Introduction to Drug Transporters - Gatekeepers Galore
- Cellular "gatekeepers": membrane proteins dictating drug flux across biological barriers.
- Vital for all ADME phases: Absorption, Distribution, Metabolism, Excretion.
- Classified into two major superfamilies:
- ABC (ATP-Binding Cassette): Active efflux pumps, ATP-driven (e.g., P-gp/MDR1 encoded by ABCB1).
- SLC (Solute Carrier): Facilitated or active uptake/efflux (e.g., OATPs, OCTs, SERT).
- Modulate drug efficacy, toxicity, and drug-drug interactions (DDIs).
⭐ > Polymorphisms in transporter genes like ABCB1 (P-gp) are key determinants of interindividual variability in drug response.
Genetic Polymorphisms in Transporters - Transporter Twists
- Genetic variations (polymorphisms) in transporter genes (e.g., ABCB1, SLCO1B1) alter drug transporter protein function.
- Single Nucleotide Polymorphisms (SNPs) are common culprits.
- Impacts drug ADME (Absorption, Distribution, Metabolism, Excretion).
- Altered drug uptake (e.g., OATPs) or efflux (e.g., P-glycoprotein/P-gp).
- Leads to:
- Varied drug efficacy.
- ↑ risk of Adverse Drug Reactions (ADRs).
- Clinical significance: Guiding drug selection & dosage.
⭐ SLCO1B1 gene polymorphism (e.g., c.521T>C, Val174Ala) significantly ↑ risk of statin-induced myopathy (e.g., with simvastatin).
Pharmacogenomics of ABC Transporters - Efflux Enigmas
and BCRP (ABCG2) pharmacogenomics)
| Gene | Common Polymorphisms | Affected Drugs | Clinical Consequences |
|---|---|---|---|
| ABCB1 (P-gp/MDR1) | - C3435T (rs1045642): T allele → ↓ P-gp expression/function. - G2677T/A (rs2032582): Altered substrate specificity. | Digoxin, tacrolimus, cyclosporine, loperamide, ondansetron, PIs (saquinavir), paclitaxel. | - C3435T (TT genotype): ↑ absorption/CNS entry (loperamide), ↑ toxicity (digoxin) or ↓ efficacy (anticancer). - G2677T/A: Variable, often ↑ exposure. |
| ABCG2 (BCRP) | - Q141K (c.421C>A, rs2231142): ↓ transporter function. | Rosuvastatin, atorvastatin, allopurinol, sulfasalazine, topotecan, imatinib, methotrexate. | - Q141K (A allele carriers): ↑ plasma concentrations, ↑ risk of toxicity (e.g., rosuvastatin-induced myopathy). |
Pharmacogenomics of SLC Transporters - Uptake Upshots
SLC (Solute Carrier) transporters mediate drug uptake into cells. Genetic variations can significantly alter drug disposition and response.
| Gene (Transporter) | Common Polymorphisms | Key Affected Drugs | Clinical Consequences |
|---|---|---|---|
| SLCO1B1 (OATP1B1) | c.521T>C (Val174Ala) | Statins (simvastatin, atorvastatin) | ↓ Hepatic uptake → ↑ plasma levels → ↑ myopathy risk (e.g., simvastatin 40mg with CC genotype) |
| SLC22A1 (OCT1) | Reduced function variants | Metformin | ↓ Hepatic uptake → ↓ glycemic response, ↑ GI intolerance |
| SLC6A4 (SERT) | 5-HTTLPR (S allele) | SSRIs (e.g., fluoxetine) | ↓ Response, ↑ adverse effects (variable evidence) |
⭐ SLCO1B1 c.521T>C polymorphism significantly increases risk of statin-induced myopathy. Individuals with the CC genotype (homozygous variant) may experience several-fold higher statin plasma concentrations.
High‑Yield Points - ⚡ Biggest Takeaways
- ABC transporters (e.g., P-glycoprotein/ABCB1) and SLC transporters (e.g., OATPs, OCTs) are key drug transporter families.
- ABCB1 (MDR1) polymorphisms (e.g., C3435T) affect drug absorption/elimination, impacting digoxin, tacrolimus.
- SLCO1B1 polymorphisms (e.g., c.521T>C) strongly link to statin-induced myopathy (e.g., simvastatin).
- OAT/OCT variants alter renal clearance of drugs like metformin (OCT2) and methotrexate (OATs).
- BCRP (ABCG2) variants (e.g., Q141K) influence rosuvastatin, allopurinol, sulfasalazine disposition.
- Transporter genotyping guides personalized dosing, optimizing therapy and minimizing adverse drug reactions (ADRs).
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