Therapeutic vulnerabilities exposed by the 9p21 loss identified through multiparametric drug screening inform rational combination strategies

Our plain-English summary of Therapeutic vulnerabilities exposed by the 9p21 loss identified through multiparametric drug screening inform rational combination strategies, by R. Bevilacqua, P. Gasperini, T. Cantore, et al (NPJ Precision Oncology, 2026).

The study

• Authors: R. Bevilacqua, P. Gasperini, T. Cantore, C. Macedo-Silva, M. Pancher, M. Radić, H. Yue, O. Quaini, T. Fedrizzi, P. Gatto, R. Seiler, B. Kiss, V. Adami, F. Lorenzin, M. Kruithof-de Julio, B.M. Faltas, F. Demichelis
• Journal: NPJ Precision Oncology
• Published: 2026;10(1)
• Read it: PubMed · Publisher · Free full text

Abstract

Homozygous loss of the 9p21 locus encompassing CDKN2A, CDKN2B, and MTAP is the most frequent copy number alteration across tumor types, making it a promising target for precision medicine strategies. To explore drug vulnerabilities exposed by this loss, we generated 9p21 locus isogenic bladder cancer (BLCA) cell models to perform a multiparametric drug screen, testing 2,349 compounds. We identified cytarabine and methotrexate as significantly more effective in the 9p21 compromised BLCA cells. Analysis of morphological alterations further supported a genotype-specific activity of nucleoside analogs, nominating gemcitabine as a drug with greater efficacy in this context. To further exploit MTAP loss, we explored drug combinations targeting MTAP synthetic lethal partners, PRMT5 and MAT2A. Synergy between cytarabine and inhibitors of PRMT5 (MRTX1719) and MAT2A (AG-270) was mediated by a differential activation of DNA damage and replication stress markers, suggesting an exploitable vulnerability. In fact, rational drug combinations with ATR/CHK1 pathway inhibitors increased efficacy while maintaining 9p21-specificity. Finally, we confirmed the effectiveness of these combinations in cell models of pancreatic adenocarcinoma and pleural mesothelioma, two tumor types with high prevalence of MTAP loss and, most notably, in bladder cancer patient-derived organoids, underscoring the strong translational potential of our findings.

© 2026. The Author(s).

In plain English

This was a laboratory study of bladder cancer cell models engineered to lack the 9p21 locus. The authors used CRISPR/Cas9 in the bladder cancer lines HT1197 and T24 to delete about 210 kb covering CDKN2A, CDKN2B and MTAP (3KO clones) alongside non-targeting control (WT) clones; HT1197 clones lacking only CDKN2A/2B (2KO) were also generated. They screened 2349 compounds at 1 micromolar for 48 hours, measuring nuclei counts and cell morphology, and identified 18 compounds that reduced viability selectively in 3KO cells; cytarabine and methotrexate were confirmed in dose-response assays, and morphology-matching nominated gemcitabine. For methotrexate and cytarabine, HT1197 2KO clones responded like WT clones, which the authors read as pointing to MTAP loss. Cytarabine showed synergy (HSA synergy score above 10) with the MAT2A inhibitor AG-270 and the PRMT5 inhibitor MRTX1719 only in 3KO clones, with increased gamma-H2AX, phosphorylated CHK1 and apoptosis. Combinations with the ATR inhibitor VX970 were also selective, and were tested in pleural mesothelioma (SPC111) and pancreatic adenocarcinoma (SW1990) lines and two bladder cancer patient-derived organoid lines.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: preclinical laboratory study: high-content multiparametric drug screen in CRISPR-engineered isogenic cancer cell lines, with validation in other cell lines and patient-derived organoids
• Who was studied: Bladder cancer cell lines HT1197 and T24 edited to isogenic 9p21 wild-type and 3KO (CDKN2A/CDKN2B/MTAP) clones, with 2KO (CDKN2A/2B only) clones generated in HT1197; pleural mesothelioma line SPC111 and pancreatic adenocarcinoma line SW1990 with MTAP knockout; two muscle-invasive bladder cancer patient-derived organoid lines (TN-001, BlCa197) from patients in Bern and Biel, Switzerland
• Exposure: Drug exposures: a 2349-compound library at 1 micromolar; then cytarabine, methotrexate, gemcitabine, the MAT2A inhibitor AG-270, the PRMT5 inhibitor MRTX1719, the ATR inhibitor VX970 and the CHK1 inhibitor AZD7762, alone and in sequential combinations
• Main results:
  • The screen flagged 18 compounds that reduced viability in 3KO cells (viability z-score at or below -2.5) but not in WT cells (z-score between -1.5 and 1.5)
  • In HT1197 clones lacking only CDKN2A/2B (2KO), sensitivity to methotrexate and cytarabine did not differ from wild type, which the authors read as MTAP loss driving sensitivity to these two drugs
  • Correlation of drug-induced morphological changes with those of cytarabine ranked gemcitabine among the top hits, and gemcitabine was more active in 3KO clones of both lines
  • Cytarabine combined with AG-270 or MRTX1719 gave Highest Single Agent synergy scores above 10, seen only in 3KO clones and not in WT or 2KO clones
  • Markers of DNA damage, replication stress and apoptosis rose in 3KO cells after treatment, including phosphorylated CHK1 with cytarabine alone or combined
  • The ATR inhibitor VX970 with MRTX1719 or AG-270 reduced viability selectively in HT1197 and T24 3KO cells (P less than 0.01, unpaired t-test)
  • In pleural mesothelioma (SPC111) and pancreatic adenocarcinoma (SW1990) models, chosen because MTAP loss occurs in 32% and 22% of these tumour types, MRTX1719 combinations with cytarabine or VX970 were more effective than single drugs in MTAP-knockout cells
  • In organoids, restoring MTAP in TN-001 removed MRTX1719 activity while MTAP knockout in BlCa197 increased it; combinations were more effective than single drugs in both lines
• The authors' conclusion: The authors concluded that nucleoside analogs are a class of drugs with more selective activity in MTAP-deficient bladder cancer, and that their data give a preclinical rationale for combining them with PRMT5, MAT2A and ATR inhibitors
• Limitations the authors state:
  • All screened compounds were tested at one fixed concentration, so drugs active only at other concentrations could have been missed
  • Absence of vulnerabilities attributable to CDKN2A/2B loss may reflect the low expression of those proteins in the HT1197 model
  • Only two patient-derived organoid lines were used; a larger panel is needed
  • Resistance mechanisms and toxicity of the combinations were not addressed

Topics

Medical terms in this study, explained in our Lexicon: CDKN2A, MTAP, Gemcitabine, Adenocarcinoma, Pleural Mesothelioma.

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