Morphological features of melanoma destruction under the influence of EGFR inhibitors: Gefitinib and a novel pyrimidine derivative.

e21539 Background: The global rise in cutaneous melanoma incidence necessitates the search for new therapeutic targets. The EGFR signaling pathway is associated with proliferation, tumor cell survival, and the development of resistance to targeted and immunotherapy, making it an attractive target for further study. The aim of this work was to investigate the effect of the EGFR inhibitor gefitinib and a novel 2-styryl derivative of 4-oxo-1,4-dihydropyrimidine (6MPSoVn), which possesses affinity for the internal domain of EGFR, on tumor morphology in the B16/F10 melanoma model. Methods: C57Bl/6 mice with transplanted B16/F10 melanoma were divided into three groups: group 1 (n=20) received oral gefitinib, group 2 (n=20) – i.p. 6MPSoVn and the control group (n=20) – i.p. vehicle. Treatment started on the day of tumor transplantation according to the schedule: 5 days of administration followed by a 2-day break; the total duration of the course was 14 days. On day 14, animals were euthanized, followed by morphological examination of the tumor tissue. Sections 5–7 μm thick were stained with hematoxylin and eosin. Microscopy was performed using a Leica DMLS2 microscope equipped with an Olympus digital camera and an image analysis system. Results: The mean tumor volume in the control group was 3.7±0.6 cm³ (M±m), while in the gefitinib and 6MPSoVn groups it was 2.3±0.5 cm³ and 2.4±0.6 cm³, respectively. In the control group, the tumor structure was characterized by a dense arrangement of cells with large polymorphic nuclei and numerous melanin granules in the cytoplasm. In the gefitinib group, the tumor structure was partially preserved; however tumor cell shrinkage due to cytoplasmic condensation without loss of plasma membrane integrity was observed. Nuclear fragmentation was accompanied by the formation of apoptotic bodies and melanin aggregation in areas of cell death. These changes are characteristic of apoptosis. In the 6MPSoVn group, extensive areas of tumor necrosis were revealed (more than 60% of the section area). Tumor cells showed signs of dystrophy and degeneration: karyopyknosis, vacuolization, cytoplasmic lysis, loss of plasma membrane integrity, and release of melanin granules into the extracellular space. Foci of destruction exhibited pronounced lymphocytic infiltration. Loose fibrous connective tissue with a histiocytic component formed at the tumor periphery. These morphological features may also indicate necroptosis, which requires further investigation using IHC methods. Conclusions: Thus, EGFR inhibitors are capable of causing irreversible damage to melanoma cells in vivo . Cell death induced by gefitinib occurs via the mechanism of apoptosis, whereas the novel compound 6MPSoVn induces B16/F10 melanoma cell death predominantly via the necrosis pathway, accompanied by connective tissue proliferation and signs of immune activation.