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Requirements for the Cure of Cancer: Formulating a Plan of Action. Workshop sponsored by the Van Andel Institute Jan. 10-11, 2007. FROM PRINCIPLES TO PRACTICE. SESSION VI(B) The development of technologies for targeting cells that express target patterns Arnold Glazier MD.

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requirements for the cure of cancer formulating a plan of action

Requirements for the Cure of Cancer: Formulating a Plan of Action

Workshop sponsored by the Van Andel Institute

Jan. 10-11, 2007

from principles to practice



The development of technologies for targeting cells that express target patterns

Arnold Glazier MD

ideal drug targeting
Ideal Drug Targeting
  • The tumor would act like a black hole for drug
  • All drug in the blood flow to the tumor would be irreversibly retained
  • No drug accumulation in non-target sites
ideal drug targeting1
Ideal Drug Targeting
  • Based on a typical blood flow of 0.15 –0.6 ml/min/gm and 24 hours, maximum average tumor levels would be about 200-800 times the average blood level
  • The biological effects can be even orders of magnitude higher
multiplicative increases in concentration can give exponential increases in effect
Multiplicative Increases in Concentration can give Exponential Increases in Effect

Surviving Cell Fraction versus Drug Concentration


Brown JM, Wouters BG.; . Cancer Res. 1999 Apr 1;59(7):1391

examples of almost perfect targeting exist
Examples of Almost Perfect Targeting Exist
  • Hormone/ receptor binding
  • Peanut allergy / anaphylactic shock
  • Nerve gas
approaches towards ideal drug targeting
Approaches Towards Ideal Drug Targeting
  • Specific, high affinity or irreversible binding
  • Slow “off rates” of drug from receptors
  • Administering the drugs at the lowest concentration needed to saturate “drug accessible” receptors
  • Decreasing nonspecific binding
  • Increasing the quantity of drug receptors (exponential PRTT)
  • Prolonging treatment time

Principles that can be applied towards achieving these goals are well known. (Multi-site binding, slow binding, covalent binding, etc..)

major issues
Major Issues
  • Chaotic and uneven blood flow
  • Limited drug penetration into tumors
  • Slow rates of drug diffusion
  • Episodic target pattern expression
  • On a given day only parts of a tumor will be drug accessible

The drugs need to be given continuously for prolonged periods of time. (6 months?)

the aim should be to deliver drug to drug accessible target patterns
The Aim Should be to Deliver Drug to “Drug Accessible” Target Patterns
  • The important pathology that sustains cancer occurs within a limited zone around blood vessels.
  • Areas close to blood vessels will be drug accessible.
  • Drug accessible cells will be killed, new layers of cancer cells will be exposed and killed over time in an “onion peeling effect”
  • Therapy needs to be sufficiently intense so that the rate of cell loss exceeds the rate of cell production

A Minor, Sustained Decrease in the Probability of Cancer Cell Survival can have Profound Effects

Data: Berman JJ, Moore GW; Anal Cell Pathol. 1992 Sep;4(5):359-68

drugs targeted to a comprehensive set of target patterns will inhibit
Drugs Targeted to a Comprehensive Set of Target Patterns will Inhibit
  • Angiogenesis
  • Vasculogenic mimicry
  • Vascular co-option

This will achieve Dr. Folkman’s vision by effectively depriving tumor cells of new blood supply, constraining growth and allowing time for the “onion peeling” killing effect to work.

non synchronous expression of target pattern elements
Non-synchronous Expression of Target Pattern Elements

Targeting specificity should be for

  • Invasiveness alone, or
  • Invasiveness and the potential for proliferation

Elements of these classes of target patterns are expressed concurrently.

effector agents should be cell cycle independent

Effector Agents Should be Cell Cycle Independent

G2/mitotic-specific cyclin-B1 in colon cancer

the microenvironmental nature of invasiveness
The Microenvironmental Nature of Invasiveness

There is a requirement for approaches that generate a zone of anticancer activity in the local volume that surrounds target patterns

major requirements
Major Requirements

The need for:

  • Pattern specificity
  • Signal amplification
  • Multiple, redundant mechanisms of cell killing or inactivation
  • Prolonged therapy
  • The ability to simultaneously give multiple drugs
  • Chemical stability
  • Lack of antigenicity
  • Modularity in design
the logic function of prtt drugs
The Logic Function of PRTT Drugs




Are all the elements of the pattern present ?



