New research suggests that the use of biopsy or liquid biopsy might offer important insights into the most beneficial sequence of anaplastic lymphoma kinase-tyrosine kinase inhibitors (ALK-TKIs) therapy following lorlatinib (Lorbrena, Pfizer) resistance in patients with ALK-rearranged non-small cell lung cancer (NSCLC). 

Reporting at the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics (abstract A125), a multi-center team of Japanese researchers -- led by Koutaroh Okada, M.D., of the Japanese Foundation for Cancer Research -- explained that there are currently five ALK-TKIs in clinical use against ALK-rearranged cancer.

Researcher with Drugs. Source: Getty Images

Of these, alectinib is one of the most common agents used as first-line therapy. Despite alectinib’s popularity, however, many patients experience alectinib resistance due, largely to secondary mutations in ALK kinase domain, including I1171N or G1202R. For its part, lorlatinib is a third-generation ALK-TKI that has shown to overcome these secondary mutations, including I1171N and G1202R. 

Although lorlatinib has demonstrated marked clinical response in ALK-TKI resistant patients with ALK-secondary mutations, multiple lorlatinib-resistant ALK compound mutations have since been reported. 

“To further understand the lorlatinib-resistance mechanisms,” the authors wrote, “we tried to discover the lorlatinib-resistance mechanisms using cell line models and in vivo models, and to explore the therapeutic strategies to overcome the resistance.”

To help achieve these goals, the investigators first explored lorlatinib-resistance mutations by performing ENU random mutagenesis screening using murine pro-B Ba/F3 cells expressing EML4-ALK-G1202R or EML4-ALK-I1171N. 

They then identified lorlatinib-resistant tumors in vivo and analyzed relevant resistance mechanisms. Finally, the scientists obtained lorlatinib-resistant cells using TKI-naïve ALK-positive NSCLC-patient-derived JFCR028-3 cells by treating them with high concentrations of lorlatinib. 

The researchers identified a total of 15 lorlatinib-resistant EML4-ALK compound mutations with G1202R or I1171N from either ENU mutagenesis or the in vivo model. Interestingly, they also found that approximately half of these lorlatinib-resistant mutations were re-sensitized to first- or second-generation ALK-TKIs such as crizotinib or alectinib. 

Using a computational simulation, structural analysis was also found to successfully predict how and why those mutations conferred initial resistance to lorlatinib and re-sensitivity to early generation TKIs. 

On the other hand, the EML4-ALK-G1202R+L1196M compound mutation found in patients’ samples was resistant to all clinically applied ALK-TKIs. Nevertheless, they found that two BCR-ABL TKIs -- AG-957 and adaphostin -- inhibited ALK-G1202R+L1196M directly. 

Finally, the researchers used JFCR-028-3 cells exposed to high-dose lorlatinib to independently establish lorlatinib-resistant cells after three months of drug treatment. Interestingly, the growth of such lorlatinib-resistant cells was not suppressed by either lorlatinib or other ALK-TKIs. 

These findings, the investigators concluded, imply that the sequence of drug administration following lorlatinib resistance may play an important role in how patients with ALK-rearranged NSCLC respond to therapy. 

“Further studies,” they wrote, “are still needed to uncover the unidentified lorlatinib resistance mechanisms.”