BPS3021 Chap.6 Cellular Delivery Barriers

Cellular Delivery Barriers

Distinguish association, internalisation, localisation, cytosolic access and biological function.

What this chapter covers

• 01

  Surface association versus internal signal

• 02

  Endosomal sorting and lysosomal degradation

• 03

  Endosomal escape

• 04

  Functional readouts and toxicity controls

Worked example · free

Progress the productive formulation

Key terms

Cell association

Total therapeutic signal attached to or contained within cells.

Internalisation

Movement of cell-associated material across the plasma membrane into the cell.

Co-localisation

Spatial overlap between labelled signals that supports shared compartment location but not necessarily molecular interaction.

Cellular Delivery Barriers FAQ

Exam move

Draw the delivery funnel and attach one assay, one valid claim and one invalid claim to every stage; A labelled therapeutic can generate a strong cell-associated signal while remaining bound to the outer membrane; Removing or quenching extracellular fluorescence distinguishes total association from internal signal;

Microscopy with compartment markers then asks where the internal material went; A cytosolic reporter or biological response is needed to show productive delivery; associationinternalisationcorrect localisationfunctional deliveryEvery barrier removes candidates that looked successful at the previous readout.Follow the cargo to its required destinationAn extracellular receptor-blocking antibody may work without internalisation;

An antibody-drug conjugate usually needs entry and trafficking that releases its payload; mRNA and siRNA need access to the cytoplasm, so sequestration in endosomes or lysosomes is generally unproductive; DNA must additionally reach the nucleus;

The same localisation can therefore be beneficial for one modality and a failure for another; Include untreated cells, free label where relevant, a delivery-negative formulation, a positive functional control and a viability measurement;

Toxicity can reduce reporter output or alter membrane integrity, creating misleading comparisons; Co-localisation is evidence of spatial overlap, not proof of molecular interaction; A high uptake percentage is useful only when the denominator and measurement method are clear;

The common lost mark is collapsing the chain into one word: “uptake.” Replace it with the exact stage; If the quenched signal is high, say internalisation increased; If endosomal co-localisation is also high and functional output remains low, identify escape as a plausible bottleneck;

If cytosolic access is high but function is low, investigate cargo integrity, translation or target biology; Candidate A shows association 180, internal fraction 82%, endosomal co-localisation 76%, cytosolic access 8% and function 4%;

Candidate B shows association 115, internal fraction 64%, endosomal co-localisation 27%, cytosolic access 44% and function 34%; B is the stronger system because less total signal produces much more productive access and function;

A mainly accumulates in vesicular compartments; A formulation is brightest on microscopy but produces no encoded protein; Answer: brightness alone may reflect surface binding, intact-particle label or vesicular trapping; Add quenching, compartment markers, cytosolic-access and functional-expression readouts;

siRNA lowers protein expression; Answer: include a non-targeting sequence and viability control to distinguish sequence-specific knockdown from general toxicity or handling effects; A defensible answer uses at least three linked readouts and avoids causal overreach;

Name the earliest failure, propose one measurement that would discriminate alternatives, and recommend the next experiment; This matches the workshop marking logic: classification, a valid conclusion, an invalid conclusion, and a control that makes the interpretation robust;

Separate total association from the fraction internalised; Use localisation to identify trapping or productive trafficking; Check cytosolic access before attributing function to uptake; Confirm viability and state what the dataset cannot prove;

· DELIVERY BARRIERS Delivery evidence WEEK 9 Uptake is not the endpoint Association, entry, trafficking, escape and function are separate claims A labelled therapeutic can generate a strong cell-associated signal while remaining bound to the outer membrane;

Removing or quenching extracellular fluorescence distinguishes total association from internal signal; Microscopy with compartment markers then asks where the internal material went; A cytosolic reporter or biological response is needed to show productive delivery;

association internalisation correct localisation functional delivery Every barrier removes candidates that looked successful at the previous readout; Follow the cargo to its required destination An extracellular receptor-blocking antibody may work without internalisation;

An antibody-drug conjugate usually needs entry and trafficking that releases its payload; mRNA and siRNA need access to the cytoplasm, so sequestration in endosomes or lysosomes is generally unproductive; DNA must additionally reach the nucleus;

The same localisation can therefore be beneficial for one modality and a failure for another; Controls turn fluorescence into evidence Include untreated cells, free label where relevant, a delivery-negative formulation, a positive functional control and a viability measurement;

Toxicity can reduce reporter output or alter membrane integrity, creating misleading comparisons; Co-localisation is evidence of spatial overlap, not proof of molecular interaction; A high uptake percentage is useful only when the denominator and measurement method are clear;

EVIDENCE SENTENCE Measured signal → physical interpretation → valid conclusion → claim that remains unsupported; The common lost mark is collapsing the chain into one word: “uptake.” Replace it with the exact stage; If the quenched signal is high, say internalisation increased;

If endosomal co-localisation is also high and functional output remains low, identify escape as a plausible bottleneck; If cytosolic access is high but function is low, investigate cargo integrity, translation or target biology;

Time points can distinguish delayed trafficking from permanent trapping; A single image may show where cargo is at one moment but miss later escape or degradation; A short time course paired with functional output makes the location evidence more informative;

· · LOCALISE FAILURE Failure localisation Find the earliest weak link Progress the candidate with productive delivery, not the brightest label EX 6 Compare two delivery systems Candidate A shows association 180, internal fraction 82%, endosomal co-localisation 76%, cytosolic access 8% and function 4%;

Candidate B shows association 115, internal fraction 64%, endosomal co-localisation 27%, cytosolic access 44% and function 34%; B is the stronger system because less total signal produces much more productive access and function;

A mainly accumulates in vesicular compartments; Separate total association from the fraction internalised; Use localisation to identify trapping or productive trafficking; Check cytosolic access before attributing function to uptake;

Confirm viability and state what the dataset cannot prove; P1 Bright but inactive Practice A formulation is brightest on microscopy but produces no encoded protein; Answer: brightness alone may reflect surface binding, intact-particle label or vesicular trapping;

Add quenching, compartment markers, cytosolic-access and functional-expression readouts; P2 Control choice Practice siRNA lowers protein expression; Answer: include a non-targeting sequence and viability control to distinguish sequence-specific knockdown from general toxicity or handling effects;

Progress the formulation that completes the biological journey, not the one that merely reaches the cell; Delivery closing move A defensible answer uses at least three linked readouts and avoids causal overreach; Name the earliest failure, propose one measurement that would discriminate alternatives, and recommend the next experiment;

This matches the workshop marking logic: classification, a valid conclusion, an invalid conclusion, and a control that makes the interpretation robust; Normalise comparisons carefully; Percent internalised can look impressive when total association is tiny, while a large absolute internal signal may still be biologically useless;

Report both the fraction and the relevant absolute or functional readout before ranking formulations; ·