Novel 4-alkoxy Meriolin Congeners Potently Induce Apoptosis in Leukemia and Lymphoma Cells

<i>Meriolins</i> (3-(pyrimidin-4-yl)-7-azaindoles) are synthetic hybrids of the naturally occurring alkaloids <i>variolin</i> and <i>meridianin</i> and display a strong cytotoxic potential. We have recently shown that the novel derivative <i>meriolin</i><b>16</b> is highly cytotoxic in several lymphoma and leukemia cell lines as well as in primary patient-derived lymphoma and leukemia cells and predominantly targets cyclin-dependent kinases (CDKs). Here, we efficiently synthesized nine novel 2-aminopyridyl <i>meriolin</i> congeners (<b>3a</b>-<b>3i</b>), i.e., <i>pyrimeriolins</i>, using a one-pot <i>Masuda</i> borylation-<i>Suzuki</i> coupling (MBSC) sequence, with eight of them bearing lipophilic alkoxy substituents of varying length, to systematically determine the influence of the alkoxy sidechain length on the biological activity. All the synthesized derivatives displayed a pronounced cytotoxic potential, with six compounds showing IC₅₀ values in the nanomolar range. Derivatives <b>3b</b>-<b>3f</b> strongly induced apoptosis and activated caspases with rapid kinetics within 3-4 h in Jurkat leukemia and Ramos lymphoma cells. The induction of apoptosis by the most potent derivative <b>3e</b> was mediated by the intrinsic mitochondrial death pathway, as it was blocked in caspase-9 deficient and Apaf-1 knockdown Jurkat cells. However, as recently shown for <i>meriolin</i><b>16,</b> derivative <b>3e</b> was able to induce apoptosis in the Jurkat cells overexpressing the antiapoptotic protein Bcl-2. Since tumor cells often inactivate the intrinsic mitochondrial apoptosis pathway (e.g., by overexpression of Bcl-2), these <i>meriolin</i> congeners represent promising therapeutic agents for overcoming therapeutic resistance.