antibody-drug conjugates

Nitrile Gloves, Not Ribbons

Posted on by Elise Johnson

Every October, the noise starts up again: it’s breast cancer’s turn for awareness. I brace for it a little every year. What bothers me isn’t the concept, it’s watching companies race to out-pink each other.

A pink ribbon on a shirt or a car can foster a certain amount of solidarity, but at the corporate level, the awareness noise is genuinely inescapable: a building lit up pink for the night, a pink yogurt lid, or a player running out onto the field in pink cleats. Many companies have run some version of the same campaign, and what actually happens to the profit from pink merchandise varies wildly: modest percentages, hard caps on total donations, or numbers that only recently moved after enough people asked questions.

In addition to the question of money is the question of effect: what does a company’s participation do? If the goal actually is awareness, I’ve never understood who remains unaware. It tends to generate goodwill instead, and the sometimes cynical among us might call that marketing, whether or not that’s the intent.

Here’s a sentence that’s true to me, one most people have their own version of: my sister had breast cancer. One in eight women in the U.S. will hear that diagnosis in her lifetime (though women aren’t the only ones who get it). So we are aware. We have been aware for a long time.

At one point, however, we actually needed awareness, in the literal sense of the word. When the American Cancer Society started its breast cancer awareness campaign in 1985, breast cancer was a disease people didn’t discuss in polite company, self-exams weren’t routine, and mammograms weren’t the norm they are now. Getting people to talk about it, check themselves, and get screened was a real, specific goal, and awareness did its job at the time. Last year marked the campaign’s fortieth anniversary, a point at which even the American Cancer Society’s own retrospective pointedly admitted: awareness alone isn’t enough anymore.

October runs on that word, awareness, as if noticing something were the same as solving it. As if on November 1st, we can dust off our hands, congratulate ourselves, and move on to the next color of the month. But breast cancer research doesn’t run on that calendar. Real, promising work has been happening. Learning about it might not change anything either, not directly, but it’s one step closer to what the American Cancer Society itself is now calling “Turning Awareness Into Action.”

More Than a Pretty Face

This starts, perhaps unexpectedly, with the axolotl, a foot-long Mexican salamander known for its perpetual smile and the feathery gills that fan out from its head like a spray of coral. The most common pet-store variety is also, conveniently for this piece, pale pink. It has become plastered across backpacks, folders, plush toys, and t-shirts. My nine-year-old niece and her friends are obsessed with them.

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ADC Development: The Questions Running in the Background

Posted on by Elise Johnson

You’ve had food stuck in your teeth at some point during a conversation you thought was going well. Or toilet paper trailing from the back of your shoe on a day you felt particularly put together. Maybe you’ve even forgotten to color in your very blonde eyebrows and spent the rest of the day looking like someone erased the top half of your face. But you had no idea. You’re walking around with the quiet, complete confidence of someone operating on incomplete information.

You weren’t wrong about anything you could see. You just couldn’t see everything, which is a different problem than getting a bad result. A bad result tells you something is wrong, but this doesn’t. This happens in the lab too. The number is clean, the program is advancing, and somewhere in the data, something is happening that your readout has no way to show you.

Antibody-drug conjugate (ADC) development has a version of this problem. The cytotoxicity readout is real, reliable, and correct. It’s also an aggregate, and an aggregate compresses everything that happened into a single number. That number can’t tell you which mechanisms produced it, which ones are underperforming, or what to change if the program stops working. It just tells you cells died, or they didn’t. You’re walking around with the quiet, complete confidence of someone operating on incomplete information.

Cytotoxicity: Where Every Program Begins

Cell viability assays were built to answer one question: did the cells die? Increase the dose, more cells die. Decrease it, fewer do. The curve is clean, the data is reliable, and the payload is doing what it was designed to do. For cytotoxicity, it’s the right question to ask.

That question has an established platform with consistent, reproducible data: our CellTiter-Glo® and RealTime-Glo™ Assays.

For most ADC programs, this is where the measurement work starts and stops, but it should only be where it starts. The question they answer well is only one of several your ADC is raising. The number means what it says, but the question it answers has a boundary, and the boundary leaves you with an incomplete picture.

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pH Reactive Dyes for Screening Antibody Internalization

Posted on by Promega
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Antibody drug conjugates (ADCs) are a new class of therapeutic drugs that uses antibodies to deliver highly toxic drug molecules specifically to the cancer cells. A key requirement for ADCs is the ability of antibody to bind to the cancer cells followed by internalization and subsequent release of drug inside the cells leading to cell apoptosis.

Traditionally, selection of lead antibody candidates for ADCs was done in a sequential workflow where antibodies were first selected based on their affinity followed by characterization involving antibody internalization and drug conjugation. However, there is evidence that high affinity doesn’t always correlate with good internalization and hence there is a need to screen antibodies for internalization properties in addition to their affinities.

Promega has developed a method that allows antibody to be screened for their internalization properties in a simple, plate-based format. The method uses pH sensor dyes (pHAb dyes), which are not fluorescent at neutral pH but become highly fluorescent at acidic pH. When antibody conjugated with pHAb dye binds to its antigen on the cancer cell membrane they are not fluorescent but upon internalization and trafficking into endosomal and lysosomal vesicles the pH drops and dye becomes fluorescent.

Fluorescence signal, for pHAb dyes conjugated using either amine or thiol chemistry, is minimal at pH>7 and increase significantly as the pH drops to pH 5.0, which is a typical pH in cell endosomal compartment. Moreover, pH response of free pHAb dye is similar to that of conjugated dye indicating that conjugation chemistry doesn’t influence the pH response of the dye.

Due to the high signal-to-background ratios of the dyes, plate-based internalization assays can be performed, enabling screening of large libraries of antibodies for their internalization properties, hopefully leading to improved identification of lead candidates for ADC applications.