Hyaluronic acid (HA) plays a crucial role in tumor growth and invasion through its interaction with cluster of differentiation 44 (CD44), a non-kinase transmembrane glycoprotein, among other hyaladherins. CD44 expression is elevated in many solid tumors, and its interaction with HA is associated with cancer and angiogenesis. Despite efforts to inhibit HA-CD44 interaction, there has been limited progress in the development of small molecule inhibitors. As a contribution to this endeavour, we designed and synthesized a series of N-aryltetrahydroisoquinoline derivatives based on existing crystallographic data available for CD44 and HA. Hit 2e was identified within these structures for its antiproliferative effect against two CD44⁺ cancer cell lines, and two new analogs (5 and 6) were then synthesized and evaluated as CD44-HA inhibitors by applying computational and cell-based CD44 binding studies. Compound 2-(3,4,5-trimethoxybenzyl)-1,2,3,4-tetrahydroisoquinolin-5-ol (5) has an EC₅₀ value of 0.59 μM against MDA-MB-231 cells and is effective to disrupt the integrity of cancer spheroids and reduce the viability of MDA-MB-231 cells in a dose-dependent manner. These results suggest lead 5 as a promising candidate for further investigation in cancer treatment.

CD44, a cell surface glycoprotein, plays a crucial role in cancer progression by enhancing cell proliferation and resistance to apoptosis. Targeting CD44 with small molecules is a promising cancer therapy strategy. Building on our previous work with the tetrahydroisoquinoline (THIQ) derivative SRT1, we designed and synthesized a series of analogues (SRT2-SRT10) to explore their anticancer potential. Among these, the sulfonate esters SRT5 and SRT6 were the most promising in CD44⁺ MDA-MB-231 breast cancer cells. They effectively inhibited the HA-CD44 interaction, as demonstrated by binding assays and cell viability studies. In addition, molecular dynamics simulations predict that these esters interact with the same key residues within the CD44-HABD domain as those involved in HA recognition. In CD44⁺ lung cancer cell lines (A549 and NCI-H23), SRT1 exhibited the strongest antiproliferative activity (EC₅₀ = 0.88 and 0.42 μM, respectively), while SRT5 and SRT6 also showed significant efficacy, particularly in NCI-H23 cells. Interestingly, only SRT1 induced apoptosis, suggesting distinct mechanisms of cell death. Kinase profiling revealed that SRT5 and SRT6 inhibited CD44-associated kinases, particularly SRC, contributing to their anticancer effects. In contrast, SRT1 appeared to act through a kinase-independent pathway. All compounds displayed high selectivity for cancer cells over non-tumoral lung cells. ADME predictions suggested favorable pharmacokinetic properties. Overall, our results underscore the potential of N-benzylTHIQ derivatives, as selective agents for targeted therapy of lung cancer and support further in vivo validation and mechanistic investigations.

Molecular interactions at the cell surface, in particular between hyaluronic acid (HA) and the cluster of differentiation 44 (CD44) receptor, are crucial in several biological processes and diseases such as cancer. Thus, inhibition of the HA-CD44 interaction has become a promising therapeutic strategy. Etoposide was the only antitumor compound known to inhibit the binding of CD44 to HA, thereby disrupting key functions that drive malignancy. However, our recent research led to the development of N-alkyl and N-aryl THIQ derivatives, which represented a significant advancement in this field. Here, we further explore the structure-activity relationships of a series of newly designed N-alkylcarbonyl THIQ and study the structural parameters that define both the CD44 inhibitory and antiproliferative activities. Compounds 5d and 7d showed the most improvement of the antiproliferative activity compared to the N-alkylketone 1. Cell viability, competitive binding assays and molecular dynamics studies demonstrated effective inhibition of HA-CD44 binding by compounds 5d and 7d. This work not only expands the arsenal of potential therapeutic agents targeting HA-CD44 interactions but also highlights the potential for new treatments that could more effectively disrupt cancer progression.