Small Molecule Drug Conjugate Hybrids of Naphthalene Sulfonamide and Phospholipid Conjugates Are Microtubule-Disrupting Antitumor Agents

Background: Antimitotic agents are very successful antitumor therapies, but lack tumor selectivity, causing toxicity. Antitumor alkylphospholipids (APLs) selectively accumulate in tumor cells but display low potencies. Hypothesis: Incorporating APL moieties onto antimitotic N-trimethoxyphenyl naphthalene sulfonamides (TMNS) might afford SMDCs with the potency of antimitotics and the tumor selectivity of APLs. Methods: 24 new TMNSs with spacers of different lengths (4 to 9 atoms) and nature (alkanes or ethers) on the sulfonamide nitrogen and capped with phosphorus-containing groups such as diethylphosphonates, phosphonic acids, and hydrogenophosphonate esters of aminoalcohols (diethylaminopropanol, choline, or dimethylaminoethanol) were designed and synthesized. Their antiproliferative effects against several cancer cell lines and their cotreatment with verapamil to assess whether they are substrates of MDR pumps were evaluated. The mechanism of action was studied: cell cycle effects, apoptosis induction, and immunofluorescence microscopy. Computational studies considered binding to tubulin and pharmacokinetics. Results: Diethyl phosphonates and phosphonic acids are antiproliferative in the micromolar to submicromolar range. P-gp inhibitor verapamil renders inactive compounds active, suggesting that efflux, not binding, removes activity. Mechanistic studies agree with an antimitotic action. Proposed binding to tubulin is similar to TMNS, with the phospholipid-like substituent projecting towards the interdimer space. Conclusions: Hybridization of TMNSs with potentially tumor–targeting APLs yields microtubule-disrupting antitumor compounds. However, the modifications assayed turn the compounds into substrates of MDR. These compounds are a proof of concept of the strategy that might succeed if future modifications avoid MDR and might target the compounds towards cancer cells.