In-Depth Notes on Antibody Drug Conjugates and mRNA Vaccines for Cancer Treatment

Antibody Drug Conjugates (ADCs)

• Definition: ADCs integrate monoclonal antibodies (mAbs) with cytotoxic drugs, following Paul Ehrlich's "magic bullet" concept to minimize toxicity of chemotherapeutics by targeting cancer cells specifically.

• aim to limit toxicity of small molecules used in chemotherapy.

• Fab region gives specificity.

• cytotoxic drug connected by linker- this is either cleavable by chemical or enzymatic reaction. Can be non cleavable- in this case the antibody will go through full metabolism.

  • Tumor-specific mAbs must consider affinity, internalization, pharmacokinetics (PK), and conjugation chemistry.

  • Components:

  • Linker Types: Cleavable (chemical/enzyme) vs. non-cleavable; stability in plasma is crucial.

  • Cytotoxic Payload:

    • Conventional Targets: Include tubulin and DNA.

    • Unconventional: e.g., topoisomerase inhibitors, immune stimulants.

    • Drug to Antibody Ratio (DAR): indicates potency and efficacy of ADC. The number of cytotoxic payloads attached to one monoclonal antibody.

• Clinical Developments:

  • Hundreds of ADCs are in development, with only a few approved (around 12 globally).

  • Key examples include:

  • Trastuzumab (Herceptin™): Targets HER-2 in breast cancer.

  • TDM-1 (Kadcyla™): Emtansine payload with a DAR of 3.5.

  • T-DXd (Enhertu™): Deruxtecan payload with a DAR of 8, lower overall cytotoxicity.

• Adcs follow MOA like Mabs, then the payload of a small drug.

• When released, cytotoxic drug relies on 3 mechenisms:

• - microtubule polymerisation inhibiton

• tipoisomerase 1 inhibition

• DNA alkylation

• DNA alkylation: This mechanism involves the covalent binding of the drug to DNA, leading to cross-linking and subsequent apoptosis of cancer cells.

Maximun tolerated dose- thought that ADCs would improve max tolerated dose and decrease the dose needed to be effective.

But, trials suggest that ADCs do not increase the MTD of conventional chemotherapeutics .

ADCs with a lower DAR have higher antibody dose as they have less cytotoxic payload.

• Efficacy and Challenges:

  • ADCs often show greater efficacy in cancers unresponsive to regular chemotherapeutics. For instance, T-DXd exhibited a 42% response rate vs. 12% for chemotherapy alternatives.

  • Toxicity remains a significant issue; many ADCs maintain similar or worse toxicity profiles (incidence >90%), however they remain very efficacious.

  • Although, lots of unknowns- no randomised trials been done.

Instability and Drug Release

• Linker Instabilities: linkers can either be cleavable (release drug via proteolysis, reduction, pH etc) or non cleavable (follow full catabolism).

  • Types:

  • Linker-Drug Instability: Intended drug release occurs. prefer to have linker still attached to antibody, and only the drug is released from it.

  • mAb-Linker Instability: More problematic, can lead to undesired drug release. If the linker goes separately from mab can be problem.

  • Approved ADCs often use thio-maleimide conjugates:

  • Different linkers show varying stability (e.g., caproyl linkers lead to rapid release).

• Comparative Analysis:

  • ADCs with lower DAR require higher antibody doses, though the normalized cytotoxin content remains similar to conventional drugs. The effectiveness of lower vs. higher DAR requires further research.

Distribution and Biodistribution of ADCs

• When using radiolabeled mAbs like Trastuzumab:

  • Distribution data indicates:

  • 1/3 in circulation; 15% in liver, 4% in spleen/kidney, and 5-7% in adipose tissue (may increase in obesity).

  • Less than 1% reaches tumor lesions, indicating the challenge of targeted delivery.

  • might get small amount of ADC on tumour target, but receptor could match others in the body- ADR?

• TOXICITY:

• Drug release off target, or on tatget off tumour

• some ADCs can induce neuropathy, liver tox, thrombocytopenia

• Pre targetung with mAb before using ADC can reduce off target toxicity.

DELIVERY:

• Use in sequence of 2 ADCs sharing same taget but different payload - MOA doesnt give significant cross resistance.

• mAb can be tuned to improve the pH of dependent binding affinity to receptor, or using bispecific to improve selectivity, tolerability, PK.

Summary of Key Concepts in mRNA Vaccines

• Function: Used to induce or boost anti-tumor immune responses using synthetic mRNA encoding tumor-specific antigens.

• None approved yet.

• Main problem- do not know all the antigens that a specific tumour has - need to be able to identify these biomarkers to target.

• Advantages:

  • Non-infectious, well tolerated, and easily degradable.

  • Quick and inexpensive production.

• Delivery Methods:

  • Non-formulated

  • formulated (lipid based)

  • Delivery via dendritic cells for personalized medicine.

• Mechanism of Action:

  • mRNA is taken up by cells, translated into proteins which then trigger immune responses by activating T cells through MHC class I and II pathways.