Kill Cell

Spare Cell

Specificity is for the pattern, not the individual elements.


1. Binding

2. Chemical bond formation

3. Breakage of chemical bonds

4. Catalysis of a reaction

5. Dissolution or precipitation

Medicinal Chemistry Boils Down To:

modular building blocks
Modular Building Blocks
  • Targeting ligands
  • Triggers
  • Triggering agents
  • Effector agents
  • Linkers and scaffolds
  • Male and female adaptors
  • Masking groups
  • Molecular clocks
  • Intracellular transport ligand
  • Solubility modifiers

These components exist and are within the scope of current technology.

targeting ligands
Targeting Ligands

Ligand Receptor Complex

Ligands are chemical groups that bind together like a lock and key to target receptors.

a urokinase selective ligand
A Urokinase Selective Ligand

Kd is in the low nanomolar range.

Tamura S Y., et al., Bioorganic Med Chem Lett,

10:983-987 (2000)

triggers and triggering agents
Triggers and Triggering Agents






Chemically altered drug

Triggers are chemical groups then when acted upon by a triggering agent undergo a chemical change.

Enzymes and non-enzymes can serve as triggering agents.

applications of triggers
Applications of Triggers
  • To turn on or off a chemical process
  • To activate a toxin
  • To inactivate a toxin
  • To unmask a ligand
  • To release a toxin
effector agents
Effector Agents
  • Toxic agents that kill cells
  • Agents that irreversibly block the potential for cell proliferation
  • Agents that trigger an immune response
  • Agents that amplify a response
linkers and scaffolds
Linkers and Scaffolds





Targeting Ligands

Structural elements that provide the backbone of the drug

cyclodextrins as scaffold
Cyclodextrins as Scaffold

Rigidity, multiple sites for linker attachment,

solubility, spatial separation of components,

low toxicity

male and female adaptors
Male and Female Adaptors

The male and female parts bind specifically and tightly.

In the ideal case the binding is irreversible.

masking groups







Masking Groups

A masking group blocks a receptor.

A triggering agent can unmask the receptor.

molecular clocks
Molecular Clocks




Chemical change

Molecular clocks provide an adjustable time delay between a triggering event and a chemical change.

intracellular transport ligands
Intracellular Transport Ligands



Cell Receptor

Transport into Cell


Transport Ligand



Intracellular transporter groups can also work by physical, non-receptor mediated mechanisms.

Tumor Cell

Tumor Cell

A wide range of pattern targeting technologies can be developed by combining these modular building blocks in logical ways.
prtt approaches
PRTT Approaches
  • Targeted delivery of a targeted agent
  • Targeted delivery of a trigger activated drug
  • Independently targeted synergistically toxic drugs
  • Multi-site binding
  • Exponential Pattern Recognition Targeting
  • Combinations of the above
  • Other
targeted delivery of a targeted cytotoxic agent2
Targeted Delivery of a Targeted Cytotoxic Agent

The cytotoxic agent is toxic only if its target is present

targeted delivery of a trigger activated drug1
Targeted Delivery of a Trigger Activated Drug

Only cells that have both the target receptor and the triggering

enzyme will be killed.

a urokinase activated gmcsf receptor targeted diphtheria toxin
A Urokinase-Activated GMCSF Receptor Targeted Diphtheria Toxin


Urokinase activates

Diphtheria toxin

Binds to GMCSF

Receptor on cells

The drug targets the pattern of urokinase and GMCSF receptor.

Ralph J. Abi-Habib, Shihui Liu, Thomas H. Bugge, Stephen H. Leppla, and Arthur E. Frankel; Blood, 1 October 2004, Vol. 104, No. 7, pp. 2143

targeting the microenvironment
Targeting the Microenvironment

The drug is targeted to the microenvironment, released by the triggering enzyme, diffuses to the tumor cell and kills it.

advantages of releasing a toxin into the tumor microenvironment
Advantages of Releasing a Toxin into the Tumor Microenvironment
  • Invasiveness is a property of both the cancer cell and its microenvironment
  • A zone of toxicity is created making it easier to kill all the cancer cells

Approaches that produce a zone of toxicity are strongly preferred.


