# A novel, short isoform of the +TIP microtubule (MT) binding protein CLIP170 confers taxane resistance by obstructing the MT pore.

> **NIH NIH R01** · WEILL MEDICAL COLL OF CORNELL UNIV · 2022 · $501,039

## Abstract

The taxanes are amongst the most commonly used chemotherapy drugs in clinical oncology, and are a mainstay of treatment in
gastric cancer. However, despite their use in both first and second line therapy, patients commonly exhibit intrinsic resistance
resulting in marginal benefit. A post hoc analysis of taxane therapy in an international clinical trial (TAX-325) confirmed this
observation; we found that GC patients with diffuse histological subtype did not benefit from DTX therapy, suggesting that
diffuse GC is may be intrinsically resistant to taxanes. To date, despite the wide use of taxanes in oncology, the molecular underpinnings
of clinical taxane resistance remain poorly elucidated. Using preclinical models of GC intrinsic resistance, we identified a novel
faster-migrating isoform of the microtubule (MT) plus-end binding protein CLIP-170, hereafter CLIP-170S, which was enriched
in GC cell lines with intrinsic taxane resistance. The canonical full-length CLIP-170 protein belongs to the family of MT plus-
end-tracking proteins (+TIPs) which accumulate at the distal ends of growing MTs, linking MT ends to various cell structures
and regulating MT dynamics. Mass-spec proteomics and 5’RACE revealed that CLIP-170S was missing the first 150 amino acids,
including the first Cap-Gly (domain, required for proper +TIP localization. Confocal microscopy experiments showed that
CLIP-170S was miss-localized from the MT ends to the MT lattice. Live-cell imaging of native cytoskeletons using fluorescently-
labeled paclitaxel (Flutax) revealed significantly faster dissociation rates of Flutax from MTs in the cells expressing CLIP-170S,
indicating transient interaction with MTs. Taxane binding to MTs is a two-step process. First, taxanes bind to the MT outer
surface by interacting with their low affinity binding site at the MT pore, then, they get internalized to the MT lumen where they
bind to their high affinity luminal binding site. Our data using chemical probes specific for the outer and inner surface of the
MT pore showed that CLIP-170S expression was associated with decreased binding affinity of taxanes for MTs. Stable knock-
down (KD) of CLIP-170S reversed completely taxane resistance (~300-fold)— while KD of the canonical CLIP-170 had no
effect on drug activity— thereby, suggesting a cause-effect relationship between CLIP-170S expression and taxane resistance. Together
these data led us propose a model where CLIP-170S blocks the MT-pore, impairs taxane binding to the MT outer surface inhibiting
taxane access to the high-affinity luminal binding site resulting in drug resistance. We have developed a drug discovery platform,
BANDIT (Bayesian Analysis to Identify Drug Interaction Targets), which allows for accurate identification of target proteins
for orphan drugs or small molecules. BANDIT identified Imatinib as a drug predicted to be active in taxane-resistant GC cells.
Experimental validation showed that Imatinib not only was able to completely rev...

## Key facts

- **NIH application ID:** 10437609
- **Project number:** 5R01CA228512-05
- **Recipient organization:** WEILL MEDICAL COLL OF CORNELL UNIV
- **Principal Investigator:** Olivier Elemento
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2022
- **Award amount:** $501,039
- **Award type:** 5
- **Project period:** 2018-04-19 → 2024-03-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10437609

## Citation

> US National Institutes of Health, RePORTER application 10437609, A novel, short isoform of the +TIP microtubule (MT) binding protein CLIP170 confers taxane resistance by obstructing the MT pore. (5R01CA228512-05). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/10437609. Licensed CC0.

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