance **
**	****	****(b) decrease clearance**
**	****	****(c) decrease pharmacologic effect **
**	****	****(d) increase infusion-associated reactions**
**	****	****(e) all of above  **
**	****	****(f) none of above**

## Answer to Question 3: (e)

## Exploratory IND Guidance

## Question 1. (true or false)
	Upon completion, the Exploratory IND is withdrawn. If appropriate, studies may be continued under a conventional IND that is supported by a full appropriate battery of preclinical studies.

**	****Upon completion, the Exploratory IND is withdrawn. If appropriate, studies may be continued under a conventional IND that is supported by a full appropriate battery of preclinical studies.**

## Answer to Question 1: (True)

## Question 2. (multiple choice)

**Which of the following statements describes basic outline of Exploratory INDs? **

- (a)	Limited human exposure with no therapeutic or diagnostic intent (e.g., screening studies, micro dose studies)
- (b) 	Administration of either sub-pharmacologic doses or 	doses expected to produce a pharmacologic, but not a 	toxic effect
- (c) 	Limited number of human subjects with a limited dose 	range for a limited period of time
- (d) 	Less risk to human subjects than traditional Phase 1 	studies that look for dose-limiting toxicities
- (e) 	None of above
- (f) 	All of above

## Answer to Question 2: (f)