Agent 1

Agent 2

Paired, Independently Targeted

Synergistically Toxic Drugs


Individually, Agent 1 and Agent 2 are Nontoxic, But Toxic in Combination:

Agent 1

Agent 1

Agent 2

Agent 2

Tumor cell

Normal cell

Type B

Normal cell

Type A

No Toxicity Toxicity No Toxicity

multi site binding and pattern recognition
Multi-Site Binding and Pattern Recognition

Multi-site binding can give an enormous increase in the tightness of binding compared to single site binding


A Ten Billion Times Increase in Affinity due to Three Site Binding




Tri- Ala-Ala

Kd = 10 – 6

Kd = 10 –17

  • Rao J, Lahiri J, Isaacs L, Weis RM, Whitesides GM; Science 280:708-11 (1998)
multi site binding1



Tumor cell

Normal cell

Multi-Site Binding

No Binding

Tight Binding

At low concentrations the drug can bind tightly to cells with the target pattern without binding to cells that express only one element of the pattern

advantages of multi site binding
Advantages of Multi-Site Binding
  • Specificity for the pattern
  • Potency
  • Slow off rate
  • Immense reductions in the dose of drug required
  • Reductions in side effects
exponential pattern recognition targeting

Exponential Pattern Recognition Targeting

From one receptor create two, from two create four ….


Exponential Pattern Recognition Targeting

Instead of consuming receptors, the targeted drug will in effect increase the target receptor density.

The more drug that is delivered, the more drug that can be delivered.

components of exponential pattern recognition targeting
Components of Exponential Pattern Recognition Targeting

Masked Female Adapter


Targeting Ligand

Male Ligand

1 2

The male and female parts bind with very high affinity.

triggering enzymes unmask the female adaptor
Triggering Enzymes Unmask the Female Adaptor
  • Many enzymes that are over-expressed by tumors can be utilized
  • The triggering enzyme can also be independently targeted to tumor cells
exponential pattern recognition targeting1
Exponential Pattern Recognition Targeting

Triggering enzyme

Tumor cell

Tumor cell

1.) Component 1 binds to cell receptors.

2.) Triggering enzyme(s) unmask female adapter.




Triggering enzyme

Tumor cell

Tumor cell

3) Component 2 binds to the unmasked female adaptor.

4) The triggering enzyme unmasks twice as many

new female adaptors.







Tumor cell

Repetition of the cycle can deposit a large quantity of drug in a tree like structure

massive amounts of drug can be delivered to a tumor cell
Massive Amounts of Drug can be Delivered to a Tumor Cell

The quantity can increase exponentially

self amplifying exponential prtt

Self-Amplifying Exponential PRTT

The very binding of a male ligand and female adaptor creates two new female adaptors without the need for a triggering enzyme.


Unmasked Female Adaptor


Female Adaptor



Male and Female

Covalently Bound


Female Adaptor


Female Adaptor


Female Adaptor


Masked Female Adaptor

Masked Female Adaptor

Bulky Group

Masked Male Adaptor


Unmasked Female Adaptor

Female Adaptor from

a second molecule

Bulky Group


Female Adaptor

female adaptors can transform different patterns into a common target
Female Adaptors can Transform Different Patterns into a Common Target

This can enable the efficient delivery of multiple drugs to each target pattern and prevent the development of drug resistance.


A wide range of possibilities and emergent properties can arise with drugs that interact with each other.


Amplification and positive feedback can be achieved by delivering enzymes to adaptors which in turn unmask additional adaptors.


An other approach is to deliver a marker to the target patterns that make it look to the immune system like a bacterial infection.


Massive signal amplification is possible along with a change in scale.

To attract and activate one neutrophil requires only a small number ofchemotactic molecules.

each neutrophil can deliver billions of molecules of
Each neutrophil can deliver billions of molecules of:
  • Hydrogen peroxide
  • Myeloperoxidase
  • MMP-9
  • Urokinase
  • Elastase
  • Catepsins
the system exhibits positive feedback
The system exhibits positive feedback:
  • Myeloperoxidase activates neutrophils
  • ROS inactivate protease inhibitors
  • Ros activate MMP’s
  • Ros stimulate MMP production
  • Cathepsins

The protease released can also activate MMP-2, MMP-9, and plasminogen.


The net result could be a massive signal amplification in and around the target pattern and… a change in scale.