  • Alternative moa- internalised by endocytosis so mrna is transpirted in the cytoplams and undergoes antigen processing so the mrna is released and goes into ribosome. Ribosome produces proteins and the production of the proteins leads to MHC class 1 and 2 system to work - activate cd8+ and cd4+ cells and give immune response.

• Lipid nanoparticles- made of 4 components plus mrna mixed in microfluidic systems:

• cationic ionisable liquid

• cholesterol - to solidify the product

• phospholipid

• PEGylated lipid- stabilises the particles- reduces plasma protein adsorption on lipid nanoparticle- less recognisable to immune system.

release is pH triggered during endosomal maturation - change of lipid arrangements and release of mRNA.

Allergic responses were rare, but worse than with normal vaccines. Usually well tolderated.

none currently available for cancer.

• Challenges

  • Storage and distribution issues must be addressed.

  • Personalized medicine might require tailored mRNA vaccines for individual patients.

  • need for rapid and large scale good manufacturing practice productuion of individualised mrna vaccines.- difficult when each vaccine could be different.

• Clinical Trials:

  • Current trials assess efficacy and immune response, some showing promise in generating antibody responses or inducing remission in patients.

Conclusion on ADCs and mRNA Vaccines

• ADCs are a promising avenue in cancer treatment but come with significant challenges regarding toxicity and biodistribution.

• mRNA vaccines are emerging therapeutics showing potential for cancer treatment, though more work is needed to translate these findings into approved therapies and widespread clinical practice.

• Future research should focus on optimizing drug delivery and formulation to enhance efficacy while minimizing toxicity.

CELL AND GENE THERAPY

ADVANCED THERAPY MEDICINAL PRODUCTS (ATMP)

GT- gene therapy medicinal product = type of ATMP containing active substance which consisrs of - recombinant nucleic acid adminstered to humans with view to regulating, repairing, replacing, adding or deleting a genetic sequence. Therapeutic, prophylactic or diagnostic effect relates directly to the recombinant nucleic acid sequenceit contains, or to the priduct of genetic expression of this sequence.

SC- somatic cell therapy medicinal product= cells or tissues that have been subject to manipulation so that biological characteristics, physiological functions/ structural properties relevant for intended clinical use have been altered, or of cells or tissues not intended to be used for same essential fucntion in the recipient ans the donor- has properties for / administered with a view to treating, preventing / diagnosing disease.

gene therapy and somatic cell therapy are interlinked.

TE- tissue engineered priduct- engineered cells/ tissues and is presented as having properties for or is administered to humans woth view to regenerate/ repair/ replace human tissue.

pitential for these cell and gene therapies-

gt- use virus, modify content inside, admin to pt.

tissue engineering- modify tissue and grow in large numbers so can modify organs inside pt.

AUTOLOGOUS- take cells from patient , choose right cells, modify and grow, inject back into patient.

ALLOGENIC- use suitable donor, then inject into patient.

Viral vectors can be used for gene therapy. 4 types- adenovirus, AAV, retrovirus, lentvirus. relies on specialist companies.

Combination of gene therapy and cell therapy:

few centres in the uk that do this.

Car T cells

cancer can block t cell defences- genetically engineer patients own t cells to make them smarter, seeking out to destroy cancer.

car t cell therapy is a version of this.

T cells are customised to focus on specific kind of cancer cell.

Pt blood is filtered through a machine that separates t cells and other WBCs from the rest.

They mix collected t cells with a virus that has been disabled so will not cause illness, instead that virus carries genetic instructions for the t cells to grow an artificial receptor= chimeric antigen receptor (CAR). this will track its cancer target and perpare for an attack.

Millions of copies of these engineered cells are grown in a lab and then given back to patient IV.

Once in bloodstream, CAR-T cells find the antigen and grab hold- then release toxic chemicals that trigger cell death in the cancer cells. then they move on to other cancer cells in the patient’s bloodstream.

Summarised:

Take blood from pt, extract t cells, create car t cells using virus , transfect t cells with virus, then get car t cells – express car receptors on surface, then grow in lab, when have enough, give back to patient via infusion, car t cells eill then attack the cancer cells.

Toxicities of CAR-T cell therapy

• leads to release of IL-6 cytokines - leads to cytokine release syndrome - the first line treatment for this is mAb.

• None of these new therapies come without drawbacks.

Somatic cell therapy

Adult cells autologous or allogenic - multipotent stem cells, chondrocelect( use differentiated cells from suitable donor), cartilage report.

embryonic stem cells have applications in blindness and spinal injury.

induced pluripotent cells, xenognic cells

Tissue engineering product-

may contain:

cell/tissue of human or animal origin (or both)

cells / tissues may be viable or non viable

has been used to replace cornea

grow cells in vitro and create new oegans - then go back to be provided to patient- complicated and labour intensive.

Implications for pharmact

• regulations

• handling requorememts

• toxicity monitoring and reporting.